PLUME-LIKE NEON IN A METASOMATIC APATITE FROM THE AUSTRALIAN LITHOSPHERIC MANTLE

The nature of metasomatizing fluids and melts in the mantle are of int erest for understanding the chemical evolution of the Earth's interior (1-3). The study of noble-gas isotopes in appropriate mantle-derived s amples has the potential to provide valuable insight into this questio n, by constraining the origin of the fluids and the timing of metasoma tic events. Here we report the application of neon-isotope systematics to investigate the metasomatic history of apatite grains in spinel-lh erzolite xenoliths from the Australian lithospheric mantle. We find th at the apatite has a neon-isotope signature similar to that associated with plume-related volcanism, as is found in Hawaii, whereas coexisti ng mineral phases (olivine and amphibole) and non-apatite-bearing Iher zolites have isotope signatures more typical of mid-ocean-ridge basalt s. The occurrence of plume-like neon in the apatite implicates deep pl ume-like material beneath southeastern Australia as the source of the metasomatizing agent.