Mineralogical and geochemical features of the Allan Hills tephra, South Victoria Land: Implications for mid-Pleistocene volcanic activity in Antarctica

Abstract

More than 100 volcanoes have been discovered in Antarctica, however, the sources of many Antarctic tephras are not yet constrained. In this study, four tephra samples recovered from the environment of Site 27 on an area of blue ice at Allan Hills, South Victoria Land, provide information on magma and crustal sources for the tephra erupted in Antarctica. We report data on the chemistry of Antarctic tephra glasses and minerals analysed by electron microscopy, electron probe microanalysis and laser ablation inductively coupled plasma mass spectrometry. The tephra amphibole chemistry indicates magma residence at ~1 GPa and ~1100 °C. Abundant Ca–Al–Si-rich minerals imply that the magma ascended from a reservoir at 29.4 ± 2.7 km depth was affected by the assimilation of calc-silicate crust. The high Fe and Ti contents in the magmatic minerals and the trace element patterns of the glasses typical of a hydrothermally altered oceanic crust suggest that the Allan Hills tephra originated from a mantle plume-derived magma. The fragmented morphology of the glasses implies that the magmatic activity was associated with explosive eruptions during the mid-Pleistocene. The chemistry of the glasses and the presence of rhönite and Al-rich spinel minerals suggest that the magma might be genetically related to the currently active McMurdo volcanic group.