Tectonic framework of Qilian orogen: reveal from an aeromagnetic anomaly feature  

祁连造山带及邻区构造格架--来自航磁异常特征的启示

作　　者：Yang Hai Xiong Shengqing Liu Qiankun Zhou Daoqing Yang Xue Fan Zhengguo Jia Zhiye Li fang Gao xiuhe Liu fuxiang 杨海;熊盛青;刘前坤;周道卿;杨雪;范正国;贾志业;李芳;高秀鹤;刘福香(中国自然资源航空物探遥感中心,北京100083;中国科学院地质与地球物理研究所岩石圈演化重点实验室,北京100083)

机构地区：[1]China Aero Geophysical Survey and Remote Sensing Center for Natural Resource,Beijing,100083,China [2]State Key Laboratory of Lithospheric Evolution,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing,100029,China

出　　处：《Applied Geophysics》2024年第3期528-548,618,619,共23页应用地球物理（英文版）

基　　金：supported by the National Natural Science Foundation of China grant(U2244220);China Geological Survey Project grant(DD20190551,DD20230351)。

摘　　要：The Qilian Orogenic belt is one of the typical orogenic belts globally and a natural laboratory for studying plate tectonics.Many researchers have studied the ophiolite and high pressure and ultra-high pressure metamorphic rocks in the Qilian orogen and obtained valuable achievements.However,a hot debate exists on the basement property,the distribution of ophiolite,and the boundaries of tectonic units.Large-scale high-precision aeromagnetic surveys have recently been conducted in the Qilian Orogenic belt and adjacent areas.In this study,we are trying to analysis the tectonic framework of the Qilian Orogen using 1:500,000 aeromagnetic data.The results provide geophysical perspectives for studying the structural framework and deformation of this area.According to the aeromagnetic∆T anomaly map,the central and Southern Qilian have the same magnetic anomaly feature that noticeably differs from the North Qilian Orogenic belt and the Qaidam Block.This result indicates that the central and Southern Qilian have a unified magnetic basement and differ from the North Qilian orogenic belt and Qaidam Block.The map shows the distribution of ophiolite in the North Qilian orogenic belt.Linear magnetic anomalies represent the ophiolites because the mafic–ultramafic rocks usually have high magnetic susceptibility.The ophiolite belts are continuously distributed in the western part of North Qilian orogenic belt and have a large scale.However,the scale of the ophiolite belt and the outcropping of mafic–ultramafic rocks reduces when they pass through Qilian County to the east.The results indicate differences in the evolution process between the eastern and western parts of North Qilian,with Qilian County as the transition zone.This study also systematically defines the geophysical boundaries of the Qaidam Block,Qilian Block,North Qilian Orogenic belt,and Alxa block.It is proposed that the sinistral displacement of the Altun Fault is adjusted and absorbed by the series of NE-trending faults in the Qilian orogen and merge into th祁连造山带是世界上典型的造山带之一,是研究板块构造的天然实验室。大量的学者对祁连造山带的蛇绿岩和高压-超高压变质岩开展了研究,取得了许多新的认识,但仍然在基底性质、蛇绿岩分布以及构造单元边界的划分等问题上存在较大分歧。近年来,在祁连造山带及邻区开展了大比例尺高精度航磁调查,为祁连造山带及邻区构造格架及变形作用研究提供了地球物理视角。基于最新的航磁异常图,祁连造山带呈现出深部东西向分段,浅部南北向分带的特征。东、西段为正负块状磁异常,中段为块状正磁异常。中、南祁连具有相似的磁场特征,与北祁连造山带和柴达木地块有明显的区别,这一结果说明中南祁连可能具有统一的磁性基底,且不同于北祁连造山带和柴达木地块。北祁连与阿尔金北并不相连,在地球物理场上不一样。磁场特征清晰的显示了北祁连蛇绿岩的分布。蛇绿岩通常具有较强的磁性,能引起线性条带状磁异常。蛇绿岩带在北祁连西段分布连续,规模也较大,但经过祁连县向东,蛇绿岩带的规模减小,且基性超基性岩的出露也明显减少。结果表明,以祁连县为转折端,北祁连东段和西段的演化过程可能存在差异。本次研究还系统划分了祁连造山带及邻区的构造单元,提出阿尔金断裂左行平移量被加里东期系列北西向左行走滑断裂所调节和吸收,并最终归并于龙首山-固始断裂。新构造运动使北祁连造山带剪切方向拉张作用增强,将北祁连造山带分割为几段,形成系列北东向断裂。

关 键 词：Qilian orogen tectonic framework aeromagnetic anomaly feature mafic–ultramafic 

分 类 号：P542.2[天文地球—构造地质学] P631.222[天文地球—地质学]