Structural attitudes of large scale layering in Valles Marineris, Mars, calculated from Mars Orbiter Laser Altimeter data and Mars Orbiter Camera imagery

Valles Marineris, located on the flank of the Tharsis Ridge uplift on Mars, exposes layering within the canyon walls interpreted to be volcanic flood lavas. By combining 1/128°×1/128°Mars Orbiter Laser Altimeter elevation data with wide-angle Mars Orbiter Camera images using Orion structural analysis software, we computed the attitude of some of this large-scale layering. Multilinear regression was used to fit planes to three-dimensional coordinates of points selected along exposed layer traces, giving the plane attitude and various fitting statistics. By measuring the same layer using different images, we found the measurements to be quite reproduceable. Errors in dip angle were typically only a few degrees or less. Analysis of the data indicates that most layers dip gently into the adjacent chasma. We interpret this orientation to be the result of the crustal subsidence, probably related to the formation of the early collapse basins, rather than the result of rotations produced by extensional faulting. Since the dip is consistent far away from the edge of the current chasmata we suggest that the scale of the depressions was on the order of hundreds of kilometers, exceeding the dimensions of the current chasmata.