Abstract The tectonic evolution of the Cenozoic mountain ranges, fault systems and basins that comprise the roughly east-west Caribbean/ South America plate boundary zone from Colombia to Trinidad was controlled principally by highly-oblique dextral convergence between the Caribbean and South American Plates. The Caribbean Plate is pinned by the Central American and Lesser Antilles subduction zones and is stationary in a mantle reference frame whereas the South American Plate is moving westwards in that frame. The Caribbean Plate is of Pacific provenance and has, since early Cenozoic time, progressively invaded at an average rate of 20-25 mm/yr the Proto-Caribbean oceanic gap between North and South America, Thus, the Lesser Antilles are terminated southward by a dextral transpression zone that lengthened progressively throughout Cenozoic time. This zone showed strong partitioning between easi-west dextral strike slip faults, such as the Oca and El Pilar faults, and south-southeast ward-directed thrust nappes. The nappes loaded the South American craton to generate a coupled flexural foreland basin and peripheral bulge that migrated eastwards. At any time during this evolution, the zone between the thrust complex and the crest of the peripheral bulge was a zone of potential updip hydrocarbon migration, which moved eastwards in tandem with the relatively eastward migrating Caribbean Plate. Ln several cases, especially in Oligocene and younger Cenozoic times, E-W trending strike-slip and normal faults decoupled parts of the thrust load from the South American craton and allowed flexural recovery, the rapid uplift of coast ranges, and thick sedimentation in transtensional basins. All deformation in the Venezuela nappe pile pertaining to arc-continent collision between the Caribbean and South American crusts is of Cenozoic age and youngs from west to east. Our evolutionary tectonic reconstruction of the Caribbean/South American plate boundary zone is critically dependent upon a precise restoration of the geometry of northwest South America immediately before the Caribbean Plate began its relative eastward motion. This involved our determining the amounts of relative motion along the various faults and deformation zones of Colombia and Venezuela that have developed mainly since the late Oligocene. Retro-restoring motion on these faults allows a construction of the Cenozoic nappe front prior to 25 Ma and the shape of northwest South America prior to 60 Ma. Displacements include about 110 km of sinistral motion on the Santa Marta Fault Zone, up to 150 km of dextral slip in the Merida Andes zone, 25 km of shortening across the Sierra de Perijti, and at least 65 km and 90 km of dextral motion on the Oca Fault Zone in Colombia and Venezuela, respectively. On a retrodeformed paleogeographic grid which takes into account all of these restorations as well as removal of accreted tetranes, the paleogeographic development of Venezuela and Trinidad is traced through Cenozoic time, and important tectonic processes and controls on hydrocarbon accumulations are defined and discussed.

Abstract The strongly curved zone of Cretaceous island arc rocks underlying the Greater Antilles, Aves ridge, and Leeward antilles of the Caribbean region constitutes the remnants of the elongate, east-facing Great Arc of the Caribbean (GAC) that formed in the early Cretaceous along the eastern margin of the Pacific and entered and consumed the proto-Caribbean Sea. The exact location of the suture between arc rocks of the docked GAC and the South American continental margin has remained poorly known in northwestern South America, especially in the area where the suture was subjected to post-collisional, right-lateral strike-slip displacements up to 100 km (62 mi) in magnitude. An improved location of the suture is significant for oil exploration because basins overlying South American continental rocks have higher-quality source and reservoir rocks and much larger oil reserves than basins overlying the GAC. To define the GAC suture location in known or active areas of petroleum exploration in the Falcon Basin, Gulf of Venezuela, La Vela Basin, and Leeward Antilles, we use modeling, filters, and enhancements on two regional gravity and magnetic databases. Regional maps of observed gravity, Bouguer and magnetic anomalies, and filtered and enhanced gravity data show that the elongate GAC has a distinctive character that can be mapped as a continuous feature in the areas of the Leeward Antilles and Paraguana-eastern Falcon areas of western Venezuela. Map view restorations of the right-lateral Oca–Ancon fault zone by realigning offset magnetic highs and lows show an approximate right-lateral displacement within the GAC suture zone area between 80 km and 100 km (50 mi and 62 mi) that is consistent with published estimates for the Oca–Ancon fault zone based on outcrop mapping. Finally, four regional gravity profiles, incorporating other forms of previous data including refraction results and wells to basement, were modeled across the GAC–South American suture zone area. A more precise location of the GAC–South American suture zone is proposed in western Venezuela that is defined by an elongate zone of distinctive magnetic highs.

