In situ U–Th–Pb geochronology of monazite and xenotime from the Jack Hills belt: Implications for the age of deposition and metamorphism of Hadean zircons
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- 作者：Birger Rasmussen ; Ian R. Fletcher ; Janet R. Muhling ; Simon A. Wilde
- 关键词：Jack Hills ; Monazite ; Xenotime ; U– ; Pb ; Geochronology ; SHRIMP ; Narryer Terrane
- 刊名：Precambrian Research
- 出版年：2010
- 出版时间：June 2010
- 年：2010
- 卷：180
- 期：1-2
- 页码：26-46
- 全文大小：2891 K
文摘
Quartz-pebble conglomerate and quartzite at Eranondoo Hill in the Jack Hills belt in the northwestern Yilgarn Craton, Australia, contain monazite and xenotime grains in heavy mineral layers. In situ SHRIMP U–Th–Pb geochronology of detrital monazite and xenotime, as well as monazite and xenotime inclusions in detrital quartz, gives ages between 3.3 and 3.1 Ga. The conglomerates, which host abundant Hadean zircon grains, contain metamorphic monazite in the muscovite matrix that yields an age of 2653 ± 5 Ma. This date is interpreted to represent the time of low-grade metamorphism and therefore is a direct minimum age for sediment deposition. The conglomerates also contain authigenic xenotime that gives an age of 800 ± 25 Ma, which suggests that part of the succession was affected by a previously unrecognised Neoproterozoic event. Authigenic xenotime in conglomerate immediately to the east of Eranondoo Hill gives an age of 2660 ± 10 Ma. Metamorphic monazite in garnet-bearing quartz-mica schist from the middle of the belt records an age of 1858 ± 6 Ma, which likely reflects an episode of deformation and low-grade metamorphism associated with major shearing. Several monazite grains from the schist indicate that the centre of the belt also experienced metamorphism at 2.65 Ga. Massive magnetite–hematite ore from banded iron formation in the northeastern part of the belt contains authigenic xenotime that formed at 3080 ± 20 Ma. Co-existing monazite gives a similar age (3080 ± 35 Ma), indicating that at least part of the belt was deposited before 3.08 Ga. A second population of xenotime was identified, indicating a later episode of heating and fluid flow at 1820 ± 25 Ma, possibly related to reactivation during the 1.83–1.78 Ga Capricorn orogeny. The sedimentary rocks dated in this study were deposited before 2.65 Ga, and in some cases, before 3.08 Ga, indicating that much of the Jack Hills belt is Neoarchean or older. The metasedimentary rocks, and the Hadean zircons they preserve, experienced a protracted history of deformation and heated fluid flow spanning more than two billion years (3080-800 Ma).