Silicate weathering in the Ganges alluvial plain

• DOI: 10.1016/j.epsl.2015.06.049
• Publication Date: 2015-07-16T15:30:58Z
• Authors: Patrick J. Frings; Wim Clymans; Guillaume Fontorbe; William Gray; Govind J. Chakrapani; Daniel J. Conley; Christina De La R...
• Keywords: Alluvial plain; Eluvium; Alluvial fan

The Ganges is one of the world's largest rivers and lies at heart a body literature that investigates interaction between mountain orogeny, weathering global climate change. Three regions can be recognised in basin, with Himalayan orogeny to north plateaus peninsular India south together delimiting alluvial plain. Despite constituting approximately 80% processes peninsula plain have received little attention. Here we present an analysis 51 water samples along transect plain, including all major tributaries. We focus on geochemistry silicon its isotopes. Area normalised dissolved Si yields are twice as high Himalaya origin than tributaries (82, 32 kmol SiO2 km−2 yr−1, respectively). Such fluxes not widely used rate indicators because large but variable fraction DSi mobilised during initial process retained secondary clay minerals. However, isotopic composition (expressed δ30Si) varies from +0.8‰ mainstem front +3.0‰ streams appears controlled by congruency, i.e. degree incorporation into phases. higher δ30Si values therefore reflect decreasing congruency lowland river catchments. This exploited quantify removal using Rayleigh isotope mass balance model, consequently derive silica mobilisation rates 200, 150 107 for Himalaya, respectively. Because non-Himalayan dominate catchment area, majority primary minerals occurs (41% 34%,