Abstract

The island of Barbados exposes the crestal zone of the accretionary prism of the Lesser Antilles forearc. Tertiary rocks at Bath, Barbados, include four lithic suites: (1) inter-bedded volcanogenic and mainly calcareous pelagic rocks (the Oceanic beds), (2) radiolarite, (3) siliceous hemipelagic rocks, and (4) mélange. Suites 1–3 are in structurally discrete groups of fault packets; mélange occurs in apparently diapiric crosscutting bodies. The Oceanic beds occupy a pre-Pleistocene nappe complex that underlies much of Barbados. Radiolarite and hemipelagic rocks belong to a thick accretionary basal complex and constitute the relative autochthon to the Oceanic nappes. Fault rocks of the sub-Oceanic fault zone developed during emplacement of the Oceanic nappes. The lower portion of the tectonic stack is deformed in a major south-verging fold couple with wavelength of ∼250 m. Lower, early emplaced Oceanic nappes are restricted to the core of the major synform and are increasingly deformed with depth. Structures suggest easterly transport of Oceanic nappes and upward younging of nappe emplacement, indicating that the deformation of Oceanic beds propagated westward. The Oceanic nappes provided a seal to rising fluids; transport of nappes may have been facilitated by elevated fluid pressure beneath their sole thrust. Pre- and post-nappe folds record north-south shortening about shallow, west-plunging axes, consistent with folded accretionary strata elsewhere on Barbados. Deformation occurred under shallow nonmetamorphic conditions.

The Oceanic beds are interpreted as being trapped outer forearc-basin strata that have been tectonically shouldered by the arcward migrating prism flank or crest. The hemipelagic and radiolarite suites may be offscraped abyssal-plain and trench-wedge accumulations. Paleogene-lower Miocene Oceanic strata were deposited at depths between 2.0 and 4.8 km. Middle Miocene Oceanic beds accumulated at shallower depths (1–1.5 km); thus, early Miocene was the probable time of inception of major uplift and arcward shouldering in the crestal zone of the accretionary prism. Accretion of the basal complex of Barbados probably occurred in late Eocene time.

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