Stable isotope compositions of olivine and dolomite in peridotites formed by deserpentinization,Darrington area,North Cascades,Washington |
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| Authors: | Michael Johnson Michael A Dungan Joseph A Vance |
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| Institution: | Department of Geology, Rice University, Houston, Texas 77001, U.S.A.;NRC Resident Research Associate, NASA, Johnson Space Center Houston, Texas 77058, U.S.A.;Department of Geological Sciences, University of Washington, Seattle, Washington 98195, U.S.A. |
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| Abstract: | Oxygen isotope analyses of five olivines from the Darrington peridotite, Washington, yield δO18 values of +7.3 to +8.9%. which are consistent with derivation of these rocks from a serpentinite precursor. The isotopic data are compatible with mineralogical, textural and chemical evidence that most of the Darrington peridotites have formed by deserpentinization. Olivine from a single, petro-graphically distinct peridotite sample has a δO18-value of +5.2%. which is within the field of high-temperature olivines. The isotopic and textural evidence indicate that this is a partially recrystallized peridotite tectonite.Oxygen and carbon isotope analyses of dolomites from olivine-carbonate rocks indicate that they could have originated by introduction of atmospheric CO2 via meteoric waters during the formation of ophidolomites or ophicalcites. Subsequent metamorphism and reequilibration have modified the δO18-values. |
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