“K 'I.‘ ‘ 4 0 v 5‘, .I” .w . .‘_I \r , 2111:3Q’42“ \ fifla"! ‘ ' I a r *‘afi‘w‘fi’. . v. -;.":‘—1 , r . ‘3' xx“ 2 ‘ [5.1: x‘. [35“? ‘ - 4313:, V I ABSTRACT MESOSCOPIC AND MICROSCOPIC FABRIC RELATIONSHIPS ACROSS THE CATOCTIN MOUNTAIN-BLUE RIDGE ANTICLINORIUM OF CENTRAL VIRGINIA by Villard S. Griffin, Jr. The Catoctin Mountain-Blue Ridge anticlinorium of central Virginia has been subdivided into three parallel zones by previous workers. These zones are: l) the eastern Piedmont, Upper Precambrian-Lower Cambrian volcanics and metasediments, 2) the central core of Precambrian base- ment gneisses and granodiorite, with a complex deformational history, and 3) the western, Upper Precambrian-Lower Cambrian volcanics and metasediments of the Blue Ridge. This investigation is concerned with variations of mesoscopic and microscOpic structural elements among and within these three anticlinorium subdivisions. The mesoscopic fabric elements considered are, bedding, cleavage, foliation, Jointing, and lineations. The microscopic fabric elements studied are, quartz optic axes and mica cleavage pole orienta- tions. On the mesoscOpic scale, the bedding, cleavage, folia- tion, and lineation have characteristic orientations within the three anticlinorium subdivisions. The western zone, .Lower Cambrian sediments show the effects of a more gentle deformational and metamorphic history than do the basement Villard S. Griffin, Jr. and Piedmont units. Excepting the Swift Run Formation, the sedimentary units along the eastern and western side of the anticlinorium are B-tectonites, with fold axes and most lineations paralleling the regional north-eastward strike. The basement gneisses show a very strong a lineation, and are consequently different from the younger units along the anticlinorium flanks. Joints have a strong tendency to cross-cut the regional trend in all three subdivisions of the anticlinorium. There is also a weaker tendency to parallel the regional trend. The granodioritic Pedlar Formation, from the basement, shows some anomalous foliation orientations. The gneissic banding or foliation, which is expressed by quartz and feld- spar grain alignment, has several orientations. Three are northeastward and parallel the foliation of the gneisses, as well as the bedding, cleavage, and foliation of the younger units along the flanks, however, one does not parallel the regional trend. The quartz and mica fabrics show variations among the three anticlinorium zones. The quartz optic axes of the western units, excepting the Swift Run Formation, show con- centrations around the b-axis in individual diagrams. Also, the quartz axes have a horizontal girdle tendency in the horizontal cumulative-summary diagrams. The mica orientation in these units tends to agree with orientations of the bed- ding and cleavage surfaces. The quartz fabrics of the basement complex gneisses show intersecting girdles, horizontal and at high angles. Villard S. Griffin, Jr. The mica fabrics show pronounced girdles about the a linea- tion. Within an Antietam formation shear zone, along the western flank of the anticlinorium, quartz Optic axes form a girdle about the pronounced a, or shear, lineation. There- fore, presumably, the basement gneiss quartz and mica fabrics also show a history of shearing in 2. Insufficient mica is present in the Pedlar Formation for orientation analysis. The quartz fabric itself is difficult to interpret, but may be more similar to that of the gneisses than to that of other units. The quartz axes of the Piedmont units subparallel the lineation and form girdles trending northeast in horizontal master diagrams. The quartz fabric of the Mount Athos quartzite is difficult to fit into this picture completely. The mica fabric appears to reflect the influence of the steep- ly dipping Paleozoic foliation which strikes northeastward. The symmetries of most mesoscOpic and microscopic subfabrics throughout the anticlinorium appear to be rather consistent. The most pronounced symmetry planes trend north- westward. A monoclinic symmetry tendency is strongest, which reflects the northwestward asymmetry of the structures. In some subfabrics, especially that of Jointing, an orthorhom- bic tendency is possible. Triclinic symmetry tendencies are noted in the Swift Run and Mount Athos quartz fabrics and in the Pedlar foliation fabric. MESOSCOPIC AND MICROSCOPIC FABRIC RELATIONSHIPS ACROSS THE CATOCTIN MOUNTAIN-BLUE RIDGE ANTICLINORIUM OF CENTRAL VIRGINIA by Villard s. Griffin, Jr. A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Geology 1965 ACKNOWLEDGEMENTS Many persons and several organizations have offered valuable guidance, assistance, and encouragement during this investigation. Special appreciation must be acknowledged to Dr. Chilton Prouty, Dr. James Trow, Dr. Justin Zinn, and Dr. Harold Stonehouse, of the Department of Geology at Michigan State University, for their guidance during the field and laboratory research, and in the writing of this paper. Special thanks also must be given to the members of the Department of Geology at the University of Virginia, especially Dr. R. S. Edmundson and Dr. R. S. Mitchell, for their generous assistance, guidance, and encouragement during the summer of 1963 and 1964. Dr. R. O. Bloomer, of St. Lawrence University, has offered valuable information and criticisms, in addition to lending the writer an unpublished manuscript concerning the geology of the area under considera- tion. Dr. Frank Trainer of the United States Geological Survey has discussed with the writer possible implications of some of the mesoscopic Joint diagrams. Dr. J. L. Calver and Dr. Seymore Greenburg of the Virginia Division of Mineral Resources, as well as other members of the staff, have extended encouragement and advice. In addition, they offered helpful services during the summer of 1963. Appreciation is also extended to Norman Haimila, and Michael Katzman, who as students of this writer, produced several petrofabric diagrams which served as a check on the writer's own plotting methods. 11 Appreciation is extended to the Society of the Sigma Xi and the Research Society of America for a "Grant-in Aid" for field work during the summer of 1963. Also, the writer is grateful to the graduate office of Michigan State Univer- sity for graduate tuition scholarships covering the academic years of 1962-1963, and 1963-1964. Officials of the National Park Service were courteous and helpful to the writer during his work along the Blue Ridge Parkway. Finally, the writer is deeply indebted to his parents for their constant en- couragement and financial assistance, without which this investigation would not have been possible. It is to his parents that this paper is dedicated. 111 TABLE OF CONTENTS Introduction Purpose of the Investigation . . . . Previous Studies within the General Area Geologic Setting Stratigraphy of the Area General discussion . . . . . . . Basement complex . . . . Upper Precambrian or Lower Cambrian Paleozoic rocks . . . . . . . . . Later rocks . . . . . . . . . . . Structure of the Area General discussion . . . . . . . Macroscopic structures . . . . . Mesoscopic structures . . . . . . Tentative Fabric Orientations Introduction to the Investigations . . Chilhowee Group . . . . . . . . . . . Antietam formation* . . . . . Mesoscopic fabric relations. Microscopic fabric relations Harpers formation MesoscOpic fabric relations. Microscopic fabric relations *Unicoi Formation Mesoscopic fabric relations. Microscopic fabric relations Upper Precambrian or Lower Cambrian Rocks (West Limb) Swift Run Formation Mesoscopic fabric relations. Microscopic fabric relations Basement Complex Pedlar Formation MesoscOpic fabric relations. Microscopic fabric relations Marshall formation Mesoscopic fabric relations. Microscopic fabric relations Lovingston formation Mesoscopic fabric relations. Microscopic fabric relations Upper Precambrian or Lower Cambrian Rocks (East Limb) Lynchburg formation Mesoscopic fabric relations. iv rocks 0 O O O O O O O O O Page 10 l4 16 2O 37 37 42 48 51 51 55 62 67 76 80 93 97 103 107 113 118 134 138 149 Microscopic fabric relations Evington Group Candler Formation Mesoscopic fabric relations. MicroscOpic fabric relations Mount Athos Formation MesoscOpic fabric relations. Microscopic fabric relations Resume of Salient Petrofabric Facts General discussion . . . . . . . The Chilhowee group Mesoscopic fabric. Microscopic fabric . . . . . The Swift Run Formation Mesoscopic fabric. . . . . . MicroscOpic fabric . . . . . The basement complex Mesoscopic fabric. . . . . . MicroscOpic fabric . The Lynchburg formation-Evington group Mesoscopic fabric. . . . . . Microscopic fabric . . . . . Interpretations . . . . . . General Discussion . . Joints . . . ~ The Chilhowee Fabric . The Piedmont Fabric. . Shear zone Fabrics . . The Marshall and Lovin The Pedlar Fabric . . The Swift Run Fabric . Conclusions . . . . . gst eeeOeeeeee t3 '2] eeemeeeeee 0‘ oeefiee.eee H“ 0000000000 CO References Cited . . . . . . . . . . . . . Page 154 164 169 178 182 188 189 190 193 194 196 198 200 202 206 206 206 207 209 215 218 221 224 225 228 *The use of Formation as opposed to formation depends upon whether the unit was originally designated by the name "formation" or by another name, such as "gneiss" "sandstone”. 01‘ TABLE Page Formations within the Catoctin-Mountain-Blue Ridge anticli- norium in central Virginia . . . . . . . . . . . . LIST OF FIGURES Figure 1. oc~zoxu1 «FUN 17. 18. 19. 20. 21. 22A. 22B. 23A. 23B. 24. 25A. 25B. 26. 27A. Map showing the geographic location of the area investigation in Virginia . . . . . . . . . . Antietam formation Bedding and cleavage diagram (40 poles) . . Statistical s-surfaces (defined by Fig. 2). Bedding and cleavage pole plot (40 poles) Joint diagram (103 poles) . . . . . . . . . Statistical Joint sets (defined by Fig. 5). Quartz Quartz Quartz Quartz Quartz Quartz Quartz Quartz Quartz Quartz, horizontal cumulative-summary diagram (5 diagram diagram diagram diagram diagram diagram diagram diagram diagram (235 (250 (268 (249 (259 200 250 (200 from maxima centers) . Optic Optic optic Optic Optic optic optic Optic shear axes) axes) axes) axes) axes) axes) axes) axes) zone (2OO Harpers formation optic Bedding and cleavage diagram (38 poles) Statistical s-surfaces (defined by Fig. 17) . Bedding and cleavage pole plot (38 poles) . . Joint diagram (lOl poles) . . . . Statistical Joint sets (defined by Fig. 20) . Quartz diagram (215 Optic axes) . . Muscovite-sericite diagram (98 cleavage poles) Quartz diagram (180 optic axes) O O O O O O O O O O O O O O O O O O O O O O O O O axes) Muscovite-sericite diagram (108 cleavage poles) Quartz diagram (179 Optic axes) Quartz diagram (166 optic axes) Muscovite- sericite diagram (115 216 optic axes) Quartz diagram 200 optic axes) Quartz diagram vi cleavage poles) . . . 9 Page of O O O C O O O O I O O O O O U1 (I) i O C\ H q 0 Figure 27B. Sericite diagram (100 cleavage poles) . . . . . . 28A. Quartz diagram (200 optic axes) . . . . . . . . 28B. Sericite diagram (100 cleavage poles) . . . . . . 29A. Quartz diagram (195 Optic axes) . . . . . 29B. Muscovite- sericite diagram (102 cleavage poles) . 30. Quartz, horizontal cumulative-summary diagram (95 maxima centers- of-gravity). . . . . . 31. Mica, horizontal cumulative-summary diagram (28 maxima centers-o f—gravity). 32. Statistical mica s-surfaces (defined by Fig. 31). Unicoi Formation 33. Bedding and cleavage diagram (57 poles). . . . . 34. Statistical s-surfaces (defined by Fig. 33) . . . 35. Bedding and cleavage pole plot (57 poles) . . . . 36. Joint diagram (118 poles). . . . . 37. Statistical Joint sets (defined by Fig. 36) . . . 38. Quartz diagram 2OO optic axes . . . . . . . . . 39A. Quartz diagram 204 optic axes . . . . . . 39B. Muscovite- sericite diagram (103 cleavage poles) . 40A. Quartz diagram (205 Optic axes) . . . . 40B. Muscovite- sericite diagram (lOO cleavage poles) . 41A. Quartz diagram (195 Optic axes). . . . . . . 41B. Muscovite-sericite diagram (95 cleavage poles). . 42A. Quartz diagram (200 Optic axes) . . . . . . . . . 42B. Sericite diagram (100 cleavage poles). . . . . 43A. Quartz diagram (218 optic axes) . . . . . . . 43B. Muscovite-sericite diagram (101 cleavage poles) . 44A. Quartz diagram (200 Optic axes) . . . . . . . . . 44B. Sericite diagram (100 cleavage poles) . . . . . . 45. Quartz diagram 220 Optic axes) . . . . . . . . . 46. Quartz diagram 51 optic axes). . . . . . . . 47A. Quartz diagram 2OO optic axes) . . . . . . . . 47B. Sericite diagram (lOO cleavage poles) . . . . . . 48. Quartz diagram 172 Optic axes) . . . . . . . . . 49A. Quartz diagram 2OO Optic axes) . . . . . . . . . 49B. Sericite diagram (100 cleavage poles) . . . . . . 50. Quartz diagram 200 optic axes . . . . . . . . . 51A. Quartz diagram 249 optic axes . . . . . . . . . SIB. Muscovite-sericite diagram (lOO cleavage poles) . 52. Quartz, horizontal cumulative- -summary diagram (167 maxima centers-of—gravity) . . . . 53. Mica, horizontal cumulative-summary diagram (33 maxima centers-of—gravity). . 54. Statistical mica s-surfaces (defined by Fig. 53). Swift Run Formation 55. Bedding and foliation plot (10 poles). . . . . 56. Lineation plot (8 lineations). . . . . . . . . 57. Joint diagram (22 poles). . . . . . . 58. Statistical Joint sets (defined by Fig. 57) . . . vii Page 72 72 72 72 74 74 74 74 95 95 95 95 Figure 59A. 59B. 60A. 60B. 61A. 61B. 62A. 62B. 63. 64. 65. 66. 67. 68. 69. 70. 71. 72. 73. 74. 75. 75. 77. 78A. 78B. 79. 80. 81. 82. 84. 85A. 85B. 86A. 86B. 87A. 87B. 88A. 88B. 89A. 89B. 90A. 90B. Quartz diagram (200 Optic axes). Sericite diagram (100 cleavage poles) Quartz diagram (200 Optic axes) . . Sericite diagram (100 cleavage poles) Quartz diagram (2OO optic axes) . . Sericite diagram (100 cleavage poles) Quartz diagram (2OO optic axes) . . Sericite diagram (100 cleavage poles) Quartz, horizontal cumulative- -summary diagra (56 centers-of—gravity) . . . . . . . . . Mica, horizontal cumulative-summary diagram (18 centers-of—gravity). . Statistical mica s- -surfaces (defined by Fig. 64): Pedlar Formation Gneissic banding diagram (100 poles) . Statistical s-surfaces (defined by Fig. Joint diagram (168 poles). . . . Statistical Joint sets (defined by Fig. Quartz diagram 200 optic axes Quartz diagram 2OO Optic axes Quartz diagram 197 Optic axes Quartz diagram 200 Optic axes) Quartz diagram (200 optic axes Quartz diagram 182 optic axes Quartz diagram 2OO Optic axes . Quartz diagram from shear zone (96 Optic axes). Quartz diagram from shear zone (200 Optic axes) Sericite diagram from shear zone (100 cleavage 0\0 (DO\ eeeeeeveVe eeeeeeeO‘e eeeeeeeeeee p01es). O O O O O O O O O O O I O O O O Quartz, horizontal cumulative-summary diagram (97 maxima centers-of-gravity). . . . . . . Marshall formation Foliation diagram (100 poles). . . Statistical s-surfaces (defined by Fig. 80) Lineation diagram (68 lineations). . . . Joint dia.gram (lOO poles). . Statistical Joint sets (defined by Fig. 83) Quartz diagram (195 Optic axes) . . . Muscovite-sericite diagram (lOO cleavage pol Quartz diagram (200 Optic axes) . . . . Biotite diagram (lOO cleavage poles). . Quartz diagram (135 Optic axes) . . . . Biotite diagram (lOO cleavage poles). . Quartz diagram (2OO optic axes) . . . Biotite diagram (lOO cleavage poles). . 8 Quartz diagram (190 optic axes) . . . Biotite diagram (100 cleavage poles). Quartz diagram (200 Optic axes). . Biotite diagram (100 cleavage poles). eeeeeeeeeemeeeeee eeeeeeeeeeveeeeee viii 0000000000... Page 95 95 100 100 100 100 100 100 102 102 102 106 106 106 106 106 106 110 110 110 110 110 110 112 112 112 116 116 116 116 116 116 121 121 121 121 121 121 123 123 123 123 123 Figure 91A. 91B. 92A. 92B. 93A. 93B. 94A. 94B. 95L 95B. 96L 96B. 97A. 97B. 98A. 98B. 99A. 99B. 100. 101. 102. 103. 104. 105. 106. 107. 108A. 108B. 109A. 109B. 110A. 110B. 111A. 1118. 112A. 112B. 113A. 113B. 114A. 1148. 115A. 115B. 116A. 116B. 117A. 117B. Quartz diagram (200 optic axes) . . Biotite diagram (100 cleavage polesL Quartz diagram (200 Optic axes) . . . Mica diagram (100 cleavage poles) . . Quartz diagram (200 optic axes) . . . Sericite diagram (98 cleavage poles). Quartz diagram (200 Optic axes) . . Biotite-sericite diagram (92 cleavage Quartz diagram (192 Optic axes) . . . Sericite diagram (101 cleavage poles) Quartz diagram (200 Optic axes) . . . Biotite diagram (100 cleavage poles). Quartz diagram (200 Optic axes) . . . Sericite diagram (99 cleavage poles). Quartz diagram (188 optic axes) . . . Biotite diagram (97 cleavage poles) . Moneta quartz diagram (97 Optic axes). 00.000.013.000... 0 ooooooooHooooooo (0 00000000310000... Moneta biotite diagram (100 cleavage poles) Quartz, horizontal cumulative-summary diagra (185 maxima centers-of-gravity) . . . . . Mica, horizontal cumulative-summary diagram (78 maxima centers- of-gravity). ) m Mica statistical s- -surfaces (defined by Fig. 101) Lovingston formation Foliation diagram (106 poles) . . Statistical s-surfaces (defined by Fig. 103) Lineation diagram (59 lineations) . . Joint diagram (118 poles) . . Statistical Joint set (defined by Fig. 106) Quartz diagram (201 optic axes) . . Biotite-muscovite-sericite diagram (100 poles). . . . . . . Quartz diagram (201 Optic axes) . . Biotite diagram (100 cleavage poles) Quartz diagram (200 optic axes) . . Mica diagram (100 cleavage poles) . Quartz diagram (200 optic axes). Biotite diagram (100 cleavage polesL Quartz diagram (205 Optic axes) . . . Biotite diagram (100 cleavage Oles). Quartz diagram (210 Optic axes) Biotite diagram (100 cleavage poles). Quartz diagram (200 optic axes) . . Quartz diagram (193 Optic axes) . . . Biotite diagram (99 cleavage poles) . Quartz diagram (203 optic axes) . . . Biotite diagram (94 cleavage poles) . Moneta quartz diagram (81 optic axes) Muscovite-sericite diagram (100 cleavage pol ) Moneta biotite diagram (100 cleavage pol s ix clea 6 00.000000000000000.400.000 (D oooooovooooooococoomoooooo Page 123 125 125 125 125 125 125 127 127 127 127 127 127 129 129 129 129 129 129 132 132 136 136 136 136 136 136 141 141 141 141 141 141 143 143 143 143 143 143 145 145 145 145 145 145 147 Figure 118. 119. 120. 121. 122. 123. 124. 125. 126. 127A. 1278. 128A. 128B. 129A. 1298. 130A. 1308. 131A. 131B. 132A. 132B. 133A. 133B. 134A. 134B. 135. 136. 137. 138. 139. 141. 142. 143A. 143B. 144A. 144B. 145A. 1453. 146A. 146B. 147A. 147B. Quartz, horizontal cumulative-summary diagram (107 maxima centers- Of-gravity) . . . . . . . . Mica, horizontal cumulative-summary diagram (45 maxima centers-of— gravity) . Mica statistical s-surfaces (defined by Fig. 119) Lynchburg formation Bedding and foliation diagram (100 poles) . Bedding and foliation plot (100 poles). Statistical s-surfaces (defined by Fig. Lineation diagram (38 lineations) . . . Joint diagram (102 poles) . . Statistical Joint sets (defined by Fig. Quartz diagram (203 optic axes) . . . Muscovite diagram (100 cleavage polesL Quartz diagram (200 Optic axes) . . . Muscovite diagram (100 cleavage polesL Quartz diagram (193 Optic axes). . . Muscovite diagram (94 cleavage poles) Quartz diagram (194 optic axes) . . . Muscovite diagram (100 cleavage poles) Quartz diagram (200 Optic axes) . . . Mica diagram (100 cleavage poles) . . Quartz diagram (200 optic axes). . Muscovite-sericite diagram (100 cleavae Quartz diagram (200 Optic axes) . . . Muscovite diagram (100 cleavage poles). Quartz diagram (200 optic axes) . . . Muscovite diagram (102 cleavage poles). 86 Quartz, horizontal cumulative-summary diagram (80 maxima centers-Of-gravity). . . 121) iaé) P 0000000000000. Mica, horizontal cumulative-summary diagram (27 maxima centers-Of-gravity). H 00000000000000.0000... m 0 O O O V. O O O O O O O O O O O C O O O . Mica statistical s-surfaces (defined by Fig. 136) Candler Formation Foliation diagram (64 poles). Statistical s- -surfaces (defined by: Fig. Lineation diagram (71 lineations) . . Joint diagram (100 poles) . . Statistical Joint sets (defined by Fig. Quartz diagram (200 optic axes) . . . . Mica diagram (100 cleavage poles). . . Quartz diagram (200 optic axes) . . Muscovite diagram (100 cleavage poles). Quartz diagram (200 Optic axes). . . . Muscovite diagram (100 cleavage poles). Quartz diagram (200 optic axes) . . . . Muscovite-sericite diagram (100 Quartz diagram (200 Optic axes). . . . Muscovite diagram (100 cleavage poles). X OOOOOOOHOOHO cleavage p U4 .p ooOoooooooI—‘oomo v V OOQOOOOOOOOOOOO 1 m C O V. O O O O O O O O O O O Page .147 O 147 .147 o 151 .151 .151 .151 .151 .151 .157 .157 0157 0157 .157 -157 ~159 .159 .159 ~159 -159 ~159 .161 .161 .161 .161 .161 .163 .163 .167 .167 .167 .167 o 167 .167 .172 .172 .172 .172 .172 .172 o 174 O 174 .174 Figure Page 148A. Quartz diagram (171 optic axes). . . . . . . . .174 148B. Sericite diagram (100 cleavage poles) . . . . . . .174 149A. Quartz diagram (200 Optic axes) . . . . . .174 149B. Muscovite-biotite- chlorite diagram (100 cleavage poles). . . . . . . . . . . . .176 150. Quartz, horizontal cumulative-summary diagram (76 maxima centers-of—gravity). . . . . . . . .176 151. Mica, horizontal cumulative-summary diagram (31 maxima centers-of—gravity). . . .176 152. Mica statistical s- -surfaces (defined by Fig. 151) .176 Mount Athos Formation 153. Bedding and foliation diagram (49 poles). . . . . .180 154. Bedding and foliation plot (49 poles) . . . . . . .180 155. Statistical s- -surfaces (defined by Fig. 153). . . .180 156. Lineation diagram (34 lineations) . . . . . . . . .180 157. Joint diagram (113 poles) . . . . . . . . . .180 158. Statistical Joint sets (defined by Fig. 157). . . .180 159. Quartz diagram (200 optic axes; . . . . . . . . . .185 160. Quartz diagram 200 Optic axes . . . . . . . . . .185 161A. Quartz diagram 200 Optic axes) . . . . . . . . .185 161B. Sericite diagram (100 cleavage poles) . . . . . . .185 162. Quartz diagram (200 Optic axes) . . . . . . . . . .185 163. Quartz diagram (200 Optic axes; . . . . . . . . . .185 164A. Quartz diagram (200 optic axes . . . . . . . . . .187 164B. Sericite diagram (100 cleavage poles) . . . . . . .187 165. Quartz diagram (200 optic axes) . . . . . . . . . .187 166. Quartz, horizontal cumulative-summary diagram (87 maxima centers-of—gravity). . . . . . . . . .187 167. Mica, horizontal cumulative-summary plot (6 maxima centers-of—gravity). . . . . . . . . . . .187 LIST OF PLATES Plate P889 1. Index map of the Catoctin Mountain-Blue Ridge (Pocket) anticlinorium of central Virginia . . . . . . 2. Exposures of Moneta, Lovingston, and Marshall formations . . . . . 21 3. Exposures of the Pedlar, and Lynchburg formations . 23 . Exposures of the Unicoi, Harpers, and Antietam formations o o o o o o o o o 25 Candler, and Mount Athos formations . . . . . . 27 . Photomicrographs of the Lovingston, Marshall, and Pedlar formations . . . . 29 . Photomicrographs of the Lynchburg, Swift Run, and Unicoi formations . . . . . . . . . . . . . . 31 4 5. Exposures of the Rockfish Congiomerate, the 6 7 xi Plate 8. 9. Photomicrographs of the Harpers, and Antietam (sheared and non-sheared) formations . . . Photomicrographs of the Candler, and Mount Athos formations . . . . . . . . . . . . . xii Page INTRODUCTION Purpose Of The Investigation The geologic structure or fabric Of an area may be divided into three categories according to magnitude. They are the macroscopic, the mesoscOpic, and the microscopic fabric scales. The macroscopic scale is concerned with structures larger than those Observed in outcrops. The mesoscOpic scale involves structures seen in outcrops or in handspecimens. The micrOSOOpic scale involves structures revealed only in thin section, and it has a less Obvious relation to the other two scales than those scales have to each other. In reality, however, these divisions are artifi- cial and are justified only as aids in interpretating the total structural picture. Most structural investigations cited in the literature are concerned with structures of the macroscOpic and mesoscopic scales. Microscopic investigations apparently have been neg- lected. This state of affairs is most probably due to the great time-consuming Operations necessary in Obtaining micro- fabric data, and to the great ambiguity of the data itself once obtained. A few notable investigators, such as Ernst 01003 (1946), 01003 and A. Hietanen (1941), H. W. Fairbairn (1939, 1949), E. B. Knopf (1933). Knopf and E. Ingerson (1938), Bruno Sander (1930, 1934), Walter Schmidt (1925, 1926, 1932), F. J. Turner (1948), and Turner and L. E. Weiss (1963), have 1 2 demonstrated that microscopic fabric studies may provide information in certain cases which investigation Of the mesoscopic and macroscopic fabrics cannot provide alone. However, these workers remind us that microscopic fabric studies without an accompanying treatment of the macroscOpic and especially of the mesoscopic fabric scales may lead to erroneous conclusions, and should be avoided. This writer intends to demonstrate how valuable is a study of the microscopic structural elements (quartz Optic axes and mica cleavage poles) within the Catoctin Mountain- Blue Ridge anticlinorium of central Virginia. Following the advice Of the earlier microfabric investigators, mentioned above, a consideration of mesoscOpic structural elements (bedding, cleavage, foliation, Joints, and lineations) is included as well. Because Of the different structural and lithologic zones within the anticlinorium, indicated by previous mesoscopic and macroscopic studies, this is a desirable locality in which to check the validity of a micro- fabric study in determining structural differences among different assemblages of rocks. The area under consideration here is located in central Virginia (Figure 1). It extends from the Piedmont province :Ln.the east, across the Blue Ridge province into the Valley aJnd Ridge province in the west, a distance of about 29 miles. 1316 area contains approximately 970 square miles. Specifical- ly, it is located within the Vesuvius, Lovingston, Amherst, axui Shipman fifteen minute quadrangles (Plate 1). 