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

William Marsh Rice University, Houston TX

Investigators

Abstract

0549268 Lee Intellectual 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.