Abstract
The Gondwana pre-break up related formations in Bafoussam area are transitional calc-alkaline doleritic dykes exhibiting high Alumina and low Ti-Mg contents. Their REE compositions are similar to those of E-MORB (Nd/Nb≈1, Zr/Nb≤20). A high partial melting of about 20% of Garnet peridotites source having primitive mantle composition, is inferred to the studied rocks. They are slightly evolved 50<Mg#<54, and its clinopyroxenes are augite of high temperature (600°C-1100°C). The studied dykes were emplaced in a within-plate tectonic setting and yield a 40Ar-39Ar plateau ages of 229±7Ma. These ages are slightly different from those of dolerites from the Oban-Obudu massif (Nigeria), from the basaltic dyke of the Cameroon Volcanic Line and from the Karoo-Ferrar mafic magmatism, all interpreted as magmatism that preceded the break-up of Gondwana. The emplacement age of 229±7Ma of dolerites from Bafoussam area relates them to the very early stage of Gondwana pre-break up magmatism in central Africa.
Highlights
In Cameroon, the basement formations are made up of Archean to Paleo-Proterozoic rocks related to the Congo Craton and of Neoprotorozoic rocks related to Pan-African orogeny; this basement is overlain in some places by tertiary to recent volcanic rocks or by sedimentary formations (Fig. 1A)
Based on the fact that transitional lavas are related to the extension of the lithosphere, we suggest that dolerites from Bafoussam area may represent an early stage of the maximum extension of the lithosphere reported below the Cameroon line in Cenozoic times (Kuepouo et al, 2006)
The main conclusions of this paper are: 1) Dolerites from Bafoussam area are transitional calc-alkaline basalts, with high Alumina and low Mg contents. Their parental magma evolved mostly by fractional crystallization and their REE compositions are similar to those of the E-MORB. 2) The clinopyroxenes of dolerites from Bafoussam area are similar to those of transitional basaltic lavas and other basaltic dykes described in Cameroon
Summary
In Cameroon, the basement formations are made up of Archean to Paleo-Proterozoic rocks related to the Congo Craton and of Neoprotorozoic rocks related to Pan-African orogeny; this basement is overlain in some places by tertiary to recent volcanic rocks or by sedimentary formations (Fig. 1A). Doleretic dykes have been reported by Vicat et al, (2001) in the Adamawa Plateau, within the Northern Domain of the Pan African Fold Belt in Cameroon These authors related the doleritic dykes from Adamawa plateau to a magmatic activity anterior to the Cenozoic alkaline volcanism of the Cameroon Line. The mafic dykes of Lake Nyos studied by Aka et al, (2018) are alkaline and sub alkaline, they yield K-Ar ages of 231.1 ± 4.8 Ma and 224.8 ± 4.7 Ma respectively The authors correlate it with the initiation of west Gondwana fragmentation to form the Atlantic Ocean. After recalling the main petrochemical characteristics, we present the pyroxene chemistry and the Argon-Argon geochronology of dolerites dykes in Bafoussam region These new data will constraint their sources and will contribute to understand the geodynamic evolution of the Central Africa within the Gondwana geological setting
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