Hydrogeochemistry of the Northern Barbados Accretionary Complex Transect: Ocean Drilling Project Leg 110

Gieskes, Joris M.; Vrolijk, Peter; Blanc, G.

doi:10.1029/jb095ib06p08809

Cited by 112 publications

(64 citation statements)

References 28 publications

(5 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Low-chlorinity pore waters have been documented near the toe of the Barbados accretionary prism, especially in the vicinity of the basal décollement (Gieskes et al, 1990b;Shipboard Scientific Party, 1995a, 1995b. Previous investigators suggested that these pore waters evolved during smectite-to-illite reactions within deeper domains of underplating and then migrated toward the prism's toe (Gieskes et al, 1990a;Wilkens et al, 1990;Vrolijk et al, 1991).…”

Section: Thematic Backgroundmentioning

confidence: 99%

Clay mineralogy and clay geochemistry in the vicinity of the décollement zone, northern Barbados Ridge

Underwood¹,

Deng²

1997

Proceedings of the Ocean Drilling Program, 156 Scientific Results

View full text Add to dashboard Cite

Fine-grained sediments recovered during Leg 156 of the Ocean Drilling Program contain assemblages of clay minerals that change considerably with depth. Key structural and stratigraphic features within the toe of the northern Barbados accretionary prism include the basal décollement and a sharp boundary between lithologic Units II and III; this lithologic boundary occurs within the décollement zone. We analyzed three size fractions (4−8 µm, 1−4 µm, and <1 µm) by X-ray diffraction and obtained chemical data from the <1-µm size fractions by scanning electron microscopy coupled with energy dispersive spectroscopy. Relative proportions of expandable clay minerals increase significantly, but erratically, near the top of the décollement zone. Proportions of discrete smectite and smectite-rich illite/smectite (I/S) mixed-layer clays decrease steadily down the décolle-ment zone. The base of the décollement zone is characterized by unusually high concentrations of illite. These changes in clay mineralogy influence the shear strength of claystones at the deformation front and help control the position of the décollement.Relative abundances of illite within all lithofacies units increase in coarser size fractions, and this trend is consistent with a detrital source. Kaolinite does not display any systematic partitioning within Unit II, but its proportions increase in the finer size fractions within Unit III. The smectite content of Unit II increases with decreasing grain size; Unit III shows the opposite trend between particle size and % smectite. Bentonite-like samples probably originated through in situ alteration of disseminated volcanic ash, but we believe that the pyroclastic material was mixed into a background sediment that already contained abundant detrital smectite. Illitic mixed-layer clays within the underthrust domain (Unit III) also appear to be detrital in origin. Correlations among both % smectite and % kaolinite and most major-element oxides are statistically significant, but correlations for illite are not. Expandable clays vary considerably in their chemical make-up; the most common type appears to be a Mg-poor, K-rich, Fe-Al-beidellite. We rely upon actualistic provenance connections for late Quaternary clays to guide our interpretations of Miocene and Oligocene sediment dispersal. If these analogues are valid, then the proto-Orinoco and protoAmazon Rivers were the most important detrital sources for the older hemipelagic and turbidite deposits of Barbados Ridge.

show abstract

Section: Thematic Backgroundmentioning

confidence: 99%

Clay mineralogy and clay geochemistry in the vicinity of the décollement zone, northern Barbados Ridge

Underwood¹,

Deng²

1997

Proceedings of the Ocean Drilling Program, 156 Scientific Results

View full text Add to dashboard Cite

show abstract

“…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

View full text Add to dashboard Cite

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.

show abstract

“…More fluid is present below thrust faults penetrated at Site 829, which implies that the faults may channelize fluid flow similar to the Barbados accretionary wedge (Mascle, Moore, et al, 1988). Moreover, the deepest samples at Site 829 are characterized by low chloride and high methane concentrations, a covariance that also characterizes the pore-fluid chemistry within the décollement at the Barbados accretionary wedge (Gieskes et al, 1990). Thus, the fluid near the deep thrust fault at Site 829 may have been derived from the décollement and subduction-related processes.…”

Section: Resultsmentioning

confidence: 92%

Summary and Conclusions

1992

Proceedings of the Ocean Drilling Program

View full text Add to dashboard Cite

Leg 134 of the Ocean Drilling Program investigated the influence of ridge collision and subduction on the structural evolution of island arcs by drilling at a series of sites in the collision zone between the d'Entrecasteaux Zone and the central New Hebrides Island Arc. The d'Entrecasteaux Zone is an arcuate Eocene to Oligocene submarine chain of ridges and basins extending from the northern New Caledonia ridge to the New Hebrides Trench. Near the New Hebrides Trench, the zone comprises two parallel, east-west-trending morphologic highs: the fairly continuous North d'Entrecasteaux Ridge and the South d'Entrecasteaux Chain, composed of seamounts and guyots whose easternmost member is the Bougainville Guyot. The impingement of the d'Entrecasteaux Zone upon the central New Hebrides Island Arc has greatly disrupted and tectonically modified the forearc and arc morphology and structure. Holes at Sites 827 and 829 were drilled to penetrate the lowermost accretionary wedge and the interplate thrust fault (décollement). The primary objective of drilling at Site 828 was to obtain a critical reference section of the north ridge rocks. Sites 830 and 831 are located where the Bougainville Guyot has collided with the arc. At Site 830 we aimed to penetrate imbricated arc rocks, and at Site 831 we sought to determine the lithology, age, paleobathymetry, and mechanical properties of the guyot. Sites 832 and 833 are located in North Aoba Basin, an intra-arc basin that is considerably deeper than any other basin along the arc summit and that occurs directly east of the collision. This basin contains several unconformities that appear to document the structural evolution of the central New Hebrides Island Arc.Preliminary interpretations of the results of Leg 134 suggest that each ridge of the twin-ridge d'Entrecasteaux Zone causes different forearc deformation. The sedimentary and surficial basement rocks of the North d'Entrecasteaux Ridge, whose basement rocks (MORB) are denser than those of the Bougainville Guyot, appear to have been scraped off and accreted to the forearc during subduction. This accretion has formed the Wousi Bank, which consists of uplifted forearc rocks and stacked thrust sheets. The South d'Entrecasteaux Chain impacts the forearc in a different manner: a narrower, less distinct form of deformation has occurred compared to the North d'Entrecasteaux Ridge collision zone, although the chain is converging at the same rate and at the same angle as the north ridge. Major compositional changes of pore fluids in the collision zone result from diagenetic alteration of volcanic sediment and are manifested as chloride and calcium concentrations greater than seawater values and sodium, potassium, and magnesium concentrations lower than seawater values. Variations in these solute concentrations correspond to structural features, particularly across thrust faults at Site 829 and in a fractured zone at Site 830. More fluid is present below thrust faults penetrated at Site 829, which implies that the faults may chan...

show abstract

Hydrogeochemistry of the Northern Barbados Accretionary Complex Transect: Ocean Drilling Project Leg 110

Cited by 112 publications

References 28 publications

Clay mineralogy and clay geochemistry in the vicinity of the décollement zone, northern Barbados Ridge

Clay mineralogy and clay geochemistry in the vicinity of the décollement zone, northern Barbados Ridge

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

Summary and Conclusions

Contact Info

Product

Resources

About