Petrography and Geochemistry of Dolerite Dykes from Cretaceous Bamwa Half Grabben (North Cameroon, Central Africa)

Abstract

Petrography and geochemistry of dolerite dykes from cretaceous Bamwa half grabben of North Cameroon in Central Africa have been done. Field work study have shown that dykes swarms of Bamwa basin exceptionally occurred as well exposed dykes vertically overhanging the local granitoids of the basement along trending direction of N155E. Dykes are 1 to 26 m wide and extend on 400 to 500 m. Microscopic observations have revealed various textures, from ophitic, sub-ophitic, classical dolerite to microlitic porphyritic. All dolerites are petrographically composed of plagioclase, oxides, clinopyroxene, rare apatite, chlorite and amphibole crystals, marked by alteration signs. ICP-AES and ICP-MS geochemical analyses of Bamwa dolerites have distinguished the dolerites lavas of basaltic trachyandesite, andesite, dacite and rhyolite composition. Bamwa dolerites are giant dykes which exhibit the geochemical characters of continental tholeiites of low TiO2 composition (TiO2 < 2 wt. %). Petrographic and geochemical studies of the dolerite dykes of Bamwa basin have shown that studied dolerites have experienced a complex petrogenetic history through assimilation and fractional crystallization, fluid infiltration and varying degrees of crustal contamination processes, after a relatively high partial melting rate of enriched subcontinental lithospheric mantle source. Studied dolerites stand as fingerprints of post Pan African magmatic events of arc-back arc setting after subduction.