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Contributions to Mineralogy and Petrology

, Volume 57, Issue 3, pp 297–303 | Cite as

K-Ar Radiometric Age Determinations of White Micas from the Piemont Zone, French-Italian Western Alps

  • Michel Delaloye
  • Jacqueline Desmons
Article

Abstract

K - Ar radiometric data are presented suggesting a different metamorphic history for both parts of the Piemont zone in the Western Alps: the Combin zone to the west, considered to have escaped the late Cretaceous metamorphic event, and the Zermatt-Saas zone to the east, where ophiolites predominate, and which has been affected by a first metamorphism during late Cretaceous.

Paragonite lenses within serpentinite give an isotopic ratio dating a serpentinization phase, or representing mixed ages. Late Cretaceous ages are found in the Zermatt-Saas zone and in the melange areas. The Combin zone gives only Eocene-Oligocene ages, as well as that part of the Zermatt-Saas zone that is closer to the Lepontine thermal high (dated as 38 m.y.). No late Oligocene-early Miocene ages (as previously obtained on Na-amphiboles) have been found among the investigated micas.

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Notes

Acknowledgments

The support of the “Fonds national suisse pour la recherche scientifique” is gratefully acknowledged. Thanks are due to Dr. J.C Hunziker for critical reading.

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Copyright information

© Springer-Verlag 1976

Authors and Affiliations

  • Michel Delaloye
    • 1
  • Jacqueline Desmons
    • 2
  1. 1.Département de Minéralogie de l’Université de GenèveGenève 4Switzerland
  2. 2.Institut DolomieuLaboratoire de Géologie AlpineGrenoble CedexFrance

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