Archaean Sedimentation, Canadian Shield

Abstract

Abstract The resedimented (turbidite) facies association dominates the Archaean rock assemblages of the volcanic-sedimentary (greenstone) belts of the Canadian Shield. The alluvial-fan braided-fluvial facies association is widespread but of secondary importance. Both facies associations contain an abundance of felsic volcanic detritus, and in many greenstone belts, it is the dominant material. Rapid resedimentation of pyroclastic sediment from felsic centers seems to have been common. Plutonic detritus may have had either a synvolcanic or a granitic cratonic provenance. Major gneissic subprovlnces consist largely of paragneisses whose protoliths may have had a volcanic parentage similar to the sediments of the greenstone belts. The original total volume of erupted felsic volcanic material, if the large amounts in the metasedimentary rocks of the greenstone belts and in the paragneisses of the gneiss subprovinces are included, may have been an order of magnitude greater than the volume of felsic volcanic rocks exposed today. The total volume of felsic volcanic material may have been greater than the total volume of intermediate-mafic volcanic material. Numerous quartzarenite and carbonate occurrences have been described, indicating that at least several portions of the Canadian Shield were tectonically stable as early as 2980 Ma.