4 Previous Studies Within The General Area The earliest known work having any bearing on the area under consideration is that of William Maclure (1809). Before 1835, William Barton Rogers investigated the geology of Virginia, and his findings were published in 1884, after his death, as a volume entitled, Geology of the Virginias. Several years prior to this, William Fontaine (1875). pub- lished a report entitled, Strata g: the Primordial Period in Virginia. Geologic maps of Virginia were published in 1911, 1916, 1928, and 1963. The studies of T. L. Watson and J. H. Cline (1916) initiated the more modern investigations of the geology in regard to the structure, petrology and age relations of the Blue Ridge and its adjacent regions. A. I. Jonas (1927, 1935) working alone, and later collaborating with G. W. Stose (1939). carried out a comprehensive reconnaissance of this region, providing a basis for later studies. H. H. Hess (1933) investigated soapstone bodies located in the eastern part of the area. A contemporary, C. H. Moore (1938, 1940), did structural and petrological work in Amherst county. The structural and age relations of certain metamorphic rocks, within the Lynchburg quadrangle were reported by W. R. Brown (1941, 1951). At the same time, R. R. Bloomer (1941) studied the petrology and age relations of the basal Cambrian volcanics in the Blue Ridge, included in an area directly southwest Of the area involved in this thesis. In 1947, two Opposing views on the Cambrian-Precambrian 5 boundary in Virginia were brought to light. R. 0. Bloomer and R. R. Bloomer, advanced the belief that two formations previously thought to be Precambrian, the Catoctin and Lynch- burg formations, are really Cambrian in age. In Opposition to this view, A. S. Furcron advanced a view which accepts the established age of these two formations as correct. In a later paper, R. 0. Bloomer (1950) maintained his earlier view by stating that he found a continuous sedimentary sequence from "the base of the Lynchburg into the Chilhowee," or lower Cambrian rocks. A contemporaneous paper by W. A. Nelson (1950) supported Bloomer's hypothesis by concluding that there is no evidence of a major unconformity between the lower Cambrian and Catoctin formations. H. B. Cooke (1952), a student of W. A. Nelson, investigated the structure and petrology Of the Rockfish conglomerate, which according to Nelson is the base of the Lynchburg formation. W. R. Brown (1953) reported on the structural frame- work of the Virginia Piedmont. His paper is a survey Of the geology and mineral resources, and contains a geologic map of the Piedmont and Blue Ridge, along with a map of some structural elements in the Lynchburg quadrangle. Later in 1958, he published a detailed geologic report on this same quadrangle. Gilbert Espenshade (1952, 1954) mapped and studied the stratigraphic and structural relations along the southeastern edge of the thesis area and of the Lynchburg quadrangle, directly to the south. His work tends to confirm that of R. 0. Bloomer, W. R. Brown and W. A. Nelson concern- ing the developmental history of the area from Lynchburg 6 time and thereafter. One year later, R. 0. Bloomer and H. J. Werner (1955) published the results of a comprehensive struc- tural, stratigraphic and petrologic study of this area, bordering Espenshade's area and extending northwest across the Blue Ridge. This study demonstrates the inconsistency in the usage of several formational names. During the same year, R. V. Dietrich (1955) Questioned the concept of the Rockfish Conglomerate being a basal con- glomerate of the Lynchburg formation, and "unequivocal" evidence for a great unconformity between the Lynchburg for- mation and the Older Precambrian basement complex. In 1958, a paper by E. 0. Gooch appeared concerning downfolded meta- sedimentary rocks, possibly Of late Precambrian age, within the axial zone of the Catoctin Mountain-Blue Ridge anticlino- rium, directly north Of this thesis area. More recently, R. 0. Bloomer has written a paper as yet unpublished, which is concerned with relationships within the basement complex of this area. Notable in this paper. is a rather well outlined and supported hypothesis for graniti- zation of these basement rocks. The author (1961) has made a preliminary reconnaissance petrofabric study with the quartz and mica microscOpic fabrics. Interesting relationships suggested by this study caused this present investigation to be undertaken. More recently, several works have been published on the geology of adjacent areas. W. A. Nelson (1962) published a report on the geology of Albeuarle County, bordering the thesis area on the northeast. In 1963, R. M. Allen, Jr., 7 published a report on the geology of Madison and Greene Counties, directly northeast of Albemarle County. Finally, J. Smith, R. Milici, and S. Greenberg (1964) have published a report concerning the geology of Fluvanna County, lying in the Piedmont to the north and east Of the area under con- sideration herein. GEOLoggc SETTING STRATIGRAPHY OF THE AREA General Discussion The stratigraphic relations and geologic history Of the formations of the Catoctin Mountain-Blue Ridge anti- clinorium in central Virginia are controversial. Realizing that any one interpretation may not be the correct one, it was necessary to make a choice, in order that this investi- gation might have an explicit basis from which to Operate. Consequently, the works of Espenshade (1954), Bloomer and Werner (1955). and Bloomer (unpublished manuscript) are utilized herein as the basis for this study. There are several reasons for using the work of these investigators. Their work is the most recent, detailed and comprehensive within the actual area of this investigation. Brown's work (1958) has supported certain geologic interpretations worked out by Bloomer and Werner, and Espenshade directly south of this area. Also, R. Allen (1963) supports the work of Bloomer and Werner to a degree in his studies in two counties to the northeast Of this area. A generalized geologic column for central Virginia, based on the work of Espenshade, and Bloomer and Werner, may be seen on page 9 . The geology of the eastern side of the anticlinorium is based on Espenshade's paper (1954), while the remainder is based on those of Bloomer and Werner (1955), and Bloomer (unpublished). Only those units which are starred 8 TABLE - Formations Within Catoctin Mountain-Blue Ridge Anticlinorium in Central Virginia Western Area Central Area Eastern Area Shady-Tomstiwn formation Q (Slippery Creek 3 d ( formation a o *4 a '2 “3 (Mt. Athos a Antietam n ( Formation 8 a, formation 8 ( 9 “3 Archer Cree a o 6 g' Harpers 5 ( Formation 35 8 formation 5 *4 E ‘10 Candler * c: Unicoi * Formation --Eormation ........................................... ::n 33 Catoctin Catoctin a;. formation formation ".3.” as on) Swift Run Lynchburg 33$ Fbrmation* formation* 3 :3 a as. =>o Angular Unconformity : ‘3 Basement Complex 9 .0 B * * * * g Pedlar , Marshall , Lovingston , Harris Cove, Moneta , a Roseland formations a. * Formations studied for fabric relationships. 1. The use of Formation as Opposed to formation depends upon whether the unit was originally designated by the name "formation" or by another name, such as Hgneiss or "sandstone" 2. Correlations between the Chilhowee and Evington groups are problematic. NO Specific correlations are to be inferred from this table. 10 in the table were studied. The quartz and/or mica content were critical to this study, and only those formations possessing sufficient quantities were considered. The following is a brief and general summary Of the most important stratigraphic relations and petrologic characteristics of these units. The reader is referred to Plate 1 for the aerial distribution Of these formations, and for the sampling localities. Basement Complex According to Bloomer and Werner. (1955).and Bloomer (unpublished) the important formations of the Precambrian basement complex are, the Moneta Gneiss, the Lovingston Gneiss, the Harris Cove Granite, the Marshall Gneiss, the Pedlar Formation, and the Roseland Anorthosite. These in- vestigators state that these bodies have gradational contacts with one another, and are most probably a granitized series of Precambrian sedimentary rocks. These formations increase in regional metamorphic rank in the order given above essentially, from the almandine-amphibolite facies up into the granulite facies, which is represented here by most of the Pedlar and Roseland formations. This increase is from east to west, which is the reverse of that attributed to the later Paleozoic metamorphisms of this same region. Moneta Gneiss - The Moneta Gneiss, which has been termed "basement complex gneiss", by Bloomer and Werner, is a dark, biotite-and hornblende-bearing schistose rock, con- taining quartz, oligoclase, potassic feldspar and garnet 11 (Plate 2, Fig. A). It is generally Of fine-grained texture and occurs widely in lens-like bodies (skialiths or xeno- liths) in the Lovingston and Marshall formations, and to a much lesser degree in the Pedlar Formation. Contact between the Moneta Gneiss and its surrounding rock may be both grada- tional or Sharp. Bloomer and Werner, and Bloomer believe that the Moneta is the original formation Of the Precambrian basement prior to its "granitization", and that these present lenses are ungranitized remnants. Lovingston formation - The Lovingston Gneiss forms an elliptical body approximately 25 miles long in the basement complex. Bloomer and Werner (1955), and Brown (1958) dis- tinguish it from the Marshall formation by its characteristic development Of potassic feldspar augen (Plate 2, Fig. B; Plate 6, Fig. A). The augen are contained in a matrix com- posed of biotite, quartz, potassic feldspar and oligoclase- andesine. Due to the biotite and some amphibole, it is gener- ally a dark rock. Its texture is medium-grained,and Bloomer places it in the almandine-amphibolite facies of regional metamorphism. Harris Cove Formation - The Lovingston Gneiss grades into both the Harris Cove granite, formerly the Lovingston Granite (Bloomer and Werner, 1955; Bloomer, unpublished), and into the Marshall gneiss. The Harris Cove Formation, included within the same metamorphic facies as the Moneta, Lovingston and Marshall formations, has a typical granitoid appearance in the hand specimen, though in some cases it .appears faintly gneissic. It possesses more feldspar and 12 less mica than does the Lovingston; otherwise it is similar in composition. Its main mass lies within the body of the Lovingston Gneiss. Marshall formation - The Marshall formation has the greatest aerial extent of any rock unit within the investi- gation area. In many cases, it appears quite similar to the Lovingston formation, except that the feldspar porphyroblasts present are usually not as large nor do they posses the augen-shapes as they do in the Lovingston (Plate 2, Fig. C; Plate 6, Fig. B). Moneta Gneiss inclusions are as abundant in this unit as they are in the Lovingston. Because it generally possesses more feldspar and less biotite than the Lovingston Gneiss, as does the Harris Cove Granite also, Bloomer considers that it is higher in the almandine amphi- bolite facies and has been granitized, similarly to the Harris Cove granite, to a degree intermediate between the Lovingston and Pedlar formations. This writer has Observed that the Marshall formation indeed possesses a granitic (essentially mica-free) facies within its outcrOp area in the Shipman quadrangle. Pedlar Formation - By virtue of its composition and texture, Bloomer places most of the Pedlar Formation within the granulite facies of regional metamorphism and applies 'to it the name charnockite. Within this formational unit, laowever, the character Of the rock varies considerably. Generally, it is granitic and gneissic in appearance, but 111 some places it is quite sheared and may resemble either 1316 Marshall or Lovingston gneisses to the casual Observer 13 (Plate 3, Figs. A and B; Plate 6, Fig. C). The Pedlar occurs as two major masses within this region. The larger mass underlies most Of the present Blue Ridge in the Vesuvius quadrangle, while the smaller mass lies within the Marshall gneiss in the central portion of the Amherst quadrangle. Smaller bodies occur throughout the basement area; many lie within the Harris Cove Formation and grade into it. In the area of this investigation the Pedlar generally shows a green or greenish gray color due mainly to the pres- ence of greenish feldspar, but at some localities it may have a creamy white or a pinkish color, especially in the unakite zones along the Blue Ridge. Grain size varies con- siderably from place to place, but it is in general medium to coarse grained. Along Tye River gap in the Blue Ridge, for example, feldspar grains become quite large, even ex- ceeding 5 centimeters in length. According to Bloomer and Werner (1955) and Bloomer (unpublished), the Pedlar formation contains in decreasing abundance, perthite, quartz, oligoclase, andesine-Oligoclase, chlorite, and other minor minerals such as albite, biotite, muscovite, diOpside, hypersthene, ilmenite, sphene, almandine, sericite, epidote, apatite, tremotite, and "well rounded zircon" (Bloomer, unpublished manuscript, p. 26). Because of its hypersthene content at certain localities, Jonas and Stose originally termed these rocks "hypersthene granodio- rites". Roseland Anorthosite - Bloomer and Werner (1955, 13. 582) state that the Roseland Anorthosite is an "oval 14 body about 13 miles long and 2.5 miles wide in the middle of the basement complex . . ." Its origin is problematical and has been attributed by workers to either magmatization or granitization processes or both. Most handspecimens are a medium to coarse textured white rock, sometimes con- taining blue quartz blebs, and more rarely ilmenite and/or rutile. Bloomer states that the rock is crudely layered and consists Of andesine-Oligoclase in the monomineralic portions Of the body. In other areas, the rock may contain up to 30 percent of quartz and potash feldspar in addition to the andesine-Oligoclase. Near the edges of this body nelsonite bodies occur, some of which have been mined for titanium in the past. Nelsonite consists of ilmenite and/or rutile, with equal amounts of apatite, in addition minor amounts Of andesine-oligoclase, blue quartz, rutile and zircon occur. Bloomer places this anorthosite body in the granulite facies of regional metamorphism. flpper Precambrian 93 Lower Cambrian Rocks Lynchburg formation - In the eastern portion Of the Catoctin Mountain-Blue Ridge anticlinorium the basement com- plex is overlain unconformably by the Lynchburg formation. In several localities the basal Lynchburg is represented by the Rockfish conglomerate member (Plate 5, Fig. A). At JRockfish, Virginia, the basal conglomerate ground-mass is {graywacke in composition, and looks much like the rocks from vflaich it was derived. The cobbles are composed mainly Of Iflarris Cove granite from the basement. At the base, the 15 rock grades downward, from a well-stratified conglomerate, into a poorly-foliated rock. Bloomer and Werner (1955) believe that this is a regolith developed upon the basement complex upon which the Lynchburg was deposited. The Lynchburg has an outcrop width of about 4.5 miles, from southeast to northwest, within the study area. It contains many rock types (Plate 3, Fig. C; Plate 7, Fig. A). In general, graywacke predominates, but shales or schists, quartzites, graphitic slates, conglomerates, amphi- bolites, and talcose and serpentine bodies occur. According to Bloomer and Werner (1955, p. 586), the Lynchburg formation lies partly within the greenschist facies and partly in the almandine-amphibolite facies Of regional metamorphism. Swift Run Formation - The Swift Run Formation is be- lieved to be equivalent to the upper part of the Lynchburg formation. In the area under study here, it is exposed only in the western part Of the anticlinorium, along the eastern flanks of the Blue Ridge, where it lies unconformably on the basement complex. However, in Albemarle County, just to the north of this area, Nelson (1962) names the upper part of what many call the Lynchburg formation, the Swift Run Formation. The Swift Run Formation generally consists of volcanic rocks, subgraywackes, and graywackes, epidotized in places (Plate 7, Fig. B). It is a very thin unit com- paratively and has a small outcrop extent (see Plate 1.). Catoctin formation - The Catoctin formation conform- ably overlies the Swift Run and the Lynchburg formations (lying within the Lynchburg formation outcrOp area in part), l6 and where the Swift Run is absent, overlies unconformably the basement complex in the Blue Ridge. The Catoctin forma- tion is a sequence Of metamorphosed basic flows of spilitic composition, with small lenses of arkoses, graywackes and tuff. Pillow structures and amygdules are commonly Observed at many localities. In the Blue Ridge this formation is rather thick, showing sections in excess Of 5,000 feet at a few places, but generally thinning and finally disappear- ing in the Vesuvius quadrangle area. In the Piedmont to the east, the Catoctin formation is much thinner, but it still shows the same characteristics as that in the Blue Ridge. The Catoctin formation is mainly composed of albite replac- ing andesine and epidote, and chlorite; it has a schistose appearance. It is placed in the greenschist facies. Paleozoic rocks Evington Group The Evington group crOps out in the eastern side of the anticlinorium and is believed by Espenshade (1954) and Brown (1953, 1958) to be a sequence of lower Cambrian rocks. The Candler Formation is placed at the base Of the group by the above workers, although Furcron (1935) has the sequence reversed. According to Espenshade, the Candler lies con- formably upon the Lynchburg formation, though separated in places by a small fault. Brown (1958), in the area farther south Of the one discussed here, stated that the contact is gradational. l7 Candler Formation - The Candler Formation is general- ly a lustrous, greenish-white or gray phyllite, and looks very much like some phyllitic members Of the Lynchburg (Plate 5, Fig. B; Plate 9, Fig. A). It is mainly composed of sericite, chlorite, quartz, and albite (Espenshade, 1954, p. 15). There are small lenses Of marble and quartzite ly- ing within this main phyllitic mass. Greenburg and Melici (personal communication, summer 1963) have investigated by x-ray methods a considerable number of samples of this phyllite from an area in Fluvanna County and have found that paragonite is the principal micaceous mineral here. The high sodium content indicates that much of the Candler Formation is a metavolcanic tuff sequence. Archer Creek Formation - If Espenshade (1954) and Brown (1959) are correct in their stratigraphic interpreta- tions, the Archer Creek Formation lies conformably upon the Candler Formation. It is a relatively thin unit consisting mainly of graphitic schists and marbles. It was not selected for study in this investigation mainly because Of its re- ported low quartz content. Mt. Athos Formation - The Mount Athos Formation over- lies the Archer Creek Formation and is essentially a quart- zite (Plate 5, Fig. C; Plate 9, Figs. B and C), though it does contain marble lenses in some areas. The quartzite is not pure in all places. Some horizons contain mica and chlorite and may appear schistose, although usually showing ggood bedding in most exposures. The formation is not very 'thick and is repeated many times by folding, as are all the 18 units Of the Evington group. This formation is economically significant because Of the manganese concentrations found within it. Slippery Creek formation - Brown (1958) has named the greenstone lying above the Mount Athos quartzite the Slip- pery Creek Greenstone. Both Brown and Espenshade contend that this unit is not equivalent to the Catoctin formation lying farther west, as Furcron (1939) suggests, but is actually younger. However, if Furcron were correct, then the entire Evington sequence would have to be reversed. However, Furcron requires several fault contacts, and in general, a more complex geologic picture than Brown's and Espenshade's hypothesis. Both Brown and Espenshade outline their evidence in detail and it appears relatively convincing to this writer Chilhowee Group Most geologists hesitate to say that the Chilhowee group is correlative, formation for formation, to the Evington group, but many do believe that both groups may be correlative to some unknown degree. Bloomer and Werner (1955) and Brown (1958) believe that the Chilhowee group is the miogeosynclinal equivalent Of the eugeosynclinal Evington group. Unicoi Formation - The oldest formation classified by Bloomer and Werner as definitely Cambrian is the Unicoi Iflcrmation, although Nelson (1962) disagrees and places it 111 the upper Precambrian or rather in his "ProtOpaleozoic". 19 According to Bloomer and Werner, the Unicoi lies conformably upon the Catoctin formation in this area, even containing Catoctin-like flows and tuffaceous shales near its lower boundary, although King (1949, 1950), Stose and Stose (1949), and Reed (1955), working in other areas, have recognized an unconformable contact between the two formations. 0b- viously such an unconformity could not represent a great time span if it cannot be recognized everywhere. The Unicoi Formation, in addition to containing flows and tuffs, is composed of subgraywackes, pebbly arkoses and pebbly quart- zites (Plate 4, Fig. A; Plate 7, Fig. C). Harpers formation - The Harpers formation conformably overlies the Unicoi Formation, and consists Of subgraywackes which are irregularly interbedded with quartzite (Plate 4, Fig. B; Plate 8, Fig. A). The subgraywackes are generally fine—grained. The Harpers may be considered a transitional unit between the Unicoi and the Antietam Quartzite, although at several places the Harpers appears, in handspecimen, nearly indistinguishable from some Unicoi types. Antietam formation - The Antietam formation is the uppermost formation of the Chilhowee group. Bloomer and Werner state that the Antietam formation is partially equiva- lent to the Erwin Quartzite to the southwest. It is a very homogeneous orthoquartzite, consisting of 96 to 99 percent quartz (Plate 4, Fig. C; Plate 8, Figs. B and C). Tomstown formation - Although not part of the Chilhowee gyroup nor included in this study, the Tomstown (Shady) forma— ‘tion must also be considered here in order to complete the 20 stratigraphic picture Of this area. The formation consists mainly of dolomite and grades downward into the Antietam quartzite. It grades upward into the Rome-Waynesboro forma- tion of the Valley and Ridge province. The Tomstown forma- tion is poorly exposed but underlies various portions Of the western flanks Of the Blue Ridge. Later rocks Few rocks are present in the area of investigation representing time later than lower Cambrian. None Of them show effects of regional metamorphism. Specifically, these are Triassic dikes and Quarternary alluvium. NO significant Triassic basin sediments are tO be found in this area. Triassic rocks — The Triassic dikes are, according to Bloomer and Werner (1955, p. 599), "1-100 feet thick and up to several miles long . . ." Generally these dikes trend northwest-southeast, but some trend northeast-southwest, approximately paralleling the regional trend of the Older rocks. Espenshade (1954) maps the dikes in his area as branching out from one another. They are generally composed of diabase. Quarternary rocks - The Quarternary rocks are repre- sented by Recent alluvium. Usually, these are restricted to present flood plains along drainage ways, but some occur at higher elevations as terraces, indicating recent and per- sistent uplift Of the entire area. 21 PLATE 2 FIGURE A - Exposure of Moneta gneiss surrounded by Lovings- ton Gneiss, approximately 1/4 mile south of Va. 151 on Va. 6. FIGURE B - Exposure of the Lovingston formation near Spring Mountain, along U. S. 29. The gneissosity is prominent. FIGURE C - Exposure of the Marshall formation showing gneissosity. Photograph taken along eastern front of the Blue Ridge, north central Amherst quadrangle. ' 22 PLATE 2 PLATE 3 23 FIGURE A - Exposure of the Pedlar Formation along Va. 60 about 11/2 miles south of the Blue Ridge Park- way, showing gneissic banding trending from the tOp to the bottom of the photograph. FIGURE B - Exposure of the Pedlar Formation along the Blue FIGURE C - Ridge Parkway showing large feldspar crystals. A faint gneissic banding trends from the lower right to the upper left-hand corner Of the photograph. Exposure of a shaley member of the Lynchburg formation near Elmington, Virginia. A small fold, approximately two feet across, may be seen in the center of the photograph. 24 PLATE 3 25 PLATE 4 FIGURE A - Exposure of the Unicoi Formation at Tye River Gap. The beds above the hammer are arkose, while those below are red tuffs. FIGURE B - Exposure of the Harpers formation at Tye River Gap. This out-crOp of graywacke shows prominent bedding 0 FIGURE C - Exposure of the Antietam quartzite at Tye River Gap. Cleavage, dipping gently to the southeast, intersects the steeply dipping beds. 26 PLATE 4 27 PLATE 5 FIGURE A - Exposure of the Rockfish Conglomerate at the type area. Bedding trends from the right to the left of the photograph. ‘ FIGURE B - Exposure of the Candler phyllite near Norwood, Virginia. The foliation is nearly vertical. FIGURE C - Exposure of the Mount Athos Formation about one mile north of Buffalo Station, Virginia. The quartzite beds dip steeply. PLATE 5 29 PLATE 6 FIGURE A - Lovingston formation showing quartz (Q) with sutured grain contacts and tiny quartz grains smeared out in the foliation plane. A portion of an auge of oligoclase-andesine (F) is to be seen in the upper right-hand corner. Crossed nicols; X75. FIGURE B - Marshall formation with three types of quartz. The large detrital (7) quartz grain (D. Q.) shows pronounced undulose extinction. Quartz grains with sutured boundaries may be seen, as well as the tiny quartz grains, and biotite (B). All are elongated in the direction of foliation. Crossed nicols; X75. FIGURE C - Pedlar Formation illustrating rounded quartz blebs (Q) within large oligoclase-andesine (F) grains. Hypersthene grains (H) appear in the right side of the photograph. Crossed nicols; X75. 30 PIATE 6 PLATE 7 FIGURE A - FIGURE B - 31 Lynchburg formation showing muscovite (M) roughly following the trend of the s-surface from the right to the left edge across the photo- graph. Detrital (D. Q. ) and recrystallized quartz (Q) may also be seen. Crossed nicols; X75. Swift Run Formation showing rounded detrital quartz grains (D. Q.) surrounded by a fine matrix of quartz (Q), and sericite (S). Crossed nicols; X75. FIGURE 0 - Unicoi Formation illustrating detrital quartz grains (D. Q.) elongated in the foliation sur- face. The grains are cemented by hematite (H). Crossed nicols; x75. 52 PLATE '7 33 PLATE 8 FIGURE A - Harpers formation showing quartz grains (Q), and sericite (S) oriented in an s-surface trending from the right to the left side of the photograph. Crossed nicols; x75. FIGURE B - Antietam formation with over 99% equant, detri- tal quartz grains cemented by overgrowths of secondary quartz. Crossed nicols; X75. FIGURE C - Antietam formation in a shear zone (see Figure 15). Detrital quartz grains have been extensive- ly deformed and show pronounced undulose extinc- tion. Crossed nicols; X75. PLATE 8 35 PLATE 9 FIGURE A - Candler Formation with recrystallized quartz (Q), and muscovite (M) grains elongated in the s-surface. Crossed nicols; x125. FIGURE B - Mount Athos Formation showing equant quartz grains with sutured boundaries. Crossed nicols; 175. FIGURE C - Mount Athos Formation illustrating larger de- formed detrital quartz (D. Q.), smaller re- cr stallized quartz grains (Q), and sericite (S). Crossed nicols; x75. 56 PLATE 9 37 STRUCTURE OF THE AREA General discussion The Catoctin Mountain-Blue Ridge anticlinorium, trending northeast-southwest, is the most conspicuous struc- tural feature within the area of this investigation (see Plate 1). Of lesser importance than the anticlinorium, but still Of major importance, is the intricate pattern of thrust and reverse faults and large folds along the eastern and western edges of this large structural feature. Next in magnitude are transverse faults. Structures within the mesoscopic realm occurring throughout the area include bedding, minor folds, foliation, cleavage, lineation and joints. iacrOSCOpic structures The Catoctin Mountain-Blue Ridge anticlinorium measures approximately 25 miles across from southeast to northwest. According to Bloomer and Werner (1955), and Bloomer (unpublished manuscript), this structure should be regarded as an "undation", dividing the eugeosyncline to the east from the miogeosyncline to the west and representing a structural high on the basement complex throughout the Precambrian and Paleozoic sedimentation of the Appalachians. Following from this, the Catoctin Mountain-Blue Ridge anti- clinorium perhaps may also be termed an intrageosynclinal geanticline, in the classical sense of the concept of geo- syulclinal development (M. Kay,l951, p. 17). 