The Sudbury Structure (Ontario,Canada): a tectonically deformed multi-ring impact basin |
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Authors: | A. Deutsch R. A. F. Grieve M. Avermann L. Bischoff P. Brockmeyer D. Buhl R. Lakomy V. Müller-Mohr M. Ostermann D. Stöffler |
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Affiliation: | (1) Institut für Planetologie, Universität Munster, Wilhelm-Klemm-Str. 10, D-48149 Münster, Germany;(2) Geological Survey of Canada, KlA OY3 Ottawa, Canada;(3) Geologisch-Paläontologisches Institut, Universität Münster, Corrensstr. 24, D-48149 Münster, Germany;(4) Institut für Geologie, Universität Bochum, Postfach 102148, D-44780 Bochum, Germany;(5) Present address: Museum für Naturkunde der Humboldt-Universität Berlin, Invalidenstr. 43, D-10115 Berlin, Germany |
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Abstract: | The occurrence of shock metamorphic features substantiates an impact origin for the 1.85 Ga old Sudbury Structure, but this has not been universally accepted. Recent improvements in knowledge of large-scale impact processes, combined with new petrographic, geochemical, geophysical (LITHOPROBE) and structural data, allow the Sudbury Structure to be interpreted as a multi-ring impact structure. The structure consists of the following lithologies: Sudbury Breccia —dike breccias occurring up to 80 km from the Sudbury Igneous Complex (SIC); Footwall rocks and Footwall Breccia — brecciated, shocked crater floor materials, in part thermally metamorphosed by the overlying SIC; Sublayer and Offset Dikes, Main Mass of the SIC and Basal Member of the Onaping Formation (OF) — geochemically heterogeneous coherent impact melt complex ranging from inclusion-rich basal unit through a dominantly inclusion-free to a capping inclusion-rich impact melt rock; Grey Member of OF — melt-rich impact breccia (suevite); Green Member of OF — thin layer of fall back ejecta; Black Member of OF — reworked and redeposited breccia material; Onwatin and Chelmsford Formations — post-impact sediments. Observational and analytical data support an integrated step-by-step impact model for the genesis of these units. Analysis of the present spatial distribution of various impact-related lithologies and shock metamorphic effects result in an estimated original rim-to-rim diameter of the final crater of 200 or even 280 km for the Sudbury Structure, prior to tectonic thrusting and deformation during the Penokean orogeny. |
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Keywords: | Sudbury Structure Impact crater Multi-ring basin Penokean orogeny Rb/Sr Sm/Nd Rare earth elements |
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