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

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 up...

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Autores principales: Gallet, S., Jahn, B.-M., Van Vliet Lanoë, B., Dia, A., Rossello, E.
Formato: JOUR
Materias:
Geochemistry
Loess
Rb/Sr
Sm/Nd
Upper crust
continental crust
geochemistry
loess
upper crust
Acceso en línea:http://hdl.handle.net/20.500.12110/paper_0012821X_v156_n3-4_p157_Gallet
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Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA) de Universidad de Buenos Aires
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spelling todo:paper_0012821X_v156_n3-4_p157_Gallet2023-10-03T14:10:26Z Loess geochemistry and its implications for particle origin and composition of the upper continental crust Gallet, S. Jahn, B.-M. Van Vliet Lanoë, B. Dia, A. Rossello, E. Geochemistry Loess Rb/Sr Sm/Nd Upper crust continental crust geochemistry loess upper crust 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 Na2C/Al2O3 and K2O/Al2O3 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 (87Sr/86Sr = 0.706-0.709, ∈Nd(0) = -6 to - 1.5) from all other loess deposits (87Sr/86Sr = 0.712-0.730, ∈Nd(0) = -13 to -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 MT. 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. © 1998 Elsevier Science B.V. All rights reserved. JOUR info:eu-repo/semantics/openAccess http://creativecommons.org/licenses/by/2.5/ar http://hdl.handle.net/20.500.12110/paper_0012821X_v156_n3-4_p157_Gallet
institution Universidad de Buenos Aires
institution_str I-28
repository_str R-134
collection Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA)
topic Geochemistry
Loess
Rb/Sr
Sm/Nd
Upper crust
continental crust
geochemistry
loess
upper crust
spellingShingle Geochemistry
Loess
Rb/Sr
Sm/Nd
Upper crust
continental crust
geochemistry
loess
upper crust
Gallet, S.
Jahn, B.-M.
Van Vliet Lanoë, B.
Dia, A.
Rossello, E.
Loess geochemistry and its implications for particle origin and composition of the upper continental crust
topic_facet Geochemistry
Loess
Rb/Sr
Sm/Nd
Upper crust
continental crust
geochemistry
loess
upper crust
description 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 Na2C/Al2O3 and K2O/Al2O3 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 (87Sr/86Sr = 0.706-0.709, ∈Nd(0) = -6 to - 1.5) from all other loess deposits (87Sr/86Sr = 0.712-0.730, ∈Nd(0) = -13 to -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 MT. 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. © 1998 Elsevier Science B.V. All rights reserved.
format JOUR
author Gallet, S.
Jahn, B.-M.
Van Vliet Lanoë, B.
Dia, A.
Rossello, E.
author_facet Gallet, S.
Jahn, B.-M.
Van Vliet Lanoë, B.
Dia, A.
Rossello, E.
author_sort Gallet, S.
title Loess geochemistry and its implications for particle origin and composition of the upper continental crust
title_short Loess geochemistry and its implications for particle origin and composition of the upper continental crust
title_full Loess geochemistry and its implications for particle origin and composition of the upper continental crust
title_fullStr Loess geochemistry and its implications for particle origin and composition of the upper continental crust
title_full_unstemmed Loess geochemistry and its implications for particle origin and composition of the upper continental crust
title_sort loess geochemistry and its implications for particle origin and composition of the upper continental crust
url http://hdl.handle.net/20.500.12110/paper_0012821X_v156_n3-4_p157_Gallet
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