Particular H2O dissolution mechanism in iron‐rich melt: Application to martian basaltic melt genesis

Abstract

AbstractMartian basalts are different from Earth by their iron‐rich abundance with 18 wt% FeOtot in average for Mars upper crust. The H2O dissolution mechanism in this atypical melt composition is not well understood. We have synthesized H2O‐bearing martian basaltic glass analogs (10 < FeOtot < 16 wt%) under high pressures (0.5–1.5 GPa) and temperatures (>1500°C) conditions. We used Raman and Fourier transform infrared spectroscopies to investigate the effect of H2O as well as the high FeOtot content on the molecular structure of Fe‐rich glasses. Increasing Fe content appears to inhibit the dissolution of H2O in the melt. In fact, it appears that Free OH groups are formed at relatively low H2O content in Fe‐rich melts (1 wt%), whereas they only appeared at high H2O content (~6.5 wt%) for Fe‐poor glasses. We suggest that the Free OH are bonded to Fe2+ cations in the melt forming isolating clusters of Fe (OH)2. Such configurations are suspected to induce an increase in the melt polymerization. The presence of free hydroxyls dissolved in the melt is likely to have a major impact on the genesis of aqueous fluid phase at the surface of Mars.