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![Zr/Y vs Nb/Y for rocks from BKVF along with alkaline rocks from Mount Cameroon [7,53], alkaline and transitional tholeiitic lavas from Bana [21], Bangou [12] and Bamoun Plateau [31,32]. DEP, deep depleted mantle; DM, depleted mantle; PM, primitive mantle; UC, upper crust; HIMU, high U/Pb mantle source; EM1 and EM2, enriched mantle sources; EN, enriched component; REC, recycled component [4]. Diagramme Zr/Y vs Nb/Y des laves de BKVF et du mont Cameroun [7,53] ; les domaines des basaltes alcalins et des basaltes à affinité transitionnelle de Bana [21], de Bangou [12] et du plateau Bamoun [31,32] sont présentés. DEP, manteau fortement appauvri ; DM, manteau appauvri ; PM, manteau primitif ; UC, croûte continentale ; pôles mantelliques HIMU (rapport 238 U/ 204 Pb élevé), EM1 and EM2 (enrichis) ; EN, composant enrichi ; REC, composant recyclé [4].](profile/Jules-Tamen/publication/248548400/figure/fig8/AS:312676057141255@1451559189811/Zr-Y-vs-Nb-Y-for-rocks-from-BKVF-along-with-alkaline-rocks-from-Mount-Cameroon-7-53.png)
Zr/Y vs Nb/Y for rocks from BKVF along with alkaline rocks from Mount Cameroon [7,53], alkaline and transitional tholeiitic lavas from Bana [21], Bangou [12] and Bamoun Plateau [31,32]. DEP, deep depleted mantle; DM, depleted mantle; PM, primitive mantle; UC, upper crust; HIMU, high U/Pb mantle source; EM1 and EM2, enriched mantle sources; EN, enriched component; REC, recycled component [4]. Diagramme Zr/Y vs Nb/Y des laves de BKVF et du mont Cameroun [7,53] ; les domaines des basaltes alcalins et des basaltes à affinité transitionnelle de Bana [21], de Bangou [12] et du plateau Bamoun [31,32] sont présentés. DEP, manteau fortement appauvri ; DM, manteau appauvri ; PM, manteau primitif ; UC, croûte continentale ; pôles mantelliques HIMU (rapport 238 U/ 204 Pb élevé), EM1 and EM2 (enrichis) ; EN, composant enrichi ; REC, composant recyclé [4].
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![Fig. 3. Nomenclature of the BKVF volcanics in a TAS diagram [22]....](profile/Jules-Tamen/publication/248548400/figure/fig3/AS:312676057141250@1451559189654/Nomenclature-of-the-BKVF-volcanics-in-a-TAS-diagram-22-Ankaramites-have-basalt_Q320.jpg)
The Barombi Koto volcanic field (BKVF) is located northeast of Mount Cameroon and constitutes a portion of the Kumba graben, one of the monogenetic volcanic fields of the Cameroon volcanic line (CVL). Tortonian fissural eruptions yielded picritic flows reworked by subsequent explosive eruptions, which generated two maars and ten cinder cones. The l...
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... we suggest an interpretation in terms of heterogeneity of the characteristics of the mantle source. Lavas from Mt Cameroon plot close to alkali basalts of BKVF and corroborate the mantle heterogeneity recently demonstrated [53]. More mantle source characteristics, as mantle components, can be inferred from element ratio systematics [4]. In Fig. 8, BKVF define a population above the DNb line in the plume basaltic source. They range from the HIMU endmember to mid-way to EM2. These chemical features may suggest that the mantle source region was modified prior to the melting by recycled oceanic crust (HIMU) with trapped melt fractions (EM2) or probable subducted continental ...
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... the HIMU endmember to mid-way to EM2. These chemical features may suggest that the mantle source region was modified prior to the melting by recycled oceanic crust (HIMU) with trapped melt fractions (EM2) or probable subducted continental sediments (EM2) [4]. As a result of such multi-component mixing, the mantle source is likely heterogeneous. Fig. 8 also shows that alkaline basaltic lavas from Mount Cameroon [7,53], Bamoun Plateau [31,32] and Bana [21] are rather close to the recycled component. Indeed, in order to unravel the source and processes of basaltic magmatism in Mount Cameroon, Yokoyama et al. [53] acquired various data comprising major and trace elements, Sr-Nd-Pb ...
