Systematic Variations in the Age and Thickness of Subducting Crust as a Control on Regional Structure; the Barbados Accretionary Prism, the Island of Trinidad and the Associated Offshore Areas, and Implications for Hydrocarbon Prospectivity

Variations in crustal thickness and elastic properties of subducting crust play a fundamental role in determining structural style, uplift history, basin types, and trap types along convergent margins. We integrate results from satellite gravity maps, gravity modeling, ~5500 km of ≥12000 ms seismic reflection data tied to 25 wells, 120 earthquake focal mechanisms, 200 heat flow data points, and p-wave and coda tomography of 1000 earthquakes to reveal the presence of four distinct crustal provinces actively subducting to the north and northwest beneath the arcuate, southeastern margin of the Caribbean plate; a region that includes the petroleum provinces of offshore Trinidad.

From east to west, these provinces include: 1) Province 1, a 40-50-km-thick crust; Precambrian basement of the South American continent, overlain by 8.5-14 km of Cretaceous to recent sediments and characterized by few, intermediate depth earthquakes of mixed thrust and normal fault mechanisms; 2) Province 2, a 70-km-wide, 30-km-thick, thinned continental crust adjacent to the continent-ocean boundary (COB) overlain by 15 km of Cretaceous to recent sediments and characterized by a cluster of intermediate depth earthquakes with mainly normal mechanisms and inferred fault planes oriented parallel to the thrust margin; 3) Province 3, a ~230-km-wide, 7-12-km-thick Jurassic oceanic crust characterized by fewer shallow to intermediate depth earthquakes and low heat flow consistent with older oceanic crust; and 4) Province 4, a 5-7-km-thick crust of Late Cretaceous age with few earthquakes.

We interpret the four provinces on the subducting plate and their basin and structural styles in terms of their elastic strength: the strongest continental area to the west has the highest flexural rigidity, bends the least resulting in a broad and deep Maturin foreland basin. Province 2 crust adjacent to the COB is thinner, weaker and bends more readily, indicated by normal fault earthquakes aligned along the zone of maximum flexure and a narrow but deep Columbus foreland basin. Thin Mesozoic oceanic crust in provinces 3 and 4 flex easily without breakage, few earthquakes and the formation of a peripheral bulge beneath the 300-km-wide accretionary prism. Basin style, subsidence history, and structural trap types in the overriding Caribbean plate and Trinidad area can be related to the type of incoming crust; thicker incoming crust results in greater shortening, uplift, and shallower top basement surface.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California