University of Montana ScholarWorks at University of Montana Graduate Student Theses, Dissertations, & Professional Papers Graduate School 1992 Structure stratigraphy and contact relationships in Mesozoic volcanic and sedimentary rocks east of Pemberton southwestern British Columbia Janet M. Riddell 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 Riddell, Janet M., "Structure stratigraphy and contact relationships in Mesozoic volcanic and sedimentary rocks east of Pemberton southwestern British Columbia" (1992). Graduate Student Theses, Dissertations, & Professional Papers. 7499. https://scholarworks.umt.edu/etd/7499 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]. Maureen and Mike MANSFIELD LIBRARY Copying allowed as provided under provisions of die Fair Use Section of the U.S. COPYRIGHT LAW, 1976. Any copying for commercial purposes or financial gain may be under^en only with the author’s written consent. MontanaUniversity of STRUCTURE, STRATIGRAPHY AND CONTACT RELATIONSHIPS IN MESOZOIC VOLCANIC AND SEDIMENTARY ROCKS, EAST OF PEMBERTON, SOUTHWESTERN BRITISH COLUMBIA by Janet M. Riddell B.Sc., University of British Columbia, Vancouver, 1984 presented in partial fulfillment of the requirements for the degree of Master of Science University of Montana 1992 Approved by: Cqairman, Board of Examiners Dean, Graduate ScfeoT ' Date UMI Number: EP38300 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 OtRMTtation Püblishina UMI EP38300 Published by ProQuest LLO (2013). Copyright in the Dissertation held by the Author. Microform Edition © ProQuest LLO. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code uesf ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 Riddell, Janet M., M.S., June 1992 Geology Structure, stratigraphy, and contact relationships in Mesozoic volcanic and sedimentary rocks, east of Pemberton, southwestern British Columbia (162 pages) Director: James W. Sears East of Pemberton, British Columbia, Mesozoic volcanic and sedimentary rocks crop out in a northwesterly striking body that is almost entirely surrounded by voluminous late Cretaceous to late Tertiary plutons of the Coast Plutonic Complex. On previous maps, the rocks in this body are correlated with the Upper Triassic Cadwallader Group. This paper describes the results of a mapping study of the part of this body that is exposed in the Tenquille Lake, Owl Creek, and Lillooet Lake pendant areas. I spent six months mapping these rocks at 1:25(XX) scale in order to produce more detailed geological maps, to confirm and/or establish valid regional correlations, and to identify important structural features. The north-northwest striking Owl Creek fault bisects the study area. Rocks that correlate with the Cretaceous Gambier Group lie in the footwall; in the hanging wall, rocks that are correctly correlated with the Cadwallader Group are overlain unconformably by a late Mesozoic volcanic and sedimentary sequence, herein called the Cerulean Lake unit. Movement sense on the Owl Creek fault is northeast-side-up with a component of right lateral oblique slip. There are no oceanic rocks or tectonic melange in the exposures of the fault zone, so it appears to be an ordinary fault rather than a tectonic suture. Rocks in the hanging wall have suffered a long complex structural history, and consequently exhibit strong to intense brittle and ductile structural features, both in Cadwallader Group and in Cerulean Lake unit rocks. Gambier Group rocks in the footwall of the fault are far less complex structurally. The Cerulean Lake unit consists of a lower volcanic member and an upper sedimentary member. This unit overlies the Cadwallader Group on an angular unconformity that represents a depositional hiatus of at least 50 million years. Cerulean Lake unit conglomerates and sandstones contain material derived from the Cadwallader Group, from 158 to 160 Ma granitoids, and from the Cerulean Lake unit volcanic member. The Cerulean Lake unit shares some characteristics with the upper parts of the Gambier Group, but as its age is unknown, a positive regional correlation has not yet been established. 11 ACKNOWLEDGEMENTS Financial and logistical support for this project was provided by British Columbia Geoscience Research Grants #s 89-24 and 89-38, by the Geological Survey of Canada, and by Teck Exploration. I am very grateful to Murray Joumeay for offering me the opportunity to undertake this project and for his support and direction during the fieldwork. Robin Shropshire, Shelley Higman, Laurie Welsh, David Bilenduke, and Scott Helm helped me in the field during the summers of 1989 and 1990. 