STRATéGRAP‘HY AH}? SITRIEECTQRE Q? TE‘EE MCCASEMN EJES‘FR‘ECR wzsrcwm Thesis Too Hm Dogma 05 pin Dc MECMGM‘T STATE UNWER‘SETY Joseph John Mameugo 1960 This is to certify that the thesis entitled STRATIGRAPHY AND STRUCTURE OF THE MCCASLIN DISTRICT, WISCONSIN presented by JOSEPH JOHN MANCUSO has been accepted towards fulfillment of the requirements for \. . \ft’ Ufi;:;\() WA] Major was»? Date lth \b \OX‘LOD k L I B R A R Y Michigan Sta tc University OVERDUE FINES: 25¢ per du per item RETURNING LIBRARY MATERIALS x." Place in book return to remove charge from circulation records ' \ J: x 1 n l "w ' 4' A -.-, 3;: - 11 ‘ “3/ STRATIGRAPHY AND STRUCTURE OF THE MCCASLIN DISTRICT, WISCONSIN By JOSEPH JOHN MANCUSO AN ABSTRACT Submitted to the School for Advanced Graduate Studies of Michigan State University of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Geology 1960 Approved Sada—Lieu a /\ Jos eph John Mancuso ABSTRACT A combined field and laboratory study was carried on to determine the stratigraphy and structure of the McCaslin district of northeastern Wisconsin. The district lies along the parallel 450 21' north latitude and between the meridians 880 11' and 880 48' west longitude. The dominant structure in the district is the McCaslin syncline which trends approximately east-west. The trough opens to the west and appears to close to the east but is disrupted by the intru- sive High Falls granite. The oldest rocks in the district are the Waupee series which is distributed about the outer borders of the trough. The series is a complex of metamorphosed volcanic flows, agglomerates and tuffs with large included bodies of granite and diorite. The McCaslin formation lies unconformably upon the Waupee series. It is composed of a basal conglomerate which grades upward into clean quartzite. The formation reaches a maximum thickness of close to 5000 feet. The McCaslin formation furnishes the structural framework for the regional syncline. The Hager rhyolite porphyry lies unconformably upon the McCaslin formation. It flowed out onto a terrain of fairly high relief and is confined mainly to the synclinal trough. Joseph John Mancuso The youngest rocks in the district are the intrusive High Falls and Belongia granite masses. The High Falls granite was seen in direct contact with the McCaslin formation in six different localities and shows definite intrusive relationships. A well developed meta- morphic aureole related to the High Falls granite can be traced by progressive metamorphic changes in the Hager, McCaslin and Waupee formations. The metamorphic mineral assemblages indicate a maximum temperature of 700 degrees centigrade for the granite intrusion and a maximum depth of 15 feet for penetration of granite fluids into the quartite. A petrofabric and a joint study were made to supplement the structural data obtained in the field. Both agree with the major structure and indicate that the direction of maximum stress release was nearly horizontal and parallel to the strike of the bedding. The exact stratigraphic position of the Precambrian formations of the district can be determined only approximately and conjecturally because of their isolation and complete separation from the main Precambrian regions to the north. The Waupee series is considered Lower Precambrian and a possible correlative of the Quinnesec formation of Iron and Dickinson Counties, Michigan. The McCaslin formation is considered to be Middle Precambrian or Huronian, but its exact position in the Huronian system is not clear. 4 Joseph John Mancuso . The extrusion of the Hager rhyolite porphyry and the intrusion of the High Falls and Belongia granites along with the regional deformation are thought to be part of a great post-Huronian--pre-Keweenawan orogeny (Killarney revolution?) which occurred about 1000 to 1100 million years ago. STRATIGRAPHY AND STRUCTURE OF THE McCASLIN DISTRICT, WISCONSIN BY JOSEPH JOHN MANCUSO A THESIS Submitted to the School for Advanced Graduate Studies of Michigan State University of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Geology 1960 (l / :37 ’70 I4,» [ft/é! Figure 1. \» \VM7\~V~7\‘- \v\y~\‘ ‘7: , View of McCaslin Mmmtain ii 8 ea ”W”? '3‘ 3i 11- ” ‘35, ,3... ‘ ' “ill iii 1.. t. A J i ‘1‘; E i :4". (“1.1” ”1". 5:: EEOOK Page LIST OF FIGURES ........................................... v LIST OF TABLES ........................................... V111 LIST OF MAPS .............................................. ix INTRODUCTION ............................................. 1 Acknowledgments 1 Previous Investigations 2 Geography and Topography 3 Regional Geology 6 GEOLOGY OF THE MCCASLIN DISTRICT ...................... 7 Waupee Volcanics and Basement Complex 7 McCaslin Formation 12 Quartzite 13 Conglomerate 16 Environment of Deposition 20 Structure of the McCaSIin Formation 21 Hager Rhyolite Porphyry 28 High Falls Granite 32 Structure of the McCaslin District and the Relationship of the High Falls Granite to the Areal Distribution of the Quartzite Ranges 40 Relationship of the High Falls Granite to the Hager Rhyolite Porphyry 44 METAMORPHISM ............... 1 ............................ 51 Waupee Volcanics and Granite Complex 52 Hager Rhyolite Porphyry 61 McCaslin Formation 65 Temperature of Metamorphism and Granite Intrusion 77 ANALYSES OF JOINTS ....................................... 83 PETROFABRIC ANALYSES ................................... GEOLOGIC HISTORY REGIONAL GEOLOGY AND CORRELATION ..................... REFERENCES iv 86 88 92 97 Figure 10. 11. 12. l3. 14. 15. 16. LIST OF FIGURES View of McCaslin Mountain ......................... Index map, area of investigation ..................... Cross-bedded quartzite in McCaslin formation ......... Quartzite resting on conglomerate, McCaslin formation. Paleo-current map of Precambrian quartzites of the Lake Superior region Quartzite inclusions in the Hager rhyolite porphyry ..... High Falls granite (Gt)-McCaslin formation (Qtz) contact exposed in the bed of the Peshtigo River in sec. 25, T. 34 N., R. 18 E. .............................. High Falls granite (Gt)-McCaslin formation (Qtz) contact exposed in the rift in sec. 28, T. 34 N. , R. 17 E. . . . Joint fractures in quartzite filled with secondary quartz, McCaslin formation .............................. Brecciated quartzite cemented by secondary quartz, McCaslin formation .............................. Flow foliation in the High Falls granite ............... Flow foliation and inclusion in the High Falls granite . . . Waupee inclusions in the High Falls granite ........... Fluorite (F) in the High Falls granite, plain light (Sample 41) ....................... . .............. Fluorite (F) in the High Falls granite, crossed nicols (Sample 41) ............................... . ...... .Fluorite (F) in the Hager rhyolite porphyry, plain light (Sample 74) ...................................... Page ii 15 15 19 30 34 35 38 38 41 42 42 47 47 48 Figure 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. Sample location map, metamorphic geology .......... Diorite of the Waupee series altered to mineral assemblage characteristic of greenschist facies (Sample 5) ......... . . . . . . ....................... Garnets (G) and zoisite (Z) in the Waupee volcanics (Sample 47) ..................................... Feldspar assemblage microcline-perthite-albite in the Waupee volcanics (Sample 46) .................... Feldspar assemblage microcline-perthite-albite in the Waupee volcanics (Sample 46) ........ . ............ Biotite (B) and muscovite (M) in the Waupee volcanics (Sample 93) ..................................... Hornblende (H) in the Waupee volcanics (Sample 65) . . . Fine grained groundmass and phenocrysts with sharp boundaries, Hager rhyolite porphyry (Sample 74) . . . Recrystallized groundmass and overgrown feldspar phenocrysts, Hager rhyolite porphyry (Sample 78). . . Slightly recrystallized quartz with interstices filled by fine sericite, McCaslin formation (Sample 73) ...... Highly recrystallized quartz exhibiting undulatory extinction, McCaslin formation (Sample 42) ........ Coarse, optically continuous muscovite filling interstices between adjacent quartz grains, McCaslin formation (Sample 39) .................... . ................ Andalusite filling interstices between quarts grains, McCaslin formation (Sample 51) ................... Coarse sillimanite needles formed within andalusite, McCaslin formation (Sample 66) . ._ ................. aaaaa vi Page 53 54 57 58 58 60 60 63 63 66 66 68 68 74 vii Figure Page 31. Fine sillimanite needles formed along quartz boundaries from remnant sericite, McCaslin formation (Sample 66) . . . ................ . ................... 74 32. Feldspar assemblage (F) microcline-perthite-albite occupying interstices between quartz grains, McCaslin formation at High Falls granite contact (Sample 83). . . . 75 viii LIS T OF TABLES Table Page 1. Sequence of rocks in the McCaslin district .......... 8 2. Analyses of the High Falls granite ................. 45 3. Analyses of the Hager rhyolite porphyry ........... 46 4. Metamorphic mineral assemblages ................. 55 5. Correlation of the McCaslin district to Iron and Dickinson Counties, Michigan ................... 93 II III IV LIST OF MA PS Geologic map of the McCaslin district Tectonic A, Band C axes from joint analyses Petrofabric analyses McCaslin syncline, regional geology ix Pocket Pocket Pocket Pocket INTRODUCTION Northeast Wisconsin contains large areas of relatively unexplored Precambrian rock sequences. One of these areas, the McCaslin district of Marinette, Langlade, Oconto and Forest Counties is described here. This research was undertaken because there is reason to believe that deposits of valuable minerals may exist in this part of Wisconsin; concentrations of pyrrhotite are found near Mountain, and concentrations of molybdenum are located near Middle Inlet. No deposits of minable size have been found to date, but the local concen- trations constitute evidence that economic bodies of valuable minerals may occur in the vicinity. A detailed field and laboratory study of the exposed rock formations is considered the. logical approach to the detection of economic mineral deposits. After having spent three field seasons studying the Pre- cambrian formations of northern Wisconsin, the author and an assistant completed the field work during the summer of 1959. This field season was devoted to mapping the outcrops and to a study of the geologic structure and stratigraphy of the McCaslin region. During the academic year 1959-1960, laboratory investigations were made at Michigan State University to supplement the field data. Acknowledgments The field work was supported by a National Science Foun- dation Summer Fellowship for Teaching Assistants, and the writer gratefully acknowledges this financial assistance. To Samual Alguire the writer is deeply indebted for capable assistance in the field. Appreciation is due to Dr. Justin Zinn, Dr. James Trow, Dr. William Hinze, Dr. B. T. Sandefur and Dr. H. B. Stonehouse for their constructive criticism and interested guidance. The writer would also like to acknowledge the use of facilities and the helpful assistance of the United States Forestry station at Lakewood, Wisconsin. Previous Inve stigations The quartzite of the McCaslin range is briefly mentioned in the Wisconsin Geological Survey publication Geology of Wisconsin, 1873-1879, but a detailed geological exploration was not undertaken by the geological survey at that time. In 1943, F. V. Hoffman compiled a geological map of McCaslin Mountain from aerial photographs. General outcrop locations and rock descriptions were based on field work by O. M. Wheelwright. Hoffman concluded that the northern and southern ridges of the eastern range were the limbs of a local syncline. Roberts, 1951, concluded that the High Falls granite is the result of granitization of an impure quartzite. He maintained that structural activity was a major factor in the granitization process. In 1957, the author mapped the rock exposures in the vicinity of Mountain, Wisconsin, and concluded that the rock sequence exposed was the southern limb of a large regional syncline. The author also conducted a general reconnaissance of the geology of northeast Wisconsin. In addition, general geological and geophysical surveys have been made in the McCaslin region by a number of mining com- panies, but their findings are not available. Geography and Topography The McCaslin district lies in northeast Wisconsin along the parallel 450 21' north latitude and between the meridians 880 11' and 880 48' west longitude south of the Menominee River and northwest of Green Bay (Figure 2). The district, as described in this report, occupies parts of Marinette, Langlade, Forest and Oconto Counties and contains topographic features such as McCaslin Mountain, Deer Lookout Tower Hill and Thunder Mountain which are underlain by massive quartzite and conglomerate. The district covers an area of approximately 375 square miles. McCaslin Mountain is the main topographic feature of the area forming a ridge of moderate relief rising up to 300 feet above the surrounding countryside and trending N. 600-90o E. It ranges from two to five miles in width and extends laterally for a distance of MICHIGAN WISCONSIN 50 miles Area of Investigation INDEX MAP approximately 25 miles in Tps. 33 and 34 N. , Rs. 14, 15, 16, 17 and 18 E. The highest altitude on the ridges is slightly in excess of 1500 feet at the McCaslin lookout tower in the SE 1/4 sec. 25, T. 34 N. , R. 16 E. Deer Lookout Tower Hill which occupies most of sec. 2, T 34 N. , R. 16 E. is an isolated circular knob that rises 200 feet above its surroundings. Thunder Mountain is a ridge trending slightly west of north and rising 300 feet above the adjacent countryside in secs. 30 and 31, T. 33 N., R. 18 E. and secs. 25 and 36, T. 33 N., R. 17 E. The entire region has been glaciated and the topography has been modified by abrasion and deposition of glacial material. Pre- glacial drainage has been disrupted by the drift, so that swampy ground and lakes are common in the region. Principal streams, such as the Peshtigo, North and East Branches of the Oconto, Knowles, Otter and McCaslin rivers, all emptying into Green Bay, occupy channels that are a combination of pre- and post-glacial drainage. The thickness of the glacial drift is not uniform, and over large areas the ice has removed the mantle and exposed scoured and polished bedrock. Large portions of the area where quartzite lies at or near the surface are covered with hardwood forests. Farming, lumbering and tourists provide the principal occupations in the region. The principal town is Wabeno with a population of 800. Lakewood, Carter and Townsend are smaller unincorporated communities in the district. The Chicago and North- western Railway is the only railroad crossing the region. State highways 32 and 64 are the main thoroughfares servicing the district. Regional Geology The stratigraphy of the Precambrian of northeast Wisconsin is still a matter of dispute because of the extensive cover of glacial drift, the lack of distinctive rock units and the lack of concentrated geologic study. In general, as shown on the geologic map of Wisconsin, revised by E. F. Bean, 1949, the regional stratigraphy is as follows: Upper Cambrian sandstones and dolomites lap over undifferentiated Huronian and Laurentian rocks (chiefly granites, gneisses, gabbros, porphyries, metasediments and metavolcanics). Scattered outliers of Keweenawan igneous rocks (basic lava flows, gabbros, diabases and acid extrusives) and Upper, Middle and Lower Huronian (quartzites, slates and iron formations) occur in the undifferentiated Huronian and Laurentian of northern Wisconsin. GEOLOGY OF THE McCASLIN DISTRICT Waupee Volcanics and Granite Complex A sequence of rocks outcropping near Mountain, Wisconsin and designated as the Waupee volcanics was described by the author following field work done during the summer of 1957 as follows: The Waupee volcanics are a thick sequence of tuffs, agglomerates, basalts, and basalt porphyries which have been cut by two separate granite intrusives, metamorphosed to the amphibolite facies, and in part silicified. The volcanics are extensively exposed in the area drained by the Waupee Creek, west of the Little Waupee Swamp in T. 31 N. , R. 16 and 17 E. , east of Mountain, Wisconsin. The composition of the volcanics ranges from 100 percent hornblende in the amphibolites to almost pure quartz in the silicified areas. Feldspar is often absent, but may be present to the extent of 50 percent as an essential con- stituent or as phenocrysts in the porphyries. The grain size ranges from less than 1 mm to over 5 mm. Thin banding or bedding is common, but in many cases the rock is dense and massive. The general trend of the banding and bedding is from N. 500 E. to N. 800 E. with steep dips to the north and south, but forming no apparent anticlinal or synclinal folds. Many local dips and strikes vary from this general trend, but they are probably the result of the distortion during one or the other of the granite intrusions. The Waupee volcanics are