Palaeoproterozoic accretion processes of Australia and comparisons with Laurentia

摘要

The Palaeoproterozoic rocks of Australia and Laurentia preserve an excellent record of the accretionary tectonics associated with transitions between the Columbia (Nuna) and Rodinia supercontinents. The geologic records of Australia and Laurentia suggest that the dominant tectonic driver was one or more subduction zones in which several episodes of crustal accretion occurred between ca. 1790 Ma and 1620 Ma. Correlated orogenic events include the ca. 1800–1780 Ma Yapungku–Yambah (Australia)–Medicine Bow (Laurentia) orogenies, ca. 1740–1690 Ma Strangways–Kimban (Australia)–Nimrod (Antarctica)–Yavapai (Laurentia) orogenies, and the ca. 1650–1620 Ma Leibig–Ooldea (Australia)–Mazatzal (Laurentia) orogenies. There are major differences in the style of accretion: Laurentia is characterized by accretion of dominantly juvenile arc terranes, whereas accreted Australian terranes are more evolved and are isotopically similar to the continental nucleus. Adjacent to its plate margin, the Australian continent contained regions of elevated heat production compared with the Laurentian margin. Brace-Goetze lithospheric strength models for ca. 1700 Ma indicate that the Australian plate margin was significantly weaker than that of Laurentia. This variation in lithospheric strength is interpreted to impact the behaviour of the overriding plate during subduction roll back. Attenuation of the Australian lithosphere during ductile extension caused rifting of large continental fragments from the plate margin. Their subsequent accretion resulted in the re-amalgamation of pre-existing continental lithosphere similar to the lithosphere in the overriding plate. Subduction roll back adjacent to the cold and rigid Laurentian margin (e.g. the Wyoming Craton) had relatively little impact on the overriding plate, with oceanic back-arc basins and juvenile arc terranes developing outboard of the plate margin. Inversion of these arc and oceanic back-arc terranes resulted in episodic continental growth.