부산대학교 도서관

Oxygen isotope analyses of well developed, fissure-grown quartz, adularia, and calcite crystals are related to downhole temperatures and other data from the Ohaki-Broadlands geothermal field. The bore no. BR 7 profile shows how oxygen isotope analyses of geothermal minerals provide quantitative evidence on subsurface hydrology, particularly with regard to zones of boiling, and on the past stability of a geothermal system. The lower part of this profile permits correlation of a temperature of 275/sup 0/C with 10/sup 3/ ln ((/sup 18/O//sup 16/O)/sub quartz/(/sup 18/O//sup 16/O)/sub K-feldspar/) = 3.3. Based on the constraints gained from Broadlands, on the 600/sup 0/C quartz--K-feldspar fractionation from Blattner and Bird (1974), and on earlier data of O'Neil and Taylor (1967, 1969) and O'Neil, Clayton, and Mayeda (1969), quartz-feldspar, quartz-calcite, and quartz-muscovite oxygen isotope geothermometers may be calibrated independently of isotopic analyses of solutions. The corresponding new equations are 10/sup 3/ ln ..cap alpha.. (quartz--K-feldspar) = 0.82 + 0.74 10/sup 6/ K/sup -2/, 10/sup 3/ ln ..cap alpha.. (quartz-muscovite) = 1.30 + 1.27 10/sup 6/ K/sup -2/, and 10/sup 3/ ln ..cap alpha.. (quartz-calcite) = 0.37 + 0.88 10/sup 6/ K/sup -2/ (NBS-28 = 9.8/PDB = 30.36). The constant of the quartz-calcite equation depends directly on the scales of reporting used for silicates and carbonates respectively. (auth)