『Abstract
　To quantify rates of rind formation on weathering clasts under tropical and humid and to determine factors that control weathering reactions, we analyzed Uranium series isotope compositions and trace element concentrations in a basaltic andesite weathering clast collected from Basse-Terre Island in Guadeloupe. U, Th, and Ti elemental profiles reveal that Th and Ti behave conservatively during rind formation, but that U is added from an external source to the rind. In the rind, weathering reactions include dissolution of primary minerals such as pyroxene, plagioclase, and glass matrix, as well as formation of Fe oxyhydroxides, gibbsite and minor kaolinite. Rare earth element (REE) profiles reveal a significant Eu negative anomaly formed during clast weathering, consistent with plagioclase dissolution. Significant porosity forms in the rind mostly due to plagioclase dissolution. The new porosity is inferred to allow influx of soil water carrying externally derived, dissolved U. Due to this influx, U precipitates along with newly formed clay minerals and oxyhydroxides in the rind. The conservative behavior of Th and the continuous addition of U into the rind adequately explain the observed systematic trends of (²³⁸U/²³²Th) and (²³⁰Th/²³²Th) activity ratios in the rind. Rind formation rates, determined from the measured U-series activity ratios with an open system U addition model, increase by a factor of 〜1.3 (0.18-0.24 mm/kyr) from a low curvature to a high curvature section (0.018-0.12 mm^-1) of the core-rind boundary, revealing that curvature affects rates of rind formation as expected for diffusion-limited rind formation. U-series geochronometry thus provides the first direct evidence that the curvature of the interface controls the rate of regolith formation at the clast scale. The weathering rates determined at the clast scale can be reconciled with the weathering rates determined at the watershed or soil profile scale if surface roughness equals values of approximately 1399-2200.』

1. Introduction
2. Geological setting
3. Methods
　3.1. Field sampling and clast preparation
　3.2. Analytical methods for U-Th isotopes
　3.3. Analytical methods for trace elements
4. Results
　4.1. Major and trace element profiles
　4.2. U and Th activity ratios
5. Discussion
　5.1. Mobility of elements during rind formation
　5.2. ²³⁸U-²³⁴U-²³⁰Th disequilibrium during rind formation
　5.3. Rind formation rates calculated from ²³⁸U-²³⁴U-²³⁰Th disequilibria
　5.4. Control of curvature on rind formation rates
　5.5. Comparison of chemical weathering rates to published estimates
6. Conclusions
Acknowledgements
Appendix A. Solving the continuous U addition model
References