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Article

Paleoproterozoic Mafic and Ultramafic Rocks from the Mako Belt, Senegal: Implications for Back-Arc Basin Origin

by
Ibrahima Dia
1,
Tanya Furman
2,*,
Kaan Sayit
3,
Shelby Bowden
2,4,
Mamadou Gueye
5,
Cheikh Ibrahima Faye
5 and
Olivier Vanderhaeghe
6
1
Polytech Diamniadio, Amadou Mahtar Mbow University, Dakar 45927, Senegal
2
Department of Geosciences, Pennsylvania State University, University Park, PA 16803, USA
3
Department of Geological Engineering, Middle East Technical University, 06800 Ankara, Turkey
4
Savannah River National Laboratory, Aiken, SC 29808, USA
5
Ecole Nationale Supérieure des Mines et de la Géologie, Cheikh Anta Diop University, Dakar 10700, Senegal
6
GET-OMP, Universite de Toulouse, UPS, CNRS, IRD, CNES, 14 Avenue E. Belin, 31400 Toulouse, France
*
Author to whom correspondence should be addressed.
Minerals 2025, 15(10), 1057; https://doi.org/10.3390/min15101057
Submission received: 25 August 2025 / Revised: 23 September 2025 / Accepted: 30 September 2025 / Published: 5 October 2025
(This article belongs to the Section Mineral Geochemistry and Geochronology)
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Abstract

The Mako Belt in the Kédougou-Kéniéba Inlier (eastern Senegal) preserves Paleoproterozoic (2.3–1.9 Ga) mafic and ultramafic rocks that record early crustal growth processes within the southern West African Craton (WAC). Basalt bulk rock compositions preserve primary melt signatures, whereas the associated ultramafic cumulates are variably serpentinized and are better assessed through mineral chemistry. Basalts occur as massive and pillow lavas, with MgO contents of 5.9–9.1 wt.% and flat to slightly LREE-depleted patterns (La/Smₙ = 0.73–0.88). Primitive mantle-normalized diagrams show subduction-related signatures, including enrichment in Ba, Pb, and Rb and depletion in Nb and Ta. Most basalts and all ultramafic rocks display (Nb/La)PM > 1, consistent with enriched mantle melting in a back-arc setting. Harzburgites and lherzolites have cumulate textures, high Cr and Ni contents, and spinel with chromian cores (Cr# > 0.6) zoned sharply to Cr-rich magnetite rims that overlap basalt spinel compositions. Integration of the petrographic, mineralogical, and whole-rock geochemical data indicates the presence of mafic melts derived from a subduction-modified mantle wedge and likely formed in a back-arc basin above a subducting slab, rather than from a plume or mid-ocean ridge setting. Regional comparisons with other greenstone belts across the WAC suggest that the Mako Belt was part of a broader arc–back-arc system accreted during the Eburnean orogeny (~2.20–2.00 Ga). This study supports the view that modern-style plate tectonics—including subduction and back-arc magmatism—was already active by the Paleoproterozoic, and highlights the Mako Belt as a key archive of early lithospheric evolution in the WAC.

Graphical Abstract

1. Introduction

The question of when and how modern-style plate tectonics began operating on Earth remains one of the central debates in Precambrian geodynamics. While some authors argue for the onset of subduction, arc magmatism, and terrane accretion as early as the Mesoarchean [1,2], others maintain that many Archean and Paleoproterozoic belts may reflect non-uniformitarian processes such as plume-driven lithospheric overturn or stagnant-lid tectonics [3,4]. Resolving this debate requires detailed studies of well-preserved early Proterozoic orogenic belts, particularly those that contain both mantle- and crust-derived components and that preserve magmatic, structural, and geochemical evidence for subduction-related processes.
The West African Craton (WAC) provides a unique setting to address this issue. The WAC comprises two major Paleoproterozoic to Archean domains: the Archean Kénéma-Man Domain (KMD) and the Paleoproterozoic Baoulé-Mossi Domain (BMD) (Figure 1). Paleoproterozoic greenstone-granitoid terranes are particularly well exposed in the Kayes and Kédougou Kéniéba inliers [5,6]. These regions contain calc-alkaline and tholeiitic mafic sequences intruded by granitoids and are bounded by large-scale shear zones that reflect polyphase deformation and orogenic assembly [7,8,9]. The greenstone terranes formed during the Eburnean orogeny (~2.20–2.00 Ga), a key period in Earth’s tectonic evolution that many consider as marking the onset of modern-style plate tectonics (e.g., [1,7,10]). Crustal growth in this region likely resulted from successive accretion of island arcs and back-arc basins, possibly resembling a modern convergent margin system [10,11,12], although some authors invoke non-uniformitarian models such as plume-related tectonics or pre-plate tectonic mechanisms [13,14].
The Kédougou-Kéniéba Inlier forms the northernmost exposure of the BMD in eastern Senegal and western Mali (Figure 1). This region offers rare exposures of both juvenile volcanic sequences and associated ultramafic units, making it an ideal location to investigate the tectonomagmatic conditions of early crustal growth. The Kédougou-Kéniéba Inlier covers ~16,000 km2 and comprises two primary lithostratigraphic groups: the predominantly volcanic-plutonic Mako Supergroup to the west, and the mainly sedimentary Dialé-Daléma Group to the east [9,15,16]. These units are separated by the Main Transcurrent Zone (MTZ), a major crustal-scale shear zone marking a tectonic boundary characterized by intensive deformation and granitic intrusions [8,9]. Regionally, NE-SW trending Birimian greenstone belts are localized along crustal-scale transcurrent shear zones such as the Senegal-Mali Shear Zone (SMSZ) and the MTZ (Figure 2). The Kédougou-Kéniéba Inlier records multiple stages of Paleoproterozoic crustal evolution: (1) formation of volcanic and plutonic rocks at ~2.20–2.16 Ga [13,17], (2) sedimentation in the Dialé-Daléma basin (~2.12–2.11 Ga; [18]), and (3) regional metamorphism and plutonism during the Eburnean orogeny (2.09–2.06 Ga; [19]). The Mako Belt consists of a thick, conformable sequence of mafic volcanic flows—both massive and pillowed—interbedded with volcaniclastics and cut by syn- to late-tectonic calc-alkaline plutons [6,20]. These rocks exhibit pervasive greenschist facies metamorphism, typical of Birimian greenstones throughout the region. Ultramafic rocks (e.g., harzburgites, lherzolites) crop out as isolated lenses within this mafic sequence and are variably serpentinized [11,12]. These ultramafic bodies are typically thrust over the mafic units and aligned along NE-SW trending structural corridors (Figure 2; [8]). Geochronological constraints (e.g., Sm-Nd and Pb-Pb isochrons at ~2.19–2.06 Ga) on Mako Belt igneous units [12,17] suggest prolonged magmatic activity that preceded regional deformation. The eastern part of the belt includes granitoids of the Saraya Batholith (U-Pb zircon ages ~2.072–2.079 Ga) that intrudes the Dialé-Daléma metasediments [19].
Despite its limited spatial extent (~20 km x < 100 km; Figure 2), the Mako Belt offers a valuable window into Paleoproterozoic tectonomagmatic processes. The juxtaposition of arc-like tholeiitic basalts and cumulate ultramafic rocks, the presence of basalt pillows, and the enrichment in subduction-related trace elements all suggest formation in an arc to back-arc setting [11,12] rather than an oceanic plateau (e.g., [13,14,15,21]). Most studies have focused on either the mafic volcanic series or the ultramafic units in isolation, and few have integrated petrographic, geochemical, and mineralogical data to evaluate whether these rocks can be convincingly attributed to modern-style tectonic processes such as subduction and arc extension. We present new whole-rock major and trace element geochemical data, along with mineral chemistry and petrographic descriptions, from a representative suite of mafic and ultramafic rocks in the Mako Belt, the westernmost greenstone belt in the Kédougou-Kéniéba Inlier. Our objective is to determine whether these rocks record geochemical signatures consistent with subduction-related settings—particularly back-arc basin environments—and to assess their implications for Paleoproterozoic geodynamics in the West African Craton. We use systematic variations among the less-fluid-mobile trace elements to document and evaluate the effects of subduction-related processes in basalt melt genesis. By integrating our new data with published results from other SWAC belts we clarify the tectonic setting of the Mako Belt and evaluate the role of modern-style plate tectonics during the early Proterozoic. Our work therefore provides key insights into the mechanisms of crustal growth, mantle melting, and lithospheric assembly in one of Africa’s oldest continental nuclei.

