Meso – and Neoarchean tectonic evolution of the northwestern Superior Province: Insights from a U-Pb geochronology, Nd isotope, and geochemistry study of the Island Lake greenstone belt, Northeastern Manitoba by Jennifer E. Parks A thesis presented to the University of Waterloo in fulfillment of the thesis requirement for the degree of Doctor of Philosophy in Earth Sciences Waterloo, Ontario, Canada, 2011 ©Jennifer E. Parks 2011 Author’s Declaration I hereby declare that I am the sole author of this thesis. This is a true copy of the thesis, including any required final revisions, as accepted by my examiners. I understand that my thesis may be made electronically available to the public. ii Abstract What tectonic processes were operating in the Archean, and whether they were similar to the “modern-style” plate tectonics seen operating today, is a fundamental question about Archean geology. The Superior Province is the largest piece of preserved Archean crust on Earth. As such it provides an excellent opportunity to study Archean tectonic processes. Much work has been completed in the southern part of the Superior Province. A well-documented series of discrete, southward younging orogenies related to a series of northward dipping subduction zones, has been proposed for amalgamating this part of the Superior Province. The tectonic evolution in the northwestern Superior Province is much less constrained, and it is unclear if it is related to the series of subduction zones in the southern part of the Superior Province, or if it is related to an entirely different process. Such ideas need to be tested in order to develop a concise model for the Meso – and Neoarchean tectonic evolution of the northwestern Superior Province. To this end, a field mapping, U-Pb geochronology, Nd isotope, and lithogeochemistry study was undertaken in the Island Lake greenstone belt. This granite-greenstone belt is part of the northern margin of the North Caribou terrane, a larger reworked Mesoarchean crustal block located in the northwestern Superior Province. U-Pb TIMS zircon geochronology data shows that the Island Lake greenstone belt experienced a long and complex geological history that included the deposition of three distinct volcanic assemblages at ca. 2897 Ma, 2852 Ma, and 2744 Ma, as well as a younger clastic sedimentary group, the Island Lake group. All of these volcanic assemblages include felsic and mafic volcanic rocks, as well as a suite of contemporaneous plutonic rocks. The U-Pb data set shows that the Savage Island shear zone, a regional fault structure that transects the Island Lake greenstone belt, is not a terrane-bounding feature as correlative supracrustal assemblages are observed on both sides of it. The Nd isotope data shows that the volcanic assemblages and contemporaneous plutons iii have been variably contaminated by an older ca. 3.0 Ga crustal source. The mafic volcanic rocks in the assemblages have two distinct geochemical signatures, and show a pattern of decreasing crustal contamination with decreasing age. Together these data suggests that the Meso – and Neoarchean volcanic assemblages are part of an intact primary volcanic stratigraphy that were built on the same ca. 3.0 Ga basement and have autochthonous relationships with each other. This basement is the North Caribou terrane. The youngest sedimentary group in the belt, the Island Lake group, was deposited between 2712 Ma and 2699 Ma. It consists of “Timiskaming-type” sedimentary rocks, and is the youngest clastic sedimentary package in the belt. A detailed study of detrital zircons in units from the stratigraphic bottom to the top of the sedimentary group indicates an age pattern of detrital zircons that is most consistent with a scenario in which sediments were deposited in inter-diapiric basins created by diapirism and sagduction (i.e., vertical tectonic) processes. During the diapiric ascent of the felsic material, inter-diapiric basins were formed in the synclines between adjacent domes, into which sediments were deposited. U-Pb zircon TIMS geochronology identified two ages of deformation in the Island Lake greenstone belt. Two dykes that crosscut an older, D1 foliation place a minimum age of ca. 2723 Ma on the D1 deformation, and two syn-kinematic dykes date movement along two transpressional shear zones to 2700 Ma. Together all these data indicate that the tectonic evolution in the Island Lake greenstone belt and in the northwestern Superior Province took place in three main stages. The first two stages involved the generation of Meso – and Neoarchean volcanic assemblages and contemporaneous plutonic rocks due to southward dipping subduction under the North Caribou micro-continent. The third stage involved the deposition of late “Timiskaming-type” sediments