71-23,263 ZAINUDDIN, Syed Mohammad, 1939PETROLOGY OF THE GRANITIC ROCKS IN THE VICINITY OF REPUBLIC TROUGH IN THE UPPER PENINSULA OF MICHIGAN* Michigan State University, Ph.D., 1971 Geology University Microfilms, A XEROX Company , A nn Arbor, M ichigan PETROLOGY OF THE GR A N I T I C IN THE V I C I N I T Y OF R E P U B L I C ROCKS TROUGH IN THE U P P E R P E N I N S U L A O F M I C H I G A N By Syed Mohammad A Zainuddin THESIS Submitted Michigan partial State fulfillment for to University of the the deg r e e requirements of D O C T O R OF P H I L O S O P H Y D e p a r t m e n t of 1971 Geology PLEASE NOTE: Several pages contain colored illustrations. F i l m e d in t h e best possible way. UNIVERSITY MICROFILMS ABSTRACT PETROLOGY OF THE GRANITIC ROCKS IN THE VICINITY OF REPUBLIC TROUGH IN THE UPPER PENINSULA OF MICHIGAN BY Syed Mohammad Zainuddin Republic Trough Is a narrow, tightly folded syncline of Animlkle metasediments, located towards the western part of Marquette County In the upper peninsula of Michigan. 4 surrounding the trough. Granitic rocks are exposed in the area The number of granitic intrusions and their age relations have been a subject of controversy for many years. The present study was conducted to determine the number of geneti­ cally different types of granite based on field observations and petrographic variation. The field relation and textural variation indicate the occurence of three types of granitic rocks of significant areal extent; an even-grained granite gneiss, foliated porphyritic granite with small phenocrysts, and the coarse porphyritic granite. (The foliated porphyritic granite and coarse porphyritic granite have not been differentiated by earlier workers.) The modal composition of the three granites can not be used to resolve them into genetically different types since the variation within one type is greater than the difference between two types. elements composition is also not significantly different. The trace K/Rb ratios in the K-feldspars of the three granite types are generally similar and range within the published values for granites. However, the Na/K ratios in the K-feldspars of the two porphyritic granites show a bi-modal distribution and are significantly higher for the coarse porphyritic Syed M. Zainuddin granite. Statistical analyses of the plagioclase twin types clearly demonstrate that the samples of the foliated porphyritic granite and the coarse porphyritic granite belong to significantly different populations. The granite gneiss is texturally and mineralogically very hetero­ geneous, probably reflecting varying conditions of the genesis of the rock type. Xenoliths of the granite gneiss have been found in the other two granites which indicate that the granite gneiss is the oldest of the three granitic rocks. The intrusive relation of the gneiss into the pelitic schist suggest a magmatic origin of the gneiss. Unlike the other granites in the area, granite is mineralogically homogeneous. the foliated porphyritic The modes plotted on the Qtz-Or-Ab ternary phase diagram are restricted to the low temperature trough. This Indicates a slow cooling of the rock maintaining chemical equilibrium. The highly ordered structural state of the K-feldspar and the distribution coefficient of albite between coexisting feldspars also support this view. The macro measurements and petrofabric analysis of the foliated porphyritic granite indicate that a strong NW-SE foliation, parallel to the axial plane of Republic Syncline, was superimposed on an earlier N25W-S25E foliation. The structural relation indicates a pre-Animlkie age of the rock type. A younger granite, referred to as coarse porphyritic granite, was emplaced along the anticlinal axis between the Republic Syncline and Marquette Syncline. The granite shows great mineralogical variation ranging from granite to trondhjemite in composition. General lack of NW-SE foliation, as observed in the field and revealed b y petrofabric analysis, suggests a post-Animikie age of the coarse porphyritic granite. ACKNOWLEDGMENTS The study was instigated and carried through under the guidance of Dr. James W. Trow. For his k e e n personal interest in the study, and for the genial atmosphere provided, the author extends a deep sense of gratitude. The writer is especially indebted to Dr. untiring offer of his time. Thomas A. Vogel for His consultations and suggestions during the course of the investigation, and his m a n y editorial efforts on this manuscript are gratefully acknowledged. Dr. H. B. Stonehouse, Dr. C. E. Prouty, Dr. Robert Ehrlich, and Dr. W. J. Hinze have offered encouragement a nd m a n y suggestions whi c h are incorporated in the text. Acknowledgment is also extended to the Cleveland-Cliffs Iron Company, Ishpeming, for permitting me to m a k e use of their facilities. ii TABLE OF CONTENTS Page LIST OF T A B L E S ................................................ v LIST OF FIGURES................................................ vi INTRODUCTION .................................................. 1 Purpose o£ the Study..................................... 1 Geography ................................................ 1 Geological Setting. 3 . . . . . . ........................ Field M a p p i n g ........................................... GENERAL LITHOLOGY OF THE GRANITIC ROCKS 8 ................... 9 Granite Gneiss........................................... 9 Foliated Porphyritic Granite............................ 10 Coarse Porphyritic Granite.............................. 10 GENERALIZED SCHEMATIC MAP OF REPUBLIC TROUGH A R E A ........... 13 PETROLOGY O F THE GRANITES..................................... 18 A) Modal Analysis of the Granites...................... 18 B) General Texture of the Granitic Rocks ............. 24 Granite Gneiss ..................................... 24 Foliated Porphyritic Granite........................ 29 Coarse Porphyritic Granite. 34 C) . ...................... Composition of the Coexisting Feldspars in the Granites............................................. 39 An content of Plagioclase ............... 39 . . . . . Ab content of the K-feldspar........................ lii 40 Page D) Structural State of K-feldspar ..................... 46 E) Plagioclase Twinning ................................ 52 Statistical Treatment................................ 57 Distribution of trace Elements in K-feldspars. 59 F) . . SUMMARY A N D CONCLUSION......................................... 67 LIST OF REFERENCES............................................. 71 APPENDIX A. Locations of xenollths found in foliated porphyritic granite and coarse porphyritic grani t e . APPENDIX B. Method of separation of K-feldspar from the rock. APPENDIX C. X-ray method for determination of structural state of K-feldspar. iv L I S T O F TAB L E S Table 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. Page Age Relations of the Rocks of Southern Complex (after Dickey, 19 38).......................................... 6 Sequence of Precambrian Rocks In Northern M ichigan (from Gair and Thaden, 1 9 6 8 ) ................................ 7 Mineral Composition of the Three Types of Granitic R o c k s .......................................................... 19 Average Composition of K-feldspars (10 samples of each type of g r a n i t e ) ....................................... 41 K-feldspar Composition of Six Samples of Coarse Porphyritic Granite from the Same O u t c r o p ................ 43 Triclinicity of K-feldspars in the Three Granite Types (4 samples of each) . . . . . ................... . . . . . 50 Average Frequencies of Plagloclase Twin Types in the Three Types of Granite (20 samples e a c h ) .................. 55 Frequencies of Twinned and Untwinned Plagioclases in Coarse Porphyritic Granite and Foliated Porphyritic G r a n i t e ....................................................... 57 Comparison of the A, C, and U Plagloclase Twin Frequencies in Samples of Coarse Porphyritic Granite and Foliated Porphyritic G r a n i t e ............................ 58 Comparison of the Means of Plagloclase Twin Counts in Coarse Porphyritic Granite and Foliated Porphyritic Granite using t-te s t.......................................... 59 Ionic Properties of the Elements that can substitute for Alkalies in the Feldspar L a t t i c e ....................... 60 Substitution Possibilities for K in K-feldspar (after Nockolds, 1966) . . . . . . . . . . . . 61 Arithmetic Means and Ranges of Concentrations of K, R b , and Ba in K-feldspars in the Three Types of Granite (6 samples of e a c h ) ................................ 63 v LIST OF FIGURES Figure 1. Page Index map showing location of the Republic Trough A r e a .............................................. 2 2. Map showing sample locations............................ 12 3. Geologic map of Republic Area, Marquette County, Michigan................................................... 15 Ternary diagram of quartz-plagioclase-microcllne modal values for granite g n e i s s ........................ 20 Ternary diagram of quartz-plagloclase-microcline modal values for foliated porphyritic granite ......... 22 Ternary diagram of quartz-plagioclase-microcllne modal values for coarse porphyritic granite ......... 23 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. . Mlcrocline (M) - plagloclase (P) intergrowth. Crossed polars...................... 25 Antiperthitic plagloclase. Plagloclase (P) replacing mlcrocline (M). Crossed polars ............. 25 Recyrstallization exhibited by mosaic arrangement of subhedral crystals of plagloclase. Crossed polars..................................................... 27 Plagloclase crystals showing mosaic texture. Crossed polars............................................ 27 Antiperthitic plagloclase. Mlcrocline (M) mantling quartz (Qtz). Crossed polars ........................... 28 Vein perthite - mlcrocline (M) and plagloclase (P). Crossed polars............................................ 28 Quartz (Q) crystals exhibiting recrystallization texture. Crossed polars ................................. 30 Rim of albite (A) mantling plagloclase (P) on plagloclase - mlcrocline (M) interface. Crossed polars..................................................... 32 vi Figure 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. Page Clear albite rim (outlined in ink) restricted to mlcrocline (M) - plagloclase (P) contact. No rim on mlcrocline - quartz (Q) and plagloclase quartz Interface. Crossed polars .......................... 32 Nucleation of albite exsolved from mlcrocline (M) on plagloclase (P) boundary. Crossed p o l a r s ............... 32 Albite (clear blebs) exsolved from mlcrocline (M) is intergrown with plagloclase (P).Crossed polars . . 33 Rods of quartz in twinned plagloclase. The rods extend across the twin plane without any distortion. Crossed polars.''.............................................. 33 Zoning in plagloclase. The more calcic core is altered. Crossed pol a r s ..................................... 35 Zoned plagloclase (P). The lamellae cross from core to rim without deflection. Crossed p o l a r s ................. 35 Replacement and resorption of mlcrocline (M) by plagloclase (P) . Crossed pola r s ............................. 37 Myrmekite on mlcrocline (M) - plagloclase (P) interface. Crossed polars ................................................. 37 Mole percent albite in solid solution plotted against mole percent total albite in K-feldspar ................... 42 Geothermometer based on the distribution of albite between K-feldspar and plagloclase in granite gneiss (x), foliated porphyritic granite (•)» and coarse porphyritic granite (v), (after Perchuk and Ryabchikov, 1 9 6 8 ) .......................................................... 45 Plots of 26 (060) against 26 (204) C u K ^ for K - f e l d ­ spars in granite gness (x), (after Wright, 1968). . . . 47 Plots of 20 (060) against 20 (204) CuK^ for K-feld­ spars in foliated porphyritic granite, shown by dots (•)» (after Wright, 1968)............................... 48 Plots of 20 (060) against 20 (204) CuK^ for K-fe l d ­ spars in coarse porphyritic granite, shown by (v), (after Wright, 1968).......................................... 49 Glide twinning in plagloclase. The lamellae thin in unison. Crossed polars. . . . . ........................ 54 vii Figure 29. 30. 31. 32. Page Displacement of twin lamellae in plagloclase b y a later phase of deformation. C r o s s e d polars. . . . 54 Plots of twinned (A+C) against untwinned p l a g l o ­ clase frequencies in foliated porphyritic granite (■) and coarse porphyritic granite (v)...................... 56 Percent K vs ppm Rb in granite gneiss (x), foliated porphyritic granite (*), and coarse porphyritic granite ( v ) .................................................... 65 ppm Kb plotted against pp m Ba in K-feldspar. Granite gneiss is shown b y cross (x)f foliated porphyritic granite b y dots (•), and coarse p o r ­ phyritic granite b y ( v ) .................................... 