From Frontal Subduction To A Compressional Transform System: New Geophysical Data On The Structure Of The Caribbean-South America Plate Boundary In Southeastern Caribbean

The transition between the deformation belt of the east Caribbean active margin and the transform margin of the north of the south America plate develops mostly offshore, east of Trinidad, at the southern edge of the Barbados accretionary prism. The south of the Barbados Ridge constitutes a huge mature accretionary prism where Cretaceous oceanic crust and probably late Jurassic oceanic crust to the south is being subducted below the Caribbean plate with a relative plate motion between South America and the Caribbean plate at a rate of about 2 cm/year, in an E-W direction. The CARAMBA marine survey conducted in this hinge area, in January 2002, onboard the French O/V Atalante, provided about 60 000 km2 of multibeam data acquired together with more than 5000 km of high resolution seismic reflection data and 3.5 kHz sediment penetrator data. These new constraints on the structure and the deformation processes of this area show that approaching the South America continental margin, the Orinoco River and delta clastics influxes develop on both the flexured continental margin and the compressional accretionary complex. The multibeam and seismic data show linear ramp anticlines developing at the leading edge of the prism, while a more complex arrangement of shorter, discontinuous folds is apparent at the southern lateral border of the prism. Notably, at the deformation front of the southernmost part of the prism, the fold-&- thrust system vanished out toward the south with enechelon geometry. Normal listric faults as well as active E-W dextral strike-slip faults with mega-tension gashes deforming the sea bottom are obvious to the south at the vicinity of the South America Margin. Also, the survey spectacularly evidences that a large active belt of mud volcanoes and shale diapirs is widely developed in the area and extends SW, in the onshore Trinidad. These mud volcanoes are well developed along ramp anticlines and on top of sigmoid rises of shale diapirs.