The Physical And Chemical Changes And Their Weathering Indications Of Weatherable Minerals In Granite Weathering Crust

Weathering of rocks and minerals is the basis of the source of sedimentary materials,and granite is the original carrier for studying the origin of sediments.Because the granite facies are uniform and stable,the minerals in the rock body are more evenly distributed and the degree of differentiation is small.The degree of weathering of different minerals in the weathering crust of granite is coordinated with the location of the weathering zone.The biotite,hornblende and feldspar in granite belong to silicate minerals,which are important minerals on the surface of the earth.They are the more easily weathered mineral components in the weathering crust,and there are various types of weathering products.The weathering is the surface layer of the earth.An important geochemical process of the material cycle has a significant impact on the global CO₂cycle and climate change,the formation of soil and clay minerals,and the cycle of nutrient elements.Therefore,this paper selects a representative region of the warm temperate zone,the vicinity of Yantai in the Shandong Peninsula for the study.In this area,the weathering crust of the Yuangezhuang granite body and its main minerals,biotite,hornblende and feldspar are the research objects to explore its performance characteristics in different layers of the weathering crust and during the weathering process.On the basis of detailed field geological survey,the collected samples were crushed,washed,screened,magnetically separated,and selected under the microscope,and then subjected to density analysis,XRD diffraction analysis,geochemical testing of trace elements,strontium Isotopic testing and other experimental procedures have studied the color,hardness,density changes and mineral phase transitions of biotite in the weathering crust;the weathering degree and element migration changes of three single minerals and weathering crust debris in different layers are studied.The law and the characteristics of strontium isotope changes,a comprehensive analysis of its weathering characteristics and weathering mechanisms,and the following results are obtained:(1)The weathering of biotite is obvious in the weathering crust,as the degree of weathering increases,its color changes from black to brown to reddish brown;gloss changes from bright to dark;hardness decreases;elasticity decreases and flexibility increases;mineral structure level The net spacing becomes larger;the density is greatly reduced.The main components and structure of biotite have undergone major changes and lead to mineral phase transitions.The change trend is biotite?mica-type mixed layer minerals?water biotite-vermiculite mixed layer minerals?vermiculite.(2)The upper part of the weathering crust of Yuangezhuang granite is at a moderate degree of weathering.The degree of weathering of single minerals in the weathering crust is in the order of biotite>hornblende>feldspar,and the weathering degree of biotite and amphibole is the highest in the subsurface layer;The overall weathering of feldspar is not significant,and the degree of weathering on the top of the crust is slightly higher than that of other layers.(3)In the process of rock mineral weathering,the weathering crust is enriched in Fe and Al elements as a whole,among which biotite Si and Al are enriched,but K and Na are lost.The amphibole element changes little,and the feldspar changes from Al,Ca,P and other elements from the bedrock to the subsurface layer have varying degrees of leaching.Most of the trace elements of single minerals have extreme values at the subsurface layer,which are related to the migration of water and gas in the top layer of the weathering crust,the growth of vegetation and the deposition of the subsurface layer.(4)The content of rare earth elements in the weathered crust and its single minerals is relatively high.The content is in descending order of hornblende>residual whole sample>biotite>feldspar.The common feature is that the content of light rare earth elements is higher than that of heavy rare earths.,Are mainly based on?Ce family elements.(5)Rb element is mainly enriched in biotite minerals in weathered crust,and Sr element is present in feldspar.The ratio of ⁸⁷Sr/⁸⁶Sr in biotite is much higher than that of feldspar,residual whole sample and hornblende.With the increase of weathering,the content of Rb in biotite and the ratio of⁸⁷Sr/⁸⁶Sr gradually decrease.The ratio of weathering crust and different minerals Rb/Sr is positively correlated with the ratio of⁸⁷Sr/⁸⁶Sr.(6)The climate and precipitation conditions of Yuangezhuang are the main factors affecting the weathering degree of the weathering crust and its single minerals at low to medium level.The topography and the tectonic genesis type of the weathering crust,biological influencing factors and mineral crystal structure factors are secondary factors.factor.