南天山英买来花岗岩的地质、地球化学特征及其地质意义  

Geology and Geochemistry of the Yingmailai Granitic Intrusion in the Southern Tianshan and Its Implications

作　　者：马乐天[1,2] 张招崇[1] 董书云[1] 张舒[1] 张东阳[1] 黄河[1] 

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室,北京100083 [2]北京大学地球与空间科学学院,北京大学地质博物馆,北京100871

出　　处：《地球科学（中国地质大学学报）》2010年第6期908-920,共13页Earth Science-Journal of China University of Geosciences

基　　金：国家科技支撑计划(No.2007BAB25B05);“111计划”(B07011)资助

摘　　要：新疆英买来岩体位于南天山中段,其主体由黑云母钾长花岗岩组成,局部有二云母钾长花岗岩,形成于晚二叠世.岩体中有两种少量椭球状的包体,一是暗色细粒包体,二是浅色包体.花岗岩和包体的地球化学特征基本相似,它们在主量元素特征上以高Si、富K、富碱,贫Mg、Ca为特征,微量元素特征上表现为富Rb、Ba、Th以及轻重稀土的高度分馏和Nb、Ta、Zr、Hf等的负异常.花岗岩和包体的Harker图解显示出一致的变化趋势,表明它们是同源岩浆演化的产物.其A/CNK值为0.99～1.08,显示出准铝-过铝的特点,而稀土元素配分曲线则显示出强烈富集轻稀土和明显的负Eu异常.结合其高的(87Sr/86Sr)t值(0.71036～0.71585)和负的εNd(t)值(-1.67～-6.45),推测岩浆起源于壳源含斜长石的角闪石质岩石脱水条件下的部分熔融(深度<50km),其母岩浆在就位前发生了以黑云母和斜长石为主伴随有磁铁矿等副矿物的分离结晶作用.英买来花岗岩体的岩石类型以及地球化学特征表明其是介于A型和S型之间的一种过渡类型花岗岩类,其形成时的构造环境为碰撞晚期或接近碰撞结束向后碰撞过渡阶段.The Late Permian Yingmailai granitic intrusion is located in the middle part of the southern Tianshan.It consists predominantly of biotite K-feldspar granite with minor two-mica K-feldspar granite.Two types of ellipse-shaped xenoliths including dark-color fine-granular xenolith and light-color granitic xenolith have been recognized in the granitic intrusion.The xenoliths share geochemical similarities with granites.They are characterized by high SiO2 contents,enrichment of K and total alkali coupled with low MgO and CaO contents.Furthermore,they display the enrichment in Rb,Ba,Th and REE as well as significant fractionation of LREE from HREE,and negative Nb,Ta,Zr and Hf anomalies on the ORG normalized trace element patterns.The similar variation trends of major oxides between granites and xenoliths on the Harker diagram suggest that they derived from a common parental magma.The A/CNK ratios range from 0.99 to 1.08,meta-aluminous to per-aluminous feature.The chondrite-normalized REE patterns are characterized by strong enrichment of LREE relative to HREE and significantly negative Eu anomalies.In combination with their high（87Sr/86Sr）t ratios（0.710 36 to 0.715 85） and negative εNd（t） values（-1.67 to-6.45）,it can be inferred that the magmas might have been produced by dehydration melting of crust-source amphibole-bearing mafic rocks（〈50 km）,and that crystal fractionation of biotite and plagioclase with minor magnetite might have occurred before emplacement.The petrological and geochemical characteristics of the granitic rocks suggest that the intrusion is a transition type between A and S types,and formed in the late or end stage of collision between Tarim and Kazakhstan plate in Late Permian time.

关 键 词：二云母花岗岩 地球化学 壳源 二叠纪 南天山. 

分 类 号：P596[天文地球—地球化学]