Stable Isotope Geochemistry of Quartz, Clay Minerals and Zeolites Under Sedimentary/Diagenetic/Low Grade Metamorphic Conditions

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Fundamental data on the oxygen isotopic behavior of sedimentary/diagenetic/low-grade metamorphic silicate minerals (quartz, clays and zeolites) are needed. The research includes calibration of mineral-water oxygen isotopic fractionations for quartz and for zeolites and calibration of intracrystalline isotopic fractionations in clays. It also includes research on techniques for the oxygen isotopic analysis of zeolites and on the kinetics of isotopic exchange between zeolites and water. The quartz-water oxygen isotope fractionation will be calibrated at approximately 0, 25, 50 and 75 degrees C by growing quartz crystals in aqueous solution under carefully controlled conditions. The results, when combined with published fractionation data for 200 degrees C and above, should yield reliable metamorphic temperature range. In addition to providing information about quartz, the results will be useful in our attempts to estimate other mineral-water isotopic fractionations. Studies aimed at measuring and calibrating intra-crystalline isotopic fractionations in clays will be based both on partial fluorination and on thermal dehydroxylation. This will permit an estimate of both the temperature of the clay formation and the isotopic composition of the clay-forming fluid. The ability to do this would be especially useful in the isotopic study of sandstones, where cogenetic mineral pairs are very rarely encountered. The proposed studies of the isotopic behavior of zeolites will indicate the degree to which the isotopic compositions of various minerals in this common diagenetic/low-grade-metamorphic group provide useful information about the conditions of their formation and enhance applications of oxygen isotope techniques to the understanding of low temperature processes.