Pecularities of Structure and Development of Caucasian Segment of Alpine-Hymalayan Collizion Zone: Evidence from Geological, Volcanological, and Geophysical Data

The Caucasus is a part of huge Late Cenozoic Alpine-Himalayan zone collision of continental plates, lasted throughout the Eurasian continent. At that the Greater Caucasus is an edge of the Eurasian plate, raised along the large reverse fault - the Main Caucasian Fault. This fault, in turn, is a part of the super-fault, stretching from the Kopetdag to the Trans-European Suture Zone (zone Tornquist-Teisseyre). The Caucasus is limited from its both sides by large depressions of Black and Caspian seas, which "cut off" pre-Pliocene structures both the Caucasus and the Kopetdag; origin of these seas is associated with downward currents in the mantle ("cold plumes"). The peculiar structure of the region is north-south Transcaucasian Rise, which is located in the northern part of Caucasian-Arabian syntaxis. Large positive isostatic anomaly is confined with it, apparently indicating presence here of the mantle plume head. Along the zone of syntaxis the belt of Neogene-Quaternary volcanism occurs which begins in Eastern Anatolia and traced through the Lesser to Greater Caucasus. Two types of volcanic rocks are represented here: (1) prevailing volcanics of calc-alkaline series, very close in petrological and geochemical characteristics to suprasubduction type, and (2) extensive lava plateaus formed by basalts of intraplate (plume related) type. However, subduction zone under the Caucasus region, as well as throughout the Caucasian-Arabian syntaxis, is absent and relatively shallow earthquakes (50-60 km) are dominated here. We considered that origin of calc-alkaline magmas is associated with interaction between the mantle plume head, and crustal material at shallow depths under conditions of deformation at high pressures, leading to melting of the material in the zone of collision. Reduction of space in the area of Caucasian-Arabian syntaxis, which occurred during the Late Cenozoic, reached 400 km; such shortening in absence of subduction was apparently achieved mainly due to tectonic "diffluence" of the crustal material to both sides before hard "stop" of the East European Craton under the pressure of the Arabian indenter. Situation in the region continues to develop now mainly due to deep-seated mantle processes, gradually destroying structure of the pre-Pliocene collision zone on the surface.