Détail de la notice
Titre du Document
Blueschists, eclogites, and decompression assemblages of the Zermatt-saas ophiolite : High-pressure metamorphism of subducted Tethys lithosphere
Auteur(s)
BUCHER Kurt ; FAZIS Yvonne ; DE CAPITANI Christian ; ...
Résumé
The Zermatt-Saas ophiolite of the Swiss Alps represents a complete sequence of Mesozoic Tethys oceanic lithosphere. The ophiolite was subducted during early phases of the Alpine orogeny and the mafic rocks were transformed to eclogites and blueschists. Metabasalts locally preserve pillow structures in which glaucophanite forms rims on eclogitic pillow cores. Omphacite-garnet-glaucophane-epidote-ferroan dolomite-Mg-chloritoid-talc-paragonite-chlorite-rutile form characteristic coeval blueschist- and eclogite-facies assemblages. Omphacite + garnet + glaucophane + epidote + rutile represents an equilibrium assemblage that formed during deformation and in the period when the rocks reached the greatest depth of subduction. In rocks containing this assemblage, an additional significant mineral pair is Mg-chloritoid + talc. Coarse chloritoid (XMg ∼ 0.45) and talc formed in dispersed clusters after the last penetrative deformation. The assemblage may require > 2.7 GPa pressure to form. It developed at maximum pressure conditions corresponding to the return-point of the ophiolite in the subduction zone. Coarse paragonite and chlorite replaced parts of the earlier formed assemblages and removed free H2O from the rocks. Exhumation of the HP to UHP ophiolite rocks was accompanied by development of symplectite rims and other replacement products along grain boundaries of the eclogite minerals by decompression reactions in a fluid-deficient regime. Particularly notewor
Editeur
Mineralogical Society of America
Identifiant
ISSN : 0003-004X CODEN : AMMIAY
Source
The American mineralogist A. 2005, vol. 90, n° 5-6, pp. 821-835 [15 pages]
Langue
Anglais
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