Magnetic provinces, recognized by trend geometry and anomaly character, are delineated in western Venezuela utilizing aeromagnetic data from the 1950s oil company surveys. In northwestern Venezuela, the Guajira-Paraguaná province (east-west anomalies) lies north of a proposed east-west fault zone extending from the southern Para-guaná Peninsula across the Gulf of Venezuela and south of the pre-Tertiary outcrops on the Guajira Peninsula. South of this fault zone and on the west is the Perijá province (northeasterly trends) and on the east the Coro province (northwesterly trends). The Oca zone province (east-west trends) separates the northern and southern parts of the Perijá province. Geologic features which can result in these magnetic anomalies are fault blocks, east-west faults, some in sets, faults oblique to east-west shear, and probably intrusions into the crust parallel to these features. These have been produced by differential motion between the major zones of dislocation resulting from right-lateral offsets on east-west transcurrent faults during extension in the Tertiary. Thus, the magnetic anomalies locate a complex zone of Cenozoic interaction on this margin of the Caribbean-South American plate boundary. South of the Oca fault, the Perijá province trends are related to the geologic trends of the Sierra de Perijá, and the Jurassic La Quinta graben complex and the Central Lake Graben. There are only modest, trendless anomalies in the eastern Maracaibo Basin, the Falcón Basin, and the area to the south. Magnetic basement rocks here are probably igneous and metamorphic Paleozoic units, similar to those exposed in the Venezuelan Andes. Southeast of the Andes, a major lineation between the Barinas and Río Meta provinces is correlated with the projection of the Altamira fault. Unmetamorphosed lower Paleozoic sedimentary rocks are preserved in a block dropped down to the north. This is possibly an extension of the Espino Graben complex, which is 300 km to the northeast and in which Jurassic basalt is preserved. Strong magnetic anomalies west and south of the El Baúl Uplift are probably associated with Jurassic volcanics, similar to those exposed in the uplift, perhaps preserved in the same graben complex. These appear as major features of the interior plains (llanos) north of the Guayana Shield. The primary subdivision of the magnetic provinces is two-fold. North of and including the Oca fault-Coro area, magnetic anomalies document the complex zone of interaction related to east-west shear in Cenozoic time. South of this, magnetic anomalies are related to the distribution of pre-Cretaceous rocks, some of which were involved in the plate boundary interactions, but others to the south are related to the development of the pre-Cretaceous terrane north of the Guayana Shield.

