New 3D models for the subducted lithosphere of the Eastern Mediterranean Basin

We present a new regional three-dimensional (3D) slab reconstruction of the Eastern Mediterranean Basin utilising the UU-P07 global tomography model and two earthquake data packages (GCMT and ISC) to produce 3D slab models to a depth of 2900 km. The model data are permissive of the presence of a south-eastward-propagating horizontal tear in the Aegean slab beneath the Rhodope Massif in the Balkanides extending towards the Thermaic Gulf. Alternatively: i) the local pattern of reduced amplitudes at ~ 200km depth could also reflect a different type of lithosphere; and/ or ii) tearing might have been preceded by down-dip stretching, resulting in abrupt thinning of the lithosphere in the extended zone.

Further to the southeast, beneath the Peloponnese and Crete, the model data support the existence of multiple subduction-transform (or STEP) faults. The subduction–transforms have since themselves begun to founder, and to roll back towards the southeast.  Even further east, beneath Cyprus, the model data appears to support the existence of yet another STEP fault, linking the slab to the east flank of the Arabia indenter.  

The 3D geometry of the subducted slabs demonstrates ‘lithological steps’ that formed as the lithosphere tore and bent while descending. Previous 3D reconstructions of the region’s deep lithospheric geometry confirmed the presence of fragmented segments but details on: i) the vertical extent of the descended slabs; and ii) the correlation between surface deformation structure and geometry at depth had yet to be established. In order to allow such a correlation, the 3D model was floated [or returned to the planet surface] utilizing a wire mesh with a Delaunay tessellation, using the program Pplates. This enabled area-balancing and therefore a more accurate approximation to the areal extent of the slabs prior to their subduction. The floated slab(s) can be incorporated in a 2D+time tectonic reconstruction to provide additional constraints not available using surface geology. The inferred tears correlate with surface structures such as the Strabo and Pliny trenches between the Hellenic Arc (Aegean Trench) and the Cyprian Trench near the Cyprus Arc, as well as with the seaward extent of the East Anatolian Fault separating the Cyprus Arc and the Arabian indenter. Such correlations between surface and deep lithospheric structures have four-dimensional (4D) implications for episodic closure of the West Tethys suture from its Mesozoic onset, through the tectonically active Tertiary to the present-day.