Bibliographische Detailangaben
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Personen und Körperschaften:
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Guitreau, M (VerfasserIn); Blichert-Toft, J (VerfasserIn); Mojzsis, S J (VerfasserIn); Roth, A S G (VerfasserIn); Bourdon, B (VerfasserIn); Cates, N L (VerfasserIn); Bleeker, W (VerfasserIn) |
| Format: |
Elektronische Zeitschrift
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| Sprache: |
English
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| veröffentlicht: |
Elsevier BV, 2014 |
| Gesamtaufnahme: |
GEM: Geo-mapping for Energy and Minerals
, Geochimica et Cosmochimica Acta vol. 135, 2014 p. 251-269, Natural Resources Canada, Contribution Series
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| Schlagwörter: |
Northwest Territories;
Zeitschrift;
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| Quelle: |
GEOSCAN
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| Zusammenfassung: |
The Acasta Gneiss Complex (AGC) is a remnant Hadean-Eoarchean terrane compo...
The Acasta Gneiss Complex (AGC) is a remnant Hadean-Eoarchean terrane composed of strongly deformed polyphase mafic to felsic gneisses which preserve a multi-stage history of magmatic emplacement, inheritance, and subsequent tectono-thermal modifications. The complexities encountered in such an old terrane fragment have been documented in previous geochronological studies of the AGC (e.g. zircon U-Pb, 147Sm-143Nd), and are evident also in its Lu-Hf isotope systematics. Here, we report new Lu-Hf isotope whole-rock measurements which show that some AGC gneisses were severely disturbed by migmatization and associated mineral segregation, while others preserve their Lu-Hf isotope systematics relatively intact with mostly near- to sub-chondritic initial 176Hf/177Hf ratios. Results reveal identifiable Eoarchean and later (Paleoarchean) magmatic events at around 3960Ma and again at 3600Ma, with a major metamorphism of the complex at 3750Ma. The oldest and least disturbed gneisses have a Lu-Hf regression age of 3946±87Ma, in good agreement with U-Pb zircon geochronology. A role of yet older crust (4000-4200Ma) in the formation of the AGC is also evident, but seems not to have influenced to first order the Lu-Hf isotope systematics of the 3960Ma group. The ca. 3960Ma group is proposed to be representative of its mantle source based on the absence of correlation between ?Hf(t) and Ce/Pb. It is further suggested that these two parameters show that the ca. 3600Ma gneisses were sourced in part from a mafic lithology belonging to the 3960Ma group, and that multiple sources (mantle and crust) were involved in AGC formation. The identification of preserved Lu-Hf isotope systematics in AGC gneisses means that complementary geochemical and isotopic studies bearing on the petrogenesis of pre-3900Ma rocks are possible. Despite its history of strong deformation and alteration, carefully selected domains within the AGC carry surviving information about the evolution of the mantle-crust system at the Eoarchean-Hadean boundary. © 2014.
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