Nova Terra 52

Alcudian (Central Iberian Zone) were isotopically younger than those for the Serie Negra (Ossa-Morena Complex), what at first would in- dicate deposition of the first at a greater distance from the West Africa Craton. The differences found in the Sm-Nd isotopic sources make it hard to sustain that the siliciclastic rocks of the Lower Alcudian and Serie Negra were deposited close to one another, as they are observed today. With the data at hand, the most probable scenario is that the deposition of the Lower Alcudian and Serie Negra took place at distant sections within the Gondwana margin, either in rather distant sections of the same sedimentary basin (e.g., two flanks of a back-arc basin), or even in two separate basins within the same arc-system. Comparative provenance analysis based on U-Pb geochronology of detrital zircons favors a more eastern Ediacaran position of the Central Iberian Zone relative to the Ossa-Morena Complex along the peri- Gondwanan realm (Fig. 8; Díez Fernández et al., 2010; Fernández- Suárez et al., 2014; Albert et al., 2015a, Cambeses et al., 2017). This is yet another evidence on the tectonic transport needed to explain the current juxtaposition of the Ediacaran series of the Central Iberian Zone and Ossa-Morena Complex (Fig. 2). Such tectonic transport could have been achieved during any of the three main orogenic events recorded in the Iberian Massif after deposition of the Ediacaran series, namely: (i) latest Ediacaran convergence, (ii) Early Paleozoic rifting, or (iii) Var- iscan collision. On a preliminary analysis, the current juxtaposition of the Central Iberian Zone and the Ossa-Morena Complex would require a component of dextral lateral movement along the margin of Gondwana over at least one major fault (Fig. 8). Although no lateral movements have been proved for the Early Paleozoic rifting stage, we cannot rule out the possibility that some lateral movement occurred at this time. Never- theless, the rifting stage would not explain alone the current terrane Range of Nd Model ages for: West Avalonia (Atlantic Canada) East Avalonia (Uriconian, outhern Britain) s East Avalonia (southern Britain -1) West Africa Craton Carolina Florida Reservoirdominatedby Grenvillianandpost-Grenvillian/ pre-Cadomiancrust Reservoirdominatedby pre-Grenvilian (>0.9-1.1Ga)cratoniccrust 3200 Ma Amazonian Craton Sunsas-Grenvillian (Amazonian Craton, eastern part) -25 -20 -15 -10 -5 0 5 10 5.2 0.2 5.1 0.1 5.0 0 Fig. 6. ε Nd vs Age diagram showing T DM values of the Late Ediacaran siliciclastic rocks of the Lower Alcudian and Serie Negra series. The range of Nd model ages of selected regions are shown for comparison (Linnemann and Romer, 2002). E. Rojo-Pérez et al. 3UHFDPEULDQ 5HVHDUFK ² &KDSWHU