Study On Hf Isotopic Composition Of Jingchuan Red Clay From The Loess Plateau

The Quaternary Loess Plateau and the Tertiary Red Clay,as terrestrial sediments,contain information on the late Cenozoic climate change and plateau uplift.For the loess in the Loess Plateau,the researchers have achieved good results in the early stage,and think that red clay and loess are all caused by wind.In this study,Nd-Hf isotopes were used to study the isotope characteristics of different sizes of red clay in the Jingchuan section of the Loess Plateau,and to determine the differences in material sources and their contribution to the“seawater array”and the North Pacific dust.Based on the Nd-Hf isotope characteristics,the following conclusions are obtained:（1）The Hf isotope of Jingchuan Red Clay 28～45μm and 5～28μm is consistent,indicating that the source is the same;zircon in red clay is mainly present in components>45μm,so there is no zircon effect in components between 28-45μm and 5-28μm.The<5μm component is mainly a distant source,which may be from the Gobi Altai Mountains.（2）Compared with the Hf isotopes of Jingchuan and Lingtai red clay（28～45μm）,Jingchuan red clay is relatively stable.The large fluctuations of Hf isotopes in Qin’an and Lingtai red clays indicate that the spatial and temporal factors have a significant effect on Hf isotopes,and the mechanism of change in Hf isotopes of red clays in the Loess Plateau is complex.（3）The characteristics of the Nd-Hf isotope also indicate that the source materials of the components of 28～45μm and 5-28μm are basically the same,coming from desert regions such as the Badain Jaran Desert and Tengger Desert on the loess plateau,and the 5～28μm component is the main particle size of red clay,and its transmission distance is relatively long,which may come from the fine-grained material mainly in Badain Jaran Desert and Tengger Desert.The 28～45μm component is a near-source,which may come from the Tengger Desert,which is near-source windward on the Loess Plateau.（4）The different granularity components of Jingchuan Red Clay in theε_Nd-ε_Hf isotope diagram,5～28μm and 28～45μm are distributed on the“zircon-free array”,indicating that the zircon content in these two grades is very small,indicating that the Nd-Hf decoupling contributes to the zircon effect.The reason for the increase in the Hf value of the<5μm component is firstly the inconsistency in the source,and secondly,the weathering has also affected the decoupling of its Nd-Hf isotope.（5）By analyzing the Nd-Hf isotope composition of components less than 5μm,it is believed that the Jingchuan red clay and the North Pacific deep-sea dust material have similar material sources,that is,the desert adjacent to the Badain Jaran Desert,the Taklimakan Desert,and the plateau area in northern Mongolia indicate that the Gobi Desert in northwestern China has a certain contribution to the source of dust in the North Pacific.