cut by and appear as inclusions in the Macauley granite, a gray foliated horn- blende granite which is typically exposed along the Macauley Creek in sec. 5, T. 31 N. , R. 17 E. , east of Mountain, Wisconsin. The foliation of the Macauley granite and the alignment of volcanic inclusions follow the same general N. 500 E. to N. 800 E. trend, but again, there are many local deviations. The Macauley granite is of Z to 5 mm grain size and varies greatly in composition, ranging from that of quartz diorite to that of mafic syenite. The mafic minerals, mainly hornblende with minor biotite, amount to 70 percent in extreme cases. In the McCaslin district, rocks similar in lithologic character to the Waupee series crop out north of the main McCaslin quartzite ridge and also east of the Thunder Mountain quartzite exposures. The exposures are widely separated and vary greatly in extent, some consisting of one small or large outcrop and others of several separated outcrops near one another. Exposures north of the main McCaslin ridge are found near the center of sec. 28, T. 34 N. , R. 16 E. ; in the S and SE 1/4 sec. 23, T. 34 N. , R. 16 E. ; and in the NE 1/4 sec. 5, and the N 1/4 sec. 4, T. 33 N. , R. 15 E. Exposures are most numerous and largest east of Thunder Mountain in secs. 31, 32, and 33, T. 33 N., R. 18 E., the NW 1/4 sec. 5, T. 32 N., R. 18 E. and the SE 1/4 sec. 25, T. 33 N., R. 17 E. The rocks grouped under the general heading of Waupee volcanics and granite complex include a variety of types. Mega- scopically they are gray-black, finely banded or massive rocks which appear to be rich in fine grained quartz. The grain size seldom is more than 2 mm. The rock characteristically shows iron staining on the weathered surface and is very hard, and breaks under a stroke of the hammer producing a sharp conchoidal fracture. The fine banding, where evident, is best observed on the weathered surface and is the result of differential weathering of quartz rich and mafic mineral rich layers less than 5 mm in SEQUENCE OF ROCKS IN THE MCCASLIN DISTRICT Pleistocene Precambrian Glacial drift UNCONFORMTTY High Falls granite Intrusive contact Hager rhyolite porphyry Unconformity McCaslin formation Unconformity waupee volcanics and granite complex Table l o 10 width. Individual layers are not traceable over great distances because of the fineness of the banding and scarcity of continuous outcrops. Near the center sec. 28, T. 34 N., R. 16 E. a massive, equigranular rock of diorite composition with grain size less than 3 mm is interbedded with the finely laminated portions of the Waupee. The diorite exhibits a slightly pink color on the weathered surface. A small exposure in the S 1/4 sec. 23, T. 34 N. , R. 18 E. is fine-grained, dark and does not show banding or foliation. In sec. 4 and 5, T. 33 N. , R. 15 E. the Waupee complex takes on a coarser, igneous appearing texture and varies in composition from granitic to dioritic. The grain size is 3-5 mm, the color is slightly pink and the rock is massive. The outcrop as a whole, however, contains a boxwork of veins two inches and less in width filled with either epidote, quartz, pink granite or granite pegmatite. In the NE 1/4 sec. 5 the rock is a hornblende diorite with an average grain size of 5 mm. Hornblende laths in small zones attain lengths of 1-2 inches and may comprise as much as 40-60 percent of the rock. Pyrite occurs as a visible accessory of less than one percent in small scattered patches. A small outcrop in this area shows a complex relationship of amphibole rich host rock invaded by a complex of light pink granite veins. The relationship of the Waupee complex to the over— lying quartzite in the McCaslin district is that of an unconformable 11 base upon which the quartzite was deposited. The basal phase of the quartzite is a coarse, dark conglomerate containing pebbles of material similar to that of the Waupee complex. Dips and strikes of the Waupee are not generally conformable with those of the basal conglomerate or the quartzite. Numerous outcrops of the Waupee complex are found immediately east of the Thunder Mountain quartzite exposures. The Waupee is characteristically finely banded, dark gray-black, very dense and exhibits a conchoidal fracture. The grain diameter is generally less than 2. mm. The fine banding is traceable over the length of the outcrops, which may be a distance of 300 feet. The strike of the banding is N. 10° w. and the dip is 55° W. The attitude is conformable with that of the overlying basal conglomerate and that of the main quartzite body which underlies this topographic high. Faint cross bedding in an exposure in the SE 1/4 sec. 32, T. 33 N. , R. 18 E. , indicates that the top of the formation is to the west and that the general source of sediments is from the north. The general source direction and tops of beds as indicated by cross-bedding in the Waupee corresponds to that in the later quartzite. Portions of the Waupee series in this area probably represent water-laid volcanic materials interbedded with the flows and pyroclastic s . 12 McCaslin Formation The McCaslin formation consists of two kinds of rock, the quartzite which makes up the bulk of the range and the con- glomerate at its base. Three separate ranges of exposures occur in the district; the McCaslin Mountain exposures, those at Deer Lookout Tower Hill and those at Thunder Mountain. McCaslin Mountain is a narrow (1-3 miles) range of continuous exposures that extend in a N. 600-90O E. direction for a distance of some 25 miles. The western portion which extends from the Ada Lake lookout tower in sec. 4, T. 33 N. , R. 14 E. to Knowles Creek in sec. 4, T. 33 N. , R. 16 E. consists of a single ridge which rises 100-300 feet above the surrounding country- side. Outcrops are fairly sparse, but the prominent elevation of the ridge and the abundance of large boulders of conglomerate and quartzite leave little doubt as to the presence of quartzite or conglomerate very near to the surface. The eastern portion of the range which trends N. 700-900 E. from Knowles Creek in sec. 4, T. 33 N. , R. 16 E. to the Peshtigo River in T. 34 N. , R. 17 E. consists of a distinct ridge to the north and another to the south separated by a narrow lowland less than one mile wide occupied by lakes and swampy ground. The north ridge, composed mainly of conglomerate, trends N. 700-900 E. and disappears beneath glacial drift in sec. 20, T. 34 N. , R. 17 E. 13 The south ridge, mainly made of hard gray to white, vitreous quartzite, extends in a N. 700 E. direction to a large rift in sec. 28, T. 34 N. , R. 17 E. East of the rift the ridge trends approximately east to the vicinity of a pronounced bend in the Peshtigo River where it is terminated in sec. 2.5 and 2.6, T. 34 N. , R. 17 E. by the intrusive High Falls granite. The Deer Lookout Tower Hill exposures in sec. 2, T. 34 N., R. 16 E. consist of two N. 50.100 w. trending ridges of clean, gray—white quartzite separated by an arm of intrusive granite 300 feet in width. A few pebbles are scattered through the quartzite, but no continuous conglomeratic layers were seen. Glacial drift borders the knob of quartzite on all sides. The Thunder Mountain exposures extend in a N. 00-100 W. direction for a distance of l. 5 miles from sec. 31, T. 33 N. , R. 18 E. to sec. 25, T. 33 N., R. 17 E. The quartzite is conformable with the Waupee complex to the east and is terminated by the High Falls granite to the north. Exposures of conglomerate at the east portion of Thunder Mountain give way to a fine vitreous gray-white quartzite to the west. Quartzite--The great bulk of the McCaslin formation is a hard, brittle, vitreous quartzite which was originally sandstone that was changed through the processes of metamorphism. The texture varies from rounded grains of quartz of medium size l4 cemented together by secondary interstitial quartz to a recrystallized mosaic of interlocking quartz grains with little or no interstitial material. There is a general increase in grain size and decrease in interstitial quartz from west to east because of more intense metamorphism as the vicinity of the High Falls granite is approached. The color of the quartzite is generally white, varying through gray and pink to purplish-red and at some places brick red. The latter is due to finely disseminated hematite. Bedding is apparent in many exposures because of slight changes in grain size, color or hematite staining. Bedding joints are often well developed even where true bedding is in- conspicuous. Cross-bedding is very common throughout the district. On the McCaslin range cross-bedding indicates that the tops of the beds are to the south, and that the general source of sediments or current direction is from west to northwest. Ripple marks are extremely well preserved in the s 1/4 sec. 29, T. 34 N., R. 17 E. They are of the oscillation type and indicate that the top of the beds is to the south. Cross bedding at Thunder Mountain indicates that the top of the quartzite is to the west and that the source or current direction is from the north. Silty or clayey material was not found interbedded with the quartzite in the district. If it does exist, it is most likely hidden by the vegetation cover or has been removed more deeply 15 » .i, «*»=~ s»\‘_b-\,‘\\_\‘\ \\i»_ .’ I rr’ff’f~J—J ”fr’v I l I r gl‘, xr_\_,‘\\i_.\-\ <\ l ,¥\‘\\m\-‘ E _V Figure 11. Quartzite resting on conglomerate, McCaslin for- nation. 16 by selective erosion. Therefore, fracture cleavage, drag folds and boudinage structure, common in other quartzite areas such as the Baraboo Hills of Wisconsin, were not seen in the district. The quartzite in places (EC 1/4 sec. 27, T. 34 N. , R. 18 E. ; NE 1/4 sec. 28, T. 34 N., R. 17 E.; SE 1/4 sec. 29, T. 34 N., R. 17 E.;SW1/4 sec. 35, T. 34 N., R. 16 E.; s 1/4 sec. 34, T. 34 N., R. 16 E.;NW 1/4 sec. 4, T. 33 N., R. 15 E.) consists of a mass of angular fragments of gray quartzite firmly cemented by white, secondary quartz. The brecciated areas are generally linear in extent and parallel to the bedding direction. In general, they are located along the southern border of the range or near areas of inferred cross flexing or faulting. The breccia is of deformational origin and developed by differential movement of the brittle quartzite layers during the regional folding and the intrusion by the High Falls granite. Conglomerate-~The conglomerate exposed at the base on the McCaslin formation is a true basal conglomerate. It is abundant and shows conclusively the unconformable position of the sedimentary series above the rocks of the Waupee complex. The conglomerate is found as a fairly continuous series of exposures along the northern border of the western McCaslin range and on the north ridge of the eastern McCaslin range. An exposure in the SE 1/4 sec. 30, T. 33 N., R. 18 E. indicates that conglomerate lies to the east and below the clear gray quartzite and stratigraphically above the Waupee complex in the Thunder Mountain area. 17 Gray and red quartzite and white vein quartz make up by far the dominant portion (50-70 percent) of the pebbles in the conglomerate. The remainder is a mixture of fragments of the Waupee complex, banded hematite iron formation and red jasper. The pebbles attain a maximum size of seven inches in diameter at the west end of the western range in sec. 4, T. 33 N. , R. 14 E. Other outcrops indicate that the pebbles are coarsest (4-5 inches in diameter) at the extreme northern border of the ranges which is the base of the formation and become finer in the upper beds eventually giving way to clean gray quartzite. The proportion of quartzite and quartz pebbles increases from less than 50 percent at the base of the formation to almost 100 percent in the finer conglomeratesabove the base. This change is easily recognized by the color gradation from dark gray or black at the base to clear white or light gray toward the top. The degree of roundness and sphericity is maximum for the quartzite and quartz pebbles, but varies from angular to sub- rounded for the Waupee and iron formation pebbles. This suggests a distant source for the quartz pebbles and a fairly close source for the pebbles of Waupee complex and iron formation. Outcrops of Waupee are within 500 feet of the conglomerate in sec. 5, T. 33 N. , R. 15 E. and the SE 1/4 sec. 23, T. 34 N. , R. 16 E. , and many others are seen within one-half mile to the north of the quartzite. No outcrops 18 of iron formation are found in the district, but iron rich layers were noted in the Waupee complex south of Mountain, Wisconsin, thus it is quite possible that they may also exist in the Waupee complex north or west of McCaslin. No possible source of quartzite or quartz was seen in the immediate vicinity of the McCaslin district, however, exposures of quartzite are quite common in the Florence, Menominee, Iron River and Crystal Falls districts less than fifty miles to the north. The matrix of the conglomerate is a mixture composed of fine grains of rounded quartz, quartzite and dark rock fragments. The proportion of dark fragments decreases from the base upward, thereby causing a change in overall color from dark gray-black at the base to light gray or white toward the top. Interbedded with the conglomerate leyers are beds ranging in composition from dirty gray or red arkose to clean white quartzite which increases in number in higher horizons. Cross—bedding in the finer grained beds indicates a general source of the sediments from the west and northwest, and that the top of the formation is to the south. At Thunder Mountain the general trend of the conglomerate layers is N. 00-100 W. Pebbles become smaller and are more quartzitic and the matrix becomes cleaner with less dark fragments toward the west or from the bottom to the top of the formation. Cross-bedding in the beds of finer material between conglomerate layers indicates a general source from the north and west, and that the tops of the beds are to the west. l9 EDGE OF PALEOZOIC IESMRC ’ SYUROEOI I|$SISSAOI ? % LORRAIN LOIIMN ‘ unsoo " MILES Figure 5. Paleo—current map of Precambrian quartzites of the Lake Superior region (from Pettijohn, 1957). Areas shown in black are principally quartzite. Mean-current azimith is shown by arrows. The McCaslin quartzite has been added to Pettijohn's original map. 20 Environment of Deposition-—The composition and sedi- mentary structures of the McCaslin formation indicate that the sediments were deposited upon the bottom of a shallow but extensive body of water. The sediments do not seem to be fluvial deposits, as the sands which form a large part of the unit are generally clean, well sorted and, in general, well stratified. Furthermore, such fluvial characteristics as cut-and-fill and the development of lenticular beds on a limited scale are not apparent. The sedimentary conditions that existed in the McCaslin basin of deposition were similar to those existing in present standing bodies of water. Gravels would be localized along beaches and would, ideally, grade outward toward deeper water into a fine, clean sand. From the stratigraphic position of the conglomerates and clean quartzitic sediments, and from the location of the logical source area to the north, it appears that the McCaslin formation was deposited in a sea transgressing northward over a Waupee terrain of low relief and fed by streams from the north and west (Figure 5). However, the exact shore and the direction of the encroachment of the seas is still a matter of conjecture because of inadequate information from the conglomerate exposed in the Mountain area to the south. Furthermore, the deposition of over 5000 feet of gravel and sand indicates that the site of deposition probably was subsiding. 21 Structure of the McCaslin Formation--The overall extent and attitude shown by the McCaslin formation indicate the structural framework of the district as a whole. Frequent reference should be made to the accompanying geologic map (Map I). The discussion of the structure might well begin with the western portion of the McCaslin range in the vicinity of the Ada Lake lookout tower. The north and south ridges of the eastern range, Deer Lookout Tower Hill and Thunder Mountain will be treated in consecutive order. The western exposures of the McCaslin formation extend in a general easterly direction from the Ada Lake lookout tower in sec. 4, T. 33 N., R. 14 E. to Knowles Creek in sec. 33, T. 34 N., R. 16 E. Conglomerate is the dominant rock exposed along the western range although a few exposures of fairly clean quartzite were noted along the southern slopes of the ridge. Cross-bedding indicates that the beds are right side up. A structural interpretation of the extreme western portion of the range in secs. 4, 3, 2 and l, T. 33 N. , R. 15 E. and sec. 6, T. 33 N. , R. 15 E. is difficult because of poor and questionable outcrops, but the continuity of the formation is fairly evident because of the continuous range of hills trending east which rises abruptly 100-300 feet above the surrounding lowlands. The lithology of many large boulders on the ridge indicates that it is underlain by conglomerate and quartzite. 