CO2 Solubility in Primitive Martian Basalts Similar to Yamato 980459 and the Evolution of the Martian Atmosphere

Abstract

There is considerable evidence that liquid water was stable on the ancient Martian surface during at least some parts of the late Noachian and early Hesperian epochs. Yet there remains considerable uncertainty as to how this greenhouse was created and maintained and how it evolved to the current thin, modern atmosphere. To understand possible volcanogenic fluxes of CO2 to the early Martian atmosphere, we investigated experimentally carbonate solubility in a synthetic melt based on the shergottite meteorite Yamato 980459 (Y980459), a picritic rock (19.08 wt.% MgO) thought to be a near-primary liquid derived from high temperature (>1540 °C) partial melting of the Martian mantle at high temperature. Previous work on the CO2 solubility in synthetic Martian basalts based on the Humphrey Adirondack-class basalt showed that degassing of CO2 to the atmosphere may not be sufficient to create greenhouse conditions required by observations of liquid surface water (Stanley et al, 2011, GCA). However, solubilities are predicted to be greater for depolymerized melts similar to Y 980459, possibly allowing degassing of increased amounts of dissolved CO2 and a significant contribution of volcanogenic CO2 to an early Martian greenhouse.

A series of piston-cylinder experiments were performed at 1-2 GPa and 1600-1650 ºC in Fe-doped Pt capsules. CO2 contents in experimental glasses were determined using Fourier transform infrared spectroscopy (FTIR) and range from 0.45-1.26 wt.%. These are nearly identical to solubilities documented for Humphrey basalt and do not show enhanced solubility owing to depolymerization. Thus the experimentally-determined solubility of synthetic picritic shergottite basalts confirm that the Martian mantle is incapable of degassing sufficient CO2 to sustain a thick greenhouse atmosphere in the Late Noachian. Therefore, models of Martian atmospheric evolution considering only the greenhouse effects of CO2 should be reexamined and additional volatiles such as SO2 and CH4 should be considered.