THE GREATER CAUCASUS MOUNTAINS: A COMPLETE TRANSECT FROM ACTIVE SUBDUCTION TO CONTINENTAL COLLISION IN A SINGLE OROGENIC SYSTEM

The Greater Caucasus Mountains lie at the northern margin of the Arabia-Eurasia collision and accommodate the majority of plate convergence at their longitude. Marked, and contradictory, variations in along-strike geodetic convergence rates, distribution of seismicity, and depth of upper-plate exposure and total shortening have confounded an integrated understanding of the Caucasus as a coherent Late Cenozoic orogenic system driven by the northward collision of the Lesser Caucasus oceanic island arc with the southern margin of Eurasia. Recent geologic studies, including balanced cross-section restorations and low-temperature thermochronology, geochemical studies of Mesozoic and Cenozoic volcanic rocks, and recent and ongoing geophysical investigations have elucidated the tectonic evolution, neotectonic activity, seismotectonics, and crustal structure of the Greater Caucasus.

We propose that the Greater Caucasus are best understood by division into four distinct tectonic zones. From east to west, these zones are (i) the Caspian Zone, beneath the Caspian Sea, where subduction of the South Caspian Basin beneath the Apsheron Sill is ongoing, but the construction of a substantial accretionary prism or other tectonic edifice is lacking; (ii) the eastern Greater Caucasus, where ongoing subduction of the oceanic-floored Kura Basin drives lithospheric deformation forming a terrestrial accretionary prism in the Greater Caucasus range; (iii) the central Greater Caucasus, where incipient subduction of the ~40 km thick crust of the Lesser Caucasus arc has resulted in the uplift and erosion of the Kura foreland basin, development of a fold-thrust belt spanning the entire width of the foreland basin, and a bivergent accretionary wedge in the Greater Caucasus, and (iv), the western Greater Caucasus, where subduction is complete and continental collision now drives lithospheric deformation throughout the upper plate, suture zone, and lower plate of the Caucasus orogenic system.

Such an interpretation reconciles outstanding discrepancies in along-strike observations of the orogen from a geophysical, geodetic, and geologic perspective and constructs a coherent framework in which the Greater Caucasus can be understood as reflecting a continuum of stages in the transition from oceanic subduction to continental collision.