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Metamorphism and Migmatization of Metasediments in the Precambrian English River Subprovince, Western Ontario Rodney M

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Metamorphism and Migmatization of Metasediments in the Precambrian English River Subprovince, Western Ontario Rodney M University of North Dakota UND Scholarly Commons Theses and Dissertations Theses, Dissertations, and Senior Projects 1985 Metamorphism and migmatization of metasediments in the Precambrian English River subprovince, western Ontario Rodney M. Baumann University of North Dakota Follow this and additional works at: https://commons.und.edu/theses Part of the Geology Commons Recommended Citation Baumann, Rodney M., "Metamorphism and migmatization of metasediments in the Precambrian English River subprovince, western Ontario" (1985). Theses and Dissertations. 13. https://commons.und.edu/theses/13 This Thesis is brought to you for free and open access by the Theses, Dissertations, and Senior Projects at UND Scholarly Commons. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of UND Scholarly Commons. For more information, please contact [email protected]. "'[ ..} _--;/ ;' '"'I ~I ! I METAMORPHISM AHD HIGMATIZATION OF HETASEDIMEIITS IN THE PRECAMBRIAN ENGLISH RIVER SUBPROVINCE, WESTERN ONTARIO by Rodney H, Baumann Bachelor of Science, Horth Dakota State University, Fargo, North Dakota, 1981 A Thesis Submitted to the Graduate Faculty of the University of Horth Dakota in partial fulfillment of the requirements for the degree of lfal!lter of Arts Grand Forks, North Dakota May 1985 This thesis submitted by Rodney M. Baumann ln partial fulfillment of the requirements for the degree of Master of Arts from the University of North Dakota ls hereby approved by the Faculty Advisory Collllllittee under whom the work has been done. I This thesis meets the standards for appearance and conforms to the style and format requirements of the Graduate School of the University of North Dakota, and is hereby approved. ii Permission Title METAMORPHISM AND HIGMATIZATION OF METASEDIMENTS IN THE PRECAMBRIAN EHGLISH RIVER SUBPROVINCE, WESTERN ONTARIO Department-=Geo=l::.:o:..gy.._ ____________________ Degree Master of Arts In presenting this thesis in partial fulfillment of the requirements for a graduate degree from the University of North Dakota, I agree that the Library of this University shall make it freely available for inspection. I further agree that permission for extensive copying for scholarly purposes may be granted by the professor who supervised my thesis work or, in his absence, by the Chairman of the Department or the Dean of the Graduate School, It is understood that any copying or publication or other use of this thesis or pa.rt thereof for financial gain shall not be allowed without my written permission. It is also understood that due recognition shall be given to me and the University of North Dakota in any scholarly use llhieh may be made of any material in my thesis. iii CONTENTS LIST OF FIGURES • • • .vi LIST OF TABLES • • .ix ACKNOWLEDGEMENTS. • X ABSTRACT • • • • • • • • • .xi INTRODUCTION. • 1 Objectives of the Study 1 Location and General Geology • • • 2 Techniques 8 Migmatites 9 Definition of a Migmatite • 9 Layered Migmatites and their Origins • .10 Previous Works in the English River subprovince • • • .10 Meta.sediments. • 10 Plutonic Rocka. • • • • 13 Age Determinations • • • 111 METAMORPHISM AND MIGMATIZATION. • • .16 Petrography of Pelite Metasediments and Phase Equilibria ••• 16 Petrography of Wacke Metasediments and Phase Equilibria • 33 Plagiocla.se Chemistry Comparisons of Banded and Isolated Leucosomes to their Meta.sedimentary Hosts .119 Petrography and Outcrop Structures of Migmatizing Leucosomes .•50 TEMPERATURE, PRESSURE, AND WATER ACTIVITY ESTIMATES • 77 Geothermometry. .77 Geobarometry. • .83 Water Activity. • .88 iv CONCLUSIONS • • • .93 APPENDICES. • • • .95 Appendix A: Outcrop Locality Maps. .96 Appendix B: Mineralogy of Thin-Sectioned Samples. • 102 Appendix C: Chemistry of Selected Minerals. • 110 REFERENCES CITED. • • • • • 137 V LIST OF FIGURES Figure 1. Subprovinces of the Superior province •••• 3 2. English River subprovince showing gneissic, sodic, and potassic plutonic rocks ••••• . .. 5 3. Alternating units of pelite (coarser-grained) and wacke (finer-grained) ••••••••• 17 4. Pelite sa.111ples showing regions of leucocratic material thought to represent crystallized 111elt (anatectite) 20 4A. Outcrop of alternating pelite and wacke with light colored blebs of anatectite occurring in pelite layers •.••••••••••••••• 22 5. Microphoto of relatively coarser-grained anatectite bleb containing microcline. 24 6. Map of field area showing positions of isograds. 