稀土元素地球化学对太古宙花岗岩类成因的判别

The Discrimination to Archean Granitoids Genesis Using Rare Earth Elements Geochemisty

太古宙花岗岩类的成因是地学界争论颇久的问题。本文以稀土元素地球化学理论论证了北京、辽吉地区某些花岗岩为岩浆成因而非混合岩构成的“地层”。文章论述了主元素特征为钾质花岗岩的岩体实是钾化的TTG岩体 ,论述了主元素成分相同的TTG岩石具不同的稀土图谱 ;被长英质细脉注入的TTG岩石受混染作用改造稀土图谱也发生了变化 ;各种各样非TTG成分的岩石由于硅质的渗透被改造为TTG质岩石。这些实例说明 ,必须进行岩石学、矿物学和地球化学的综合研究才能判定太古宙形形色色的花岗质岩石。

The genesis of Archean granitoids are a long controversy problem. This paper demonstrates some rock genesis discrimination about Archean gray gneiss based upon REE geochemistry. Such as: some Archean granites were actually magmative intrusive origin not migmatization origin; some Kaligranite bodies determined by major elements are actually preserved TTG features of REE patterns. They are TTG granite bodies which suffered potassium metasomatism; TTG rocks with similar major elements compositions have different REE patterns indicating variety mineralogy component of accessory minerals; REE pattern of TTG rocks injected by felsic veinlets were modified by hybridization; Various non-TTG rocks would had been reconstructed as TTG rocks both in major elements chemistry or in REE abundant by siliceous permeation. All examples mentioned above are of important significant in Archean crustal evolution and in metallogeny. It must be taken a comprehensive survey such as field geology chemical geology and mineralogy in discriminating Archean granitoid.