Mobility of U-series nuclides during basalt weathering: An example from the Deccan Traps (India)

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 in high physical erosion and peat areas.