38 These writers further state that the anticlinorium is not a typical tectonic flexure but appears to have re- sulted more or less from epeirogenic movements. Consequent- ly its amplitude is not great. However, some writers (Nelson, 1961, Allen, 1962), reporting on areas to the northeast, find a tendency for overturning in the northwest limb Of this feature. Bloomer and Werner believe that this is the result only Of later tilting to the northwest as the anticlinorium rose under the influence Of epeirogenic forces, and is not due to flexural overturning. Apparently portions of the anticlinorium served as sources for the clastic units which overlie it on both sides. This belief is supported especially by the basement complex fragments and minerals composing the Rockfish, Lynchburg, Swift Run, and Unicoi units. Thrust and moderate to high angle reverse faults occur along the northwest side of the anticlinorium. The faults parallel the northeast-southwest regional grain. These structures occur to a lesser degree along the south- eastern limb. The great majority Of these faults dip con- sistently to the southeast. Although, the moderate to high angle reverse faults appear more abundant than the thrusts. It is possible that many Of these steeper faults are bottomed by low angle overthrusts and may be nothing more than a system of imbricate faults. Bloomer and Werner suggest this for the reverse fault development in the western side of the anticlinorium. They believe that this may indicate that the basement high (undation) acted as a moving buttress 39 against which the overlying strata were shoved during the orogenic thrusting. In the eastern limb Of the anticlinorium, some Of the reverse and thrust faults seem to have developed along forma- tional contacts and boundaries between smaller units of varying composition. Some faults have develOped also synchro- nously with the development Of tight folds. Espenshade (1954, p. 32) states that many "isoclinal folds have been faulted by high-angle reverse faults which have sheared out the western limbs Of the anticlines." Bloomer and Werner have also noted a similar tendency within the Blue Ridge. Bloomer and Werner (1955). and Bloomer (unpublished, and personal communication, 1963) have noted that thrust and reverse faults in the Blue Ridge appear to die out into the basement complex foliation or into the overlying stratified layers. The most recent workers in central Virginia and sur- rounding areas, especially Brown, Espenshade, and Bloomer and Werner, have found no trace Of the large displacement "Martic thrust" postulated by Jonas (1929, 1932), and accepted by Furcron (1939). As presented by Jonas, this thrust is be- lieved to extend from Pennsylvania into central Virginia, and even farther south, along the eastern edge Of the Catoctin Mountain—Blue Ridge anticlinorium. It is thought to have thrust the rocks Of the Evington group (Jonas' Glenarm series), in a nappe-like fashion, 15 to 20 miles westward onto the Lynchburg formation and the rocks of the basement complex. The Candler formation (Jonas' Wissahickon formation) was be- lieved to represent mylonite develOped by this great movement, 40 and its low metamorphic rank (greenschist facies) believed to be the result of diaphthoresis brought about by the ex- tensive shearing. Further northeast, Ernst Cloos and Anna Heitanen (1941) have cast doubt on the existence of the Martic over- thrust in Pennsylvania and Maryland after applying various structural techniques, including petrofabrics, to the prob- lem. Some transverse, strike-slip faults, with a general northwest-southeast trend exist in the Blue Ridge side of the anticlinorium, while a lesser number exist in the eastern or Piedmont side. Many of these may be tear faults in the hanging wall of thrust sheets and moderately dipping reverse faults. Bloomer and Werner state that they seem to dip steeply and have an extent Of only a few miles at most. A few do appear to have no genetic relation to thrust and re- verse faults. Large-scale folding is rather common throughout the entire investigation area, and the fold axes consistently trend northeast-southwest. In the formations along the eastern limb of the anticlinorium, Espenshade, and Bloomer and Werner note the tendency for development of isoclinal folding, with axial surfaces dipping southeast. In the Evington group especially, this is well-develOped and intri- cate in nature. In general, however, these eastern folded strata lie within a larger synclinorium, the lowest unit lying within it being the Lynchburg. This James River syn- clinorium flanks the eastern side Of the basement undation 41 or anticlinorium. The strata within the western side Of the anticlinori- um or undation show well-develOped folds, but isoclinal folds are not as common as in the eastern side. The larger folds are generally more Open, though there is a strong tendency for overturning to the northwest, with the axial plane sur- faces dipping southeast. These strata appear to lie within a larger synclinorium in a fashion similar to those in the Piedmont, although to the southwest Of this area a small anticlinorium (Buena Vista anticline) is developed just west of this synclinorium. This synclinorium, between the large Catoctin Mountain-Blue Ridge anticlinorium and the smaller Buena Vista anticlinorium, has been considerably shortened by thrusting (Bloomer and Werner, 1955, p. 601). Within the basement complex core of the major anti- clinorium there exists much evidence Of folding on a macro- scopic scale, neglecting the anticlinorium itself. South of the thesis area, Bloomer and Werner have noted isoclinal folds within these basement units, which become more Ob- scured as they are traced northeastward into the area under consideration here, presumably because Of the increased effects of granitization (Bloomer, unpublished, p. 51-54; Bloomer and Werner, 1955, p. 604). Bloomer (personal communication, 1963) has indicated that in the western limb of the anticlinorium the Pedlar formation of the basement complex, participated in the fold- ing Of the overlying strata. This is indicated by the fre- <1uent occurrence of the Pedlar within the ereded axial zones 42 of anticlines in the Blue Ridge (see Plate 1). Further evidence of macroscopic folding in the basement is the Mechum River syncline, just to the northeast of this area within Albemarle county. This is a slightly faulted syncline of Lynchburg-like strata lying along the axis of the anti- clinorium, trending northeast and varyingly overturned to the northwest. Normal faulting, though reported in other areas adjacent to this area and by some earlier workers within this particular area, has not been found to be significant here by Espenshade, and Bloomer and Werner. Most normal faulting within the Appalachians appears to be of Triassic age. Mesoscopic structures Bedding is of significance only within rocks Of young- er age than those Of the basement complex, although Bloomer and Werner, and Bloomer believe that traces Of bedding may be found throughout the basement, especially to the south of the area considered here. Virtually all bedding has been deformed into small and moderate scale folds, usually with the northwestern limb overturned. Because Of the asymetric folding in the Blue Ridge and isoclinal folding in the Pied- mont, the majority of the bedding dips to the southeast. However, within the more competent strata of the Antietam quartzite within the Blue Ridge and the Mount Athos quartz- ite within the Piedmont, a significant number of limbs do clip to the northwest. Bedding consistently strikes north- east-southwest. 43 Bloomer and Werner have termed much of the minor folding in the Blue Ridge intraformational folding, since the small-scale folds do not appear to be drag folds along the limbs of the larger folds but may be termed disharmonic folds instead. Their axial surfaces bear no conceivable parallel relationship with those of the larger folds. Bloomer and Werner postulate three episodes of folding with- in the Blue Ridge: 1) the mesoscopic folding, resulting in increased competency of the units, 2) the macroscopic folding, 3) and finally the folding Of later thrust sheets. Espenshade finds somewhat different relationships within the Piedmont. Drag folds appear to exist in abun- dance, although he admits the possibility that they may not all be drag folds. Within the incompetent phyllite units, especially within the Candler Formation, both bedding and minor folds rarely appear. Cleavage and foliation are manifest in one form or another in every formation older than Triassic throughout this entire area. They are better develOped within some units than in others. Bloomer and Werner (1955, p. 604) list three general categories for cleavage within the Blue Ridge units: "1) a mimetic or bedding-plane cleavage, 2) a close-spaced joint set or wide-spaced fracture cleavage, and 3) a cleavage closely related tO thrust faulting . . ." Of the first two, the second category is the most obvious ‘within the Chilhowee formations, though the first is apparent in thin section in the Unicoi and Harpers units. The cleavage inelated to thrusting, the third category, is pronounced within 2.4 the Catoctin and Swift Run formations, though at certain localities it is well developed within the Unicoi, Harpers, and Antietam formations. All cleavages of the above three categories trend northeast-southwest and dip moderately to steeply to the southeast. In the Piedmont several foliations are developed in the Lynchburg, and Catoctin formations and in the Evington group. As Opposed to the cleavages found in the western side of the anticlinorium, these foliations are true schis- tosity, in that they are defined by parallel alignment Of minerals (especially mica). All trend northeast and dip moderately to steeply to the southeast, and are best developed within the phyllitic and schistose members. According to Espenshade (1954, p. 29-31), there appears to be an Older foliation that parallels the isoclinally folded bedding, and is only rarely Observed cutting the bedding. Several younger foliations intersect this Older s-surface at varying dip angles and trend angles, resulting in a crinkling of the older schistosity surface. Espenshade states that these later s-surfaces might be considered fracture cleavage by some, but he would rather consider them "slip cleavage", since they are quite similar to slip cleavage found in an area in Vermont studied by W. S. White (1949). The Candler Formation shows the above complex relations between the several s-surfaces quite well, while the Lynchburg and Mount Athos formations Show them very poorly or not at all. The gneisses of the basement complex possess a well- develOped foliation, usually defined by mica, especially 45 biotite. This foliation trends northeast and dips steeply to the southeast. Though it parallels the younger foliations and cleavages developed in the overlying strata on both sides Of the anticlinorium, it was developed within the base- ment gneisses in Precambrian time. This is evidenced by the foliation being truncated by overlying beds Of the Lynchburg, Swift Run, Catoctin, and Unicoi formations, as well as by the foliated basement gneiss cobbles contained in the Rockfish Conglomerate (Bloomer and Werner, 1955, and Bloomer, unpublished). This basement foliation has been traced farther to the southwest from this thesis area by Bloomer and Werner (1955, p. 604) and has been found to bear a relationship with isoclinally folded "bedding", in the less "granitized" gneisses, similar to axial plane foliation. Within the Pedlar Formation the foliation is poorly developed, mainly because of the decrease in mica and in- crease in feldspar content. However, a gneissic banding is widely prevalent, which Bloomer (unpublished) attributes to quartz lenticles. It is comprised of moderate to closely spaced layers of round blebs Of blue and milky quartz. R. Allen (1963) has found this same banding farther north- east in the Pedlar of Greene and Madison counties. The writer has also noted this banding in several outcrops of Marshall gneiss and granite, especially where it contains somewhat less mica than usual. The banding does not strike northeast and dip southeast as consistently as does the basement gneiss foliation. In many cases, it strikes east- west or northwest and dips northwest or more commonly 46 southwest. Bloomer's and Warner's shear or thrust cleavage is well-developed in some areas within the large Pedlar mass, along the eastern side of the Blue Ridge. Presumably, these are shear zones. The granitoid Pedlar has been changed by this cleavage development into a schistose rock, appear- ing much like the Marshall gneiss upon casual handspecimen examination. The only important lineations to be found within the lower Cambrian rocks along the western side Of the anti- clinorium are those due to intersection of various s-surfaces, such as bedding and cleavage, and those lineations found in zones of Bloomer's and Warner's thrust cleavage. Those lineations due to intersection of s-surfaces trend parallel tO the regional structure and loosely may be termed linea- tions in Q. Those found along shear surfaces generally trend to the northwest and may be termed lineations in 3. Among the late Precambrian and lower Cambrian strata along the eastern border Of the anticlinorium, only one significant lineation is outstanding. This is the crinkling or crenulation develOped by the intersection of the several foliations mentioned previously. The Candler shows these best; within some single exposures, two outstanding crinkle lineations have been Observed, and at least one lineation exists in every exposure of Candler phyllite visited by this writer. The Lynchburg rarely shows two crinkle directions, but it does frequently Show one. The same may be said con- cerning the Mount Athos Formation. These lineations parallel 1", 47 the regional trend and may be termed lineations in Q. Within the basement complex gneisses, one important lineation has been Observed lying along the foliation sur- faces and trending approximately normal to the regional structure. It is defined by stretched mica, quartz, and feldspar grains. Bloomer and Werner, and Bloomer attribute it to shearing. It has been found in every outcrop of gneiss examined by this writer. As with the thrust cleavage linea- tion in the Blue Ridge, it may be termed a lineation in a. In rare localities within this investigation area, Bloomer (unpublished) has found crinkle b lineations, where apparent remnant bedding remains visible in the altered gneisses. This is apparently more prevalent in the Moneta Gneiss zones. Joints are abundant throughout the entire area Of the anticlinorium. These joint sets trend in varying directions, but in general tend to cut across the regional trend at vary- ing angles toward the northwest. Most dip steeply, but some have a low dip and are most probably due to sheeting effects. Joints appear tO be late mesoscopic structures, but this investigator has found some within the Lovingston Gneiss along which movement must have taken place. These particular joints have a biotite lineation developed along the surfaces, possibly suggesting movement along them during metamorphism or mimetic crystallization. Joints are best developed in the granitic units, such as the Pedlar formation, and least developed in the phyllitic units, such as the Candler forma- tion. TENTATIVE FABRIC ORIENTATIONS INTRODUCTION TO THE INVESTIGATION This study is intended to investigate the nature Of the microscopic fabric. In order to do this, in any valid sense, it is necessary to consider the mesoscopic fabric also. Through the mesoscOpic fabric, the microscopic fabric may be related to that Of the macroscOpic fabric and to the "total" fabric. This premise is based on Bruno Sander's (1930) contention that all fabrics are related, if formed by the same deformation, and all should reflect in their sym- metry the same movement picture derived from the structural deformation of the region, though some fabrics may record more details of the movement than others. This premise is supported by Ernst Cloos (1946), Fairbairn (1949) and Turner and Weiss (1963). Because of certain limitations imposed on this study, especially limitations of time, this investigation must be restricted to considering only certain characteristics of the microscopic and mesoscopic fabric. Because quartz is abun- dant present in all units selected, it was selected for microfabric analysis. However, because mechanisms of quartz orientation under the influence Of deforming forces is ob- scure (H. W. Fairbairn, 1939). mica was also selected for orientation study. Ernst Cloos (1941, p. 56) states the case for utilizing mica, in addition to quartz, in orienta- tion studies: "Quartz maxima cannot always be related 48 49 to obvious field data, and the correlation must be made by means of the mica diagrams . . ." Unfortunately, mica is not everywhere present in formations in the central Blue Ridge region, but was measured where available. The mesoscopic fabric elements to be studied here are bedding, foliation and cleavage, various lineations, and joints. It is believed that these provide the most informa- tion for the least amount of time spent in finding and measuring them. By referring to Plate 1, the reader will be able to find the various sampling localities, and thus be able to understand the sampling procedure and distribution. The field sampling of specimens for microfabric analysis and the measuring of mesoscopic structural elements was carried out according to standard procedures. All statistical orienta- tion data have been plotted in the lower hemisphere on the Schmidt met. In addition, all quartz and mica diagrams are non-selective, in that all quartz, muscovite, biotite, or sericite grains were measured irrespective of size, subtype, or paragenesia. There are certain limitations which prevent this study from being truly statistical. These are: l. The unrepresentative nature Of the field sampling. a) Exposures are not everywhere present, due to deep soil covering. b) Because Of limitations of time and funds, only a relatively small number of samples and field readings were taken. c) Inaccuracies in measurements of strikes, bearings, dips and plunges in the field. 50 These are caused by: (1) Variations in orientation of bedding, cleavage, foliation, lineation, joints, etc., within the single outcrop. (2) Normal limitations in the Brunton compass, and human error. d) Variation in geometric configuration and in aerial extent of one formation as com- pared with others. 2. Inaocuracies and limitations in laboratory procedures include: a) Inaccuracies of orientation developed during rock slabbing. b) Limitations in the accuracy of the universal stage and in the plotting techniques. c) Due to limitations of time, a small number of mineral grains were measured from each slide (approximately 200 quartz optic axis and 100 mica cleavage poles). d) Use of centers of maxima for rotation into cumulative summary geographic diagrams, rather than rotating all points into hori- zontal plan view for each contributing diagram. Much of the following discussion will be related to symmetry of fabric. Here symmetry is meant to be actually a tendency toward a particular symmetry, not true symmetry. True symmetry is realized in crystallography, while in petro- fabrics symmetry is not so well defined. The following discussion will begin with the Antietam quartzite in the western side of the anticlinorium and move eastward, ending with the Mt. Athos quartzite in the eastern- most side. 51 CHILHOWEE GROUP Antietam formation Mesoscopic fabric relations Bedding:cleavagg - Figure 2 is a diagram of 40 poles to bedding and cleavage in the Antietam quartzite plotted in the lower hemisphere of the Schmidt net.v Because the number Of poles is small, the density concentrations were not per- cent contoured. On initial inspection, the most outstanding character- istic of this diagram is the girdle - the approximate symme- try plane Of which lies N51W, 86 SW. Because only one con- ceivable symmetry plane may be passed through this girdle, the symmetry tends toward monoclinicity. The normal to the symmetry plane is tentatively designated b; by definition the fold axis (Sander, 1930). It bears N39°E and plunges 4°NE. Figure 3 shows the ideal statistical planes defined by these three maxima. Essentially, a statistical fold is defined, with two orientations being most prominent: The west limb striking N65°E, 8°NW and the east limb, along with some cleavage, striking N18°E, 24°SE. The girdle and the submaxima indicate other surface orientations of lesser importance in the fold. The greater concentration of points in the northwestern maximum indicates a slight overturning to the northwest. The third and northwesternmost maximum FIGURE 2 FIGURE 3 FIGURE 4 FIGURE 5 FIGURE 6 FIGURE 7 52 Antietam. Diagram of 40 poles to bedding and cleavage. Contours: 5, 4, 3, 2, l, and 0 point zones. Horizontal view. Antietam. Ideal, statistical s-surfaces defined by the maxima of Figure 2. Horizontal view. Antietam. Plot of 40 Oles to bedding and cleavage (heavy points). Refer to Figure 2. Horizontal view. Antietam. Diagram of 103 poles to joints. Contours: 7-4%, 3%, 2%, 1%, and 0%. Horizontal view. Antietam. Ideal, statistical joint sets defined by 3% (weak lines), and 4-7% (strong lines) maxima. Horizontal view. Antietam. Quartz diagram of 235 optic axes. Contours: 4%, 3%, 2%, 1%, and 0%. Diagram attitude: N65W, 90; looking northward. 53 54 indicates that much of the cleavage dips steeply to the southeast, and may be termed an axial plane cleavage. This cleavage strikes N33°E, 83°SE; the remaining cleavage paral- lels the southeastern dipping beds and may be termed bedding plane cleavage. The fold plunges 4°NE. Two important maxima lie along the girdle trend. Both are defined by bedding poles (Figure 4), however, the more northwestern maximum also contains some cleavage poles. The smaller maximum near the northwestern edge Of the diagram, as well as the other minor concentrations along the edge, are solely the result of cleavage poles. Joints - In Figure 5, the statistical orientation of 103 joint poles from the Antietam formation may be seen. Symmetry is not as Obvious here as in the s-surface diagram above. In general, the maxima and submaxima define a hori- zontal girdle. The best possible symmetry plane which may be passed through this girdle strikes Nll°W, 90°. A mirror plane normal to the first one might almost be considered as well as a horizontal mirror plane. However, the possibility of these latter two symmetry plans seems not to be as great as that of the first plane alone. Consequently, the joint fabric symmetry may be considered to have a monoclinic tendency but possesses a lesser orthorhombic tendency. Figure 6 shows the ideal statistical joint sets de- fined by the joint maxima of Figure 3. These statistical joint trends are: A. Joint sets defined by maxima of 4% or greater: 1. n 10E, Boonw 55 2. N 240E, 90° . N 130w, 90° 4. N 370W, 80°NE 5. N 710w, 90° 6. N 88°E, 70°SE B. Joint sets defined by maxima Of 3% 1. N 110E, 56°NW 2. N 55°E, 45°SE 3. N 65°E, 82°SE 4. N 75°E, 56°Nw . N 30°w, 66°Sw 6. N 83°w, 67°NE Four of the six joint sets defined by the high maxima trend in a northerly direction, while four of the six joint sets defined by the three percent maxima trend eastward. Consequently, the stronger joint sets trend more generally northward, while the weaker sets trend more generally east- ward. To summarize, there is a group Of six north trending joints approximately perpendicular to a group of six east trending joints in the Antietam formation. Microscopic fabric relations Scalar fabric aspects - Detrital quartz commonly accounts for about 96 to 99 percent of the rock (Plate 8, Fig. B). The quartz grains generally show pronounced wavy extinction that is quite pronounced. In some grains Boehm lamellae intersect the wavy extinction direction nearly at right angles. Except in shear zones (Plate 8, Fig. C), 56 these features probably are the result of deformation in the parent rock from which the Antietam quartz clasts were derived. The average size of the quartz grains is approxi- mately 0.3 mm. In shear zones, the length Of elongated grains may be as much as 2.3 mm, and the length-width ratio may be as much as 11:1. Silica cements the quartz grains. Metaquartzite fragments are rare. Microcline, orthoclase, and plagio- clase exist in minor quantities, 0.5 to 3 percent, associ- ated with sericite and clay minerals, which account for less than 3 percent of the rock. Epidote, hematite, rutile, tourmaline, and zircon comprise less than 2 percent of the rock. . Vectorial fabric aspects - Figures 7 through 14 show quartz fabric diagrams of Antietam quartzite. The sections from which these diagrams were made were cut perpendicular to the strike of the bedding at each locality. The tendency for the very strong maxima to group within less than 50 degrees of the center of each Of the diagrams (b axis) is quite noticeable, except in Figure 10. Also, these maxima tend to lie nearly in the plane of bedding (81). Figures 7 and 8, being only a little more than two miles apart, show fabrics that are quite similar. Figures 11 and 12, 13 and 14 also show similarities to one another. This indicates that there are probably local domains of fabric homogeneity within the Antietam. Figure 9 may possibly be related to Figures 7 and 8, especially since the sample was taken a little more than a FIGURE 8 - FIGURE 9 - FIGURE 10- FIGURE 11- FIGURE 12- FIGURE 13- Antietam. Contours: attitude: Antietam. Contours: attitude: Antietam. Contours: tude: Antietam. Contours: tude: Antietam. Contours: attitude: Antietam. Contours: attitude: 57 Quartz diagram Of 250 optic axes. 4% 3%, 2%, 1%, and 0%. Diagram N84E, 90; looking northward. Quartz diagram Of 268 Optic axes. 4%, 3%, 2%, 1%, and 0%. Diagram N44W, 90; looking northward. Quartz diagram of 249 Optic axes. 3%, 2%. 1%. and 0%. Diagram atti- N20W, 90; looking northward. Quartz diagram of 259 Optic axes. 3%, 2%, 1%, and 0%. Diagram atti- N67W, 90; looking northward. Quartz diagram of 200 optic axes. 5-4%, 3%, 2%, 1%, and 0%. Diagram N57W, 90; looking northward. Quartz diagram of 250 Optic axes. 4%, 3%, 2%, 1%, and 0%. Diagram N26W, 90; looking northward. 58 59 mile from that of Figure 8. Figure 10 represents a problem in that its fabric appears less oriented and has a different configuration from that of the others. By reference to Plate 1, the reader will notice that a fault has been inferred just to the northwest Of this sample locality by Bloomer and Werner (1955, Plate 1). It is possible that this faulting movement was responsible for erasing or disturbing the pre- existing fabrie orientation of the quartzite (umpragung), causing a fabric of poor orientation. Figure 15 represents a quartz fabric developed within a shear zone near Sherando. In this zone, quartz grains have been elongated in the shear surface (82) and have length-width ratios as great as 11:1. Also, wavy extinction and Boehm lamallae are well develOped and the intersection of both tend to be bisected by the shear surface(82). The quartz fabric is a pronounced girdle around the g or shear lineation lying in 82. It must be assumed that this fabric is the result of shearing the quartzite, when it was in a rather plastic state. The Antietam can be considered an a-tectonite at this locality. Robert Balk (1952), Anders Kvale (1945), and Trygve Strand (1944) have found similar bc-girdles developed within shear zones in quartzites of the Taconic mountains of New York and in the Caledonian mountains of Norway, respectively. Fifty one centers-of—gravity of 4 percent maxima and 3 percent maxima from each quartz diagram, with the excep- tion of Figure 15, were rotated into the horizontal and then contoured. The resulting cumulative-summary, plan view 60 FIGURE 14 - Antietam. Quartz diagram of 200 optic axes. Contours: 5-4%, 3%, 2%, 1%, and 0%. Diagram attitude: N57W, 90; looking northward. FIGURE 15 - Antietam (shear zone). Quartz diagram of 200 Optic axes. Contours: 7-4%, 3%, 2%, 1%, and 0%. Diagram attitude: N26W, 90; looking northward. FIGURE 16 - Antietam. Quartz optic axis maxima, cumula- tive-summary diagram. Fifty one maxima centers. Contours: lO-6%, 4%, 2%, and 0%. Horizontal view. 62 diagram is represented in Figure 16. Centers of four (or greater) and three percent maxima were chosen for rotation in the analysis of this formation and of the others for two reasons. The first is that they represent the significant concentration of quartz optic axes. Secondly, it is much quicker and more feasible to rotate and contour, for example, 51 to 80 centers than to rotate and contour 1600 quartz axes for a single cumulative- summary diagram. In geographic view, the quartz optic axis maxima tend to develOp a horizontal girdle or one dipping a few degrees to the northwest. One symmetry plane seems to be conceivable here. This mirror plane strikes N47W, 90°; the microfabric b axis, normal to the mirror plane, bears N43°E, 40°NE. The b_of the quartz fabric has a bearing 4° farther east than §_of the bedding and cleavage. Both axes have the same northeastward plunge. The quartz fabric may be considered to possess a monoclinic symmetry tendency. ggrpers formation Mesoscopic fabric orientations Bedding - cleavage - Figure 17 represents the con- toured diagram Of 38 poles to bedding and cleavage in the Harpers formation. As in the Antietam formation, the diagram was not percent contoured due to the low number Of poles plotted. Similar to the s-surface diagram of the Antietam FIGURE 17 FIGURE 18 FIGURE 19 FIGURE 20 FIGURE 21 FIGURE 22A- 63 Harpers. Diagram of 38 poles to bedding and cleavage. Contours: 6, 5, 4, 3, 2, l and 0 point zones. Horizontal view. Harpers. Ideal, statistical s-surfaces defined by the maxima of Figure 17. Horizontal view. Harpers. Plot of 38 poles to bedding and cleavage (heavy points). Refer to Figure 17. Horizontal view. Harpers. Diagram of 101 poles to joints. Contours: 8-4%, 3%, 2%, 1%, and 0%. Hori- zontal view. Harpers. Ideal, statistical joint sets defined by 3% (weak lines), and 4-8% strong lines) maxima. Horizontal view. Harpers. Quartz diagram of 215 optic axes. Contours: 6-4%, 3%. 