66 vlll INTRODUCTION Purpose of Study The granitic rocks around the Republic Trough in Marquette County, Michigan called "Basement Complex" by Van Hise (1911) and "Republic Granite" by Lamey (19 33), have been a subject of discussion since 1850. The controversy among the different workers is related to the actual number of granitic intrusions in the area and their relative age. There is, however, a general agreement that at least two types of granites are exposed in the area. The relationship of the granites with the Animikie metasediments and the relative areal extent of the granites is still a matter of controversy. Most of the discussions by the previous workers in the area are attempts to explain the age relation of the granites and the Animikian rocks based largely on field relations; the petrology of the granites has not been described clearly. The purpose of the present study was to determine the number and range of granite types in the area and to determine the extent that petrographic variations coupled with field observations could resolve the granitic rocks into a combination of genetically different types. Geography The Republic Trough is a narrow syncline of Animikian rocks located towards the western part of Marquette County in the Upper Peninsula of Michigan (Figure 1). The area mapped surrounds the trough and covers about sixty square INOEX l*OM MAP t !~------- h 0K »0» «• IT* Figure 1. II* N* 14* Index Map Showing Location of the Republic Trough Area. miles encompassed within latitudes 46°20' 8 7 ° 5 3 l and 8 8 ° 0 6 * west. and 30 west. and 46°28' north; longitudes It Includes Townships 46 and 47 north; Range 29 The area is dissected b y the Michigamme River flowing southeast along the axis of the trough. The town of Republic, towards the southeast of the trough, is located on State Highway M 93 and is also accessible by a few county roads. The southern part of the area is traversed b y few pave d roads accessible by automobile; the northern part has only a few logging roads and is completely inaccessible by automobile. The outcrops of rocks are v e r y few and sporadic, covering less than five per cent of the area, but road cuts have exposed the rock at many places. New State Highway M 93 runs north-south along the whole length of the area, and the cuts along the road provide the best exposures for study and expose fresh unweathered rocks for sampling. mainder is covered b y sand plains; Most of the r e ­ swamps cover the shallow depressions. Exposures of rocks are seen on the summits and flanks of small isolated knobs separated b y wide cover of glacial deposit. Geological Setting The area known as the Southern Complex (Dickey, composed of granite, outside the Republic Trough. 19 36) is dominantly Reconnaissance survey revealed the presence of three texturally distinct types of granites of significant areal extent, an even-grained granite gneiss, foliated p o r ­ phyritic granite with small phenocrysts and coarse porphyritic granite lacking any visible foliation. The foliated porphyritic granite and coarse porphyritic granite have not be e n differentiated by previous workers in the area and have commonly been referred to as "Republic Granite" since first named b y Lamey (19 33). The number of granitic Intrusions in the area and their age rela­ tions with the Animikie xnetasediment have been a matter of controversy since 1850. Van Hise and Leith (1911) reviewed the problem and work up to 1909 and concluded that there are two intrusions of granite in the area: one pre-Animikie (pre-Huronian), and the other post-Animiklan. The relative areal extent of pre-Animikie and post-Animlkie granites have also been a controversial problem. Lamey (1937) believes that most of the granites of the Southern Complex are post-Animikie, whereas Dickey (1936) contends that much of the Southern Complex consists of preAnimikie granites. the area, Foster and Whitney (1851), the earliest workers in suggested that the granite of the Southern Complex is intru­ sive into the Animikian. Lamey (1937) has compiled an excellent review and evaluation of the many writings and work on the problem of the granitic rocks of the Southern Complex. In a series of articles, he has concluded that the entire area of the Southern Complex with minor exceptions is Intruded by granites of post-Animlkie age. Lamey has reported the intrusion of granite into quartzite, presumably of Animikie age, south of National Mine in Ishpeming. His idea is further supported by the metamorphism of Animikie sediment which he attributes to the contact effect of postAnimlkie granite (Lamey, 1934). Metamorphism of Animikie sediment has been cited as evidence for the post-Anlmikie age of porphyritic granite by some other workers (Swanson, 1929; Zinn, 1930; Snelgrove, Seaman and Ayres, 1944). Swan­ son (1929) and Zinn (1930) have also recognized the occurrence of an older heterogeneous gneiss in the area upon which Animikie was laid down. Swanson (1929) also reported the intrusion of granite into Animikie sediment seen In a drill hole in Section 20, T47N, R28W, lated this granite with the Republic granite. tion is, however, and has corre­ The basis of his correla­ not mentioned. Dickey (1936) has dated the porphyritic granite as pre-Animikie in age and cited the following evidences in support of his view: (a) Lack of intrusion of porphyritic granite in Animikie (Huronian) rock. (b) Deformation and shearing of granite after solidification. (c) Basal Animikian conglomerate containing boulders of porphyritic granite. The conglomerate was exposed at the southeastern end of the Repub­ lic Trough in the northeast quarter of Section 18, T46N, R29W. Accord­ ing to Dickey, boulders of porphyritic granite up to five feet in diameter are included in the conglomerate; the foliations in the boulders are at varying angles to the general foliation of porphyritic granite. The conglomerate was first described by Smyth (189 3) who also reported the presence of boulders of granite in the conglomerate. Lamey did not find any evidence of granite boulders in the c on­ glomerate and disputes the finding of Dickey in a later paper (Lamey, 19 37). According to Lamey, the conglomerate is chiefly quartzitic. The total absence of porphyritic granite in Animikie conglomerate has also been reported by Marsden, Tyler et al (1940). The outcrop has since been covered by waste material from the Republic Mine and could not be examined during the course of this study. Dickey (1938) has recognized a post-Animikie granite in Republic area which he called "Klllarney Granite." He reports that this granite is sporadic in occurrence and that it is exposed in disconnected small areas. He has attributed its origin to the partial fusion of porphyritic granite during the Klllarne y orogeny. The periods of g r a n i t i c i n t r u s i o n in the Southern Complex and their age relation w i t h o t h e r P r e c a m b r i a n rocks of the area, Table 1. as recognized b y Dickey, are shown in T a b l e 1. Age Relations of the Rocks of Southern C o m p l e x (after Dickey, 1938) Era Paleozoic Period Formation Cambrian Keweenawan Algonkian Precambrian Lipaiian i n t e r v a l - ------Kllla r n e y granite Upper Huronian Middle Lower CaParcneau interval-Granite-porphyry — - Laure n t i a n Granite of the A r c h e a n i n j e c t i o n gneiss A r chean Keewatin James Schi sts (1958) proposed the c l a s s i f i c a t i o n of the P r e c a m b r i a n rocks of N o rthern M i c h i g a n into Lower, Middle, and Upper Precambrian. three-fold nomenclature has been adop t e d b y the U. This S. G e o l o g i c a l Survey. James also p r oposed the term A n i m i k i e for the m e t a s e d i m e n t s p reviously called Huronian. Table 2 shows the succe s s i o n of the P r e ­ cambrian rocks in Northern Michigan, rium. adapted to the M a r q u e t t e Synclino- 7 Table 2. Sequence of Precambrian Rocks In Northern Michigan (from Gair and Thaden, 1968) Upper Precambrian Keweenawan Series Diabase dikes Perldotlte Pegmatite Middle Precambrian age uncertain Mafic Intrusive rocks of uncertain age Animikie Series Menominee Group Siamo Slate Ajlbik Quartzite Unconformity or DisconformityWewe Slate Chocolay Group Kona Dolomite Mesnard Quartzite Enchantment Lake Formation Lower Precambrian -UnconformityMetamorphosed mafic intrusive rocks of uncertain agemay be partly or entirely of Animikie age , Intrusive -.... Compeau Creek Gneiss and related dikes -Intrusive contactMetamorphosed mafic intrusive rock — — — — — Intrusive contact---------Mona Schist including Lighthouse Point Member Field Mapping Field work for this investigation was carried out during the summers of 1966 and 1967 and continued for part of the summer in 1968. An area of about 60 square miles covering parts of Republic SW, Republic, Witch Lake NE, and Witch Lake 7.5 minute quadrangles, was studied. U. S. Geological Survey topographic maps on 1 inch to 2000 feet scale were used as base maps. Wherever available, county roads and logging roads were used for traverses; other traverses were taken along section lines. Outcrops were plotted by pace and compass met h o d of survey, pass. is densely forested, which prevents the easy location of The area available exposures. using a Brunton Com­ This handicap wa s partly overcome by the use of aerial photographs in locating positions of outcrops. Deviation of compass reading was noted near the Animikie rocks due to the presence of iron formation; deviations as much as 80° were re­ corded in some localities. The compass reading in areas of magnetic disturbance was corrected using the sun chart compass correction method of Fraser (1963). Sun compass was also used for some readings, but was not very practical because of the long time required for each reading. Based on textural variation and field relations, types of granites were recognized: granite with small phenocrysts, granite gneiss, three distinct foliated porphyritic and a coarse porphyritic granite. GENERAL LITHOLOGY OF THE GRANITIC ROCKS Granite Gneiss The rock is massive, fine to m e d i u m grained, and is composed p r i ­ marily of mlcrocline perthlte, quartz,and plagioclase in vary i n g p r o ­ portions. The granite gneiss is very heterogeneous in composition, ranging from a quartzose granite (location: along M 95) through granodloritic (location; Section 29, T47N, R29W; (b) S W hi north of M i c h i g a m m e River (a) northern part of of Section 25, T47N, R29W) to true massive granite. Textural variation in the rock is also v e r y prominent. The p a r a l ­ lel aligned biotite flakes at places form banding and attain a true gneissic texture. At a few locations, Ht-par-lit injection of granitic liquid into pelitic and semi-pelitic Low e r Precambrian rocks has resulted in the formation of injection gneiss w h i c h consists of coar s e l y c r y s t a l ­ line quartzo-feldspathic bands alternating w i t h biotite quartz bands. Near the trough, outcrops of granite gneiss generally flank Animikie metasediments; and also mantle the coarse porphyritic granite in the northern sector of the area. Near Republic, the granite gneiss occurs in juxtaposition with foliated porphyritic granite; at places they are much intermingled. The rock possesses a NW-SE foliation w h i c h was superimposed on a N25W-S25E foliation, parallel to the axis of the syncline, probably developed by Animikie folding. 