TY - JOUR
T1 - Timing of geological events in the lunar highlands recorded in shocked zircon-bearing clasts from Apollo 16
AU - Joy, Katherine
AU - Snape, J F
AU - Nemchin, A A
AU - Tartese, Romain
AU - Martin, D M
AU - Whitehouse, M J
AU - Vishnyakov, V
AU - Pernet-Fisher, John
AU - Kring, D A
PY - 2020/5/22
Y1 - 2020/5/22
N2 - 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.
AB - 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.
M3 - Article
SN - 2054-5703
VL - 7
JO - Royal Society Open Science
JF - Royal Society Open Science
IS - 6
M1 - doi.org/10.1098/rsos.200236
ER -