Publication:
Deeply subducted continental fragments – Part 2: Insight from petrochronology in the central Sesia Zone (western Italian Alps)

cris.virtual.author-orcid0000-0001-8303-0771
cris.virtual.author-orcid0000-0002-9492-1497
cris.virtual.author-orcid0000-0003-0697-2719
cris.virtualsource.author-orcidcd81c621-e986-443c-8777-bd1d216c38ce
cris.virtualsource.author-orcid7e421314-0d5f-49d7-8385-bfe4b093cd38
cris.virtualsource.author-orcid017585d2-2329-41da-8c43-7a2662444659
cris.virtualsource.author-orcid9b40e94d-7769-41f2-90ef-b431465b0840
cris.virtualsource.author-orcid2ebc4067-4063-476c-b041-d99d8a5030ae
datacite.rightsopen.access
dc.contributor.authorGiuntoli, Francesco
dc.contributor.authorLanari, Pierre
dc.contributor.authorBurn, Marco
dc.contributor.authorKunz, Barbara Eva
dc.contributor.authorEngi, Martin
dc.date.accessioned2024-10-08T15:42:41Z
dc.date.available2024-10-08T15:42:41Z
dc.date.issued2018
dc.description.abstractSubducted continental terranes commonly comprise an assembly of subunits that reflect the different tectono-metamorphic histories they experienced in the subduction zone. Our challenge is to unravel how, when, and in which part of the subduction zone these subunits were juxtaposed. Petrochronology offers powerful tools to decipher pressure–temperature–time (P–T–t) histories of metamorphic rocks that preserve a record of several stages of transformation. A major issue is that the driving forces for re-equilibration at high pressure are not well understood. For example, continental granulite terrains subducted to mantle depths frequently show only partial and localized eclogitization. The Sesia Zone (NW Italy) is exceptional because it comprises several continental subunits in which eclogitic rocks predominate and high-pressure (HP) assemblages almost completely replaced the Permian granulite protoliths. This field-based study comprises both main complexes of the Sesia terrane, covering some of the recently recognized tectonic subunits involved in its assembly; hence our data constrain the HP tectonics that formed the Sesia Zone. We used a petrochronological approach consisting of petrographic and microstructural analysis linked with thermodynamic modelling and U–Th–Pb age dating to reconstruct the P–T–t trajectories of these tectonic subunits. Our study documents when and under what conditions re-equilibration took place. Results constrain the main stages of mineral growth and deformation, associated with fluid influx that occurred in the subduction channel. In the Internal Complex (IC), pulses of fluid percolated at eclogite facies conditions between 77 and 55Ma with the HP conditions reaching  ∼ 2GPa and 600–670°C. By contrast, the External Complex (EC) records a lower pressure peak of  ∼ 0.8GPa for 500°C at  ∼ 63Ma. The juxtaposition of the two complexes occurred during exhumation, probably at  ∼ 0.8GPa and 350°C; the timing is constrained between 46 and 38Ma. Mean vertical exhumation velocities are constrained between 0.9 and 5.1mmyear−1 for the IC, up to its juxtaposition with the EC. Exhumation to the surface occurred before 32Ma, as constrained by the overlying Biella Volcanic Suite, at a mean vertical velocity between 1.6 and 4mmyear−1. These findings constrain the processes responsible for the assembly and exhumation of HP continental subunits, thus adding to our understanding of how continental terranes behave during subduction.
dc.description.numberOfPages32
dc.description.sponsorshipInstitut für Geologie
dc.identifier.doi10.7892/boris.129160
dc.identifier.publisherDOI10.5194/se-9-191-2018
dc.identifier.urihttps://boris-portal.unibe.ch/handle/20.500.12422/65738
dc.language.isoen
dc.publisherCopernicus Publications
dc.relation.ispartofSolid Earth
dc.relation.issn1869-9510
dc.relation.organizationDCD5A442C18FE17DE0405C82790C4DE2
dc.relation.organizationDCD5A442C02AE17DE0405C82790C4DE2
dc.subject.ddc500 - Science::550 - Earth sciences & geology
dc.titleDeeply subducted continental fragments – Part 2: Insight from petrochronology in the central Sesia Zone (western Italian Alps)
dc.typearticle
dspace.entity.typePublication
dspace.file.typetext
oaire.citation.endPage222
oaire.citation.issue1
oaire.citation.startPage191
oaire.citation.volume9
oairecerif.author.affiliationInstitut für Geologie
oairecerif.author.affiliationInstitut für Geologie
oairecerif.author.affiliationInstitut für Geologie
oairecerif.author.affiliationInstitut für Geologie
oairecerif.author.affiliationInstitut für Geologie
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unibe.date.licenseChanged2019-10-24 04:46:23
unibe.description.ispublishedpub
unibe.eprints.legacyId129160
unibe.refereedtrue
unibe.subtype.articlejournal

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