Cambrian orogeny in the Ribeira Belt (SE Brazil) and correlations within West Gondwana: ties that bind underwater

Abstract

AbstractA 530–490 Ma tectono-metamorphic event, the Búzios orogeny, is recognized within the Ribeira Belt, along the coast of SE Brazil. Tectonic evolution started with a Late Neoproterozoic marine basin and volcanic activity at c. 610 Ma. The rocks in this basin were affected by high-grade metamorphism at c. 530 Ma, coeval with deformational phases D1–D2, which generated compressive low-angle tectonic structures with top-to-NW tectonic transport. Large recumbent folds with NW–SE axes parallel to the main stretching lineation formed during D3 as the Cabo Frio tectonic domain, the focus of this study, collided with the Oriental terrane to the NW. D4 sub-vertical shear zones are limited in extent. A new U–Pb age of 501±6 Ma is reported for zircon from an amphibolite-facies shear zone related to either D3 or D4. Post-tectonic 440 Ma pegmatites mark the final stage of tectono-magmatic activity. The Cabo Frio tectonic domain has African affinities and is exotic to the Ribeira Belt. Middle Cambrian deformational and metamorphic ages are also reported from the ‘Angolan’ Pan-African belt, the southern Kaoko and Damara belts in Namibia, and the Cuchilla Dionisio–Punta Del Este terrane in Uruguay. The occurrence of Cambrian metamorphic rocks along the present African and South American coastlines shows that Mesozoic rifting closely follows Palaeozoic sutures of West Gondwana.