2. Materials and Methods

2.1. Field Observations and Sampling

Field sampling was conducted across the Mako Belt region of the Kédougou-Kéniéba Inlier in eastern Senegal (Figure 2). The basaltic units of the Mako Belt occur as both massive flows and well-preserved nested pillow lavas (Figure 3a,b and Figure 4a). Individual pillows range from 40 to 100 cm across and exhibit clear chilled margins and devitrified glass rims. Vesicles, observed sporadically along flow tops, are locally flattened. Ultramafic rocks form resistant ridges and isolated lenses and consist primarily of coarse-grained harzburgites and lherzolites, commonly serpentinized (Figure 3c,d and Figure 4b–f). These rocks are characterized by coarse-grained textures and dark green to black coloration. At the regional scale they exhibit signs of polyfolding, typically with dome and basin structures. A total of 12 representative samples were selected for detailed analysis, comprising five basalts and seven ultramafic rocks (primarily harzburgite and lherzolite).
Sampling emphasized outcrops that showed minimal visible weathering or alteration to preserve primary textures and geochemical signals as much as possible. Specific attention was paid to avoiding samples with extensive hydrothermal overprinting, which is pervasive in this region [11,12]. To target the least altered materials, we used consistent field criteria to distinguish less-altered from strongly hydrothermally altered rocks (Figure 3e,f). In basalts, less-altered outcrops display intact pillow/massive textures with dark, fine-grained interiors, crisp selvages, rare or thin mm-scale veins, and limited bleaching; amygdales (where present) are sparse and small. Strongly altered basalts exhibit pervasive bleaching, epidote–chlorite–calcite veining and selvages, oxidized (hematite/limonite) rinds, softening along fractures, and abundant, coalescing amygdales infilled by secondary carbonates/epidote. In ultramafic rocks, less-altered exposures show coarse relict textures with localized mesh-serpentine and minor magnetite, whereas strongly altered examples show pervasive mesh- to ribbon-serpentinization, abundant magnetite veining, local talc–chlorite replacement along shear bands, and carbonate ± silica infill in fractures. These field criteria guided selection of sampling spots, which were then further screened petrographically and geochemically.

2.2. Sample Processing and Analytical Methods

Thin sections were prepared by Spectrum Petrographic for petrographic observation and electron probe microanalysis (EPMA). EPMA was conducted at the Materials Characterization Laboratory, Pennsylvania State University, using a CAMECA SX-50 instrument (Gennevilliers, France) with a 15 kV accelerating voltage, 30 nA beam current, and 2 µm spot size. The instrument was standardized for Na, Al, Si, and Ca on plagioclase, Mg and Cr on pyrope, K on orthoclase, Ti on synthetic sphene, and Mn on almandine. Mineral analyses reported are averages of three spots per grain, except for spinels, for which single-spot transects were used to document zoning. Mineral composition data are presented in Table S1.
Samples were prepared for geochemical analysis at the Pennsylvania State University. Fresh rock fragments were first slabbed (~1 cm thick) and pieces with visible traces of vein material (e.g., discoloration along fractures) were discarded. The slabs were then broken into ~5 mm chips using a non-metallic alumina micro-chipper and sieved to eliminate fines, which may disproportionately contain altered materials. The resulting coarse fractions were powdered in a tungsten carbide mill to produce homogenized sample powders.
Analyses of major and trace element abundances (Table 1) were performed at the Pennsylvania State University Laboratory for Isotopes and Metals in the Environment (LIME) on a Thermo iCAP 7400 Inductively Coupled Plasma Emission Spectrometer and a Thermo iCAP RQ Inductively Coupled Plasma Mass Spectrometer (Waltham, MA, USA), respectively. Prior to major element analyses, powdered samples were prepared via lithium metaborate fusion [22]. A total of 50–100 mg of powdered sample was mixed with 400 mg of lithium metaborate powder and transferred to graphite crucibles. The mixtures were heated to 900 °C for 10 min and the melt beads were added to 100 mL of 5% HNO3 solution in Teflon beakers for 20 min. Samples were further diluted by combining a 2.5 mL aliquot of the sample with 10 mL each of 2% HNO3 and lutetium internal standard solutions. Prior to Sc analysis, powdered basalt samples and hand-picked plagioclase-free glassy matrix materials (50 mg) were weighed into clean Teflon vials for acid digestion. Concentrated acid was used to digest the samples. Three milliliters of HF, one milliliter of HClO4, and one milliliter of HNO3 were added to the powder initially and the vial was sealed and heated at 100 °C for 24 h. Then, the samples were dried at 120 °C to drive off the HNO3 and HF, and 0.5 mL of HClO4 was added before heating at 120 °C overnight. Upon cooling, reverse aqua regia was added to the vial (3 mL of HNO3 and 1 mL of HCl). Samples were reacted at room temperature for one hour before being sealed and heated overnight at 150 °C. Samples were then completely dried down at 160 °C and resuspended in 4 mL of 4N HNO3 for analysis. After acid digestion, the samples were diluted by combining a 0.1 mL aliquot of digested sample with 5.9 mL of 2% HNO3. Analytical accuracy and precision were assessed using international rock standards (BHVO-1, BIR-1, JA-1, W-2, BCR-1). Major element reproducibility was typically <3%, and <1% for elements such as SiO2, Sr, Y, Zr, Nb, La, and Ce; <3% for other major elements, Ba, Rb, Cs, Cr, Sc, V, Co, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Hf and Ta; <5% Ni, Yb, Lu, Pb, Th and <8% for U. Loss on ignition (LOI) values were obtained by measuring weight loss after heating powdered samples to 900 °C for 8–12 h. Major element oxide values used in figures have been renormalized to 100 wt.% anhydrous with 15% of the total iron as Fe+3.

