Preserved interactions between acid and intermediate magmas in a 2.15–2.10 Ga Rhyacian continental arc: Insights from petrographic, geochemical and isotopic data of the Macuco de Minas metagranitoid, Mineiro belt, Brazil

The Mineiro Belt originated by Siderian (2470 to 2330 Ma) to Rhyacian (2250 to 2110 Ma) arcs amalgamated to the Neoarchean foreland of the southern margin of the São Francisco Craton, Brazil. The Macuco de Minas metagranitoid is one of the most important plutons related to the Rhyacian Ritápolis arc that developed close to the Siderian crust akin to the older Cassiterita and Resende Costa arcs. We integrate new U-Pb ages, coupled geochemistry and Sr-Nd-Hf isotopes, and thermobarometry data together with compiled information in order to unravel the petrogenesis of the Macuco de Minas metagranitoid and its role in the formation of the Mineiro belt. This pluton is essentially represented by porphyritic granodiorites to monzogranites which exhibit centimetric microcline phenocrysts immersed in a medium-grained matrix mainly composed of quartz, oligoclase, biotite, and titanite. These rocks exhibit well-preserved mixing and mingling features (homogeneous hybrid rocks, mafic clots, magmatic enclaves, diorite injections with cuspate-lobate shape, and back-veining) suggesting interaction with a dioritic/tonalitic magma, similar to the coeval Rio Grande metadiorite that occurs nearby. The Macuco de Minas (and hybrid) rocks are magnesian, medium- to high-K calc-alkaline, metaluminous to slightly peraluminous, and display a high Ba-Sr signature. These exhibit enrichment in LILE and LREE compared to HFSE and HREE, as well as low Sr87/Sr86(2.1 Ga) (0.7027 to 0.7037), εNd(2.1 Ga) values from −2 to −7, and εHf(2.1 Ga) values from +3 to −7. The Nd-TDM model ages vary from 2.3 to 2.7 Ga and the zircon Hf ones from 2.38 to 2.77 Ga. The Macuco de Minas sample yielded a LA-ICP-MS zircon U-Pb crystallisation age of 2144 ± 16 Ma, and metamorphic age (titanite) of 2071 ± 42 Ma. The crystallisation age is similar to the 2140 ± 17 Ma Rio Grande metadiorite. However, the latter contains inherited grains as old as 2200 ± 19 Ma and 2263 ± 21 Ma, not observed in the Macuco de Minas pluton. The bulk geochemical and isotopic signature of the studied granitoids point to a mantle source with a subordinated contribution of juvenile Siderian rocks of the Cassiterita and Resende Costa arcs and subducted sediments from the Archean rocks of the São Francisco Craton. From a tectonic point of view, the Macuco de Minas and Rio Grande plutons are compatible with the second stage of the Ritápolis arc development, to date the youngest episode of arc generation recognised in the Mineiro belt. •Diorit