Strain distribution over the east Mediterranean ridge: A synthesis incorporating new Sea-Beam data

Abstract

We present the results of several multi-narrow-beam (Sea-Beam) traverses of the Mediterranean ridge on board R.V. “Jean Charcot”. These results can be considered to be complementary, in resolution and coverage, to the previously published long-range side-scan sonar (Gloria) results. A characteristic of the Mediterranean ridge is the presence over about half of its surface of an extensive fold system affecting the Messinian and Plio-Quaternary cover, which is dissected by conjugate strike-slip faults. The resolution of Sea-Beam was used to map the main characteristics of folding and faulting. This analysis, together with previously available data, enables us to define the strain pattern over the Mediterranean ridge. We thus now have an overall view of the strain pattern from a marginal basin (Aegea) through the Hellenic trench and adjacent sea-floor to the opposite continent. The bottom of the Hellenic trench is a boundary between an extensional domain to the north and a compressional one to the south. The southern domain is strongly affected by the presence of the Lybian promontary. It is related to the formation of an accretionary ridge due to the inability of the upper 3–4 km of sediments to subduct. This ridge is similar to the accretionary prism but it is much wider with respect to its height, probably because of the existence of a decollement over a level of overpressure. The Hellenic trench then is in the situation of a fore-arc basin. Its origin is due to the fact that the Aegean continental slope is not vertical but rather has a small 4° dip. As a result, a sedimentary wedge, symmetric but shorter than the main accretionary wedge develops over the buried portion of the slope. It is characterized by landward thrusts. Such an origin probably applies to fore-arc basins in general.