NEODYMIUM ISOTOPIC CONSTRAINTS FOR THE ORIGIN OF MESOPROTEROZOIC FELSIC MAGMATISM, GAWLER-CRATON, SOUTH AUSTRALIA

Mesoproterozoic felsic magmatism of the Gawler Range Volcanics and Hil taba Suite granites occurred at 1585-1595 Ma across much of the Gawler Craton, South Australia. Nd isotopic analysis of this felsic magmatis m, combined with petrological and geochemical arguments, suggest deriv ation by partial melting of both Paleoproterozoic and Archean crust. T he majority of samples analyzed have Nd isotopic and geochemical chara cteristics compatible with the involvement of Paleoproterozoic crust s tabilized during the 1.85-1.71 Ga Kimban orogeny as sources for the Me soproterozoic magmatism; others require derivation from sources domina ted by Archean rocks. This cycle of Paleoproterozoic crustal stabiliza tion followed by involvement of this crust Mesoproterozoic felsic magm atism is one previously documented from many parts of Mesoproterozoic Laurentia. On the basis of models proposing East Australia - Antarctic a to be the conjugate landmass at the rifted margin of western North A merica, it appears that the voluminous magmatism of South Australia is another example of a typically Mesoproterozoic style of magmatism lin ked to Laurentia. This Mesoproterozoic magmatism appears temporally Li nked to regional high-temperature, low-pressure metamorphism of the re gion, and together with the presence of mantle-derived magmas, implica tes the operation of large-scale tectonothermal processes in the origi n of felsic magmatism at 1590 Ma.