ST
Professeur
Scientific activity
Researcher profile
Faculty researcher at the University of Yaoundé I. Grade: Professeur.
Scientific publications
Diddi Hamadjoda Djamilatou, Nils Lenhardt, Pierre Christel Biakan à Nyotok, Safianou Ousmanou, Guillaume Boudoire, Petrus le Roux and 3 more
Geochemistry
Benoît Joseph Mbassa, Olivier Vanderhaeghe, Michel Gregoire, Mathieu Benoît, Zenon Itiga, Caroline Ngwa Neh and 1 more
Springer Link (Chiba Institute of Technology)
The sub-continental lithospheric mantle (SCLM) beneath the Cameroon Volcanic Line (CVL) is vertically and laterally heterogeneous, consisting of a complex mixing of DMM, HIMU, and EM1, affected by modal or cryptic metasomatism, depending on the area. The petrography, whole-rock geochemical data, and minerals’ chemical composition of lavas and mantle xenoliths from the Bini Warack area, combined with Sr isotope compositions, provide constraints on the origin and thermochemical evolution of the SCLM beneath this sector of the CVL. The host lavas are basanite, basalt, and latite with OIB affinity, characterized by moderate to high silica and alkali contents (SiO2 = 42.35–56.56 wt%, K2O+Na2O = 2.34–7.07 wt%), a high Ba/Rb ranging from 12.2 to 26.1, a low Rb/Sr from 0.03 to 0.08, strong enrichment in LREE relative to HREE (LaN/YbN: 9.3–30), and moderate enrichment in radiogenic isotopes (e.g., 0.702987 < 87Sr/86Srinitial < 0.703206; 0.512854 <143Nd/144Ndinitial < 0.512918) with positive εNdinitial (+4.84 to +6.09). These features are consistent with an origin of the lavas by a low degree of partial melting (<2%) of a lherzolitic mantle source containing 2% to 6% garnet. These lavas have then evolved by fractional crystallization without any evidence of crustal contamination. The studied mantle xenoliths are spinel-bearing lherzolites, characterized by U/Th ratios typically lower than 1, a slight enrichment in LILE relative to HFSE, and mainly consist of minerals with fertile composition (Fo84-91; spinel Cr#: 0.1–0.22; Al-rich pyroxenes). They are consistent with refractory mantle peridotite that evidences low partial-melting degrees. Trace element concentrations of host lavas (high Ba/Rb: 12.2–26.1 and low Rb/Sr: 0.03–0.08), together with olivine’s crystals chemical features (high Ca/Fe and 100*Mn/Fe ratios; low 100*Ni/Mg ratios) and low Ca/Al ratios (<5) of clinopyroxenes in spinel-bearing lherzolite xenoliths suggest that the SCLM beneath the Bini Warack area is likely a juvenile lithospheric mantle which that undergone a carbonate-rich metasomatism.
Benoît Joseph Mbassa, Olivier Vanderhaeghe, Michel Gregoire, Mathieu Benoît, Zénon Itiga, Caroline Ngwa Neh and 1 more
Bulletin de la Société Géologique de France
The sub-continental lithospheric mantle (SCLM) beneath the Cameroon Volcanic Line (CVL) is vertically and laterally heterogeneous, consisting of a complex mixing of DMM, HIMU, and EM1, affected by modal or cryptic metasomatism, depending on the area. The petrography, whole-rock geochemical data, and minerals’ chemical composition of lavas and mantle xenoliths from the Bini Warack area, combined with Sr isotope compositions, provide constraints on the origin and thermochemical evolution of the SCLM beneath this sector of the CVL. The host lavas are basanite, basalt, and latite with OIB affinity, characterized by moderate to high silica and alkali contents (SiO 2 = 42.35–56.56 wt%, K 2 O+Na 2 O = 2.34–7.07 wt%), a high Ba/Rb ranging from 12.2 to 26.1, a low Rb/Sr from 0.03 to 0.08, strong enrichment in LREE relative to HREE (La N /Yb N : 9.3–30), and moderate enrichment in radiogenic isotopes ( e.g. , 0.702987 < 87 Sr/ 86 Sr initial < 0.703206; 0.512854 < 143 Nd/ 144 Nd initial < 0.512918) with positive εNd initial (+4.84 to +6.09). These features are consistent with an origin of the lavas by a low degree of partial melting (<2%) of a lherzolitic mantle source containing 2% to 6% garnet. These lavas have then evolved by fractional crystallization without any evidence of crustal contamination. The studied mantle xenoliths are spinel-bearing lherzolites, characterized by U/Th ratios typically lower than 1, a slight enrichment in LILE relative to HFSE, and mainly consist of minerals with fertile composition (Fo 84-91 ; spinel Cr#: 0.1–0.22; Al-rich pyroxenes). They are consistent with refractory mantle peridotite that evidences low partial-melting degrees. Trace element concentrations of host lavas (high Ba/Rb: 12.2–26.1 and low Rb/Sr: 0.03–0.08), together with olivine’s crystals chemical features (high Ca/Fe and 100*Mn/Fe ratios; low 100*Ni/Mg ratios) and low Ca/Al ratios (<5) of clinopyroxenes in spinel-bearing lherzolite xenoliths suggest that the SCLM beneath the Bini Warack area is likely a juvenile lithospheric mantle which that undergone a carbonate-rich metasomatism.
