Timing of geological events in the lunar highlands recorded in shocked zircon-bearing clasts from Apollo 16

Katherine Joy, J F Snape, A A Nemchin, Romain Tartese, D M Martin, M J Whitehouse, V Vishnyakov, John Pernet-Fisher, D A Kring

Research output: Contribution to journalArticlepeer-review

Abstract

Apollo 16 soil-like regolith breccia 65745,7 contains two zircon-bearing clasts. One of these clasts is a thermally annealed silica-rich rock, which mineralogically has affinities with the High Alkali Suite (Clast 1), and yields zircon dates ranging from 4.08 Ga to 3.38 Ga. The other clast is a KREEP-rich impact melt breccia (Clast 2) and yields zircon dates ranging from 3.97 to 3.91 Ga. The crystalline cores of both grains, which yield dates of ca. ~ 3.9 Ga, have undergone shock pressure modification at <20 GPa. We interpret that the U-Pb chronometer in these zircon grains have been partially reset by the Imbrium basin-forming event when the clasts were incorporated into the Cayley Plains ejecta blanket deposit. The zircon grains in Clast 1 have been partially decomposed, resulting in a break-down polymineralic texture, with elevated U, Pb and Th abundances compared with those in the crystalline zircon. These decomposed areas exhibit younger dates around 3.4 Ga, suggesting a secondary high-pressure, high-temperature event, likely caused by an impact in the local Apollo 16 highlands area.
Original languageEnglish
Article numberdoi.org/10.1098/rsos.200236
JournalRoyal Society Open Science
Volume7
Issue number6
Publication statusAccepted/In press - 22 May 2020

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