Structure and evolution of the Pamir—Hindu Kush region lithosphere

Abstract

The deep structure of the Pamirs—Hindu Kush region is considered. Using the geological and tectonic data a conclusion is reached on the sliding of the 30 km uppercrustal layer and its disharmony relative to the upper crust. On the basis of the methods of the three dimensional wave velocity model of the lithosphere, obtained by the seismic tomography algorithm, and of the investigations of the recurrency law of the earthquakes in the Pamirs—Hindu Kush mantle focal zone, developed by the author's, a considerable horizontal inhomogeneity is recognized in the structure of the region up to a depth of 300 km. All these data indicate that the movement of the lithosphere plates is brought about not by simple subduction, but by their twisting, differentiated at various levels, occurring in the upper mantle notless but perhaps even more intensively than in the Earth's crust. The mixing of the crustal and mantle materials accompanying this process can account for the decrease in the upper mantle average density in certain parts of the region.