Enrichment characteristics of rare earth elements in the middle reaches sediments of the Yarlung Tsangpo River

As a vital component of the big river systems on the Tibetan Plateau, the Yarlung Tsangpo River (YTR) receives a large volume of weathered and eroded materials from various geological units including the Lhasa Block, Yarlung Tsangpo Suture Zone, and Tethyan Himalayas. The enrichment of rare earth elements (REEs) in its sediments is of significance for deciphering source to sink processes of plateau-derived river sediments and exploring REEs resources. In this study, the floodplain sediment and suspended particulate matter were collected from the middle reaches of the YTR mainstem and its main tributaries (Lhasa River, Nyang River, and Parlung Tsangpo River) in the north, and the REEs compositions of the detrital components of these sediments were systematically analyzed. The results show that the total content of REEs in the YTR sediments is generally higher than that of major rivers in the world, and exceptionally high in some tributaries. These river sediments exhibit pronounced negative Eu anomalies but no significant Ce anomalies, mainly inheriting the provenance characteristics of bedrocks such as the granite in the Lhasa Block, which has high content of REEs and obvious Eu anomalies. Furthermore, the significant correlation between contents of total REEs (∑REEs) and elements such as U, Zr, Th, P indicates that heavy minerals basically control the REE composition of detrital sediment. Combined with regional heavy mineral investigations, we infer that the heavy minerals such as apatite, zircon, and garnet are the main reasons for the abnormally high REE contents observed in these river sediments.