A Pilbara perspective on the generation of Archaean continental crust

The Archean crust contains direct geochemical information of the Earth's early planetary differentiation. A major outstanding question in the Earth sciences is whether the volume of continental crust today represents nearly all that formed over Earth's history or whether its rates of creation and destruction have been approximately balanced since the Archean. Analysis of neodymium isotopic data from the oldest remnants of Archean crust suggests that crustal recycling is important and that preserved continental crust comprises fragments of crust that escaped recycling. Furthermore, the data suggest that the isotopic evolution of Earth's mantle reflects progressive eradication of primordial heterogeneities related to early differentiation.

Hadean

Early Earth

10.1126/science.7667634

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Citations (308)

Geochemical Constraints on the Growth of the Continental Crust

The Journal of Geology (1982)

S. M. McLennan S. R. Taylor

Several lines of evidence indicate that the Archean upper crust was considerably more mafic than the present-day upper crust. There has been no significant change in REE and Th abundances in post-Archean clastic sedimentary rocks, suggesting that there has been no change in the composition of the upper crust during the post-Archean. This indicates that if there have been any additions to the post-Archean upper crust, they must have had similar composition to the upper crust itself. Geochemical modelling of REE and Th abundances in sedimentary rocks suggests that the minimum ratio of post-Archean to Archean upper crustal composition required to eliminate the Archean upper crustal trace element signature, within analytical uncertainty, is about 4:1. Such a model also is supported by isotopic data. Using plausible assumptions regarding the volume of Archean crust, isostatic relations, and extreme models of the earth's degassing history, it is proposed that approximately 65-75% of the continental crust formed during the period of 3.2-2.5 Ga, and that between 70-85% of the continental crust had formed by 2.5 Ga. Such a model is consistent with relatively constant continental freeboard during the past 2,500 million years. Thus, the constant freeboard model does not provide unique evidence for large-scale recycling of continental material through the mantle.

10.1086/628690

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Citations (251)

Archaean geochemistry: The origin and evolution of the archaean continental crust

Chemical Geology (1986)

Jan D. Kramers

10.1016/0009-2541(86)90015-x

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Crustal structure along the northern ‘Fennolora’ profile

Precambrian Research (1987)

Carl‐Erik Lund