Mantle sources and melting processes beneath East Antarctica: geochemical and isotopic volcanoes

• Published in: Contributions to mineralogy and petrology 2022-04, Vol.177 (4)
• Main Authors: Panter, K. S, Li, Y, Smellie, J. L, Blusztajn, J, Reindel, J, Odegaard, K, Spicuzza, M. J
• Format: Article
• Language: English
• Subjects: Basalt; Breccia; Magnetite; Mid-ocean ridges; Volcanism; Volcanoes
• ISSN: 0010-7999
• DOI: 10.1007/s00410-022-01914-9

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 pahoehoe 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 peridotiteâmelt reaction in a mantle that is heterogeneous on a small-scale. Both magma types have geochemical and isotopic signatures that differentiate them from most of the volcanism found within the West Antarctic rift system. Data trends in Sr-Nd-Pb isotope space indicate mixing of at least two-distinct mantle sources: (1) a relatively depleted component similar to sources for mid-ocean ridge basalt from the extinct Antarctic-Phoenix spreading center, and (2) an enriched component similar to sources for mafic magmas of the Jurassic KarooâFerrar large igneous provinces. The availability of these mantle source types was facilitated by the detachment, sinking and heating of metasomatized continental lithosphere (enriched source) that released volatiles into the surrounding asthenosphere (depleted source) to promote flux melting. Volcanism triggered by lithospheric detachment is, therefore, explicitly applied to Mount Early and Sheridan Bluff to explain their isolation and enigmatic tectonic setting but also to account for source heterogeneity and the ephemeral change in degree of mantle partial melting recorded in their mafic compositions.