Pre‐ to syn‐tectonic emplacement of early Palaeozoic granites in southeastern South Australia

Abstract

Abstract Stratigraphic and structural observations indicate that the Encounter Bay Granites concordantly intruded the youngest formations of the Kanmantoo Group in the Mount Lofty Ranges metamorphic belt prior to the culmination of the first phase of folding and associated schistosity development recorded during the early Palaeozoic Delamerian Orogeny. Metamorphic textures in the metasediments of the Kanmantoo Group suggest that cordierite crystallized locally near the granites prior to and during the F 1 folding, whereas andalusite crystallized on a regional scale during the F 1 folding and in the post‐F 1 and pre‐F 2 static phase. Rb‐Sr isotope data for total‐rock, feldspar, and muscovite samples of the meta‐sediment‐contaminated border facies and the uncontaminated inner facies of the Encounter Bay Granites indicate that the granites were emplaced between 515 ± 8 m.y. and 506 ± 6 m.y. ago in the Late Cambrian epoch. Rb‐Sr and K‐Ar data for biotite from the granites record variable radiogenic Sr loss un...