Characteristics And Genetic Analysis Of Analcite-bearing Rocks In The Fourth Member Of Shahejie Formation In The Western Sag Of Liaohe River

This thesis is guided by theories of sedimentology,mineral petrology,geochemistry and other disciplines,making full use of drilling,logging,regional geological information and other laboratory data,combing with some research measures such as core observation,thin section identification,X-ray diffraction analysis,electron probe analysis,scanning electron microscope analysis,cathodoluminescence analysis and homogenization temperature of inclusion to describe in detail the petrological and geochemical characteristics of the analcime-bearing rocks,analyzed their material sources and paleo-sedimentary environments.Above all the researches and combined with structural fractures and sedimentary evolution characteristics,this thesis discussed the formation of analcime-bearing rocks and initially established its cause model in the fourth member of Shahejie Formation(Sha 4th member).The analcime-bearing rocks of the Sha 4th member are composed of clay minerals,dolomite,quartz,feldspar,analcite,calcite,pyrite,aragonite,siderite,gypsum.Analcime has three kinds of occurrences:laminar,nodular and cemented.The lamellar analcime has an amorphous colloid under the microscope,and the micellar lamellar enrichment,with the rich dolomite and clay mineral laminated interlayer.The nodular analcime is a scattered distribution in the granular layer of powder and fine grain,and usually develops with the sedimentary deformation layer,which may be caused by the local enrichment of the smooth layer of zeolite during the sedimentary period.The cement-filled analcime is distributed in the crack and the hole margin,and has a high degree of self-image,and the grain size is bright,and it is mainly produced by fine grain.The analcime-bearing rocks is mainly composed of laminar sedimentary structure,hot water breccia structure,vein structure,enveloping layer and tuberculosis also can be seen in local.The diagenesis mainly includes compaction,dissolution,filling and recrystallization.Analcime is mainly distributed in Gaosheng layer and Dusan layer of Sha 4th member,other layers of analcime are almost invisible,and the distribution of analcite is controlled by the deposition center and the fracture.According to the analysis of the homogenization temperature of analcime mineral inclusions in fracture,this type of analcime has different causes:Uniform high temperature peak analcime for late hydrothermal Wells,the aluminum silicate gel in fluid to congeal slowly,the genesis of analcime marginal distribution along the fissures,cracks on the edge of micritic dolomite heated fluid influence the formation of recrystallization powder crystal dolomite.Uniform low temperature peak analcime the same temperature as its buried formation,may be the early diagenesis phase,amorphous lamellar analcime may be affected by organic acid occurred slowly cemented after dissolution.According to the distribution pattern of rare earth elements,it is found that both the analcime and the basalt are derived from the mantle source material.The origin of analcime is related to the mantle source material based on the characteristics of Sr isotope.The anlysis of mineral composition and rare earth element indicate that the analcime is formed in the reducing sedimentary environment of high salinity and temperature.And it can be concluded that the salinity of study area is between 22.65?32.05‰,and the equilibrium temperature is between 27.35?74? by the anlysis of the characteristics of carbon and oxygen isotopes.This paper predicts the depth change of the lake on the basis of the value of Th/U,the analcime were relatively developed in the shallow stage of the lake basin.Comprehensive analysis of the above results.Fracture is formed in strong tectonic movement.Hydrothermal fluid carrying large amounts of silicate colloid and alkali metal ions,spewing into the low temperture water of the lake along the fracture.Due to the decrease of pressure and temperature,the hydrothermal fluid reacts with lake water to form precipitation.Its reaction formed the analcime in larger salinity of the lake during the drought period.But during the relatively humid period,the salinity of the lake water is relatively small,which is more conducive to the formation of clay minerals.The analcime formed during the diagenesis is formed by dissolving the stratiform analcime and re-precipitating in the dissolved pores and cracks.