Thermal and mechanical models of continent-continent convergence zones

Abstract

The thermal regimes of continent-continent convergence zones are modelled by a finite difference technique, assuming that there is some subduction of continental crust. Gravity and heat flow profiles are generated from the thermal models. Subducted crust and slab remain cool except at the upper surface where frictional heating is important. Crustal rocks may be metamorphosed or melted by friction while the plates are converging or by radioactive self-heating more than 30 m.y. after the plates have stopped. In the former case, melting requires frictional shear stresses between 500 and 2000 bars at a plate velocity of 5 cm/yr. At lower velocities the upper limit of frictional stress is greater. The total work performed in continental subduction may be minimized if the angle of underthrusting becomes more shallow, changing the location of subduction. A model for the geometry of oceanic and continental slabs in the Zagros Mountains is presented which satisfies gravity, heat flow, seismic, and geologic,constraints. Continental underthrusting is beginning along a new fracture at the edge of the Persian Gulf, isolating the Arabian continental shelf from the subduction process. Slippage along this fault is Pleistocene and probably does not exceed 30 km. Subduction of continental crust at the crush zone is probably insignificant. o KM 200 , ß ß ß \ ß

Source and Propagation Effects of Rayleigh Waves from Central Asian Earthquakes

“…It should be mentioned that Bird's 55km crustai model (Bird, 1976) Before going on to discuss mantle conditions, the model, PLATEAU-3, ais given in Table 5 To meet the constraint on the long period dispersion base must be 4.9km/sec which is .2km/sec higher than for stable models as was also found for the Tectonic province.…”

“…The formation of orogenic belts (Dewey and Bird, 1970), the seismicity, stress field, faulting Molnar and Tapponnier, 1975) and the mechanical and thermal evolution of structures in southern Asia (Bird, 1976) proto-lithospheric plates (Hamilton. 1970).…”

‘On the eclogites of Norway’—65 years later

“…10: Spinel lherzolite/garnet lherzolite transition (O'Hara et al, 1971). 11: P, T path, Zagros, top of slab (Bird et al, 1975).…”

Comments on ‘Initiation of intracontinental subduction in the Himalaya’ by Peter Bird

“…The temperature regime is contended to be partly controlled by thrust-related frictional heating and radioactive heating through doubling of the continental crust [Bird et al, 1975]. Bird [1978] rejected these possibilities, however, and suggested a process of lithospheric delamination and mantle upwelling to explain the thermal history and the subsequent generation of the MCT.…”