Crustal thickness effects on chemical differentiation and hydrology on Mars

Abstract

The thermal state of planetary crusts depends primarily on heat flow from the mantle to the crust and the depth-integrated radioactive heat generation in the crust. The latter scales with crustal thickness, such that for a given concentration of heat-producing elements, the thicker the crust, the hotter it will be. If estimates of Martian crustal thickness are correct and if these thicknesses are representative of the Noachian crust, thermal modeling shows that the thick crust underlying the southern highlands should have been hot enough 4–3 billion years ago to produce widespread partial melting in the lower crust, whereas the thinner crust beneath the northern lowlands would not have been hot enough to melt. Widespread melting of the lower crust in the southern highlands should have generated significant amounts of silicic magmas, such as granites, as direct partial melts or by fractional crystallization of such melts. Silicic plutons are thus predicted to lie at depth beneath the southern highlands, now hidden beneath a carapace of younger basaltic flows. High surface heat flux imparted by the thick southern highlands crust would also have reduced the extent of permafrost, generating an underlying, stable aquifer of liquid water in the Martian regolith during the Noachian. Tapping of this aquifer by volcanoes or impacts may have caused episodic flooding on an otherwise frozen planet.