H_2O-CO_2-NaCl体系石英溶解度模型(适用于高达1000℃、1.5GPa的高温高压环境)

A thermodynamic model of quartz solubility in H_2O-CO_2-NaCl systems up to 1000℃ and 1.5GPa

石英在热水溶液中的溶解度对地球化学和岩石学的研究都极为重要。我们提出一个能够适用于H2O-CO2-NaCl复杂流体成分,高温高压(0～1000℃,0～1.5GPa)条件下的石英溶解度计算模型,形式如下:其中A(T)、B(T)、C(t)均为温度T(K)和t(℃)的多项式。xH2O和V*H2O分别代表流体中水的摩尔分数和有效偏摩尔体积。V*H2O值由公式Vmix=xHOV*H2O+ΣxsVs计算得到。其中,Vmix代表流体混合物的摩尔体积,由Maoetal.(2010)的最新模型计算得到,xs和Vs分别代表溶质的摩尔分数和本征体积。具体采用VCO2=29.9cm3/mol、VNaCl=30.8cm3/mol。本模型精度较前人模型有所提高,并且适用深达下地壳的温度-压力-成分环境,如:巴罗式变质带、板块俯冲带等。另外,本模型可被用于建立石英地质温度计,加深人们对于石英脉及有关矿床成因的认识,并且可用来指导实验及工程。本模型的在线计算程序可通过以下网站获得:www.geochem-model.org。

There are numerous experimental measurements of quartz solubility has been studied over a broad spectrum of aqueous fluid compositions and temperature-pressure range. Here, we proposed an equation, which can calculate the solubility of aqueous silica in H2O-CO2-NaCl fluid mixture at high temperatures and high pressures from 0 - 1000℃ and 0 - 1.5GPa, as follows ： log m so2=A（T）＋B（T）·log M H2O/V· H2O＋C（t）·log x H2O Here A（T） ,B（T） and C（t） are polynomials of temperatures T（K） and t（ ℃）, x H2O and V H2O stand for the mole fraction and effective partial molar volume of H2O in fluid, respectively. The value of V H2O is calculated from the relation Vmix = x HO V ＊H2O＋∑ xs Vs,where Vmix represent the molar volume of the fluid mixture, which is calculated from the recent model of Mao et al. （2010）, xs and Vs denote the mole fraction and the intrinsic volume of the solute, respectively. Values Vco2 = 29. 9cm3/mol and VNaCl = 30. 8cm3/mol were adopted by this thermodynamic model. The accuracy of our model is better than previous models, and our model is able to predict the solubility of quartz over a much wider T-P-x, conditions relevant to the deep crust, so that it could be used to evaluate aqueous silica transport in Barrovian metamorphic belts and subduction zones and so on. In addition, our model is helpful to establish quartz geothermometer, discover the formation mechanics of deposits relevant to the quartz veins. Online calculation of the solubility of quartz is available on： www. geochem-model, org.