羌塘地块西部晚三叠世灰岩古地磁研究及其构造意义  

Paleomagnetic study of the Late Triassic limestones in the western portion of the Qiangtang Block and its tectonic implications

作　　者：曹勇[1,2] 孙知明 李海兵[2] 叶小舟[1] 潘家伟[2] 张蕾[2] 刘栋梁 刘晨光[1] CAO Yong;SUN Zhiming;LI Haibing;YE Xiaozhou;PAN Jiawei;ZHANG Lei;LIU Dongliang;LIU Chenguang(MNR Key Laboratory of Paleomagnetism and Tectonic Reconstruction,Institute of Geomechanics,Chinese Academy of Geological Sciences,Beijing,100081;MNR Key Laboratory of Deep-Earth Dynamics,Institute of Geology,Chinese Academy of Geological Sciences,Beijing,100037)

机构地区：[1]中国地质科学院地质力学研究所,自然资源部古地磁与古构造重建重点实验室,北京100081 [2]中国地质科学院地质研究所,自然资源部深地动力学重点实验室,北京100037

出　　处：《地质学报》2019年第10期2463-2476,共14页Acta Geologica Sinica

基　　金：国家自然科学基金项目(编号：41672218和41672211);中国地质调查项目(编号：DD20160022-03和DD20190059);中国地质科学院基本科研业务费项目(编号：JYYWF201810);自然资源部深地动力学重点实验室开放基金项目资助成果

摘　　要：青藏高原羌塘地块和拉萨地块汇聚-碰撞拼合过程的研究对认识青藏高原中部隆升历史及其动力学过程具有重要的科学意义,而羌塘地块古地磁研究对理解上述问题至关重要。通过对羌塘地块西部改则地区晚三叠世灰岩的系统古地磁测定,获得其高温剩磁分量。但是这一高温剩磁分量未通过褶皱检验,表明为后期重磁化的结果。研究剖面高温特征剩磁平均方向在地理坐标下为Dg=349.3°,Ig=40.4°,κg=45.4,α95=6.5°,相应的古地磁极为76.4°N,311.1°E,dp/dm=4.7°/7.9°。这一古地磁极与羌塘地块早白垩世约110~100Ma的古地磁极在古地磁误差范围内重合,表明其重磁化的时代为早白垩世约110~100Ma。综合分析羌塘地块和拉萨地块古地磁结果,并结合海相地层、蛇绿岩和洋岛等地质证据,显示班公湖-怒江特提斯洋西段闭合的时间发生在早白垩世晚期约110~100Ma。改则地区晚三叠世灰岩的早白垩世晚期重磁化作用与羌塘/拉萨地块西部的碰撞密切相关。The processes of the collision between the Qiangtang and Lhasa blocks is a key factor to understanding the evolution history and geodynamics of the central Tibetan Plateau.The paleomagnetic study for the Qiangtang block is critical to understand these questions.A paleomagnetic study of the Late Triassic limestones from the Gaize area in the western portion of the Qiangtang block has been carried out and a remagnetization component has been obtained.The mean direction of the characteristic remanent component in geographic coordinates is Dg=349.3°,Ig=40.4°,κg=45.4,α95=6.5°,corresponding to a paleopole at 76.4°N,311.1°E with dp/dm=4.7°/7.9°.This pole coincides with the Early Cretaceous(ca.110~100Ma)paleomagnetic pole of the Qiangtang block,indicating the age of the remagnetization is 110~100Ma.Our new results,combined with previous reliable Cretaceous paleomagnetic results from the Qiangtang and Lhasa blocks and synthesize stratigraphy,ophiolite and ocean island evidence,suggested that the final closure of western portion of the Bangong-Nujiang Tethys Ocean may have occurred during 110~100Ma.Furthermore,the late Early Cretaceous remagnetization of the Late Triassic limestones in the Gaize area was closely related with the Qiangtang-Lhasa collision.

关 键 词：羌塘地块 古地磁 重磁化 羌塘-拉萨地块碰撞 班公湖-怒江洋 

分 类 号：P31[天文地球—固体地球物理学]