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 High-grade metamorphic rocks – marble, charnockite, meta-anorthosite, metapelite, clinopyroxenite and garnet amphibolite – have been found in northwestern Venezuela. They occur as: (a) xenoliths in the Oligo-Miocene lavas of Cerro Atravesado, Central Falcón; (b) possibly olistoliths in Nuezalito Formation, NW Portuguesa; (c) in Cerro El Guayabo, an elongated east–west oriented hill in the Nirgua Complex, Yaracuy; (d) rounded clasts of marble in the basal conglomerate of Casupal Formation, Falcón; (e) rounded clasts of anorthosite and sillimanite gneiss in a conglomerate of Matatere Formation, Lara; and (f) basement cores extracted from La Vela Gulf, Falcón. These high-grade rocks probably suffered a retrograde metamorphism to amphibolite facies of Palaeozoic age, and an even more retrograde event to the greenschist facies during Early Cenozoic, together with strong shearing and hydrothermal alteration. They indicate the possible existence of an extensive high-grade basement, or a mosaic of such blocks, under northwestern Venezuela, especially below the Falcón petroleum basin. Similar rocks crop out extensively in northern and central Colombia, Mexico, Ecuador and Peru. This is the first time they are described from Venezuela. Their high-grade lithology, pre-Mesozoic positions, and the tectonic evolution of Northern South America allow interpretation of a possible Grenvillian affinity, related to the supercontinents of Rodinia and Pangaea.