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... Dy/Yb vs. La/Yb ( Fig. 7) and La/Sm vs. Sm/Yb (not shown) also point to low degrees ( < 10%) of partial melting of a garnet-rich peridotite to produce the ratios’ values observed in picrobasalts and basanites from BKVF. Lavas from Mt Cameroon plot close to alkali basalts of BKVF. Yokohama et al. [53] estimated that 2 – 3% of accumulated melts are necessary to produce the La/Yb and Gd/Yb ratios of the neighbouring Mt Cameroon lavas from a lherzolitic source comprising only 4 – 8% garnet. In Fig. 7, the values of the Dy/Yb ratio may be reached almost at 8% of melt accumula- tion. Along the Cameroon pluto-volcanic line, transitional tholeiitic basalts are reported in many massifs (Mbam [31], Bangou [12], Bana [21]), and in the Bamoun Plateau [32]. Their origin by high-degree melting of the mantle has been proposed, based on their low Zr/Y values (5.3 – 6.6 at Bangou, 5.4 – 7.4 at Bana and 6 – 11 on the Bamoun Plateau). This conclusion is in agreement with their position in Fig. 7. One of the most critical issues when basaltic magma source is addressed is that of its lithospheric or asthenospheric origin. Hopefully, highly incompatible trace elements in mantle minerals and in less differentiated basalts are valuable indicators. Table 1 provides worthwhile highly incompatible elements ratios of the primitive mantle (PM), the continental crust (CC), mid-ocean ridge basalts (MORB), ocean islands basalts (OIB), and rocks of this study. It appears that the latter display values in the range of primordial mantle and OIB. Bogaard and Wörner [3] used Dy/Yb vs La/Yb diagrams to discriminate between melting of garnet and spinel peridotite based on the compatibility of Yb and the incompatibility of La in garnet and the different rates of fractionation of La/Yb and Dy/Yb ratios during melting stages in the garnet stability field. The studied rocks display two trends (Fig. 7). The trend formed by basanite and picrobasalts fairly parallels the melting curve of garnet peridotite with decreasing values of La/Yb and Dy/Yb ratios, pointing probably to different degrees of melting of a garnet peridotite. On the contrary, the trend formed by alkali basalts is located in the garnet-poor peridotite field and shows decreasing values of La/Yb ratio at constant or increasing Dy/Yb ratio values. This figure shows that BKVF lavas resulted from low degrees (8 – 10%) of partial melting of a garnet-peridotite mantle compared to the high degrees (15 – 16%) of melting that yielded transitional lavas of Mts Bangou and Bana. Taking into consideration the scattering of its values, we suggest an interpretation in terms of heterogeneity of the characteristics of the mantle source. Lavas from Mt Cameroon plot close to alkali basalts of BKVF and corroborate the mantle heterogeneity recently demonstrated [53]. More mantle source characteristics, as mantle components, can be inferred from element ratio systematics [4]. In Fig. 8, BKVF define a population above the D Nb line in the plume basaltic source. They range from the HIMU end- member to mid-way to EM2. These chemical features may suggest that the mantle source region was modified prior to the melting by recycled oceanic crust (HIMU) with trapped melt fractions (EM2) or probable subducted continental sediments (EM2) [4]. As a result of such multi-component mixing, the mantle source is likely heterogeneous. Fig. 8 also shows that alkaline basaltic lavas from Mount Cameroon [7,53], Bamoun Plateau [31,32] and Bana [21] are rather close to the recycled component. Indeed, in order to unravel the source and processes of basaltic magmatism in Mount Cameroon, Yokoyama et al. [53] acquired various data comprising major and trace elements, Sr – Nd – Pb isotopes and precise measurements of 238 U – 230Th – 226 Ra disequilibria in lavas. The data point out the involve- ment of various components (HIMU, FOZO, mantle heterogeneity, subcontinental lithosphere, plume activity). These authors suggested that the geochemical characteristics of Mt Cameroon samples might result from an interaction of melt derived from the astheno- spheric mantle with the overlying sub-continental lithospheric mantle, which has suffered a Late Mesozoic metasomatism, presumably related to ancient St Helena plume activity. Many previous studies of volcanics of the Cameroon line have concluded that the magma mantle source is heterogeneous [14,15,26,39]. A recent study of lherzolite xenoliths encountered in alkali basalts from the northern part of the Kumba plain [49] reveals that they display a narrow mineralogical and chemical composition range. Therefore, the sampled mantle zone is fertile or simply affected by a very low degree of partial melting and cryptic metasomatism. These authors conclude that the upper mantle beneath the corresponding volcanoes is homogeneous and very different from the one beneath the Nyos volcanic plain. This assertion is valuable only with the assumption that the sampled mantle zone ranges from the bottom to the top of the upper mantle, and does not correspond to a limited pocket [29]. However, a study of the basalts (host of the peridotite xenoliths) is needed for highlighting the characteristics of the magma mantle source there. The metasomatic effects constitute another relevant point on the mantle source characteristics. Magmas resulting from the melting of a metasomatised mantle may display modal or cryptic testimonies. Along the CHL, Déruelle et al. [8] indicated that hydrated (kaersutite and biotite) and/or carbonate minerals in the lamprophyres (e.g., camptonites from Mt Cameroon) may be considered as the fingerprints of the melting of an infra-lithospheric metasomatised mantle. In Mt Etinde, modal and cryptic metasomatic effects coexist. In addition to carbonate minerals, nephelinites show unusual (high) values of Zr/Hf (92 – 50) ratio, which probably reflects a carbonate metasomatism in the mantle source [39]. Cryptic metasomatism is also evidenced in the peridotite xenoliths from the Kumba graben [49]; this cryptic metasomatism may have reached the BKVF mantle source. Key results on the mantle source characteristics of BKVF comprise the low degrees of partial melting of a garnet-peridotite infra-lithospheric mantle, their chemical characteristics, similar to those of an OIB mantle source, the heterogeneity of the mantle and a possible cryptic metasomatism. The mantle modifier component as the HIMU should remain a hypothesis until it is confirmed or challenged by He, Sr, Nd, Pb isotopes. Lavas from BKVF range from picrobasalts to hawaiite through basanites and alkali basalts. Due to their high Ni, Co, Cr, and MgO contents, they correspond to primitive or less differentiated rocks. Their major and trace element compositions are similar to those of alkaline lavas from other monogenetic volcanic fields of the Cameroon Volcanic Line. The scattering of many elements on bivariate plots and the wide range of values of incompatible element ratios are interpreted in terms of independent volcanoes formed by low-degree melting of distinct zones of a heterogeneous asthenospheric mantle. The ratios preclude any crustal contamination of the magmas en route to the surface. They rather indicate a mantle source characterized by a HIMU prevailing component. We are thankful to Andrea Marzoli, Anton Le Roex, Jacques Touret, and an anonymous reviewer for the thorough reviews that improved this paper. This work was funded by the Swiss Natural Sciences Association (field trip) and the Swiss Commission for Foreign Students (scholarship to the first author) on the support of Prof. Dr Volker Dietrich (Swiss Polytechnic High School, ...
