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131 (Supplementary Table 1). Given that the HFSE have a great capacity to differentiate types of magmas and are considered the most immobile elements in postmag- matic processes (Pearce 2014), these variable concentra- tions suggest that the igneous typology of the mafic rocks of the ophiolite is varied. This compositional varia- bility is also reflected in the different concentrations recorded by some compatible trace elements, such as Ni (<20–240) and Cr (<29–940). The REE contents are also quite variable (ΣREE = 9.77–87.56), as are the REE pat- terns normalized to chondrite (Nakamura 1974), which show variable enrichment, positive and negative anoma- lies of Eu and low fractionation, with variable values of (La/Yb) N between 5.44 and 17.23. One sample is highly depleted in LREE and shows a different normalized pat- tern (Figure 5a). The two samples of metatonalites are different in relation to their major element content, with very different values in SiO 2 (69.21, 81.39), Al 2 O 3 (8.66, 13.27), FeO(t) (1.51, 4.25) and CaO (0.83, 3.66). However, the contents in HFSE are generally more similar and moderate. High REE contents are also relatively compar- able (ΣREE = 104.02, 170.99), with normalized patterns showing strong fractionation ((La/Yb) N = 23.95, 113.93) (Figure 5b). According to their projection on the Co-Th diagram (Figure 5c; Hastie et al . 2007), the mafic rocks of the Mérida Ophiolite have basaltic compositions that corre- spond to tholeiitic and calc-alkaline igneous series. This different classification corresponds well with the com- positional variability observed in the contents of major and trace elements. The two metatonalitic bodies iden- tified in the ophiolite lie on the boundary between normal and high-K calc-alkaline series. Identification of the tectonic setting in which these lithologies formed is a key question for understanding the Mérida Ophiolite in the peri-Gondwanan domain. The diagram of Mullen (1983) uses the contents of some major elements (Ti- Mn-P) that are relatively immobile during postmag- matic processes and have been shown to be effective in discriminating the tectonic environment for the gen- eration of Ediacaran ophiolites (Arenas et al . 2018). In this diagram, the mafic rocks are also classified as both tholeiitic (island-arc tholeiites) and calc-alkaline types, and various samples can be considered boninitic (Figure 5d). The same igneous series can be identified using the diagram of Wood (1980), based on the con- tents of Hf-Th-Nb, HFSE of pronounced postmagmatic immobility (Figure 5e). Also based on highly immobile elements with a high discriminating capacity, the Nb/ Yb-Th/Yb diagram (Figure 6a; Shervais 1982; Pearce 2008, Pearce 2014) clearly differentiates the oceanic affinity of basaltic types (MORB–OIB array), characteris- tic of ophiolites generated in divergent settings, including those formed in supra-subduction zone (SSZ) environments, that is, in convergent settings related to the dynamics of magmatic arcs (volcanic-arc array), where the generation of oceanic lithosphere can be associated with the formation of fore-arc or back-arc basins. The mafic rocks of the Mérida Ophiolite plot in sectors corresponding to SSZ settings, far from the MORB-OIB array, in an intermediate domain between convergent environments linked to oceanic arcs or con- tinental arcs. Considering only these convergent envir- onments, the Ti-V diagram (Figure 6b; Shervais 1982; Pearce 2014) does not permit the proximity of the slab to the domain where the protoliths of these mafic rocks were generated to be defined, although it does confirm the boninitic character of those lithologies most depleted in HFSE. However, the original affinity of these mafic rocks with oceanic or continental arcs can be resolved using the La/Yb-Th/Nb diagram (Figure 6c; Hollocher et al . 2012), where all the analysed samples plot in the field of continental domains. Finally, the patterns of the mafic rocks normalized to N-MORB clearly confirm their generation in supra-subduction zone (SSZ) settings, as can be seen from the negative anomalies of Ta-Nb, Hf-Zr and Ti, and positive anomaly for Sm (Figure 6d; Pearce 2014). Furthermore, these patterns of variation appear to be unique to mafic rocks generated in environments proximal to the sub- duction trench (Pearce 2014). This region would in principle permit three dynamic settings for the genera- tion of mafic rocks, a back-arc basin, a fore-arc basin, or the base of the magmatic arc itself. The first possibility has been suggested by Díez Fernández et al . (2022), while the third possibility was initially proposed by Bandrés et al . (2004). As will be shown below, the Sm- Nd isotopic geochemical data allow us to specify the initial tectonic setting. With regard to the two intercalations of metatonalitic rocks recognized in the ophiolite, the characteristics of their compositional pattern normalized to a common ORG (Figure 7a; Pearce et al . 1984), is different from those considered representative of ocean floor plagio- granites characteristic of ophiolites. Indeed, their con- tents of Rb, Y, Nb, Ta, and Yb are more closely related to granitoid types generated in volcanic arcs (Figures 7b and 7c; Pearce et al . 1984). Thus, the mafic and felsic rocks of the Mérida Ophiolite were likely generated in a common dynamic setting, namely a supra-subduction zone domain linked to a peri-Gondwanan volcanic arc. 5.1.2. Sm-Nd isotopic geochemistry The mafic rocks of the Mérida Ophiolite have relatively constant Ɛ Nd (0) values, which range between 2.5 and 5.6, with corresponding TDM values of 548–960 Ma. They INTERNATIONAL GEOLOGY REVIEW 11 Mérida Ophiolite (SW Iberia)