Petrographic and Geochemical Study of the Yandingui-Yangba Massif (Bafia, Central Cameroon): Geodynamic Implications

Abstract

Several diverse models and hypotheses have been proposed to understand the dynamics of the Central African Pan-African Belt. The lack of agreement among these proposals suggests that it would be better to continue large scale mapping to provide answers to this regional issue. In this perspective, the NE-SW oriented Yandingui-Yangba rock massif, located about thirty kilometers north of Bafia, and intrudes a Precambrian metamorphic basement. The petrographic study of the massif reveals two lithological units: the metamorphic unit, which includes orthogneiss and amphibolite enclaves, and the intrusive magmatic unit, composed of amphibole-biotite granites. Geochemically, the rocks of Yandingui-Yangba (67.85 < SiO<sub>2</sub> < 71.06) are metaluminous I-type granites (A/CNK < 1.1), associated with the shoshonitic series and of magnesian nature (0.67 < FeOt/(MgO + FeOt) < 0.78). Mantle-normalized trace element spectra show a subparallel pattern between the granites and orthogneiss, indicating a common origin. These rocks were emplaced in a volcanic arc setting in a subduction-collision context. The presence of positive anomalies in U, K, Pb, and Zr, and negative anomalies in Th, Nb, and Ti, is characteristic of crustal-derived rocks. The magma that generated these granites resulted from the partial melting of metagreywackes in the lower crust, as evidenced by the low concentrations of Ni and Cr. This melting was likely facilitated by heat influx from mantle-derived magma during the Pan-African orogeny.