Structural features of mud volcanoes and the fold system of the Mediterranean Ridge, south of Crete

Abstract

New information on the geometry of the mud volcanoes, folds and faults located in the central part of the Mediterranean Ridge is provided from long range and deep-tow sidescan sonar images, high resolution seismic and low frequency echosounder profiles, and gravity cores obtained on the R/V Gelendzhik during the 1993 UNESCO-ESF Training Through Research cruise. Symmetrical gentle folds, with a mean wavelength of 750 m, deform predominantly Pliocene-Quaternary sediments, but also perhaps as old as Messinian. In most areas of the Mediterranean Ridge, the north-northeast directed subduction of the African plate below the Eurasian plate at the Hellenic arc produces folds with hinge lines subparallel to the trend of the ridge. However, the hinge lines of the folds curve around the southern part of the area with highest concentration of mud volcanoes and produce an irregular U-shape fold belt. Some of the folds show an intrusive nucleus and, in some of them, mud breccia appears to have flowed from the flanks of the folds into the troughs. The mud volcanoes consist of domes of interlayered pelagic sediments and mud breccias containing sediments and rock fragments of Late Aptian to Pleistocene ages. Mud breccia flows are mainly extruded radially from vents, although rare fissure extrusions are also observed. The mud volcanoes have an irregular to elliptical shape, with diameters up to 16 km. The distribution of mud volcanoes in the area is irregular, but they are more frequent in an area called the Olimpi Field. Faults in the uppermost part of the Mediterranean Ridge are rare. Most of the faults are normal and subparallel to fold limbs. In addition, N20°E and N100°E subvertical faults are found controlling the shape of the mud volcanoes.