Abstract

The Currywongaun–Doughruagh intrusion comprises a folded sequence of ultrabasic cumulates, anorthosites–norites-pyroxenites, all with plagioclase more calcic than An80. Acid gneisses and granite dykes and pegmatites occur in intimate association with the ultrabasic rocks. Due to faulting the intrusion is separated into two masses: Gurrywongaun constitutes the lower, layered parts of the intrusion; Doughruagh forms the higher levels and consists of massive norites that are in places extensively replaced by acid gneiss. Within each part there is a progressive Fe-enrichment towards the axial planes of the major structures (inverted synclines), with the overall trend in Currywongaun continued by a similar trend in Doughruagh.

Early crystallizing cumulates of the basic magma are thought to be represented in the nearby Dawros peridotite that was tectonically separated during strong F2 movements. Subsequently the magma crystallized the Currywongaun cumulates and during later folding (F3) the remaining magma was squeezed out and ultimately crystallized as the Doughruagh norites. Accompanying crystallization of the ultrabasic rocks, upward migration of acid components and water culminated in the segregation of acid magma in the uppermost levels of the intrusion. Silica-rich hydrous phases emanating from this acid residuum metasomatised the Doughruagh norites, while renewed F3 deformation imparted the acid gneiss foliation. Finally the acid residuum injected and agmatised the ultrabasic rocks.

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