STRUCTURAL STYLES ALONG OBLIQUELY CONVERGENT OROGENS: THE EASTERN CARIBBEAN-SOUTH AMERICA PLATE BOUNDARY

The Caribbean-South America plate boundary in NE Venezuela and northern Trinidad exposes an E-W oriented mountain belt of deformed and metamorphosed sediments deposited on the northern South America passive margin in early Mesozoic time. Northern Trinidad and NE Venezuela display contrasting styles of deformation developed during oblique collision and wrenching between the Caribbean and South American plates in the past 50 million years. In northern Trinidad, metamorphic conditions increase from east to west with structures evolving from upright in the east to recumbent in the west, across the brittle-ductile transition. In ductilely deformed rocks, foliation is subhorizontal and lineation is ~E-W, parallel to the belt. Sense of shear is ambiguous. In NE Venezuela, metamorphic grade is similar to the western part of northern Trinidad; foliation dips moderately to steeply to the S and lineation plunges moderately to the SW. In general, sense of shear criteria parallel to lineation show top (down) to SW relations, indicating increased exhumation of the northern part of the belt. Oblique collision and wrenching in the Caribbean-South American plate boundary may have generated a complex deformation history, which evolved diachronously from west to east to produce the two styles of deformation displayed in northern Trinidad and NE Venezuela. Two models have been proposed to account for the generation and exhumation of this belt. In the first model, deformation is concentrated in a retro-wedge developed in front of the rigid Caribbean plate indenter, which deformed the softer South American continental crust. Vertical stretch decreases southward, exhumation rate increases to the north and deformation ages are younger to the east due to diachronous collision. The second model implies a midcrustal coupling zone that deforms ductilely due to translation of upper crustal blocks and transpression of the system. Subhorizontal fabrics develop contemporaneously parallel to the rheological layering of the lithosphere. For both models, spatial and kinematic variations of fabric orientation, cooling ages, and exhumation rates, are key elements to understand the overall deformation history of this region and are currently being studied.