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November 2013

Using CitcomCU to Model Farfield Deformation in Alaska

Jadamec et al.’s (2013) recent paper 3-D numerical models of flat slab subduction and the Denali fault driving deformation in south-central Alaska investigates the relative effect of flat slab subduction, an intra-continental shear zone, and a non-Newtonian rheology on overriding plate deformation. Numerous hypotheses have been previously put forth to explain the far-field deformation in Alaska and mountain building in the Alaska Range, in which is located the tallest mountain in North America, Mt. McKinley. However, these hypotheses had not previously been tested with a geodynamic model that includes both a subducting plate and overriding plate to determine if the present balance of forces in the subduction zone can actually produce the localized mountain building inboard of the plate boundary. Jadamec et al. (2013) show the localized intra-continental mountain building in the central Alaska Range, including Mt. McKinley, can be produced by the modern flat slab configuration combined with a vertical lithosphere scale shear zone representative of the Denali fault. A first order consequence of including the Denali fault shear zone, is to decouple the portion of south-central Alaska between the Denali fault and the Aleutian trench from the rest of North America, forming an independently moving fore-arc sliver which correlates to the Wrangell block. Thus, the overall effect of including the Denali fault and using a Non-Newtonian viscosity is to isolate a portion of the overriding plate such that it can be translated by flat slab subduction into a North American continental backstop, with the central Alaska Range located at this juncture. The 3D models were run with the CIG maintained code CitcomCU. To resolve the overriding plate, the plate interface, as well as the flat slab geometry, the models required high resolution (up to 2.35 km) and were run on the TeraGrid/XSEDE high performance computing resources, with 17,000 compute hours per model. Figure. 3-D cartoon showing the inter-relation of the modern tectonic configuration and overriding plate deformation in south-central Alaska.