Nguihdama Dagwai, Pierre Kamgang, Mbowou Gbambié Isaac Bertrand, Gilles Chazot, Ismaı̈la Ngounouno
Open Journal of Geology
The alkaline volcanism of the Cameroon Volcanic Line in its northern domain has raised many fresh enclaves of peridotites. The samples selected come from five (05) different localities (Liri, in the plateau of Kapsiki, Mazélé in the NE of Ngaoundéré, Tello and Ganguiré in the SE of Ngaoundéré and Likok, locality located in the west of Ngaoundé). The peridotite enclaves of the above localities show restricted mineralogical variation. Most are four-phase spinel-lherzolites, indicating that this is the main lithology that forms the lithospheric mantle below the shallow zone. No traces of garnet or primary plagioclase were detected, which strongly limits the depth range from which the rock fragments were sampled. The textures and the wide equilibrium temperatures (884˚C - 1115˚C) indicate also entrainment of lherzolite xenoliths from shallow depths within the lithosphere and the presence of mantle diapirism. The exchange reactions and equilibrium state established in this work make it possible to characterize the chemical composition of the upper mantle of each region and test the equilibrium state of the phases between them. Variations of major oxides and incompatible elemental concentrations in clinopyroxene indicate a primary control by partial melting. The absence of typical “metasomatic” minerals, low equilibration temperatures and enriched LREE patterns indicate that the upper mantle below septentrional crust of Cameroun underwent an event of cryptic metasomatic enrichment prior to partial melting. The distinctive chemical features, LREE enrichment, strong U, Ce and Pr, depletion relative to Ba, Nb, La, Pb, and T, fractionation of Zr and Hf and therefore ligh high Zr/Hf ratio, low La/Yb, Nb/La and Ti/Eu are all results of interaction of refractory peridotite residues with carbonatite melts.
Luc Achille Ziem A Bidias, Leandre Harold Njeuatchoua Kameni, Amidou Moundi, Pierre Kamgang
International Journal of Geoheritage and Parks
This study was carried out in the Foumbot-Kouomboum region (Noun Plain, Cameroon Volcanic Line), with the main objective of presenting (i) the geomorphological characteristics of the volcanic landforms and (ii) the inventory and evaluation of the main geomorphosites in the Foumbot-Kouomboum region. All the geomorphosites selected in this study are of volcanic origin and include four crater lakes (Monoun Lake, Mfouet Lake, Negop-Ghang Lake, Ngouondam Lake) and four strombolian cones (Mfomben, Chapchap, Makwet, Nord-Njitande). Most of these volcanic geomorphosites are accessible and have volcanic features that highlight the geological significance of this region, warranting national and international recognition. These volcanic landscapes have relatively high scientific and additional values. The integrity of many of the selected geomorphosites is preserved and they are representative of the regional geomorphology. Some artisanal and industrial quarries, as well as agro-pastoral activities, tend to degrade certain geomorphosites that currently lack legal protection. The results of the inventory and evaluation of the selected geomorphosites show that they have enormous geotourism, educational and cultural potential that can be studied in depth with the aim of creating an UNESCO Global Geopark. Therefore, it is highly recommended to implement geoconservation policies for these geomorphosites. This will help to safeguard and enhance the natural beauty and unique volcanic landscapes they possess.
Nguihdama Dagwaï, Pierre Kamgang, Mbowou Gbambié Isaac Bertrand, Gilles Chazot, Ismaı̈la Ngounouno
Advances in Geological and Geotechnical Engineering Research
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.
