Structural setting and tectonic control of mud volcanoes from the Central Mediterranean Ridge (Eastern Mediterranean)

Based on a recent marine geophysical data set, including swath bathymetry, acoustic imagery and six-channel seismics, recorded over a large area of the Mediterranean Ridge (MR) in early 1998 during the Prismed 2 survey, this paper presents a study of the various relationships observed between tectonic features cutting across the Central Mediterranean Ridge accretionary wedge and massive mud expulsions (known as mud volcanoes), identified over large areas of the ridge.Regional mapping of two of the mud volcano fields previously only partly investigated (Olimpi and United Nations Rise) revealed the presence of many new mud expulsion centres and a third new mud volcano field has been identified. All the mud features show great variability in morphology, size and backscatter strength of their surrounding mud flows. Based on their contrasting morpho-acoustic characteristics, we propose a classification into three main groups of mud construction: (1) "mud volcanoes", these consist of subcircular and prominent reliefs, often associated with high backscatter mud flows; (2) "mud domes", similar to mud volcano, but smaller, these occurrences correspond to weakly reflective mud constructions; (3) "mud plateaus" represent a third category which appears as wide, often highly reflective and rather flat mud extrusions. From all available data, an attempt to explain the different mud ascent processes and driving forces is discussed, in relation to the initial collision structural setting of the Central Mediterranean Ridge. Within this area, most of the mud constructions have been observed to be associated with tectonic features and, in particular, with strike-slip faulting for the first time. As a hypothesis, we propose in this paper two different ascent processes to explain the contrasting mud constructions: (1) "extrusion" for the mud volcanoes and plateaus and (2) "intrusion" for the mud domes, connected to two different mud levels controlled by the crustal geometry of this pre-collision area and especially the southwards extension of the Cretan continental crust below the Mediterranean Ridge accreted sediments.