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Paleomagnetism, Geochemistry, and U-Pb Geochronology of Proterozoic Mafic Intrusions

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Paleomagnetism, Geochemistry, and U-Pb Geochronology of Proterozoic Mafic Intrusions Paleomagnetism, Geochemistry, and U-Pb Geochronology of Proterozoic Mafic Intrusions in the High Arctic: Relevance to the Nares Strait Problem by Steven Walter Denyszyn A thesis submitted in conformity with the requirements for the degree of Doctor of Philosophy Graduate Department of Geology, University of Toronto © Steven Walter Denyszyn 2008 Library and Bibliotheque et 1*1 Archives Canada Archives Canada Published Heritage Direction du Branch Patrimoine de I'edition 395 Wellington Street 395, rue Wellington Ottawa ON K1A0N4 Ottawa ON K1A0N4 Canada Canada Your file Votre reference ISBN: 978-0-494-39837-1 Our file Notre reference ISBN: 978-0-494-39837-1 NOTICE: AVIS: The author has granted a non­ L'auteur a accorde une licence non exclusive exclusive license allowing Library permettant a la Bibliotheque et Archives and Archives Canada to reproduce, Canada de reproduire, publier, archiver, publish, archive, preserve, conserve, sauvegarder, conserver, transmettre au public communicate to the public by par telecommunication ou par Plntemet, prefer, telecommunication or on the Internet, distribuer et vendre des theses partout dans loan, distribute and sell theses le monde, a des fins commerciales ou autres, worldwide, for commercial or non­ sur support microforme, papier, electronique commercial purposes, in microform, et/ou autres formats. paper, electronic and/or any other formats. The author retains copyright L'auteur conserve la propriete du droit d'auteur ownership and moral rights in et des droits moraux qui protege cette these. this thesis. Neither the thesis Ni la these ni des extraits substantiels de nor substantial extracts from it celle-ci ne doivent etre imprimes ou autrement may be printed or otherwise reproduits sans son autorisation. reproduced without the author's permission. In compliance with the Canadian Conformement a la loi canadienne Privacy Act some supporting sur la protection de la vie privee, forms may have been removed quelques formulaires secondaires from this thesis. ont ete enleves de cette these. While these forms may be included Bien que ces formulaires in the document page count, aient inclus dans la pagination, their removal does not represent il n'y aura aucun contenu manquant. any loss of content from the thesis. Canada Paleomagnetism, Geochemistry, and U-Pb Geochronology of Proterozoic Mafic Intrusions in the High Arctic: Relevance to the Nares Strait Problem Steven Walter Denyszyn To fulfill the requirements for the degree of Doctor of Philosophy, 2008 Department of Geology, University of Toronto Abstract The paleomagnetism, geochemistry, and geochronology of mafic intrusions in Arctic Canada and Greenland were investigated with the primary purpose of resolving the Nares Strait Problem, a controversy regarding the location of a plate boundary between Greenland and North America and the relative displacement between the two plates. E/W-trending dykes in Arctic Canada and northwest Greenland have an age of 721 ±2 Ma and are associated with the Franklin magmatic event. Their geochemistry is comparable and the mean paleopole for the Canadian dykes (5.8°N, 188°E, N=12, A95=9.9°) is broadly similar to that of the Greenlandic dykes (8.8°N, 178.7°E, N=10, A95=7.2°) indicating that they are of the same swarm, but that of the Canadian dykes is offset from that of the Greenland dykes by a direction and magnitude consistent with a -200 km displacement along a fault beneath Nares Strait, in accordance with other lines of evidence such as dyke distribution and age boundaries in the bedrock The paleopole from the Canadian dykes is significantly different (p=0.05) from that of Franklin rocks elsewhere, suggesting rapid plate motion over the duration of magmatism. Also associated with Franklin magmatism are the N/S-trending Clarence Head dyke swarm, dated at 715±1 Ma, and the Thule sills, dated for the first time, ii at 712±2 Ma. Two Clarence Head dykes have been chemically remagnetized, likely as a result of fluids expelled by the Ellesmerian Orogeny. Three dykes of the Melville Bugt dyke swarm were sampled, one dated at 1622±4 Ma. The measured pole (6.1°N, 267.7°E, dp=2.36°, dm=3.76°) indicates that Laurentia and Baltica drifted separately at this time. Though the Melville Bugt swarm's extension was not found in Canada, a possible candidate, a dyke at Dundas Harbour, was dated at 1337±2 Ma, a previously unknown age of dyke emplacement in North America, with a VGP of 12.1°S, 250.8°E, dp=6.7°, dm=13.4°. This study includes the first analysis of the effects of alpha recoil in baddeleyite, which could have a strong influence on analyses of very small crystals. The effect is apparently not as significant in baddeleyite as in zircon, as the higher density of baddeleyite's crystal lattice may restrict recoil distances iii Acknowledgments My sincere gratitude is extended to my supervising committee of Henry Halls, Don Davis, and Russ Pysklywec, whose support, advice, and availability