10 Foliated Porphyritic Granite (with small phenocrysts) The rock is generally grey in color showing a well-developed planar foliation marked by parallel alignment of biotite flakes. anhedral phenocrysts of mlcrocline and plagloclase, fairly prominent linear structure in the foliation. Subhedral to sometime form a The phenocrysts are usually one to two cm in length, and display an augen appearance in a few localities. The trend of the early foliation in general is N25W-S25E with a very steep to vertical dip. The granite was probably folded with the Animikie rocks and in the process acquired a NW-SE orientation. The foliation is generally concordant with the Animikie metasediments near the contact, but at a location south of Republic Mine (NE k, of Section 18, T46N, R29W), the discordant relation of the granite with the m e t a ­ sediments is clear. The field relation of the rocks at this location indicates that the N25W-S25E foliation in the granite developed before the folding of the Animikie rocks, was folded later with them. Unlike the other two types of granite in the area, the rock is generally homogeneous in composition. Coarse Porphyritic Granite (with big phenocrysts) The rock lacks any planar foliation but shows a strong linear orientation marked by parallel to subparallel arrangements of euhedral to subhedral phenocrysts of mlcrocline. The large (3 to 4 cm long) phenocrysts of mlcrocline are set in a coarse matrix of quartz, plagioclase, and biotite, with accessories. The feldspar phenocrysts in the rock are arranged linearly in a N65W-S65E direction, probably caused by flow. The trend of llneation in the rock has a very discordant relation with the foliation of the foliated porphyritic granite in the central part of the outcrop, but gradually attains parallelism near the contact with the foliated p o r ­ phyritic granite. The phenom e n o n is well illustrated b y the change in lineation trend from sample location 5 7 (Section 32, T47N, ceeding southwest to sample locations 58, contact (see Figure 2). R29W), pro­ 59, 60, and 185 near the The lineation changes gradually from N62W-S62E to N25W-S25E at location 185. This suggests that the development of lineation is due to flow and that the change in the trend as the contact is approached is a result of interference b y the wall rock (Balk, 19 37). HUP SHOWING LOCATION OF SAMPLES jr Figure 2. Map Showing Sample Locations GENERALIZED SCHEMATIC M A P OF REPUBLIC TROUGH AREA The structure of the Republic Trough area is very complex. are clear evidences of many phases of deformation, There each phase having partially deformed the structure developed by earlier phases. The various phases of deformation have complicated the field relations of the different granitic rocks. Field observation to resolve the relation­ ship of the granites was greatly handicapped by the lack of sufficient rock exposures in the area. The granite gneiss is exposed mainly around the Animikian rocks along the trough. The contact relations of the two rocks could not be observed at any place; commonly an erosional valley separates the granite gneiss and Animikie metasediments. The intrusive relation of the granite gneiss into hornblende-quartz-schist is very clear at a few locations south of the Michigamme River. The gneiss is also seen to be generally mantling the coarse porphyritic granite, but field relations are difficult to determine since the outcrops are ver y small and iso­ lated. Xenoliths of granite gneiss, varying in size from a fraction of a meter to a few meters, are found in coarse porphyritic granite as well as foliated porphyritic granite. The presence of xenoliths clearly indi­ cates that the granite gneiss is the oldest of the three granitic rocks in the area. The field relations of foliated porphyritic granite and coarse 13 14 porphyritic granite are not ver y clear. The outcrops of the two rock types are everywhere separated by glacial deposits; the transition between the two types is sharp. There are, however, a few small sporadic outcrops of well-foliated coarse porphyritic granite at the following locations: (a) Eastern part of Section 13, T46N, R30W (b) Southern part of Section 36, T47N, (c) Northwestern % of Section 19, T46N, R30W R29W The rock is well-foliated and has been map p e d as foliated porp h y r i ­ tic granite. It may alscx be related to coarse porphyritic granite and have acquired the foliation as the result of flow during intrusion. The margin of coarse porphyritic granite at places has developed planar foliation presumably due to the flow along the contact. Figure 3 shows the general bedrock geology of the area. Pegmatite and amphibolite have not been shown o n the map because of their small outcrops. Petrofabric analysis of 13 rock samples (5 each of coarse porp h y r ­ itic granite and foliated porphyritic granite and 3 of granite gneiss) was carried out to determine the age relation of the rocks by the number of phases of deformation and their effect on the rock. The samples were collected from scattered outcrops to get a representation of the whole area. Two oriented sections were cut from each r o c k — one parallel to the horizontal plane and the other from a vertical plane. Orientation of C-axis (the principal axis) of quartz wa s recorded for 200 quartz grains in each section. The plot of the vertical section was rotated along the N-S axis to bring it to a horizontal plane. C-axis emergence on lower hemisphere was plotted on a "Schmidt equal area net." A GEOLOGIC MAP OF REPUBLIC AREA. MARQUETTE COUNTY. MICHIGAN Figure 3. Geologic Map of Republic Area, Marquette County, Michigan 16 composite plot of the two sections In each rock was contoured at a one percent Interval. Plot of two sections at right angles to each other Is likely to eliminate bias in the selection of the plane of observa­ tion. The petrofabric analysis of the rocks revealed that the granite gneiss and the foliated porphyritic granite have a strong orientation in NW-SE direction, which is concordant with the axis of the Republic Trough. It is likely that the development of this orientation is syn­ chronous with the folding of the Animikie metasediments and is super­ imposed on the earlier formed planar foliation striking N25W-S25E. The age of emplacement of coarse porphyritic granite is not very clear. Lack of planar foliation and a general absence of NW-SE orienta­ tion in petrofabric analysis (only two of the five rocks examined have any significant concentration in NW-SE direction) suggest a post-Animikie age of the coarse porphyritic granite. The rock appears to have been emplaced as a sheet with a general strike of N60W-S60E and occupies the anticlinal axial position between the Republic Syncline and Marquette Syncline. It intruded along the axial plane of the anticline after or during the waning phase of Animikie folding. The metamorphism of the Animikie rocks may be related to the in­ trusion of the coarse porphyritic granite. It Is also likely that only the roof of the coarse porphyritic granite pluton is exposed in the area and the rock extends more widely at depth. The presence of xenoliths in the rock and the extensive metamorphism of the Animikie metasediments supports this idea. Weak orientation in E-W and NE-SW direction is revealed by a few samples of all the three types of granite in the area. These orientations 17 developed after the emplacement of coarse porphyritic granite and may be associated with the numerous pegmatite and amphibolite intrusions in the area. Taylor (1967) studied the structure of the Lower Precambrian rocks in the Champlon-Republic area. He recognized four phases of deformation by the measurements of minor structures. P E T R O L O G Y O F T HE G R A N I T E S A) Modal Analysis of the Gran i t e s Determination of the m i n e r a l s and their relative p r o p o r t i o n s in the three types of granitic rocks wa s c a r r i e d out to study the m i n e r ­ alogy of the granites and exam i n e the diffe r e n c e b e t w e e n the various types. The point count m e t h o d of Chayes (1956) w as e m p l o y e d for d e t e r ­ m i ni n g the relative proportions of m i n e r a l s in thin sections. About 1200 to 1400 points w e r e coun t e d in e a c h section of coarse p o r p h y r i t i c granite; whereas 1000 to 1200 p o i n t s w e r e coun t e d in the other lithologies, the number b e ing deter m i n e d b y the c o a r s e n e s s of the rock. The three types of g r a n i t e s are simi l a r in mine r a l composition; v ariation w i t h i n a type is sometimes g r e a t e r t h a n the difference betw e e n the types. The average m o d e s of the three gran i t e s are p r e s e n t e d in Table 3, and these are p l o t t e d on the K - f e l d s p a r - p l a g i o c l a s e - q u a r t z ternary diagrams (Figures 4, 5, a nd 6). The plots for the granite gneiss (Fig. 4) are c o n c e n t r a t e d mainly in the central part of the diagram, w h i c h c o rresponds to the low temperature trough on the q u a r t z - o r t h o c l a s e - a l b i t e diagram of James and H a milton (1969). Fe w samples c o m p l e t e l y devoid of K - f e l d s p a r w e r e c o l l e c t e d from granite gneiss-coarse p o r p h y r i t i c granite contact zone, one which is from an outcrop n o r t h of R e p u b l i c w h e r e the granite gneiss is intermingled w i t h the foliated p o r p h y r i t i c granite. 18 except for The d e p l e t i o n Table 3. Mineral Composition of the Three Types of Granitic Rocks Average Mode of Granite Gneiss (18 samples) Mineral Microcline Quartz Plagioclase Biotite Muscovite Chlorite Myrmekite Zircon Epidote Apatite Calcite Opaque * Mean 20.5 30.1 35.4 5.3 5.3 1.7 1.0 Tr. Tr. Tr. Tr. Tr. Range 0.0 7.0 21.1 0.0 0.0 Tr. 0.0 Standard Deviation . - 33.7 39.1 74.3 13.8 15.1 3.9 2.9 0.0 - 1.8 10.7 8.6 14.0 Foliated Porphyritic Granite (18 samples) Mean 30.0 31.3 25.4 4.2 6.2 1.4 0.7 Tr. Tr. Tr. Tr. Tr. Range 15.4 22.9 11.6 1.4 2.0 0.3 0.0 Standard Deviation - 39.4 41.6 37.6 7.7 16.0 6.7 2.7 0.0 - 1.8 *Allanite, garnet and hornblende were identified in fev rocks. 6.0 5.0 6.8 Coarse Porphyritic Granite (18 samples) Mean 25.0 35.6 27.8 3.6 5.6 1.2 1.0 Tr. Tr. Tr. Tr. Tr. Range 0.0 13.9 15.0 0.3 3.1 Tr. 0.0 - 54.1 55.4 54.2 8.6 10.1 3.2 2.6 Standard Deviation 15.2 10.3 13.0 20 QUARTZ 7T FLAGIOCIASE Fig. 4 M ICROCLINE Ternary d i a g r a m of quartz-plagioclasemicrocline mod a l values for granite gneiss 21 of K-feldspar in the rock may have been caused by the replacement of microcllne by albite. Evidence of such replacements is seen in a few rocks (Figure 7). The average modal composition of the granite gneiss is 20.5% K-feldspar, 30.1% quartz, 35.4% plagioclase (An6-18)» 5.3% biotite, 5.3% muscovite, 1.7% chlorite, 1.0% myrmekite and traces of zircon, epidote, apatite, calcite, and ferruginous opaques. Allanite, garnet, and hornblende are rare accessories (Table 3). All the values for the foliated porphyritic granite fall with­ in a strikingly restricted area near the low temperature trough (Figure 5). This indicates that the rock cooled slowly, maintaining perfect equilibrium throughout the cooling. Unlike the other granites in the area, the foliated porphyritic granite is fairly uniform in composition. The average modal compositions of the granites, given in Table 3, indicate that in comparison with the coarse porphyritic granite, the foliated porphyritic granite is richer in K-feldspar but poorer in quartz and plagioclase. Zircon, epidote, clinozoisite, and apatite are rare and occur only as inclusions in the plagioclase, probably formed later by the alteration of the plagioclase. Plots of the coarse porphyritic granite (Figure 6) are very dispersed and do not follow any regular pattern with relation to its location in the field. Most of the values are concentrated near the center, slightly away from the plagioclase field. Five samples have less than five per cent K-feldspar and their plots lie on or near the plagioclase-quartz tie line. Most of these rocks are located in the contact zone with granite gneiss. The low K-feldspar rocks are generally rich in plagioclase, whereas the quartz content remains about average. 22 QUARTZ MICROCLINE PLAGIOCLASE Fig. 5 Ternary diagram of quartz-plagioclaaemicroc line modal values for foliated porphyritic granite 23 QUARTZ PLAGIOCLASE Fig. 6 M ICROCLINE Ternary diagram of quartz-plagioclasemicrocline modal values for coarse porphyritic granite 24 There is no significant correlation with the An-content of the plagio­ clase and the variation in the plagioclase:microcline ratio. Na-metasomatism during or after the emplacement of coarse porphyritic granite has probably caused the replacement of mlcrocllne by albite. Fractionation of alkalies between a fluid phase and crystalline feldspar is mainly dependent on temperature; the physical condition of the fluid has very little effect on the alkali ratio (Orville, 1963). According to Orville, the colder rocks will be enriched in K-feldspar, whereas the warmer rocks will be depleted in K-feldspar. Replacement of K-feldspar by albite in these rocks m a y be attributed to the thermal gradient established near the contact by the emplacement of hot granite magma into the cold country rock. Evidences of such replacements are seen in samples of coarse porphyritic granite (Figure 8). The modal composition of coarse porphyritic granite is very variable; the average mode (Table 3) indicates that in comparison to foliated porphyritic granite the rock is poorer in K-feldspar and richer in average plagioclase content. are much more common accessories. Epidote, apatite, and calcite The total muscovite formed by the alteration of feldspar is significantly more. B) General Texture of the Granitic Rocks Granite Gneiss The granite gneiss is extremely heterogeneous both in the mineralogy and texture. It varies from even grained massive granitic texture to banded gnelssic texture; a few samples have metasedimentary appearance. The granite gneiss is the oldest of the granitic rocks in the area which can be inferred by its occurrence as xenoliths in the other Figure 7. Microcllne (M> - plagioclase Crossed polars. (P) intergrowth. Figure 8. Antlperthltic plagioclase. Plagioclase replacing microcllne (M). Crossed polars. (P) 26 two types of granites. Evidence of m e t a m o r p h i s m on the rock is indicated b y r e c r y s t a l l i z a t i o n texture w h i c h is c l e a r l y e x h i b i t e d b y the m o s a i c type arrangement of small 10). subhedral p l a g i o c l a s e crystals (Figures 9 and However, p r e s e n c e of zoning and C a r l s b a d twinning of p l a g i o c l a s e in a few