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... Dy/Yb vs. La/Yb ( Fig. 7) and La/Sm vs. Sm/Yb (not shown) also point to low degrees ( < 10%) of partial melting of a garnet-rich peridotite to produce the ratios’ values observed in picrobasalts and basanites from BKVF. Lavas from Mt Cameroon plot close to alkali basalts of BKVF. Yokohama et al. [53] estimated that 2 – 3% of accumulated melts are necessary to produce the La/Yb and Gd/Yb ratios of the neighbouring Mt Cameroon lavas from a lherzolitic source comprising only 4 – 8% garnet. In Fig. 7, the values of the Dy/Yb ratio may be reached almost at 8% of melt accumula- tion. Along the Cameroon pluto-volcanic line, transitional tholeiitic basalts are reported in many massifs (Mbam [31], Bangou [12], Bana [21]), and in the Bamoun Plateau [32]. Their origin by high-degree melting of the mantle has been proposed, based on their low Zr/Y values (5.3 – 6.6 at Bangou, 5.4 – 7.4 at Bana and 6 – 11 on the Bamoun Plateau). This conclusion is in agreement with their position in Fig. 7. One of the most critical issues when basaltic magma source is addressed is that of its lithospheric or asthenospheric origin. Hopefully, highly incompatible trace elements in mantle minerals and in less differentiated basalts are valuable indicators. Table 1 provides worthwhile highly incompatible elements ratios of the primitive mantle (PM), the continental crust (CC), mid-ocean ridge basalts (MORB), ocean islands basalts (OIB), and rocks of this study. It appears that the latter display values in the range of primordial mantle and OIB. Bogaard and Wörner [3] used Dy/Yb vs La/Yb diagrams to discriminate between melting of garnet and spinel peridotite based on the compatibility of Yb and the incompatibility of La in garnet and the different rates of fractionation of La/Yb and Dy/Yb ratios during melting stages in the garnet stability field. The studied rocks display two trends (Fig. 7). The trend formed by basanite and picrobasalts fairly parallels the melting curve of garnet peridotite with decreasing values of La/Yb and Dy/Yb ratios, pointing probably to different degrees of melting of a garnet peridotite. On the contrary, the trend formed by alkali basalts is located in the garnet-poor peridotite field and shows decreasing values of La/Yb ratio at constant or increasing Dy/Yb ratio values. This figure shows that BKVF lavas resulted from low degrees (8 – 10%) of partial melting of a garnet-peridotite mantle compared to the high degrees (15 – 16%) of melting that yielded transitional lavas of Mts Bangou and Bana. Taking into consideration the scattering of its values, we suggest an interpretation in terms of heterogeneity of the characteristics of the mantle source. Lavas from Mt Cameroon plot close to alkali basalts of BKVF and corroborate the mantle heterogeneity recently demonstrated [53]. More mantle source characteristics, as mantle components, can be inferred from element ratio systematics [4]. In Fig. 8, BKVF define a population above the D Nb line in the plume basaltic source. They range from the HIMU end- member to mid-way to EM2. These chemical features may suggest that the mantle source region was modified prior to the melting by recycled oceanic crust (HIMU) with trapped melt fractions (EM2) or probable subducted continental sediments (EM2) [4]. As a result of such multi-component mixing, the mantle source is likely heterogeneous. Fig. 8 also shows that alkaline basaltic lavas from Mount Cameroon [7,53], Bamoun Plateau [31,32] and Bana [21] are rather close to the recycled component. Indeed, in order to unravel the source and processes of basaltic magmatism in Mount Cameroon, Yokoyama et al. [53] acquired various data comprising major and trace elements, Sr – Nd – Pb isotopes and precise measurements of 238 U – 230Th – 226 Ra disequilibria in lavas. The data point out the involve- ment of various components (HIMU, FOZO, mantle heterogeneity, subcontinental lithosphere, plume activity). These authors suggested that the geochemical characteristics of Mt Cameroon samples might result from an interaction of melt derived from the astheno- spheric mantle with the overlying sub-continental lithospheric mantle, which has suffered a Late Mesozoic metasomatism, presumably related to ancient St Helena plume activity. Many previous studies of volcanics of the Cameroon line have concluded that the magma mantle source is heterogeneous [14,15,26,39]. A recent study of lherzolite xenoliths encountered in alkali basalts from the northern part of the Kumba plain [49] reveals that they display a narrow mineralogical and chemical composition range. Therefore, the sampled mantle zone is fertile or simply affected by a very low degree of partial melting and cryptic metasomatism. These authors conclude that the upper mantle beneath the corresponding volcanoes is homogeneous and very different from the one beneath the Nyos volcanic plain. This assertion is valuable only with the assumption that the sampled mantle zone ranges from the bottom to the top of the upper mantle, and does not correspond to a limited pocket [29]. However, a study of the basalts (host of the peridotite xenoliths) is needed for highlighting the characteristics of the magma mantle source there. The metasomatic effects constitute another relevant point on the mantle source characteristics. Magmas resulting from the melting of a metasomatised mantle may display modal or cryptic testimonies. Along the CHL, Déruelle et al. [8] indicated that hydrated (kaersutite and biotite) and/or carbonate minerals in the lamprophyres (e.g., camptonites from Mt Cameroon) may be considered as the fingerprints of the melting of an infra-lithospheric metasomatised mantle. In Mt Etinde, modal and cryptic metasomatic effects coexist. In addition to carbonate minerals, nephelinites show unusual (high) values of Zr/Hf (92 – 50) ratio, which probably reflects a carbonate metasomatism in the mantle source [39]. Cryptic metasomatism is also evidenced in the peridotite xenoliths from the Kumba graben [49]; this cryptic metasomatism may have reached the BKVF mantle source. Key results on the mantle source characteristics of BKVF comprise the low degrees of partial melting of a garnet-peridotite infra-lithospheric mantle, their chemical characteristics, similar to those of an OIB mantle source, the heterogeneity of the mantle and a possible cryptic metasomatism. The mantle modifier component as the HIMU should remain a hypothesis until it is confirmed or challenged by He, Sr, Nd, Pb isotopes. Lavas from BKVF range from picrobasalts to hawaiite through basanites and alkali basalts. Due to their high Ni, Co, Cr, and MgO contents, they correspond to primitive or less differentiated rocks. Their major and trace element compositions are similar to those of alkaline lavas from other monogenetic volcanic fields of the Cameroon Volcanic Line. The scattering of many elements on bivariate plots and the wide range of values of incompatible element ratios are interpreted in terms of independent volcanoes formed by low-degree melting of distinct zones of a heterogeneous asthenospheric mantle. The ratios preclude any crustal contamination of the magmas en route to the surface. They rather indicate a mantle source characterized by a HIMU prevailing component. We are thankful to Andrea Marzoli, Anton Le Roex, Jacques Touret, and an anonymous reviewer for the thorough reviews that improved this paper. This work was funded by the Swiss Natural Sciences Association (field trip) and the Swiss Commission for Foreign Students (scholarship to the first author) on the support of Prof. Dr Volker Dietrich (Swiss Polytechnic High School, ...
