Martian meteorite Tissint records unique petrogenesis among the depleted shergottites

Tissint, a new unaltered piece of Martian volcanic materials, is the most silica-poor and Mg-Fe-rich igneous rock among the depleted olivine-phyric shergottites. Fe-Mg zoning of olivine suggests equilibrium growth (<0.1 degrees Ch(-1)) in the range of Fo(80-56) and olivine overgrowth (Fo(55-18)) through a process of rapid disequilibrium (similar to 1.0-5.0 degrees Ch(-1)). The spatially extended (up to 600 m) flat-top Fe-Mg profiles of olivine indicates that the early-stage cooling rate of Tissint was slower than the other shergottites. The chemically metastable outer rim of olivine (