Ochs FA, Lange RA
Department of Geological Sciences, University of Michigan, Ann Arbor, MI 48109-1063, USA.
Science. 1999 Feb 26;283(5406):1314-1317. doi: 10.1126/science.283.5406.1314.
Density measurements on several hydrous (</=19 mole percent of H2O) silicate melts demonstrate that dissolved water has a partial molar volume (V&cjs1171;H2O) that is independent of the silicate melt composition, the total water concentration, and the speciation of water. The derived value for V&cjs1171;H2O is 22.9 +/- 0.6 cubic centimeters per mole at 1000 degrees C and 1 bar of pressure, whereas the partial molar thermal expansivity ( partial differentialV&cjs1171;H2O/ partial differentialT) and compressibility ( partial differentialV&cjs1171;H2O/ partial differentialP) are 9.5 +/- 0.8 x 10(-3) cubic centimeters per mole per kelvin and -3.2 +/- 0.6 x 10(-4) cubic centimeters per mole per bar, respectively. The effect of 1 weight percent dissolved H2O on the density of a basaltic melt is equivalent to increasing the temperature of the melt by approximately 400 degrees C or decreasing the pressure of the melt by approximately 500 megapascals. These measurements are used to illustrate the viability of plagioclase sinking in iron-rich basaltic liquids and the dominance of compositional convection in hydrous magma chambers.
对几种含水（水含量≤19摩尔百分比）硅酸盐熔体的密度测量表明，溶解水的偏摩尔体积（(V_{\bar{H_2O}})）与硅酸盐熔体成分、总水浓度以及水的形态无关。在1000℃和1巴压力下，得出的(V_{\bar{H_2O}})值为22.9±0.6立方厘米/摩尔，而偏摩尔热膨胀系数（(\frac{\partial V_{\bar{H_2O}}}{\partial T})）和压缩系数（(\frac{\partial V_{\bar{H_2O}}}{\partial P})）分别为9.5±0.8×10⁻³立方厘米/摩尔·开尔文和 -3.2±0.6×10⁻⁴立方厘米/摩尔·巴。1重量百分比的溶解水对玄武质熔体密度的影响相当于将熔体温度升高约400℃或使熔体压力降低约500兆帕。这些测量结果用于说明斜长石在富铁玄武质液体中下沉的可行性以及含水岩浆房中成分对流的主导地位。
