E.S. Michlovich, S.F. Wolf, M.S. Wang, S. Vogt, D. Elmore, M.E. Lipschutz

We report 36Cl (301-kyr half-life) data obtained by accelerator mass spectrometry allowing nominal terrestrial ages to be determined for 39 Antarctic H4-6 chondrites for which contents of volatile trace elements are known. The compositional difference between these Antarctic meteorites and 58 non-Antarctic falls increases with terrestrial age and, using multivariate statistical techniques, becomes highly significant for Antarctic samples with ages >50 kyr. The compositional difference is inconsistent with trivial causes such as weathering and seems to reflect differences in thermal histories of parent sources. Temporal source variations for the H chondrite flux on Earth thus exist not only on a short-term 40 years, basis (Dodd et al., 1993) but also on a long term, >50 kyr, basis.