Three-dimensional normal faulting models of the Valles Marineris, Mars, and geodynamic implications

Inversion of Martian topography, using a three-dimensional boundary element model, permits revised estimates of fault dip angle, depth of faulting, paleogeothermal gradient, and extensional strain in the Valles Marineris region. The major normal faults dip at 40 degrees -55 degrees to depths of similar to 60-75 km with comparatively small footwall uplifts (< 500 m for throws to 10 km), implying that paleogeothermal gradients during faulting were similar to 10 K km(-1) or less, assuming relatively rapid strain rates appropriate to the extending Martian crust. Accumulation of dip-slip offsets along the main normal faults likely was associated with anticlinal flexure and deformation of preexisting strata within the troughs. The magnitudes of the predicted vertical and horizontal displacements outside the troughs, as well as extensional strains, are spatially variable, depending on both cross- and along-strike position relative to the troughs. The predicted displacements and strains attain maximum values at the troughs and decay to background values at cross-strike distances of similar to 250 km, corresponding to 3-4 times the depth of faulting, with an average province-wide strain of 4-15%. By implication, the aggregate strain field surrounding Tharsis is a highly variable spatial and temporal composite of the inhomogeneous strain fields, each associated and scaling, in size with an individual graben, from the smallest structures through the largest Valles Marineris troughs.