Sistema Sm-Nd em rocha-total aberto versus fechado: comportamento isotópico em zonas de alta deformação

Abstract

High strain shear zones of Brasiliano age, developed in Paleoproterozoic basement gneiss of the Caicó region, Borborema Province, NE Brazil, were associated with medium- to low-grade metamorphism and deformational processes that transformed porphyritic augen gneiss into muscovite quartzite, modifying their original mineralogy and chemical properties. During the last hydrothermal event mobility of major, minor and trace elements was great, whereas the pattern of Rare Earth Elements was not changed. We carried out a Sm-Nd isotopic study in these rocks in order to understand the behavior of Nd isotopes during mylonite generation. T DM model ages at around 2.6 Ga and µNd (t) values for both protolith and transformed rock suggest that the Nd isotopic system remained closed, recording the original source rock signature, despite undergoing two superposed metamorphic events.These new Sm-Nd results provide important information on the geologic evolution of basement rocks in the central Rio Grande do Norte Terrane of the Borborema Province, NE Brazil.