Eastern Pontides and Black Sea: gravity inversion, crustal structure, isostasy and geodynamics

Lacking detailed seismic data on the crustal structure of Anatolia and the transition to the Black Sea, it is attempted to invert gravity for crust-mantle structure with constraints from the limited a priori information available, as average continental and oceanic crust, local topography, an isostatic model, published marine seismic data and a tentative "fix point" from recent seismological receiver functions near the Black Sea coast. An initial 2D-model for a north–south profile along about 40°E longitude is constructed and adjusted to fit the Bouguer anomaly taken from a published Turkish map and results from satellite radar altimetry. Isostasy, seismic data and gravity inversion concur in suggesting that the Moho under the eastern Black Sea is about 25 km deep with 15 ± 1 km thick sediments (4–7 km unconsolidated). Under eastern Anatolia where the average elevation is about 2 km, the Moho comes out to be about 55 ± 5 km deep. No constraints exist for the upper-lower crust transition. The gravity fitting model is not far from an isostatic mass balance, but the high topography of ~2 km seems slightly overcompensated with the Moho ~3 km deeper than predicted by the isostatic model; a slightly increased mantle density beneath eastern Anatolia would restore the isostatic balance without contradicting gravity. We favour such a vertical balance over a regional or lateral mass balance inherited from the initial opening of the Black Sea basin.