A型花岗岩的微量元素地球化学

Trace Element Geochemistry of A-Type Granites

本文总结和评述了A型花岗岩典型的微量元素特征,如富集Ga、稀土元素(除Eu外)和高场强元素, 亏损Ba、Sr和明显的Eu负异常。分别讨论了影响微量元素特征的多种制约因素,主要包括源区性质、岩浆的物理化学条件、岩浆作用过程和络合作用。通过对比世界范围内几个地区相伴生的碱性A型花岗岩和铝质A型花岗岩的微量元素地球化学特征,发现前者Ga、F含量更高,而轻重稀土比值小,Eu、Ba、Sr等元素含量更低,显示了前者的岩浆分异作用更强,同时说明了碱性A型花岗岩可以由与之伴生的铝质A型花岗岩分异而来。

Typical characteristics of trace element geochemistry of A-type granites are reviewed and summarized in this paper. They include the enrichment of Ga, REE （except Eu） and high-field-strength elements （such as Zr, Nb）, the depletion of Ba and St, and the obvious negative Eu anomaly. Several factors controlling features of trace elements are discussed respectively. They include the character of source materials, physical-chemical conditions of the magmas, magmatic processes, and complexation in magmas. The comparison of trace element geochemical characteristics of alkaline A-type granites and those of the associated aluminous A-type granites in several areas show that the alkaline A-type granites has higher Ga and F concentrations, smaller LREE/HREE ratios, lower Eu, Ba, Sr concentrations than those of the associated aluminous A-type granites. These features imply that the alkaline A-type granitic magma was more strongly differentiated than the aluminous A-type granitic magma. This could imply that the alkaline A-type granitic magma could be derived through crystal fractionation from the aluminous A- type granitic magma.