2%, 1%, and 0%. Diagram attitude: N52W, 90; looking northward. Figure 19 64 65 formation, the most outstanding characteristic of this diagram is the vertical girdle. The best conceivable symmetry plane strikes N40W and dips 865W; the pole normal to this plane, the b axis, bears N50E, 4NE. The symmetry is monoclinic. The asymmetry of the girdle toward the northwest suggests a statistical fold overturned to the northwest. The two most outstanding maxima define two ideal planes dipping to the southeast (Figure 18). From Figure 19 it is to be noted that cleavage is mainly responsible for the northwesternmost maximum, while bedding is responsible for most Of the other maxima and for the girdle. Since the cleavage (82) lies so closely to the bedding (81), it may be designated bedding-plane cleavage. Axial plane cleavage, unlike the case of the Antietam, is not so evident here. Joints - The poles to 101 joints are represented by the statistical diagram in Figure 20. A horizontal girdle is the most obvious characteristic of this diagram. If symmetry planes may be passed through any part of this girdle, the writer suggests one N300W, 90. The difficulty of reflecting the larger maximum ()>4%) in the northwestern edge of the diagram immediately across to the smaller maximum (2%) is obvious. However, by referring to Figure 21, in which the ideal statistical joint sets defined by the various maxima of Figure 21 are represented, the reader will note that this symmetry plane of N3OW, 90 appears more credible now. As in the case of the Antietam joint diagram, an 66 argument may be made for an orthorhombic symmetry tendency. If this is valid, a symmetry plane of N6OE, 90 and one hori- zontal would be possible. However, the maxima in the south- eastern portion Of the diagram are closer to the edge than those in the northwestern portion. In addition there are three southeastern maxima and only two northwestern ones. However, by again referring to Figure 21, these Objections seem less important. In summary, the joint fabric of the Harpers formation may be either orthorhombic or monoclinic, with the latter being the more likely possibility. The statistical joint set trends as illustrated in Figure 21 are: A. Joint sets defined by maxima of 4% or greater : 1. N40E, 67SE 2. N2W, 878W 3. N2W, 70NW 4. N18W, 868W 5. N42W, 808W 6. N57W, 84NE B. Joint sets defined by maxima of 3%: l. N64E, BONE 2. N8W, 523W 3. N44W, 76NE 4. N88W, 82NE Five of the six joints defined by the high maxima trend in a northwesterly direction. Only two of the four joint sets defined by the three percent maxima trend in a 67 definite northwesterly direction; one set is almost east- west. Most joint sets then trend northwest-southeast, es- pecially the stronger ones. Microscgpic fabric relations Scalar fabric aspect - Detrital quartz (original grains) forms 40 to 60 percent of the rock and has a size range of 0.7 mm to 0.1 mm (Plate 8, Fig. A). Undulose ex- tinction is common to most quartz grains, and Boehm lamellae are present in scattered occurrences. Because the extent of penetrative deformation is not intense within this for- mation, it is unlikely that the wavy extinction and Boehm lamellae were develOped after deposition and are presumed to be Older than the Harpers formation. Recrystallized quartz may be observed in some sections, but its role is only of minor importance. Most Harpers samples were col- lected from the subgraywacke units. Mica comprises from 3 to 20 percent of the rock; fine grained, freshly crystallized muscovite and detrital- diagenetic sericite are nearly equally represented. The size range for muscovite is 0.4 to 0.05 mm, for sericite it is 0.2 to 0.02 mm. Orthoclase, microcline, and plagioclase form between 5 to 20 percent Of the rock. Metaquartzite clasts are scarce, and limonite and hematite comprise about 10 percent of the rock in some specimens. Other minerals present in the Harpers formation are epidote, tourmaline, zircon, rutile, and ilmenite. Bedding lamination is the most persistent and common 68 s-surface observed in thin section. However, in some speci- mens, an s-surface intersects the bedding surface at a rather high angle. In such specimens, quartz grains tend to line up with their longest dimensions in the plane of this a- surface. Some mica conforms to and emphasizes the s-surface. Vectorial fabric aspect - The quartz and mica diagrams of the Harpers formation are represented in Figures 22 through 35. All were prepared from slides out normal to the strike of the specimen, as discussed in the previous section on the Antietam fabric. Very little significance may be attributed to the quartz diagrams individually. The diagrams from the Harpers of the vesuvius quadrangle (Figures 22A, 25A, 24, 25A and 26) generally have a high concentration of maxima within 50 degrees of the center of the diagram, tentatively b. To a degree, the diagrams are somewhat similar to those of the Antietam similarly situated along strike. The strong quartz fabric maxima of the Harpers in the Lovingston quadrangle are less concentrated and suggest girdles trending from the lower right hand edge toward the upper left hand edge (Figures 27A, 28A, 29A). Figure 30 represents a cumulative-summary master dia- gram, in geographic view, prepared by the methods outlined in the previous section, for centers of 95 optic axis maxima from the Harpers quartz diagrams. Figure 31 was prepared in a similar manner from the centers of 27 important maxima from the mica diagrams. The quartz optic axis maxima show a horizontal girdle 69 FIGURE 22B - Harpers. Muscovite-sericite diagram of 98 FIGURE 23 FIGURE 24 FIGURE 25 cleavage poles. Contours: 9-7%. 4-3%, 2-1%, and 0%. Diagram attitude: N52W, 90; looking northward. Harpers. (A) Quartz dia ram Of 180 optic axes. Contours: 5-4%, 3 , 2%, 1%, and 0%. (B) Muscovite-sericite dia ram of 108 cleav- age poles. Contours: 10-8 , 7-6%, 5-4%, 3-2%, 1%, and 0%. Diagram attitudes: N47W, 90; looking northward. Harpers. Quartz diagram of 179 optic axes. Contours: 5-4%, 3%, 2%, 1%, and 0%. Diagram attitude: NllW, 90; looking northward. Harpers. (A) Quartz diagram of 166 Optic axes. Contours: 4%, 3%, 2%, 1%, and 0%. (B) Muscovite-sericite diagram of 115 cleav- age poles. Contours: l6-ll%, lO-9%. 8-7%, 6-5%, 4-3%, 2%, 1%, and 0%. Diagram attitudes: N10E, 90; looking northward. '70 FIGURE 26 - FIGURE 27 - FIGURE 28 - FIGURE 29A - 71 Harpers. Quartz diagram Of 216 optic axes. Contours: 5-4%, 3%, 2%, 1%, and 0%. Diagram attitude; N58W, 90; looking northward. Harpers. (A) Quartz diagram of 200 optic axes. Contours: 4%, 3%, 2%, 1%, and 0%. (B) Sericite diagram of 100 cleavage poles. Contours: 11-10%, 9-7%, 6-3%, 2-1%, and 0%. Diagram attitudes: N59W, 90; looking north- ward. Harpers. (A) Quartz diagram of 200 Optic axes. Contours: 5-4%, 3%, 2%, 1%, and 0%. (B) Sericite diagram of 100 cleavage poles. Contours: 34-10%, 9-8%, 7-3%, 2-1%, and 0%. Diagram attitudes: N65W, 90; looking north- ward. Harpers. Quartz diagram of 195 optic axes. Contours: 5-4%, 3%, 2%, 1%, and 0%. Diagram attitude: N47W, 90; looking northward. 73 FIGURE 29B - Harpers. Muscovite-sericite diagram of 102 cleavage poles. Contours: 22-l4%, l3-ll%, 10-8%, 7-5%, 4-2%, 1%, and 0%. Diagram atti- tude: N47W, 90; looking northward. FIGURE 30 - Harpers. Quartz Optic axis maxima, cumulative- summary diagram of 95 maxima centers. Contours: 6-4%, 3%, 2%, 1%, and 0%. Horizontal view. FIGURE 31 - Harpers. Mica cleavage pole maxima, cumulative- summary diagram of 28 maxima centers. Contours: 3, 2, 1, and 0 point zones. Horizontal view. FIGURE 32 - Harpers. Ideal, statistical s-surfaces defined by maxima of Figure 31. Horizontal view. 74 75 tendency. In this respect it is similar to that of the Antietam quartz fabric. A Monoclinic symmetry tendency is more pronounced here than in the Antietam quartz fabric. The single symmetry plane strikes N50W, 90°. The tendency toward girdle development is pronounced in the mica fabrics. According to F. J. Turner's classifi- cation of mica fabrics (1948, pp. 272-273) these may be classified as B-tectonites (movement along two or more 3- surfaces as indicated by two or more sets of strong maxima) except the mica fabrics of the two extreme northeastern localities in the Lovingston quadrangle (Figures 28B and 29B) These must be considered S-tectonites probably (those fabrics having only one active s-surface Of deformation, as indicated by one strong set of maxima). However, even these show the girdle tendency and are not pure S-tectonites. Bedding appears to be an important surface along which the mica tends to be oriented as in the cases Of Figures 23B, 24B and 29B, the latter two diagrams having the S-tectonite mica fabric. In the other diagrams, bedding appears not to be the important surface of mica orientation, but one or more other surfaces inclined at various angles to bedding appear to be significant. The mica master diagram (Figure 32) shows one definite vertical girdle and probably another less definitely defined. The former trends N52W, 883W, while the latter trends New,' BONE. The symmetry is triclinic. The two high maxima lying in the well-defined girdle 76 express ideal statistical planes shown in Figure 32. Both mica s-surfaces correlate more closely with the bedding sur- faces than with those of cleavage (see Figure 18) contrary to the conclusion made. The line of intersection of these two mica s-surfaces, the mica fabric b_axis, bears N33E, 1 NE, while the 2 defined by bedding and foliation poles bears N50E, 4NE. Unicoi Formation MesoscOpic fabric orientations Bedding-cleavage - The configuration of poles to bedding and cleavage surfaces within the Uhicoi Formation is represented in Figure 33. Since the number of poles exceeds fifty, the diagram is percent contoured and not point con- toured as in the case of the Antietam and Harpers formations. Similar to the bedding-cleavage (s-surface) fabrics of the two previously discussed formations, the s-surface fabric here is a vertical girdle. The most probable symmetry plane strikes raw and dips 86°sw. The fold axis or 2, nor- mal to the girdle symmetry plane, bears N57E, hNE. Here again, as in the two previous formations, the asymmetry of the girdle toward the northwest suggests a statistical fold overturned to the northwest. Seven strong maxima (3 percent or greater) define seven outstanding statistical surfaces. These are illus- trated in Figure 34. Five dip to the southeast, while two FIGURE FIGURE FIGURE FIGURE FIGURE FIGURE 33 34 35 36 37 38 77 Unicoi. Diagrams of 57 poles to bedding and cleavage. Contours: 5, 4, 3. 2, l, and 0 point zones. Horizontal view. Unicoi. Ideal, statistical s—surfaces defined by the maxima of Figures 33. Horizontal view. Unicoi. Plot of 57 poles to bedding and cleavage (heavy points). Refer to Figure 33. Unicoi. Diagram of 118 poles to Joints. Con- tours: 7-4%, 3%, 2%, 1%, and 0%. Horizontal view. Unicoi. Ideal, statistical Joint sets defined by 3% (weak lines), and 4-7% (heavy lines) maxima. Horizontal view. Unicoi. Quartz diagram of 200 optic axes. Contours: 4%, 3%, 2%, 1%, and 0%. Diagram attitude: N2E, 90; looking northward. '78 79 dip northward; all strike northeast. These surfaces are: N17E, 28SE N39E, SOSE (entirely cleavage) N50E, 603E N66E, 705E (entirely bedding) N68E, 185E (two thirds cleavage) NYOW, 12NE N64E, 32NW Figure 35 shows a breakdown of the distribution of cleavage and bedding. Cleavage poles are nearly as scattered over the diagram as the bedding poles. However, the north- western maximum normal to the ideal s-surface of N39E, 505E and the northcentral maximum normal to the ideal s-surface of N68E, 185E are entirely and almost entirely the result of cleavage, respectively. Only the maximum normal to the plane N66E, 708E is entirely the result of bedding. Cleav- age appears to manifest itself both as bedding-plane and axial plane varieties. Joints - Figure 36 represents the diagram of 118 poles to Joints from the Unicoi Formation. The horizontal girdle present in the Joint pole diagrams of the Antietam and Harpers formations is present here to a lesser degree. The most feasible symmetry plane that may be passed through this girdle strikes N25W, 90°. Reference to the ideal statistical Joint sets (Figure 37) defined by the various maxima of Figure 36 supports this. However, as in the case of the previous two formations, there is also a lesser orthohombic tendency here. Two addi- J‘. 4“. IL 4‘ 80 tional symmetry planes might be possible, a vertical one of N65E, 90° and a horizontal one. The statistical Joint trends for the Harpers formation from Figure 37 are: A. Joint sets defined by maxima of #1 or greater: 1. N12E, 90° 2. N13W, 82NE 3. N18w, 875w 4. N33W, 83NE B. Joint sets defined by maxima of 3%: 1. N56E, 688E 2. N38E, 76NW 3. N29W, 42NE 4. N71W, 868W The more strongly defined Joint sets trend in a more northerly direction than do the Joint sets defined by 3% maxima. Only one weak Joint set strikes in a very northward direction. Microscopic fabric relations §9a1ar fabriciaspects - Detrital or original quartz grains account for about 50 percent of the rock (Plate 7, Fig. 0). The quartz grains usually are distorted, show wavy extinction, and are fractured considerably. In some sections, the grains are elongated subparallel to the plane of the s-surface visible in these slides. Generally, they are not elongated but equant. The grain size varies between 0.1 mm and 1.0 mm. 81 Recrystallized quartz takes the form of tiny, unde- formed grains. In some sections this type of quartz forms stringers, or rods, which cut across feldspar grains and extend into the groundmass. Also, this recrystallized quartz has been noted around the boundaries of the original quartz grains. Inclusion trains crossing grain boundaries may also be seen in some sections. Sericite in some specimens accounts for about 30 percent of the rock: grains vary between .02 mm and 1.0 mm in length. Muscovite is also important in some sections; grains vary between .02 mm and 1.8 mm. Epidote accounts for about 5 percent of the rock. Chlorite, biotite, limo- nite and clay minerals exist in minor amounts. Feldspar occurs as sericitized grains, in most thin- sections examined, and comprises from 10 to 40 percent of the rock. Orthoclase, microcline and plagioclase are present, along with microperthite, or microantiperthite. Vectorial fabric aspects - Figures 38 through 51 represent quartz and mica diagrams, of the Uhicoi Formation. In the quartz diagrams, most of the strongest maxima tend to lie within 50 degrees of the b_axis of each diagram. In every diagram, at least one strong maximum lies in or near the bedding surface (31). Most diagrams have a similar general appearance, perhaps indicating a characteristic similarity of quartz fabric from location to location within this formation. As with the prior two units, little attempt will be made here to give a critical evaluation of the 82 FIGURE 39 - Unicoi. (A) uartz diagram of 204 optic axes. FIGURE 40 - Contours: 5-4 , 3%, 2%, 1%, and 0%. (B) Muscovite- sericite diagram of 103 cleavage poles. Contours: 15-12%, 11'10%9 9-8%! 7'61! 5' %9 3-1%: and 0%. Diagram attitudes: N28W, 90; looking northward. Unicoi. (A) uartz diagram of 205 Optic axes. Contours: 5-4 , 3%, 2%, 1%, and 0%. (B) Muscovite-sericite diagram of 100 cleavage poles. Countours: 16-12%, ll-lo%. 9-8%. 7-6%. 5-4%. 3-1%, and 0%. Diagram attitudes: N39w, 90; looking northward. FIGURE 41 - Uhicoi. (A) uartz diagram of 195 Optic axes. Contours: 5-4 , 3%, 2%, 1%, and 0%. (B) Muscovite-sericite diagram of 96 poles to clea- vage. Contours: 24-19%, 18-16%, 15-13%, l2-10%, 9-7%, 6-4%, 3-11, and 0%. Diagram attitudes: NSOW, 90; looking northward. FIGURE 42 - FIGURE 43 - FIGURE 44 - 84 Unicoi. (A) Quartz diagram of 200 optic axes. Contours: 4%, 3%, 2%, 1%, and 0%. (B) Seri- cite diagram of 100 cleavage poles. Contours: 14-10%, 9-7%, 6-3%. 2-1%, and 0%. Diagram atti- tudes: N47W, 90; looking northward. Unicoi. (A) uartz diagram of 218 optic axes. Contours: 5-4 , 3%, 2%, 1%, and 0%. (B) Mus- covite-sericite diagram of 101 cleavage poles. Contours: 11-9%. 8-7%. 6-5%. 4-3%, 2-11, and 0%.d Diagram attitudes: N6W, 90; looking north- war . Unicoi. (A) Quartz dia ram of 200 optic axes. Contours: 4%, 3%, 2%, l , and 0%. (B) Sericite diagram of 100 poles to cleavage. Contours: 23%-lg%. 9%. 8%. 7%. 6%. 5%. 4%. 3%. 2%. 1%. and 0 . Diagram attitudes: N22W, 90; looking northward. 85 FIGURE 45 FIGURE 46 FIGURE 47 FIGURE 48 FIGURE 49A 86 Unicoi. Quartz diagram of 220 optic axes. Contours: 4%, 3%, 2%, 1%, and 0%. Diagram attitude: NSW, 90: looking northward. Unicoi. Quartz diagram of 51 optic axes (quartz- poor rock). Contours: 8-6%, 4%, 3%, 2%, 1%, and 0%. Diagram attitude: N40W, 90; looking northward. Unicoi. (A) Quartz diagram of 200 optic axes. Contours: 4%, 3%, 2%, 1%, and 0%. (B) Seri- cite diagram of 100 cleavage poles. Contours: 9-8%, 7-5%, 4-3%, 1%, and 0%. Diagram atti- tudes: N48E, 90; looking northward. Unicoi. Quartz diagram of 172 Optic axes. Contours: 4%, 3%, 2%, 1%, and 0%. Diagram attitude: N39W, 90; looking northward. Unicoi. Quartz diagram of 200 optic axes. Contours: 5-4%, 3%, 2%, 1%, and 0%. Diagram attitudes: N4OW, 90; looking northward. 87 88 individual quartz diagrams. Figure 52 is the horizontal, cumulative-summary dia- gram of 167 centers-of-gravity of quartz optic axis maxima from the above listed Unicoi diagrams. As in the Antietam and Harpers formations, a certain symmetry tendency is sug- gested. The best possible symmetry plane strikes N36W, 90°. The fabric is pronounced in its monoclinic symmetry tendency. The horizontal girdle tendency is less pronounced here than in the quartz fabric of the previously discussed formations. The greatest maxima congregate about the northeast and south- west edges of the diagram. The individual mica fabric diagrams show a peripheral girdle tendency. All may be classified as B-tectonite types, except those of Figures 41B, and 44B. These may be better classified as S-tectonites. Again, as in the case of the Harpers mica fabric, bedding surfaces tend to exert the most significant orienting influence in the S-tectonites. The B-tectonite maxima in- dicate little or no relationship to bedding generally, but appear to be influenced by one or several s-surfaces inter- secting the bedding at various angles. Figure 53 is the horizontal, cumulative-summary diagram of the centers-of—gravity of 33 mica maxima from the diagrams shown in this chapter. Due to the low number of points, the diagram was not percent contoured. A partial vertical girdle is evidenced here, but is less well-defined than that of the Harpers formation. Its orientation is 89 FIGURE 49B - Unicoi. Sericite diagram of 100 cleavage poles. FIGURE 50 Contours: 34-10%, 9-71, 6-3%, 2-11, and 0%. Diagram attitude: N4OW, 90; looking northward. - Unicoi. Quartz diagram of 200 optic axes. Contours: 5-4%, 3%, 2%, 1%, and 0%. Diagram attitude: N81W, 90; looking northward. FIGURE 51 - Unicoi. (A) uartz diagram of 249 optic axes. FIGURE 52 - Contours: 5-4 , 3%, 2%, 1%, and 0%. (B) Muscovite-Sericite diagram of 100 cleavage poles. Contours: l6-1l%, 10-9%. 8-7%, 6-5%. 4-3%, 2-1%, and 0%. Diagram attitudes: N84W, 90; looking northward. Unicoi. Quartz optic axis maxima, cumulative- summary diagram of 167 maxima centers. Con- tours: 3.2%, 2.5%: 1.7%: 0.8%, and 0%. Hori- zontal view. 90 91 FIGURE 53 - Unicoi. Mica cleavage pole maxima, cumulative- summary diagram of 33 centers. Contours: 5, 4,3,2,1, and 0 point zones. Horizontal view. FIGURE 54 - Unicoi. Ideal, statistical s-surfaces defined by maxima of Figure 53. Horizontal view. 92 93 N52W, 863W, defining the quartz subfabric b axis of N37E, 4NE. Three important maxima exist here. The two central ones define two nearly flat-lying ideal statistical planes, as illustrated in Figure 54. The southeast dipping surface (N71E, 148E ) may be associated more with cleavage than with bedding, because it most nearly parallels the surface N68E, 185E of Figure 34 which is 66.7 percent influenced by cleav- age (probably of the bedding-plane type). The other gently dipping surface (N77E, SNW) most nearly parallels the ideal s-surface N7OW, 12NE of Figure 34, and like this surface, is most probably strongly influenced by bedding. The remaining maximum, near the northwestern edge of the diagram is Figure 53, defines the remaining steeply dipping plane (N34E, 748E) in Figure 54. This surface may be due to cleavage of the axial plane variety, since it most closely parallels the axial plane cleavage surface N39E, 505E of Figure 36. UPPER PRECAMBRIAN OR LOWER CAMBRIAN (WEST LIMB) Swift Run Formation Mesoscopic fabric relations S-surfaces - Due to the small number of s-surfaces available for measurement, the s-surface data for the Swift Run Formation (Figure 55) have not been contoured. More caution must be used in interpreting these particular data FIGURE 55 FIGURE 56 FIGURE 57 FIGURE 58 FIGURE 59 94 Swift Run. Plot of ten poles to bedding and folia- tion. Horizontal view. Swift Run. Plot of eight lineations (mineral stretching). Horizontal view. Swift Run. Diagram of 22 poles to Joints. Contours: 3, 2, 1, and 0 point zones. Hori- zontal view. Swift Run. Ideal, statistical Joint sets de- fined by maxima of Figure 57. Horizontal view. Swift Run. (A) Quartz dia ram of 200 optic axes. Contours: 6-4%, 3%,.2fl, 1 , and 0%. (B) Seri- cite diagram of 100 cleavage poles. Contours: ll-8%, 7-6%, 5-3%, 2-1%, and 0%. Diagram atti- tudes: Nllw, 90; looking northward. 95 96 than that of the Chilhowee Group. However, certain tenta- tive statements may be made concerning the fabric of this formation. ' The plane NSOH, 900 appears to define the trend of these plotted data best. The normal to this plane (the 2- axis) bears N40E, OONE. Eight of the ten poles lie in the northwestern portion of the diagram and, providing this sampling is valid, indicate a predominance of southeastern dipping s-surfaces. The foliation generally parallels bed- ding in these ten outcrops available for study. The symmetry tendency is monoclinic. Lineation - Figure 56 represents eight lineations from the Swift Run Formation. The lineations are concentrated within the southeastern portion of the diagram and lie along the foliation surfaces represented in Figure 57. These structures tentatively lie in the direction of the a fabric axis. The direction best representing the trend of these data has a bearing of NSSW, and is plunging to the southeast. Joints - Twenty two poles of Joints in the Swift Run are represented in the contoured diagram of Figure 58. These data were not percentage contoured because of their small number. Important concentrations occur in the north- east and southwest regions of the diagram. A symmetry plane striking N32W, 788W is conceivable. The symmetry shows a monoclinic tendency. Figure 58 illustrates two strong and three lesser, ideal statistical Joint sets: 97 A. Joint sets defined by maxima of 3 poles: l. N28W, 64SW 2. N42W, 765W B. Joint sets defined by maxima of 2 poles: l. N33W, 74NE 2. N39W, 503w 3. NSOW, 478W All Joint sets trend northwest, and all but one set dip to the southwest. Microscopic fabric relations §ga1ar fabric aspects - Detrital or original quartz grains-comprise between 10 and 20 percent of the rock in the thin sections studied (Plate 7, Fig. B). These quartz grains are generally elongated in the direction of the prevailing s-surface. Undulose extinction and fracturing are evident. These grains range in size from .01 cm to 0.5 cm, for the maximum dimension. Peripheral or recrystallized quartz is also present. It accounts for 5 to 20 percent of the rock. -The size averages approximately .05 cm. These grains occur around the periphery of the larger original grains and are smeared out into the foliation surface. undulose extinction is not very pronounced. Sericite is the prevalent mica. It accounts for between 20 and 70 percent of the rock. The average grain size is about 0.05 cm. Sericite generally appears in thin 98 section to lie in or near, and to emphasize, the prevailing s-surface. Feldspar occurs as small elongated and fractured grains and as larger grains containing rounded quartz blebs. The size range for the feldspar is approximately between .01 cm and 0.5 cm. Feldspar accounts for about 5 to 40 per- cent of the rock. Egctorial fabric aspects - Figures 59A, 60A, and 62A represent orientation diagrams of quartz optic axis cut from speciments having a noticeable lineation. As shown in Figure 57, this lineation is down-dip and lies in 5. Host 4% (or greater) maxima lie within 40° of the center of the diagram 3 axis. Figure 62A is from a specimen without linea- tion, hence it was cut normal to the strike of the foliation. Three of its four 4% (or greater) maxima lie within 40° of the center of the diagram (tentatively the b axis). In all four diagrams one high maximum lies in, or close to, the foliation surface. In the horizontal cumulative-summary diagram of quartz maxima centers (Figure 63) there is a weak tendency toward monoclinic symmetry. The best possible mirror plane has an attitude of N40H, 90°. The maxima in the northeastern half of the net are better developed than those of the southwest- ern half. However, the strong northeastern maxima are most probably weakly reflected by the weaker southeastern maxima. A northwest trending girdle tendency also is present. It is definitely a single girdle up to the position of the strong maximum near the center of the diagram. From there 99 FIGURE 60 - Swift Run. (A) Quartz diagram of 200 optic axes. Contours: 5—4%, 3%, 2%, 1%, and 0%. (B) Sericite diagram of 100 cleavage poles. Contours: 22-10%, 9-7%, 6-3%, 2-1%, and 0%. Diagram attitudes: NlOW, 90: looking northward. FIGURE 61 - Swift Run. (A) Quartz diagram of 200 optic axes. Contours: 6-4%, 3%, 2%, 1%, and 0%. (B) Seri- cite diagram of 100 cleavage poles. Contours: 30-10%, 9-7%, 6-3%. 2-1%, and 0%. Diagram attitudes: N82w, 90; looking northward. FIGURE 62 - Swift Run. (A) Quartz diagram of 200 optic axes. Contours: 5-4%, 3%, 2%, 1%, and 0%. (B) Sericite diagram of 100 cleavage poles. Contours: lS-8%. 7-4%. 3-l%, and 0%. Diagram attitudes: N28E. 57NW: looking northward. 100 101 FIGURE 63 - Swift Run. Quartz optic axis maxima, cumulative- summary dia ram of 56 maxima centers. Contours: 6-4%, 3%, 2 , 1%, and 0%. Horizontal view. FIGURE 64 - Swift Run. Mica cleavage pole maxima, cumulative- summary diagram of 18 centers. Contours: 3, 2, 1, and 0 point zones. Horizontal view. FIGURE 65 - Swift Run. Ideal, statistical s-surfaces de- fined by maxima of Figure 64. Horizontal view. 102 103 it bifurcates. If symmetry may be assumed here, it must be monoclinic. The mica diagrams which accompany these quartz dia- grams, (Figures 59B through 62B) show a strong tendency toward peripheral girdle development. In the case where shearing has been pronounced, with the resulting development of linea- tion in g, the girdles lie in a plane normal to this lineation. In Figure 63B, where shearing was not intense enough to devel- op a lineation, a mica girdle appears to be develOped normal to the strike of the foliation. Typically, the mica cumulative-summary diagram shows a better defined fabric than that of the corresponding quartz cumulative-summary diagram. The mica fabric is a girdle, the symmetry plane of which strikes and dips NllW, 883w, with a b axis orientation of N80E, 2NE. This trend is seen to be more northward than the trends of the other Swift Run subfabrics. The strongest concentrations of mica maxima centers lie in the two supermaxima in the northern edge of the diagram. Figure 65 represents the ideal statistical s- surfaces defined by these two maxima. The attitudes of these two surfaces are: N78E, 688E, and N78E, 78E. BASEMENT COMPLEX Pedlar Formation Mesoscopic fabric relations Gneissic banding - In almost every exposure of the 104 Pedlar formation examined in this study, a gneissic banding or layering of quartz lenticles was observed. One hundred poles to these s-surfaces appear in the diagram of Figure 66. Four strong maxima are present, two being stronger than the others. The lesser pole concentrations in the diagram tend to form a horizontal girdle. Figure 67 represents the ideal statistical s-surfaces determined by important concentrations of these poles. The strongest maximum of Figure 67 defines a plane N49E, 695W. The second strongest maximum defines a plane N81W, 698W. The first s-surface is Appalachian in trend, while the latter one is non-Appalachian. The remaining two maxima define s- surfaces of lesser importance: N68E, 438E, and N79E, 878E. These follow the regional trend. Joints - Joints are well-develOped in the Pedlar formation, perhaps better develOped than in any rock unit within the area. Figure 68 is the diagram of poles to 168 Joint surfaces in the Pedlar formation. Symmetry is fairly conceivable here, with a symmetry plane trending N4OW, 90°. There is a definite asymmetry toward the northwest, which indicates that this fabric has a monoclinic tendency. Figure 69 illustrates the attitude of the ideal stratistical Joint sets, as defined by the maxima of Figure 69. These are: A. Joint sets defined by maxima of 4% or greater: 1. N14W, 66NE 2. N23W, 90° FIGURE 66 FIGURE 67 FIGURE 68 FIGURE 69 FIGURE 70 FIGURE 71 105 Pedlar. Diagram of 100 poles to gneissic band- ing. Contours: 8-4%, 3%, 2%, 1%, and 0%. Horizontal view. Pedlar. Ideal, statistical s-surfaces defined by the 4-8% maxima of Figure 66., Horizontal view. Pedlar. Diagram of 168 poles to Joints. Con- tours: 6-4%, 3%, 2%, 1%, and 0%. Horizontal view. Pedlar. Ideal, statistical Joint surfaces de- fined by 3% (weak lines), and 4-6% (strong lines) maxima. Horizontal view. Pedlar. Quartz diagram of 200 optic axes. Con- tours: 5-4%, 3%, 2%, 1%, and 0%. Diagram atti- tude: N14W, BNE; looking northward. Pedlar. Quartz dia ram of 200 optic axes. Con- tours: 6-4%, 3%, 2 , 1%, and 0%. Diagram atti- tude: N84E, 88E; looking northward. 