Extrusion dynamics of mud volcanoes on the Mediterranean Ridge accretionary complex

Abstract

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 60-300kma-', 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 4-50 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 d6collement 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.

Significance of Mud Volcanism

“…The first values agree well with cemented chimneys in the ancient Verrua MV in Italy [Cavagna et al, 1998]. Also, theoretical considerations and calculations based on Stokes' law indicate similar diameters of 2-3 m for the Mediterranean Ridge MVs [Kopf and Behrmann, 2000]. However, some controversial data are reported for the feeder geometry at depth.…”

“…The low vitrinite reflectance measured makes it unlikely that the solid component has experienced elevated temperatures or deep burial. These results are supported by another, more theoretical approach based on quasistatic modeling of the ascent of mud [Cherskiy, 1961;Kopf and Behrmann, 2000]. The latter estimate of a mud mobilization depth of 1.7 km is bracketed by the less well constrained 1-2 km depth of burial from the maturity data [Kopf et al, 2000b].…”

“…A total of five active MVs are identified on Sakhalin, and the average emission of predominantly methane gas per vigorous eruption has been calculated to be ϳ14,400 m 3 [Gorkun and Siryk, 1968]. The equations used for the gas flux estimates are further used to estimate the mobilization depth of the ejecta, which again bears some errors (see discussion and equations of Kopf and Behrmann [2000]). Although detailed fieldwork in the exhumed accretionary complex on the island of Sakhalin revealed shaly and olistostromal series [Kimura et al, 1992], no close relationship between these beds and the ejecta has been established.…”

Structure of mud volcano systems and pockmarks in the region of the Ceuta Contourite Depositional System (Western Alborán Sea)

“…A suite of mechanisms is proposed for the movement and migration of fluids from one reservoir to the next or from the reservoir to the surface: hydraulic fracturing of sediments as a consequence of increasing pore fluid pressures that will produce fluid conduits (Kopf and Behrmann, 2000;Dimitrov, 2002;Hustoft et al, 2007;Van Rensbergen et al, 2007;Moss and Cartwright, 2010), lateral and vertical migrations due to variations in the properties within the contourite sediments (grain size and porosity) and probably other diagenetic processes (Stewart and Davies, 2006).…”

Spatial variation in fluid flow and geochemical fluxes across the sediment–seawater interface at the Carlos Ribeiro mud volcano (Gulf of Cadiz)

“…Wallmann et al (2006) estimate that the total CH 4 emission into the ocean via fluid flow through submarine MVs is of the order of 10 10 mol yr À1 , excluding the contributions from gas ebullition ($2 Â 10 10 mol yr À1 ) and mud extrusions ($12.5 Â 10 10 mol yr À1 ). Thus, although these estimates are based on very few data (Kopf and Behrmann, 2000;Sauter et al, 2006;Sahling et al, 2009), the magnitude of methane emissions via quiescent dewatering is very similar to gas ebullition. This is most likely because of the more constant and continuous nature of fluid flow and its widespread occurrence at MVs, in contrast to gaseous fluxes which are rich in CH 4 but episodic.…”