Experimental constraints on the solidification of a hydrous lunar magma ocean

1Yanhao Lin,2,3Hejiu Hui,4Xiaoping Xia,2Sheng Shang,1Wim van Westrenen
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13425]
1Department of Earth Sciences, Faculty of Science, Vrije Universiteit Amsterdam, De Boelelaan 1085, 1081 HV Amsterdam, the Netherlands
2State Key Laboratory for Mineral Deposits Research & Lunar and Planetary Science Institute, School of Earth Sciences and Engineering, Nanjing University, 163 Xianlin Dadao, Nanjing, 210023 China
3CAS Center for Excellence in Comparative Planetology, Hefei, 230026 China
4State Key Lab of Isotope Geochemistry, Guangzhou Institute of Geochemistry, CAS, No 511, Kehua Street, Tianhe District, Guangzhou, 510640 China
Published by arrangement with John Wiley & Sons

The identification of hydrogen in a range of lunar samples and the similarity of its abundance and isotopic composition with terrestrial values suggest that water could have been present in the Moon since its formation. To quantify the effect of water on early lunar differentiation, we present new analyses of a high‐pressure, high‐temperature experimental study designed to model the mineralogical and geochemical evolution of the solidification material equivalent to 700 km deep lunar magma oceans first reported in Lin et al. (2017a). We also performed additional experiments to better quantify water contents in the run products. Water contents in the melt phases in hydrous run products spanning a range of crystallization steps were quantified directly using a secondary ion mass spectrometry (SIMS). Results suggest that a significant but constant proportion (68 ± 5%) of the hydrogen originally added to the experiments was lost from the starting material independent of run conditions and run duration. The volume of plagioclase formed during our crystallization experiments can be combined with the measured water contents and the observed crustal thickness on the Moon to provide an updated lunar interior hygrometer. Our data suggest that at least 45–354 ppm H2O equivalent was present in the Moon at the time of crust formation. These estimates confirm the inference of Lin et al. (2017a) that the Moon was wet during its magma ocean stage, with corrected absolute water contents now comparable to estimates derived from the water content in a range of lunar samples.

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