Geology of Gabon
From Wikipedia, the free encyclopedia
Gabon is situated at the northwestern margin of the Congo Craton—a region of stable, ancient crust—and preserves very ancient rock units across 75% of the country, with overlying sedimentary units from the Cretaceous and other more recent periods.[1]
Proterozoic (2500-541 Ma)
The oldest rocks in Gabon are granitoid Archean basement rocks, 2.8 to 2.6 Ga old, that span into Cameroon, Equatorial Guinea and the Republic of Congo. The basements rocks are divided between the Chaillu Massif and North Gabon Massif. Like many other Archean cratons, the granitoid rocks are associated with potassic rocks, granite, monzonite, syenite and diorite-tonalite-granodiorite sequences. A large charnockitic body—a series of metamorphic rocks with varying chemical composition—exists in southern Gabon. Unlike other parts of Africa, Gabon lacks greenstone belt development.
The Franceville Supergroup is made up of approximately 2 Ga Paleoproterozoic rocks, located in the east-central part of the country. The Ogooue orogenic belt in west-central Gabon also dates to the Paleoproterozoic, made up of heavily deformed metasedimentary and metavolcanic rocks from a fold and thrust belt. In the southwest, the Mayombe-Nyanga terrane contains high-grade Paleoproterozoic basement rocks, the Lambarene migmatite belt, as well as Doussa Supergroup metasedimentary rocks. Granites appear after the tectonic activity ended and are 1.9 Ga. The Mayombe Supergroup, within the Mayombe-Nyanga terrane, along with Franceville dolerite dykes from 970 Ma are the only remnants of the Mesoproterozoic rocks. The Nyanga Basin and de-la-Noya in the western part of Gabon expose the Neoproterozoic West Congolian Supergroup, with deformed volcanic and sedimentary sequences, similar to others in southern Africa. A small carbonatite formation was deposited 669 Ma in the Lambarene region.
Cretaceous-Quaternary (145 million years ago to the present)
A horst from the Early Cretaceous splits the Lambarene-Chincoua basement rocks and divides the overlying western sedimentary basin in two. The eastern, interior basin is made of a mix of lacustrine and continental sedimentary rocks, while marine sediments are common in the western basin, from the Cretaceous to as recently as the Quaternary in the past 2.5 Ma.[3]