1 am especially grateful to Robin; her sense of humour was a great benefit during the very difficult first weeks of the mapping; to David, he aggressively hunted for and found fossils; and to Scott, for his excellent mapping contribution. Jean Pautler of Teck Exploration hired me to work with her in the Tenquille Lake area in 1990; I was able to accomplish far more than I originally planned as a result of this collaboration with Jean. I received help with processing and identification of microfossils from Trish Weaver, Du Yue, and Charles Miller (University of Montana), Peter Krause and Mike Orchard (G.S.C), and Glenn Rouse (University of British Columbia). I want to thank the members of my thesis committee, Jim Sears, Donald Hyndman, and Bill van der Sluys, for their help and advice. I am especially grateful to Jim for constructive criticism and many interesting discussions, and to Don for his excellent editorial advice. Many of my friends and coworkers at the British Columbia Geological Survey Branch were very supportive of this project; most of all Paul Schiarizza, who was very generous with his time and ideas. The office staff and my fellow students at the University of Montana Geology Department pro\ ided a friendly and stimulating working environment. I cannot acknowledge all of them in this space, but these good friends helped me with this project in ways that are immeasurable. 1 could not have undertaken this project without the financial security provided for me by my late grandmother, Allison Riddell, and my parents, Neill and Ann Riddell. Most importantly of all , I want to express my heartfelt thanks to John Gaix cr, Robert Gaba, and Dorothy Payne, for turning me on to geology again, and helping me to find the courage to go back to school. Ill TABLE OF CONTENTS Abstract ii Acknowledgements iii Table of Contents iv List of Figures vi List o f Plates vii CHAPTER 1 - INTRODUCTION 1 1.1 General statem ent 1 1.2 Previous work 3 - 1.2.1 History of the study and nomenclature of the Cadwallader Group 3 - 1.2.2 Previous work on the Gambier Group and the Fire Lake Group 7 - 1.2.3 Previous work in the Tenquille/Lillooet Lake area 7 1.3 Purpose of this study 9 1.4 Method 9 1.5 Location and physiography 10 CHAPTER 2 - ROCK UNITS 11 2.1 The Cadwallader Group 11 - 2.1.1 Introduction 11 -2.1.2 Mafic volcanic rocks 12 -2.1.3 Unbedded tuffs 14 -2.1.4 Bedded tuffs and sedimentary rocks 15 - 2.1.5 Rhyolite flows and tuffs 17 - 2.1.6 Plutonic rocks at the south end of Lillooet Lake 18 -2.1.7 Lithofacies'relationships in the Triassic section 18 -2.1.8 Correlation with the Cadwallader Group 27 2.2 The Gambier Group 29 - 2.2.1 Introduction 29 - 2.2.2 Peninsula Formation 29 - 2.2.3 Brokenback Hill Formation 31 - 2.2.4 “Upper” unnamed unit 32 - 2.2.5 Correlation with the Gambier Group 34 2.3 The Cerulean Lake unit 36 - 2.3.1 Introduction 36 - 2.3.2 Volcanic member 36 - 2.3.3 Sedimentary member 39 2.4 Tertiary volcanic rocks 41 iv CHAPTERS - STRUCTURE 43 3.1 Introduction to Chapter 3 43 3.2 Structural zones in the Tenquille/Lillooet Lake area 44 3.3 The Owl Creek fault zone 44 3.4 Zone 1 49 - 3.4.1 Folding of Gambier Group rocks adjacent to the Owl Creek fault 52 - 3.4.2 The “Warm Lake" fault 52 - 3.4.3 The Gambier Group/Pemberton Diorite Complex intrusive contact 56 3.5 Zone 2 56 - 3.5.1 The contrast in structural style across the Owl Creek fault 56 - 3.5.2 The Bastion Range fault 58 - 3.5.3 Folding in Zone 2 58 3.6 Zone 3 59 -3.6.1 Faults and shear zones in Zone 3 59 - 3.6.2 Folding in Zone 3 Cadwallader Group rocks 62 - 3.6.3 Folding in the Cerulean Lake unit 63 - 3.6.4 The Cadwallader/Cerulean Lake unconformity 64 3.7 Neogene tension cracks - found in all zones 64 3.8 Discussion of structural features 67 CHAPTER 4 - DISCUSSIONS AND CONCLUSIONS 69 4.1 Discussion of the stratigraphy 69 - 4.1.1 Cadwallader Group stratigraphy and island arcs 69 - 4.1.2 Tectonic history of the Cadwallader Group 71 4.1.2.1 The Cadwallader Group and the Cadwallader terrane 71 4.1.2.2 Relationships between the Cadwallader terrane and the 73 Bridge River terrane 4.1.2.3 The Cadwallader and Bridge River terranes and their 74 relationship with the Stikine