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(168). For further details on analytical protocol and data processing see Gerdes and Zeh (2006). Geological interpretations (see below) are based solely on concordant analyses with concordance com- prised between 95% and 105%. Concordant analyses with anoma- lously large errors were also excluded. U and Pb content and the Th/U ratio were calculated relative to the GJ-1 zircon standard and are accurate to approximately 10%. Analytical results of U– Th–Pb isotope ratios and calculated U–Pb ages are given in Supple- mentary Tables S3.1 to S3.5. In order to separate age clusters within each sample we used the function Unmix Ages in Isoplot to determine the number of superimposed Gaussian distributions. Then we proceeded to ‘‘build clusters” starting at the youngest end and adding analyses that are equivalent, i.e. will give a Concordia age with low MSDW until the first analyses that is not equivalent is found, and this analysis is used as the starting point of the next older cluster and so on. Zircon populations with more than three concordant and overlapping analyses have been considered as consistent concordant populations. 4.4. Whole-rock Sr-Nd isotopic analysis Sr–Nd isotope analyses were performed using Thermal Ioniza- tion Mass Spectrometry (TIMS) at the Geochronology and Isotope Geochemistry Service of the Universidad Complutense de Madrid. Samples were dissolved with ultrapure reagents (HF-HNO 3 -HCl). After that, Rb-free Sr fractions were separated from the bulk matrix in a first step of chromatography (Resin Dowex AG 50x8), fol- lowed by the separation from Sm of the Nd fractions in a second step (Ln-Resin ). Sr and Nd samples were analysed in an Iso- topX–Phoenix mass spectrometer (TIMS), following a dynamic multicollection mode. 87 Sr/ 86 Sr ratios were corrected for possible 87 Rb interferences and normalized to the average 86 Sr/ 88 Sr value of 0.1194 (Nier, 1938), used for conventional internal correction. Final Sr isotope ratios were also corrected in view of the isotopic Sr standard ratios (NBS 987 - Standard Reference Material 987), analysed along with the samples, and yielding an average value of 87 Sr/ 86 Sr = 0.710246 (±0.000017; 2 r ) for 10 replicate analyses. Moreover, to correct procedural and instrumental mass fractiona- tion, the resulting 143 Nd/ 144 Nd ratios were corrected for 142 Ce and 144 Sm potential interferences and normalized to 146 Nd/ 144 - Nd = 07219 value (O’Nions et al., 1979). Potential drifts of the sam- ples isotope ratios were corrected using the Nd isotope standard reference values (JNdi-1; Lugmair et al., 1983), by analysing the standard along with the samples, with an average value of 143 - Nd/ 144 Nd = 0.512112 for 7 replicas and an internal precision of ± 0.000009 (2 r ). Analytical errors on the 87 Sr/ 86 Sr and 143 Nd/ 144 - Nd ratios were estimated to be lower than 0.01% and 0.006%, respectively. Sr and Nd procedural blanks are always under 0.5 and 0.1 ng, respectively. The results of Sr and Nd isotopic analyses are given in Supplementary Table S4. 5. Results 5.1. Whole-rock geochemistry Metabasite rocks emplaced in the lowest exposed levels in the Montemolín Formation have a common geochemical pattern (Sup- plementary Table S2). These mafic rocks do not present high values in Al 2 O 3 , Sc or Ni, which allows to discard that they represent types of accumulated (Pearce, 1996a). They are characterized by rela- tively high SiO 2 contents between 51.01 and 56.41 wt%, along with Fig. 4. Microphotographs of representative samples from the Mérida Massif. (a) and (b) metagranodiorites of Valle Real Metaigneous Complex (PPL); note the large size of amphibole, plagioclase and secondary epidote crystals. (c) and (d) deformed Valverde metagranites (XPL, strained rim areas). E. Rojo-Pérez, U. Linnemann, M. Hofmann et al. Gondwana Research 109 (2022) 89–112 The Ediacaran arc section