New Constraints on Crust and Mantle Structure Surrounding the Beaufort Sea, Western Canadian Arctic, from a New Broadband Seismic ArrayWednesday, November 21, 2018 - 16:30 to 19:00 Multiplex Gym (DND)
The formation and evolution of the western Canadian Arctic Archipelago represents a long-standing tectonic puzzle. The eastern Beaufort Sea rifted margin juxtaposes young (<150 Ma) Arctic Ocean lithosphere with Paleo-Proterozoic continental lithosphere of the Canadian Shield underlying Banks Island. Controlled source off-shore seismic data suggest that Banks Island represents the western edge of the rifted margin established during the opening of the Arctic Ocean. In this scenario rifting caused Banks Island to subside and accumulate sediments rich in petroleum source material. Conversely, surface-wave based velocity models of North America indicate velocities at 100-150 km depths similar to those beneath Canada’s diamond mines in the central Slave craton. These results suggest Banks Island basement is part of the Canadian Shield and any kimberlites found thereon are promising diamond candidates. Furthermore, the southern Beaufort Sea Mackenzie Delta margin represents a well-developed fold and thrust belt of Cretaceous to present age but has only been recently recognized as likely active. This belt accommodates either slow thrusting of continental crust over the oceanic crust, or underthrusting of the oceanic crust beneath the margin.
We exploit data from new land broadband seismic networks to investigate crustal structure and seismicity around the Beaufort Sea. One of the key questions is how one can reconcile mantle structure typical of the Canadian Shield with crust typical of a rifted passive margin. Specifically, the inference of thick cratonic-like lithosphere underlying Banks Island is incompatible with this being a tectonically disrupted and thinned margin of the Canada Basin. Preliminary results of crust and mantle structure from dispersion analysis (ambient noise and teleseismic earthquakes), 1D inversion, and receiver function analyses, indicate a ~30 km deep Moho beneath the Beaufort Sea and Banks Island, with slight thinning northwards towards Prince Patrick and Melville Islands. Mantle velocities remain elevated, indicative of cooler lithosphere. Anisotropy orientations from SKS splitting indicate margin parallel fabrics, perpendicular to those expected for a tectonically extended margin; however, the source depth of these fabrics remains elusive.