Abstract Present-day Venezuela may be divided into the following major structural provinces—Perijá Mountains Goajira-Paraguaná arch, Maracaibo basin, Falcon, Venezuelan Andes, Caribbean ranges, Barinas-Apure basin, Eastern Venezuela basin, and Guayana shield. The pre-Cretaceous history is little known. A Paleozoic geosyncline may have existed in Western Venezuela, but any important regional metamorphism there was pre-Devonian. ? Mid-Ordovician, Late Devonian or early Carboniferous, and Permian to Triassic deformations may be postulated, but their trends cannot be evaluated at present. Toward the end of the Paleozoic widespread uplift, accompanied by faulting and volcanism, raised the whole country above sea level. The Perijá, Maracaibo, Andes, and Barinas-Apure provinces owe their character as distinct units to the Tertiary Andean deformation, with the basins sinking as the mountains arose. The Cretaceous and Eocene oil fields of Western Venezuela owe their existence to the Andean orogeny; the middle to late Tertiary fields are less directly linked to it. There is some indication that movements began first in the northwest (Sierra de Perijá) during the Eocene, progressed southeastward across the more-or-less stable Maracaibo platform, reached the Andes at the close of the Eocene, and culminated in the Mio-Pliocene. The mountains, with dominant trend of N. 35° E. for the Perijá and N. 50° E. for the Andes, are essentially complexly folded and faulted structural arches with high angle reverse, normal, and wrench faults. Mountainward-dipping reverse faults are thought to bound their flanks. Both the Maracaibo and Barinas-Apure basins have asymmetrical cross sections with deepest zones close to the flanks of the Andes. The displacement on a large northeast Bocono fault trend may have to be taken into account in reconstructing the deformation of the Andes. Beginning in the Late Jurassic, the Caribbean sea began an extensive transgression of northern and western Venezuela. An east-west trending Caribbean geosyncline developed in the extreme north. Volcanism and major deformation of the Caribbean geosyncline began about Middle Cretaceous time, leading to the folding, faulting, and metamorphism of the previously deposited Mesozoic rocks. However, sedimentation, volcanism, deformation, and metamorphism, although on decreasing scale, continued throughout Late Cretaceous and Paleocene time and perhaps into the early Eocene. Dominant structural features in the Caribbean ranges trend N. 60°---80° E.; wrench (strike-slip) faulting is common. To many geologists, an outstanding tectonic feature of northern Venezuela is a series of long east-west trending, right-lateral wrench faults, that are located close, and roughly parallel, to the coast. Best known of these are the Oca fault in the west and the Pilar fault in the east. It is possible that these faults are at least as old as Cretaceous, that they are related to the tectonic history of the general Caribbean area, as suggested by Bucher and others, and that they have played a major role in the deformation of all of Venezuela. The importance of these faults as dominant features has yet to be proved and caution is advised in evaluating their significance in the tectonic history of Venezuela.

The Falcón Basin in northwestern Venezuela and adjacent offshore basins developed within a zone of extensional tectonics during Oligocene and Miocene times. Extension resulted from right-lateral motion along offset, east-west-trending, transcurrent faults, including the Oca fault in western Venezuela, the Cuiza fault in northern Colombia, and the San Sebastián fault along the coastal areas of central Venezuela. On both local and regional scales, transcurrent and normal faults were active during the early evolution of the basins. These faults define rhomb-shaped pullapart basins in map plan. Extension occurred in a northeast direction causing normal faulting along north-west trends. Basin subsidence was accompanied by crustal thinning and injection of basaltic magmas. Evidence of Oligocene magmatic activity is found in the central part of the Falcón Basin where volcanic rocks and hypabyssal intrusions are exposed. These rocks are similar to other suites of continental igneous rocks typically associated with rifting environments. Basaltic rocks of both alkalic and subalkalic affinities are present. Xenoliths of the underlying crust and mantle are abundant. Felsic igneous rocks are relatively rare. Other structures within the Falcón and Bonaire basins formed during later stages of basin development. These include folds and reverse faults of northeast trend and conjugate sets of small transcurrent faults. These structures were amplified by greater compressional stresses during late Miocene and Pliocene time. A similar Tertiary tectonic regime is postulated for the larger area of the Bonaire Crustal Block, a block that includes the Falcón and Bonaire basins. This block is a broad region of extensional pullapart structures which developed during the Oligocene to Miocene, right-lateral motion between the Caribbean and South American crustal plates. Minimum extension within the northern part of the block, along the Venezuelan and Netherlands Antilles and the Paraguaná and Guajira peninsulas, is estimated at 35 to 45 km in an east-west direction. The extension within this nonrigid block should be considered when determining Tertiary movements between the Caribbean and South American plates.