中地壳的地球化学动力学和矿石成因  

Geochemical Kinetics and Ore Genesis in Middle Crust

作　　者：张荣华[1] 胡书敏[1] 张雪彤[1] 

机构地区：[1]中国地质科学院矿产资源研究所地球化学动力学实验室,北京100037

出　　处：《地球学报》2006年第5期460-470,共11页Acta Geoscientica Sinica

基　　金：国土资源部项目(编号:20010302);科技部项目(编号:2001DEA20023;2001DEA30041;2003DEA2C021;G1999043212);国家自然科学基金项目(编号:4003011;49473196;20373064)联合资助。

摘　　要：笔者重点进行了大于300℃--在近临界区至超临界区条件下的硅酸盐矿物与水反应动力学实验.矿物(钠长石Ab、透辉石Di、阳起石Act和磁铁矿Mt)的溶解反应动力学实验是使用流体通过叠层反应器的开放体系在25～400℃和22MPa下完成的.实验发现矿物在300℃至400℃范围,在跨越水临界点时出现反应速率的涨落.各种多金属氧化物硅酸盐与水反应时,各个元素溶解到溶液里的释放速率一般不一样,常称为一致溶解作用.但是,在近300℃变为一致溶解作用.实验发现在22 MPa时硅酸盐矿物的最大溶解反应速率多是在300℃,如硅的最大释放速率是在300℃.其余元素如Na、K、Mg、Ca、Fe、Al等释放速率在＜300℃22 MPa时都高于硅的释放速率,在＞300℃时硅的释放速率要高于其它元素的释放速率.确切地说,金属与氧之间的键的性质决定了它们(金属氧化物)与水之间反应速率.在一般情况下,Na-Obr,Ca-Obr,Mg-Obr,Al-Obr和Si-Obr的键桥(br),它们之间相对地由具有离子键性质逐步变为具有极性键的性质.由常温常压到亚临界区(300～374℃22 MPa),再到大于临界点374℃、22MPa进入超临界区,水的性质随温度、压力变化.水由容易溶解离子键逐渐变为容易打破极性键.笔者还研究了黑钨矿、锡石(玄武岩、花岗闪长岩)与水在250～400℃条件下的反应动力学过程,得出了相同的结果.实验均发现在跨越水临界点时矿物(或岩石)与水反应的动力学涨落.这些实验结果可以用于说明中地壳上部的水/岩相互作用的特征.发生于中地壳的水、岩相互作用大多是在300～450℃和20～50 MPa条件下进行的.各地区的地壳厚度不一,中地壳温度压力并不完全相同.模拟中地壳条件下水/岩相互作用实验,目的主要是研究矿物(或岩石)在300～450℃条件下反应动力学过程.已有热液矿床矿物流体包体数据表明:有一批矿床的主要矿石形成于300～500℃The authors performed lots of kinetic experiments on silicate-water reactions at temperatures > 300℃ and under the conditions from a sub-critical state to a super-critical state of water. The dissolution kinetic experiments of such minerals as albite, actinolite and diopside and basalt were carried out by using packed bed reactor, in the temperature range of 250 to 400℃ and at 22MPa. Experiments show that dissolution rates behave a fluctuation in dissolution rates, in the case of crossing the critical state of water, i.e., over the temperature range of 300 to 400℃. When a multi-oxide silicate mineral was dissolved in water, different dissolved aqueous metals behaved different release rates, which is called an incongruent dissolution. Usually congruent dissolution in water occurred at 300℃, for example, congruent dissolution of albite appeared at 300℃. Experiments also show that the maximum dissolution rates of silicate minerals always occur at 300℃, for example, the maximum release rate of Si is at 300℃. When temperature was lower than 300℃, the release rates of Na, K, Mg, Ca, Fe and Al were higher than those of Si. On the contrary, the release rates of Si of silicate minerals were higher than those of other metals when the temperature was above 300℃. The bonding properties of the metal-oxygen bridge accurately determined the reaction rates between metal-oxide and water. Generally speaking, under the room condition, the sequence of Na-Obr,Ca-Obr,Mg-Obr,Al-Obr and Si-Obr exhibited the properties of relative change from the ionic bond to the polar bond. Water properties changed with temperature and pressure from the room condition to a sub-critical region (300～374℃,22 MPa), and then to a supercritical region (>374℃,22 MPa). As a result, water molecules were gradually not liable to break ionic bonds but liable to break polar bond. Besides, the authors performed the kinetic experiments of magnetite and cassiterite in water in the temperature range of 250 to 400℃, and obtained the same signif

关 键 词：化学动力学 临界态 矿物与水反应 中地壳 

分 类 号：P5[天文地球—地质学]