A revised Ordovician age for the Miranda do Douro orthogneiss, Portugal. Zircon U-Pb ion-microprobe and LA-ICPMS dating
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Universidad de Barcelona; Instituto de Ciencias de la Tierra Jaume Almera
U-Pb datingOllo de SapoPre-VariscanCentral Iberian ZoneGneiss
Bea Barredo, F.; et al. A revised Ordovician age for the Miranda do Douro orthogneiss, Portugal. Zircon U-Pb ion-microprobe and LA-ICPMS dating. Geologica Acta, 4(3): 395-401 (2006). [http://hdl.handle.net/10481/32070]
PatrocinadorThis work was financially supported supported by the Spanish DGCYT grant BTE2002-04618-C02-01, the SYNTHESIS grant SE-TAF 528 and the NATO Collaborative Project EST-CLG-978997.
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.