The Element Geochemical Characteristics Of Weathering And Pedogenic Process Of Basalt In Eastern Jilin Province

Basalt is widely distributed in China,ranging from the Greater Khingan Range in the northeast to Hainan Island in the southern tip.The research area is located in the eastern part of Jilin Province and involves areas such as Jiaohe,Baishan and Tonghua.It is mainly controlled by the east-west,north-east,and north-north-east tectonic belts.In the Cenozoic era,especially in the Neogene and Quaternary,multi-phase and large-scale volcanic activities took place.Thus the largest Quaternary basalt platform in China formed,which has a total area of more than 10,000 square kilometers.This article starts from the perspective of basalt weathering in the eastern part of Jilin Province in order to provide some new information for the study of basalt in this area.Select representative sampling points from 173 rock-soil sampling points.Collect parent rock?R?-parent material layer?C?-deposition layer?B?-leaching filter?A?-decay layer?O?samples in vertical profile.A total of 4 groups were used to analyze and test the contents of their major elements,rare earth elements and trace elements.The characteristics of major elements indicate that the lithologies of R65,R90,and R121 in the eight soil-rock combination samples are coarse-faced basalts,the lithologies of R44,R74,R120,R122,and R145 are basalts;The lithology of SR21 is basalt,and the parent rock samples SR79,SR45 and SR119 in the remaining three sets of soil profiles are basalt basalts.In the major elements of the soil-rock combination samples,the content of SiO₂ in the soil samples increase relative to that of the parent rock samples,and the contents of Al₂O₃,TFe₂O₃,CaO,MgO,Na₂O,TiO₂,and P₂O₅ all decrease relatively,while the K₂O and The MnO content rises and falls.In the four soil profile samples,the content of SiO₂ is relatively enriched in the evolution process of R?parent rock??A?leaching layer?,and relatively loss in the evolution process of A?leaching layer??O?humic layer?;Except for some samples,the contents of Al₂O₃,TFe₂O₃,CaO,MgO,Na₂O,K₂O,TiO₂,and P₂O₅ are relatively deficient in the evolution process of R?parent rock??O?humic layer?;while the MnO rule is not obvious,and the total content changs little.The characteristics of rare earth elements indicate that in the three soil-rock samples,the differences between light and heavy rare earths are obvious,and the lighter rare earth is relatively enriched in the negative slope right tilt pattern.Eu and Ce do not show obvious abnormalities.In the four soil samples and parent rock samples,the differences between light and heavy rare earths are obvious,and the lighter rare earth is relatively enriched in the negative slope right tilt pattern.And all samples have no Ce anomaly,while the SS21 soil samples show weak negative anomalies.The soil samples in the SS45 soil samples show weak negative anomalies in the soil samples of layers A and C,and strong negative Eu anomaly in the soil samples of layer B.There is a significant negative Eu anomaly in the SS91 soil sample.The trace element content indicates that the contents of Ba,Nb,Ni,Sr,V,and Zn in the parent rock sample of the 8 pairs of soil-rock combination samples are higher than those in the soil sample.It indicates that these elements suffer leaching loss in the process of weathering.And for elements such as Cr,Pb,Be,Rb,Y,Li,U,Th,As,Sb,and Hg,the content of the parent rock sample is lower than that of the soil sample,indicating that these elements have been relatively enriched during weathering.The contents of Co,Nb,Sr,and Sb in the corresponding parent rock samples of the four soil profiles are significantly higher than the upper continental crust elemental abundances?UCC?.Rb,Li,As,and Hg are relatively low,and other elements are equivalent to UCC.In addition,the weathering degree of the basalt in the study area is also analyzed by calculating the relative mobility rate of elements,chemical alteration index,silicon-iron index,and silicon-aluminum index.The relative mobility rate of elements in profile SS21 and profile SS45 are similar,the relative mobility rate of SiO₂ and K₂O is positive,while the relative mobility rate of other principal components is negative;the relative mobility rate characteristics of profile SS79 and profile SS119 are similar.The relative mobility rate of Al₂O₃ in the soils of the B-layer,and SiO₂ in that of the O-layer,A-layer,and B-layer are only positive,and the mobility rate of other elements in the remaining layers are negative.Comprehensive analysis of the silicon-iron index of the four soil profiles show that the characteristics of all profiles remain the same.The silicon-iron index of the soil in the A-layer is the highest,and the silicon-iron index in the C-layer of soil is the lowest.And the range is very large,indicating that the silicon-iron index of each layer has obvious difference.For the silicon-aluminum index,the characteristics of profile SS21,profile SS45,and profile SS79 are the same.It is also that the A-layer has the highest silicon-aluminum index,and the C-layer soil has the lowest silicon-aluminum index,and the range is very large.However,for profile SS119,unlike the other three profiles,the O-layer soil has the highest silicon-aluminum index,and the B-layer soil has the lowest silicon-aluminum index.The characteristics of the chemical alteration index show that the four groups of profiles belong to the moderate degree of chemical weathering under warm and humid weather conditions.