SILICIC VOLCANISM ON KOZUF MAUNTAINS EVIDENCED BY TRIDIMITE AND PERLITE IN HIGH-SiO2 SEDIMENTARY ROCK AT ALSAR CALDERA

Abstract

The volcanic caldera Allchar is located in the western area of the volcanic complex in the Kozuf Mountain at the
frontier of the Vardar zone and the metamorphic complex Elen Supe, a relic of the old Precambrian continental
crust. The volcanic activity in this area of the volcanic complex in the Kozuf Mountain is represented by igneous
rocks with Dacitic-Rhyolitic composition. There are many sediment pyroclastic rocks in the composition of the
caldera, represented by volcanoclastic tuffs with layers of tridymite and layers of perlite. Tridymite appears in
layers, few meters thick and its color is white. Tridymite and perlite are usually associated with Silicic volcanism.
There is also crystobalit and smaller amount of opal in tridymit’s composition. The appearance of opal is due to the
diagenetic changes of the high temperature SiO2 glass. This paper presents the mineralogical and geochemical
investigations of tridymite and perlite using XRD, FUS-ICP-MS, SEM-EDS methods. Normalized values of the rare
element earth show distribution in the same manner as in the igneous rocks at the volcanic caldera of Allchar.