Lithogeochemical and Nd-Sr isotope data of the orthogranulites of the Juiz de Fora complex, SE-Brazil: insights from a hidden Rhyacian Orogen within the Ribeira belt

Abstract

New petrography, geochemistry and Sm-Nd and Sr data from the orthogranulites of the Juiz de Fora complex in southern Rio de Janeiro State and compiled information provide insights on the petrogenetic and tectonic evolution. The complex comprises several geochemical groups including mafic orthogranulites (three tholeiitic and one alkaline) and felsic orthogranulites (three calc-alkaline and one tholeiitic/low K calc-alkaline). New geochemical and isotope data, combined with available U-Pb data suggest a long evolutionary history from the Paleoproterozoic to the Neoproterozoic. The oldest magmatic episode produced juvenile to slightly contaminated arc-type Rhyacian rocks, as well as granitic rocks related to collision or post-collision episodes. Altogether these rocks integrate part of a dismembered Rhyacian orogen within the Ribeira belt. Few T DM Nd model ages yielded 2.75 to 2.58 Ga, suggesting minor Archean contribution for magma genesis. Some of the basic granulites' bodies yield Meso-to Neoproterozoic T DM Nd model ages, which may refer to an extensional magmatism. Orthogranulites present granulite facies paragenesis, related to the youngest tectonic episode in the Juiz de Fora Complex (Brasiliano Orogeny). The new data are potentially important for Paleoproterozoic reconstruction models, due to the predominantly juvenile character of the Juiz de Fora complex, as similarly worldwide.

Evidence for a complex accretionary history preceding the amalgamation of Columbia: The Rhyacian Minas-Bahia Orogen, southern São Francisco Paleocontinent, Brazil

“…iii) the accreted Piedade Block is interpreted as an Archean microcontinent, juxtaposed against the Mantiqueira Complex by the Ponte Nova Shear Zone, a Paleoproterozoic suture zone Peres et al, 2004). The rocks of the Piedade Block are Neoarchean TTGs and sanukitoids and associated mafic bodies, whose isotopic signatures indicates reworking of a pre-existing continental crust, and minor Paleoproterozoic granitoid rocks with post-collisional signatures Silva et al, 2002); iv) and the Mantiqueira and Juiz de Fora complexes, both accreted Paleoproterozoic magmatic arcs Araújo et al, 2019b;Kuribara et. al., 2019;Degler et.…”