Post tectonic magmatism investigated by means of geochronological methods U-Pb and Lu-Hf, Pedra Branca Complex, Rio de Janeiro - RJ

Post tectonic magmatism investigated by U-Pb and Lu-Hf geochronological methods, Pedra Branca Complex, Rio de Janeiro - R

Abstract

The Pedra Branca complex is located in the western region of Rio de Janeiro city. Tectonically it is inserted in the Coastal Domain, which is part of the central segment of Ribeira Belt. The lithologies that formed this rocky complex were generated in events related to the Brasiliano Orogeny (~ 600Ma), thus contains pre- to- post-collisional rocks. The study of post-tectonic granite bodies belonging to Ribeira belt reveals that the magmatism event occurred in two different pulses, with ~ 30Ma between them. The study developed here analysed 9 samples from the Pedra Branca Complex, by means of the geochronogical methods U-Pb and Lu-Hf, with focus on the Pedra Branca granite, which may represent the older pulse and Favela granite, which may represent the younger pulse, in order to improve the understanding of the post-tectonic magmatism in the area. The majority of the results confirm the previously described ages in the literature, however some results show that the magmatism in the complex actually occurred in a more progressive form, with a lower interval between them (~ 20Ma). The petrogenetic indicator εHf showed participation of crustal and mantelic sources , giving to magmatism a bimodal feature.