Bibliographische Detailangaben
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Personen und Körperschaften:
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Mojzsis, S J (VerfasserIn); Cates, N L (VerfasserIn); Caro, G (VerfasserIn); Trail, D (VerfasserIn); Abramov, O (VerfasserIn); Guitreau, M (VerfasserIn); Blichert-Toft, J (VerfasserIn); Hopkins, M D (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. 133, 2014 p. 68-96, Natural Resources Canada, Contribution Series
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| Schlagwörter: |
Zeitschrift;
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| Quelle: |
GEOSCAN
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| Zusammenfassung: |
The oldest compiled U-Pb zircon ages for the Acasta Gneiss Complex in the N...
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-wstite) to <FMQ (fayalite-magnetite-quartz) oxygen fugacities. A ca. 3920Ma emplacement age for the AGC is contemporaneous with bombardment of the inner solar system. Analytical bombardment simulations show that crustal re-working from the impact epoch potentially affected the precursors to the Acasta gneisses.
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