New U-Pb Zircon Ages by LA-ICP-MS of Metagranitoids of Interference Zone between the Southern Brasília Belt and the Central Ribeira Belt, in South Region of Rio de Janeiro State, Brazil

Abstract

In the towns of Resende and Itatiaia, south of Rio de Janeiro State, there are magmatic rock bodies traditionally inserted in the geotectonic context of the Ribeira belt. More recently, other works relate the region to the Interference Zone between the Brasília and Ribeira belts. Contributing to discussions about these interpretations, four metagranitoid bodies were selected for U-Pb analyses of zircon (LA-ICP-MS): a) Córrego das Cruzes, granodioritic inequigranular K-feldspar-biotite gneiss, crystallization and metamorphic ages of 1690±8.6Ma and 606±6.6Ma respectively; b) Engenheiro Passos, megaporphyritic hornblende-biotite metagranitoid, crystallization and metamorphic ages of 652.2±3.6Ma and 621.1±3.7Ma respectively; c) Marimbondo, hololeucocratic metagranite, crystallization and metamorphic ages of 605±2.4Ma and 585±4.8Ma respectively; d) Pedra Selada, granitic to granodioritic porphyritic (hornblende)-biotite metagranitoid, crystallization age of 590.7±1.5Ma. The oldest metagranitoid presents a crystallization age compatible with extensional events, however, this body is still poorly studied. The other bodies present Neoproterozoic crystallization ages correlated to different stages of the Brasília belt: pre-collisional, late-collisional and post-collisional, respectively. The metamorphic ages between 621-605Ma coincide with metamorphism related to the Brasília belt, whereas 585Ma would be associated with Ribeira belt metamorphism. These data corroborate interpretations that place the area in the Interference Zone between the Brasília and Ribeira belts.