The emplacement of the Wuluma granite: melt generation and migration along steeply dipping extensional fractures at the close of the Late Strangways orogenic event, Arunta Block, central Australia

• Published in: Precambrian research Vol. 72; no. 1; pp. 43 - 67
• Main Authors: Lafrance, B., Clarke, G.L., Collins, W.J., Williams, I.S.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.03.1995
• ISSN: 0301-9268; 1872-7433
• DOI: 10.1016/0301-9268(94)00046-T

During the Paleoproterozoic, the Strangways Metamorphic Complex in the Arunta Block, central Australia, underwent two major deformation events under granulite-facies conditions, namely, the Early Strangways event (∼ 1800-1780 Ma) and the Late Strangways event. The Early Strangways event ( D 1 M 1 ) produced a regional, granulite-facies gneissic foliation, which outlines structural trends in the Strangways Metamorphic Complex. The Late Strangways event ( D 2 M 2 ) is a compressional event, which produced spectacular regional sheath folds and high-temperature shear zones. Melt segregations bearing orthopyroxene + garnet + cordierite + K-feldspar + quartz overprint these structures and mark the end of the second granulite-facies event (M 2). In the Wuluma Hills, SW Strangways Metamorphic Complex, pressures of 5–6 kbar and temperatures greater than 750°C were reached during this event. The Wuluma granite consists of steeply dipping sheets of granites, which overprint the Late Strangways structures and are parallel to the regional gneissic foliation. The rotation and steepening of the regional gneissic foliation occurred during the Late Strangways event. The Wuluma granite formed at the close of the Late Strangways event as extensional fractures opened parallel to the steeply dipping gneissic foliation. Fluids migrated into these extensional cracks causing in situ partial melting of the granulites. The introduction of hydrous fluids and their subsequent release during the crystallization of the granitic melts generated a pervasive, metasomatic event (M 3), which is characterized 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 granite) with regional folding under granulite-facies conditions (M 2) and ended 1728 Ma ago with the formation of the Wuluma granite and pervasive, regional retrogression (M 3).