Removing the “heavy mineral effect” to obtain a new Pb isotopic value for the upper crust
Article first published online: 13 SEP 2013
©2013. American Geophysical Union. All Rights Reserved.
Geochemistry, Geophysics, Geosystems
Volume 14, Issue 9, pages 3324–3333, September 2013
How to Cite
2013), Removing the “heavy mineral effect” to obtain a new Pb isotopic value for the upper crust, Geochem. Geophys. Geosyst., 14, 3324–3333, doi:10.1002/ggge.20219., , , , and (
- Issue published online: 24 OCT 2013
- Article first published online: 13 SEP 2013
- Accepted manuscript online: 10 JUL 2013 05:55AM EST
- Manuscript Accepted: 2 JUL 2013
- Manuscript Revised: 1 JUL 2013
- Manuscript Received: 20 FEB 2013
- Lead isotopes;
- continental crust
 Based on the concept that sedimentary processes average large areas of exposed crust, sediment data have been widely used to estimate the average Pb isotopic composition of the upper continental crust. However, the possible effects of mineral sorting processes on sediment Pb isotopes have never been fully investigated. Here, we report Pb isotopic compositions of Himalayan river sediments as well as those of several grain-size fractions and mineral separates. We demonstrate that Pb isotopes of both bed loads and suspended loads are biased toward more radiogenic values than their source rocks due to a “heavy mineral effect” caused by mineral sorting during fluvial transport on continents. The sparse zircons, monazites and allanites present in all samples (<1 wt%), including suspended loads, generate a Pb isotopic variability as large as that observed in the Earth's mantle. After correction of this effect, we propose an average value for the composition of the upper Himalayan crust together with a new Pb isotopic value for the Earth's upper continental crust. We conclude that mineralogical effects must be evaluated carefully before using Pb isotopes of sediments as provenance and anthropogenic tracers.