Benoît Joseph Mbassa, Zénon Itiga, Caroline Neh Ngwa, Moïse Bessong, Mfomou Ntepe, Emmanuel Njonfang and 1 more
Arabian Journal of Geosciences
Nicaise Blaise Tchuimegnié Ngongang, Merlin Patrick Njombie Wagsong, François Mvondo Owono, Innocent Badriyo, Philippe Essomba, Natalie Love Ngongang Tchikankou and 3 more
Open Journal of Geology
Alkaline basalts of Bafang and its environs are consisted of feldspars, olivines, pyroxenes and oxides which appear as phenocrysts, microphenocrysts and microcrysts. Feldspars are plagioclases (An67.97-15.84Ab69.19-30.43Or20.59-1.51) and anorthoclases (Ab68.11-61.20Or33.87-20.91An10.98-4.93). Plagioclases are the most abundant amount these feldspars. Anorthoclases appear only in mugearite (BAF 3 and BAF 37) the most differentiated of the studied alkaline-basalts. In High Magnesian basalt, (HMg-B) plagioclases are labradorites (An67.97-59.30Ab38.74-30.43Or2.75-1.60) and sanidine (An45.44-31.82Ab62.66-51.79Or5.52-2.77), whereas in Low Magnesian basalt (LMg-B) there are labrador (An67.4.75-51.96Ab44.98-33.72Or3.06-1.51), andesine (An45.44-31.82Ab62.66-51.79Or5.52-2.77), oligoclase (An26.65-15.84Ab69.19-63.57Or20.59-8.55) and anarthoclase (Ab68.11-61.20Or33.87-20.91An10.98-4.93). Olivines are magnesian (Fo86.7-50.1) and ferriferous (Fo48.8-37.8). In HMg-B, olivine are only magnesian. These olivines are chrysolites and hyalositerite. In LMg-B, olivines are magnesian and ferriferous with the predominance of ferriferous. They are chrysolites, hyalositerite and hortonolite. Pyroxenes are Ca, Mg and Fe clinopyroxenes. There are diopsides (Wo51.94-45.02En44.41-33.16Fs16.42-10.70) and augites (Wo44.88-43.64En41.03-37.04Fs18.25-14.43). Oxides are magnetites represented by ulvospinel (Usp90-75Sp2-7Mt5-23). Fractionation of ferromagnesian minerals (opaque oxide, olivine and pyroxene) is the main differentiation process. Two stages of fractional crystallization can be distinguished: the first stage comes with basanites and the second with hawaiites to mugearites. Chemical compositions of phenocrystals in studied basaltics lavas record signatures of magma recharge by pulsatory intrusions of new magma into the existing magma reservoir before the eruptions.
Nguihdama Dagwaï, Pierre Kamgang, Mbowou Gbambié Isaac Bertrand, Gilles Chazot, Ngounouno Ismaà ̄la
International Journal of Advanced Geosciences
Spinel-lherzolite xenoliths trapped within the alkali basalts flow in the Liri region (Kapsiki Plateau) have a protogranular texture and consist of olivine, orthopyroxene, clinopyroxene and spinel crystals. These xenoliths are residues of partial melting of the primitive mantle, with the low titanium content in clinopyroxene crystals (TiO2 < 0.5 wt.%). The clinopyroxene of the spinel-lherzolite xenoliths from Liri, are divided into two distinct groups according to their trace element characteristics. The variations in the rare earths elements make it possible to classify the different clynopyroxenes in two groups: the first group consisting of the samples of Liri (Liri 1, Liri 02, Liri 3, Liri 05 and Liri 5) rich in light rare earths elements (LREEs), with ratios (Ce/Yb)N normalized which vary between 3.00 and 7.78. It is probably a cryptic metasomatism due to the absence of hydrated minerals (such as amphibole) which caused these enrichments. The second group comprises samples of Liri (Liri 01, Liri 2, Liri 04, Liri 4) depleted in light rare earths elements, with the ratio in (Ce/Yb) N < 1.2. This depletion in rare earths elements results from the extraction of the melting liquid.   Â
Merlin Gountié Dedzo, Asobo Nkengmatia Elvis Asaah, Eric Martial Fozing, Boris Chako Tchamabé, Ghislain Zangmo Tefogoum, Nguihdama Dagwaï and 4 more
Journal of African Earth Sciences
Benoît Joseph Mbassa, Emmanuel Njonfang, Michel Grégoire, Zénon Itiga, Pierre Kamgang, Mathieu Benoît and 3 more
Arabian Journal of Geosciences
Benoît Joseph Mbassa, Pierre Kamgang, Michel Grégoire, Emmanuel Njonfang, Mathieu Benoît, Zénon Itiga and 4 more
Comptes Rendus Géoscience
The Mbengwi plutonics consist of intermediate to felsic granitoids forming a continuous magmatic series from monzonite to granite and mafic intrusions. Their mineralogical composition consists of quartz, plagioclases, K-feldspars, biotite, muscovite, and amphibole. The accessory phase includes opaque minerals + titanite ± apatite ± zircon, while secondary minerals are pyrite, phengite, chlorite, epidote, and rarely calcite. These plutonics are assigned high–K calc–alkaline to shoshonitic series, metaluminous to weakly peraluminous and mostly belong to an I–type suite (A/CNK = 0.63–1.2). They are typically post–collisional, with a subduction signature probably being inherited from their protoliths emplaced during the subduction phase. The Sr and Nd isotopic data evidence that these plutonics result from melting of the lower continental crust with variable contribution of the oceanic crust. Their geochemical features are similar to those of western Cameroon granitoids related to the Pan–African D 1 event in Cameroon.
