Cenozoic volcanism of the Caucasian mobile belt in Georgia, its geological-petrological peculiarities and geodynamic conditions

Abstract

The Caucasian mobile belt is situated in the area of Late Cenozoic collision of the large Afro-Arabian and Eurasian lithospheric plates. Extensive volcanic activity in the Georgian part of the Caucasian mobile belt took place during the Late Miocene-Holocene. Five volcanic regions have been identified in Georgia; each of them reveals in a greater or lesser degree similarity of tectonic and magmatic processes. Volcanic products are represented by basaltic, doleritic, andesitic basaltic, andesitic dacitic, rhyolitic lavas and their pyroclastics with andesites and dacites prevailing. Using petrochemical and geochemical data the volcanics can be divided into two main rock groups: calc-alkaline and subalkaline series. The marker petrogeochemical series is presented by the medium- to high-K calc-alkaline volcanics. Relative to the heavy elements (HFSE) Y, Nb they are enriched in some large ion lithophile elements (LILE) Rb, Sr, Ba and light rare earth elements (REE) La, Ce. This confirms the leading role of fractional crystallization in forming the volcanics of the study area. These volcanics have the characteristics of pre-collision subduction (increased LILE content and high La/Nb ratios) geodynamic regimes. Volcanic rocks derived from sources displaying different tectonic environments show close petrogeochemical resemblance, indicating the similarity of the melting substrates of magmatic chambers. The findings also allow us to give priority to the magma generation conditions, to its periodical renewal and depths of inception in comparison with the geodynamical factors. Isotopic data (87Sr/86Sr) have confirmed that the subduction-enriched lithospheric mantle material was more important than that of the continental crust components. Sr isotopic ratios do not show marked dependence on the values of the petrochemical composition of the enclosing rocks and on the time of their formation. © TÜBİTAK.