22 In sec. 4, T. 33 N. , R. 15 E. outcrop relationships indicate that a right hand fault trending approximately N. 300 W. and with a lateral displacement of 1/4 to 1/2 mile transects the western range. A deep valley, through which pass State Highway 32 and the Chicago and Northwestern Railroad, crosses the range in this area. The ridge is offset at this place to the south on the east side of the valley. A comparison of the attitudes of the beds on the two sides (less than 3/4 miles apart) indicates that lateral offset has taken place. The strike of the bedding changes abruptly from N. 359-80O W. on the west side of the valley to N. 730 E. on the east side. When projecting the trend of the bedding of the most northerly conglomerate exposures on the west side of the valley across the lowland to the east side, exposures of the Waupee complex are encountered, indicating that the stratigraphic sequence on the east side of the valley has been offset 1/4 to 1/2 mile to the south. Brecciated quartzite cemented by secondary white quartz found on both sides of the valley supports the fact that movement has taken place. A large exposure in the SW 1/4 NE 1/4 sec. 4, T. 33 N., R. 15 E. consists of very intensely brecciated conglomerate and quartzite. The breccia grades to the south into unbrecciated quartzite and conglomeratic layers. An examination of the transition zone shows that the initial forces causing the brecciation produced a joint system with one set of joints striking N. 100 W. and dipping very steeply to the SE. and another set striking N. 700 W. and dipping very steeply to 23 the NE. More intense movement caused fracturing and rotation of the quartzite fragments so that the original pattern of jointing is not discernable in the intensely brecciated northern portion of the outcrop. Later solutions filled the joints and open spaces between the fragments with secondary white quartz. Also, evidence of brecciation was noted on the west side of the valley in an outcrop located a few hundred feet south of the Carter lookout tower in the NE 1/4 sec. 5, T. 33 N., R. 15 E. Joints 1-2 feet wide trending north and dipping 630 E. filled by clean, white quartz cut the quartzite and inter-bedded conglomerate. Fragments of quartzite up to 10 inches in size are imbedded in the joints and indicate by their position that they have been moved and rotated. Exposures are rather scarce in secs. 3, 2 and 1, T. 33 N. , R. 15 E. in the region where the North Branch of the Oconto River crosses the western range, but the general topography of the region suggests that the ridge is fairly continuous. The strike of the bedding ranges from N. 900 E. to N. 730 E. , and the dips are to the south at 50-67 degrees. An exposure of exceptionally well preserved cross— bedding near the center of sec. 3, T. 33 N. , R. 15 E. (Figure 3) indicates that the beds are right side up and that the source of the sediments or current direction was from the west. There are many good outcrops along the western range from the valley of the North Branch of the Oconto River eastward to the Valley ofKnowles Creek. Outcrops, together with the tOpographic ex- Pression of the ridge, indicate that the quartzite ridge widens from less than 24 1/4 mile at the valley of the North Branch of the Oconto River to over 1 1/4 miles in the vicinity of Knowles Creek. This change in thickness of the ridge is not caused by divergence of the beds but appears to be related to the encroachment of the quartzite from the south by the over- lying Hager rhyolite porphyry because of a post-McCaslin--pre—Hager erosion of the quartzite formation. Conglomerate is most abundant along the northern portions of the ridge giving way to clean white quartzite to the south. The gradation is especially marked in a large outcrop near the center of NW 1/4 sec. 6, T. 33 N. , R. 16 E. The conglomerate has a dirtier matrix and a greater percentage of dark pebbles on the northern portion of the outcrop. The matrix becomes cleaner, quartz pebble content increases and interbedded clean quartz sand becomes more abundant to the south, and finally, the southern extremity of the outcrop is made up of clean vitreous quartzite with no pebbles. The gradation from conglomerate to clean quartzite from the base upward is also apparent in the vicinity of Knowles Creek. Outcrops near the center of sec. 33, T. 34 N. , R. 16 E. are entirely conglomeratic; whereas outcrops in the SE 1/4 NW 1/4 sec. 4, T. 33 N. , R. 16 E. are entirely clean white quartzite. The strike of the bedding varies from N. 900 E. to N. 600 E. and the dips range from vertical to 550 S. Good cross-bedding of the interbedded quartzite layers in the conglomerate and in the non— conglomeratic quartzite indicates that the tops of the beds are to the s outh. 25 The eastern portion of the McCaslin range which extends from Knowles Creek eastward to the vicinity of the Peshtigo River valley consists of two ridges separated by a swampy lowland. The northern ridge is underlain mainly by conglomerate with a few interbedded thin quartzite layers. In the NW 1/4 sec. 34, T. 34 N. , R. 16 E. outcrops of conglomerate form the east bank of Knowles Creek. The strike is N. 700 E. and the dip is 800 S. A short distance to the east in sec. 26, T. 34 N. , R. 16 E. the prevailing strike is N. 800 E., while the prevailing strikes in the NE 1/4 sec. 25, and the SE 1/4 sec. 24, T. 34 N., R. 16 E. are N. 800-900 w. There appears, therefore, to be a slight flexing or bending of the north ridge. The dips are consistently to the south ranging from 350 to 800. In general, the moderate dips are along the northern edge of the ridge and the steeper dips to the south. The separate topographic expression of the north ridge terminates abruptly near the western margin of sec. 20, T. 34N., R. 17 E. The southern ridge of the eastern portion of the range is . composed of clean, vitreous quartzite. It forms the most impressive topographic feature of the district. The strike of the beds varies from N. 670 E. near Knowles Creek to N. 900 E. near the rift in the NE 1/4 sec. 28, T. 34 N. , R. 17 E. to N. 650 W. on the east side of the rift. The dip of the beds is to the north ranging from 400 to 800. However, many scattered exposures of good cross—bedding and a series of ripple 26 marked surfaces in the SE 1/4 SW 1/4 sec. 29, T. 34 N., R. 17 E. indicate that the tops of the beds are to the south; therefore, the quartzite beds which make up the south ridge are overturned. In the NE 1/4 sec. 28, T. 34 N., R. 17 E. a large rift trending approximately N. 300 W. transects the quartzite range. Nearly vertical cliffs of quartzite 100 feet high are separated by 500 feet of flat swampy ground. The opposite walls of the rift, as viewed from an air photo, appear to match except for a slight southward adjustment of the eastern wall. Trends of the quartzite bedding are, in general, N. 709-800 E. on the west side of the rift, but change to N. 650-800 W. on the east side of the rift. The topographic expression of the quartzite bedrock, as also noted on air photos, indicates very clearly that the segment of the range east of the rift has been bent southward. In the immediate vicinity of the rift, the base of the quartzite is in direct contact with the intrusive High Falls granite and has been brecciated and later recemented by secondary white quartz. The relationship of the quartzite to the granite will be discussed in a later section. A large outcrop of highly fractured quartzite healed by secondary quartz is found in the NE l/4 SE 1/4 sec. 27, T. 34 N. , R. 17 E. The general strike of a faint bedding or banding is N. 350 W. and dips 750 SW. The anomalous attitude in this exposure suggests that this large outcrop may not be in place, but detached from the main range and rotated somewhat during the intrusion of the High Falls granite. 