The sampling zone is located in Figure 2 . The spinel lherzolitic xenoliths are light green, dense, generally subangular to sub-rounded, sometimes elongated, and shaped by the host lava. Their size ranges from 1.5 to 10 cm in length ( Figure 3 ) and they are well preserved in the host lavas with coarse-grained olivines. The contact with the host lava is unambiguous, and the spinel lherzolitic xenoliths appear to be affected by the host lava, which can also infiltrate through their cracks. These spinel lherzolitic xenoliths might be residues of melting rock, removed and incorporated into the ascending host lava.

The textures observed in the spinel lherzolitic xenoliths studied are similar to the coarse-grained structure described in various alkali basalt xenoliths worldwide [21] . Currently, we have no recorded occurrences of garnet, plagioclase, phlogopite, or amphibole minerals described in various xenoliths worldwide.

The Quaternary spinel lherzolitic xenoliths from Mamelle are larger (3 to 7 cm) and exhibit a protogranular structure ( Figure 4(A)-(F) ; Figure 5(A) and Figure 5(B) ). They consist of automorphic to subautomorphic minerals of olivine, pyroxene, and spinel.

The tertiary xenoliths from Manual Cape are small (2 to 5 cm) and composed of olivines, pyroxenes, and spinels. Xenoliths also have a protogranular texture ( Figure 5(C)-(E) ). Small olivine crystals are sometimes partially or totally embedded in pyroxenes.

Interstitial pyroxenes between olivines are destabilized by subsequent thermal disruption. In some areas, the minerals exhibit intergranular sliding and basaltic infiltration along fractures.

The Madelen Island xenoliths are found in prismatic basanites and are small (2 to 4 cm). They have a protogranular structure Figure 5(F) . Some minerals show a reaction aureole in contact with the host lava and intergranular sliding. They consist mainly of olivine and pyroxene, with spinel being very rare. Olivine is fractured and shows intergranular sliding. Interstitial pyroxene is often associated with spinel. The spinel is vermicular, poly-lobed, elongated, or appears as small, aligned grains.

Automorphous to subautomorphous pyroxenes are interstitial and have been corroded near the contact with the host lava. Rectilinear or curvilinear boundaries defining polygonal junctions or triple junction points between olivine or olivine and pyroxene phases indicate that these xenoliths are close to textural equilibrium ( Figure 6(A) and Figure 6(B) ). Some minerals are partially or totally altered, with a reaction aureole around the contact between hosted rocks and xenoliths ( Figures 6(C)-(F) ).

Spinels are generally small along the shorter axis (0.1 to 3 mm). They are rectangular ( Figure 7(A)-(D) ), polylobed, elongated Figure 7(F) , Figure 8(D)-(F) or amoeboid ( Figure 7(E) and Figure 7(F) , Figure 8(A)-(C) ). Some are interstitial, while others are grouped in diverticulate aggregates or small grains aligned between olivine and pyroxene crystals or embedded in other mineral phases ( Figure 7(A) , Figure 7(B) , and Figure 7(D) ). Spinels, closely associated with pyroxenes and olivines, take on different forms, reflecting their primary or early spinel nature in the xenoliths studied.

The sharp contact between protogranular spinel lherzolitic xenolith studies and porphyritic microlitic host basanites is generally irregular or rectilinear ( Figure 7(C)-(F) ). The minerals in xenoliths have fractures that can be filled by magmatic fluid, creating a glassy film that can act as a contaminant. These fractures, accompanied by intergranular sliding, are evidence of the interaction between host basalts and mantle xenoliths.

Some olivines have sharp, curved, polygonal contours Figure 8(A) and Figure 8(B) . Other olivines, often severely fractured during mobilization, show intergranular slippage or corrosive action when in contact with host lavas. The fractured olivine can also be penetrated by magmatic juices, which may act as basaltic contamination. Recrystallization is nonexistent, and some olivines seem to be affected by the host basalt, which explains their primary nature. In any case, the olivines are not transformed and remain in equilibrium with the host lava. Their intense fracturing results from their re-mobilization in the host lava.

