A revised Ordovician age for the Miranda do Douro orthogneiss, Portugal. Zircon U-Pb ion-microprobe and LA-ICPMS dating


  • F. BEA Departamento de Mineralogía y PetrologíaCampus Fuentenueva, Universidad de Granada, 18002 Spain.
  • P. MONTERO Departamento de Mineralogía y PetrologíaCampus Fuentenueva, Universidad de Granada, 18002 Spain.
  • C. TALAVERA Departamento de Mineralogía y PetrologíaCampus Fuentenueva, Universidad de Granada, 18002 Spain.
  • T. ZINGER Institute of Precambrian Geology and Geochronology, Russian Academy of SciencesMakarova Emb. 2, St. Petersburg, 199034 Russia.




U-Pb dating, Ollo de Sapo, Pre-Variscan, Central Iberian Zone, Gneiss


The Miranda do Douro orthogneiss was believed to be the oldest magmatic rock of the Central Iberian Zone, on the base of a U-Pb discordia upper intercept of 618 ± 9 Ma. Nevertheless, new ion-microprobe and LA-ICPMS U-Pb zircon dating revealed that the crystallization age was 483 ± 3 Ma. The orthogneiss also contains a 605 ± 13 Ma zircon population that indicates that the source-rock for the Ordovician magma was Pan-African. Moreover, a few ~3.17 Ga zircon grains were also recorded. These grains are the oldest found so far in Iberia, and its occurrence would suggest the involvement of an Archean crust in the Pan-African orogeny.


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