Abstract U/Pb zircon and 40 Ar/ 39 Ar hornblende ages of medium- to high-grade metamorphic basement rocks from La Vela Bay in the Falcon Basin and of granitic gneiss rocks from a basement inlier in the southeastern Guajira Peninsula, northwestern Venezuela, measured by laser ablation–inductively coupled plasma–mass spectrometry and sensitive high-resolution ion microprobe, document the presence of Meso- to Neoproterozoic crust related to the Putumayo orogen, which probably correlates with the Chibcha terrane, in Colombia. Metawackes, metapelites, and granitic gneisses from these localities showed a high-grade metamorphism peak between 1.0 Ga and 0.98 Ga. Ages of inherited zircon cores of 1212 ± 11 Ma, 1214 ± 10 Ma, 1227 ± 9 Ma, 1366 ± 38 Ma, 1519 ± 9 Ma, and 2707 ± 8 Ma, are interpreted as relicts of detrital igneous grains that were originally incorporated from the Amazon craton into the sedimentary protolith. In addition, 40 Ar/ 39 Ar ages of hornblende crystals in metapelites preserve younger events between 923 Ma and 916 Ma, which indicate cooling under 530°C after the granulite facies peak. Radiometric ages presented in this study support the idea that these basement rocks probably formed part of a single orogenic belt in western South America, that formed in an active margin located in the northwestern part of the Amazon craton, which gave rise to a continental collision with Baltica during the Neoproterozoic assemblage of Rodinia.

Abstract A multi-event tectonic episode that affected the Caribbean and South American Plate boundaries as well as Cenozoic oil generation is based on new structural and geochemical data from the western Falcón Basin, Venezuela. It involves Late Cretaceous to Middle Eocene emplacement of the Lara Nappes followed by Late Eocene to Early Miocene tectonic collapse and graben formation, Middle Miocene inversion and out of sequence thrusting. Oil-source rock correlation of seeps in the northern part of the basin suggests a Cenozoic siliciclastic source rock deposited under suboxic to anoxic conditions. Potential Cenozoic source rocks and Late Cretaceous La Luna Formation were used to evaluate the generation conditions using one- and two-dimensional thermal modelling. A heat flow of c . 190 mW m −2 was reached during the Oligocene–Early Miocene in the central part of the basin. As a result the Cretaceous source rock is overmature, while the primary Cenozoic source rocks are in the oil window. The thermal modelling also suggests that hydrocarbon accumulations are mainly located on the flanks of the graben, with small amounts possible in the centre, due to erosion during basin inversion. This modelling is highly consistent with the proposed polyphase tectonic model.