多世代旋转正断层对断陷盆地沉积迁移的控制——柴达木早、中侏罗世盆地性质

Control of Multi-generation Rotary Normal Faults on Sediment Migration in Rift Basin: An Example from the Early and Middle Jurassic Qaidam Basin

基于盆-山耦合关系、地震剖面解释及盆地沉积特征,认为早侏罗世柴达木为箕状断陷盆地,具“南断北超”性质,中侏罗世亦为箕状断陷盆地,具“北断南超”性质。昆仑山北缘正断层与阿尔金左行、鄂拉山右行走滑断裂,分别控制了早侏罗世柴西、柴东箕状断陷盆地;随着昆仑山隆升向北扩展,北倾的高角度正断层逐渐旋转上凸,柴南早侏罗世地层逐渐剥蚀而缺失,仅残存于柴北缘鄂博梁、冷湖构造带等地区。下侏罗统与基底接触带发育的“鱼鳞式”构造,为地壳不均匀隆升时,多世代旋转正断层先后切割所致。柴西南隆升导致中侏罗世地层向北、北东迁移,并出现反向箕状断陷盆地。因此,柴达木早—中侏罗世箕状断陷盆地的反向与沉积迁移,记录了青藏高原北部地壳由水平拉张转换为垂向隆升并向北扩展的地质过程。

Based on the coupling relations between basins and mountains, interpretation of seismic sections and sedimentary characteristics of basins, the Early Jurassic Qaidam Basin is confirmed as a haft-graben fault basin with characters of ＂faulting in the south and overlapping in the north＂, while the Middle Jurassic Qaidam Basinas a haft-graben fault basin with the characters of ＂faulting in the north and overlapping in the south＂. Normal faults at the northern margin of the Kunlun Mountains, together with the left-lateral strike-slip Altun Tagh fracture and right-lateral strike-slip Elashan fracture, respectively, controlled the formation of Early Jurassic haft-graben fault basins in the western and eastern Qaidam Basin. Along with the uplift of the Kunlun Mountains expanding toward the north, north-inclined high-angle normal fault planes gradually rotated and rose, which resulted in a tectonic denudation and disappearance of Early Jurassic strata in the southern Qaidam Basin and relics of Early Jurassic strata are remained only in the Lenghu structural and Eboliang structural belts and other belts in the southern Qaidam Basin. Fish-scale-like structures formed at the contact surface between lower Jurassic and basement might result from mutual incision of multi-generation rotary normal faults in turn because of asymmetrical uplift of crust. Uplift in the southwestern Qaidam Basin led to the migration of Middle Jurassic strata to the north and west, and resulted in the formation of inverted haft-graben fault basin. Therefore, the dip of normal faults controlling the Early Jurassic haft-graben fault basins was contrary to that of the Middle Jurassic haft-graben fault basins, and there was a sedimentary migration from the Early Jurassic to Middle Jurassic. It recorded a geological process that the crust of the northern Qinghai-Tibetan Plateau changed from horizontal extension to vertical uplift.