Seismic structure, crustal architecture and tectonic evolution of the Anatolian-African Plate Boundary and the Cenozoic Orogenic Belts in the Eastern Mediterranean Region

Abstract

The modern Anatolian-African plate boundary is represented by a north-dipping subduction zone that has been part of a broad domain of regional convergence between Eurasia and Afro-Arabia since the latest Mesozoic. A series of collisions between Gondwana-derived ribbon continents and trench-roll-back systems in the Tethyan realm produced nearly East -West-trending, subparallel mountain belts with high elevation and thick orogenic crust in this region. Ophiolite emplacement, terrane stacking, high-P and Barrovian metamorphism, and crustal thickening occurred during the accretion of these microcontinents into the upper plates of Tethyan subduction roll-back systems during the Late Cretaceous-Early Eocene. Continued convergence and oceanic lithospheric subduction within the Tethyan realm were punctuated by slab breakoff events following the microcontinental accretion episodes. Slab breakoff resulted in asthenospheric upwelling and partial melting, which facilitated post-collisional magmatism along and across the suture zones. Resumed subduction and slab roll-back-induced upper plate extension triggered a tectonic collapse of the thermally weakened orogenic crust in Anatolia in the late Oligocene-Miocene. This extensional phase resulted in exhumation of high-P rocks and medium-to lower-crustal material leading to the formation of metamorphic core complexes in the hinterland of the young collision zones. The geochemical character of the attendant magmatism has progressed from initial shoshonitic and high-K calc-alkaline to calc-alkaline and alkaline affinities through time, as more asthenosphere-derived melts found their way to the surface with insignificant degrees of crustal contamination. The occurrence of discrete high-velocity bodies in the mantle beneath Anatolia, as deduced from lithospheric seismic velocity data, supports our Tethyan slab breakoff interpretations. Pn velocity and Sn attenuation tomography models indicate that the uppermost mantle is anomalously hot and thin, consistent with the existence of a shallow asthenosphere beneath the collapsing Anatolian orogenic belts and widespread volcanism in this region. The sharp, north-pointing cusp (Isparta Angle) between the Hellenic and Cyprus trenches along the modern Anatolian-African plate boundary corresponds to a subductiontransform edge propagator (STEP) fault, which is an artifact of a slab tear within the downgoing African lithosphere.

Neotethyan closure history of western Anatolia: a geodynamic discussion

“…It is supported by geochemical fingerprints of metasomatised mantle melting; field evidence for post-tectonic magmatic activity; and a clear temporal distinction with the Late Cretaceous arc-related magmatic activity north of the Marmara Sea (see Gülmez et al 2013 and reference therein). It further provides an explanation for the slab-like positive anomaly displayed below the Izmir-Ankara Suture in some seismic tomography models (Dilek and Sandvol 2009;Salaün et al 2012). Yet, it raises some issues.…”

“…Dilek et al developed a tectonic model based on the study of the Cenozoic magmatic history of western Anatolia (Dilek and Altunkaynak 2009;Altunkaynak et al 2012;Altunkaynak and Dilek 2013) and constraints from seismic-tomographic images (Dilek and Sandvol 2009). These images, in contrast to others (e.g.…”

Zagros orogeny: a subduction-dominated process

“…From our present-day knowledge of magmatism, the Iranian plateau may thus resemble E Turkey, where magmatism and deformation take place through a mixture of slab break-off, mantle delamination and strike-slip faulting (Keskin, 2003;Al-Lazki et al 2004;Keskin, Genç & Tüysüz, 2008;Sengör et al 2008). Such complex magmatic patterns are now recognized below W Turkey too (Dilek & Sandvol, 2009;Dilek, Altunkaynak & Oner, 2010). Future research should therefore aim at better documenting gradients in magmatic type such as were reported for Turkey (i.e.…”

Integrating geologic fault data into tsunami hazard studies

“…(2012). Tomographic analyses by various authors suggest the presence of the slab at very deep depth by revealing a large high velocity anomaly beneath the Aegean Sea that reaches the 660 km discontinuity (Piromallo and Morelli, 2003;Dilek and Sandvol, 2009;Suckale et al, 2009).…”