Petrology and geochemistry of the mafic dyke swarm of the Treinta Y Tres Region, Northeast Uruguay.

Transitional basalts of the Treinta y Tres region intrude late Proterozoic granites in northeast Uruguay. The age of the swarm is assumed to be close to 750 Ma. Major and trace geochemical diagrams indicate gabbro type fractionation, which is supported by MPR plots. In comparison to the Florida and Nico Perez suites, the Treinta y Tres swarm is enriched in Ti, P, Zr and Sr and depleted in LILE and REE. These features and the Sro and Ndo isotope values are discussed in terms of source heterogeneity and crustal contamination. The geochemical characteristics do not support crustal contamination. The Treinta y Tres suite is better explained by a source affected by two melting episodes. The dikes were originated from the latter melting, which occurred in a an isotopically heterogeneous source. Diagrarns related to several incompatible elements ratios indicate that the mantle source of Uruguaian dikes and of continental basalts of Brazil have similar geochemical features since Early Proterozoic up to Mesozoic.