samples suggest that total r e c r y s t a l l i z a t i o n has not occurred. Suwa (1965) o b s e r v e d that the C a r l s b a d twin n i n g in p l a g i o c l a s e gradu a l l y disappears w i t h p r o g r e s s i v e recrystallization. A n t i p e r t h i t i c i n t e r g r o w t h of m i c r o c l l n e and p l a g i o c l a s e is v e r y commonly o b s e r v e d in the g r a n i t e gneiss. In a few rock samples, the antiperthites m a y have o rig i n a t e d b y the e x s o l u t i o n of K - f e l d s p a r w h i c h was p r obably f a c i l i t a t e d b y the str a i n due to shearing stress on the rock (Sen, 1969). A n t i p e r t h i t e s of r e p l a c e m e n t o r i g i n hav e also be e n recognized in some rocks (Figure 7). Vogel, Smith, and G o o d s p e e d (1968) have reported the development of a n t i p e r t h i t e due to n u c l e a t i o n of K-feldspar o n low e n e r g y surfaces in the c h a r n o c k i t i c rocks of New J e r ­ sey. F o r m a t i o n of antiperth i t e in a fe w samples of granite gneiss m a y be attributed to the growth of m i c r o c l l n e on low energy surfaces w i t h i n earlier formed plagioclase. within plagioclase, formed m i c r o c l l n e The b o u n d a r y of quartz crystal, enclosed act e d as a favor a b l e site for the n u c l e a t i o n of latet (see Figu r e 11). The s e r o c k samples have a v e r y h i g h content of p l a g i o c l a s e a n d the i r m o d e s plot in the p l a g i o c l a s e field on the q u a r t z - o r t h o c l a s e - a l b i t e t e r n a r y p h a s e diag r a m of James and Hami l t o n (1969), w h i c h suggests that the p l a g i o c l a s e crystallized early. The interstitial growth of m i c r o c l l n e b e t w e e n p l a g i o c l a s e crystals also i n d i cate later c r y s t a l l i z a t i o n of m i c r o c l l n e in these rocks. The m i c r o c l l n e in m o s t of the granite gneiss samples is not very perthitic. V e i n perthlte, o b s e r v e d in a fe w rocks (Figure 12) » Is 27 Figure 9. RecryBtallizatlon exhibited by mosaic arrange­ ment of subhedral crystals of plagioclase. Crossed polars. Figure 10. Flagioclase crystals showing mosaic texture. Crossed polars. Figure 11. Antlperthltlc plagioclase. Microcllne mantling quartz (Qtz). Crossed polars. (M) v V* a Figure 12. clase V e i n perthlte - microcllne (P). Crossed polars. (M) and plaglo~ 29 believed to be of exsolution origin (Deer, Howe, a nd Zussman, Rims of albite ma n t l i n g the h i g h e r An-plagloclase, seen in the other two granites, 1963). commonly are g e n e r a l l y l a c k i n g in gran i t e gneiss. Lack of such rims m a y be attributed to the m e t a m o r p h i s m of the rock. Foliated Porphyritic Granite The rock type has a p o r p h y r i t i c text u r e w i t h p h e n o c r y s t s of microcllne and plagioclase set in an e v e n - g r a i n e d coa r s e m a t r i x of quartz, plagioclase, K-feldspar, and biotite. Th e p h e n o c r y s t s form a prominent linear structure in the s t r o n g f o l i a t i o n d e f i n e d b y p l a n a r orientation of musc o v i t e and biotite flakes. of twin lamellae of plagioclase Bending and displacement (Figures 28 and 29) of the rock after solidification. indi c a t e d e f o r m a t i o n G r a n u l a t i o n of the p h e n o c r y s t s f r e ­ quently observed in the rock provides further e v i d e n c e of deformation. Aggregates of quartz e x h i b i t i n g a m o s a i c texture are i n t e r ­ preted as h a v i n g be e n formed by r e c r y s t a l l i z a t i o n occurrence of albitic rims s u rrounding p l a g i o c l a s e crystallization is not complete. (Figure 13). However, suggests that the r e ­ C a r l s b a d t w i n n i n g and zon i n g o b s e r v e d in the plagioclase in a few rocks are i n d i c a t i v e of original features that have escaped later r e c r y s t a l l i z a t i o n (Suwa, igneous 1965). The texture of the foliated p o r p h y r i t i c g r a n i t e indic a t e s that the plagioclase crystallized b o t h earl i e r and l a t e r than microcllne. The earlier formed euhedral to subhedral c r y s t a l s of p l a g i o c l a s e are enclosed w i t h i n micro c l l n e and have a h i g h l y s e r i c l t l z e d core of m o r e calcic plagioclase surrounded b y c l e a r albi t i c rims. plagioclases, Later formed interstitial b e t w e e n m i c r o c l l n e and quartz, are low in Am-content. The clear albitic rims m a n t l i n g a m o r e calcic core are Figure 13. Quartz (Q) crystals exhibiting recrystalli-’ zation texture. Crossed polars. Figure 14. R i m of albite (A) mantling plagioclase (P) on plagioclase - microcllne (M) interface. Crossed polars. interpreted to have f o r m e d b y the e x s o l u t i o n of albite from the m i c r o ­ cllne and m i g r a t i o n to a favorable site. P l a g i o c l a s e g r a i n b o u n d a r y in contact w i t h m i c r o c l l n e appears to be the m o s t favorable site as the albitic rims are u s u a l l y restricted to m l c r o c l l n e - p l a g i o c l a s e contact (Figures 14 and 15 c l e a r l y demonstrate this fact). The r i m is well developed on the m l c r o c l l n e - p l a g i o c l a s e b o u n d a r y but is c o m p l e t e l y l a c k ­ ing on p l a g l o c l a s e-plagiocla s e i nterface in Fig u r e 14. The a b s e n c e of the rim on the p l a g i o c lase-q u a r t z contact is evident in Figure 15. The restricted occurrence of the albite ri m o n p l a g i o c l a s e - m l c r o c l i n e i n t e r ­ face suggests that the rim has d e v e l o p e d b y the reaction b e t w e e n m i c r o ­ cllne and plagioclase. The albite is likely to have e x s o l v e d from microcllne and w a s nucl e a t e d on the p l a g i o c l a s e boundary. Albite e x ­ solved from m i c r o c l l n e is seen to be m i g r a t i n g towards p l a g i o c l a s e and is nucleating on the grain b o u n d a r y (Figure 16). In some rocks, exsolved albite from m i c r o c l l n e is intergrown as belbs into plagi o c l a s e as seen in Figure 17. The sharp contact of the rims w i t h m i c r o c l l n e Indicates a reaction in the solid state after the c r y s t a l l i z a t i o n of the magma. In a few cases, p a r t i c u l a r l y w h e r e the albite rims occur on p l a g i o c l a s e - quartz Interface, the rims m a y have b e e n formed b y the e x s o l u t i o n of albite from the plagioclase and m i g r a t i o n to the gra i n boundary. Vermicular intergrowth of q u a r t z in p l a g i o c l a s e is fai r l y c o m ­ mon and is considered to be e x s o l u t i o n m y r m e k i t e b e c a u s e of its frequent association w i t h m i c r o c l l n e (Hubbard, 1967). I n one sample, clear belbs of quartz extend across a twin pla n e in p l a g i o c l a s e without any d i s t o r ­ tion (see Figure 18) w h i c h suggests that the m y n n e k i t i z a t i o n took pla c e after the development of twinning in the p l a g i o c l a s e and is p r o b a b l y a late stage phenomena. 32 Figure 15. Clear albite rim (outlined in ink) restricted to microcline (M) - plagioclase (P) contact. No rim on microcline - quartz (Q) and plagioclase - quartz Interface. Crossed polars. Figure 16. Nucleation of albite exsolved from microcline (M) on plagioclase (F) boundary. Crossed polars. 33 Figure 17. Albite (clear blebs) exsolved from microcline (M) is intergrown w i t h plagioclase (P). Crossed polars. Figure 18. Rods of quartz in twinned plagioclase. The rods extend across the twin plane without any d i s ­ tortion. Crossed polars. 34 M i c r o c l l n e In the foli a t e d p o r p h y r i t i c granite is g e n e r a l l y not v e r y p e r t h l t i c (average 5.5 m o l e % exsolved albite as compared to Ab in coarse porphyritic granite). 1 2 .3 % A n t i p e r t h i t e is, however, v e r y c o m ­ m o n in the rock. Coarse Porphyritic Granite Unlike the foliated porphyritic granite, the coarse p o r p h y r i t i c granite is not m u c h deformed and lacks an y well d e v e l o p e d foliation. The modal composition of the rock is v e r y variable, rock is fairly homogeneous. but textu r a l l y the Large pheno c r y s t s of m i c r o c l i n e are set in a m a t r i x of plagioclase, quartz, microcline, muscovite, and biotite. The parallel alignment of the p h e n o c r y s t s form a promi n e n t l i n e a t i o n in the rock. The plagioclase crystals in some rocks are zoned and generally have h i g h l y corroded cores w h i c h are h e a v i l y charged w i t h epidote, cllnozoisite, calcite, and sericite. The dirty cores are su r r o u n d e d b y clear less calcic rims (Figure 19), w h i c h are opti c a l l y continuous w i t h the cores. Where twinning is present, the lamellae cross from the core to the rim w i t h o u t deflection (Figure 20). The K-feldspar content of the rock is v e r y v a r i a b l e ranging from 0.0 to 54.1%. Replacement and resor p t i o n of m i c r o c l i n e b y p l a g i o ­ clase is i n d i c a t e d in a few rocks (Figure 21). cline and plagioclase, throughout. und e r cros s e d nicols, The interg ro w t h of m i c r o exhibits a com m o n extinctio Such optical c o n t i n u i t y p r o b a b l y reflects a growth control imparted b y the p r e - existin g microcline. The texture of some rocks also indicates the replacement of microcline, p r o b a b l y due to N a - m e t a ­ somatism after the solidif i c a t i o n of the rock. A l b i t i c rim m a n t l i n g the p l a g i o c l a s e is v e r y c o m m o n in the rock 35 Figure 19. Zoning in plagioclase. is altered. Crossed polars. The more calcic core Figure 20. Zoned plagioclase (P). The lamellae cross from core to rim without deflection. Crossed polars. 36 occurring generally on the plagioclase-microcline Interface. The plagioclase in the trondhjemltic variety w i t h little or no microcline significantly lacks any albitic rim. The frequency of albitic rim and the amount of myrmekite is directly related to the microcllne content of the rock. Generally, the plagioclase at the contact of microcline either has a clear rim of albite or has inclusions of blebs of quartz forming myrmekite. Lack of albitic rim on the microcline-myrmekite Interface may be attributed to the assimilation of albite with the plagioclase in the myrmekite during the exsolution process. In some cases, the albite exsolved from microcline is intergrown as blebs into plagioclase (Figure 17). Myrmekite is ve r y common in the coarse por- phyrite granite which may indicate a high crystallization temperature of the rock (Hubbard 1967). The close association of myrmekite with microcline (Figure 22) suggests an exsolution origin of myrmekite (Hubbard, 1966 and 1967). Hubbard (1967) indicated that a significant proportion of the anorthlte molecule m a y be included in alkali feldspar as solid solution at high crystallization temperature. Wyart and Sabatier (1965) have demonstrated that the alkali feldspar can take up to 30% of Ca^AlSl^Og into solid solution at 600°c. Calcium is accepted in alkali feldspar in the form of "Schwankte*s(1909) high silica an o r ­ thlte molecule." This anorthlte molecule is accommodated in normal lattice sites I I in alkali feldspar. For each cation accepted in the monovalent lattice framework, a vacancy defect in the corresponding site will be generated. The ability of the lattice to retain vacancies is strongly dependent on the temperature. Therefore, acceptance of significant amounts of calcium in the ternary alkali feldspar suggests high 37 Figu r e 21. Replaceme n t and resorption of m i c r o c l l n e b y plagioclase ( P ) . Cros s e d polars. Figu r e 22. M y r m e k i t e on m i c r o c l l n e Interface. Crossed polars. (M) - plagioclase (M) (P) 38 crystallization temperature. With cooling, growth of anorthlte and quartz takes place as the vacancies are annihilated. ^ > A l S i 308 )2 ----- > CeAl2Si208 Vacancy "High silica anorthlte" Anorthlte + 4 Sio2 + quartz The precipitating albite from the ternary feldspar would com­ bine with anorthlte to form plagioclase. The new plagioclase finds an ideal growth site along the periphery of pre-existing plagioclase and forms as an overgrowth which advances into K-feldspar (Figure 22). In case of low crystallizing temperature, there will be low concentration of anorthlte in the original ternary feldspar which will result in the absence of quartz from the plagioclase aggregate. The coarse porphyritic granite magma cooled very slowly pre­ sumably under deep-seated conditions which resulted in the growth of large crystals that form the phenocrysts in the rock. The finer texture of the groundmass may be attributed to an increase in the rate of cool­ ing, probably due to the intrusion of magma to a shallower depth. this process, to flow. In the early formed phenocrysts developed a parallelism due Formation of muscovite and serlcite at the expense of feld­ spar and alteration of epidote to chlorite is commonly observed in the rock indicating a retrograde effect, probably