Abstract. Geochemical studies of Wyoming Precambrian graywackes derived from continental crust older than 3.2 × 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 × 10 9 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 × 109 years.
|Number of pages||3|
|Publication status||Published - 1967|