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Geological Society, London, Special Publications; 2000; v. 174; p. 169-204;
DOI: 10.1144/GSL.SP.1999.174.01.10
© 2000 Geological Society of London

Shale Intrusions

Extrusion dynamics of mud volcanoes on the Mediterranean Ridge accretionary complex

Achim Kopf1 & Jan H. Behrmann2

1 Géosciences Azur, B.P. 48, 06235 Villefranche-sur-Mer Cédex, France kopf{at}obs-vlfr.fr
2 Geologisches Institut, Albert-Ludwigs-Universität Freiburg, Albertstrasse 23B, 79104 Freiburg, Germany

Drilling of two submarine mud domes situated in the Olimpi field on the northern flank of the Mediterranean Ridge accretionary complex has documented episodic eruptive activity over the last 1 to >1.5 Ma. Mud extrusion is related to plate convergence between Africa and Eurasia, having caused backthrust faulting of accreted strata containing overpressured mud at depth. The domes mainly consist of mud breccia with up to 65% of polymictic clasts embedded in a clayey matrix. On the basis of modifications of Poiseuille’s and Stokes’ laws, mud extrusion rates were calculated for Milano and Napoli mud domes. Mud ascent velocities are estimated to be up to 60–300 km a–1, and are comparable with those of silicate magmas. Using physical property, structural and flux data of the mud breccias, and compiled data from mud domes on land, the diameter of the feeder channel and the depth of origin for the overpressured muds could be reliably estimated for the first time. Feeder channels are likely to be only a few metres wide. Gas efflux estimates constrain a source depth to c. 1700 ± 50 m below sea floor in the Olimpi field, which is considerably shallower than estimations made from the thermal maturity of solid organic carbon in the mud breccias. The efflux data suggest that the overpressured muds were not mobilized at décollement depth, but at a shallower level within the accretionary prism. A comparison of mud ascent rates (as determined from Poiseuille flow) and the total volumes of mud extruded indicate that only a fraction of the time span constrained from biostratigraphic data (c. 1 Ma) is needed to build up the Milano and Napoli mud domes. Durations of 12–58 ka of extrusive activity suggest mud volcanism here to have been a highly episodic phenomenon.





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A. Deyhle, A. J. Kopf, and G. Aloisi
Boron and boron isotopes as tracers for diagenetic reactions and depth of mobilization, using muds and authigenic carbonates from eastern Mediterranean mud volcanoes
Geological Society, London, Special Publications, 2003; 216: 491 - 503.
[Abstract] [PDF]