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Article

The Subduction-Related Metavolcanic Rocks of Maroua, Northern Cameroon: New Insights into a Neoproterozoic Continental Arc Along the Northern Margin of the Central African Fold Belt

by
Pierre Christel Biakan à Nyotok
1,
Merlin Gountié Dedzo
2,*,
Diddi Hamadjoda Djamilatou
1,3,
Nils Lenhardt
3,
Moussa Ngarena Klamadji
4,
Periclex Martial Fosso Tchunte
1 and
Pierre Kamgang
5
1
Department of Earth Sciences, Faculty of Science, University of Maroua, Maroua P.O. Box 814, Cameroon
2
Department of Life and Earth Sciences, High Teachers’ Training College, University of Maroua, Maroua P.O. Box 55, Cameroon
3
Department of Geology, University of Pretoria, Private Bag X20, Pretoria 0028, South Africa
4
Département des Sciences de la Vie et de la Terre, Faculté des Sciences Techniques et de la Technologie, Université de Pala, Pala P.O. Box 28, Chad
5
Department of Earth Sciences, University of Yaoundé I, Yaoundé P.O. Box 812, Cameroon
*
Author to whom correspondence should be addressed.
Geosciences 2024, 14(11), 298; https://doi.org/10.3390/geosciences14110298
Submission received: 15 September 2024 / Revised: 26 October 2024 / Accepted: 29 October 2024 / Published: 5 November 2024
(This article belongs to the Section Geochemistry)
Browse Figures
Versions Notes

Abstract

:
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.

1. Introduction

Despite forming the link between the Precambrian shield of Central Africa and the regions to the north that include the West African Shield and the central Sahara domain, the Central African Fold Belt (CAFB) is the least well-known of all major Pan-African belts [1]. In fact, central Africa, situated north of the Congo basin, is geologically poorly known. Up till now, it holds an essential key to unraveling geologic relations in Africa between the Precambrian shield of central Africa and the areas to the north that comprise the central Sahara domains and the West African Shield. The amalgamation of the Archean and Paleoproterozoic blocks (<1600 Ma) in Central Africa has been carried out in several phases, from the Mesoproterozoic (1600–1000 Ma) to the Neoproterozoic (1000–540 Ma) by the accretion of the various pan-African belts, such as the CAFB. The first phase contributed to the construction of the supercontinent Rodinia, while the second phase helped to build the supercontinent Gondwana [2]. The assembly of this latter continent involved the closure of the intervening Neoproterozoic basins and subduction of the oceanic lithosphere along a convergent margin [3,4]. In the Cameroonian part, especially in the northern part, previous work described the volcano–sedimentary sequence in the Poli, Bibemi-Zalbi, and Rey Bouba Greenstone belts [1,5,6,7].
The Poli Belt, to which the metavolcanic rocks of Maroua belong, is a syn- to pre-collisional basin established upon or in the environs of young magmatic arcs. The filling up of this depression occurred in a docking-arc/back-arc setting [8]. It comprises Neoproterozoic schists and gneisses of low and medium-to-high grade with sedimentary, volcano–sedimentary and volcanic origin. Metavolcanic rocks are calc-alkaline rhyolite and tholeiitic basalt emplaced in an extensional crustal setting [9,10]. Their depositional age is about 700–665 Ma; detrital sources include ca. 736, 780, 830 and 920 Ma magmatic rocks [8,11].
The Bibemi–Zalbi Belt covers the Cameroonian and Chadian territories and is locally named Bibemi–Zalbi Greenstone Belt. It is dated around 777 ± 5 Ma on epiclastite [12] and 700 ± 10 Ma on metabasalt [13]. According to [14] assumption of a back-arc and an arc basin system associated with a subduction in the Adamawa-Yadé Domain (AYD), [15] interpreted the region in terms of back-arc basin, volcanic arc and fore-arc basin that were accreted eastward to the AYD, alongside the Tcholliré–Banyo shear zone.
The Rey Bouba Greenstone belt (RBGB) principally comprises sedimentary and volcano–sedimentary rocks, felsic volcanic to greenschist-facies mafic rocks associated with pre-, syn- and post-tectonic dykes and granitoids [7]. It is a back-arc basin related to the subduction of an oceanic plate below the southeastern continental margin of the AYD [4,15]. Nevertheless, few geochronological data acquired by Pb–Pb minimum ages on single zircon are available for the RBGB, indicating ages of 750 ± 20 Ma for the Gatougel dacitic tuff [14] and 557± 17 Ma for the post-tectonic Vaimba granite. More recently, U–Pb zircon dating of felsic metavolcanic of RBGB fixed the maximum age for the volcanic activity at ca. 670 Ma [7]. The Balda granite pluton, with U-Pb age of 732.7 ± 7.5 Ma [16], located near the Maroua area, is identified as deformed alkaline granite and formed within a syn-orogenic extensional back-arc basin [16]. These sequences were generally interpreted as pre-tectonic back-arc basins intruded by or associated with the calc-alkaline TTG suite [8,15,16]. However, in the Maroua area, these sequences have been poorly studied, and information concerning their geochemistry and their geodynamic setting is very rare or almost nonexistent.
In this study, to better understand the petrogenesis and geodynamic evolution along the northern margins of the CAFB, petrography and geochemistry of metavolcanic rocks of the Maroua area are presented, and their petrology and tectonic setting are discussed.

