Late Ordovician island-arc volcanic rocks, northern Capertee Zone, Lachlan Fold Belt, New South Wales

Late Ordovician (ca 450 Ma) units (Sofala Volcanics, Coomber Formation, Burranah Formation, Tucklan Formation) in the northern Capertee Zone of the northeastern Lachlan Fold Belt in central New South Wales are part of an extensive pile of mafic volcanic and volcaniclastic strata and associated shallow intrusions known collectively as the Molong volcanic province. Lavas and large clasts in volcaniclastic rocks comprise basalt (clinopyroxene-phyric) and basaltic andesite (plagioclase-phyric). Alteration mineral assemblages suggest prehnite-pumpellyite to prehnite-actinolite facies metamorphism. Geochemical data for samples with minimal alteration indicate shoshonitic affinity for these Ordovician magmatic rocks and are characterised by depletion of Ta, Nb, Zr, Ti and Y relative to Rb, Ba and K. Initial Sr-87/Sr-86 ratios and epsilon(Nd) values are similar to those reported from other Ordovician volcanic suites in the Molong volcanic province and indicate minimal crustal input. The geochemical and isotopic signature of these rocks indicates their genesis in a subduction-related island-arc setting.