Age and characteristics of the Loma del Aire unit (SW Iberia): Implications for the regional correlation of the Ossa-Morena Zone

Abstract

Finding of ca. 620 Ma old zircons in a volcanic rock of the Loma del Aire unit, one of many structural divisions in the Ossa Morena Zone, some years ago, attracted much attention to this unit, which would contain, if proven, the oldest rocks so far dated not only in Ossa Morena but also in the entire Iberian Massif. In this paper, new field, petrographic, whole-rock geochemical and Sm–Nd isotope data as well as new TIMS U–Pb zircon ages are presented, which collectively allow a much better characterization and dating as Cambrian of the rock sequence in the Loma del Aire unit; the previously found ca. 620 Ma old zircon population is now interpreted as xenocrysts incorporated in the Cambrian magma. Our data together with recently published provenance studies, bear important implications concerning the nature and evolution of the underlying lithospheric basement of the Ossa Morena Zone, which shares many characteristics with the Neoproterozoic peri-West-African craton arc systems currently exposed in the Precambrian inliers of the Moroccan Anti-Atlas, the North Armorican Zone of Brittany, Normandy and the Channel Islands (Cadomian Arc), and the Saxo-Thuringian and Teplá-Barrandian Zones of the Bohemian Massif. A correlation of the Ossa Morena zone with these arc systems in the Neoproterozoic and Early Paleozoic is thus proposed.