A review of the geologic history of the Himalayan-Tibetan orogen suggests that at least 1400 km of north-south shortening has been absorbed by the orogen since the onset of the Indo-Asian collision at about 70 Ma. Significant crustal shortening, which leads to eventual construction of the Cenozoic Tibetan plateau, began more or less synchronously in the Eocene (50–40 Ma) in the Tethyan Himalaya in the south, and in the Kunlun Shan and the Qilian Shan some 1000–1400 km in the north. The Paleozoic and Mesozoic tectonic histories in the Himalayan-Tibetan orogen exerted a strong control over the Cenozoic strain history and strain distribution. The presence of widespread Triassic flysch complex in the Songpan-Ganzi-Hoh Xil and the Qiangtang terranes can be spatially correlated with Cenozoic volcanism and thrusting in central Tibet. The marked difference in seismic properties of the crust and the upper mantle between southern and central Tibet is a manifestation of both Mesozoic and Cenozoic tectonics. The form...

Geologic Evolution of the Himalayan-Tibetan Orogen

Topography extracted from swath profiles along the northern, southern, and eastern margins of the Tibetan Plateau show two end-member morphologies: steep, abrupt margins and longwavelength, low-gradient margins. Because the lack of significant upper crustal shortening across much of the eastern plateau margin implies that the crustal thickening occurs mainly in the deep crust, we compare regional topographic gradients surrounding the plateau to model results for flux of a Newtonian fluid through a lower crustal channel of uniform thickness. For an assumed 15-km-thick channel, we estimate a viscosity for the lower crust of 10 18 Pa·s beneath the low-gradient margins, 10 21 Pa·s beneath the steep margins, and an upper bound of 10 16 Pa·s beneath the plateau. These results indicate that the large-scale morphology of the eastern plateau reflects fluid flow within the underlying crust; crustal material flows around the strong crust of the Sichuan and Tarim Basins, creating broad, gentle margins, and “piles up” behind the basins creating narrow, steep margins. These results imply that this portion of the Eurasian crust was heterogeneous, but largely weak, even prior to construction of the Tibetan Plateau.

http://basin.earth.ncu.edu.tw/Course/SeminarII/abstract2014_1/2014.10.02_Sun,%20Yuan-Cheng/Topographic%20ooze%20building%20the%20eastern%20margin%20fo%20Tibet%20by%20low%20crustal%20flow.pdf

Topographic ooze: Building the eastern margin of Tibet by lower crustal flow

Field observations and satellite geodesy indicate that little crustal shortening has occurred along the central to southern margin of the eastern Tibetan plateau since about 4 million years ago. Instead, central eastern Tibet has been nearly stationary relative to southeastern China, southeastern Tibet has rotated clockwise without major crustal shortening, and the crust along portions of the eastern plateau margin has been extended. Modeling suggests that these phenomena are the result of continental convergence where the lower crust is so weak that upper crustal deformation is decoupled from the motion of the underlying mantle. This model also predicts east-west extension on the high plateau without convective removal of Tibetan lithosphere and without eastward movement of the crust east of the plateau.

http://www.geosci.usyd.edu.au/users/prey/Teaching/Geos-3003/geos3003papers/RoydenScience98.pdf

Surface Deformation and Lower Crustal Flow in Eastern Tibet

Global positioning system velocities from 553 control points within the Tibetan Plateau and on its margins show that the present-day tectonics in the plateau is best described as deformation of a continuous medium, at least when averaged over distances of .;100 km. Deformation occurs throughout the plateau interior by ESE-WNW extension and slightly slower NNE-SSW shortening. Relative to Eurasia, material within the plateau interior moves roughly eastward with speeds that increase toward the east, and then flows southward around the eastern end of the Himalaya. Crustal thickening on the northeast- ern and eastern margins of the plateau occurs over a zone ;400 km wide and cannot be the result of elastic strain on a single major thrust fault. Shortening there accommodates much of India's penetration into Eurasia. A description in terms of movements of rigid blocks with elastic strain associated with slip on faults between them cannot match the velocity field.

Continuous deformation of the Tibetan Plateau from global positioning system data

The geological evolution of the Tibetan plateau is best viewed in a context broader than the India-Eurasia collision zone. After collision about 50 million years ago, crust was shortened in western and central Tibet, while large fragments of lithosphere moved from the collision zone toward areas of trench rollback in the western Pacific and Indonesia. Cessation of rapid Pacific trench migration (∼15 to 20 million years ago) coincided with a slowing of fragment extrusion beyond the plateau and probably contributed to the onset of rapid surface uplift and crustal thickening in eastern Tibet. The latter appear to result from rapid eastward flow of the deep crust, probably within crustal channels imaged seismically beneath eastern Tibet. These events mark a transition to the modern structural system that currently accommodates deformation within Tibet.

http://science.sciencemag.org/content/sci/321/5892/1054.full.pdf

The Geological Evolution of the Tibetan Plateau

The Longmen Shan region includes, from west to east, the northeastern part of the Tibetan Plateau, the Sichuan Basin, and the eastern part of the eastern Sichuan fold-and-thrust belt. In the northeast, it merges with the Micang Shan, a part of the Qinling Mountains. The Longmen Shan region can be divided into two major tectonic elements: (1) an autochthon/parautochthon, which underlies the easternmost part of the Tibetan Plateau, the Sichuan Basin, and the eastern Sichuan fold-and-thrust belt; and (2) a complex allochthon, which underlies the eastern part of the Tibetan Plateau. The allochthon was emplaced toward the southeast during Late Triassic time, and it and the western part of the autochthon/parautochthon were modified by Cenozoic deformation. The autochthon/parautochthon was formed from the western part of the Yangtze platform and consists of a Proterozoic basement covered by a thin, incomplete succession of Late Proterozoic to Middle Triassic shallow-marine and nonmarine sedimentary rocks interru...

Liu Yupinc

Papers

Tectonics of the Longmen Shan and Adjacent Regions, Central China