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... It is in the Kumba Volcanic Field (KVF), a Miocene to Recent volcanic graben adjacent to the Mount Cameroon stratovolcano (Figure 1a,b). The volcanics in the field are picritic basalts, basanites, alkali basalts and hawaiites (Cornen et al., 1992;Nkouathio et al., 2002;Tamen et al., 2007), and they exhibit the geochemical characteristic of magmas derived from low degrees of partial melting of a garnetperidotite mantle characterized by a HIMU prevailing component (Asaah et al., 2020;Tamen et al., 2007). The volcanic activities in the KVF were generated through two major time-spaced volcanic episodes, the first during the Tortonian Age ($11.5 Ma; dominated by an effusive-type eruption that generated wide-spread aphyric flows; the second volcanic episode is of Calabrian Age ($1 Ma) and characterized by Strombolian-and phreatomagmatic-type explosive eruptions that generated tens of scoria cones, and four maars including the BMM, Dissoni, Barombi Koto and Mbwadong (Figure 1b). ...
... It is in the Kumba Volcanic Field (KVF), a Miocene to Recent volcanic graben adjacent to the Mount Cameroon stratovolcano (Figure 1a,b). The volcanics in the field are picritic basalts, basanites, alkali basalts and hawaiites (Cornen et al., 1992;Nkouathio et al., 2002;Tamen et al., 2007), and they exhibit the geochemical characteristic of magmas derived from low degrees of partial melting of a garnetperidotite mantle characterized by a HIMU prevailing component (Asaah et al., 2020;Tamen et al., 2007). The volcanic activities in the KVF were generated through two major time-spaced volcanic episodes, the first during the Tortonian Age ($11.5 Ma; dominated by an effusive-type eruption that generated wide-spread aphyric flows; the second volcanic episode is of Calabrian Age ($1 Ma) and characterized by Strombolian-and phreatomagmatic-type explosive eruptions that generated tens of scoria cones, and four maars including the BMM, Dissoni, Barombi Koto and Mbwadong (Figure 1b). ...
... The volcanic activities in the KVF were generated through two major time-spaced volcanic episodes, the first during the Tortonian Age ($11.5 Ma; dominated by an effusive-type eruption that generated wide-spread aphyric flows; the second volcanic episode is of Calabrian Age ($1 Ma) and characterized by Strombolian-and phreatomagmatic-type explosive eruptions that generated tens of scoria cones, and four maars including the BMM, Dissoni, Barombi Koto and Mbwadong (Figure 1b). While the Dissoni and Mbwadong maars have not yet received a detailed volcanostratigraphic study, Tamen et al. (2007) showed that Barombi Kotto is made of two short lava flows embedded in units of phreatomagmatic lapillituff deposits, likely formed during a single eruptive episode, recording eruptive style changes (Hawaiianphreatomagmatic -Strombolian). ...
Using a multidisciplinary approach to understand the subsurface processes behind the formation of maar‐diatreme volcanoes is of growing interest. While geophysical characterization can visualize the diatreme and the feeding dike system beneath the volcano at a reasonable scale, such data are rare and generally unavailable. Stratigraphic‐controlled sampling and geochemical analysis of pyroclasts within the ejecta ring can, however, provide substantial information on dike evolution and the influence of the magmatic plumbing system on the growth of these volcanoes. Such investigation is presented here for the Barombi Mbo Maar (BMM), a complex maar of the Cameroon Volcanic Line (CVL) composed of a pile of tephra units linked to multiple explosive phases that were grouped into three eruptive episodes. Major and trace element compositions of lavas collected from the different eruptive units indicate that the erupted magmas at BMM consist mainly of basalt, trachybasalt and basanite, with Oceanic Island Basalts (OIB) and high μ ( μ = ²³⁸ U/ ²⁰⁴ Pb) (HIMU) signatures. Compositional modelling suggests that partial melting occurred at different degrees in the garnet‐to‐spinel transition zone from one episode to another. The repetition of eruptions with big gaps between them, the presence of another large adjacent old maar crater next to the 2.5 km crater of the BMM, and the overall similarity in geochemical compositions from one eruption to another suggest a deep high‐productive zone in the mantle beneath the BMM. The latter productive zone was capable of generating magma batches episodically to fuel several individual monogenetic eruptions at the same location.
... The Pan-African Precambrian metamorphic and Cretaceous sequences consist of sandstones, clays, and conglomerates [3]. Mount Manengouba (2420 m) at the north of the zone is formed of basalt, trachyte, and rhyolite lavas [13]. The Kumba Trough pit is made up of Precambrian metamorphic and plutonic basement rocks overlain by Cretaceous-Cenozoic coastal sandstones. ...
