Mineral Chemistry of Mantle Eclogites

该项目将利用各种分析和理论方法，更好地了解南部非洲金伯利岩中榴辉岩包裹体的来源。第一个目标是描述原生相之间的主量元素和微量元素以及稳定的和放射性成因的同位素关系。P.I.将完成并公布对一系列不同化学成分的样品的初步研究结果，包括常量元素和微量元素以及氧、Sm-Nd和Rb-Sr同位素的数据。要做到这一点，他将需要柯石英的氧同位素数据和石榴石的Sm-ND和Rb-Sr数据。除了完成初步研究外，他还将对这些岩石中的主要和微量元素以及氧同位素分馏进行晶体化学模拟，其基础是可压缩性测量和在室温和高温下的额外结构精炼。第二个目标是确定在这些样品的细脉和晶界中形成的第二相的主元素和微量元素化学特征，这些第二相似乎是深层交代作用的结果。这将通过电子探针以及分析性的扫描电子显微镜和透射电子显微镜对这些似乎与寄主榴辉岩化学相关的相进行显微岩石学分析来完成。这些研究应该更好地确定榴辉岩成分变化的原因，从而更好地了解上地幔的化学动力学。这项提议的供资水平低于最初请拨的123 603美元，这将导致分析较少，并减少使用分析透射电子显微镜，这是最昂贵的分析技术。我们也将无法在这项研究中支持全日制研究生，尽管我们确实预计会从其他来源获得学生支持，这些来源可能部分应用于此项目。此外，T.McCormick的支持率从全职的25%略降至20%。所附两年订正预算约为78400美元，反映了这些变化。就所附订正预算的供资水平而言，我们预计今后两年在了解上地幔化学动态方面将取得重大进展。

This project will utilize various analytical and theoretical methods to better understand the origin of eclogite inclusions in kimberlites of southern Africa. The first objective is to characterize the major and trace element and stable and radiogenic isotopic relationships among primary phases. The P.I. will complete and publish the results of a preliminary study on a chemically diverse suite of samples, including data on major and trace elements, and oxygen and Sm-Nd and Rb-Sr isotopes. To do this he will require additional oxygen isotopic data on coesite and Sm-Nd and Rb-Sr data on garnet. In addition to completion of the preliminary study, he will undertake crystal chemical modeling of major and trace element and oxygen isotope fractionation in these rocks, based on compressibility measurements and additional structure refinements at room temperature and elevated temperature. A second objective is to characterize the major and trace-element chemistry of the secondary phases that have formed in small veins and grain boundaries in these samples, and appear to be the result of metasomatism at depth. This will be done by electron microprobe together with analytical SEM and TEM micropetrography of these phases which appear to be chemically related to the host eclogite. These studies should better define the causes of eclogite compositional variation which will yield a greater understanding of the chemical dynamics of the upper mantle. Funding of this proposal at a level reduced from the originally requested $123,603 will result in fewer analyses and reduced usage of the analytical TEM, which is the most expensive of the analytical techniques. We also will be unable to support a full- time graduate student in this study, although we do anticipate having student support from other sources which may be partly applied to this project. Also, support for T. McCormick is slightly reduced from 25% to 20% of full-time. The attached revised budget at approximately $78,400 over two years reflects these changes. At the funding level of the attached revised budget, we anticipate significant progress in understanding the chemical dynamics of the upper mantle over the next two years.