Modelling inversion of two stages shortening overprinted pre-existing grabens: A case study of Huoerguosi-Manasi-Tugulu fold-and-thrust belt, northern Tian Shan, China

The Huoerguosi-Manasi-Tugulu (HMT) fold-and-thrust belt, which is located in the southern Junggar Basin, has formed in response to contraction during Late Cenozoic. However, the tectonic environment for its formation before Late Cenozoic is still controversial. In this paper, we conducted geometric and kinematic analysis of seismic profiles and outcrop data to reveal the Late Jurassic deformation characteristics in this area. Angular unconformity between Cretaceous and Jurassic is well preserved in Qigu anticline belt south to the HMT fold-and-thrust belt. This unconformity also exists in the HMT fold-and-thrust belt, indicating that HMT fold-and-thrust belt started to active during Late Jurassic. We use surface data, recently collected and processed subsurface seismic refection data, isopach map of Lower Jurassic and balanced sections to propose pre-existing half-graben system developed in the Lower Jurassic with this fold-and-thrust belt. We also use results of a series of scaled sandbox analogue models, where industrial CT apparatus was used to monitor deformation, to simulate the evolution of this fold and thrust belt. We suggest that the segmented shape of the HMT fold-and-thrust belt is a response to the presence of thrust ramps, which were formed during early Jurassic. During late Jurassic and Cenozoic shortening, the Lower Jurassic syn-rift sediments served as major detachment horizon, making a pre-existing normal fault act as a stress concentration zone leading to steeping of a thrust-ramp over the normal fault and cover detachment overstep the underlying half-grabens. Modeling results reveal that the presented structural framework has close resemblance with paleostructures especially in the intracontinental environment, which underwent a complex multicycle evolution process, and provide a new prospective for the interpretation of natural examples.