Geology and tectonic evolution of the Palaeoproterozoic Bryah, Padbury and Yerrida Basins (formerly Glengarry Basin), Western Australia: implications for the history of the south-central Capricorn Orogen

Abstract

The Palaeoproterozoic Bryah, Padbury and Yerrida Basins are situated along the northwestern margin of the Archaean Yilgarn Craton, central Western Australia. These basins form part of the Capricorn Orogen, which developed between 2.0 and 1.8 Ga as a result of the collision between the Archaean Pilbara and Yilgarn cratons. The Bryah, Padbury and Yerrida Basins, which at the present day cover a total area of ca 20 000 km 2, were formerly considered as one geological entity, the Glengarry Basin. These three basins are characterized by distinct stratigraphy, igneous activity, structural and metamorphic history, and mineral deposit types. Igneous activity only affected the Bryah and Yerrida Basins, with voluminous eruptions of tholeiitic magma. In the Bryah Basin tholeiitic volcanic rocks are Mg-rich and have mixed MORB to oceanic island chemical signatures, but with a boninitic (subduction-related) component. In the Yerrida Basin tholeiites are Fe-rich and have chemical signatures that suggest a mixed tectonic environment ranging from oceanic to continental. It is considered possible that this tholeiitic magmatism is related to a mantle plume. Two models for the tectonic evolution of the Bryah, Padbury and Yerrida Basins are proposed: (1) the Bryah and Yerrida Basins were formed in a back-arc setting, whilst the Padbury Basin developed as a retro-arc foreland basin over the Bryah Basin; and/or (2) strike-slip transtension, during and following the Pilbara-Yilgarn collision, created the Bryah and Yerrida strike-slip pull-apart Basins. A change in regional stress regime resulted in the inversion of the basins and the development of a foreland basin in the northwest (Padbury Basin).