Protolith ages and exhumation histories of (ultra)high-pressure rocks across the Western Gneiss Region, Norway

Emily O. Walsh, Bradley R. Hacker, Phillip B. Gans, Marty Grove, George Gehrels

Research output: Contribution to journalArticlepeer-review

62 Scopus citations


The timing of protolith formation, ultrahigh-pressure (UHP) subduction, and subsequent exhumation for the ultrahigh-pressure to high-pressure units across the eastern part of the Western Gneiss Region, Norway, were assessed using U/Pb zircon, Th/Pb monazite, and 40Ar/39Ar white mica ages. U/Pb zircon ages from eclogites demonstrate that oceanic and continental allochthons were emplaced onto the Baltica basement before the entire mass was subducted to (ultra)high pressure. Eclogites within the allochthons across the entire Western Gneiss Region are Caledonian and show a degree of zircon (re)crystallization that increases with peak pressure, permitting the interpretation that the entire region underwent synchronous subduction. 40Ar/39Ar white mica ages of 399 Ma indicate that the eastern part of the Western Gneiss Region had been exhumed to shallow crustal levels while UHP metamorphism was ongoing farther west, indicating a westward dip to the slab. The 40Ar/39Ar white mica ages also show a clear east-to-west gradient across the entire Western Gneiss Region, indicating that the Western Gneiss Region rose diachronously to crustal levels from east to west between 399 and 390 Ma.

Original languageEnglish (US)
Pages (from-to)289-301
Number of pages13
JournalBulletin of the Geological Society of America
Issue number3-4
StatePublished - Mar 2007


  • 4Ar/Ar
  • Exhumation
  • Laser ablation inductively coupled plasma-mass spectrometry
  • Secondary ion mass spectrometry
  • Ultrahigh pressure
  • Western Gneiss Region

ASJC Scopus subject areas

  • Geology


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