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Geotermobarometria de granulitos do Cinturão Ribeira na porção norte do estado do Rio de Janeiro: seção Italva (RJ) – Patrocínio do Muriaé (MG)

2009; Sociedade Brasileira de Geologia; Volume: 39; Issue: 3 Linguagem: Inglês

10.25249/0375-7536.2009393519532

2177-4382

Tiago da Rocha Karniol, Rômulo Machado, Essaïd Bilal, Jacques Moutte,

Geological and Geochemical Analysis

This work focuses on the metamorphic pattern of a segment of the Ribeira Belt in the northern region of the State of Rio de Janeiro based on geothermobarometric analyses carried out on granulites and gneisses with garnet from the Italva (RJ) - Patrocínio do Muriaé (MG) section. Granulites of the western portion from Itaperuna presented intervals of 754-775°C and 7,9-8,6 kbar. However, granulites of the eastern region of Itaperuna showed intervals of 702-722 °C and 8.0-9.1 kbar. Relative lower geothermobarometric conditions - 50 to100 °C and 2,0 to 3,0 Kbar - were calculated from aluminous gneisses exposed between Itaperuna and Italva. We noted that the intervals of pression and temperature are mostly higher if we consider mineral nuclei analyses, up to 2,0 Kbar and approximately 100ºC. Furthermore, when compared with other studies of the region, our results present about the same temperature and 2,0 Kbar higher. Based on a thermal gradient of 30º/km for the studied rocks, which is common for Pre-Cambrian ultrahigh-temperature (UHT) granulitic belts, we estimate a crustal thickness of at least 25 km for the granulites from Itaperuna region. We suggest in this work that granulites of Itaperuna region were exhumated in tranpressive regime related to the process of tectonic extrusion.