Coupling Relationship Between Chemical Weathering Of Red Soil Yellow Soil And Environmental Magnetism In Subtropical Multi Terrain Scale

The essence of chemical weathering is the chemical reaction between the water solution rich in oxygen and carbon dioxide and the minerals that make up the rocks,which makes the elements that make up the original minerals migrate until the formation of stable new mineral assemblages in the supergene environment.As one of the final products of the chemical weathering of silicate minerals containing iron,epiiron oxides are widely enriched in the tropical and subtropical epiphytic environment,forming the iron rich soil sequence of Latosol red soil red soil red soil.It is of great significance to study the temporal and spatial variation of iron oxide phase and its control mechanism in the tropical and subtropical zone for monitoring the continental weathering process,improving the continental weathering theory,and correctly evaluating the environmental effect and the feedback of the mesosphere during the continental weathering process.As an environmentally sensitive mineral formed by prior weathering of iron bearing minerals,pedogenic magnetic particles are of great significance for soil classification,erosion assessment,pollution monitoring and climate reconstruction.In the soil topographical sequence,the iron oxide produced by chemical weathering caused by the redistribution of water and heat and material appears obvious migration and transformation.Based on this,this paper selected the multi-scale iron rich soil shape sequence in the subtropical granite area of China,and carried out the coupling study of chemical wind and environmental magnetism of slope sequence(FJS),vertical zone sequence(FJM)and mountain plain transition sequence(FJL).(1)From uphill to downhill,the total amount of iron oxide in raw soil controlled by chemical weathering decreased slightly,but the total amount of iron oxide in raw soil controlled by water activity decreased significantly.At the same time,the change of Gt is not obvious,but the amorphous iron oxide is enriched under the slope.Except for the fine SP particles,the ferromagnetic particles decreased with the decrease of HM.However,the contribution of the finer ferromagnetic particles to the coarser ferromagnetic particles and the contribution of the ferromagnetic particles to the antiferromagnetic particles increased.It verified the genetic relationship between ferromagnetic particles and HM,but in the granite soil with low Hm/(Hm+Gt),the growth and transformation of ferromagnetic particles to HM are more rapid.In addition,the smallest SP particles separated from HM may be enhanced by transport with amorphous iron oxide or by downhill transformation from amorphous iron oxide rich.(2)The chemical weathering from coastal plain to inland mountainous area in Southeast granite area has a nonlinear relationship with altitude.The non-linear relationship is related to the non synchronous change of topometeorological elements.The high weathering intensity in the foothills near 100 m above sea level corresponds to the high temperature in the region,the high weathering intensity in the low mountains near 500 m above sea level corresponds to the high precipitation in the region,and the high weathering intensity in the middle mountains of 1000 mm corresponds to the high altitude in the region.The chemical weathering on the scale of vertical zone and slope also shows the common control of climate and altitude.The response of free iron,Gt and Hm to chemical weathering is similar,but the response of Hm and magnetic parameters is more sensitive.(3)The chemical weathering in the granite area of Southeast China has an obvious effect on the enricHment of free iron.The lower the Si Al ratio is,the more the free iron is.However,the enrichment rate of different iron oxide phases is different.The enricHment rate of Gt is the same as that of free iron,the enrichment rate of Hm is obviously slower,and Fe_o is the slowest.In addition,the process of mountain scale erosion and deposition may lead to the high Fed,high Gt and low Hm of some high Si Al samples in the Piedmont hills,which may be related to the migration of goethite dominated free iron to the Piedmont.(4)The main component of free iron oxide is Gt,followed by Hm,and Fe_o content is low.There was a positive correlation between Gt and free iron.The growth rate of Hm with Fe_d is related to the hydrothermal gradient of the sequence.Fe_o and Fe_d are basically in synchronization,but under the condition of low Fe_d and low weathering,Fe_o components may also increase significantly.(5)There is a general correlation between different granular magnetic minerals and iron oxides,which confirms the genetic relationship between magnetic components and iron oxides.But the relationship between different iron oxide components and magnetic minerals is different.In low magnetic soil,GT has a general contribution to different magnetic particles,while Fe_o has a contribution to fine magnetic particles.In the high magnetic soil,HM has a general contribution to the magnetic particles.(6)The distribution of magnetic particles changed with magnetic enricHment.There is a general lack of the finest SP particles in the granite area,which may be related to the high erosion in the area.SD,MD ferrous particles and antiferromagnetic particles are enriched synchronously with magnetism,but the growth rate of each part is similar in low susceptibility soil;however,in high susceptibility soil,some of the magnetic particles of some samples decrease,but keep a faster growth with magnetism,and the coarser the particle size is,the faster the growth rate is,suggesting that there are different magnetic enricHment modes between low and high weathering soil.