Mechanism of the thermo-tectonic evolution of the uplift of the tibetan plateau

Abstract

The forty-million years long uplift-erosion history of the Tibetan Plateau has been investigated from a genetic point of view on the basis of data of the multidisciplinary paleogeographic method and the method of isotopie chronology. The most prominent features of the plateau uplift are summarized to establish and verify a preliminary genetic model of the thermo-tectonic evolution of the plateau's uplift. In the derivation of the mathematical expressions of the model, the true (absolute) and apparent (relative) uplift rates ( uand u′), together with the regional average erosion rate ( e ), as well as four model parameters, i.e.: (1) x-depth of a mechanically neutral plane, (2) H-peak elevation of the plateau surface at a characteristics time, (3) t 0-characteristic age separating crustal shortening due to thickening and that due to mass-sliding, and (4) h-elevation of the regional peneplain by the end of the Tertiary are tentatively introduced for the first time. Thus, the model is three-dimensional in nature, though expressed in a rather simplified way: shortening in the direction of principal stress, thickening in the vertical direction and lateral extension in the form of strike-slip mass-sliding. Full consideration is given to erosion in the course of undulation of the plateau's surface in the light of three possible modes of erosion distribution: (1) e = const., (2) e = e 0 + mt and (3) e = f( t), and a large variety of erosion rates. The role and effect of isostatic compensation is estimated in conjunction with the status of the stress field, using a modified lithospheric thinning model suggested by Morgan (1983). Comparing the best-fitting curve of the plateau's surface evolution with the model-calculated curve of tectonic uplift and the estimated curve of isostatic uplift, the author has distinguished the following three stages in the whole history of the Tibetan Uplift: (1) a slow uplift stage (40-20 Ma), (2) an undulating uplift stage (20-2 Ma) and (3) a rapid uplift stage (2-0 Ma).