Metamorphic evolution and U-Pb zircon SHRIMP geochronology of the Belizário ultramafic amphibolite, Encantadas Complex, southernmost Brazil

The integrated investigation of metamorphism and zircon U-Pb SHRIMP geochronology of the Belizárioultramafic amphibolite from southernmost Brazil leads to a better understanding of the processes involvedin the generation of the Encantadas Complex. Magmatic evidence of the magnesian basalt or pyroxeniteprotolith is only preserved in cores of zircon crystals, which are dated at 2257 ± 12 Ma. Amphibolite faciesmetamorphism M1 formed voluminous hornblende in the investigated rock possibly at 1989 ± 21 Ma. Thisultramafic rock was re-metamorphosed at 702±21 Ma during a greenschist facies eventM2; the assemblageactinolite + oligoclase + microcline + epidote + titanite + monazite formed by alteration of hornblende. Themetamorphic events are probably related to the Encantadas Orogeny (2257±12 Ma) and Camboriú Orogeny(∼ 1989 Ma) of the Trans-Amazonian Cycle, followed by an orogenic event (702±21 Ma) of the BrasilianoCycle. The intervening cratonic period (2000-700 Ma) corresponds to the existence of the SupercontinentAtlantica, known regionally as the Rio de la Plata Craton.