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Scientific article
English

Post-granulite facies monazite growth and rejuvenation during Permian to Lower Jurassic thermal and fluid events in the Ivrea Zone (Southern Alps)

Contributors

Vavra, Gerhard; Schaltegger, Urs

Published in

Contributions to mineralogy and petrology, vol. 134, no. 4, p. 405-414

Publication date

1999

Abstract

U-Pb analyses of single monazite grains from two granulite facies metapelites in the Ivrea Zone (Southern Alps) reveal the presence, in both samples, of at least three different ages and prove that earlier interpretations of supposedly concordant monazite data as cooling ages are unwarranted. One group of monazite data defines a subconcordant discordia line with an upper intercept age of 293.4 ± 5.8 Ma and a lower intercept age of 210 ± 14 Ma. The upper intercept is interpreted as the real cooling age of the monazites. The lower intercept is interpreted as an episode of fluid-driven Pb-loss, indicated by the presence of internal and external corrosion structures not only of the monazites but also of the zircons in the same samples that are also rejuvenated at 210 ± 12 Ma. Another group of monazite data lies above the concordia. The presence of excess 206Pb indicates that these crystals have grown below the monazite blocking temperature, thus after the granulite facies metamorphism. The age of growth of the new monazite crystals is approached by their 207Pb/235U ages that range between 273 and 244 Ma. The two groups of post-cooling age (post-293.4 ± 5.8 Ma) monazite data correspond to two distinct late- and post-Variscan geotectonic regimes that affected the Southern Alps, (1) Permian transtension with decompression and anatectic melting; (2) Upper Triassic to Lower Jurassic rifting with geographically dispersed hydrothermal activity and alkaline magmatism.

Keywords

  • Ivrea Zone
  • Variscan
  • Monazite
  • U-Pb Triassic

UNIGE affiliation entities

UNIGE research groups

Citation (ISO format)

VAVRA, Gerhard, SCHALTEGGER, Urs. Post-granulite facies monazite growth and rejuvenation during Permian to Lower Jurassic thermal and fluid events in the Ivrea Zone (Southern Alps). In: Contributions to mineralogy and petrology, 1999, vol. 134, n° 4, p. 405–414. doi: 10.1007/s004100050493

Main files (1)

Article (Published version)

Identifiers

Additional URL for this publication

http://link.springer.com/10.1007/s004100050493

Journal ISSN

0010-7999
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Technical informations

Creation

10/06/2013 16:00:00

First validation

10/06/2013 16:00:00

Update

14/03/2023 20:18:39

Status update

14/03/2023 20:18:39

Last indexation

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