HR: 1340h
AN: T33B-1377    [Abstracts]
TI: Structural, Thermochronological, Topographic, and Precipitation data of the Transpressional Orogen of the Venezuelan Paria Pen¡nsula, SE Caribbean-South American Plate Boundary
AU: * Cruz, L
EM: cruz0031@umn.edu
AF: University of Minnesota, 310 Pillsbury Drive SE, Minneapolis, MN 55455 United States
AU: Fayon, A
EM: fayon001@umn.edu
AF: University of Minnesota, 310 Pillsbury Drive SE, Minneapolis, MN 55455 United States
AU: Teyssier, C
EM: teyssier@umn.edu
AF: University of Minnesota, 310 Pillsbury Drive SE, Minneapolis, MN 55455 United States
AU: Weber, J
EM: weberj@gvsu.edu
AF: Grand Valley State University, 1 Campus Dr., Allendale, MI 49401 United States
AB: New structural and thermochronological data as well as published structural, topographic, and precipitation data from the Paria Pen¡nsula suggest a general model for the exhumation and deformation of rocks in the SE Caribbean-South American plate boundary. The mountain belt of the Paria Peninsula in eastern Venezuela is composed of deformed and metamorphosed sediments that were deposited on the northern South America passive margin in early Mesozoic time. This belt is currently bounded by the active right-lateral strike-slip El Pilar fault to the south and the Coche/North Coast fault to the north. Metamorphic grade increases from sub-greenschist facies in the south to amphibolite facies in the north. In eastern Paria Pen¡nsula, the focus of our study, foliation (S1) dips steeply to the south along the southern coast and gradually shallows to the north to $25-30\deg$ dip. In general, S1 strikes approximately 060-075\deg subparallel to oblique to the general trend of the metamorphic belt. Elongation lineations (L1) are defined by the preferred orientation of elongated quartz grains that plunge subhorizontally to the SW. Quartz c-axes fabric patterns from samples along and across the region show top-to-SW or oblique-normal sense of shear, and suggest activation of the basal$<$a$>$, prism $<$a$>$, and rhomb $<$a$>$ slip systems under relatively low temperature ($300-400\deg$C). Apatite and zircon fission-track ages obtained for individual samples plot within 2 sigma error of each other, which we interpret as due to rapid cooling. Apatite and zircon FT ages range from 29 Ma in the south to 4-5 Ma in the north. The rapid cooling rates in the temperature range for zircon and apatite ($350 \deg$C -$120 \deg$C) are similar across the peninsula, but the event was diachronous from south to north. The topography of the Paria Pen¡nsula and its precipitation pattern are both asymmetric (approximately 1 m/yr on the southern flank, and 2-3 m/yr on the northern flank). Rivers in the northern flank flow perpendicular to the main divide with steep gradients, short distances, and high discharge rates while drainage patterns in the southern flanks are characterized by lower gradients, with fluvial plains and alluvial fans. This orogen shows significant similarities to the Southern Alps orogen in New Zealand, in terms of internal deformation, exhumation patterns, topography, erosion rates, and precipitation. Therefore, a general model for a transpressional double wedge is proposed for both orogens. In this model, material is extruded toward one side of the orogen by "channel-like" flow. This model accounts for the asymmetric profiles of deformation and erosion rates in both orogens. Internally, the direction of material accretion is the main variable that controls the orogen's internal particle path and deformation. Externally, the configuration of the orogen is controlled by erosion that "facilitates" localization of exhumation and deformation. Interaction among exhumation, deformation, and erosional processes characterize this type of setting and possibly dictate orogenic evolution.
DE: 8102 Continental contractional orogenic belts
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting