Journal
CHEMICAL GEOLOGY
Volume 203, Issue 1-2, Pages 75-90Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.chemgeo.2003.09.002
Keywords
lead isotopes; river sediments; Upper Continental Crust
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The lead isotopic composition of river sediments is reported in the present work for the Earth's major river basins, from old cratonic to young orogenic areas and from subarctic to tropical climates. Sediment samples from these large river basins provide a useful tool to calculate the average upper crustal composition because they are large-scale integrated samples of the weathering products of the,present-day Upper Continental Crust (UCC). Two different and complementary calculations were done to estimate the average lead isotopic composition of the UCC. The first, based on the flux weighted average of particulate lead delivered by the rivers, gave values of 19.07, 15.74 and 39.35 for Pb-206/Pb-204, Pb-207/Pb-204 and Pb-208/Pb-204 ratios, respectively. To avoid over-estimating the contribution of orogenic areas, which produces a bias (because the flux of particulate lead depends strongly on the physical erosion rate), a second calculation was done by averaging with drainage areas of each river basin. This gave values of 18.93, 15.71 and 39.03 for Pb-206/Pb-204, Pb-207/Pb-204 and Pb-208/Pb-204 ratios, respectively. These direct calculations of the lead isotopic composition of the UCC are similar and are in agreement with previous estimates made using an indirect approach. (C) 2003 Elsevier B.V All rights reserved.
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