Geochemical Characteristics And Carbon Occurrence Of Fault Gouges In Guanxian-Anxian Fault Zone,Sichuan Province

"Wenchuan Earthquake Fault Zone Scientific Drilling?WFSD?"is a national science and technology support project jointly organized by the Ministry of Science and Technology,the Ministry of Land and Resources and the Seismological Bureau of China after the Wenchuan Earthquake.Its purpose is to study seismic mechanisms,capture aftershock information,improve aftershock monitoring,and earthquake warning and forecasting capabilities.After the earthquake,different scholars excavated a number of shallow trenches on the earthquake surface rupture zone,and carried out systematic research on the fault rock in the trench.It is one of the effective methods to explore the mechanism of earthquakes by studying the information of fluid action and mechanical milling during fault rock.Based on the“Wenchuan Earthquake Fault Scientific Drilling?WFSD?”project,this paper takes the fault mud,gray-green sandstone and red sandstone of the Jiulong trench on the front edge fault of the Longmenshan fault zone?the Guanxian-Anxian fault zone?as the research object.Using a combination of polarized light microscopy,laser Raman,X-ray fluorescence spectroscopy?XRF?and other methods to analyze the sample of the trench,the following understanding is obtained:?1?Calcite veins were found in the fault mud of the Jiulong trench in the frontal fault of the Longmenshan fault zone,revealing the fluid action in the fault zone.The fault mud in the trench has the characteristics of relative enrichment of Al,Cr,Fe,K,Ti and Mn,and relative loss of Ca,Cu,Mg and Si.The water-rock reaction of the main slip zone of the fault is more intense.The accumulation of Ti and Cr is found in this part,the loss of K,and the rutile clastic and chromite are found,indicating that a strong water-rock reaction has occurred,making the activity The sexual elements are taken away by the fluid,and the stable elements are enriched.The elemental anomalies of the fault zone may be related to the type of surrounding rock.?2?A large amount of pyrite is found in the fault mud,and the iron mineral in the gray-green sandstone is magnetite,indicating that Fe³⁺is reduced to Fe²⁺during the formation of fault mud.Therefore,it is speculated that the formation environment of the pro source fault of the Longmenshan fault zone is a reducing environment.?3?Guanxian-Anxian fault zone is generally rich in carbon,and is classified into four occurrence states according to microstructural analysis,namely:unbroken internal breccia in fault mud Initial state;angular distribution of angular carbonaceous matter;carbonaceous vein;fragmented lithified carbonaceous veins in four states.Laser Raman shows that the carbonaceous materials in the four modes of fault mud have almost the same degree of graphitization,and the characteristics of the slip zone slip mechanism may affect the degree of graphitization of carbonaceous.Laser Raman spectroscopy did not show the presence of a G-peak containing graphite crystals alone,indicating that the carbonaceous material in the Anxian-Gengxian fault zone did not undergo high-temperature friction heating,and the low-angle thrust of the fracture zoneThe quality of the fault zone is a slow slip process during the earthquake.Therefore,the fault is a mechanism of low temperature slow slip,that is,a creep mechanism.