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Basement Architecture in the Southern Caribbean Basin, Guajira Offshore, Colombia


Basement distribution in the Guajira Offshore Basin in Colombia appears to be the result of a complex assemblage of a series of tectonic blocks of diverse origin, including suspect terranes accreted to the South American autochthon. This is consistent with a multiphase tectonic history of the Southern Caribbean that includes an Early Mesozoic rifting episode followed by a drifting period separating the North and South American plates. Later, the advent of the Caribbean plate and its convergence with the northern edge of the South American Plate from Late Cretaceous to Recent grounds the current tectonic framework of the Southern Caribbean Basin in the Guajira Offshore area. Potential field and 2D seismic data and well information were used to assess the nature and distribution of the basement in the Guajira Offshore Basin. Results show that the crust in the Guajira Offshore Basin can be divided in four main domains: 1) Block tectonics represented by two systems of pre-Paleogene grabens and half-grabens that appear to be remnants of the Proto-Caribbean plate attached to South America along the Chimare Suture in the north, and in the Tayrona sub-basin in the south. 2) The main Guajira basement block of continental affinity that was part of a continental-ocean transition boundary during the Mesozoic rifting phase. The thickness of the crust in this block decreases abruptly across the margin over a distance of ∼80 km, from ∼20 km near the coast line to less than ∼3 km near the so-called Tayrona sub-basin. This abrupt decrease in crustal thickness is consistent with modern day transform margins. 3) The Chirrinche, Chinchorro and Mochila paleohighs, outboard of the main basement block, with a unique seismic character and magnetic imprint, represent a series of accreted suspect terranes that collided with the Guajira margin before Early Paleogene. 4) The Tayrona and Chimare sub-basins related to a Neogene transcurrent phase that could be interpreted from strike-slip faults and associated pull-apart and transpressional structures. Additionally, the diverse nature of the inboard crystalline basement reported in the area also favors an assemblage of exotic but small terranes accreted to the autochthonous South American Plate. These observed features likely rule out the reported accretion of the Great Arc of the Caribbean to most of the Guajira Offshore terrane.