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In this study, field descriptions of the dolerite dykes cross‐cutting the Pan‐African basement (DPB) and the dolerite and gabbroic dykes cross‐cutting the Cretaceous sedimentary basin (DGCSB) are used together with petrographic, bulk‐rock geochemistry, as well as Sr–Nd–Pb isotopic data to constrain the geodynamic setting and origin of these mafic (basanite, basalt and basaltic andesite in composition) rocks that outcrop in the Figuil–Léré area. The DPB dykes are alkaline with SiO2 of 46.63–49.03 wt% and MgO of 3.93–7.11 wt%. In contrast, the DGCSB dykes are subalkaline with SiO2 ranging between 50.24 and 53.16 wt% and MgO fluctuating between 5.22 and 7.90 wt%, comparable to dykes described in other regions of the Cameroon Line (CL). The rocks studied belong to the tholeiitic series and were emplaced in within‐plate basalts (WPB) and mid‐ocean ridge basalts (MORBs) setting. The variations in major and trace elements from the basanite to basaltic andesite compositions are dependable with fractional crystallization (FC) of different mineral phases such as opaque minerals, olivine, clinopyroxene, amphibole and alkali feldspar. Most samples exhibit negative Nb–Ta and positive Sr anomalies, which together with the negative correlation between MgO and 87Sr/86Sr, and isotopic ratio of 206Pb/204Pb <19.5 (18.27–19.49) suggests interactions of crustal components. Nevertheless, this contamination seems limited because there is a positive correlation between SiO2 and 143Nd/144Nd plot and low Ba contents (72–210 ppm) of the samples compared to the mid‐continental crust (259–628 ppm). Trace element modelling proposes a derivation of the Figuil–Léré dykes from parental melts generated by 4%–15% partial melting of a source containing garnet peridotite in the mixed lithospheric–asthenospheric mantle. The isotopic data of the dykes studied with hybrid magma composition are characterized by more radiogenic 87Sr/86Sr, 143Nd/144Nd and 206Pb/204Pb isotopic ratios with a dominant mixing of depleted MORB mantle (DMM)–enriched mantle 1 (EM1)–enriched mantle 2 (EM2), like those of other mafic dykes of the CL. [ABSTRACT FROM AUTHOR]

Abstract The most important part of geochemical studies of lavas along the Cameroon Volcanic Line (CVL) has so far focused on the southern and central segments of the line leaving behind the northern-most part of the CVL with few and incomplete data. This study presents the case of the Gawar, Zamay and Minawao volcanoes, for which, for the first time, petrological and geochemical data comprising major and trace elements, and Strontium-Neodymium-Lead isotopes have been used to investigate the mantle source and the genetic relation between the felsic and mafic lavas in these areas. Volcanics in the Gawar are mainly basanites while those from Minawao and Zamay are essentially trachytes. The Nb/Ta and Zr/Hf ratios are similar for both the mafic and felsic rocks suggesting a dominant evolution of the magma by fractional crystallization. Primitive-mantle normalized multi-element diagrams of the mafic lavas are comparable to those reported in other volcanoes along the CVL; characterized by the depletion of Heavy Rare Earth Elements (HREE) and enrichment of Light Rare Elements (LREE), indicative of an enrichment and the presence of garnet in the source. Modeled results for melting using primitive mantle normalized values of Sm/Yb vs La/Sm indicate a low degree (<2%) of partial melting of a source with less than 4% garnet. This is consistent with chondrite normalized REE patterns characterized by the fractionation of HREE relative LREE. Trace elements composition and isotope data preclude the significant role of the continental crust in the magmatism of the mafic rocks. However, during evolution to the felsic lavas, the role of the crust became more important. The ranges for 87Sr/86Sr (0.70356–0.70362), 143Nd/144Nd (0.512928–0.512931), 206Pb/204Pb (19.62–19.72), 207Pb/204Pb (15.65–15.68) and 208Pb/204Pb (39.31–39.45) isotopic composition for mafic samples (Gawar) are limited and fall within the range of mafic lavas studied along the CVL. The isotopic signatures and trace element characteristics are consistent with an asthenospheric origin, however with contribution from the sub-continental lithospheric Mantle (SCLM). The two sources have imparted characteristics of more than two mantle components involving the Depleted MORB-like mantle, HIMU and Enriched mantle (EM1). Highlights • Geochemical data and Sr-Nd-Pb isotopes have been used to explore the mantle source. • Similar Nb/Ta and Zr/Hf ratios suggest magma evolution by fractional crystallization. • Sm/Yb vs La/Sm graph show <2% partial melting of a source with ≈4% garnet. • The ranges for isotopic data of mafic samples are within the range of CVL lavas. • Isotopic and trace element data are consistent with an asthenospheric origin. [ABSTRACT FROM AUTHOR]

Abstract: The concentrations of major and trace elements and the isotopic compositions were measured in felsic lavas of the Bamenda Mountains, an extinct volcanic center of the West Cameroon Highlands (WCH), in order to assess the relative roles of mantle versus crustal magma sources in the evolution of silicic magmatic systems. These silicic volcanics are composed of benmoreites, trachytes and rhyolites associated with alkaline basaltic lavas and have characteristics of A-type magmas. Chemical diagrams show two magmatic lineages based on the ratios of HFSE/LILE (e.g. Hf/Rb: 0.19–0.34 and 0.11–0.23), the degree of fractionation (La/Sm: 5.2–6.4 and 6.5–7.5) and the contents of REE; they are respectively referred to as less-differentiated felsic lavas (LDFL) and high-differentiated felsic lavas (HDFL). Their evolution is mainly governed by alkali feldspar-dominated fractional crystallization. The K/Ar ages on trachytes range from 27.40±0.50 to 12.74±0.25Ma with the HDFL being mostly younger. Their ε Nd range mostly between −0.88 and+2.43 with one value at −3.43 precluding their derivation from melting of a continental crust. Besides the most negative value (−3,43) obtained in trachyte BA63 remains high compared to −20.28 calculated for a Bamemda Pan-African granitoid suggesting very low crustal contamination. However, the fact that this lower ε Nd in BA63 is not followed by the corresponding low Ce/Pb and high La/Nb rather indicates a selective role of crustal contamination. This feature seems characteristic of the felsic lavas of the whole Cameroon Volcanic Line. The isotopic and trace element variations observed for the Bamenda felsic lavas are most consistent with a source in the continental lithospheric mantle. [ABSTRACT FROM AUTHOR]