An example of a Palaeoproterozoic back-arc basin: Petrology and geochemistry of the ca. 1864 Ma Stubbins Formation as an aid towards an improved understanding of the Granites–Tanami Orogen, Western Australia

The Palaeoproterozoic Stubbins Formation is a newly defined succession of turbiditic and pelagic sedimentary rocks interbedded with volcanic and abundant dolerite sills. Based on preliminary SHRIMP U–Pb data from various parts of the Stubbins Formation, the age of the formation is ca. 1864 Ma, which is about 30 million years older than that interpreted for other successions included in the Granites–Tanami Orogen of Western Australia and the Northern Territory. A study of the geochemistry of dolerite and spatially restricted basalt from the top 200 m of the Stubbins Formation indicates that these rocks: (1) have tholeiitic to calc-alkaline affinities; (2) are related to the same magmatic events; and (3) based on comparisons with modern analogues, were deposited in a back-arc basin to island-arc setting between the Halls Creek and Arunta Orogens. Deposition in the basin ceased during compressional (collisional) deformation about 1850 Ma. This was followed by collisional tectonics at ca. 1800 Ma, which is associated with orogenic lode-gold deposits in the region.