^1,2,3Mark C. Nottingham,⁴Finlay M. Stuart,⁴Biying Chen,⁴Marta Zurakowska,⁴Jamie D. Gilmour,^1,2Louise Alexander,^1,2Ian A. Crawford,³Katherine H. Joy
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13783]
¹Department of Earth and Planetary Science, Birkbeck College, University of London, Malet Street, London, WC1E 7HX UK
²The Centre for Planetary Sciences at UCL-Birkbeck, Gower Street, London, WC1E 6BT UK
³Department of Earth and Environmental Sciences, The University of Manchester, Oxford Road, Manchester, M13 9PL UK
⁴Isotope Geosciences Unit, Scottish Universities Environmental Research Centre (SUERC), East Kilbride, G75 0QF UK
Published by arrangement with John Wiley & Sons

We report the concentrations and isotope ratios of light noble gases (He, Ne, Ar) in 10 small basalt fragments derived from lunar regolith soils at the Apollo 12 landing site. We use cosmic ray exposure (CRE) and shielding condition histories to consider their geological context. We have devised a method of using cosmogenic Ne isotopes to partition the CRE history of each sample into two stages: a duration of “deep” burial (shielding of 5–500 g cm−2) and a duration of near-surface exposure (shielding of 0 g cm−2). Three samples show evidence of measurable exposure at the lunar surface (durations of between 6 ± 2 and 7 ± 2 Myr). The remaining seven samples show evidence of a surface residence duration of less than a few hundred thousand years prior to collection. One sample records a single-stage CRE age range of between 516 ± 36 and 1139 ± 121 Myr, within 0–5 g cm−2 of the lunar surface. This is consistent with derivation from ballistic sedimentation (i.e., local regolith reworking) during the Copernicus crater formation impact at ~800 Myr. The remaining samples show CRE age clusters around 124 ± 11 Myr and 188 ± 15 Myr. We infer that local impacts, including Surveyor crater (180–240 Ma) and Head crater (144 Ma), may have brought these samples to depths where the cosmic ray flux was intense enough to produce measurable cosmogenic Ne isotopes. More recent small impacts that formed unnamed craters may have exhumed these samples from their deep shielding conditions to the surface (i.e., ~0–5 g cm−2) prior to collection from the lunar surface during the Apollo 12 mission.

^1,2Yan Fan,¹Shijie Li,¹Shen Liu,³Hao Peng,⁴Guangming Song,⁵Thomas Smith
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13789]
¹State Key Laboratory of Continental Dynamics and Department of Geology, Northwest University, Xi’an, 710069 China
²Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, 550081 China
³Xi’an Astronautics Composite Materials Institute, Xian, 710025 China
⁴Beijing Institute of Spacecraft Environment Engineering, Beijing, 100094 China
⁵State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029 China
Published by arrangement with John Wiley & Sons

In recent years, numerous meteorites have been collected in desert areas in northern and western China. We describe the environment of some deserts in this region, and the petrological and mineralogical characteristics of 49 of the recovered ordinary chondrites. They consist of 14 H chondrites, 33 L chondrites, and 2 LL chondrites. Of the 300 desert meteorites with approved names from deserts in China, there have been 287 ordinary chondrites, six iron meteorites, one CO3 chondrite, one diogenite, one ureilite, one brachinite, one eucrite, and one EL7 chondrite. Forty-two dense meteorite collection areas (DCAs) have been defined, mainly located in northern and western China. The meteorites collected are mainly from the Kumtag DCA, followed by the Alatage Mountain, Loulan Yizhi, Hami, and Lop Nur DCAs. After tentative pairing of the meteorites, we estimate that the ordinary chondrites account for 72% of the desert meteorites collected in China, with 63 H chondrites, 133 L chondrites, and 20 LL chondrites. This dominance of L chondrites contrasts with other deserts, which may result from the insufficient collection or bias in pairing of ordinary chondrites. The mass distribution of meteorites from different DCAs in China is consistent with that from DCAs in Africa. Based on the available information and the meteorite flux model proposed by previous studies, we suggest that the time over which meteorites have been accumulated in the southern Hami DCA might be >10 kyr. Therefore, the southern Hami region is currently the most suitable area for meteorite collection in China.