Rb-Sr isotopic systematics of lherzolitic shergottite Yamato-793605

We have undertaken a Rb-Sr isotopic study of the lherzolitic shergottite, Yamato (Y)-793605. The acid-leaching experiment designed to remove secondary Pb contamination during previous work with U-Th-Pb systematics did not significantly affect the Rb-Sr systematics. A Rb-Sr internal isochron obtained for combined data of leachates and residues yielded an age of 173±14Ma with an initial ^Sr/^Sr ratio of 0.71042±0.00007,using λ (^Rb)=1.402×10^y^. The Rb-Sr age, initial ^Sr/^Sr ratio and trace element abundance pattern of Y-793605 are all similar to those of lherzolitic shergottites, ALH 77005 and LEW 88516. We favor the 173Ma age for the time of igneous crystallization, because this interpretation is more consistent with characteristics of both the isotopic systematics and mineral chemistry. A minor disturbance of U-Pb systems observed in residue fractions indicate that shock event(s) occurred more recently, without affecting Rb-Sr system