THE EMPLACEMENT OF THE WULUMA GRANITE - MELT GENERATION AND MIGRATIONALONG STEEPLY DIPPING EXTENSIONAL FRACTURES AT THE CLOSE OF THE LATE STRANGWAYS OROGENIC EVENT, ARUNTA BLOCK, CENTRAL AUSTRALIA

During the Paleoproterozoic, the Strangways Metamorphic Complex in the Arunta Block, central Australia, underwent two major deformation even ts under granulite-facies conditions, namely, the Early Strangways eve nt (similar to 1800-1780 Ma) and the Late Strangways event. The Early Strangways event (D-1/M(1)) produced a regional, granulite-facies gnei ssic foliation, which outlines structural trends in the Strangways Met amorphic Complex. The Late Strangways event (D-2/M(2)) is a compressio nal event, which produced spectacular regional sheath folds and high-t emperature shear zones. Melt segregations bearing orthopyroxene + garn et + cordierite + K-feldspar + quartz overprint these structures and m ark the end of the second granulite-facies event (M(2)). In the Wuluma Hills, SW Strangways Metamorphic Complex, pressures of 5-6 kbar and t emperatures greater than 750 degrees C were reached during this event. The Wuluma granite consists of steeply dipping sheets of granites, wh ich overprint the Late Strangways structures and are parallel to the r egional gneissic foliation. The rotation and steepening of the regiona l gneissic foliation occurred during the Late Strangways event. The Wu luma granite formed at the close of the Late Strangways event as exten sional fractures opened parallel to the steeply dipping gneissic folia tion. Fluids migrated into these extensional cracks causing in situ pa rtial melting of the granulites. The introduction of hydrous fluids an d their subsequent release during the crystallization of the granitic melts generated a pervasive, metasomatic event (M(3)), which is charac terized by the retrogression of cordierite to sillimanite + biotite titanomagnetite. A U/Pb ion probe zircon age of 1728 +/- 3 Ma for the Wuluma granite constrains the timing of M(3). Thus, the Wuluma granite is part of an orogenic cycle which began 1745 Ma ago (Anamarra granit e) with regional folding under granulite-facies conditions (M(2)) and ended 1728 Ma ago with the formation of the Wuluma granite and pervasi ve, regional retrogression (M(3)).