Present‐day kinematics of Asia derived from geologic fault rates

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Abstract
Active fault geometry, available Quaternary rates on major faults, and the far‐field plate motion are used to determine crustal kinematics in the collision zone between India and Asia. Using a finite element formalism to construct a spherical shell model of the Asian continent with embedded faults, we seek a velocity solution approaching the motion of rigid blocks by minimizing the elastic strain energy in the fault‐bounded blocks. By doing so, we test the assumption that long‐term deformation within continents is mostly localized into major faults. In the solution, fault motion accounts for more than 80% of the deformation, allowing us to describe our velocity model in terms of quasi‐rigid block rotations on the sphere. South China is rotating clockwise about a pole located southwest of Borneo, implying an E‐ESE velocity vector of ∼11 mm/yr for a point at Shanghai, in agreement with the velocity vector determined by very long baseline interferometry [Heki et al., 1995]. The eastward movement of south China is accommodated by oblique extension along the Red River fault at a rate of 10 ± 5 mm/yr in the south and by the combination of left‐lateral strike‐slip motion on the Qinling‐Dabie Shan fault and the counterclockwise rotation of the Ordos and adjacent blocks in the north. The Tarim rotates clockwise with respect to Dzungaria about a pole located at 44°N, 92°E, consistent with increasing crustal shortening toward the west throughout the Tien Shan. Assuming incompressibility, a crustal volume budget over a domain encompassing the Tertiary mountain ranges in Asia shows that, over the last 10,000 years, 73 ± 4% of the north‐south shortening between India and Asia has been absorbed by thickening of the lithosphere, and 27% has been accommodated by lateral extrusion of continental blocks. The present‐day predominance of thickening in Asia results from the relatively slow eastward motion of south China, controlled by strike‐slip faulting in the Qinling Shan and oblique extension in northeastern China.