Composition of the Ancient North American Crust

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Science  24 Feb 1967:
Vol. 155, Issue 3765, pp. 1013-1015
DOI: 10.1126/science.155.3765.1013


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.