Abstract

Widespread evidence of ultrahigh-pressure metamorphism is reported from the Nordfjord and Stadtlandet area of the Western Gneiss region in Norway, outlining a distinct ultrahigh-pressure province. Coesite has been found as inclusions in garnet, omphacite, or kyanite in eclogite from 5 new localities, and quartz pseudomorphs after coesite occur in eclogite minerals at an additional 12 localities. Quartz pseudomorphs after coesite, within garnet and clinozoisite, are reported for the first time from associated gneisses, which is evidence for in situ ultrahigh-pressure metamorphism, at least at a local scale. The boundary to an ultrahigh-pressure province is defined by a metamorphic break from lower pressure (<2.5 GPa) eclogites to coesite or quartz pseudomorph after coesite eclogites (>2.8 GPa) within a 10-km-wide mixed zone in the Nordfjord area. This zone may mark the disrupted tectonic boundary to a small ultrahigh-pressure unit and casts doubt on the assumption that the Western Gneiss region behaved as a coherent terrane during burial and exhumation.

You do not currently have access to this article.