| Active faults are the root cause of structural earthquakes.Research on fault activity is to prevent earthquakes from the source.As a direct product of fault activity,mineralogical characteristics,structural characteristics,and geochemical characteristics of fault gouges contain information on fault activity and evolution.Zhejiang is one of the most economically active provinces in China.It has major projects such as nuclear power plants and railways.It has experienced many tectonic movements,complicated geological structures,and developed fracture structures.There have been many earthquakes along the Jiangshan-Shaoxing deep fault zone.As a result of the excavation of building construction,6 small size fresh faults exposed in Wujialong of Jiangshan City,Zhejiang Province,which was sub-branch of Jiangshan-Shaoxing deep fault.In the fault zone,black fault gouge has just been discovered,in order to explore whether the black fault gouge is the product of the latest fault activity.Field geological survey,X-ray fluorescence analysis,X-ray powder diffraction,Scanning Electron Microscopy and Energy Dispersive and M?ssbauer spectroscopy were used to study the mineral composition,chemical constituents,micro-morphology of quartz particles and iron species of fault gouges and wall rocks of F1,F2 and F3 faults in Wujialong Fault.After comparative analysis and research we found that:(1)The mineral composition of the wall rocks and fault gouges are mainly quartz and clay minerals,and it also contains a small amount of albite and calcite.The clay minerals are mainly composed of illite,K/S layer and I/S layer,and also contain small amount of chlorite,kaolinite and trace amount of vermiculite and montmorillonite.Except the JS07 sample,the rock forming minerals content of fault gouges is lower than wall rocks' whereas to the clay content of fault gouges is higherthan wall rocks'.(2)By comparing the chemical composition of wall rocks and fault gouges,it was found that the content of active elements such as Al,Na,Mg,Si and Fe varied greatly in the fault gouges,and the relative enrichment and loss of elements were consistent with the mineral compositions shown by XRD.(3)The SEM-EDS experimental results show that the Wujialong fault sliding modes are non-shock creep and have low activity frequency since the Holocene.The intense activity of the F1 fault is mainly in the Pliocene and early Pleistocene.The F2 fault activity mainly concentrated in the early Pleistocene,and there were weaker activities in the Pliocene.The strong activity of the F3 fault is mainly concentrated in the Middle Pleistocene,and there are relatively weak activities in the late Pleistocene and early Pleistocene.(4)The clay mineral type of F1 fault gouges is single and contains only illite,revealing that the fault zone is a relatively stable environment.The content of illite in the F2 and F3 fault gouges is relatively lower than that of the wall rocks.The relatively high content of montmorillonite and I/S layer shows that they are in a moist,strong oxidizing environment..The high content of reduced iron of wall rocks in F1 may suggest that the formation of wall rocks is involved in the process of reducing substances,the high levels of oxidized iron of F1,F3 fault zone and F3 hanging wall,indicating either F1,F3 faults are inactive and/or they are inner-block fault.(5)The types and association of clay minerals in the fault zone and the redox environment generally show that the Wujialong fault is in a relatively stable environment,however,the content of illite in the fault zone is high,which is conducive to the fault activity.The activity of Wujialong fault and the possibility of earthquake should be taken into consideration seriously. |
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