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Growth of continental crust: Clues from Nd isotopes and Nb-Th relationships in mantle-derived magmasIsotope and trace element geochemistry of Precambrian mantle derived rocks and implications for the formation of the continental crust is discussed. Epsilon Nd values of Archean komatiites are variable, but range up to at least +5, suggesting that the Archean mantle was heterogeneous and, in part, very depleted as far back as 3.4 to 3.5 Ga. This may be taken as evidence for separation of continental crust very early in Earth history. If these komatiite sources were allowed to evolve in a closed system, they would produce modern day reservoirs with much higher epsilon Nd values than is observed. This implies recycling of some sort of enriched material, perhaps subducted sediments, although other possibilities exist. Archean volcanics show lower Nb/Th than modern volcanics, suggesting a more primitive mantle source than that observed nowadays. However, Cretaceous komatiites from Gorgona island have similar Nb/Th to Archean volcanics, indicating either the Archean mantle source was indeed more primitive, or Archean magmas were derived from a deep ocean island source like that proposed for Gorgona.
Document ID
19880020821
Document Type
Conference Paper
Authors
Arndt, N. T. (Max-Planck-Inst. fuer Chemie Mainz, Germany)
Chauvel, C. (Max-Planck-Inst. fuer Chemie Mainz, Germany)
Jochum, K.-P. (Max-Planck-Inst. fuer Chemie Mainz, Germany)
Gruau, G. (Max-Planck-Inst. fuer Chemie Mainz, Germany)
Hofmann, A. W. (Max-Planck-Inst. fuer Chemie Mainz, Germany)
Date Acquired
September 5, 2013
Publication Date
January 1, 1988
Publication Information
Publication: Lunar and Planetary Inst., Workshop on the Growth of Continental Crust
Subject Category
GEOPHYSICS
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.
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