The sub-Antarctic Antipodes Volcano: a

Abstract

The sub-Antarctic Antipodes Islands group, located on the edge of the Campbell Plateau, is composed of Surtseyan-like tuff cones, porphyritic lavas and dykes, overlain by scoriaceous cinder cones. The youthful nature is indicated by well-preserved cones and craters, raised boulder beaches, pollen and spores comparable to the present-day vegetation in peat underlying one lava flow, and published Ar/Ar ages of ≤0.5 Ma. The alkaline crystalline rocks record a fractionation lineage that was controlled by progressive removal of clinopyroxene and olivine at shallow depths with minimal interaction with continental crust. A compilation of isotopic data confirms that the magmas were derived from a mantle source containing a high-time integrated U/Pb (HIMU)-like component. Although this source component has been recognised in many Zealandia intraplate volcanoes, the Antipodes Volcano lavas contain consistently high 206Pb/204Pb and low 87Sr/86Sr ratios, making the geochemical suite an excellent baseline for HIMU studies. The distinctive isotope ratios and chemistries are comparable with those of some anhydrous Pb- and K-depleted peridotitic mantle xenoliths from intraplate volcanoes in Zealandia. If the lithospheric mantle contributed to the source of Antipodes Volcano, the Pb and K anomalies in the lavas may not require residual amphibole/phlogopite and/or sulphide in their source region. Furthermore, comparison with the peridotite suite indicates that the Zealandia lithospheric mantle is isotopically heterogeneous and thus not all the Zealandia Cretaceous–Cenozoic intraplate volcanoes need have tapped a HIMU-like reservoir.