3. Results

3.1. Petrography and Mineral Chemistry

The basaltic rocks are broadly metamorphosed to greenschist facies, with primary phases (plagioclase, olivine, clinopyroxene) replaced pervasively by chlorite, epidote, actinolite, and albite. Vesicle fillings commonly include quartz, carbonate, and secondary micas [11,23,24]. Pillow margins are aphanitic to sparsely phyric (up to 1 vol.% olivine phenocrysts ~0.2 cm dimension) while pillow interiors have holocrystalline textures with ~200 µm crystals of plagioclase feldspar, relict olivine + clinopyroxene and Fe-Ti oxides. Fe-Ti oxides in basalt MMK are Cr-bearing magnetites with over ~95 wt.% total iron (average 45.8 wt.% Fe2+ and 50.6 wt.% Fe3+) and up to 8 wt.% Cr2O3.
Cumulate textures are widespread, with euhedral clinopyroxene and olivine crystals up to several millimeters across. Sample LM is distinct in that it contains over 50 vol.% euhedral clinopyroxenes up to 1 cm across in a matrix of plagioclase feldspar. The ultramafic rocks typically contain optically continuous clinopyroxene crystals approaching 3 cm across in poikilitic growth around euhedral olivines ~200 µm in dimension.
Clinopyroxenes from ultramafic samples are dominantly diopsidic (Wo41–44En50–54Fs2–8), with minor augite in some samples (e.g., LM, KL1) (Figure 5). Orthopyroxenes occur in lesser abundance (e.g., KL2, LA). The diopsidic clinopyroxenes and orthopyroxenes have low Al2O3 (<3.75 wt.%) and TiO2 (<1.5 wt.%); augitic pyroxenes have higher Al2O3 (LM 8–12 wt.%, KL1 ~9.5 wt.%) and TiO2 (LM 1–2.5 wt.%, KL1 > 4 wt.%) contents (Table S1). Olivine compositions vary between samples but are quite homogeneous within each of the ultramafic samples (KL1 Fo82–83, KL2 Fo80–81, LA Fo84; Table S1).
Individual spinel crystals range from Al-chromite and picotite (Cr# 0.5–0.6; Cr# = Cr/[Cr + Al]) through Fe-chromite/Cr-magnetite to magnetite with compositions overlapping those analyzed in basalt sample MMN (Figure 6a–c). Many Al-Cr rich spinels are zoned to magnetite at their outermost rims, consistent with hydrothermal overprint (Figure 6b). Spinel Cr# values range from 0.5 to >0.6, indicative of arc-related magmatic affinity [25,26].

3.2. Whole Rock Major and Trace Element Geochemistry

Major element oxide compositions of massive and pillow basalt samples range from 5.7 to 8.9 wt.% MgO and 50.6–56.5 wt.% SiO2. Abundances of incompatible major elements K2O and P2O5 do not correlate with either MgO or SiO2 in the Mako basalt suite and are higher in samples with 8–9 wt.% MgO than they are in more evolved lavas with <8 wt.% MgO. This precludes a simple role for fractionation of the lava compositions. Loss on ignition (LOI) values for the basalts range from 0.6 to 3.1 wt.%, consistent with petrographic observations of pervasive but weak hydrothermal alteration. Most of the basalts are quartz normative (2.2–13 vol.%), but BAM contains 4.3 vol.% normative olivine. Their total alkali and silica contents (Figure 7a) place them broadly in the basaltic andesite field; these results may reflect alkali mobility during hydrothermal alteration but are still comfortably within the published range of samples defined as Mako basalts [13,20].
The ultramafic rocks have LOI values between 4.5 and 22.4 wt.%, consistent with petrographic observations of moderate to complete serpentinization. Normalized (anhydrous) major element oxide values are therefore considered cautiously; the samples contain 40.1–45.5 wt.% SiO2 and 33.3–44.0 wt.% MgO, typical of olivine- and pyroxene-rich cumulates (Table 1). Strong serpentinization makes classification of the Mako Belt ultramafic rocks challenging. Mako Belt samples have been characterized as harzburgite, lherzolite or wehrlite [11,12]; our samples are dominantly harzburgites to lherzolites (Figure 7b).
Trace element compositions of the basalts reflect moderate to low degrees of fractionation. Cr and Ni contents (163–298 ppm and 83–116 ppm, respectively) are consistent with limited olivine and pyroxene removal from primary mantle melts. Chondrite-normalized rare earth element (REE) patterns are broadly flat (~10× chondrite), with minor LREE depletion (La/Smₙ = 0.73–0.88, Lan/Ybn 0.75–0.97) and weak Eu anomalies in some samples (Figure 8a). Primitive mantle-normalized diagrams show consistent enrichment in LILE (Ba, Rb, Pb) over HFSE (Nb, Ta, Ti), with a notable positive Pb anomaly (Figure 8b). Massive lavas from the northern portion of the sampled area are characterized by (Nb/La)PM < 1, whereas pillow basalts from central and southern areas have (Nb/La)PM > 1, a signature consistent with back-arc settings [31]. Incompatible trace element abundances (e.g., La, Zr) are higher in samples with 8–9 wt.% MgO than in the lower-MgO samples. Mako Belt lavas are highly enriched in Ba, K and Pb suggesting shallow mantle incorporation of subduction zone fluids, and moderately enriched in Rb, Th, U, and LREE suggesting addition of a deeper subduction component. Negative anomalies in Nb are typical of arc-related magmatism. Notable distinctions between the groups are the lack of K enrichment and Nb depletion in the ultramafic rocks.
Ultramafic cumulates contain high Cr (2252–3882 ppm) and Ni (810–1500 ppm), consistent with accumulation of olivine into a basaltic liquid. REE patterns are generally flat or slightly concave-down (La/Smₙ = 0.81–1.3; La/Ybₙ = 1.0–1.9) (Figure 8c). Primitive mantle-normalized patterns show low incompatible element abundances but systematic positive Pb anomalies (Figure 8d). On MORB-normalized multi-element diagrams (Supplementary Figure S1) the ultramafic samples display lower incompatible element abundances than the basalts but retain a significant positive Pb anomaly, suggesting interaction with basaltic melts and/or subduction-related fluids [12].
The multi-element patterns of our samples broadly overlap the published range of Mako Belt basalts, but several differences are noteworthy (Figure 8). First, LILE behavior is variable: some literature samples are strongly LILE-enriched whereas others are only weakly so, matching the spread observed in our suite. Second, HFSE anomalies are selective rather than universal in both datasets: negative Nb–Ta anomalies occur in some samples, while Ti and Hf are generally flat or show slightly negative anomalies. Third, a few published samples exhibit more pronounced negative anomalies at Zr than seen in our basalts. These differences likely reflect a combination of (i) heterogeneous source and/or fractionation histories and (ii) variable alteration. To minimize alteration effects, we emphasize immobile-element relationships and ratios (e.g., Ti, Zr, Nb, Hf systematics) in the subsequent tectonic assessment, and we avoid relying on alteration-sensitive proxies. Overall, the integrated pattern suggests overlapping geochemical characteristics between the new and published datasets, with variability that cautions against single-proxy tectonic assignments.

