柴达木盆地西部地区晚新生代构造变形及其意义

The Late Cenozoic tectonic deformation in the Western Qaidam Basin and its implications

青藏高原东北缘构造变形研究是认识整个青藏高原隆升过程、机制以及印欧板块碰撞远程效应的重要途径。受控于昆仑山断裂、阿尔金断裂、祁连山断裂的柴达木盆地,新生代地层发育,较完整地记录了高原东北缘的构造变形信息。尤其柴达木盆地西部地区,构造变形强烈,晚新生代地层出露完整,是研究其晚新生代构造变形历史及驱动机制的理想地区。文中应用平衡剖面和古地磁构造旋转方法,结合最新的磁性地层年代,定量恢复该地区的构造变形历史。结果表明,在挤压应力的控制下该地区自22 Ma以来,构造变形主要表现为地层缩短与构造旋转,且其强度呈阶段性增长,具体又可划分为3个阶段:22～9.1 Ma构造活动平静期、9.1～2.65Ma构造变形相对加强期、2.65Ma以来构造变形顶峰期。研究表明,造成柴西地区地层持续缩短和顺时针旋转的关键推动力是印欧板块晚新生代的持续向北推挤、昆仑山—祁曼塔格山向柴达木盆地强烈挤压推覆以及阿尔金左旋走滑断裂大规模的复活。

The research of tectonic deformation of northeastern Tibetan Plateau is an important way to recognize the process and mechanism of the entire plateau uplift,and the remote effects of Indo-European plate collision,too.The Qaidam Basin is bounded by the Kunlun fault,Altyn Tagh fault and Qilian fault to the northwest,south and northeast,respectively,developed the thick Cenozoic sediments and have recorded the tectonic deformation information of northeastern Tibet.Especially,the western Qaidam Basin has undergone strong tectonic deformation and well exposed the Late Cenozoic strata,which is the ideal area to study the Late Cenozoic tectonic deformation history and driving mechanism.Combined with the latest high-precision paleomagnetic age,the balanced cross-section restoration and paleomagnetic structure rotation were used to reconstruct the Late Cenozoic tectonic deformation history of the western Qaidam Basin.The results show that the tectonic deformation was mainly manifested as the strata shortening and the structure rotation under the compressive stress since 22 Ma.The extent of the shortening and the amount of the rotation presented a phasic growth.The deformation history can be divided into three stages： quiet period of tectonic activity（22-9.1 Ma）;tectonic deformation relatively strengthened（9.1-2.65 Ma）;and the tectonic movement reaching the peak（since 2.65 Ma）.The Late Cenozoic strata shortening and clockwise rotation of the western Qaidam Basin resulted from the Late Cenozoic Indo-European plate continually extruding northward,the Kunlun-Qimen Tagh Mountains strongly thrusting to the Qaidam Basin,and the Altyn Tagh sinistral strike-slip fault being revived on a large scale.