Strain decoupling across the decollement of the Barbados accretionary prism

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doi: 10.1130/0091-7613(1996)024<0127:SDATDO>2.3.CO;2
Author(s): Housen, Bernard A.; Tobin, Harold J.; Labaume, Pierre; Leitch, Evan C.; Maltman, Alex J.; Shipley, T.; Ogawa, Y.; Ashi, J.; Blum, P.; Brückmann, W.; Felice, F.; Fisher, A.; Goldberg, D.; Henry, P.; Jurado, M. J.; Kastner, M.; Laier, T.; Meyer, A.; Moore, J. C.; Moore, G.; Peacock, S.; Rabaute, A.; Steiger, T.; Underwood, M.; Xu, Y.; Yin, H.; Zheng, Y.; Zwart, G.
Ocean Drilling Program, Leg 156, Shipboard Scientific Party, College Station, TX
Author Affiliation(s): Primary:
University of Minnesota, Institute for Rock Magnetism, Minneapolis, MN, United States
Other:
University of California at Santa Cruz, Santa Cruz, CA, United States
Laboratoire de Géophysique Interne et Tectonophysique, Grenoble, France
Sydney University of Technology, Australia
University of Wales Aberystwyth, United Kingdom
Volume Title: Geology (Boulder)
Source: Geology (Boulder), 24(2), p.127-130. Publisher: Geological Society of America (GSA), Boulder, CO, United States. ISSN: 0091-7613 CODEN: GLGYBA
Note: In English. 21 refs.; illus.
Summary: The interrelation between deformation styles and behavior of fluids in accretionary prisms is under debate, particularly the possibility that overpressuring within the basal decollement may enable mechanical decoupling of the prism from the subducting material. Anisotropy of magnetic susceptibility (AMS) data from sediments spanning the basal decollement of the Barbados accretionary prism show a striking progression across this structure that strongly supports the hypothesis that it is markedly overpressured. In the accretionary prism, above the decollement, the minimum AMS axes are subhorizontal and oriented nearly east-west, whereas the maximum AMS axes are oriented nearly north-south and shallowly inclined. At the top of the decollement, the minimum AMS axes orientations abruptly change to nearly vertical; this orientation is maintained throughout the decollement and in the underthrust sediments below. The AMS orientations in the prism sediments above the decollement are consistent with lateral shortening due to regional tectonic stress, as the minimum axes generally parallel the convergence vector of the subducting South American plate and the maximum axes are trench-parallel. Because the orientations of the AMS axes in deformed sediments usually parallel the orientations of the principal strains, the AMS results indicate that the incremental strain state in the Barbados prism is one dominated by subhorizontal shortening. In contrast, the AMS axes within and below the decollement are consistent with a strain state dominated by vertical shortening (compaction). This abrupt change in AMS orientations at the top of the decollement at Site 948 is a direct manifestation of mechanical decoupling of the off-scraped prism sediments from the underthrust sediments. The decoupling horizon occurs at the top of the decollement zone, coinciding with the location of flowing, high-pressure fluids.
Year of Publication: 1996
Research Program: ODP Ocean Drilling Program
Key Words: 07 Marine Geology and Oceanography; 18 Geophysics, Solid-Earth; Accretionary wedges; Atlantic Ocean; Barbados Ridge; Decollement; Decoupling; Faults; Leg 156; Maghemite; Magnetic minerals; Magnetic susceptibility; Magnetite; Marine sediments; North Atlantic; Ocean Drilling Program; Oxides; Paleomagnetism; Plate tectonics; Preferred orientation; Sediments; Strain; Underthrust faults
Coordinates: N153133 N153224 W0584207 W0585106
Record ID: 1996019609
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