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TitreAge, origin and thermal evolution of the ultra-fresh 1.9 Ga Winnipegosis komatiites, Manitoba, Canada
AuteurWaterton, P; Pearson, D G; Kjarsgaard, B A; Hulburt, L; Locock, A; Parman, S; Davis, B
SourceLithos vol. 268-271, 2017 p. 114-130,
Séries alt.Secteur des sciences de la Terre, Contribution externe 20160281
Documentpublication en série
Mediapapier; en ligne; numérique
Lat/Long OENS-101.1667 -97.0000 55.1667 52.0000
Sujetsdatations au zircon; datation au uranium-plomb; pétrographie; Ceinture de Circum-superior ; Orogenèse de Trans-hudson ; Protérozoïque
Illustrationslocation maps; photomicrographs; graphs; diagrams; geological sketch maps
ProgrammeCoordination de IGC-4, Initiative géoscientifique ciblée (IGC-4)
Résumé(disponible en anglais seulement)
The Proterozoic spans the longest portion of earth's history, yet in contrast to the Archaean, the record of komatiites and related high MgO igneous rocks from this Eon is sparse. This paper describes the pristine Palaeoproterozoic Winnipegosis Komatiites, from Manitoba, Canada, which form part of the Circum-Superior Belt large igneous province. We present a comprehensive petrographical investigation, mineral and bulk rock geochemistry, and Al-in-olivine thermometry for the Winnipegosis Komatiites, along with new U-Pb SHRIMP
dating of zircons from a mafic unit, which yield an age of 1870.3 ± 7.1 Ma for the Winnipegosis Komatiite Belt. The komatiites are Al-undepleted and dominated by massive olivine porphyritic flows with a median thickness of 6 m. Differentiated flows containing layers of olivine spinifex are present, but rare. Trace element data indicate the komatiites were derived fromdepleted mantle, and subsequently contaminated with 2-% continental crust. Temperatures from Al-in-olivine thermometry are consistent with a nominally dry melt, and combined with olivine-melt Mg-Fe partitioning, suggest a parental melt with ~24 wt% MgO and a liquidus (olivine) temperature of ~1501 °C, approximately 100 °C cooler than their hottest Archaean counterparts. At ~1424 °C chromite joined olivine as a crystallising phase. Olivine and chromite phenocrysts were re-mixed with residual melt shortly before or during komatiite eruption, which occurred by the time the magma had cooled to ~1321 °C. Combined geochemical and geological evidence requires that the Winnipegosis Komatiites erupted
onto rifting continental crust. Their high liquidus temperatures require anomalously hot mantle. Considering the Winnipegosis Komatiites in the context of the broader Circum-Superior Belt, we suggest that these magmas formed from a mantle plume that was deflected towards the margins of the Superior craton by strong gradients in lithospheric thickness. This interpretation of the mode of formation of the Circum-Superior Belt casts doubt on ambient mantle potential temperatures as high as 1600 °C during the Proterozoic.
Résumé(Résumé en langage clair et simple, non publié)
Détermination de l'évolution et de la source du magma de la region Winnipegosis.