caused by the concentra­ tion of volatiles during the later stage of rock formation. The source of the volatiles for the retrograde change in the rock m ay be intrusion of pegm&tite In the area, but the widespread occurrence of the feature does not favor the idea of an external source. the later 39 C) Composition of the Coexisting Feldspars In the Granites The feldspar composition is a quali t a t i v e indication of the thermal history of the rock and m a y be used to compare the granites in the area. During the crystallization of the rock, between potassium feldspar and calcium feldspar. albite is distributed The distribution coefficient (the ratio of albite in alkali feldspar to albite in plagioclase) is a function of the temperature'of~ crystallization (Barth, However, 1962). the temperature recorded represents a chemical equilibrium at a certain temperature in the process of the formation of the rock and may be lower than the highest temperature the rock had attained. An Content of rlagioclase The composition of the plagioclase of 60 samples, 20 each of the three types of granites, was determined b y the Rittmann m e t h o d (Emmons, 1943). Ten to twelve grains were studied in each of 60 samples. The dispersion method (Tsuboi, chart based on the 1923) and the use of a revised dispersion oc'001 curve (Morse, 1968) we r e employed to check some of the results of the R i t t m a n n method. The results of the two methods were remarkably similar. The average composition of the plagioclase in the three types of granitic rocks is fairly similar; generally in calcium. The the plagioclase is poor plagioclase in the granite gneiss of 11.5% A n (range An^_^g, contains an average Standard Deviation = 2.4). The average plagioclase composition of the foliated porphyritic granite is A n ^ ranging from An^ to An^g (S.D. = 1.9); whereas the coarse porphyritic granite ranges from Anj_^g (S.D. = 3.2), 11.1% An. g the average of 20 samples being There is no systematic vari a t i o n in the An- content of the plagioclase with relation to the occurrence of the rock in the area. 40 Ab Content of the K-Feldspar The composition of potassium feldspar was determined by (201) X-ray method of Orville (1958, 1967). KBr03 was used as an internal standard to prepare the smear mount for X-ray diffraction runs. samples, ten each of the three rock types, were analyzed. Thirty The result of the analysis is given in Table 4. The 201 peak of K-feldspar is a measure of the mole percent albite in solid-solutions in the K-feldspar. The bulk composition of K-feldspar (i.e., the total amount of albite in solid solution and ex­ solved) was determined by dry homogenization of the feldspar at 1050° C. for 48 hours (after Orville, 1967). The difference in the analysis of homogenized sample (total Ab in K-feldspar ) and the unheated sample (Ab in solid solution) determined the amount of exsolved albite in the K-feldspar. The amount of Ab in solution in the crystal structure of K-feldspar after homogenization represents the amount that the lattice could hold at the fixation temperature. Mole percent Ab in solid solution in K-feldspar is plotted against total Ab content of K-feldspar for foliated porphyritic granite and coarse porphyritic granite in Figure 23. K-feldspars in the coarse porphyritic granite have much higher Ab content than K-feldspars of foliated porphyritic granite. ever, is generally similar. The amount of Ab in solid solution, how­ Table 4. Average Composition of K-feldspars (10 samples of each type of granite). Mole percent Ab in solid solution Rock Type Mean Range Mole percent exsolved Ab Mean Mole percent total Ab Range Mean Range Granite gneiss 3.4 0.0 - 4.8 7.9 1.2 - 22.0 11.3 7.3 - 26.8 Foliated porphyritic granite 4.2 2.1 - 6.3 5.5 2.5 - 8.8 9.7 7.3 - 13.1 Coarse porphyritic granite 3.9 2.1 - 5.8 12.3 6.8- 29.5 16.2 10.0 - 32.2 Solution Solid 10 In V V V v Mole % Ab V 2 - j i■ i i I — i___ i 10 i i L 20 30 Mole % Total Ab In K-feldspar Figure 23 Mole percent albite in solid solution plotted against mole percent total albite in K-feldspar. Foliated porphyritic granite (•) and coarse porphyritic granite (v) are indicated. 43 Six samples of the coarse porphyritic granite, collected at 10 feet apart from a single outcrop, were analyzed to check the varia­ tion within the rock type In a small area. The K-feldspar composition, determined by the (201) method, were remarkably similar (Table 5). Table 5. K-feldspar Composition of Six Samples of Coarse Porphyritic Granite from the Same Outcrop. Mole percent total Ab in K-feldspar Mole percent Ab in solid solution 16. 2 18.8 18.8 18.8 19.3 18.8 4.8 3.2 3.8 4.8 3.2 3.8 Mean = 3,9 Mean = 18.4 Standard Deviation = 0 . 6 Standard Deviation = 1.1 The dependence of distribution coefficient of Ab between co­ existing feldspars on temperature has been suggested by many workers (Barth, 1931 and 1962; Orville, 1962; Perchuk and Ryabchikov, 1968). Virgo (1969) studied the partitioning of sodium between coexisting feld­ spars from some metamorphlc rocks and found an overlap in the data from rocks of different metamorphlc facies. He concluded that the compositions of coexisting feldspars do not give any indication of their temperature of crystallization. However, in the present study, temperature deter­ mined by feldspar composition corresponds with the temperature indicated by trace element distribution. This suggests a correlation of coexist­ ing feldspar composition with temperature. 44 The curves In Figure 24 represent the isotherm of Ab distribu­ tion between coexisting plagioclase and K-feldspar in equilibrium at 1000 Kg/cm^ (after Perchuk and Ryabchikov, 1968). The plots of six samples of each type of granite indicate that the approximate tempera­ ture of crystallization of the granite gneiss ranges from 430°C to 560°C; the foliated porphyritic granite ranges from 440°C to 480°C; whereas the coarse porphyritic granite varies from 460°C to 580°C. Recrystallization of the rock m a y affect the distribution c o ­ efficient of Ab, and the temperature indicated may actually represent the recrystallization temperature rather than the fixation temperature during magmatic cooling. However, lower metamorphlc environment in most of the area suggests the temperature of the feldspars represent fixation at the end of magmatic cooling and not the metamorphlc thermal condition. The narrow range of crystallization temperature of foliated porphyritic granite probably Indicates that the rock cooled very slowly, maintaining chemical equilibrium during the process. The significantly higher Ab content of K-feldspar in coarse p o r ­ phyritic granite (than in the other two types of granite) Indicates a higher temperature of crystallization of the rock. High temperature favors the solubility of sodium in K-feldspar (Heier, 1962). Most of the albite in the K-feldspar is, however, exsolved and this is inter­ preted to have been facilitated by the concentration of volatile consti­ tuents during the late stage of crystallization. Indication of volatile concentration is provided by the formation of secondary muscovite at the expense of feldspar which is commonly observed in the rock. The altera­ tion of the plagioclase probably released calcium to form calcite, apa­ tite, and epidote which occur interstitially within the plagioclase in 45 90 VI lOO c 80 70 . 60 30 20 10 10 20 30 4 0 50 60 70 80 90 M ° le AB/ 1 b + OR * 100 Figure 24 Geothermometer based on the distribution of albite between K feldspar and plagioclase in granite gneiss (x), foliated porphyritic granite (•) and coarse porphyritic granite (v). (after Perchuk and Ryabchikov, 1968). 46 the rock. D) Structural State of K-Feldspar The structural state of K-feldspar was determined to compare the thermal histories of the three types of granite. The distribution of Al and Si in the tetrahedral sites of feldspars is controlled by the rate of cooling of the rock; duration of time that the feldspar was held near the temperature of transformation may have great effect on the A l :Si arrangement (Wright, 1967). The nature and extent of the ordering of Al and Si ions in the feldspars determine the structural state of the mineral. In all low feldspars, there is an idealized, ordered arrange­ ment; whereas a high energy environment causes random arrangement of the Al and Si ions and the structure is considered disordered (MeGaw, 1959). A method to determine structural state and composition of alkali feldspar by using cell dimensions has been described by Orville (1967); Wright and Stewart (1968). three reflections, (201), Measurement of 20 values for the (060), and (204) can be used to determine unit cell parameters a, b, and c respectively (Wright, 1968). Orville (1967) has reported that the variation in 'a' is only slightly dependent on Al:Si ordering. However, 'a1 varies greatly with composition. The alkali feldspars have been termed "anomalous" by Wright and Stewart (1968) if the 20 value for (201) estimated from (060) and (204) plot differs from the 20 value measured directly for (201) by 0.1° 20. The structural state of the ‘Anomalous" feldspar can, however, be deter­ mined by (201) method (Wright, 1968). 20 values for (060) plotted against (204) for the three types of granite (12 samples each) are shown in Figures 25, 26, and 27. It is evident from the figures that the K-feldspars in the three granites are 47 | i i i H i i i Hi p i i | i i i i | i i n | i Mi | i i i i | i i i n ii* n Mi i | i i i i | i i i r T n m i i i i | m r|H i 'i r i i > f | i * i i | i i i i | i n i | i i i n r T iiiiii L «w 49.90 - a l b It• 40 r H i g h «lbit» 29 OCOC«K«, 2 0 49.00 r - ■ 1.4 * High aonltflna .......“ . I " ......... 90.40 .90 .90 TO ..I I . . . I . . . ........ 90 .90 . 91.00 . 10 20 .30 .40 .90 91-90 CO *04 CwK„, Figure 25 Plots of 29 (060) against 20 (204) C u K M for K — feldspars In granite gneiss (x), (after Wright, 1968). »Hi>M|nnTiinpfinrm7iTT>Tim|iiii|ir»r|iiimni[ini|iiii|iMi|mi|»iiHinni **.0* JtLn* *lblt* 40 High a lh f t * i«o«ociv ,IO 41.00 .60 -TO .40 High 80 4 .50 70 .50 .10 .90 .40 .50 51.60 Figure 26 Plots of 20 (060) against 20 (204) C u K ^ for K - feldspars In foliated porphyritic granite, shown by dots (•)» (after Wright, 1968). [TTirinnji1111M1111111r11M|■11f11fiI]■11 u 0 . m < - • » 4 lb H « SO .50 JtO • IT * ze owc .k* JO 45.00 .to ■ M o n im u S P in lc r o c lin * .70 50.40 .50 .60 70 .50 JO I 51.00 50 804 Cut*., 20 .30 .40 .50 5160 Figure 27 Plots of 20 (060) against 20 (204) C u K k for K - feldspars in coarse porphyritic granite, shown by (v), ■ (after Wright, 1968). highly ordered and m a y be termed as "maximum Microcline" (after Wright 1968). Another m ethod of the determination of the structural state of K-feldspar is a measure of triclinicity (A) using the difference in spacing of the diffraction peaks of (131) and (l3l), Goldsmith and Laves (1954). as suggested by The triclinicity (^) is calculated as follows: A = 12.5 d(131)-d(131) The values observed b y this m e t h o d for the three types of gran­ ite, are shown in Table 6. Table 6. Triclinicity of K-feldspars in the Three Granite Types (4 samples of each). Range of A - v a l u e Rock Type Granite gneiss 0.89 - 0..95 Foliated porphyritic granite 0.95 - 0..96 Coarse porphyritic granite 0.90 - 0..93 The triclinicity index corresponds ve r y well state determination using (060) and <2 0 4 ) reflections. to the structural The highly ordered structural state of K-feldspars of all the three types of granites suggests a very slow rate of cooling of the rocks. Mackenzie and Smith (1961) determined the temperature of inver­ sion from monocllnlc to triclinic symmetry of K-feldspar as 525°C. Tomi- saka (1962) produced a monoclinic K-feldspar at a temperature as low as 400°C under a water pressure of 350 bars. Steiger and Hart (1967) have 51 concluded that the transition temperature is around 400°C. Wright (1967) in his study of the K-feldspar in pegmatites in the contact aureole of the Eldora Stock, Colorado agrees with the findings of Steiger and Hart and concludes that the upper stability limit of "maximum microcllne" is 375+ 50°C. The structural state of K-feldspar is related to a number of factors other than temperature. MacKenzie and Smith (1961) have sug­ gested that the pressure and volatile content may have sufficient effect on the temperature of inversion. Many other parameters such as total hydrostatic pressure and composition of the original material may in­ fluence the orthoclase-microcline transition (Steiger and Hart, 1967). Little is known about the effect of total pressure or partial pressure of water on the phase transformation in the K-feldspar. Experiments performed by Tomisaka (1962) indic&te that the partial water pressure or total pressure has very little effect on the inversion temperature. MacKenzie and Snith (1961) and Wright (1967) have suggested a great de­ pendence of the inversion temperature upon the Na-content of K-feldspar. The orthoclase-microcline conversion temperature increases with the amount of sodium dissolved in K-feldspar (Wright, 1967). The quantita­ tive data on this are, however, not available. The highly ordered K-feldspar in the coarse porphyritic granite may represent a higher temperature of transformation due to the high Ab content of K-feldspar in the rock type (average = 16.2 mole % A b ) . The amount of albite in the K-feldspars of foliated porphyritic granite is generally low (average = 9 . 