Sources of mud volcano fluids in the Gulf of Cadiz - indications for hydrothermal imprint.

Hensen, Christian , Nuzzo, Marianne, Hornibrook, E., Pinheiro, L. M., Bock, Barbara, Magalhães, V. H. and Brückmann, Warner (2007) Sources of mud volcano fluids in the Gulf of Cadiz - indications for hydrothermal imprint. Geochimica et Cosmochimica Acta, 71 (5). pp. 1232-1248. DOI 10.1016/j.gca.2006.11.022.

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Mud volcanism in the Gulf of Cadiz occurs over a large area extending from the shelf to more than 3500 m water depth and is triggered by compressional stress along the European–African plate boundary, affecting a deeply faulted sedimentary sequence of locally more than 5 km thickness. The investigation of six active sites shows that mud volcano (MV) fluids, on average, are highly enriched in CH4, Li, B, and Sr and depleted in Mg, K, and Br. The purity of the fluids is largely controlled by the intensity of upward directed flow. Flow rates could be constrained by numerical modelling and vary between <0.05 and 15 cm yr−1. Application of δD–δ18O systematics identifies clay mineral dehydration, most likely within Mesozoic and Tertiary shales and marls, as the major source of fluids. Hence, Cl and Na in the pore fluids are mostly depleted below seawater values, following a general trend of dilution. However, deviations from this trend occur and are likely caused by the dissolution of halite in evaporitic deposits. Other secondary processes overprinting the original fluid composition may occur along the flow path, such as dissolution of anhydrite or gypsum and/or the formation of calcite and dolomite. Different sources of fluids are also indicated by variations in 87Sr/86Sr, which range from 0.7086 to 0.7099 at the different sites. Dehydration may be induced primarily by overburden and tectonic compression; however, very high concentrations of Li and B, specifically at Captain Arutyunov MV (CAMV) indicate additional leaching at temperatures above 150 °C, which could be explained by the injection of hot fluids along deep penetrating, major E–W strike–slip fault systems. This hypothesis is supported by the occurrence of generally thermogenic, but significantly CH4-enriched, light volatile hydrocarbon gases at CAMV which cannot be explained by shallow microbial methanogenesis. Li and Li/B ratios from different types of hot and cold vents are used to infer that high temperature signals seem to be preserved at various cold vent locations and indicate a closer coupling of both systems in continental margin environments than outlined in previous studies.

Document Type: Article
Keywords: Mud volcano fluids; Gulf of Cadiz; RV Sonne; SO175
Research affiliation: OceanRep > SFB 574 > B5
OceanRep > SFB 574
OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-MG Marine Geosystems
OceanRep > SFB 574 > B2
OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-P-OZ Paleo-Oceanography
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1016/j.gca.2006.11.022
ISSN: 0016-7037
Projects: METROL, MVSEIS, Future Ocean, SFB574
Contribution Number:
SFB 574103
Date Deposited: 20 Jan 2009 08:50
Last Modified: 23 Sep 2019 21:55

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