Thesis defense of Vicky BOUÉNITELA

Le domaine paléoprotérozoïque (éburnéen) de la chaîne du Mayombe (Congo-Brazzaville) : origine et évolution tectono-métamorphique.

Abstract

Structural analysis of Palaeoproterozoic domain formations revealed a compressive deformation generated by Eburnean and Pan-African orogenies, which are characterized respectively by NW-SE and NE-SW shortening.

Eburnean metamorphism is marked by garnet-biotite-plagioclase paragenesis in Loémé and Loukoula Groups while Pan-African metamorphism is reflected by assemblages of amphibolite facies in the Loémé Group and by chlorite-albite-epidote intermediate facies in the Loukoula Group. The Bikossi Group displays monocyclic metamorphism with garnet-biotite-muscovite and garnet-chloriteoid-chlorite assemblages ; the latter is stable between 510-568 ° C and 8 kbar.
Geochronological analyzes allowed to : (i) constrain the age of crystallization of orthoderived rocks, (ii) trace the sources of the sediments of paraderived rocks and (iii) date the tectono-thermal events which affected the Palaeoproterozoic domain. U-Pb zircon dating shows evidence of Archean relic (2700-3000 Ma), Eburnean magmatism (2070-2040 Ma), post-Eburnean magmatism (925 Ma), and Neoproterozoic-Cambrian disruptions. The 40Ar-39Ar analyzes on biotite, muscovite and amphibole situate the Pan-African tectono-thermal event between 615 and 496 Ma.