Detrital zircon populations in the lower formations of the South Portuguese Zone (SW Iberia, Variscan Orogen)

Resumen

Detrital zircon age populations from five lithostratigraphic units of the South Portuguese Zone have been analyzed in order to determine provenance sources and to test the Avalonian or Gondwanan affinity of this terrane. Samples were collected in Devonian-Carboniferous rocks from the Pulo do Lobo belt (Horta da Torre, Ribeira de Limas and Santa Iría formations), located just south of the Ossa-Morena Zone/South Portuguese Zone boundary, and from the lowermost outcropping rocks of the Iberian Pyrite belt (Ronquillo and PQ formations). The most relevant results are as follows: (i) the strong Avalonian imprint in the Horta da Torre formation, which shows Mesoproterozoic and Caledonian-Amazonian zircon populations, and can thus be considered as the only “exotic” formation in all the South Portuguese Zone; (ii) the Ribeira de Limas formation (Pulo do Lobo belt) and the Ronquillo formation (Iberian Pyrite belt) can be considered as equivalent according to their zircon content, age, lithology and polyphasic deformation; (iii) the youngest Santa Iría and PQ formations, which unconformably overlie the Ribeira de Limas and Ronquillo formations respectively, contain an important zircon peak at 365-375 Ma that is attributed to a missed Variscan magmatic arc.