Abstract

Geochemical and geophysical data indicate that the average potash content of young calc-alkaline volcanics increases in approximately a linear manner with crustal thickness. If such a relationship existed during the Precambrian, potash contents of early Precambrian (graphic billion years) calc-alkaline volcanics in the Canadian Shield indicate that these volcanics were erupted onto a crust that was approximately 10–25 km thick. Since 3–13 km of these volcanics are now exposed, the total thickness of the early Precambrian crust prior to the Kenoran orogeny may have approached or reached presentday crustal thicknesses.

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