2. Regional Geology and Tectonic Setting

The Central African Fold Belt (CAFB), or ‘mobile zone’ [17,18], is a vast belt area located between the Dahomeyide belt in the west, on the edge of the West African craton, and the Oubanguide belt in the east [19]. It is bounded in the north by the East Saharan metacraton and in the south by the Congo craton (Figure 1a,b). In Cameroon, the CAFB is divided into three geotectonic domains [20,21,22]. These domains are dominated by various shear zones, one of the most important of which is the Cameroonian Centre Shear Zone (CCSZ) at N70°E [23]. The geotectonic domains include, successively, the following: (1) the Southern Domain, identified as a synthetic basin comprising deposits of less than 625 Ma; (2) the Central Domain, marked by the presence of relics of the Paleoproterozoic basement and which was metamorphosed during the Pan-African orogeny and by the intrusion of batholiths; (3) the Northern Domain, which is considered a back-arc basin that formed between 830 Ma and 665 Ma.
The Southern Domain is bounded to the north by the Sanaga fault and to the south by the northern border of the Congo craton. Three lithological groups are identified in this area: the Yaoundé [26,27,28], the Mbalmayo [29] and the Ntui–Betamba groups [20]. The area also includes two petrographic units: (1) one unit of metasedimentary rocks (disthene–biotite–garnet gneiss, biotite–muscovite–garnet gneiss, silicate–calcite rocks, and quartzite); (2) one unit of pyroxene and amphibolite–gneiss. These two units recrystallized at temperatures between 750–800 °C and P ≥ 9–1.3 GPa [20] and correspond to the rocks that were deposited north of the Congo Craton.
The Central or Adamawa-Yadé Domain [7,30] is located between the Buffle Noir–Mayo Baleo (BNMB) fault in the north and the Sanaga fault (FS) in the south [22]. It is characterized by the presence of numerous WSW-ENE Pan-African decay corridors and is composed of several lithological units represented by the following: (i) Paleoproterozoic formations; (ii) Neoproterozoic gneiss; (iii) igneous intrusions of Pan-African age. The Paleoproterozoic formations include plutonic rocks primarily composed of diorites and granodiorites, as well as volcano–sedimentary or metasedimentary rocks such as amphibole and biotite gneisses, garnet and biotite gneisses, meta-arkoses, and meta-quartzites. These formations that are often migmatized, have undergone a remobilization during Pan-African times and have only retained a few relics of granulite assemblages. Geochronological data (U-Pb on zircon) reveal ages for these rocks that are between 2100 Ma and 600 Ma [21,31].
The Northern Domain, or Poli Group [32], to which our study area belongs, is also known as the West Cameroon Domain [7,30]. It is bounded to the west by the Buffle Noir–Mayo Baleo (BNMB) fault (Figure 1b). This area is considered to be a back-arc basin with an age between 830 and 665 Ma, which is composed of metavolcanic rocks (the object of this study) associated with calc-alkaline tholeiitic bimodal volcanism (tholeiitic basalts, calc-alkaline rhyolites). Furthermore, the Northern Domain includes calc-alkaline intrusions (diorite, granodiorite and granite) that have formed syn- to post-tectonically between 733 and 580 Ma [21,33]. The intrusions penetrated the Paleoproterozoic schists to form NNE–SSW directional batholiths [22]. Furthermore, this domain is characterized by a regional N-S to NNE-SSW foliation.
The Maroua study area (Figure 2) is situated between the latitudes 10°36’40” N and 10°37’30” N and the longitudes 14°19′ E and 14°20′ E. It is composed of felsic and mafic metavolcanic lavas, located on the boundary between the Northern Domain and the East Saharan metacraton.

3. Analytical Methods

For this study, geochemical data of selected samples of the Maroua metavolcanic rocks were obtained. Whole-rock major and trace element concentrations of twenty-one (21) samples were measured by X-ray fluorescence (XRF) and an inductively coupled plasma mass spectrometer (ICP-MS). All samples were finely ground using a tungsten carbide milling pot at the University of Pretoria. For the XRF analyses, major elements and selected trace elements of all samples were analyzed using a Thermo Fischer ARL Perform X Sequential XRF instrument with OXSAS software (version 2.2). SARM 49 was used for quality control, with accuracy better than 1% for the major element oxides.
At the University of Witwatersrand (WITS), trace element analysis was performed using a Perkin Elmer DRC-e ICP-MS and certified primary solution standards. To ensure the reliability of the data, all the samples were analyzed in conjunction with BCR-1, BHVO-1 and BIR-1 international reference materials. The samples were prepared using the CEM Mars microwave system for HF-HNO3 digestion and, after drying, were placed in solution with 2% HNO3. For the ICP-MS analysis, the samples were diluted 1000 times and combined with internal Re, Rh, Bi and In standards to provide the needed mass range. Primary external calibration standards were created in the range of 5–100 ppb. Every ICP-MS determination was carried out in the presence of the control standards BCR-1, BHVO-1 and BIR-1. All elements deviated less than 10% from the recommended values.

4. Results

The immobile trace element diagram [35] classified the felsic and mafic volcanic rocks sampled for this investigation as basalts, andesites and dacites (Figure 3a). Almost all mafic samples were chemically classified as subalkaline basalts (Nb/Y = 0.08–0.29) according to the Nb/Y vs. Zr/TiO2 diagram (Figure 3a). The SiO2 contents of the mafic rocks (basalt) varied from 49.63 to 60.40 wt% and from 68.00 to 75.25 wt% for the felsic lavas (andesite and dacite). The basalts appeared tholeiitic in composition (Figure 3b), whereas the andesite and dacites appeared calc-alkaline in nature [36] (Figure 3b). Using the SiO2 vs. K2O classification diagram of [37], the studied rocks were also found to belong to the calc-alkaline medium-K and low-K tholeiite series (Figure 3c). On the SiO2 vs. Fe2O3t/(Fe2O3t + MgO) plot [38], the mafic samples are essentially magnesian, whereas all the felsic rocks are ferroan (Figure 3d).
The metavolcanic rocks of Maroua are massive and outcrop as blocks and bowls on the slopes of the massifs (Figure 4a,c,e). All samples exhibited microlitic porphyritic and aphyric textures. In the basaltic samples, olivine, clinopyroxene, amphibole, plagioclase and oxides (pyrite was visible in hand specimens of Figure 4b and in thin sections) were the main mineral phases (Figure 5a). The andesites and dacites were found to be mainly composed of quartz (together with feldspar, visible in hand specimens; Figure 4d,f), sanidine, plagioclase, clinopyroxene, biotite and opaque minerals (Figure 5b–d). The matrix of felsic metavolcanic rocks (dacites and andesites) were devitrified and contained abundant, very small crystals of quartz (Figure 5a–c), suggesting that recrystallization had occurred. Fragmented plagioclase, often with flexuous twinning, in mafic and felsic lavas indicated that these rocks were subjected to high pressures after their emplacement.

4.1. Geochemistry

Major and trace elements data for representative samples of the Maroua lavas are presented in Table 1 and Table 2.

4.1.1. Major Elements

To minimize the effects of alteration on the samples, the concentrations of major element oxides in the studied lavas were recalculated to 100% on an anhydrous basis. Mg# was calculated as the mole ratio of MgO/(MgO + FeO), assuming FeOt = Fe2O3 × 0.8998 Fe2O3. The mafic rocks showed a wide range in their MgO (3.07–5.04 wt%), TiO2 (0.96–1.28 wt%) and Fe2O3 (9.11–12.71 wt%) contents, with a Mg number (Mg#) varying from 43.10 to 50.90.
The felsic lavas, on the other hand, were characterized by low MgO (0.13–1.08 wt%), TiO2 (0.19–0.50 wt%) and Fe2O3 (3.24–5.81 wt%) contents and a low Mg# (6–31.10). In the Harker diagrams of major element oxide content against SiO2 concentration (Figure 6a–f), the concentrations of Fe2O3, TiO2, Al2O3, MgO, P2O5 and CaO decrease from basalts to dacites. The Na2O and K2O values, on the other hand, rise in the mafic samples and then decrease abruptly in the felsic samples (Figure 6g,h).