The main objective of this study is to characterise the superficial structures of Foumban area. To achieve this, a sample of data from the gravity map of Cameroon is used to build a new Bouguer map to the studied area. The finite element method is used to separate the Bouguer anomalies into regional and residual anomalies. Given that the signatures of gravity anomalies related to surface structures are perceptible on the residual anomaly map, a qualitative analysis of this map helped to identify three anomaly domains in the north-western, central and north-eastern parts of the studied area. These three anomalies peak at 19 mGal, -24 mGal and 27 mGal, respectively. Spectral analysis is used to obtain the appropriate energy spectrum for different profiles that were selected, to estimate the average depth of the intrusive bodies. Thus, thanks to 3D modelling of the anomalous structures of the crust, a gravimetric interpretation is carried out. This interpretation leads correlatively to the geology of the region to conjecture the presence of sediments (clays, conglomerates, sandstones, sands) in the center of the study area; metamorphic rocks (gneisses, micaschists) and magmatic rocks (granites) responsible for positive anomalies in the rest of the area
... Trace elements and Sr and Nd isotopic compositions of the Mokolo-Kosséhone lavas are consistent with a mixture of different source materials from the sub-continental lithospheric mantle (SCLM) and the asthenosphere with minor crustal contamination. The source composition is analogous to those described in the northern portion of the CVL (Rankenburg et al., 2005;Gountié Dedzo et al., 2019) and other volcanic massifs along the CVL (e.g., Marzoli et al., 2000;Déruelle et al., 2007;Tamen et al., 2007;Yokoyama et al., 2007;Aka et al., 2008;Kamgang et al., 2013;Asaah et al., 2015aAsaah et al., , 2015bAsaah et al., , 2020Asaah et al., , 2021Tchuimegnie et al., 2015). Gurenko et al. (2006). ...
This study presents major and trace elements, and Sr-Nd-Pb isotope data of the Mokolo-Kosséhone volcanic rock (basanite, trachybasalt, trachyte, and rhyolite) from the northernmost segment of the Cameroon Volcanic Line (CVL). The basanite sample exhibits primitive character (MgO: 12–14 wt%; Mg#: 69–72; Ni: 327–427 ppm; Cr: 524–599 ppm; Co: 57–60 ppm). Trace element and isotopic signatures of the mafic lavas are similar to those of OIB. The trends observed in the major oxides and compatible trace elements against SiO2 from basanite to rhyolite are attributed to the fractionation of different mineral phases such as Fe-Ti oxides, olivine, clinopyroxene, feldspar, and quartz. The enrichment in LREEs and depletion in HREEs associated with (La/Yb)N > 5 (12.39–32.65), (Tb/Yb)N > 1.7 (1.71–2.89), and Dy/Yb > 2 (2.16–3.63), suggest the presence of a garnet phase in a mantle source. The lavas were produced at varying depths by low degrees of partial melting (< 4%) of a source containing less than 5% of garnet peridotite. The 206Pb/204Pb values of basanite (19.69630–19.79122) are similar to those of FOZO (206Pb/204Pb > 19.5). The trachybasalt samples with 206Pb/204Pb values of 19.25 and 19.37 suggest the probable enrichment of magma with a high-μ (HIMU) signature (206Pb/204Pb < 19.5) by a crustal component. Trace elements and isotopic compositions (87Sr/86Sr: 0.70308–0.70378, 143Nd/144Nd: 0.51287–0.51296, 206Pb/204Pb: 19.24652–19.79122) of the Mokolo-Kosséhone lavas are consistent with a mixture of different source material from the sub-continental lithospheric mantle (SCLM) and the asthenosphere with minor crustal contamination. The composition of the source is analogous to those described in the northern portion of the CVL and other volcanic massifs along the CVL.
... A detailed understanding of the origin of the volcanic activity is further limited by the scanty and scattered radiometric age data for the entire CVL (see Table 1 and Aka et al., 2018). Tectonic, petrographic and geochemical aspects of the CVL are covered in reviews and regional studies by, e.g., Sato et al. (1990), Déruelle et al. (1991Déruelle et al. ( , 2007, Tamen et al. (2007), Nkouathio et al. (2008), Njome and de Wit (2014), Asaah et al. (2015), Yamgouot et al. (2016), Ngwa et al. (2017), Tiabou et al. (2019) and Temdjim et al. (2020). ...
Volcanic eruptions represent hazards for local communities and infrastructure. Monogenetic volcanoes (usually) erupt only once, and then volcanic activity moves to another location, making quantitative assessment of eruptive hazards challenging. Spatio-temporal patterns in the occurrence of these eruptions may provide valuable information on locations more likely to host future eruptions within monogenetic volcanic fields. While the eruption histories of many stratovolcanoes along the Cameroon Volcanic Line (CVL) are relatively well studied, only fragmentary data exist on the distribution and timing of this region's extensive monogenetic volcanism (scoria cones, tuff rings, maars). Here, we present for the first time a catalog of monogenetic vents on the CVL. These were identified by their characteristic morphologies using field knowledge, the global SRTM Digital Elevation Model (30 m resolution), and satellite imagery. More than ~1100 scoria cones and 50 maars/tuff rings were identified and divided into eight monogenetic volcanic fields based on the visual assessment of clustering and geological information. Spatial analyses show a large range of areal densities between the volcanic fields from >0.2 km⁻² to 0.02 km⁻² from the southwest towards the northeast. This finding is in general agreement with previous observations, indicating closely spaced and smaller edifices typical of fissure-fed eruptions on the flanks of Bioko and Mt. Cameroon in the southwest, and a more focused plumbing system resulting in larger edifices of lower spatial density towards the northeast. Spatial patterns were smoothed via kernel density estimates (KDE) using the Summed Asymptotic Mean Squared Error (SAMSE) bandwidth estimator, the results from which may provide an uncertainty range for a first-order hazard assessment of vent opening probability along the CVL. Due to the scarce chronological data and the complex structural controls across the region, it was not possible to estimate the number of vents formed during the same eruptive events. Similarly, the percentage of hidden (buried, eroded) vents could not be assessed with any acceptable statistical certainty. Furthermore, the impact of different approaches (convex hull, minimum area rectangle and ellipse, KDE isopaches) to define volcanic field boundaries on the spatial distribution of vents was tested. While the KDE boundary definition appears to reflect the structure of a monogenetic volcanic field better than other approaches, no ideal boundary definition was found. Finally, the dimension of scoria cones (approximated by their basal diameters) across the CVL was contrasted to the specific geodynamic setting. This region presents a complex problem for volcanic hazard analysis that cannot be solved through basic statistical methods and thus, provides a potential testbed for novel, multi-disciplinary approaches.