The modal compositions of the peridotite samples studied show the predominance of olivines (69% - 73%), followed by pyroxenes (6% - 25%) and spinel (0.17% - 3.5%).

These proportions place the xenoliths in the field of Harzburgites, Dunites, and Lherzolites ( Figure 9(A) ) and are comparable to xenoliths from the sub-oceanic mantle ( Figure 9(B) ) in an active margin context ( Figure 9(C) ).

Olivine, orthopyroxenes, and clinopyroxenes form the mineral paragenesis of spinel lherzolitic xenoliths, completed by an aluminous phase, the spinel. The compositions of these mineral phases in the spinel lherzolitic are given in Tables 1-7 .

The Fo content (Fo = Mg/(Mg + FeT)*100) ranges from 89.1 to 91.8 in olivines from Mamelle xenoliths, 90.3 to 91.8 in olivines from Madelen Island, and 75.9 to 92.4 in olivines from Manual Cape xenoliths ( Table 1 , Table 2 ). These high Fo contents, combined with the absence of olivine zonation, are characteristic of peridotite xenoliths found in alkaline basalts worldwide. Globally, these Fo olivine contents are significantly higher than the range estimated for the primitive mantle (88.7 - 90.1), as noted in [26] . The Fo contents of olivines in the studied xenoliths consistently remain higher than those of olivines in the host alkaline basalts (Fo 60 - 91.5) [14] .

The NiO content of olivines ranges from 0.151% to 0.425% for olivines from Mamelle xenoliths, 0.057% to 0.442% for those from Madelen Island, and 0.039% to 0.351% for those from Manual Cape. These NiO contents fall within the normal range (0.28% to 0.30% by weight) of olivines from the primitive mantle (PM) [26] .

Correlations between NiO content and Mg# ( Figure 10 ) show a positive trend from Cape Manuel to Mamelle spinel lherzolitic xenoliths. These variations are similar to the Lherzolite xenolith type [21] .

CaO contents remain globally low, ranging from 0.0129% to 0.478% in the olivines of the Mamelle xenoliths, from 0% to 0.79% for the Manual Cape olivines, and 0.048% to 1.352% for those of Madelen Island.

Chromium content oscillates between 0 and 0.094 in the olivines of the Mamelle xenoliths, 0 to 0.603 in the olivines of Manual Cape, and 0 to 0.406 in those of Madelen Island.

These variations in the chemical elements Fo, NiO and CaO are compatible with a mantle origin of the xenoliths studied.

The pyroxenes in the xenoliths studied are augite or diopside for the clinopyroxenes (Wo_37.16-51.27-En_37.02-65.52-Fs_3.2-11.72) and clinoenstatites for the orthopyroxenes (Wo_1.31-1.53-En_90.08-90.54-Fs_8.01-8.55) in the Morimoto classification diagram [27] ( Figure 11 ).

1) Clinopyroxenes

Clinopyroxenes in quaternary xenoliths (Mamelle) ( Table 3 ) have Cr₂O₃ contents ranging from 0.82 to 1.27%, TiO₂ from 0.00 to 0.21% and Al₂O₃ from 1.21 to 4.69%.

Clinopyroxenes in tertiary lava xenoliths ( Table 4 ) from Manual Cape have higher Cr₂O₃ (0.4% - 4.66%), TiO₂ (0.06% - 2.22%), and Al₂O₃ (0.5% - 7.92%) contents than those from Madelen Island, where these values are 0.434% - 4.656%, 0.00% - 0.217% and 0.579% - 7.92% respectively. Na₂O contents remain comparable, ranging from 0.49% to 2.24% for clinopyroxenes from Manual Cape xenoliths, compared with 0.47% to 2.286% for xenoliths from Madelen Island.

Al^IV/Al^VI ratios, ranging from 0.16 to 19.32, are comparable to those of clinopyroxenes from subcontinental upper mantle peridotites, GERM see [26] .