4.1.2. Trace Elements

The contents of the compatible trace elements Sc, Ni, Co and Cr ranged from 27.14 to 33.36 ppm, 0.73 to 17.93 ppm, 26.21 to 46.01 ppm and 0.47 to 35.28 ppm, respectively, in the mafic lavas, while for the felsic samples, these concentrations were relatively low (8.56–16.01 ppm, 0.73–2.12 ppm, 17.25–35.16 ppm and 0.49–2.06 ppm).
The concentrations of the incompatible trace elements Zr, Nb and La varied widely between the mafic lavas (16.11–44.59 ppm, 1.36–4.77 ppm and 4.52–11.11 ppm, respectively) and the felsic rocks (94.92–223.90 ppm, 2.59–10.36 ppm and 7.23–22.64 ppm, respectively). The plots of selected trace element content vs. SiO2 concentration display negative correlations, with a continuous decrease in Sc, Ni, V and Sr concentrations (Figure 7a–d). Positive correlations were observed with increasing Zr, Nb, Ba and La contents (Figure 7e–h). In Figure 8, the concentrations of the selected rare earth elements (REEs) and trace elements are normalized to those of chondrite and primitive mantle according to [39] and specified, respectively, by the (N) and (PM) subscripts. On the chondrite-normalized REE diagram, mafic and felsic rocks display fractionated patterns with enrichment in the light REEs and depletion of the heavy REEs (Figure 8a,b; LaN/YbN = 1.41–5.38). The felsic samples display a negative Eu anomaly (Eu/Eu* = EuN/(SmN × GdN)1/2 = 0.59–0.87), while the mafic lavas exhibit practically no or a positive Eu anomaly (Eu/Eu* = 1.03–1.35). There are no obvious Ce anomalies (Ce/Ce* = 0.9–1.05) in any of the samples. On the primitive mantle-normalized trace element diagram, the rocks show negative Ti and Nb–Ta anomalies for most samples (0.08–0.9 and 0.54–0.74, respectively) and negative (0.28–0.58 for mafic samples) to positive (1.05–3.14 for felsic samples) Hf–Zr anomalies.

5. Discussion

5.1. Assessment of Alteration and Trace Element Mobility

The relatively high loss on ignition (LOI) values of the volcanic rocks of Maroua (1.34–3.54 wt%) are consistent with the fact that the samples were altered. In addition to geochemical alteration, the studied rocks underwent post-magmatic metamorphic processes, and therefore, an assessment of the degree of trace element mobility was important before any petrogenetic interpretation of such rocks. The Alumina Saturation Index (ASI) and the Alteration Index (AI) are good indicators to evaluate the intensity of weathering that has affected magmatic rocks. Unaltered island-arc basalts and mid-ocean-ridge basalts have average AI values of 34 ± 10% and 36 ± 8%, respectively [40]. In contrast, ASI values ˃1 are due to alkali loss and linked to hydration and/or alteration [41]. All samples of Mts. Kossel Béi and Mbalgaré exhibited ASI values between 0.80 and 1.1 (Table 1) and AI values between 10.61% and 39.18% (Table 1), suggesting that they were somewhat fresh and thus had not undergone significant alteration.
Earlier studies (e.g., [42,43,44]) revealed that mobile elements, such as K, Fe, Na, Ca, P, Rb, Ba, Sr and Cs, are alteration-sensitive and could be mobilized during metamorphism and post-magmatic crystallization. Some elements are known to remain generally immobile during alteration and metamorphism up to amphibolite facies, i.e., Ti, Al, Cr, Ni, V, Sc, Nb, Zr, Ta, Hf, Y, Th, Sm and the heavy REEs (e.g., [45]) and were thus considered suitable for the petrogenetic interpretation of the Maroua volcanic rocks. Furthermore, the robust correlations in the Harker diagrams (Figure 6 and Figure 7) and the coherent presentation of the REE and trace element patterns (Figure 8) without any noticeable Ce anomalies (e.g., [46]) were taken as evidence that the major elements, trace elements and light REEs were not significantly mobilized during the low-grade metamorphism and post-magmatic alteration.
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Figure 8. (a,b) Chondrite-normalized rare earth element (REE) diagrams and (c,d) primitive mantle-normalized multi-element diagrams for the Maroua volcanic rocks. Normalizing values are from [41].
Figure 8. (a,b) Chondrite-normalized rare earth element (REE) diagrams and (c,d) primitive mantle-normalized multi-element diagrams for the Maroua volcanic rocks. Normalizing values are from [41].
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5.2. Fractional Crystallization

The relatively low and wide range of Mg# (6.2–50.9) and MgO (0.13–4.95 wt%), Ni (0.73−17.93 ppm), Co (17.25−46.01) and Cr (0.47−35.28) contents shown by the Maroua volcanic rocks suggest that they do not represent compositions of a primitive magma. Instead, these characteristics imply that they underwent extensive fractional crystallization (FC) from primary magmas either en route to the surface or in magma chambers [47]. This primitive magma generally has Mg# of 68–72 and very high abundances of these components: MgO > 10 wt%; Ni, 300–400 ppm; Co, 50–70 ppm; and Cr, 300–500 ppm [48,49]. FC played an important role in the differentiation of the Maroua lavas, as evidenced by the robust correlation in the Harker diagrams and trace element distribution patterns. The Yb vs. La/Yb and Zr/Nb vs. Ba/La diagrams (Figure 9a,b) also confirmed that crystal fractionation played a significant role in the genesis of these rocks. The decrease in Fe2O3 and TiO2 with SiO2 (Figure 6a,b) indicates a stage of fractionation of Fe-Ti oxide minerals during magmatic differentiation. The FC of olivine in mafic samples is inferred from the decreasing Ni (Figure 7b) and MgO (Figure 6d) concentrations with increasing silica content, whereas the crystal fractionation of clinopyroxene is evidenced by a decrease in the CaO and Sc (Figure 6e and Figure 7a) contents with increasing SiO2 content. The negative correlation between Dy/Yb ratios and SiO2 content (Figure 9c) illustrates the fractionation of amphibole rather than clinopyroxene in most of the volcanic rocks. The increase in K2O and Na2O concentrations with differentiation, along with the significant variation of the Ba/La ratios (13.86–50.49) and the constant values of Y/Nb (4.27–8.4) in the felsic lavas, could be attributed to an important alkali feldspar fractionation at the end of the FC process [50,51]. The decrease in CaO and Sr content with that of SiO2, combined with Sr and Eu anomalies, particularly in the most differentiated rocks, is consistent with the fractionation of plagioclase. The plot of Sr vs. Rb/Sr (Figure 9d) with a negative correlation also illustrates that the fractionation of K-feldspar and plagioclase was the principal mechanism in the course of magmatic differentiation. The volcanic rocks outcropping in Mts. Kossel Béi and Mbalgaré presented clear linear correlations on the Harker diagrams (Figure 6 and Figure 7), suggesting that the felsic rocks were derived from more basaltic parental magmas by fractional crystallization.

