Niobium/Uranium Evidence for Early Formation of the Continental Crust
Abstract
Niobium/uranium ratios in greenstone-belt basalts and gabbros indicate that parts of the Late Archean mantle beneath Western Australia underwent a level of melt extraction, resulting in formation of the continental crust, comparable to that seen in the present mantle. The implication is either that (i) the amount of continental crust that formed before 2.7 × 109 years ago was much greater than generally thought or (ii) crustal growth occurred by severe depletion of small volumes of the mantle rather than by moderate depletion of a large volume of mantle.
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REFERENCES AND NOTES
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A single crustal contaminant cannot produce the two types of enriched basalts. Although Paringa and Devon Consuls basalts have different Nb/U, Nb/Th, La/Sm, and Th/La ratios, consistent with different amounts of crustal contamination by a single contaminant, concentrations of Nb and Sm in the two basalt types are about the same, inconsistent with this interpretation.
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Published In
Science
Volume 275 | Issue 5299
24 January 1997
24 January 1997
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© 1997 American Association for the Advancement of Science.
Submission history
Received: 6 August 1996
Accepted: 15 November 1996
Published in print: 24 January 1997
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Cited by
- Evolution of the Continents and the Atmosphere Inferred from Th-U-Nb Systematics of the Depleted Mantle, Science, 283, 5407, (1519-1522), (1999)./doi/10.1126/science.283.5407.1519
- Early Evolution of Continents, Science, 275, 5299, (498-499), (1997)./doi/10.1126/science.275.5299.498
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