Evolutionary model of the Himalaya-Tibet system: geopoem based on new modelling, geological and geophysical data

A two-dimensional thermo-mechanical laboratory modelling of continental subduction was performed. The subducting continental lithosphere includes a strong brittle upper crust, a weak ductile lower crust, and a strong upper mantle. The lithosphere is underlain by a low viscosity asthenosphere, Subduction is produced by a piston (push force) and the pull force from the mantle lithospheric layer, which is denser than the asthenosphere, The lithospheric layers are composed of material whose strength is sensitive to and inversely proportional to temperature. Throughout the experiment the model surface was maintained under relatively low temperature and the model base at higher temperature, The subduction rate satisfied the Peclet criterion, Modelling confirms that the continental crust can be deeply subducted and shows that slab break-off, delamination and tectonic underplating are fundamental events with drastic consequences on the subsequent evolution of the convergent system. Combining these results with previous, purely mechanical modelling, we elaborate a new evolutionary model for the Himalaya-Tibet convergent system. The principal successive stages are: (1) subduction of the Indian continental lithosphere to 200-250 km depth following subduction of the Tethys oceanic lithosphere; (2) failure and rapid buoyancy-driven uplift of the subducted continental crust from ca, 100 km depth to some depth that varies along the mountain belt (20-30 km on average); (3) break-off of the Indian subducted lithospheric mantle with the attached oceanic lithosphere; (4) subduction/underplating of the Indian lithosphere under Asia over a few to several hundred kilometers; (5) delamination, roll-back, and break-off of the Indian lithospheric mantle: (6) failure of the Indian crust in front of the mountain belt (formation of the main central thrust) and underthrusting of the next portion of Indian lithosphere beneath Tibet for a few hundred kilometers. At the beginning of stage (6), the crustal slice corresponding to the Crystalline Himalayas undergoes 'erosion-activated' uplift and exhumation. (C) 2000 Elsevier Science B.V. All rights reserved.