Dufek Layered Mafic Intrusion, Antarctica: Perspective on Differentiation from Nd-Sr-Pb Isotopic Compositions, PGE Abundance Patterns and Trace Element Modeling

Phase paragenetic relationships preserved in layered mafic intrusions are the basis of much of our present knowledge about mafic magma differentiation. Initial 87Sr/86Sr, 143Nd/144Nd and Pb ratios in plagioclase and pyroxene from the 182.1 ± 0.8 Ma Dufek layered mafic intrusion in Antarctica can vary both between one mineral type in different rocks and between different mineral types in the same rock. Differences between minerals in the same rock become more pronounced toward the top of the intrusion, explicable by the assimilation of a small amount of the Precambrian to Permian metasedimentary rocks. Both mechanical mixing of crystals equilibrated in different magma systems and assimilation of local country rocks are important differentiation processes in the intrusion. PGE concentrations in the Dufek intrusion and other Ferrar rocks have coherent but highly fractionated abundance patterns reflecting source compositions and melting processes, but not the complex magma mixing revealed by the isotopic ratios. Infiltration and compaction in the intrusion is modeled using the MELTS algorithm that is coupled with standard diffusion and advective one-dimensional mass transport equations. The results of the modeling are best explained by infiltration of a liquid compositionally similar to basalts from a nearby dike into a homogeneous crystal-liquid mush compositionally similar to local leucogabbros, followed by compaction.