新疆哈密白干湖花岗岩地球化学特征及构造背景分析

Petrogeochenistry Characteristics and Tectonic Analysis of Baiganhu Granite in Hami,Xinjiang

新疆哈密白干湖花岗岩体主要由钾长花岗岩、二长花岗岩和石英闪长岩组成。为确定该岩体源区性质和地质背景,对其进行了地球化学、构造环境研究,认为白干湖岩体具高硅(SiO_(2)=69.73%~77.59%),富碱(Na_(2)O+K_(2)O=5.48%~9.18%)特征,岩石里特曼指数δ=0.92~2.62,属钙碱性系列;铝过饱和指数A/CNK=0.868~1.02,为准铝质系列岩石;稀土总量偏高,轻稀土元素富集,(La/Yb)_(N)平均值为6.59,轻、重稀土元素分馏明显,Eu弱负异常(δEu=0.27~0.79)。富集轻稀土和大离子亲石元素,HFSE,Sr,Nb,Ba,P等元素相对亏损。研究表明,白干湖岩体属“I”型花岗岩,具陆陆碰撞型花岗岩特征,属同碰撞阶段,为壳幔混合源花岗岩类型。

The Baiganhu granite in Hami,Xinjiang is mainly composed of potassium feldspar granite,monzogranite,and quartz diorite.In order to find out the origin and tectonic actting of the granites,in this area,studies of tectonic environment and geochemistry were carried out.We have learnt that granite in research areas si rich in silicon(SiO_(2)=69.73%-77.59%)and alkali((Na_(2)O+K_(2)O=5.48%-9.18%)).The Ritman index of granite is 0.92-2.62,which shows a characteristics of calcalkaline series.The aluminum overanturated index(A/CNK)of granite is 0.868-1.02,which is a metaluminous series.The granite is characterized by highΣREE,LREE enrichment,notable light and heavy REE fractionation(the average value of(La/Yb)_(N)is 6.59),negative Eu anomaly(δEu=0.27-0.79),rich LILEs such as Rb,K,Th and depleted HFSEs such as Nb,Ba,P and Sr.These characteristics suggest that the granite in research areas is typical I-type granite and may be continentcontinent collisional granite,which is produced during the stage of syn-collision.The granite magma is proved to be acrustmantle mixing origin.