IGNIMBRITE DIFFERENTIATION AND ESTIMATION OF THE VOLUME OF MAGMA EJECTED DURING IGNIMBRITE FORMING ERUPTIONS IN EAST KAMCHATKA

Abstract

This study was carried out in the central segment of the East Kamchatka volcanic belt, known for its wide development of ignimbrites which cover an area of -4000 km2. Ignimbrites fill several calderas located in the central parts of three major volcanic centers: Karymskii, Bolshoi Semyachik, and Uzon-Geizernyi. They range from 35 to 180 thousand years in age. Ignimbrites were examined in the Novyi Semyachik R. valley stretching along a boundary between the Karymskii and Bolshoi Semyachik volcanic centers, where their sequences were described in detail. The study of their mineral compositions revealed differences between the rocks produced by different volcanoes. As a result, the limits of the ignimbrite fields were defined more exactly, and the ignimbrite volumes were calculated. The total volume of the rhyodacite magma ejected during the eruptions that had occurred in East Kamchatka during the last 180 000 years was estimated as 1.2 km3/thou. years.