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The Petrology and Geochemistry of Feldspathic Granulitic Breccia NWA 3163: Implications for the Lunar Crust
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Author and Affiliation:
McLeod, C. L.(Houston Univ., Dept. of Earth and Atmospheric Sciences, TX, United States);
Brandon, A. D.(Houston Univ., Dept. of Earth and Atmospheric Sciences, TX, United States);
Lapen, T. J.(Houston Univ., Dept. of Earth and Atmospheric Sciences, TX, United States);
Shafer, J. T.(Houston Univ., Dept. of Earth and Atmospheric Sciences, TX, United States);
Peslier, A. H.(Engineering and Science Contract Group, Houston, TX, United States);
Irvine, A. J.(Washington Univ., Dept. of Earth and Space Sciences, Seattle, WA, United States)
Abstract: Lunar meteorites are crucial to understand the Moon s geological history because, being samples of the lunar crust that have been ejected by random impact events, they potentially originate from areas outside the small regions of the lunar surface sampled by the Apollo and Luna missions. The Apollo and Luna sample sites are contained within the Procellarum KREEP Terrain (PKT, Jolliff et al., 2000), where KREEP refers to potassium, rare earth element, and phosphorus-rich lithologies. The KREEP-rich rocks in the PKT are thought to be derived from late-stage residual liquids after approx.95-99% crystallization of a lunar magma ocean (LMO). These are understood to represent late-stage liquids which were enriched in incompatible trace elements (ITE) relative to older rocks (Snyder et al., 1992). As a consequence, the PKT is a significant reservoir for Th and KREEP. However, the majority of the lunar surface is likely to be significantly more depleted in ITE (84%, Jolliff et al., 2000). Lunar meteorites that are low in KREEP and Th may thus sample regions distinct from the PKT and are therefore a valuable source of information regarding the composition of KREEP-poor lunar crust. Northwest Africa (NWA) 3163 is a thermally metamorphosed ferroan, feldspathic, granulitic breccia composed of igneous clasts with a bulk anorthositic, noritic bulk composition. It is relatively mafic (approx.5.8 wt.% FeO; approx.5 wt.% MgO) and has some of the lowest concentrations of ITEs (17ppm Ba) compared to the feldspathic lunar meteorite (FLM) and Apollo sample suites (Hudgins et al., 2011). Localized plagioclase melting and incipient melting of mafic minerals require localized peak shock pressures in excess of 45 GPa (Chen and El Goresy, 2000; Hiesinger and Head, 2006). NWA 3163, and paired samples NWA 4481 and 4883, have previously been interpreted to represent an annealed micro-breccia which was produced by burial metamorphism at depth in the ancient lunar crust (Fernandes et al., 2009). This is in contrast to the interpretation of Hudgins et al. (2009) where NWA 3163 was interpreted to have formed through contact metamorphism. To further constrain its origin, we examine the petrogenesis of NWA 3163 with a particular emphasis on in-situ measurement of trace elements within constituent minerals, Sm-Nd and Rb-Sr isotopic systematics on separated mineral fractions and petrogenetic modeling.
Publication Date: Jan 01, 2013
Document ID:
20130003579
(Acquired Jan 29, 2013)
Subject Category: LUNAR AND PLANETARY SCIENCE AND EXPLORATION
Report/Patent Number: JSC-CN-27801
Document Type: Conference Paper
Meeting Information: Lunar and Planetary Science Conference; 18-22 Mar. 2013; The Woodlands, TX; United States
Meeting Sponsor: Lunar and Planetary Inst.; Houston, TX, United States
Financial Sponsor: NASA Johnson Space Center; Houston, TX, United States
Organization Source: NASA Johnson Space Center; Houston, TX, United States
Description: 3p; In English; Original contains color illustrations
Distribution Limits: Unclassified; Publicly available; Unlimited
Rights: Copyright; Distribution under U.S. Government purpose rights
NASA Terms: METAMORPHISM (GEOLOGY); MINERALOGY; PETROLOGY; LUNAR CRUST; BRECCIA; LUNAR SURFACE; PETROGENESIS; ROCKS; TERRAIN; PHOSPHORUS; MINERALS
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