Component geochronology in the polyphase ca. 3920Ma Acasta Gneiss

S. Mojzsis, Nicole L. Cates, Guillaume Caro, Dustin Trail, Oleg Abramov, Martin Guitreau, Janne Blichert-Toft, Michelle D. Hopkins, Wouter Bleeker

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43 Citations (Scopus)

Abstract

The oldest compiled U-Pb zircon ages for the Acasta Gneiss Complex in the Northwest Territories of Canada span about 4050-3850Ma; yet older ca. 4200Ma xenocrystic U-Pb zircon ages have also been reported for this terrane. The AGC expresses at least 25km2 of outcrop exposure, but only a small subset of this has been documented in the detail required to investigate a complex history and resolve disputes over emplacement ages. To better understand this history, we combined new ion microprobe 235,238U-207,206Pb zircon geochronology with whole-rock and zircon rare earth element compositions ([REE]zirc), Ti-in-zircon thermometry (Tixln) and 147Sm-143Nd geochronology for an individual subdivided ~60cm2 slab of Acasta banded gneiss comprising five separate lithologic components. Results were compared to other variably deformed granitoid-gneisses and plagioclase-hornblende rocks from elsewhere in the AGC. We show that different gneissic components carry distinct [Th/U]zirc vs. Tixln and [REE]zirc signatures correlative with different zircon U-Pb age populations and WR compositions, but not with 147Sm-143Nd isotope systematics. Modeled DWRzircon [REE] from lattice-strain theory reconciles only the ca. 3920Ma zircons with the oldest component that also preserves strong positive Eu* anomalies. Magmas which gave rise to the somewhat older (inherited) ca. 4020Ma AGC zircon age population formed at ~IW (iron-wüstite) to

Original languageEnglish
Pages (from-to)68-96
Number of pages29
JournalGeochimica et Cosmochimica Acta
Volume133
DOIs
Publication statusPublished - May 15 2014

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Geochronology
geochronology
gneiss
zircon
Rare earth elements
rare earth element
Chemical analysis
Rocks
ion microprobe
history
granitoid
hornblende
Isotopes
rock
terrane
plagioclase
slab
emplacement
outcrop
Iron

ASJC Scopus subject areas

  • Geochemistry and Petrology

Cite this

Mojzsis, S., Cates, N. L., Caro, G., Trail, D., Abramov, O., Guitreau, M., ... Bleeker, W. (2014). Component geochronology in the polyphase ca. 3920Ma Acasta Gneiss. Geochimica et Cosmochimica Acta, 133, 68-96. https://doi.org/10.1016/j.gca.2014.02.019

Component geochronology in the polyphase ca. 3920Ma Acasta Gneiss. / Mojzsis, S.; Cates, Nicole L.; Caro, Guillaume; Trail, Dustin; Abramov, Oleg; Guitreau, Martin; Blichert-Toft, Janne; Hopkins, Michelle D.; Bleeker, Wouter.

In: Geochimica et Cosmochimica Acta, Vol. 133, 15.05.2014, p. 68-96.

Research output: Contribution to journalArticle

Mojzsis, S, Cates, NL, Caro, G, Trail, D, Abramov, O, Guitreau, M, Blichert-Toft, J, Hopkins, MD & Bleeker, W 2014, 'Component geochronology in the polyphase ca. 3920Ma Acasta Gneiss', Geochimica et Cosmochimica Acta, vol. 133, pp. 68-96. https://doi.org/10.1016/j.gca.2014.02.019
Mojzsis, S. ; Cates, Nicole L. ; Caro, Guillaume ; Trail, Dustin ; Abramov, Oleg ; Guitreau, Martin ; Blichert-Toft, Janne ; Hopkins, Michelle D. ; Bleeker, Wouter. / Component geochronology in the polyphase ca. 3920Ma Acasta Gneiss. In: Geochimica et Cosmochimica Acta. 2014 ; Vol. 133. pp. 68-96.
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