Nova Terra 52

MgO contents between 4.24 and 6.63 wt%. These values are consis- tent with those of transitional to calc-alkaline rocks (Ross and Bédard, 2009). As regards other major elements, they have low contents of Al 2 O 3 , CaO and Ti 2 O (avg. 13.96, 5.05 and 1.27 wt%, respectively), and slightly high of Fe 2 O 3 (T), K 2 O and Na 2 O (avg. 10.78, 1.45 and 3.17 wt%, respectively), with relatively low MgO/ MgO + FeO ratios (0.26–0.42 wt%). Samples belonging to the metagranitic complexes described in the Mérida Massif do not show a common geochemical pattern, which prevents them from being described as a single set (Supple- mentary Table S2). Samples taken from San Andrés and Valverde metaigneous complexes are the most silica-rich (avg. SiO 2 < 70- wt%), whereas the samples from Don Álvaro and Valle Real metaig- neous complexes have average values of 56.17 and 55.43 wt%, respectively. The rocks of San Andrés and Valverde metaigneous complexes show low average values of Fe 2 O 3 (2.44 and 1.64, respectively), MnO (avg 0.06 and 0.05, respectively), MgO (0.78 and 0.51, respectively) and CaO (1.34 and 2.29, respectively), while the rocks belonging to Don Álvaro and Valle Real metaigneous complexes have higher values in those oxides (Supplementary Table S2). The Al 2 O 3 values are very similar in Don Álvaro and Val- verde rocks (around 15 wt% on average), while the Valle Real group presents the highest average values (avg. 18.31 wt%), and the felsic orthogneiss of San Andrés the lowest values (avg. 12.69 wt%). Don Álvaro Metaigneous Complex has slightly lower average Na 2 O val- ues than the rest of the groups (avg. 2.73 wt%), while the Valverde Metaigneous Complex shows slightly higher K 2 O contents than the rest of the groups (avg. 2.29 wt%). As a whole, the four metaigneous complexes are close to the compositions known in Cordilleran batholiths and I-type granites (Frost et al., 2001). All of them appear represented as magnesian granites in relation to their nFe, and as calcic and calc-alkalic granites into the MALI diagram (Supplementary Fig. S1). The rock assemblages of Don Álvaro and Valle Real complexes have a metaluminous character in the A/ CNK vs. A/NK diagram (Shand, 1948), with an A/CNK ranging from 0.64 to 1.02 (Fig. 5a). The San Andrés and Valverde metaigneous complexes are more peraluminous, with an average A/CNK ranging from 1.0 to 1.32 (Fig. 5a). The moderate effect of weathering pro- cesses is supported by values of the Hashimoto alteration index (AI; Ishikawa et al., 1976) ranging in average from 30 to ca. 40 for all studied samples. Rock material loss of ignition (LOI) at 1100 C is in some cases higher than 2 wt%, even higher than 3 wt%, which prevents using classical TAS diagram (Le Maitre et al., 1989) as common classifica- tion criterion for all samples. In these cases, it is important to remark that using elements with high mobility might reflect nei- ther the geochemical composition of the protolith nor its magma source. For this reason, it is necessary to use more reliable analo- gous classifications, based on trace element proxies which remain more immobile under deformation/metamorphic conditions. The Nb/Y-Zr/Ti diagram (Winchester and Floyd, 1977, modified by Pearce, 1996a; Fig. 5b) was used following these criteria. According to this classification, the metabasites from the Montemolín Forma- tion plot in the gabbro/basalt field. Don Álvaro samples appear restricted to the gabbro and gabro/diorite field, which is the same occupied by the Valle Real samples. The classification for the San Andrés samples into this diagram is restricted to the monzonite- monzogranite field, whereas the samples belonging to the Valverde Metaigneous Complex are more dispersed on this diagram, mainly due to their low Zr and Ti contents with respect to the rest of the analysed samples. The total Chondrite-normalized rare earth element contents (Sun and McDonough, 1989; Supplementary Table S2) are quite similar for the whole metabasites located into the Upper Schist- Metagranitoid Unit. Their incompatible, immobile REE patterns (Fig. 5c)vary from almost flat to slightly fractionated LREE ((La/ Sm) n = 1.54–2.36) with rather flat HREE patterns ((Gd/ Yb) n = 1.25–1.38) and without significant Eu anomalies (Eu/Eu* = 0.76–0.91), compatible with plagioclase fractionation. These rocks (a) 5 10 15 20 25 30 35 0 50 100 150 200 High/P fractional crystallization Arc basalt re-melting Slab melting Adakites Normal Arc-Rocks Y S/Y 10 20 30 40 0 50 100 150 (b) Adakites Normal Arc-Rocks ) bY / a L( N Yb N 0.01 0.1 1 10 0.10 001 01 1 MORB-OIB Array E- MORB N- MORB OIB SSZ Oceanic Arc Continental Arc Magma- crust interaction Deep- crustal recycling bY / h T Nb/Yb (c) SHO CAB CAB IAT Fig. 6. (a) Sr/Y - Y discrimination diagrams for adakite-like rocks and common volcanic-arc magmas (Defant and Drummond, 1990; MacPherson et al., 2006). (b) (La/Yb) N - Yb N discrimination diagrams for adakite-like rocks and common volcanic-arc magmas (Defant and Drummond, 1990). (c) Th/Yb - Nb/Yb diagram (Pearce, 2008, 2014) for the metabasites of the Montemolín Formation; SHO: shoshonite, CAB: calc-alkaline basalts, IAT: island arc tholeiites, SSZ: Supra- subduction zone, N-MORB; normal-mid ocean ridge basalts, E-MORB; enriched- mid ocean ridge basalts, OIB: ocean island basalts. Symbols are the same as in Fig. 5. E. Rojo-Pérez, U. Linnemann, M. Hofmann et al. Gondwana Research 109 (2022) 89–112 The Ediacaran arc section