Geochemical evidence from Lower Permian volcanic rocks of northeast New South Wales for asthenospheric upwelling following slab breakoff
The ca 280 Ma Alum Mountain Volcanics and Werrie Basalt were erupted in northeast New South Wales, Australia, during Early Permian lithospheric extension that separated discrete episodes of subduction of Carboniferous and Late Permian — Triassic age. The Alum Mountain rocks, which are preserved in two major synclines in the southeast Tamworth Belt, are mostly basalt, but andesite and rhyolite are also present. The Werrie Basalt found further north in the Tamworth Belt and in the floor of the Gunnedah Basin is composed mainly of basalt, but includes more evolved rocks in the vicinity of several eruptive centres. The Alum Mountain rocks have REE abundances similar to N‐MORB, with flat REE patterns, (La/Sm) N ratios ranging from 0.54 to 1.07, and (La/Yb) N ratios from 0.94 to 2.78, suggesting an origin by large degrees of partial melting of asthenosphere at a depth
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