Controls on the distribution and fractionation of rare earth elements in recent sediments from the rivers along the west coast of India

The sediments of 90 rivers from five states along the west coast of India were analysed for their chemistry. The major element ratios of sediments suggest lateritic soils in Kerala, lateritic soils admixed with particulates weathered from Fe–Mn ores in Karnataka and Goa and, non-lateritic, chemically weathered soils in Maharashtra and Gujarat. The sediments from the Archean-Proterozoic (A-P) terrain are strongly weathered, while those from Deccan Traps (DT) terrain are intermediate to strongly weathered. The mean total rare earth elements content (∑REE) of sediments from the rivers of Kerala is much higher than in other states. ∑REE shows strong positive correlation with oxides of Fe, Mn and P from A-P terrain and Al, Fe and Ti from DT terrain and, strong positive correlation with heavy metals (Zr, U, Hf and Th) from both terrains. The low Sm/Nd and Y/Ho ratios corresponding to high chemical index of alteration (CIA) and, high ratios corresponding to high and low CIA are typical. The Post-Archean average Australian shale (PAAS)-normalized REE shows LREE- and MREE-enriched patterns in the sediments of Kerala and MREE- and HREE-enriched patterns in other sediments. Distinct positive Ce anomaly occurs in the sediments of Karnataka, Goa and south Maharashtra and, weak positive to weak negative Ce anomaly in the sediments of other states. The Eu anomaly is negative in the silts of south Kerala and positive in all other sediments. The primary sources for REEs are adsorbed REEs onto secondary mineral phases and clay minerals and, heavy minerals. The change in REE patterns is primarily related to the source rock composition. Fractionation of REEs is related to the intensity of chemical weathering, supply of REE and transport processes. The average REE composition of river sediments from peninsular India is more mafic than in UCC and World Rivers Average Clay.