(U-Th)/He dating of Taki pseudotachylyte, Ryoke granites

Yamada, Kunimi; Takagi, Hideo*; Tagami, Takahiro*; Danhara, Toru*

Taki pseudotachylyte first found along the MTL was formed after mylonitization of the Hatai Tonalite under amphibolite to greenschist facies conditions, and had been post-dated by cataclasis. We dated some zircons from the mylonited Tonalite around the pseudotachylyte using the (U-Th)/He method, the age corresponds approximately to the FT ages of the pseudotachylyte, not the Tonalite. This suggests that the ambient temperature for generating the pseudotachylyte was higher than the closure temperature of ZHe, and this is consistent with cataclasis temperature. In this case we can not say the age of the pseudotachylyte, however, we can constrain something for the age and cooling-denudation history of this fault. Now we continue to date zircons from the pseudotachylyte.