Merlin Gountié Dedzo, Pierre Kamgang, Emmanuel Njonfang, Ghislain Zangmo Tefogoum
Current Research in Geoscience
Hazards related to pyroclastic density current continue to raise victims on many volcanoes in our planet. The Cameroon is not spared to this type of hazard because deposits of pyroclastic flows and surges are found on Mount Bamenda; products of this volcano are relatively young (27-0 Ma). Besides Mount Bamenda, Mounts Bambouto and Oku are the only volcanoes located in the central part of the Cameroon Volcanic Line where these ignimbritic deposits are found. Several factors highlight dangerousness and damage that can cause ignimbritic flows on the flanks of this volcano. This is essentially the high aspect ratio of these ignimbrites, the important population (about 750,000 people) that lives on the slopes and around the volcano. In order to have an idea of a nowadays ignimbritic eruption scenario on Bamenda volcano, the Anisotropy of Magnetic Susceptibility (ASM) method is used in this study to highlight the palaeoflow in ancient deposits of ignimbrites which are mostly discontinuous and isotropic. Results of AMS study are used to produce map of hazards and assess risks that may be related with such eruptions in Bamenda volcano.
Merlin Gountié Dedzo, Pierre Kamgang, Emmanuel Njonfang, Ghislain Zangmo Tefogoum, D. G. Nkouathio, Armand Kagou Dongmo
British Journal of Applied Science & Technology
International audience
Nicaise Blaise Tchuimegnié Ngongang, Pierre Kamgang, Gilles Chazot, Arnaud Agranier, Hervé Bellón, Philippe Nonnotte
Journal of African Earth Sciences
Nguihdama Dagwai, Gilles Chazot, Pierre Kamgang, Mbowou Gbambié Isaac Bertrand, Ismaı̈la Ngounouno
International Journal of Geosciences
Spinel-bearing lherzolite xenoliths from the Hossere Garba (1272 m.a.s.l) volcano on the Adamawa Plateau, is located in Likok village, at about 35 km to WSW of Ngaoundere. These xenoliths (~11 cm size) have been sampled into the host basaltic lava flows from the NE flank of the Hossere Garba volcano. These xenoliths characterized by porphyroclastic texture consisted of olivine (~55 vol.%), orthopyroxene (~19 vol.%) and clinopyroxene (~21 vol.%) crystals. Spinel crystals (~5 vol.%) are red brown and interstitial between the crystals of olivine and pyroxenes. CaO contents are low (VI/AlIV ratio range between 1.1 and 1.3 for the Cr-diopside crystals from Hossere Garba xenoliths. The constant value of the volumes V(Cell) and V(M1) for clinopyroxene compositions, indicates the similar pressures. Hossere Garba represents a residual sequence issued from partial melting of a mantle source. Similar compositions have been recorded in minerals of ultramafic xenoliths from other ultramafic xenoliths domains of the Cameroon Line and the Adamawa Plateau.
Pierre Kamgang, Gilles Chazot, Emmanuel Njonfang, Nicaise Blaise Tchuimegnié Ngongang, Félix M. Tchoua
Gondwana Research
Benoît Joseph Mbassa, Emmanuel Njonfang, Mathieu Benoît, Pierre Kamgang, Michel Grégoire, Stéphanie Duchêne and 3 more
Mineralogy and Petrology
Emmanuel Njonfang, Alexandre Nono, Pierre Kamgang, Vincent Ngako, Félix M. Tchoua
Geological Society of America eBooks
Alkaline magmatism along the Cameroon Line has been active for at least 67 m.y. and is currently defined by an almost SW-NE geological lineament (mean value: N30°E). Available petrological, geochemical, and structural data obtained over the last 20 yr lead us to reappraise its mechanism of emplacement. Known as the second most important geological curiosity in Africa, after the East African Rift system, it displays a continental part and an oceanic part, a unique feature in Africa and even in the world. The continental part contains both plutonic and volcanic massifs, and the oceanic part consists only of volcanic massifs. Plutonic rocks as a whole define a complete series of gabbro-diorite-monzonite-syenite-granite type, whereas volcanic rocks display abundant basic (basalt-hawaiite) and felsic (trachyte-phonolite-rhyolite) lavas with very few intermediate ones (mugearite-benmoreite). The formerly entire alkaline nature of these rocks is here ruled out by the discovery of volcanoes with geochemically transitional affinities in some areas of the continental sector. On the other hand, new K-Ar and 40Ar/39Ar dates confirm the absence of any age migration associated with the SW-NE linear trend. This lack of steady time-space migration and the SW-NE trend have also been observed in the magmatic provinces of Nigeria and Benue Trough, which share similar geochemical features with the Cameroon Line, and along the NE-SW major igneous lineaments in South Africa. The mechanism of such episodic emplacement of alkaline magmatism can be better explained in terms of complex interactions between hotspots and lithospheric fractures during African plate motion.
