Luke Beranek has published the article “A magma-poor rift model for the Cordilleran margin of western North America” in the December 2017 issue of Geology.
The Cordilleran margin of western North America has an uncertain rift evolution that includes >300 Myr of lithospheric extension, breakup, and syn- to post-breakup magmatism. Published models for Cordilleran rift evolution since the 1980s have called for homogeneous pure shear or heterogeneous simple shear extension to explain Neoproterozoic-early Paleozoic deformation and magmatism along western North America. In this article, I use the Newfoundland-Iberia rift system as a modern analogue to propose a new magma-poor rift model for the Cordilleran margin. Based on North Atlantic analogues, it is predicted that early Cambrian lithospheric breakup resulted in a base-level fall and generation of the basal Sauk I megasequence boundary along western North America. A lower to middle Cambrian breakup succession developed over this lithospheric breakup surface and from bottom to top consists of lowstand, transgressive, and highstand systems tract deposits. Lower Cambrian volcanic strata are recognized in proximal breakup successions and predicted to be more voluminous in outboard regions with hyperextended crust and exhumed mantle. Off-axis, post-breakup volcanic strata were generated during the release of in-plane tensile stresses and focusing of extension toward the nascent plate boundary. The Beranek research group is currently studying Newfoundland-Iberia stratigraphy and tectonics to further understand North Atlantic rift evolution and apply these ideas to ancient rift margins, including the Cordilleran, Franklinian, and Iapetan margins of North America. Comments are closed.
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