岩石圈中的降压作用及其相变过程

Depressurization and related phase transition in the lithosphere

岩石圈中许多地质过程,都曾经历过降压作用。岩石圈中的压力是一个极为重要的参数,压力的降低将改变地质作用过程的其他物理化学性质,包括导致相变。通过岩石圈中降压过程性质和机制的研究,重点探讨降压所引起的相变及其地质意义,试图从新的研究角度提出一些认识和思路。(1)降压是岩石圈中许多地质作用发生的必要条件,降压的性质不同对应不同的地质现象。(2)岩石圈物质的相变线(含两端点)及邻区的物理化学行为突变有重要研究价值。降压可导致岩石圈中的水发生一、二级相变,影响着热液成矿和油气成藏,是"构造降压-水相变耦合成矿(藏)"新模式的理论核心。降压导致岩石圈中固体熔融相变,是岩浆形成的必要条件,降压性质差异决定着岩浆岩的种类和结构。降压过程中,矿物组合随之调整,因各种矿物的相变线不同,矿物变形行为表现各异,地压梯度明显降低,影响超高压变质作用和变形、岩石圈减薄等的解释。(3)降压通常是岩石圈局部升温和聚集水的前提。岩石圈中若没有降压,就不会出现明显升温和聚集水的现象。

There is always the depressurization in many geological processes of the lithosphere.The pressure is an important parameter in the lithosphere,and the pressure reducing will change other physico-chemical properties of some geological processes and cause the phase transitions.Through the study of the properties and mechanisms of depressurization,this paper mainly discusses the phase transitions caused by depressurization and their relative geological significance,and tries to propose some new knowledge and ideas from a new view.Some new ideas are showed below.（1）The depressurization is the essential condition for many geological processes in the lithosphere,and the variations of depressurization properties correspond to different geological phenomena.（2）The physico-chemical behavior mutations of the phase transition line（including two endpoints）and their adjacent areas of material in the lithosphere have important research values.The depressurization can lead to the occurrence of the first-order or second-order phase transitions of water and impact the hydrothermal mineralization and hydrocarbon accumulation,which is the theoretical core of water phase controlling hydrothermal mineralization（WPCHM）and hydrocarbon accumulation.The depressurization is essential to form magma because it will cause the phase transition of solid,and the types and textures of the igneous rocks depend on the diversity of depressurization properties.Because of the difference of phase transition line of various solid minerals,the mineral assemblage is adjusted in the process of depressurization,and the behavior of the mineral deformation is different.The pressure gradient is decreased obviously with the change of system properties,which will influence the explanations of the lithospheric thinning,the metamorphism and deformation of ultrahigh-pressure（UHP）rocks.（3）The depressurization is usually aprerequisite for the local warming and adding water in the lithosphere.If in the lithosphere there is no depressurization,it is unlikely that there will be a noticeable warming and adding water.