Supercomputer simulation of continental collision in Precambrian: lithosphere thickness effect
Many aspects of Precambrian tectonics remain unclear due to the indeterminate influence on geodynamic processes that is exerted by a number of key physical parameters (the mantle temperature, lithosphere thickness, etc.) which in the Precambrian time significantly differ comparing to those at present. This paper presents results of thermo-mechanical-petrological two dimensional (2D) numerical modeling which simulates the convergence process at the velocity of 5 cm/year depending on continental lithosphere thickness. In the model continental lithosphere thickness ranged from 100 km to 200 km, the upper mantle temperature exceeded the modern temperature by 150 °С, and the radiogenic heat production of continental crust is 1.5 times higher than that at present. The numerical modeling has shown that in the case of lithosphere thickness of 100 to 160 km the subduction terminates with the detachment of the oceanic plate from the continental plate (slab break-off) followed by the formation of a broad magmatic province (oceanic plateau) which takes place between the continents instead of the orogenesis. The time and the place of occurrence of the slab break-off depend on lithosphere thickness, the thinner it is the earlier and the closer to the surface the slab break-off occurs. For instance, in the model with a relatively thin continental lithosphere of 150 km, the slab is detached in 10,3 m.y. at the depth 150 km, whereas in the case of thin lithosphere of 100 km the slab detaches in 5,1 m.y. and almost at the very surface. In the latter case, the magma generation area is much larger due to the formation of magmatic provinces on both sides of the oceanic slab (instead of one side as it was observed in other models). Continental collision with a very thick lithosphere (of 200 km and more) proceeds without slab break-off and is not followed by any significant volcanism. Thus, modeling performed in the present paper demonstrates an impact of SLAB PULL mechanism on processes in plate convergence zones.