Martian rifts: Structural geology and geophysics

Abstract

Large extensional tectonic surface structures on Mars are investigated on the basis of image and topographic data. These features have lengths of up to 1400 km, typical widths of tens of kilometers, and depths of up to 3000 m. Their structural architecture is characterized by segmentation with changing style, the development of asymmetric basins with changing polarity, and accommodation zones between such basins. Most structures are associated with varying degrees of volcanism. Based on these observations and a comparison to terrestrial continental rifts, we interpret these series of basins or grabens as rift systems. Crater counts of rift-related geologic surface units indicate that rifts on Mars are �4.0 to 3.5 Ga old. Modelling of rift flank uplift yields heat flows ranging between 28 and 66 mW m�2, and a corresponding thickness of the elastic lithosphere in the order of �10 km at the time of rifting. The radial orientation of some rifts with respect to Tharsis is consistent with a rifting mechanism related to regional extensional stresses in the lithosphere. Rifts with other orientations might have formed in response to stress fields induced by horizontal gradients of the gravitational potential energy, modulated by magmatic zones of lithospheric weakness.