DRIVING MECHANISM OF ASTHENOSPHERIC FLOW BENEATH EASTERN ANATOLIA: INSIGHT FROM GRAVITY DATA MODELLING

The Eastern Anatolian region is part of a young continental collision zone between the Arabian and Eurasian plates. The lithosphere in Eastern Anatolia is underlain by a low-velocity zone associated with asthenospheric flow in the upper mantle. The driving mechanism of asthenospheric flow beneath Eastern Anatolia and the isostatic state of the Anatolian Plateau are not well understood. Two hypotheses have been suggested to explain the driving mechanism of asthenospheric flow beneath Eastern Anatolia: 1) lithospheric delamination and 2) slab break-off.

To determine the driving mechanism of asthenospheric flow in the uppermost mantle beneath Eastern Anatolia, a 2.5-D gravity model was developed. The gravity modelling was based on terrestrial and satellite-derived gravity data. The 2.5-D gravity model shows significant lithospheric thicknesses variations across the Anatolian and Arabian plates. The lithospheric mantle in Eastern Anatolia is thinner (~62 – 74 km) than the Arabian Plate (~84 - 95 km), indicating that the Anatolian lithosphere may be delaminated. Furthermore, the 2.5-D gravity model shows the presence of a detached Arabian slab below 300 km depth, which is consistent with results of seismic tomography. Thus, the asthenospheric flow beneath Eastern Anatolia might have been induced by slab break-off and lithospheric delamination. The widespread volcanism in Eastern Anatolia and the rapid uplift of the Anatolian plateau can be considered as evidence of slab break-off and lithospheric delamination in the region.

The topography in Eastern Anatolian is not isostatically compensated. There is a residual topography of approximately 1.7 km that cannot be explained by crustal roots. Thus, part of the Eastern Anatolian Plateau may be dynamically supported by asthenospheric flow in the upper mantle.