West Antarctic mantle deduced from mafic magmatism

Abstract

AbstractDistinct mantle compositions recorded in primitive West Antarctic magmatic rocks vary by tectonic setting and time. Deep asthenospheric mantle-plume sources or shallow metasomatized mantle sources may operate either coincidently or independently to supply melts for magmatism. For example, contemporaneous subduction and plume dynamics produced the Ferrar–Karoo Large Igneous Province; subduction-related melting followed by slab-rollback or melting of slab-hosted pyroxenite explains Antarctic Peninsula volcanism through time; Marie Byrd Land magmatism results from plume materials variably mixed with subduction-modified mantle; while magmatism in Victoria Land and western Ross Sea is best explained by plate dynamics and melting of asthenospheric and metasomatized lithospheric sources, and not by an upwelling plume. Element and isotopic ratios show a fundamental change between Marie Byrd Land and Victoria Land mantle domains. Specifically, Pb isotopes indicate that Victoria Land magmatism sources have a stronger focal zone (FOZO) mantle component, while Marie Byrd Land magmatism possesses more of the high μ = high 238U/204Pb (HIMU) mantle component that leads to high 206Pb/204Pb over time. The chemical and isotopic heterogeneity of relatively unfractionated igneous rocks in West Antarctica reflects fundamental differences in mantle domains and melting conditions. This mantle variability coincides with changes in crustal structure and composition, and has a geophysical signature that is manifest in seismic data and tomographic models.