Interaction of deformation and metamorphism during subduction and exhumation of hydrated oceanic mantle: Insights from the Western Alps (Articolo in rivista)

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  • Interaction of deformation and metamorphism during subduction and exhumation of hydrated oceanic mantle: Insights from the Western Alps (Articolo in rivista) (literal)
Anno
  • 2012-01-01T00:00:00+01:00 (literal)
Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#doi
  • 10.1111/j.1525-1314.2012.00990.x (literal)
Alternative label
  • REBAY G., SPALLA M.I., ZANONI D. (2012)
    Interaction of deformation and metamorphism during subduction and exhumation of hydrated oceanic mantle: Insights from the Western Alps
    in Journal of metamorphic geology
    (literal)
Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#autori
  • REBAY G., SPALLA M.I., ZANONI D. (literal)
Pagina inizio
  • 687 (literal)
Pagina fine
  • 702 (literal)
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  • http://onlinelibrary.wiley.com/doi/10.1111/j.1525-1314.2012.00990.x/full (literal)
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  • 30 (literal)
Rivista
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  • 16 (literal)
Note
  • Scopus (literal)
  • ISI Web of Science (WOS) (literal)
  • Google Scholar (literal)
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  • Dipartimento di Scienze della Terra e dell'Ambiente, Università degli Studi di Pavia, Via Ferrata, 1-27100 Pavia, Italy (gisella.rebay@unipv.it) Dipartimento di Scienze della Terra, Università degli Studi di Milano and CNR-IDPA, Via Mangiagalli, 34 - 20133 Milano, Italy (literal)
Titolo
  • Interaction of deformation and metamorphism during subduction and exhumation of hydrated oceanic mantle: Insights from the Western Alps (literal)
Abstract
  • Petrological investigations supported by multi-scale structural analysis of eclogitized serpentinite in the Zermatt-Saas Zone of the Western Alps allows for the determination of mineral assemblages related to successive fabrics, upon which the P-T-d-t path of these hydrated mantle rocks can be inferred. Serpentinites of the upper Valtournanche, with lenses and dykes of metagabbro and meta-rodingite, display an Alpine polyphase metamorphic evolution from eclogite to epidote-amphibolite facies conditions associated with three successive foliations having different parageneses in these rocks. Serpentinite mainly consists of serpentine with minor magnetite; however, where S1 and S2 foliations are pervasive, metamorphic olivine, together with Ti-clinohumite and clinopyroxene, are also found. The mineral assemblage associated with D1 includes serpentine1, clinopyroxene1, opaque minerals, titanite ± olivine1, Ti-clinohumite1 and ilmenite; the D2 assemblage is the same (±chlorite) but minerals have different compositions. The assemblage associated with D3 comprises serpentine3, opaque minerals, ±chlorite3, ilmenite and amphibole3. Ti-clinohumite is associated with veins that are older than D2 and pre-date D3. Veins that post-date D3 are characterized by amphibole + chlorite or by serpentine. P-T conditions for S2 parageneses evaluated using two pseudosections for different bulk compositions suggest that these rocks experienced pressures >2.5 ± 0.3 GPa at temperatures slightly higher than 600 °C. The late epidote-amphibolite facies re-equilibration associated with D3 and D4 developed during late syn-exhumation deformation related to folding and testifies to a small temperature decrease. These results, which were integrated in the regional framework, suggest that different portions of the Zermatt-Saas Zone registered different P-T peak conditions and underwent different exhumation paths. In addition, the inferred P-T-d-t path suggests that the Valtournanche serpentinites re-equilibrated close to the UHP conditions registered by the Cignana meta-cherts. These results imply that tectonic slices exhumed after UHP metamorphism might be wider than previously reported or that small-size UHP units, tectonically sampled during the Alpine convergence, are more abundant than those that have been detected to date. (literal)
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