27 Isolated portions of the south ridge are found in the NW 1/4 SW 1/4 sec. 26, T. 34 N., R. 17 E. and in the SW 1/4 NE 1/4 sec. 25, T. 34 N. , R. 17 E. The latter is in direct contact with the High Falls granite and is bordered by it on the west and north. These outcrops are interpreted as being large xenoliths detached from the main quartzite range and moved to the present position by the granite intrusion. The group of quartzite exposures at Deer Lookout Tower Hill appear to be isolated from the main McCaslin Mountain range. The attitudes of the quartzite bedding are extremely varied and un- related to the east-northeast regional trend, and cross-bedded exposures at close intervals give contrasting and anomalous results concerning the tops of the beds and the source of the sediments. The quartzite is cut by a 300 foot wide arm of intrusive granite, and the conclusion is that the Deer Lookout Tower Hill quartzite is a very large xenolith which was detached from the main McCaslin range and carried to its present position by the motion of the intruding High Falls granite. The quartzite exposures on Thunder Mountain offer an important clue to the regional structural interpretation of the McCaslin district, which is discussed in detail in a later section. The strike of the quartzite beds is consistently N. 00—100 W. , and the dips are SOC-70O W. Cross—bedding indicates that the beds are right side up and that the source of the sediments or current direction was from the 28 north and northwest. The consistent overall agreement of clips and strikes and cross-bedding at various locations on Thunder Mountain and the conformable relationship to the underlying Waupee complex indicate that the Thunder Mountain exposures are ”in place" with respect to the regional structural pattern which is synclinal. Hager Rhyolite Porphyry The Hager rhyolite porphyry was originally described by the author near Mountain, Wisconsin (Mancuso, 1957). The main body of the Hager is a distinct rock type, easily recognized by the quartz phenocrysts that exhibit a rounded appearance on a broken or weathered surface. Under the microscope, the groundmass appears to be a mosaic of anhedral quartz, orthoclase, plagioclase (An15_20) and biotite. The quartz is late and occurs filling the interstitial spaces between the feldspars and as myrmekitic intergrowths with the feldspars. Brown pleochroic biotite occurs as laths or aggregates that are aligned to give the rock a definite flow structure. The foliation bends around the phenocrysts. Accessory sphene is associated with the biotite. The phenocrysts are rounded and embayed due to resorbtion, and fractures in the pheno- crysts are filled by the crystalline groundmass. The few plagioclase and microcline phenocrysts are mottled with quartz and biotite inclusions. The nature of the rock type and its origin was established in the M. S. thesis: The coarse grain size and great thickness of the Hager rhyolite porphyry may suggest that it is an intrusive granite, but field evidence seems to indicate a volcanic origin. Contact relationships with the conglomerate are those of an extrusive flow and not that of the ordinary intrusive. No dikes of the Hager were seen cutting the conglomerate or any of the forma- tions to the south, and no xenoliths of the conglomerate were seen in the Hager. Flow lines and the general bedded 29 appearance of the Hager conform to the general trend of the underlying contact. A large outcrop in the NE 1/4 sec. 21, T. 32 N. , R. 17 E. exhibited a breccia pattern with cement and fragments of the same general material. This is interpreted as a brecciated flow top with fractures filled by a later flow. The rather coarse grain size could result from slow cooling in the central portions of this very thick flow. The Hager rhyolite porphyry in the McCaslin district is seen as a fairly continuous string of exposures along the southern border of the main McCaslin range and west of the quartzite exposures at Thunder Mountain. The rhyolite porphyry was not seen in direct contact with the quartzite, but in the NW l/4 sec. 6, T. 33 N., R. 16 E. The WC 1/2 sec. 4, T. 33 N., R. 16 E. ; the SE 1/4 sec. 35, T. 34 N., R. 16 E. ; the NW 1/4 sec. 31, T. 34 N., R. 17 E. and the NW 1/4 sec. 32, T. 34N., R. 17 E. it outcrops within 100 feet of quartzite exposures. The age of the Hager rhyolite porphyry with respect to the McCaslin formation was definitely established in an exposure in the SE 1/4 NW 1/4 sec. 6, T. 33 N. , R. 16 E. Angular fragments of the quartzite are engulfed in the rhyolite porphyry (Figure 6). The rhyolite exhibits a good flow banding of mafic minerals and phenocrysts trending o N. 70 W. and dipping 480 NE. The foliation flows around the inclusions. The quartzite inclusions, up to 6 inches in diameter, generally are scattered at random throughout the rhyolite outcrop, but in a few cases a series of inclusions are aligned parallel to the flow banding. The contacts are extremely sharp with no apparent change or alteration of the quartzite or rhyolite. Figure 6. Qumrtsite inclusions in the Hager rlwolite por- phwryo 30 31 In the vicinity of the North Branch of the Oconto River, a marked thinning of the western range is apparent. Outcrops of Hager rhyolite porphyry are found immediately south of the quartzite exposures (less than 200 feet) and exhibit a flow banding which trends parallel to the outline of the quartzite ridge. An outcrop of rhyolite north of the quartzite on the east Side of Forestry Road No. 2349 in the NW 1/4 sec. 29, T. 34 N., R. 16 E. indicates that the rhyolite completely crossed the quartzite ridge possibly by way of an ancient erosional valley now reformed in the less resistant rhyolite and occupied by the North Branch of the Oconto River. The age of the Hager rhyolite porphyry with respect to the High Falls granite is not definitely established, but evidence suggests that it is older than the granite. They were not seen in direct contact with each other in the district, but they outcrop in close proximity in secs. 27 and 28, T. 34 N. , R. 17 E. There is an increase in the grain size of the groundmass of the rhyolite from west to east and the phenocrysts show signs of secondary enlargement and recrystallization near the granite. The position or locality of the rhyolite seems to have been controlled by the structure of the quartzite, and both in turn have been modified by the force of the granite intrusion. Therefore, the extrusion of the Hager rhyolite porphyry followed or was synchronous with the deformation of the quartzite, but preceeded the intrusion of the High Falls granite. The possibility does exist, 32 however, that the Hager rhyolite porphyry and the High Falls granite stem from the same original source and were part of a long orogenic period in the later Precambrian. The relationship of the Hager rhyolite porphyry to the High Falls granite will be discussed in detail in a later section. High Falls Granite This research does not attempt a complete study of the High Falls granite. Only those portions that extend into the McCaslin district and that affect the structural interpretation of the McCaslin formation will be discussed in detail. The granite is found as a series of large and small exposures scattered throughout the vicinity of the High Falls and Caldron Falls Reservoirs in west-central Marinette County. It terminates the McCaslin district on the north and east. A pink granite with an average grain size of 5-10 mm containing laths of orthoclase up to 1/2 inch in length outcrops near the High Falls Reservoir in the SW 1/4 sec. 19, T. 33 N., R. 18 E. The composition averages microcline-perthite-albite 60 percent, quartz 25 percent and biotite 15 percent. Accessory minerals include zircon, fluorite, apatite, and titanite. This exposure probably represents the true composition of uncontaminated High Falls granite. The texture is hypidiomorphic granular. Westward, toward the east end of the McCaslin range and 33 Thunder Mountain, the granite contains numerous inclusions of the Waupee complex in various stages of digestion (Figures 12 and 13). The color varies from red to gray-black, and the texture is gneissic with segregation and alignment of the mafic constituents due to flow (Figure 11). Isolated outcrops, such as those found in the NW 1/4 sec. 19, T. 33 N., R. 18 E. and secs. 28, 29, 32, and 33, T. 34 N., R. 18 E. , indicate by the attitude of their flow banding and the number of inclusions that the general locality of the main granite body is to the east and northeast of the McCaslin district. The granite was seen indirect contact with the McCaslin formation in several localities. In an outcrop in the bed of the Peshtigo River near the center of sec. 25, T. 34 N. , R. 17 E. , the contact is extremely sharp with very little penetration of the quartzite by granite veins (Figure 7). The granite becomes porphyritic, dark gray-red in color and fairly syenitic in composition at the contact. The mafic mineral content increases and flow banding parallels the trend of the contact. The quartzite appears highly recrystallized and at the immediate contact contains stringers and scattered grains of pinkish orange microcline, perthite and albite. The extreme straigntness and sharpness of the contact suggests that it was controlled by original fractures or joints in the quartzite. From the field location and relationship to the regional structural picture, it seems that the quartzite in this outcrop may be part of a large block completely engulfed by the granite and detached from the main body of the quartzite range. ,_ ,4 , a ,4 f, ’4 4/,A,4...