Global Positioning System measurements from eastern Tibet and their implications for India/Eurasia intercontinental deformation

Abstract

We present and interpret Global Positioning System (GPS) measurements of crustal motions for the period 1991–1998 for a network encompassing the eastern part of the Tibetan Plateau and its foreland. Relative to a Eurasian frame defined by minimizing the velocities of 16 GPS stations in Europe, central Asia, and Siberia, stations within all parts of the plateau foreland in south China move 6–10 mm/yr east‐southeast, indicating that the eastward movement within the plateau is part of a broader eastward movement that involves the plateau and its eastern and northern foreland. North of the plateau, foreland stations move northeastward at ∼10 mm/yr, indicating that the northern boundary of the deformation zone lies north of the plateau. With this realization of a Eurasian frame, the velocity of the GPS station at Bangalore in southern India implies that the northward motion of India is 5–12 mm/yr slower than that predicted from the NUVEL‐1A plate reconstruction. Viewed relative to the South China Block, stations of the northeast plateau, bounded on the north by the Qilian Shan and the Altyn Tagh fault, move NNE to NE with velocities ranging from 19 mm/yr within the plateau to 5–11 mm/yr in its foreland. The Altyn Tagh fault shows left‐lateral slip of ∼10 mm/yr at 95°E and shortening across the fault of <5 mm/yr. Stations south and west of the Xianshuihe/Xiaojiang fault system define a crustal fragment rotating clockwise at ∼10 mm/yr relative to the South China Block around the eastern Himalayan syntaxis. The GPS measurements indicate no significant shortening (< 3 mm/yr) within the Longmen Shan of the central eastern plateau and its adjacent foreland, although the Longmen Shan rise over 6 km in <100 km horizontal distance. Geological studies indicate that the deformational field was established diachronously in late Miocene to Pliocene time, was characterized by no east‐west shortening of Tibetan crust, and has an inhomogeneous style of deformation resulting from a balance of different tectonic processes.