3.7.2 Large scale neotectonics of the Caucasus and surrounding areas

The Greater Caucasus, located at the cross-road of Europe, Asia and Arabia, is Europe’s highest mountain range (Khain, 1975; Adamia et al., 1977; Gamkrelidze and Gamkrelidze, 1977; Adamia et al., 1981; Khain, 1997). At its eastern termination, in Azerbaijan, the Greater Caucasus plunges into the Caspian Sea where it forms the Apsheron Sill. The Caspian Sea is one of the world’s major oil provinces, and an area of geostrategic and geopolitical importance. The sediments that host the oil reservoirs in the Southern Caspian Sea were deposited in a very deep basin (> 20km). The provenance/source of these sediments is the Greater Caucasus from where erosion products were carried by large rivers such as the Volga, Samur and Kura into the Caspian Basin. Similarly, the Black Sea represents a major sediment sink at the western termination of the Greater Caucasus.

The continued growth of the Greater Caucasus since the Early Tertiary and the important subsidence of the South Caspian Basin is crucial to the understanding of erosion and sedimentation processes in this area. The Greater Caucasus is not only Europe’s highest mountain range, but also the fastest growing one. This growth is due to the convergence of the Arabian plate with the Eurasian plate at rates of 22-24 mm/y, leading to continued earthquake activity and growth of the mountain range (Zonenshain et al., 1990; Priestley et al., 1994; Nilforoushan et al., 2003; Allen et al., 2004).

As tectonic activity is expressed in the morphology, the Greater Caucasus is a unique natural laboratory to investigate links between lithospheric, tectonic, and surface processes. The present topography is also the surface we live on and any dramatic changes or ruptures in this surface are likely to cause important economic damage and possible loss of human life. Slope instabilities associated with heavy rainfall regularly causes landsides and other mass wastage processes, resulting in major changes in landscape. Active crustal shortening across the Greater Caucasus and the resulting uplift are associated with constant seismicity. Igneous activity unrelated to the Lesser Caucasus volcanic arc, is manifest in the border area between Georgia and Russia, with Mount El'brus being the most outstanding example.

The Greater Caucasus developed in response to the final closure and inversion of a Mesozoic back-arc basin that had undergone repeated phases of extension and compression during Triassic to Cretaceous times in response to activity along Tethyan subduction systems located south of the Pontides and the Lesser Caucasus. The Caucasus orogeny commenced during the Late Eocene and persisted until the present. The southern margin of the Greater Caucasus Trough is partly preserved in the western Greater Caucasus near the Black Sea in Georgia (Banks et al., 1997), but is unknown to the east near the Caspian Sea in Azerbaijan. This margin was flanked to the south by the subduction-related volcanic arc of the Lesser Caucasus that had been active since the Early Jurassic (Philip et al., 1989; Ershov et al., 1999; Mikhailov et al., 1999; Nikishin et al., 2001; Brunet et al., 2003; Ershov et al., 2003; Nikishin et al., 2003). The main topographic relief of the Greater Caucasus began to develop during the Middel Miocene and younger tectonic phases. The transition from subsidence of the Greater Caucasus Trough to its inversion and the resulting rise of the mountain chain is documented by the sedimentary record of basins flanking it to the north (Indol-Kuban and Terek-Caspian depressions) and to the south (Rioni and Kura basins) (Ershov et al., 2003). This record needs to be further explored in terms of the gradual rise of the Greater Caucasus mountain range. Although important amounts of sediments were deposited during the Late Eocene and Oligocene in the Caspian Sea – Black Sea Paratethys realm, it remains unclear whether already at these times the Greater Caucasus had formed a major topographic feature or barrier, or whether it formed lowlands prior to its rapid Mid-Miocene uplift (Popov et al., 2004). How is dynamic topography linked to tectonic and surface processes during the Tertiary to recent development of the Greater Caucasus Orogen? What lithospheric processes were involved in the development of the crustal roots that support the present-day topography?