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Dating of eclogite-facies zircons: the age of Alpine metamorphism in the Sesia-Lanzo Zone (Western Alps)

Rubatto, Daniela; Gervers, Michael; Compagnoni, Roberto

Description

Zircons from eclogite-facies rocks of the Sesia-Lanzo Zone have been investigated by cathodoluminescence and dated by ion microprobe (SHRIMP). Most of the zircons show a oscillatary or sector zoned core, which is surrounded by a weakly zoned or unzoned rim, irregular in shape. The U-Th-Pb analyses revealed that, opposite to the cores, the zircon rims have low U- and Th-contents, very low Th/U ratios and that their U-Pb systems were reset or they lost lead at the time of metamorphism. This study...[Show more]

dc.contributor.authorRubatto, Daniela
dc.contributor.authorGervers, Michael
dc.contributor.authorCompagnoni, Roberto
dc.date.accessioned2015-12-13T23:35:23Z
dc.identifier.issn0012-821X
dc.identifier.urihttp://hdl.handle.net/1885/93886
dc.description.abstractZircons from eclogite-facies rocks of the Sesia-Lanzo Zone have been investigated by cathodoluminescence and dated by ion microprobe (SHRIMP). Most of the zircons show a oscillatary or sector zoned core, which is surrounded by a weakly zoned or unzoned rim, irregular in shape. The U-Th-Pb analyses revealed that, opposite to the cores, the zircon rims have low U- and Th-contents, very low Th/U ratios and that their U-Pb systems were reset or they lost lead at the time of metamorphism. This study provides evidence that the zircon rims recrystallized and changed their internal zoning as well as their chemical and isotopic composition during high-pressure (15-18 kbar) moderate temperature (550-600°C) metamorphism. In the Sesia-Lanzo Zone, eclogite-facies zircons from three different localities and four different rock types were analysed. The age of metamorphic zircon rims was obtained from an eclogite from Monte Mucrone (65 ± 5 Ma), an eclogitic micaschist from the Aosta Valley (65 ± 3 Ma) and two mafic rocks from Cima di Bonze (68 ± 7 Ma). The ~65 Ma age is further supported by the ages of the youngest zircon rims in three other samples. These results constrain the age of eclogite-facies metamorphism in the Sesia-Lanzo Zone. An age of 76 ± 1 Ma determined on zircons from a hydrothermal vein is interpreted as dating the prograde formation of the vein at temperatures well below 550°C. The age results suggest a maximum rate of 0.7 cm/y for the subduction of the Sesia-Lanzo Zone to eclogite-facies conditions. The Cretaceous-Tertiary age for the eclogite-facies metamorphism in the Sesia-Lanzo Zone implies that this continental unit was not subducted together with either portions of the Adriatic margin or the neighbouring Mesozoic Tethys. We suggest that the Seisa-Lanzo Zone behaved as a separate continental block at the time of Alpine convergence.
dc.publisherElsevier
dc.sourceEarth and Planetary Science Letters
dc.subjectKeywords: Alpine orogeny; eclogite; geochronology; metamorphism; zircon; Switzerland Alpine Orogeny; Eclogite facies; Regional metamorphism; Sesia-Lanzo zone
dc.titleDating of eclogite-facies zircons: the age of Alpine metamorphism in the Sesia-Lanzo Zone (Western Alps)
dc.typeJournal article
local.description.notesImported from ARIES
local.description.refereedYes
local.identifier.citationvolume167
dc.date.issued1999
local.identifier.absfor040203 - Isotope Geochemistry
local.identifier.ariespublicationMigratedxPub25316
local.type.statusPublished Version
local.contributor.affiliationRubatto, Daniela, College of Physical and Mathematical Sciences, ANU
local.contributor.affiliationGervers, Michael, University of Toronto
local.contributor.affiliationCompagnoni, Roberto, University di Torino
local.description.embargo2037-12-31
local.bibliographicCitation.startpage141
local.bibliographicCitation.lastpage158
local.identifier.doi10.1016/S0012-821X(99)00031-X
dc.date.updated2015-12-12T09:39:44Z
local.identifier.scopusID2-s2.0-0033561610
CollectionsANU Research Publications

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