The Earth's oldest known crust; a geochronological and geochemical study of 3900-4200 Ma old detrital zircons from Mt. Narryer and Jack Hills, Western Australia

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doi: 10.1016/0016-7037(92)90062-N
Authors:Maas, Roland; Kinny, Peter D.; Williams, Ian S.; Froude, Derek O.; Compston, William
Author Affiliations:Primary:
Aust. Natl. Univ., Res. Sch. Earth Sci., Canberra, Australia
Other:
Curtin Univ. Technol., Australia
Univ. Edinburgh, United Kingdom
Volume Title:Geochimica et Cosmochimica Acta
Source:Geochimica et Cosmochimica Acta, 56(3), p.1281-1300. Publisher: Pergamon, Oxford, International. ISSN: 0016-7037
Publication Date:1992
Note:In English. 129 refs.; illus. incl. 4 tables
Summary:U, Th, Pb elemental and isotopic analyses are presented of zircons separated from Jack Hills metaconglomerate, one group older than 3900 m.y. and the other younger than 3750 m.y. Hf, Zr and REE analyses are also presented of these zircons and zircons from Mt Narryer quartz arenites, with Sc additionally given for the Jack Hills zircons. Data on grain morphology and inclusion mineralogy are also summarized. Diverse trace-element compositions especially in the REE of the old Mt Narryer zircons, point to a range of source rocks and differentiated crust existing 4150-4200 m.y. ago. Positive Ce anomalies are attributed to the presence of Ce4+ during crystallization. Inter-element covariations are independent of age and isotopic characteristics, e.g. that between Lu and Hf. Although no single minor- or trace-element abundance characteristic of the pre-4000 m.y. zircons is diagnostic of the source lithology, mineral inclusions, zircon morphology and similarity of composition to younger zircons in the same detrital populations indicate a felsic granitic provenance of continental type. The results indicate that sialic crust was differentiated with a polyphase history as indicated by the distinct zircon age groups. Overgrowths of low Th/U zircon of probable metamorphic origin suggest that by approx 3900 m.y. continental crustal thickness was sufficient to allow metamorphic zircon growth to occur. [R.K.H.]
Subjects:Absolute age; Archean; Dates; Geochronology; Nesosilicates; Orthosilicates; Paleoarchean; Pb/Pb; Precambrian; Silicates; U/Th/Pb; Zircon; Zircon group; Australasia; Australia; Jack Hills; Western Australia; Mount Narryer
Abstract Numbers:92M/3735
Record ID:1992012462
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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