--> Crustal Modeling of the Caribbean- South American Plate Boundary, at Venezuelan Central Coast
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Crustal Modeling of the Caribbean- South American Plate Boundary, at Venezuelan Central Coast

Abstract

The central coast of Venezuela is a tectonically complex transpressive plate boundary zone between Caribbean and South American plates, which offers an excellent location to study accretionary processes (e.g. Leeward Antilles to South America). In the last decades, hundreds of works have been carried out in the zone, but there is still not enough information to get a full image of the lithospheric structure, and there are also several hypotheses related to the origin of the Caribbean plate. This study is looking for additional insights for the understanding of the crustal structure at the plate boundary zone between Caribbean and South American plates, at latitudes 10∫N — 13∫N, and longitudes 63∫W to 67∫W. The geological expressions and crustal geometry obtained from the modeling of geological and geophysical data, helped to subdivide the area of study in three main geological provinces, from north to south: 1) Venezuelan basin, 2) Leeward Antilles, and 3) Tertiary basins. The data used to build this crustal model consisted of: bathymetric, gravimetric, Previous HitmagnetometricTop, and seismic data. The gravimetric data corresponds to the combined geopotential model EGM2008 used to calculate the Bouguer anomaly (GarcÌa, 2009). The Bouguer anomalies in the area vary from -210 to 213 mGal, and confirmed the subdivision mentioned before, showing three different patterns corresponding to each zone, mainly constant gravity values at the Venezuela basin, pairs of gravimetric lows and highs NW-SE oriented at the Leeward Antilles belt, and W-E lineaments at the Tertiary basins zones. From the gravimetric regional-residual separation the depth for the deep source was estimated at 18km at the Leeward Antilles area and at 28km at the San Sebastian-El Pilar fault system. The residual gravimetric map for the study area confirmed the subdivision defined from the Bouguer anomaly map (Figure 1). The magnetic data corresponds to the combined model of the terrestrial magnetic field EMAG2 (Maus, et al., 2009). The magnetic anomaly values vary from 196 to -117nT, and confirmed the subdivision of 113 three main areas, showing pairs of magnetic lows and highs NW-SE oriented, in the central area W-NW to E-SE lineaments at the Leeward Antilles area, and in the south a flat area of almost regular value corresponding to the San Sebastian — El Pilar fault zone. From the magnetic regional-residual separation the depth of the deep source was estimated to be around 20km at the north to 25 km at the south. The seismic data used for the Cretaceous basement interpretation corresponded to 2D reflection data and 2D seismic sections published in previous studies (Paolini, 2012; Escalona, et al., 2009; Ysaccis, 1997). The gravimetric and magnetic model was carried out using an inverse modeling approach. The gravimetric model was adjusted in order to match the observed and calculated gravities, getting as outcomes the estimated crustal depths and geometry. The resulting crustal geometry shows variations of the cortical thickness from 15km at the north in the Venezuelan basin zone, to 28 km at the south at the San Sebastian — El Pilar (SSEP) fault system, showing an abrupt change in the topography, suggesting two different blocks at each side of the SSEP fault system (Figure 2). Velocity vectors measured from SIRGAS2000 stations located at the Caribbean and South American plates show different ranges and orientations corroborating the hypothesis of two different blocks at the north and south side of the fault system (Liberal, 2015; Perez, et al., 2001). The Caribbean velocity vectors has an orientation NE, while the South American ones has orientations NW (Figure 2). The outcomes from this study support the hypothesis that the San Sebastian — El Pilar fault system corresponds to a lithospheric element that is part of the plate boundary zone.