Contrasting isotopic sources (Sm-Nd) of Late Ediacaran series in the Iberian Massif: Implications for the Central Iberian-Ossa Morena boundary

In the Iberian Massif, westernmost sector of the Variscan Orogen, the nature of the boundary between the Central Iberian Zone and the Ossa Morena Complex has been largely discussed. Peri-Gondwanan Ediacaran series similar in age (c. 565 Ma) but different in composition occur at both sides of that boundary. The Lower Alcudian Series (Central Iberian Zone) is located to the north, while the Serie Negra (Ossa-Morena Complex) can be found to the south of the boundary. Major and trace element compositions and Sm-Nd isotopic systematics of siliciclastic rocks from both series suggest a common active margin setting for their deposition, the Serie Negra likely occupying a more external (fore-arc) position within the arc-system relative to the Lower Alcudian Series, which would have been deposited within a large back-arc domain. TDM ages for these two series are notably different, yielding values of 1421-2040 Ma and 1256-1334 Ma for the Serie Negra and Lower Alcudian, respectively. These values suggest higher input from old cratonic sources in the Ossa Morena Complex, with probable participation of the West African Craton, which would be less prominent in the Central Iberia Zone. The whole data set indicate deposition of the Ediacaran series in separated basins, probably far away from each other along/across the margin of Gondwana. Current juxtaposition of these basins is explained by Variscan and probably also pre-Variscan tectonics. Similar conclusions could be also be extended to other similar boundaries in the Variscan Orogen.