5.3. Source Characteristics, Tectonic Setting and Geodynamic Model

Before characterizing the magmatic source of the studied rocks, it was important to check whether this magma had not been contaminated during its ascent by crustal material. The Nb/Yb vs. Th/Yb crustal input plot (Figure 10a) [55] shows that the majority of the samples are displaced off the MORB-OIB-OPB primitive array, indicating some enrichment in crustal material. The MORB-OIB-OPB primitive array contains nearly all of the mafic lavas from the Kossel Béi Mountain, which suggests that they are uncontaminated lavas. The Nb/Yb vs. TiO2/Yb diagram (Figure 10b) [55] also shows the group of uncontaminated mafic lavas, which correspond to the tholeiitic series, as previously indicated in Figure 3b. The great majority of the Kossel Béi mafic lavas on the Nb/U vs. Ce/Pb diagram [56] (Figure 10c) are plotted far from Precambrian basement samples [57], thus reflecting the fact that the source magma of these rocks was less contaminated by crustal components. Furthermore, compared to felsic lavas (positive Zr-Hf anomaly: 1.08–3.14; high Zr/Sm: 14.48–41.2), these mafic samples were characterized by negative Zr-Hf anomalies (0.28–0.58) and low Zr/Sm ratios (5.65–9.45), which therefore suggests very limited crustal contamination [58,59,60]. In the Nb/La vs. La/Yb plots [61] of the Maroua volcanic rocks (Figure 10d), the values of Nb/La vary from 0.30 to 0.57, which brings them closer to the field of the average lower crust, thus indicating a lithospheric mantle source for most of the studied rocks. It is worth noting that the uncontaminated mafic samples plotted near the limit of the lithospheric mantle and the zone of lithosphere–asthenosphere interaction, thus reflecting the fact that the mafic magma was more or less contaminated by crustal material, albeit to a limited extent.
Using these five (5) mafic samples, which were significantly less contaminated than the others, the mineralogical composition and the melting degree of the source of the Maroua volcanic rocks could be modelled on REE ratio plots from the melting equations [62]. The presence of garnet in the mantle source of the studied rocks was characterized by Dy/Yb > 2 (2.00–2.94) for these mafic uncontaminated samples [63,64] (Figure 11a).
According to [65], the presence of a garnet phase in the source was also suggested by the enrichment in LREE over HREE, since garnet has an important HREE affinity and depletes these elements from melts. The Sm/Yb vs. La/Sm variation diagram [66] (Figure 11b) confirmed the presence of residual garnet in the mantle source of the studied Maroua rocks. The REE patterns of the mafic samples presented a negative slope (Figure 8a) and probably indicated their origin from a relatively low degree of partial melting from an enriched mantle source. In Figure 11b, this percentage of partial melting fluctuates between 5 and 10%.
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Figure 11. Plots of uncontaminated mafic lavas of Mt. Kossel Béi in the (a) Dy/Yb vs. La/Yb diagram (after [63,64]) and (b) Sm/Yb vs. La/Sm diagram (after [66]). PM: primitive mantle; DMM: depleted MORB mantle.
Figure 11. Plots of uncontaminated mafic lavas of Mt. Kossel Béi in the (a) Dy/Yb vs. La/Yb diagram (after [63,64]) and (b) Sm/Yb vs. La/Sm diagram (after [66]). PM: primitive mantle; DMM: depleted MORB mantle.
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The Maroua volcanic rocks showed a negative slope from LILE (Ba, K and Th) to HFSE (Nb, Hf, and Ti) on the primitive mantle-normalized spider diagrams and presented negative Eu anomalies for the felsic lavas. These geochemical features are compatible with those of subduction-related magmas [67] and active continental margins [68,69]. The negative anomalies of Nb-Ta and Zr-Hf on the multi-element spider diagrams also suggest contributions or interactions of a pre-existing subducted crustal component or assimilation of the upper crust by the magma. Figure 12 displays geotectonic discriminant diagrams of the Maroua volcanics. On the La/10-Y/15-Nb/8 diagram [70], the rocks plot in the syn- to post-orogenic, active margin setting (Figure 12a). In the Th-Ta-Hf/3 triangular diagram (Figure 12b) [71], the samples fall in the volcanic arc field or the supra-subduction-zone basalt field. The Y vs. Zr plot (Figure 12c) [72] also illustrates the fact that the Maroua metavolcanic rocks belong to the fields of arc-related active margin settings. In the Y vs. Nb and Y + Nb vs. Rb diagrams [69], all the investigated samples fall within the volcanic arc granite field (Figure 12d,e). The Th/Nb vs. Ba/Th diagram (Figure 12f) [73] shows that the studied samples plotted toward the subducted slab-derived fluid. Therefore, the parental magma of the Maroua volcanic samples was probably generated during the interaction between the subducted crustal components and the lithospheric mantle, as previously suggested.
Figure 13 proposes a geodynamic model comprising different stages that led to the emplacement of the Maroua volcanic rocks. The increase in the dip angle of the subducted slab following the convergence of the Congo craton (Adamawa-Yadé Domain) and the Saharan craton (Western Cameroon Domain) resulted in lithospheric thinning via extension, which caused slab detachment, upwelling and slab melting of the asthenosphere. The partial melting of the enriched lithospheric mantle, with input of lower continental crust, then generated the primary mafic magmas, which produced the volcanic rocks of Maroua through fractional crystallization.

