Existence de dykes doléritiques anciens à composition de tholéiites continentales au sein de la province alcaline de la ligne du Cameroun. Implication sur le contexte géodynamique

n the Adamawa Plateau (Northern Cameroon), doleritic dykes belong to a magmatic activity which predated the Cenozoic alkaline volcanism of the Cameroon Line. They have the chemical composition of continental tholeiites with Nb-Ta- and Ti-negative anomalies. This magmatism is interpreted as being derived from a sub-continental lithospheric source, which may have been contaminated during a former subduction event, linked to the Pan-African convergence. It is related to an early stage of continental break-up, which was contemporaneous or predated the Cretaceous tholeiitic magmatism of predominantly asthenospheric origin, which indicates a lithospheric thinning

Geochemistry and Geochronology of the Nlonako Alkaline Complex, Central Africa

The Nlonako Anorogenic Complex (NAC) is located in the southern continental sector of the Cameroon Line (CL). It intrudes the Cretaceous sediments and the Pan-african granitogneissic basement and is characterized by an association of diversified plutonic and volcanic rocks. Geochemical studies of major, trace and rare earth elements reveal an alkaline series which corresponds to a gabbro-diorite-monzonite-syenite-granite type. This series comprises two suites: a metaluminous suite made of basic and intermediate rocks, fayalite alkali granite and syenites; and a peralkaline suite including rhyolite and other granites. Both suites are derived from a single, hot and dry magma of basaltic composition. The evolution of the magma is dominated by fractional crystallization of mantle material and was progressively affected by crustal contamination at the end of the differentiation process. The conventional whole-rock Rb/Sr method was performed on three syenites and five granites. The ages obtained range between 44.6 and 49.7 Ma, confirming the Tertiary time of emplacement of the NAC.Keywords: Nlonako Anorogenic Complex (NAC), alkaline series, magma, fractional crystallization, crustal contamination, tertiary age

Ti-bearing aenigmatite from Djinga Tadorgal (Adamawa plateau) and Sao Tomé (Cameroon Line) phonolites: geochemical implications and application of the QUILF thermobarometer for the crystallization conditions

The chemical and structural compositions of aenigmatite from Djinga Tadorgal and Sao Tomé phonolites were compared to those previously described in the felsic lavas and nephelinite from the Adamawa Plateau and Cameroon Line, in order to determine their crystallization temperatures and pressures. Chemical analysis results and the application of QUILF thermobarometer, indicated the equilibrium temperatures between 655 °C and 791 °C, oxygen fugacity (fO2) below the FMQ buffer, pressures near 0.1 GPa and silica activities less than 1.0 for Djinga Tadorgal and Sao Tomé phonolites. The Ti-bearing aenigmatite from Djinga Tadorgal and Sao Tomé phonolites are a late and accessory mineral, resulting from the reaction between Tirich magnetite and Na2O-rich magmatic liquid.Keywords: Peralkaline lavas, mineral chemistry, silica activity, thermodynamic condition

A Typical Sublithospheric Mantle beneath the Tello Region, SE-Ngaoundéré (Cameroon Line)

Peridotite xenoliths, raised to the surface by alkaline basalts or kimberlites,provide us direct information on the processes and composition of the upper mantle. They are the major source of information on the state of stress,pressure and temperature in the deep mantle. They are thus a source of petrological and geochemical information that is generally not available on the Earth’s surface. Fresh spinel-lherzolite xenoliths exhibit a protogranular components of the Tello volcano. The Tello is the continental sector of the Cameroon Line, located in the South East of the town of Ngaoundéré at 75 km approximately between (N7° 13’, N7° 14’) and (E13° 40’ and E13° 60’). Minerals’ composition of the xenoliths is ~64% olivine, ~24% orthopyroxene, ~11% clinopyroxene and ~1% spinel. Significant variation in (Cr/Cr + Al) of the system shows the reciprocal nature of the spinel solution.The Tello spinel lherzolites show internal chemical homogeneity and represent a normal upper mantle. Their mineral chemistries suggest equilibrium condition of 830° - 925° and 1.4 GPa-2.3 GPa. These data suggest that there is good correlation bracket between increasing activity of Al2O3 and decreasing of practionning of TiO2 into spinel. The AlIV and AlVI contents vary by 0.05-0.2 and 0.03-0.2 respectively. The majority of samples caracterise the lithospheric mantle

Evaluation of the impact of gold mining activities on the waters and sediments of Lom River, Wakaso, Cameroon and the restorative effect of Moringa Oleifera seeds

