Geochemistry and geochronology of the Méiganga metadiorite: implications on the timing of D2 deformational phase in Adamawa Yadé Domain in Cameroon

Abstract

The metadiorite of Méiganga forms an ovoid body intruding metasedimentary gneisses in the area of Méiganga city. It shows schistosity, banded structure and is made up of green hornblende, biotite, antiperthitic plagioclase, quartz, zircon, opaque minerals and chlorite. Imprints of D2, D3 and D4 deformation phases are identical in the metadiorite and the amphibole biotite gneiss, leaving no doubt as to the syn-D2 emplacement and crystallization of the protolith of the metadiorite. The metadiorite samples display high-K calc-alkaline to shoshonitic characteristics and possess features of I-type granitoids. They exhibit relative low enrichment of LREE with respect to HREE, (La/Yb)_N = 9.5-11.3, and moderate negative Eu anomalies (Eu/Eu* =0.80-0.83). Optical features of the zircon grains of the metadiorite and its syn-D2 emplacement and crystallisation indicate that the zircon evaporation ²⁰⁷Pb/²⁰⁶Pb ages (614.1 ± 3.9 Ma and 619.8 ± 9.8 Ma) of this rock date the D2 deformation phase in the Méiganga area. Comparison with other sectors of the Adamawa Yadé Domain (AYD) shows the close synchronic character of the D2 deformational phase in central Cameroon (Méiganga, Tibati, Ngaoundéré areas) and the diachronic character of this phase in central and western Cameroon. We found that a similar chronological evolution has been demonstrated in the Macururé Domain of the Sergipano Belt (NE Brazil).

Keywords: syn-D2 granitoid; ²⁰⁷Pb/²⁰⁶Pb age; Central Pan-Africa Fold Belt; Sergipano Belt