Evolução geológica do Complexo Quirino, Terreno Paraíba do Sul, Setor Central da Faixa Ribeira, com base em dados isotópicos de Sm-Nd e Sr

Abstract

The study area is part of the Ribeira Belt, Central Segment Mantiqueira Province (Almeida et al., 1973, 1977, 1981), which represents one of fold-thrust belt in neoproterozoic/cambrian generated during the Brasiliano Orogeny, at the edge south / southeast of the São Francisco Craton (Almeida, 1971, 1977, Cordani et al., 1967, 1973, Brito Neves & Cordani, 1982, Teixeira and Figueiredo, 1991). In this context, the Quirino Complex is the reworked basement of Paraiba do Sul Terrain (Heilbron et al., 2004). Quirino Complex is formed by extensive bodies of foliated orthogneisses the homogeneous, the leuco mesocratic, average particle size of the thick, compositionally ranging from tonalitic granitoids / granodioritic to granitic, and featuring enclaves of ultramafic, mafic and calcium silicate (rich in tremolite). The tonalite orthogneiss / granodioritic present porphyroblasts of plagioclase and hornblende as mafic main, contrasting with those of granitic composition showing porphyroblasts of K-feldspar and biotite predominates. Accessories appear as zircon, titanite, apatite and epidote. Also associated with these orthogneisses, neoproterozoic granitoids that make up individual bodies or lenses in the set anatetics paleoproterozoic. These are composed predominantly of biotite gneiss and hornblende-biotite gneiss. Lithogeochemical analysis of orthogneiss from Quirino Complex suggest the existence of two distinct magmatic series. The first belongs to the high-K calc-alkaline series composition shows a more expanded granitic-adamelític/granodioritic/tonalitic and is correlated to some orthogneisses and bt-hb-bt-orthogneiss. The medium-K orthogneisses series feature predominantly tonalitic composition, and correlated to most of the hornblende-biotite gneiss. Lenses enclaves metapiroxenitics and amphibolites occur in many outcrops. Neoproterozoic granitoids also occur composition of granitic to quartz-monzonitic. The isotopic study of Sm-Nd and Sr showed that the high-K calc-alkaline series orthogneisses and those of medium-K calc-alkaline series, have TDM model ages ranging from Archean to Paleoproterozoic, consistent with U-Pb data zircon from the literature. The high-K calc-alkaline series is older (2308 ± 9.2 Ma to 2185 ± 8 Ma) than medium-K calc-alkaline series (2169 ± 3 to 2136 ± 14 Ma) and occurs the existence of zircons inherited with minimum ages of 2846 Ma and 2981 Ma for medium-K series and 3388 ± 16 for high-K series. The brasiliano granitoids have neoproterozoic crystallization ages correlated to Brasiliano Orogeny (602-627 Ma) (Viana, 2008, Valladares et al., 2002). Based on data of Sr and Sm-Nd was possible to identify four distinct groups. Groups 1 and 2 are formed by rocks of Paleoproterozoic (2.1 to 2.3 Ga) TDM model ages ranging from 2.9 to 3.4 Ga, εNd between -8.1 and -5.8 and 87Sr / 86Sr ratios (t) = 0.694707 (Group 1) and TDM ranging from 2.5 to 2.7 Ga, εNd between -5.8 and -3.1 and 87Sr/86Sr (t) = 0.680824 (Group 2), formed with the assistance of a Paleoproterozoic Archean. The third group consists of Paleoproterozoic juvenile rocks with crystallization ages ranging between 2.0 and 2.2 Ga and TDM model ages ranging from + 2.1 to + 2.2 Ga and εNd between +1.5 and +1.2. Group 4 is formed during the Neoproterozoic (645 Ma) of rocks with Paleoproterozoic age possibly TDM model ages exceeding 1.7 Ga and εNd= -8.3.