H2O storage capacity diagrams of Martian (a; average model estimate of this study) and terrestrial (b; Dong et al., 2021) mantle assemblies between 3 and 22 GPa. The bulk H2O storage capacities at each P–T were estimated from the H2O storage capacities of the stable phases and their relative abundances. Thermodynamically stable mantle assemblages were calculated for a massive silicate Mars composition (Taylor, 2013) and a MORB-depleted Earth mantle composition (Workman and Hart, 2005) using the thermodynamic code HeFESTo (Stixrude and Lithgow-Bertelloni , 2005, 2011). Anhydrous mantle solids for Mars and Earth are from Duncan et al. (2018) and Herzberg et al. (2000), respectively. The mantle phases are labeled as follows: ol→olivine, wd→wadsleyite, rw→ringwoodite, fp→ferropericlase, cpx→clinopyroxene, opx→orthopyroxene, hpcpx→high pressure clinopyroxene, ak→akimotoite, st→stishovite and capv→CaSiO3 perovskite.
Water has been stored in the Martian mantle since its formation, mostly in nominally anhydrous minerals. The early, short-lived hydrosphere and intermittently flowing water on the Martian surface may have been fed and replenished by magmatic outgassing of mantle water.
Estimating the water storage capacity of the solid Martian mantle imposes important constraints on its water inventory and helps to elucidate sources, sinks and temporal variations of water on Mars. In this study, we applied a bootstrap aggregation method to investigate the effects of iron on water storage capacities in olivine, wadsleyite, and ringwoodite, based on high-pressure experimental data compiled at from the literature, and we provide a quantitative estimate of the upper bound. bulk water storage capacity in the FeO-rich solid Martian mantle.
Along a series of areotherms at different potential mantle temperatures (Tp), we estimated a water storage capacity equal to 9.0+2.8−2.2 km global equivalent layer (GEL) for the current Martian mantle at Tp = 1600 K and 4.9+1.7 -1.5 km GEL for the initial Martian mantle at Tp = 1900 K. The water storage capacity of the Martian mantle increases with secular cooling over time, but due to the lack of an efficient water recycling mechanism on Mars, its actual water content in the mantle may be significantly lower than its water storage capacity today.
Junjie Dong, Rebecca A. Fischer, Lars P. Stixrude, Carolina R. Lithgow-Bertelloni, Zachary T. Eriksen, Matthew C. Brennan
Comments: 52 pages including supplements, 14 figures, 13 tables; manuscript accepted for publication in Icarus
Subjects: Geophysics (physics.geo-ph); Terrestrial and planetary astrophysics (astro-ph.EP)
Cite as: arXiv:2205.15450 [physics.geo-ph] (or arXiv:2205.15450v1 [physics.geo-ph] for this version)
From: Junjie Dong
[v1] Mon, May 30, 2022 10:17:14 PM UTC (9,863 KB)
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