Mud Volcanoes and Dome-Like Structures at the Eastern Mediterranean Ridge

Abstract

The Mediterranean Ridge is interpreted as a large accretionary complex, which originated due to the northern subduction of the African lithosphere below the Eurasian one and the partial collision of those two continents; more precisely, between the African and Aegean Microplates. The main goals of the UNESCO-TTR 5 (Training Through Research) cruise, carried out by several methods including high resolution seismic profiling, included the investigations of mud volcanoes, the distribution of the Messinian evaporites, and mapping the seafloor structures. The high resolution seismic data were confirmed with other geoacoustic methods as sidescan sonars (short-ORETECH and long-range OKEAN) and subbottom sampling. The area of investigation is designed to run parallel to the Mediterranean Ridge on the eastern end towards the Florence Rise, and is situated between the northern and southern deformation fronts of the ridge. The seismic data were preprocessed onboard (band pass filtering, horizontal stack and attenuation level) and predictive deconvolution. New mud volcanoes and structures were discovered at the western part of the target area, named 'United Nations (UN) Rise' to celebrate the fiftieth anniversary of the United Nations. With respect to fluid expulsion, three mud volcanoes were imaged, all of which show different backscattering characteristics. The investigated area shows complex structures and the UN area within the inner deformation front of the Mediterranean Ridge, is much more complicated. Some features are similar to mud volcanoes, but with some important differences. The typical characteristics of these features are a positive (up-doming) structure on the seafloor relief, no acoustically transparent zone, a strong low-frequency reflector (M-reflector?) down-bent near this object and some of these features are symmetrical. The Mud volcanism can exhibit itself only where the evaporitic layer is thin or absent. The mud volcanism on the Mediterranean Ridge reflects the general tectonic evolution of the accretionary complex presently progressing.