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 language | English |
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Article number | doi.org/10.1098/rsos.200236 |
Journal | Royal Society Open Science |
Volume | 7 |
Issue number | 6 |
Publication status | Accepted/In press - 22 May 2020 |
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Planetary Science
Gilmour, J., Joy, K., Lyon, I., Burgess, R., Jones, R., Tartese, R., Holland, G., Clay, P., Crowther, S., Pernet-Fisher, J., Ruzie, L., Assis Fernandes, V., MacArthur, J., Nottingham, M., Bell, S., Baker, E., Hartley, M., Neave, D., Snape, J. & Almayrac, M.
Project: Research