Assessment of global and regional tectonic models for faulting in the ancient terrains of Mars

Abstract

Structural landforms within parts of the heavily cratered terrain of Mars were studied in order to test various models of global fracturing. Landforms analyzed were scarps, grabens, simple ridges, and channel wall scarps. Many of these landforms predate graben formation in Tharsis. Very few structural landforms were found to be either radial to Tharsis or normal to principal stress trajectories calculated for Tharsis isostasy or flexural loading. These results suggest either that the structures are locally derived or, if they were produced by Tharsis activity, that the state of stress in Tharsis was different from that which produced the classic graben systems. Association of narrow valley networks with subdued grabens in one portion of Margaritifer Sinus suggests that one episode of narrow valley formation coincided with flexural loading in Tharsis. Crustal fracturing in Oxia Palus that predates outflow channel formation does not correlate with Tharsis tectonism and may reflect fracturing by the proposed Chryse multiring basin to the north. In contrast to previous studies, no evidence was found for either an orthogonal Martian grid or conjugate sets of shear fractures. It is concluded that Mars probably did not experience significant tidal despinning. Calculations of thermal stress within a cooling early lithosphere performed for varying lithospheric thicknesses predict large‐scale tensile near‐surface failure. Many of the large ridges in Memnonia that predate classical Tharsis‐centered tectonism may reflect normal faulting generated in part by thermal stress.