Reworking of Hadean crust in the Acasta gneisses, northwestern Canada: Evidence from in-situ Lu-Hf isotope analysis of zircon

Tsuyoshi Iizuka, Tsuyoshi Komiya, Simon P. Johnson, Yoshiaki Kon, Shigenori Maruyama, Takafumi Hirata

Research output: Contribution to journalArticle

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Abstract

The Acasta Gneiss Complex of northwestern Canada comprises early Archean orthogneisses and includes the oldest known terrestrial rocks (3.94-4.03 Ga). Previous zircon geochronological studies revealed the presence of zircon xenocrysts with ages up to 4.2 Ga in the oldest rocks, indicating that the source of early Archean granitoids contained Hadean (> 4.03 Ga) crust. In this study, we have determined the Lu-Hf isotopic compositions of zircon grains extracted from the early Archean Acasta gneisses to evaluate the extent of the Hadean crust contribution to the formation of these granitoids. Analyses of the Lu-Hf isotopes were carried out using in-situ laser ablation inductively coupled plasma mass spectrometry combined with cathodoluminescence images of the internal structure of the grains. Two ca. 3.59 Ga granitoids have εHf(T) of - 2.4 ± 2.2 and - 3.2 ± 2.5, suggesting that the source of the granitoids was extracted from the mantle as far back as 3.8 Ga. This is consistent with the presence of abundant zircon xenocrysts with ages up to 3.9 Ga. The Hf isotopic composition of a 3.72 Ga granitoid is significantly less radiogenic, with an εHf(T) of - 6.1 ± 2.5. This indicates that the granitoid formed by remelting of very old crust. The εHf(T) values for the two oldest rocks, the ca. 3.97 Ga tonalites, are - 1.2 ± 3.3 and - 3.3 ± 1.7, respectively, indicating that even the oldest known granitoids contain reworked older crustal materials. These results suggest that Hadean crust had significantly contributed to the genesis of some of the early Archean Acasta granitoids.

Original languageEnglish
Pages (from-to)230-239
Number of pages10
JournalChemical Geology
Volume259
Issue number3-4
DOIs
Publication statusPublished - Feb 25 2009
Externally publishedYes

Fingerprint

Hadean
reworking
Isotopes
Archean
zircon
isotope
crust
Rocks
granitoid
isotopic composition
rock
Inductively coupled plasma mass spectrometry
Remelting
Cathodoluminescence
cathodoluminescence
Laser ablation
Chemical analysis
ablation
gneiss
mass spectrometry

Keywords

  • Ancient zircon
  • Crustal evolution
  • Crustal reworking
  • Hadean
  • LA-MC-ICPMS
  • Lu-Hf isotope

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geology

Cite this

Reworking of Hadean crust in the Acasta gneisses, northwestern Canada : Evidence from in-situ Lu-Hf isotope analysis of zircon. / Iizuka, Tsuyoshi; Komiya, Tsuyoshi; Johnson, Simon P.; Kon, Yoshiaki; Maruyama, Shigenori; Hirata, Takafumi.

In: Chemical Geology, Vol. 259, No. 3-4, 25.02.2009, p. 230-239.

Research output: Contribution to journalArticle

Iizuka, Tsuyoshi ; Komiya, Tsuyoshi ; Johnson, Simon P. ; Kon, Yoshiaki ; Maruyama, Shigenori ; Hirata, Takafumi. / Reworking of Hadean crust in the Acasta gneisses, northwestern Canada : Evidence from in-situ Lu-Hf isotope analysis of zircon. In: Chemical Geology. 2009 ; Vol. 259, No. 3-4. pp. 230-239.
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