4. Discussion

4.1. Classification and Tectonic Setting of Mako Belt Mafic and Ultramafic Rocks

Although many samples preserve primary textures, the pervasive greenschist metamorphism and serpentinization in the Mako Belt [6,24] necessitate cautious interpretation of fluid-mobile elements (e.g., Ba, Pb, K). Accordingly, our geochemical interpretation emphasizes relatively immobile elements (e.g., Th, Nb, Yb, Zr) and integrates multiple discriminant diagrams to minimize the effects of alteration [31,34,35].
The subalkaline character of the studied mafic rocks of the Mako Belt, along with their enrichment in mobile elements such as Ba, K, and Pb, suggests a subduction-related tectonic setting. In an AFM diagram (Figure 9a), the samples plot near the tholeiitic–calc-alkaline transition. Classification based on elements that have low mobility in hydrothermal fluids (MnO-P2O5-TiO2/10; Figure 9b) places most samples in the field of island arc tholeiites. This interpretation is supported by the Zr/TiO2 vs. Nb/Y diagram (Figure 9c), where the samples plot within the sub-alkaline basalt field. These trends suggest moderate evolution and subduction-related magmatism [35,36].

4.2. Geochemical Evidence for Subduction Influence in the Basalts

The Mako basalts exhibit flat to slightly LREE-depleted chondrite-normalized REE patterns (La/Smₙ = 0.73–0.88) and primitive mantle-normalized trace element abundances that show variable enrichments in LILE (e.g., Ba, Pb, Rb) and depletions in HFSE (e.g., Nb, Ta) (Figure 8a,b). In particular, some samples display negative Nb-Ta±Zr anomalies, and most have weak to absent negative Ti and Hf anomalies. The combination of LILE enrichment with Nb-Ta depletion is consistent with arc-like signatures where fluids or melts released from the subducted slab metasomatize the overlying mantle wedge [31]. We note that this signature is not present in all of our samples, and we therefore treat the trace element evidence as suggestive rather than diagnostic, and evaluate tectonic setting using the integrated geochemical dataset together with field and petrographic constraints.
The covariation of immobile elements such as Cr and Y (Figure 10a) places the Mako basalts within the field of island arc tholeiites and suprasubduction zone lavas [39]. Ti-V systematics (Figure 10b) also overlap the arc/MORB field boundary [40]. Our samples lie within the region of published Mako Belt data and Birimian greenstone samples from Boromo and Houndé (Figure 1). We note that not all of the Birimian greenstones are genchemically alike: Liptako lavas extend to more classical arc-like compositions, while lavas from Ashanti, Sefwi, Boundiali and Haute-Comoé (Figure 1) include MORB-like Ti/V values. We note that the Nb/Yb–Ba/Yb and Th/Nb–Ba/Nb diagrams (Figure 10c,d) point to subduction enrichment at shallow mantle depths, consistent with a metasomatized source in a back-arc setting (e.g., [31,41]). At a given Nb/Yb, Ba/Yb values are systemically higher than those of lavas within the MORB array (N- to E-MORB), indicating fluid-related enrichment (e.g., [31]). Our usage of the MORB array follows standard global datasets, and the distinction from OIB-like yet slab-modified basalts is consistent with recent applications of Nb/Yb–Ba/Yb systematics in NE China [42]. Considering the relative fluid-immobile nature of Th, the greater enrichment in Th relative to Ba of these rocks indicates metasomatism and a contribution from sediment-derived melts within the mantle wedge [31,41].
Perhaps the most compelling evidence for a back-arc setting is the observation that several samples display (Nb/La)PM > 1.0. In typical arc environments, Nb is depleted due to its retention in rutile in the subducted slab, while in back-arc basins—where the slab influence is diluted by influx of asthenospheric mantle—Nb can be enriched relative to La and Th [41]. This feature is seen in the central and southern Mako Belt lavas and aligns with geodynamic models where slab rollback or arc extension facilitates partial melting of a heterogeneously enriched mantle source [34,43]. Such Nb enrichment is rare in plume-free arc settings and contrasts sharply with both MORB and OIB, which lack the full suite of arc-like trace element features observed here (e.g., positive Pb anomalies, low Th/Nb). The few samples that exhibit mild E-MORB-like traits coexist with strong arc-type signals, indicating a source hybridized by both depleted and enriched domains—typical of back-arc basins formed above a retreating slab [44,45]. Taken holistically, the comparative multi-element diagrams (Figure 10) show the Mako mafic suite spanning arc-line fields with excursions toward back-arc behavior consistent with a variably enriched supra-subduction zone source.
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Figure 10. Trace element systematics of southern WAC lavas with >4 wt.% MgO. Individual samples from our study are labeled; black circles are Mako Belt lavas from the Kedougou-Kenieba Inlier. Liptako samples lack published Cr data. (a) Y-Cr plot (after [39]). (b) Ti-V plot (after [40]). (c) Nb/Yb-Ba/Yb plot (after [31]). Most southern WAC data lie above the enriched portion of the MORB array in a region characteristic of back-arc and supra-subduction zone lavas. (d) Th/Nb-Ba/Nb plot (after [31]). Mako Belt samples record shallow enrichment in Ba, while samples from other portions of the Man-Leo Shield preserve evidence for both deep and shallow enrichment processes. Data sources: Mako Belt [11,13,20,46]; Ashanti belt [47,48]; Sefwi Belt [49,50,51]; Liptako [13,52]; Boromo and Houndé Belts [53]; Boundiali [54]; Haute Comoé [55,56,57].
Figure 10. Trace element systematics of southern WAC lavas with >4 wt.% MgO. Individual samples from our study are labeled; black circles are Mako Belt lavas from the Kedougou-Kenieba Inlier. Liptako samples lack published Cr data. (a) Y-Cr plot (after [39]). (b) Ti-V plot (after [40]). (c) Nb/Yb-Ba/Yb plot (after [31]). Most southern WAC data lie above the enriched portion of the MORB array in a region characteristic of back-arc and supra-subduction zone lavas. (d) Th/Nb-Ba/Nb plot (after [31]). Mako Belt samples record shallow enrichment in Ba, while samples from other portions of the Man-Leo Shield preserve evidence for both deep and shallow enrichment processes. Data sources: Mako Belt [11,13,20,46]; Ashanti belt [47,48]; Sefwi Belt [49,50,51]; Liptako [13,52]; Boromo and Houndé Belts [53]; Boundiali [54]; Haute Comoé [55,56,57].
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4.3. Nature and Origin of the Ultramafic Rocks