made a direct and significant contribution to the development and ultimate success of this research. Henry in particular is thanked for initiating this project as part of the Nares Strait Geocruise in 2001, and for giving me the opportunity to pursue this study. Thanks also to my family, and to friends at the Geology department at the University of Toronto where I have been for less than ten years for moral (and technical) support. Especially noteworthy in this regard are Sarah Hirschorn, Halan Wang, Chris Charles, Chris White, AH Marin, and the many and various noodle-merchants of Toronto's Chinatown. I would also like to acknowledge the staff of the Jack Satterly Geochronology Lab at U. of T., particularly Mike Hamilton and Kim Kwok, for their generosity with their time in teaching me the ropes of geochronology, for assisting in the lab, and for providing the sort of camaraderie that made it a joy to fiddle with microscopic grains of baddeleyite. Funding for this project was provided by the Natural Sciences and Engineering Research Council and the Northern Scientific Training Programme. The Canadian Polar Continental Shelf Project provided efficient and valuable logistical support for fieldwork in the High Arctic, without which, it seems, no work would get done in Canada's north. Ray Mercredi of Grise Fiord, Ellesmere Island and Hans Jensen of Qaanaaq, Greenland are thanked for sharing their knowledge of how things get done up there. Finally, thanks to Monica. Your patience and support and more patience have meant so much. This thesis is dedicated to you. iv Table of Contents Abstract ii Acknowledgments iv Table of Contents v 1. Introduction 1 The Nares Strait Problem 1 Plate kinematic history of the Arctic region 6 Geology and tectonic history of the Arctic region 14 The Eurekan Orogeny 24 Proposed plate boundaries 26 Mafic intrusions 29 The Melville Bugt dyke swarm 30 Proterozoic diabase dykes of unknown affinity 31 The Franklin igneous event 33 2. Methodology 38 Paleo-/Rock Magnetism 38 Petrography and Geochemistry 45 Tectonic reconstruction 47 Geochronology 48 3. Results 55 Geochronology 56 Franklin dyke swarm 57 Clarence Head Swarm (N/S dykes) 58 Melville Bugt swarm 63 Dundas Harbour dyke 63 Geochemistry and Petrography 67 Franklin dyke swarm 67 Clarence Head Swarm (N/S dykes) 77 Melville Bugt swarm 77 Dundas Harbour dyke 77 Paleo-/Rock Magnetism 80 Franklin dyke swarm 80 Clarence Head Swarm (N/S dykes) 97 Melville Bugt swarm 102 Dundas Harbour dyke 106 v 4. Discussion 110 Nares Strait Problem 110 Correlation of Neoproterozoic mafic dykes Across Nares Strait 113 Does the Kap Leiper dyke extend into Canada? 118 Reconstruction of the Nares Strait region 128 Geochronology of baddeleyite in the Franklin intrusions 133 Emplacement of orthogonal dykes and the remagnetization of the "Clarence Head" dykes 137 New Ages of Proterozoic Arctic Magmatism and its effect on the Apparent Polar Wander Path of Laurentia 142 Differences in paleopole measurements across the Franklin intrusions 148 5. Conclusions 160 6. References 164 Appendix A; Paleomagnetic data by specimen 180 Appendix B: Geochemical data 193 VI 1 1. Introduction The Nares Strait Problem Controversy about the existence of a major sinistral fault lying between Greenland and Ellesmere Island (the "Nares Strait problem" of Dawes and Kerr 1982a) originated with early reconstructions of the two landmasses by Taylor in 1910 and Wegener in 1915 (Figure 1.1). Taylor (1910) proposed a sinistral fault with an offset of about 300 km to explain the generation of Tertiary mountain chains by land drifting away from polar regions. Later, Wegener (e.g., 1929) incorporated these ideas into his theory of continental drift and the fault thereafter became known as the "Wegener Fault". The problem arises because, subsequently, several workers have compared the stratigraphy of the Proterozoic and Paleozoic sedimentary rocks on either side of the Nares Strait (Figure 1.2) and concluded that no more than 70 km of lateral movement is permissible (Dawes & Kerr 1982b and references therein; Harrison 2006). However, this conclusion has been questioned and alternative solutions more in harmony with plate tectonic expectations have been presented (e.g., Miall 1983; Johnson & Srivastava 1982). In support of the plate tectonic model, geological and geophysical studies (particularly of marine magnetic anomalies) indicate that oceanic crust underlies the Labrador Sea and that the opening of the Labrador Sea and Baffin Bay occurred between ~85 and 56 My ago (Srivastava et al 1981; Oakey 1994; Chalmers & Laursen 1995), with Greenland moving in a NNE direction with respect to Canada. The Nares Strait Problem remains a significant controversy in plate tectonics in which all the "classic" elements indicating plate motion are present, but the onshore geology has been interpreted as telling a very different story. The primary objectives of this thesis involve studying a combination of distinctive characteristics - paleomagnetism, petrography, geochemistry and U-Pb geochronology - to Figure 1.1: Speculative reconstructions of Greenland and North America by a) Taylor (1910) and b) Wegener (1915).
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