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powdering of the samples were first performed at the Universidad Complutense of Madrid (Spain). Lithium metaborate/tetraborate was used for fusion, and the elements were measured by Inductively Coupled Plasma analysis (ICP-OES and ICPMS). The quality of the performed analyses is high, with a detection limit of ~0.01% for the majority of the major elements and ~0.001% for MnO and TiO 2 , and that for trace elements varying from 0.002 ppm for Lu to 30 ppm for Zn. Detection limits for each element, the composition of the standards used for this run of analyses, and the analytical details of each element can be found in Arenas et al . (2021a). Locations of all the samples are given in Supplementary Metadata 1. Sm-Nd isotope analysis (ID-TIMS) was performed at the Geochronology and Isotope Geochemistry Facility of the Universidad Complutense (https://www.ucm.es/iso tope; Supplementary Table 2). Spiked samples ( 149 Sm- 150 Nd tracer) were dissolved using a strong acid digestion (HF+HNO 3 + HCl). Sm and Nd fractions were separated by means of a two-step chromatographic pro- cess, by using AG® 50 × 8 resin to separate REE from the bulk matrix of the samples and Ln-Resin (Eichrom Technologies, Inc., USA) to recover purified Sm and Nd Figure 3. Petrographic microphotographs of garnet amphibolites from the Mérida Ophiolite showing details of the large garnet porphyroblasts and the common non-retrogressed nematoblastic matrix composed of pargasite, plagioclase, clinozoisite, quartz and ilmenite. INTERNATIONAL GEOLOGY REVIEW 7 Mérida Ophiolite (SW Iberia)