Magnetic Properties Of Weathering Laterite Derived From Basalt,Panan,Zhejiang,and Its Responses To Soil-forming Processes

Basaltic weathered laterite is a typical soil of parent material development,which is distributed in all tropical and subtropical regions of China.The process of weathering and the changes in the physical and chemical properties of the process are unique,and the study of the soil is very important to know the red soil of the southern bedrock.The environmental magnetic is widely used to study the characteristics and processes of soil formation,development and evolution.This paper took basalt weathered laterite section?XZ section?of Panan county,Zhejiang province as the research object.The magnetic properties and its influencing factors of basalt weathered laterite are studied by using environmental magnetism,combining with geochemistry,diffuse reflection spectrum,particle size,color and organic matter,etc.The relationship between magnetic properties and soil-forming process is discussed,and the feasibility of studying the degree of weathering of bedrock weathering crust soil by means of magnetism is discussed.The main conclusions are as follows.From the bottom of the section to the top,the soil magnetization first decreases and then increases,and the soil magnetism in the upper part of the section reaches the highest.Ferrous magnetic minerals?magnetite,titanomagnetite,etc.?dominate the magnetic section,at the same time,incomplete antiferromagnetic minerals?hematite,goethite?contribute.With the depth of the soil becomes shallow,the magnetic particles tend to become thinner,from PSD-MD particles to SP-SD magnetic mineral particles.The particle size composition is dominated by clayey silt,and the content of clay and sand decreases with the decrease of depth,whereas the silt and average particle size are opposite.Soil color is shown as,high brightness,high yellowness and low redness.Organic matter content is relatively low,the increased organic matter content at the top may be related to plant roots and human activities.The chemical elements in the section are mainly Si,Al and Fe,while the other elements is very low.The change of soil weathering degree has an influence on the leaching rate of each element.There is a correlation between element content and soil magnetic minerals.Metallic elements such as Fe and Ti are mainly concentrated in soil magnetic minerals in the form of primary minerals such as magnetite and titanomagnetite.The degree of soil weathering as reflected by chemical weathering indexes such as CIA,Sa,R,Saf and Ba are not in accordance with the weathering characteristics of the laterite section of the mother material development,indicating that these indexes are difficult to accurately characterize the weathering process of the soil of weatherin laterite derived from basalt in Panan,Zhejiang.The mother material is the main factor affecting the magnetic properties of the section,which determines that the background of the magnetic minerals in the section is ferrite magnetite.Climate,biology,soil formation time and particle size all have different effects on the type,content and particle size of soil magnetic minerals.In addition,the chromaticity index can reflect the soil magnetic mineral type to a certain extent.The magnetic properties of XZ section soil reflect the soil-forming process of basaltic weathered laterite.In the early stage of soil formation,the soil was in the state of semi-weathering or weak weathering,and the magnetism of the soil was high,mainly composed of primary MD ferromagnetic minerals?magnetite,titanomagnetite?;With the enhancement of weathering into soil,the primary ferromagnetic minerals in the soil gradually oxidize into incomplete anti-ferromagnetic minerals?hematite,goethite,etc.?,the soil magnetism decreases,the SP-SD magnetic particles increase,and the magnetic particles become fine.When the soil enters the stage of strong weathering,the primary ferromagnetic minerals are further reduced,while the anti-ferromagnetic minerals still show a certain high value.At the same time,a large number of secondary ferromagnetic minerals?magnetite?of fine particles are gradually generated,the soil magnetization rate continues to increase,and the magnetic particles of SP-SD are further increased.The magnetic properties can reflect the soil-forming mechanism of basalt weathered laterite.Environmental magnetism can be used as an important means to study the development of laterite soil in south China especially in subtropical weathered crust.The ratio parameters ?_ARM/SIRM and frequency susceptibility ?_fd%can reflect the development degree of this type of soil by the change of magnetic mineral content of fine particles.