wAbstract
@This study presents lithium isotope and elemental data for the
dissolved phase and suspended and bedload sediments of the major
Icelandic rivers. For the dissolved phase, Β7Li values
range between 10.1ρ and 23.8ρ, while river sediments display lower
and much more homogeneous values (Β7Li = 3.1ρ-4.8ρ),
close to the composition of unweathered Mid-Ocean Ridge Basalt
(MORB). High Β7Li values are associated with high K/Li,
Na/Li and Mg/Li ratios, in waters draining mainly old and weathered
basalt catchments, whereas low Β7Li rivers are located
in younger parts of the island. Simple mixing between precipitation,
Li-rich hydrothermal springs and basalt weathering is unable to
explain the entire range of Β7Li values. Instead, a
simple model of Li uptake by secondary minerals, associated with
clay-water Li isotope fractionation (’7Li ranging from
-1ρ to -7.5ρ) can explain both water and sediment Β7Li
values. A negative correlation is observed between basalt chemical
erosion rates and Β7Li measured in Icelandic rivers,
and an empirical law is inferred. Comparison with literature data
suggests that this relationship may be applicable at a more global
scale, and, if confirmed, could be of particular use for estimating
the evolution of continental weathering preserved in marine sedimentary
records. However, more data are now needed for rivers draining
silicates typical of the continental crust, in order to refine
large scale modelling.
Keywords: Li isotopes; basalt; silicate weathering; erosion; riversx
1. Introduction
2. Sampling area
3. Analytical procedure
@3.1. Li contents
@3.2. Li isotopes
4. Results
@4.1. Li contents
@4.2. Li isotopes
5. Discussion
@5.1. Sources of dissolved Li
@5.2. Assessing the link between riverine Β7Li and
silicate erosion rates
@5.3. Modelling clay-water Li isotope fractionation
6. Summary and conclusion
Acknowledgements
References