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lead composition. Concordant ages range from 631 to 507 Ma (Fig. 11c). The oldest concordant age found was 637 ± 14 Ma. The majority of concordant ages (45/48) are Ediacaran to Cambrian with clusters at 612 ± 7 Ma (n = 3; MSWD = 2.3), 590 ± 5 Ma (n = 5; MSWD = 0.44), 568 ± 3 Ma (n = 19; MSWD = 0.106) and 554 ± 2 Ma (n = 17; MSWD = 1.07). The age of the youngest cluster is consid- ered to represent the best estimate for the crystallisation age (Fig. 11d) of this rock and agrees within uncertainty with the age obtained for the non-deformed Valverde Metaigneous Complex (551 ± 5 Ma, see above). Three non-equivalent concordant analyses yield younger ages of 532 ± 11 Ma (VALMIC 50), 519 ± 11 Ma (VAL- MIC 111) and 507 ± 10 Ma (VALMIC 96). 5.3. Sm-Nd and Rb/Sr isotope geochemistry Sr and Nd initial ratios and equivalents at the crystallization age obtained for each group have been calculated and included in Sup- plementary Table S4, along with the diagrams shown in Fig. 12. Based on the intrusion relationship between the metabasic rocks and the oldest rocks dated in this work, we have used the age of the latter as a reference for the calculation of Nd analyses in the metabasite samples. Supplementary Table S4 also included new Sr analyses obtained from the metasedimentary rocks of the Serie Negra Group. The metabasites of the Montemolín Formation show a wide variation in 87 Sr/ 86 Sr (t) ratios, from 0.7038 to 0.7061. A similar range is found in the samples from San Andrés and Valverde, whose 87 Sr/ 86 Sr (t) ratios ranges between 0.7033–0.7056 and 0.7035–0.7050, respectively. The samples belonging to Don Álvaro and Valle Real metaigneous complexes present lower 87 Sr/ 86 Sr (t) ratios, ranging 0.7031–0.7042. On the other hand, the wide varia- tion of f Sm/Nd and 147 Sm/ 144 Nd ratios in all the rocks studied sug- gests influence of recycling processes, and argues against isotopic homogenization. The samples from the metagranitoid complexes display negative e Nd (0) values. The lowest values correspond to those samples belonging to the San Andrés and Valverde metaig- neous complexes, describing a narrow range between 7.3 and 5.1; meanwhile the Don Álvaro and Valle Real metaigneous com- plexes present a wider range, between 4.9 and 0.2. On the other hand, the samples belonging to Montemolín metabasites show negative to slightly positive e Nd (0) values, ranging from 0.4 to 3.3. The largest variations in e Nd (t) are shown by the Montemolín metabasites, which range from positive to negative values (2.1 to 1.0), followed by the Valverde samples (2.4 to 0.5). Samples belonging to San Andrés metaigneous complex have e Nd (t) values varying between 2.7 and 0.5, meanwhile Don Álvaro and Valle Real samples show the least variation in the e Nd (t) values, ranging from 2.8 to 1.4 and from 2.2 to 0.5, respectively (Supplementary Table S4 and Fig. 12). TDM model ages (DePaolo, 1988) obtained for the metabasites of the Montemolín Formation are significantly older than the age of crystallization suggested for the igneous protolith (pre- c. 602 Ma), ranging between 1316 and 2110 Ma. These rocks show a clear overlap with the Serie Negra Group metasediments from the northern and southern sections of the OMC (Fig. 12a; Rojo- Pérez et al., 2019, 2021), suggesting that, at least in part, these metabasites share an ancient isotopic source with the metasedi- mentary rocks of the Serie Negra Group. However, the obtained e Nd (t) values for the metabasites are significantly more positive than those obtained for the metasedimentary rocks, showing more radiogenic 87 Sr/ 86 Sr (t) ratios than those calculated for the Serie Negra Group (Fig. 12b), indicative of strong mantle signature. TDM model ages obtained for the four metagranitoid assemblages are Neoproterozoic, also older than their protolith’s crystallization ages (see above), varying in a narrow range between 818 Ma and 1145 Ma. On the other hand, the isotopic sources of the meta- Fig. 12. (a) e Nd vs. age diagram showing TDM values for Late Proterozoic to Early Paleozoic metaigneous complexes from Mérida Massif. The range of Nd model ages of equivalent metagranites (ranging 580–609 Ma) from the North Africa Cadomian basement (Errami et al., 2009; El Haïbi et al., 2021) are shown for comparison. (b) e Nd (t) vs. 87 Sr/ 86 Sr (i) diagram for the metagranitic rocks from Mérida Massif. The values for the metasedimentary rocks of the Serie Negra Groupare also included. Red and green arrows show the mixing lines calculated by Castro et al., 2021. The two evolved end members correspond to the midpoints on the fields of the Chilean accretionary complex and the North Patagonian massif. The juvenile end member (not represented here) is the altered oceanic crust (AOC) (from Pankhurst et al., 1999; Kelley et al., 2003; Castro et al., 2021). The extended path of the red arrow overlaps the Serie Negra Group isotopic source. The relative position of the continental crust and enriched mantle type I (EM I) and Type II (EMII) geochemical reservoirs are also plotted. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) E. Rojo-Pérez, U. Linnemann, M. Hofmann et al. Gondwana Research 109 (2022) 89–112 &KDSWHU