Second-Phase Isotopic and Trace Element Studies of the DufekLayered Mafic Intrusion and Comparisons with Dikes and Sillsof the Ferrar Magmatic Province

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This award, provided by the Office of Polar Programs of the National Science Foundation, supports research to continue isotopic and trace element studies of the Dufek layered mafic intrusion in the Pensacola Mountains, Antarctica. This research utilizes 338 samples that were collected on field expeditions in 1993 and 1995. The Dufek intrusion is one of the largest bodies of its kind in the world, and mineralogical relationships preserved in it offer insights crystallization and chemical differentiation processes in large volumes of relatively homogeneous magmas. New work to be done under this project will focus on measuring elemental concentrations and isotopic ratios of Nd, Sr, and Pb within individual mineral grains from two stratigraphic intervals in the intrusion (the Frost Pyroxenite to Spear Anorthosite section and the Lower Inclusion Member to Upper Inclusion Member section). These analyses will be used to model chemical differentiation of key minerals during the crystallization process and to identify possible chemical signatures of magma chamber recharge event or magma contamination by melting of the surrounding wall rocks which are known to occur in large mafic magma bodies. Both sequences of rock contain abrupt changes in mineralogy and chemical composition. These chemical and mineralogical studies will allow comparison of the Dufek to the intrusive sills of the Ferrar Group from other parts of the Transantarctic Mountains. Inasmuch as data from the first phase of study suggested that assimilation and fractional crystallization were important processes in the Dufek magma chamber, the new data acquired under this project will also be modeled using differential equations that calculate the mass rate of assimilation of surrounding rock relative to crystallization within the intrusion.