106 figure 70 107 3. N35W, 44NE 4. N40W, 70NE 5. N47w. 90° 6. N74W, 523W B. Joint sets defined by maxima of 3%: l. N68E, 79NW 2. N42E, 575E 3. N38E, 848E 4. N6W, 42NE. All strongly defined statistical Joint sets trend northwestward across the regional strike. The weaker Joint sets, save one, trend toward the northeast and parallel the regional trend. Numerically, more Joint sets trend north- west, and of this group, only one set dips to the southwest. Microscopic fabric relations Scalar fabric aspects - The maJority of the quartz grains, large or small, are rounded (Plate 6, Fig. 0). These blebs give the appearance of having been replaced, primarily by plagioclase. Supporting this is the fact that many neighboring blebs, within feldspar crystals, be- come extinct at almost the same angle under crossed nicols. The larger grains are commonly distorted and frac- tured, while the smaller grains are commonly undistorted. The size range varies between .001 cm to 0.5 cm; quartz accounts for between 20 to 40% of the rock. Sericite is the only mica present. However, it 108 accounts for only five percent or less of the mineral compo- sition, as determined by thay analysis of those specimens not from shear zones. Generally, it appears to have devel- oped from the alteration of the plagioclase. It is of great- er importance in the samples taken from shear zones. Feldspar usually occurs as large grains that are fractured or cleaved and are sericitized. Also significant are the inclusions of quartz blebs mentioned above. The grain size varies between .05 cm and 1.0 cm. in the thin sections examined. Feldspar accounts for between 30 to 70 percent of the minerals present. Pyroxene is present sporadically as hypersthene and diOpside. It varies in size from .05 cm to 0.5 cm, for the maximum dimensions, and it accounts for between zero and ten percent of the rock. No obvious dimensional alignment of minerals can be seen in thin section. This is probably due to the coarse texture of the rock. Vectorial fabricgaspect - The quartz diagrams of Figures 70 through 76 represent the fabric of typical Pedlar Formation samples. Besides Jointing, the most persistent feature observed in exposures is the gneissic banding men— tioned previously. These diagrams were prepared from sec- tions cut normal to the plane of this banding, but parallel to the strike of the banding. Absence or insignificance of mica prevented the preparation of mica diagrams. Most of the important quartz optic axis maxima lie FIGURE 72 FIGURE 73 FIGURE 74 FIGURE 75 FIGURE 76 FIGURE 77 109 Pedlar. Quartz dia ram of 197 optic axes. tours: 9-4%, 3%, 2 , 1%, and 0%. Diagram tude: N2E, 98E: looking northward. Pedlar. Quartz dia ram of 200 optic axes. tours: 5-4%, 3%, 2 , 1%, and 0%. Diagram tude: N64E, 56NW; looking northward. Pedlar. Quartz diagram of 200 optic axes. tours: 5-4%, 3%, 2%, 1%, and 0%. Diagram tude: N3E, 20NE: looking northward. Pedlar. Quartz dia ram of 182 optic axes. tours: 9-4%, 3%, 2 , 1%, and 0%. Diagram tude: N37E, 7NW; looking northward. Pedlar. Quartz diagram of 200 optic axes. tours: 5-4%, 3%, 2%, 1%, and 0%. Diagram tude: NSBE, 71NW; looking northward. Con- atti- Con- atti- Con- atti- Con- atti- Con- atti- Pedlar (shear zone). Quartz diagram of 96 optic axes (quartz-poor). Contours: 5-4%, 3%, 2%, 1%, and 0%. Diagram attitude: N41W, 36NW; looking northward. 110 111 FIGURE 78 - Pedlar (shear zone). (A) uartz diagram of 200 optic axes. Contours: 6-4 , 3%, 2%, 1%, and 0%. (B) Sericite diagram of 100 cleavage poles. Contours 8%, 7-6%, 5-3%, 2-1%, and 0%. Diagram attitudes: N2E, 27NW, looking northward. FIGURE 79 - Pedlar. Quartz Optic axis maxima, cumulative- summary diagram of 97 maxima centers. Contours: 8-4%, 3%, 2%, 1%, and 0%. Horizontal view. 112 113 within 40 to 50 degrees of the center of the diagrams. There also appears to be a weak tendency for some maxima to lie in or near to the gneissic banding plane.* Figures 77 and 78 are from shear zones that are young- er than the gneissic banding they cross-cut. This shearing trends northeastward and has an a lineation. Both of these diagrams are from sections cut normal to this down-dip lineation, and both figures show a strong girdle development. In Figure 77 the girdle is slightly inclined to the plane of the diagram but normal to the s-surface. In Figure 78A the girdle lies almost normal to the plane of the diagram and at an acute angle to the s-surface. The mica diagram (Figure 78B) which accompanies the quartz diagram, shows a well-develOped girdle normal to the s-surface and also nor- mal to the quartz girdle. The horizontal cumulative-summary diagram prepared from 97 maxima center points from Figures 70 through 76 is presented in Figure 79. The strongest maxima comprise a vertical girdle. A symmetry plane possibly may be passed through this girdle which has an attitude of N56W, 86NE. The symmetry is not perfect, but there is much in the con- figuration of the various maxima which suggests a strong tendency toward monoclinic symmetry. Marshall formation Mesoscopic fabric relations Foliation - The foliation within the Marshall formation 114 is well defined by mica, quartz and feldspar grain alignment, mica being the most conspicuous in the hand specimen. Figure 80 illustrates the orientation of over one hundred poles to foliation. The diagram indicates a strong foliation devel- opment in this formation. Figure 81 shows the two important statistical folia- tion surfaces, as defined by the three high zones of the previous diagram. The most important s-surface is that of N44E, 583E. This statistical foliation surface is defined by a maximum of 14 percent. The lesser s-surface has an attitude of N76E, 708E and is defined only by a five percent maximum. The two percent maximum in Figure 80 is due to a gneissic banding similar to that observed in the Pedlar Formation. It was sporadically seen in some exposures where the mica content was small. The symmetry tendency is monoclinic, and the best feasible symmetry plane is N47H, 90°. The Q axis is normal to this plane and bears N43E, 0°. Lineation - Lineation is pronounced within this forma- tion, and is the result of elongated mica, quartz, and feld- spar grains within the surface of foliation. This is well illustrated by the diagram of 68 lineations in Figure 82. As determined by the point of highest concentration within the lineation maximum (X), the statistical bearing of this lineation is N59W, 818E. This is essentially in the dip direction of foliation, and parallel to the a fabric axis direction. 115 FIGURE 80 - Marshall. Diagram of 100 poles to foliation. FIGURE 81 FIGURE 82 FIGURE 83 FIGURE 84 FIGURE 85A- : 9 9 9 s e 969 9 2%?tggf82%,lig, :5: 0%?% Hgiizgitazxvieg. 5% Marshall. Ideal, statistical s-surfaces defined by the maxima of Figure 80. Horizontal view. Marshall. Diagram of 68 lineations (mineral stretching). Contours: 18-9%, 8-7%, 6-3%, 2-1%, and 0%. Horizontal view. Marshall. Diagram of 100 poles to Joints. Contours: 7-4%, 3%, 2%, 1%, and 0%. Horizontal view. Marshall. Ideal, statistical Joint surfaces defined by the 3% (weak lines), and by 4-7% (strong lines) maxima of Figure 83. Horizon- tal view. Marshall. Quartz diagram of 195 Optic axes. Contours: 4%, 3%, 2%, 1%, and 0%. Diagram attitude: N50E, 123E; looking northward. 116 Figure 82 Figure 64 “8“" 55“ 117 Joints - Figure 83 illustrates the orientation of 100 Joint poles. The tendency is toward the development of a horizontal girdle. Symmetry is suggestive here, with a mirror plane of N32W, 90° being plausible. The maxima to be reflected across this symmetry plane are not every- where equal in intensity, but this may be a minor point. Due to the two pairs of symmetrically opposed maxima in the central southeastern portion of the diagram, and to the fact that there are none in the northwestern portion, the symmetry tendency is monoclinic. By referring to Figure 84, the sta- tistical Joint sets defined by these maxima may be noted. These Joint sets are: A. Joint sets defined by maxima of 4% or greater: 1. N36E, 86NW 2. N18E, 84 SE 3. N12E, 85NW 4. N12W, 82NE 5. N32W, 79NE 6. N53W, 853W B. Joint sets defined by maxima of 3%: 1. N85E, 79NW 2. N82E, 645E 3. N80E, 825E 4. N67E, 56NW 5. N47E, 62NW 6. N68w, 2ONE 7. N76W. 90° 118 The girdle tendency is well illustrated by the arrange- ment of these ideal Joint sets fairly regularly about the net. The stronger sets tend to cut across the regional trend, while the weaker sets tend more to parallel the regional structural grain. However, this distinction is not as clear- cut as in the case of some_of the previously discussed for- mations. The two low dipping Joint sets may express sheet- ing, that is Jointing due to relief of vertical pressure near the surface. This type structure is quite evident in certain exposures. Microscopic fabric relations Scalar fabric aspects - "Original" quartz varies from three percent in some sections to 20 percent in others (Plate 6, Fig. B). In every case, the grains have very pro- nounced wavy extinction. The grains are fractured, or splin- tered, and in many cases these fractures are "healed" with later quartz. The fracture directions are commonly sub- parallel to the direction of shear, and some grains tend to be elongated in this direction also. The average grain size is 0.8 mm. Another type of quartz, less than 0.1 mm in size, has sutured grain contacts and little or no undulose extinction. This type of quartz occurs on the rims of the larger quartz grains, and is found smeared out into the direction of the s-surface. Superindividuals, composed of discrete grains of this type of quartz, exist in some sections. The amount present in the average thin section is about 20 percent. 119 Biotite is the most abundant mica present, being the chief mica in over half the thin—sections studied from the Marshall formation. Sericite is next in abundance, with muscovite being least abundant. Both biotite and sericite account for between 20 and 25 percent of the minerals in the sections where each predominate over the other. The average grain size for biotite is .01 cm.. and .005 cm for sericite. Muscovite averages .01 cm. The biotite and mus- covite appear as fresh crystals. While sericite has a lesser tendency to occur this way. Feldspar accounts for 40 to 60 percent of the rock, generally. The grains are usually fractured and sericitized. Plagioclase is the most important feldspar, while microcline occurs less frequently. ygctorial fabric aspects - The individual quartz dia- grams from the Marshall formation are illustrated in Fig- ures 85A through 98A. All sections were cut normal to the predominant down-dip lineation discussed above. The most striking characteristic of the quartz fabric is the tendency for fewer maxima to occur near the center of the diagram than along the periphery of the dia- grams, although a notable portion still occurs within 40 degrees of the center (the 5 axis). This peripheral girdle tendency is stronger in some diagrams than in others, but is present to a degree in almost every diagram. In Fig- ures 94A, 95A, and 96A there is a strong suggestion of inter- secting girdles (BfixB' tectonite fabric). 120 FIGURE 85B - Marshall. Muscovite-sericite diagram of 100 cleavage poles. Contours: 14-85. 7-6%, 5-3%, 2-1%, and 0%. Diagram attitude: N50E, 128E: looking northward. FIGURE 86 - Marshall. (A) Quartz diagram of 200 optic axes. Contours: 5-4%, 3%, 2%, 1%, and 0%. (B) Biotite diagram of 100 cleavage poles. Contours: 11-8%. 7-6%. 5-3%, 2-1%, and 0%. Diagram attitudes: N22E, 42NW; looking northward. FIGURE 87 - Marshall. (A) Quartz diagram of 135 cptic axes (quartz-poor). Contours: lO-4%, 3%, 2%, 1%, and 0%. (B) Biotite diagram of 100 cleavage poles. Contours: 8-6%, 5-3%, 2-1%, and 0%. Diagram attitudes: N64E, 49NW; looking northward. FIGURE 88A - Marshall. Quartz diagram of 200 optic axes. Contours: 4%, 3%, 2%, 1%, and 0%. Diagram attitude: NlW. 373W: looking northward. 122 FIGURE 88B — Marshall. Biotite diagram of 100 cleavage FIGURE 89 FIGURE 90 poles. Contours: 10-8%. 7-6%, 5-3%, 2-1%, and 0%. Diagram attitude: le, 37SU: look- ing northward. Marshall. (A) Quartz diagram of 190 cptic axes. Contours: 4%, 3%, 2%, 1%, and 0%. (B) Biotite diagram of 100 cleavage poles. Contours: 9%, 8-7%, 6-5%, 4-3%, 2-1%, and 0%. Diagram attitudes: N42E, 26nw: looking northward. . Marshall. (A) Quartz diagram of 200 optic axes. Contours: 4%, 3%, 2%, 1%, and 0%. (B) Biotite diagram of 100 cleavage poles. Contours: 8%, 7-6%, 5-3%, 2-1%, and 0%. Diagram attitudes: N65E, 16NW: looking northward. FIGURE 91A - Marshall. Quartz diagram of 200 optic axes. attitude: N4OE, 4ONW: looking northward. 1225 124 FIGURE 91B - Marshall. Biotite diagram of 100 cleavage poles. Contours: 8%. 7-6%, 5-3%, 2-1%, and 0%. Diagram attitude: N4OE, 40NW: looking northward. FIGURE 92 - Marshall. (A) Quartz diagram of 200 optic axes. Contours: 4%, 3% 2%, 1%, and 0%. (B) Mica (non-selective) diagrams of 100 cleavage poles. Contours: above 8%, 8-7%, 6-5%, 4-3%, 2-1%, and 0% (by M. M. Katzman). Diagram attitudes: NllW, 288W; looking northward. FIGURE 93 - Marshall. (A) Quartz diagram of 196 optic axes. Contours: 5-4 , 3%, 2%, 1%, and 0%. (B) Sericite diagram of 98 cleavage poles. Contours: 9-8%, 7-6%, 5-4%, 3-1%, and 0%. Diagram attitudes: N54E, 2NW; looking northr ward. FIGURE 94A - Marshall. Quartz diagram of 200 optic axes. Contours: 5-4%, 3%, 2%, 1%, and 0%. Diagram attitude: N34E, 36NW; looking northward. 1 25 Pi (u r e 9 2 B Figu :- e 9 3 A 4.4 @V FIGURE 94B FIGURE 95 FIGURE 96 FIGURE 97A 126 - Marshall. Biotite-sericite diagram of 92 cleavage poles. Contours: l4-7%, 6-5%, 4-3%, 2-1%, and 0%. Diagram attitude: N34E, 36NW: looking northward. Marshall. (A) Quartz diagram of 192 optic axes. Contours: 4%, 3%, 2%, 1%, and 0%. (B) Sericite diagram of 101 cleavage poles. Contours: 12-7%. 6-5%. 4-3%, 2-1%, and 0%. Diagram attitudes: N59E, 9NW; looking northward. Marshall. (A) Quartz diagram of 200 optic axes. Contours: 4%, 3%, 2%, 1%, and 0%.. (B) Biotite diagram of 100 cleavage poles. Contours: 8%, 7-6%, 5—3%, 2-15, and 0%. Diagram attitudes: N57E, 4ONW; looking northward. - Marshall. Quartz diagram of 200 optic axes. Contours: 3%. 2%, 1%, and 0%. Diagram attitude: N32E, 38NW; looking northward. 127 128 FIGURE 97B - Marshall. Sericite diagram of 99 cleavage poles. Contours: l6-l3%, 12-11%, 10-9%, 8-7%, 6-5%. 4-3%, 2-1%, and 0%. Diagram atti- tude: N32E, 38NW; looking northward. FIGURE 98 - Marshall. (A) Quartz diagram of 188 optic axes. Contours: 4%, 3%, 2%, 1%, and 0%. (B) Biotite diagram of 97 cleavage poles. Contours: 9-8%, 7-6%, 5-4%, 3-1%, and 0%. Diagram attitudes: N22E, 38NW: looking north- ward. FIGURE 99 - Marshall (Moneta zone). (A) Quartz diagram of 97 optic axes (quartz-poor). Contours: 6-4%, 3%, 2%, 1%, and 0%. (B) Biotite dia- gram of 100 cleavage poles. Contours: 10-8%, 7-6%, 5-3%, 2-11, and 0%. Diagram attitudes: N61E, 9NW; looking northward. FIGURE 100 - Marshall. Quartz optic axis maxima, cumula- tive-summary dia ram of 185 maxima centers. Contours: 4%, 3 , 2%, 1%, and 0%. Horizontal view. 129 130 The horizontal cumulative-summary diagram of 185 centers of the quartz optic axis maxima from the above dia- grams has a noticeable symmetry tendency (Figure 100). This possible symmetry plane has an orientation of N23W, 90? Maxima intensity balance is not perfect on either side of this symmetry plane, because maxima on the eastern side of the mhnor plans have a lower value and a somewhat different configuration from those on the western side. However, the suggestion of symmetry is definite. This symmetry tendency is monoclinic, for the greater proportion of maxima lie to the northwest. Another observation to be mentioned is the suggestion of a girdle dipping at a low angle to the northwest. It is stretching the imagination to say that it is.a definite girdle, yet the suggestion is strong. The peripheral girdle tendency is very strong in the individual mica cleavage pole diagrams (Figures 87B - 983). Where the girdle tendency is less, the alignment of the mica flakes within the foliation surface appears to be im- portant. However, in most cases the tendency is toward there being several maxima of relatively small area dis- tributed fairly evenly about the girdle. Because eadh sec- tion was cut normal to the lineation, as mentioned above, the girdleathen lie in a plane normal to the lineation. Figure 101 is the horizontal cumulative-summary dia- gram of 78 centers of maxima from the girdles of these mica diagrams. There is a very strong girdle tendency here. This 131 FIGURE 101 - Marshall. Mica cleavage pole maxima, cumula- tive-summari%diagram of 78 maxima centers. Contours: , 3% , 2%, 1%, and 0%. Horizontal Viewe FIGURE 102 - Marshall. Ideal, statistical mica s-surfaces defined by maxima of Figure 101. Horizontal view. 1.32 133 girdle dips gently to the northwest and has a remarkable symmetry tendency. The best symmetry plane through the girdle has an attitude of N37W, 86NE. The symmetry tendency is monoclinic. The poorly defined quartz cptic axis girdle of Figure 100 roughly coincides with this mica girdle. Both statistical girdles lie in planes that are approximately normal to the statistical lineation direction defined in Figure 82. The ideal s-surfaces defined by the mica supermaxima of Figure 101 are illustrated in Figure 102. The circular configurations of these ideal planes reaffirm the existence of a mica girdle. There is a slightly greater number of these s-surfaces trending to the northwest, than to the northeast. One sample was taken from the Moneta gneiss lying within the Marshall formation. Both a non-selective quartz and mica diagram were prepared from this specimen. The dia- grams may be seen in Figures 99A and 99B. The section from which these diagrams were prepared was cut normal to the pre- vailing down-dip lineation. Both diagrams look very much like their counterparts in the Marshall formation. The quartz diagram possesses a well defined peripheral girdle, with a less well defined central girdle. The mica diagram shows a peripheral girdle tendency, with two large maxima lying in the partial girdle. Girdles in both diagrams lie within a plane normal to the lineation. 134 Lovingston formation Mesoscopic fabric relations Foliation - The foliation of the Lovingston formation is very similar to that of the Marshall formation. It is well defined by mica, elongated quartz, and feldspar grains; it is persistent and widespread. Figure 103 represents a contoured diagram of over 100 poles to this foliation. The statistical foliations (s-surfaces) defined by the high maxima from this diagram are represented in Figure 104. The strongest maximum represents the plane N59E, 808E: the lesser maximum defines the plane N43E, 77SE. Both are Appalachian in attitude, and the weak northwest foliation trend of the Marshall formation is even weaker here in the Lovingston gneiss. The symmetry tendency is monoclinic. The best pos- sible mirror plane is N44W, 865W. The b axis is normal to this plane and has a bearing of N46E, 4°NE. Lineation - This mesoscopic structure is as pronounced within this unit as it is within the Marshall formation. Its orientation and character are illustrated by Figure 105. Here 59 lineations have been plotted and contoured giving a diagram quite similar in character to that of the Marshall lineation fabric. The highest point of lineation concentra- tion within the maximum area (X) bears N42M, 833E. As in the case of the Marshall formation, this lineation is due to mica, quartz, and feldspar grains elongated in the dip direction of the foliation (5 axis). AIK FIGURE 103 FIGURE 104 FIGURE 105 FIGURE 106 FIGURE 107 FIGURE 108A- 135 Lovingston. Diagram of 106 poles to foliation. Contours: 12-5%, 4%, 3%, 2%, 1%, and 0%. Horizontal view. Lovingston. Ideal, statistical s-surfaces defined by the maxima of Figure 103. Horizontal view. Lovingston. Diagram of 59 lineations (miner- al stretching). Contours: 27-10%, 8%, 7%, 5%, Horizontal view. 3%, 2%, 0 . Lovingston. Joint diagram of 118 poles. Contours: 7-5%: 4-3%. 2%, 1%, and 0%. Horizontal view. Lovingston. Ideal, statistical Joint sets defined by maxima of Figure 106. Horizontal view. Lovingston. Quartz diagram of 201 optic axes. Contours: 5-4%, 3%, 2%, 1%, and 0%. Diagram attitude: N13E, 388E: looking northward. 156 Figure 107 137 Joints - The diagram of 118 Joint poles is seen in Figure 106 and indicates a horizontal girdle. This girdle is better developed than in the case of the Marshall forma- tion. In addition to the girdle, a strong maximum lies near the center of the diagram, indicating the strong develOpment of sheeting. Attempting to pass symmetry planes through the dia- gram is difficult. By examining this diagram carefully and by examining the accompanying diagram, Figure 107, contain- ing the statistical Joint sets defined by maxima from Fig- ure 106, the writer believes that the only conceivable sym- metry plane is the plane N58E, 85NE. Probably the reason for the difficulties in determining mirror planes is due to the Joint fabric possessing a rather strong axial sym- metry tendency. This may apply to the Joint fabrics of other units under discussion in this thesis as well, especially the Antietam formation. The ideal statistical Joint sets (Figure 107) are as follows: A. Joints defined by maxima of 5% or greater: 1. N27E, 76SE 2. NlW, 86NE 3. N23W, 823W 4. N50W, 63W (sheeting) 5. N66w, 90° 6. N75W, 66NE 7. N82E, 888E 138 B. Joint set defined by a 3-4% maximum - N45W, 90? Most of these Joint sets out across the regional strike of the rocks. MicroscOpic fabric relations Scalar fabric aspects - Original quartz grains account for between three and 20% of the rock (Plate 6, Fig. A). This quartz type exhibits pronounced undulatory extinction and is commonly fractured. Some grains are elongated in the direction of foliation. The grains vary in size from 0.5 mm to 1.5 mm. A second variety of quartz is more abundant, account- ing for 20% of the rock. Size varies between 0.1 mm and 0.2 mm. Sutured contacts exist between the individual grains, and most grains have some undulose extinction. In a few sections the grains are fractured and commonly are smeared out in the foliation surface. Probably these grains are of paradeformational origin, inasmuch as they show undulose extinction but also have sutured boundaries. Mica is quite abundant in thin sections. Mostly it occurs as fresh, euhedral or subhedral crystals. Biotite is the most common type of mica observed, accounting for 10 to 20 percent of the rock, with a size range of .001 cm to 0.1 cm. Muscovite varies between three to five percent and has a size range of .01 cm to 0.1 cm. Sericite generally ac- counts for less than three percent of the rock and varies in size between .001 cm and .01 cm. The micas are bent around 139 the augen structures and emphasize the foliation. Large crystals, or augen, of feldspar are common and generally exhibit fractures and cleavage. Almost all grains are sericitized to varying degrees. The amount of grains present varies between 40 and 60 percent. The augen may be as much as 2 cm in size. Egctorial fabric aspects - The sections for petro- fabric analysis were cut normal to the prominent §_11neation. This procedure is identical with that used in studying the previous formation. The individual quartz diagrams are seen in Figures 108A through 116A. There also appears here a strong peri- pheral girdle tendency. However, in contrast with the indi- vidual quartz diagrams of the Marshall formation, there is also a strong tendency for grouping maxima into a second girdle within 40 to 50 degrees of the center of the diagram (the 5 axis). The diagram of Figure 112A suggests an inter- secting girdle fabric (BAB' fabric). The symmetry exhibited in the horizontal master diagram for quartz maxima is good. This diagram of 107 maxima is illustrated in Figure 118. The fabric is monoclinic, and only one symmetry or mirror plans may be passed through it. This plane has an attitude of N28W, 80SW. The symmetry on either side of this mirror plane is excellent, the best from any subfabric of this entire study. There appear to be four girdles in this cumulative- summary diagram. One girdle dips very gently to the southeast, FIGURE 108B - FIGURE 109 - FIGURE 110 - FIGURE 111A - 140 Lovingston, Biotite-muscovite-sericite diagram of 100 cleavage poles. Contours: 10'9%9 8'7%9 6-5%: 4-3%: 2'1%: and 0%- Diagram attitude: N13E, 385E: looking northward. Lovingston. (A) Quartz diagram of 201 optic axes. Contours: 4%, 3%, 2%, 1%, and 0%. (B) Biotite diagram of 100 cleavage poles. Contours: 12-11%, 10-9%: 8-7%. 6-5%, 4-3%, 2-1%, and 0%. Diagram attitudes: N45E, l7NW; looking northward. Lovingston. (A) Quartz diagram of 200 cptic axes. Contours: 3%, 2%, 1%, 0.5%, and 0% (by N. Haimila). (B) Mica (un- differentiated) diagram of 100 cleavage poles. Contours: 9%. 8-7%. 5-5%. 4-3%. 2-11. and 0% (by N. Haimila). Diagram attitudes: N56E, 28NW; looking northward. Lovingston. (A) Quartz diagram of 200 cptic axes. Contours: 5-4%, 3%, 2%, 1%, and 0%. Diagram attitude: N34E, 208E: looking northward. 141 FIGURE 111B - FIGURE 112 - FIGURE 113 - FIGURE 114A - 142 Lovingston. Biotite diagram of 100 cleavage poles. Contours: 9-8%. 7-6%, 5-3%, 2-1%, and 0%. Diagram attitude: N34E, 208E; looking northward. Lovingston. (A) Quartz diagram of 205 optic axes. Contours: 5-4%, 3%, 2%, 1%, and 0%. (B) Biotite diagram of 100 cleavage poles. Contours: 14-13 , 12-1%%, 10-9%: 8-7%, 6-5%. 4-3%, 2-1 , and o . Diagram attitudes: N32E, 24NW; looking northward. Lovingston. (A) Quartz diagram of 210 optic axes. Contours: 5-4%, 3%, 2%, 1%, and 0%. (B) Biotite dia ram of 100 cleavage poles. Contours: 22-20%, 19-17%, 16-13%, l2-9%, 8-5%. 4-1%, and 0%. Diagram attitudes: N4OE, 128E; looking northward. Lovingston. Quartz diagram of 200 optic axes. Contours: 5-4%, 3%, 2%, 1%, and 0%. Diagram attitude: N4W, 415W; looking northward. FIGURE 114B - FIGURE 115 - FIGURE 116 - FIGURE 117A - 144 Lovingston. Muscovite-sericite dia ram of 100 cleavage poles. Contours: 9-8 , 7-6%, 5-3%, 2-1%, and 0%. Diagram attitude: N4W, 418W; looking northward. Lovingston. (A) Quartz diagram of 193 optic axes. Contours: 4%, 3%, 2%, 1%, and 0%. (B) Biotite dia ram of 99 cleavage poles. Contours: 14-1;%, 12-11%, lO-9%, 8-7%, 6-5%, 4-3%, 2-1 , and 0%. Diagram attitudes: N72E, 4NW; looking northward. Lovingston. (A) Quartz diagram of 203 optic axes. Contours: 5-4%, 3%, 2%, 1%, and 0%. (B) Biotite diagram of 94 cleava e poles. Contours: 12-9%, 8-7%, 6-5%, 4-3 , 2-1%, and 0%. Diagram attitudes: N52E, 215E; looking northward. Moneta in Lovingston. Quartz diagram of 81 optic axes (Quartz-poor). Contours: 4%, 3%, 2%, 1%, and 0%. Diagram attitude: N28W, 678W; looking northward. 145 146 FIGURE 117B - Moneta in Lovingston. Biotite diagram of FIGURE 118 FIGURE 119 FIGURE 120 100 cleavage poles. Contours: 19-8%. 