Petrology and Structure Bayonne Batholith Southeastern British Columbia
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University of Montana ScholarWorks at University of Montana Graduate Student Theses, Dissertations, & Professional Papers Graduate School 1982 Petrology and structure Bayonne batholith southeastern British Columbia Philip M. Barrett The University of Montana Follow this and additional works at: https://scholarworks.umt.edu/etd Let us know how access to this document benefits ou.y Recommended Citation Barrett, Philip M., "Petrology and structure Bayonne batholith southeastern British Columbia" (1982). Graduate Student Theses, Dissertations, & Professional Papers. 7084. https://scholarworks.umt.edu/etd/7084 This Thesis is brought to you for free and open access by the Graduate School at ScholarWorks at University of Montana. It has been accepted for inclusion in Graduate Student Theses, Dissertations, & Professional Papers by an authorized administrator of ScholarWorks at University of Montana. For more information, please contact [email protected]. COPYRIGHT ACT OF 1976 Th is is an unpublished m a n u sc r ipt in w hich c o p y r ig h t sub s i s t s . Any further r e p r in t in g of it s contents must be approved BY THE AUTHOR. MANSFIELD L ibrary Un iv e r s it y of Montana Da t e ! ____1 9 8 2 PETROLOGY AND STRUCTURE, BAYONNE BATHOLITH, SOUTHEASTERN BRITISH COLUMBIA by Philip M. Barrett B.S., University of Washington, 1974 Presented in partial fu lfillm e n t of the requirements for the degree of Master of Science UNIVERSITY OF MONTANA 1982 Approved by: c l / 1 / 7 g / t ' cTLtyytytxXOri. Chairman, Board of Examiners Dean, Graduate Scnbol ___________7 -X 7 ' S x - Date UMI Number: EP37885 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. UMT OwMKtatkm Pubtishing UMI EP37885 Published by ProQuest LLC (2013). Copyright in the Dissertation held by the Author. Microform Edition © ProQuest LLC. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code ProQuesf ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106 - 1346 ABSTRACT B arrett, Philip M ., M.S., Summer, 1982 Geology Petrology and Structure, Bayonne Batholith, Southeastern British Columbia Director: David M. Fountain o j^ < k 'T V • The primary purpose of this study is to determine i f a major fa u lt lies buried in the Purcell Trench near the southern end of Kootenay Lake in southeastern British Columbia and how such a fa u lt might be related to the structural evolution of the Selkirk metamorphic core complex (SMCC) to the south. Pétrographie data indicates the existence in the Bayonne batholith of two previously unrecognized granitic phases, one an S-type granite. S- and I-type plutons in the region may have been emplaced during separate intrusive events. The most westerly and north westerly occurrences of S-type granites in the region broadly coincide with the location of the Kootenay Arc, and this boundary may mark the western edge of autochthonous Precambrian continental crust. A roughly north-south-trending zone of ductile and cataclastic deformation has developed in rocks of the Bayonne batholith. Three stages of deformation history, possibly representing two separate tectonic events, can be distinguished. Later ductile deformation produced conjugate east- and west-dipping mylonite shears for which a normal sense of displacement is indicated. The conjugate shears indicate a subhorizontal, ENE-WSW extension. Later ductile and cataclastic structures could have been produced by stresses of the same orientation during a single tectonic event. Stratigraphie offsets and contrasts in metamorphic grade and late thermal histories of intrusive rocks across the Purcell Trench near the southern end of Kootenay Lake suggest a major fault buried in the trench. The structures exposed near Kootenay Landing may be subsidiary to the postulated Purcell Trench fa u lt. The presence of the features suggesting the postulated Purcell Trench fault and a slickenside lineation parallel to one measured 65 km to the south expand to the north the range of the terrane that can be considered the SMCC. The second tectonic event of this study correlates at least with the later cataclastic deformation event of the SMCC and other core complexes and is interpreted to have occurred during the Eocene. 11 ACKNOWLEDGMENTS I would like to dedicate this thesis to my wife, Karen, who nurtured i t and me in many ways over the years and drafted most of the figures. I sincerely appreciate the unwavering support that my committee members, Dave Fountain, Don Hyndman and Rob Ream, have given me throughout the evolution of the study. F in ally, I want to thank Doug Archibald, Fred M iller and Ray Price for graciously sharing their knowledge with me. 111 TABLE OF CONTENTS Page ABSTRACT................................................................................................................ii ACKNOWLEDGMENTS............................................................................................i i i LIST OF FIGURES.............................................................................................v ii LIST OF TABLES ............................................................................................... ix LIST OF PLATES ................................................................................................. x CHAPTER 1. INTRODUCTION.................................................................. 1 Location and Access ............................................................. 3 Structural Setting ............................................................ 3 Kootenay A r c .............................................................................. 6 St. Mary fa u lt ..........................................................................6 Selkirk metamorphic core complex ................................. 7 2. IGNEOUS PETROLOGY ....................................................................... 10 Petrology of the Bayonne Batholith ............................... 10 General features ................................................................. 10 Mine s t o c k ...............................................................................10 Main mass of the Bayonne ba th o lith ................................14 Kootenay Landing Granite .......................................... 16 Areal Extent of Bayonne Batholith Phases .................... 17 Age of the Bayonne B a th o lith .............................................. 17 Regional Igneous Petrology .......................................... 21 i V CHAPTER Page Regional correlation ......................................................... 21 S-type and I-type granites ............................................ 21 Spatial Separation of S- and I-type Granites . 25 Temporal Separation of S- and I-type Granites . 26 3. STRUCTURAL GEOLOGY ...................................................................... 33 Ductile deformation ............................................................. 33 Mesoscopic and macroscopic description .................. 33 Microscopic textures .................................................... 37 Indicators of sense of shear ....................................... 41 Cataclastic Deformation .................................................... 51 Slickensided surfaces .................................................... 51 Microbreccia ..................................................................... 52 Deformation History ............................................................. 54 4. REGIONAL TECTONIC IMPLICATIONS ............................................ 62 Purcell Trench Fault ............................................................. 63 N55°W Cross-faults and Continuations of the Purcell Trench Fault .................................................... 65 Selkirk Metamorphic Core Complex ................................... 68 Complex Deformational Histories of Core Com plexes .......................... 69 Timing of Regional Tectonic Events .............................. 70 St. Mary Fault .............................................................................. 74 Fault Near Jersey C re e k .........................................................74 V CHAPTER Page 5. SUMMARY AND CONCLUSIONS..............................................................76 Igneous Petrology .................................................................... 76 Structural Geology .... .............................................. 78 Regional Tectonic Implications ...................................... 80 REFERENCES.........................................................................................................83 VI LIST OF FIGURES Figure Page 1. Plutonic rocks and major structures of the Selkirk-Priest River region .................................................... 2 2. Geologic map, including sample locations ...................... 5 3. QAP plot of estimated modes of 26 samples from Bayonne batholith ...................................................................... 12 4. Absolute total magnetic fie ld contours and contacts inferred from them .................................................. 19 5. Equal-area projection of 19 poles to mylonite fo liatio n from the deformation zone exposed near Kootenay