U-Pb geochronology and Sm-Nd isotopic composition of Proterozoic gneisses, Channel Islands, UK

• Published in: Journal of the Geological Society Vol. 155; no. 4; pp. 609 - 618
• Main Authors: Samson, Scott D, D'Lemos, Richard S
• Format: Journal Article
• Language: English
• Published: London Geological Society of London 01.07.1998; The Geological Society of London; Geological Society; Geological Society Publishing House
• Subjects: absolute age; accuracy; amphibolite facies; Cadomian Orogeny; chemical composition; concentration; Crystalline rocks; crystallization; dates; Earth sciences; Earth, ocean, space; English Channel Islands; Europe; Exact sciences and technology; facies; geochemistry; Geochronology; Geological time; Geology; gneisses; igneous and metamorphic rocks; Igneous and metamorphic rocks petrology, volcanic processes, magmas; intrusions; Islands; Isotope geochemistry. Geochronology; isotopes; lithogeochemistry; metamorphic rocks; metamorphism; Petrology; Precambrian; Proterozoic; Sm/Nd; Stone; U/Pb; United Kingdom; upper Precambrian; Western Europe; United Kingdom; English Channel Islands; Western Europe; Guernsey Island; United Kingdom > UK; Isle of Sark; Sm/Nd; Cadomian Orogeny; absolute age; U/Pb; English Channel Islands; nesosilicates; lower Proterozoic; gneisses; single crystals; Europe; xenocrysts; protoliths; metamorphism; amphibolite facies; Precambrian; metamorphic rocks; orthogneiss; intrusions; zircon; Proterozoic; silicates; dating; concordia diagram
• ISSN: 0016-7649; 2041-479X
• DOI: 10.1144/gsjgs.155.4.0609

A precise date of 2061 ± 2 m.y., determined by single zircon U-Pb techniques, confirms the Palaeoproterozoic age of the Icart gneiss of Guernsey. Positive initial εNd values for this and other gneisses on Guernsey (Lihou Island, Pea Stacks, Soldier's Bay) indicate that pre-Cadomian basement was an important site of new crustal production at ∼ 2100 m.y. These data, combined with the age of the Icart gneiss, provide a more robust link between Cadomian basement and the ∼ 2100 Birimian terrains of West Africa than could be made solely on general age similarities. High-precision U-Pb dating has shown that the protolith to an orthogneiss at Port du Moulin, Sark, is 616+4-2 m.y. rather than being Palaeoproterozoic. These new dates, combined with published 40Ar/39Ar data, show that deformation, magmatism and amphibolite-facies metamorphism took place at ∼ 605-615 m.y. in this region.