ST
Maître de Conférences
Activité scientifique
Profil chercheur
Enseignant-chercheur à l’Université de Yaoundé I. Grade : Maître de Conférences.
Publications scientifiques
Madi Boukar, Mero Yannah, Bernard Njom, Robert Temdjim, Amidou Moundi, Roger Bissaya et 3 autre(s)
Arabian Journal of Geosciences
Mebara Onana François Xavier, Robert Temdjim, Njombie Wagsong Merlin Patrick, Gilles Chazot, Tiabou Feudjio Anicet, Lucas Mouafo et 1 autre(s)
Arabian Journal of Geosciences
Patrick Merlin Wagsong Njombie, Robert Temdjim, Nicaise Blaise Ngongang Tchuimegnie, Stephen Foley, François Xavier Onana Mebara
Chemical Geology
A.M. Fagny, Oumarou Faarouk Nkouandou, Jacques‐Marie Bardintzeff, Hervé Guillou, Ovidiu Gabriel Iancu, Zénab Nouraan Njankouo Ndassa et 1 autre(s)
Journal of African Earth Sciences
Robert Temdjim, Merlin Patrick Njombie Wagsong, Arnold Julien Nzakou Tsepeng, Stephen Foley
Geoscience Frontiers
Mantle peridotites entrained as xenoliths in the lavas of Ngao Bilta in the eastern branch of the continental Cameroon Line were examined to constrain mantle processes and the origin and nature of melts that have modified the upper mantle beneath the Cameroon Line. The xenoliths consist mainly of lherzolite with subordinate harzburgite and dunite. They commonly contain olivine, orthopyroxene, clinopyroxene and spinel although the dunite is spinel-free. Amphibole is an essential constituent in the lherzolites. Mineral chemistry differs between the three types of peridotite: olivines have usual mantle-like Mg# of around 90 in lherzolites, but follow a trend of decreasing Mg# (to 82) and NiO (to 0.06 wt.%) that is continuous in the dunites. Lherzolites also contain orthopyroxenes and/or clinopyroxenes with low-Mg#, indicating a reaction that removes Opx and introduces Cpx, olivine, amphibole and spinel. This is attributed to reaction with a silica-undersaturated silicate melt such as nephelinite or basanite, which originated as a low-degree melt from a depleted source as indicated by low Al 2 O 3 and Na 2 O in Cpx and high Na 2 O/K 2 O in amphibole. Thermobarometric estimates place the xenoliths at pressures of 11–15 kbar (35–50 km) and temperatures of 863–957 °C, along a dynamic rift geotherm and shallower than the region where carbonate melts may occur. The melt/rock reactions exhibited by the Ngao Bilta xenoliths are consistent with their peripheral position in the eastern branch of the Cameroon Volcanic Line in an area of thinned crust and lithosphere beneath the Adamawa Uplift.
Anicet Feudjio Tiabou, Robert Temdjim, Pierre Wandji, Jacques‐Marie Bardintzeff, Vivian Bih, Edith Etakah Bate Tibang et 2 autre(s)
Acta Geochimica
Merlin Patrick Wagsong Njombie, Robert Temdjim, Stephen Foley
Contributions to Mineralogy and Petrology
Aminatou Fagny Mefire, Oumarou Faarouk Nkouandou, Jacques‐Marie Bardintzeff, Robert Temdjim, Hervé Guillou
HAL (Le Centre pour la Communication Scientifique Directe)
International audience
Aminatou Fagny Mefire, Oumarou Faarouk Nkouandou, Robert Temdjim, Jacques‐Marie Bardintzeff, Hervé Guillou, D. Stumbea et 1 autre(s)
HAL (Le Centre pour la Communication Scientifique Directe)
International audience
Fagny Mefire Aminatou, Nkouandou Oumarou Faarouk, Robert Temdjim, Jacques‐Marie Bardintzeff, Hervé Guillou, Dan Stumbea et 1 autre(s)
International Journal of Advanced Geosciences
Tchabal Mbabo in Central Africa is a voluminous volcano massif composed of alkali lava series. K-Ar geochronology data obtained from three samples of basanite - trachyandesite composition defined at least two volcanic activities. The first at end Eocene (38.22 ± 0.80 Ma) and the second during Oligocene (28.88 ± 0.61 and 28.60 ± 0.60Ma). The distribution of different ages along the Cameroon Volcanic Line is difficult to council with any migration of magmatic activity, as previously suggested. The most realistic scenario for the formation of Cameroon Line is that the ascent of lavas has been favored by the crustal discontinuities inherited from the Pan-African orogeny and reactivated during Mesozoic and Cenozoic. ICP MS and ICP AES analyses show that basanite lavas are the result of 2 % melting of sub-lithospheric mantle source containing garnet and phlogopite phases; the trachyandesites are formed by fractional crystallization of K-feldspar, amphibole, clinopyroxene and Fe-Ti oxides.
