内蒙古敖汉旗地区晚泥盆世-早石炭世双峰式火山岩的发现及其地质意义  

Discovery of the Late Devonian–Early Carboniferous bimodal volcanic rocks in the Aohanqi,Inner Mongolia,and their geological significance

作　　者：王森 渠洪杰[1] 王欢 宋殿兰[1] 程慕利 谭春亮 冉灵杰 冯跃文 陈英富 崔玉良 岳永东 林广利 WANG Sen;QU Hong-jie;WANG Huan;SONG Dian-lan;CHENG Mu-li;TAN Chun-liang;RAN Ling-jie;FENG Yue-wen;CHEN Ying-fu;CUI Yu-liang;YUE Yong-dong;LIN Guang-li(Beijing Institute of Exploration Engineering,China Geological Survey,Beijing 100083,China;Inner Mongolia Mining Development Limited Liability Company,Hohhot 010010,China;China University of Geosciences(Beijing),Beijing 100083,China;Inner Mongolia No.10 Institute of Geology and Mineral Exploration and Development,Chifeng 024005,China)

机构地区：[1]中国地质调查局北京探矿工程研究所,北京100083 [2]内蒙古矿业开发有限责任公司,内蒙古呼和浩特010010 [3]中国地质大学(北京),北京100083 [4]内蒙古自治区第十地质矿产勘查开发院,内蒙古赤峰024005

出　　处：《地球化学》2020年第2期150-167,共18页Geochimica

基　　金：中国地质调查局地质调查项目(DD20201127,DD20190021,DD20160062)。

摘　　要：在内蒙古中东部荒漠草原浅覆盖区1∶5万填图试点工作基础上,对内蒙古敖汉旗北部波罗和硕-萨力巴-步登皋一带原划分为二叠系额里图组火山岩进行了岩石学、地球化学及同位素年代学研究。岩石学特征表明这套火山岩以玄武岩和流纹岩组合为主,局部发生弱变质作用,两者呈相间或互层出露。地球化学成分上由基性和酸性两个岩石端元组成,在中性岩的范围出现了明显的间断,表现出典型的“双峰式”火山岩组合特征。选取4件代表性流纹岩样品开展了LA-ICP-MS锆石U-Pb测年研究,分别获得了(361±2)Ma、(359±2)Ma、(350±28)Ma和(338±1)Ma的成岩年龄,时代上属于晚泥盆世末期-早石炭世,根据区域对比应将其划为朝吐沟组(D3-C1ch)。流纹岩表现出高硅富碱贫铝铁的地球化学特征,属于高钾钙碱性系列,与典型的A型花岗岩或碱性流纹岩平均成分接近,属于造山后火山岩。玄武岩相对低MgO、高FeO,具有板内玄武岩的特征,成因上可能与弧陆碰撞后伸展造山环境有关;结合区域已有研究成果及认识,认为华北板块北缘赤峰地区晚泥盆世伸展作用持续到早石炭世,根据本文获取的最近年龄结果,将该期伸展作用的时间上限确定为338 Ma。Based on the preliminary work of geological mapping at a 1:50000 scale in the desert and grassland shallow-overburden area in central and eastern Inner Mongolia,a comprehensive study of petrology,geochemistry,and isotopic chronology was carried out for volcanic rocks distributed in the Boluoheshuo-Saliba-Budenggao area of north Aohanqi,which were originally divided into the Permian Elitu Formation.These volcanic rocks were mainly composed of basalts and rhyolites lithologically,with weak alteration.These two kinds of rocks were either interbedded or distributed at intervals.Their geochemical compositions were basic and acidic end-members,with a significant discontinuity of neutral rocks,thus showing typical features of“bimodal”volcanic rocks.In this study,four representative rhyolite samples were selected for LA-ICP-MS zircon U-Pb dating,which yielded diagenetic ages of(361±2)Ma,(359±26)Ma,(350±2)Ma,and(338±1)Ma,respectively,which belong to the Late Devonian–Early Carboniferous.These volcanic rocks should be classified as the Chaotugou Formation(D3-C1ch)according to a regional geological comparison.The rhyolites were geochemically characterized by a high silicon content,rich alkali content,and poor aluminum content,and belonged to the high-potassium-calcium-alkaline series,which was close to the average composition of the typical A-type granite or alkaline rhyolite,which belong to the post-orogenic volcanic rocks.The basalts contained a relatively low MgO content and high FeO content,thus exhibiting features of intraplate basalts,and may be related to the post-collision of arc-land.In consideration of former research in the region,an new understanding is put-forward:the Late Devonian extension continued until the Early Carboniferous in the Chifeng area,which is the northern margin of the North China Craton,with a probable time limit of 338 Ma.

关 键 词：双峰式火山岩 朝吐沟组 玄武岩 流纹岩 敖汉旗 

分 类 号：P597.3[天文地球—地球化学] P591.1[天文地球—地质学]