Deng, Xinhua and Underwood, Michael B. (1996): Influence of clay mineralogy on location of the decollement zone, Barbados accretionary complex

Leg/Site/Hole:
ODP 110
ODP 156
Identifier:
1997-066334
georefid

Creator:
Deng, Xinhua
University of Missouri-Columbia, Department of Geological Sciences, Columbia, MO, United States
author

Underwood, Michael B.
author

Identification:
Influence of clay mineralogy on location of the decollement zone, Barbados accretionary complex
1996
In: Anonymous, Geological Society of America, 28th annual meeting
Geological Society of America (GSA), Boulder, CO, United States
28
7
439
Decollement zones (plate-boundary faults) separate offscraped and underthrust sequences in subduction zones. ODP Legs 156 and 110 penetrated the toe of the northern Barbados accretionary complex. Clay mineralogy and geochemistry (by XRD, SEM/EDS, and XRF) have added more insights into what controls the stratigraphic position of the Barbados decollement (a 32-m-thick zone). A sharp lithologic boundary occurs within the middle of the decollement zone between Miocene pelagic-hemipelagic clays (Unit II) and Oligocene fine-grained turbidites (Unit III). This zone also coincides with a pronounced mineralogic gradient from smectite-rich sediments at the top (>60 wt-% smectite in bulk) to illite-rich sediments at the base (<10 wt-% smectite). The smectite-rich interval retains higher porosity, abnormally high pore fluid pressure, and mechanical weakness. Mixed-layer I/S clays in Unit II are approximately 20 % less illitic that those in Unit III, which also lowers shear strength. Chemical and XRD data indicate that smectite in Unit II is montmorillonite, whereas smectite in Unit III is more Fe-rich and includes beidellite and nontronite. Relative clay-mineral abundances are partitioned by grain sizes, but smectite shows no significant variations in chemical composition between the <1 and <0.2 micro size fractions. We found no evidence to support an in situ diagenetic origin for these mineralogic changes. Instead, we attribute the variations to shifts in detrital provenances and sediment dispersal pathways from a continental source from South America (Unit III) to a mixed continental-volcanic source (Unit II).
English
Coverage:Geographic coordinates:
North:15.3224
West:-59.4500East: -58.4207
South:13.0000

Solid-earth geophysics; Sedimentary petrology; accretionary wedges; Antilles; Barbados; Caribbean region; Cenozoic; chemical composition; clay mineralogy; decollement; diagenesis; faults; hemipelagic environment; in situ; Leg 110; Leg 156; Lesser Antilles; marine environment; Miocene; Neogene; Ocean Drilling Program; Oligocene; Paleogene; partitioning; pelagic environment; plate boundaries; plate tectonics; pore water; porosity; provenance; sediments; SEM data; shear strength; spectra; strength; subduction zones; Tertiary; variations; West Indies; X-ray diffraction data; X-ray fluorescence spectra;

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