浆混花岗岩专题填图方法初探——以东昆仑加鲁河地区为例

Geological mapping approach to hybrid type granitic batholiths:A case study of the Jialuhe complex from East Kunlun orogen

东昆仑造山带花岗岩中广泛发育暗色微粒包体,含有丰富的壳幔岩浆混合作用的证据,被认为是研究岩浆混合作用的天然场所。适逢近阶段同源花岗岩谱系填图方案在造山带岩浆混合(浆混)花岗岩图区实践时深受质疑,本研究以东昆仑加鲁河地区浆混花岗岩为例,开展浆混花岗岩区专题填图试点工作,旨在探索一套适合浆混花岗岩填图的岩石单位划分方案。从野外地质、岩相学、岩石和矿物化学等不同角度论证了加鲁河花岗闪长岩及其内部包体形成于开放体系下的壳幔岩浆混合作用。在填图工作中,将图区内的岩浆岩划分为浆混花岗岩和非浆混花岗岩2个超单元。以岩浆混合作用为理论依据,将浆混花岗岩超单元划分为基性端元、酸性端元和浆混产物3个二级单位,对于2个端元岩石单位按照其矿物组成、结构构造等方面的差异(岩浆演化导致)再次划分最基本岩石单位——侵入体,对于浆混产物单位,建议可按照岩浆混合程度差异或者内部包体变化规律灵活划分基本岩石单位——浆混体。由此建立了一套可与同源花岗岩谱系单位相兼容的浆混花岗岩谱系单位划分方案,为岩浆混合花岗岩区开展填图工作提供了初步探索方案。

Mafic enclaves are widespread in the granitic rocks of Eastern Kunlun orogen. They provide essential evidence for mixing events of magmas from the mantle and the crust,and thus the Eastern Kunlun granite belt is considered to be a natural laboratory of magma mixing. In recent years,arguments appear in applying comagmatic granitical mapping method to hybrid type granitic batholiths in an orogen environment. In this paper,the authors studied the Jialuhe hybrid type granite complex from East Kunlun orogen,aiming to shed some new lights on mapping methods of hybrid type granites. Based on field work,petrography,mineral and rock chemistry information,it is concluded that the Jialuhe granodiorite and the mafic enclaves inside resulted from magma mixing event under open systems. During the work,the authors divided the igneous rocks into two supper units,i.e.,hybrid unit and un-hybrid unit. Based on the theory of magma mixing,three sub-units were further established: mafic end-member,felsic end-member andhybrid products. The basic unit for end-member rocks is pluton according to differences in mineral assemblages and textures of rocks.Likewise,the hybrid products could be further divided into different mixing units based on the different degrees of mixing or on the variations of enclave distributions. This mapping method is somehow similar to the traditional comagmatic granitical mapping method,and provides a preliminary exploration scheme for mapping work of hybrid type granite batholiths.