Tectono-thermal evolution of central Transcaucasia: Thermal modelling, seismic interpretation, and low-temperature thermochronology of the eastern Adjara-Trialeti and western Kura sedimentary basins (Georgia)

Structural interference along the boundaries of adjacent tectonic domains generates complex subsidence and exhumation patterns. In this paper we study a key segment of the convergence zone between the interfering south-verging Greater Caucasus and north-verging Lesser Caucasus retro-wedge. The study area comprises the along-strike transition between the Paleogene Adjara-Trialeti back-arc basin and the Oligocene-Neogene Kura foreland basin of eastern Georgia. During the Neogene, despite their difference in age and subsidence mecha-nisms, both basins have been progressively inverted to various extent within the overall context of the Arabia-Eurasia continental collision. Thermal modelling of borehole data from the Adjara-Trialeti basin allowed to reconstruct two phases of rapid subsidence, late Paleocene-Early Eocene and Middle-Late Eocene, respectively correlated to flexural loading by the Lesser Caucasus retro-wedge and continental rifting. Integration of thermal modelling, apatite fission-track statistical inverse modelling, and seismic interpretation detected a third subsi-dence phase in the Early Miocene, possibly related to strike-slip tectonics. Thermal maturity data dictate that 1.0-1.3 km of the Adjara-Trialeti sedimentary succession has been eroded since the onset of structural inversion in the mid-Miocene. The burial history of the western Kura Basin outlines intermittent and asymmetrical episodes of flexural subsidence from the Oligocene to the Late Miocene, due to competing loading by the Lesser Caucasus, the Adjara-Trialeti fold-and-thrust belt and the Greater Caucasus. Finally, during latest Miocene times southward propagation of deformation from the Greater Caucasus induced an additional tectonic loading (1.3-1.8 km) due to the emplacement of thin-skinned thrust sheets, mostly eroded during the Plio-Quaternary.