Abstract
The Einasleigh Metamorphics form part of the Etheridge Group and are interpreted as the lowest exposed part of the Georgetown Inter 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 co 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.
Original language | English |
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Pages (from-to) | 385-401 |
Number of pages | 17 |
Journal | Australian Journal of Earth Sciences |
Volume | 52 |
Issue number | 3 |
DOIs | |
Publication status | Published - Jun 2005 |