Affiliation:
1. Lunar and Planetary Institute, 3600 Bay Area Boulevard, Houston, Texas 77058, U.S.A.
2. AstrobiologyOU, School of Environment, Earth and Ecosystem Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, U.K.
Abstract
Abstract
A centimeter-sized fragment of dunite, the first recognized fragment of Moon mantle material, has been discovered in the lunar highlands breccia meteorite Northwest Africa (NWA) 11421. The dunite consists of 95% olivine (Fo83), with low-Ca and high-Ca pyroxenes, plagioclase, and chrome spinel. Mineral compositions vary little across the clast and are consistent with chemical equilibration. Mineral thermobarometry implies that the dunite equilibrated at 980 ± 20 °C and 0.4 ± 0.1 gigapascal (GPa) pressure. The pressure at the base of the Moon’s crust (density 2550 kg/m3) is 0.14–0.18 GPa, so the dunite equilibrated well into the Moon’s upper mantle. Assuming a mantle density of 3400 kg/m3, the dunite equilibrated at a depth of 88 ± 22 km. Its temperature and depth of equilibration are consistent with the calculated present-day selenotherm (i.e., lunar geotherm).
The dunite’s composition, calculated from mineral analyses and proportions, contains less Al, Ti, etc., than chondritic material, implying that it is of a differentiated mantle (including cumulates from a lunar magma ocean). The absence of phases containing P, Zr, etc., suggests minimal involvement of a KREEP component, and the low proportion of Ti suggests minimal interaction with late melt fractionates from a lunar magma ocean. The Mg/Fe ratio of the dunite (Fo83) is significantly lower than models of an overturned unmixed mantle would suggest, but is consistent with estimates of the bulk composition of the Moon’s mantle.
Publisher
Mineralogical Society of America
Subject
Geochemistry and Petrology,Geophysics
Reference108 articles.
1. Mineralogical study of new lunar meteorite Yamato 981031;Arai;Lunar and Planetary Science Conference 33rd,2002
2. Spinel cataclasites in 15445 and 72435—Petrology and criteria for equilibrium;Baker;Lunar and Planetary Science Conference Proceedings,1980
3. Introduction to Metamorphic Textures and Microstructures;Barker,2013
4. Lunar meteorite Northwest Africa 11962: A regolith breccia containing records of titanium-rich lunar volcanism and the high alkali suite;Bechtold;Meteoritics & Planetary Science,2021
5. The problem of the origin of symplectites in olivine-beating lunar rocks;Bell,1975
Cited by
1 articles.
订阅此论文施引文献
订阅此论文施引文献,注册后可以免费订阅5篇论文的施引文献,订阅后可以查看论文全部施引文献