Geochronology and petrogenesis of the Pan-African granitoids from Mbondo-Ngazi Tina in the Adamawa-Yadé Domain, Central Cameroon

The Mbondo-Ngazi Tina area belongs to the eastern part of the Adamawa-Yadé Domain (AYD), which corresponds to the central domain of the Central African Fold Belt (CAFB) in Cameroon. This area comprises three groups of granitoids including granites, syenites, and diorites, which are chemically similar to quartz monzonites and nepheline syenites, and monzodiorites, respectively. These granitoids are metaluminous and I-type rocks, with the dioritic rocks being ferroan and high-K calc-alkaline, while others are magnesian and shoshonitic rocks. The Ti-in-zircon thermometer suggests crystallization temperatures of 678–811 °C and 658–768 °C for monzonites and syenites, respectively. Their zircon trace element distribution and patterns coupled to the whole-rock geochemical features indicate that the Mbondo-Ngazi Tina granitoids were most likely originated from the mixture between crust- and mantle-derived melts, with high crustal portion for the quartz monzonites and nepheline syenites, and strong involvement of mantle component for the monzodiorites. The Ce/Ce*, Eu/Eu*, Th/U, and Zr/Hf of zircons suggest that the crystallization of magma melts took place under variable oxidizing and oxygen fugacity conditions at temperature of 678–768 °C. LA-ICP-MS U–Pb zircon analyses yield emplacement age of 576.4 ± 1.9 Ma and 585.9 ± 2.1 Ma for the quartz monzonites and nepheline syenites, respectively. These ages suggest that these rocks are post-tectonic granitoids emplaced during relaxation stages after the collision between the Amazonian-West African cratons and the São Francisco-Congo and Saharan cratons. The post-collisional extensional regime is related to the development of large shear zones across the Pan-African/Brasiliano belts, which played a role for the ascent and emplacement of post-tectonic granitoids in response to lithospheric delamination. This explains that such granitic plutons are widespread in the CAFB and adjacent Brasiliano belt.