扬子地块西北缘侏罗纪重磁化及其大地构造意义  

Jurassic remagnetization in the northwestern margin of the Yangtze Block and its tectonic implications

作　　者：李海燕[1,4] 谷志东[2] 张世红[1,4] 颜丹平[3,4] 杨昆昆 钟涛 杨天水[1,4] 吴怀春[1,4] LI HaiYan;GU ZhiDong;ZHANG ShiHong;YAN DanPing;YANG KunKun;ZHONG Tao;YANG TianShui;WU HuaiChun(State Key Laboratory of Biogeology and Environmental Geology,China University of Geosciences,Beijing 100083,China;Research Institute of Petroleum Exploration and Development(RIPED),PetroChina,Beijing 100083,China;State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences,Beijing 100083,China;Frontiers Science Center for Deep-time Digital Earth,China University of Geosciences(Beijing),Beijing 100083,China)

机构地区：[1]中国地质大学生物地质与环境地质国家重点实验室,北京100083 [2]中国石油勘探开发研究院,北京100083 [3]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 [4]中国地质大学(北京)深时数字地球前沿科学中心,北京100083

出　　处：《地球物理学报》2024年第12期4698-4716,共19页Chinese Journal of Geophysics

基　　金：国家重点研发计划项目(2022YFF0800103);国家油气重大科技专项(2016ZX05004005-001);国家自然科学基金项目(41802028);111引智项目(B20011);深时数字地球前沿科学中心“深时数字地球”中央高校科技领军人才团队项目(2652023001)联合资助.

摘　　要：造山过程通常伴随着重磁化的广泛发生,因而造山带的重磁化研究有助于厘定其构造定型的时间.为了确定扬子地块西北缘逆冲推覆构造的定型时间,本文对大巴山弧形逆冲带西北端的西乡地区和龙门山逆冲带北段的宁强至广元地区成冰纪—寒武纪多个岩石单元开展了古地磁学、岩石磁学和岩相学研究,揭示出广泛的侏罗纪重磁化作用.样品的退磁特征、岩石磁学和扫描电镜观察结果显示,该重磁化分量为化学剩磁,载磁矿物为自生磁铁矿和赤铁矿,其形成与造山作用引发的流体迁移有关.结合研究区已发表的侏罗纪重磁化数据,大巴山弧形逆冲带和西乡—宁强地区记录了一致的侏罗纪重磁化方向,表明这一带逆冲构造格架的形成不晚于侏罗纪,而广元地区青林乡和陈家坝剖面的重磁化方向相对发生了~60°的逆时针旋转,表明该地区逆冲构造格架的形成晚于侏罗纪,但该区灌县—安县断层以东的近四川盆地区域未受影响,没有发生旋转.The study of remagnetization in orogenic zones is conducive to determine the timing of their formation,since the orogenesis is usually accompanied by ubiquitous remagnetization.To constrain the age of the thrust framework of the northwestern margin of the Yangtze Block,an integrated paleomagnetic,rock magnetic and petrographic study has been carried out on the Cryogenian-Cambrian strata,including the Xixiang area to the northwest of the Dabashan thrust belt and the Ningqiang-Guangyuan area in the northern part of the Longmenshan thrust belt.Extensive Jurassic remagnetization is revealed.Demagnetization characteristics,rock magnetic results and scanning electron microscopy observations of these rock units suggested a chemical remagnetization carried by authigenic magnetite and hematite,whose growth was related to fluid migration resulting from the Jurassic orogenesis.Together with the published Jurassic remagnetization data of the studied area,the consistent Jurassic remagnetization direction was discovered from the Dabashan thrust belt and the Xixiang-Ningqiang area and this implied that the thrust framework formed no later than Jurassic.Whereas,the remagnetization component of the Guangyuan area of the northern part of the Longmenshan thrust belt anticlockwise rotated~60°relatively and this suggested that the thrust framework formed after Jurassic.But the area close to the Sichuan basin in the Guangyuan area east to the Guanxian-Anxian fault was not affected,with no obvious rotation being observed.

关 键 词：扬子地块西北缘 侏罗纪 重磁化 构造旋转 化学剩磁 

分 类 号：P318[天文地球—固体地球物理学]