Nova Terra 52

481 International Journal of Earth Sciences (2021) 110:467–485 13 of the Late Ediacaran series from Iberian and Bohemian massifs, and the number of rocks sampled in the different locations are presented in Figs. 2, 3 and 8. The diagram CaO vs. ε Nd ( T ) (Fig. 7) shows the influ- ence of felsic or mafic (more juvenile) contributions in the siliciclastic rocks, as well as the contribution of old crus- tal areas. CaO contents in the Tentudía Formation show uniform distribution, similar to the distribution followed by the Saxo-Thuringian rocks, in both cases suggesting mixed felsic–mafic sources. However, the samples from the Montemolín Formation show a different trend directed toward less evolved source areas. The higher CaO values (avg. 1.93 wt%) are consistent with the presence of a sig- nificant volume of metamafic igneous rocks interbedded in this sequence. In Fig. 7, the Ediacaran samples show a wide variation in CaO with little changes in ε Nd (t ) values. Most samples fall into a restricted range of ε Nd ( t ) values, ranging between −7 and −11 (Figs. 7 and 8). Three samples show less negative values of ε Nd (t ) , probably due to the addition of juvenile material derived from an active magmatic arc. The homogeneous distribution, with little or no variation in ε Nd ( t ) , can be interpreted as evidence for a common isotopic source area, which should have remained available for a long time in the (North African) margin of Gondwana. This uni- formity and availability are also reflected in the ε Nd (0) values of the Bohemian series compared. Linnemann and Romer (2002) obtained highly negative ε Nd (0) values for the SXTZ series, ranging between − 16.6 and − 12.8, except for the three samples mentioned above with larger juvenile input. The ε Nd vs. time diagram presented in Fig. 8 shows a comparison between the isotopic composition of the SXTZ (North Bohemia) samples and the siliciclastic rocks of the Serie Negra Group. The Nd model ages obtained for the Bohemian samples define a relatively narrow age group ranging between 1570 and 1976 Ma. This age range is somewhat greater than that defined by the Montemolín and Tentudía formations of the Serie Negra Group. However, the two groups of samples are similar in relation to their isotopic sources, which very likely indicate a common source area for the North Bohemian and SW Iberian massifs during Ediaca- ran times. Their source area must have remained available at least during the depositional time of all the Ediacaran series. As a result, these data seem to indicate a common palaeo- graphic context in the (North African) margin of Gondwana for the two regions. Ediacaran proto- North Bohemia and proto- SW Iberia were probably part of the same (or closely connected) sedimentary basin(s), where turbiditic siliciclas- tic series that shared common source areas were deposited (Fig. 9). Discussion In the southwest part of the Iberian Massif, the Ossa–Morena Complex represents the most external section of the Gond- wana margin (Díez Fernández and Arenas 2015). This sec- tion and its prolongation in the allochthonous complexes of NW Iberia, was affected by an intense Variscan deformation Fig. 9 Paleogeographic reconstruction at c. 570 and 540 Ma, showing the paleo-position inferred for the deposition of the Late Ediacaran series located in the Ossa-Morena Complex (OMC), Armorican Mas- sif (AM), Saxo-Thuringian Zone (SXTZ) and Central Iberian Zone (CIZ) along the (North African) margin of Gondwana. The arrows indicate the location of the source areas and the direction of sediment transport into the peri-Gondwanan basin. Gondwana paleogeography based on von Raumer and Stampfli (2008), Meert and Bruce (2008) and Díez Fernández et al. (2010) Iberian–Bohemian correlations