Magnetic fabrics and emplacement of an anorogenic granitic pluton: case of the Yoli microgranite along the Cameroon Volcanic Line

The purpose of this study is to assess the magnetic fabrics and anisotropy of magnetic susceptibility (AMS) of the Yoli anorogenic microgranite to infer its emplacement mechanism. The Yoli massif is one of the numerous Cenozoic plutons of the Cameroon Magmatic Line cutting across the Central African Pan-African Fold Belt. The pluton, emplaced as result of the reactivation of the N–S oriented Pan-African Mayo Nolti major shear zone, is made of fine-grained and porphyritic microgranite showing evidence of magmatic and submagmatic state deformations. It mostly shows ferromagnetic behavior marked by the presence of the pure magnetite crystals as susceptibility carrier. The pluton internal geometry inferred from magnetic fabrics allows to distinguish two main domains: domain I shows steep plunges and dips magnetic fabrics suggesting fan-like vertical ascent of the magma whereas magnetic fabrics in domain II indicate multidirectional moderate to low plunging lineation suggesting horizontal magma flow following steep dipping planes. These structural features suggest that the magma ascended in domain I through the reactivated N–S fault and flowed toward the south and east. Low P j values (≤1.20) is inferred to magmatic flow, whereas the AMS oblate shapes suggest internal high stress flowing condition during emplacement, probably due to forceful emplacement through ballooning.