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SUMMARY Evidence from seismology, geology and geodynamic studies suggests that regional-scale lower crustal flow occurs in many tectonic settings. Pressure gradients caused by mantle processes and crustal density heterogeneity can provide driving force for lower crustal flow. Numerically modelling such flow can be computationally expensive. However, by exploiting symmetry in the physical system, it is possible to represent the vertical component of flow in terms of its lateral components, thereby reducing the problem’s spatial dimension by one. Here, we present a mathematical formulation for flow in a viscous channel below an elastic upper plate, which is optimized for solution by common numerical methods. Our formulation drastically reduces the computational load required to simulate lower crustal flow over large areas and long timescales. We apply this model to two example problems, with and without an elastic upper plate, identifying combinations of parameters that are capable of generating measurable geologic uplift. 

Buoyancy anomalies within Earth’s mantle create large convective currents that are thought to control the evolution of the lithosphere. While tectonic plate motions provide evidence for this relation, the mechanism by which mantle processes influence near-surface tectonics remains elusive. Here, we present an azimuthal anisotropy model for the Pacific Northwest crust that strongly correlates with high-velocity structures in the underlying mantle but shows no association with the regional mantle flow field. We suggest that the crustal anisotropy is decoupled from horizontal basal tractions and, instead, created by upper mantle vertical loading, which generates pressure gradients that drive channelized flow in the mid-lower crust. We then demonstrate the interplay between mantle heterogeneities and lithosphere dynamics by predicting the viscous crustal flow that is driven by local buoyancy sources within the upper mantle. Our findings reveal how mantle vertical load distribution can actively control crustal deformation on a scale of several hundred kilometers.