The Early Mesozoic evolution of the Western Greater Caucasus (Russia): Triassic–Jurassic sedimentary and magmatic history

Abstract

Abstract The Greater Caucasus (GC) forms a high Alpine fold-and-thrust belt on the southern margin of the East European Platform (EEP). The Triassic, and particularly, the Jurassic history of the Western Greater Caucasus region is important for our understanding of the palaeogeographic and tectonic evolution of the western Tethys area. In order to better constrain the nature and relevance of these events in the evolution of the region, which are classically described as the Late Triassic to Late Jurassic Cimmerian events, a field campaign in the Western Greater Caucasus was undertaken. Analysis of structural, sedimentological and petrological data from 41 sites in the Fore-Caucasus (Malaya Laba, Mount Tkhach-Belaya River), the Central Greater Caucasus (Georgievskoye, Otdaleni) and Southern Slope (Krasnaya Poliana) areas of the Western Greater Caucasus revealed that a broad asymmetric basin, with associated emergent volcanic islands, formed in the area in Jurassic times. Incipient back-arc rifting in Pliensbachian times was coeval with similar rifting episodes in the Pontides and South Caspian Sea areas. The synchroneity of these events may have been related to the renewal of the Tethys subduction to the south of the Eo-Cimmerian accretionary belt. Rift reactivation, with significant thinning of the continental lithosphere, occurred in the Aalenian. Despite the strong Alpine tectonic overprinting, some structural data confirms that the extension trend was east–west (almost parallel to the active margin) resulting in the formation of a series of pull-apart basins in the GC and the South Caspian region behind the Eastern Pontides–Lesser Caucasus subduction-related volcanic belt. In Bajocian times, subduction-related volcanic activity largely expanded from the Eastern Pontides–Lesser Caucasus to encompass the Transcaucasus, the southern part of GC and the Crimea region. Such widening of the volcanic arc was probably due to a shallowing of the northward subducting slab. In the back-arc GC region, this signalled the onset of the post-rift stage. The return of the slab to normal steepness resulted in subsidence in the back-arc region and in the GC with extensive accommodation space creation. This was subsequently filled by the Late Jurassic, Cretaceous and Cenozoic sedimentary successions.