~ Figure 7. 4\ .4\ \ 4a_\,,\_\,\¥\4 >.4\ ,l\_ High Falls granite (Gt)-McCaslin formation (Qtz) contact exposed in the bed of the Peshtigo River in sec. 25, ’1‘. 311 N., R. 18 E. 314 High Falls granite (Gt)-Mc0aelin formation (Qtz) contact exposed in the rift in sec. 28, T. 311 N., R. 17 E. 35 36 In the NE 1/4 sec. 28, T. 34 N. , R. 17 E. , associated with a large rift transecting the quartzite range, the granite is again in direct contact with the quartzite. Here again the granite becomes dark and syenitic with a decrease in grain size and an increase in mafic mineral content, mainly biotite. At the northeast corner of the rift, small exposures of the granite-quartzite contact indicate that joints or fractures in the quartzite played a major part in governing the avenues of granite invation; however, veins and stringers of pink feldspar and granite are numerous throughout the quartzite forming the east wall of the rift. The most interesting and revealing granite-quartzite contact exposures are found on the west side of the rift at the base of a large mass of highly brecciated quartzite cemented by secondary white quartz (Figure 8). In the vertical wall of the rift a continuous transition exists from granite to quartzite invaded by large granite veins and dikes, to quartzite breccia healed by later secondary quartz. At the base of the rift wall granite predominates and contains numerous inclusions of quartzite; however, no quartz healed quartzite breccia inclusions were seen in the granite. Flow banding in the granite follows around the quartzite inclusions. Upward from the base of the cliff quartzite predominates but is invaded by numerous veins and stringers of granite up to 2 feet wide which exhibit a flow banding that very closely parallels the walls of the veins. From the mid-point to 37 the top of the rift wall the granite veins and stringers are no longer seen. The quartzite becomes a mass of brecciated fragments, some of whose outlines match, cemented by clean white quartz. In a few cases the white secondary quartz can be traced downward to an origin in a granite vein or stringer. The transition zone to the northwest, where brecciated quartzite passes into massively bedded unbrecciated quartzite, indicates that the brecciation began with the development of two major fracture or joint sets whose strikes and dips respectively are: N. 20° E., 48° NW. and N. 80° W., 15° SW. More intense pressure and movement caused intense fracturing and rotation of the quartzite blocks between the original fractures or joints. In sec. 36, T. 34 N. , R. 16 E. , on the northern border of the south ridge of the eastern range and in the rift in sec. 28, T. 34 N. , R. 17 E. , the granite lies directly adjacent to the quartzite. The granite typically is dark in color, deficient in quartz and flow banded parallel to the quartzite contact. The quartzite is very highly re- crystallized near the contact and, under the microscope, exhibits secondary microcline perthite and albite that have grown between the original quartz grains at the expense of the muscovite. These exposed contacts along with the evidence cited below suggest that the area between the north and south quartzite ridges is occupied by the High Falls granite. The granite most probably intruded along a bedding plane of the quartzite and caused the splitting of the ridges, a flexing 38 Figure 9. Joint fractures in quartzite filled with secondary quartz, McCaslin formation. ./ f,— r”, z//4«,/,//, ,g ,4. 4\\i.,‘\4¥4,\44‘\\ ,.\ ‘4,\,\U.\.-¥,\\\g,‘\4‘ l I I 1 I 1 Figure 10. Brecciated quartzite cemented by secondary quartz, McCaslin formation. 39 of the northern ridge and overturning of the south ridge. The relation- ship of the granite to the structure of the quartzite is discussed in detail in a later section. An indirect evidence of granite intrusion is found along the sharp bend of Knowles Creek near the east boundary of sec. 33, T. 34 N. , R. 16 E. The quartzite is highly jointed and recrystallized, contains numerous small veins and stringers of pink granite and is stained pinkish-orange in color similar to quartzite exposures that occur in direct contact with the granite. Fine secondary microcline, perthite and albite occupy the interstices between the quartz grains. At Deer Lookout Tower Hill an arm of granite 300 feet wide transects the quartzite in a N. 100 W. direction with a dip of 800 to the southwest. The granite is highly banded parallel to the contact, porphyritic and fairly dark in color. The quartzite has a variable attitude, but appears to have a pronounced secondary foliation parallel to the granite body due to the alignment of secondary muscovite flakes and sillimanite. At Thunder Mountain, 700 feet west of the northeast corner of sec. 25, T. 33 N. , R. 18 E. , a granite sill three feet wide invades an outcrop of banded Waupee complex. The trend of the Waupee and the granite sill is north-south and dips 350 to 500 to the west. The granite has a grain size of 1/4 inch or more, is pink in color and contains coarse books of muscovite. 40 Structure of the McCaslin District and the Relationship of the High Falls Granite to the Areal Distribution of the Quartzite Ranges The broad regional structure of the McCaslin district can best be described as the northern limb of a large synclinal trough, the southern limb of which is found in the vicinity of Mountain, Wisconsin, approximately fifteen miles south of the main McCaslin range of hills. The axial line of the regional structure trends N. 600-90O E. and plunges slightly to the west. The quartzite exposures at Thunder Mountain probably represent part of the broad eastern nose of the syncline. The High Falls granite batholith terminates the syncline to the east and northeast. From the granite—quartzite relationships described on the preceding pages, the following conclusions seem justified concerning the relationship of the High Falls granite to the regional structure of the McCaslin district and to the areal distribution of the quartzite ranges. The main body of the High Falls granite lies to the east and northeast of the McCaslin district. The granite has invaded the rocks of the McCaslin district by forceful injection, stoping and assimilation. The Waupee complex and the McCaslin formation vary greatly in physical and chemical characteristics; therefore, they reacted differently and offered unlike resistance to the granite intrusion. Figure 11. Flow foliation in the High Falls granite. Wfi—v 4 Av“, 4 Figure 12. Flow foliation and inclusion in the High Falls granite. [—r ,4( I. / ,4- ,frpx’,, Figure 130 waupee inclusions in the High Falls granite. 112 43 The Waupee complex offered little resistance to the granite body; veins and dikes seem to have invaded the Waupee with seemingly little regard for original fracture Systems, bedding planes or other controls inherent in the Waupee rocks. Inclusions of the Waupee because of their greater density, sank into the mass of the granite and were assimilated and digested. Near the extremities of the granite body, the process of assimilation was not carried to completion and the granite contains Waupee inclusions in various stages of digestion (Figure 13). The quartzite, however, offered resistance to the force of the intrusion as a massive unit. The avenues of the granite intrusion were primarily governed by pre-existing weaknesses in the quartzite such as joints, fractures or bedding planes. Therefore, the quartzite suffered flexing, bending and fracturing on a regional scale with local areas of brecciation in zones of differential movement. The region between the north and south ridges of the eastern range is occupied by an intrusive arm or sill of granite which intruded along the plane of the bedding. The force of the intrusion caused a spreading of the two ridges, a flexing of the northern ridge, and overturning of the southern ridge. The large zones of brecciation noted in outcrops in the NW 1/4 NE 1/4 sec. 3, T. 33 N. , R. 16 E. ; the SW 1/4 sec. 35, T. 34 N., R. 16 E. and the SE 1/4 sec. 29, T. 34 N. , R. 17 E. are found near the southern border of the range 44 and are most probably caused by the differential movement of brittle quartzite layers during the process of overturning. The granite terminates the quartzite range to the northeast where large blocks were detached from