Configuration of the Colombian Caribbean Margin: Constraints from 2D Seismic Reflection data and Potential Fields Interpretation

Abstract

The active Colombian Caribbean margin has evolved since late Cretaceous time, resulting in an intricate deformation history involving oblique subduction – accretion, extension, and tectonic inversion during the Cenozoic. The combined interpretation of 2D seismic refl ection, gravity and magnetic data provides new insights into the confi guration of the Colombian Caribbean margin and the crust- types present along it. The margin displays the morphological and tectonic character- istics of a typical accretion-dominated subduction complex. The 3D gravity modelling suggests that the Caribbean Plate is subducting beneath NW Colombia at a low angle of about 5° in E to SE direction. The major tectonic domains forming the margin include, from west to east: trench, active accretionary prism, outer high and forearc basins. The trench axis coincides with the toe of the active accretionary prism. The active prism corresponds to the external part of the Sinú-Colombia Accretionary Wedge. The outer high domain includes the major structural complex formed by the easternmost part of the Sinú-Colombia Accretionary Wedge and the San Jacinto Fold Belt. It represents the fossil part of the accretionary prism, which today acts as a dynamic backstop to the active accretionary prism. The outer high comprises several small sedimentary basins containing post-kinematic Plio-Pleistocene deposits, which fossilize the complex outer high structure. The landward boundary of the outer high is marked by the well-developed positive fl ower structure of the Romeral North or San Jacinto Fault System, which represents a structural break between the smaller basins deformed by mud diapirism to the west and the main and deeper forearc San Jorge Basin to the east. The basement-type present along outer high-forearc transition (San Jacinto Fold Belt-San Jorge Basin) is still discussed controversially. The results of 3D gravity and 3D magnetic modelling in this study support the presence of an oceanic “basement complex” (mixture of basalts and sediments) underlain by a con- tinental tectonic wedge (CTW) which belongs to the overriding South American Plate. The emplacement of oceanic affi nity rocks over continental basement is inter- preted as offscraping and backthrusting of Caribbean material onto the continental margin during the initiation of the oblique subduction of Caribbean crust beneath NW South America. The continental crust of the South American arc framework provided the static backstop, against which the material of the later dynamic backstop was accreted. The existence of a continental tectonic wedge (CTW) beneath the oceanic “basement complex” in the San Jacinto Fold Belt (west of the Romeral Zone) indicates that the Romeral North Fault System does not form the tectonic boundary between oceanic crust to the west and continental crust to the east. The Romeral Fault and its associated structures form a dextrally transpressive fault system developed within continental crust (the static backstop) as a result of the oblique convergence between Caribbean and South American plates. From the crustal model proposed here, two tectonic limits are identifi ed as ocean-continental crust boundaries: an upper one, which represents a major east-directed backthrust that detached oceanic basalts and sediments from the downgoing slab, emplacing them over the continental tectonic wedge (CTW), and a lower one, which corresponds to the east-dipping boundary between the downgoing Caribbean and overriding South American plates.