Asymmetric radial thrusting of the Pamir Salient since the Late Quaternary: Implications from the spatio-temporal varations in deformation rates

Abstract

The Pamir Salient is one of the most tectonically active belts within/along the India-Eurasia collision zone. A series of active fault systems formed or have been reactivated along the arcuate margin of the Pamir Salient since the Cenozoic. The formation of the northward-pointing arcuate shape of the Pamir Salient has been a focus in recent decades. However, the timing, formation mechanism, and evolution process of the Pamir Salient remain controversial. The spatio-temporal variation in the kinematics of these active fault systems is key to revealing the formation and evolution of the Pamir Salient. However, few studies concentrate on the multi-timescale deformation of these structures. Based on different tectonic styles of these arcuate fault systems, we summarized the deformation rates of main active structures at different timescales(million-year, millennial and decadal)and analyzed their spatio-temporal variations. The results show that the tectonic deformation of the frontal Pamir Salient has remained relatively stable and the deformation rates of main structures along the frontal Pamir have kept relatively constant since the Late Quaternary. In the western margin of the Pamir, the sinistral-slip rate of the Darvaz fault is about 10~15 mm/a. Within the Tajik basin, the Tajik fold-and-thrust belt experienced E-W shortening at a rate of 6 mm/a. Along the northern boundary of the Pamir, the total N-S shortening rate between the Pamir and the Alai valley is about 13 mm/a and the dextral-slip rate accommodated by the Pamir frontal thrust is 5~6 mm/a. To the east, the shortening rate is approximately 6 mm/a, absorbed by the east part of the Pamir frontal thrust. In the eastern edge of the Pamir, the tectonic activity is weak and the dextral-slip rate on the Kashgar-Yecheng transfer system is 2~4 mm/a. Meanwhile, the thrust and strike-slip rates of the front show a strongly asymmetric pattern. On one hand, the shortening mainly concentrates on the western and northern margin of the Pamir, and the rate is high in the middle(about 13 mm/a)but smaller in both sides(about 6 mm/a). On the other hand, the sinistral-slip rate is very high(about 10~15 mm/a)along the western margin while the dextral-slip rate is low(about 4 mm/a)along the northern and eastern edge. Based on these observations, we suggest that the kinematic model of the Pamir Salient has been reasonably consistent since the Late Quaternary under an asymmetric radial thrusting, which may be controlled by the difference in boundary conditions along the Pamir Salient.