Asymmetric spreading formed Shatsky-Ojin-Hess conjugate (SOHCO) oceanic plateau that subducted under North America

Jonny Wu, University of Arizona
Edward Clennett, Birkbeck, University of London, UK
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Abstract

The subduction history of the North American Cordillera during Laramide times is debated and may involve subduction of conjugate oceanic plateau related to the Shatsky-Hess Large Igneous Provinces (LIPs) in the central Pacific. We review updated geologic constraints and present a plate tectonic reconstruction of the Shatsky-Hess LIPs and their conjugates on the Farallon plate, which we call SOHCO (Shatsky-Ojin-Hess conjugates). We use an optimization routine to produce new poles for asymmetric Farallon-Pacific seafloor spreading during Shatsky-Hess Rise formation, which is likely because the Shatsky-Hess LIPs are associated with plume-ridge interaction. Our SOHCO model implies a ~4300 km-long system of amalgamated conjugate plateau and seamount chain that is >40% longer than previously modeled. SOHCO subducted continuously under western North America over a protracted 30 Myr period, which may help to explain the extended duration of the long-lived Laramide orogeny from Late Cretaceous to Paleogene. Our main model assumes Shatksy conjugate subduction under the southern Sierra Nevadas at 90 Ma and produces SOHCO subduction under Southern California and northern Mexico from ~90 to 60 Ma. An alternative assumption of Hess conjugate subduction under the Mojave at 70 Ma produces an earlier and more northerly Shatsky conjugate arrival along northern California at 95 Ma that continues in a trajectory towards Idaho, Wyoming and Montana by 90 Ma. Our new Farallon-Pacific asymmetric seafloor spreading poles provide a new framework to link ancient Pacific plate motions to western North America.

Session

Large-scale tectonics