The age of the Mesoproterozoic Stoer Group sedimentary and impact deposits, NW Scotland

John Parnell, Darren Mark, Anthony E. Fallick, Adrian Boyce, Scott Thackrey

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42 Citations (Scopus)


The Mesoproterozoic Stoer Group of the 'Torridonian' has been dated at 1177 +/- 5 Ma (2 sigma), based on Ar-40/Ar-39 dating of authigenic K-feldspars precipitated in degassing structures within the Stac Fada Member, interpreted previously as an impact ejecta deposit. Fluid inclusion analysis of the K-feldspar shows that it precipitated from hot fluids, and so must immediately post-date emplacement of the ejecta blanket. The oxygen isotopic composition of K-feldspar is remarkably constant at 9.7 +/- 0.2 parts per thousand (V-SMOW) and is consistent with derivation from evaporated lake water. The new age supports previous determinations of 1199 +/- 70 Ma from Pb-Pb dating of limestone and 1180 Ma from palaeomagnetic data, but provides much higher precision.

Original languageEnglish
Pages (from-to)349-358
Number of pages10
JournalJournal of the Geological Society
Issue number2
Publication statusPublished - Mar 2011


  • moine thrust zone
  • Northwest Scotland
  • fluid-flow
  • geochronology
  • pseudotachylite
  • geochemistry
  • provenance
  • seawater
  • events
  • origin

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