The radiometric age of the Albany Granite and the Stirling Range Beds, Southwest Australia

Abstract The reported age of 1,100 ± 50 m.y. for the Albany Granite is taken as marking the waning stages of the main orogeny in the south coast of Western Australia. The high initial 87Sr/86Sr for this granite, 0.7118 ± 0.0064, suggests an anatectic or rheomorphic origin which is consistent with petrographic evidence for the absence of a later metamorphism. Shales from the Stirling Range Beds indicate a metamorphic event at 1,150 ± 40 m.y. which is considered to be the time of upthrusting of rocks of higher metamorphic grade to their present position adjacent to the Stirling Range Beds. The minimum age of deposition for the Stirling Range Beds is postulated as 1,340 m.y.