Transition from alkaline to calc-alkaline volcanism during evolution of the Paleoproterozoic Francevillian basin of eastern Gabon (Western Central Africa) - Ecole Nationale du Génie de l'Eau et de l'Environnement de Strasbourg Accéder directement au contenu
Article Dans Une Revue Journal of African Earth Sciences Année : 2014

Transition from alkaline to calc-alkaline volcanism during evolution of the Paleoproterozoic Francevillian basin of eastern Gabon (Western Central Africa)

Résumé

We report new geochemical data for the volcanic and subvolcanic rocks associated with the evolution of the Francevillian basin of eastern Gabon during Paleoproterozoic times (c. 2.1-2 Ga). Filling of this basin has proceeded through four main sedimentary or volcano-sedimentary episodes, namely FA, FB, FC and FD. Volcanism started during the FB episode being present only in the northern part of the basin (Okondja sub-basin). This volcanism is ultramafic to trachytic in composition and displays a rather constant alkaline geochemical signature. This signature is typical of a within-plate environment, consistent with the rift-setting generally postulated for the Francevillian basin during the FB period. Following FB, the FC unit is 10-20 m-thick silicic horizon (jasper) attesting for a massive input of silica in the basin. Following FC, the FD unit is a c. 200-400 m-thick volcano-sedimentary sequence including felsic tuffs and epiclastic rocks. The geochemical signatures of these rocks are totally distinct from those of the FB alkaline lavas. High Th/Ta and La/Ta ratios attest for a calc-alkaline signature and slight fractionation between heavy rare-earth suggests melting at a rather low pressure. Such characteristics are comparable to those of felsic lavas associated with the Taupo zone of New Zealand, a modern ensialic back-arc basin. Following FD, the FE detrital unit is defined only in the Okondja region, probably associated with a late-stage collapse of the northern part of the basin. It is suggested that the alkaline to calc-alkaline volcanic transition reflects the evolution of the Francevillian basin from a diverging to a converging setting, in response to the onset of converging movements in the Eburnean Belt of Central Africa.
Fichier non déposé

Dates et versions

hal-01176735 , version 1 (15-07-2015)

Identifiants

Citer

Denis Thiéblemont, Pascal Bouton, Alain Préat, Jean-Christian Goujou, Monique Tegyey, et al.. Transition from alkaline to calc-alkaline volcanism during evolution of the Paleoproterozoic Francevillian basin of eastern Gabon (Western Central Africa). Journal of African Earth Sciences, 2014, 99 (2), pp.215-227. ⟨10.1016/j.jafrearsci.2013.12.007⟩. ⟨hal-01176735⟩
152 Consultations
0 Téléchargements

Altmetric

Partager

Gmail Facebook X LinkedIn More