SM/ND DATA OF METASEDIMENTARY ROCKS FROM THE CENTRAL SEGMENT OF RIBEIRA BELT, SOUTHEASTERN BRAZIL

DIANA RAGATKY, MIGUEL TUPINAMBÁ, BEATRIZ PASCHOAL DUARTE

Resumo


The central segment of Ribeira Belt, southeastern Brazil, comprises several tectonic domains where, during the Proterozoic, extensive detritic material was deposited over pre-1.8 Ga basement rocks. This paper presents Sm-Nd isotopic data on the high-grade metasedimentary rocks of this belt and discusses some possible implications on their sedimentary provenance. The pre-1.8 Ga basement rocks display different Nd isotopic evolution and thus can be promptly discriminated as sources of different Nd model ages (TDM) and isotopic characteristics such as: Mantiqueira Complex, 3.0 and 2.6 Ga TDM isochrons ages; Juiz de Fora Complex, 2.2 Ga TDM isochron age and Quirino Complex, 2.0 Ga and 3.2 Ga TDM ages. At the Juiz de Fora Domain, metapelites from the Andrelândia Depositional Cycle display a very narrow range of Sm/Nd values (0.15 to 0.17) and TDM ages between 1.8 and 2.0 Ga. The corresponding measured εNd values [εNd(0)] vary between – 20.8 and –29.1. The metapsammopelites of the Jardim Glória Unit, in the same geologic domain, display very different isotopic characteristics: higher Sm/Nd ratios (0.22 and 0.24), lower εNd(0) values (–15.3 and –18.3) and Neoarchean TDM ages (2.5 and 2.6 Ga). At the Paraíba do Sul Klippe, the analyzed metapelites from the middle unit of Paraíba do Sul Group show TDM ages close to 1.7 Ga with eNd(0) values of -14.10 and -17.34. The metapsammopelites from the basal and uppermost units plot along the 2.0 Ga TDM isochron and display εNd(0) values varying between -21 and –32. An isolated TDM of an amphibolitic body, probably intrusive in the metasedimentary rocks of Paraíba do Sul Group, yields 1.0 Ga TDM age, with a 147Sm/144Nd value of 0.1428.

Palavras-chave


Neodymium isotopes; Sedimentary provenance; Ribeira Belt; Proterozoic.

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