Quaternary episodic growth of the Pamir Frontal Thrust: Insights from the Biertuokuoyi piggyback basin, western end of Tarim Basin

The Quaternary Biertuokuoyi piggyback basin was deposited and synchronously deformed at the hanging wall of Pamir Frontal Thrust (PFT), western end of Tarim Basin, recording its kinematic information. Well imaged stratigraphic configuration of the piggyback basin in seismic data provides us an opportunity to quantitatively characterize the magnitude and slip rate of the PFT. Stratified by the Base Cenozoic detachment, the PFT system is characterized by 5 lower ramp thrusts that cutting Paleo-Mesozoic strata and an upper ramp thrust (subdivided into 3 domains) that cutting Cenozoic strata. The shortening of the Pamir region transmits from the 5 lower ramps through the detachment into the upper ramp thrust (PFT) and Mushi anticline. During the formation of piggyback basin, a slip of ~8.4 km derived from the lower ramp thrusts was determined, and ~5.0 and ~3.4 km was compensated by the upper ramp thrust and Mushi anticline, respectively. Coeval thrusting of the 5 lower ramp thrusts is recommended, which is constrained by the basement geometry of the piggyback basin. The growth strata in the distal part were folded with constant-dip kink-band migration, where the dip (~18.5°) is similar with the upper ramp thrust domain II. Caused by the synclinal fault bend, several growth unconformities and different widths of kink-bands are identified. These growth unconformities as well as the correlated conformable stratigraphic surfaces, constitute 5 growth sequence boundaries, indicating 6 stages episodic growth. The measured 6 stages slips are 1760 m, 375 m, 1750 m, 357 m, 48 m, and 328 m, respectively. Combined with published chronology data, the calculated average slip rate (since ~3.3 Ma) of the upper ramp thrust domain II is ~1.4 mm/yr, corresponding to a slip rate of ~1.6 mm/yr on the surface thrust (Aismaola segment). This paper is an application of the fault-related folding theory in fold-thrust belts and highlights the piggyback basin as a powerful tool to constraint the deformation.