Abstract: Evolution of the Tibetan Plateau Viewed from the Perspective of Eastern Tibet

BURCHFIEL, B. CLARK
Schlumberger Professor of Geology, Massachusetts Institute of Technology, Cambridge, Massachusetts

The tectonics of the eastern part of the Tibetan plateau and its foreland are key elements to resolve problems relating to Cenozoic evolution of the plateau and its relation to post-collisional intracontinental deformation within the India/Eurasia convergent system. Most fruitful has been the attempt to examine the latest Cenozoic and active deformation and work backward in time to the inception of the collision. The youngest and active tectonic framework can be developed more rapidly from geodesy, seismology, and active deformation than by extensive mapping of older surface geology where it is more difficult to establish contemporaniety of structures and events within this vast region. Evidence from young and active tectonism shows that deformation in the eastern Tibetan plateau is inhomogeneous and can be divided into three different areas of different structural style. Geodetic results show that relative to south China velocities of crustal material within the plateau do not extend beyond the eastern limit of the plateau and northeast of the plateau show only slow northward velocity. The velocity structure confirms a three part tectonic division of the eastern plateau developed from geology. Tectonism in these three areas can be projected back 6-10 m.y. in different places. Prior to that time the pattern of deformation shows both similarities and differences to the young and active deformation. The similarities can be shown to be related to the continual northward penetration of India into Eurasia, and the differences may be related to structural controls by crustal anisotropy. From these data we have developed a hypothesis for crustal evolution of the plateau that is different from existing models and involves formation of a fluid lower or middle crust that flows laterally in response to topographically generated potential energy modifying that part of plateau development that is related to deformation caused by intracontinental convergence between India and Eurasia.