成矿流体动力学与大地构造环境的关系

摘要

热液矿床的形成需要大量流体，而流体的运移需要包括地势差、岩石变形、热梯度及热异常等多种驱动力。这些流体驱动力与构造环境及过程有密切关系。流体压力状态和热场及地势差的组合决定了压性构造环境流体以向上运动为主，如造山型成矿系统，而张性构造环境流体以对流为主，如 VMS 和 SEDEX 成矿系统。造山作用造成的地势差及水平挤压作用所产生的超压可以驱动流体侧向迁移数百公里，如 MVT 成矿系统。但是，具体的成矿流体动力学过程比较复杂，且随构造演化而变化。在经历过多个大地构造演化阶段的地区，如地洼区，老的成矿流体动力系统不断被新的系统叠加或取代；新的构造单元需要来自地幔的流体源补充才有利于成矿。成矿学研究的是成矿作用与大地构造的关系，而流体动力学系统与大地构造环境密切相关，因此，成矿流体动力学应成为成矿学的一个重要组成部分。%The formation of most mineral deposits requires circulation of large amounts of fluids, which may be driven by various geologic forces. In this paper, we demonstrate that such forces are intimately related to tectonic settings. Geologic fluid flow may be driven by topographic relief at the surface, mechanical deformation of the rocks, and thermal gradients and anomalies, all of which are related to tectonic environments and processes. The combination of fluid pressure regime, thermal regime, and topographic relief is such that upward fluid flow is dominant in compressional environments, such as the orogenic gold mineralization systems, whereas convection systems are better developed in extensional environments, e.g., VMS and SEDEX mineralization systems. Topographic relief and horizontal shortening associated with compressional stress regime in an orogen may drive fluid flow for hundreds of kilometers laterally through the foreland basin to stable platform areas, such as in the MVT mineralization systems. The detailed fluid flow patterns, however, are much more complex than this generalization, and evolve with tectonic processes. In areas that have experienced multiple tectonic cycles, such as the diwa regions, mineral deposits formed in early cycles may be overprinted by those formed in late cycles, and new fluid input from the mantle may be required for mineralization in the late stages. As metallogeny deals with the relationships between mineralization and tectonic settings, and hydrodynamics of mineralization is closely related to tectonic setting, therefore, it is important to integrate hydrodynamic studies of mineralization into metallogenic modeling.