The ultramafic bodies are not mantle residues but rather represent crystallization products of arc-derived magmas ponded at depth—hence their affinity with arc cumulates rather than ophiolitic peridotites. This interpretation is supported by the REE patterns of the ultramafic rocks (Figure 8c), which are parallel to those of the basalts and plot within the field of lherzolitic cumulates rather than residual mantle compositions. Olivine compositions (Figure 11) fall in compositional space between peridotite and pyroxenite, consistent with arc-related magmatic cumulates refertilized by basaltic melt. The presence of diopsidic clinopyroxenes aligns with suprasubduction zone ultramafic cumulates documented in modern arc/back-arc complexes (e.g., [37,38]). Their trace element signatures, particularly weak LREE enrichment and Pb anomalies, imply interaction with metasomatized melt or fluids, reinforcing a subduction-influenced magmatic origin.
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Figure 11. Olivines in Mako Belt ultramafic samples have compositions intermediate to values expected for olivines in equilibrium with melts formed from peridotitic and pyroxenitic sources [58].
Figure 11. Olivines in Mako Belt ultramafic samples have compositions intermediate to values expected for olivines in equilibrium with melts formed from peridotitic and pyroxenitic sources [58].
Minerals 15 01057 g011
Key evidence for this interpretation comes from spinel compositions. Abundant chromian spinels with Cr# > 0.60 in the ultramafic samples overlap compositions reported in volcanic arcs and are distinct from lower-Cr# spinels associated with mid-ocean ridge lavas [25]. The Mako Belt ultramafic rock spinels show clear trends from mantle-like Cr-Al-rich compositions to magnetite as observed in the basalts (Figure 6a,b), supporting petrographic observations that the ultramafic rocks record equilibration with basaltic melts followed in many cases by secondary alteration at low temperatures. These trends are apparent in zoning patterns of individual crystals as well as through spot analyses of multiple spinels in each sample (Figure 6a,b). Neither the spot analyses nor the transects record evidence for melt removal, i.e., depletion of the ultramafic rocks by separation of a basaltic melt, but rather a wide range in Mg/(Mg+Fe+2) values at constant Cr/(Cr+Al) that has been attributed to melt-rock reaction [30], which we postulate occurred in concert with melt addition and equilibration (Figure 6c). Spinel rim compositions (which overlap those of groundmass spinels in the basalts) fall within the range of greenschist to amphibolite-facies magnetites, indicating late-stage hydrothermal alteration [26,59].
The mineralogical and petrographic features of the Mako Belt mafic and ultramafic rocks are best explained by a convergent margin environment, more specifically a back-arc basin setting associated with subduction-related processes. This interpretation is supported by a convergence of petrological, mineralogical, and geochemical evidence that, when critically assessed, rules out alternative origins such as mid-ocean ridge (MOR) or plume-related settings. We recognize that this interpretation is non-unique, particularly in the context of evolving models for Paleoproterozoic geodynamics. Recent studies have emphasized that Archean and Paleoproterozoic mafic rocks, including those outside of known subduction zones, can display arc-like signatures such as LILE enrichment and HFSE depletion [60,61]. These signatures, while diagnostic of subduction in Phanerozoic settings, may in older terranes also result from metasomatism unrelated to slab-derived fluids, such as recycling of lithospheric components during crustal overturn or delamination. We emphasize that our geochemical interpretations rest on abundances of elements that are not readily mobilized by hydrothermal processes or metamorphism through greenschist facies, e.g., the occurrence of Nb-enriched samples (Nb/LaPM > 1.0) alongside strong arc-like features argues against simple alteration or random metasomatism. Instead, this duality reflects selective melting of an enriched subarc mantle wedge with back-arc asthenospheric input, a scenario incompatible with purely stagnant-lid or plume models.

4.4. Regional Tectonic Implications: Arc Accretion and WAC Architecture

The Mako Belt forms a small region of the SWAC Birimian terranes (Figure 1), but its tectonic significance extends beyond its local context. When viewed alongside greenstone belts from the Baoulé-Mossi Domain—such as Boromo, Houndé, Boundiali, and Haute-Comoé—the Mako samples fit into a broader regional pattern consistent with protracted subduction-accretion processes during Paleoproterozoic crustal assembly [7,10,62].
Discrimination diagrams (Figure 10) reveal that mafic rocks from Mako, Houndé, and Boromo share geochemical traits diagnostic of island arc or back-arc settings: low Nb/Yb, high Ba/Yb, and elevated Cr. These features are distinct from the MORB-like or enriched arc signatures found further east in the Ashanti, Sefwi, and Liptako belts. This spatial gradient in geochemical signatures may reflect variations in slab geometry, subduction polarity, or progressive crustal thickening along the evolving orogen. Such trends support a geodynamic model involving the sequential accretion of volcanic arcs and back-arc basins, followed by terminal collision during the Eburnean orogeny (~2.1–2.0 Ga). The Mako Belt, situated at the northwestern fringe of the SWAC, likely represents one of the earlier-formed back-arc systems that was later sutured onto the craton margin [7,10].
The presence of cogenetic mafic and ultramafic rocks, coupled with trace element signatures indicative of fluid-mediated mantle metasomatism, suggests that the Mako Belt records a snapshot of arc extension and mantle hybridization during early WAC assembly. These processes are not isolated: analogous cumulate facies and back-arc affinities have been documented in ultramafic complexes across Burkina Faso [53], Niger [63], and Ghana [64], pointing to a craton-scale subduction system.

