Eastern Anatolia: A hotspot in a collision zone without a mantle plume

Abstract

Eastern Anatolia is one of the best examples of an active continental collision zone in the world. It comprises one of the high plateaus of the Alpine-Himalaya mountain belt, with an average elevation of similar to 2 km above sea level. Almost two-thirds of this plateau is covered by young volcanic units related to collision. They range in age from 11 Ma to Recent and have a thickness of up to 1 km in places. The collision-related volcanic province is not confined to Eastern Anatolia, but extends across much of the Caucasus in the east, including Eastern Turkey, Armenia, Azerbaijan, Georgia, and Southern Russia, spanning a distance of some 1000 km. The region covered by the collision-related volcanic sequences comprises a regional domal shape (similar to 1000 km in diameter), and this unique morphology is comparable to that of the Ethiopian high plateau except for its north-south shortened asymmetrical shape. Recent geophysical data reveal that the lithospheric mantle is exceptionally thin or absent beneath this regional dome, indicating that the dome is currently supported by the asthenospheric mantle. Because of these features, the Eastern Anatolia-Iranian plateau and the Lesser Caucasus region as a whole can be regarded as the site of a "melting anomaly" or "hotspot" closely resembling the setting proposed for mantle plumes. However, geologic and geochemical data provide evidence against a plume origin. Instead, the results of recent geophysical studies, coupled with geologic, geochemical, and experimental findings, support the view that both domal uplift and extensive magma generation can be linked to the mechanical removal of a portion or the whole thickness of the mantle lithosphere, accompanied by passive upwelling of normal-temperature asthenospheric mantle to a depth as shallow as 40-50 km. Mechanical removal of the mantle lithosphere might be controlled by delamination in the north beneath the Erzurum-Kars plateau, while it might be linked to slab steepening and break-off in the south. Therefore, magma generation beneath Eastern Anatolia may have been controlled by adiabatic decompression of the asthenosphere. The Eastern Anatolian example is important in showing that not only plumes but also shallow plate tectonic processes have the potential to generate regional domal structures in the Earth's lithosphere as well as large volumes of magma in continental intraplate settings.