Water Storage Capacity Of The Martian Mantle Through Time

By Keith Cowing
June 1, 2022
Filed under
Water Storage Capacity Of The Martian Mantle Through Time
H2O storage capacity diagrams of Martian (a; model-averaged estimate from this study) and terrestrial (b; Dong et al., 2021) mantle assemblages 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. The thermodynamically-stable mantle assemblages were calculated for a bulk silicate Mars composition (Taylor, 2013) and a terrestrial depleted MORB mantle composition (Workman and Hart, 2005) using the thermodynamic code HeFESTo (Stixrude and Lithgow-Bertelloni, 2005, 2011). The anhydrous mantle solidi for Mars and Earth are from Duncan et al. (2018) and Herzberg et al. (2000), respectively. Mantle phases are labeled as: 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, primarily in nominally anhydrous minerals. The short-lived early hydrosphere and intermittently flowing water on the Martian surface may have been supplied and replenished by magmatic degassing of water from the mantle.

Estimating the water storage capacity of the solid Martian mantle places important constraints on its water inventory and helps elucidate the 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 from the literature, and we provide a quantitative estimate of the upper bound of the bulk water storage capacity in the FeO-rich solid Martian mantle.

Along a series of areotherms at different mantle potential temperatures (Tp), we estimated a water storage capacity equal to 9.0+2.8−2.2 km Global Equivalent Layer (GEL) for the present-day 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 through time, but due to the lack of an efficient water recycling mechanism on Mars, its actual mantle water content 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 supplementary materials, 14 figures, 13 tables; manuscript accepted for publication in Icarus
Subjects: Geophysics (physics.geo-ph); Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2205.15450 [physics.geo-ph] (or arXiv:2205.15450v1 [physics.geo-ph] for this version)
Submission history
From: Junjie Dong
[v1] Mon, 30 May 2022 22:17:14 UTC (9,863 KB)

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