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Sm‐Nd isotopic evidence on the age of eclogitization in the Zermatt‐Saas ophiolite

Sm‐Nd isotopic evidence on the age of eclogitization in the Zermatt‐Saas ophiolite ABSTRACT Rocks within the Zermatt‐Saas ophiolite of the western Alps have undergone eclogite facies metamorphism during subduction prior to the Alpine collision. The metamorphic history of these rocks is well defined, with eclogitic assemblages being followed by the limited growth of blueschist assemblages of glaucophane and paragonite. Subsequent greenschist alteration occurs adjacent to faults, veins and metasediments. Away from such sources of water, retrogression is very limited. Sm‐Nd isotopic analyses of an essentially unretrogressed eclogitic metabasalt suggest that eclogite facies metamorphism occurred at 52 ± 18 Ma. The large uncertainty is due to the presence of very small amounts of Nd‐rich epidote present as inclusions within garnet. As the closure temperature of garnet to Sm & Nd is thought to be >600d̀C, resetting due to post‐high‐pressure diffusion is thought to be insignificant. Given the fine‐grained protolith to the sample analysed, and its extensive deformation under eclogite facies conditions, incomplete homogenization of pre‐metamorphic isotopic variations is also considered unlikely to be responsible for the young age. A Tertiary age of eclogitization means that models of early Alpine evolution based on the cessation of high‐pressure metamorphism in the Cretaceous need to be revised. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Metamorphic Geology Wiley

Sm‐Nd isotopic evidence on the age of eclogitization in the Zermatt‐Saas ophiolite

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References (43)

Publisher
Wiley
Copyright
Copyright © 1994 Wiley Subscription Services, Inc., A Wiley Company
ISSN
0263-4929
eISSN
1525-1314
DOI
10.1111/j.1525-1314.1994.tb00013.x
Publisher site
See Article on Publisher Site

Abstract

ABSTRACT Rocks within the Zermatt‐Saas ophiolite of the western Alps have undergone eclogite facies metamorphism during subduction prior to the Alpine collision. The metamorphic history of these rocks is well defined, with eclogitic assemblages being followed by the limited growth of blueschist assemblages of glaucophane and paragonite. Subsequent greenschist alteration occurs adjacent to faults, veins and metasediments. Away from such sources of water, retrogression is very limited. Sm‐Nd isotopic analyses of an essentially unretrogressed eclogitic metabasalt suggest that eclogite facies metamorphism occurred at 52 ± 18 Ma. The large uncertainty is due to the presence of very small amounts of Nd‐rich epidote present as inclusions within garnet. As the closure temperature of garnet to Sm & Nd is thought to be >600d̀C, resetting due to post‐high‐pressure diffusion is thought to be insignificant. Given the fine‐grained protolith to the sample analysed, and its extensive deformation under eclogite facies conditions, incomplete homogenization of pre‐metamorphic isotopic variations is also considered unlikely to be responsible for the young age. A Tertiary age of eclogitization means that models of early Alpine evolution based on the cessation of high‐pressure metamorphism in the Cretaceous need to be revised.

Journal

Journal of Metamorphic GeologyWiley

Published: Mar 1, 1994

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