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Journal of Geosciences and Geomatics. 2020, 8(2), 58-75
DOI: 10.12691/JGG-8-2-2
Original Research

Mineral Chemistry and Descriptive Petrology of the Pan-African High-K Granitoids and Associated Mafic Rocks from Mbengwi, NW Cameroon: Petrogenetic Constraints and Geodynamic Setting

Benoît Joseph Mbassa1, , Emmanuel Njonfang2, Caroline Neh Ngwa1, Michel Grégoire3, Zénon Itiga4, Pierre Kamgang5, Mfomou Ntepe1, Jesús Solé Viñas6, Mathieu Benoit3, Jacques Dili-Rake1 and Ferdinand Mbossi Eddy1

1Institute for Geological and Mining Research, Branch for Geophysical and Volcanological Research, P.O. Box 4110, Yaoundé Cameroon

2Higher Teacher Training College, University of Yaoundé I, P.O. Box 47, Yaoundé, Cameroon

3Géosciences-Environnement-Toulouse, UMR 5563, Université Paul-Sabatier, 14 avenue Édouard-Belin. 31400 Toulouse, France

4Department of Earth Sciences, University of Douala, P.O. Box 24157, Douala, Cameroon

5Department of Earth Sciences, University of Yaoundé I, P.O. Box 812, Yaoundé, Cameroon

6Instituto de Geología, Universidad Nacional Autónoma de México (UNAM), Cd. Universitaria, Coyoacán, 04510 Cd. de México, MEXICO

Pub. Date: July 01, 2020
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Benoît Joseph Mbassa, Emmanuel Njonfang, Caroline Neh Ngwa, Michel Grégoire, Zénon Itiga, Pierre Kamgang, Mfomou Ntepe, Jesús Solé Viñas, Mathieu Benoit, Jacques Dili-Rake and Ferdinand Mbossi Eddy. Mineral Chemistry and Descriptive Petrology of the Pan-African High-K Granitoids and Associated Mafic Rocks from Mbengwi, NW Cameroon: Petrogenetic Constraints and Geodynamic Setting. Journal of Geosciences and Geomatics. 2020; 8(2):58-75. doi: 10.12691/JGG-8-2-2

Abstract

The Mbengwi Pan-African high-K calk-alkaline I-type plutonic rocks consist of granitoids and monzodiorites. These granitoids have a rather homogeneous mineralogical composition made up of calcic amphiboles, ferromagnesian and lithio-aluminous micas, quartz, feldspars, oxides, titanite and incidentally of sulphides, magmatic epidote, apatite, zircon, chlorites and carbonates. Plagioclase compositions range from Na-albite to andesine. Micas are Mg-biotite in monzodiorites and Mg-biotite, Fe-biotite, siderophyllite, lepidomelane, muscovite and phengite in granitoids. Magmatic amphiboles are made up of Fe-hornblende, Mg-hornblende, Fe-edenite, Mg-hastingsite or edenite whereas post-magmatic amphiboles are actinolite. Trace elements analyses reveal: i) low rare earth elements content in monzodiorites (average = 199.9 ppm) compared to granitoids (average = 404.65 ppm); ii) a weak to strong fractionation ((La/Lu)N = 4.5 - 102.96), iii) an enrichment in LILE and LREE relative to HFSE and HREE, and iv) negative anomalies in Rb, K, Sr, Ti, Eu and positive ones in Th and La. Mineralogical and whole rock geochemical results reveal that magmas were produced by vapor-present partial melting of one or several heterogeneous igneous protoliths relatively rich in potassium. The investigated rocks were emplaced between 4 and 34 km deep, at pressure ranging from 1.2 to 9.4 Kbars and were not subjected to post-magmatic alterations according to their Zr/Hf values (> 20). Their differentiation process is the combined result of fractional crystallization and multiple mixing and mingling.

Keywords

Mbengwi, Northwest Cameroon, Pan-African, minerals chemistry, geochemistry

Copyright

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