Recent Mountain Building of the Central Alpine-Himalayan Belt

摘要

From the end of the Eocene through the Pliocene, the Alpine-Himalayan Belt underwent colli-sional shortening induced by convergence of the Gondwana plates with the Eurasian Plate and varied in orientation from the north-northwestern to the northeastern directions. The collisional shortening was expressed in folding, thrusting of continental crustal tectonic sheets over one another, and closure of the residual basins of Neotethys and its backarc seas; it resulted in local thickening of the crust and its isostatic uplifting. As a rule, the uplifts were not higher than ～1.5 km. In other words, before the Pliocene, the growth of local mountain edifices was caused by collisional shortening of the belt. Isostatic uplifting of the thickened crust was continued in the Pliocene and Quaternary even more intensely than before, but the general rise of the mountain systems was superposed on this process. The rise substantially exceeded in amplitude the contribution of the uplift caused by shortening and did not depend on the preceding Cenozoic history of either territory. Not only the mountain ridges but also most adjacent basins were involved in rising, which eventually led to the contemporary mountain topography of the belt. The spread of the hot and fluid- enriched astheno-sphere of the closed Tethys beneath the orogenic belt could have been a cause of such additional rising. The uplift was an isostatic reaction to decompaction of the lithospheric mantle partly replaced with asthenosphere and of the lower crust subject to retrograde metamorphism under the effect of cooled asthenospheric fluids. The deep transformations are also probably responsible for deepening of some basins in the Pliocene-Quaternary and more contrasting transverse segmentation of the belt.