Resumo

UGHI, Antonio. Study of the cortical structure in the north-central Venezuela through bending plate analysis. Rev. mex. cienc. geol [online]. 2014, vol.31, n.1, pp.93-103. ISSN 2007-2902.

We conducted a gravity study, based on a 700 m spaced, regular grid of satellite data, aimed at defining the geometry of cortical blocks in the north-central region of Venezuela. The elastic behavior of the South American plate and its tectonic relationship with the Caribbean plate was modeled over four transects chosen from the complete Bouguer anomaly map, for which the geometries and densities of cortical blocks have been defined. We found that the north central Venezuelan crust can be divided into three different terranes: 1) continental crust bounded at north by the San Sebastián-Morón system fault, 2) transitional crust between the San Sebastián-Morón system fault and the South Caribbean deformed belt, and 3) oceanic crust to the north of the South Caribbean deformed belt. Each crust type has specific gravity signatures distinguishable on vertical and horizontal gravity gradient maps. High negative gravity gradients were expected over the thick sedimentary sequences of the Bonaire basin; however, we found high positive gravity gradients. There are two possible explanations: 1 ) crustal tectonic thinning putting the Moho discontinuity near the surface and thus increasing the gravity gradient, and 2) anomalous thermal flux beneath the transitional lithosphere changing rock density and increasing the gravity gradient. The results of flexural models show that the time of loading of the continental crust was between Upper Cretaceous and Early Paleocene and the time of loading of the transitional crust was between early Eocene and late Oligocene.

Palavras-chave : gravity; plate flexure; regional isostasy; geodynamics; modeling; Venezuela.