Abstract

A 4000 to 7000 m sequence of amphibolite-facies Archean layered gneisses in the Pakwash Lake – Lac Seul area of Northwest Ontario has been examined to determine its origin. The micaceous, relatively fine grained gneisses are concluded to be metasedimentary rocks. They were probably deposited from aqueous suspension as graded beds. The provenance of the detrital material was dacitic volcanics. Apparently there was little chemical alteration prior to metamorphism. An unmetamorphosed analog for these deposits is the volcaniclastic Eocene Ohanapecosh Formation in the Mt. Rainier area of Washington, U.S.A. Seventeen new chemical analyses are used to describe the rocks and decipher their origin.Similar rocks occur for at least 100 km east and west from the area of detailed study, suggesting a major sedimentary basin or series of basins in the area of the present English River Gneiss Belt.

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