封闭体系中水与玄武岩作用的研究

玄武岩与水的作用主要表现在硅酸盐及铝硅酸盐矿物的水解作用。本文首先从理论上论述硅酸盐及铝硅酸盐矿物的界面反应过程。然后结合水─岩作用实验，探讨水与玄武岩在封闭条件下的作用特点及其动力学机制。为模拟自然界中深部封闭体系地下水与玄武岩的作用，我们将采自六合玄武地区的上第三系上新统黄岗组（Ｎ２Ｈ）碱性徽榄玄武岩粉碎后分别与具不同酸碱性的水溶液密封于塑料瓶中，分析其封闭条件下浸泡不同时间后水溶液的化学组成，探讨玄武岩与水的作用规律。研究结果表明：（１）封闭体系中水与玄武岩作用，水溶液的ｐＨ值普遍增高；在初始环境为酸性条件下，水中可溶性ＳｉＯ２含量呈对数曲线变化，在弱酸性、中性及碱性条件下，则呈抛物线状变化；水─岩作用过程中元素释放规律亦随条件不同而不同。（２）控制硅酸盐及招硅酸盐矿物水解反应速度的化学反应速度和弥散速度，在酸性条件下，前者占主导作用，在弱酸性、中性和碱性条件下则是弥散速度控制了水解反应速度。最后，本文将理论推导出的矿物水解反应速度方程与水─岩作用实验结果相比较，并绘出拟合图形，表明理论与实际相吻合。

STUDY ON THE INTERACTIONS BETWEEN WATER AND BASALT IN A CLOSED SYSTEM

Hydrolysis of silicate and aluminosilicate minerals is dominating in the water--rock interactions. Firstly, the paper expounded in theory the surface reactions between the water and the minerals during the hydrolysis. Then in combination with the results from the waterrock interactions in laboratory, the paper discussed the hydrochemical characteristics during the interactions between water and basalt in a theed system, and studied the dynamic mechanism of the dissolution of siliccate and aluminesilicate minerals.In order to simulate the water-rock interactions in the closed system which is in deep protions of the Earth's crust, we collected the alkali-oilivine basalt of Huanggang Formation (Pliocene of the Neogene, N2H) from Luhe (Jiangsu Province), crushed it, put it into several plastic bottles with different solutions with pH range from 3 to 9 and sealed the bottles hermetically. Then we analysed the variations of chemical compositions of the solutions in the course of interactions between the basalt and water in the closed system and studied the law of the interactions between basalt and water.The main results obtained are as follows:(1)During the interactions between water and basalt in a closed system, the pH of the solution goes up generally. The variation of the soluble SiO2 concentration of the solution taxes the form of a logarithmic curve when the initial solution is acid. In the contrast, it can be described with a parabolic function when the initial solution is weak acid, neutral or basic. Moreover, the regular pattern of element releasing from rock to water varies in accordance with the pH of the initial solution.(2) The rate of the chemical reaction and that of the diffusion determine the rate of hydrolytic reaction of silicate and aluminosilicate minerals. Under the acid circumstances, the rate of chemical reaction is dominant, while under the weak acid, neutral or basic circumstances,the rate of diffusion is dominant.Furthermore, the paper compared the curves of SiO2] variations drawn from the theoretical rate equation of the hydrolytic reaction with the data obtained from the experiment of water--rock interactions. The results indicate that the theory is identical with the realty.