A model of the crust and upper mantle structure of the Hellenic and Cyprus subduction zones constrained by gravity and seismic data
The Aegean-Anatolian region is one of the most dynamically complex and seismically active tectonic settings on Earth. The dynamic evolution of this region is dominated by the African plate subduction along the Hellenic and Cyprus trenches and collision between the Anatolian and Eurasian plates. The region is characterized by active volcanism, large-scale continental extension, uplift, slab rollback, slab break-off and slab-tear. Several seismic tomography studies suggest the presence of a low-velocity zone in the upper mantle beneath southwestern Anatolia. The low-velocity zone is interpreted as asthenospheric material rising up through a slab window (slab-tear) in the subducting African plate. The slab-tear and possible detachment of the subducting African lithosphere from the surface plates are attributed to the differential retreat rates between the Hellenic and Cyprus trenches. The hot asthenosphere might have induced thermal erosion on the crust beneath southwestern Anatolia. To determine the effects of the hot asthenospheric material on crustal structure, 2.5-D and 3-D gravity models of the Aegean-Anatolian region (24°-33° E and 34°-40° N) have been developed. The gravity model is based on satellite-derived and terrestrial gravity data from the European Improved Gravity Model of the Earth (EIGEN-6C2). The EIGEN-6C2 model includes terrestrial and satellite gravity data from GRACE (Gravity Recovery and Climate Experiment) LAGEOS (Laser Geodynamics Satellites), and GOCE (Gravity field and steady-state Ocean Circulation Explorer) missions. The results of the gravity modeling, as constrained by geophysical data and models such as receiver function and seismic tomography, show that the crust above the low-velocity zone is relatively thin. The crustal thickness within the asthenospheric window area ranges from 24 to 29 km, and the thickness increases outside the asthenospheric window area (30 - 42 km). The observed crustal thinning might be attributed to thermal erosion induced by upwelling hot asthenosphere and extensional tectonics related to the Southwest retreating Hellenic trench and westward movement of the Anatolian micro plate. The magmatic centers and high geothermal gradients in the Menderes Massif Complex are indicative of an upwelling asthenosphere beneath southwestern Anatolia. Thus, asthenospheric flow may have played a role in the genesis of the crustal structure of southwestern Anatolia.