International Journal of Earth Sciences

, Volume 91, Issue 6, pp 964–978

Zircon U–Pb geochronology of Ordovician magmatism in the polycyclic Ruitor Massif (Internal W Alps)

Authors

  • François Guillot
    • UMR Processus et Bilans des Domaines Sédimentaires, Univ. Sci. Tech. Lille bâtiment SN5
  • Urs Schaltegger
    • Department of Earth SciencesFederal Institute of Technology ETH
  • Jean Bertrand
    • Laboratoire de Géodynamique des Chaînes Alpines, Université de Savoie
  • Étienne Deloule
    • Centre de Recherches Pétrographiques et Géochimiques, BP 20
  • Thierry Baudin
    • Bureau de Recherches Géologiques et Minières
Original Paper

DOI: 10.1007/s00531-002-0280-0

Cite this article as:
Guillot, F., Schaltegger, U., Bertrand, J. et al. Int J Earth Sci (Geol Rundsch) (2002) 91: 964. doi:10.1007/s00531-002-0280-0

Abstract.

Among the Middle Penninic basements of the Internal NW-Alps, the Ruitor massif shows the best preserved remnants of pre-Permian metamorphic rocks. Their Barrovian-type mineral associations are somewhat masked by the greenschist to blueschist Alpine metamorphism of Tertiary age. Four Ruitor gneisses have been analysed, showing geochemical characters of granitoids from orogenic zones. Zircon morphology also suggests magmatic protoliths and a crustal source; some of the morphological zircon types suggest anatectic granites. The first U–Pb ages on zircon for this massif have been obtained concurrently through conventional multigrain and ion microprobe dating. Two metavolcanic rocks at 471±5 and 468±22 Ma could be slightly older than the porphyritic augen gneisses at 465±11 and 460±7 Ma. Regional data from the other Internal basement massifs suggest that the Variscan event is poorly recorded, except in Ruitor-type units. Ruitor and Sapey gneisses belonged to the same unit (Nappe des Pontis), which was affected by a 480–450-Ma event including volcanism and anatexis and ended with a late calc-alkaline granite emplacement at 460–450 Ma. The distribution of Variscan basement units roughly parallels Alpine zonation.

Internal Alps Polycyclic metagranite U–Pb geochronology Variscan Zircon morphology
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Copyright information

© Springer-Verlag 2002