Abstract:
Analysis of the Earth's shell composition permits one to estimate quantitatively the matter exchange between the lower and upper mantle. On the basis of available data, the intensity of magmatism, as the important mechanism of matter exchange in the upper shells, is quantitatively estimated in mid-oceanic ridges (MORs), island arcs, and hot spots. The intensities of effusive lavas in island arcs and spreading regions are compared with their theoretically calculated values. On the basis of the criterion characterizing the conditions of volcanism generation, avolcanic regions under lava subduction are revealed. It has been established that in MORs the periods of active magmatism, when magmatic products almost completely effuse onto the surface, alternate with the periods of plum magmatism, when the most part of magma stays at depth. Magmatism of active margins depends primarily on the spreading intensity, but in the period of great collisions it manifests itself only slightly or is replaced by collisional granites. The variety and interrelation of these processes ensure a stability in thermal processes in the Earth's shells.