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the mafic rocks of the Mérida Ophiolite appears to be primitive with only a slightly modified isotopic composi- tion, essentially in equilibrium with its age. The two samples of tonalitic orthogneisses have an isotopic composition similar to that which characterizes the granitic massifs of the Upper Schist-Metagranitoid Unit (Rojo-Pérez et al . 2022), with Ɛ Nd (0) values of −1.3 and −5.2 and TDM of 664 and 831 Ma (Figure 8b). The generation of the tonalites is therefore compatible with that of the granitoids and may have occurred in the same peri-Gondwanan volcanic arc tectonic setting. Indeed, Rojo-Pérez et al . (2022) have suggested that these granitic rocks result from the partial melting of diapiric mélanges involving the mantle wedge, subducted sedimentary rocks, and the oceanic crust that formed part of the subductive slab. 5.2. Zircon U-Pb geochronology 5.2.1. Metagabbro OM-2 Only a few zircon crystals were obtained from metagabbro OM-2. These are small xenomorphic or fragmentary grains Figure 7. Typology and tectonic setting of the felsic rocks. a) ORG-normalized patterns (normalizing values after Pearce et al . 1984). b), c) Discrimination diagramas based on incompatible elements (Pearce et al . 1984). Symbols are as in Figure 3 14 R. ARENAS ET AL. &KDSWHU