Anicet Feudjio Tiabou, Robert Temdjim, Caroline Neh Ngwa, Vivian Bih, François Xavier Onana Mebara
Journal of Geography and Geology
This paper presents principally the textural and geothermometric evidence of polymagmatic activity at a monogenetic volcano along the Cameroon Volcanic Line (CVL) in a bid to contribute to the global understanding of how such volume-limited basaltic magmatic systems operate. Preliminary geochemical data presented show that the lavas are alkali basalt and basanite (SiO2: 40.42 – 47.59 wt%, MgO: 7.61 – 9.13 wt%) and are petrographically indistinguishable. They outcrop as low mounds of columnar basalts associated with sparse pyroclastic materials. The lavas are fine porphyritic with phenocrysts of olivine and clinopyroxene set in a plagioclase microlite-dominated hypocrystalline groundmass. Olivine has two distinct populations: grains that are anhedral to glomerocrystic with spinel and plagioclase inclusions and usually have resorbed margins (olivine 1); and grains that are euhedral, sometimes skeletal, with a thin and well preserved rim (olivine 2). Similarly two clinopyroxene crystal populations are recognizable: clinopyroxene grains that are resorbed, dismembered, with sieve-textured cores and irregular core-rim margins (clinopyroxene 1); and euhedral clinopyroxene grains partially enclosing olivine phenocrysts with hour glass and sector zoning (clinopyroxene 2). These textural features suggest that the eruption was caused by an influx of a fresh batch of magma (that crystallized olivine 2 and clinopyroxene 2) into a fractionated crystal mush (olivine 1 and clinopyroxene 1) in the chamber. The crystal mush was re-heated by the intruding basaltic magma resulting in a broad pre-eruption liquidus temperature of 1040 – 1156oC calculated using mineral chemistry of equilibrium olivine-clinopyroxene pairs. Keywords: Cameroon volcanic line, geothermometry, monogenetic volcano, olivine-clinopyroxene pairs
Njilah Isaac Konfor, Robert Temdjim, Charles Richard, Nzolang Ghogomu, Rose Tchuitchou, Humphery Ajonina
Revista Facultad de Ingeniería Universidad de Antioquia
The Oku massif occupies the central position amongst the continental sector volcanoes of the Cameroon Volcanic Line (CVL). Field observations, petrographic major, trace and REE geochemistry show that lavas are basanite/alkali basalt-trachyte/rhyolite suited with a distinct compositional gap within the benmoreite field. This gap, which cannot be explained by sampling bias, may therefore reflect density filtration within the magmatic plumbing system. However, accumulation and fractionation of major mineral phases: pyroxenes, olivines and plagioclases appear to have controlled magma evolution. Fractional crystallization has been shown to be the major differentiation process that gave rise to the spectrum of magmas of this stratovolcano though crustal contamination in high level magma chambers cannot be precluded in this intraplate continental setting. K-Ar age determinations show that the volcanic activity in Mt. Oku occurred in three distinctive episodes 25-22 Ma, 18-14 Ma and < 1 Ma. There is no evidence for volcanic activity between 14 and 1Ma. Less than 1 Ma BP, activity resumed creating abundant cones and craters.
Oumarou Faarouk Nkouandou, Robert Temdjim
Journal of Geosciences
Spinel-bearing lherzolite xenoliths have been recovered from Mio-Pliocene alkaline basalt flows of the Ngao Voglar volcano, 35 km northwest of Ngaoundere in the Adamawa volcanic Massif (Cameroon).They have been examined to characterize the petrography, mineralogical composition, and equilibrium conditions of the upper mantle beneath the Ngaoundere region.The xenoliths exhibit protogranular textures and consist of four main minerals: olivine (Fo 89-90 ), Mg-enstatite (En 89-91 Wo 1 Fs 8-10 ), Cr-diopside (En 49-52 Wo 44-49 Fs 1.5-5 ) and spinel (Mg# ~79.2, Cr# ~10.7).Thermobarometric calculations show equilibrium temperatures ranging between 850 and 950 °C and pressures of 8 to 17 kbar consistent with the spinel lherzolite stability field.These data suggest that the xenoliths come from a depth of 28-31km in the uppermost mantle situated just below a thinned crust; they are in agreement with the geophysical data previously determined in the Adamawa Massif.On the basis of these features, and considering the evidence for textural, mineralogical, and chemical equilibrium in the studied xenoliths prior to their entrainment in the host magma, we conclude that the source of these xenoliths was a chemically and petrographically homogeneous, spinel lherzolite lithospheric mantle.But the occurrence of mantle-derived xenoliths of various types (dunite, lherzolite, wehrlite, harzburgite, websterite, clinopyroxenite, and orthopyroxenite) in alkali basalts from many other localities of Cameroon (Oku Massif, Lake Nyos area and Mount Cameroon) is consistent with upper-mantle heterogeneities on a regional scale and implies that the nature of the upper mantle beneath the continental sector of the Cameroon Volcanic Line varies under its different volcanic centres.
Merlin Isidore Teitchou, Michel Grégoire, Robert Temdjim, Raphael T. Ghogomu, Caroline Neh Ngwa, Festus Tongwa Aka
Geological Society of America eBooks
Basaltic lavas of Nyos volcano (Cameroon) mostly contain mantle peridotite xenoliths consisting of spinel-bearing lherzolites and harzburgites. Based on the trace-element patterns, especially rare earth element (REE) patterns, two groups of samples have been distinguished: group 1 samples are characterized by spoon-shaped REE patterns, and group 2 samples show light (L) REE–enriched patterns. Mineralogical characteristics together with major- and trace-element compositions point to a low degree of partial melting (less than 5%) and metasomatic processes. The latter mechanism explains in particular the LREE content of bulk rocks and clinopyroxenes and the occurrence of hydrous minerals in some samples. All the...
Jean Pierre Tchouankoué, Robert Temdjim, C. Tchawoua
Congres Geologique International, Resumes
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
Robert Temdjim, Pierre Boivin, Gilles Chazot, Claude Robin, Émilie Rouleau
Comptes Rendus Géoscience
Les dépôts volcaniques du lac Nyos (Cameroun) contiennent des enclaves ultrabasiques de natures variées : lherzolites, harzburgites et webstérites, dont certaines contiennent de l'amphibole. Les compositions en éléments majeurs et en éléments traces des amphiboles et des clinopyroxènes permettent de mettre en évidence un épisode ancien de fusion partielle. Deux épisodes d'enrichissement en éléments incompatibles sont identifiés, l'un riche en terres rares légères et affectant des échantillons préalablement appauvris, l'autre très riche en U et Th et plus pauvre en terres rares. La relation entre ces deux derniers épisodes n'est pas établie.
Der‐Chuen Lee, Alex N. Halliday, G.R. Davies, Eric J. Essene, J. Godfrey Fitton, Robert Temdjim
Journal of Petrology
Major element, trace element and Sr−Nd−Pb isotopic compositions of ultramafic xenoliths and megacrysts from the continental Cameroon line provide evidence for metasomatism of the upper most lithospheric mantle by enriched melts during the Mesozoic The megacrysts probably crystallized within the lower continental crust from melts similar to the host magmas. All the xenoliths originated as depleted residues after the extraction of basaltic melts, but some indicate evidence of interaction with enriched partial melts before entrainment. The U−Pb isotopic data on garnet are consistent with cooling through >900°C at >300 Ma. The Sm−Nd isotope systematics in constituent phases appear to have been in equilibrium on a xenolith scale at the time of entrainment, indicating derivation from mantle that remained at temperatures >600°C until eruption. Spinel therzolies that show simple light rare earth element (LREE) depletions are characterized by isotopic compositions that are comparable with, but slightly more depleted than Atlantic N-MORB, suggesting that the unmetasomatized sub-continental lithosphere of the Cameroon line may be isotopically similar to that of sub-oceanic lithosphere. The Nd-depleted mantle model ages of these xenoliths are consistent with late Proterozoic depletion, similar in age to much of the overlying continental crust. In contrast, samples that have LREE-enriched clinopyr-oxenes (La/Yb =4.7–9.4) contain trace amounts of amphibole, are enriched in U and have more radiogenic Pb and Sr. These xenoliths yield U−Pb and Sm−Nd model ages consistent with Mesozoic enrichment, in agreement with the age of enrichment of the source regions of the basalts, as deduced from Pb isotopic compositions. Clinopyroxenes record three orders of magnitude enrichment in U and LREE accompanied by progressive K depletion associated with the growth of trace amphibole, with K/U ratios that range from 12000 to 1. The ratios of the trace elements thought to have similar bulk D in mantle melting, Ce/Pb, Ba/Rb and Nd/Sr ratios, display regional variations related to the time integrated history of enrichments indicated by Nd isotopic compositions. Mass balance calculations suggest that the melts responsible for the most recent enrichment of the lithosphere had higher La/Yb and U/Pb than Cameroon line host magmas, and were probably the product of small degrees of partial melting associated with the earliest stages of the breakup of Pangea.
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