Park Volcanics, Murihiku Terrane, New Zealand: Petrology, petrochemistry, and tectonic significance

Abstract

Abstract The Late Triassic to Early Jurassic Park Volcanics Group comprises minor shallow intrusive and extrusive bodies emplaced during mainly marine sedimentation of the Murihiku Terrane, southern New Zealand. Gowan Andesite in western Southland and Glenham Porphyry andesites in eastern Southland are high‐K andesites. Glassy examples have commonly lost K during alteration. Orthoclase contents of Or3.6–3.7 in plagioclase phenocrysts at An50 confirm the high‐K nature of the melts at the time of phenocryst crystallisation. The Gowan andesites have higher Fe/Mg than the Glenham and related differences in minor element chemistry suggesting lower fO 2during fractionation of the parent magma. Pinney Volcanics in western Southland are mostly high‐K trachydacites but, like Glenham Porphyry, include minor rhyolite. Barnicoat Andesite in the Nelson area is medium‐K olivine andesite, marginally tholeiitic in terms of its FeO∗/MgO versus SiO2behaviour, but otherwise is typically calc‐alkaline, as are the Gowan, Glen...