Aberswyth University of Wales, United Kingdom

Authigenic carbonates and muds from six mud volcanoes in the eastern Mediterranean Sea were recovered during the French/Dutch MEDINAUT cruise utilizing the submersible Nautile in November 1998. The mud volcanoes are active seafloor vents in two areas at the plate boundary between the converging African and Eurasian Plates: the Mediterranean Ridge accretionary prism near Crete (Greece) and the Anaximander Mountains south of Turkey. B contents and delta (super 11) B signatures were measured with the aim of identifying the diagenetic processes and source depths of the material in the collision zone. B concentrations of the carbonate precipitates cover a range of 8-45 ppm and vary isotopically from +15.6 to +22.9 per mil (corresponding to a parent solution of 34.9-42.2 per mil at pH7). Both the B-enrichment and a delta (super 11) B valve slightly lower than seawater suggest the mud domes originate from a moderately deep fluid source, with local admixture of seawater. B contents and delta (super 11) B of the mud show distinct differences between the areas: the Mediterranean Ridge mud domes have lower B contents and higher delta (super 11) B (average 3.9 per mil) compared to Anaximander Mountains mud volcanoes (delta (super 11) B average -0.6 per mil). These B results attest the release of structurally bound B from clay mineral lattices, probably due to stronger deformation near Turkey. These mudstones, which had previously been affected by deep-seated thrusting beneath the Antalya Complex, may have been liquefied and remobilized in their present setting. By contrast, the mud on the Mediterranean Ridge represents offscraped clay-rich strata that was incorporated into the large accretionary wedge.