Complex burial histories of Apollo 12 basaltic soil grains derived from cosmogenic noble gases: Implications for local regolith evolution and future in situ investigations

Nottingham, M. C., Stuart, F. M. , Chen, B., Zurakowska, M., Gilmour, J. D., Alexander, L., Crawford, I. A. and Joy, K. H. (2022) Complex burial histories of Apollo 12 basaltic soil grains derived from cosmogenic noble gases: Implications for local regolith evolution and future in situ investigations. Meteoritics and Planetary Science, 57(3), pp. 603-634. (doi: 10.1111/maps.13783)

Abstract

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.

• Item Type: Articles
• Additional Information: MCN, LA, IAC, and KHJ thank the Leverhulme Trust for financial support (RPG-2015-020 and RPG-2019-222). KHJ acknowledges funding from Royal Society grants RS/UF140190 and URF\R \201009, and KHJ and JDG acknowledge STFC grants ST/R000751/1 and ST/V000675/1.
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Zurakowska, Dr Marta and CHEN, BIYING and Stuart, Professor Fin
• Authors: Nottingham, M. C., Stuart, F. M., Chen, B., Zurakowska, M., Gilmour, J. D., Alexander, L., Crawford, I. A., and Joy, K. H.
• College/School: College of Science and Engineering > Scottish Universities Environmental Research Centre
• Journal Name: Meteoritics and Planetary Science
• Publisher: Wiley
• ISSN: 1086-9379
• ISSN (Online): 1945-5100
• Published Online: 07 February 2022
• Copyright Holders: Copyright © 2022 The Authors
• First Published: First published in Meteoritics and Planetary Science 57(3): 603-634
• Publisher Policy: Reproduced under a Creative Commons licence