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Integration of Geophysical Data to Define a Structural Model in the North-Central Coast of the Venezuelan Platform

Abstract

The study area is located in La Orchila – La Tortuga region, in the Caribbean Sea, to the north of the central part of Venezuelan coast, in La Blanquilla and Tuy – Cariaco basins, between latitudes 10° and 12.5° north and longitudes −66.5° and −64° west. In the last years the country has been affected by several seismic events, this generates the necessity to define a structural model for the offshore northern area of Venezuela, emphasizing the neotectonic activity. This model will allow a better understanding of the active structures that may be affecting the seismic activity in this area. The structural model has been created from the integration of geophysical and geological data, allowing the interpretation of six different geological provinces in the area: 1) Leeward Antilles (Orchila zone); 2) Leeward Antilles (Eastern Blanquilla Basin); 3) Western Blanquilla Basin; 4) Margarita–La Tortuga Platform; 5) Margarita–Los Testigos Platform; and 6) Tuy-Cariaco Basin, including the San Sebastian – El Pilar fault system. The cortical thickness shows a general trend to decrease northward, with some exceptions, in La Tortuga high and in Margarita Platform, associated to the volcanic arc of the Leeward Antilles. The cortical thickness is increasing southwards, with an abrupt change to the south of the fault system, the average thickness in the north side is 16 km and in the south is 25 km. The Moho discontinuity goes shallower northwards, deepening southwards. The depths range varies between 27 km and 16 km, with an average of 27 km in the coast and 18 km in the Leeward Antilles area. These results are similar to the ones obtained from the regional gravimetric anomaly; however, due to the size of the window used to perform the spectral analysis, dividing the area in four blocks, the total component for the mantle spectrum could not be covered. This data cross correlated with GPS vector data show the possible existence of two different blocks to each side of the fault system, one to the north associated to the Caribbean Plate and one to the south associated to the South American Plate, suggesting that this fault system corresponds to a structural feature which is affecting not only the crust but also the upper mantle, establishing the San Sebastian – El Pilar fault system as a lithospheric element which is part of the plate boundary, between the Caribbean and South American Plate.