The petrological expression of early Mars volcanism

Abstract

Crystallization products of liquids produced by partial melting of a possible Martian mantle for conditions covering the earliest Noachian era to the most recent Amazonian times have been modeled using the MELTS thermodynamic calculator. The results imply a transition from low‐calcium pyroxene dominated assemblages in the Noachian to high‐calcium pyroxene assemblages in the Hesperian and Amazonian, which is remarkably consistent with observations made by orbiting visible and near‐infrared spectrometers. This transition is interpreted as the consequence of the thermal evolution of the mantle, with no need for exotic conditions, such as higher water content or nonchondritic Ca/Al ratio of the mantle source, to produce low‐calcium pyroxene rich lithologies. Our results are compatible with numerical models of the thermal evolution of Mars that predict high production rates of crust on early Mars, implying that Noachian rocks exposed at the surface may be petrological expressions of this volcanism rather than being associated with mantle overturn following the crystallization of a magma ocean.