从地球物理场信息探讨阿尔金断裂带东北尾端效应和延伸

据区域地球物理资料分析,阿尔金—祁连山弧形巨型重力梯级带展布在青藏高原东北边缘,构成青藏地块与塔里木、华北地块的分界,NEE向密集重力梯级带反映出阿尔金断裂带呈左行走滑兼有逆冲;祁连山西段NWW向弧形重力高、重力低相间分布,反映出祁连造山带内挤压推覆、逆冲叠置、盆山耦合的构造格局;在敦煌—金塔之间,基于阿尔金左行走滑断裂带东北段存在尾端效应,产生一系列与NEE向走滑断裂伴生的NNE向拉分断陷盆地,大陆碱性玄武岩充填在拉分空间,引起与重力低对应的磁异常;由于能量的消减和转换致使阿尔金断裂终止于金塔盆地花海断陷,向东并未延伸。

A TENTATIVE DISCUSSION ON THE TAIL EFFECT OF NORTHEAST ALTUN FAUL TBELT IN THE LIGHT OF GEOPHYSICAL FIELD INFORMATION

According to the regional geophysical data, the Altun-Qilian arc giant gravity gradient zone is located at the northeastern edge of the Qinghai-Tibet block and forms the boundaries between Qinghai-Tibet block, Tarim basin and North China block. With the NEE-trending gravity gradient zone, this zone reflects the Altun fault characterized by both sinistral strike-slip and thrust. West Qilian is characterized by alternate NWW-trending arc gravity high and gravity low, which reflects the framework of squeeze nappe, thrust superposition and basin-range coupling within the Qilian orogenic belt. Between Dunhuang and Jinta, due to the tail effect of northeast Altun fault, a series of NNE-trending pull-apart fault basins associated with NEE-trending strike-slip fault and filling of mainland alkaline basalt in the pull-apart space were produced, which caused corresponding magnetic anomalies characterized by gravity low. Due to energy reduction and conversion, the Altun fault terminated in Huahai fault of Jinta basin, thus not extending eastward.