Polymetamorphism in the Central Ribeira belt, SE Brazil: New constraints on the P–T–t–d evolution of the Outer Magmatic arc System and Cabo Frio Terrane from phase equilibria modelling and monazite–titanite geochronology

Precambrian orogens record polycyclic histories marked by multiple episodes of subduction, accretion, and crustal reworking during successive continental collisions. The Araçuaí–Ribeira Orogenic System (AROS), southeastern Brazil, is a Neoproterozoic–Cambrian orogen formed through diachronous collisions involving magmatic arcs, microcontinents, and cratonic blocks. This study reconstructs the P–T–t–d evolution of metasedimentary/amphibolite rocks located between the Outer Magmatic Arc System (OMAS) and the Cabo Frio Terrane in the Central Ribeira Orogen. Petrography, mineral chemistry, phase equilibria modeling, and U–Th–Pb geochronology of monazite and titanite reveal three main metamorphic events: M1, high-temperature event related to collision between the OMAS and the Inner Magmatic Arc System; M2, high-pressure event attributed to collision between the OMAS and the Angola Craton; and M3 retrograde stage. In the Bt–Crd–Grt gneiss from the OMAS back-arc basin, four generations of monazite were identified. Mnz I (574–568 Ma) enriched in Y + HREE formed during M1 prograde metamorphism. Mnz II (560 Ma) and Mnz III (553 Ma) are depleted in Y + HREE. Mnz II reprecipitated from dissolution of Mnz I, marking the partial melting, whereas Mnz III constraints the M1 temperature-peak (5.3–6.5 kbar, 760–820 °C) during decompression, supported by monazite included in cordierite (554 Ma). The M2 pressure-peak overprint occurred at 540–535 Ma under 8–9 kbar and 730–790 °C. Mnz IV (527 Ma) reflects garnet breakdown during M3. In the Bt–Ky–Grt gneiss from the Cabo Frio Terrane, three monazite generations were recognized. Mnz I (543 Ma) records M2 high-pressure metamorphism (∼12 kbar, 800 °C). Mnz II (536 Ma), enriched in Y + HREE, reflects M3 retrogression during isothermal decompression, whereas Mnz III (517 Ma) formed during garnet growth associated with orogenic collapse. Titanite U–Pb ages (522 Ma) in amphibolite from the Cabo Frio Terrane record cooling and exhumation.