Presence of high-grade rocks in NW Venezuela of possible Grenvillian affinity

Abstract

AbstractHigh-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.