6. Conclusions

The Maroua metavolcanic rocks are located at the northern margin of the Central African Fold Belt in northern Cameroon and include basalts, andesites and dacites. The chemistry of the studied rocks showed that the mafic samples are essentially magnesian, whereas the felsic rocks are ferroan and belong to the calc-alkaline medium-K and, mainly, low-K tholeiite series. Major and trace element systematics of the volcanic rocks suggest that the lavas originate from a similar mantle source with compositional variations mainly caused by fractional crystallization. The modelled results indicate a derivation of the studied rocks 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 oceanic crust and the lithospheric mantle and which evolved chemically through fractional crystallization and assimilation. The features exhibited by the studied rocks are similar to those of subduction-zone melts and are characterized by the fact that on chondrite-normalized REE diagrams and primitive mantle-normalized spidergrams, (i) the mafic and felsic rocks display fractionated patterns with enrichment in the light REEs and depletion of the heavy REEs (LaN/YbN = 1.41–5.38); (ii) negative Nb–Ta (0.54–0.74), Ti (0.08–0.9) and Eu (0.59–0.87) anomalies were found for most samples.

Author Contributions

Conceptualization, P.C.B.à.N. and M.G.D.; methodology, P.C.B.à.N., M.G.D., D.H.D., N.L., M.N.K., P.M.F.T. and P.K.; validation, P.C.B.à.N., M.G.D. and N.L.; formal analysis, P.C.B.à.N., M.G.D., D.H.D., N.L., M.N.K. and P.M.F.T.; investigation, P.C.B.à.N., M.G.D. and N.L.; resources, P.C.B.à.N., M.G.D. and N.L.; data curation, P.C.B.a.N., M.G.D., P.K. and N.L.; writing—original draft preparation, P.C.B.à.N., M.G.D. and N.L.; writing—review and editing, P.C.B.à.N., M.G.D., D.H.D., N.L., M.N.K., P.M.F.T. and P.K.; supervision, M.G.D., N.L. and P.K.; project administration, M.G.D. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

The original contributions presented in the study are included in the article and further inquiries can be directed to the corresponding author.

