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- Volume 92 (1969)
- Fascicule 2
- Ages Pb/U, Sr/Rb et Ar/K de formations métamorphiques et granitiques du sud-est du Brésil (États de Rio de Janeiro et de Minas Gerais)
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Ages Pb/U, Sr/Rb et Ar/K de formations métamorphiques et granitiques du sud-est du Brésil (États de Rio de Janeiro et de Minas Gerais)
Abstract
Field and petrological data and Pb/U, Sr/Rb and Ar/K radiometric results establish the existence of two superposed orogenesis in the Paraíba Belt (S. E. Brazil, States of Rio de Janeiro and Minas Gerais).
Banded granulites of the « Paraíba Serie » represent sediments metamorphosed during a first orogeny dated at about 2000 m.y.
Migmatitic and granitic gneisses of the Serra dos Órgãos are syntectonic gneisses of an orogeny dated at 620 ± 20 m.y.
Results published previously date the last granites at 540 ± 60 m.y., pegmatites at 464 ± 11 m.y. and the youngest event (apparent ages of biotite) at 450 ± 30 m.y. These are late to post-tectonic events of the second orogeny which is also the last to have affected the area.
One young diabase, which cuts the aforementioned formations, is dated at 133 ± 6 m. y.