27 7. Thin, leucosome lamellae within pelite 29 8. Top microphoto is of sillimanite coexisting stably with biotite, quartz, and plagioclase. Bottom microphcto shows how sillimanite may exist as a metastable phase. • • • • • • • • • • • • • • • • 31 9. Sample of wacke consisting of quartz, plagioclase, and biotite ••••••• . .. • .. .. • • 314 10. Wacke sa.111ple containing diffuse, leucocratic regions which are thought to represent anatectite •••••• 38 11. P-T diagram indicating the region of biotite stability upon reaction of quartz, plagioclase, and biotite •••••••••••••••••• 42 12. Thin, discontinuous leucosome lamellae in wacke. • • • • • • • • • • • • • • • • • • • • • 44 vi 13. Outcrop (top) and hand sa.111ple (bottom) depicting pinitized cordierite (dark crystals) within leucosome bands contained in wacke •••••••••• q7 1q. Outcrop of a layered migmatite within the field area ••••• . • .. • • • • 51 15. Large, volwainous outcrops of leucosome material in the field area thought to have been emplaced by forceful magmatic activity. • • • • • • • • • •••• 53 16. Range in composition of leucosome material plotted using Streckheisen's classification system for igneous rocks .. • . 56 17. Photos of large alwainous phases (garnets) associated with leucosome material •••••••• 59 18. Left photo shows thick leucosome bands adjacent to u11111odified wacke and pelite paleosome layers. Right photo shows a close-up of one of the leucosome bands as being adjacent to unmodified wacke paleosome ••••••••••• 62 19. Outcrop where mafic selvedge does not appear extensive enough such that melanosome + leucosome = paleosome ••••••••••••• 65 20. Photos of leucosome material cross-cutting metasedimentary banding •••••••• 67 20A. Field area outcrop of cross-cutting leucosome bands. • 69 21. Top photo shows anastomosing leucosome system. Bottom photo shows a migmatite breccia (agmatite). • 71 22. Outcrops of leucosome depicting injection structures in medium-grade metasediments outside the field study area •••••••••••.•••• 75 23. Diagram illustrates temperature variations for a given value of lnK between the three goethermometer calibrations used in this study ••••••• 78 24. Regions of temperature-pressure estimates for each of the three geothermometer calibrations used in this study. • • • • • • • • • • • • • • 81 25. Temperature (0 c) plot which shows relatively higher equilibration temperatures occurring central to the field area ••••. 84 25A. Water activity plot for.pelite assemblages 86 vii 26. Map of outcrops outside the enlarged region of figure 26A •••••••• . • • • • • .. • • 97 26A. Map of outcrops (enlarged) within the heavy bordered region of figure 26 •••••••••••••••• 99 viii LIST OF TABLES Table 1. Temperatures (°C) obtained from various biotite-garnet geothermometer calibrations • • • • • .. .. • • 80 2. Pressures (kb) obtained from geobarometers used in this study • • • • • • , , • , • • . .. 89 3. Water activity values and calculation variables. 91 II. Mineralogy of thin-sectioned samples • 1011 5, Garnet chemistries •• , 1111 6. Biotite chemistries. • • 121 7. Cordierite chemistries. • • . • 128 8. Plagioclase chemistries. • .132 9. Orthopyroxene chemistries. .136 ix I wish to thank Dr. Dexter Perkins for llis valuable ideas and insight which contributed to this thesis, and Dr. Frank Karner and Dr. Don Halvorson for their critical reviews of the manuscript. I aa grateful for funding provided by Sigma Xi Research Society and the University of North Dakota Graduate School. Thanks is also extended to my friend and colleague, Steve Chipera, for the many discussions we shared concerning each of our research endeavors. l< ABSTRACT Metasediments of the Precambrian English River subprovince, a subdivision of the Superior province, are conspicuously migmatized by 'bands of light-colored, igneous-appearing material. The metasediments them.selves consist of alternating layers of pelite and wacke lithologies, which represent original mudstones and graywackes respectively. Their deposition is thought to represent subaqueous turbidity flows. For the metasediments of the study area, a 250 square kilometer portion of the English River subprovince, metamorphic grade increases southward from the English River subprovince's northern border. Two isograds have been mapped: the disappearance of muscovite and the disappearance of stable sillimanite. Geothermometry studies are consistent with the trend in metamorphism and temperature values indicate an essentially east-west trending thermal anticline near the center of the subprovince's northern metasedimentary domain. Granulites, defined by the presence of orthopyroxene, occur in the high­ grade metasediments near the center of the thermal anticline. Water activities appear to decrease with increased metamorphic grade. Melting reactions in both pelites and wackes are consistent with phases in small, leucocratic, isolated patches of what is thought to be xi anatectite in the metasediments. These llallle melting reactions cannot always explain the conspicuous layered leucosome
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