花岗岩类岩石成因的磷灰石微区地球化学和同位素示踪

In-situ apatite geochemical and isotopic insights into the petrogenesis of granitoids.

花岗岩类岩石是大陆地壳最重要的组成部分,通常伴生金属矿产,其成因研究可用来探索大陆地壳的形成、演化及动力学机制,并指导矿产资源的勘探。花岗岩类岩石是由岩浆经过结晶分异、地壳混染和岩浆混合等复杂演化过程形成的,且其母岩浆通常来源于不同的岩浆源区。如何准确示踪岩浆源区性质和精细刻画岩浆演化、岩石成岩过程是花岗岩成因研究的关键。磷灰石作为花岗岩类岩石中常见的副矿物,其结晶历史时间长——贯穿整个岩浆演化阶段,且富含F、Cl等挥发分和Sr、REE等微量元素,其化学特征和同位素组成在示踪花岗岩岩浆源区和成岩过程方面有独特的优势。随着微区分析技术的发展,磷灰石的微区地球化学成分记录了寄主岩浆的成分及其变化过程,可从微观角度揭示花岗岩的成因。本文结合前人研究成果及作者近年来的相关工作,系统综述磷灰石微区地球化学研究的进展,探讨如何在岩相学观察的基础上利用磷灰石的结晶过程、微区成分环带和微区同位素组成示踪岩浆源区、岩浆演化和成岩过程,以期为探索花岗岩精细成岩过程提供有效示踪方法。

Granitoids(including granites and related mafic rocks),commonly associated with metal ore deposits,are the main component of the continental crust.Their petrogenesis are the key to revealing the geodynamic mechanism and the formation and evolution of continental crust,and to guiding the exploration of mineral resources.Granitoids are commonly formed by complicated magmatic evolution,including partial melting,fractional crystallization,crustal assimilation and magma mixing.Moreover,they are derived from distinct source rocks.The key to understanding the petrogenesis of granitoids is how to well constrain the sources of magmas and to accurately trace the petrogenetic processes.Apatite,as a common accessory mineral in granitoids,has a long-term crystallization history and can crystalize from the host magmas throughout the whole magmatic evolution process.Importantly,apatite contains high contents of F,Cl,Sr,REE and other elements.Its geochemical features and isotopic compositions have a unique advantage in tracing the magmatic sources and detailed petrogenesis of its host granitoids.With the development of laser ablation techniques,in-situ elemental and isotopic analysis of apatite not only record the geochemical features of host magma at different stages of magmatic evolution but also can be used to reveal the petrogenesis of granitoids from micro perspectives.Based on previously published data and our recent work,this paper overviews the advances in geochemical and isotopic features of apatite in each type of granitoids,and shows how to use the crystallization history,micro-component zoning and isotopic compositions of apatite to trace the magmatic source and evolution and petrogenesis of the host granites on the basis of petrographic observations,in order to provide a new method to well constrain the origin of granitoids.