Zircon Inheritance Refines the Cambrian Orogenic Architecture of Southeast Australia

The Selwyn Block is one of the few accreted terranes identified in the vast Paleozoic Tasmanides of eastern Australia and its incorporation into this orogen marks a first-order event in the tectonic evolution of the Pacific margin of Gondwana. However, the age, composition, and paleogeography of the Selwyn Block are poorly understood because it is almost completely concealed in the middle and lower crust. The prevailing hypothesis suggests the Selwyn Block is a northern continuation of the Proterozoic Western Tasmania Terrane. We test this hypothesis by comparing inherited zircon U-Pb ages (n = 881) from early Paleozoic granitoids intruding the Selwyn Block and the Western Tasmania Terrane. Phase equilibria modelling confirms that typical Western Tasmania Terrane lithologies are melt-fertile and would have contributed inherited zircon grains to local granitoids. The inherited zircon age signature of granitoids in the Western Tasmania Terrane mirrors detrital zircon ages from local Proterozoic strata with age populations at ca. 1430 Ma and 1800--1600 Ma. In comparison, granitoids intruding the Selwyn Block have ca. 600--500 Ma and ca. 1200--900 Ma inherited zircon age populations, likely derived from local Paleozoic strata. Previously published wholerock radiogenic Sr isotopic data and new zircon radiogenic hafnium isotope data also imply distinct melt sources with granitoids intruding the Selwyn Block granitoids having lower initial 87Sr/86Sr and higher initial