7-6%, 5-3%, 2-11, and 0%. Diagram attitude: N28W, 678W; looking northward. Lovingston. Quartz optic axis maxima, cumula- tive-summary diagram of 107 maxima centers. Contours: 6-4%, 3%, 2%, 1%, and 0%. Hori- zontal view. Lovingston. Mica cleavage pole maxima, cumulative-summary diagram of 45 maxima centers. Contours: 5, 4, 3, 2, 1, and 0 point zones. Horizontal view. Lovingston. Ideal, statistical s-surfaces defined by maxima of Figure 119. Horizontal view. 14 '7 148 while another is horizontal. More striking than these two subhorizontal girdles are the two steeply dipping ones, the acute angle of which is bisected by the symmetry plane. One has the attitude of N52W, 74NE and the other is NOOE, 450W. The individual mica diagrams are shown in Figures 108B through 116B. The peripheral girdle tendency is strong, but there is also a tendency to develOp strong maxima of large area within these girdles. These maxima appear to be strongly influenced by mica lying within the foliation. The girdles lie in a plane normal to the pronounced lineation. The plan-view cumulative-summary diagram of 45 centers of the mica diagram maxima (Figure 119) shows a strongly developed girdle dipping slightly to the northwest. The symmetry tendency is moderate, with the best possible symmetry plane having an attitude of N42W, 90°. Another symmetry plane possibly may be N48E, 0°, and still another may almost lie within the plane of the diagram, dipping gently northwest, indicating that an orthorhombic symmetry tendency is possible. Figure 120 illustrates the ideal mica s-surfaces de- fined by the maxima of Figure 119. There is a circular con- figuration of these mica s-surfaces which reiterate the existence of the mica girdle. The zone of intersection of the greatest number of these surfaces is Just to the south- east of the center of the diagram and it is within the general vicinity of the greatest lineation concentration, as 149 seen in Figure 105. As in the case of the Marshall formation, one speci- men was taken from a Moneta gneiss inclusion in the Lovings- ton formation. The non-selective quartz and mica diagrams made from this sample are Figures 117A and 117B. The thin section prepared from this diagram is perpendicular to the prevailing lineation, which parallels the dip direction. In the quartz diagram, the central girdle tendency is noticeable, as well as that of the peripheral girdle. However, as in so many Of the other mica diagrams Of the Lovingston formation, the develOpment of a large area maximum normal to the foliation is pronounced. Consequently, both diagrams are very similar to their counterparts in the Lovings- ton formation. UPPER PRECAMBRIAN OR LOWER CAMBRIAN (EAST LIMB) Lynchburggformation -Mesoscopic fabric relations Foliation and Bedding - Figure 121 is the diagram of over 100 poles to foliation and some bedding surfaces Of the Lynchburg formation. Figure 122 is the scatter diagram for Figure 121, the heavy points being bedding poles. From this diagram, the bedding is seen to be parallel to the foliation for the most part. The foliation is both of the bedding- plane and axial plane varieties, inasmuch as the bedding appears to be mainly isoclinal. FIGURE FIGURE FIGURE FIGURE FIGURE FIGURE 121 122 123 124 125 126 150 Lynchburg. Diagram of 100 poles to bedding and foliation. Contours: 15-l4%, l3-l2%, lO-7%: 6-3%, 2-1%, and 0%. Horizontal view. Lynchburg. Plot of 100 poles to bedding (heavy points) and foliation. Horizontal view. Lynchburg. Ideal, statistical s-surfaces defined by the maxima of Figure 121. Hori- zontal view. Lynchburg. Diagram of 38 lineations (cre- nulations). Contours: 4, 3, 2, 1, and 0 point zones. Horizontal view. Lynchburg. Joint diagram of 102 poles. Contours: 6-4%, 3%, 2%, 1%, and 0%. Hori- zontal view. Lynchburg. Ideal, statistical Joint sets defined by maxima Of Figure 125. Horizontal view. 151 Figure 121 152 The statistical s-surfaces normal to the maxima Of Figure 121 are illustrated in Figure 123. The two most im- portant s-surfaces, as defined by 15 and 14 percent maxima respectively, are N31E, 848E, and N40E, 81SE. The three other lesser s-surfaces are listed here in declining impor- tance: N37E, 70NW, N59E, 748E, and N37E, 70NW. Because many of the foliations measured are trans- posed bedding, or lying within bedding planes, the picture shown here is one of mutually parallel bedding surfaces and foliation, dipping steeply to the southeast and northwest with the former being the more frequent. The statistical fold axis (b) bears N36E, 0°, and the plane normal to it is N54W, 90°. This is the best symmetry plane, and the symme- try is monoclinic. Lineation - The lineation pattern revealed in Figure 124 for 38 lineations from the Lynchburg formation profoundly differs from that previously discussed from the Swift Run and basement units. Rather than resulting from mineral stretching in the direction of shear (g), the lineations in the Lynchburg are crenulations (crinkles) and appear to be due to intersecting s-surfaces. The general trend of the lineation pattern is that of a girdle which bears N45E, 90°. The normal or axis of the girdle trends N45H, 0°. The statistical lineations defined by the maxima of Figure 124 are: A. Lineations defined by 4 point and 3 point maxima: 1. N47E, 288E 153 2. N53E, 81NE 3. N51E, 59NE 4. N57E, 28E 5. N36E, SSE B. Lineations defined by 2 point maxima: 1. N36E, 34NE 2. N4OW, 72NW. Joints - Symmetry is moderately well develOped in the Joint fabric pattern. The symmetry tendency is mono- clinic with a single mirror plane of N43W, 90? The hori- zontal girdle tendency, so prevalent in some formations previously discussed, is apparent here, but not pronounced. The partial girdle dips gently NW. Figure 125 illustrates statistical Joint sets defined by the maxima of Figure 126. These ideal statistical Joint sets are as follows: A. Joints defined by maxima of 4% or greater: 1. N52E, 708E 2. N16W, 828W 3. N18W, 68NE 4. N37W, 82NE 5. N57W, 858W 6. N7ow, 535w B. Joints defined by maxima Of 3%: 1. N80E, 808E 2. N-S, 64H 3. N71W, 203W ‘Y‘ ’\ 154 4. N81H, 888W 5. N84W, 58NE 6. N87E, SONW. Five of the six strong statistical Joint sets trend across the regional grain. The weaker Joint sets are less cross-cutting with the regional trend. However, most of them intersect the regional strike at a steep angle. MicroscOpic fabric relations Scalar fabric aspects - Original (detrital) grains comprise between seven and twenty percent of the rock (Plate 7. Fig. A). These quartz grains have pronounced wavy extinc- tion and are commonly fractured. The grain size varies from 0.2 mm to 1 mm. Smaller, equant quartz grains occur with an average size of 0.2 mm. Wavy extinction rarely is exhibited. The grains tend to group together in discrete units, or aggre- gates, and they possess sutured contacts with their neighbor- ing grains. This quartz type is more abundant than the orig- inal quartz grains, and accounts for 20 to 60 percent of the rock. Most of the mica appears as fresh euhedral crystals which vary in size between 0.01 mm and 1.0 mm. Muscovite generally accounts for between 15 and 60 percent of the rock, and biotite accounts for seven to ten percent. Feldspar accounts for between three to ten percent of the total mineral content. It occurs as both large and small 155 grains. All of the feldspar is sericitized to varying de- grees. Vectorial_fgbricaspects - The thin sections from which microfabric elements of the Lynchburg formation were studied were cut normal to the lineation, where present. In cases where the lineation was absent, the sections were cut normal to the strike of the foliation or bedding. The individual quartz diagrams may be seen in Figures 127A through 134A. A girdle about the center of the diagram and within 40 degrees Of the center (the b axis) is the most common and characteristic feature of the quartz fabric. Not as well develOped, but yet significant, is a tendency for the development Of a peripheral girdle. The area between the two girdles is relatively barren of quartz Optic axes in most diagrams. The centers of the maxima from the above diagrams yield an interesting picture in the horizontal cumulative- summary diagram of Figure 135. In this figure there is a distinctive northeastern trending girdle which parallels the lineation girdle (see Figure 124). There also appears to be definite symmetry here: a mirror plane with an attitude N47W, 828W may be assumed. The symmetry is monoclinic. The individual mica diagrams may be seen in Figures 1273 through 134B. The girdle tendency is much less impor- tant in the mica fabric of this formation as compared with that Of previously discussed formations. This is probably due to the strong influence of the foliation surfaces in FIGURE 127 - FIGURE 128 - FIGURE 129 - 156 Lynchburg. (A) Quartz diagram Of 203 optic axes. Contours: 5-4%, 3%, 2%, 1%, and 0%. (B) Muscovite-diagram of 100 cleavage poles. Contours: 32-8%, 6%, 4%, 2%, 1%, and 0%. Diagram attitudes: N39W, 268W; looking north- ward. Lynchburg. (A) Quartz diagram of 200 optic axes. Contours: 5-4%, 3%, 2%, 1%, and 0%. (B) Muscovite diagram of 100 cleavage poles. Contours: 27-8%, 7-6%, 5-3%, 2-1%, and 0%. Diagram attitudes: N55W, 888W; looking northward. Lynchburg. (A) Quartz diagram of 193 optic axes. Contours: 5-4%, 3%, 2%, 1%, and 0%. (B) Muscovite diagram of 94 cleavage poles. Contours: 9%-8%, 7-6%, 5-4%, 3-1%, and 0%. Diagram attitudes: N62W, 508W; looking north- ward. 158 FIGURE 130 - Lynchburg. (A) Quartz diagram of 194 Optic axes. Contours: 4%, 3%, 2%, 1%, and 0%. (B) Muscovite diagram of 100 cleavage poles. Contours: l2-ll%, 10-9%. 8-7%. 6-5%. 4—3%, 2-1%, and 0%. Diagram attitudes: N56W, 90: looking northward. FIGURE 131 - Lynchburg. (A) Quartz dia ram Of 200 Optic FIGURE 132 - axes. Contours: 3.5%: 2.5 , 1.5%, 0.5%, and 0% (b N. Haimila). (B) Mica (non- selective diagram of 100 cleavage poles. Contours: 25-16%, 15-11%, lO-6%, 4-1%, and 0% (by N. Haimila). Diagram attitudes: N28E, 168E; looking northward. Lynchburg. (A) Quartz diagram of 200 Optic axes. Contours: 5-4%, 3%, 2%, 1%, and 1%. (B) Muscovite-sericite diagram of 100 Optic axes. Contours: 26-23%, 22-21%, 20-17%, l6-l3%. 12-9%. 8-5%. 4-1%, and 0%. Diagram attitudes: N29W, 90; looking northward. 159 FIGURE 133 - FIGURE 134 - FIGURE 135 - 160 Lynchburg. (A) Quartz dia ram Of 200 Optic axes. Contours: 4%, 3%, 2 , 1%, and 0%. (B) Muscovite diagram of 100 cleavage poles. Contours: 14-8%. 7-6%. 5-3%, 2-1%, and 0%. Diagram attitudes: N50W; 90; looking north- ward. Lynchburg. (A) Quartz diagram of 200 Optic axes. Contours: 4%, 3%, 2%, 1%, and 0%. (B) Muscovite diagram of 102 cleavage poles. Contours: 14-12%, 11%, 10-9%. 8-7%, 6-5%, 4-3%, 2-1%, and 0%. Diagram attitudes: N20W, 28W: looking northward. Lynchburg. Quartz Optic axis maxima, cumula- tive-summary diagram Of 80 maxima centers. Contours: 8-5%, 4%, 2%, 1%, and 0%. Hori- zontal view. 161 162 FIGURE 136 - Lynchburg. Mica cleavage pole maxima, cumula- tive-summary diagram of 27 maxima centers. Contours: 3, 2, 1, and 0 point zones. Hori- zontal view. FIGURE 137 - Lynchburg. Ideal, statistical s-surfaces defined by maxima Of Figure 136. Horizontal view. 163 164 directing the growth of the micas during metamorphism. Following from this, it is not surprising that these large area maxima generally lie normal to the prominent s-surfaces in each diagram. Figure 136 is the horizontal cumulative-summary diagram of the centers of the mica maxima from the above individual diagrams. This diagram is quite similar to the one showing poles to foliation and bedding (Figure 121). Maxims both in the northwest and southeast portion of the diagram, without a definite intervening girdle, indicate strongly develOped s-surfaces in the mica fabric approximately paralleling the foliation and isoclinally folded bedding. The 2 axis for the mica fabric is oriented N28E, lONE, and the plane normal to this, the approximate symmetry plane, is N64W, 808W. The symmetry tendency is probably monoclinic. In Figure 137. the ideal mica cleavage s-surfaces have been represented, as determined by the maxima Of Figure 136. The two s-surfaces are N32E, 805E, and N18E, 85NW. The former closely corresponds to one of the two strongly devel- Oped s-surfaces in Figure 123. EVINGTON GROUP Candler Formation Mesoscopic fabric relations Foliation - No bedding was Observed in the Candler Formation by this writer. Consequently, 64 poles to 165 foliation only have been plotted and are illustrated in Figure 138. The configuration of the foliation is actually quite similar to that Of the Lynchburg formation. The foliation is well defined by mica. There is a slight girdle tendency, but only slight. The best symmetry plane is N55W, 80SW. The normal to this plane is b, and it bears N36E, lONE. The symmetry is monoclinic. Figure 139 shows the ideal statistical planes determined by the maxima Of.the previous diagram. The strongest planes dip to the southeast, all striking northeast. The stronger trends are N46E, 68SE, N36E, 848E, and N16E, 703E. A weaker s-surface is N45E, 48NW. Lineation - The pattern of 71 lineations of the Candler Formation is strikingly similar to that Of the Lynch- burg formation. These lineations, which Figure 140 repre- sents, are the result of the intersection of s-surfaces, and they may be termed crenulations or crinkles. The lineation pattern is that of a northeastern trending girdle. The trend Of this girdle is N36E, 0°, and the normal to the plane Of the girdle is N54W, 0°. The statistical lineations de- fined by the maxima Of Figure 140 are: A. Lineations defined by 3%, 4%, and 6% maxima: l. N36E, 0° (6%) 2. N23E, 725w (4%) 3. N21E, 463w (3%) 4. N28E, 348W (3%) FIGURE FIGURE FIGURE FIGURE FIGURE FIGURE 138 139 140 141 142 143A 166 Candler. Diagram of 64 poles to foliation. Contours: 12-11%, 9-5%, 3-2%, and 0%. Horizontal view. Candler. Ideal, statistical s-surfaces defined by the maxima of Figure 138. Horizontal view. Candler. Diagram of 71 lineations (crenula- tions). Contours: 6%, 5%, 3%, 2%, 1%, and 0%. Horizontal view. Candler. Joint diagram of 100 poles. Con- tours: 6-4%, 3%, 2%, 1%, and 0%. Horizontal view. Candler. Ideal, statistical Joint sets defined by 3% (weak lines) and 4-6% (strong lines) maxima of Figure 141. Horizontal view. Candler. Quartz diagram Of 200 optic axes. Contours: 5-4%, 3%, 2%, 1%, and 0%. Diagram attitude: N73W, 90; looking northward. 167 Figure 138 Figure 142 168 B. Lineations defined by 2% maxima: l. N29E, 4lNE 2. N64E, 6NE. Joints - The orientation pattern Of 100 Joint poles, shown in Figure 141, suggests a fairly well developed, hori- zontal girdle. Furthermore, there is a suggestion of a vertical, northwest trending girdle also. Symmetry is fairly conceivable here, and is most probably monoclinic. The best possible symmetry plane is N44W, 90°. Figure 142 shows the ideal statistical Joint sets Obtained from Figure 141. These are: A. Joints defined by maxima Of 4% or greater: 1. N81E, 86NW 2. N68E, 428E 3. NlE, 82SE 4. NlOW, 900 5. Nl6W, 743w 6. N39W, 778W 7. N49W, 84NE 8. N62w, 69NE 9. N73W, 67SW B. Joints defined by maxima of 3%: l. N89E, 21NW 2. N67E, 698E 3. N3W, 16NW . The stronger Joint sets are more abundant. Seven of 169 these tend to be transcurrent to the region strike. One of the weaker Joint sets also cuts the regional trend at a high angle. The nearly horizontal statistical Joint sets are possibly the result Of sheeting. Microscopic fabric relations Scalar fabric aspects - The Candler Formation being a phyllite unit, quartz is generally not as abundant as in other formations of this region (Plate 9, Fig. A). It ac- counts for between 10 and 40 percent Of the rock and varies in size from between .01 cm and 0.1 cm. Commonly, the grains are scattered throughout a matrix of mica and are elongated into the surface of foliation. The length—width ratios may be as much as 10:1 or greater. The grains are fresh appear- ing, with little or no undulose extinction and possess sutured contacts. In many cases several grains may be grouped to- gether as elongated superindividuals. In some cases bubble trains cross several grains, regardless of the boundaries. Sericite and minor quantities of muscovite account for approximately 40 to 80 percent Of the rock. The mica empha- sizes the schistosity and frequently is kinked by late s- surfaces intersecting the foliation, yielding chevron mica folds. These grains are fresh appearing and are assumed to be paradeformational. Smaller grains, which are unbent and trend along both s-surfaces, are assumed to be post deforma- tional. The grain length for mica varies between .005 cm and .07 cm. 170 Feldspar occurs as fresh looking grains, elongated into the schistosity surface. In every respect, these feld- spar grains have an appearance similar to the quartz. Con- sequently, the feldspar is difficult to distinguish except by use of the universal stage. Vectorial fabric aSpects - The thin sections from which the petrofabric diagrams were prepared were cut normal to the lineation. If two lineations were present, the sec- tions were cut normal to the most outstanding lineation. Figures 143A through 149A represent the individual quartz diagrams for the Candler Formation. These diagrams resemble those of the Lynchburg to some degree. The most outstanding characteristic is a noticeable develOpment Of a girdle within 40 to 50 degrees of the center of the diagrams (the b axis). The lesser peripheral girdle tendency is also present, along with relatively barren zone between the central and peripheral girdles. Figure 150 is the horizontal cumulative-summary dia- gram Of 76 maxima center points from the individual quartz diagrams. 0n inspection the similarities between it and that of the Lynchburg formation may be readily seen. How- ever, it is not so well defined as the pattern of the Lynch- burg. The northeast-southwest trend is present, but less pronounced. Symmetry is also much more vague, but the ten- dency is present. The best symmetry plane is N55W, 90°: the trend of the girdle, which is normal to this mirror plane, is N36E, 0°. The symmetry tendency is assumed to be 171 FIGURE 143B - Candler. Mica (non-selective) diagram Of FIGURE 144 FIGURE 145 100 cleavage poles. Contours: l3-8%, 7-6%, 5-3%, 2-1%, and 0%. Diagram attitude: N73W, 90; looking northward. Candler. (A) Quartz dia ram of 200 Optic axes. Contours: 5-4%, 3 , 2%, 1%, and 0%. (B) Muscovite diagram of 100 cleavage poles. Contours: 36-8%, 6%, 4%, 2%, 1%, and 0%. Diagram attitudes: N57W, 90; looking north- ward. - Candler. (A) Quartz diagram of 200 Optic axes. Contours: 7-4%, 3%, 2%, 1%, and 0%. (B) Muscovite diagram Of 100 cleavage poles. Contours: 9-8%. 7-6% 5-3%, 2-1%, and 0%. Diagram attitudes: N49W, 90; looking north- ward. FIGURE 146 A- Candler. Quartz diagram Of 200 Optic axes. Contours: 5-4%, 3%, 2%, 1%, and 0%. Diagram attitudes: N64W, 90; looking northward. FIGURE 146B - FIGURE 147 - FIGURE 148 - FIGURE 149A - 173 Candler. Muscovite-sericite dia ram of 100 cleavage poles. Contours: 32-8 , 6%, 4%, 2%, 1%, and 0%. Diagram attitude: N64W, 90; looking northward. Candler. (A) Quartz diagram of 200 Optic axes. Contours: 5-4%, 3%, 2%, 1%, and 0%. (B) Muscovite diagram Of 100 cleavage poles. Contours: 23-8%, 7-6%, 5-3%, 2-1%, and 0%. Diagram attitudes: N48W, 288W; looking northward. Candler. (A) Quartz diagram of 171 optic axes. Contours: 5-4%, 3%, 2%, 1%, and 0%. (B) Sericite diagram of 100 cleavage poles. Contours: ll-8%, 7-6%, 5-3%, 2-1%, and 0%. Diagram attitudes: NlOW, 348W; looking northward. Candler. Quartz dia ram Of 200 Optic axes. Contours: 4%, 3%, 2 , 1%, and 0%. Diagram attitude: N56W, 74NE; looking northward. 1'74 175 FIGURE 149B - Candler. Muscovite-biotite-chlorite diagram FIGURE 150 - FIGURE 151 - FIGURE 152 - Of 100 cleavage poles. Contours: 12-8%, 7-6%, 5-3%, 2-1%, and 0%. Diagram attitude: N56w, 74NE; looking northward. Candler. Quartz optic axis maxima, cumula- tive-summary diagram of 76 maxima centers. Contours: 9-5%. 4%, 3%, 2%, 1%, and 0%. Horizontal view. Candler. Mica Cleavage pole maxima, cumula- tive-summary diagram of 31 centers. Con- tours: 3, 2, 1, and 0 point zones. Horizon- tal view. Candler. Ideal, statistical mica s-surfaces defined by maxima of Figure 151. Horizontal view. 1'76 177 monoclinic. The mica cleavage pole diagrams corresponding tO the quartz diagrams are illustrated in Figures 143B through 149 B. The girdle tendency is stronger here than in the mica fabric diagrams of the Lynchburg formation. However, the tendency still remains for the occurrence of single, large area maxima within these girdles. The prevailing 3- surface (foliation) appears to have a strong influence on the develOpment Of these maxima, because most maxima tend to be normal to it. The horizontal, cumulative-summary diagram of 31 mica cleavage maxima center points, Figure 151, shows a strong vertical girdle tendency, with the partially formed girdle trending northwest. The b axis of this girdle bears N28E, 0°. The plane of the girdle, normal to b, is N61W, 90°. The strongest concentrations of maxima centers-Of-gravity are in the northwest and southeast edges of the diagram, especially the former. The relationship between this diagram and that Of the foliation poles (Figure 138) is close. Figure 152 represents the s-surfaces defined by the two maxima Of Figure 151. These surfaces are planes having the following attitudes: N28E, 638E, and N44E, 84NW. There are no close correlations between these mica s-surfaces and those defined by foliation pole maxima of Figure 140. How- ever, the trends of all s-surfaces are Appalachian in char- acter. 178 Mount Athos Formation Mesoscopic fabric relations Bedding and foliation - Bedding is more important than foliation in the Mount Athos Formation. Figure 153 is a diagram of 49 poles to this bedding and to the less fre- quently observed foliation. There is a slight tendency for development of a north- west trending, vertical girdle. However, the maJor concen- trations of poles lie within the northwestern area of the diagram, while a lesser concentration lies at the southeastern edge Of the diagram. Poles to foliation tend to concentrate near the northwestern edge Of the diagram (Figure 154), and none are found in the southeastern portion of the diagram. The symmetry tendency is monoclinic, and the best symmetry plane is N52W, 86NE. The ideal s-surfaces, as defined by the maxima in Figure 153, areshown.in Figure 155. There are two Of these s-surfaces; both have a similar strike, which is close to the N42E, 4°SW trend of 9, defined by the partial girdle of Fig- ure 153. The attitudes of these surfaces are: N39E, 79SE, and N41E, 518E. The more steeply dipping surface is the result of both bedding and foliation. Apparently, isoclinal folds which are overturned to the northwest predominate, along with an axial plane foliation that is also essentially a bedding plane foliation. Lineation - Lineation in the Mount Athos Formation is FIGURE 153 - FIGURE 154 - FIGURE 155 - FIGURE 156 - FIGURE 157 - FIGURE 158 - 179 Mount Athos. Diagram of 49 poles to bedding and foliation. Contours: l3-12%, ll-lO%, 9%, 8-7%, 6-5%, 4-3%. 2-1%, and 0%. Hori- zontal view. Mount Athos. Plot of 49 poles to bedding and foliation (heavy points). Horizontal view. Mount Athos. Ideal, statistical s-surfaces defined by maxima of Figure 153. Horizontal view. Mount Athos. Diagram of 34 lineations (crenulations). Contours: 12-10, 9-7, 6-4, 3-1, and 0 point zones. Horizontal view. Mount Athos. Joint diagram of 113 poles. Contours: 7-4%, 3%, 2%, 1%, and 0%. Hori- zontal view. Mount Athos. Ideal, statistical Joint sets defined by maxima in Figure 157. Horizontal view. 180 Figure 158 181 illustrated by the statistical diagram Of 34 lineations in Figure 156. In some respects the lineation pattern resembles quite closely the lineation patterns of the Candler and Lynchburg formations. The northeast trending vertical girdle is present, however, it is not so completely develOped as in the above two formations. The plane Of the girdle has an orientation of N41E, BOSE. The lineation appears as crenulations or crinkles on the bedding and foliation surfaces. It is presumably due to the intersection of s-surfaces. Below are listed the impor- tant statistical lineations defined by maxima of Figure 156: A. Lineations defined by 4 point maxima: l. N41E, 28W 2. N24E, 545W 3. NlE, 398W 4. NSW, 818E B. Lineations defined by 2 point maxima: l. N45E, 24NE 2. N29E, 258W. Joints - The orientation Of 113 Joints is illustrated in the pole diagram in Figure 157. The horizontal girdle tendency witnessed in the Joint fabrics of the previous two units is nonexistent here. Instead two maxima lie along the northeast and southwest peripheries of the diagram. A symmetry plane of N45W, 90° may be likely. Possibly two other planes of symmetry may be credible in this diagram, one within the plane of the diagram and another N45E, oo. 182 If this is possible, the symmetry tendency is orthorhombic. The ideal Joint sets, as determined by the maxima of Figure 157, are shown in Figure 158. They are: A. Joint sets defined by 4% or greater maxima: 1. N3OW, 75SW 2. N60w, 90° B. Joint sets defined by 3% maxima 1. N49w, 54NE 2. N87W, 70NE. All of these statistical Joint sets tend to cross-cut the regional northeast structural trend. Microscopic fabric relations Scalar fabric aspects - The quartz content of this rock varies between 90 and 100 percent, depending upon wheth- er or not it is micaceous (Plate 9, Figs, B and C). There are three general quartz types in thin section. One is the original or detrital variety. In size it varies between .08 cm and 0.2 cm. It shows pronounced wavy extinction and is elongated into the shear surface with length—width ratios Of up to 10:1, or greater. In some cases these grains are super- individuals, that is polycrystalline aggregates of smaller quartz grains sutured together. This variety Of quartz ac- counts for between zero and ten percent Of the rock. A second variety is a very fine grain type with a size range of .005 to .01 cm. These grains have sutured con- tacts with one another, show undulose extinction, and are 183 drawn out into the prevailing s-surface. The quantity seen in thin section varies between zero and 100 percent. The third type occurs as fresh, equant grains with sutured contacts. The size range for this quartz type is between .01 cm and 0.1 cm. These grains are believed to be recrystallized quartz and consequently are probably post- deformational in origin. Lack of undulose extinction is characteristic Of this type. Sericite is the mica present in the Mount Athos forma- tion. It is present in amounts varying between zero and ten percent, as determined by eray analysis. Because Of this small concentration, it is difficult to utilize it for micro- fabric analysis. Vectorial fabric aspects - As in the case of the Lynchburg formation, all thin sections were cut normal to the prominent lineation. If no lineation was present, the section was cut normal to the strike of the bedding or folia- tion. The individual quartz fabrics, as illustrated in Figures 159, 160, 161 A, 162, 163, 164 A and 165 are some- what different from their counterparts in the previous two units discussed. In three Of the diagrams, Figures 159, 160 and 164 A, the central girdle tendency is present to varying degrees. However, in Figure 160, there appears to be a girdle normal to the plane of the diagram, cutting the s- surface at an intermediate angle. Figure 161 A suggests a girdle normal to the plane of the diagram but paralleling 184 FIGURE 159 - Mount Athos. Quartz diagram of 200 optic axes. Contours: 5-4%, 3%, 2%, 1%, and 0%. Diagram attitudes: N6OW, 90: looking north- ward. FIGURE 160 - Mount Athos. Quartz diagram of 200 Optic axes. Contours: 7-4%, 3%, 2%, 1%, and 0%. Diagram attitude: N34W, 90; looking northward. FIGURE 161 - Mount Athos. (A) Quartz dia ram Of 200 optic axes. Contours: 4%, 3 , 2%, 1%, and 0%. (B) Sericite diagram of 100 cleavage poles. Contours: 10-8%. 7-6%, 5-3%, 2-1%, and 0%. Diagram attitudes: N47W, 66NE; looking northward. FIGURE 162 - Mount Athos. Quartz diagram Of 200 Optic axes. Contours: 5-4%, 3%, 2%, 1%, and 0%. Diagram attitude: N4W, 48SW; looking north- ward. FIGURE 163 - Mount Athos. Quartz diagram of 200 Optic axes. Contours: 6-4%, 3%, 2%, 1%, and 0%. Diagram attitude: N80W, 90; looking north- ward. . 