A MODEL OF OUTFLOW GENERATION BY HYDROTHERMAL UNDERPRESSURE DRAINAGE IN VOLCANO-TECTONIC ENVIRONMENT, SHALBATANA-VALLIS (MARS)

The survey of the Shalbatana Vallis course and the analysis of the dis tribution of the concentric peripheral and radial systems of faults ea st of Tharsis allow us to propose a model that demonstrates the effect of volcano-tectonic strains generating crossing fault systems where h eat points allowed hydrothermal drainage of confined aquifers and gene rated headwater systems. This model is qualitatively consistent with t he strain of the spherical buldge of Tharsis expressed by extensional faults intersected by radial faults in the upper lithosphere. The sout hward course of the channel is oriented parallel to extensional faults that are related to the wrinkle ridge field of Lunae Planum. The chan nel is perpendicular to the normal radial faults of eastern Tharsis be tween the equator and -20 degrees lat. The intersection of these two f ault systems generated weak points where magmatic material originating from the lithosphere entered the upper crust through the self-sealing ice-saturated cryosphere. We demonstrate that the system of fault int ersections can explain: (a) the hydrothermal drainage of underground a quifers by convective heat flux and dike intrusion that formed chaotic terrains where source areas were generated beneath the cryosphere and (b) the linear course of the sharp-rimmed, U-shaped Shalbatana Vallis intersected by successive chaos developments as governed by the under lying peripheral fault system, The physics of thermal underpressure va por diffusion and the condensation into water is described as the exch ange of heat between the magmatic intrusion and the ice-rich confined layers beneath the chaotic terrains. (C) 1997 Academic Press.