Segmented flat-slab Caribbean subduction beneath northernmost South America from teleseismic receiver function imaging

Segments of the southwestern portion of the Caribbean Plate are subducting beneath northern Colombia at a low angle. Using the teleseismic receiver function technique, we were able to image this shallowly subducting Caribbean Plate, in the vicinity of the highly elevated Santa Marta Massif, a singular topographic feature in the Caribbean coast of Colombia. Two major wave conversions across different broadband seismological stations have been interpreted as the continental and oceanic crust–mantle boundaries (Moho), corresponding to the overriding continental South American Plate and the shallowly subducting oceanic Caribbean Plate. A convergence–parallel cross section reveals that at less than ∼100 km from the coastline, a continental Moho conversion is absent, and an oceanic Moho is suggested at depths between ∼40 and 80 km beneath the surface, getting progressively deeper towards the continental interior. At greater distances from the coastline, two Mohos can be identified, defining a subduction angle of ∼11° along a distance of at least 150 km, before the slab sinks beneath the Maracaibo Block in Venezuela. A convergence–oblique cross section shows the segmented nature of the Caribbean Plate in the coastal area of northernmost Colombia, where the west-east striking Oca-Ancón Fault acts as a boundary between a shallowly subducting segment to its south, and an underthrusting segment to its north.