186 FIGURE 164 - Mount Athos. (A) Quartz diagram Of 200 Optic FIGURE 165 - FIGURE 166 - axes. Contours: 5-4%, 3%, 2%, 1%, and 0%. (B) Sericite diagram of 100 cleavage poles. Contours: 22-8%, 7-6%, 5-3%, 2-1%, and 0%. Diagram attitudes: N29W, 388W; looking northward. Mount Athos. Quartz diagram of 201 optic axes. Contours: 7-4%, 3%, 2%, 1%, and 0%. Diagram attitude: N6W, 90; looking northward. Mount Athos. Quartz Optic axis maxima, cumulative-summary diagram Of 87 maxima centers. Contours: 5-4%, 3%, 2%, 1%, and 0%. Horizontal view. FIGURE 167 - Mount Athos. Mica cleavage maxima pole plot of 6 maxima centers. Horizontal view. ‘_“—‘ ——_——' _“—'— 188 the s-surface. The maxima relationships of Figures 163 and 164 are similar, but the fabrics appear to have a strOng triclinic tendency. The horizontal cumulative-summary diagram of 81 quartz maxima center points is even more distinctly different from the corresponding diagrams of the Lynchburg and Candler forma- tions. The maJor pattern revealed here is apparently that of two intersecting girdles in a fashion such that the re- sulting symmetry is triclinic. The best develOped girdle is defined by the plane N63E, 6ONW; the remaining girdle is defined by the plane N49W, 80NE. The mica is scarce in the Mount Athos Formation. Only two diagrams were prepared as a consequence Of this. Both Figures 161B and 164B have a girdle tendency. However, there is also a development of a few maxima of large area, which are well defined by the s-surfaces. Figure 167 shows the six center points of these maxima plotted in plan view. The plane N3OW, 90°appears to define the trend suggested by this scanty data. If these points are representative of the mica orientation in this formation, then the mica super fabric is that Of a vertical, northeast trending girdle. RESUME 0F SALIENT PETROFABRIC FACTS ngeral discussion The preceding has been a detailed description of the fabric character of the individual formations under study. It may be advisable now to summarize the more significant 189 fabric characteristics from the above discussion, as well as making a comparison of fabric characteristics among the var- ious units. Certain groupings Of formations may be conveniently used in the discussion here, because their fabrics are some- what similar. The Chilhowee group, The Swift Run Formation, the basement complex, and the Lynchburg formation-Evington group are specifically these groups and will be used in the following summary. The Chilhowee group Mesoscopic fabric S-surfaces - Both bedding and cleavage are the promi- nent mesoscopic s-surfaces in the Chilhowee group, with bed- ding surfaces being the most abundant. In all plan view (horizontal) s-surface pole diagrams (Figures 2, 16 and 33), the vertical northwest trending girdle is the rule. The axis normal to these girdles are designated as the statis- tical fold or p axis. The average attitude of the p axis is N49E, 4NE, and it is a typical Appalachian trend. These girdles are all overturned to the northwest and show a tendency toward monoclinic symmetry. Cleavage poles and bedding poles are moderately well segregated in the Antietam and Harpers diagrams. In both, the bedding poles account for the central maxima and thus indicate beds dipping low to the southeast and northwest. The Unicoi diagram indicates both low and steeply dipping bedding 190 surfaces. The more steeply dipping beds dip only to the southeast. Only the Antietam formation appears to have well- defined axial plane cleavage, while the Uhicoi diagram shows a moderate develOpment, and the Harpers diagram shows no Obvious development at all. All three units apparently have bedding plane cleavage, being best developed in the Unicoi and Harpers formations and least developed in the Antietam formation. Joints - The horizontal Joint pole diagrams (Figures 5, 20, and 36) all show a tendency for horizontal girdle devel- Opment. The Antietam shows this tendency best and the Unicoi diagram the least. It is difficult to decide which symmetry tendency is strongest, monoclinic or orthorhombric. In any case, the most obvious symmetry planes, to this observer, appear to trend north-northwest. The average trend for the Chilhowee Joint fabric symmetry planes appears to be N22W, 90? This is more northward than the symmetry plane trends for the s-surface diagrams. While the above symmetry discussion may be Open to argument, the fact that the better defined statistical Joint sets tend to cut across the regional grain is indisputable. There is also a definite tendency for the weaker Joint sets to more or less parallel the regional structural trend. Microscopic fabric Scalar aspects - Detrital quartz is the most abundant 191 mineral in the Chilhowee group, accounting for 40 percent of the rock in the Harpers formation (Plate 8, Fig. A) and 99 percent in the Antietam formation (Plate 8, Fig. B). Re- crystallized quartz, other than that of overgrowths, occurs only in the Unicoi Formation (Plate 7, Fig. B). The detrital grains are equant in the Antietam forma- tion but are somewhat elongated in the prominent s-surface in the Harpers and Unicoi formations. Within a shear zone in the Antietam formation, quartz elongation is extremely pronounced, with length-width ratios of as much as 11:1 (Plate 8, Fig. C). Most quartz grains in the Chilhowee units possess undulose extinction, presumably of a predepositional‘ origin. Feldspar occurs in all units but is important in the graywacke and subgraywacke members of the Harpers and Unicoi formations. Sericite is the most abundant of the micas, with some muscovite occurring. No mica occurs in the Antietam forma- tion. In the other two units mica accounts for between three and thirty percent of the rock. It generally does not have a fresh appearance and lies within both the bedding and cleavage surfaces. Vectorial aspects - The individual quartz diagrams vary in configuration, not only between formations but within each formation. However, the diagrams of the Harpers are somewhat similar to their counterparts in the Antietam. The Unicoi individual quartz diagrams differ in appearance from 192 both the Antietam and Harpers. In all three cases though, the greater number Of maxima lie between approximately 40 to 50 degrees of the centersof the diagrams, which are normal to the strike direction of the bedding. The diagram prepared from the sample taken from the shear zone in the Antietam formation (Figure 14) shows a different quartz fabric from the above diagrams. Here a girdle is developed around the direction of shearing, which is indicated by an 3 lineation due to the elongated quartz grains. The horizontal cumulative-summary diagrams of the maxima center points from these individual quartz diagrams (Figures 15, 30, and 52) show a sub-horizontal girdle ten- dency. This is best develOped in the Antietam diagram and poorest develOped in that of the Unicoi. The strongest maxima occur along the northeast and southwest edges of the diagram in the Uhicoi diagram. This tendency is seen in the Antietam and Harpers diagrams, but it is not so pronounced. All three quartz master diagrams show monoclinic symmetry tendencies, with the average mirror plans being N44W, 90? The Antietam diagram suggests a slight orthor- . hombic tendency but the monoclinic tendency is stronger. The individual mica diagrams, accompanying the individ- ual quartz diagrams, from the Harpers and the Unicoi forma- tions (the Antietam is devoid of mica) show a strong tendency for peripheral girdle development. In cases where there are several small area maxima lying along the girdle, the girdles 193 are presumably the result of the several intersecting 8- surfaces normal to these maxima. These fabrics are consid- ered B-tectonites, after Turner (1948, p. 272-273). In fewer cases, single, large area maxima occur in partially developed girdles. This fabric is assumed to fit better in the s-tectorite category. The horizontal, cumulative-summary diagrams for the Harpers and Unicoi mica fabrics (Figures 31 and 53) show the cleavage pole maxima in northwest trending, vertical girdles. The Unicoi mica fabric is only a partial girdle. The south- eastern portion is not developed, whereas the Harpers girdle is rather well developed, but there may also be another north- northeast trending girdle in this diagram. If this is so, then the Harpers master diagram is that Of two intersecting girdles, and the symmetry is triclinic. Disregarding this problematic girdle, the average p (microfold axis) trend for the Harpers and Unicoi mica fabrics is N38E, 3NE. This p trend is eleven degrees closer to due north than is the p trend of the mesoscopic s-surfaces. The statistical cleavage surfaces (Figures 18 and 34), defined by the supermaxima, tend to correlate more closely with bedding than with cleavage. The Unicoi statistical cleavage surfaces on the other hand, tend to correlate with both bedding and axial plane cleavage. The Swift Run Formatigp MesoscOpic fabric S-surfaces - There are too few measurements to make 194 any definite statements concerning the mesoscOpic s-surface fabric of the Swift Run Formation. However, it may be stated that both bedding and bedding-plane cleavage appear to occur here. The scatter diagram (Figure 55) shows the greatest number of poles lying in the northwest portion Of the diagram, while only two poles occur in the southeast portion of the diagram. A vertical girdle tendency is suggested here with a northwest trend. The p axis is approximately N40E, 0°. The symmetry tendency is probably monoclinic. Lineation - Again there are too few measurements for making any definite statements. The lineations are grouped in an area to the southeast of the center of the diagram (Figure 56). They are considered lineations in 9, due tO mineral stretching in shear zones, which are frequent in the Swift Run formation. Their trend is NSSW, plunging south- east. Joints — The pole orientation Of Joints show a fabric pattern with maxima concentrated in the northeastern and southwestern portions of the diagram (Figure 57). There is almost no noticeable girdle development. A monoclinic sym- metry tendency prevails, with a symmetry plane Of N32W, 783W. All statistical Joint sets, both strong and weak, trend northwest across the regional strike (Figure 58). Microscopic fabric Scalar aspects - Although detrital quartz is present in this unit, recrystallized quartz is almost equally abundant. 195 (Plate 7, Fig. B). Recrystallized quartz occurs around the periphery of the larger grains and is also smeared out into the foliation surfaces, as well. The detrital grains are very much deformed; this is evidenced by their elongation in the s-surface direction and by the pronounced undulatory extinction they exhibit under crossed nicols. Sericite is the prevalent mica, but it generally ap- pears fresher than that seen in thin sections from the Harpers and Unicoi formations. Mica alignment emphasizes the prevailing s-surfaces. Feldspar is present. Many grains appear to have been derived from the Pedlar Formation, inasmuch as rounded quartz blebs are contained in them. Vectorial aspects - Three Of the four thin sections prepared were cut normal to the a lineation. The maxima in the individual diagrams tend to group about the 2 axis, that is within 50 degrees of the center Of the diagram. The mica cleavage poles tend to show a peripheral girdle tend- ency about this a lineation in the individual mica diagrams accompanying the quartz diagrams. The horizontal master diagram of quartz maxima center points (Figure 63) also differ from those of the Chilhowee group. It is easier to conceive Of a triclinic symmetry tendency than that of monoclinic symmetry. In any case, the symmetry tendency is weak. Possibly a northwest trending girdle may be interpreted (N4OW, 90), which bificates in the northwest portion of the diagram. 196 The mica master diagram (Figure 64) has a rather well develOped vertical girdle with an attitude Of Nllw, 888W and with the p axis trending N80E, 2NE. This extreme northward trend is rather anomalous. The basement complex Mesoscopic fabric S-surfaces - Foliation, due to mica, elongated quartz and feldspar grains, is the predominant s-surface present in the Lovingston and Marshall formations. In the Pedlar Formation a gneissic banding is the primary s-surface, and is the result of the lining up of quartz lenticles and fold- spar grains. The differentiation of these two types of s-t surfaces into formational environments is not clear-cut, because the Pedlar-like gneissic banding may be found in the less micaceous zones of the Lovingston and Marshall forma- tions, and Lovingston-like foliation is develOped in shear zones within the Pedlar Formation. The foliation diagrams for the Marshall and Lovingston units (Figures 80 and 103) are quite similar, indicating an average foliation trend of N56E, 72SE. The Pedlar s-surface diagram (Figure 66) indicates a more complex situation. The greatest gneissic banding pole concentrations are within the northwestern part of the diagram, the largest maximum indi- cating an s-surface with an orientation Of N49E, 758E. There is, however, a large maximum in the northeastern part of the diagram indicating a statistical s-surface of N81W, 698W, 197 which is non-Appalachian. There is, furthermore, a horizontal girdle tendency in the Pedlar diagram. The diagrams of the Lovingston and Marshall units indicate a monoclinic symmetry tendency, while that Of the Pedlar Formation is probably triclinic. Lineation - NO lineation occurs in the Pedlar Forma- tion, excluding the a lineation in shear zones. In the Lovingston and Marshall formations, however, a strong linea- tion is developed by elongation of mica, quartz, and feldspar grains in the down dip (2 axis) direction. The average bear- ing and plunge determined from the Marshall and Lovingston lineation diagrams (Figures 82 and 105) are N42W, 833E, and N59W, 818E, respectively. Joints - The Lovingston Joint diagram (Figure 106) shows a strong horizontal girdle tendency, with a maximUm at the center indicating shooting. The Marshall diagram (Figure 83) shows the girdle tendency, but not as well as that Of the Lovingston, and the Pedlar diagram (Figure 68) shows this tendency even less. Symmetry is questionable in all diagrams but that of the Pedlar. This particular fabric has a strong monoclinic tendency, with a mirror plane Of N40W, 90°. The Marshall Joint diagram has a not so Obvious monoclinic tendency, with a mirror plane Of N32W, 90°. The Lovingston Joint diagram presents difficulties in determining symmetry tendencies. The strongest statistical Joint sets of the Pedlar and Marshall formations generally cut across the regional 198 structural trend, while the weaker sets tend to more or less parallel the northeast-southwest trend. NO clearcut rela- tionship is seen in the case Of the Lovingston Joint fabric. In this particular diagram two Joint set directions seem prominent, a north trending one and an east trending one. Microscopic fabric Scalar aspects - The scalar fabric aspects of the Lovingston (Plate 6, Fig. A) and Marshall (Plate 6, Fig. B) formations are quite similar but very much different from that of the Pedlar Formation (Plate 6, Fig. C). In the Pedlar, quartz grains, both large and small, are rounded and have been called blebs by Bloomer and Werner (1955), and Bloomer (unpublished). The larger quartz grains are fractured and show undulose extinction, while the smaller grains are usually undistorted. The maJority Of both types occur in large feldspar crystals. Quartz appears in two forms in the other two units: original quartz, and recrystallized quartz. The original grains are larger, show undulose extinction, and are elongated into the foliation surface, whereas the re- crystallized grains are generally equant and possess no wavy extinction properties. Mica is important in the Lovingston and Marshall fabrics, and emphasize the foliation. 0f the three micas present, biotite, muscovite and sericite, biotite is the most important. The biotite crystals are fresh appearing. 199 Sericite in very minor quantities is the only mica Of impor- tance in the usual Pedlar rock. Feldspar is Of great importance in the Pedlar mineral- ogy, but of lesser importance in the mineralogy Of the other two units. In all cases feldspar shows evidence of alteration to sericite and clay. Vectorial aspects - As the previously discussed characteristics of the Lovingston and Marshall formations are as much alike as those Of the Pedlar Formation differ from them both, such is also the case concerning the vectorial fabric aspect. No comparison may be made with the Pedlar concerning mica fabric, because it has none essentially. The individual quartz diagrams of the Pedlar Forma- tion are difficult to interpret. However, they are quite different from those of the Lovingston and Marshall forma- tions, with the single exception of one diagram from a shear zone. Here a peripheral girdle is well developed which is similar to those of the two gneisses. In fact, this diagram looks more like certain Marshall quartz diagrams, in that the central girdle tendency is almost non-existant, rather than the Lovingston individual diagrams with generally well- developed central as well as peripheral girdles. In the individual quartz diagrams of the Marshall and Lovingston formations, some girdles lie in a plane normal to the linea- tion, and others, especially in the Lovingston diagrams, lie at angles other than 90 degrees to the g lineation. The quartz horizontal cumulative-summary diagrams for 200 the two gneissic units (Figures 100 and 118) suggest sub- horizontal girdles. The Marshall girdle is poorly defined but appears to dip gently to the northwest. The Lovingston diagram suggests two sub-horizontal girdles and two others which are better pronounced, lying parallel to g, and inter- secting one another, in addition to intersecting the two sub- horizontal girdles. On the other hand, the Pedlar diagram (Figure 79) shows a northwest trending vertical girdle. Symmetry is monoclinic for all diagrams, being best developed in the Lovingston fabric and poorest develOped in the Marshall fabric. The average symmetry plane Of the quartz fabric of the basement complex is N36W, 855W: the symmetry planes of the Marshall and Lovingston diagrams correlate better with one another than with the Pedlar. The individual mica diagrams Of the Lovingston and Marshall formations show a strong tendency to develop peri- pheral girdles normal to the lineation. This is even more pronounced in the Marshall fabric. The horizontal cumulative- summary diagrams of mica maxima (Figures 101 and 119) ro- flect this by showing well-developed sub-horizontal girdles lying in a plane normal to the g lineation. Symmetry is difficult to interpret. Both fabrics may have a strong axial symmetry tendency. The Lypchburgpforpation - Evington group Mesoscopic fabric S-surfaces - Foliation predominates in the Lynchburg 201 and Candler formations (no bedding was observed by this writer in the Candler Formation), while bedding predominates over foliation in the Mount Athos Formation. The bedding orienta- tions Observed in these units are the result of isoclinal folding. Bedding plane foliation is indicated both in the Lynchburg and Mount Athos s-surface diagrams, with a sugges- tion Of some axial plane foliation in the Mount Athos. Most surfaces dip moderately to steeply toward the southeast. This characteristic is best develOped in the Lynchburg fabric and poorest develOped in that of the Mount Athos. The Lynchburg and Candler diagrams (Figures 121 and 138) look very much alike. Both show a slight northwest trending girdle tendency. The Mount Athos diagram (Figure 153) looks somewhat different, this being due to the preva- lence Of moderately southeastward dipping bedding surfaces rather than the steeply dipping surfaces prevalent in the other two diagrams. Its girdle tendency is consequently more pronounced. The average p axis trend for these forma- tions is approximately N38E, 1°SW. Lineation - The lineation of all three units is due to the crinkling of bedding and the oldest foliation by younger intersecting and less penetrating cleavages. The typical lineation pattern is that of a northeast trending girdle or partial girdle (Figures 124, 140, and 156), the average trend of which is N4lE, 90°. The most persistent lineation within these formations is horizontal and essentially parallels the gross trend of 202 the girdle. However, other important statistical lineation trends are present in these girdles. The maxima which define these lineation trends lie along the girdle trend but plunge between 24 and 81 degrees in various directions (see page ). Joints - The horizontal Joint pole girdle develOpment is present both in the Lynchburg and Candler Joint diagrams (Figures 125 and 141) but is pronounced only in the case Of the Candler. The Mount Athos diagram (Figure 157) shows only a concentration Of poles in the northeast and southwest edges of the diagram without any intervening girdle. The symmetry tendency may be monoclinic, but an orthor- hombic tendency may be interpreted as well in the Mount Athos diagram. Nevertheless, the average orientation Of the most obvious symmetry plane is N44W, 90. for these units. The strong statistical Joint sets tend to cross-cut the regional grain, and the weaker statistical sets have a tendency to be sub-parallel to regional northwest-southeast trend. Microscopic fabric Scalar aspects - Original quartz is commonly present in the Lynchburg (Plate 7, Fig. A) and Mount Athos (Plate 9, Fig. B and C) units. It has the appearance Of subrounded grains, elongated in the direction of the prevailing s-sur- face, and generally possesses wavy extinction. These grain are commonly the largest quartz grains in the rock. Recrystallized quartz is abundant and occurs in all 203 three units. However, it is generally equant in the Lynch- burg fabric and in some Mount Athos fabrics, and it is elon- gated into the foliation direction in all of the Candler thin sections (Plate 9, Fig. A), and also in several from the Mount Athos formation. Lack of undulose extinction, lack Of inclusions, and the presence of sutured contacts are the characteristics Of this type of quartz. Feldspar is present in significant amounts in the Candler and Lynchburg formations. Some feldspar is difficult to distinguish from quartz in appearance, this is especially true in the Candler fabric. Mica is present in all three units. It is very abun- dant in the Candler Formation but scarce in the Mount Athos Formation. Muscovite and biotite with a fresh appearance are the micas present in the Lynchburg formation, while sericite accounts for the largest part Of the mica in the other two units. Mica emphasizes the prevailing s-surface and in the Candler fabric is crinkled by the later cleavage. Vectorial aspects - All fabric diagrams were prepared from slides cut normal to the prevailing lineation, and where absent, cut normal to the strike Of the s-surface. The individual quartz diagrams of the Lynchburg have a strong development of central girdles about the lineation or strike lines with little tendency to develop peripheral girdles. This is also true for the Candler quartz diagrams. The Mount Athos diagrams are different from those of the above two formations, and are more difficult to interpret. In 204 some Mount Athos diagrams there appear to be large circle (peripheral) girdles cutting across the plane of the diagram at high angles. The horizontal, quartz maxima master diagrams for the Lynchburg and Candler units (Figures 135 and 150) are rather similar to one another, with that of the Lynchburg being best defined. This particular diagram shows the maxima forming a girdle which trends toward the northeast. The Candler girdle is broader and less well-defined. The average trend for both units is N39E, 0°. The Mount Athos diagram (Figure 166) is quite different from that of the above two units and is more difficult to interpret. Possibly the fabric shows two intersecting girdles. The girdles have the following attitudes: N63E, 60NW, and N49W, 8ONE. The sym- metry tendency of the Lynchburg and Candler quartz fabrics is monoclinic, with an average symmetry plane of N51E, 28W. Probably the Mount Athos diagram shows a triclinic symmetry tendency. The individual mica diagrams show a poorer peripheral girdle tendency than in some of the previous units. Single, large area maxima are the most common features. These maxima Often lie within a much weaker girdle or partial girdle. Apparently the prominent s-surface had a great in— fluence on the development Of the mica fabric. The Lynchburg and Candler horizontal cumulative- summary mica diagrams (Figures 136 and 151) show a vertical northwest girdle trend. The girdle is best develOped in 205 the Candler diagram; little may be said about the Mount Athos scatter diagram (Figure 167) because Of the small num- ber of maxima Obtained for plotting. However, it may be similar to the others. The average p determined from these diagrams is N29E, 0°. This trend is nine degrees farther north than the p trend of the mesoscopic s-surfaces. The statistical mica s-surfaces dip steeply southeast and parallel the prevalent bedding and foliation s-surfaces. INTERPRETATIONS GENERAL DISCUSSION This analysis Of the microscopic and mesoscopic fabrics across the Catoctin Mountain-Blue Ridge anticlinori- um has demonstrated that the different assemblages of rocks possess characteristic fabric patterns. The Chilhowee fabric is significantly different from that Of the basement complex, and both of these differ from the fabric Of the Piedmont units. The Swift Run quartz fabric is difficult to interpret, but the other Swift Run subfabrics may be similar to those of the Marshall and Lovingston gneisses Of the basement com- plex. Throughout this area most mesoscopic and microscopic subfabrics possess a monoclinic symmetry tendency, with the symmetry plane trending northwest and normal to the regional structural trend. This agrees with previous mesoscopic and macroscOpic studies, which have established the prevalence of structures overturned toward the northwest. JOINTS Joints are characteristic of all formations through- out the area and generally appear to be the result Of rather late deformation in the region, perhaps Triassic. The most pronounced Joints definitely cross-cut the regional strike at high angles and are probably gg,JOints. Others trend 206 207 northeast-southwest and are considered pp or aleoints, depending on whether they resulted from compression or from tension. Hadley and Goldsmith, 1963 (p. 95B-96B) mention simi- lar Joint relationships in the eastern Smoky Mountain area of North Carolina and Tennessee. P. D. King 1964 (p. 128) has also found cross-cutting (pp) and parallel Joint trends, with the pp trend being the most pronounced in_the central Smoky Mountain region of Tennessee. Farther north, in the Maryland and Pennsylvania area, S. L. Agron (1950, p. 1289) finds pp Joints more prevalent than others in the Peach Bottom Slate, also C. H. Broedel, (1937, p. 186) finds pp Joints in the gneiss domes near Baltimore. Ernst Cloos (1937, p. 74) states that ". . . in the Piedmont Of Maryland and Pennsylvania cross Joints are most abundant . . ." Similar Joint relationships have been recognized also in other orogenic belts. Wahlstrom and Kim, 1959 (p. 1236) find Joints cutting the regional grain in the Precambrian rocks of the Front Range of Colorado. Sutton and Watson (1951, p. 278) mention cross-cutting pp Joints in the Scottish highlands and state, ". . . in all parts of the complex, the last effect of pressure was to produce a series of strong vertical Joints . . . perpendicular to the strike . . ." THE CHILHOWEE FABRIC The fabric of the Chilhowee group in the western edge of the anticlinorium shows a history of less penetrative deformation compared with that of the basement complex and 208 Piedmont domains. Examination of the scalar aspects of the fabric shows minor metamorphic recrystallization, predeposi- tional strained quartz grains, and fine-grained, ill-defined sericite grains, all indicative of a sedimentary history with lesser deformation on the microscopic scale and little or no metamorphism. The individual quartz diagrams show a general ten- dency for maxima to be concentrated within 40 degrees or so of the p axis of each diagram. This effect has been observed by Rowland (1939. p. 458-459) who states that maxima arranged about, and 20 to 40 degrees from the p axis of the fabric, have been interpreted as demonstrating a "sedimentary orien- tation in which the Oblong grains as well as those making up the maxima lie with their optic axes approximately parallel to the planes Of motion in the sedimentary medium". Wayland (1939) concurs with this statement. He states that the Optic axes, generally parallel the longest dimensions Of sedimen- tary sand grains, this direction presumably being longest because of its greater resistance to wear. Furthermore, the longest dimensions of sand grains commonly parallel shore- lines (Twenhofel, 1932, p. 36). If these statements are valid, then coupled with the above observations on the Chilhowee scalar and vectorial fabric aspects, a sedimentary fabric, in part or in entirety, may be indicated for the rocks of the Chilhowee group. The present quartz orientation then possibly may be attributed to currents paralleling the ancient shorelines Of the deposi- tional area, with minor modification by a mildly penetrative 209 deformation. The mica subfabric possibly may better reflect ef- fects of deformation than the quartz. Some maxima in the master horizontal diagrams for mica of the Harpers and Unicoi formations apparently show the influence of postlithifica- tion cleavages. The strike of bedding in the Chilhowee units, especial- ly in the Antietam and Harpers formations, is variable be- cause of the low dips (see Figures 2 and 17). The strikes of the thin sections from which the fabric diagrams were prepared are consequently variable also. This may ex- plain the horizontal girdle in the cumulative-summary dia- grams of quartz maxima of the Antietam and Harpers formations (Figures 15 and 30), in spite of the concentrations of maxima within 40 degrees or so of the microfabric b axis for the individual diagrams. THE PIEDMONT FABRIC As opposed to the fabric of the Chilhowee group, that of the Lynchburg, Candler and Mount Athos formations show definite effects of metamorphism and recrystallization. Strained, elongated original quartz grains are common in these units, but elongated and equant recrystallized quartz is as common, if not more abundant. The mica also shows a freshness due to recrystallization, especially in the Lynchburg formation. Deformation has also been more intense in these units 210 than in those of the Chilhowee. As Opposed to the mesoscOpic s-surface pole girdles in the Chilhowee units, these Piedmont units show no mesoscopic s-surface girdles; their diagrams indicate steeply dipping and well defined foliation and isoclinally folded bedding. The major foliation in these Piedmont units is of the bedding plane variety, as postulated by Espenshade (1954, p. 29-31). This is supported by the s-surface diagrams. The secondary cleavage which intersect the bedding and the bedding plane foliation is not evident in the diagrams be- cause of the difficulty of finding exposed surfaces of this particular cleavage in outcrops. However, the crinkle linea- tion which it produces with the bedding and bedding folia- tion has been statistically presented in the lineation dia- grams. The peculiar lineation girdles trending northeast- southwest, which these diagrams show, have been found farther north in the Peach Bottom slate of Pennsylvania and Maryland by S. L. Agron (1950). The girdles here and in Pennsylvania and Maryland trend parallel to the regional b axis, and they possess maxima that are both subhorizontal (parallel to b) and steeply dipping, indicating sub-horizontal crenulations and steeply plunging crenulations. Other workers report similar crenulations in the Maryland-Pennsylvania areas to the north (Cloos and Hietanen, 1941, p. 160, and C. Ch'ih, 1950, p. 938) and in the North Carolina-Tennessee areas to the south (Hadley and Goldsmith, 1963, p. B92 - B95, and P. B. King, 1964, p. 127). 