【作者】 张驰；

【导师】 段振豪；

【作者基本信息】 中国地质大学（北京） ， 地球化学， 2010， 博士

【摘要】 流体是推动地球的演化和发展的重要组成部分。脱水脱气、部分熔融、岩浆活动、深变质作用和地幔对流等一系列深部过程都离不开流体的参与。观测、实验和计算是认识上地幔流体的三种基本方法。然而,由于很难获取地幔样品且无法实现原位测量,直接观测的数据非常有限；而高温高压下的流体成分往往具有强腐蚀性和高流动性,相关实验测量的难度也很大；所以理论预测在地球深部流体的研究中具有特别重要的意义。本研究通过综合量子力学、分子动力学、统计力学和热力学等方法,研究和预测了上地幔流体体系的化学组成、物理化学性质及其地球化学作用机制。我们首先利用量子力学从头计算结果,获取不同流体分子之间的相互作用势能,在此基础上,进行大量分子动力学模拟以获取不同条件下C-O-H流体体系的物理化学性质,随后通过综合分子模拟数据和现有的实验数据,建立了适用于上地幔条件的C-O-H流体通用型状态方程,可以用来计算和预测上地幔条件下H₂O.CO₂、CH₄、C₂H₆、H₂、O₂、CO等流体组分在宽广温度压力范围内的PVTx性质和逸度系数,以这些工作为基础,结合统计热力学计算的标准态热力学性质,本研究最后建立了相应的热力学模型,通过自由能优化方法实现对上地幔温度压力条件下流体的组成和物理化学性质的预测。利用来自地球深部共生矿物对测量的氧逸度资料作为边界条件,模型计算显示水是古老克拉通底部上地幔流体中最重要的物种,而地球深部的还原环境中有无机成因甲烷生成的可能。在宏观性质以外,我们也利用分子动力学方法对二氧化硅熔融体在上地幔条件下的微观结构进行了分析,并通过高效的Voronoi图分析了熔融体中孔隙数量随压力的变化,探讨了氩在地球深部熔融体中溶解的微观机制。研究发现,氩的溶解度与二氧化硅熔融体结构中的填间孔隙数量随压力的变化密切相关,以此为基础建立的热力学模型成功地解释了高压下氩在二氧化硅熔融体中溶解度的突降。更多还原

【Abstract】 Fluid is the key part the evolution of the Earth system. It plays critical role in degassing, partial melting, magma activity, deep metamorphism and mantle convection. Observation, experiment and calculation are three basic methods to investigate the properties of fluid in the Earth’s upper mantle. However, due to the scarcity of sample from the mantle and it is impossible to measure properties in situ, the data from direct observations are very limited. The causticity and flexibility of fluids also make the experimental study to be very hard. So the theoretical predictions become particularly important in the study of fluid in the Earth deep interior.This study synthesizes the quantum mechanics, molecular dynamics, statistical mechanics and thermodynamics method and it gives prediction to the composition, the thermodynamics properties and the mechanism in fluids and melts in geological processes.We first evaluate the interaction force between different species from the ab initio potential surface, then we done extensive molecular simulations to get to PVTx properties in C-O-H system under various TP conditions. After that, we build a general equation of state for major species of C-O-H fluids in the upper mantle. It well reproduce and predict the PVTx properties and fugacity of H₂O, CO2, CH4, C2H6, H₂, O₂, CO and their mixtures. Based on these results and statistical method, we build the thermodynamics model of the composition and properties of C-O-H system in various temperature, pressure and geological environment with Gibbs energy minimization. In an application to the fluid composition in mantle under ancient craton, the model predict the H₂O is the always the dominant fluid species and it is possible to generate methane even ethane under reductive mantle conditions.Besides the macroscopic properties, this thesis gives microscopic picture of the solution of Ar in silica melts under upper mantle conditions. The structure of silica melts under pressure is investigated with an effective Voronoi diagram method, and it indicated the solubility of Ar is closely related to number of the interstitial voids large enough to accommodate Ar. The thermodynamics model based on the molecular simulation data well explains the drop of Ar solubility in silica melts under pressures in the mantle.更多还原