U-Pb SHRIMP zircon ages of Ediacaran-Cambrian granitic bodies in central Brazil: Implications for the tectonic evolution of the Araguaia belt

The small granitic plutons of the Ramal do Lontra, Presidente Kennedy, Barrolandia and Santa Luzia are emplaced into the Estrondo Group metasedimentary rocks of the Neoproterozoic Araguaia Belt. They have similar petrographic and compositional characteristics and are coeval with the medium-grade regional meta-morphism of the belt. New U-Pb SHRIMP zircon data yielded quite robust ages. These results fall within the experimental error, and the integrated Concordia age of 542 +/- 3 Ma was chosen as representative of their magmatic crystallization. A relevant number of inherited grains are present, showing overgrowth rims with high-U content, formed during the later stage of magmatic crystallization. LA-ICP-MS U-Pb dating on detrital zircon grains from a metasedimentary rock of the Estrondo Group yielded several Paleoproterozoic ages and a few Neoarchean ages, but the major peak in the histogram was between 1000 and 1200 Ma. The youngest grains indicate an Ediacaran age near 600 Ma, which is considered a reasonable upper limit for the deposition of the Estrondo Group. The Araguaia Belt started as an intracontinental system, segmenting the Amazonian Craton, formed by rifting during the breakup of Rodinia and was after occupied by a sedimentary basin which evolved to form an oceanic lithosphere. In the Ediacaran, the huge continental collisions that formed the West Gondwana Orogen most likely caused its remote activation, producing tectonic inversion with vergence to the west. Granitic plutons were emplaced in the last stages of the evolution of the Araguaia Belt, during the Brasiliano-PanAfrican orogenesis, at the Ediacaran-Cambrian boundary. (AU)