Temporal And Spatial Differences And Its Mechanism Of The Frontal Thrust Belt Of The West Kunlun Mountains In The NE Pamir

The Radial thrusting model in the western margin of Pamir is widely accepted, while the development on the east side of Pamir cannot reach an agreement. Cowgill (2010) proposed that the development on the east side of Pamir was due to the transpressional right-slip transfer faulting. Then Sobel et al. (2011) affirmed that the right-slip transfer faulting have ceased since～5 Ma. In Likang’s opinion (2014), orthogonal the strike of the frontal thrust belt, tear faults systems exist between fold-thrust belts to accommodate the different displacements of these zones from the Pliocene to the present.Previous researchers have done a lot of research in the spatial-temporal differences of the fold-thrust belts in the northeast margin of Pamir. But they cannot reach a consensus on the deformation style, deformation time and the evolution process of the fold-thrust belts. What’s more, the deformation in front of West Kunlun Mountains have formed a thick foredeep since 5 Ma, in contrast to the time of uplift-exhumation in the mountains was before 20～25 Ma. The onset timing of the flexural subsidence and the related deposition of the basin has not been determined.This article focused mainly on deformation style, deformation time and the tectonic evolution of the thrust belt in front of West Kunlun Mountains, on the basis of the field observation, well data, seismic interpretation in Qimugen segment and the adjacent regions by the method of structural analysis, growth strata analysis and balanced cross section. The main findings lead to the following conclusions:1. In the Qimugen segment, new observations revealed a foredeep in the Wuqia Group, which constrained the onset timing of the flexural subsidence and the related deposition of the basin. However, in other adjacent segments, no foredeeps were found in Wuqia Group. The thermochronological results also demonstrate a fast cooling event in the west Kunlun orogen at similar time. Additionally, we also found a foredeep in Atushi formation in the Qimugen segment in a position which is more closer to the basin. These results support that the foredeep migrate towards the foreland with the eastward propagation of the northwest striking Qimugen fold-thrust system.2. Along the strike of the frontal thrust belt, the deformation of the Qimugen segment started later than the other adjacent segments;3. The amounts and rates of shortening exhibits 20km and 21% in Qimugen segment,46km and 30.5% in Sugaite segment,64.2km and 29.5% in Kedong segment, indicating that the deformation intensity of Qimugen segment is weaker than the nearby segments.4.1 propose the mechanism and evolution process of the spatial-temporal differences of the fold-thrust belts in the northeast margin of Pamir:In the early Miocene, a unified foredeep was formed in front of West Kunlun Mountains. From the Pliocene to the present, the spatial-temporal differences were dominated by two NE striking strike-slip faults in the Qimugen segment. The western fault is a left-slip fault, while the eastern fault is a right-slip fault. The development of the strike-slip faults has two effects on the structural style of the study region. On the one hand, it outlined the Qimugen segment an arc-shaped bilge; on the other hand, it made the deformation later and weaker in this area. Only the foredeep in the Wuqia Group of the Qimugen segment survived for this reason.