Abstract

A numerical thermodynamic model is proposed for one of the most important geological fluid system, ternary H₂O–CO₂–CaCl₂ system, at P-T conditions of the middle and lower crust and crust–mantle boundary. The model is based on the previously proposed equation for concentration dependence of the excess Gibbs free energy and on the first obtained P-T dependencies of the coefficients of the equation of state (EOS) expressed via molar volumes of the components. The EOS allows to predict the properties of the fluid participating in the majority of deep petrogenetic processes: its phase state (homogeneous or multi-phase), densities of fluid phases, concentrations of components in the co-existing phases, and the chemical activities of the components. The model precisely reproduces all available experimental data on the phase state of the ternary H₂O–CO₂–CaCl₂ fluid system in the ranges of temperatures 773.15–1073.15 K and pressures 0.1–0.9 GPa and also allows the correct application of the EOS beyond the experimentally studied range of temperatures and pressures up to P = 2 GPa and T = 1673.15 K. The possibility of the correct extrapolation of our EOS is ensured by using the parametrization of P-T dependencies via the molar volume of water. The latter remains in the experimental domain of values or falls slightly beyond its boundaries, when increasing temperatures and pressures.

中文翻译：

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H 2 O–CO 2 –CaCl 2流体系统的状态方程和中，下地壳的Р-Т参数下的流体相性质

摘要

针对最重要的地质流体系统之一，三元H ₂ O–CO ₂ –CaCl ₂系统，在地壳中下部和地壳幔边界的PT条件下，提出了一个数值热力学模型。该模型基于先前提出的过量吉布斯自由能与浓度的相关性方程式以及第一个获得的PT状态方程（EOS）的系数的依赖性通过组件的摩尔体积表示。EOS可以预测参与大多数深层成岩过程的流体的特性：其相态（均相或多相），流体相的密度，共存相中各组分的浓度以及组件。该模型精确地再现了三元H ₂ O–CO ₂ –CaCl ₂流体系统在773.15–1073.15 K温度和0.1–0.9 GPa压力范围内的相态的所有可用实验数据，并且还允许正确应用EOS超出了实验研究的温度和压力范围，最高可达P  = 2 GPa和T  = 1673.15K。通过水的摩尔体积使用PT依赖性参数化，可以确保正确推断我们的EOS 。当温度和压力升高时，后者保留在值的实验范围内或略微超出其界限。