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Neoarchean Arc Magmatism, Subsequent Collisional Orogenesis University of Massachusetts Amherst ScholarWorks@UMass Amherst Doctoral Dissertations Dissertations and Theses July 2016 Neoarchean Arc Magmatism, Subsequent Collisional Orogenesis, and Paleoproterozoic Disruption within the Western Churchill Province: Implications for the Growth and Modification of Lower Continental Crust Sean P. Regan University of Massachusetts Amherst Follow this and additional works at: https://scholarworks.umass.edu/dissertations_2 Part of the Tectonics and Structure Commons Recommended Citation Regan, Sean P., "Neoarchean Arc Magmatism, Subsequent Collisional Orogenesis, and Paleoproterozoic Disruption within the Western Churchill Province: Implications for the Growth and Modification of Lower Continental Crust" (2016). Doctoral Dissertations. 662. https://doi.org/10.7275/8224352.0 https://scholarworks.umass.edu/dissertations_2/662 This Open Access Dissertation is brought to you for free and open access by the Dissertations and Theses at ScholarWorks@UMass Amherst. It has been accepted for inclusion in Doctoral Dissertations by an authorized administrator of ScholarWorks@UMass Amherst. For more information, please contact [email protected]. NEOARCHEAN ARC MAGMATISM, SUBSEQUENT COLLISIONAL OROGENESIS, AND PALEOPROTEROZOIC DISRUPTION WITHIN THE WESTERN CHURCHILL PROVINCE: IMPLIACATIONS FOR THE GROWTH AND MODIFICATION OF LOWER CONTINENTAL CRUST A Dissertation Presented By SEAN P. REGAN Submitted to the Graduate School of The University of Massachusetts Amherst in partial fulfilment of the requirements for the degree of DOCTOR OF PHILOSOPHY May 2016 Geosciences © Copyright by Sean P. Regan 2016 All Rights Reserved NEOARCHEAN ARC MAGMATISM, SUBSEQUENT COLLISIONAL OROGENESIS, AND PALEOPROTEROZOIC DISRUPTION WITHIN THE WESTERN CHURCHILL PROVINCE, CANADA: IMPLICATIONS FOR THE GROWTH AND MODIFCATION OF LOWER CONTINENTAL CRUST A Dissertation Presented By SEAN P. REGAN Approved as to style and content Michael L. Williams, chair Michael J. Jercinovic, member Sheila J. Seaman, member Kevin Mahan, member Laurie Brown, member Rolf Karlstrom, external member Julie Brigham-Grette, Department head Geosciences ACKNOWLEDGEMENTS First and foremost, I would like to extend a special thanks to my advisor, Dr. Michael L. Williams for constant patience, support, and an undying enthusiasm for my education. He has been a phenomenal advisor and mentor, and has made a serious impact on both my personal and professional life. Dr. Michasel J. Jercinovic has aided in numerous ways and both facilitated much of the data acquired herein, and also taught me how to be a good analyst. The entire research group at the University of Massachusetts, Amherst has been a constant source of peer support and I have gained much insight in various discussions, interactions, and seminars. These people include: Dr. Chris Koteas, Dr. Julien Allaz, Jeffrey R. Webber, Amanda VanLankvelt, Calvin Mako, Phillip S. Geer, and Claire Pless. Dr. Kevin H. Mahan (CU Boulder) has been an excellent external mentor and impactful on my education despite his location approximately 2000 miles away. Greg Walsh (USGS) has contributed a great deal of time and resources in support of completion of the below work. Excellent field support and friendship is owed to Mark E. Holland, and Omero F. Orlandini. This work was funded by several sources. Primary funding came from the National Science Foundation (NSF) research grants EAR-0948560 awarded to Kevin H. Mahan and Dr. Michael L. Williams, EAR-1045515 awarded to Laurie Brown. Other sources of funding were two student research grants awarded to Sean P. Regan. Also, five student research awards from the Department of Geosciences, University of Massachusetts, Amherst have supported various components of the presented research. Many others have contributed to this dissertation including best friends and colleagues Jeffrey Chiarenzelli and Mark Holland. All the work presented herein is collaborative. Chapter 2 was published in the Canadian Journal of Earth Sciences with coauthors: Dr. Michael L. Williams, Shannon Leslie, Dr Kevin Mahan, Dr. Michael Jercionivic, and Mark Holland. Chapter 3 is currently being prepared for iv submission to Geology with coauthors Michael L. Williams, Michael Jercinovic, and Matthew Wielicki (University of California, Los Angeles). The fourth chapter will be submitted in the next several months to Precambrian Research with coauthors Dr. Michael L. Williams, Dr. Kevin H. Mahan, Dr. Greg Dumond, Dr. Michael J. Jercinovic, and Omero Felipe Orlandini. The final chapter is a ‘work in progress’ but will likely be submitted to Precambrian Research with coauthors Dr. Jeffrey R. Chiarenzelli, Dr. Michael L. Williams, Dr. Lawrence Aspler, and Dr. Michael J. Jercionivc. v ABSTRACT NEOARCHEAN ARC MAGMATISM, SUBSEQUENT