Acknowledgments

The authors would like to warmly thank the anonymous reviewers for their comments, which deeply improved the paper.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. (a) Pan-African shear zone network in a pre-Mesozoic reconstruction (modified from [24]); (b) Pan-African structural map of Cameroon [23] (modified and reinterpreted from [21]). The inferred boundary of the Saharan metacraton was drawn following [25]. Thick lines indicate shear zones (SZs): BSZ Balché SZ, BNMB Buffle Noir–Mayo Baléo, CCSZ Central Cameroon SZ, GGSZ Godé–Gormaya SZ, MNSZ Mayo Nolti SZ, RLSZ Rocher du Loup SZ, SSZ Sanaga SZ. I, Paleoproterozoic basement and Pan-African syn-tectonic granitoids; II, Meso- to Neoproterozoic volcano–sedimentary basins.
Figure 1. (a) Pan-African shear zone network in a pre-Mesozoic reconstruction (modified from [24]); (b) Pan-African structural map of Cameroon [23] (modified and reinterpreted from [21]). The inferred boundary of the Saharan metacraton was drawn following [25]. Thick lines indicate shear zones (SZs): BSZ Balché SZ, BNMB Buffle Noir–Mayo Baléo, CCSZ Central Cameroon SZ, GGSZ Godé–Gormaya SZ, MNSZ Mayo Nolti SZ, RLSZ Rocher du Loup SZ, SSZ Sanaga SZ. I, Paleoproterozoic basement and Pan-African syn-tectonic granitoids; II, Meso- to Neoproterozoic volcano–sedimentary basins.
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Figure 2. Location of the study area. (a) Location of Cameroon in Africa; (b) geological map of Northern Cameroon (redrawn from [34]); (c) Google map image of the study area with location of the samples for the geochemical analysis.
Figure 2. Location of the study area. (a) Location of Cameroon in Africa; (b) geological map of Northern Cameroon (redrawn from [34]); (c) Google map image of the study area with location of the samples for the geochemical analysis.
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Figure 3. (a) Nb/Y versus (vs.) Zr/Ti discrimination diagram plotted for the Maroua felsic and mafic volcanics [35]; (b) AFM diagram [36] for the Maroua lavas. Basalts exhibit tholeiitic trends, whereas felsic volcanics are tholeiitic and calc-alkaline in nature. A: Na2O + K2O; F: FeOt; M: MgO; (c) K2O vs. SiO2 diagram [37]; (d) [Fe2O3t/(Fe2O3t + MgO)] vs. SiO2 diagram [38].
Figure 3. (a) Nb/Y versus (vs.) Zr/Ti discrimination diagram plotted for the Maroua felsic and mafic volcanics [35]; (b) AFM diagram [36] for the Maroua lavas. Basalts exhibit tholeiitic trends, whereas felsic volcanics are tholeiitic and calc-alkaline in nature. A: Na2O + K2O; F: FeOt; M: MgO; (c) K2O vs. SiO2 diagram [37]; (d) [Fe2O3t/(Fe2O3t + MgO)] vs. SiO2 diagram [38].
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Figure 4. Field outcrop (a,c,e) and hand specimen (b,d,f) photos of the sampled Maroua lavas. (a,b) Basalt of Mt. Mbalgaré; (c,d) andesite of Mt. Mbalgaré; (e,f) dacite of Mt. Kossel Béi.
Figure 4. Field outcrop (a,c,e) and hand specimen (b,d,f) photos of the sampled Maroua lavas. (a,b) Basalt of Mt. Mbalgaré; (c,d) andesite of Mt. Mbalgaré; (e,f) dacite of Mt. Kossel Béi.
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Figure 5. Thin-section photomicrographs of the Maroua lavas. (a) Dacite of Mt. Kessel Béi; (b) dacite of Mt. Mbalgaré; (c) andesite of Mt. Mbalgaré; (d) basalt of Mt. Balgaré.
Figure 5. Thin-section photomicrographs of the Maroua lavas. (a) Dacite of Mt. Kessel Béi; (b) dacite of Mt. Mbalgaré; (c) andesite of Mt. Mbalgaré; (d) basalt of Mt. Balgaré.
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Figure 6. Harker diagrams showing the content of major element oxides ((a) Fe2O3; (b) TiO2; (c) Al2O3; (d) MgO; (e) CaO; (f) P2O5; (g) Na2O; (h) K2O) vs. SiO2 concentration.
Figure 6. Harker diagrams showing the content of major element oxides ((a) Fe2O3; (b) TiO2; (c) Al2O3; (d) MgO; (e) CaO; (f) P2O5; (g) Na2O; (h) K2O) vs. SiO2 concentration.
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Figure 7. Harker diagrams showing selected trace elements ((a) Sc; (b) Ni; (c) V; (d) Sr; (e) Zr; (f) Ba; (g) Nb; (h) La) vs. SiO2 concentration.
Figure 7. Harker diagrams showing selected trace elements ((a) Sc; (b) Ni; (c) V; (d) Sr; (e) Zr; (f) Ba; (g) Nb; (h) La) vs. SiO2 concentration.
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Figure 9. (a) Zr/Nb vs. Ba/La (after [52]) and (b) Yb vs. La/Yb (after [53]) plots of fractional crystallization as the main petrogenetic process for the studied rocks. (c) Plot of SiO2 concentration vs. Dy/Yb showing abundant crystallization of amphibole rather than clinopyroxene (after [54]). (d) Binary Sr vs. Rb/Sr plot showing a negative correlation and illustrating K-feldspar and plagioclase fractionation. Cpx: clinopyroxene; Gt: garnet; Amp: amphibole; OIB: oceanic island basalt.
Figure 9. (a) Zr/Nb vs. Ba/La (after [52]) and (b) Yb vs. La/Yb (after [53]) plots of fractional crystallization as the main petrogenetic process for the studied rocks. (c) Plot of SiO2 concentration vs. Dy/Yb showing abundant crystallization of amphibole rather than clinopyroxene (after [54]). (d) Binary Sr vs. Rb/Sr plot showing a negative correlation and illustrating K-feldspar and plagioclase fractionation. Cpx: clinopyroxene; Gt: garnet; Amp: amphibole; OIB: oceanic island basalt.
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Figure 10. (a) Nb/Yb vs. Th/Yb diagram [55] illustrating crustal input projection, where higher Th/Nb ratios indicate more crustal contamination; the non-contaminated mafic lavas of Mt. Kossel Béi plot between E-MORB and OPB; (b) TiO2/Yb-Nb/Yb diagram [55] showing residual garnet projection in the source; (c) Ce/Pb vs. Nb/U plots after [56]. The data for the Precambrian basement are from [57]. (d) Nb/La vs. La/Yb plots of the Maroua volcanics [61]. OIB: oceanic island basalt; MORB: mid-ocean-ridge basalt; E-MORB: enriched mid-ocean-ridge basalt; IAB: island-arc basalt; EM-OIB: enriched-mantle ocean island basalt; CAB: continental-arc basalt; OPB: oceanic-plateau basalt.
Figure 10. (a) Nb/Yb vs. Th/Yb diagram [55] illustrating crustal input projection, where higher Th/Nb ratios indicate more crustal contamination; the non-contaminated mafic lavas of Mt. Kossel Béi plot between E-MORB and OPB; (b) TiO2/Yb-Nb/Yb diagram [55] showing residual garnet projection in the source; (c) Ce/Pb vs. Nb/U plots after [56]. The data for the Precambrian basement are from [57]. (d) Nb/La vs. La/Yb plots of the Maroua volcanics [61]. OIB: oceanic island basalt; MORB: mid-ocean-ridge basalt; E-MORB: enriched mid-ocean-ridge basalt; IAB: island-arc basalt; EM-OIB: enriched-mantle ocean island basalt; CAB: continental-arc basalt; OPB: oceanic-plateau basalt.
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Figure 12. Geotectonic discriminant diagrams of the Maroua volcanics. (a) La/10-Nb/8-Y/15 diagram [70]; (b) Th-Hf/3-Ta diagram [71]; (c) Y vs. Zr diagram after [72]; (d) Y vs. Nb and (e) Y + Nb vs. Rb diagrams after [69]; (f) Th/Nb vs. Ba/Th diagram after [73]. Primitive-mantle normalizing values were from [74]. SSZ: supra-subduction-zone basalts; VAG: volcanic-arc granitoids; syn-COLG: syn-collisional granitoids; WPG: within-plate granitoids; ORG: oceanic-ridge granitoids.
Figure 12. Geotectonic discriminant diagrams of the Maroua volcanics. (a) La/10-Nb/8-Y/15 diagram [70]; (b) Th-Hf/3-Ta diagram [71]; (c) Y vs. Zr diagram after [72]; (d) Y vs. Nb and (e) Y + Nb vs. Rb diagrams after [69]; (f) Th/Nb vs. Ba/Th diagram after [73]. Primitive-mantle normalizing values were from [74]. SSZ: supra-subduction-zone basalts; VAG: volcanic-arc granitoids; syn-COLG: syn-collisional granitoids; WPG: within-plate granitoids; ORG: oceanic-ridge granitoids.
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Figure 13. Schematic geotectonic model for the genesis of the Maroua volcanic rocks (adapted from [7]). The color of melts generated from the slab melting, partial melting of crust and mantle, and welling magma in the continental crust are different because their composition are evolutionary.
Figure 13. Schematic geotectonic model for the genesis of the Maroua volcanic rocks (adapted from [7]). The color of melts generated from the slab melting, partial melting of crust and mantle, and welling magma in the continental crust are different because their composition are evolutionary.
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Table 1. Whole-rock major and trace element composition of Maroua volcanic rocks, Mount Kossel Béi.
Table 1. Whole-rock major and trace element composition of Maroua volcanic rocks, Mount Kossel Béi.
