U-Pb zircon geochronological evidence for Neoproterozoic events in the Glenfinnan Group (Moine Supergroup): the formation of the Ardgour granite gneiss, north-west Scotland |
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| Authors: | C R L Friend P D Kinny G Rogers R A Strachan B A Paterson |
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| Institution: | (1) Department of Geology, Oxford Brookes University, Oxford, OX3 0BP, UK, GB;(2) School of Applied Geology, Curtin University of Technology, GPO Box U1987, Perth. WA 6001, Australia, AU;(3) Isotopi Geosciences Unit, Scottish Universities Research and Reactor Centre, East Kilbride, Glasgow, G75 0QF, UK, GB |
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| Abstract: | The age and Precambrian history of the Moine Supergroup within the Caledonide belt of north-west Scotland have long been contentious
issues. The Ardgour granite gneiss is essentially an in situ anatectic granite formed during deformation and regional high-grade
metamorphism from Moine metasediments. High-precision TIMS and SHRIMP U-Pb zircon dating shows that the age of the anatectic
Ardgour granite gneiss and its enclosed segregation pegmatites is 873 ± 7 Ma. This demonstrates the reality of a Neoproterozoic
episode of high-grade metamorphism in the Glenfinnan Group Moine and, contrary to previous evidence, the absence of Grenvillian-aged
metamorphism. This conclusion places constraints on Neoproterozoic palaeogeographic reconstructions of the North Atlantic
region, indicating that the Moine rocks cannot be used as a link between the Grenvillian belt of North America and the Sveconorwegian
orogen in Scandinavia. SHRIMP ages of between c. 1100 and 1900 Ma were obtained from detrital, inherited zircons and reflect
the provenance of the Glenfinnan Group Moine sediments which must, therefore, have been deposited between c. 1100 and 870 Ma.
Potential sources are found as relatively minor, tectonically bounded basement inliers within the British Caledonides, although
more widespread source areas occur outside Britain in both Laurentia and Baltica. The most important feature of the provenance
is the absence of detrital Archaean grains. This suggests that the Archaean Lewisian gneiss complex, which forms the basement
component of the western foreland to the Caledonides in Britain, was not a major contributor to the Glenfinnan Group basin.
Received: 16 June 1996 / Accepted: 29 January 1997 |
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