Composition of the Ancient North American Crust

Abstract

Geochemical studies of Wyoming Precambrian graywackes derived from continental crust older than 3.2 x 10⁹ years indicate that their source area was at least as highly differentiated as most younger Precambrian crust. The composition of this early crust (approximately that of calcium-rich granite) is not unlike that of the 2.5 to 3.2 x 10⁹ year old North American crust. Limited geochemical data suggest that the composition of North America may not have changed significantly during the last 3.0 to 3.5 x 10⁹ years.