花岗岩侵位机制与成矿作用

Granite Magma Ascent and Emplacement Mechanisms and Their Relation to Mineralization Process

在地壳不同层次侵位的花岗岩浆具有不同的温度压力条件,与围岩之间存在不同的密度差和粘度差,加之不同地壳层次存在着不同的岩石流变学特征,导致花岗岩浆在地壳不同层次具有相异的侵位机制和侵位构造特征。一般来说,在下地壳层次侵位的岩体形成于封闭—半封闭环境,不利于岩浆系统中物质和能量的交换以及矿床的形成;在中上地壳层次侵位的岩体因处于相对开放环境,且又经历过一定程度的分异演化过程,因而有利于形成诸如接触交代或其他岩浆热液矿床。由于不同侵位机制的岩浆体系具有不同的机械力和化学活动性,从而产生不同特征的侵入接触构造体系,营造出不同的侵入接触成矿环境。在中上地壳层次侵位的杂岩体以多次脉动、增量式生长为特征,其增量生长方式可表现为反环带-外侵式、正环带-内侵式和不规则-离散式,其中有利于成矿的杂岩体往往表现为反环带-外侵式。

This paper provides in-depth reviews and discussions on granitic magma ascent and emplacement mechanisms and their relations to mineralization process. Granite-related mineralization is part of granitic magma evolution process. Consequently, ores generated by the mineralization process are products of the magmatic evolution process. Due to distinct temperature and pressure conditions and different density and viscosity contrasts with their country rocks, granitic magmas emplaced at various rheological crustal levels demonstrate different emplacement mechanisms and mineralization styles. Granites emplaced at deeper crust levels are unlikely mineralized due to a close or near-close magmatic system and lack of elemental and energy exchange with their country rocks. Granites emplaced at shallower crust levels, however, tend to generate a contact-zone mineralization system and/or a hydrothermal mineralization system due to the opening environment and frequent interaction with their country rocks, as well as a prolonged differentiation and fractionation process of the granites themselves. The contact zone systems of granites could also differ from one another due to their distinct emplacement mechanisms at various crust levels, and therefore may show different mineralization styles and characteristics. Examination of growth styles of composite plutons and their likelihood of mineralization suggests that those with reverse concentric zonation and constructed by outward-incremental emplacement of multiple pulses of magmas may tend to significantly contribute to hydrothermal and skarn-type mineralization.