Geochemical Process Of Rock Weathering Under Wind Erosion At The Northern Piedmont Of Yinshan Mountain

The process of rock weathering and soil formation is the main form of continental surface layer interaction which is concerned by surface earth system science and is an important link of element geochemical cycle.Its essence is the process of element transfer and redistribution.Under the joint influence of the rock itself and the external environment,the geochemical behavior of the elements in the profile will show different evolution characteristics in the process of rock weathering into soil.It is of great significance to study the mechanism of soil development and infer the law of environmental evolution in arid and windy areas to study the migration of elements in the process of rock weathering and soil formation under the action of wind.The Yinshan Mountains,which run across the middle of Inner Mongolia in northern China,belong to the semiarid zone of the middle temperate zone and are strongly influenced by the wind.The main part of the mountain range is composed of Archean metamorphic rock series and magmatic rocks of different ages.Under the influence of climate,geomorphology,lithology and other factors,these rocks have formed different rock weathering profiles,which provides a good research material for exploring the process and law of rock weathering and soil formation under the influence of wind power in mountainous and hilly areas.In this paper,the weathering profile of rocks in the north piedmont of Yinshan Mountain in central Inner Mongolia is taken as the research object.Through analyzing the lithologic characteristics of parent rocks in different profiles and the distribution and evolution characteristics of major elements and trace elements in the profiles,the change rule of these elements is discussed,and the evolution process of elements in the weathering process of rocks in the north piedmont of Yinshan under the action of wind force is discussed.Fifteen rock profiles with a total of 6 different lithologies distributed in different geomorphic locations were selected in the hilly region at the northern piedmont of Yinshan Mountains,and samples of soil layer,semi-weathered layer and bedrock layer of each profile were collected respectively.The elements of the 45 samples were tested,and 15 bedrock samples were identified under the microscope.In addition,the grain sizes of 15 soil samples were tested.Based on this,the geochemical properties and evolution characteristics of the elements in the profiles were analyzed.(1)Among the 15 rock weathering profiles in the study area,except for a few samples,CIA values are all lower than 65,indicating a low degree of chemical weathering.The chemical weathering degree of soil layer is less than that of semi-weathered layer due to the influence of wind erosion on some rock weathering profiles.(2)Compared with the reference element Th,the major elements in each section all have different degrees of leaching loss.Different contents of major elements lead to different migration characteristics of some elements in different lithologic weathering profiles.For example,the contents of K and Na in granite are higher,and the leaching rate during weathering is obviously higher than that of basalt.The contents of Ca and Ti in the basalt are high and weathering is more likely to occur.The contents of Ca and Ti in the soil layer drop sharply under wind erosion.(3)Wind force and geomorphic factors are the most important factors affecting rock weathering in the study area.The terrain in the north foothills of Yinshan Mountain is high in the south and low in the north,and the wind direction is mainly north and northwest.In the west part of the study area,the geomorphology type is low mountain and hilly,which is less affected by the wind effect and only exists the exchange of fine particles.The central geomorphologic type of the study area is Zhongshan,which is less affected by wind force and is dominated by the migration of foreign materials.The eastern part of the study area belongs to the basalt platform,and the terrain is relatively flat and open,which is more affected by the wind effect.The soil layer is subjected to strong wind erosion,and the chemical weathering degree of the soil layer is less than that of the semi-weathered layer.