Formation of the Neoarchean Bad Vermilion Lake Anorthosite Complex and spatially associated granitic rocks at a convergent plate margin,Superior Province,Western Ontario,Canada |
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| Institution: | 1. Department of Earth and Environmental Sciences, University of Windsor, Windsor, ON, Canada N9B 3P4;2. Department of Earth Sciences, The University of Western Ontario, London, N6A 5B7 ON, Canada;3. Faculty of Earth Sciences, China University of Geosciences, Wuhan 430074, China;4. Great Lakes Institute for Environmental Research, University of Windsor, Windsor, ON, Canada N9B 3P4;1. Department of Geological Engineering, Karadeniz Technical University, 61080 Trabzon, Turkey;2. Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA;3. Department of Earth Sciences, University of Adelaide SA 5005, Australia;4. School of Earth Sciences and Resources, China University of Geosciences, 29 Xueyuan Road, Beijing 100083, China;5. CAS Key Laboratory of Crust–Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China;6. Korea Basic Science Institute, YangCheong 804-1, Ochang, Cheongwon, Chungbuk 363-883, South Korea;7. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China |
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| Abstract: | The Bad Vermilion Lake Anorthosite Complex (henceforth, the BVLA Complex) in western Ontario is one of the well-exposed, anorthosite-bearing, Archean layered intrusions in the Superior Province, Canada. This study presents new whole-rock major and trace element data for the various units of the Complex, oxygen isotope data for the anorthosite, and major and trace element data for the spatially associated granitic rocks intruding the BVLA Complex to constrain their petrogenetic and geodynamic origin. Zircons from granitic rocks have yielded a 207Pb/206Pb age of 2716 ± 18 Ma, constraining the minimum intrusion age of the Complex.Despite deformation and greenschist facies metamorphism, primary igneous textures are locally well preserved in the BVLA Complex. Its whole-rock major and trace elemental compositions and the oxygen isotopic systematics appear not to have been substantially modified by deformation and metamorphism. Mantle-like oxygen isotope signatures and major and trace element compositions are inconsistent with significant crustal contamination of the BVLA Complex during its emplacement. The existence of primary calcic igneous plagioclase, coherent negative Nb anomalies (Nb/Nb* = 0.08–0.88), and geochemical similarities between gabbros from the BVLA Complex and gabbros from Cenozoic arcs collectively suggest an intra-oceanic subduction zone geodynamic setting for the Complex. Near-flat REE patterns in the various units of the BVLA Complex suggest that they were derived from melting of a shallow source beneath a subarc mantle wedge. Trends in immobile major (e.g., MgO) and trace (e.g., Zr) element data indicate that the mineralogical composition of the Complex can be explained by fractional crystallization and accumulation of olivine, orthopyroxene, clinopyroxene, plagioclase and possibly amphibole.Compositionally, the bordering granitic rocks are A2-type and strongly enriched in Th and REE (> 100 times chondrite) and depleted of Ba, Sr, Eu and Ti. We suggest that they formed in a post-collisional, extensional, tectonic regime following emplacement of the BVLA Complex in an oceanic arc. |
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