Pierre Kamgang, Emmanuel Njonfang, Alexandre Nono, Merlin Gountié Dedzo, Félix M. Tchoua
Journal of African Earth Sciences
Pierre Kamgang, Gilles Chazot, Emmanuel Njonfang, Félix M. Tchoua
Comptes Rendus Géoscience
Mafic rocks from the Bamenda volcanic province along the Cameroon Volcanic Line have been dated from 17 to 0 Ma. Associated with some trachytes and rhyolites, this volcanism covers a period of more than 25 Ma. The studied rocks are basalts to mugearites. Most of them have been contaminated by continental crust during their transit to the surface. The oldest rocks are the most contaminated. One group of samples shows high Eu, Sr and Ba contents. This characteristic is not due to crustal contamination process, but has a mantle source origin. We argue that these characteristics have been acquired by mixing of melts formed by partial melting of mantle pyroxenites with melts formed in mantle peridotites. Such pyroxenites have been observed as mantle xenoliths in the Adamaoua province, and their chemical and isotopic compositions are consistent with such a model.
Pierre Kamgang, Emmanuel Njonfang, Gilles Chazot, Félix M. Tchoua
Comptes Rendus Géoscience
Les laves felsiques des monts Bamenda, au cœur de la ligne volcanique du Cameroun, sont principalement représentées par des trachytes, et par quelques benmoréites et rhyolites alcalines à hyperalcalines. Les données géochronologiques K–Ar définissent deux épisodes de volcanisme, le premier entre 18 et 22 Ma, le deuxième entre 12,5 et 13,5 Ma. Les données géochimiques montrent que les laves acides sont formées par cristallisation fractionnée de magmas basiques et mettent en évidence une contamination significative par les roches crustales pendant la différenciation. Dans l’ensemble, ces données sont en accord avec l’absence d’évolution dans le temps de la localisation du volcanisme le long de la ligne du Cameroun, et montrent un mécanisme identique de genèse des roches acides au cours du temps et pour les différentes provinces volcaniques adjacentes (Bamenda, Oku et Bambouto).
Robert Temdjim, I Konfor Njilah, Pierre Kamgang, Charles Nkoumbou
African Journal of Science and Technology
On the Adamawa plateau (Cameroon volcanic line), alkali basalt lava flows are dated at 6.5 ± 0.2 Ma by K-Ar method. Associated phonolitic and trachytic plugs were put in place 6.8 to 6.2 ± 0.2 Ma ago. The most recent volcanic episode aged 0.91 ± 0.06 Ma yielded maars and scoria cones with associated basaltic lava flows. The microlitic groundmass of miaskitic phonolites comprise of euhedral phenocrysts nepheline, anorthoclase, hastingsite, salite-ferrosalite, sphene and apatite. In the agpaïtic phonolites, interstitial anhedral crystals of aegirine-augite, aenigmatite and lavenite mould euhedral phenocrysts of anorthoclase, nepheline, sodalite and noseane. Through the felsic lava series, pyroxene defines an evolutionary trend from salite to aegirine augite with gradual acmite enrichment. Amphibole trend shows a limited range (kaersutite in trachytic lavas and hastingsite in miaskitic phonolites). Genetically, phonolites are linked to trachytes by crystal fractionation mechanism but this mechanism alone cannot account for the overall Na2O and MnO enrichments in lavenite-bearing agpaitic phonolites. At this stage, a migration of dissolved volatilemetal complexes may have accompanied crystal fractionation to produce lavenite: (Na, Ca)2(Mn, Fe2+)(Zr, Nb, Ti)Si2O7(OH, F).Keywords: agpa ïtic phonolites, migration of volatile-metal complexes, laveniteRésuméDans la rgion de Ngaoundr, (plateau de l'Adamaoua, Ligne volcanique du Cameroun), des coules de