Chemical studies of H chondrites: 5. Temporal variations of sources

Abstract

We report 36 Cl (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.