Volatile-rich mantle beneath eastern Australia

Evidence for the geochemical characteristics of mantle metasomatism in eastern Australia is provided by primitive magma compositions and by mantle-derived xenoliths. Trace-element and isotopic compositions of the magmas indicate definable heterogeneous mantle domains on cm, km, and 50 km scales. High ⁸⁷Sr/⁸⁶Sr values in the basaltic rocks correlate with the presence of amphibole + or - mica + or - apatite in deep-seated xenoliths entrained in these or associated host rocks in the same province. The xenoliths may also contain fluid inclusions which reflect the composition of trapped mantle fluid phases. Both isotopic data and xenolith microstructures suggest that repetitive, discrete episodes of mantle metasomatism have occurred throughout the evolution of the eastern Australian lithosphere. Therefore the timing of mantle metasomatism relative to a given volcanic episode is variable. -J.M.H.