... Gas bubbles from the near-shore bottom of Lake Wum were found to be simply dissolved air, judging from carbon and hydrogen isotopic compositions. However, out of the about 34 volcanic lakes along the CVL (Kling, 1988), only four; the Barombi Koto maar (Tamen et al., 2007), the Debunsha maar (Ngwa et al., 2010), the Barombi Mbo maar (Cornen et al., 1992;Chako-Tchamabé et al., 2013;2015;Asaah et al., 2020) and Nyos maar (Hasegawa et al., 2019), have received both a volcano and lithostratigraphic constraints that shed lights on their eruptive evolution. The others are just briefly described in some books, technical reports, papers, or thesis (e.g., Nana, 1991;Eno Belinga and Njilah, 2001;Manjeh-Ma'ah, 2016). ...
... The vesicular lava flow unit lying directly on the basement granite and occurring as recycled lava blocks in subsequent SC U1 deposits likely corresponds to the first erupted volcanics in the Wum area. Such flows are observed at many monogenetic volcanic field settings along the CVL like Tombel graben (also known as the Kumba plain, Nkouathio et al., 2002;Tamen et al., 2007;Chako-Tchamabé et al., 2013, 2015, and the Noun plain (Wotchoko et al., 2005). In fact, in those monogenetic volcanic fields, fissural lavas have been identified as the product of initial widespread Tortonian volcanism along the CVL. ...
Field investigations of tephra deposits and morphometric characterisation were used to constrain the eruptive history and the complexity of the Wum Maar Volcano (WMV) on the Northwestern foot of the Oku Volcanic Group (Cameroon Volcanic Line). The WMV is a compound volcanic edifice made up of an irregular horse-shoe-shaped maar-crater bordered by overlapping scoria cones and a small lava flow field. The bulk ejecta volume computed using ArcGIS.10.3 and field topographic measurements is ∼0.133 km³. The deposits were subdivided into older volcanics, a pre-maar member composed of four Strombolian scoria cones and a maar-member made up of interbedded layers of lapilli-tephra, lapilli-ash, and ash-breccia deposits. The bedding characteristics (structure, bedding dip, direction, attitude, and contact relations) coupled with the componentry analysis of maar deposits indicate phreatomagmatic-derived fallouts and pyroclastic density currents emplaced under both dry and wet conditions due to variations in magma-water ratio during the different phreatomagmatic explosions. The thick paleosol between older volcanics and the pre-maar and the maar deposits suggests that before the formation of the WMV, an eruptive activity took place and comprised an effusive outpouring of a basaltic magma batch that exploited the network of fractures within the basement rocks to reach the surface. Long after this stage, other batches of basanitic and trachybasaltic magmas richer in volatiles erupted explosively (Strombolian eruptive dynamism) around the northern and southern rims of the maar crater, leading to the emplacement of several overlapping scoria cones. The last stage was characterised by the formation of the Wum maar crater through a phreatomagmatic explosion when batches of basanitic magma came in contact with groundwater. The volcanics are sub-aphyric and host mantle xenoliths. Although evenly distributed across the different maar units, these mantle xenoliths are frequent and large enough to suggest a rapid magma ascent. The center of the maar crater compared to the location of the scoria cones suggest that the explosion locus migrated eastwards. The relative proportion of lithic granite within the pyroclastic succession increases upward (highest in MU4), and the depth of the maar varies from <10 m at the western border to about 124 m at the eastern one, suggesting a vertical and a lateral migration of the explosion locus. The intensity of the phreatomagmatic explosion reduced with time as indicated by the clast-size distribution, with a progressive reduction in water availability wherein the eruption became more internally controlled, changing in style from phreatomagmatic to Strombolian at the end. We conclude that even with very small magma volumes, monogenetic eruptions can have very complex histories, as shown by the WMV, because of the taping system, multiple vents, change in eruptive style, vertical and lateral migration of eruption foci, and multiple magma batches.
... It has been demonstrated that CVL magmatism is characterised by contributions from both the asthenosphere and the lithospheric mantle (Halliday et al., 1990;Yokoyama et al., 2007), involving at least three Fig. 7. Chondrite normalised REE diagrams for dykes studied along the CL. Data for average peridotites beneath the CVL is obtained from Lee et al., 1996;Tamen et al., 2007;Teitchou et al., 2011;Temdjim, 2012;Asaah, 2015;Tedonkenfack et al., 2019. Normalising values and data for OIB, N-MORB and E-MORB are from Sun and McDonough (1989). ...
... However, the mixing of this nature would be characterised by significant Nb-Ta anomalies on the PM-normalised multi-element patterns for the dykes. Therefore, the hybrid isotopic composition in such mixing would have more radiogenic 87 Lee et al., 1996;Tamen et al., 2007;Teitchou et al., 2011;Temdjim, 2012;Asaah, 2015;Tedonkenfack et al., 2019. Normalising values and data for OIB, N-MORB and E-MORB are from Sun and McDonough (1989). ...
