@article{184,
  author = {Pavel Pitra and Marc Poujol and Jean Van Den Driessche and Eloise Bretagne and Caroline Lotout and Nathan Cogn{\'e}},
  title = {Late Variscan (315 Ma) subduction or deceptive zircon REE patterns and U{\textendash}Pb dates from migmatite-hosted eclogites?(Montagne Noire, France)},
  abstract = {Eclogites hosted in sillimanite-bearing migmatites in the Montagne Noire dome (French Massif Central) have an oceanic protolith and recorded a prograde P{\textendash}T path from ~19.5 kbar, 700{\textdegree}C to the pressure peak at ~21 kbar, 750{\textdegree}C (pseudosection modelling), suggesting metamorphism in a subduction setting. Subsequent exhumation to low-P high-T (LP{\textendash}HT) conditions (~6 kbar, 730{\textdegree}C) is constrained by the equilibration conditions of the embedding migmatite. In samples of a fresh and a retrogressed eclogite, all zircon crystals but one display similar REE patterns (no Eu anomaly, flat HREE), usually ascribed to crystallization under eclogite-facies conditions. Yet, the U{\textendash}Pb apparent ages of zircon crystals from both eclogites spread from c. 360 Ma to a dominant data cluster at c. 315 Ma. The c. 315{\textendash}310 Ma zircon U{\textendash}Pb dates obtained from the embedding migmatite are interpreted as the age of crystallization of the partial melt during the LP{\textendash}HT metamorphic stage. First-order geological evidence, in particular the sedimentary record, excludes the existence of a subduction zone in the region at this period. Unless calling upon a major reappraisal of the tectonics of the European Variscan orogen, this suggests an ambiguous relation between REE patterns and U{\textendash}Pb dates in the zircon population. Various scenarios that could account for the observations are discussed. Combining our data with the results of a previously published Sm{\textendash}Nd dating of garnet, and regional considerations, we consider that 360 Ma is the best approximation of the minimum age of the eclogite-facies event. We hypothesize that the eclogites formed farther north and were transferred to their present location by lower-crustal flow. It is inferred that during the subsequent exhumation, eclogite-facies zircon grains recrystallized and underwent partial to total resetting of their U{\textendash}Pb system, whereas the REE system remained mostly unmodified. These results caution against the use of REE patterns as the only criterion to associate a specific zircon age with HP metamorphism in eclogites occurring in migmatitic domes.},
  year = {2021},
  booktitle = {Journal of Metamorphic Geology},
  journal = {Journal of Metamorphic Geology},
  series = {Journal of Metamorphic Geology},
  institution = {Wiley Online Library},
  organization = {Wiley Online Library},
  publisher = {Wiley Online Library},
  school = {Wiley Online Library},
  doi = { https://doi.org/10.1111/jmg.12609},
}