Quantitative mapping of active mud volcanism at the western Mediterranean Ridge-backstop contact
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ORIGINAL RESEARCH PAPER
Quantitative mapping of active mud volcanism at the western Mediterranean Ridge-backstop contact Alain Rabaute Æ Nicolas Chamot-Rooke
Received: 30 January 2007 / Accepted: 23 July 2007 / Published online: 6 September 2007 Springer Science+Business Media B.V. 2007
Abstract Based on a new quantitative analysis of sidescan sonar data combined with coring, we propose a revised model for the origin for Mediterranean Ridge mud volcanism. Image analysis techniques are used to produce a synthetic and objective map of recent mud flows covering a 640 · 700 km2 area, which represents more than half of the entire Mediterranean Ridge mud belt. We identify 215 mud flows, extruded during the last 37,000–60,000 years. This time period corresponds to the limit of penetration of the sonar, that we evaluate through geoacoustic modeling of the backscattered signal returned by the mud brecciahemipelagites contact, and calibrate by coring. We show that during this period, at least 96% of the mud volume has been extruded at the Mediterranean Ridge-Hellenic backstop contact, the remaining being scattered over the prism. We suggest that the source is a Messinian (5–6 Ma) mud reservoir that remained close to the backstop contact, at variance with the classical transport-through-the-wedge model. A revised mud budget indicates that steady-state input is not needed. We propose that the source layer was deposited in deep and narrow pre-Messinian basins, sealed by Messinian evaporites, and finally inverted in postMessinian times. Onset of motion of the Anatolia-Aegea microplate in the Pliocene resulted in change from slow to fast convergence, triggering shear partitioning at the edges of the backstop and basin inversion. Mud volcanism initiation is probably coeval with the latest events of this kinematic re-organization, i.e. opening of the Corinth Gulf and activation of the Kephalonia fault around 1–2 Ma.
A. Rabaute (&) N. Chamot-Rooke Laboratoire de Ge´ologie, Ecole normale supe´rieure, CNRS UMR 8538, 24, Rue Lhomond, Paris Cedex 05 75231, France e-mail: [email protected]
Keywords Mediterranean Ridge Mud volcanism Acoustic characterization Backscatter Geodynamics Messinian evaporites Accretionary prism Backstop Strike-slip faults
Introduction Mud volcanoes have been found in various geological contexts in the Mediterranean seas, including Tertiary and Mesozoic basins (Alboran Sea, Black Sea, Levantine Basin, see Pe´rez Belzuz et al. (1997), Ivanov et al. (1996b), Netzeband et al. (2006)), Neogene accretionary prisms (Mediterranean Ridge; Calabrian Prism, see Ceramicola et al. (2006); Gulf of Cadiz, see Van Rensbergen et al. (2005) and Hensen et al. (2007)), and sedimentary cones (Nile, see Loncke et al. (2004)). In the Eastern Mediterranean, mud volcanism is present as one more or less continuous belt along the Mediterranean Ridge referred to as the Mediterranean Ridge mud diapiric belt (Limonov et al. 1996). As in other marine accretionary environments associated with mud volcanism, and in
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