Trapped remnant of the Tethyan realm: the influence of ancient tectonics on the present-day geodynamics of the eastern Mediterranean

The eastern Mediterranean Sea preserves crust that was trapped during the collision of Africa with Eurasia and the closure of the Neo-Tethyan Ocean. Thick sedimentary blanketing (10 to 15 km) complicates our ability to assess the nature of the crust, and therefore it has remained one of the least understood regions of the collision belt. In this presentation, I review recent marine geophysical observations (surface and deep-tow magnetics, high-resolution bathymetry and seismic reflection data) and discuss their geodynamic implications. The surface total field and vector magnetic anomalies from the Herodotus Basin reveal a sequence of long-wavelength NE-SW lineated anomalies that straddle the entire basin suggesting a deep two-dimensional magnetic source layer. The magnetic vector data indicate an abrupt transition from a 2D to a 3D magnetic structure along the eastern edge of the Herodotus Basin and west of the Eratosthenes Seamount, where a prominent gravity feature is found. These findings indicate that the Herodotus Basin preserves remnants of oceanic crust accreted along a mid-ocean ridge system that spread in an NW-SE direction. The African Plate's continuous northward and counterclockwise motion during the Paleozoic and Mesozoic allow predicting the crustal remanent magnetization directions, which dictate the shape of the present-day magnetic anomalies. The shape of the Herodotus anomalies best fit Carboniferous magnetization directions. The combination of surface and deep-tow magnetic data, as well as thermal and magnetic forward modeling, suggest that spreading was slow (~25 km/myr half spreading rates) and that the upper oceanic crust has been entirely demagnetized, probably due to the heating effect induced by the thick sedimentary coverage.

 

The stretched continental crust of the Levant Basin, found east of the Herodotus Basin, preserves a series of horsts and grabens that generally orient in an orthogonal direction relative to the spreading direction, suggesting that they may have formed concurrently with the initial opening of the Herodotus Basin. Earthquake data and long NW-SE bathymetric scars found within the northern edge of the Nile deep-sea fan suggest that an active fault belt transfers the motion from the Gulf of Suez toward the northern convergence boundaries. This fault belt is directed toward, and merges with, the continental-ocean boundary that straddles the eastern Herodotus Basin. This observation may indicate that the mechanical transition from the rather weak and stretched continental crust of the Levant to the relatively strong oceanic Herodotus crust has guided the location of the western boundary of the Sinai Microplate, formed during the Oligocene by the fragmentation of the African Plate.