Study On The Transformation Of The Clay Mineral In The Fault Gouge And Its Experimental Simulation

Based on the observation of the field samples which were obtained from the fault gouge of Devonian Niqiuhe formation in the Dayangshu basin,the characterization and the distribution of clay mineral in the fault gouge was analyzed.High temperature and pressure hydrothermal experiments were taken on the aspect of mineral phase,composition and structure to simulate clay mineral transformation as the increasing of temperature and pressure.At the same time,molecular dynamics method was used to simulate the transformation process of the phase and the structure that obtained from the hydrothermal experiments.And then,the influence of interlayer organic matter（OM）on the transformation of smectite illitization was explored by high temperature and pressure hydrothermal experiments.Finally,the influence of fluid composition-the concentration of K⁺on the clay mineral transformation was also discussed.The main content of this thesis are as follows:1.Mineralogy of clay minerals in the fault gouge of Devonian Niqiuhe formation in the Dayangshu basin and their significance of temperature rise induced by fault activityThe phase,composition and microstructure of clay minerals in the fault gouge of Devonian Niqiuhe formation in the Dayangshu basin was characterized by XRD,XRF and HRTM.The results showed that the fault gouge was composed of mixed-layer chlorite/smectite and illite.The highest chlorite content in the mixed-layer chlorite/smectite was found on the edge of the fault gouge,and even some chlorite exist.The chlorite compositional geothermometer was used to determine the temperature,and the result indicated that the highest temperature exist on the edge of the fault gouge.The maximum temperature on the edge of the fault gouge was 175°C,and the minimum temperature appeared in the core of the fault gouge was 153°C.Thus,the difference between the maximum and minimum temperature was 22°C,which indicated the maximum value of temperature rise induced by fault activity.Therefore,the characteristic analysis of mineral phase and composition can not only highlight the transformation and distribution of clay mineral in the fault gouge,but also offer basic parameters to analysis the slightly temperature rise induced by fault activity.2.Conversion reactions from dioctahedral smectite to trioctahedral chlorite and their structural simulationsIn this study,hydrothermal devices were selected as the instruments to simulate the clay mineral transformation process.And dioctahedral smectite dominated mudstone was tested in the temperature range of 250⁵50°C and the pressure range of 5²80 MPa,with reactions lasting 24 hours and the liquid/solid ratio of 1:1,in the solution of saturated KCl.The mineralogical character of the clay minerals was tested by XRD,XRF,SEM,FTIR and HRTEM.Molecular simulation was performed to determine the structure and behavior of interlayer cations and interlayer water changes of clay minerals.And the transformation series was obtained as follows:from dioctahedral smectite to dioctahedral randomly interstratified illite/smectite to dioctahedral ordered illite/smectite to coexistence of dioctahedral and trioctahedral ordered illite/smectite and finally to trioctahedral chlorite and illite/smectite.This work illustrated the dioctahedral smectite alteration and transformation process and showed a continuous octahedral sheet transformation from dioctahedral smectite to trioctahedral chlorite.This series of clay minerals transformation provided an important experimental basis for understanding the geochemical conditions where clay minerals were exposed in the geological environment and will offer basic parameters to establishing a quantitative link between composition and formation conditions.3.Experimental investigation of the influence factors on the transformation of smectite illitizationIn this study,hydrothermal experiments which were taken at the temperature range of250⁶50°C and the pressure range of 200³25 MPa,with reactions lasting 24 hours and the liquid/solid ratio of 1:1 were used to study on the influence of organic matter（OM）on the transformation of smectite illitization.The mineralogical character of the clay minerals was tested by TG,XRD,XRF,SEM and FTIR.The results clearly show that the decomposition temperature range of the OM was 350-500°C,and the presence of OM have different impacts at the different temperature and pressure.The illitization transformation at 250°C and 200 MPa are accelerated in the presence of OM.While,at the temperature and pressure conditions of 350°C 215 MPa and 450°C 245 MPa,the crystal structure of clay minerals was destroyed by the decomposition of the interlayer OM and generation of fluid composition.Then,the illitization of samples that with OM delayed.At the conditions of 650°C and 325 MPa,the illitization of samples with and without OM was in the same rate because of the absence of OM in the interlayer of smectite.This study revealed that the existence and occurrence of OM could influence the smectite illitization in different temperature and pressure,and OM was the important influence factor to be considered in diagenesis,very low-grade and low-grade metamorphism.Further study on the interactions between OM and clay minerals was needed to facilitate our understanding on the mechanism of smectite illitization as well as its geological applications.Another influence factor,the K⁺concentration（saturated KCl,1M KCl and H₂O）on the clay mineral transformation has been studied.The hydrothermal experiments were taken at the temperature of 200°C,with reactions lasting 24 hours and the liquid/solid ratio of 60:1.The mineralogical evolution of the clay minerals was characterized by XRD,the results clearly showed that the higher concentration of K⁺results in the higher rate of illitization.The concentration of K⁺promoted the smectite illitization.Hydrothermal experiments were used to study the influence of the temperature and pressure on the clay minerals transformation.The simulation experiments were taken at the fixed liquid/solid ratio,fluid composition and reaction time.As the increasing of temperature and pressure,the transformation process of smectite illitization was smectite to disordered illite/smectite minerals to ordered illite/smectite minerals.