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Preservation of Permian allanite within an Alpine eclogite facies shear zone at Mt Mucrone, Italy: Mechanical and chemical behavior of allanite during mylonitization

Cenki-Tok, B.; Oliot, E.; Rubatto, Daniela; Berger, A.; Engi, Martin; Janots, E.; Thomsen, T.B.; Manzotti, P.; Regis, Daniele; Spandler, Carl; Robyr, M.; Goncalves, P.; Berger, Alfons

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This study addresses the mechanical and chemical behavior of allanite during shear zone formation under high-pressure metamorphism. Understanding physico-chemical processes related to the retention or resetting of Pb isotopes in allanite during geological processes is essential for robust petrochronology.Dating of allanite in meta-granodiorite showing variable amounts of strain (from an undeformed protolith to mylonite) at Monte Mucrone (Sesia Zone, NW Italy) gave surprising results. Based on...[Show more]

dc.contributor.authorCenki-Tok, B.
dc.contributor.authorOliot, E.
dc.contributor.authorRubatto, Daniela
dc.contributor.authorBerger, A.
dc.contributor.authorEngi, Martin
dc.contributor.authorJanots, E.
dc.contributor.authorThomsen, T.B.
dc.contributor.authorManzotti, P.
dc.contributor.authorRegis, Daniele
dc.contributor.authorSpandler, Carl
dc.contributor.authorRobyr, M.
dc.contributor.authorGoncalves, P.
dc.contributor.authorBerger, Alfons
dc.date.accessioned2015-12-10T23:26:21Z
dc.identifier.issn0024-4937
dc.identifier.urihttp://hdl.handle.net/1885/67724
dc.description.abstractThis study addresses the mechanical and chemical behavior of allanite during shear zone formation under high-pressure metamorphism. Understanding physico-chemical processes related to the retention or resetting of Pb isotopes in allanite during geological processes is essential for robust petrochronology.Dating of allanite in meta-granodiorite showing variable amounts of strain (from an undeformed protolith to mylonite) at Monte Mucrone (Sesia Zone, NW Italy) gave surprising results. Based on structural and petrographic observations the shear zones at Mt Mucrone are Alpine, yet allanite located within an eclogite facies mylonite yielded Permian ages (208Pb/232Th average age: 287±7Ma). These mm-sized allanite grains are rimmed by an aggregate of coarse-grained garnet+phengite, thought to derive from former epidote. These aggregates were immersed in a weak matrix that experienced granular flow, and they were thus chemically and mechanically shielded during Alpine mylonitization. In undeformed samples (8a and 8b), two populations of epidote group minerals were found. Allanite forms either coronas around Permian monazite or individual grains with patchy zoning. Both types yield Permian ages (208Pb/232Th age: 291±5Ma). On the other hand, grains of REE-rich clinozoisite of Cretaceous age are found in undeformed rocks. These grains appear as small fragments with embayed surface outlines and minute satellites or rims around Permian allanite. These (re)crystallized grains are Sr-rich and show mosaic zoning.These results indicate that allanite crystals retained their chemical and isotopic characteristics, and thus their Permian age, as a result of strong strain partitioning between the epidote group porphyroclasts and the eclogite facies matrix in HP-mylonites. The observed partial mobilization of Pb isotopes, which lead to the Cretaceous-aged rims or grains in undeformed samples was facilitated by (re)crystallization of allanite and not by mere Pb diffusion alone under the HP conditions.
dc.publisherElsevier
dc.sourceLithos
dc.subjectKeywords: allanite; dating method; eclogite; facies; geochronology; high pressure; lead isotope; metamorphism; mylonitization; Permian; preservation; shear zone; uranium series dating; Italy; Sesia Allanite; Mt Mucrone; Sesia zone; Shear zone; U-Th-Pb ages; Western Alps
dc.titlePreservation of Permian allanite within an Alpine eclogite facies shear zone at Mt Mucrone, Italy: Mechanical and chemical behavior of allanite during mylonitization
dc.typeJournal article
local.description.notesImported from ARIES
local.identifier.citationvolume125
dc.date.issued2011
local.identifier.absfor040303 - Geochronology
local.identifier.absfor040312 - Structural Geology
local.identifier.ariespublicationf2965xPUB1509
local.type.statusPublished Version
local.contributor.affiliationCenki-Tok, B., University of Bern
local.contributor.affiliationOliot, E., Universite de Franche Comte
local.contributor.affiliationRubatto, Daniela, College of Physical and Mathematical Sciences, ANU
local.contributor.affiliationBerger, A., University of Copenhagen
local.contributor.affiliationEngi, Martin, University of Bern
local.contributor.affiliationJanots, E., Universite Joseph Fourier
local.contributor.affiliationThomsen, T.B., University of Bern
local.contributor.affiliationManzotti, P., University of Bern
local.contributor.affiliationRegis, Daniele, University of Bern
local.contributor.affiliationSpandler, Carl, James Cook University
local.contributor.affiliationRobyr, M., University of Bern
local.contributor.affiliationGoncalves, P., Universite de Franche Comte
local.contributor.affiliationBerger, Alfons, University of Bern
local.description.embargo2037-12-31
local.bibliographicCitation.startpage40
local.bibliographicCitation.lastpage50
local.identifier.doi10.1016/j.lithos.2011.01.005
local.identifier.absseo970104 - Expanding Knowledge in the Earth Sciences
dc.date.updated2016-02-24T08:14:41Z
local.identifier.scopusID2-s2.0-79958833140
local.identifier.thomsonID000292663600004
CollectionsANU Research Publications

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