Rock TypeBasaltDaciteDaciteBasaltAndesiteBasaltAndesiteBasaltBasaltBasaltDacite
Lon. (°E)
Lat. (°N)		14.32929
10.61238		14.32976
10.61216		14.33117
10.61356		14.33074
10.61399		14.33133
10.61435		14.33059
10.61441		14.32931
10.61502		14.32868
10.61400		14.32868
10.61279		14.32868
10.61262		14.32876
10.61221
Sample IDMP1MP2MP3MP4MP5MP6MP9MP10MP11MP12MP13
SiO2 (Wt%)50.3175.0773.1251.2373.4549.6368.0051.7757.2251.1774.96
TiO21.090.280.361.220.351.050.501.040.970.960.31
Al2O318.9314.5813.4018.3913.3519.1914.8018.2616.9720.2013.09
Fe2O311.113.524.0511.074.0511.125.8110.9410.549.773.64
MnO0.170.070.100.220.100.190.150.180.180.180.07
MgO4.890.570.724.990.734.951.085.043.674.470.57
CaO9.920.791.008.320.7710.082.748.025.859.470.54
Na2O2.844.426.643.976.643.015.664.253.642.895.77
K2O0.500.600.500.330.470.521.110.220.740.590.95
P2O50.250.090.100.280.100.270.150.270.230.300.09
LOI2.261.571.842.181.902.792.373.013.422.471.5
Mg#49.7026.5028.750.4028.75029.450.9043.9050.7026.10
AI29.7318.3513.8030.2313.9529.4620.6630.0431.7129.0819.44
ASI0.811.561.010.831.040.800.950.840.970.891.14
Li (ppm)15.9274.824.23512.8772.51216.9983.92411.64116.7569.4072.676
P923.899325.253297.797925.674123.642922.976473.773935.297929.275736.994298.553
Sc31.66510.93410.58533.3558.56331.66515.6132.20127.30927.14210.456
Ti6186.032051.0031945.5236248.1411130.256261.122823.3246357.1695675.7275953.721933.763
V294.2557.826.939328.1178.424282.69932.773306.601222.053268.94610.287
Cr34.9770.4910.53628.2351.52135.2842.06430.65825.5557.0860.497
Co40.84220.73829.54535.45927.97842.53127.89636.95346.00835.9333.04
Ni16.8791.1671.09512.8241.75317.9292.12414.60514.8836.9451.072
Cu78.0224.7010.78377.5544.97977.62115.72275.72771.0558.6417.747
Zn91.76899.13264.87388.96120.76892.93997.45794.388.436102.13779.323
Ga17.12616.60715.76519.10314.93516.72216.76517.4441616.92816.092
AS0.4360.5680.5050.4720.4830.4390.5410.5062.290.4180.521
Rb7.95410.3445.7134.23313.448.07312.0982.5298.4511.71111.163
Sr149.33162.13942.604176.411113.444148.25131.548167.268138.4237.62131.73
Y15.69744.22750.84514.87740.08616.04334.22116.37615.53324.31542.815
Zr19.001222.455223.2127.82139.13216.111110.98826.9528.93444.585216.571
Nb3.51410.369.4164.5744.7744.1187.9643.4513.6554.7699.435
Sn1.4672.9662.8821.0491.5581.5591.9430.9580.631.3462.519
Sb0.5360.4090.2041.7860.1110.3860.5711.1282.2380.6270.15
Cs0.0490.1190.0850.0730.0290.0581.2030.0470.0510.0840.044
Ba227.327413.464301.865165.894267.374216.201383.92156.334275.752281.047528.082
La8.24520.26419.3168.58911.5158.01816.0538.13311.1099.84322.643
Ce17.15444.16942.30517.88726.37917.25635.99918.47923.50322.24850.004
Pr2.6785.685.4772.7623.6622.3284.6072.4892.6912.976.111
Nd11.12525.37525.57512.24717.8111.07120.98911.80612.61614.2126.624
Sm3.1026.4666.2233.0974.9222.8545.4023.0283.0623.816.442
Eu1.2241.421.3171.1561.2211.1151.6281.2381.1441.3791.395
Gd2.9567.3187.3933.1226.0383.1716.1633.3133.2754.3787.229
Tb0.5871.2141.2660.4781.0330.48610.5070.4890.7061.183
Dy3.2038.2148.7343.1787.0593.0566.5933.2493.0454.697.925
Ho0.7571.7511.8850.6431.4980.6251.3740.6530.6160.9631.69
Er1.8145.175.4711.6584.3741.6783.8541.761.6542.624.985
Tm0.3290.7610.7740.2270.6380.2290.5440.2390.2270.3670.759
Yb1.4235.4525.521.4324.7481.4473.6481.4761.4812.2915.403
Lu0.1780.8130.8180.1790.6340.1890.5060.1880.2060.2960.795
Hf0.7886.0956.1131.7454.0870.8923.0511.161.0871.5955.967
Ta0.2540.6160.5810.1590.3010.2480.4870.1950.1980.2870.564
W35.97373.97798.17733.75693.83336.02473.75335.83546.64932.944104.903
Pb1.7640.052.2292.24918.1161.7974.8062.0272.2193.0180.021
Th0.3453.1142.8860.3441.290.3262.0130.3130.3030.9984.754
U0.1622.9851.2060.2470.6110.1520.7860.1540.1410.4072.772
LaN/YbN4.162.672.514.301.743.973.163.955.383.083.01
Eu/Eu*1.240.630.591.140.681.130.861.191.101.030.62
Nb/Nb*0.710.450.430.870.420.860.470.730.680.520.40
Ti/Ti*0.770.120.120.870.080.900.200.860.780.610.12
Hf/Hf*0.282.722.420.581.810.321.050.400.410.462.63
Ce/Ce*0.901.011.010.901.000.981.031.011.051.011.04
Mg# = molar ratio of [MgO/(MgO + FeO)] × 100); assuming FeOt = Fe2O3 × 0.8998Fe2O3; AI = [(MgO + K2O)/(MgO + K2O+ CaO + Na2O)] ×100; ASI = [Al2O3/(CaO+ Na2O + K2O)] molar. (*) refer to normalizing values of Eu, Nb, Ti, Hf and Ce.
Table 2. Whole-rock major and trace element composition of Maroua volcanic rocks, Mount Mbalgaré.
Table 2. Whole-rock major and trace element composition of Maroua volcanic rocks, Mount Mbalgaré.
Rock TypeAndesiteDaciteBasaltDaciteDaciteBasaltAndesiteBasaltDaciteAndesite
Lon. (°E)
Lat. (°N)		14.32875
10.61855		14.32836
10.62064		14.32909
10.62423		14.32863
10.62193		14.32879
10.62221		14.32959
10.62585		14.33079
10.62454		14.33070
10.62537		14.33132
10.62331		14.33183
10.62101
Sample IDMB2MB3MB4MB5MB6MB8MB11MB12MB13MB17
SiO2 (Wt%)73.1375.2560.1773.3974.9249.8872.4360.4073.7274.64
TiO20.300.191.050.240.201.280.280.970.230.26
Al2O313.5512.3415.4513.1212.5718.6913.8214.9113.2213.04
Fe2O34.763.459.474.003.4912.714.439.113.853.24
MnO0.180.180.200.190.150.210.140.210.220.11
MgO0.490.513.360.400.474.950.133.070.520.65
CaO0.801.624.321.311.297.771.225.191.861.55
Na2O6.355.014.916.174.762.585.985.294.645.63
K2O0.361.410.751.152.091.721.510.521.680.81
P2O50.090.050.330.020.060.210.060.330.040.06
LOI1.641.652.741.501.343.541.502.591.762.61
Mg#18.7024.9044.4018.323.246.706.243.1023.2031.10
AI10.6122.4230.8117.1529.6739.1818.4925.5025.2916.87
ASI1.100.970.920.951.010.921.010.801.031.01
Li (ppm)5.6284.5866.2772.6422.72410.41.7584.1093.2255.132
P267.841304.3961073.705144.781143.745646.183147.295995.549120.828178.029
Sc16.01311.13227.40711.7059.68631.06213.35927.22912.10710.578
Ti1686.7011968.2935966.21367.5861197.8437490.1881591.5745552.2911341.1771375.951
V0.876.971152.9856.97110.574379.9480.145158.2087.28714.35
Cr0.6580.6220.4671.51.6854.6110.5082.1131.5041.842
Co17.25335.15926.20925.47428.94144.2326.6332.81922.35635.095
Ni0.7261.1330.8311.4611.59710.9430.8011.3891.5131.62
Cu1.5581.1694.293.244.251175.5710.6425.8334.787.818
Zn102.39169.10290.542120.78888.37294.918107.68295.773110.5668.281
Ga15.05615.80714.37316.45114.78216.21916.72215.50716.43211.666
AS0.4170.4570.450.50.4730.170.5250.2310.4420.831
Rb3.6145.3746.12711.71620.97819.09711.3145.08315.379.242
Sr55.37944.665176.42170.998160.814357.882123.88595.015116.06772.274
Y29.46139.15221.72642.94538.95212.76542.42319.45741.06328.967
Zr98.986223.89744.427126.06995.47930.36894.9225.07102.322114.415
Nb2.5939.4171.75.2374.8191.3915.991.5444.9762.753
Sn1.3142.051.4331.9831.9360.4581.5320.6461.8481.247
Sb0.2670.1740.2660.0740.140.1010.1290.1110.1180.1
Cs0.0370.0860.0420.1170.0530.0870.0290.3880.0280.155
Ba160.748284.24479.863206.581532.9291030.16478.942264.699343.072385.587
La7.22616.5035.59114.90312.664.51616.3464.92514.0757.637
Ce18.84137.58213.77833.36930.3249.88534.04812.17131.54516.096
Pr2.6914.982.0694.5394.2061.465.1721.7824.4692.241
Nd13.44221.94610.79721.84120.0827.43624.749.29221.56510.243
Sm3.8595.493.1796.0185.4892.0986.5532.7125.8542.777
Eu1.2091.1671.2261.741.4221.0071.8161.0721.6640.86
Gd4.7086.0873.9157.1846.4452.4947.663.3967.0253.773
Tb0.7980.9990.6251.2141.0980.3941.260.5541.1970.67
Dy5.4836.824.2198.2637.4642.5358.3973.628.0194.759
Ho1.1831.4860.8741.741.5730.5181.7380.7611.6661.054
Er3.484.7542.4634.9154.3621.4084.852.1444.6823.25
Tm0.5240.7490.3480.7070.6150.1940.6830.3040.6690.486
Yb3.6795.5532.3764.7844.0571.2754.5422.164.6793.619
Lu0.5430.8180.320.6630.5150.1760.5560.2820.5790.504
Hf2.96.4391.3633.873.0250.9332.9280.9333.1453.441
Ta0.1760.5950.1190.3240.2950.0940.3550.1060.2970.184
W55.816120.60134.44986.07792.28129.777107.45666.16582.66123.004
Pb00.040.7563.7364.4721.1391.4341.1310.210.084
Th3.0092.1190.4141.3521.2490.2551.2710.373.5381.58
U0.82.8860.2970.6180.5610.1260.50.221.2340.963
LaN/YbN1.412.131.692.232.242.542.581.642.161.51
Eu/Eu*0.620.871.060.810.731.350.781.080.790.81
Nb/Nb*0.370.460.380.400.410.440.450.390.400.34
Ti/Ti*0.160.140.710.090.081.390.090.760.090.17
Hf/Hf*1.081.960.413.141.670.441.410.300.841.88
Ce/Ce*1.051.020.990.991.020.940.911.010.980.95
Mg# = molar ratio of [MgO/(MgO + FeO)] × 100); assuming FeOt = Fe2O3 × 0.8998Fe2O3; AI = [(MgO + K2O)/(MgO + K2O+ CaO + Na2O)] ×100; ASI = [Al2O3/(CaO+ Na2O + K2O)] molar. (*) refer to normalizing values of Eu, Nb, Ti, Hf and Ce.
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Biakan à Nyotok, P.C.; Gountié Dedzo, M.; Djamilatou, D.H.; Lenhardt, N.; Klamadji, M.N.; Fosso Tchunte, P.M.; Kamgang, P. The Subduction-Related Metavolcanic Rocks of Maroua, Northern Cameroon: New Insights into a Neoproterozoic Continental Arc Along the Northern Margin of the Central African Fold Belt. Geosciences 2024, 14, 298. https://doi.org/10.3390/geosciences14110298

