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

该奖项由国家科学基金会极地方案办公室提供，支持继续对南极洲彭萨科拉山脉Dufek层状镁铁质侵入体进行同位素和微量元素研究。本研究利用1993年和1995年野外考察收集的338个样品。Dufek侵入体是世界上同类岩体中最大的岩体之一，其中保存的矿物学关系提供了大量相对均匀岩浆中结晶和化学分异过程的见解。 在该项目下将要完成的新工作将侧重于测量侵入体中两个地层间隔（霜辉石岩至矛状斜长岩段和下包体段至上包体段）中单个矿物颗粒内Nd、Sr和Pb的元素浓度和同位素比值。 这些分析将用于模拟结晶过程中关键矿物的化学分异，并确定岩浆房补给事件或已知发生在大型镁铁质岩浆体中的周围围岩熔融造成的岩浆污染的可能化学特征。 这两个岩石序列都包含矿物学和化学成分的突变。 这些化学和矿物学研究将使Dufek与来自跨南极山脉其他地区的Ferrar群的侵入岩床进行比较。 由于研究第一阶段的数据表明，同化和分离结晶是Dufek岩浆房的重要过程，因此，本项目下获得的新数据也将使用微分方程进行建模，计算侵入体内围岩同化相对于结晶的质量速率。

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.