Archean high-pressure metamorphism in the western Canadian Shield

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doi: 10.1127/ejm/7/6/1251
Authors:Snoeyenbos, David R.; Williams, Michael L.; Hanmer, Simon
Author Affiliations:Primary:
University of Massachusetts, Department of Geosciences, Amherst, MA, United States
Other:
Geological Survey of Canada, Canada
Volume Title:European Journal of Mineralogy
Source:European Journal of Mineralogy, 7(6), p.1251-1272. Publisher: Schweizerbart'sche Verlagsbuchhandlung (Nägele u. Obermiller), Stuttgart, Federal Republic of Germany. ISSN: 0935-1221
Publication Date:1995
Note:In English. 34 refs.; illus., incl. 4 plates, 4 tables, geol. sketch map
Summary:The 'upper deck' of the 3200-2600 m.y. E Athabasca mylonite triangle in N Saskatchewan consists mainly of crustal rocks metamorphosed at >><[dollar]I> 15 kbar and 1000°C. The T is constrained to ≥ 1000°C by homogenization thermometry of ternary feldspars in felsic gneisses and by garnet-clinopyroxene exchange thermometry in mafic rocks; the minimum P of 15 kbar is indicated by the presence of matrix kyanite in association with the high-T feldspars. Primary corundum in certain garnet-clinopyroxenites also indicates a P of ≥ 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 terrain, 400 km2 in area and 10 km thick; elevation of this terrain into juxtaposition and fusion with granulite-facies lower crustal mylonites occurred within a 2600 m.y. intracontinental strike-slip shear zone. The upper deck is one of the very few high-P crustal metamorphic provinces known in the Americas and at 2600 m.y. is among the oldest such, worldwide. [R.A.H.]
Subjects:Archean; Athabasca Formation; Chain silicates; Clinopyroxene; Crust; Crystal structure; Feldspar group; Felsic composition; Framework silicates; Garnet group; Gneisses; High pressure; High temperature; Kyanite; Mafic composition; Metamorphic rocks; Metamorphism; Mica group; Mineral composition; Muscovite; Mylonites; Nesosilicates; Orthosilicates; Oxides; P-T conditions; Precambrian; Pressure; Proterozoic; Pyroxene group; Rutile; Shear zones; Sheet silicates; Silicates; Temperature; Upper Precambrian; Zircon; Zircon group; Canada; Canadian Shield; North America; Saskatchewan; Western Canada
Coordinates:N590000 N600000 W1053000 W1063000
Abstract Numbers:96M/2445
Record ID:1996014800
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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