Relationship between crustal melting and magma emplacement during the final stages of West Gondwana agglutination recorded in high-grade terranes of SE Brazil

High-grade metamorphism, partial melting and differentiation of the continental crust played an important role in the Ediacaran-Cambrian Búzios collisional orogen, in West Gondwana. To constrain the timing of subduction, collision and partial melting, U-Pb secondary-ion mass spectrometry (SIMS) and Lu-Hf laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon analysis were performed in migmatites from a reworked Paleoproterozoic crust. Two melt crystallization phases at ca. 570 Ma and 530 Ma are shown and compared with the magmatic evolution of the flanking Neoproterozoic terrane, the Oriental Terrane, which is juxtaposed to the investigated terrane along an inferred suture zone. The former represents the location of a batholith (600-570 Ma) to the West and a more recent Ediacaran magmatic arc (570-540 Ma) to the east. The Ediacaran magmatic arc is situated near the contact with the Paleoproterozoic continental crust in the Cabo Frio Tectonic Domain, which is the study area and is interpreted as the paleo-margin of the Angola Craton. The first melt crystallization phase is coeval with the Ediacaran magmatic arc and might be related to the beginning of the subduction of the paleo-margin.  Then, there is an absence of melt crystallization (570-530 Ma), as prograde metamorphism enables monazite-zircon dissolution at granulite facies. During 530-515 Ma, the Cabo Frio Tectonic Domain has the second and larger melt crystallization phase, while the Oriental Terrane shows a gap of magmatic record. Although both terranes were now in tectonic contact, no inter-terrane melt migration occurred, probably due to horizontal stresses and onset of collision. The correlation between magma emplacement in the Oriental Terrane and melting in the Cabo Frio Tectonic Domain is controlled by the tectonic setting where the Paleoproterozoic continental crust underwent partial subduction below the Neoproterozoic terrane, the more buoyant upper plate.