Lateral fault growth in the Kashi anticline (Chinese Tian Shan): Insights from seismic interpretation, shortening distribution and tri-shear methods

Deciphering the relationship between lateral growth of faults and along-strike deformation (i.e., shortening and uplift) in the Earth's upper crust remains a challenge. Here we gain insight into the relation between these processes by studying the Kashi anticline, an asymmetric, doubly plunging thrust-fault related fold located in the southwest Tian Shan, China. We use seismic interpretation and field observations, together with 2D tri-shear and excess area methods, to quantify the distribution of shortening along this structure. The shortening distribution along strike of the Kashi anticline is non-linear and has a peaked, asymmetric, bell-shape, with a maximum value of 5.9±0.2 km. After comparing the 3D structural model of the Kashi anticline and our tri-shear models, we propose that lateral propagation-to-maximum shortening ratio, initiation fault length and lateral propagation rate control the lateral fault propagation process and the fold terminations. Moreover, the 3D fault morphology and the ages of the growth strata suggest that the Kashi anticline experienced two stages of lateral growth with propagation rates of 60 km/Ma between 1.4±0.2 Myrs and 0.9±0.3 Ma, and ~67 km/Myrs from 0.9±0.3 Ma to present. These observations highlight the relation between the evolution of lateral fault growth and the along-strike shortening distribution, allowing us to use the latter (which we can measure) to infer the former (which we cannot). These novel insights from the Kashi anticline can be used to understand lateral growth of thrust and normal faults worldwide.