| It takes a long time for rocks to develop into soils.The mineral composition and structure of rocks affect the time of soil formation and development.The main minerals of basalt are basic plagioclase and pyroxene,which contain a small amount of olivine,amphibole and biotite.These minerals have weak weathering resistance and are easy to weathering form soil.In addition to this mineral composition,basaltic volcanic ballast has the characteristics of cryptocrystalline or vitreous structure and multi-porous structure.Under supergene conditions,basaltic volcanic ballast is a good material for studying the occurrence and development of soil because of its easy weathering of minerals,unstable vitreous structure and porous structure,which also increases the area of contact between rock or mineral surface and supergene environment.As for the soil developed by volcanic ejecta,no scholar has studied its genetic characteristics from various angles.In this study,the genesis characteristics of basaltic volcanic ejecta from Darinol,Datong,Inner Mongolia and Kuandian,Liaoning Province were studied in terms of morphology,mineralogy,physical and chemical properties,and the genesis rules of basaltic volcanic ejecta were analyzed and compared.The results show that:(1)Physical and morphological characteristics of the tested profiles: there are more basalt volcanic debris in Darinol and Datong soils,and the volume is larger.With the deepening of the soil profile,the content of basalt volcanic debris increases and the volume disappears.There was a significant increase.The soil texture of Darinol and Datong profiles is mainly sandy soil,while that of Kuandian profiles is mainly loam soil.Darinol and Datong sand grains are mostly angular with obvious stomata,while Kuandian sand grains are mostly subcircular-subangular with almost no stomata.(2)Volcanic glass is the main primary mineral in all soil profiles,and the content of volcanic glass is Kuandian < Darinol < Datong.Quartz formed by devitrification can be seen in all soils tested,and the deeper the profile is,the larger the grain size is,the less the quartz content is;Quartz content is: Kuandian section > Darinol ash section > Darinol ballast section > Datong section.There are also a few plagioclase and pyroxene in the soil profile of semi-arid area,while there are almost no plagioclase and pyroxene in the profile of wet area.Datong soil does not contain crystalline clay minerals;Darinol soil has less crystalline clay minerals and lower crystallinity;Kuandian soil has more clay minerals and higher crystallinity.The contents of amorphous clay minerals(diaspore)are as follows: Kuandian section > Darinol volcanic ash section > Darinol volcanic ballast section > Datong section.(3)Carbonate content: Darinol < Datong,Kuandian has no carbonate.Si O2,Fe2O3 and Al2O3 are the main components of the major elements in all sections.The contents of Si O2,Ca O,Mg O,Na2 O and K2 O in Darinol and Datong are relatively high,while the contents of Fe2O3 and Al2O3 in Kuandian are relatively high.The loss of Ca,Mg,Na,P and Mn in each section is different,with Kuandian losing the most,Darinol losing the second and Datong losing the least,and Kuandian's Si losing to a certain extent in Kuandian,Darinol losing almost nothing in Datong.Fe and Al were enriched in different degrees,with Kuandian > Darinol > Datong,clay > silt > sand.(4)The occurrence law of basaltic volcanic eruptions in soils: large boulders are weathered and broken into small boulders,sand grains are changed from angular to sub-circular,stomata gradually disappear,soil texture gradually becomes sticky;carbonate in soils is leached first,followed by K,Ca,Na and Mg in minerals,and with the loss of Si,Fe and Al are relatively enriched.Volcanic glass,pyroxene and plagioclase in soil gradually decreased,devitrified quartz gradually increased,clay minerals increased,mineral types changed from volcanic glass to short-range ordered mineral diaspore,and then to crystalline minerals illite,vermiculite and kaolinite. |
PDF Full Text Request