We report whole-rock geochemistry and Sr–Nd–Pb isotopic compositions of mafic dykes intruded in the Precambrian granito-gneissic basement complex, exposed at Nyos, Batibo, Dschang and Foumban on the Cameroon Line. The dykes are alkaline (Batibo), transitional (Foumban), and subalkaline (Nyos, Batibo and Dschang) with SiO2 of 45–54 wt% and MgO of 2–9 wt%, similar to dykes reported in other areas of the Cameroon Line (CL) and the Central Atlantic Magmatic Province (CAMP). The abundances of rare earth elements (REE) and the Primitive Mantle normalised patterns for the Nyos, Batibo and Dschang dykes are similar to those of MORB, indicating that the dykes formed at shallower depths by a higher degree of partial melting relative to the Foumban dykes and the alkaline lavas of the CL. The transitional basaltic dykes with steeper REE patterns have their sources at deeper levels in the lithospheric mantle, possibly the garnet-spinel transition zone and were generated by a lower degree partial melting of the lithospheric and plume components. The Nyos and Batibo subalkaline dykes show similar isotopic compositions with a spectrum extending from depleted (DMM-like) to enriched (EM1-like) mantle, indicating the similarity in their source components. The Dschang dykes show distinct isotopic characteristics with relatively unradiogenic Nd-Pb isotope compositions compared to the Batibo and Nyos dykes. The Foumban transitional dykes with characteristic wide ranges in Sr-Nd-Pb isotopic compositions reveal varying contributions from enriched mantle components (EM1 and EM2) in addition to its plume signature similar to those of CL lavas. The Nyos and Batibo dykes alongside other dykes on the CL have low TiO2 abundances (<2 wt%), negative PM-normalised Nb-anomalies, and moderately to strongly enriched REE patterns, and isotopic composition that overlaps with those of CAMP, suggesting a similar lithospheric origin.
... The study area is limited by the longitudes 09 00 and 11 00 east and the latitudes 04 00 and 07 00 north (Figure 1b), in the Pan-African sector made up of syntectonic granitoids. According to Tamen et al. (2007), Mount Cameroon is one of the horsts of the Kumba. It is made up of basanitic, basaltic and hawaiitic lava flows, and cinder cones (Deruelle et al., 1991). ...
Volcanic scoriae from the southern part of the Cameroon Volcanic Line (Limbé, Loum-Tombel, Yamba, Doupé, Njinkouo, Foumbot, Manjo-manengollé, Galim and Djoungo) were investigated in order to determine their chemical and mineralogical composition, to deduce their origin and to identify their natural characteristics which may be useful to the cement industry. The mineralogical composition was determined by X-ray Diffractometer (XRD); X-ray Fluorescence (XRF) and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) instruments provided geochemical data. In order to establish the relationship between the natural characteristics of volcanic scoriae and the properties of cements, the amount of amorphous phases was determined by dissolution using sodium hydroxide solution and the pozzolanic activity by thermogravimetric analysis. Field observations show that these rocks are basalts, basanites, hawaiites and picrobasalts. Their mineralogical composition includes augite, olivine, plagioclase, enstatite, feldspars, ettringite, portlandite and Fe-Ti minerals. Overall, they are characterized by high MgO, Fe2O3, CaO, and TiO2 contents. The behavior of major and trace elements suggests that volcanic scoriae have an evolution dominated by partial melting. Besides, high chondrite normalized La/Yb (8–22), Tb/Yb (> 1.9) and Dy/Yb (> 2) values suggest that the melting corresponds to the garnet lherzolite stability field. The scoriae exhibit good pozzolanic reactivity after 28 days according to their considerable amount of amorphous phases, low CaO contents and their large specific surface area. According to ASTM C618 standard, the sum of SiO2, Al2O3 and Fe2O3 (SAI = 65.96–76.34 wt.%); LOI (-0.1–16.99 wt.%), and of CaO, Fe2O3 and MgO (CIM = 23.43–34.06 wt.%) suggest that those less weathered materials seem appropriate as an additive in cement manufacture. The suitable use of volcanic scoriae in the cement industry closely depends on the petrological features of amorphous phases.
... Oku lavas show steep patterns of HREE depletion (e.g., (Sm/Yb) N and (Dy/Yb) N > 1), indicating the presence of residual garnet in the source. The ratio of Sm/Yb for the lavas (3.9-5.8) is higher than those of peridotite xenoliths from Mt. Oku (<3.7; Tamen et al., 2007;Sababa et al., 2015;Asaah, 2015;Tedonkenfack et al., 2019;Liu et al., 2020), corroborating with their origin at greater depths relative to the latter. The similarities in HFSE ratios (e.g., Zr/Hf, Nb/Ta and U/Th) and Sr-Nd isotopic composition suggest the lavas originated from a heterogeneous mantle source. ...
... Partition coefficients are taken from Holbrook and Kelemen, (1993). Trace element data for peridotites are from Asaah, 2015;Tamen et al., 2007;Sababa et al., 2015;Tedonkenfack et al., 2019. ( Fig. 11a), although having slightly higher Ta/Yb and Th/Yb relative to average OIB. ...
This study presents geochemical data for mafic lavas from Mt. Oku to investigate the mantle source for Mt. Oku lavas and regional variations in isotopic ratios along the Cameroon Volcanic Line (CVL). The investigated mafic lavas present trace element and isotope signatures akin to ocean island basalts (OIB) and cover the entire range of the CVL. Major and trace element compositions of the studied lavas indicates that they have undergone fractionation of olivine + clinopyroxene + Fe-Ti oxide ± Cr–spinel with insignificant crustal contamination. The lavas were generated by <2% partial melting from a heterogeneous source containing less than 4% garnet. Major and trace elements abundances indicate the presence of hydrous minerals indicative of modal metasomatism.
The highest value of radiogenic ²⁰⁶Pb/²⁰⁴Pb (20.7) so far measured along the CVL is reported in this study. The isotopic features of the lavas suggest that the HIMU signatures are dominantly inherited from the asthenosphere (primary source) and melting of enriched components hosted in the subcontinental lithospheric mantle (SCLM; secondary source). Lavas from Mt. Oku present more comprehensive ranges of Sr–Nd–Pb isotopic composition than those from the continent-ocean-boundary (COB). The isotopic composition of Mt. Oku lavas with ²⁰⁶Pb/²⁰⁴Pb > 19.5 differs from those of the COB but are similar to FOZO.
