Rheological stratification of the lithosphere: A direct inference based upon the geodetically observed pattern of the glacial isostatic adjustment of the North American continent

A sequence of new analyses of the process of glacial isostatic adjustment (GIA) is described. The focus is upon the resolution of a recognized flaw in the currently prevalent model of this process, that denoted ICE-5G(VM2). The flaw concerns a previously noted inability of the model to simultaneously reconcile the VLBI and GPS measured rates of vertical and horizontal motion in the region of the North American continent that lay outboard and to the south of the Laurentide Ice-Sheet (LIS) at Last Glacial Maximum. This characteristic misfit of the model to the data has been suggested to be reconcilable only by recourse to models that explicitly incorporate the influence of lateral viscosity heterogeneity. It is demonstrated herein that, on the contrary, this flaw is entirely and unambiguously attributable to the rheological stratification of the lithosphere, an influence not previously accounted for in global models of the GIA process but which must exist on a priori grounds.