HR: 1340h
AN: T33B-1382    [Abstracts]
TI: Structure and Stratigraphy of the Barbados Accretionary Prism and the Tobago Forearc Basin
AU: * Chaderton, N A
EM: nchaderton@mail.utexas.edu
AF: Jackson School of Geosciences, University of Texas at Austin, Austin, TX 78704 United States
AU: Wood, L J
EM: lesli.wood@beg.utexas.edu
AF: Jackson School of Geosciences, University of Texas at Austin, Austin, TX 78704 United States
AU: Mann, P
EM: paulm@utig.ig.utexas.edu
AF: Jackson School of Geosciences, University of Texas at Austin, Austin, TX 78704 United States
AB: The relationship between the Lesser Antilles island arc, the Tobago forearc basin, and the Barbados accretionary prism shows classic convergent margin geometry. Barbados is the only emergent part of the accretionary prism with 80% of the island's land area being covered by Pleistocene limestone. Erosion of the limestone cap in the northeastern part of the island exposes older rocks of the prism. A 450-km2 2-D seismic data volume allows extension of these stratigraphic units offshore and definition of a regional structural framework. The relationship between the unit identified onshore as the Early Eocene to Middle Miocene Oceanic Formation and the basal unit, the intensively folded and faulted Eocene prism rocks of the Scotland Group, has long been debated. Previous proposals claim that the Oceanic Formation, consisting of pelagic clays with some ash beds, is allochthonous and has been thrusted into its present position above accreted sediments of the Scotland Group. However, seismic data show no evidence of nappes-the basis for the overthrusting hypothesis. Seismic interpretation presented here supports the opposing view that the Oceanic Formation and its offshore equivalent in the offshore Tobago forearc basin was deposited in situ and onlap the older, more highly deformed rocks of the accretionary prism. Previous workers proposed that the region's extensive mud diapirism (identified onshore as the Joes River Formation) has caused the emergence of Barbados, which continues to rise 0.44 mm/yr. However, seismic lines suggest that the island's emergence and present-day uplift is related to footwall uplift along a large, NE-striking normal fault off the east coast of the island.
DE: 8010 Fractures and faults
DE: 8099 General or miscellaneous
DE: 8150 Plate boundary--general (3040)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting