Evolution of early continental crust

Abstract

The present article reviews the evolution of continental crust since the time the earth began to inscribe a permanent history in rocks of the cratonic nuclei. The existence of a sialic crust prior to 4200 Ma ago, soon after the permobile stage of the earth, is documented by detrital zircon in the Precambrian metaconglomerate of Neyerer Complex, Western Australia. The evolution of Archaean crust (> 2500 Ma) is discussed in terms of currently used Nd model-age calculations, based on a depleted mantle evolutionary model. The model fits the generally accepted assumption that LREE depletion of the upper mantle commenced very early in the earth's history and that the present-day MORB is the best representative for the Nd-isotopic composition of today's depleted mantle. Finally, the mechanisms for growth or accretion of the continental crust and the incompatibility of thickened crust during Archaean time are discussed.