AN ISOTOPIC PERSPECTIVE ON GROWTH AND DIFFERENTIATION OF PROTEROZOIC OROGENIC CRUST: FROM SUBDUCTION MAGMATISM TO CRATONIZATION

The in situ chemical differentiation of continental crust ultimately leads to the long-term stability of the continents. This process, more commonly known as ‘cratonization’, is driven by deep crustal melting with the transfer of melts to shallower regions resulting in a strongly chemically stratified crust, with a refractory, dehydrated lower portion overlain by a complementary enriched upper portion. Since the lower to mid portions of continental crust are rarely exposed, investigation of the cratonization process must be through indirect methods. In this study we report in situ Hf and O isotope compositions of both magmatic and inherited zircons from several well-dated felsic magmatic suites in the Capricorn Orogen of Western Australia to highlight the differentiation history (i.e. cratonization) of this portion of late Archean to Proterozoic orogenic crust. The Capricorn Orogen shows a distinct tectonomagmatic history that evolves from an active continental margin through to intraplate reworking, ultimately leading to thermally stable crust that responds similarly to the adjacent Archean Pilbara and Yilgarn Cratons. The data define not only the source components from which the magmas were derived, but a range of physical and chemical processes that operated during magma transport and emplacement. These data also identify a previously unknown crustal reservoir in the Capricorn Orogen that may represent the remnants of an Ophthalmian-aged magmatic arc.