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

K H Joy; J F Snape; A A Nemchin; R Tartèse; D M Martin; M J Whitehouse; V Vishnyakov; J F Pernet-Fisher; D A Kring

doi:10.1098/rsos.200236

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

R Soc Open Sci. 2020 Jun 3;7(6):200236. doi: 10.1098/rsos.200236. eCollection 2020 Jun.

Authors

K H Joy¹, J F Snape², A A Nemchin^{2

3}, R Tartèse¹, D M Martin⁴, M J Whitehouse², V Vishnyakov⁵, J F Pernet-Fisher¹, D A Kring⁶

Affiliations

¹ Department of Earth and Environmental Sciences, School of Natural Sciences, The University of Manchester, Manchester, UK.
² Department of Geosciences, Swedish Museum of Natural History, Stockholm, Sweden.
³ Department of Applied Geology, Curtin University, Perth, Australia.
⁴ European Centre for Satellite Applications and Telecommunications (ECSAT), European Space Agency, Fermi Avenue, Harwell Campus, Didcot, Oxfordshire OX11 0FD, UK.
⁵ School of Computing and Engineering, University of Huddersfield, Huddersfield, UK.
⁶ Center for Lunar Science and Exploration, Lunar and Planetary Institute, Universities Space Research Association, Houston, TX 77058, USA.

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 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 less than 20 GPa. We interpret that the U-Pb chronometer in these zircon grains has 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 breakdown 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, probably caused by an impact in the local Apollo 16 highlands area.

Keywords: Apollo 16; Pb-Pb age dating; lunar samples; regolith breccias; shock-zircon; zircon.

Associated data

figshare/10.6084/m9.figshare.c.5001047