A new estimate for the composition of weathered young upper continental crust from alluvial sediments, Queensland, Australia

Kamber, BS, Greig, A and Collerson, KD (2005) A new estimate for the composition of weathered young upper continental crust from alluvial sediments, Queensland, Australia. Geochimica Et Cosmochimica Acta, 69 4: 1041-1058.


Author(s) Kamber, BS
Greig, A
Collerson, KD
Title A new estimate for the composition of weathered young upper continental crust from alluvial sediments, Queensland, Australia
Journal name Geochimica Et Cosmochimica Acta
Publication date 2005
Sub-type Article
Volume number 69
Issue number 4
ISBN 0016-7037
ISSN 0016-7037
Start page 1041
End page 1058
Total pages 18
Place of publication Oxford, England
Publisher Pergamon-Elsevier Science Ltd
Collection year 2005
Subject C1
260301 Geochronology and Isotope Geochemistry
780104 Earth sciences
Abstract We present new major element, trace element and Nd-isotope data for 30 alluvial sediments collected from 25 rivers in Queensland, E Australia. Samples were chosen to represent drainage from the region's most important lithologies, including Tertiary intraplate volcanic rocks, a Cretaceous igneous province (and sedimentary rocks derived thereof) as well as Proterozoic blocks. In most chemical and isotopic aspects, the alluvial sediments represent binary or ternary mixing relationships, with absolute abundances implied to reflect the proportion of lithologies in the catchments. When averaged, the studied sediments differ from other proxies of upper continental crust (UCC) mainly in their relative middle rare earth element enrichment (including an elevated Sm/Nd ratio), higher relative Eu abundance and higher Nb/Ta ratio. These features are inherited from eroded Tertiary intraplate basalts, which commonly form topographic highs in the studied region. Despite the high degree of weathering strong to excellent coherence between similarly incompatible elements is found for all samples. From this coherence, we suggest revisions of the following upper crustal element ratios: Y/Ho = 26.2, Yb/Tm = 6.37, Th/W = 7.14, Th/Tl = 24 and Zr/Hf = 36.9. Lithium, Rb, Cs and Be contents do not seem depleted relative to UCC, which may reflect paucity of K-feldspar in the eroded catchments. Nickel, Cr, Pb, Cu and Zn concentrations are elevated in polluted rivers surrounding the state capital. River sediments in the Proterozoic Georgetown Inlier are elevated in Pb, Cu and Zn but this could be a natural phenomenon reflecting abundant sulphide mineralisation in the area. Except for relative Sr concentrations, which broadly anticorrelate with mean annual rainfall in catchments, there is no obvious relationship between the extent of weathering and climate types, which range from and to tropical. The most likely explanation for this observation is that the weathering profiles in many catchments are several Myr old, established during the much wetter Miocene period. The studied sediment compositions (excluding those from the Proterozoic catchments) are used to propose a new trace element normalisation termed MUQ (MUd from Queensland), which serves as an alternative to UCC proxies derived from sedimentary rocks. Copyright (C) 2005 Elsevier Ltd
Keyword(s) Geochemistry & Geophysics
Chemical-composition
Refined Solution
Terrestrial Pb
Core Formation
Evolution
Petrogenesis
Elements
History
Origin
Mantle
 
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