Petrography, mineralogy, and geochemistry of a new lunar magnesian feldspathic meteorite Northwest Africa 11460

1Haijun Cao,1,2Zongcheng Ling,1Jian Chen,1,2,3Xiaohui Fu,4Yongliao Zou
Meteoritics & Planetary Science (in Press) Link to Article []
1Shandong Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, School of Space Science and Physics, Institute of Space Sciences, Shandong University, Weihai, Shandong, 264209 China
2CAS Center for Excellence in Comparative Planetology, Chinese Academy of Sciences, Hefei, China
3State Key Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology, Taipa, Macau, China
4State Key Laboratory of Space Weather, National Space Science Center, Chinese Academy of Sciences, Beijing, 100190 China
Published by arrangement with John Wiley & Sons

Lunar meteorite Northwest Africa (NWA) 11460 has been classified as a polymict breccia, composed of feldspathic clasts, mafic-rich clasts (gabbroic and troctolitic fragments), granulites, and a wide range of impact melt breccias and dimict breccias. The non-mare clasts have chemical affinities in major element composition to the Apollo ferroan anorthosites (FAN) and magnesian-suite plutonic rocks. In contrast, incompatible trace element (ITE) compositions of the Mg-richer clasts are more consistent with those of FANs rather than magnesian-suite rocks. NWA 11460 has a Mg-rich feldspathic bulk composition (FeO = 4.53 wt%, Al2O3 = 25.87 wt%, and Mg# = 73.8) and relatively ITE-poor (i.e., Th = 0.31 ppm and Sm = 0.65 ppm) characteristics. Feldspathic impact melt materials are approximately similar in composition to the estimated composition for the upper feldspathic lunar crust (as defined by Korotev et al., 2003). The ITE-poor and Mg-rich characteristics different from Apollo 16 feldspathic impact melts indicate that this meteorite has been possibly derived from a region distal to the nearside lunar highlands. Our analysis further suggests that NWA 11460 most likely originated from the farside of the Moon. Compositionally, Mg-rich ITE-poor clasts within NWA 11460 as well as those observed in other feldspathic lunar meteorites (which probably came from many different lunar regions) reveal that Mg-rich rocks with low-ITE components represent an important constituent of lunar crustal rocks. The diversities of highly magnesian non-mare clasts and the low-ITE chemistry provide geochemical clues for the genetic relationship between KREEP components and magnesian plutonic magmatism on the lunar farside.


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