basaltes alcalins dats 6,5 ± 0,2 Ma sont accompagnes de necks et pitons trachytiques et phonolitiques, phonolites dates 6,8 et 6,2 ± 0,2 Ma par la mthode K-Ar. L'pisode ultime des cnes stromboliens, maars et coules basaltiques remonte 0,91 ± 0,06 Ma. L'ensemble des laves appartient une srie alcaline sodique. La msostase des phonolites miaskitiques englobe des phnocristaux automorphes d'anorthose, nphline, sodalite, nosane, hastingsite, salite-ferrosalite, sphne et apatite. Dans les phonolites agpaïtiques, les cristaux interstitiels xnomorphes de pyroxnes agyriniques, anigmatite et lavnite moulent les cristaux automorphes d'anorthose, sanidine, nphline, sodalite et nosane. Dans l'ensemble des laves felsiques, le pyroxne volue des salite et ferrosalite dans les trachytes et phonolites miaskitiques aux augite agyrinique et agyrine dans les phonolites agpaïtiques. La variation des compositions des amphiboles est limite (kaersutite dans les trachytes hastingsite dans les phonolites). Sur le plan ptrogntique, les phonolites drivent des trachytes par un mcanisme de cristallisation fractionne. A la fin de la diffrenciation, ce mcanisme a t coupl la migration des complexes mtaux-volatiles dissous dans les fluides magmatiques pour former des phonolites hyperalcalines agpatiques lavnite, subnsosilicate complexe de Ti et Zr de formule (Na, Ca)2(Mn, Fe2+)(Zr, Nb, Ti)Si2O7(OH, F). Mots cls: phonolites agpaïtiques, migration des complexes mtaux-volatiles, lavnite African Journal of Science and Technology Vol. 5(2) 2004: 113-123
Emmanuel Njonfang, Pierre Kamgang, Raphael T. Ghogomu, Félix M. Tchoua
Journal of African Earth Sciences
M. Caen‐Vachette, P. Tempier, Pierre Kamgang
Journal of African Earth Sciences (1983)
Pierre Christel Biakan à Nyotok, Merlin Gountié Dedzo, Djamilatou Diddi Hamadjoda, Nils Lenhardt, Moussa Ngarena Klamadji, Périclex Martial Fosso Tchunte and 1 more
Geosciences
The metavolcanic rocks around Maroua in the Far North Region of Cameroon are located at the northern margin of the Central African Fold Belt (CAFB) and have not been studied to date. The petrographic and whole-rock geochemical data presented in this paper highlight their magma genesis and geodynamic evolution. The lavas are characterized by basaltic, andesitic, and dacitic compositions and belong to the calc-alkaline medium-K and low-K tholeiite series. The mafic samples are essentially magnesian, while the felsic samples are ferroan. On a chondrite-normalized REE diagram, mafic and felsic rocks display fractionated patterns, with light REE enrichment and heavy REE depletion (LaN/YbN = 1.41–5.38). The felsic samples display a negative Eu anomaly (Eu/Eu* = 0.59–0.87), while the mafic lavas are characterized by a positive Eu anomaly (Eu/Eu* = 1.03–1.35) or an absence thereof. On a primitive mantle-normalized trace element diagram, the majority of the samples exhibit negative Ti and Nb–Ta anomalies (0.08–0.9 and 0.54–0.74, respectively). These characteristic features exhibited by the metavolcanic rocks of Maroua are similar to those of subduction-zone melts. This subduction would have taken place after the convergence between the Congo craton (Adamawa-Yadé domain) and the Saharan craton (Western Cameroonian domain). Petrological modelling using major and trace elements suggests a derivation of the Maroua volcanics from primitive parental melts generated by the 5–10% partial melting of a source containing garnet peridotite, probably generated during the interaction between the subducted continental crust and the lithospheric mantle and evolved chemically through fractional crystallization and assimilation.
