Particular H 2 O dissolution mechanism in iron‐rich melt: Application to martian basaltic melt genesis

Martian basalts are different from Earth by their iron‐rich abundance with 18 wt% FeO tot in average for Mars upper crust. The H 2 O dissolution mechanism in this atypical melt composition is not well understood. We have synthesized H 2 O‐bearing martian basaltic glass analogs (10 < FeO tot < 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 H 2 O as well as the high FeO tot content on the molecular structure of Fe‐rich glasses. Increasing Fe content appears to inhibit the dissolution of H 2 O in the melt. In fact, it appears that Free OH groups are formed at relatively low H 2 O content in Fe‐rich melts (1 wt%), whereas they only appeared at high H 2 O content (~6.5 wt%) for Fe‐poor glasses. We suggest that the Free OH are bonded to Fe 2+ 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.