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ABSTRACT

Recent studies of the Cordillera de la Costa belt of northern Venezuela on Margarita Island and Araya Peninsula as well as ongoing studies along the central Venezuelan coastal region from Cabo Codera to Puerto Cabello, have yielded two surprising conclusions: (1) the deformational history is virtually the same throughout the entire length (about 550 Km) of the bell, and (2) the deformational structures suggest a kinematic history, far more complicated than expected from simple models of subduetion, transpression, and transtension.

The metamorphic Cordillera de la Costa belt consists of an “oceanic” assemblage, a “continental-margin” sequence and granitic rocks. The first assemblage underwent high-pressure, low-temperature meiamorphism (eclogite and blueschist facies), typical of subduction complexes, and the second and third underwent lower-pressure metamorphism. These assemblages are now thoroughly intermixed.

Since amalgamation, all assemblages underwent similar deformational histories. Five generations of synmeiamorphic structures were recognized (D1a to D1e) and two generations of non-metamorphic structures (D2 and D3). The D1 structures formed during the Late Cretaceous in a subduction zone (Farallon - Proto-Caribbean); D1a occurred at a depth of about 45 Km and D1b to D1e at successively shallower depths (from about 30 Km to 15 Km). The kinematic significance of D1a and D1b structures could not be established as they are disrupted by D1c. D1c structures (east-west trending foliations and stretching lineations with dextral kinematic indicators) have formed during right-oblique plate convergence. Did structures are minor folds with northeast- and rarely northwest-striking axial planes; they may have formed in similar tectonic environment as D1c. The D1e deformation (conjugate sets of ductile shears) resulted in east-west extension, caused by increased obliquity of plate convergence due to the arcuate nature of the volcanic arc. D2 structures are related to thrust faults (north-vergent on Margarita Island; south-vergent on the Venezuelan mainland) and may be the result of the Tertiary emplacement of the belt onto the South American continent. The Late Tertiary D3 structures (north-south trending folds) and several sets of faults may be related to eastward passage of the Caribbean past the South American plate.

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