Exhumation and deformation processes in transpressional orogens: The Venezuelan Paria Peninsula, SE Caribbean-South American plate boundary

The Paria Península in eastern Venezuela exposes an E-W-oriented mountain belt 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. Foliation (S _t ) dips steeply to the south along the southern coast and progressively gentler to the north to 25-30°. S ₁ strikes ∼060-075° subparallel to oblique to the general trend of the metamorphic belts. Stretching lineation (L _t ) plunges variably to the SW. The pattern of crystallographic preferred orientation (CPO) of quartz c-axes indicates a transition from symmetric coaxial strain to weak top-to-SW or oblique-normal sense of shear. The fabric patterns suggest activation of the basal >a<, prism >a<, and rhomb >a< slip systems under relative low-temperature (300-400 °C). Apatite fission-track ages range from 29 Ma in the south to 5 Ma in the north. Similarly, samples in the northern and central zone yielded the youngest zircon fission track (FT) ages, ranging from 5 Ma to 9 Ma, and the southern zone yielded slightly older ages ca. 13 Ma. From the FT ages we estimate a diachronous cooling from south to north and a cooling rate in the range of 16-56 °C/m.y. (∼1-2 mm/yr of exhumation). That many of the cooling ages postdate pre-10 Ma transpression suggests that tectonically driven vertical extrusion alone cannot account for the observed exhumation. The topography of the Paria Peninsula and its current precipitation pattern are both asymmetric. Exhumation, deformation, topography, erosion, and precipitation patterns from the transpressional orogen of the Paria Peninsula are comparable to those described in the Southern Alps of New Zealand. A general model for these two-sided transpressional wedges is proposed based on geologic observations. Obliquity of the compression and erosion seems to play an important role in the evolution, exhumation, and deformation of these two naturally deformed orogens.