Some recent Russian studies of ignimbritic rocks

Abstract

Abstract Summarised translations of recent papers by the Russian geologists Vlodavetz, Petrov, Maleyev, Piip, Aprelkov, and Bykovskaya and Rottman are presented and discussed. Current classifications of volcanic rocks in the U.S.S.R. include a group of rocks, called “tufolavas”, not generally recognised elsewhere. They are reported to be like ash-flow tuffs or ignimbrites, but are characterised by lens-like inclusions and have a “fluidal” or lava-like matrix. Their distinction from welded tuffs deposited at high temperature is not clear in the literature. In the U.S.S.R. ignimbrites and tufolavas have been studied in detail in the Quaternary volcanics of Armenia and Kamchatka. Other, older deposits have been found in volcanic provinces in eastern Siberia, in the Urals, and in the high mountain ranges south of Kazakhstan. Chemically, they range mainly between rhyolite and dacite. Most writers ascribe their origin to some degree of magmatic differentiation. Phenocryst modes differ in the different volcanic ...