A new approach to the opening of the eastern Mediterranean Sea and the origin of the Hellenic subduction zone. Part 2: The Hellenic subduction zone

Abstract

We discuss the structure of the present Hellenic subduction zone. We show that the present Hellenic subduction zone was formed at about 15 Ma when it started to consume the Mediterranean lithosphere and to form the large accretionary wedge that covers a large part of the eastern Mediterranean. We establish that there is independent evidence that the very large Hellenic Trough that it created was formed simultaneously. Shortly before, an 8–10 km thick backstop that extends 200 km southward, where it presently abuts the African margin, was put into place. We reconstruct the northern margin of the eastern Mediterranean Sea prior to the Hellenic subduction in a new and independent way. The faults recently identified by Sachpazi et al. (2016a . Geophysical Research Letters, 43: 651–658) and Sachpazi et al. (2016b . Geophysical Research Letters, 43: 9619–9626) within the Hellenic seismic slab are a key element of our reconstruction. This is because the slab, which is part of the Nubia plate, is rigid and the faults within it coincide with the lines of slip congruent with the relative motion of the Aegean block over it. These faults demonstrate that about 400 to 500 kilometers of eastern Mediterranean lithosphere have been subducted with essentially the same southwestward direction of motion during the last 15 Myr. Our reconstruction shows that before the onset of the Hellenic subduction, the northern margin of the eastern Mediterranean Sea coincided with a major Jurassic transform fault that limited the eastern Mediterranean to the north during its formation in the Jurassic and Early Cretaceous as proposed in part 1. We discuss the implications of this reconstruction on the Neogene evolution of the Anatolia–Aegea block and its geodynamics.

The aetiology of the neotectonic evolution of Turkey

“…Faccenna et al (2006Faccenna et al ( , 2013 hold the thermal flow of the Afar plume and the effect of the slab break in the Bitlis area responsible for the lateral motion of Anatolia. We have been unable to find any corroborating evidence, e.g., possible distortions of the subducting slabs below the Anatolian Scholle due to the suggested mantle flow, for such a motive for the westerly flight of the Anatolian Scholle (e.g., Spakman et al 2008;Mutlu and Karabulut 2011;Bakırcı et al 2012;Le Pichon et al 2019).…”

“…This high plateau existed since at least the earliest Miocene, because the Taurus thrusts thickening it had ceased their activity during the Burdigalian (Gutnic et al 1979; see also Şengör and Yılmaz 1981;. Therefore, there is at least some 2-3 Ma between the initiation of the Hellenic Trench at approximately 13 Ma ago (Le Pichon et al 2019) and the final culmination of the height of the West Anatolian/Aegean high plateau (at the latest 15 Ma ago). By contrast, the Hellenic Trench became activated almost as soon as the North Anatolian Fault formed.…”

Assessment of the Coastal Vulnerability to the Ongoing Sea Level Rise for the Exquisite Rhodes Island (SE Aegean Sea, Greece)

“…This long-term ground elevation, albeit not uniform throughout Rhodes, seems to be more effective on the evolution of the island's coastal zone than the glacio-eustatic cycles. Uplift rates as high as 12 mm y −1 have been estimated for the broader setting of the fragmented forearc of the Hellenic subduction zone [44,88,95,114,115] as a result of the inconsistent slide (rates of <5-35 mm y −1 ; [116]) of the Nubian (north Africa) plate below the Aegean (south Eurasia) microplate. In general, in the active plate margins, the vertical ground movement is the dominant process for the configuration of the coastal zones [117][118][119], and therefore, it has to be considered as a fundamental CVI variable.…”

Methoni Mw 6.8 rupture and aftershocks distribution from a dense array of OBS and land seismometers, offshore SW Hellenic subduction

“…Our findings in the present study of the southwestern part of the subduction zone are consistent with these characteristics of background seismicity of the Ionian Islands. The normal fault earthquakes are in the lower plate crust and trenchwards of the thickened Hellenic continental margin and may mark the lower plate bending to underthrust the southwestwards advancing upper plate (Le Pichon et al, 2019). The plate interface may be thus defined as the boundary (at the 24-25km depth range)…”

“…Black barbed line: outer limit of backstop, thrust contact of the accretionary wedge of the Mediterranean Ridge over it. Black dashed NW-SE trending line: Inner limit of the backstop at the transition between the Matapan Trough to the SW and the Hellenic continental margin to the NE from Le Pichon et al (2019). (b) Distribution of post-seismic slip over the offshore forearc as afterslip according to geodetic data modeling (Howell et al, 2017a) with the higher >0.2 resolution area marked by a green rectangle.…”