西昆仑塔尔一带志留纪花岗质岩石的地球化学特征及构造意义  

Geochemical characteristics and tectonic significance of the Silurian granite rocks in the Taer region of the Western Kunlun

作　　者：黄建国[1] 崔春龙[1] 杨剑[1] 朱余银[1] HUANG Jian-guo;CUI Chun-long;YANG Jian;ZHU Yu-yin(College of Environment and Resources, Southwest University of Science and Technology, Mianyang 621010, China)

机构地区：[1]西南科技大学环境与资源学院,四川绵阳621010

出　　处：《地球化学》2017年第5期435-445,共11页Geochimica

基　　金：西南科技大学博士基金(14zx7126);新疆维吾尔自治区政府1﹕5万区调项目(XJQDZ2006-18)

摘　　要：西昆仑塔尔一带志留纪中酸性侵入岩广泛分布,以阿勒马力克杂岩体为代表,据野外接触关系可分为3个序次的岩浆侵位,主体岩石为钙碱性石英二长岩,岩石具有中硅(SiO_2含量为57.6%~65.1%)、高钾(K_2O含量为3.84%~6.55%)、高钙(CaO含量为3.21%~5.23%)和准过铝质(A/CNK为0.78~1.00)等特征。锆石U-Pb年龄为432~434 Ma,结合其围岩侵位关系厘定为志留纪。岩石稀土元素总量较高(∑REE为257~502μg/g),富集轻稀土元素(LREE/HREE为9.16~21.7),轻重稀土元素分馏明显((La/Yb)N为9.71~37.7)和中等负Eu异常(δEu为0.80~1.04),总体上表现出I型花岗岩特征。据岩石中锆石饱和温度计算,结合Sr和Yb的含量变化及δEu、Rb/Sr、Rb/Ba、Nd/Th、Nb/Ta和La/Sm等指标特征,认为岩石是在温度约为876℃、压力8~15 kbar(或深度为30~50 km)的条件下,由中下地壳的英云闪长岩或砂质岩经角闪石的脱水熔融而形成,产于昆北洋壳(向南)俯冲消减向碰撞后伸展拉伸转化的构造环境中。Silurian intermediate-acid intrusive rocks represented by the Alemalike complex rock mass aredistributed widely around the Taer region of the Western Kunlun.The intrusive rocks can be subdivided intothose of three periods according to their contact relationships.The main rock type is calc-alkaline quartzmonzonite characterized by medium SiO2(the content of SiO2is57.6%-65.1%),high K(the content of K2O is3.84%?6.55%),high Ca(the content of CaO is3.21%-5.23%),as well as by being quasi peraluminous(theratio of A/CNK is0.78-1.00).Zircon U-Pb ages are in the range of432?434Ma.In combination with thecontact relationship the rocks are determined to be Silurian in age.The rocks have slightly higher REE contents(ΣREE257-502μg/g),are more enriched in LREEs(LREE/HREE9.16-21.7).The rocks also show obviousLREE/HREE fraction((La/Yb)N9.71-37.7)and moderate negative Eu anomaly(δEu0.80-1.04).As a whole,the rocks show the characteristic features of the type-I granites.According to the calculation of zircon saturationtemperatures in rocks,in combination with the content varitatione of Yb and Sr and the characteristics ofequivalent indices forδEu,Rb/Sr,Rb/Ba,Nd/Th,Nb/Ta,La/Sm,etc.,we believe that the rocks were formedby tonalities or sandy rocks sourced from the middle and lower crusts through dehydration-melting ofhornblendes under such conditions that the temperature was at about876℃and the pressure at8?15kbar(orat the depth of30-50km);the complex rock mass was formed in the tectonic environment of transformation,which extends from the North Kunlun Ocean’s subduction(southward)to extensional structure after collision.

关 键 词：西昆仑 志留纪 I型花岗岩 构造环境 阿勒马力克杂岩体 

分 类 号：P581[天文地球—岩石学]