COLLISIONAL OROGENESIS, AND PALEOPROTEROZOIC DISRUPTION WITHIN THE WESTERN CHURCHILL PROVINCE, CANADA: IMPLICATIONS FOR THE GROWTH AND MODIFICATION OF LOWER CONTINENTAL CRUST MAY 2016 SEAN P. REGAN, B.S., ST. LAWRENCE UNIVERSITY M.S., UNIVERSITY OF MASSACHUSETTS, AMHERST Ph.D., UNIVERSITY OF MASSACHUSETTS, AMHERST Directed by: Professor Michael L. Williams The growth and modification of continental lithosphere are fundamental geologic processes that have had a profound effect on Earth’s evolution. The lower continental crust can play a myriad of roles pertaining to these processes depending on the strength, age, temperature, and composition of the rocks present. However, the lower continental crust is impossible to sample in-situ, and thus observations of modern lower continental crust are limited to seismic studies and xenolith studies, which provide mere snap shots of the lower crust. High pressure granulite terranes provide 4 dimensional, and spatially resolvable, analogues of lower continental crust. The Athabasca granulite terrane (AGT), along the eastern margin of the Rae subprovince of the western Churchill Province, is underlain by >20,000 km2 of high pressure granulite, and is arguably to be the largest intact exposure of lower continental crust in the North America. Work presented herein provides a detailed temporal and tectonic framework for interpreting rocks of the AGT, and evaluates rocks ca. 400 km along strike to test for spatial consistency. Results suggest that the Paleoproterozoic involved the juxtaposition of various lithotectonic blocks along major ductile shear zones that vary in metamorphic conditions, timing and kinematics. Sinistral kinematics within the Cora Lake shear zone within the AGT, for instance, are explained by accretion of the Lynn-Lake and La Ronge arcs along the southern periphery of the Churchill vi Province at ca. 1.88 Ga at the waning phases of granulite-facies conditions. Ca. 1.9 Ga deformation involved upright folding, and the development of a regionally extensive dextral transpressive fabrics, and appears to be spatially related to the Chipman dike swarm. This event may have been driven by accretionary and collisional tectonics between the Slave and western Churchill Province. IN-SIMS micro zircon geochronology suggests a ca. 2.1 Ga emplacement age for the Chipman dikes, and may be indicative of an incipient rift, which was the locust for ca. 1.9 Ga reactivation. Preceding these events was a major crustal thickening event that occurred immediately after widespread arc-like magmatism interpreted to represent early subduction and subsequent collisional orogenisis. Rocks along strike, 400 km to the northeast of the AGT, share a similar Neoarchean history, and dike swarm, but contain little evidence of regionally extensive Paleoproterozoic granulite-facies reactivation. The reasoning for this is unknown at current, but perhaps it is due to an increasing distance from the bounding Paleoproterozoic orogens. These data provide a four dimensional framework to evaluate changes in lower crustal properties and behavior for greater than 600 my. vii TABLE OF CONTENTS Page ACKNOWLEDGEMENTS ............................................................................................................ iv ABSTRACT .................................................................................................................................... vi LIST OF TABLES .......................................................................................................................... xi LIST OF FIGURES ...................................................................................................................... xiii CHAPTER 1: INTRODUCTION ....................................................................................................................... 1 Introduction ............................................................................................................................... 1 Purpose and General Approach ................................................................................................. 3 Dissertation Organization .......................................................................................................... 3 Summary ................................................................................................................................... 5 2: THE CORA LAKE SHEAR ZONE, ATHABASCA GRANULITE TERRANE, AN INTRAPLATE RESPONSE TO FAR-FIELD OROGENIC PROCESSES DURING THE AMALGAMATION OF LAURENTIA……………………………………………………....12 Introduction ............................................................................................................................. 12 Geologic setting ......................................................................................................................
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