Proterozoic evolution of part of the Embu Complex, eastern Sao Paulo state, SE Brazil

摘要

This paper presents detrital zircon ages obtained in rocks of the Embu Complex, southeastern Sao Paulo State, Brazil. The Embu Complex encompasses a Paleoproterozoic basement represented by migmatitic hornblende and biotite orthogneisses covered by (kyanite)-(sillimanite)-(garnet) bearing biotite-muscovite schists and paragneisses with decametric intercalations of quartzites and calcsilicate rocks. In the studied area this metasedimentary sequence is intruded by the porphyritic Serra do Quebra Cangalhagranite. Through field and microstructural studies, four ductile deformational phases were-identified. Metamorphic events related to the Brasiliano Orogeny that affected the studied rocks were dominantly under medium temperature and pressure conditions, from greenschist to middle amphibolite facies. Detrital zircon crystals from a similar to 10 m thick quartzite layer were analyzed by LA-ICP-MS resulting in a wide range of ages between 2100 and 600 Ma that fall mainly in four groups: the first group between 2.1 and 1.6 Ga, with apex at 1.7 Ga; two less expressive Mesoproterozoic groups with values between 1.6 and 1.2 Ga; and a fourth group with values between 1.2 and 0.6 Ga. Considering the geochronological data, the sedimentation of the basin began after 852 +/- 40 Ma (the youngest igneous grain) and finished before similar to 786 Ma (metamorphic rim). The age of the intrusive Serra do Quebra Cangalha granite (similar to 680 Ma) is consistent with this minimum age. The opening of the basin could be related to the break-up of Rodinia, which resulted in several small continents, among them the Paranapanema and Sao Francisco paleocontinents. Comparing these data with similar provenance data from the Apiaiterrane, itseems probable that the Embu Complex was physically connected with it during most of their evolution. (C) 2017 Elsevier Ltd. All rights reserved.