during vertical tectonic processes in iv conjunction with horizontal tectonic movement along late transpressional shear zones at ca. 2.70 Ga. At the end of this process the North Superior superterrane was terminally docked to the North Caribou terrane along the North Kenyon fault. This study shows that while a version of horizontal or “modern” style plate tectonics were operating in the Archean, vertical tectonic processes were also occurring and that these processes operated synchronously in the Neoarchean. v Acknowledgements I would like to thank the following organizations for financial support for this project: LITHOPROBE, NSERC and NSERC discovery grants to Shoufa Lin and Larry Heman, the Northern Scientific Training Program, the University of Waterloo, the Ontario Graduate Scholarships, and the Ontario Graduate Scholarships Science and Technology program. The Manitoba Geological Survey has played an important part of Ph. D. project. They provided financial, logistical, and technical support. In particular I’d like to thank Ric Syme for access to samples he collected in the field and for use of his field notes. I’d like to thank Tim Corkery for helping me make sense of things in the field, and for his moral support and his infectious enthusiasm when talking about rocks in the northwestern Superior Province. The second chapter of this thesis is a modified version of the publication: Parks, J., Lin, S., Davis, D., and Corkery, M.T., 2006: New high-precision U-Pb ages for the Island Lake greenstone belt, northwestern Superior Province: implications for regional stratigraphy and the extent of the North Caribou Terrane. Canadian Journal of Earth Sciences. v 43, p.789-803 The version presented here includes minor modifications and editorial changes. Appendix A is 40 x 26 inch geological map which is included in a pocket at the back of the thesis in printed copies. The map has been published by the Manitoba Geological Survey. Neither the map nor chapter two require written permission to reproduce. Many people have assisted me in different stages of research during my PhD. I’d like to thank Shoufa for his advice and being patient, as well as the rest of my committee for helping me in different stages of this processes. Scott Snider, Matt Chalaturnyk and Daniel Martin are thanked for assistance in the field, and Neill Brandson is thanked for logistical support during the field season. I would like to thank Don Davis, John Ketchum, Kim Kwok, Sandra Kamo, and Tom Pestaj for assistance with geochronology at the Jack Satterly Laboratory, and Larry Heman, Antony Simonetti, vi Rob Creaser, Judy Shultz and Kendra Siemens and the rest of the staff at the Radiogenic Isotope Facility at the University of Alberta. As well, thanks to Kirsty Tomlinson for assistance in the field and with preliminary Nd isotope and geochemical data interpretation. Greg Stott and Gary Beakhouse are thanked for providing comments and suggestions on an early version of Chapter three. At the University of Waterloo I’d like to thank Sue Fisher for helping me to navigate the bureaucracy of being a graduate student at UW, and for always providing helpful advice and a supportive shoulder. I would not have learned or enjoyed myself as much over the past few years without the support of the Shoufa Squad. Thanks to Edith, Andy, Sandra, A.J., Paul, Justin, Matt, Yvette, Nathan and Ben as well as other fellow graduate students at UW and the University of Alberta. Outside of school I need to thank the following people for helping me keep my sanity: my Toronto friends (Heather and Jenever- thanks for letting me crash), the 2006 Edmonton Oilers, the Melrose Crew, Mathryn, Randrea, too many roommates to count, and anyone I ever shared a beer with at Ethels. Last but not least I need to thank my family for always being supportive and only asking me a few times why it was taking me so long to finish my thesis. Super thanks BP. vii Dedication Thanks Mom For N.A.P. viii Table of Contents Author’s Declaration .............................................................................................................................. ii Abstract ................................................................................................................................................. iii Acknowledgements ............................................................................................................................... vi Dedication ........................................................................................................................................... viii Table of Contents .................................................................................................................................. ix List of Figures