Arc magmatism in the Nkoula granitoid suites, Central African Fold belt in Cameroon: evidence of a metasomatized high oxidized S- and I- type magma

• Published in: International journal of earth sciences : Geologische Rundschau Vol. 111; no. 4; pp. 1223 - 1250
• Main Authors: Ntieche, Benjamin, Wokwenmendam Nguet, Pauline, Moundi, Amidou, Mekala, Ram Mohan, Mounjouohou, Mahomed Aziz, Atsalang, Chimene Grace Staelle, Nchouwet, Zakari
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.06.2022; Springer Nature B.V
• Subjects: Amphiboles; Asthenosphere; Barium; Biotite; Chemical composition; Continental crust; Crystallization; Depletion; Earth and Environmental Science; Earth Sciences; Feldspars; Fractional crystallization; Geochemistry; Geology; Geophysics/Geodesy; Isotopes; Lanthanum; Lava; Magma; Melting; Mineral Resources; Niobium; Ocean circulation; Oceanic crust; Original Paper; Orogeny; Orthoclase; Oxidation; Petrography; Petrology; Plagioclase; Quartz; Rocks; Sedimentology; Structural Geology; Subduction; Tantalum; Titanite; Titanium; Trace elements; Upwelling; Nkoula granitoid suites; High-K calc-alkaline; Adamawa-Yade; I-and S-type; Subduction
• ISSN: 1437-3254; 1437-3262
• DOI: 10.1007/s00531-022-02175-4

Situated in the Tikar plain, the Nkoula granitoid suites consist of granites, quartz monzonites and syenites. The petrography, mineral chemistry and whole-rock geochemistry of the studied granitoids were done. The rocks are mainly made up of quartz, K-feldspar, plagioclase, amphibole, biotite ± sphene ± epidote. They are I-and S-type, metaluminous to peraluminous, magnesian and belong to high-K calc-alkaline to shoshonitic series. K-feldspars are orthoclase and plagioclases have the chemical composition of oligoclase. Biotites are reequilibrated primary Mg-rich while amphiboles are magmatic, calcic and essentially magnesian. All the granitoids display LREE enrichment and HREE depletion with negative Eu anomaly. The primitive mantle normalized trace element patterns display Rb, Ba, U, Th and Pb enrichment and depletion in Nb, Ta, Ti and P. The major and trace element variations indicate that fractional crystallization plays an important role during the magmatic processes of the S-type magma. The trace element ratios Ba/Rb, Nb/Ta, Y/Nb, Th/La, Sm/La, Hf/Sm and Ta/La, along with the biotite and amphibole chemistry, point to a crust-mantle mixed source for the Nkoula granitoid suites. The granitoids emplaced in the syn-collisional and volcanic arc setting. The most likely processes for the Nkoula granitoid consist of the partial melting of the subducted slab and the probable contribution of a mantle component. The break-off of the subducted slab may have favored the upwelling of the asthenosphere that supplies heat for the partial melting of the slab and crust components. The Nkoula granitoid magma displays 3–5 wt.% of water and was formed under high oxidizing conditions. They were emplaced at relatively shallow depth (3–9 km) and crystallized at about 800–900 °C in the Adamawa-Yade continental crust due to the subduction of the Yaounde oceanic crust under the Adamawa-Yade domain during the Pan-African orogeny.