Tectonics in the Greater Caucasus (Georgia – Russia): From an intracontinental rifted basin to a doubly verging fold-and-thrust belt

Abstract

The Greater Caucasus doubly-vergent orogenic system has its origin in a Mesozoic-Early Cenozoic back-arc-type basin, floored by an extensively stretched and heavily intruded continental crust that has subsequently been inverted. Our field investigations along the Georgian Military Road in the eastern Central Greater Caucasus provide insights in its tectonic structure and reveal a bivergent orogenic wedge geometry. The southward propagating pro-wedge comprises the Southern Slope tectonic imbricate system developed in the Mesozoic-Early Cenozoic basin infill and the Transcaucasian Kartli foreland fold-and-thrust belt and is actively underthrust by the Transcaucasian Dzirula-Shatsky Block. The retro-wedge, on the other hand, incorporates the Northern Slope tectonic zones (including the Homocline Range) and the North Caucasian Terek-Sunzha foreland fold-and-thrust belt that developed in the Mesozoic-Cenozoic cover of the Scythian Platform. The Main Range forms the axial zone of the mountain belt where crystalline, pre-Mesozoic basement is locally brought to the surface at almost 3000 m altitude along the Main Caucasus Thrust.Our study of the regional geology, in combination with paleotectonic reconstructions suggests that the present-day tectonic units of the Caucasus correspond to distinct pre-collisional paleotectonic domains that existed in the Mesozoic-Early Cenozoic Neotethys-Eurasia ocean-continent convergence zone. The focus of our study lies on the tectonic interpretation of the Greater Caucasus fold-and-thrust belt. We propose to interprete the major thrusts of the orogen as former normal listric detachments occurring in the Greater Caucasus Basin, that were reactivated as reverse faults and thrusts during the collisional events of the Arabia-Eurasia convergence since the Late Eocene-Oligocene (Alpine inversion stage).