4.5. Geodynamic Model

We interpret the Mako Belt mafic and ultramafic rocks as part of an arc–back-arc system that developed above a subducting oceanic plate during the early stages of West African Craton growth approximately 2.2–2.1 Ga (Figure 12). The initial convergence between juvenile terranes and a proto-cratonic nucleus (possibly part of the Kénéma-Man Domain) generated an island arc sequence characterized by tholeiitic to calc-alkaline volcanism. Continued slab rollback or trench retreat promoted arc extension, resulting in the opening of a back-arc basin where mantle upwelling facilitated partial melting of a heterogeneously metasomatized source.
Mafic lavas (both massive and pillowed) and associated ultramafic cumulates crystallized in this extensional back-arc domain. Their emplacement likely occurred in a shallow marine basin, as suggested by the preservation of pillow structures, submarine volcaniclastics, and transitional geochemical signatures. The presence of Nb-enriched yet arc-affinity basalts suggests a melt source influenced by both slab fluids and asthenospheric input—typical of modern back-arc basins such as the Lau or Mariana systems [31,45]. As subduction continued, the arc and back-arc units were accreted onto the craton margin during the main phase of the Eburnean orogeny (~2.1–2.0 Ga), resulting in regional deformation, low-grade metamorphism, and granitoid intrusion. The current juxtaposition of mafic, ultramafic, and metasedimentary units across the Main Transcurrent Zone reflects this collisional episode and subsequent transpressional reworking [8,9]. We recognize the absence of classical ophiolitic markers (e.g., sheeted dikes, blueschists) and limited structural constraints, but note that the presence of cumulate ultramafic rocks, pillow basalts, and coherent geochemical patterns argues for tectonic juxtaposition of units within a subduction-related context.
Our results build upon and refine previous interpretations of the Mako Belt units [11,12,13,21,65]. The subalkaline nature of the Mako lavas suggested a potential ophiolitic affinity with N-MORB/OIB-like compositions [48]. Our study confirms the subaqueous environment (e.g., pillow basalts) and cumulate textures but rejects the MORB/OIB scenario in favor of arc-related magmatism, based on robust trace element systematics (e.g., high Ba/La, (Nb/La)PM > 1) and spinel chemistry (high Cr#). While juvenile or depleted Sr-Nd isotopic signatures have been interpreted as evidence for plume-related oceanic plateau basalts [11,13,21], our new petrological and geochemical constraints suggest that these units instead formed in a suprasubduction back-arc basin where depleted mantle source material is available. Recent work on Mako Belt lavas [12,21] noted transitional characteristics between E-MORB and arc tholeiites and emphasized the cumulate nature of the ultramafic rocks in both the Mako Belt and Loraboué (Burkina Faso) and interpreted their tectonic setting as ambiguous between island arc and active margin. In contrast, our integrated mineralogical, petrochemical and tectonic analyses argue for a coherent arc–back-arc system during the Eburnean orogeny, thereby reinforcing the operation of plate tectonic processes in the Paleoproterozoic West African Craton.
Our model for the Mako Belt is consistent with recent synthesis of the southern West African Craton [10], which describes a multi-terrane architecture resulting from progressive accretion of arcs and back-arcs onto a proto-cratonic core. Within this framework, the Mako Belt represents one of the westernmost back-arc basins, later sutured against other juvenile belts such as Boromo and Boundiali. Geochemical gradients observed across the SWAC—from MORB-like lavas in eastern belts to more enriched back-arc signatures in the west—support this spatial reconstruction. The Mako Belt’s dual geochemical nature (arc and back-arc) highlights the importance of trench-parallel variations in mantle source composition and subduction flux, features now recognized in both modern and ancient convergent systems (e.g., [34,41]). This model contributes to the growing body of evidence that modern-style plate tectonic processes, including subduction, arc magmatism, and back-arc basin formation, were already operative by the Paleoproterozoic. The tectonic architecture recorded in the Mako Belt—an arc–back-arc system accreted onto a proto-craton, later reworked by orogenic processes—finds analogs in present-day settings such as the western Pacific or Tethyan domains.

5. Conclusions

This study provides new constraints on the tectonomagmatic evolution of the Mako Belt in eastern Senegal based on integrated petrographic, mineralogical, and whole-rock geochemical data from mafic and ultramafic rocks.
  • Mafic lavas in the Mako Belt—preserved as massive and pillowed flows—exhibit geochemical features consistent with magmatism in a subduction-modified mantle wedge. Some samples display (Nb/La)PM > 1, indicating partial melting of an enriched source, typical of back-arc basin environments. Harzburgites and lherzolites with cumulate textures, high Cr and Ni contents, and spinel Cr# > 0.6 have REE patterns parallel to those of the basalts, supporting a cogenetic relationship.
  • The geochemical data are best explained by formation in a Paleoproterozoic back-arc basin associated with subduction, rather than by plume-related or mid-ocean ridge processes. The coexistence of arc-like and back-arc-like geochemical traits is interpreted as the result of melt generation in a heterogeneously metasomatized subarc mantle wedge, possibly influenced by slab rollback.
  • Comparison with other SWAC greenstone belts (e.g., Boromo, Boundiali) suggests that the Mako Belt was part of a broader convergent margin system. These belts likely formed in distinct arc and back-arc settings and were progressively accreted onto the West African Craton during the Eburnean orogeny (~2.10–2.00 Ga).
  • The proposed geodynamic model reinforces the view that modern-style plate tectonics—including subduction and arc–back-arc magmatism—was already active in the Paleoproterozoic. The Mako Belt offers an important window into these early processes and contributes to ongoing debates on crustal growth mechanisms during the assembly of early cratonic nuclei.
Future work combining high-precision geochronology, isotopic studies, and structural analysis will be essential to further refine the timing and dynamics of arc–back-arc evolution in the southern West African Craton.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/min15101057/s1, Table S1: EPMA analyses of Mako Belt samples. Figure S1: Incompatible trace element abundances of (a) Mako Belt lavas and (b) ultramafic rocks normalized to mid-ocean ridge basalt.

Author Contributions

Conceptualization, I.D. and T.F.; methodology, I.D. and T.F.; formal analysis, I.D., T.F. and S.B.; investigation, I.D., T.F., K.S., M.G. and C.I.F.; resources, M.G. and C.I.F.; data curation, I.D., T.F. and S.B.; writing—original draft preparation, I.D. and T.F.; writing—review and editing, I.D., T.F., K.S., S.B., M.G., C.I.F. and O.V.; visualization, I.D. and K.S.; project administration, I.D. and T.F.; funding acquisition, I.D. All authors have read and agreed to the published version of the manuscript.

Funding

The work has been conducted with the financial support of the US Department of State through a Fulbright Program Scholarship granted to Ibrahima Dia.

Data Availability Statement

Datasets generated during this study are presented herein.

Acknowledgments

Liz Andrews, Laura Liermann and Dongxiang Wang were invaluable in sample analysis through the LIME lab. We thank the staff at the West African Exploration Initiative (WAXI) for their thoughts. Constructive comments from two anonymous reviewers and the editor helped us to clarify text and figures and greatly improved the manuscript.

