摘要 : Stable oxygen isotopic fractionation during inorganic calcite precipitation was experimentally studied by spontaneous precipitation at various pH (8.3<pH<10.5), precipitation rates (1.8<logR<4.4 mu mol m(-2) h(-1)) and temperature... 展开 Stable oxygen isotopic fractionation during inorganic calcite precipitation was experimentally studied by spontaneous precipitation at various pH (8.3<pH<10.5), precipitation rates (1.8<logR<4.4 mu mol m(-2) h(-1)) and temperatures (5, 25, and 40 degrees C) using the CO2 diffusion technique. The results show that the apparent stable oxygen isotopic fractionation factor between calcite and water (alpha(calcite-water)) is affected by temperature, the pH of the solution, and the precipitation rate of calcite. Isotopic equilibrium is not maintained during spontaneous precipitation from the solution. Under isotopic non-equilibrium conditions, at a constant temperature and precipitation rate, apparent 10001n alpha(calcite-water) decreases with increasing pH of the solution. If the temperature and pH are held constant, apparent 10001n alpha(calcite-water) values decrease with elevated precipitation rates of calcite. At pH = 83, oxygen isotopic fractionation between inorganically precipitated calcite and water as a function of the precipitation rate (R) can be described by the expressions 10001n alpha(calcite-water) = -1.102 log R + 34.56 10001n alpha(calcite-water) = -1.094 log R + 30.87 10001n alpha(calcite-water) = -0.534 log R + 26.80 at 5, 25, and 40 degrees C, respectively. The impact of precipitation rate on 10001n alpha(calcite-water), value in our experiments clearly indicates a kinetic effect on oxygen isotopic fractionation during calcite precipitation from aqueous solution, even if calcite precipitated slowly from aqueous solution at the given temperature range. Our results support Coplen's work [Coplen T. B. (2007) Calibration of the calcite-water oxygen isotope geothermometer at Devils Hole, Nevada, a natural laboratory. Geochim. Cosmochim. Acta 71, 3948-3957], which indicates that the equilibrium oxygen isotopic fractionation factor might be greater than the commonly accepted value. 收起