U-Pb dating of detrital zircon from the Mt. Alfred area, Yilgarn Craton, Western Australia
2016 (English)Licentiate thesis, comprehensive summary (Other academic)
Hadean and Paleo-Eoarchean aged detrital zircon provide a rare glimpse into the nature of the early Earth. Thus, the characterisation of new localities with rocks that host Hadean and Paleo-Eoarchean zircon provide invaluable insight into the Earth’s early crust. We report high spatial resolution SIMS U-Th-Pb data in detrital zircon from five samples of the Mt. Alfred Archean quartzite located in the Illaara Greenstone Belt, Yilgarn Craton in Western Australia. To date, only two studies have published detrital age data for this locality (Wyche et al., 2004; Thern and Nelson, 2012). A total of 487 spots in 450 zircon grains have been analysed for U-Th-Pb and the internal structure of the grains has been studied by cathodoluminescence imaging. Concordant 207Pb/206Pb ages range between 3109 ± 17 and 3918 ± 16 Ma (2σ), with three main age peaks at ca. 3640, 3690 and 3760 Ma. 207Pb/206Pb ages of up to 4067 ± 5 Ma were found, but these were highly discordant. At least two Pb-loss events are evident during the Neoarchean and Permian-Triassic. The Neoarchean event is implied from highly metamict zircon cores producing 207Pb/206Pb ages ca. 2.7-2.8 Ga, younger than a crosscutting quartz-tourmaline vein formed at 2.94 Ga. Single-grain discordia trends define the more recent Pb-loss event, with eight grains producing a weighted average lower intercept age of 224 ± 35 Ma (2σ).We propose that the similarity of ages between the Mt. Alfred detrital zircon age distribution and the Meeberrie gneiss of the Narryer Gneiss Complex (NGC) imply the distal transport of these sediments over ca. 300 km, or the previous existence of NGC-like rocks near the Illaara greenstone belt. The noticeable lack of detrital zircon aged ca. 3.34 Ga as observed in all other detrital populations of the Illaara Formation suggests a different provenance for the Mt. Alfred quartzites.
Detrital zircons of hadeisk and paleo- eoarkeisk age gives a unique insight into the early Earth's nature. Investigation of the new premises with rocks that contain had genomic and paleo- eoarkeiska zircons therefore provides an invaluable insight into the earliest history of the Earth's crust. We report SIMS U-Th-Pb data with high spatial resolution of detrital zircons from five samples from the Archaean Mt. Alfred quartzite located in Illaara Greenstone Belt, Yilgarn-Craton, Western Australia. So far, only two studies published detrital data from this local (Wyche, et al., 2004; Thern and Nelson, 2012). A total of 487 points in 450 zirkonkristaller analyzed for U-Th-Pb and the internal structures of the crystals have been studied by cathodoluminescence imaging. Concordant 207Pb / 206Pb-ages vary between 3109 ??} 17 and 3918 ??} 16 Ma (2ƒÐ), with three Alders peaks at ca. 3640, 3690 and 3760 Ma. 207Pb / 206Pb-ages on up to 4067 ??} 5 Ma were found but these were highly discordant. At least two lead loss episodes can be observed and these have neoarkeisk and Permian-Triassic age. The neoarkeiska hand notification can be derived from strong metamikta zirkonkarnor giving 207Pb / 206Pb-ages ca. 2.7-2.8 Ga, younger than the cutting end of quartz-tourmaline-Adra formed at 2.94 Ga. Diskordialinjer within the same crystal defines a more recentchanges lead loss. Atta crystals provide a weighted mean value of 224 ??} 35 Ma (2ƒÐ) for the lower interceptaldern.Vi argue that the similarity in ages between the detrital zirkonerna from Mt. Alfred and from Meeberrie gneiss in Narryer Gneiss Complex (NGC) suggest long range transport of these sediments over ca. 300 km or previous existence of NGC-like rocks nara Illaara greenstone belt. The clear lack of detrital zircons with ages ca. 3:34 Ga, which is found in all other detrital populations in Illaara Formation, indicating a different provenance Mt. Alfred kvartsiterna.
Place, publisher, year, edition, pages
Stockholm University: Stockholm University, 2016. , 83 p.
Detrital zircon, Geochronology, Archean, Hadean, Western Australia
Research subject Geochemistry; Geology
IdentifiersURN: urn:nbn:se:su:diva-135618OAI: oai:DiVA.org:su-135618DiVA: diva2:1047047
2016-12-06, DeGeersalen, 10:00 (English)
Johansson, ÅkeAndersson, Jenny
Whitehouse, Martin, Adjunct ProfessorNemchin, Alexander, ProfessorPease, Victoria, Professor
FunderKnut and Alice Wallenberg Foundation, 440811