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

The Palaeoproterozoic Bryah, Padbury and Yerrida Basins are situated a long the northwestern margin of the Archaean Yilgarn Craton, central W estern Australia. These basins form part of the Capricorn Orogen, whic h developed between 2.0 and 1.8 Ga as a result of the collision betwee n the Archaean Pilbara and Yilgarn cratons. The Bryah, Padbury and Yer rida Basins, which at the present day cover a total area of ca 20 000 km(2), were formerly considered as one geological entity, the Glengarr y Basin. These three basins are characterized by distinct stratigraphy , igneous activity, structural and metamorphic history, and mineral de posit types. Igneous activity only affected the Bryah and Yerrida Basi ns, with voluminous eruptions of tholeiitic magma. In the Bryah Basin tholeiitic volcanic rocks are Mg-rich and have mixed MORB to oceanic i sland chemical signatures, but with a boninitic (subduction-related) c omponent. In the Yerrida Basin tholeiites are Fe-rich and have chemica l signatures that suggest a mixed tectonic environment ranging from oc eanic to continental. It is considered possible that this tholeiitic m agmatism is related to a mantle plume. Two models for the tectonic evo lution of the Bryah, Padbury and Yerrida Basins are proposed: (1) the Bryah and Yerrida Basins were formed in a back-are 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 P ilbara-Yilgarn collision, created the Bryah and Yerrida strike-slip pu ll-apart Basins. A change in regional stress regime resulted in the in version of the basins and the development of a foreland basin in the n orthwest (Padbury Basin). (C) 1998 Elsevier Science B.V.