Contribution of Subduction Dynamic Topography to the Formation of the Maturin Foreland Basin Eastern Venezuela

The Maturín Basin in Eastern Venezuela, which formed during the Neogene adjacent to the Serranía del Interior Thrust Belt, is considered a good example of a peripheral foreland basin. Earthquake and tomographic data indicate that Eastern Venezuela is underthrust by the oblique subduction of the South American Plate underneath the Caribbean Plate. Our objectives are to understand the processes responsible for the formation of the Maturin Basin, and to quantitatively determine the contribution of thrust sheet loading and continental subduction. A sequence of new forward flexural isostatic models was generated from Middle Miocene to Present for 3 profiles across the Serranía del Interior Thrust Belt and Maturín Foreland Basin in order to determine the contribution of thrust sheet loading to foreland basin subsidence. The predictions of these models are constrained using seismic reflection and well data. The flexural isostatic modelling shows that thrust-sheet loading associated with the Serranía del Interior Thrust Belt is insufficient to generate the observed subsidence within the Maturín Basin. The modelled basin depth is shallower than observed by 2 km in the west and 6 km in the east. A topography and basin mass balance study, and comparison with free air gravity anomalies for other foreland basin and mountain belt systems, confirms that the mass deficiency in the Monagas Basin is too large to be regionally compensated by the mass excess in the Serranía Thrust Belt. Dynamic fluid flow modelling of subduction related dynamic topography of Eastern Venezuela has been used to investigate the influence of South American subduction on the generation of the accommodation space observed in the Maturín Basin. Fluid flow modelling of subduction related dynamic topography suggests that the subduction of the South American lithospheric mantle caused downward deflection of the South American crust affecting the Maturín Basin and the Serranía Thrust Belt. This result is consistent with earthquake and tomographic evidence. The total subsidence predicted using preferred thrust sheet loading and fluid flow models is comparable with the wavelength and amplitude of the subsidence observed in the eastern part of the Maturín Basin. This modelling suggests that the Maturín Basin subsidence has two components: 55% in amplitude related to thrust sheet loading and 45% driven by continental subduction. The subduction-related subsidence is greater in the eastern than in the western parts of the basin, consistent with the South American subduction decreasing to the west.