Lake Bonneville Uplift and a Fluid Lower Crust

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Recent numerical modeling of the Basin and Range extension process indicates that the lower crust must have a low viscosity in order for the Moho to remain flat, as required by seismic observation. Assuming this modeling is correct, the Lake Bonneville uplift should be re-examined with the goal of searching for earth models with low-viscosity lower crusts which satisfy the Lake Bonneville relict shoreline data. Preliminary modeling using an approximation to the Lake Bonneville load indicates that such models may successfully predict the Lake Bonneville uplift. The PI will examine a range of plausible low-viscosity lower-crustal earth models using a realistic model of Lake Bonneville and assuming linear viscoelastic rheologies. He will undertake finite- element modeling to incorporate such effects as power-law flow and an elastic-brittle upper crust. The modeling is significant because it may revise previous estimates of the upper-mantle viscosity beneath the Basin and Range, as well as indicate whether the Lake Bonneville uplift is compatible with the fluid lower crust required by other modeling.