Collaborative Research: Sr-Nd-Pb-Hf Isotope Studies of Deep Crustal Xenoliths from the Southwestern U.S.A. and Northern Mexico

PIs建议对西德克萨斯Davis Mountains-Big Bend地区和墨西哥Chihuahua Camargo玄武岩田麻粒岩相包体进行岩石学、地球化学、Sr-Nd-Pb-Hf同位素和常规U/Pb锆石综合研究。此外，他们将分析来自新墨西哥州基尔伯恩洞的含石榴石的变质岩，以确定其Hf同位素组成。基尔伯恩洞（Kilbourne Hole）和其他地方的矿石的Nd(0)变化有限，但176Lu/177Hf的比值范围很广，包括极值（0.5）。含石榴石熔体提取的Hf模型年龄应该远比基于Nd的模型年龄更明确。这将是第一个整合Sr、Nd、Pb和Hf同位素的下地壳捕虏体的系统研究，也是迄今为止最详细的常规U/Pb锆石研究。虽然这次合作的直接目标是研究地壳下部，但加州大学圣克鲁斯分校的工作人员将在威斯康星大学麦迪逊分校获得最先进的Hf同位素分析的宝贵经验，包括联合开发新的标准和尖峰。这种方法将使加州大学圣克鲁斯分校能够有效地启动Hf同位素研究项目。

9318687 Cameron The PIs propose to make a combined petrologic, geochemical, Sr-Nd-Pb-Hf isotope and conventional U/Pb zircon study of granulite facies xenoliths from the Davis Mountains-Big Bend region of west Texas and the Camargo basalt field in Chihuahua, Mexico. In addition, they will analyze garnet- bearing metaigneous restites from Kilbourne Hole, New Mexico, for their Hf isotope compositions. Restites from Kilbourne Hole and the other locations have only limited variation in Nd(0) but a wide range of 176Lu/177Hf ratios including extreme values (0.5). Hf model ages for melt-extraction from garnet-bearing restites should be far less ambiguous than model ages based on Nd. This will be the first systematic study of lower crustal xenoliths that integrates Sr, Nd, Pb, and Hf isotopes, and it will be by far the most detailed conventional U/Pb zircon study to date. Although the immediate goal of this collaborative effort is the study of the lower crust, U.C. Santa Cruz workers will gain valuable experience at U.W. Madison in state-of-the-art Hf isotope analysis, including joint development of new standards and spikes. This approach will allow U.C. Santa Cruz to efficiently start-up a program in Hf isotope work.