Luc Achille Ziem A Bidias, Sahada Mouchili Nguegni, Dieudonné Charles Isidore Ilouga, Hermine Suzinie Kenna, Amidou Moundi, Pierre Kamgang
International Journal of Geoheritage and Parks
This study was conducted in Kouoptamo, located in the Noun plain in Western Cameroon, with the main objective of inventorying and evaluating the geological heritage, and promoting the protection and geoconservation of geosites, and their use in geotourism development. Geosites in the region include dammed lakes (Petpenoun lakes), maars (Sanka Ndoumkain maar, Tchoua maar), scoria cones (Nkoambeng, Kechuentim, Ngouen volcanoes), a dome (Njigoumbé dome) and a managed natural area (Petponoun domain). Most geosites have a high scientific, aesthetic and educational value. The method used for the inventory and assessment of geosites in this work is according Reynard, et al. (2016), which is more suitable for geological heritage on a regional scale. The scientific value in this method is composed of four criteria, namely: rarity, representativeness, integrity and palaeogeographical interest. Each of these criteria is evaluated independently by a numerical score ranging from 0 (nil) to 1 (very high) in intervals of 0.25. The overall average scientific value of the Kouoptamo geosites is 0.77. Nkoambeng volcano has the highest scientific value (0.88), followed by Tchoua maar, Sanka Ndoumkain maar, Njigoumbé dome and Ngouen volcano, all of which score 0.81, while Kechuentim volcano and Petpenoun domain score 0.75 and 0.69 respectively. The integrity of several of these geosites is preserved, mainly the Petpenoun lakes, the Tchoua maar, and the Sanka Ndoumkain maar. Geosites such as Sanka Ndoumkain maar, Tchoua maar, Njigoumbé dome and the Nkoambeng, Kechuentim, and Ngouen volcanoes are representative of the regional geomorphology. Artisanal quarries (Nkoambeng volcano) and industrial quarries (Njigoumbé dome), as well as agro-pastoral activities, tend to degrade these geosites, which in general do not benefit from any legal protection. It is strongly recommended that geoconservation policies be adopted for these geosites, in order to preserve and develop these sites for their considerable geotourism potential while taking into account the current resource and land usage to find an optimum, sustainable strategy.
Benoît Joseph Mbassa, Caroline Neh Ngwa, Jacques Dili-Rake, Moïse Bessong, Zénon Itiga, Mero Yannah and 2 more
Arabian Journal of Geosciences
Merlin Gountié Dedzo, Eric Martial Fozing, Boris Chako Tchamabé, Pierre Christel Biakan à Nyotok, Djamilatou Diddi Hamadjoda, Asobo Nkengmatia Elvis Asaah and 3 more
Arabian Journal of Geosciences
Rikangsou Tchouhla, Merlin Gountié Dedzo, Boris Chako Tchamabé, Gervais Onana, Djamilatou Diddi Hamadjoda, Pierre Christel Biakan à Nyotok and 3 more
Geosciences Journal
Innocent Badriyo Agama, Gilles Chazot, Pierre Kamgang
Acta Geochimica
Henri Appolinaire Kenzo, Victor Metang, Willy Stephane Segue, Legrand Joseph Tchop, Lucas Mouafo, Diane Marilyn Nkamga Mbakam and 3 more
Arabian Journal of Geosciences
Philippe Essomba, Gilles Chazot, Nicaise Blaise Tchuimegnié Ngongang, Arnaud Agranier, Pierre Kamgang, Hervé Bellón and 3 more
Acta Geochimica
Nathalie Love Ngongang Tchikankou, Pierre Kamgang, Gilles Chazot, Arnaud Agranier, Hervé Bellón, Philippe Nonnotte and 2 more
Arabian Journal of Geosciences
Merlin Gountié Dedzo, Ghislain Zangmo Tefogoum, Boris Chako Tchamabé, Eric Martial Fozing, Emmanuel Njonfang, Pierre Kamgang
Journal of Geography Environment and Earth Science International
Ignimbritic flow deposits which derived from pyroclastic density currents (PDCs) are mostly observed in West-Cameroon Highlands located in the central portion of the Cameroon Volcanic Line (CVL), especially in Bambouto (21.12 - 0.50 Ma) and Bamenda (27.40 - 0 Ma) volcanoes. These deposits covering approximately 27% (≈195 km2) of the volcanoes surface with thickness ranging from 30 to 200 m representing a total volume estimated at 20 km3. Because of the intense weathering of the ignimbritic formations after their setting up and being buried by basaltic and trachtytic flows, the initial volume of these pyroclastic deposits is really much larger. Soil fertility has fostered an important population growth (more than 1,200,000 people) in these volcanoes. The economic and agropastoral activities on the flanks and inside the caldera of the volcanoes are estimated at about $US7.5 billion. In this paper, we evaluate and realize cartography of the hazards associated to ignimbritic eruptions which are most disastrous in term of volcanic process in this region. Magnetic studies, specifically, Anisotropy of Magnetic Susceptibility (AMS) method has been utilized for the determination of flow directions in visually nearly isotropic ignimbritic deposits outcrops. The AMS data reported from the Bamenda and Bambouto volcanoes ignimbrites produced significant informations about the depositional scheme of the PDCs. In most sites, magnetic lineations and principally magnetic foliation are reliably parallel to downhill directions, frequently with an upslope imbrication. Inferred palaeoflow directions based on the field indicators, orientation of minerals and other objects in oriented thin sections and the directional AMS data show that Bambouto caldera, Oku crater and Santa-Mbu caldera are the sources of main PDCs of Bambouto and Bamenda volcanoes. These AMS results have aided us to produce a hazard and risks maps related to potential future pyroclastic flows on these volcanoes. The assessment of risks in these volcanoes was based on populations in the study area, infrastructures (houses and roads) and average income of breeding activity.
