A revised Ordovician age for the Miranda do Douro orthogneiss, Portugal. Zircon U-Pb ion-microprobe and LA-ICPMS dating
Abstract
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.
Keywords
U-Pb dating; Ollo de Sapo; Pre-Variscan; Central Iberian Zone; Gneiss.
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PDFDOI: https://doi.org/10.1344/105.000000353
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Facultat de Ciències de la Terra Geociències Barcelona Institut de Diagnosi Ambiental Universitat Autònoma de Barcelona
Universitat de Barcelona i Estudis de l'Aigua (CSIC)
Geologica Acta (ISSN-1695-6133)
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Phone: +34 93 403 19 89 | E-mail: geologica-acta@ictja.csic.es