Loess geochemistry and its implications for particle origin and composition of the upper continental crust

Loess geochemistry and its implications for particle origin and composition of the upper... Chemical and Nd Sr isotopic compositions of loess samples from Argentina, Europe and Spitsbergen were analyzed to examine the nature of source terrains, the origin of silt-size particles and the suitability of using loess as starting material for estimating the average chemical composition of the upper continental crust. From the relations between Na 2 O/Al 2 O 3 and K/ 2 O/Al 2 O 3 ratios and CIA values (chemical index of alteration), the loess protoliths must have undergone previous sedimentary differentiation and subjected to moderate chemical weathering. REE patterns are remarkably uniform with (La/Yb) N ≈ 10 , which is characteristic of the upper continental crust (UCC). Negative Eu anomalies, expressed in Eu/Eu * ratios, vary from 0.65 for European loess to 0.8 for Pampean loess from Argentina. All loess deposits have nearly constant La/Th or Th/U ratios, which are very similar to those of the average UCC or post-Archean shales. These ratios are not fractionated in size-fractions relative to the whole-rock values. Nd and Sr isotopic compositions clearly distinguish Argentinean loess ( 87 Sr 86 Sr = 0.706–0.709, ε Nd (0) = −6to−1.5 ) from all other loess deposits ( 87 Sr 86 Sr = 0.712–0.730, ε Nd (0) = −13to−8 ). The REE and isotopic results clearly indicate a significant contribution of young Andean volcanics to the Pampean loess deposits, whereas multi-recycled and well-mixed ancient sediments are principal sources for the other deposits. The present results reinforce the earlier conclusion reached by S.R. Taylor, S.M. McLennan and M.T. McCulloch (Geochemistry of loess, continental crustal composition and crustal model ages, Geochim. Cosmochim. Acta 47 (1983) 1897–1905) that the average chemical composition of UCC can be obtained from eolian deposits as well as from fine-grained clastic sediments. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Earth and Planetary Science Letters Elsevier

Loess geochemistry and its implications for particle origin and composition of the upper continental crust

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Publisher
Elsevier
Copyright
Copyright © 1998 Elsevier Science B.V. All rights reserved
ISSN
0012-821X
eISSN
1385-013X
DOI
10.1016/S0012-821X(97)00218-5
Publisher site
See Article on Publisher Site

Abstract

Chemical and Nd Sr isotopic compositions of loess samples from Argentina, Europe and Spitsbergen were analyzed to examine the nature of source terrains, the origin of silt-size particles and the suitability of using loess as starting material for estimating the average chemical composition of the upper continental crust. From the relations between Na 2 O/Al 2 O 3 and K/ 2 O/Al 2 O 3 ratios and CIA values (chemical index of alteration), the loess protoliths must have undergone previous sedimentary differentiation and subjected to moderate chemical weathering. REE patterns are remarkably uniform with (La/Yb) N ≈ 10 , which is characteristic of the upper continental crust (UCC). Negative Eu anomalies, expressed in Eu/Eu * ratios, vary from 0.65 for European loess to 0.8 for Pampean loess from Argentina. All loess deposits have nearly constant La/Th or Th/U ratios, which are very similar to those of the average UCC or post-Archean shales. These ratios are not fractionated in size-fractions relative to the whole-rock values. Nd and Sr isotopic compositions clearly distinguish Argentinean loess ( 87 Sr 86 Sr = 0.706–0.709, ε Nd (0) = −6to−1.5 ) from all other loess deposits ( 87 Sr 86 Sr = 0.712–0.730, ε Nd (0) = −13to−8 ). The REE and isotopic results clearly indicate a significant contribution of young Andean volcanics to the Pampean loess deposits, whereas multi-recycled and well-mixed ancient sediments are principal sources for the other deposits. The present results reinforce the earlier conclusion reached by S.R. Taylor, S.M. McLennan and M.T. McCulloch (Geochemistry of loess, continental crustal composition and crustal model ages, Geochim. Cosmochim. Acta 47 (1983) 1897–1905) that the average chemical composition of UCC can be obtained from eolian deposits as well as from fine-grained clastic sediments.

Journal

Earth and Planetary Science LettersElsevier

Published: Mar 30, 1998

References

  • Plio-Pleistocene megacycles: record of climate and tectonics
    Kukla, G.; Cilek, V.
  • Aeolian sediments in the Quaternary record: an introduction
    Derbyshire, E.
  • Making the material: the formation of silt-sized primary mineral particles for loess deposits
    Smalley, I.
  • Stratigraphy, geochemistry, and thermoluminescence ages of Lower Mississippi valley loess
    Pye, K.; Jonhson, R.
  • Patterns of elemental transport in the bedload of the Meurthe River (NE France)
    Albarède, F.; Semhi, K.
  • The nature, origin and accumulation of loess
    Pye, K.
  • Evolution of the Kaapvaal Craton as viewed from geochemical and Sm Nd isotopic analyses of intracratonic pelites
    Jahn, B.M.; Condie, K.C.

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