Original paper

Archean high-pressure metamorphism in the western Canadian Shield

Snoeyenbos, David R.; Williams, Michael L.; Hanmer, Simon

European Journal of Mineralogy Volume 7 Number 6 (1995), p. 1251 - 1272

33 references

published: Dec 27, 1995
manuscript accepted: Jun 21, 1995
manuscript received: Feb 20, 1995

DOI: 10.1127/ejm/7/6/1251

BibTeX file

ArtNo. ESP147050706017, Price: 29.00 €

Download preview PDF Buy as PDF

Abstract

Abstract The upper deck of the 3.2-2.6 Ga East Athabasca mylonite triangle, northern Saskatchewan, Canada consists predominantly of crustal rocks metamorphosed at conditions exceeding 15 kbar and 1000°C. Mylonitic quartzofeldspathic gneisses and gneiss-hosted metabasite alike record these conditions. Temperature is constrained to at least 1000°C by homogenization thermometry of ternary feldspars in the felsic gneisses and by garnet-clinopyroxene exchange thermometry in mafic rocks. Minimum pressure of 15 kbar is indicated by the presence of matrix kyanite in association with the high-temperature feldspars. Primary corundum in certain garnet-clinopyroxenites also indicates pressure of at least 15 kbar. Unusual mineral compositions such as Ti-rich muscovite, Cr-bearing kyanite, and possible zircon exsolution from rutile are found in several locations. Oriented rutile needles in garnet, interpreted as exsolution, are pervasive. The upper deck is a discrete metamorphic terrane, 400 km2 in area and 10 km in thickness. Elevation of this terrane into juxtaposition and fusion with granulite-facies lower crustal mylonites occurred within a 2.6 Ga intracontinental strike-slip shear zone. The upper deck is one of the very few high-pressure crustal metamorphic provinces known in the Americas and at 2.6 Ga it is among the oldest such, worldwid

Keywords

ArcheanCanadathermobarometryhigh-pressure metamorphism