大兴安岭北段斯木科北山“低Sr低Yb型”花岗岩年代学、岩石地球化学特征及地质意义  

Geochronology,geochemistry and geological implications of low-Sr and low-Yb granites in northern margin of Simuke Mountain,northern Great Xing’an Range

作　　者：赵天雪 孙国胜[1] 晋瑞香 何欣[1] 王广伟 ZHAO Tian-xue;SUN Guo-sheng;JIN Rui-xiang;HE Xin;WANG Guang-wei(College of Earth Sciences,Jilin University,Changchun 130061,China)

机构地区：[1]吉林大学地球科学学院

出　　处：《世界地质》2019年第3期668-680,共13页World Geology

基　　金：内蒙古地勘基金项目(NMKD2014--38)

摘　　要：对大兴安岭兴安地块上发现的斯木科北山“低Sr低Yb”花岗岩进行了研究。斯木科北山花岗岩中锆石具有明显的岩浆成因特征,LA-ICP-MS锆石U-Pb测年^206 Pb/^238 U加权平均年龄为137.6±2.2 Ma,表明其形成于早白垩世早期。全岩主量元素高Si、富碱,低Fe、Ca、Mg,属于准铝质-弱过铝质、高钾钙碱性岩石。微量元素Rb、Th、U、Ce、Zr、Hf富集;Nb、Ta、Sr、Ba、P、Ti亏损;基性相容组分Co、Ni、Cr含量较低,Sr、Yb含量低,为“低Sr低Yb”花岗岩;轻稀土分馏明显,重稀土分馏较弱,中稀土亏损(Yb N>Ho N);具有弱-中等的Ce/Ce^*正异常和弱-中等的Eu/Eu^*负异常;表明岩石形成于较强的氧化环境。岩石样品点在Rb-Y+Nb构造环境判别图解中,位于后碰撞花岗岩区;在10 000Ga/Al比值为基础的花岗岩成因类型判别图解中,均投入到A型花岗岩区,暗示其形成于蒙古—鄂霍茨克洋闭合造山的后碰撞伸展构造背景。The low-Sr and low-Yb granites in northern margin of Simuke Mountain of Xing an Block in northern Great Xing an Range has been studied.Zircon from the granites have obvious magmatic genetic characteristics.The weighted average age of LA-ICP-MS zircon U-Pb dating ^206 Pb/^238 U is 137.6±2.2 Ma,indicating that it was formed in Early Cretaceous.Major element compositions of whole rock are characterized by high Si and alkali contents,but low Fe,Ca and Mg contents,belonging to high K calc-alka-lineseries and quasi aluminum to weak peraluminous rocks.Trace element compositions are characterized by enrichment in Rb,Th,U,Ce,Zr and Hf,but depletion in Nb,Ta,Sr,Ba,P and Ti.Compatible Co,Ni,Cr,Sr and Yb contents are low,indicating they are low-Sr and low-Yb granites.Rare-earth element(REE)compositions exhibit light-REE fractionation,weak heavy-REE fractionation,and also show a depletion of middle REEs(Yb N>Ho N),with weak-medium positive Ce/Ce^*anomalies and negative Eu/Eu^*anomalies,suggesting the rocks were formed in a strongly oxidized environment.In the Rb-(Y+Nb)tectonic discrimination diagram,the granite samples fall into the post-collision granite field,and in the 10 000 Ga/Al genetic discrimination diagram,the samples fall into the A-type granite field,implying that the rocks were formed in a post-collision extensional setting related to the closure of Mongol-Okhotsk Ocean and associated orogenic activity.

关 键 词：大兴安岭北段 低Sr低Yb花岗岩 岩石成因 年代学 岩石地球化学 

分 类 号：P597[天文地球—地球化学] P595[天文地球—地质学]