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| Titel |
A legacy of Hadean silicate differentiation inferred from Hf isotopes in Eoarchean rocks of the Nuvvuagittuq supracrustal belt (Québec, Canada) |
| VerfasserIn |
Martin Guitreau, Janne Blichert-Toft, Stephen J. Mojzsis, Antoine S. G. Roth, Bernard Bourdon |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250077581
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| Zusammenfassung |
| New Lu-Hf isotopic data for mafic and felsic rocks from the Nuvvuagittuq supracrustal belt
(NSB) in northern Québec (Canada) yield an Eoarchean age of 3864 ± 70 Ma consistent with
both zircon U-Pb and whole-rock 147Sm-143Nd chronology, but in disagreement with ca.
4400 Ma ages inferred from the 146Sm-142Nd chronometer (O’Neil et al., 2008). The Lu-Hf
result is interpreted as the mean emplacement age of the different autochthonous
units of the NSB. An observed alignment of the data along a Lu-Hf “scatterchron”
precludes a Hadean age for the NSB because its isotopic characteristics appear to
be controlled by long-term radiogenic ingrowth. Emplacement of the NSB in the
Hadean (e.g., 4362 Ma; re-calculated in Kinoshita et al., 2012) should have caused
age differences of hundreds of millions of years to manifest as strong deviations
from the Lu-Hf scatterchron. Combined Lu-Hf and Sm-Nd data on the same NSB
amphibolite samples (Ca-poor cummingtonite- and hornblende-bearing) define a
mixing hyperbola at ca. 3800 Ma with end-member compositions representative
of the compositional groups identified for these lithologies (O’Neil et al., 2011).
Anomalously low 142Nd/144Nd values relative to Bulk Silicate Earth are endemic to
“low-TiO2” amphibolites; this is attributable to an ancient multi-stage history of
their mantle source as indicated by rare-earth element patterns. Modeling shows
that the 142Nd/144Nd deficits could have developed in response to a re-fertilization
episode within a mantle domain depleted by primordial crust extraction at 4510 Ma. |
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