Migration of Tharsis volcanism on Mars caused by differential rotation of the lithosphere

The two most striking surface features on Mars are the Tharsis Rise and the crustal dichotomy. The crustal dichotomy, an elevation difference of ∼5 km between the southern highlands and the northern lowlands, is the oldest geological feature on Mars, and the Tharsis Rise is a vast volcanic construct in the equatorial region of the planet, near the dichotomy boundary. Tharsis volcanism was initiated in the southern highlands and the main volcanic centre subsequently migrated to its current location, suggesting relative motion between the lithosphere and the underlying mantle. However, as a one-plate planet, Mars cannot have large-scale motion of the lithosphere according to the standard theory of stagnant-lid convection. Here I use three-dimensional spherical shell models of mantle convection to demonstrate that a unique mode of horizontal motion of the lithosphere, differential rotation, is readily excited for Mars by one-plume convection and lithospheric thickness variations. The suggested mechanism explains the temporal and spatial patterns of Tharsis volcanism and offers a path to a unified model for Tharsis rise and the crustal dichotomy, with implications for volcanism, tectonics and true polar wander on other one-plate planetary bodies. © 2009 Macmillan Publishers Limited. All rights reserved.