Structural study of the Foréké-Dschang trachytic dome (Mount Bambouto, West Cameroon): An anisotropy of magnetic susceptibility (AMS) approach

Abstract

The Tertiary trachytic dome of Foréké-Dschang is located on the southwestern slope of Mount Bambouto. This dome, made of porphyritic and microlitic lavas which enclose sanidine, pyroxene and oxides, is dated at 16–8.8Ma and was emplaced in gneisses belonging to the Pan-African basement. The mean magnetic susceptibility magnitude Km values of the trachytic dome show a ferromagnetic behavior in 79% of the stations, likely due to the presence of more or less maghemitized titanomagnetite based on thermomagnetic and hysteresis data.The Foréké-Dschang dome is elliptical and strikes NE–SW, parallel to a border fracture. The Pan-African host gneisses display N70° striking and steeply dipping foliations crosscut by the dome. Some Tertiary sinistral reworking of these foliations may have induced the opening of a local tension gash in agreement with the regional model suggesting that the N30° Cameroon Volcanic Line opened as a mega-tension gash with respect to the N70° Adamawa fault zone. Two petrographic types are recognized in the trachytic dome, aphyric (domain I) or porphyritic (domain II). The magnetic foliations show an outward-dipping concentric pattern in domain I. A flat lying zone with the highest magnetic anisotropy (18%) is regarded as overlying the vent. The organization of magnetic fabrics suggests that domain II was emplaced before domain I. As a whole, the Foréké-Dschang trachytes represent a multilobate dome emplaced in a pulsatory manner.