129Xe-128Xe and 40Ar-39Ar chronology of two Antarctic enstatite meteorites

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^<129>(Xe)-^<128>(Xe) and ^<40>(Ar)-^<39>(Ar) analyses have been performed on two Antarctic enstatite meteorites, the chondrite Y-691 and the aubrite (enstatite achondrite) ALH-78113. Both meteorites have complex ^<40>(Ar)-^<39>(Ar) release patterns to which no unambiguous age assignment is possible. Both give apparently satisfactory ^<129>(Xe)-^<128>(Xe) correlations corresponding to unusual ages. The I-Xe age of the chondrite Y-691 is 16 Ma after Bjurbole, not unusual for chondrites in general but 10Ma later than previously known ages for enstatite chondrites. The I-Xe age of the aubrite ALH-78113 is 210Ma after Bjurbole, the latest age (rather than a limit) so far observed by the I-Xe technique, but this age assignment must be considered tentative because of the possibility that it is significantly influenced by terrestrial I contamination.
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