Abstract

The distribution of the basement in the Guajira Offshore Basin in Colombia appears to be consistent with the evolution of the autochthonous South American Block as part of a continent-ocean transform fault of the late Jurassic rift system that created the proto-Caribbean Sea between the North and South American plates. Later, rotation, accretion of suspect terranes, and the collision-subduction with the Caribbean plate framed current architecture of the basement in the basin. In addition to the Mesoproterozoic crust found in the onshore Alta Guajira area, a set of terranes of diverse age including late Triassic metamorphic rocks, early Cretaceous meta-sediments, late Cretaceous granites and serpentines, Eocene plutonic intrusions, and a chain of undifferentiated-age suspect blocks, can also be identified in the offshore basin.

Although the current architecture of the basement in the Guajira Offshore Basin does not show a preferential tectonic arrangement, four different types of crustal-fabric can be identified: (1) a Pre-Cambrian autochthonous block that exhibits an abrupt thickness change across the margin over a distance of ca 80 km (49.7 mi), from ca 20 km (12.4 mi) near the coast line to less than ca 3 km (1.8 mi) near the so-called Tayrona Subbasin. This abrupt decrease in crustal thickness resembles modern-day transform margins involving continent-ocean transition; (2) two areas exhibit what appear to be systems of horsts and grabens, typical of block-tectonics settings. One area is identified north of the Chimare suture and the other is located further south in the Tayrona Subbasin. Even though their age is currently difficult to establish, they may correspond to stretched continental crust and proto-Caribbean remnants of the rift-system that separated North America from South America during Jurassic time; (3) the Chirrinche, Chinchorro, and Mochila paleohighs whose non-magnetic character separated these suspect terranes from the autochthonous basement further east; and 4) The South Caribbean deformed Belt (SCDB) and the Tayrona and Chimare Neogene Subbasins associated with transcurrent fault systems generated by the oblique convergence of the Caribbean and the South American plates. A simplified evolution model of the Guajira Offshore Basin, based on basement distribution, includes four main phases: opening of the proto-Caribbean seaway during late Jurassic; subduction of this oceanic crust under the continental South American plate and associated volcanism during the Cretaceous period; collision of the Caribbean Large Igneous Province (CLIP) with the continental block, effectively stopping the ongoing subduction process in the late Cretaceous–early Paleogene time; and the development of the still active SCDB mostly on Caribbean oceanic crust since middle Paleogene times. Our observations preclude the pervasive presence of the Great Arc of the Caribbean (GAC) in the Guajira Offshore Basin.