From Subduction to a Compressional transform system: Diffuse Deformation Processes at the Southeastern Boundary of the Caribbean Plate

Geophysical data acquired in the southeastern Caribbean marine area (CARAMBA survey of the French O/V Atalante) provide new information about the deformation processes occurring in this subduction-to-strike-slip transitions zone. The 65 000 km2 of multibeam data and 5600 km of seismic reflection and 3.5 kHz profiles which have been collected evidence that the connection between the Barbados accretionary prism and the south Caribbean transform system is partitioned between a wide variety of recently active tectonic superficial features (complex folding, diffuse faulting, and mud volcanism), which accommodate the relative displacement between the Caribbean and the South America plates. The active deformation within the sedimentary pile is mostly aseismic (creeping) and this deformation is relatively diffuse over a large diffuse plate boundary. There is no direct fault connection between the front of the Barbados prism and the strike-slip system of northern Venezuela. The toe thrust system at the southern edge of the Barbados prism, exhibits clear en-echelon geometry. The geometry of the syntectonic deposits evidence the diachronism of the deformation processes. Notably, it is well evidenced that early folds have been sealed by the recent turbidite deposits, whereas, some of the fold and thrust structures were active recently. Within this active compressional region, extension growth faults develop on the platform and on the slope of the Orinoco delta along a WNW-ESE trending en-echelon fault system that we called the Orinoco Delta Fault Zone (ODFZ). This fault system is clearly oblique with respect to the present-day Orinoco delta slope. These faults are not simply related to a passive gravitary collapse of the sediments accumulated on the Orinoco platform. Though there a decoupling between the shallow deformation processes in the sediments and the deep deformation characterized by earthquake activity, the ODFZ is inferred to be partly controlled by deep structures associated the shearing of the lithosphere at depth (probably at the Continent-Ocean Boundary).