Coeval generation of TTG-sanukitoid magmatism in the Rhyacian tectonic evolution of the Juiz de Fora Complex, São Francisco Paleocontinent (SE Brazil)

TTG-sanukitoid rocks are typical of the Archean, where cycles of generation of TTG magmas and, only later, the generation of sanukitoid magmas are described. Paleoproterozoic TTG-sanukitoid magmatism is described mainly in the Minas-Bahia Orogenic System (a set of orogenic belts developed in the collage of the São Francisco Paleocontinent, in eastern Brazil) and the orogenic belts of the North China Craton and has been interpreted as evidence of global diachronic of changes from a typically Archean tectonic to a tectonic similar to modern plate tectonics. In this context, this work presents new data on Whole-rock geochemistry and isotopes of Sm-Nd and Sr, and zircon U-Pb geochronology (LA-Q-ICP-MS and LA-MC-ICP-MS) for orthogranulites from the Juiz de Fora Complex – one of the components of the Minas-Bahia Orogenic System (eastern Brazil), reconstructs its tectonic history and discusses the coeval generation of TTG-sanukitoid magmas. Felsic orthogranulites have a granodioritic to tonalitic composition and TTG geochemical signature, with high SiO₂ content (>67.01% wt.), low ferromagnesian element content, enrichment in Na₂O (>4.07% wt.), low K₂O (<1.85% wt.), affinity with the magnesian and weakly peraluminous series, strong fractionation between LREE and HREE, high (La/Yb)_N ratio (>30.17), positive Eu anomalies, high Sr/Y ratios (>134), and low HFSE content (Nb, V, Zr, and Yb). Two dated samples from this group show ages of 2191 ± 20 and 2110 ± 17 Ma, both are juvenile, with positive εNd_t (2.5-5.6), T_DM ages near to crystallization ages, and low radiogenic Sr content. These rocks can originate from the melting of an amphibolite with variable garnet content, and minimal or absent rutile.The intermediate orthogranulites have a quartz-dioritic to granodioritic composition and a sanukitoid geochemical signature, with ranging SiO₂ contents (50.78-65.28wt. %), low K₂O/Na₂O ratios (0.31-1.60), moderate to high Mg# (0.41-0.67), affinity with the magnesian and metaluminous series, strong fractionation between LREE and HREE, moderate to high ratios (La/Yb)_N (11.12-46.72), Eu anomalies absent at weakly negative/positive, high content of mobile fluid elements, such as Ba (525-1733 ppm) and Sr (377-807 ppm), and moderate to high contents of compatible elements, such as Cr (20-200 ppm), Co (22- 336 ppm) and Ni (20-50 ppm). The four ages obtained for this group are between 2186 ± 20 and 2176 ± 18 Ma, all with εNd_t near to the CHUR (-2.7 to +0.2), T_DM ages between 2.34 and 2.52, and little radiogenic Sr. For these rocks, the data suggest an origin in the partial melting of a mantle enriched by sediment-derived melts. The group of mafic orthogranulites, in turn, is more heterogeneous, with OIB-type rocks, dated at 2162 ± 26 Ma, with negative εNd_t (-4.9), T_DM age of 2.69 Ga and higher Sr content radiogenic, and rocks with E-MORB geochemical signature, without zircon for dating. As conclusions, the integration of new data obtained with compiled data allows the reconstruction of an intra-oceanic to continental magmatic arc in the Rhyacian evolution of the Juiz de Fora Complex (2.22-2.06 Ga), marked by the continuous and coeval generation of TTG- sanukitoid magmatism, possible in a hot, high-angle subduction scenario, with generation of TTG magmas in the melting of the subducting slab in a region closer to the trench, and sanukitoid magmatism by partial melting of the enriched mantle above the subducting slab. The generation of OIB and E-MORB magmas between 2.16 and 2.14 Ga would be a reflection of a rollback and upwelling of the asthenosphere, separating a more juvenile stage of the magmatic arc (2.22-2.16 Ga), and a mature stage (2.13-2.06 Ga). Thus, in the Rhyacian, the accretionary processes developed in the formation of the São Francisco Paleocontinent recorded the development of magmatic arcs similar to those of modern plate tectonics.