Conflicts of Interest

The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

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Figure 1. Geological map of the southern West African Craton showing the distribution of Archean and Paleoproterozoic terranes, greenstone belts, granitoids, and sedimentary basins. The sampling area of this study within the Mako Belt is indicated by a blue ellipse. Compiled and redrawn based on [10]. Numbers correspond to Birimian greenstones discussed in the text: 1, Liptako; 2, Boromo; 3, Houndé; 4, Houte-Comoé; 5, Boundiali; 6, Sefwi; 7, Ashanti.
Figure 1. Geological map of the southern West African Craton showing the distribution of Archean and Paleoproterozoic terranes, greenstone belts, granitoids, and sedimentary basins. The sampling area of this study within the Mako Belt is indicated by a blue ellipse. Compiled and redrawn based on [10]. Numbers correspond to Birimian greenstones discussed in the text: 1, Liptako; 2, Boromo; 3, Houndé; 4, Houte-Comoé; 5, Boundiali; 6, Sefwi; 7, Ashanti.
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Figure 2. Geological map of the Kédougou-Kéniéba Inlier showing sampling locations of basalts and ultramafic rocks from this study. The Senegal-Mali Shear Zone (SMSZ) and Main Transcurrent Zone (MTZ) are indicted on the map. Inset: location of the study area within the West African Craton.
Figure 2. Geological map of the Kédougou-Kéniéba Inlier showing sampling locations of basalts and ultramafic rocks from this study. The Senegal-Mali Shear Zone (SMSZ) and Main Transcurrent Zone (MTZ) are indicted on the map. Inset: location of the study area within the West African Craton.
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Figure 3. Outcrop photographs of Mako Belt samples. (a) Pillow basalt BAM; (b) pillow basalt MMK; (c) ultramafic KNL; (d) ultramafic MN; (e,f) hydrothermally altered, pervasively veined regions are recognizable in the field and were avoided during sampling.
Figure 3. Outcrop photographs of Mako Belt samples. (a) Pillow basalt BAM; (b) pillow basalt MMK; (c) ultramafic KNL; (d) ultramafic MN; (e,f) hydrothermally altered, pervasively veined regions are recognizable in the field and were avoided during sampling.
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Figure 4. Photomicrographs of Mako Belt samples. (a) Massive basalt SPL (ppl); (b) cumulate LM (ppl); (c) serpentinized portion of ultramafic OR (ppl); (d) ultramafic LA (ppl; relict pyroxene outlined in yellow); (e) detail of anhydrous portion of sample LA (xpl); (f) detail of serpentinized portion of sample LA (xpl) showing olivine fully replaced with serpentine. (cpx = clinopyroxene (relict or fresh); oliv = olivine (relict or fresh); ppl = plane polarized light; xpl = crossed polarized light).
Figure 4. Photomicrographs of Mako Belt samples. (a) Massive basalt SPL (ppl); (b) cumulate LM (ppl); (c) serpentinized portion of ultramafic OR (ppl); (d) ultramafic LA (ppl; relict pyroxene outlined in yellow); (e) detail of anhydrous portion of sample LA (xpl); (f) detail of serpentinized portion of sample LA (xpl) showing olivine fully replaced with serpentine. (cpx = clinopyroxene (relict or fresh); oliv = olivine (relict or fresh); ppl = plane polarized light; xpl = crossed polarized light).
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Figure 5. Pyroxene compositions in Mako Belt ultramafic rocks.
Figure 5. Pyroxene compositions in Mako Belt ultramafic rocks.
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Figure 6. Spinel compositions within Mako Belt samples (after [27,28]). Shaded gray field is mantle chromite [29]; dashed arrow labeled BR indicates Cr-Al trend [26]. (a) Spinels in ultramafic samples range from Al-chromite to magnetite; cumulate LM contains only magnetite. (b) EPMA transects across individual crystals in ultramafic rocks PG1, MN and basalt MMK indicate core compositions of picotite and Al-chromite zoned sharply to rims of magnetite. (c) Cr# vs. Mg# of Mako Belt spinels (after [28,30]). Individual data points as in panel (a); gray field encloses transect analyses in panel (b). Blue trend labeled DB is the range of mean mid-ocean ridge low- to high-Al peridotite spinels [25].
Figure 6. Spinel compositions within Mako Belt samples (after [27,28]). Shaded gray field is mantle chromite [29]; dashed arrow labeled BR indicates Cr-Al trend [26]. (a) Spinels in ultramafic samples range from Al-chromite to magnetite; cumulate LM contains only magnetite. (b) EPMA transects across individual crystals in ultramafic rocks PG1, MN and basalt MMK indicate core compositions of picotite and Al-chromite zoned sharply to rims of magnetite. (c) Cr# vs. Mg# of Mako Belt spinels (after [28,30]). Individual data points as in panel (a); gray field encloses transect analyses in panel (b). Blue trend labeled DB is the range of mean mid-ocean ridge low- to high-Al peridotite spinels [25].
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Figure 7. Classification of study samples. (a) Total alkalis–silica diagram for basalt samples. Shaded field encloses Mako basalts (from [13,20]). (b) CIPW normative classification of Mako series ultramafic rocks (gray symbols this study, green symbols are data from [12]).
Figure 7. Classification of study samples. (a) Total alkalis–silica diagram for basalt samples. Shaded field encloses Mako basalts (from [13,20]). (b) CIPW normative classification of Mako series ultramafic rocks (gray symbols this study, green symbols are data from [12]).
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Figure 8. Chondrite normalized REE profiles and primitive mantle normalized incompatible trace element contents of Mako Belt samples. (a,b) Basalts. Shaded field encloses analyses of Mako Belt pillow basalts [11]; individual analyses shown in panel (b). (c,d) Ultramafic rocks. Shaded fields enclose analyses of Mako Belt lherzolites [12] and Ashanti and Boromo ultramafic cumulates ([32] and references therein); individual analyses are shown in panel d. Normalizing values from [33].
