Constraints on the formation of carbonates and low‐grade metamorphic phases in the Martian crust as a function of H₂O‐CO₂ fluids

Abstract

Low-grade metamorphic hydrous minerals and carbonates occur in various settings on Mars and in Martian meteorites. We present constraints on the stability of prehnite, zeolites, serpentine, and carbonates by modeling the influence of H 2 O-CO 2 fluids during low-grade metamorphism in the Martian crust using compositions of a Martian basalt and an ultramafic cumulate. In basaltic compositions with 5 wt% fluid, our models predict prehnite in less oxidized, CO 2 -poor conditions (≤0.44 mol kg À1 CO 2 ) on warmer geotherms of 20 °C km À1 . At fluid-saturated conditions, epidote and laumontite are replaced by quartz, calcite, chlorite, and muscovite. In ultramafic compositions with 5 wt% fluid, antigorite (serpentine) is stable at CO 2 -poor conditions of ≤0.33 mol kg À1 , while talc forms at 0.05-0.56 mol kg À1 CO 2 . At fluid-saturated conditions, antigorite is replaced by talc and chlorite, and at higher X(CO 2 ) by magnesite and quartz. Our models therefore suggest that prehnite, zeolites, and serpentine have formed in a CO 2 -poor environment on Mars implying that fluids during their formation either did not contain high amounts of CO 2 or had degassed CO 2 . Carbonates and potentially talc would have formed in the presence of a CO 2 -bearing fluid and therefore at different alteration stages than for prehnite, zeolites, and serpentine either in the same hydrothermal event during which the fluid composition changed gradually due to cooling and precipitation or by separate and successive alteration events with fluids of different compositions.

Recycled carbonates elevate the electrical conductivity of deeply subducting eclogite in the Earth’s interior

“…A part of them was devolatilized or stagnated at relatively shallower depths (~50 km in the hot subduction zone and ~100 km in the cold subduction zone), while the residual carbonates was sequestrated in the eclogitic slab into deep mantle further. Decarbonation (metamorphism, carbonate dissolved 5,6 , and carbonate molten 4,[7][8][9] ), carbonate stagnation, and carbonates deep subduction decide the deep Earth carbon cycling paths and flux as a research hotspot in the last decade [1][2][3][4]6,[8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] . Until now, details of these procedures are still exploring constantly.…”