大兴安岭东南段中三叠世岩浆岩年代学、地球化学特征及其对古亚洲洋构造演化时限的制约  

Geochronology and geochemistry of the Middle Triassic magmatic rocks in the southeastern part of the Da Hinggan Mountains and their constraints on the tectonic evolution of Paleo-Asian Ocean

作　　者：贺宏云[1] 李英雷 刘汇川 柳永正 张海平[1] 王东星[1] 郭永烈 秦江东 肖剑伟[1] HE Hongyun;LI Yinglei;LIU Huichuan;LIU Yongzheng;ZHANG Haiping;WANG Dongxing;GUO Yonglie;QIN Jiangdong;XIAO Jianwei(Inner Mongolia Key Laboratory of Magmatic Mineralization and Ore-Prospecting/Geological Survey Institute of Inner Mongolia,Hohhot 010020,Inner Mongolia,China;School of Earth and Space Sciences,Peking University,Beijing 100871,China;Institute of Mineral Resources,Chinese Academy of Geological Sciences,Beijing 100037,China;State Key Laboratory of Petroleum Resources and Prospecting,China University of Petroleum/China University of Petroleum(Beijing),Beijing 102249,China;College of Geosciences,China University of Petroleum(Beijing),Beijing 102249,China)

机构地区：[1]内蒙古自治区地质调查院/内蒙古自治区岩浆活动成矿与找矿重点实验室,内蒙古呼和浩特010020 [2]北京大学地球与空间科学学院,北京100871 [3]中国地质科学院矿产资源研究所,北京100037 [4]中国石油大学油气资源与探测国家重点实验室/中国石油大学(北京),北京102249 [5]中国石油大学(北京)地球科学学院,北京102249

出　　处：《地质通报》2020年第7期1046-1061,共16页Geological Bulletin of China

基　　金：中国地质调查局项目《内蒙古1∶5万沙巴尔吐等六幅区域地质矿产调查》(编号:DD20160048-09);国家自然科学基金项目(批准号:41502210)。

摘　　要：大兴安岭东南缘扎赉特旗老山门地区新发现了中三叠世中基性火山岩和花岗岩。锆石U-Pb定年结果显示安山岩喷出年龄为238.8±1.8 Ma,花岗岩结晶年龄为242.2±2.1 Ma。中基性火山岩属于高钾钙碱性系列,为偏铝质,A/CNK值为0.92~0.97,Mg#值为41~45,稀土元素配分图和微量元素蛛网图右倾明显,基本无负Eu异常,高场强元素Nb、P、Ti亏损,稀土元素总量为120.61×10^-6~130.19×10^-6,具典型的大陆岩石圈地幔受俯冲板片作用影响改造后的特征。花岗岩为I-A过渡型花岗岩,属高钾钙碱性系列,总体为弱过铝质,A/CNK值为0.91~1.17,稀土元素配分图和微量元素蛛网图右倾明显,可见明显Ba、Nb、Sr、P、Ti、Eu负异常,稀土元素总量偏低,为81.24×10^-6~290.52×10^-6。老山门中基性火山岩来源于较深的原始地幔,源区岩浆在上涌过程中经过强烈的分离结晶作用,并受到一定程度的地壳混染。而老山门侵入岩为上涌的中基性岩浆加热下地壳形成。老山门中三叠世中基性火山岩和花岗岩形成于古亚洲洋碰撞-后碰撞-拉张的转换期,时间为240~220 Ma,属于碰撞造山作用演化晚期的区域性挤压为主并逐渐转为弧后伸展的构造环境。Middle Triassici ntermediate-basic volcanic rocks and contemporaneous granite in the Laoshanmen area on the southeastern margin of the Da Hinggan Mountains were identified.Zircon U-Pb dating results show an eruption age of 238.8±1.8 Ma for the andesite and a crystallization age of 242.2±2.1 Ma for the granite.The intermediate-basic volcanic rock samples belong to the high potassium calc-alkaline series,and are aluminous,with A/CNK being 0.92~0.97 and Mg#being 41~45.Their chondrite and primitive mantle normalized REE patterns and spidergrams show no negative Eu anomaly but significant depletion of high field strength elements,such as Nb,P and Ti(Nb*=0.19~0.39;Eu*=0.89~0.99).These are typical characteristics of continental lithospheric mantle modified by plate subduction action.The granite samples are weakly peraluminous I to A type transitional granite,and belong to high potassium calc-alkaline series,with A/CNK being 0.91~1.17 and Eu*being 0.06~0.66.These observations indicate that the Laoshanmen intermediate-basic volcanic rocks originated from the deep primitive mantle source,which underwent strong fractional crystallization during upwelling and was contaminated by the crust.The granites were formed by the lower crust which was heated by the upwelling intermediate-basic magma.They were formed in the transitional period of collision-post collision-extension in the Paleo-Asian Ocean,which lasted from 240~220 Ma and belonged to the tectonic environment of regional compression in the late evolution of collision orogeny and gradually turned into back-arc extension.

关 键 词：大兴安岭 中三叠世 I-A过渡型花岗岩 古亚洲洋 碰撞-伸展转换 

分 类 号：P534.51[天文地球—古生物学与地层学] P597.3[天文地球—地质学]