211 However, none of these writers specifically report any crenulations that are not sub-horizontal and do not parallel the regional b axis. These workers appear to agree that the displacement (crenulation) of the foliation is the result of slip-cleavage which was active during the latter phase of compressive deformation. However, Agron believes that the crenulations in the Peach Bottom slate are the result of the intersection of the older foliation with later fracture cleavage rather than slip-cleavage. A British worker, M. J. Rickard (1961, p. 324), does not like the term "slip-cleavage” or "strain-slip cleavage". Instead, he proposed to replace it with the term "crenulation cleavage." He considers this descriptive term more widely applicable than the older generic strain-slip cleavage. This writer believes that Richard's non-genetic "crenulation cleavage" may be preferable since the crenulations are attri- buted to more than one variety of cleavage by workers in the Appalachian region. Agron (p. 1289) suggests that the crenulation linea- tion girdle is the result of rotation of the local 2 axes (crenulations) about 3 in the ab plane. 0n the other hand, Donath and Parker (1964, p. 59) contend that "lineations parallel to the axial plane will fall about a point maximum unless the field is noncylindrical, in which case they will define the axial plane." They prOpose that "a great-circle distribution of lineations need not reflect rotation of pre- existing lineations (as Agron suggests) but may be produced l\ L J’\ I. 212 by a later, possibly unrelated episode of deformation." This was earlier suggested as a possibility by Turner and Weiss (1963. p. 449). The present writer believes that these crenulation girdles or great-circles are not necessarily the result of rotation of the local 3; axis (crenulations) about 3 in the a); plane nor need to be produced by later non-rotational de- formations.’ All crenulation data in this study were taken over a relatively wide area, and local variations in the attitude of the "crenulation cleavage" as it cuts the older foliation, due to local inhomogeneities, may have produced varying attitudes in the lineation from place to place. No more than two obvious crenulations have been observed by this writer in a single specimen or exposure, and only one lineation per exposure is usual. One should expect to find a few exposures containing several (more than two or three) crenulations, if these structures are due to either an ex- tensive rotational deformation or to later extensive defor- mations. Figures 123 and 139 indicate that the older folia- tion has a moderate variation in trend throughout the area. Consequently, even a crenulation cleavage of very regular orientation, if this were the case, would produce crenula- tions of varying attitudes with the older foliation, because this older foliation itself varies in orientation. A careful analysis of the younger foliations will be necessary if any definite conclusions concerning this particular problem can be made. l A'\.. J‘\ .2". 1‘ 213 The existence of girdles produced by the quartz maxima center points in the horizontal cumulative-summary diagrams is of great interest when seen in relation to the lineation girdles. These quartz supermaxima girdles are essentially parallel in trend with the lineation girdles. The individual quartz diagrams for both the Lynchburg and Candler units are from sections cut normal to the crenu- 1ation in the outstanding s-surfaces (or in a few cases normal to the strike of this s-surface when lineation was not visible). Small circle girdles about the center of the diagrams is the outstanding feature of these individual dia- grams, especially in the case of the Lynchburg formation. Consequently, these quartz girdles and their maxima vary in orientation as the lineation varies, and the lineation here forms girdles. The quartz orientation is then apparently very closely related to these crenulated lineations in origin. Many workers have reported quartz girdles normal to b lineations or crenulations, but small circle girdles appar- ently are not so common as great circle girdles. It is pos- sible that these girdles are similar to those discussed by Rowland and Wayland, which have been attributed to a sedi- mentary origin, however, this writer does not believe so, but believes them due to deformation and perhaps recrystal- lization, since they have such a constant relationship with the crenulated lineation. The Mount Athos quartz fabric is not obviously similar to that of the Lynchburg or Candler formations. The 214 horizontal cumulative-summary diagram shows two steeply dip- ping, intersecting girdles which bear no apparent relation- ship to the lineation. The symmetry is triclinic. Whether this anomalous quartz fabric is the result of a different type of deformation or whether it indicates that the Mount Athos quartz fabric developed along different lines because of the lithologic dissimilarities between it and the other two formations, cannot be definitely known. However, con- sidering the relationship of the Mount Athos total fabric with that of the Lynchburg and Candler formations, one must be careful not to place undue emphasis on this one difference. The one most important difference between the Mount Athos Formation and the other two units is that the Mount Athos Formation has a very high quartz content, and this particu- lar factor may account for the unusual quartz orientation. The individual mica diagrams generally show both well- developed maxima normal to the prevailing s-surface and poorly develOped girdles normal to the lineation. This is probably the result of the extensive recrystallization of the mica of these units under the influence of metamorphic conditions. The Lynchburg mica fabric is best develOped in this respect. This then may be termed a development of mica fabric by mimetic recrystallization along pro-existing 3- surfaces. The horizontal cumulative-summary diagrams of the Lynchburg and Candler mica cleavage poles show that these mimetic s-surfaces parallel the isoclinal bedding and bedding 215 plane foliation surfaces reasonably well. Apparently these two surfaces influenced the development of the present mica fabric of these two formations. It should be noted also that the Candler master mica diagram reflects, in the partial girdle, a poorer recrystallization of mica than in the case of the Lynchburg. Little may be said concerning the mica fabric of the Mount Athos Formation because of the meager data available. From the horizontal plot of the few mica cleavage pole maxima available, Figure 167 shows a tendency toward development of a mica girdle trending northwest, coinciding with the trend of the partial girdle for Mount Athos mesoscopic 3- surface poles. ‘ Because the total fabrics of the Lynchburg and Candler formations have so many characteristics in common, this writer believes that both show the same deformational history. If the Candler Formation were the shear zone for the great "martic overthrust," logically its fabric would probably be distinctly different from that of the Lynchburg formation, lying in the foot—wall. What faulting that did take place within the Candler Formation, or between it and the Lynchburg formation, was not of such magnitude to develop a distinct and unique fabric in the Candler Formation. SHEAR ZONE FABRICS Unique fabrics have been found in obvious shear zones along the eastern edge of the Blue Ridge, and the most 216 outstanding example of this is the previously-mentioned shear zone in the Antietam (Figure 14). The quartz grains in this very pure orthoquartzite have been stretched in the direction of shear, yielding length-width ratios of as much as 11:1. Pronounced undulose extinction occurs as sets of intersecting bands, the angles of which are bisected by the direction of shear, or the a fabric axis. The quartz optic axis diagram shows a girdle normal to this a lineation. Other workers have found similar rela- tionships in shear zones in the Caledonians of Scandinavia and Scotland. Two recent Norwegian workers especially have demonstrated the develOpment of quartz optic axes in girdles normal to the 9 axis, which parallels the stretching linea- tion. T. Strand (1945, p. 14) has observed this effect in a sheared conglomerate 100 miles northwest of Oslo. The movement was toward the southeast which is indicated by the lineation (strakeningen); the conglomerate cobbles are elongated in a northwest-southeast direction. Of 19 quartz diagrams studied, only one shows a girdle parallel to the direction of thrusting, the other eighteen have girdles normal to a, as was found here in the Antietam formation shear zone. A.Kvale (1945, p. 193), the other Norwegian investi- gator, has found mica and quartz partial girdles normal to the stretching lineation in Caledonian shear zones east of Bergen (Bergsdalen Quadrange area). Robert Balk (1952, p. 415-535) finds the quartz fabric of shear zones in a quartzite from the Taconic area of New York similar to that 217 reported by these Norwegian workers. According to Ernst Cloos (1946, pp. 28, 29, and 44), many other reports concern- ing a lineation in shear zones occur in the geologic litera- ture. In the central Virginia area, this girdle effect is further observed in shear zones within the Pedlar Formation. Figure 77 shows a girdle subnormal to the a shearing linea- tion (strakeningen). In addition, a mica diagram also from the Pedlar Formation, Figure 78B, shows a cleavage pole girdle normal to this lineation, but the companion quartz diagram, Figure 78A, shows a girdle essentially normal to the mica girdle and parallel to the ab plane. Perhaps this correlates with the above mentioned exception Strand found. Ernst Cloos (1946, p. 26-28, 35-36) believes that the character of deformation producing quartz and mica girdles normal to the a lineation is that of Bruno Sander's "cylindrical flow". Presumably where shearing takes place in a rock body under plastic conditions, a strong stretching of minerals will develop in the direction of shear (along the 5 axis). Furthermore, "the lineation would result in a strong waviness (microscopic folds parallel to a) and fluctuation of mica around it, resulting in a girdle" (p. 35). The quartz grains would also participate in this rotation, but in exactly what manner is open to debate. Some investi- gators find girdles normal to the b axis lying in the ag plane, while some, such as Kvale and Balk, find quartz girdles lying normal to the a lineation. Others, such as 218 Strand and the present writer, find both types of girdles. THE MARSHALL AND LOVINGSTON FABRICS Bloomer and Werner (1955, p. 603-604) consider the well-develOped lineation of the basement complex gneisses (the Lovingston and Marshall formations) to be lineation in 3, produced by shearing along this direction. They observe also that Blue Ridge thrusts disappear into the basement foliation. P. B. King (1964, p. 127) cites similar down- dip lineations in basement gneisses of the Great Smoky Mountains of Tennessee and terms them lineations in a. Ernst Cloos (l946, p. 44) observes similar lineation in the South Mountain volcanics of Maryland and Pennsylvania. He considers the lineation there to be the result of elongation in 5, also. From the fabric data obtained in this study, this writer concurs with the conclusions of Bloomer and Werner. This lineation, lying within the very regularly striking and dipping foliation, has itself a very definite and regular attitude. It plunges steeply toward the southeast and is concentrated within a limited area in each of the lineation diagrams, indicating a very high degree of preferred orienta- tion. Further, the individual mica diagrams show well- developed girdles normal to this lineation, and many individ- ual quartz diagrams show to a lesser extent girdles about the lineation. The two cumulative-summary, horizontal mica diagrams show very pronounced girdles normal to the lineation. 219 The cumulative-summary, horizontal quartz diagram for the Marshall formation (Figure 100) shows a weak girdle essentially coinciding with the well-developed mica cumula- tive-summary girdle. However, the corresponding cumulative- summary quartz maxima diagram for the Lovingston formation (Figure 118) shows more complex relationships. Here one horizontal and one subhorizontal girdle may be discerned, both being subnormal to this a lineation. But there are two additional and better developed girdles subparallel to the a direction. Both girdles intersect one another and their intersection angle is bisected by the symmetry plane of the diagram. Moreover, the plane of intersection is nearly normal to the planes of the two subhorizontal girdles. BJB' tectonite quartz patterns have been cited by many observers within sheared rocks. Fairbairn (1949, p. 59 and 61) mentions such observations by W. Larsson (1938). Larsson finds that the quartz fabric from a granite mylonite in Sweden yields two intersecting girdles very similar in appearance to Figure 118 of this paper. Presumably then, the Lovingston quartz girdles are a direct result of the a direction shearing. The array of girdles here is more complex than in the case of the Marshall formation, or that of the Antietam shear zone. However, the symmetry of the arrangement of these Lovingston girdles is of the first order and clearly must be the effects of movement in the a direction. The reader will recall that within one Pedlar shear zone the quartz girdle lay parallel to the 3 axis, while the 220 corresponding mica diagram shows a girdle normal to 9 (Figures 78A and B). Also, one of Strand's shear zone dia- grams shows a quartz girdle parallel to the shear direction. The Lovingston quartz, cumulative-summary diagram may show the entire range of girdles produced by shearing. In conclusion, the mica fabric appears to yield 'girdles normal to the direction of movement during cylindri- cal flow under relatively plastic conditions in the basement gneisses. The quartz fabric may also produce girdles normal to the a direction, but it may also develop girdles parallel to it, or even intersecting girdles subparallel to it. Consequently, quartz fabrics are less easy to interpret than those of mica. It must be pointed out here that the scalar aspect of the fabric in these two gneisses shows elongated and strained original quartz grains with crush quartz and minor recrystallized quartz within the interstices. The mica also shows the effects of deformation. All of this evidence considered together strongly supports an intense and penetrative shearing of these gneisses, under relatively plastic conditions. This shearing pre- sumably took place in pre-Appalachian time, because cobbles of the Lovingston, having this foliation, have been found in the Rockfish conglomerate by several workers. Moreover, the deformation which affected these gneisses is of a dif- ferent nature from that which develOped the fabric of the Chilhowee group and the Lynchburg formation-Evington group. The only exceptions are those fabrics in shear zones affecting 221 younger rocks, the Antietam shear zone especially. It is possible that during the more recent deformation, these old foliation surfaces in the basement gneisses were reactivated in local areas, especially in the western part of the Blue Ridge. This is not difficult to conceive because of the similarity in orientation of the basement gneiss foliation and younger Appalachian foliations and isoclinally folded beds. THE PEDLAR FABRIC Although being an important part of the basement complex and grading into both gneisses, the Pedlar Formation and its fabric are very distinct from the gneisses and their fabrics. Unfortunately, little or no mica is present and no lineations were observed in the Pedlar Formation, outside of the restricted shear zones. Consequently, these aspects of the fabric are not available in considering the fabric development of the Pedlar Formation. The granitic-like composition and gneissic banding are typical of this formation. Some of the banding parallels the foliation of the gneisses, but a significant portion does not. The quartz fabric does not help much in determin- ing the significance of the orientation of the banding, because the quartz fabric is quite ambiguous without accom- panying mica diagrams. The only definite statement that may be made about the quartz fabric is that in the horizontal cumulative-summary diagram of maxima from the individual 222 quartz diagrams (Figure 79) the symmetry plane trends northwest-southeast, and in this respect it is similar to the other master quartz diagrams of the basement complex. The only definite statements that may be made concern- ing this puzzling banding of quartz and feldspar grains are that it is highly variable in orientation, and it is older than the regular northeast-southwest shear zones that are developed within the Pedlar. Bloomer (unpublished, p. 53) has reported finding drag folds within the banding at certain locations. How this relates to the picture obtained in this study is uncertain, since none were observed by this writer. The Pedlar Formation's domal, oval shape, its intimate association with the basement gneisses, and its gneissic banding all have been observed in other old basement complexes in various parts of the world. M. O. Oyawoye (1964, p. 138-144) cites a charnockite-biotite gneiss association in northern Nigeria. The charnockite body is of an elongated lensoid shape and its relation with the gneiss suggests ". . . a common petrogenic history," to at least some degree. Oyawoye suggests that the charnockite develOped from the gneiss by some sort of granitization process. Banding parallel to the foliation in the adjacent gneiss is mentioned. C. H. Broedel (1937. p. 186, and 168) discusses the oval shape of the gneiss domes in the Piedmont near Baltimore, Maryland. Important among his observations are that the domes are oval shaped, and that the "banding", composed of platy minerals, is "bent into a semicircle following the 223 periphery of the domes . . ." Broedel suggests that the banding is in some way related to the uplift of the domes, though he specifically states that he does not necessarily wish to imply an igneous origin for the banding. Broedel did not present these structures in a fabric diagram, but logically the circular banding arrangement would produce a horizontal girdle or partial girdle, possibly even somewhat similar to the gneissic banding diagram for the Pedlar Formation in central Virginia. Further observations in the field must be made concerning this gneissic banding in each of the two large oval Pedlar bodies in central Virginia to determine specifically whether this gneissic banding does indeed follow the oval outline of the large domal bodies. Pentti Eskola (1948, p. 461-476) makes several generali- zations on the association of oval granitic bodies and adja- cent gneisses in ancient basements. Some of these do not apply here but others may. In eastern Finland, within the Karelidic zone, several elongated basement domes are mantled with basal conglomerates containing cobbles direct- ly derived from the gneisses of the basement. Quartzites, dolomites, and mica schist lie above the conglomerates. These strata are "layered parallel to the dome contacts and the foliation of the gneiss". In some of these areas the basement has not been altered since erosion and the subsequent deposition of the mantle upon it. Others have been remobilized during a later orogeny producing migmatiza- tion and varying degrees of palingenesis in the basement. 224 Eskola suggests that these occurrences are "exactly the same" as those "in Maryland and elsewhere within the Appalachian range of North America." (p. 461). Certainly these descriptions are suggestive of the basement complex upwarp and the mantle of younger, deformed sediments along its flanks within central Virginia. It is obvious that a greater awareness of and interest in the work being carried on in other basement complex areas of the world, and especial- ly a closer contact among the workers involved in similar problems from widely separated areas, may shed light on the problems within the central Virginia area and in other areas of the world. THE SWIFT RUN FABRIC The remaining unit to be considered is the Swift Run Formation. As stated several times previously, a paucity of information unfortunately exists because of difficult access to and the very small stratigraphic thickness of this unit. The fabric of the Swift Run Formation, from the data at hand, is different from that of the Chilhowee group. It is also different from that of the Lynchburg formation- Evington group. The Swift Run Formation s-surface and lineation subfabrics (Figures 55 and 56) are possibly similm' to those of the basement complex, and to that of the shear zone within the Antietam formation. The foliation and bed- ding dip steeply to the southeast and strike regularly 225 northeast. The lineation lies essentially in a down-dip direction, parallel to 3. However, the mica cumulative- summary diagram (Figure 64) does not show the characteristic girdle about a found in the basement, but possibly lies subnormal to the regional b axis. The quartz cumulative- summary diagram is ambiguous and thus difficult to interpret. It may possess triclinic symmetry and consequently reflect a complex movement picture. The scalar fabric character shows elongated quartz and mica grains, deformed and sug- gestive of shearing. Because this unit lies within the Blue Ridge thrust zone, it must be assumed that in general the total fabric reflects the effects of shearing, but to what degree other factors are involved is unknown at present. CONCLUSIONS Very little is known of the mechanism or mechanisms by which quartz is oriented during deformation. A few notable studies have been made which attempt to provide an experimental basis for theories concerning quartz orienta- tion (Griggs and Bell, 1938; Griggs, Turner, and Heani, 1960, pp. 75—79; Carter, Christie, and Griggs, 1961). Al- though these studies show promise, definite information on the orienting mechanisms of quartz is not available. This lack of eXperimental knowledge has been a handi- cap in analyzing the quartz fabric of the Catoctin Mountain- Blue Ridge anticlinorium. As a consequence any genetic interpretations made concerning quartz orientation are 226 inconclusive, and are not based on sound fact. Quartz was.chosen here because of its presence in all units studied. Mica, however, has provided a better tool in the interpretation of the microscOpic fabric, and mica orientation is more easily related to the orientation of mesoscopic structures. Unfortunately, mica is not present in all units studied in central'Virginia. One intent of this paper has been to demonstrate microfabric differences among the different suites of rocks Within the anticlinorium. This has been done in a descrip- tive sense. However, the quality of information has been poor in comparison with the effort required to obtain it. The opposite may be said of information obtained from the meSOSCOpic subfabrics. In.most cases the mesoscOpic data shows the variation of structural characteristics among the various suites of rocks as well as, or better than, did that obtained from the microscopic subfabrics. Several recommendations for further studies in cen- tral Virginia may be suggested here. First, an investiga- tion would be desirable concerning whether the scarceness of mica in the Mount Athos formation is responsible for the anomalous quartz fabric. It would be interesting to see if the Candler-like and Lynchburg-like individual quartz fabrics from the Mount Athos can be directly correlated with.a higher mica content. 227 Another interesting study would be an.attempt to explain why the Lynchburg formation is of a higher metamorphic rank than is the Candler Formation. The present fabric study supports previous investigations which have indicated that both the Lynchburg and Candler units have undergone a similar deformational history. The question that must be answered is why these two units do not record a similar metamorphic history also. The basement complex presents several problems for future investigations. An examination of the several types of quartz and mica in the Lovingston and.Marshall formations by means of partial diagrams may yield specific information concerning the number of deformational and.metamorphic episodes which these rocks have undergone. Also, a detailed microscopic and mesoscOpic fabric study of the Pedlar found in the anticline cores of folded Chilhowee rocks along the Blue Ridge may yield information concerning therheologic state of the Pedlar during Appalachian folding. Finally, a detailed study of the mesoscOpic and microscOpic character of the Swift Run formation.may indicate what role this unit played during regional thrusting. Agron, Allen, REFERENCES CITED S. L., 1950, Structure and petrology of Peach Bottom slate, Pennsylvania and Maryland, and its environment: G601. SOC. Am., Bull., V. 61, p. 1265-1306. R. M., Jr., 1963, Geology and mineral resources of Greene and Madison Counties: Virginia Div. Min. Resources, Bull., n. 78, 94p. Balk, R., 1952, Fabric of quartzites near thrust faults: Jour. Geology, v. 60, p. 415-435. Bloomer, R. 0., 1950, Late Pre-Cambrian or Lower Cambrian formations in central Virginia: Am. Jour. 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Virginia Division of Mineral Resources, 1963, Geologic map of Virginia. Wahlstrom, E. E., and Kim, 0. J., 1959. Precambrian rocks of the Hall Valley area, Front Range, Colorado: Geol. Soc. Am., Bull., v. 70, p. 1217-1244. Watson, T. L., and Cline, J. H., 1916, Hypersthene syenite and related rocks of the Blue Ridge region, Virginia: Geol. Soc. Am., p. 193-234. Wayland, R. J., 1938, Optical orientation in elongate clastic quartz: Qm. Jour. Sci., v. 236, p. 99-109. White, W. S., 1949, 1949, Cleavage in east-central Vermont: Am. Geophys. Union, Trans., v. 30, p. 587-594. GRIFFIN -4”..- 3.-.; -‘D- nut-h. b“. ____L.‘_ "a. I‘-' 4.1+' '7’: _ :719‘1'119 first" —‘." l' MAP .,,., OFTHE CATOCTHNEflOUNIAINJMJHZPUDGE.ANTKHJNORHMJ OF CENT RAL VIRGINIA (75 [gig <9"? F77 S»... I.“ / a //// ‘ i" / .. . Fl ..., ,A W ,, WfiMHrR‘Tr‘mnbA (|r _ (HIf-‘MAN O‘I nDA“ ‘- AFTER E 3‘?“3o’ wur' ”W ’IWWIIWLEGEND M MOUNT were 4m€A~ANTIETAM r... 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