Figure 8. Chondrite normalized REE profiles and primitive mantle normalized incompatible trace element contents of Mako Belt samples. (a,b) Basalts. Shaded field encloses analyses of Mako Belt pillow basalts [11]; individual analyses shown in panel (b). (c,d) Ultramafic rocks. Shaded fields enclose analyses of Mako Belt lherzolites [12] and Ashanti and Boromo ultramafic cumulates ([32] and references therein); individual analyses are shown in panel d. Normalizing values from [33].
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Figure 9. Classification diagrams for Mako belt samples. Symbols as in Figure 7, white dashed fields enclose basalts (from [13]). (a) AFM diagram; sample BD is a silicified massive basalt. Field of ultramafic cumulates from [37,38]. (b) Tectonic classification diagram for Mako basalts after [35]. (c) Tectonic classification diagram for Mako basalts and ultramafic samples after [36].
Figure 9. Classification diagrams for Mako belt samples. Symbols as in Figure 7, white dashed fields enclose basalts (from [13]). (a) AFM diagram; sample BD is a silicified massive basalt. Field of ultramafic cumulates from [37,38]. (b) Tectonic classification diagram for Mako basalts after [35]. (c) Tectonic classification diagram for Mako basalts and ultramafic samples after [36].
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Figure 12. Geodynamic sketch of the evolving arc environment of the southern WAC. Yellow arrows indicate subduction direction; blue arrows indicate slab rollback; orange shapes are granitoid magmas and pluton. The final panel shows interfingered slices of granitoid calc-alkaline rocks and back-arc basin crustal slices following the Eburnian orogeny.
Figure 12. Geodynamic sketch of the evolving arc environment of the southern WAC. Yellow arrows indicate subduction direction; blue arrows indicate slab rollback; orange shapes are granitoid magmas and pluton. The final panel shows interfingered slices of granitoid calc-alkaline rocks and back-arc basin crustal slices following the Eburnian orogeny.
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Table 1. Bulk rock analyses.
Table 1. Bulk rock analyses.
Mako Belt Extrusive RocksMako Belt Ultramafic Rocks
SampleBAMBG1GL1MMKLMSPLKL1KL2LAMNPG1SBPSF2
Lat13.104412.829513.131813.184713.603113.187612.905812.904812.834212.848812.846513.189712.9644
Long−12.1029−12.3807−12.0980−12.0671−12.0269−12.1084−12.2462−12.2450−12.3300−12.3598−12.3583−12.1105−12.1526
SiO250.6252.7152.3251.8251.7456.5338.1842.7039.3739.6039.7141.6330.51
Al2O314.8814.2414.2615.459.9712.302.151.902.282.443.234.261.65
TiO20.810.740.790.741.260.900.210.240.360.200.250.360.15
Fe2O3 *10.217.9610.908.7215.357.2312.9012.2311.717.878.7910.197.48
MnO0.200.160.180.190.180.160.190.210.200.150.170.170.14
MgO8.916.605.728.738.817.9134.1831.7134.9736.5834.3630.6533.49
CaO9.6211.409.1911.679.289.601.956.492.312.042.643.950.92
Na2O3.002.933.401.792.142.200.120.190.120.070.090.170.09
K2O0.050.080.070.420.790.540.030.040.040.030.040.050.03
P2O50.080.070.070.070.080.090.030.020.050.020.040.050.02
LOI2.463.132.560.980.641.249.324.508.5610.099.557.4922.42
Total100.82100.0099.44100.56100.2398.6799.24100.2099.9599.0798.8498.9596.90
Sc32.3431.4532.8332.5640.1024.3110.2419.2310.779.5610.1211.996.50
V232.6207.0225.7206.8405.3183.167.082.476.754.160.676.942.2
Cr214.4163.0180.4297.872.5220.73337255933642864235022523882
Co35.838.938.437.261.432.1112.3104.4103.4101.297.382.997.3
Ni84.288.183.4115.556.197.2116981011881500144910391340
Cu62.066.475.467.6136.372.755.321.321.148.627.434.111.2
Zn59.955.564.860.266.454.059.553.357.147.949.351.842.4
Rb2.71.51.27.011.114.00.10.20.40.30.60.70.1
Sr81.965.9132.168.6207.055.16.88.83.85.87.630.77.6
Y14.812.314.411.816.215.12.13.15.02.53.24.51.2
Zr24.718.120.519.431.143.05.07.814.48.513.214.43.2
Nb14.23.73.41.74.34.50.70.81.40.81.01.5bdl
Cs11.22.92.90.71.58.3bdlbdl0.35bdlbdlbdlbdl
Ba27.740.616.730.8155.9173.93.114.322.71.733.29.04.3
La1.801.751.911.408.336.150.320.490.900.630.881.190.24
Ce4.924.705.234.1421.6214.520.911.362.581.572.053.200.65
Pr0.780.750.820.683.241.970.160.230.420.240.320.470.11
Nd4.113.874.253.6214.918.990.811.202.191.141.512.270.57
Sm1.401.311.401.243.582.450.260.390.700.330.440.670.16
Eu0.560.510.540.480.890.720.110.140.200.130.160.220.06
Gd2.051.822.011.723.382.880.350.530.910.430.540.820.22
Tb0.380.340.390.330.540.480.060.090.150.070.100.140.04
Dy2.602.272.622.253.202.990.390.590.960.480.600.870.24
Ho0.570.490.570.480.640.600.080.120.200.100.120.180.05
Er1.731.421.691.421.811.710.240.350.560.280.360.520.15
Tm0.250.200.240.200.250.240.030.050.080.040.050.070.02
Yb1.651.291.571.351.581.500.230.320.490.270.340.480.14
Lu0.240.180.230.200.230.220.030.050.070.040.050.070.02
Hf5.491.001.010.771.431.420.240.310.540.310.440.510.11
Ta15.584.044.382.444.093.831.201.161.661.441.172.040.67
Pb0.400.220.220.722.641.780.210.290.160.510.320.370.39
Th6.280.270.220.001.850.62bdlbdlbdlbdlbdlbdlbdl
U0.0340.0290.0280.0260.4350.163bdlbdlbdl0.0080.0230.041bdl
Note: “bdl” = below detection limit. Fe2O3 * indicates all iron measured as Fe3+.
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Dia, I.; Furman, T.; Sayit, K.; Bowden, S.; Gueye, M.; Faye, C.I.; Vanderhaeghe, O. Paleoproterozoic Mafic and Ultramafic Rocks from the Mako Belt, Senegal: Implications for Back-Arc Basin Origin. Minerals 2025, 15, 1057. https://doi.org/10.3390/min15101057

AMA Style

Dia I, Furman T, Sayit K, Bowden S, Gueye M, Faye CI, Vanderhaeghe O. Paleoproterozoic Mafic and Ultramafic Rocks from the Mako Belt, Senegal: Implications for Back-Arc Basin Origin. Minerals. 2025; 15(10):1057. https://doi.org/10.3390/min15101057

Chicago/Turabian Style

Dia, Ibrahima, Tanya Furman, Kaan Sayit, Shelby Bowden, Mamadou Gueye, Cheikh Ibrahima Faye, and Olivier Vanderhaeghe. 2025. "Paleoproterozoic Mafic and Ultramafic Rocks from the Mako Belt, Senegal: Implications for Back-Arc Basin Origin" Minerals 15, no. 10: 1057. https://doi.org/10.3390/min15101057

APA Style

Dia, I., Furman, T., Sayit, K., Bowden, S., Gueye, M., Faye, C. I., & Vanderhaeghe, O. (2025). Paleoproterozoic Mafic and Ultramafic Rocks from the Mako Belt, Senegal: Implications for Back-Arc Basin Origin. Minerals, 15(10), 1057. https://doi.org/10.3390/min15101057

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