CONTRIBUTION A L'ÉTUDE PÉTROLOGIQUE GÉOCHIMIQUE ET STRUCTURALE DU DIAPIR MlGMATITIQUE HENNEBONT-VANNES. BRETAGNE MÉRIDIONALE

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Mobilisation anatectique et déformation. Un exemple : Les migmatites du Golfe du Morbihan (Bretagne méridionale)

Note déposée le 5 mars 1976, présentée à la séance du 3 mai 1976.National audiencepas de résum

Fammenian-Tournaisian dextral ductile shear in the French Variscan belt

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New investigations in southwestern Guinea: consequences for the Rokelide belt (West Africa)

International audienceThe southern Guinean terranes belong to the “Rokelide belt” that is located in the southwestern part of the West African craton (Senegal to Liberia). Field investigations and K–Ar and 40Ar–39Ar radiometric analysis performed on samples collected from southern Guinea provide a new interpretation for metamorphic terranes not yet dated. A K–Ar whole-rock age of a gneiss and 40Ar–39Ar plateau ages of amphiboles separated from a mylonitic gneiss of the Ouankifondi formation and a gneiss from the Kissi-Kissi formation yield several Pan-African metamorphic ages at circa 650, 560, and 530 Ma, respectively. Field investigations show that these formations are unconformably capped by the Kolente group. The previous structural framework and the geodynamic evolution of the Rokelide belt based on the coeval evolution of the Ouankifondi and Kissi-Kissi formations and the Kolente group are reassessed. The Rokelide belt is linked to the Bassaride belt. Correlations with adjacent Sierra Leonean terranes and with northern Guinea and Senegal are considered

Données complémentaires sur la géométrie du plissement et sur les variations de forme et d'orientation de l'ellipsoïde de deformation dans l'arc ibéro-armoricain

Note déposée le 14 novembre 1975, présentée à la séance du 27 novembre 1975, manuscrit définitif reçu le 23 janvier 1976.National audiencepas de résum