Temperature and rheological properties of the mantle beneath the North American craton from an analysis of heat flux and seismic data

Abstract

We combine heat flux data and seismic velocity models for the North American lithosphere to derive constraints on thermal conditions and deformation mechanisms in the underlying convecting mantle. Local heat flux averages that are not affected by shallow crustal heat production contrasts allow calculation of reliable lithospheric geotherms and uncertainty ranges. For consistency with the seismic data, the mantle potential temperature beneath North America must lie within a 1290°C-1450°C range, close to that for the oceanic mantle sampled at mid-ocean ridges. The heat flux at the base of the lithosphere varies laterally from 11 ± 3 mW m-2 beneath the ∼250 km thick Archean core of the Superior province to 15 ± 3 mW m-2 beneath the thinner younger Appalachians province. It is shown that the most likely cause of such rates of heat supply into the North American continent is small-scale convection in an unstable boundary layer beneath the rigid mechanical lithosphere. This allows useful constraints on the mantle rheological properties. We show that the most likely deformation mechanism is dislocation creep in wet mantle rocks. Ranges for the mantle temperature, water content, and rheological parameters could be tightened very significantly once strong constraints are obtained on radiogenic heat production in the lithospheric mantle. Copyright © 2011 by the American Geophysical Union.