The Solidus and Melt Productivity of Nominally Anhydrous Martian Mantle Constrained by New High Pressure‐Temperature Experiments—Implications for Crustal Production and Mantle Source Evolution. Issue 4 (18th April 2020)

• Record Type: Journal Article
• Authors: Ding, Shuo; Dasgupta, Rajdeep; Tsuno, Kyusei
• Is Part Of: Journal of geophysical research. Volume 125:Issue 4(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-04-18
• Subjects: Martian mantle solidus -- effect of bulk Mg# and total alkali on the mantle solidus of Mars -- decompression melting -- crust production on Mars; Planets -- Periodicals; Geophysics -- Periodicals; 559.9
• DOI: 10.1029/2019JE006078
• Languages: English
• ISSNs: 2169-9097

Abstract

Abstract: We constrained the solidus of a model Martian composition with low bulk Mg# (molar MgO/(MgO + FeOT ) × 100 ~75) and high total alkali (Na2 O + K2 O = 1.09 wt.%) concentration at 2 to 5 GPa by experiments. Based on the new solidus brackets, we provide a new parameterization of the solidus temperature as a function of pressure of Martian mantle: T s (° C ) = − 5 P ( GPa ) 2 + 107 P ( GPa ) + 1, 068. The newly constrained solidus of the Lodders and Fegley (1997; https://doi.org/10.1006/icar.1996.5653 ) model Martian composition (LF composition) is 20 to 90 °C lower than the previous solidus of model Martian mantle with lower total alkali (~0.54 wt.%). The supersolidus experiments yield an average isobaric melt productivity, d F /d T, of 20 ± 6 wt.%/100 °C. We also bracketed the solidi of model Martian mantle compositions with low Mg# (~75) and low alkali (~0.54 wt.%), and with high Mg# (~80) and low alkali (~0.54 wt.%) at a constant pressure of 3 GPa. We find that bulk Mg# enhances the solidus temperature and bulk total alkalis suppress it. A parameterization that estimates the effect of bulk Mg# and total alkalis on peridotite solidus, including Mars and Earth, at 3 GPa can be described as: Ts (°C) = 4.23Mg # − 85(Na2 O(wt. %) + K2 O(wt. %)) + 1, 120. Based on the new solidus parameterizations, 10–40 km more Martian crust would be produced by columnar decompression melting for LF model composition compared to the low Mg#‐low alkali model composition. The quantitative constraints on the solidus shift with Mg# and total alkalis from this study can be used to assess the Martian mantle solidus change through melting and melt extraction over time and the role of mantle heterogeneity in crustal production. Plain Language Summary: Mantle solidus at a given pressure is the temperature at which the rocky planet's mantle starts to melt and generate magmas. The location of the solidus of dry Martian mantle is the most critical information required to understand the magma generation on Mars, affecting both the thickness and composition of Martian crust. We constrained the solidus of a dry Martian mantle at the depth range between 100 and 400 km using high‐pressure, high‐temperature experiments. We also investigated the effect of composition of Martian mantle on the solidus and the near‐solidus melt productivity. Based on the experimental results, we provide equations to calculate the mantle solidus temperature as a function of pressure and mantle composition, respectively. Our results are used to estimate crustal thickness on a Martian mantle melting column. Our data can be used to predict how the mantle solidus and melt productivity changed through time for differentiation in a single plate planet without crustal recycling. Key Points: We constrained the solidus of a model Martian composition with low bulk Mg# and high total alkalis We developed a parameterization to estimate the effect of bulk Mg# and total alkalis on peridotite solidus We calculated the initial melting depths and crustal thickness on Mars with different Martian mantle compositions