Evaluation of the orogenic belt hypothesis for the formation of the Thaumasia Highlands, Mars

Abstract

Thrust faults along the southern margin of the Thaumasia Highlands, Mars, comprise a set of discrete subparallel south verging structures. Previous work proposed that the faults collectively define a narrow Earth‐like orogenic belt composed of a deformed lithospheric section translating southward through Tharsis above a regional décollement. This hypothesis is tested here by comparing topographic slopes across the Thaumasia Highlands to the values required by thrust faulting in a critical taper wedge setting. In general, topographic slopes across the Thaumasia Highlands, 0.418–1.017°, are too shallow for the Martian lithosphere to have deformed as a critical taper wedge, assuming reasonable values for pore fluid pressure ratios and frictional strengths of the wedge material and putative décollement. Combined with the absence of a mechanism to provide the necessary values of horizontal shortening (hundreds of km), nearly lithostatic pore fluid pressure ratios, and nearly frictionless décollements over regional scales on Mars that would be necessary for lithospheric translation as a wedge, the results are consistent with thrust fault deformation across Mars that is not integrated at depth into subhorizontal structures, but which function instead as discrete structures.