Paleoproterozoic Minas-Bahia Orogenic System in the southernmost São Francisco Paleocraton (Brazil): Siderian-Rhyacian magmatism associated with the Mineiro belt

The São Francisco Paleocraton involves amalgamation and reworking of Archean nuclei metasedimentary rocks associated with the Archean-Paleoproterozoic Transition and Paleoproterozoic magmatic arcs-metasedimentary basins developed during Siderian to Orosirian time interval, occurring in Brazil and West Africa counterpart (Congo Craton). Paleoproterozoic tectonic-metamorphic-magmatic event developed in Brazil was designated as Minas-Bahia Orogenic System. In the southernmost São Francisco Paleocraton, the evolution of this orogenic system was denominated Minas Orogeny and comprises: (i) part of the Minas and Bom Sucesso basins with depositional ages between 2.4–2.1 Ga, including BIF deposits; (ii) three magmatic arcs with different ages: Mineiro belt (2.47–2.04 Ga), Mantiqueira (2.20–2.00 Ga) and Juiz de Fora (2.44–2.00 Ga) complexes; and (iii) six metavolcanic-sedimentary successions and associated metasedimentary basins. The Mineiro belt focused here can be subdivided into two blocks (North and South) and is the most preserved magmatic arc of the Minas Orogeny (medium-to upper crust) exhibiting rocks with primary features and textures, such as: (i) magmatic mingling between diorites and granites; (ii) magmatic foliation associated to magma flow; (iii) porphyritic textures in mafic-felsic rocks; (iv) hornblende cumulates (hornblendites) associated to diorites; (v) spinifex textures in metaultramafic rocks; and (vi) magmatic corrosion in feldspar and quartz phenocrysts in felsic subvolcanic-volcanic rocks. In contrast, Mantiqueira and Juiz de Fora complexes are high deformed and comprise granulites, orthogneisses and migmatites (lower crust). The magmatism in the Mineiro Belt can be subdivided into six intervals: (i) 2.47–2.41 Ga; (ii) 2.36–2.31 Ga; (iii) 2.25–2.20 Ga; (iv) 2.19–2.16 Ga; (v) 2.15–2.10 Ga; (vi) 2.04-2.03 Ga. The two first pulses are Siderian, genetically associated to igneous protoliths of orthogneisses, occurs only in the North Block and show geochemical features of TTG and TTG-like rocks. The predominantly juvenile Hf and Nd isotopic constraints point to derivation from short-lived and Paleoproterozoic protoliths (2.5-2.4 Ga) through successive oceanic slab subductions. The third pulse is Rhyacian, occurring only in the South Block and comprises gabbros-tonalites and subvolcanic-volcanic juvenile rocks with positive ε_Nd, indicating a relationship with oceanic slab subduction too. The fourth pulse is observed in the two blocks, is associated to calc-alkaline to high-K calc-alkaline plutons and has negative ε_Nd akin to a continental arc setting. The fifth pulse occurs in the North and South blocks, involves diorites, granitoids and pegmatites with calc-alkaline affinity, positive-negative ε_Nd and juvenile and crustal derivation. The Nb-Ta-Sn mineralized pegmatites are restricted to this pulse and occur only in the North Block. The bodies of the last two pulses are intrusive in rocks of the metavolcanic-sedimentary successions. The sixth pulse occurs only in the North Block, show high-K calc-alkaline affinity and crustal derivation with high negative ε_Nd. Based on crystallization ages, geochemical and isotopic data, tectonic evolution of the Mineiro belt is divided into four magmatic arcs: Cassiterita (2.47–2.41 Ga) and Resende Costa (2.36–2.31 Ga) arcs with Siderian ages, TTG and TTG-like signatures and juvenile Paleoproterozoic sources; Serrinha Arc (2.25–2.20 Ga) with Rhyacian age, calc-alkaline signature and juvenile Paleoproterozoic source; and Ritápolis Arc (2.19–2.10 Ga) with Rhyacian age, calc-alkaline to high-K calc-alkaline signature and juvenile, crustal and mixed juvenile-crustal source of Archean and Paleoproterozoic ages. The early five pulses built up the Mineiro belt architecture (pre-collisional phases) whereas the sixth pulse is a response from crustal shortening collision of the Mineiro belt with the Archean nuclei and the intervening Piedade Microcontinent.