Acquisition of Laser Ablation System to Quantify Matrix and Grain-boundary Trace Element Partitioning in Olivine and Pyroxenes: an Integrated Bulk and In Situ Approach

智力优势：岩浆的微量元素特征和熔融的固体残留物可以成为破译地球上熔融和岩浆分离的物理过程的有力工具。然而，只有在充分了解这些微量元素在矿物和熔体之间的分配时，才能使用这些工具。其目标是研究地幔中主要矿物相的微量元素分配，大部分熔融发生在地幔中。重点将放在橄榄石和斜方辉石上，这两种矿物是上地幔中的主要矿物，但在分配方面了解最少。与单斜辉石相比，对分配的理解较差是由于熔体的污染效应和分析困难(橄榄石和斜方辉石中的微量元素浓度往往很低)。为了避免熔体污染的影响，建立了橄榄石、斜方辉石和单斜辉石基质中微量元素在底固相线条件下分配的半理论模型，并用地幔包体进行了标定。这些亚固相线下的基质分配系数将根据温度进行向上校正，并与已知的单斜辉石/熔体分配系数相关联，从而产生一组一致的上地幔相矿物基质/熔体分配系数。随后将检验最近的一个假设，即由于颗粒内部(基质)和边界之间的平衡分配，矿物颗粒边界(例如，边缘)是微量元素的重要储存库。通过量化与上述矩阵划分理论的偏差来评估晶界划分。这两个步骤都将通过在现有的赖斯质谱仪(ICPMS)上增加激光消融能力来促进，通过测量基质分配系数和筛选不平衡样本来实现。广泛的影响：这项研究的组成部分将被解析出来供本科生研究。获得激光也将有利于其他正在进行的研究，并通过扩大莱斯和休斯顿地区其他机构的研究项目的广度，帮助吸引更多的本科生从事研究。

0549268LeeIntellectual merit: Trace element signatures of magmas and the solid residues of melting can be powerful tools for deciphering the physical processes of melting and magma segregation on Earth. However, these tools can only be used if the partitioning of such trace elements between minerals and melt is well understood. The goal is to investigate trace element partitioning of major mineral phases in the mantle, where most melting takes place. Emphasis will be on olivine and orthopyroxene, which are the dominant minerals in the upper mantle, but the least understood in terms of partitioning. This poorer understanding of partitioning compared to that of clinopyroxene is due to contamination effects from melts and analytical difficulties (trace element concentrations in olivine and orthopyroxene are often very low). To avoid melt contamination effects, a semi-theoretical model for trace element partitioning between olivine, orthopyroxene and clinopyroxene matrices at subsolidus conditions is developed and calibrated using mantle xenoliths. These subsolidus matrix partition coefficients will then be corrected-up for temperature and related to known clinopyroxene/melt partition coefficients, yielding a consistent set of mineral matrix/melt partition coefficients for upper mantle phases. This will be followed by testing of a recent hypothesis that mineral grain boundaries (e.g., rims) are significant repositories for trace elements due to equilibrium partitioning between grain interiors (matrix) and boundaries. Grain boundary partitioning will be assessed by quantifying the deviation from matrix partitioning theory above. Both steps will be facilitated by the addition of laser ablation capabilities to existing mass spectrometry facilities at Rice (ICP-MS) by enabling the measurement of matrix partition coefficients and the screening of disequilibrium samples.Broader Impacts: Components of this study will be parsed out for undergraduate research. Acquisition of a laser will also benefit other ongoing studies as well as help to entice more undergraduates into doing research by expanding the breadth of research projects at Rice and other institutions in the Houston area.