Siyu Wang

Topic

Deformation of Tian Shan from Coseismic to Million-year Timescales

School of Earth and Ocean Sciences

Date & location

• Thursday, August 15, 2024
• 1:30 P.M.
• Clearihue Building, Room B017

Examining Committee

Supervisory Committee

• Dr. Ruohong Jiao, School of Earth and Ocean Sciences, University of Victoria (Co-Supervisor)
• Dr. Edwin Nissen, School of Earth and Ocean Sciences, UVic (Co-Supervisor)
• Dr. Lucinda Leonard, School of Earth and Ocean Sciences, UVic (Member)
• Dr. Randall Scharien, Department of Geography, UVic (Outside Member)

External Examiner

• Dr. Jessica Thompson Jobe, Geologic Hazards Science Center, U.S. Geological Survey

Chair of Oral Examination

• Dr. Niiyokamigaabaw Deondre Smiles, Department of Geography, UVic

Abstract

Intracontinental deformation is often driven by tectonic forces associated with distant plate collisions. The late Cenozoic deformation of Tian Shan is accommodated by both thrust faults bounded the mountain range and strike-slip motion within the mountain. Earthquake hazards and deformation mechanics in the far-field active regions of the Tian Shan are generally poorly quantified due to slow strain accumulation, poor data coverage, and incomplete historical earthquake records. This dissertation aims to gain a better understanding of the kinematics of deformation in this far-field intracontinental mountain belt.

I use multidisciplinary techniques to investigate the late Cenozoic deformation of the Tian Shan across different time scales ranging from coseismic to postseismic to million-year scales. I start with an earthquake that occurred in the Kepingtag fold-and-thrust belt in southwestern Tian Shan, a seismically active region and a clear example of basinward migration. I use Interferometric Synthetic Aperture Radar to measure coseismic deformation, combined with teleseismic waveform modelling and calibrated relocation of the mainshock. The results reveal a fault plane situated on the d´ecollement at the base of the folded sedimentary cover and a prevalence of seismicity at basement depths throughout the Kepingtag belt and its foreland, indicating rheological controls on earthquake depths. Then, I apply both coseismic modelling and postseismic time series analysis to study another earthquake that happened along the northern Chinese Tian Shan front, adjacent to the Southern Junggar Fold-and-thrust Belt. The findings indicate that the coseismic rupture on a shallow dipping fault plane triggers postseismic deformation that is farther north beneath the anticline. In the third part of this dissertation, I use low-temperature thermochronology, including apatite fission track and apatite U-Th/He dating systems, to model the thermal history of samples collected from the overlooked region in the northern Tian Shan. Inverse modelling of over 1000 published thermochronological data from the Tian Shan, Pamir, and northeastern Tibetan Plateau, along with new data, suggests accelerated exhumation during 15–10 Ma, which represents an acceleration of strike-slip motion.

The dissertation concludes by integrating results across various timescales to discuss deformation styles throughout the region’s tectonic evolution. This study also demonstrates that integrating techniques across multiple timescales effectively quantifies the evolution of active faulting and deformation in the Tian Shan.