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| Titel: |
U - Pb zircon ages from leucogneiss in the Etheridge Group and their significance for the early history of the Georgetown region, north Queensland |
| Auteur: |
Black, LP Withnall, IW Gregory, P. Oversby, BS Bain, JHC |
| Verschenen in: |
Australian journal of earth sciences |
| Paginering: | Jaargang 52 (2005) nr. 3 pagina's 385-401 |
| Jaar: |
2005-06 |
| Inhoud: |
The Einasleigh Metamorphics form part of the Etheridge Group and are interpreted as the lowest exposed part of the Georgetown Inlier of north Queensland. Due to a dearth of interbedded felsic igneous rocks that would be suitable for isotopic dating, the depositional age of the Etheridge Group has long been uncertain. This study presents U - Pb SHRIMP dating of zircons from leucogneiss in the Einasleigh Metamorphics. Based on field and geochemical evidence, and the nature of the contained zircons, the leucogneiss is interpreted as having a sedimentary origin derived from igneous sources. Old, poorly defined zircon components (mostly between ca 1800 and 2900 Ma) in most of the samples reflect detrital inheritance. Younger, well-defined, zircon populations in two samples of leucogneiss indicate that they were primarily derived from a possibly contemporaneous 1706 ± 6 Ma volcanic or volcano-plutonic terrane. High-grade metamorphism of these rocks occurred ∼150 million years later, and resulted in extensive zircon recrystallisation at 1562 ± 4 Ma. It is not clear whether this metamorphism and zircon crystallisation marks D1/M1 tectonothermal activity or the onset of the second major episode (D2/M2) of regional metamorphism and deformation, which peaked at ca 1552 Ma. If the latter alternative is correct, D2/M2 lasted for at least 12 million years, and D1/M1 is likely to have occurred ∼20 million years earlier at ca 1580 Ma. Two of the leucogneiss samples display evidence of isotopic resetting as young as 1500 Ma. |
| Uitgever: |
Taylor & Francis |
| Bronbestand: |
Elektronische Wetenschappelijke Tijdschriften |
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