Upper-Mantle Seismic Structure of the Eastern Mediterranean: Evidence from Body-Wave Travel-Time Tomography

The Eastern Mediterranean delineates the final stages of subduction termination by transitioning from active subduction of the world's oldest oceanic lithosphere in the west, to continental collision in the east. As such, it is the ideal location to study terminal-stage subduction. Asthenospheric or subduction processes are the main candidates for the region's 2 km uplift and Miocene volcanism, however their relative importance is debated. To address these issues, the highest resolution P-wave and first S-wave relative arrival-time tomography models of the Eastern Mediterranean, to date, have been assembled to probe upper-mantle seismic structure. 60,090 P-wave and 44,597 S-wave relative travel-times are corrected for crustal structure, then inverted using a regularised non-linear least-squares inversion procedure.

The tomographic models reveal variable fast anomalies associated with the complex structure of the subducting African lithosphere, with an intact Aegean slab in the west progressing to a fragmented Cyprean slab in the east. The Cyprean slab is therefore in early detachment and may develop akin to the Bitlis slab which sits at 500 km depth beneath eastern Anatolia. All three slabs independently interact with the mantle transition zone, descending into the lower-mantle unimpeded. Slow wavespeeds define gaps and windows that permit hot upwelling asthenosphere beneath the tectonically complex Isparta Angle, and as a horizontal tear in the Cyprean slab below the Central Anatolian Volcanic Province. Results further reveal the upper-mantle signature of the North Anatolian Fault and Dead Sea Transform. Fast wavespeeds terminate sharply at 100 km depth north of the North Anatolian Fault, consistent with the view that it is a lithospheric-scale feature. Slow structure along the Dead Sea Transform may mark a lithospheric thickness step, with hotspot material potentially flowing from Afar impacting eastern Anatolia. Slow anomalies below eastern Anatolia underlie active Holocene and Pleistocene volcanic centres, and when interpreted in light of residual topography calculations, suggest eastern Anatolia is a thermally eroded, dynamically uplifted, continent. Some of the fast velocity structures may therefore be delaminated segments of lithospheric mantle; others may be subducted slab material.