Fluid flow at the toe of convergent margins; interpretation of sharp pore-water geochemical gradients

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doi: 10.1016/S0012-821X(03)00343-1
Author(s): Saffer, Demian M.; Screaton, Elizabeth J.
Author Affiliation(s): Primary:
University of Wyoming, Department of Geology and Geophysics, Laramie, WY, United States
Other:
University of Florida, United States
Volume Title: Earth and Planetary Science Letters
Source: Earth and Planetary Science Letters, 213(3-4), p.261-270. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X CODEN: EPSLA2
Note: In English. 20 refs.; illus., incl. sects., 1 table, sketch map
Summary: Fluid expulsion greatly impacts chemical and mass budgets at subduction zones, particularly if it is focused along faults and stratigraphic conduits. Geochemical anomalies centered at decollement zones, such as pore-water freshening and the presence of thermogenic hydrocarbons, indicate long-distance, focused flow of deeply sourced fluids. The sharp gradient of these anomalies below the decollement zone has been interpreted as evidence for recent pulses of fluid flow, initiating a few to tens of ka. However, this interpretation does not consider that underthrust sediments are moving arcward beneath the decollement zone. In addition, upward flow from the compacting underthrust sediments can modify chemical profiles. Here, we use a simple model that couples fluid flow and solute transport to evaluate these sharp chemical gradients. We find that observed geochemical anomalies at the Northern Barbados and Costa Rican subduction zones can be explained either by recent pulses of flow, or by sustained flow along the decollement zone coupled with modest vertical fluid expulsion from consolidating underthrust sediments. The latter interpretation is consistent with estimates of upward flow rate at Costa Rica based on estimated pore pressure gradients and measured permeabilities within the underthrust sediments. One important implication is that recent pulses of flow along fault conduits may not be required to explain the geochemical anomalies. Furthermore, mixing of locally derived fluids flowing upward from the underthrust sediments and deeply sourced fluids flowing along the decollement zone provides an explanation for the observed changes in pore-water freshening along the decollement at Costa Rica. Abstract Copyright (2003) Elsevier, B.V.
Year of Publication: 2003
Research Program: ODP Ocean Drilling Program
Key Words: 02 Geochemistry; 07 Marine Geology and Oceanography; Accretionary wedges; Advection; Antilles; Atlantic Ocean; Barbados; Caribbean region; Central America; Continental margin; Costa Rica; Decollement; Diffusion; East Pacific; Faults; Fluid dynamics; Fluid phase; Geochemical anomalies; Geochemistry; Hydrochemistry; Leg 110; Leg 156; Leg 170; Lesser Antilles; Marine sediments; Mixing; Models; North Atlantic; North Pacific; Northeast Pacific; Northwest Atlantic; ODP Site 1039; ODP Site 1040; ODP Site 1043; ODP Site 671; ODP Site 948; Ocean Drilling Program; Pacific Ocean; Permeability; Plate convergence; Pore pressure; Pore water; Sediments; Solute transport; Subduction zones; Underthrust faults; West Indies
Coordinates: N153133 N153133 W0584357 W0584357
N153128 N153134 W0584354 W0584356
N093823 N093823 W0861200 W0861200
N093916 N093916 W0861109 W0861109
N093943 N093943 W0861045 W0861045
Record ID: 2004085272
Copyright Information: GeoRef, Copyright 2017 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands