Limited Contribution of Preferential Dissolution to Radiogenic Uranium Isotope Disequilibrium Observed in Weathered Moraines.

Radiogenic uranium isotope disequilibrium (²³⁴U/²³⁸U) has been used to trace a variety of Earth surface processes, and is usually attributed to direct recoil of ²³⁴Th and preferential dissolution of radioactively damaged lattices at the mineral surface. However, the relative contribution of these two mechanisms in the natural environment remains unresolved, making it hard to use the extent of disequilibrium to quantify processes such as weathering. This study tests the contribution of preferential dissolution using well-characterized weathered moraines and river sediments from the southeastern Tibetan Plateau. The observations show that weathering of recent moraines where the contribution from direct recoil is negligible and is not associated with depletion of ²³⁴U at the mineral surface. It suggests a limited role for preferential dissolution in this setting. We attribute this lack of preferential dissolution to a near-to-equilibrium dissolution at the weathering interfaces, with little development of etch pits associated with radioactively damaged energetic sites. [ABSTRACT FROM AUTHOR]