Relict basin closure and crustal shortening budgets during continental collision: An example from Caucasus sediment provenance

The basin's closure is believed to have initiated at approximately 35 million years ago, coinciding with the initial collision between the Arabia and Eurasia plates along the Bitlis-Zagros suture. This event eventually led to the hard collision between the Lesser Caucasus arc and the Scythian platform, forming the Greater Caucasus Mountains. The closure of the back-arc basin is thought to have triggered deceleration of plate convergence and tectonic reorganization throughout the collision. The basin's width is estimated to have been approximately 350-400 kilometers. The postcollisional subduction of such small relict ocean basins can account for both shortening deficits and delays in plate deceleration by accommodating convergence via subduction/underthrusting. However, this shortening is easily missed if it occurs along structures hidden within flysch/slate belts. The study of the Greater Caucasus Mountains provides a unique opportunity to investigate the response of the continental lithosphere to plate collision. The region's tectonic evolution is characterized by a combination of postcollisional subduction and upper crustal shortening. The results of this study suggest that the closure of the relict back-arc basin played a crucial role in accommodating the convergence between the Arabia and Eurasia plates. The Arabia-Eurasia collision is an ideal location to investigate both shortening deficits and postcollisional deceleration of convergence. The collision is younger and slower than the India-Eurasia collision, with a total convergence of approximately 750-950 kilometers since 35 million years ago. However, the documented shortening in the region is only approximately 530 kilometers, resulting in a shortening deficit of at least 220-420 kilometers. The study of the Greater Caucasus Mountains and the Arabia-Eurasia collision provides new insights into the mechanisms of continental collision and the accommodation of convergence. The results suggest that postcollisional subduction of relict ocean basins can play a significant role in accommodating convergence and reducing the need for upper crustal shortening. This mechanism can help to explain the observed shortening deficits in collisional orogens and provide a new perspective on the tectonic evolution of these regions. The closure of the relict back-arc basin in the Greater Caucasus Mountains is believed to have occurred at approximately 5 million years ago, triggering final tectonic reorganization and the formation of the modern mountain range. The study of this region provides a unique opportunity to investigate the response of the continental lithosphere to plate collision and the accommodation of convergence. The results of this study have implications for our understanding of the tectonic evolution of collisional orogens and the mechanisms of continental collision.