Journal ArticleDOI
Zircon U-Pb ages of granulites from the Central Region of the Lewisian, northwestern Scotland
Robert T. Pidgeon,D. R. Bowes +1 more
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In this article, the U-Pb isotopic systems of zircons from two samples of hypersthene granulite from the Kylesku group have been examined and it has been shown that a major isotopic event or events took place approximately 2700 m.y.Abstract:
The overprinting of the high grade rocks of the Scourian episode, during the Inverian and Laxfordian episodes, has so far prevented a reliable estimate being made of the age of the Scourian granulite–facies metamorphism in the Central Region of the Lewisian of northwestern Scotland. In an attempt to solve this problem the U–Pb isotopic systems of zircons from two samples of hypersthene granulite from the Kylesku group have been examined. These zircons have discordant apparent ages complicating the interpretation of the results. However, by measuring a number of size fractions from each of the two zircon suites it has been possible to demonstrate that a major isotopic event or events took place approximately 2700 m.y. ago in these granulite–facies rocks. It has also been shown that the two discordance trends found for the two zircon populations can be explained in terms of episodic disturbances of the U–Pb isotopic systems at times which correspond to the known ages of ‘Laxfordian’ and ‘Caledonian’ events.read more
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Jack Hills, evidence of more very old detrital zircons in Western Australia
TL;DR: In this article, the authors reported a further occurrence of old detrital zircons, again identified using the ion-microprobe SHRIMP, in conglomerate from the Jack Hills Metasedimentary Belt4,5 (26°11′ S, 116°58′ E), ∼60km north of Narryer.
Journal ArticleDOI
Geochronological studies of the Bohemian massif, Czechoslovakia, and their significance in the evolution of Central Europe
TL;DR: U-Pb zircon and Rb-Sr whole-rock analyses from various gneisses and plutonie rocks of the Moldanubian and Moravo-Silesian zones and the stable foreland of the Hercynian (Variscan) orogenic belt indicate that most of the crust in Central Europe was first formed during the Cadomian orogeny which straddles the Precambrian-Cambrian boundary.
Journal ArticleDOI
Sm—Nd systematics of Lewisian gneisses: implications for the origin of granulites
TL;DR: In this paper, isotope systematics of Lewisian gneisses from North-west Scotland suggest that their igneous calc-alkaline precursors separated from previously undifferentiated mantle 2,920±50 Myr ago.
Journal ArticleDOI
Single zircon ages from high-grade rocks of the Jianping Complex, Liaoning Province, NE China
TL;DR: The high-grade rocks of the Jianping Complex in Liaoning Provi nce, NE China, belong to the late Archaean to earliest Proterozoic granulite belt of the North China craton and were obtained by the Pb-Pb evaporation method and SHRIMP analyses as mentioned in this paper.
Journal ArticleDOI
Pb-loss patterns in zircons from a high-grade metamorphic terrain as revealed by different dating methods: UPb and PbPb ages for igneous and metamorphic zircons from northern Sri Lanka
TL;DR: In this article, the ion microprobe SHRIMP was used to date zircons from high-grade igneous and sedimentary rocks of the Vavuniya Charnockite Province (VCP) in northern Sri Lanka, using a new vapour digestion technique and evaporation.
References
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Journal ArticleDOI
Discordant uranium‐lead ages, I
TL;DR: In this paper, a graphical procedure is described for rapid calculation of discordant uraniumlead ages resulting from multiple episodes of uranium-lead fractionation, which is extended to permit the calculation of the effect of the presence of primary radiogenic lead and constant loss of intermediate daughter products.
Journal ArticleDOI
The significance of lead isotope studies in ancient, high-grade metamorphic basement complexes, as exemplified by the Lewisian rocks of Northwest Scotland
TL;DR: Lead isotope ratios, together with uranium and lead analyses, are reported for thirty-seven whole rock samples from the Precambrian Lewisian basement complex of Northwest Scotland as discussed by the authors, which can help to decide whether a given crustal segment represents essentially juvenile addition of material from the upper mantle, or reworked older crust.
Journal ArticleDOI
Volume diffusion as a mechanism for discordant lead ages
TL;DR: In this paper, the authors used the Pb206/U238-Pb207/U235 diagram to calculate the present-day U-lead ages as a function of the parameter D/a2 yield ratios that lie on a 2800 to 600 m.y.y chord.
Journal ArticleDOI
A geochronological study of the metamorphic complexes of the scottish highlands
TL;DR: Rubidium-strontium age-determinations are presented for minerals and whole rocks from the Lewisian, Moinian and Dalradian metamorphic complexes of Scotland and from the Connemara schists of western Ireland.
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