Evolução Paleoproterozoica do Complexo Juiz de Fora – Margem SE do Paleocontinente São Francisco: Litogeoquímica, Geocronologia U-Pb e Geoquímica isotópica (Sm-Nd, Sr-Sr e Lu-Hf)

Abstract

The southern margin of the São Francisco Craton exhibits several exposures of Archean and Paleoproterozoic crustal fragments that build up the São Francisco Paleocontinent during a Rhyacian to Orosirian orogenic event. These crustal fragments occur as reworked inliers within the Neoproterozoic orogenic system in the southeasternmost margin of the São Francisco Craton. The Juiz de Fora Complex (JFC) represents an imbricated thrust system that comprises orthogranulites with a wide compositional range formed in an intra-oceanic setting during the Siderian to the Orosirian and latter was accreted to the southeastern margin of the São Francisco Paleocontinent. Here we report new petrological, geochemical, whole-rock Nd and Sr data, zircon U-Pb ages and Lu-Hf in situ isotopic analyses from felsic and mafic orthogranulites from the JFC. The new data is combined with a regional compilation that enables an evaluation of the interaction between magmatism and orogenetic episoses in the context of the consolidation of São Francisco Paleocontinent during the Rhyacian-Orosirian. Pre collisional Island Arc tholeiites (IAT), Tonalites-Trondhjemites-Granodiorites (TTGs), E-MORB and sanukitoid magmatism occurred from 2.28 Ga to 2.09 Ga. This was followed by syn and late-collisional magmatism, with minor moderately juvenile TTG inputs. The late-collisional magmatism is represented by hybrid granitoids coeval with the emplacement of E-MORB basic rocks. Crustal signatures for the Rhyacian to Orosirian evolution are highlighted by the dominance of negativeNd(t) and Nd(t) isotopic results associated with Meso- to Neoarchean Nd and Hf TDM model ages as well as inherited zircon grains from both the hybrid granitoids and TTG associations. The JFC is extensively highlighted in the literature as a primitive intra-oceanic arc, but in this thesis, we propose the reworking or recycling of ancient crustal segments within the mature arc stage of the JFC, suggesting a Mesoarchean crustal source involved in the JFC geodynamic evolution