Benoît Joseph Mbassa, Emmanuel Njonfang, Caroline Neh Ngwa, Michel Grégoire, Zénon Itiga, Pierre Kamgang and 5 more
Journal of Geosciences and Geomatics
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.
Merlin Gountié Dedzo, Djamilatou Diddi Hamadjoda, Eric Martial Fozing, Boris Chako Tchamabé, Ana Teresa Mendoza‐Rosas, Asobo Nkengmatia Elvis Asaah and 3 more
Geochemistry
Nathalie Love Ngongang Tchikankou, Jules Tcheumenak Kouémo, Nicaise Blaise Tchuimegnié Ngongang, Julie Agathe Noudiédié Kamgang, Maurice Kwékam, Pierre Kamgang
European Journal of Environment and Earth Sciences
The Fotouni volcanic rocks outcrop within mylonitic corridor, in the southern domain of the continental part of Cameroon Line (CL). The NE-SW shape display by these volcanic rocks within the mylonitic corridor is an uncommon case along the CL. Field and petrographic data and spaces image analysis were performed in order to understand the NE-SW shape display by these rocks. Geochemical data display two distinct volcanic compositional groups: alkaline lavas and transitional lavas. Alkaline series ranges in composition from basanite, basalt to hawaiite and transitional series range from basalt, trachy-basalt to basaltic trachy-andesite. Field investigations show that the Fotouni, Fangam, Song and Mbeng basalts outcrops as NE-SW trending prismatic dykes which displaying well differentiated vertical tetragonal, pentagonal and hexagonal prisms within the Fotouni-Kékem shear zone (FFSZ). The overall NE-SW orientation of hills, where these prisms outcrop suggests the tectonic control on the emplacement of these rocks. Indeed, the activation of the FFSZ developed various fracture networks that facilitate magma uplift and the emplacement of the Fomopéa and Bandja plutons during the Pan-African orogeny. These Pan-African activations of the Fotouni fault weaken the crust during the Paleozoic. These weaken zones constitute path way for emplacement of volcanic dykes during the Tertiary within the NE-SW faults, probably facilitated by the general extension at the end of Cretaceous.
Ghislain Zangmo Tefogoum, Armand Dongmo Kagou, David Guimolaire Nkouathio, Merlin Gountié Dedzo, Pierre Kamgang
Geoheritage
Zangmo Tefogoum Ghislain, Nkouathio David Guimolaire, Kagou Dongmo Armand, Gountie Dedzo Merlin, Pierre Kamgang
International Journal of Geosciences
The Bamenda Volcano (BV) (2621 m) is a stratovolcano situated in the Cameroon Line (CL). BV includes Mount Lefo (2534 m) which is situated on its southern slopes and contains one elliptical caldera (3 × 4 km). This caldera is propitious to farming and breeding activity. Despite these profitable assets, Lefo caldera (LC) is an amphitheater of the occurrence of multi-origin hazards that have direct or indirect impacts on the biodiversity and human patrimony. The most present hazards are those of meteorological origin. Numerous combined factors (steepest slopes, heavy rainfalls, weathered state of volcanic products…) rule these hazards. These factors gave rise to the occurrence of landslides, gullies erosion and rock falls which occur precisely on caldera northern and eastern rims. Hazards of anthropogenic origin are based on the destruction of the vegetation cover by the population for dealing, firewood and building issues. Moreover, during the breeding activity, the cattle covers the caldera throughout the day; this unevens the topography and destroys the meadow. Hazards of volcanological origin are not yet occurring in LC; but the recent Lake Monoun (1984) and Nyos (1986) CO2 eruptions, mount Cameroon eruptions (1999 and 2000) and mount Oku Lake event (2011) which are close to the BV and, the age of 0 Myr of basalt, constitutes a subject of controversy toward the reactivation of the Cameroonian hotspot faults. The assessment of risks in LC was based on the average income of breeding activity and house investment. The economy of LC is valued at about US$527472.527. The level of such risk will be important in case of loss of human beings and the destruction of geomorphosites’ values. In order to reduce the level of looses in this zone, hazard and risks maps are provided in this paper as well as some recommendations.
Merlin Gountié Dedzo, Anne Nédélec, Alexandre Nono, T. Njanko, Eric Font, Pierre Kamgang and 2 more
Journal of Volcanology and Geothermal Research
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