Preprints
https://doi.org/10.5194/se-2020-53
https://doi.org/10.5194/se-2020-53

  14 May 2020

14 May 2020

Review status: this preprint was under review for the journal SE but the revision was not accepted.

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

Pedro Castiñeiras1, Juan Gómez Barreiro2, Francisco J. Fernández3, Carmen Aguilar4, and José Manuel Benítez Pérez5 Pedro Castiñeiras et al.
  • 1Departamento de Petrología y Geoquímica, Universidad Complutense de Madrid, José Antonio Novais 12, 28040 Madrid, Spain
  • 2Departamento de Geología, Universidad de Salamanca, Facultad de Ciencias, Pza. de los Caidos s/n, 37008 Salamanca, Spain
  • 3Departamento de Geología, Universidad de Oviedo, Jesús Arias de Velasco s/n, 33005 Oviedo, Spain
  • 4Centre for Lithospheric Research, Czech Geological Survey, Klárov 3, 11821 Prague, Czech Republic
  • 5Centro 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.

Pedro Castiñeiras et al.

 
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Status: closed
Status: closed
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Pedro Castiñeiras et al.

Pedro Castiñeiras et al.

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