General discussion

Abstract E. V. Artyushkov (Institute of Physics of the Earth, Moscow, U.S.S.R.). Shortening of the crust has been modelled by compression of a continuous medium. It has also been supposed that compression can start in continental crust of normal thickness. Mathematical models of the same type have recently been used by some other authors. It should be noted that an intense shortening of the crust in fold belts never occurred in such a way. In the main Phanerozoic fold belts (the Urals, Appalachians, Scandinavian Caledonides, the Alpine and Verkhoyansk belts, and others) no era tonic block with a normal continental crust and lithosphere was shortened (Artyushkov & Baer 1983, 1984, 1986). An intense compression took place only in deep basins on oceanic or continental crust. Most oceanic crust disappeared from the surface in the process of subduction. Now the fold belts are mainly built up of a strongly compressed crust of deep basins on continental crust. How can it be proven that this crust was really thin?