SUBSIDENCE HISTORY OF THE BARBADOS ACCRETIONARY COMPLEX

Since Late Cretaceous the Caribbean plate has moved eastward with respect to both North and South American plates. Towards the east, and as consequence of this movement, the Caribbean Plate collided with the North and South American plates during Eocene times originating the Lesser Antilles Island Arc and Barbados accretionary Prism.

In order to describe the subsidence history of the Lesser Antilles Trench, 7 regional transepts were constructed from north to south through the eastern part of Lesser Antilles subduction zone. These transepts were assembled using seismic, seismological, gravimetric and geological published data in the area. Three sequences were interpreted based on density values. These sequences correspond to non consolidated Miocene to Present sediments (NCS, ρ< 2200 Kg/cc), consolidated Cretaceous to Eocene sediments (CS, ρ<2700 Kg/cc) and basement (BAS, ρ> 2800 Kg/cc). A series of structural and Isopach maps were created using information from the regional transepts. These maps were decompacted, to determine the original thickness of the tectono-stratigraphic units. The decompacted thickness gives information related to subsidence and sediment loading and this could be associated to the geodynamic evolution of the study area.

The decompacted isopach map of the CS unit is 1.5 km thicker than the compacted one, which represents the sediment loading of the NCS unit. The maximum decompacted thickness is parallel to the Barbados deformation front, as it is expected in a subduction prism setting. The minimum decompacted thickness is related to the Lesser Antilles Island Arc and the Barracuda Ridge. A difference of approximately 9 km between the compacted and decompacted BAS tops is observed. This difference could be associated with the total sediment loading of the area. It is observed that the Lesser Antilles Island Arc was uplifted in the Eocene. Results also shows that the accommodation space created by the Eocene collision between Caribbean and both South and North American plates, was greater in the south than in the north. In addition the BAS subsidence analysis implies that to the south of the area the sediments loading, supplied by the Orinoco and the Amazonas rivers, is insufficient to generate the total subsidence, instead both tectonic and collision obliquity may play an important role.