The present study is based on the seismic interpretation of a 2D regional cross section located in the northern portion of the Lower Magdalena Valley Basin (LMV) and the Sinú-San Jacinto fold belt of northern Colombia (10-12°N). This cross-section is composed of the regional seismic line PLN-2004-01B02 which extends from an onshore area in the western flank of the Sierra de Santa Marta, to the offshore covering part of the Magdalena Fan, NW of the city of Barranquilla. The seismic interpretation was built after tying the seismic data to twelve exploratory wells, and geological maps. The structural evolution was analysed by balancing and kinematic restoration of the horizons and faults.
The LMV towards the east is an extensional and strike-slip basin developed on continental-type basement. While the Sinú-San Jacinto province is a WNW-verging fold and thrust belt rooted in allochthonous, transitional to oceanic-type basement. Strike-slip deformation is also occurring in the older and inner San Jacinto fold-belt, whereas shallow detached thrusts characterize the younger and outer Sinú accretionary prism.
The subduction of the Caribbean plate started during the Late Cretaceous, after the accretion of an allochthonous oceanic terrane (the present San Jacinto range basement).The NW margin of Colombia is active due to the continuous subduction of the Caribbean oceanic plate below the South American plate still ongoing. The structures in the LMV are related to the Romeral dextral fault system. The Romeral fault system constitutes a fault zone with transpressive and transtensive structures. This strike-slip system was active from the Paleocene to the Eocene, and some transtensive structures were inverted by the regional compression. Extensional structures are almost absent in the area and are limited to the transtensional component during the strike-slip tectonics in Paleocene to Eocene ages.
Flat-slab subduction has been ongoing since the late Miocene, due to the subduction of a thickened segment of the oceanic crust. The change of the convergence direction in late Miocene produced strong coupling of the plates and more active compression. The occurrence of earthquakes in this region confirm the active slab subduction and permits to identify the geometry of the flat subducted slab and the active faults.
The tectonic evolution of the study area can be characterized mainly as a contractional, because of an active convergent margin. The shortening is not very important in terms of displacement, since it involves many basement structures, except for the frontal fault with recurrent activity.
- Diego Nicolas Iaffa, Daniel Adolfo Bello & Josué Alejandro Mora
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