7 mole %). It may be inferred that the phase transformation of K-feldspar in the foliated porphyritic granite occurred at about 400°C (Wright, 1967). 52 E) Plagioclase Twinning Type and nature of twinning in plagioclase m a y be a good indi­ cator of the history of formation of the rock. Plagioclase crystallized from a melt shows more varied pattern of twinning than plagioclase of metamorphlc origin (Tobi, 1962). A qualitative and quantitative analysis of the plagioclase twinning in the three types of granite was carried out to study and compare the nature and extent of deformation of the rocks, also to differentiate the granites based on statistical analysis of twinning. &nith (1962, p. 255) considers the twinning to have formed by a specific type of disturbance of crystal structure either during or after the growth and that it may have many different causes. Gorai (1951) in his study of plagioclase twins has concluded that there is a charac­ teristic difference in the type of plagioclase twin in magmatic and metamorphic rock. groups. He has classified the plagioclase twin types into two A-twins, found in Igneous as well as metamorphlc rocks include the simple and polysynthetic twins and their modification. Secondary glide twins formed due to deformation by forces external to rock after the growth of the crystal are also grouped in A-twins. The C-twins in­ cluded Carlsbad, albite-Carlsbad and penetration twins which are developed in the crystals during growth. Appreciable amounts of C-twins are characteristic of undeformed igneous rocks. This amount is, however, dependent on the An content of plagioclase; calcic plagioclase has more C-twins than sodic plagioclase. Vance (1961) has concluded that the polysynthetic twinning in plagioclase m a y represent both primary growth twin and secondary glide twin. Morphology of the twin can be used as the criteria to differentiate the two. Bending and termination of lamellae as long tapering points are indicative of secondary twinning. Baler (19 30), K o hler and Raaz (1947), (personal However, several workers such as Bnmona and M a n n (195 3), and Vogel communication) consider all polysynthetic twinning in p l a g i o ­ clase as secondary. Deformation twins are common in granite gneiss and foliated porphyritic granite (Figure 28 shows glide lamellae in granite gneiss). Fracturing and displacement of glide lamellae b y a later phase of defor­ mation is observed in some samples of foliated porphyritic granite (Figure 29). Twinning in plagioclase m a y be lost by recrystallization and intense or continued deformation (Barth, tion, 1969). W i t h increased deforma­ the twin lamellae may coalesce and assume an untwi n n e d appearance (Vance, 1961, p. 1110). Kohler (1948) and Turner (1951) have observed that plagioclases in metamorphlc rocks are untwinned or only slightly twinned. Frequencies of A and C-twin types and untwinned plagioclase were determined in 20 sections of each rock type using Gora i ' s (1951) method. About 100 - 2 0 0 grains were examined in each section; grains m a y have been counted more than once. some large It was observed that the small crystals of plagioclase in the groundmass are relatively untwinned compared to the big crystals. Apparently glide lamellae are developed in big crystals due to stress; whereas the finer crystals take up the strain b y rotation. Gorai (1951) has demonstrated that the frequency of secondary twinning in pTagioclase varies directly w i t h the grain size and composition. fairly uniform. The plagioclase composition of the three rock types is The effect of the grain size factor was m i n i m i z e d by Figure 28. Glide twinning in plagioclase. The lamellae thin in unison. Crossed polars. Figure 29. Displacement o£ twin lamellae in plagioclase by and coarse porphyritic granite (v), Figure 30 57 less than 1.0 In most of the foliated porphyritic granite which suggests that the rock type was subjected to more intense deformation. The field relation of the coarse porphyritic granite and fol­ iated porphyritic granite is not conclusive. Previous workers in the area have mapped both of the granites as the same. Statistical analysis of the plagioclase twinning of the two rock types was done to test whether samples of the two rock types are similar. Statistical Treatment A Chi-square test of the twinned and untwinned plagioclase fre­ quencies (Table 8) in coarse porphyritic granite and foliated porphyritic granite was applied to determine whether they are from the same popula­ tion (see Griffiths, 1967, p. Table 8. 353). Frequencies of Twinned and Untwinned Plagioclases in Coarse Porphyritic Granite and Foliated Porphyritic Granite Rock type Coarse porphyritic granite Twinned Untwinned 1111 683 743 808 Foliated porphyritic granite = 66.2 Degree of freedom = 1 P < 0.001 The Chi-square value is significant beyond the 0.001 confidence level. Hence, the chance that such a sample will be drawn at random from a similar population is less than 1 in 1000. Chi-square value using the A, C, and U type plagioclases in the 58 two rock types also suggests a very significant difference in the two. Table 9 represents the test. Table 9. Comparison of the A, C, and U Plagioclase Twin Frequencies in Samples of Coarse Porphyritic Granite and Foliated Porphyritic Gr a n i t e . Total A C U Coarse porphyritic granite 892 94 614 1600 Foliated porphyritic granite 679 47 874 1600 1571 141 1488 3200 Total Expected value 70.5 744.0 0 - E (coarse porphyritic) +106.5 +23.5 -130.0 0 - E (Foliated porphyritic) -106.5 -23.5 +130.0 14.4 7.8 22. 7 14.4 7.8 22. 7 28.8 25.6 (0-E)^ --- 7 (coarse porphyritic) B 2 (Foliated porphyritic) £ Total * ■0 II 785.5 89.8 •X.2 = 89.8 Degree of freedom = 2 P < 0.001 Student's "t" was also calculated in order to compare the means of twinned plagioclase frequencies in the two types of granite. The re­ sult of the test is shown in Table 10. The null hypothesis (HQ ) to be tested is that samples of coarse porphyritic granite and foliated porphyritic granite are drawn from the same population # mx — 59 Table 10. Comparison of the Means of Plagioclase Twin Counts in Coarse Porphyritic Granite and Foliated Porphyritic Granite using t-test. Mean Percent Twinned Plagioclase Rock Type Variance Foliated porphyritic granite 45.4 s 2 Coarse porphyritic 61.6 s 2 = 142.7 2 n, “ n 2 - = 196.5 16 X t = j -X 1 2 ----- J a1Z + s22/ 0-1 = 3.4 Degree of freedom = 2 (n-1) = 30 P < 0.002 The "t" value is highly significant. is rejected. Thus, the null hypothesis The chance that the two means are from the samples of the same type of rock is less than 2 in 1000. F) Distribution of Trace Elements in K-Feldspar The distribution of certain trace elements in the rock can be used to interpret the stage of fractional crystallization and the petrogenesis of the rock. Ion size and charge were considered as the main factor which controls the ionic substitution in a crystal lattice (Goldschmidt, 1937). However, exceptions to this rule suggest the influence of some other factor also. Fyfe (1951) and Rlngwood (1955) implied that the ability 60 of an ion to substitute in a crystal lattice depends on its electro­ negativity. Heier (1962) considers ionic character of the element, crystal structure, and physicochemical condition as main factors that govern the incorporation of minor elements in minerals. Table 11 lists the ionic properties of some of the elements which can occupy alkali position in feldspar lattice. Table 11. Ionic Properties of the Elements that can substitute for Alkalies in the Feldspar Lattice. K Na Ca Rb Ba Sr Electrostatic charge 1 1 2 1 2 2 Ionic radius (Ahrens, 1953) 1. 33 0.97 0.99 1.47 1. 34 1.18 Ionization potential (Ahrens, 1953) 4. 34 5.14 Electronegativity 0.8 0.9 11.9 4.2 10.0 11.03 1.0 0.8 0.9 1.0 A bonding energy function combining radius, charge, and electro­ negativity was devised by Nockholds (1966). bonds (a hypothetical Bonding energy x “° 'molecule') is = 1 1 -8 is the electrom x-o* negativity difference between the metal, X, and oxygen, and R is the bond length. The bonding energyx _Q is an approximation of bonding energies of common metals bonded to oxygen for bond lengths found in six-fold coordination. Bonding energy values should be used as relative values only, as absolute bonding energies will var y w i t h the coordination and p r obably w i t h different environments having the same coordination. The relative total bonding energies (RTBE) are the values that should be used to Interpret cation distribution. Nockolds offered two rules to explain the substitution: a) When two cations of the same v a l e n c y are capable of substitution in a crystal lattice, the one having the greater relative total bonding energy will be incor­ porated preferentially. b) When two cations of different valency involving coupled substitution are capable of substitution in a crystal lattice, that substitution will take place preferentially whose sum of relative total bonding energies is the greater. (Nockolds, 1966, p. 272) The possible substitution for K in K-feldspar is listed in Table 12. Table 12. Substitution Possibilities for K in K-feldspar (after Nockolds, 1966) RTBE Bond Length K+ 90 2.77 K+ Rb + 85 2.90 Tl + 74 Na + 100 Cation Coupled RTBE Cation Bond Length K Si 470 2.77 B a ^ Ba Al 480 2. 76 2.62 o ++ Sr Sr Al 490 2.56 2.40 „ ++ Ca Ca Al 500 2.40 : | -j SR+ + and Ba have greater RTBE than K + , hence they should enter the crystal lattice m o r e easily than K. Sr should be able to enter earlier than Ba but the bon d length of K -0 (2.77) is similar to Ba-0 (2.76); whereas the bond length Sr-0 is m u c h less. Hence, Ba is incorporated more easily in K-feldspar. With increasing fractionation of the rock, the sequence of in­ corporation of elements in "K-positlon*' in K-feldspar is: Na, Rb, Tl» and Gs in order for univalent atom; for coupled substitution the order is Ba, Sr, Ca, and Pb. Ba forms a strong ionic bond with oxygen which causes it to be captured by K-mlnerals and is relatively enriched in early formed K-feldspar. Rb is admitted into K-feldspar at a later stage of crystal­ lization; as such, the K:Rb ratio decreases with differentiation (Taylor and Heier, 1960). Taylor and Heier (1960) found the Ba/Rb ratios to be the most sensitive indicator of fractionation process in feldspars. Hany workers have used the K/Rb ratio of the rock to Interpret order of Intrusion in a sequence of genetically related rocks. (Tauson and Stravrov, 1957; Butler et al., 1962; Taylor, 1965; Reynolds et a l ., 1967). The K/Rb ratio in the early stages of fractionation does not show much variation; only in extreme cases is any marked variation ob­ served (Taylor and Heier, 1962). to a false interpretation. In some cases, the K/Rb ratio may lead Zlobin and Lebedev (1960) determined the K/Rb ratio of the two genetically related plutons, Lovozero alkalic rock and Khibina rocks, and found it to be different by as much as 1.5 times. Ba and Rb contents of K-feldspar in the three types of granitic rocks were determined by X-ray fluorescence. type were analyzed. Six samples of each rock The results are presented in Table 13. The amount of K in K-feldspar was calculated after making corrections for the Ab content of the K-feldspar. The average K/Rb ratio in the three types of rock is similar; the values are within the published range of values for other granitic Table 13. Arithmetic Means and Ranges of Concentrations of Kf Rb, and Ba in K-feldspars in the Three Types of Granite (6 samples of each) Rock Type Percent K Rb ppm K/Rb ratio Ba ppm Ba/Rb ratio Granite gneiss Mean - 11.96 Range - (10.45-13.38) 408 (350-485) 300 1294 (833 - 1917) 3.1 (2.1 - 3.9) Foliated porphyritic granite Mean - 12.78 Range - (12.3-13.14) 420 (365-470) 306 1462 (1111 - 1872) 3.6 (2.4 - 5.1) Coarse porphyritic granite Mean - 11.67 Range - (9.7-12.2) 432 (350-565) 277 1178 (734 - 1532) 2.8 (1.9 - 4.4) 64 rocks(Heier and Taylor, 1959; Aldrich et a l . , 1965; Condie et al., 1970). Plots of ppm Rb against mole percent K In K-fel d s p a r In Plgure 31 indi-. cate that the foliated porphyrltic granite and coarse porphyritic granite samples fall In separate restricted zones. The plots for granite gneiss are scattered u n s y s tematically whi c h m a y reflect vary i n g conditions of the rock formation, and this m a y be supported by the wide range of Ba content of K-fel d s p a r in the rock type (see Table 13). The slightly higher average Rb content in K-feldspar of coarse porphyritic granite and a lower average Ba content indicates that the coarse porphyritic granite is a more differentiated rock than the foli­ ated porphyritic granite and granite gneiss. The Ba:Rb ratio of the coarse porphyritic granite is considerably lower than the ratio foliated porphyritic granite. However, in the the range of Rb content of the coarse porphyritic granite is very great, probably representing a great range of temperature of formation. This supports the suggestion m e n ­ tioned earlier that the coarse porphyritic granite magma cooled very slowly generally maintaining the chemical equilibrium. few locations, particularly in the marginal not have been maintained; zone, However, the equilibrium m a y this m a y indicate higher temperature. field relations are, however, at a The inconclusive because of the lack of suf­ ficient outcrops. Plots of ppm Rb against pp m Ba in K-feldspar (Figure 32) show no systematic variation. PIM Rb in K - feldspar 600r x 300- 200 100 90 100 110 120 130 Mole Percent K in K - feldspar 140 Figure 31 Percent K vs ppm Rb In granite gneiss (*), foliated porphyritic granite (•) and coarae porphyritic granite (v). 