Slab Evolution in the Early Pliocene Establishment of the Modern Tectonic Regime in the Adria-Aegean-Anatolian Region

The Eastern Mediterranean marks a region of ongoing ocean closure, starting when Arabia collided with Eurasia around Eocene-Oligocene time, but the modern tectonic configuration has only been established since ca. 4 to 5 Ma. To identify the main drivers of this tectonic evolution and explain delays between apparent drivers and responses, we review evidence for how crustal deformation, surface elevations, and volcanism in the upper plate spanning the Dinarides-Hellenides to Eastern Anatolia evolved in the context of plate reconstructions. We also use geophysical observations to guide a reconstruction of the modern slab geometries and the positions of oceanic-continental lithosphere transitions within the slabs. We then infer how the slabs evolved through time in three dimensions, using the plate reconstructions and geologic history as guides for changes in slab geometry. From this review, we reconstruct a series of paleographic maps (15, 9, and 5 Ma) and cartoons illustrating the 3D geometry of slabs at the same time frames.

Following break-off of the Bitlis slab at least 20 million years ago, the next major event in establishing the modern tectonic regime was the acceleration of Hellenic Trench retreat around 15 Ma, likely associated with the initiation of a trench-orthogonal tear along the east side of the Aegean slab. We show that initiation of the tear could relate to entrance of the Ionian oceanic lithosphere into the subduction zone, as well as the presence of Pindos oceanic lithosphere at greater depths within the slab. The trench-orthogonal tear in turn induced accelerated Hellenic Trench retreat, faster extension in the Aegean, and the start of a “proto-escape” phase of Anatolia. At 5 to 4 Ma, segmentation of the slab beneath the Kefalonia Transfer Fault Zone and further acceleration in Hellenic Trench retreat likely facilitated the localization of the North Anatolian Fault western Turkey, the formation of the East Anatolian Fault, and independent motion of the Adria plate, establishing the modern tectonic regime. Our reconstructions highlight the role of slab dynamics in driving not only the long-term, progressive tectonic evolution of the region, but also sudden plate reconfigurations.