Paleoproterozoic Enclaves and Magma Mixing: Insights from the Minas Orogen, São Francisco-Congo Paleocontinent, Brazil

This study investigates Paleoproterozoic magmatic dynamics in the Ritápolis Arc of the Mineiro Belt, focusing on the Rhyacian (2.15–2.10 Ga) Rio Grande Pluton and Macuco de Minas granitoid. These rocks record part of the Paleoproterozoic magmatic evolution of the Brazilian sector of the São Francisco–Congo Paleocontinent, specifically within the southern sector of the Minas-Bahia Orogen. By integrating detailed field observations with petrographic, geochemical, and geochronological data, we constrain the processes of enclave formation and magma interaction and their implications for open-system magmatic evolution during the Rhyacian. The Rio Grande Pluton contains hornblendite enclaves displaying fragmentation, angular boundaries and pervasive felsic net-veining, locally forming hybrid rocks. The Macuco de Minas granitoid records magma interaction through cuspate–lobate diorite/tonalite–granite contacts, granitic back-veining, mechanical transfer of K-feldspar megacrysts into mafic enclaves and titanite-centered ocelli. Both plutons preserve microscale disequilibrium textures, including mineral resorption, zoning, and mafic clots. These observations indicate that the hornblendite enclaves are fragments of older hydrous mafic cumulate rather than in situ cognate cumulates. Repeated interaction between Rio Grande and Macuco de Minas magmas drove magma mixing and mingling highlighting the importance of open-system dynamic in the Paleoproterozoic.