FEATURES OF THE MINERAL COMPOSITION OF ANDESITES FROM THE MATEKIVSKYI AND OBAVSKYI VOLCANIC COMPLEXES OF THE VYHORLAT-HUTYNSKE RIDGE (UKRAINIAN CARPATHIANS)

Abstract

The article provides information on the mineral composition of rocks that form the Matekivskyi and Obavskyi volcanic complexes, which are the part of the Vyhorlat-Hutynske Volcanic Ridge central segment in the Ukrainian Carpathians. Rocks from the quarries in the villages of Klenovets, Shelestove and Obava are described. The quarry in Klenovets is composed of andesite-basalts, andesites and their porphyrites (total observed thickness reaches 30 m) which form columnar jointing and slab parting. The rocks are mediophyric, have dark grey colour and massive texture. Plagioclases, clino- and orthopyroxenes, and ore mineral predominate among the phenocrysts. The groundmass has hyalopylitic, andesitic or intersertal texture and is composed of acid volcanic glass, plagioclase, pyroxene and ore mineral. The dome-shaped structure is clearly visible in the quarry of Shelestove. Volcanic rocks are represented by andesites, andesite-dacites and in the upper part of the section ‒ often by tuffs or interbedding of andesites, andesite-dacites and tuffs. The results of the microprobe studies of the Matekivskyi volcanic complex rocks from quarries of the Klenovets and Shelestove (Kolchino) showed that plagioclases are represented by labradorite and bytownite, pyroxenes ‒ by orthopyroxenes of the enstatite‒ferrosilite series and clinopyroxenes (augite, diopside). A powerful flow of medio- and magnophyric andesites and andesite-basalts is exposed in the Obava- village quarry; andesite tuffs occur at the bottom of the flow. Grey andesites contain phenocrysts of labradorite, orthopyroxenes of the enstatite‒ferrosilite series and augite. The trends of change over time of mineral composition (in the direction of the central part of the phenocryst → its peripheral part → the groundmass of the rock) in the studied rocks, determined by the results of microprobe analyses, are as follows: the content of Na and K increases in plagioclases, Fe ‒ in pyroxenes and Ca ‒ in orthopyroxene. The temperature regime of magmatic systems during the formation of volcanic rocks in the studied area covered the range of 1000–700 °C.