AMA Style

Biakan à Nyotok PC, Gountié Dedzo M, Djamilatou DH, Lenhardt N, Klamadji MN, Fosso Tchunte PM, Kamgang P. The Subduction-Related Metavolcanic Rocks of Maroua, Northern Cameroon: New Insights into a Neoproterozoic Continental Arc Along the Northern Margin of the Central African Fold Belt. Geosciences. 2024; 14(11):298. https://doi.org/10.3390/geosciences14110298

Chicago/Turabian Style

Biakan à Nyotok, Pierre Christel, Merlin Gountié Dedzo, Diddi Hamadjoda Djamilatou, Nils Lenhardt, Moussa Ngarena Klamadji, Periclex Martial Fosso Tchunte, and Pierre Kamgang. 2024. "The Subduction-Related Metavolcanic Rocks of Maroua, Northern Cameroon: New Insights into a Neoproterozoic Continental Arc Along the Northern Margin of the Central African Fold Belt" Geosciences 14, no. 11: 298. https://doi.org/10.3390/geosciences14110298

APA Style

Biakan à Nyotok, P. C., Gountié Dedzo, M., Djamilatou, D. H., Lenhardt, N., Klamadji, M. N., Fosso Tchunte, P. M., & Kamgang, P. (2024). The Subduction-Related Metavolcanic Rocks of Maroua, Northern Cameroon: New Insights into a Neoproterozoic Continental Arc Along the Northern Margin of the Central African Fold Belt. Geosciences, 14(11), 298. https://doi.org/10.3390/geosciences14110298

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