Orosirian magmatic episodes in the erepecuru-trombetas domain (southeastern Guyana shield): Implications for the crustal evolution of the Amazonian craton

Abstract

The granitic rocks of the Erepecuru-Trombetas Domain, southeastern Guyana Shield, are part of two extensive volcano-plutonic associations that marked the central portion of the Amazonian Craton during the Orosirian. The older episode (2.0–1.97 Ga) encompasses the Igarapé Paboca volcanic Formation and Caxipacoré Suite and the younger episode (1.90–1.87 Ga) comprises the Água Branca and Mapuera plutonic suites and the pyroclastic/effusive rocks of the Iricoumé Group. LA-ICP-MS U-Pb zircon dating of granitoids provided ages of 1991 ± 5.9 and 1989 ± 7 Ma for the Caxipacoré Suite, 1887.5 ± 4.8 Ma for the Água Branca Suite and 1881 ± 8.1 Ma for the Mapuera Suite, which reinforce the occurrence of two Orosirian magmatic episodes in the southeastern Guyana Shield. The geochemical characteristics of the Caxipacoré granitoids suggest that they formed in an orogenic tectonic setting, related to a subduction environment, while the geochemical signatures of the Água Branca and Mapuera granitoids betray the evolution from a convergent context to an extensional intracontinental environment. Nd-TDM (2.19–2.22 Ga) and Sr-TUR (1.95–1.96 Ga) model ages and slightly positive εNd (+0.26 to +0.66) for the Caxipacoré granitoids point to an origin from melting of mantle-derived magmas with participation of Rhyacian sialic crust. The Água Branca and Mapuera granitoids display Nd-TDM (1.95–2.30 Ga) and Sr-TUR (1.84–2.02 Ga) model ages and positive to negative εNd (+2.92 to −1.96) that indicate parental magmas derived from melting of dominantly Rhyacian crustal sources with minor mantle contribution. In addition, the Nd signature and the lack of Archean inherited zircon in the plutonic rocks do not favor the existence of an Archean basement in this part of the southern Guyana Shield. This assumption together with similarities with the adjacent Uatumã-Anauá Orosirian Domain, westward, led to suggest that the Erepecuru-Trombetas Domain should not be longer interpreted as belonging to the Central Amazon Province, as defined in the current geotectonic models of the Amazonian Craton.