Neoarchean structural evolution of the Murchison Domain (Yilgarn Craton)

The progressive strengthening of the continental lithosphere triggered a secular transition in tectonic style during Neoarchean times, allowing the progressive establishment of Plate Tectonics on our planet. Structural investigations in Neoarchean cratons offer therefore a critical tool to constrain how such transition took place. The highly-mineralized Yilgarn Craton of Western Australia exposes one of the largest and best preserved portions of Archean continental crust worldwide. The Yilgarn crust was intensely deformed during the c. 2730-2650 Ma Neoarchean Yilgarn Orogeny, which was accompanied by widespread granitic magmatism, and was mostly unaffected by post-Archean pervasive tectonic events, representing therefore an ideal area for the study of Neoarchean tectono-magmatic events. Here, I combine new structural data with a re-examination of the recent regional structural literature, to offer an updated view of the structural evolution of the Murchison Domain, one of the best-exposed and mineralized portions of the Yilgarn Craton. The result is a new fourfold scheme for the structural evolution of the domain, supported by a detailed and structurally-controlled geochronological dataset. The preserved tectono-magmatic evolution of the domain started with a pre-orogenic period of dominant polydiapirism, during times of prevailing tectonic quiescence. This was followed by a sequence of orogenic deformation events that produced north-striking large-scale shear zones, along which syntectonic plutons, up to 100 km in size, were emplaced during three major tectonic pulses characterized by bulk east-west shortening, between 2730 and 2660 Ma. The deformation events identified here at the scale of the Murchison Domain are likely the local expression of Yilgarn-wide tectono-magmatic events, highlighting the importance of syntectonic granitic magmatism in shaping Neoarchean orogens.