Abstract The impact of gold mining activities on the Lom River in Wakaso (Adamawa Cameroon) and the potential of Moringa Oleifera seeds for the removal of pollutants from wastewater is evaluated on this paper. Water samples were collected for physicochemical (hydrogen potential, electrical conductivity, turbidity and suspended solids) and chemical (major ions and heavy metals) analyses. To evaluate the effect of mining activities on waters and sediments, a combination of multivariate statistical analysis (MSA) and methods to assess the sediment quality was used. The restorative effect of Moringa oleifera seeds was studied with the determination of the maximum removal efficiencies and the maximum adsorption capacities. The results of the physicochemical characterization of waters showed that these waters were slightly acidic to slightly basic (6.12–8.12), weakly conductive (185.8–584.1 μS cm−1), turbid (345–801NTU) and had high content of suspended solids (167–700 mg L−1). The average concentrations of studied heavy metals (Ni, Cd, Fe, Mn, As and Hg) in waters exceeded the limits recommended by the World Health Organization (WHO) standards. Physicochemical characterization of sediments revealed that they were acidic to neutral (5.95–6.80) and organic matter (OM) content ranged from 11.11 to 15.78%. The concentrations of studied trace metals (Ni, Cd, Fe, Hg, Mn and As) in sediments were below the limits recommended by the WHO except for Cd and Hg. The study of the capacity of Moringa oleifera seeds to remove pollutants in waters showed that 54% of the electrical conductivity, 80% of turbidity and 94% of suspended solids were reduced. The maximum removal efficiency of 91.66, 92.30 and 24.48 and the maximum adsorption capacity of 2.4, 2.6 and 16.6 mg g−1were observed for Cd (II), Hg (II) and Fe (II), respectively. Thus, the Moringa oleifera seeds which are locally available natural bio-adsorbent exhibit attractive property to treat wastewater

Geochemistry of the volcanic rocks from Bioko Island (“Cameroon Hot Line”): Evidence for plume-lithosphere interaction

Bioko Island (3008 m a.s.l) is located in the presently more active volcanic zone of the Cameroon Line and composed essentially of alkaline basalts and hawaiites, and lesser mugearites. The rocks show microlitic porphyritic texture with phenocrysts of olivine (83% < Fo < 87%) and clinopyroxene in a matrix of plagioclase, clinopyroxene and oxides. Hawaiites and mugearites also include phenocrysts of plagioclase (An62-67Ab35-32Or3-1). Major element variation diagrams show an increase in SiO2, Al2O3, Na2O and K2O with increasing MgO for the studied rock groups. The rocks are characterized by low (86Sr/87Sr)i ratios (0.70320–0.70406), high ɛNd(t) values (2.56–4.33) and high (206Pb/204Pb)i ratios (20.032–20.035) values. Basalts are enriched in LILE and LREE, and have (Hf/Sm)N = 0.57–1.16. These geochemical signatures are similar to those of the Mount Cameroon rocks, and might be attributed to low degrees of partial melting from a garnet-amphibole-bearing mantle source. The trace elements and isotopic compositions suggest that the parental magma source might have involved HIMU- and EM1-components.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Géochimie des laves basaltiques récentes des zones Nord et Est de Ngaoundéré (Cameroun, Plateau de l’Adamaoua, Afrique centrale): pétrogenèse et nature de la source

Des coulées et projections basaltiques récentes (basaltes: I.D

The Cameroon Hot Line (CHL): A unique example of active alkaline intraplate structure in both oceanic and continental lithospheres

The Cameroon Hot Line (CHL) is an active N30°E tectono-magmatic alignment, extending from Pagalu Island to Lake Chad. Its oceanic sector is comprised of six major volcanoes, and the continental sector of seven major volcanoes, numerous monogenic cones and more than sixty plutonic anorogenic ring complexes. The lavas and plutonic rocks have the typical mineralogy of the alkaline series. Nephelinites and alkaline lamprophyres are also present. The basalts from the oceanic and continental sectors have similar trace elements and Sr and Nd isotope compositions, attesting that the source is sublithospheric and that the continental crust plays no significant role in the magma genesis. Uncommon intermediate lavas originate through mixing between basaltic and felsic magmas. The evolution from basaltic to phonolitic magmas is explained through crystal fractionation. Compositions of most continental trachytes and of rhyolites require a crustal component. Metasomatism of carbonatitic affinity affected the lithospheric mantle during the magma ascent. DM and FOZO mantle components were involved in the genesis of the CHL parental magmas. © 2007 Académie des sciences.SCOPUS: sh.jinfo:eu-repo/semantics/publishe

Petrology of the bimodal Cenozoic volcanism of the Kapsiki plateau (northernmost Cameroon, Central Africa)

SCOPUS: ar.jinfo:eu-repo/semantics/publishe