Late Precambrian U-Pb titanite age for peak regional metamorphism and deformation (Knoydartian orogeny) in the western Moine, Scotland

Tanner, P.W.G. and Evans, J.A. (2003) Late Precambrian U-Pb titanite age for peak regional metamorphism and deformation (Knoydartian orogeny) in the western Moine, Scotland. Journal of the Geological Society, 160(4), pp. 555-564.

Abstract

There has been controversy over the number and timing of orogenies in the Precambrian Moine block in the Scottish Caledonides since the earliest radiometric dating in the 1960s. This work challenges a recent hypothesis, that this sector of the Laurentian margin was subjected to continuous crustal extension between greater than 900 and 470 Ma. U-Pb dating (thermal ionization mass spectrometry) of titanite from a calcsilicate pod in the Moine (Morar Group) of the western Highlands gives an age of 737 ñ 5 Ma. The titanite grew from Fe-Ti-bearing detrital minerals during the main progressive, syn-D2, amphibolite-facies (sillimanite zone) regional metamorphism, thus demonstrating that a Neoproterozoic contractional tectonothermal event (Knoydartian orogeny) affected the Moine block following the rift-related emplacement of the West Highland granite gneiss at 873 Ma. We conclude that the Sgurr Beag Thrust, a major tectonic break separating the Morar and Glenfinnan groups of the Moine, is mainly of Neoproterozoic, not Caledonian, age. The early tectonothermal event was succeeded by the Grampian Phase (Caledonian orogeny) at 460-470 Ma.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Tanner, Dr Peter
• Authors: Tanner, P.W.G., and Evans, J.A.
• Subjects: Q Science > QE Geology
• College/School: College of Science and Engineering > School of Geographical and Earth Sciences
• Journal Name: Journal of the Geological Society
• Publisher: Geological Society of London
• ISSN: 0016-7649
• Copyright Holders: Copyright © 2003 The Geological Society of London
• First Published: First published in Journal of the Geological Society 160(4) 555 -564
• Publisher Policy: Reproduced in accordance with the copyright policy of the publisher.