Reaction Kinetics and Geospeedometry

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9706107 Zhang One of the basic aims of igneous and metamorphic petrology is to infer the thermal history of rocks using observed mineral assemblages and compositions. This continuing award will support research in reaction kinetics and geospeedometry, concentrating on using kinetics of homogeneous reactions (i.e., reactions in a single phase) to infer thermal history. The focus will be on the reaction of hydrous species interconversion (H2Om+O= 2OH) in volcanic glasses, not only because of its importance in geospeedometry, but also because H2O is the most abundant volatile component in the earth and plays the critical role in explosive volcanic eruptions and in physical and chemical properties of melts. Previous research provided a geospeedometer and allows the determination of the cooling rate of hydrous volcanic glasses through IR analyses. Some of the unexpected problems encountered this previous work (e.g., the need for a new calibration) have been partially addressed. With this continuing award: (1) the IR technique will be calibrated to high total H2O content - the calibration is basic to the proposed work and that of others on hydrous systems; (2) in situ experimental studies at high temperature and pressure on speciation and kinetics of the reaction will be carried out; and (3) cooling rate profiles in natural and experimental hydrous glasses will be determined.