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111 Group or analogous metasedimentary sequences through Euro- pean Cadomian basement (e.g. Eguíluz and Abalos, 1992). The younger model ages, as well as the more radiogenic e Nd and more restricted Sr (i) obtained for the Don Álvaro and Valle Real metaig- neous complexes rather indicate great participation of mantle wedge modified by subducted crustal materials. The calc-alkaline mafic magmas generated from mantle wedge modified by the sub- ducted material, are fractionated and differentiated within the crust to form ‘‘normal” calc-alkaline granites (Castro, 2014). The observed isotopic enrichment and variation along with the change from adakitic signature to ‘‘normal” arc magmatism of these metaigneous suites require variations in the chemistry of the source itself. These variations are not possible to explain only by combination of intra-crustal assimilation combined with fractional crystallization (Bowen, 1928; DePaolo, 1981), but it is necessary a periodic variation in the subduction erosion rate. 6.3. Geodynamic implications Subduction erosion occurs at all convergent plate margins, where the removed crust can remain into the crust by underplating or contribute to the arc magmatism by addition to the mantle source region generating a source enrichment or participate in the melting of the subducted crust and sediments resulting in ada- kitic magmas that mix with other slab-derived magmas and/or interact with mantle peridotite during the ascent toward the sur- face (Stern, 2011). Subduction erosion, which remove essentially crystalline fore-arc basement is not a steady-state process (Stern and Scholl, 2010; Santosh, 2010; Stern, 2011; Straub et al., 2020) but their rates vary cyclically being higher during the superconti- nent assemblage. Adakites and TTG suites can be formed by melt- ing of subducted forearc crust or previous crystalline arc rocks. Although globally these rocks are less common than basalts in active arcs, formation of this type of magmas often reflects tran- sient events of accelerated fore-arc erosion subduction, associated with changes in subduction geometry (low subduction angles) or subduction of buoyant features (Bourgois et al., 1996; Kay, 1978, 2006). Correlation between episodes of relatively high transference of crystalline arc rocks tectonically eroded and the genesis of mag- mas with distinctive geochemical characteristics have been described in the Andean continental margin (e.g. Stern, 1990; Kay, 2006; Bourgois et al., 2000; Stern, 2011, 2020), Aleutian (Jicha and Kay, 2018) and the Central American and Trans- Mexi- can Volcanic Belts (Gromet and Silver, 1987; Goss and Kay, 2006). Subduction zones linked to this proto Gondwana margin were active during the most part of this time, favouring subduction ero- sion processes able to incorporate removed arc-rock to the related mantle wedge. This margin was also characterized by a dynamic setting with opening and closing of basins addressed by moments of extension and shortening of the margin itself. Recently it has been revealed that long- and short-term cycles of mantle activity are operating on Earth since Paleoproterozoic times (Mitchell et al., 2019; Li et al., 2019), also affecting to the peri -Gondwana realm during Neoproterozoic times (Arenas et al., 2021). Cyclical changes in the intensity of mantle upwelling can also explain vari- able subduction rates, as well as changes in the subduction angle which drive in part the petrogenesis of the arc magmatism. In the case of the Ossa-Morena Complex, it has been proposed an epi- sode of roll-back affecting the subductive slab could have gener- ated extension in the overlying plate at c. 600 Ma (Arenas et al., 2018). The metabasites of Montemolín fm. studied here, probably record the incipient opening of an intra-arc basin, however the par- ticular supra-subduction zone setting under construction requires additional interpretations, since both a net fore-arc context and an incipient generation of a back-arc basin are in principle possible. The geochemical slab-distal features appreciated in the metaba- sites of the Montemolín Fm. can be related to an incipient basin develop over a low-angle subduction setting where the upper plate was extended increasing the distance between the trench and the arc. On the other hand, the uniform projection of these rocks above the MORB-OIB array defining a single type of calc-alkaline magma, is contrary to the dispersion that would be expected for rocks gen- erated in a back-arc region (Pearce, 2014). Moreover, the propor- tion of subducted crustal components progressively decreases in the magmas erupted in the back-arc region (Stern, 1990; Jacques et al., 2014), while for the primitive mantle-derived metabasites of Montemolín fm. the exceptionally old model ages, their mostly negative e Nd values and variable 87 Sr/ 86 Sr ratios agreed with a mantle source region contaminated with tectonically eroded crust components (Fig. 13a) as observed in modern arcs (Andean vol- canic zone, Stern, 1990, 2020; Lagabrielle et al., 2000; Wieser et al., 2019). For this reason, it seems more likely that this magma- tism preceded the opening of a forearc basin on the periphery of Gondwana, which also agrees with the suggested by several authors as the most probable setting for the Serie Negra deposition. Sánchez-Lorda et al. (2013, 2016), as well as for the generation of the boninite rocks included in the Calzadilla ophiolite (Arenas et al., 2018). The Gondwana assemblage at c.600 Ma is the final result of the complex interactions between crustal blocks that involve this Pan- African Orogen. This context characterized by an extended subduc- tion is a suitable setting to return a huge volume of recycled arc material into the deep mantle, this would allow the eventual gen- eration of partial melting of this removed and subsequently meta- morphosed crystalline crust along with mafic oceanic plate material, to produce a melt component at eclogite facies with ele- vated La/Yb and Sr/Y ratios along with the highest SiO 2 values resulted from crustal assimilation as the described to the San Andrés Metaigneous Complex (Fig. 13b). This metaigneous com- plex was likely formed during (or shortly after) a period of higher subduction erosion rate agreed with the e Nd values and model ages older than the protolith crystallization age, suggesting deriva- tion from an old crustal source probably mixed with a juvenile component derived from the oceanic plate incoming. The hetero- geneous 87 Sr/ 86 Sr values also suggest mixing with juvenile materi- als with mantle signature. These rocks shared geochemical and isotopic characteristic with most current tectonic settings and likely analogous in the Andean margin (e.g. Stern, 2011, 2020 and references therein), which have been also correlated with boninite magmatism as useful tool to unravel subduction initiation settings in volcanic arcs and continental margins (Falloon et al., 2008; Polat and Kerrich, 2004). The magmatism recorded in the arc section preserved in the Mérida Massif begins around c. 645–625 Ma (according to inher- ited zircons), coinciding with the closure of the Pharusian Ocean and the development of the Trans Saharan Orogen (Brahimi et al., 2018) and continues uninterrupted until c. 540 Ma. Although there is no evidence of the existence of metaigneous rocks with crystallization ages between c. 602 and 550 Ma, at least in the studied arc section, a large volume of inherited zircons between the 580–570 Ma appears represented in most of the studied metaigneous complexes, so a priori it would not be easy to deduce what evolution would have followed the peri -Gondwana margin during this gap of 50 Ma. Previous works (Bandrés, 2001; Talavera et al., 2008) relate this period of time with the intrusion of large volumes of dioritic-tonalitic granite bodies in diverse OMC sectors. This is also the age suggested for the opening of the basin that gave rise to the Mérida ophiolite (Bandrés et al., 2004; Díez Fernández et al., 2021), which could indicate a moment of extension in the upper plate and increase in the angle of the slab subduction. The presence of zircon remnants derived from old crystalline arc rocks implies that a significant portion of the sub- E. Rojo-Pérez, U. Linnemann, M. Hofmann et al. Gondwana Research 109 (2022) 89–112 The Ediacaran arc section