Compaction and dewatering processes of the oceanic sediments in the Costa Rica and Barbados subduction zones; estimates from in situ physical property measurements

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doi: 10.1016/S0012-821X(01)00403-4
Author(s): Saito, Saneatsu; Goldberg, David
Author Affiliation(s): Primary:
University of Tokyo, Ocean Research Institute, Tokyo, Japan
Other:
Lamont-Doherty Earth Observatory, United States
Volume Title: Earth and Planetary Science Letters
Source: Earth and Planetary Science Letters, 191(3-4), p.283-293. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X CODEN: EPSLA2
Note: In English. 21 refs.; illus., incl. sects., 1 table, sketch map
Summary: During Ocean Drilling Program Legs 170 and 171A, logging-while-drilling (LWD) tools were deployed on the Costa Rica and Barbados subduction margins. High-quality density, resistivity, and natural γ-ray logs were acquired across the decollement zones on both margins. Based on a new method of "layer-by-layer" correlation of the logs, changes in thickness and volume between incoming and subducted or accreted sediments are determined with 15 m resolution and 1% accuracy. The change in sediment thickness and volume generally decreases with depth, however, this change strongly depends on the lithology. Siliceous layers such as diatomaceous and radiolarian clay tend to be fluid-bearing, and the stratigraphic position of such zones is a critical factor in the fate of the subducted sediment section. On the Costa Rica Margin, the sediment section on the Cocos plate is underthrust intact beneath the toe of the Caribbean Plate with no frontal offscraping where a siliceous fluid-bearing zone is present only in the upper part of the section. On the Barbados margin, a layer of radiolarian clay exists, providing a narrow zone of mechanical weakness and anomalously high dewatering in the middle of the sediment section. This layer divides the sediments that are subducted from those that are accreted. Accreted and subducted sediments show different compaction styles. Accreted sediments are characterized by rapid compaction with vertical thickening, whereas subducted sediments are characterized by slow compaction with vertical flattening. The vertical thickening of the accreted sediments is due to horizontal tectonic compaction and contributes to the vertical thickening of the accretionary prism as a whole in the early stages of deformation. Dewatering flux is calculated by the volume change of the sediment sequences across the trench. The dewatering flux computed from the LWD data provides an estimate of the minimum fluid flux in the subduction zone and is significantly greater than the flux estimated from laboratory experiments because of meter-scale fluid conduits which influence the downhole logs but not the centimeter-scale sample measurements. Abstract Copyright (2001) Elsevier, B.V.
Year of Publication: 2001
Research Program: ODP Ocean Drilling Program
Key Words: 07 Marine Geology and Oceanography; Accretionary wedges; Antilles; Atlantic Ocean; Barbados; Barbados Ridge; Bioclastic sedimentation; Caribbean region; Central America; Compaction; Continental margin; Continental margin sedimentation; Cores; Correlation; Costa Rica; Costa Rica Rift; Dehydration; Diagenesis; East Pacific; Gamma-ray methods; In situ; Leg 170; Leg 171A; Lesser Antilles; Marine sediments; North Atlantic; North Pacific; Northeast Pacific; ODP Site 1039; ODP Site 1043; ODP Site 1044; ODP Site 1045; ODP Site 1047; Ocean Drilling Program; Pacific Ocean; Physical properties; Pore water; Sedimentation; Sediments; Subduction; Subduction zones; Well logs; Well-logging; West Indies
Coordinates: N153150 N153150 W0584211 W0584211
N093823 N093823 W0861200 W0861200
N093916 N093916 W0861109 W0861109
N153214 N153214 W0584325 W0584325
N153211 N153211 W0584251 W0584251
N153150 N153150 W0584211 W0584211
Record ID: 2001075267
Copyright Information: GeoRef, Copyright 2017 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands