Centre for Lithospheric Research, Czech Geological Survey, Klárov 3, 11821 Prague, Czech Republic
José Manuel Benítez Pérez
Centro de Ciências e Tecnologias Nucleares, Instituto Superior Técnico, Universidad de Lisboa, Estrada Nacional 10 (km 139,7), 2695-066, Bobadela LRS, Portugal
Abstract. Zircon crystal texture and Th / U ratio have been used as a watertight argument when interpreting U-Pb ages. The wide, and sometimes indiscriminate, use of those gauges could result into misinterpretation of the geological meaning of U-Pb data. A case study is presented here where zircons from a controversial polymetamorphic eclogite unit were analyzed with SHRIMP. Both U-Pb and trace element (TE) data were collected for each point. The combination of TE and structural arguments indicates that zircon was part of the eclogite facies mineral assemblage at 390 Ma. However, using Th / U ratio and CL textures lead to a different interpretation. Our results suggest that in complex orogenic scenarios and extreme environments well-known techniques (CL) and geochemical relationships (Th / U) must be used in combination with TE data and structural relationships as provenance/process gauges. While geochronology provides accurate isotope relationships, their temporal dimension must rely on structural and petrological evidence.
How to cite. Castiñeiras, P., Gómez Barreiro, J., Fernández, F. J., Aguilar, C., and Benítez Pérez, J. M.: Resolving uncertainties in the application of zircon Th / U and CL gauges to interpret U-Pb ages: a case study of eclogites in polymetamorphic terranes of NW Iberia, Solid Earth Discuss. [preprint], https://doi.org/10.5194/se-2020-53, 2020.
Received: 12 Apr 2020 – Discussion started: 14 May 2020