SOUTH-EASTERN VOLCANIC BELT OF KAMCHATKA: STRUCTURE OF THE BASEMENT

Abstract

In the course of volcanic activity the rising magma interacts with the basement rocks. The resulting system of magma conduits, marked by dikes and subvolcanic bodies, tends to spread as volcanic events are repeated. The fields of dikes and subvolcanic bodies are comparable in area, where exposed by erosion, with the foundations of large stratovolcanoes (tens to hundreds of square kilometers). In this process the basement rocks are removed to the surface by way of disintegration and removal as xenoliths carried by lava and pyroclastic material, or the rise of relatively large blocks, this process being accompanied by the intensive assimilation of basement rocks. Geophysical data show the regions of the development of Cenozoic volcanic systems as zones of "uncertainty" caused by the high reworking of the basement and its saturation with Cenozoic dikes and sills. The uncertainty is aggravated by a similarity between the densities of these bodies and basement rocks. The dike-sill systems are supposed to extend to depths as great as 7 km.