『Abstract
　U-series disequilibria have been measured by TIMS ad MC-ICP-MS in dissolved phases and suspended sediments of the main basaltic rivers from the Deccan Trap region (India). For dissolved phases (²³⁴U/²³⁸U), (²³⁰Th/²³⁸U), and (²²⁶Ra/²³⁸U) range between 1.11 and 1.28, between 0.03×10^-2 and 1.35×10^-2, and between 0.02 and 0.16 respectively. For suspended particles, (²³⁴U/²³⁸U), (²³⁰Th/²³⁸U), and (²²⁶Ra/²³⁸U) range from 0.95 to 1.1, from 1.23 to 1.59 and from 0.1 to 0.47 respectively. ²³⁰Th-²³⁸U and ²³⁴U-²³⁸U systems show direct links with indices of weathering. The data also indicate possible redistributions between the solid and aqueous phases and indicate that erosion processes do not presently operate at steady-state because present-day physical erosion rates are higher than expected (100-400 mm/ka versus 40 mm/ka for a steady-state process) for the Narmada and the Tapti basins. Models assuming either discrete or continuous particle leaching yield timescales for chemical erosion of 40-90 ka. In contrast with basins located i Northern latitudes, erosion in the Deccan basins does not appear to have been significantly disturbed during the last glaciation.
　234U-²³⁸U disequilibria in the dissolved phase of large rivers world-wide are also explored and two key factors are highlighted in this study: the dissolution of carbonates, releasing dissolved U at secular equilibrium and, the silicate weathering rate estimated at the scale of the watershed. In particular, a positive correlation is found between dissolved (²³⁴U/²³⁸U) and basaltic weathering rates for the Deccan that could reflect a key role of physical erosion since, for silicate monolithological basins, chemical erosion rates are primarily controlled by physical erosion rates. For basins with mixed lithology, dissolved organic matter also plays a key role in the preferential release of ²³⁴U from silicate minerals. (²³⁴U/²³⁸U) ratios in rivers therefore reflect a mixture between U released by carbonate dissolution and ²³⁴U preferentially released from silicate minerals located i high physical erosion and peat areas.

Keywords: U-series disequilibria; Basalt weathering; Deccan; Erosion rate; Timescale; Leaching model』

1. Introduction
2. Sampling location
3. Sampling and analytical methods
4. Results
　4.1. Suspended loads
　4.2. Dissolved phases
　4.3. Colloidal phase (5 kDa to 0.2μm)
5. Relative mobility of ²³⁸U, ²³⁴U, ²³⁰Th, and ²²⁶Ra during weathering
6. A steady-state model of erosion
7. Models for constraining weathering timescales
　7.1. Discrete leaching model
　7.2. Steady-state open system models
　　7.2.1. Continuous leaching model
　　7.2.2. Model with leaching and adsorption
8. General constraints on ²³⁴U-²³⁸U fractionation in rivers
　8.1. Lithological control on ²³⁴U-²³⁸U fractionation
　8.2. Role of dissolved organic carbon
9. Conclusions
Acknowledgements
Appendix A
References