5004001- v * ft V • • • 300- In K - feldspar 600 ppm Rb 200100a a ,< ■ * *-------- — I----------- 1___________ i___________ s___________ ■ 500 1 ■ »___________ _ 1000 _ . --------- 1 _ 1500 i » i i j 2000 ppm Ba in K - feldspar Figure 32 ppm Rb plotted against ppm Ba in K - feldspar. Granite gneiss is shown by cross (x), foliated porphyritic granite by dots (•) and coarse porphyritic granite by (v). SUMMARY AMD CONCLUSION The classification of the granitic rocks In the area based on tex­ tural variation and field relations Is corroborated by the laboratory investigations. It may be Inferred that texturally and genetically at least three types of granite occur In the area: granite gneiss, folia­ ted porphyritic granite, and coarse porphyritic granite. Based on field relations, the granite gneiss is considered as the oldest granite in the area. The age relation of the rock type is evi­ dent by the presence of xenoliths of the gneiss in the other two types of granite. The gneiss exhibits great textural and mineralogical varia­ tion and may include more than one genetic type. The area mapped as granite gneiss (see Figure 3) may include some granitized metasediments, which could not be differentiated because of inconclusive field relations due to small and isolated outcrops. The study of the trace elements distribution in the K-feldspar indi­ cates a great variation in Ba content and K:Rb ratio in the rock (see Table 13 and Figure 31) which may be interpreted as representing vary­ ing conditions of rock formation. The occurrence of growth twinning in plagioclase and the intrusive relation of the rock into older schist observed at a few locations indicate that at least part of the granite gneiss crystallized from a melt. Such intrusions at some place have re­ sulted in the development of injection gneiss. Subsequent deformation of the granite gneiss is indicated by the bending of glide lamellae in plagioclase. Evidence of at least two phases 67 68 of deformation of the rock type is revealed by the petrofabric analysis. Such deformations may have modified the petrology of the rock. texture observed in a few rocks indicate recrystallization. Mosaic However, the presence of chlorite and low An-plaglolcase in the rock and the general absence of garnet and other high grade metamorphic minerals sug­ gest low metamorphic environment. The highly ordered K-feldspar indi­ cates very slow cooling of the rock. The rest of the area is occupied by the porphyritic granite which has not been differentiated by the previous workers in the area. The strong foliation in porphyritic granite observed near Republic is sig­ nificantly lacking In the outcrops north of Republic. Instead, the rock acquires a crude llneation marked by large feldspar phenocrysts. The distinct difference In the texture was used as a criterion to map the rock separately as foliated porphyritic granite (containing small pheno­ crysts) and a non-foliated porphyritic granite (containing large pheno­ crysts) . place. The contact between the two rock types was not observed at any However, the transition between the two is generally sharp or narrowly gradational. Statistical analysis of plagioclase twinning cor­ roborates the field observations to resolve the porphyritic granite into two genetically different types of granite (see Tables 9 and 10). This is further supported by the major- and trace-element distribution in K-feldspars of the two granite typeB (see Figures 23 and 31). The foliated porphyritic granite is both texturally and mineraloglcally homogeneous and it probably represents a uniform condition of rock formation. Occurrences of xenoliths in the rock outcrops Indicate a magmatic origin of the rock which is also supported by the presence of Carlsbad twinning in the plagioclase. The structural state of the 69 K-feldspar Indicates that the foliated porph y r i t i c granite mag m a cooled very slowly. Later metamorph i s m of the rock is exhibited b y the recrys­ tallization texture. However, lack of an y high grade metamorphic mineral indicates a low temperature metamo r p h i c condition. The age of emplacement of the rock type w h i c h has b e e n a matter of discussion for m a n y years is not ve r y clear b y the field relations. The foliation of the rock generally has a concordant relation wit h the strike of the Animlkle rocks in the contact zone. the Republic mine, served. However, at one location near a discordant relation w i t h i n a short distance was o b ­ The foliation of the granite abuts against the foliation of the Animikie metasediments. not exposed. The contact of the two rock types is, however, The field relation at this location indicates that the foliation in the rock developed before the Animikie folding and was later folded with the Animikie rocks. The fracture and displacement of glide lamellae in plagioclase suggests at least two phases of deformation of the rock. The strong N25W-S25E foliation probably represents the first phase of deformation w h i c h wa s later superimposed by NW-SB foliai tion, parallel to the axis of Republic Syncllne and was probably acquired during the Animikie folding. The structural relation of the rock and the evidence of at least two phases of deformation suggest a pre-Animikie age of the rock. The absence of the granitic material in the Animikie rocks Inside the trough (a few reported occurrences are from areas outside the trough) in spite of the nearness of outcrop is not very likely unless the granite is older. Occurrence of boulders of porp h y r i t ­ ic granite in basal conglomerate of Animlkle age reported b y some workers, also supports this inference. Occurrence of Intrusive granitic rock in Animikie metasediments, as reported by Lamey (1934) and Swanson (1929) indicates the presence of a post-Animikie granite in the areas. The metamorphism of the Animikie sediment has been attributed to the contact effect of this granite. Lack of the NW-SE foliation in the rock, parallel to the axis of Repub­ lic Syncline, suggest a post-Animikie age of the coarse porphyritic granite intrusion and this is supported by the absence of evidence of shearing and deformation of the granite. The rock is probably equiva­ lent of Klllarney granite. The granite is exposed in the axial position between the Republic Trough and Marquette Syncline and was likely Intruded as a sheet. The linear arrangement of feldspar phenocrysts probably represents a "flow structure" as indicated by the change in the trend of lineation when the contact is approached. The occurrence of xenoliths and the presence of flow structure in the rock indicate an igneous origin of the coarse porphyritic granite. Abundance of growth twinning in plagioclase also supports the magmatlc origin. In comparison to the foliated porphyritic granite, the coarse por­ phyritic granite contains more myrmekite; the K-feldspar in the rock is also high in Ab content. This may indicate a higher crystallization temperature of the rock. The granite cooled very slowly as indicated by the structural state of the K-feldspars. During the later stage of crystallization the concentration of the volatile constituents caused the exsolution of albite and the alteration of feldspar to form second­ ary muscovite. L I S T O F R E F E R E N C E S LIST OF REFERENCES Aldrich, L. T . , Davis, G. L . , and James, H. L., 1965, Ages of minerals from metamorphic and Igneous rocks near Iron Mountain, Michigan: Jour. Petrology, v. 6, pp. 445-472. Baler, E., 1930, Lamellenbau and Entmlschungsstruktur der Feldspate: Z. Krist., v. 73, pp. 465-560. Balk, Robert, 1937, Structural Behavior of Igneous Rocks: Ge o l . Soc. America Mem. 5, 177 pp. Barth, T. F. W . , 1951, The feldspar geologic thermometers: neues Jb. Miner. Abh., v. 82. ______ , 1962, The feldspar geologic thermometers: Norsk* Geol. Tidsskr. , v. 42, pp. 330-339. _______ , 1969, Feldspars: John Wiley and Sons, New York, 261 pp. Butler, J. R. , Bowden, P.f and Smith, A. Z. , 1962, K/Rb ratios in the evolution of the younger granites of the northern Nigeria: Geochim et Cosmochim. Acta, v. 26, pp. 89-100. Chayes, F., 1956, Fetrographlc modal analyses: Wiley, New York, 113 pp. Condie, K. C., Macke, John E., and Reimer, Thomas O . , 1970, Petrology and Geochemistry of early Precambrian Graywackes from the Fig Tree Group, South Africa: Geol. Soc. America Bull., v. 81, pp. 2759-2775. Deer, W. A., Howie, R. A. and Zussman, J . , 1963, Rock-forming minerals: v. 4, Longmans, London. Dickey, R. M . , 1936, The granitic sequence in the Southern Complex of Upper Michigan: Jour. Geology, v. 44, pp. 317-340. _______ » 1938, The Ford River granite of the Southern Complex of Upper Michigan: Jour. Geology, v. 46, pp. 321-335. Dietrich, R. V., 1962, K-feldspar structural states as petrogenetic Indicators: Norsk Geol. Tidssk., Bind 42, pp. 394-414. Emmons, R. C . , 1943, The universal stage: Geol. Soc. America, Mem. 8, 204 pp. _______ j and Gates, R. M . , 1943, Plagioclase twinning; Geol. Soc. America Bull., v. 54, pp. 287-304. 72 , and Mann, V., 195 3, A twln-zone relationship In plagioclase feldspar: Geol. Soc. America Mem. 52, pp. 41-54. Foster, J. W. and Whitney, J. D . , 1851, Report on the Geology and topo­ graphy of the Lake Superior Land District: 32nd Cong.,Spec. Sees., Senate Doc, v. Ill, No. 4. Fraser, D. C . , 1963, Sun chart compass correction for reconnaissance mapping and geophysical prospecting in areas of magnetic distur­ bance: Econ. Geology, V. 58, pp. 131-137. Fyfe, W. S., 1951, Isomorphism and bond type: Amer. Mineralogist, v. pp. 538-542. 36, Gair, J. E. and Thaden, R. E . , 1968, Geology of the Marquette and Sands Quadrangles, Marquette County, Michigan: U. S. Geol. Survey Prof. Paper 397, 77 pp. Goldschmidt, V. M . , 19 37, The principles of distribution of chemical elements in minerals and rocks: J. Chem. Soc., 1937, pp. 655-673. Goldsmith, J. R. and Laves, F . , 1954, The mlcrocllne-sanidine stability relations: Geochim. et Cosmochim. Acta, v. 5, pp. 1-19. Gorai, M . , 1951, Petrological studies of plagioclase twins: Am. M i n e r a l ­ ogist, v. 36, pp. 884-901. Griffiths, J. C., 1967, Scientific method in analysis of sediments: McGraw Hill, New York, 508 pp. Heier, K. S., 1962, Trace elements in feldspars— a review: Norsk Geol. Tidssk., Bind 42, pp. 415-454. ________, and Taylor, S. R . , 1959a, The distribution of Li, Na, K, Rb, Cs, Rb, and T1 in Southern Norwegian pre-Cambrian alkali feldspars: Geochim. et Cosmochim. Acta, v. 15, pp. 284-304. ________, 1959b, Distribution of Ca, Sr and Ba in Southern Norwegian preCambrian alkali feldspars: Geochim. et Cosmochim. Acta, v. 17, pp. 286-304. Hubbard, F. H . , 1966, Myrmekite in charnockite from Southwest Nigeria: Am. Mineralogist, v. 51, pp. 762-773. ________ , 1967, Exsolution myrmekite: Geologiska Foreningnesi Stockholm Forhandlingar, v. 89, pp. 410-422. James, H. L., 1955, Zones of Regional Metamorphism in the Precambrian of Northern Michigan Bull. Geol. Soc. Amer., v. 66, pp. 1455-1488. . 