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Origins of high δ 18 O in 3.7-3.6 Ga crust: A zircon and garnet record in Isua clastic metasedimentary rocks

Gauthiez Putallaz, Laure; Nutman, Allen P.; Bennett, Vickie; Rubatto, Daniela

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Elevated δ18O is used as a marker for the presence of continents and surficial alteration in the Eoarchean and Hadean. This study establishes a timeline for δ18O enrichment in Eoarchean metasedimentary rocks of the Isua supracrustal belt in Greenland. The source-rocks for the protolith of these metasedimentary rocks are mafic to intermediate magmatic rocks of ≥3709 ± 4 Ma, based on the age of zircons found in volcanogenic layers. The δ18O of +5.4 ± 0.4‰ of the zircon crystals indicate that the...[Show more]

dc.contributor.authorGauthiez Putallaz, Laure
dc.contributor.authorNutman, Allen P.
dc.contributor.authorBennett, Vickie
dc.contributor.authorRubatto, Daniela
dc.date.accessioned2020-12-21T22:31:22Z
dc.identifier.issn0009-2541
dc.identifier.urihttp://hdl.handle.net/1885/218988
dc.description.abstractElevated δ18O is used as a marker for the presence of continents and surficial alteration in the Eoarchean and Hadean. This study establishes a timeline for δ18O enrichment in Eoarchean metasedimentary rocks of the Isua supracrustal belt in Greenland. The source-rocks for the protolith of these metasedimentary rocks are mafic to intermediate magmatic rocks of ≥3709 ± 4 Ma, based on the age of zircons found in volcanogenic layers. The δ18O of +5.4 ± 0.4‰ of the zircon crystals indicate that the sources had a primary mantle-derived signature. However, garnet in two metasediments yields higher δ18O values of +8.7 to +9.7‰, in equilibrium with a whole-rock of +11 to +12‰ at 500-600 °C. This requires that the mafic protolith was weathered at surficial conditions, in agreement with previous conclusions based on major element geochemistry. The garnet grains with high δ18O record four growth zones, assigned to I) arc-building thermal metamorphism, II-III) terrane assembly at medium to high-pressure conditions, estimated to occur at 3660-3690 Ma and IV) late-Archaean overprint likely at ca. 2690 Ma. This shows that material with originally mantle-like δ18O was altered at low temperature (near-surface) to generate elevated oxygen isotope signatures and then recycled to middle-crustal conditions within 10-50 million years of crystallization in the Eoarchean. We propose that melting of such rocks could produce the zircon crystals with high δ18O that are found in the detrital and magmatic record in the Archean.
dc.description.sponsorshipThis work was funded by Australian Research Council projects DP120100273 and DP170100715. DR acknowledges the support of ARC grant DP110101599 and Swiss National Science Foundation grant 200021-166280.
dc.format.mimetypeapplication/pdf
dc.language.isoen_AU
dc.publisherElsevier
dc.rights© 2020 Elsevier B.V
dc.sourceChemical Geology
dc.source.urihttps://dx.doi.org/
dc.subjectEoarchean
dc.subjectWeathering
dc.subjectOxygen Isotopes
dc.subjectSHRIMP
dc.subjectIsua
dc.subjectMetasediments
dc.titleOrigins of high δ 18 O in 3.7-3.6 Ga crust: A zircon and garnet record in Isua clastic metasedimentary rocks
dc.typeJournal article
local.description.notesImported from ARIES
local.identifier.citationvolume537
dc.date.issued2020
local.identifier.absfor040203 - Isotope Geochemistry
local.identifier.ariespublicationu6269649xPUB486
local.publisher.urlhttps://www.sciencedirect.com/
local.type.statusPublished Version
local.contributor.affiliationGauthiez-Putallaz, Laure, College of Science, ANU
local.contributor.affiliationNutman, Allen P., University of Wollongong
local.contributor.affiliationBennett, Vickie, College of Science, ANU
local.contributor.affiliationRubatto, Daniela, College of Science, ANU
local.description.embargo2099-12-31
dc.relationhttp://purl.org/au-research/grants/arc/DP120100273
dc.relationhttp://purl.org/au-research/grants/arc/DP170100715
dc.relationhttp://purl.org/au-research/grants/arc/DP110101599
local.bibliographicCitation.issue0009-2541
local.bibliographicCitation.startpage1
local.bibliographicCitation.lastpage14
local.identifier.doi10.1016/j.chemgeo.2020.119474
local.identifier.absseo970104 - Expanding Knowledge in the Earth Sciences
dc.date.updated2020-09-06T08:20:31Z
local.identifier.scopusID2-s2.0-85078883067
CollectionsANU Research Publications

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