柴北缘骆驼泉剖面新生代地层磁组构特征及其构造意义  

Magnetic fabric results of Cenozoic sediments from the Luotuoquan locality in the northern Qaidam Basin and their tectonic implications

作　　者：栗兵帅 王江汇 颜茂都[2,3] 张伟林 鲍晶[1] LI BingShuai;WANG JiangHui;YAN MaoDu;ZHANG WeiLin;BAO Jing(School of Earth Sciences,East China University of Technology,Nanchang 330013,China;State Key Laboratory of Tibetan Plateau Earth System and Resources Environment(TPESRE),Institute of Tibetan Plateau Research,Chinese Academy of Sciences,Beijing 100101,China;University of Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]东华理工大学地球科学学院,南昌330013 [2]中国科学院青藏高原研究所,青藏高原地球系统与资源环境国家重点实验室,北京100101 [3]中国科学院大学,北京100049

出　　处：《地球物理学报》2024年第1期205-224,共20页Chinese Journal of Geophysics

基　　金：国家自然科学基金项目(42164005,41974080,42262023,41804065);青藏高原地球系统基础科学中心(41988101-01);第二次青藏高原综合科学考察研究(2019QZKK0707)资助。

摘　　要：青藏高原东北部新生代构造演化对理解高原隆升和变形模式具有重要意义,而目前对于该地区挤压应力方向转变过程仍存在很大争议.本文对柴北缘逆冲带北西部骆驼泉剖面新生代地层开展系统磁组构(本文特指磁化率各项异性)研究,以揭示该地区挤压应力方向的转变特征.系统岩石磁学结果表明,骆驼泉剖面新生代样品中主要磁性矿物是顺磁性组分和赤铁矿以及少量磁铁矿.通过对磁组构特征分析及其与古水流方向对比表明,骆驼泉剖面新生代地层磁组构主要为初始变形磁组构,可用于指示沉积成岩时期的挤压应力方向.磁组构结果揭示,骆驼泉地区挤压应力方向在上干柴沟组下部沉积时期为NNE-SSW向,而上干柴沟组上部和油砂山组沉积时期转变为NE-SW向.结合柴北缘逆冲带已有磁组构结果指出,该地区早期N-S向或NNE-SSW向挤压应力可能与印度—欧亚板块早新生代以来近N-S向碰撞挤压过程有关,指示印度—欧亚碰撞的挤压应力自下干柴沟组下部沉积时期就已传播至高原东北部地区;而后期NE-SW向挤压应力方向与该地区现今GPS揭示的上地壳运动方向一致,可能与该时段高原东北部巨型走滑断裂构造体系(尤其是阿尔金断裂)有关.此外,柴北缘逆冲带新生代挤压应力方向转变在其北西部起始于上干柴沟组下部沉积时期,而南东部起始于上油砂山组下部沉积时期,与地震反射剖面揭示的断裂活动等地质证据共同揭示柴北缘逆冲带新生代的构造活动自靠近阿尔金断裂的北西部向南东部传播和扩展.综合分析青藏高原东北部地区挤压应力方向转变和其他地质证据发现,挤压应力方向转变显示出自柴北缘逆冲带北西部向东、西和南向扩展特征,与阿尔金断裂在上干柴沟组下部-上油砂山组下部沉积时期剪切应力集中于断裂本身,而上油砂山组下部沉积以来开始散布于高原东北部The Cenozoic tectonic activities in the northeastern Tibetan Plateau are crucial for understanding uplift and tectonic deformation of the Tibetan Plateau.However,the transition of the compressional strain directions in this region is still controversial.Here,we conduct a detailed magnetic fabric(refer in particular to anisotropy of magnetic susceptibility,AMS) analysis on Cenozoic sediments from the Luotuoquan locality in the northwestern part of the northern Qaidam marginal thrust belt(NQMTB) to reveal the temporal variations of the compressional strain directions.Systematic rock magnetic experiments indicate that a paramagnetic component and hematite are the main magnetic contributors to the susceptibility,whereas magnetite plays a subordinate role.By analyzing magnetic fabrics and paleocurrent directions in this region,we propose that the Cenozoic magnetic fabrics are mostly embryonic tectonic fabrics and can be used to track the compressional strain directions that were induced during the deposition and lithification processes.The magnetic fabric results reveal that the compressional strain direction at the Luotuoquan locality was NNE-SSW during the deposition of the lower Shangganchaigou Formation,and changed to NE-SW during the deposition of the upper Shangganchaigou and Youshashan Formations.Together with the available magnetic fabric results along the NQMTB,we suggest that the former N-S or NNE-SSW direction was mostly related to the roughly N-S directed India-Eurasia collision,implying the compressional strain has already propagated from the collisional zone to the northeastern Tibetan Plateau during the deposition of the lower Xiaganchaigou Formation.The latter NE-SW direction is consistent with the upper crust movement from GPS observations and is likely related to the huge strike-slip faulting(especially the Altyn Tagh Fault(ATF)) after the deposition of the lower Shangyoushashan Formation.Moreover,the transition of the compressional strain directions occurred after the deposition of the lower Shangga

关 键 词：青藏高原东北部 阿尔金断裂 柴北缘 磁组构 挤压应力 

分 类 号：P318[天文地球—固体地球物理学]