Based on a complete geophysical data set and the integration with geological observations, I propose that the lithospheric crust underlying northern Colombia is continental to thinned continental (transitional) in nature, with densities between 2600 and 2700 Kg/m3. Geophysical modeling also requires a dense wedge of sediments (density 2500 Kg/m3) at the base of the modern deformed fold belt, which may represent a fossil sedimentary wedge attached to the continental margin. This wedge may have served as a backstop for the modern fold belt. The gravity modeling does not require oceanic crust to form the basement in the Sinu and San Jacinto fold belts as previously suggested. Discrete layers and thin slivers of oceanic sediments and crustal rocks could have been scrapped off the incoming plate and thrusted into an accretionary melange, and eventually exposed at the surface, as seen in the Mulatos, Chalan and Cansona locations. Pieces of the leading volcanic arc of the Caribbean Plate were accreted to the continent at the Western Cordillera, the Morrosquillo area and the Alta Guajira, but do not form a continuous belt of volcanic-arc rocks. The crust underlying the Guajira Peninsula is thinned continental (pre Cambrian granulites), intensely intruded and metamorphosed during Mesozoic and Cenozoic episodes. The Simarua - Cuiza system in the Alta Guajira represents the paleosuture between the allochthonous Caribbean Oceanic terranes on the North and the autochthonous continental crust on the South. The Tayrona depocenter north of the Oca fault, underlain by a continental basement that is tilted in a E-W direction, was formed in a transtensional setting as the Oca fault produced a right lateral releasing bend and the north block moved between 60 to 100 Km. to the East relative to the South block. Gravity data modeling of the SNSM satisfies the observed data using densities typical of continental crust (rho < 2700 Kg/m3). 2D flexural models across the SNSM using the elastic theory with a broken plate, explain successfully the observed shape of an oceanic plate plunging SE under the continental rocks of the SNSM. Two end-member models (either flat subduction or a broken slab) can explain the geometry. However, tomographic observations previously published show a plunging slab that increases its curvature under the SNSM, producing a continental Moho that bends upwards forming a bulge under the SNSM and which, if existing, would create a hydrostatic force that helps to sustain the uplifted mountain. The massif is dynamically supported to some degree by a lithospheric slab whose flexural rigidity has been estimated around 2.1E22 Nm (or an effective elastic thickness of 15 Km). My interpretation is that the reduced effective elastic thickness of the upper lithosphere corroborates the hypothesis of a continental attenuated crust overriding the Caribbean Plate in a highly oblique direction, which produces a frontal deformed belt made of continental originated sediments that resembles a subduction accretionary prism, but no consumption of the oceanic lithosphere due to the low angle of overthrusting occurs in North Colombia as evidenced by the lack of recent volcanism.
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