Caracterização Geocronológica e Metamórfica dos Complexos Embu/Paraíba do Sul e Costeiro na região Sudoeste do Estado do Rio de Janeiro

Abstract

The study area is linked to the central segment of the Ribeira Belt, encompassing the Occidental, Oriental Terranes and Central superterrane. However, recent works indicate that, mainly, the division between the Oriental and Occidental Terranes, at least in the South of the State of Rio de Janeiro and nearby regions in São Paulo, may be shifted to the South. In this new context, the objective of this work was to study the rocks that are part of these Terranes and compare them to the Embu Terrane and the Costeiro Complex. For this, petrographic and geochronological characterizations of para- and orthoderived rocks, lithogeochemical characterizations of orthoderived rocks and identification of deformational structures were carried out, to verify if these rocks have a correlation with those described in the Costeiro Complex in the state of São Paulo. The research made here follows on from the work carried out by Hoffmann (2016) with a greater focus on obtaining new geochronological and lithogeochemical data that allow us to present new visions for the study region. The rocks in the study area were divided into two distinct domains based on field observations, lithogeochemistry and crystallization and sedimentation ages. In the Embu Terrain, two metasedimentary rocks (THM 181Q and 181BQ) and two orthoderived rocks (THM 162G and 16) were dated, between paraderived rocks the maximum age of sedimentation is 1379 Ma and among orthoderived rocks the crystallization was around 2040 Ma. In the Costeiro Complex, three metasediments (THM 18, 40 and 97Q) and seven orthoderived samples (THM 60 1, 60 2, 60 3, 259, 112 and TR 04 and 05) were dated. Among paraderived rocks the maximum age of sedimentation is close to 650 Ma and among orthoderived rocks, belonging mostly to the Serra do Piloto Magmatic Arc (SPMA), the crystallization ages varies between 614 and 635 Ma. In the samples from the Embu Terrain, metamorphic overgrowths in zircon grains are rare, but one age (620 + 18) Ma was calculated, whereas in the samples from the Costeiro Complex the opposite occurs, there are several zircon grains that have this type of overgrowth, including in the SPMA rocks, so the age of metamorphism of this Complex varies between 613 and 598 Ma. Lithogeochemical analyzes showed that SPMA rocks vary from diorites to granites and samples THM 16 and THM 162G, despite being distant and belonging to the Occidental Terrane and Central Superterrane, respectively, are the same rock and classified as belonging to the basement of the study region. It is concluded that, based on the data obtained, that the rocks of the Embu Terrane and the Coastal Complex have different sources for their respective metasediments and that the Coastal Complex corresponds to both the Occidental and Oriental Terranes, pointed out mainly by recurrent intrusions of SPMA granitic dykes in rocks of the Sillimanite Granada Biotite Gneiss Unit, implying, therefore, in the displacement of the central tectonic boundary (CTB) to the south of the study region, without encompassing the Serra do Piloto (Mangaratiba - RJ).