[P-PS05] Lunar science and exploration

[PPS05-08] Chronological consideration of Luna 24 regolith sample by in-situ U-Pb analysis

*Narumi Moromoto¹, Kentaro Terada¹, Shoichiro Yokota^1,6, Yosuke Kawai¹, Tomomi Hashiguchi¹, Takahiro Matsuda¹, Yuji Sano², Takanori Kagoshima², Naoto Takahata², Masaaki Miyahara³, Norimasa Shimobayashi⁴, Eric Galimov⁵ (1.Department of Earth and Space Science, Graduate School of Science, Osaka University, 2.Atmosphere and Ocean Research Institute, the University of Tokyo, 3.Department of Earth and Planetary Systems Science, Graduate School of Science, Hiroshima University, 4.Kyoto University Graduate School of Science, 5.Vernadsky Institute of Geochemistry and Analytical Chemistry of the Russian Academy of Science, 6.Japan Aerospace Exploration Agency Institute of Space and Astronautical Science)

Keywords:Luna 24, in-situ U-Pb analysis, NanoSIMS

In 1976, Luna 24 spacecraft landed in Mare Crisium and collected regolith samples with total weight of 170 grams by drilling. So far, LUNA 24 samples have been classified into Very-Low-Ti (VLT) basalt, and thermal activity at 2.9 Ga ago has been reported, which is the the youngest among the collected lunar rocks/soils. However, it should be taken into account that individual grains of regolith have a different origin. Moreover, late impact events might have disturbed the radiometric age, making the age younger apparently. Therefore, in order to decipher the precise history of VLT magmatism, comprehensive studies on both mineralogical description and the high-spacial resolution U-Pb dating are required, which is resist to secondary events. At the meeting, we will report on the characterization of LUNA 24 regolith collected from Mare Crisium and its in-situ U-Pb ages. Most of Ca-phosphates shows U-Pb crystallization age of about 3.5 Ga, which is older than those of previous studies, and some Ca-phosphates show disturbance of U-Pb system possibly due to secondary event. Also, some grains shows different age and chemical composition, which might derive from highland of the Moon. We also compare these results with the remote-sensing data obtained the lunar orbiters (chemical composition and the crater chronology).