祁连造山带中生代古地磁新结果及其地质意义  

New Mesozoic paleomagnetic results from the Qilian Orogenic Belt and their geological significance

作　　者：谭金生 王彬 段亮[1] 孟庆任[2] 刘萍 TAN JinSheng;WANG Bin;DUAN Liang;MENG QingRen;LIU Ping(State Key Laboratory of Continental Dynamics,Department of Geology,Northwest University,Xi'an 710069,China;State Key Laboratory of Lithospheric Evolution,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China)

机构地区：[1]西北大学地质学系大陆动力学国家重点实验室,西安710069 [2]中国科学院地质与地球物理研究所岩石圈演化国家重点实验室,北京100029

出　　处：《地球物理学报》2024年第7期2744-2760,共17页Chinese Journal of Geophysics

基　　金：国家自然科学基金(91955311,41421002,2019QZKK0708)资助。

摘　　要：祁连造山带位于青藏高原北部,保存了古特提斯洋和新特提斯洋关闭过程的远程构造响应记录.为了确定祁连造山带多期次构造响应事件的变形特征,本文在南祁连构造带天峻县中三叠世及北祁连构造带祁连县早白垩世地层中进行了详细的古地磁学及岩石磁学研究.实验结果显示,三叠纪样品分离出了稳定的高温特征剩磁并在样品水平下通过了倒转检验,白垩纪样品分离出的高温特征剩磁通过了褶皱检验.代表了岩石形成时的原生磁化,相对应的古地磁极为:(T2:82.3°N, 223.6°E,A95=4.8°;K1:65.9°N, 188.3°E,A95=6.2°).对比同时代阿拉善、华北古地磁数据表明:中三叠世之后,天峻地区相对于阿拉善参考极发生了20.2±6.8°的顺时针旋转.早白垩世之后,祁连地区相对于华北参考极没有发生明显的块体旋转(0.3±8.6°).结合前人的研究成果,我们认为晚侏罗世-早白垩世拉萨/欧亚碰撞的远程效应造成祁连造山带东西两侧发生差异性构造缩短活动(西段以逆冲推覆构造缩短为主,东段以走滑活动为主),从而造成祁连整体发生顺时针旋转.早白垩世之后,祁连西段阿尔金断裂附近及东段西宁—兰州盆地发生区域性构造旋转,祁连主体以NE向构造缩短为主.The Qilian Orogenic Belt,located on the northern Tibetan Plateau,has preserved far-field tectonic evidence reflecting the reactions to the closure of the Paleo-Tethys and Neo-Tethys oceans.In this study,we conducted meticulous paleomagnetic and rock magnetic investigations on Middle Triassic strata in Tianjun County within the South Qilian tectonic belt,as well as Early Cretaceous strata in Qilian County within the North Qilian tectonic belt.We aimed to determine the deformation characteristics of the primary body of the Qilian Orogenic Belt during the Mesozoic era's multistage tectonic response.Our experiments revealed that the Triassic samples exhibited stable High-Temperature Component(HTC)and successfully passed the reversal test at the sample level.Similarly,the Cretaceous samples displayed stable HTC and passed the fold test,indicative of the primary magnetization acquired during rock formation.Subsequent calculations yielded the Middle Triassic and Early Cretaceous poles(T2:82.3°N,223.6°E,A95=4.8°;K1:65.9°N,188.3°E,A95=6.2°),which were compared with contemporaneous poles from the Alxa Block and North China Block(NCB)regions.The Middle Triassic pole exhibited noticeable clockwise rotations concerning the Alxa Block(20.2±6.8°),while the Early Cretaceous pole displayed negligible rotation relative to the NCB(0.3±8.6°).By integrating these findings with previous research,we infer that the Qilian Orogenic Belt's tectonic response to the Late Jurassic-Early Cretaceous Lhasa/Eurasian collision event involved asymmetric tectonic shortening on the northern and southern slides,leading to the overall clockwise rotation of the orogenic belt.Subsequent to the Early Cretaceous,regional tectonic rotations occurred proximate to the Altyn Tagh Fault in the western Qilian Mountains and the Xining—Lanzhou Basin in the eastern sector.The primary body of the Qilian Orogenic Belt experienced predominant NE-oriented tectonic shortening.

关 键 词：中生代 构造旋转 祁连造山带 古地磁学 

分 类 号：P318[天文地球—固体地球物理学]