The isotopic composition of Mt. Oku lavas (⁸⁷Sr/⁸⁶Sr = 0.7030–0.7036, ¹⁴³Nd/¹⁴⁴Nd = 0.5127–0.5129, ²⁰⁶Pb/²⁰⁴Pb = 17.9–20.7) suggest that the lavas are the result of contributions from the asthenosphere and the SCLM. Using a combination of Sr–Nd–Pb isotope display on a 3D plot and Sm/Yb, we identify four essential components denoted; A, B, C and D involved in the petrogenesis of Mt. Oku lavas and the approximate melting depth. While A and B are from the asthenosphere with HIMU mantle flavour, C and D owe their origin from the SCLM with EM1 and DMM characteristics, respectively. Although depleted in Sr-Nd isotopes, D is radiogenic in ²⁰⁶Pb/²⁰⁴Pb, indicating the influence of metasomatism. Therefore, the petrogenesis of Mt. Oku lavas involves the mixing of at least three mantle end-members: HIMU–DMM–EM1. The “fanning” of samples from”A" towards the other components (B, C and D) indicates a HIMU–like end–member dominance in Mt. Oku magmatism.
Considering the geophysical studies on mantle convection and plumes, we have developed a schematic model that explains the petrogenesis of the CVL lavas. The continuous spectrum from relatively depleted to HIMU characteristics of CVL lavas is associated with the progressive change in source components (i) SCLM with ± pockets of enriched metasomes to (ii) SCLM + asthenosphere sources and finally to (iii) typically asthenospheric source material ± pockets of enriched metasomes. Lavas derived from stage (i) exhibit geochemical variability involving DMM–like and EM1–like signatures. The magma generated at Stage (iii) is dominated by the HIMU mantle component and accounts for over 85% of CVL lavas.
... However, a detailed structural study is essential to shed light on the mode of contact between the magmatic occurrences and to deduce their relative chronology, as well as the magmatic chamber models. From a regional point of view, these magma source characteristics match those of the mantle beneath the Cameroon volcanic line (CVL) and the Adamawa-Yade shield, where mantle heterogeneity and polycyclic metasomatism are reported (e.g., Nkoumbou et al. 1995;Tamen et al. 2007Tamen et al. , 2015Nkouandou and Temdjim 2011;Temdjim et al. 2004, Pintér et al. 2015Tene et al. 2019;Goussi Ngalamo et al. 2017. Morever, the mantle beneath the CVL and the Adamawa-Yade shield is of Archaean age (Goussi Ngalamo et al. 2017Ngalamo et al. , 2018Liu et al. 2017). ...
The 60 km-long Pan-African Bapé massif intruded in the Adamawa-Yade Archaean block is an excellent case for the study of subduction–collision-related magmatism, its origin by interaction among magmas from various sources, and its bearing on the evolution of the Pan-African orogenic belt in Cameroon. An integrated study including mapping, petrography and geochemistry was carried out on these Ba–Sr rich quartz monzonites, quartz monzodiorites, monzonites, granodiorites (adakites), syenites and micromonzogabbros. The rocks are dominated by plagioclase + alkali feldspars + amphibole + biotite + sphene + opaque minerals + apatite + zircon ± pyroxene ± quartz assemblage. They are I-type, ferroan, metaluminous and belong to high-K calc-alkaline, shoshonitic series. REE patterns form two sets of tight closed and of highly differentiated patterns. The spider diagrams display Th, U, Nb, Ta, Zr and Hf negative and Ba, K, Pb and Sr positive anomalies. High K2O, Ba–Sr and moderate SiO2 contents and the variation of canonical ratios such as Zr/Sm, Zr/Hf, La/Sm, and Sm/Yb, point to multiple origins for the Bapé granitoids such as (i) melting of a dehydrated subducting crust (adakites) and/or the metasomatized heterogeneous mantle wedge (spinel– and phlogopite–amphibole–garnet lherzolite), or (ii) the mixing of these liquids (other granitoids). The U–Pb emplacement age (640–603 Ma), coeval with the subduction–collision between the West-African and the Congo cratons, the occurrence of adakites, combined with geophysical data, support that these granitoids are link to the southeast–northwest subduction of the hot Yaoundé oceanic crust under the Adamawa-Yadé craton, during the Neoproterozoic time.
... Green core pyroxenes were earlier reported from the alkali lavas of CVL, especially from the Bana volcano-plutonic complex (Kuepouo et al. 2006), Kumba graben (Tamen et al. 2007), Noun Plain , and Mount Bamenda (Kamgang et al. 2013). However, these studies were limited only to report the occurrence of such pyroxenes. ...
Green core clinopyroxenes are reported from the basanites of the Petpenoun volcanoes of the Noun Plain, in the Cameroon volcanic
line (CVL). These clinopyroxenes have augite and/or diopside rims and mantles, and green cores with variable chemical composition.
Compositionally, three kinds of green cores are distinguished: (i) wollastonite-hedenbergite cores (green core I); (ii) diopside cores
(green core II); and (iii) augite cores (green core III). The wollastonite-hedenbergite green cores are identified for the first time in the
mafic lavas of the CVL. The three types of green core clinopyroxenes are characterized by a significant enrichment in iron and a
corresponding decrease in magnesium, compared with their mantles or rims. These compositional patterns of green cores exhibit an
inverse zonation. The coexistence of several populations of clinopyroxenes with distinct compositions in the same sample suite is
attributed to the mixing between a mafic and a more evolved melt. Based on petrological, mineralogical, and geochemical studies, we
propose two origins to explain the varied occurrence of green core clinopyroxenes in this study: (i) the augite and diopside green cores
precipitated from relatively evolved melts which have been mixed with their present host magmas, and (ii) the wollastonite-hedenbergite
green cores precipitated from more differentiated melts which have been mixed also with mafic magma. These results
provide new constraints on the evolution of the recent lavas in the Noun Plain, Cameroon volcanic line.