The Mg# differentiation index (Mg²⁺/Mg²⁺ + Fe²⁺ + Fe³⁺ + Mn²⁺) is relatively lower in the clinopyroxenes of the Tertiary xenoliths of Manual Cap (82.8 - 89.7), slightly higher in those of Madelen Island (91.5 - 93.7) and around 91.6 to 93.2 in the clinopyroxenes of the Quaternary xenoliths of Mamelle. Na₂O shows a positive correlation with Mg# ( Figure 12(A) ), while Al₂O₃ and TiO₂ contents show a negative correlation ( Figure 12(B) and Figure 12(C) ). These variations are comparable to those observed in Lherzolites. Variations in CaO, Al₂O₃, Cr₂O₃, and NiO contents indicate a less depleted, more refractory character [28] . Ti and Na variations in clinopyroxenes display no clear trend towards simultaneously decreasing concentrations of both oxides.

2) Orthopyroxenes

The highly magnesian orthopyroxenes have Mg# (Mg²⁺/Mg²⁺ + Fe²⁺ total) + Mn²⁺ ratios that vary between 90.8 and 91.68. Al₂O₃ contents range from 3.52% to 3.786%, with Cr₂O₃ (0.468% - 0.624%), TiO₂ (0.01% - 0.105%), and Na₂O (0.022% - 0.098%) ( Table 5 ). CaO contents remain low between 0.679 and 0.781%. The variations content of Al₂O₃ and Cr₂O₃ may be attributable to the partial melting process. For almost constant Mg# values, Na₂O, Al₂O₃ and TiO₂ contents show significant variation ranges ( Figure 12(D)~(F) ) comparable to those observed in Lherzolite xenoliths [28] . Variations in other incompatible (CaO, Na₂O, K₂O) and compatible (Cr₂O₃ and NiO) elements during melting confirm the residual nature of xenoliths resulting from the partial melting process [28] .

The spinels studied in the spinel lherzolitic xenoliths are rich in alumina, chromium, iron (both ferrous and ferric), magnesium, and less abundantly in nickel and titanium ( Table 6 and Table 7 ). The Mg# ratio (= 100 Mg/[Mg + Fe²⁺ + Fe³⁺]) ranges from 62.99% to 84.24%, while the Cr# ratio (= 100 Cr/[Cr + Al]) varies from 18.05% to 44.3%. These ratios are very similar to the spinels from lherzolites defined by Arai [29] . However, they are higher than the spinels from Cameroon line peridotite xenoliths, which are aluminous with Mg# values between 74% and 78% for lower Cr# values (8.85% - 14.10%) [30] .

The values of Fe²⁺/Fe²⁺ + Mg²⁺ ratios (0.1378 - 0.3306) and Fe³⁺/(Fe³⁺ + Al + Cr) (0.0027 - 0.0348) show wide ranges of variation in xenolith spinels.

Lherzolitic spinels in xenoliths from Tertiary volcanism (Manual Cape and Madelen Island) are richer in Fe₂O₃ (0 - 7.39%), FeO (10.15% - 47.42%), TiO₂ (0.16% - 22.02%), MgO (1.90% - 18.156%), and NiO (0.0013% - 0.267%) than spinels from Quaternary volcanic peridotites (Mamelle), which have relatively higher Cr₂O₃ (21% - 33.68%) and relatively lower Fe₂O₃ (0.4% - 1.82%), FeO (9% - 10.94%), TiO₂ (0.05% - 0.16%), MgO (16.84% - 19.52%) and NiO (0.14% - 0.34%) values. These values are comparable to those of the lherzolites defined by Arai [29] .

The variations in these elements, as well as in Cr#, and the absence of inclusion in other mineral phases, support a primary and residual nature of the spinels, which likely originated in the mantle [28] [31] [32] .

Al vs. Cr and YFe (Fe³⁺/(+Cr³⁺ + Al³⁺ + Fe³⁺) vs. XFe (Fe²⁺/Fe²⁺ + Mg²⁺) diagrams of spinels show two distinct groups in xenoliths from Quaternary volcanism. Group 1 is more aluminous and less rich in iron and chromium (MA3 - MA5), while Group 2 is less aluminous and richer in iron and chromium (MA21 - MA23) ( Figure 13 and Figure 14 ). Spinels from xenoliths in the Tertiary lavas of Manual Cape (CM22 - CM24) and Madelen Island (IM1) have alumina, iron, and chromium characteristics intermediate between these two groups of spinels in the Quaternary xenoliths of Mamelle. However, two spinels show relatively low values for alumina, chromium, and iron.

