Nova Terra 52

such boundary in Iberia contribute to the understanding of equivalent boundaries throughout the Variscan orogen. The boundary between the Central Iberian Zone and the Ossa- Morena Complex has been interpreted as a stratigraphic transition zone (Martínez Poyatos, 2002), or as an extensional detachment (Martín Parra et al., 2006), or as the remnant of a major thrust (currently re- worked as an extensional detachment), which would have emplaced northward the Ossa-Morena Complex onto the Central Iberian Zone (Díez Fernández and Arenas, 2015). On the other hand, U-Pb detrital zircon data suggest that during the Ediacaran and Early Paleozoic the basins of the Central Iberian Zone were located in a more eastern po- sition along the Gondwanan margin relative to the series from the Ossa- Morena Complex, although its specific location between the West African Craton, the Tuareg Shield and the Sahara Metacraton is very uncertain (Bea et al., 2010; Díez Fernández et al., 2010; Talavera et al., 2012; Fernández-Suárez et al., 2014; Shaw et al., 2014; Albert et al., 2015a; Cambeses et al., 2017). However, the use of isotopic tracers based on whole rock geochemistry, such as the Sm-Nd methodology, is yet to be exploited as a tool to constrain the nature of the Central Iberian Zone and Ossa-Morena Complex boundary, since the isotopic sources of coeval series at both sides of it have not been compared. It is important to point out that until now, there are not appropriate data- bases to make comparisons with the section of the Gondwanan margin preserved in North Africa, since most of the Sm-Nd available data there have been obtained in granitic rocks (Bea et al., 2010). The isotopic sources of those granitoids indicate large isotopic mixing, with high input of juvenile material (Linnemann et al., 2014; Albert et al., 2015a,b), making very difficult to use them as precise tracers of isotopic sources for a specific age. Therefore, only the investigation of the iso- topic sources associated with siliciclastic sedimentary series allows a confident time-resolved comparison between different crustal sectors. This work presents a comparison of whole rock geochemical data of coeval Ediacaran siliciclastic series, located at both sides of the Central Iberian Zone – Ossa-Morena Complex boundary, which have been tra- ditionally referred to as Lower Alcudian Series and Serie Negra, re- spectively. For this purpose, we have used published major and trace elements data and Sm-Nd isotopic data of the Lower Alcudian Series (Fuenlabrada et al., 2016) and a set of new whole rock data from the Serie Negra obtained in the same laboratories and following the same methodology. The main objective is to discuss on the basis of geo- chemical data whether the Ediacaran series at each side of the afore- mentioned boundary were deposited in the same or in separate sedi- mentary basins. The comparison is established for very close domains of both regions, the southernmost sector of Central Iberian Zone and the northernmost of Ossa-Morena Complex, designated as the Obejo-Val- sequillo Domain. If these Iberian Ediacaran series were located in an initial same paleogeographic area, the proximity of both series would be consistent with the presence of similar Sm-Nd isotopic sources and thus, a deposition in a single sedimentary basin. The investigation of the tectonic setting and isotopic sources of ancient siliciclastic series, is in general possible using major and trace elements geochemistry and Sm-Nd systematics (McLennan et al., 1990; McLennan and Hemming, 1992; Taylor and McLennan, 1985). In the Iberian Massif, these methodologies have been applied to siliciclastic series laid down during the Ediacaran-Early Cambrian transition, de- posited in a magmatic arc setting in different positions along the African margin of Gondwana (Ugidos et al., 2003; Fuenlabrada et al., 2010, 2012, 2016; Díez Fernández et al., 2017). 2. Geological setting In the southern sector of the Central Iberian Zone, the Ediacaran siliciclastic series are part of the so-called Schist and Greywacke Complex (Carrington da Costa, 1950; Ovtracht and Tamain, 1970). This group includes Ediacaran turbidites (Lower Unit or Lower Alcudian; San José et al., 1990), outcropping over the cores of the Alcudia and the Centro-Extremeño anticlines (Fig. 3), and Cambrian pelitic sequences (uppermost part of the Upper Unit or Upper Alcudian, Pusa Shales) (Rodríguez Alonso et al., 2004). The northern exposures of the Ossa- Morena Complex are referred to as the Obejo-Valsequillo Domain (Apalategui and Pérez-Lorente, 1983), and the Ediacaran siliciclastic series in that area are known as Serie Negra (Black Series; Carvalhosa, Fig. 1. Zonation of the Variscan Orogen (Díez Fernández and Arenas, 2015; Arenas et al., 2016b). Based in Franke (1989), Lefort (1989), Neuman and Max (1989) and Martínez Catalán (2011). Location of the geological map presented in Fig. 3 is shown. E. Rojo-Pérez et al. 3UHFDPEULDQ 5HVHDUFK ² &KDSWHU