An unequivocal interpretation of the paleotectonic history of the Caribbean area, especially in modem plate tectonic terms, has not been possible despite recent advances in our geophysical and marine-geological unterstanding of the region. To fulfil this goal, a more detailed knowledge will be required not only of the nature of the crust and sediments of the Caribbean Sea, but also of the geology and metamorphic history of the surrounding continents and islands (i. e. “plate margins“). In this report, a detailed geological map of northeastern Margarita Island is presented, an island that occupies a key geological and tectonic position at the southeastern margin of the Caribbean Sea. The study focusses on a 2,000–3,000 meters thick sequence of metabasalts, herein defined as the La Rinconada Group, that conformably underlies Jurassic to Cretaceous metasediments of the Caribbean Mountain System of northern South America, but is not exposed on the mainland. These mafic rocks, which are interlayered with minor, siliceous, carbonaceous schists, have been metamorphosed under relatively highp vs. T conditions to amphibole gneisses containing barroisitic amphibole throughout and omphacite as well asin situ amphibole-paragonite eclogite in suitable bulk compositions in the nothern part of the area mapped. Found within the amphibole gneisses are many irregular, elongate masses of ultramafic rock from several meters to several kilometers in length, as well as numerous intrusions of granite to tonalite composition. The ultramafic rocks are highly serpentinized and deformed, and are surrounded by extensive talc, tremolite-actinolite, and chlorite metasomatic contact-reaction zones. Tonalites are the most abundant intrusives and are predominantly totally metamorphosed.