The composition and stability of chromiferous spinels in basic and ultrabasic rocks depend not only on magma composition, temperature, and pressure but also on oxygen fugacity [33] [34] . According to Fisk et al. [35] , the increase in ferric iron (Fe₂O₃) in chromiferous spinels can be explained by the decrease in temperature under constant oxygen fugacity. On the other hand, experimental studies have shown that Fe³⁺ enrichment can also result from an increase in Fe₂O₃ in the liquid (or magma) linked directly linked to the iron concentration of the liquid (or magma) at constant temperature and oxygen fugacity. Finally, regardless of temperature and composition, the Fe³⁺ content of spinels increases with oxygen fugacity.

In the xenoliths studied, Fe³⁺ enrichment is coupled with an increase in Fe²⁺ and a decrease in Mg²⁺. Spinels in xenoliths from Tertiary volcanism are richer in Fe₂O₃ (0 to 7.39%) than those in xenoliths from Quaternary volcanism (0.4 to 1.83%). These results are probably due to a higher degree of oxidation in Tertiary xenoliths.

The chemical composition of spinels can determine the origin and formation conditions of the xenoliths studied by Arai [29] . The Quaternary Mamelle and Tertiary Madelen Island spinel lherzolitic xenoliths fall within the olivine-spinel mantle area defined by Arai [29] and are classified as olivine-spinel mantles (OSMA) and continental passive margin peridotites, with a chemical composition close to fertile mantles [29] ( Figure 15 ). The degree of melting is estimated to be between 10% and 15% [29] . Cr/Cr + Al ratios in spinels range from 0.1805 to 0.443 in the Mamelle xenoliths and are constant in those from Madelen Island (0.32), for an olivine Fo of 90.5 to 91.5 and 90.3 to 90.7, respectively. These values are comparable to those of oceanic shelf basalt peridotites, oceanic hotspot peridotites, and also the sub-continental fertile peridotites group and those of the island arc of Japan [29] .

The Cr/Cr + Al ratio (<0.5%) shows little variation in spinels. The low Ti (<0.063%) and Na (<0.158%) values in clinopyroxenes, and the low Ti (<0.003%) values in orthopyroxenes of spinel lherzolitic xenoliths, are compatible with a partial melting process of 10 to 15% [29] , although the degree of partial melting may vary from one facies to another.

Geochemical data obtained are shown in Table 8 .

Quaternary xenoliths in (Mamelle) have MgO contents ranging from 43.13% to 46.486%, Al₂O₃ from 0.65% to 2.275%, Fe₂O₃ from 8.176% to 9.67%, CaO from 0.583% to 1.46%, TiO₂ from 0.007% to 0.09%, and Na₂O from 0.099% to 0.15%.

Compared to these Quaternary xenoliths, those found in Tertiary lavas have lower MgO (39.42% - 41.85%) and higher Fe₂O₃t (9.60% - 13.29%), CaO (1.75% - 2.63%), Na₂O (0.21% - 0.45%), K₂O (0.07% - 0.19%), and TiO₂ (0.12% - 0.31%).

The host lavas containing these tertiary and quaternary xenoliths are poorer in MgO (7.4% - 12.73%) and more enriched in Fe₂O₃t (9.81% - 13.41%), Al₂O₃ (11.51% - 15.04%), CaO (7.33% - 15.95%), TiO₂ (1.80% - 2.50%), and Na₂O (2.64% - 4.79%) [14] .

Mg# differentiation index values (100*MgO/(MgO + Fe₂O₃t) are higher in xenoliths from Quaternary lavas (81.679% - 84.879%) than in those from Tertiary lavas (74.791% - 81.339%). These Mg# contents in xenoliths are higher than those in the host basalts (Mg# between 41.77% and 50.34%) [14] .

Tertiary xenoliths are comparable to those described by McDonough [36] , while quaternary xenoliths are similar to those described by several authors [26] [28] [37] [38] ( Figure 16 ).

