Fluid expulsion related to mud extrusion off Costa Rica - A window to the subduction slab

Hensen, Christian, Wallmann, Klaus, Schmidt, Mark, Ranero, César R. and Suess, Erwin (2004) Fluid expulsion related to mud extrusion off Costa Rica - A window to the subduction slab Geology, 32 (2). pp. 201-204. DOI 10.1130/G20119.1.

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A large number of mound-shaped structures that originated from mud extrusions is present along the convergent continental margin off Costa Rica and Nicaragua. Active fluid venting is indicated by the existence of CH4- and H2S-rich pore fluids as well as associated benthic fauna and authigenic carbonates. End-member fluid samples from all mounds are significantly depleted in dissolved Cl and other major elements, suggesting a general process of freshwater addition and thus a common source of the fluids. Our data clearly rule out dilution by gas hydrate dissociation as a dominant source of the freshwater. Enrichments of the fluids in B (up to 2 mmol/L) and inversely correlated δ18O vs. δD values point to clay-mineral dehydration as the cause for these anomalies. Calculations assuming a δ18O vs. δD equilibrium between the pore fluid and clay minerals at depth of formation indicate temperatures of dehydration between 85 and 130 °C. This temperature range is in agreement with the B enrichments and the presence of thermogenically formed CH4. Because temperatures above 50 °C are not reached within the sediment cover of the upper plate, the fluids most likely form within the subducted sediments and flow upward along deep-seated faults from ≥12 km depth. Mound-related fluid expulsion may contribute significantly to the recycling of mineral-bound water.

Document Type: Article
Keywords: fluid dynamics, isotope geochemistry, pore water, chlorinity, active margins, Costa Rica
Research affiliation: OceanRep > SFB 574 > A3
OceanRep > SFB 574 > A1
OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-MG Marine Geosystems
OceanRep > SFB 574
OceanRep > SFB 574 > B5
OceanRep > SFB 574 > B3
Kiel University
Refereed: Yes
DOI etc.: 10.1130/G20119.1
ISSN: 0091-7613
Projects: SFB574
Contribution Number:
SFB 57437
Date Deposited: 24 Mar 2009 16:32
Last Modified: 03 Aug 2017 06:35
URI: http://eprints.uni-kiel.de/id/eprint/4961

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