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Jacques Delhal, D. Ledent & U. Cordani

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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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.

To cite this article

Jacques Delhal, D. Ledent & U. Cordani, «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)», Annales de la Société géologique de Belgique [En ligne], Volume 92 (1969), Fascicule 2, 271-283 URL : https://popups.ulg.ac.be/0037-9395/index.php?id=6742.

About: Jacques Delhal

Musée royal de l’Afrique centrale, Tervuren, Belgique

About: D. Ledent

Laboratoire de Minéralogie et de Pétrologie, Université Libre de Bruxelles, 50, Avenue F.-D. Roosevelt, Bruxelles 5, Belgique.

About: U. Cordani

Département de Pétrologie de la Faculté de Philisophie, Sciences et Lettres de l’Université de São Paulo, Brésil.