EXHUMATION AND DEFORMATION IN THE VENEZUELAN PARIA PENINSULA, SE CARIBBEAN-SOUTH AMERICAN PLATE BOUNDARY

The Paria Peninsula in eastern Venezuela exposes an E-W oriented mountain belt bounded by the El Pilar dextral fault to the south and the El Coche dextral fault to the north. This narrow (5-10 km wide) belt is composed of deformed and metamorphosed sediments that were deposited on the northern South American passive margin in early Mesozoic time. The metamorphic grade, mostly greenschist facies, decreases from north to south in a direction perpendicular to the trend of the metamorphic belt. In the north, ductilely deformed pelitic schist, quartzite, and gneiss with high amplitude isoclinal recumbent folds characterize the structural grain. Foliation dips shallowly (15-35°) to the south and strikes NE-SW, oblique to the E-W strike-slip system. The stretching lineation is consistently oblique, plunging moderately to the SW. In the south, marble and metasandstone moderately deformed in low amplitude isoclinal folds preserve original sedimentary structures. Foliation dips more steeply (35-90°) to the south and strikes subparallel to the strike-slip system. Stretching lineation plunges variably to the SW. In general, sense of shear criteria parallel to lineation show top to SW relations (oblique-normal shear) consistently throughout the region, indicating increased uplift of the northern part of the belt. Quartz c-axes fabric patterns from samples along and across the region suggest basal slip system under relatively low temperature, and top-to-southwest sense of shear. Apatite fission-track ages range from 29 Ma in the south to 5 Ma in the north, indicating recent exhumation of the rocks to the north. Given the field geometries and fabric elements shown by this region, and based on the thermochronologic results, a model has been proposed to account for the exhumation and deformation of this belt. In this model, the Caribbean oceanic lithosphere acts as a wedged-indentor that deforms the softer continental South American crust. Deformation is concentrated in the orogenic wedge that accumulates strain (metamorphic belt). According to this model, strain decreases southward, oblique lineation result from a combination of wrenching and upward extrusion, exhumation rate increases to the north, and deformation ages are expected to young to the east due to advancing and diachronous oblique collision.