Mass Spectrometry
Online ISSN : 2186-5116
Print ISSN : 2187-137X
ISSN-L : 2186-5116
Original Article
Uranium–Lead Systematics of Lunar Basaltic Meteorite Northwest Africa 2977
Narumi MoromotoYosuke Kawai Kentaro TeradaMasaaki MiyaharaNaoto TakahataYuji SanoNaoko FujikawaMahesh Anand
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2023 Volume 12 Issue 1 Pages A0115

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Abstract

Northwest Africa (NWA) 2977 is a lunar basaltic meteorite that was found in 2005 and has been classified as an olivine cumulate gabbro. This meteorite contains a shock melt vein (SMV) induced by an intense shock event. We report herein on an in-situ analysis of phosphates in the host gabbro and the shock vein for the U–Pb dating of NWA 2977 using an ion microprobe, NanoSIMS. The majority of the analyzed phosphates, in both the SMV and host-rock, lie on a linear regression in 238U/206Pb–207Pb/206Pb–204Pb/206Pb three-dimensional space, indicating a total Pb/U isochron age of 3.15±0.12 Ga (95% confidence level), which is consistent ages determined in previous isotopic studies of NWA 2977 (Sm–Nd age of 3.10±0.05 Ga, Rb–Sr age of 3.29±0.11 Ga, and Pb–Pb baddeleyite age of 3.12±0.01 Ga), and identical to the age of the U–Pb phosphate in a paired meteorite NWA 773, 3.09±0.20 Ga, derived from our dataset. There was no clear difference in the formation age between the phosphates found in the SMV and host-rock, although the shape and size of the grains and the Raman spectra show the evidence of intense shock metamorphism. Based on these findings, the cooling rate of the phosphate was very rapid, constrained to be larger than 140 K/s.

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© 2023 Narumi Moromoto, Yosuke Kawai, Kentaro Terada, Masaaki Miyahara, Naoto Takahata, Yuji Sano, Naoko Fujikawa, and Mahesh Anand. This is an open-access article distributed under the terms of Creative Commons Attribution Non-Commercial 4.0 International License, which permits use, distribution, and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.

This article is licensed under a Creative Commons [Attribution-NonCommercial 4.0 International] license.
https://creativecommons.org/licenses/by-nc/4.0/
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