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Déruelle, B., Ngounouno, I., Demaiffe, D., “The ‘‘Cameroon Hot Line” (CHL): a unique example of active alkaline intraplate structure in both oceanic and continental lithospheres”, Comptes Rendus Geosciences, 339, 589-600, 2007.

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Article

Petrological and Geochemical Characteristics of the Cretaceous Ngaou Boh Anorogenic Complex (Adamawa Plateau, Cameroon Line): Preliminary Constraints

1Department of Earth Sciences, University of Douala, P.O. Box 24157, Douala, Cameroon

2Institute for Geological and Mining Research, Laboratory of Ore mineral Processing, P.O. Box 4110, Yaoundé, Cameroon

3Department of Earth Sciences, University of Yaoundé, P.O. Box 812, Yaoundé, Cameroon

4Higher Teacher Training College, University of Bamenda I, P.O. Box 39, Yaoundé, Cameroon

5Higher Teacher Training College, University of Yaoundé I, P.O. Box 47, Yaoundé, Cameroon

6Université Paris-Saclay, Sciences de la Terre, Volcanologie, Planétologie, UMR CNRS, 8148 GEOPS, bât 504, F-91405, Orsay, France

7Université européenne de Bretagne, CNRS UMR, 6538 Domaines océaniques, UBO-IUEM, 6 avenue Le Gorgeu, CS 93837, F-29238, Brest cedex 3, France


Journal of Geosciences and Geomatics. 2021, Vol. 9 No. 4, 160-176
DOI: 10.12691/jgg-9-4-1
Copyright © 2021 Science and Education Publishing

Cite this paper:
Zénon Itiga, Benoît Joseph Mbassa, Rose Noël Ngo Belnoun, Pierre Wotchoko, Dieudonné Tchokona Seuwui, Sébastien Owona, Jacques-Marie Bardintzeff, Pierre Wandji, Hervé Bellon. Petrological and Geochemical Characteristics of the Cretaceous Ngaou Boh Anorogenic Complex (Adamawa Plateau, Cameroon Line): Preliminary Constraints. Journal of Geosciences and Geomatics. 2021; 9(4):160-176. doi: 10.12691/jgg-9-4-1.

Correspondence to: Zénon  Itiga, Department of Earth Sciences, University of Douala, P.O. Box 24157, Douala, Cameroon. Email: zenonitiga@yahoo.fr

Abstract

The Cretaceous Ngaou Boh anorogenic complex (NBAC) located in the far North Adamawa Plateau, the centre domain of the Cameroon Line constitutes a plutonic-volcanic ring association. The whole rock K-Ar datation yields a crystallization age of ca. 74 Ma. Plutonic rocks comprise abundant alkali feldspar granites, scarce clinopyroxene-amphibole gabbros and alkali feldspar syenites. Alkali feldspar granites are leucocratic, coarse to fine-grained; quartz and K-feldspars are the major rock-forming mineral, besides minor oligoclase, biotite and accessory phases as sphene, zircon and opaques. Alkali feldspar syenites are mesocratic coarse-grained, mainly composed of K-feldspars with small amounts of quartz and biotite. Volcanic rocks consist of a basanite-trachyte-rhyolite suite. Basanites contain olivine and diopside phenocrysts and a groundmass essentially composed of plagioclase and titanomagnetite. Biotite-clinopyroxene trachytes and clinopyroxene-amphibole rhyolites have an almost homogeneous modal composition, mainly made up of sanidine and anorthoclase microliths, scarce phenocrysts of quartz, and minor crystals of biotite, clinopyroxene (augite) amphibole (pargasite, sandagaite); Fe-Ti oxides (ilmenite, titanomagnetite) and fibreglass are often isolated in the groundmass. Plutonic rocks are alkaline, weakly metaluminous with some alkali feldspar granites displaying agpaitic or peralkaline feature. Incompatible Trace elements (HFSE and LILE) distribution and chondrite-normalized REE patterns evidence a significant petrogenetic link between clinopyroxene-amphibole gabbros, alkali feldspar syenites and alkali feldspar granites. All the analysed samples are enriched in incompatible elements, indicating melts from spinel and garnet-bearing mantle source close to OIB component. Indeed, the (Tb/Yb)N ratios of both basanites (2.3-2.5) and clinopyroxene-amphibole gabbros (1.4-1.9) suggest different parental magma sources. Alkali feldspar granites appear as residue of magma differentiation led by crystal fractionation of liquid derived from the partial melting of spinel peridotite mantle. Clinopyroxene-amphibole rhyolites and biotite-clinopyroxene trachytes (Mg#=0.0-15.4) derive through fractional crystallization from basanites (Mg#=64.3-60.1), the most primitive mafic parental melt. Both plutonic rocks and lavas trends evidence a bimodality highlighted by a pronounced “Daly gap”.

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