Abstract

Numerous MORB-like mafic dykes, plugs and sills intruded the Kanmantoo Group and older meta-sediments of the southern Adelaide Fold Belt from pre-D1 to post-D2 during the Delamerian orogeny. A post-D2 meta-dolerite yields a precise U–Pb zircon age of 510 ± 2 Ma. This age, combined with a published SHRIMP zircon age of 526 ± 4 Ma, reveals a rapid tectonic evolution of the fold belt during the Cambrian: events including the thick Kanmantoo Group's deposition, major mafic magmatism, low-P/high-T regional metamorphism and multiple deformations all took place from about 526 to 510 Ma. This rapid evolution supports the suggestion that the heat source for the metamorphism originated from continental extension associated with mantle upwelling and mafic magmatism.

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