Late Mio-Pliocene landscape evolution around the Chaka Basin in the NE Tibetan Plateau: Insights from geochemical perspectives

Abstract

The present NE Tibetan Plateau is characterized by a rugged mountain range and basin landforms. Knowledge of the landscape evolution, as recorded by basin sediments, will help to understand the growth history of the NE Tibetan Plateau. Our present contribution targeted the Neogene Chaka Basin south of the Qinghai Nan Shan and reports 40 geochemical Sr, Nd, trace element, and rare earth element (REE) results of the sediments. Values of εNd vary from −15.6 to −11.6 for all samples, but εNd is higher for samples younger than 5.5 Ma. 87Sr/86Sr ratios are all between 0.71441 and 0.71844, with the variation becoming less after 4.5 Ma. Little variation in the SrNd isotopes and in the REE trend indicates that the source regions have very similar geochemical features. The contribution of aeolian loess into the basin sediments after ~3.5 Ma is also speculated from the trace element and REE results. These geochemical results reveal a change in the source region to the Qinghai Nan Shan around 4.5–5.5 Ma, which is consistent with previous lithoface evidence. Since ~3.5 Ma, landscape and topographic relief were further developed; thus, aeolian loess was deposited onto the fluvial fans south of the Qinghai Nan Shan, while global cooling and aridification began to dominate. Collectively, our present geochemical study of the Chaka Basin sediments reveals stages of landscape evolution in NE Tibet since the late Miocene.