Domal uplift and volcanism in a collision zone without a mantle plume: Evidence from Eastern Anatolia (davet üzerine hazırlanan web sayfası) http://www.mantleplumes.org/Anatolia.html


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KESKİN M.

Other, pp.1, 2005

  • Publication Type: Other Publication / Other
  • Publication Date: 2005
  • Page Numbers: pp.1

Abstract

The Eastern Anatolia region is one of the best examples of a continental collision zone in the world. It also comprises one of the high plateaus of the Alpine-Himalaya mountain belt with an average elevation of ~2 km above sea level (Fig. 1). It displays shallow and diffuse seismicity (Fig. 2), indicating that the lithosphere is still being actively deformed as a result of diffuse north-south shortening. This implies that the collision is still in progress. Previous studies have shown that the Arabian plate made its initial contact with the Eurasian plate during the Late Eocene. The region underwent compressional tectonic evolution subsequently, but most of it lay beneath sea level during a period between the Late Eocene (~50 Ma) and Serravalian (~13 Ma). At about 13 Ma, the region was subjected to abrupt block uplift and consequently elevated above sea level. Uplift was followed  by subaerial volcanic activity. Volcanism intensified and had became widespread all over the region by about 7-8 Ma, while the region gradually acquired a regional domal shape comparable to that of the Ethiopian High Plateau. However, the dome structure in Eastern Anatolia has a north-south shortened asymmetrical shape, due to the compressional tectonic regime created by collision, in contrast to that of the Ethiopian High Plateau. At present, it is difficult to recognise the dome in topographic maps since the topography of the region has been strongly modified by volcanoes and river drainage systems.

Volcanism migrated to the south/southeast over time. Great volumes of volcanic material (i.e. lavas and pyroclastic units) reaching over 1 km in thickness in places were erupted onto the surface between 8 and 1.5 Ma, forming volcano-sedimentary successions, and covering almost two-thirds of the region. Thus, the Eastern Anatolia region can be regarded as the site of a "melting anomaly" or "hotspot" resembling closely the setting proposed for mantle plumes. However, geologic and geochemical data provide evidence against a plume origin. In addition, the results of new geophysical studies, coupled with geologic and geochemical 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 50 km. This process is argued to have occurred either by delamination, slab-steepening and breakoff, or a combination of both. Therefore, magma generation beneath Eastern Anatolia may have been controlled by adiabatic decompression of the asthenosphere. The presence of a subduction component and thus water in the asthenospheric mantle wedge whould have played an important role in this melting process. In addition, material derived from previously subducted slabs might have contributed to the fertility of the mantle source region.

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, as proposed by a number of recent studies.