1958, Stratigraphy of Fre-Keweenawan rocks in parts of Northern Michigan: U. S. Geol. Survey Prof. Paper 314-C, 44 pp. James, R. S. and Hamilton, D. L . , 1969, Phase relations in the system N a A l S ^ O g - K A l S i 3 <)g - CaAl 2 Si£ 0 g - SiO£ at 1 Kilobar w a t e r vapour pressure: Contr. Mineral, and Petro., v. 21, pp. 111-141. Kohler, A., 1948, Die Abhangigkeit der Plagioklasoptik vom vorange g a n g e nen W a r m e v e r h a l t e n : Min. Pet. Mitt., v. 53, pp. 24-29. ________ , and Raaz, F. , 1947, Gedanken iiber die Bildung von Feldspatzwillingen in Gesteinen: Geol. Bundesanstalt V e r h . , pp. 163-171. Lamey, C. A., Northern 19 31, Granite intrusions in the Huronian formations of Michigan. Jour. Geology, v.39, pp. 288-295. ________ , 1933, The intrusive relations of the Republic granite: Jour. Geology, v. 41, pp. 487-500. ________ , 1934, Some metamorp h i c effects of the Republic Granite: Geology, v. 42, pp. 248-263. Jour. ________ , 19 37, Republic granite or basement complex: Jour. Geology, v. 45, pp. 487-510. MacKenzie, W. S., and Sknith, J. V. , 1961, Experimental and geological evidence for the stability of alkali feldspars: Inst. "Lucas Mallada", Curs Conf. VIII, pp. 53-69. MeGaw, H. D . , 1959, Girder and disorder in the feldspars: Mineral. Mag., v. 32, pp. 226-241. Morse, S. A., 1968, Revised dispersion method for low plagioclase: Amer. Mineralogist, v. 53, pp. 105-116. Nockolds, S. R . , 1966, the behavior of some elements during fractional crystallization of magma: Geochim. et Cosmochim. Acata, v. 30, pp. 267-278. Orville, P. M . , 1958, Feldspar investigations: Carnegie Inst. Wash. Year Book 57, pp. 206-209. ________ , 1962, Comments on the two-feldspar geothermometer: Tld s s k r . , V. 42, pp. 340-348. Norsk. Geol. ________, 1963, Alkali ion exchange between vapor and feldspar phases: Am. Jour. S c i ., v. 261, pp. 201-237. ________, 1967, Unit-cell parameters of the microcline-low albite and the sanadlne-high albite solid solution series: Am. Mineralogist, v. 52, pp. 55-86. Perchuk, L. L. and Ryabchikov, I. D . , 1968, Mineral Equilibria in the system nepheline-alkali feldspar-plagloclase and their petrological significance: Jour. Petrology, v. 9, pt. 1, pp. 123-167. K a t- 74 Reynolds, R. C., Whitney, P. R. and Isachsen, Y. W., 1967, K/Rb ratios in Adirondack anorthosites and associated charnockltic rocks, and their petrogenetlc implications: (Abs.) Geol. Soc. America North­ eastern section second ann. meeting, Boston. Ringwood, A. E., 1955, The principles governing trace-element distribu­ tion during magmatic differentiation, Part 1: Geochim. et Cosmochim. Acta, v. 7, pp. 189-202. Sen, N . , Nockolds, S. R. and Allen, R . , 1958, Trace elements in minerals from rocks of the S. California Batholith: Geochim. et Cosmochim. Acta., v. 16, pp. 58-78. Sen, S. K. 1959, Potassium content of natural plagioclases and the ori­ gin of antiperthites: Jour. Geol., v. 67, pp. 479-495. Smith, J. V., 1962, Genetic aspects of twinning in feldspars: Norsk. Geol. Tidsskr., v. 42, pp. 244-263. Smyth, H. L . , 189 3, A contact between the lower Huronian and the under­ lying granite in the Republic Trough, near Republic, Michigan: Jour. Geology, v. 1, pp. 16-29. Snelgrove, A. K . , Seaman, W. A., and Ayres, V. L . , 1944,Strategic mineral Investigations in Marquette and Baraga Counties: Michigan Geological Survey Progress Report 10, 69 pp. Steiger, R. H. and Hart, H. R . , 1967, The mlcrocline-orthoclase transi­ tion within a contact aureole, Am. Mineralogist, v. 52, pp. 87-116. Suwa, K . , 1956, Plagioclase Twinning in Ryoke metamorphic rocks from the Mitsue-mura area, Kii peninsula, Central Japan: Jour. Earth Scl., Nagoya Univ., v. 4. Swanson, C. 0., 1929, Report on the portion of the Marquette covered by the Michigan Geological Survey. Range Tausen, L. V. and Stavrov, 0. D., 1957, The geochemistry of Rubidium in granitoids: Geokhlmiya, No. 8, pp. 819-824. Taylor, S. R. , 1965, The application of trace element data to problems in petrology: Riysics and chemistry of the earth, v. 6, pp. 133-214, Pergamon Press. _______ and Heier, K. S., 1960, The petrological significance of trace element variations in alkali feldspars: 21st session of Int. Geol. Cong, part XIV, pp. 47-61. Taylor, W. E. G . , 1967, The structural history of the 'Archaean' rocks of upper Michigan: Abs. 13th Annual Session, Inst, on Lake Superior Geology, p. 38. Tobi, A. C., 1962, Characteristic patterns of plagioclase twinning: Norsk. Geol. Tidsskr., v. 42, pp. 264-271. 75 Tomisaka, T., 1962, On order-dlsorder transformation and stability range of microcllne under high vapour pressure: Mineral. J., Tokyo, v. 3, pp. 261-281. Tsuboi, S., 1923, A dispersion method of determining plagioclases in cleavage flakes: Mineral. Mag., v. 20, pp. 108-122. ________, 1934, A straight line diagram for determining plagioclase by the dispersion method: Jap. Jour. Geol. Geog., v. 11, pp. 325-326. Turner, F. J., 1951, Observations on twinning of plagioclase in meta m o r ­ phic rocks: Am. Mineralogist, v. 36, pp. 581-589. Tuttle, O. F. and Bowen, N. L . , 1958, Origin of granite in the light of experimental studies in the system NaAl Si^Og-KAl Sl^Og-Si02**H20: Geol. Soc. America, Mem. 74, 152 pp. Tyler, S. A., Marsden, R. W . , Thiels, G. A.,and Grout, F. T., 1940, Studies of the Lake Superior Precambrian by Accessory Mineral Methods: Bull. Geol. Soc. Amer., v. 51, pp. 1429-1537. Vance, J. A., 1961, Polysynthetic twinning in plagioclase: Am. Mineral­ ogist, v. 46, pp. 1097-1119. Van Hise, C. R . , Bayley, W. J . , and Smyth, H. L., 1897, The Marquette Iron-Bearing District of Michigan: U.S.G.S. Monograph 28. ________, and Leith, C. K . , 1911, The Geology of the Lake Superior Region: U.S.G.S. Monograph 52. Virgo, D. 1969, Partitioning of sodium between coexisting K-feldspar and plagioclase from some metamorphic rocks: Jour. Geology, v. 77, pp. 173-182. Vogel, T. A., Smith, B. L. and Goodspeed, R. M . , 1968, The origin of antiperthites from some charnockitlc rocks in the New Jersey Precambrian: Amer. Mineralogist, v. 53, pp. 1696-1708. Wyart, J. and Sabatier, G . , 1956, Transformations mutuelles des feldspaths alcallns. Reproduction du microcllne et de 1 'albite: Bull. Soc. Fr. Mineral. Crystallogr., v. 79, pp. 574-581. Wright, T. L . , 1967, The mlcrocllne-orthoclase transformation in the contact aureole of the Eldora stock, Colorado: Am. Mineralogist, v. 52, pp. 117-136. _______ and Stewart, D. B . , 1968, X-ray and Optical study of alkali feld­ spar: I. Determination of composition and structural state from refined unit-cell parameters and 2V; Amer. Mineralogist, v. 53, pp. 38-87. Wright, T. L . , 1968, X-ray and optical study of alkali feldspar, II. A n X-ray m e t h o d for determining the composition and structural state from measurement of 20 values for three reflections: Amer. Mineralogist, v. 53, pp. 88-104. Zlnn, J . , 1930, Report on the portion of the Marqu e t t e Range betw e e n Humboldt and Lake Mlch i g a m m e covered b y the M i c h i g a n Geological Survey. Mimeographed report, 18 pp. Zlobin, B. I. and Lebedev, V. I., 1960, Geochemical relationship of Li, Na, K, Rb, and T1 in alkali m a g m a and its petrogenetlc significance Geokhimiya, No. 2, pp. 101-124. A P P E N D I C E S APPENDIX A LOCATIONS OF XENOLITHS FOUND IN FOLIATED PORPHYRITIC GRANITE AND COARSE PORPHYRITIC GRANITE Xenoliths of granite gneiss in the foliated porphyritic granite are observed at the following locations: (a) Northeast % of Section 31, T46N, R29W (b) Southwest 4; of Section 19, T46N, RZ9W (c) Northeast % of Section 13, T46n, R30W (d) Southwest % of Section 36, T47N, R30W The contact of the two rock types is not very sharp, but there is no visible Indication of any reaction between the two rocks. The grada­ tional contact near Republic suggests partial remobilization of granite gneiss. The granite gneiss occurs as xenoliths in the coarse porphyritic granite at the following locations. The margin of the xenoliths is fairly sharp. (a) Southeast 4; of Section 30, T47N, R29W (b) Southeast % of Section 23, T47N, R30w (c) Central part of Section 24, T47N, R30W (d) Northeast % of Section 29, T47N, R29W APPENDIX B M E T H O D OF SEPARATION OF K - F E L D S P A R FROM TH E ROCK A portion of the rock sample w as crushed to obtain (-) 100 to (+) 160 m e s h size particles. acquired during grinding. quartz, The sample wa s was h e d to remove all dust K-feldspar wa s separated from plagioclase, and other minerals using a "heavy liquid." The liquid was p r e ­ pared by m i x i n g tetrachloroethelane w i t h b r o m o f o r m in proporations such that the density of the liquid w a s about 2.60. by putting pieces of pure quartz, microcllne, The density was checked and albite in the liquid and ascertaining that only the m icrocllne floated; w h e r e a s the quartz and albite sank to the bottom. microscope, The separation w a s checked under the and the process wa s repeated until at least about 9 9 % pure separation of K-feldspar was obtained. APPENDIX C X-RAY METHOD FOR DETERMINATION OF STRUCTURAL STATE OF K-FELDSPAR Smear mounts were made of finely ground K-feldspar mixed with CaF 2 as an internal standard (26Cu (220) = 47.01). The mounts were run on an X-ray diffractometer at a goniometer speed of 0.4° per minute. The chart speed was set so that 1° 20 = 1 inch. Peak positions were measured at the estimated center line of approximately top 1/10 of each peak (Orville, 1967). Duplicate diffraction was run from higher to lower 26 (opposite of the first run) and an average of the two 26 values was recorded. If the difference in the two values exceeded 0.04°, a third run was taken. (201), Measurements of 26 values for the three reflections, (060), and (204) were recorded. •• « GEOLOGIC I * >GIC MAP OF REPUBLIC ARE AREA. MARQUETTE COUN 88° 00' T , X X X ^ f . x v v v t v V V V | v v V f V V v V v v v v r V v V • X* • v **. v X * V v v v v 'V.. * X* * m 0 J* tf 1 ^ >» - •. * v * x ' x 0 0 0 X n j* 0 0 Jtf 0 ** 0 » . » V V V V^f V, _ V V V V V \ V 0 * V V V v ; V m V V V *»•* 0 « V V V 0 0 * ff m 0 0 V V v v V . \ V V X * 0 V V X V v V v V X X. +j r *: ’ " i.** TjT* j* •* s 0 v V -X. V v v * V v V v * X* V v V V V v v V X 0rf 0 J* x* X ■• X 0 V v V V ■* - ^ 5 . . V V V V^ ^ \x v V V v X X v v V *' X V v I v V X • V V v V X X v V 0 X jX X X X X , X X xX xK ii xX X ”1 X X X X X ' X X X x M X ' X > x X X X X X X X X X /x x x x x x x x x x x x .x. • .V x . X X X X X X X X X X x. . • 'v v ‘*. x X X X X X X X X . ** ' V V v * •. X >' * **• \ X x X x X 7* ^ V V V V V *. X x x 'X x x x: v v v v v v\ x ^ *\X X X V v V V V V v v v ; x X X v v v v v *\x v V v •. x x x>fv ^ V V V V V V \ v v v*. xVf~v v v v vv V V V V V V V ; v v v v v v v v v v v i v V V v Mj v v v v v v v v / V V Vs^ V V V V V V V ^ / . ' x V v v V V V V V V V . X V V V V F\f V V V V V V *. ^ V v V V V V V V V V V *.. V V V V v V V\ v • v ^ v V v V v V v / v V V v V v v v v v V VV V. V #V v V V V V V v V V>^^V V -T v V V V # V V V * V V V V V V 4 ^ v M/k^ v v v v v v v v v v v v v v v v v v v v V ^/T V V V V V A v v v v v ^ v v v v v v v v v v y y y 87° 55' N X X X X X X * x 'X X X X X X X X A X X X X X X X X X V* * x X X v*. ■ x v V X X X X X X X X X \X* X X X * V**X X X H-V vX X * V ; x X X v . x x x ✓ V «.* x X X ^ ;x x x * x : X x X X X V f^ v ‘• • • x V v V " * ’V f ’V t V V V V V V V m . V V V V * .X x X X X X x X X X X X X X X •. * X x X m X X X X X X i x tf X X X X X X X X X X X X X -}“ X X X X X x X x x x x x X X X X x x x x x X X X X X . . x x X X * "x X V ™ V* •. . X X V V V ‘ *.x VI V V **-. v * V V V X X X H" X x X X X x X x X X X X x < X X X X X X . X X X x X X X x -f-X V • x Jc X X X T.47 N. T.46N 46° * 25' - h + H - + 1 l ~ b + - b 0 0 If * O a ® a m * a m ^ rf o o o o & A ' *"V 0 O aA* ry, t *1 j? fir . o • * < * v : v .fir' *r * - « 0 • V “ H' v v V V v «U §. \ X V \ V V V X X J- X X * V + X* x \- x “hv V * “ •.X '•• ♦&#l« X *. - X ar .v jar a* * .X -|_ » . xx »*. M 0 sr*• * ’r a * 0 0 0 0 fif \ * 0 ^ 0 0 ar t * X;V X * 0 •• * ar m ^ 0 x| X X *. X X' 0 *. X 0 0 Xj x n 0 0 X X a fi V V • V * * ••y .REPU&LIC * X 0 0 V E a * V >» X \x V 0 0 O ~ x X « rn V V 'm x T X V ~ «r *\ ar * y - *v v v V v • £ V V |V m V ** v ^ V v 7 v * v V y v v v X,\ • *•*'** V V v v ^ v V v v ^ V —** v v # v V V % V V V V ............... V v* . V v V V V V V V V + v V 1 V V V V V V V V V V V am *“l“ % V V V w V v4 v V ■■ V V V V - V V V V v V v V V V V V V V V V V V • P_V v V v V v v V 4 v V V v V « t V V V v m 0 0 V v \/ v V V v V V v •I W m V v ^ v V \ v •j v \ v y v V V_ V V V V ♦ V V “4 v V V v v V V V v V V Vv v ^ V v V w V V v V 4V y v V Vv # 5 ^ W V V 7 V V v / v v M V v vf • at ’*V V V V V V V V V V V V V V V V V V V * ^ 9 V V V V V V V V V v t-*. T.47 N T.46N V V V V V V V * V t V V V V ~ b V V V V 9 V V f V V V V V V V V V V V V V V V V V \y w \ 88°5 H - - h + 4- + t + ^ / 088 « n iOO 3 R.30W. R.29W. + 1 a + •* 1 /t|* a U 1 u 1 1 * * 3 / 3 3 *■ - K 0 « * 0 0 0 0 0 0 0 0 *• ,v 0 0 0 0 0 0 0 0 0 0 * + 0 ' 0 « * 9 0 + E V EH - h prr^i K X "-v* \/ ■■ V f V V V V f V V V V V V » r *. * B I « a V V V V V v V V V *. v v *«-. v v m a***. » «**.. r a *r m a L ~*\ — SJ E IE 3 V V V v v v ’**. m■ E V V v ■ V V V V V V V V V V V G E N •V V V V V V V V V V v V V V V V V V V ••'v* '• V V V V ^ V V V V V V V V V V V V V V V ■ a V w ' \J V V V v V !^Pr V v • V V V V VgmL V v V V y V V V rm )” v v V V v V V V v V a ^ v/ "■’■■■' i'/: V v V V V V v V V V v V v V V V V V V v V V v v V V V V w Vv V v v v V | V I v v v v V V V V v V V V v v V V V D COARSE PORPHYRITIC GRANITE WITH BIG PHENOCRYSTS ANIMIKIAN ROCKS CONTACT (INFERCD) FOLIATED GRANITE WITH SMALL PHENOCRYSTS CONTACT (OBSERVED) OUTCROP AREA GNEISSIC COMPLEX MAPPED BY SYED M. ZAINUDDIN CONTACT BETWEEN ANIMIKIAN ROCKS AND GRANITE ADOPTED FROM J.W. VILLAR'S MAR PARTIALLY MODIFIED BY FIELD NOTES. NOTE* DIKES ARE NOT SHOWN DUE TO SMALL SIZE. STRIKE AND DIP OF FOLIATION STRIKE OF VERTICAL FOLIATION TKENO OF MttCATlOd _JMILK SCALE 1:2 4 0 0 0 m 22 MAP SHC 205 121 sk» 120 122 118 123 2C j, 126 22 189 • 21 S 215 216 '190 M NJ £ IV) M R 30 W Nl 0% R 29 W o fl* / / /