PETROCHEMISTRY OF RHYODACITE-TRACHYTE SERIES IN A PALEOGENE VOLCANOPLUTONIC BELT IN THE SOUTHEASTERN PAMIRS

Abstract

The antidromous and most acid series of a volcanoplutonic belt in the Southeastern Pamirs was studied. It makes up a stratovolcano 1365-3150 m thick and consists of five volcanogenic formations (rhyodacites, trachydacites, toscanites, trachytes, and latites), apart from a basal one. For study, 2500 m of the series section were sampled at regular intervals; a total of 220 samples were analyzed. The petrochemical profiles showed that the series is slightly differentiated and belongs to shoshonite and latite series of margin-continental volcanogenic belts, but with a drastic predominance of acid volcanites. This excludes the hypothesis for shoshonite-magma differentiation and suggests abundant melting of acid crustal material, which was predominant during the magma syntexis. The Late Eocene age of the series and the compositional similarity of the latter to Cenozoic volcanogenic formations in Tibet and Tarim can clarify the activity of the Tien Shan-Tibet plume in the Cenozoic.