Geochemical composition of the last deglacial lacustrine sediments in East Tibet and implications for provenance, weathering, and earthquake events

Identifying and understanding the respective influence of climate and tectonic processes becomes a frontier topic in tectonically active mountain ranges. In the eastern Tibetan Plateau, earthquake occurred frequently and usually led to formation of many dammed lakes. In this study, a last deglacial section of lacustrine sediments at Xinmocun in eastern Tibet is selected for conventional X-ray fluorescence (XRF) and Scanning XRF (SXRF) elemental analysis. The high correlation of major and trace element abundances between the Xinmocun lacustrine samples and the loess-soil samples from the Chinese Loess Plateau (CLP) supports the previous view of the eolian origin of the Xinmocun lacustrine sediments. Analysis of major element abundances, ratios, and trace element ratios indicates that the dust provenance of the Xinmocun lacustrine sediments is different from that of the CLP, and is similar to that of the loess at Ganzi and Hongyuan nearby the study area. The significant variations of most geochemical elements and their close coupling with grain-size variations cannot be reasonably explained by the changes in transport dynamics of eolian dust, and is possibly caused by the intermittent changes in available dust provenance. Frequent earthquakes triggered abundant landslides and provided large amounts of dust for the study area. Accordingly, in the >16 μm fraction of the Xinmocun grain-size record, many element abundances and their ratios, such as SiO2/Al2O3, TiO2/Al2O3, CaO/Al2O3, Sr/Al2O3, Rb/Sr, and Na2O/Al2O3, can be regarded as sensitive indicators of earthquake events in the tectonically active regions. SXRF measurements at the U-channel surface can provide some cost-effective indicators of seismic events, such as Si/Al, Ti/Al, Ca/Al, Sr/Al, Zr/Rb, and Rb/Sr. Significant variations in most element abundances and their ratios of the Xinmocun lacustrine sediments correlate closely with those of its grain-size record. They all show no increasing or decreasing trends with time. These suggest that tectonic activities characterized by seismic events possibly had a major role on the landscape erosion in the eastern Tibetan Plateau, while the climatic influence seems minor.