Heat flow, tectonics, and fluid circulation at the toe of the Barbados Ridge Accretionary Prism

Foucher, J.P.; Lepichon, X.; Lallemant, S.; Hobart, Michael A.; Henry, Pierre; Benedetti, Marc F.; Westbrook, G. K.; Langseth, Marcus G.

doi:10.1029/jb095ib06p08859

Cited by 73 publications

(49 citation statements)

References 17 publications

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“…5) This value is fairly coherent with surface heat-flow determinations in the area (Foucher et al, 1990).…”

Section: Sediment Thermal Conductivity and Heat Flowsupporting

confidence: 73%

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Long-term observations of pressure and temperature in Hole 948D, Barbados accretionary prism

Foucher¹,

Henry²,

Harmegnies³

1997

Proceedings of the Ocean Drilling Program, 156 Scientific Results

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In June-July 1994, during Ocean Drilling Program (ODP) Leg 156, Holes 948D and 949C were drilled 4 and 2 km landward, respectively, of the deformation front of the Barbados accretionary prism. The two holes were equipped with subseafloor monitoring instrumentation to determine the fluid pressure in the décollement, and the thermal structure of the sediments after drilling disturbances had dissipated, and to monitor any natural temporal variations, if present. Strings of temperature and pressure sensors were suspended from circulation obviation retrofit kit (CORK) boreseals in both holes. In December 1995, data collected for 18 months were recovered by American and French scientists onboard Nautile during the joint expedition ODPNaut. In this paper, we present the results from Hole 948D. The temperature data indicate conductive heat transfer with a constant heat flow of 85 mW/m 2 at this hole. There is no thermal indication of fluid movement along the décollement or vertically through the prism sediments. The pressure record demonstrates that Hole 948D was not properly sealed from the sea bottom. One interpretation of the pressure record is that the weight of the mud column in the borehole gradually equilibrated with the fluid pressure in the décollement. According to this interpretation, the décollement is inferred to be moderately overpressured at 2.2 MPa above the hydrostatic pressure.

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“…5) This value is fairly coherent with surface heat-flow determinations in the area (Foucher et al, 1990).…”

Section: Sediment Thermal Conductivity and Heat Flowsupporting

confidence: 73%

“…Also, the constant heat flow across the décollement implies that the horizontal flow rates along it do not exceed values of the order of 10 m 3 /yr per meter along strike of the subduction zone. This estimate is at least ten times smaller than initially proposed by Fisher and Hounslow (1990) and Foucher et al (1990).…”

Section: Discussionmentioning

confidence: 47%

Long-term observations of pressure and temperature in Hole 948D, Barbados accretionary prism

Foucher¹,

Henry²,

Harmegnies³

1997

Proceedings of the Ocean Drilling Program, 156 Scientific Results

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“…The lateral and vertical pressure gradients that are established cause fluids to be expelled locally or diffusely from the thickening section (Moore et al, 1988;Davis et al, 1990;. The rates and total volumes of fluid flow are not as great as those in axial hydrothermal systems, although thermal and particularly chemical fluxes can be locally significant (Gieskes et al, 1990;Davis et al, 1990;Langseth et al, 1990;Foucher et al, 1990), and the integrated effect of the flux of expelled fluids on the diagenesis and alteration of the sediment section is suspected to be large (Kulm and Suess, 1990;Hyndman and Davis, in press).…”

Section: Holes In Accretionary Prismsmentioning

confidence: 99%

CORK: A Hydrologic Seal and Downhole Observatory for Deep-Ocean Boreholes

Davis¹,

Becker²,

Pettigrew³

et al. 1992

Proceedings of the Ocean Drilling Program

101

105

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A new tool has been developed and successfully deployed that provides a means by which cased reentry holes drilled by the Ocean Drilling Program can be hydrologically sealed and instrumented. The seal prevents flow of water into or out of a hole that would otherwise cause severe thermal and chemical disturbance to the formation drilled. The seal is capable of withstanding both positive and negative differential pressures that may be present in hydrothermally or tectonically active environments, and can be removed for later drilling operations. The instrumentation, developed for initial deployments during Ocean Drilling Program Leg 139, was designed to monitor the formation temperatures and pressures for up to 2 years during and following the recovery from drilling disturbances. A recording gauge measures absolute pressure in the borehole below the seal. A sensor string containing 10 thermistors and a fluid-sampling tube hang in the hole below the recording package. The sampling tube extends through the seal to a port, allowing the differential pressure to be measured and fluids to be tapped from deep within the hole. Data recovery and fluid sampling can be done via submersible or remotely operated vehicle.Two units were deployed in the sediment-filled Middle Valley rift of the northern Juan de Fuca Ridge. The first was installed in Hole 857D, which was drilled to a total depth of 936 meters below seafloor, through 470 m of turbidite sediment and into a highly permeable sediment-sill complex that is inferred to be a sediment-sealed hydrothermal "reservoir." The second was deployed in Hole 858G, which was drilled to a total depth of 433 meters below seafloor into a buried volcanic edifice that underlies a hydrothermal vent field. Data were recovered successfully from both holes about three weeks after deployment. Temperatures and pressures recorded in Hole 858G show that formation conditions are severely affected by drilling and by downward fluid flow into the formation through a nearby uncased exploratory hole that was not adequately sealed with cement. The differential pressure across the seal in Hole 858G was initially -0.24 MPa, and at the time of the data recovery was becoming increasingly negative. Temperatures and pressures recorded in Hole 857D appear to be recovering slowly from drilling disturbances. Initially, the differential pressure across the seal in this hole was -1.10 MPa; at the time of the data recovery, the differential had reduced to -0.55 MPa. The instruments will continue to monitor formation pressures and temperatures once per hour for 2 years.

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“…Numerous studies have indicated that the décollement, intraprism faults, highly permeable (sandy) layers, and mud volcanoes provide conduits for water flow to escape. Detailed studies of the Barbados (Foucher et al, 1990;Fisher and Hounslow, 1990), Oregon-Washington , and Japan (Henry et al, 1989) accretionary wedges document that rates of fluid expulsion from vents and mud volcanoes can be as great as, or significantly greater than, the total rate of fluids entering the subduction zone, implying that fluid vents and mud volcanoes are transient features. The Costa Rica margin probably has few sandy layers, so any elevated permeability is most likely fracture permeability.…”

Section: Fluid Effectsmentioning

confidence: 99%