CHRONOLOGY AND EVOLUTION OF THE MIDDLE PROTEROZOIC ALBANY-FRASER OROGEN, WESTERN-AUSTRALIA

Geochemical and Sm-Nd isotopic data, and 19 ion-microprobe U-Pb zircon dates are reported for gneiss and granite from the eastern part of th e Albany-Fraser Orogen. The orogen is dominated by granitic rocks deri ved from sources containing both Late Archaean and mantle-derived comp onents. Four major plutonic episodes have been identified at ca 2630 M a, 1700-1600 Ma, ca 1300 Ma and ca 1160 Ma. Orthogneiss, largely deriv ed from ca 2630 Ma and 1700-1600 Ma granitic precursors, forms a belt along the southeastern margin of the Yilgarn Craton. These rocks, toge ther with gabbro of the Fraser Complex, were intruded by granitic magm as and metamorphosed in the granulite facies at ca 1300 Ma. They were then rapidly uplifted and transported westward along low-angle thrust faults over the southeastern margin of the Yilgarn Craton. Between ca 1190 and 1130 Ma, granitic magmas were intruded throughout the eastern part of the orogen. These new data are integrated into a review of th e geological evolution of the Albany-Fraser Orogen and adjacent margin of eastern Antarctica, and possibly related rocks in the Musgrave Com plex and Gawler Craton.