Abstract

A numerical thermodynamic model is proposed for one of the most important geological fluid systems, the ternary H₂O–CO₂–NaCl system, at P-T conditions of the middle and lower crust and crust-mantle boundary (up to P = 20 kbar and up to T = 1400°C). The form of the model is analoguous to the model developed earlier for the system H₂O–CO₂–CaCl₂. The model is based on an equation for the Gibbs excess free energy for the fluid H₂O–CO₂–NaCl, also including terms responsible for the interaction of the fluid with the solid phase of NaCl. The model allows predicting physical-chemical properties of fluids, which participate in the majority of deep petrogenic processes: the phase state of the system (homogeneous or multi-phase fluid, presence or absence of solid NaCl), chemical activities of the components, densities of the fluid phases, and concentrations of the components in the co-existing phases. The P-T dependencies of coefficients of the equation for the Gibbs excess free energy are expressed via molar volumes of water and CO₂ at corresponding pressure and temperature. The numerical parameters of the model are obtained by fitting experimental data on the phase state of the fluid system in the range of pressures from 1 to 9 kbar and temperatures from 500 to 930°C. Our parametrization of the P-T dependencies provides applicability of the model for pressures and temperatures beyond the experimental region, namely up to P = 20 kbar and up to T = 1400°C. The validity of the model above these P-T parameters is limited due the properties of the thermodynamic description of the CO₂ employed.

中文翻译：

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中下地壳PT参数下H 2 O–CO 2 –NaCl流体系统的热力学模型

摘要

提出了一个最重要的地质流体系统，即三元H ₂ O–CO ₂ –NaCl系统，在中，下地壳和地幔幔边界的PT条件下（高达P = 20 kbar和最高T = 1400°C）。该模型的形式类似于先前为系统H ₂ O–CO ₂ –CaCl ₂开发的模型。该模型基于流体H ₂ O–CO ₂的吉布斯过量自由能的方程式–NaCl，也包括负责流体与NaCl固相相互作用的术语。该模型可以预测参与大多数深层成岩过程的流体的物理化学性质：系统的相态（均相或多相流体，存在或不存在固体氯化钠），组分的化学活性，密度流体相的浓度，以及共存相中各组分的浓度。在PT的方程为吉布斯过量自由能的系数的相关性通过的水和CO摩尔体积表示₂在相应的压力和温度下。该模型的数值参数是通过在1至9 kbar的压力和500至930°C的温度范围内拟合流体系统相态的实验数据而获得的。我们对PT依赖性的参数化提供了该模型适用于超出实验区域的压力和温度，即高达P = 20 kbar和高达T = 1400°C的条件。由于所用CO ₂的热力学描述的性质，在这些PT参数之上的模型的有效性受到限制。