Petrology Framework of Guido-Gormaya Dolerite Dyke in North-Cameroon, Central Africa: Petrogenesis and Geodynamic Implications

Abstract

Dolerite dykes are considered worldwide as deep-level plumbing systems consisting of giant dyke swarms, sill provinces and layered intrusions thus can be linked to regional-scale uplift, continental rifting and breakup. The local basement of Guido-Gormaya locality in the northern Cameroon at Poli region is transected by numerous doleritic dykes of NW-SE and N-S trending directions. Doleritic dykes are extend along strike from 100 to 500 m and display 4 to 10 m, up to 40 m in size. Petrographic study shows that the studied dolerites are coarse greenish and exhibit ophitic to sub-ophitic and intersertal textures. They are composed of phenocrysts and microliths of plagioclase, amphibole, clinopyroxene and oxides. Microprobe mineral analyses have shown that plagioclase composition varies widely from albite, oligoclase, and andesine to labrador. Clinopyroxene is an augite-type exhibiting wide variation in contents between Al2O3, TiO2 and Na2O. Whole rock geochemical analyses through ICP-AES and ICP-MS methods have distinguished dolerites of trachyandesite, trachyte and rhyolite composition of quartz normative and low Mg-number. Magmas should have been differentiated through fractional crystallization coupled with crustal materials contamination or mixing processes for some ones. Guido-Gormaya dolerites belong to the orogeny type basalts originated from phlogopite-bearing E-MORB type magmatic source at shallow depth, which have experienced a relatively high partial melting rate. Studied dolerites are orogenic basalts, fingerprints of an extensional phase of a specific regional-scale tectonic event, which is supposed to be a mantle plume impact.