R5: Extraterrestrial materials

[R5-11] Shock history of Northwest Africa 2139 LL6 chondrite

*Atsushi Takenouchi¹, Hirochika Sumino², Karin Shimodate², Keisuke Nagao², Akira Yamaguchi^1,3 (1. NIPR, 2. The Univ. of Tokyo, 3. SOKENDAI)

Keywords:Shock history, Ordinary Chondrite, Ar-Ar age, I-Xe age

We observed highly shocked LL6 chondrite Northwest Africa 2139 and measured its noble gas ages. Our results indicate that there was a shock event before 4.5 Ga with strong annealing, which is similar to H chondrites. Moreover, this meteorite experienced at least other two shock events inducing two distinct shock veins. Compared with the above three shock events, collisional events could become weakened or less frequently occur because accompanied annealing effects became weaker as time goes on.