RUBIDIUM-STRONTIUM AGE AND GENESIS OF ROCKS OF THE SHOSHONITE-LATITE SERIES IN THE EASTERN RHODOPE, BULGARIA

Abstract

The rubidium- and strontium-isotope distribution in volcanic rocks of the shoshonite-latite series of Bulgaria has never before been investigated. The Borovitsa volcanotectonic depression studied by us is underlain by rocks of shoshonite-latite-trachyte-trachyrhyodacite series. The volcanic structure proper occupies the northwestern part of the larger East Rhodope depression and covers an area of about 1500 km2. Clastic and volcanic rocks of Paleogene-Quaternary age here overlie the old basement, consisting of schists, gneisses, amphibolites, marbles and the like. Overall, the isotopic and chemical compositions of basaltoid rocks of the shoshonite-latite series agree well with the general petrogenetic model in which mafic magmas are regarded as products of melting of a depleted mantle substrate under the influence of transmagmatic fluids carrying incongruent, ore and rare elements from an undifferentiated mantle source.