Hydrolithosphere and Problems of Subsurface Ice in the Equatorial Zone of Mars

Abstract

It is assumed that on Mars liquid water (lower hydrolithosphere) is confined under the icy upper lithosphere (upper hydro1ithosphere), which is indeed a rigid and practically impervious carapace. The mobility of the lithospheric water and probably also of a part of the stocking rocks under the permafrost probably originates by sapping some important surface features, for instance subcircular depressions of increasing sizes, with steep slopes, aligned along the main fractures. This process is probably primordial in the origin of the Valles Marineris system. If the oscillations of the cryo-marge (basis of the permafrost) are able to make thin enough the icy upperlithosphere until a break out point, the disruption of the aquifer to the surface is possible, generating high artesian pressure in the lowest regions of the planet (supposed process of the outflows according with the Carr’s model). It seems likely that more or less important ice caps existed in some places in the equatorial zone of Mars, with the same origin (subsurface water). Three possibilities are suggested to explain the variations of the cryomarge and the thinning of the permafrost: modifications of the geothermal gradient; climatic oscillations; progressive heating of the water during the filling of the aquifers.