Petrogenesis of the St Peter Suite, southern Australia: Arc magmatism and Proterozoic crustal growth of the South Australian Craton

The Palaeoproterozoic ca. 1620–1608 Ma St Peter Suite, located in the central Gawler Craton, South Australia comprises mafic to felsic magmatic rocks. The intermediate to felsic calc-alkaline magmatic component, preserves geochemical characteristics reminiscent of subduction-related arc magmatism. The calc-alkaline magmas are enriched in large ion lithophile elements (LILE), depleted in Nb and Ti, and have moderately evolved to relatively juvenile initial Neodymium isotopic signatures (ɛNd(1620): −0.8 to +3.7). These geochemical and isotopic characteristics are comparable to other documented Proterozoic subduction-related magmatic rock suites (e.g. those in Laurentia, Baltica, central and western Australia). We propose that the St Peter Suite preserves evidence of arc magmatism and relatively juvenile crustal growth on the southern margin of Australia. At ca. 1608 Ma, subduction ceased and migrated to the present-day north as a result of collision of the Archaean Gawler nuclei with the St Peter Suite magmatic arc terrane. This interpreted collision formed part of a broader margin incorporating the development of ca. 1590–1550 Ma arc rocks in the Musgrave Province in central southern Australia. This interpreted setting situates the voluminous ca. 1595–1575 Ma Gawler Range Volcanics and Hiltaba Suite in a back-arc environment, consistent with other Proterozoic granite–rhyolite terranes of the Laurentian Margin and Baltic Shield, which are interpreted to represent an inboard expression of subduction-related convergent margin processes.