@article{76,
  keywords = {Eclogite facies dating, French Massif Central, Lu-Hf and Sm-Nd garnet dating, P-T modeling, Petrochronology, Trace Elements, U-Pb zircon and apatite geochronology, Variscan belt},
  author = {Caroline Lotout and Pavel Pitra and Marc Poujol and Robert Anczkiewicz and Jean Van Den Driessche},
  title = {Timing and duration of Variscan high-pressure metamorphism in the French Massif Central: A multimethod geochronological study from the Najac Massif},
  abstract = {Accurate dating of eclogite-facies metamorphism is of paramount importance in order to understand the tectonic evolution of an orogen. An eclogite sample from the Najac Massif (French Massif Central, Variscan belt) displays a zircon-bearing garnet-omphacite-amphibole-rutile-quartz peak assemblage. Pseudosection modeling suggests peak pressure conditions of 15{\textendash}20 kbar, 560{\textendash}630 {\textdegree}C. Eclogite-facies garnet displays Lu-enriched cores and Sm-rich rims and yields a Lu-Hf age of 382.8 {\textpm} 1.0 Ma and a Sm-Nd age of 376.7 {\textpm} 3.3 Ma. The ages are interpreted as marking the beginning of the prograde garnet growth during the initial stages of the eclogite-facies metamorphism, and the high-pressure (and temperature) peak reached by the rock, respectively. Zircon grains display chondrite-normalized REE spectra with variably negative, positive or no Eu anomalies and are characterized by either enriched or flat HREE patterns. However, they yield a well constrained in situ LA-ICP-MS U-Pb age of 385.5 {\textpm} 2.3 Ma, despite this REE pattern variability. Zr zonation in garnet, Y content in zircon and the diversity of zircon HREE spectra may suggest that zircon crystallized prior to and during incipient garnet growth on the prograde P-T path, recording the initial stages of the eclogite-facies conditions. Consequently, the zircon age of 385.5 {\textpm} 2.3 Ma, comparable within error with the Lu-Hf age obtained on garnet, is interpreted as dating the beginning of the eclogite-facies metamorphism. Accordingly, the duration of the prograde part of the eclogite-facies event is estimated at 6.1 {\textpm} 4.3 Myr. Subsequent exhumation is constrained by an apatite U-Pb age at 369 {\textpm} 13 Ma.},
  year = {2018},
  booktitle = {Lithos},
  journal = {Lithos},
  series = {Lithos},
  volume = {308-309},
  pages = {381-394},
  issn = {0024-4937},
  url = {http://www.sciencedirect.com/science/article/pii/S0024493718301178},
  doi = {https://doi.org/10.1016/j.lithos.2018.03.022},
}