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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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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Delaloye, M., Desmons, J. K-Ar Radiometric Age Determinations of White Micas from the Piemont Zone, French-Italian Western Alps. Contributions to Mineralogy and Petrology 57, 297–303 (1976). https://doi.org/10.1007/BF03542939
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DOI: https://doi.org/10.1007/BF03542939