Opposite Sense of Strike‐Slip Faulting and Crustal Rotation Accommodating Left‐Lateral Shear Between the Tianshan Mountains and Kazakh Platform

• Published in: Geophysical research letters Vol. 48; no. 24
• Main Authors: Wu, Chuanyong, Wang, Weitao, Zheng, Wenjun, Zhang, Peizhen, Yu, Zhongyuan
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 28.12.2021
• Subjects: conjugate strike‐slip faulting; Crustal deformation; crustal rotation; Deformation; deformation pattern; Fault lines; Fault zones; Faults; Geological faults; Global positioning systems; GPS; Kazakh platform; Kinematics; Mountains; Rotation; Shear; Slip; Spatial data; Strain distribution; Tectonics; Tianshan; Eurasia; Tien Shan Mountains; India
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2021GL096442

Tectonic deformation of blocks neighboring fault zones has been thought to aid in accommodating regional displacements. In general, these block‐bounding faults possess continuous geometry and similar kinematics. However, the northwestern boundary of the Tianshan Mountains (NWBTS) involves two groups of faults that strike NW and NE. GPS velocities show that contemporary deformation takes place in a zone of 300 km wide in the NWBTS and is roughly dominated by left‐lateral shear. Left‐lateral shear motion of ∼5–6 mm/yr along the NWBTS is accommodated by right‐lateral slip and counterclockwise rotation of fault wallrocks on the NW‐striking faults and left‐lateral faulting on the NE‐striking faults. Present‐day deformation associated with the ongoing India‐Eurasia collision in the NWBTS is best described as the opposite sense of strike‐slip faulting and crustal rotation. The difference in lithospheric strengthening between the Kazakh Platform and Tianshan deflects strain toward the northeast and drives the dynamic process in this region. Plain Language Summary The NWBTS has undergone notable tectonic deformation, which involves two groups of NW‐striking and NE‐striking faults instead of displacement only along a major bounding fault. How the two groups of faults interact to bound this deformation boundary belt and accommodate the regional strain associated with the ongoing India‐Eurasia collision remains unclear. Investigating the fault kinematics and strain distribution is essential for understanding the interactions between active tectonic blocks and determining crustal deformation patterns and dynamic mechanisms in this region. In this study, we utilize the latest GPS data from Wang and Shen (2020), https://doi.org/10.1029/2019jb018774 to define the kinematics and deformation rates of the major faults in the NWBTS. Left‐lateral shear of ∼5–6 mm/yr along the NE‐trending NWBTS is accommodated by right‐lateral faulting of the NW‐striking faults and left‐lateral faulting of the NE‐striking faults, which can be interpreted as a pattern resembling the opposite sense of strike‐slip faulting and crustal rotation of the surrounding rock. Our results provide clear evidence of how active deformation is distributed in this area and the tectonic role of the different faults in regional deformation. Key Points Northwestern boundary of the Tianshan Mountains involves two groups of faults that strike NW and NE Fault kinematics and deformation rates of the major faults are determined based on the GPS data Crustal deformation in the NWBTS can be interpreted as a pattern resembling the opposite sense of strike‐slip faulting and crustal rotation