Determination of Hydrogen Content of D/H Ratio of Nominally Anhydrous Minerals

California Institute Of Technology, Pasadena CA

Investigators

Abstract

Eiler EAR-0337796 In this project, the investigators plan to develop an apparatus for measuring the abundance and isotopic composition (D/H ratio) of trace hydrogen contained in mg-sized samples of nominally anhydrous minerals, and apply that method to various mantle materials that are believed to be important to the Earth's water budget. It is expected that this method will have accuracy and precision comparable to conventional vacuum extraction of hydrogen from solids, but will be applicable to samples approximately 1000 to 10,000 times smaller. This new technique is an improvement over previous ones and it will be designed to provide absolute measurements of the amounts of hydrogen in nominally anhydrous minerals. Several methods exist for measurements of relative differences in hydrogen content of minerals, and two of these (FTIR and SIMS) are more convenient and/or have better spatial resolution than the measurement the investigators will develop. However, FTIR and SIMS are dependent on reference materials having known water contents. The scarcity of such materials is a major limitation to this field. This new technique, once developed, will be used to expand the suite of inter-laboratory standards that are the foundation of studies of nominally anhydrous minerals. By coupling measurements of H abundance and isotopic composition, the PIs will be able to conduct isotopic labeling experiments that clearly separate surface and dissolved (and perhaps other) contributions to total water contents of analyzed samples. They will also survey the water contents of mineral species that have not been previously studied by FTIR or other methods (principally due to the lack of standards). Preliminary work with hydrogen isotope analyses of small samples by this laboratory indicates that it is possible to dramatically improve our knowledge of the D/H ratios of nominally anhydrous mantle minerals, and thereby constrain the role of such minerals as reservoirs for the Earth's water budget. Some of the main broader impacts of this research will be in the enhancement of analytical infrastructure for hydrogen isotope analyses that could be passed to the community, and in the education and training of students in the field of geochemistry.