Formation age of lunar Lalande crater and its implications for the source region of the KREEP-rich meteorite Sayh al Uhaymir 169
Luyuan Xu, Le Qiao, Minggang Xie, Yunhua Wu
Icarus
In Press, Journal Pre-proof, Available online 2 July 2022
“Highlights
• Lalande crater is a Copernican crater with a formation age of 410 ± 20 Ma.
• The adjacent mare basalts unit has an Imbrian age of 3.8−0.06+0.04 Ga.
• Lalande crater is not likely the source region of the KREEP-rich meteorite Sayh al Uhaymir 169.
• The pre-existing craters heavily influence the age determination of Lalande crater, and the age determination using small crater populations should be treated with caution.”
“As the most KREEP-rich lunar sample, the Sayh al Uhaymir (SaU) 169 meteorite would provide more valuable information concerning the KREEP and early lunar evolution of the Moon if its source regions can be pinpointed. Previous studies proposed Lalande crater as the source region that corresponds to the impact event of ~2.8 Ga recorded in SaU 169, whereas this linkage is highly dependent on the age determination of the potential source crater. By counting craters superposed on the ejecta blankets of Lalande and modelling the burial process of these superposed craters by Lalande ejecta, we find that the crater statistics around Lalande is heavily influenced by the existing of pre-Lalande craters larger than ~170 m in diameter, which could lead to a largely overestimated age of Lalande crater. After taking this influence into consideration, we obtain that Lalande crater is a Copernican crater with a formation age of 410 ± 20 Ma, and the adjacent mare basalts unit has an Imbrian age of 3.8−0.06+0.04 Ga. The formation age of Lalande crater is inconsistent with any of the radio-isotopic ages recorded in SaU 169, indicating that Lalande crater is unlikely to be the source region of this lunar meteorite.”
