View article

Mount Early and Sheridan Bluff (87° S) are the above-ice expression of Earth’s southernmost volcanic field and are isolated by > 1000 km from any other exposed Cenozoic volcano in Antarctica. These monogenetic, Early Miocene volcanoes consist of olivine-phyric basaltic pillow lavas and breccias (Mount Early) and pāhoehoe lavas (Sheridan Bluff) whose differentiation is controlled by the fractional crystallization of olivine with lesser quantities of clinopyroxene, plagioclase and magnetite. Fractional crystallization or contamination by crust cannot account for the coexistence of olivine tholeiite and alkaline compositions but their relationship can be explained by change from higher (5–6%) to lower (1.5–2%) degrees of partial melting concurrent with a decrease in peridotite‒melt reaction in a mantle that is heterogeneous on a small-scale. Both magma types have geochemical and isotopic signatures that …