A new crustal model of the Anatolia–Aegean domain: evidence for the dominant role of isostasy in the support of the Anatolian plateau

Hayrullah Karabulut (1) , Anne Paul (2) , Ali Değer Özbakir (3) , Tuğçe Ergün (3) , Selver Şentürk (4)

1 KOERI - Kandilli Observatory and Earthquake Research Institute
2 ISTerre - Institut des Sciences de la Terre
3 Boǧaziçi üniversitesi = Boğaziçi University [Istanbul]
4 ITÜ - Istanbul Technical University

The engines of surface deformation in the Anatolia-Aegean region are a matter of debate, including the origin of the high elevations of the Anatolian plateau. Recent publications based on geological and thermomechanical modelling emphasize the role of dynamic topography in the plateau uplift. However, quantitative estimates of the contribution of dynamic topography are affected by large uncertainties due to insufficient knowledge of the crustal structure, in particular crustal thickness and density. To reduce these uncertainties, we provide a new accurate crustal thickness map of the Anatolia-Aegean domain computed from a large volume of broadband seismic data. In addition, we display high-resolution seismic sections of the internal structure of the crust in Western and Central Anatolia. Density contrasts are derived from the same seismic data set and Bouguer gravity anomaly computed from the EGM2008 model. Our crustal thickness model is highly correlated with the topography suggesting that the Anatolian plateau is close to isostatic equilibrium. The average density difference between crust and upper mantle computed from our crustal model and Bouguer gravity anomaly is low compared to the global average, ∼0.315 ×10 3 kg m −3. The ratio of surface elevation to crustal thickness is lower than average, 1/9.4, which also indicates a low-density crust. Differences between isostatic topography and observed topography are overall small (<500 m). The east-to-west gradients of crustal thickness and topography changes are nearly constant in between the Taurides and Pontides at the northern and southern borders of Anatolia. The observed constant crustal thickness gradient may indicate a low viscosity lower crust supported by the thin mantle lithosphere evidenced by seismic tomography beneath the Anatolian plateau. We propose that viscous flow in the lower crust has smoothed out lateral changes in the crustal structure expected for such a heterogeneous collage of continental fragments. This flow may originate from gravitational potential energy differences between Eastern Anatolia (thick crust, high elevations) and the Aegean Sea (thin crust, low elevations), suggesting that gravity plays an integral part in the westward escape of Anatolia.

Mots clés: Crustal imaging; Seismic tomography; Dynamics: gravity and tectonics; Rheology: crust and lithosphere

Domaines: Géophysique [physics.geo-ph]; Tectonique

Hayrullah Karabulut, Anne Paul, Ali Değer Özbakir, Tuğçe Ergün, Selver Şentürk. A new crustal model of the Anatolia–Aegean domain: evidence for the dominant role of isostasy in the support of the Anatolian plateau. Geophysical Journal International, 2019, 218 (1), pp.57-73. ⟨10.1093/gji/ggz147⟩. ⟨hal-02156625⟩