the main body of the quartzite, floated away in the intrusive or carried along by the force of the granite flow because of the lesser density of the quartzite. Much of the quartzite has since been removed by erosion, but remnants such as those at Deer Lookout Tower Hill and those near the Peshtigo River in secs. 25, 26 and 27, T. 34 N. , R. 17 E. remain isolated from the main quartzite mass and surrounded by granite. Relationship of the High Falls Granite to the Hager Rhyolite Porphyry The High Falls granite and the Hager rhyolite porphyry appear to be genetically related although the Hager rhyolite porphyry definitely was extruded and crystallized prior to the granite intrusion, for it shows, in part, unmistakable effects of contact metamorphism. The granite and rhyolite exhibit a striking similarity in their overall mineral composition, chemical analyses and accessory mineral suites. The essential minerals of both rocks consist of the feldspar assemblage microcline-perthite—oligoclase and quartz which occur in about the same general proportions in each rock type. The dominant mafic mineral in each case is biotite with minor hornblende and secondary chlorite. ANALYSES OF THE HIGH FALLS GRANITE hS Normal High Contact Phase Belongia granite Falls granite High Falls granite mountain, Wisconsin Sample Sample Sample Sample Sample Sample Sample J;hl Jk63 J¥60 JA82 J969 20,098 20,099 8102 67.751 66.146 59.81 61,38 58.83 63.19 611.113 11203 18.99 20.05 23.61 22.50 23.911 20.511 20.32 1:20 11.192 10.71 12.66 13.51 111.31 13.91 13.21 CaO 0.5h 0.60 0.h8 0.51 0.h7 0.23 0.37 Na20 l.h0 1.56 1.2h 1.25 1.28 0.60 0.96 (Mg,Fe)0 0.12 0.59 2.07 0.78 1.09 1.h8 0.69 H20 0.01 0.03 0.11 0.06 0.06 0.05 0.02 P205 tr. tr. tr. tr. tr. tr. tr. Zr203 tr. tr. tr. tr. tr. tr. tr. T102 tr. tr. tr. tr. tr. tr. tr. F tr. tr. tr. tr. tr. tr. tr. Total 100.01 100.00 99.98 99.99 99.98 100.00 100.00 1. 2. 3. weight percents obtained by converting from volume percents which 'were determined by the "Rosiwal method" employing a 6-axis inte- grating stage. K20 is abnormally high and N820 and OaO are low because all micro- cline and perthite were calculated as KAISi308. Trace Table 2. ANALYSES OF THE HAGER RHYOLITE PORPHYRY 116 McCaslin Mountain Thunder Mountain, Mountain Wisconsin 38mg? Sample Sample Sample Sample J— J-3Lt J-78 J-67 20, 061 3102 58.951 58.87 62.16 59.37 60.11 111203 22.20 22.27 21.03 22.26 21.5h K20 11t.862 111.15 15.10 111.22 111.08 0.0 0.50 0.59 0.20 0.57 0.53 Na20 0.93 1.06 0.52 1.10 0.92 (Mg, Fe)0 1.32 1.57 0.97 1.27 1.115 H20 0.02 0.02 0.03 0.02 0.02 F9203 1.23 1.117 tr. 1.19 1.35 P205 tit-.3 tr. tr. tr. tr. 21‘203 tr. tr. tr. tr. tr. T102 tore tore tr. tr. tr. F tr. tr. tr. tr. tr. Total 100.01 100.00 100.01 100.00 100.00 1. Weight percents obtained by converting from volume percents which were determined by the "Rosiwal method" employing a 6-axis inte- grating stage. 2. K20 is abnormally high and Na20 and 080 are low because all micro- cline and perthite were calculated as KAlSi303. 3 . Trace Table 3 . Figure 111. Fluorite (F) in the High Falls granite, plain light (Sample 111). Figure 15. Fluorite (F) in the High Falls granite, crossed nicols (Sample 1.11). 147 gum , 1 o h 0 118 49 The accessory minerals are fluorite, zircon, magnetite andapatite with minor sphene and leucoxene. In both rock types zircon and fluorite are by far the dominent accessory minerals and respectively exhibit very similar properties and modes of occurrence. The zircons occur as elongate prisms usually doubly terminated by pyramid faces with fairly Sharp crystal angles. They commonly Show an internal zoning which is parallel to the external crystal shape. Most of the zircons are very clear and colorless, although some are yellowish. The birefringence is very strong. The majority of the zircons would be classified as the “normal" type zircons characteristic of post— Huronian rocks of the Lake Superior Precambrian (Tyler, Marsden, Grout, Thiel, 1940). The fluorite (Figures 14, 15 and 16) is found as irregular grains that are comparable in size to the essential mineral constituents. It is colorless to purplish-pink and exhibits the characteristic high negative relief. Its mode of occurrence in both the granite and the rhyolite suggests that it crystallized late and filled the interstices between the quartz and feldspar grains. The remarkable Similarity between the High Falls granite and the Hager rhyolite porphyry may be attributed to coincidence, however, a more plausible explanation is that they originated from the same magma reservoir at depth. During the early stages of the post-quartzite (Killarney?) revolution the rhyolite found its way to the surface through passageways which were formed by the initial stages 50 of the deformation. The main avenues of extrusion appear to have been through the central portions of the synclinal trough which most likely was highly fractured and weakened at depth. The granite, on the other hand, worked its way Slowly upward by stoping, assimilation and forceful injection and did not reach the proximity of the Hager rhyolite porphyry until after the latter had completely crystallized. The heat and fluids related to the intruding High Falls granite then initiated the pronounced sequence of changes in the rhyolite which are discussed in the subsequent section on metamorphism. 51 META MORPHISM The metamorphic zones in the McCaslin district are spatially and genetically related to the High Falls granite intrusive. The width and shape of the metamorphic zones and the degree of metamorphic response was to a great extent governed by the distance along strike or across strike respectively from the granite contact and by the original texture and composition of the country rock. The mineral assemblages developed by metamorphism were determined by temperature and by the bulk chemical composition of the country rocks. The metamorphic changes were primarily recrystallization and reconstitution of original rock 'materials except in a narrow zone less than 15 feet wide at the immediate granite contact where potash and soda were added to the quartzite from the granite intrusive. Beyond the immediate contact aureole the country rocks lie in the quartz-albite-muscovite-chlorite subfacies of the greenschist facies1 of regional metamorphism as evidenced by the vary slight amount of recrystallization of the quartzite and rhyolite, the occurrence of fine sericite in the interstices of the quartzite and the completeness of the reactions by means of which the original pyrogenetic mineral assemblage of the diorite (sample 5) was converted to secondary products. lThe metamorphic facies designations used in this paper are those defined by Turner and Verhoogen, 1960. 52 The principal secondary minerals are chlorite, pale green actinolitic hornblende, epidote and sericite (Figure 18). An albite-epidote hornfels facies and a hornblende hornfels facies, which make up the contact metamorphic aureole of the High Falls granite, are superimposed onto the regional greenschist facies. The mineral assemblages of the individual facies varies greatly, however, because of the bulk chemical composition differences of the various rock formations. A general description of the metamorphic changes is described on the following pages with reference to the various rock formations. Frequent reference should be made to the index map of sample locations on page 53 (Figure 17). Waupee Volcanics and Granite Complex The composition of the Waupee series varies considerably from area to area because of the complex of lithologic rock types classified under the general heading of Waupee volcanics and granite complex. Among the rock types included are basalts, andesites, agglomerates, acid and intermediate tuffs possibly with interbedded water laid volcanic sediments and granite and diorite masses whose origins are attributed to a combination of the processes of intrusion and granitization. However, the zones of metamorphism in the Waupee complex are here described in terms of rocks that originally had essentially equivalent overall bulk chemistry; that of an acid to inter- mediate volcanic tuff. 53 th .: 633m wwE unE NV;— Znnk ‘ 'l-l|‘ z¢m._. >oon_omo U_Idm02<._.m2 n_<_>_ ZO_._. 7v) .\ LAKEWOOD THUNDER ”I: ‘ Reservo/r ' MOUNTAIN J.,-.132; . f / MIDDLE .-,,g, , INLET T32'N \_ .. .l _7 7< \/ MOUNTAIN , /l \l “A,“ 8‘ ’ /I k 7 \ < L A4 4 L ‘J T3IN RI4E RISE RISE RI7E p.85 RISE 4 R20E MCCASLIN SYNCLINE “MSCALE o I 2 3 1 \_____J.____L___J miles MICHIGAN smTE UNIV . LIBRARIES IIlIIIIIIIIIIIIIIIIIIIIIIIIIIIIII11IlIHIIIIIIIlIIIIIII 31293102522228