The relationship between riverine U-series disequilibria and erosion rates in a basaltic terrain

N. Vigier*, K. W. Burton, S. R. Gislason, N. W. Rogers, S. Duchene, L. Thomas, E. Hodge, B. Schaefer

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

71 Citations (Scopus)

Abstract

U-series isotopes have been measured in the dissolved phase, suspended load and bedload of the main rivers draining basaltic catchments in Iceland. For the dissolved phase, (234U/238U) and (238U/230Th) range between 1.08 and 2.2, and 7.4 and 516, respectively. For the suspended load and bedload, (234U/238U) and (238U/230Th) range from 0.97 to 1.09 and from 0.93 to 1.05, respectively. Chemical erosion rates, calculated from dissolved major elements, range between 13 and 333 t km- 2 yr- 1. Physical erosion rates have also been estimated, from existing data, and range between 21 and 4864 t/km2/yr, with an average of 519 t km- 2 yr- 1. U-series disequilibria indicate that weathering in Iceland operates at close to steady-state conditions. A model of continuous weathering indicates a maximum weathering timescale of 10 kyr, with an average rate of uranium release into water of 1.6 · 10- 4 yr- 1, which is significant when compared to granitic terrains located at similar latitudes and to tropical basaltic terrains. All river waters display (234U/238U) greater than secular equilibrium, consistent with the effects of alpha-recoil. The same dissolved phase (234U/238U) exhibit a negative trend with physical erosion rates, explained by the dominant effect of close-to-congruent chemical weathering of hyaloclastites in the younger basaltic terrains. Therefore, chemical erosion rate and mineral weathering susceptibility play a major role in determining 234U-238U disequilibria in basaltic river waters. Comparison of global data for river basins in which weathering was recently strongly limited indicates a negative correlation between silicate weathering rates estimated with major elements and the age of weathering estimated with U-series disequilibria. This strongly suggests a key role of time and soil thickness on the chemical erosion of silicates.

Original languageEnglish
Pages (from-to)258-273
Number of pages16
JournalEarth and Planetary Science Letters
Volume249
Issue number3-4
DOIs
Publication statusPublished - 30 Sep 2006
Externally publishedYes

Keywords

  • basalt
  • erosion
  • Iceland
  • steady-state
  • U-series disequilibria
  • weathering timescale

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