Compared with the geotectonic sites defined by Bonati [25] , the Quaternary (Mamelle) and Tertiary (Manual Cape and Madeline Island) peridotite xenoliths are similar to the ocean basin xenoliths ( Table 9 ) with a probable melting degree of 10% to 25% or passive margins with a probable melting degree of 10% to 15% [25] .

Concentrations of compatible trace elements (Cr ranges from 2947 - 5500 ppm, Ni from 1688 - 2374 ppm, Co from 140.6 - 167.8 ppm) are relatively high.

The Fe/Mn (64.5 to 72.55), Ni/Co (11.82 to 15.57), and Ni/Cr (0.36 to 0.71) ratios of the xenoliths studied are comparable to those of the primitive mantle (Fe/Mn = 54 to 68, Ni/Co = 16.7 to 19.3, and Ni/Cr = 0.72 to 1.07), the French Massif Central [39] (Fe/Mn = 55 to 69, Ni/Co = 17.7 to 20.3, and Ni/Cr = 0.82 to 1.17), but are also close to those of spinel peridotites [36] (Fe/Mn = 50 to 70, Ni/Co = 16 to 24, and Ni/Cr = 0.55 to 0.86) see [26] .

The Rare Earth spectra of all the xenoliths studied show sub-parallel patterns with a progressive decrease from Light Rare Earth Elements (LREE) to Medium Rare Earth Elements (MREE) to Heavy Rare Earth Elements (HREE). Xenoliths in tertiary lavas show greater Rare Earth fractionation than those in quaternary lavas ( Figure 17 ).

The ratios in quaternary xenoliths [La/Sm]_N (1.8484 - 9.3225), [Sm/Yb]N (1.1315 - 2.4181), and [La/Yb]_N (2.8171 - 20.2524) show wider variation than tertiary xenoliths, which have [La/Sm]_N 2.8092 - 4.2411, [Sm/Yb]_N 3.7943 - 5.0053, and [La/Yb]_N 10.6589 - 20.7083, respectively. Such spectra show that these xenoliths come from a Rare Earth Depleted spinel lherzolite mantle source zone. Enrichment in Light Rare Earths relative to Heavy Rare Earths may result from contamination by the surrounding magma, which forms a glassy film along fractures and can contribute significantly to enrichment in these elements. This has been described in the case of peridotite xenoliths in alkaline basalts [40] . It may also be a characteristic feature of xenoliths if they represent cumulates derived from liquids enriched in Light Rare Earths [41] , or if they result from cumulates formed from a liquid enriched and fractionated in Light Rare Earths for kimberlite nodules [41] .

The low contents of incompatible elements (Ce, La), the high Ni and Cr contents, and the Mg/Mg + Fe ratio in both olivines and spinel lherzolitic xenoliths appear incompatible with the fractional crystallization process; they are more consistent with the partial melting process.

The low contents of Heavy Rare Earths may suggest that the source zone of these xenoliths is depleted in Heavy Rare Earths, such as spinel lherzolites.

The multi-element diagram ( Figure 18 ), normalized to C1 chondrites [42] , shows sub-parallel spectra reflecting enrichment in LILE (Rb, Sr, K) and HFSE (Zr, Ti, Y) with a positive Ta anomaly and a negative Hf anomaly. These variations, coupled with slight negative anomalies in Ba, Th, and Na, may indicate low partial melting of the source zone.

The distribution of normalized trace elements in early mantle xenoliths differs significantly from those in the host lavas ( Figure 19 ), with the lavas being more enriched in rare earth elements than the xenoliths. The host lavas exhibit negative anomalies in K, Pb, P, and Zr, and positive ones in Sr and Nd, whereas the xenoliths have negative anomalies in K, Pb, U, and Y, and positive ones in Ta and P. These variations indicate that the trace element compositions of the xenoliths are not significantly affected by the host lavas. Variations in highly incompatible elements such as U and Rb, which are known to be mobile in subsurface environments, show that these elements are not significantly affected by post-magmatic or secondary alteration processes.