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that the granites represent magmas derived from the magmatic arc that, on rare occasions, came to intrude domains of the back-arc. The Hf isotopic contents in zircon in the protoliths of the gabbroic rocks show a clear juvenile character, which differs from the older isotopic sources detected in the metatonalite (Figure 11). Once again, these data support a different origin for the mafic rocks of the Mérida Ophiolite and the few granitic rocks that intrude them, which are similar to those described in the Upper Schist- Metagranitoid Unit. This further indicates that the mafic rocks of the Mérida Ophiolite are unlikely to represent the base of the magmatic arc preserved in the Upper Schist-Metagranitoid Unit. 9.5. Tectonothermal evolution of the mafic unit The U-Pb age of c. 590 Ma provided by garnet of sample 117,350 is interpreted as dating the main event of meta- morphism and deformation that affected the Mérida Ophiolite. It is the oldest Cadomian metamorphic age obtained so far in SW Iberian Massif. Considering this gar- net age and the protolith age of the metagabbro of the ophiolite reported in this work (c. 596 Ma), it is very likely that the previous U-Pb zircon age obtained from another garnet amphibolite (c. 577 Ma; Bandrés et al . 2004)repre- sents a metamorphic age. Local partial melting was observed in these garnet amphibolites, as was also pre- dicted by pseudosection modelling. Zircon could have been formed during this partial melting event. Hence, the Sm-Nd age obtained from the garnet of the Mérida Ophiolite (c. 555 Ma; Bandrés et al . 2004) is considered unreliable (internal isochron after two points). The younger deformation and metamorphism suggested for the obduc- tion of the Calzadilla Ophiolite (540 Ma, U-Pb in zircons; Arenas et al . 2018)may also have its reflection in the Mérida Ophiolite. The U-Pb zircon age of the small bodies of granites described in the Mérida Ophiolite is similar to the age reported by the Cadomian deformation of the Serie Negra (550–560 Ma) by Blatrix and Burg (1981) and Dallmeyer and Quesada (1992), and Cadomian deforma- tion also affects granitoids of the Upper Schist- Metagranitoid Unit (Díez Fernández et al . 2022) dated at c. 550 Ma (Rojo-Pérez et al . 2022). Considering the mag- matic and metamorphic ages together, they may indicate a progressive collision of the arc with the Gondwana mar- gin, starting with the rapid closure of the back-arc and the accretion of the Mérida Ophiolite (c. 590 Ma), followed by a second tectonothermal event, ranging 560–540 Ma, that progressed through the margin and the arc until the fore- arc, favouring the obduction of the Calzadilla Ophiolite (Arenas et al . 2018; Díez Fernández et al . 2019). The P-T path obtained for the garnet-bearing amphi- bolites is an intermediate-P path, progressing from higher temperatures than those characteristic of com- mon Barrovian metamorphism (Figure 15). However, these characteristics are compatible with the rapid stack- ing of somewhat overheated rocks, as would be the case for the lithosphere of a young back-arc. On the other hand, the rapid rise in temperature may reflect the imbrication of ophiolite slices under the mantle section of previously stacked slices, in which case the garnet amphibolites may correspond to a metamorphic sole. The characteristics of the P-T path, which does not reflect high-P events, and the short time interval between the end of the back-arc opening ( c . 596 Ma) and the beginning of its closure ( c . 590 Ma) also indicate that the metamorphic path probably corresponds to the onset of subduction of the back-arc lithosphere beneath the magmatic arc. P-T paths of this type have also been related to the onset of subduction of ophiolitic sections with the characteristics of metamorphic soles (Lázaro et al . 2013; Guilmette et al . 2018; Goscombe et al . 2020). 9.6. Evolutionary model for the Ediacaran peri-Gondwanan arc The characteristics of the Mérida Massif clearly suggest that it contains some units formed in association with a peri-Gondwanan magmatic arc. This is the case for at least the two upper units. The oldest protolith ages obtained both in this massif and in the Ossa-Morena Complex are c . 600 Ma and correspond to the sedimen- tation of the siliciclastic series of the Montemolín Formation (the lower member of the Serie Negra Group) and the metasedimentary series that appears in the upper unit of the Mérida Massif. These series were intruded by mafic rocks and large granitic plutons shortly after deposition, with magmatic activity continu- ing until the Ediacaran-Cambrian boundary (Rojo-Pérez et al . 2022). To the south of the Mérida Massif, the Calzadilla Ophiolite ( c . 600 Ma) has been interpreted as a fore-arc ophiolite, based on the boninitic composition of its mafic rocks and its location on the paleomargin (Arenas et al . 2018; Díez Fernández et al . 2019). Taking these data into account, the NW African margin of Gondwana likely had characteristics similar to those shown in Figure 16a, highlighted by the presence of an active magmatic arc built on the thinned peri- continental basement. This arc would have been fronted by a fore-arc basin adjoining the trench. The Serie Negra Group was probably deposited both in the frontal area of the arc, as well as in the adjoining rear section and in the arc itself, above collapsed sections and submerged levels. Ediacaran sedimentary series were also deposited INTERNATIONAL GEOLOGY REVIEW 25 Mérida Ophiolite (SW Iberia)