The Quaternary volcanoes in North China are distributed mainly in Shanxi and Shandong Provinces. In Shanxi Province, the famous Datong volcanic cluster consists of ten odd well preserved volcanic craters, volcanic cones, and volcanic necks. In Shandong Province, isolated volcanoes are distributed in Penglai and Wudi areas. Stratigraphic correlation has revealed that the volcanic products are middle to late Pleistocene in ages, while dating data have indicated that the ages of these volcanic products are in the range of 0.8～0.1Ma, and that the climax of eruption occurred in middle Pleistocene. The Quaternary volcanics in North China can be assigned to alkaline and tholeiitic basalts. The chemical compositions of these basalts indicate that they are the products of partial melting to different extents in mantle source area, having the basic features of primitive mantle-derived magma that has not been affected by crystallization differentiation. The basalts from three localities all contain mantle xenoliths comprising mainly spinel lherzolites of proto-granular and porphyroclastic textures. The rheological parameters of the upper mantle beneath these three regions have been inferred from the detailed study of these mantle xenoliths. The differential stresses are determined to be 21～31MPa, 23～26MPa and 13～24MPa for Datong, Wudi and Penglai, respectively, while the strain rates are 10^-17～10^-15s^-1, 10^-18～10^-17s^-1 and 10^-20～10^-14s^-1, respectively. The equilibrium temperatures are 900～1 050℃ for Datong xenoliths, 840～900℃ for Wudi xenoliths and 800～1 000℃ for Penglai xenoliths. The constructed differential stress and strain rate profiles of the upper mantle beneath these three areas coincide well with those of the upper mantle in continental extension zone or rift proposed by Ave Lallemant et al (1980). Volcanism is the product of the combination action of deep-seated tectonic and shallow tectonic processes. The Datong region is a part of Shanxi depression belt, Wudi volcano lies within the North China depression, and Penglai volcano is located on the outer margin of the Bohai depression. Tectonically, volcanism bears a close relation with fault depression and down-warping tectonics. Seismic sounding data and the study of mantle xenoliths have confirmed the existence of upper mantle uplift or diapir beneath these depressions. In consideration of the scale, range and distribution of Quaternary volcanism, as well as the results of the study of mantle xenoliths, it is suggested that the features of the upper mantle of North China in Quaternary, inherit the properties of the upper mantle in Tertiary time. The volcanism in Quaternary time, however, was much weaker than that in Tertiary time.

A reliable geotherm has been constructed for the lower crust and upper mantle beneath Hanuoba, Hebei Province, China through the detailed study of xenoliths from basalts. The construted geotherm is higher than the oceanic geotherm and that for old cratonic areas. It is comparable to that for the eastern margin of Australian craton, and seems to indicate the tectonic regime of the studied area. The petrologic section derived from this geotherm indicates that the lower crust of this area consists mainly of granulite facies rocks of mafic compositions. They span from about 27km to 42km depth. The upper mantle consists of lherzolite, and it seems that there is a transition zone between spinel and garnet lherzolites. The crust mantle boundary defined by this geotherm is at 42km depth and coincides well with the seismic Moho. However, the overlapping of the equilibrium temperatures of some granulite and spinel lherzolite xenoliths indicates that granulite, spinel lherzolites and garnet pyroxynite may be interlayered in a zone above the crust mantle boundary. This may explain the layered reflectors observed at the base of lower crust. The lithosphere-asthenosphere boundary can be derived to be at about 95km depth, and the underlying asthenosphere consists of garnet lherzolite incorporated by upper mantle fluids. The obtained results may provide basic constraints for the lithosphere mapping and the construction of seismogenic model of the area.

The Quaternary basalts in Datong, Shanxi Province contain small mantle xenoliths which are generally only 2～3cm in size. These mantle xenoliths comprise mainly spinel lherzolite. The textures of the xenoliths are variable from protogranular to porphyroclastic. The dislocation substructures of olivine from the xenoliths are dominated mainly by dislocation walls representative of high temperature dislocation creep. In addition, some dislocation substructures typical of lower temperature plastic deformation and high strain rate events such as dislocation tangles and slip band can also be observed. All these indicate that at least two deformation events had occurred within the upper mantle of this area. The equilibrium temperature and pressure of these xenoliths are within the range of 900～1050℃ and 1.1～1.7Gpa, respectively, corresponding to a range of depth of 40～60km. The differential stress estimated by using microstructural piezometer is in the range of 21～31MPa, showing a tendency of decreasing with depth, while the estimated strain rate and equivalent viscosity are within the range of 10¹⁵～10¹⁷s¹ and 10²¹～10²³ Pa·s, respectively. All these results have shown that an upper mantle diapir had continued to occur during the Quaternary in this area.

The study of recent fault activity in bedrock area,where no young sediments can be observed,is often fulfilled through the study of fault zone materials.The authors proposed that the formation periods of fault zone materials should be classified through macroscopic observation in the field and the microscopic analysis of the deformation features.The radiometric dating of the materials of different periods then can be carried out separately.For some dating techniques,it is necessary to determine the degree of "annealing" of the fault zone materials.Then a decisive result with reasonable interpretation can be obtained.

To study the activity feature, phase and time of the faults in a bedrock exposing region, a series of samples of fault rocks and fault gouges are collected along the Kangding-Moxi fault segment. TL. ESR. K-Ar techniques,analyses of quartz surface texture and deformation microstructure are used for the comprehensive research. The results show that the fault segment has undergone multiperiodic activity with multiple types (ductile shearing-brittle fracture) and multiple patterns (left-lateral-right-lateral),and the lower limit of the lost strong activity was around the end of late pleistocene or the begining of Holocene (ca. 10000 years).

The characteristics of the Chaeryong River fault zone and its relation to earthquakes as well as its recent activity is described in more detail. The fault is proved to be an active fault zone, which may have a control on extending of the fault zone. The formation and evolution of the fault is discussed as well.

The rocks of dyke swarm in North China have commonly diabasic texture. Their composition is of tholeiite with low Mg and high K and Na. The swarm consists of three subswarms, which were formed 1500Ma, 1200Ma and 900 Ma ago, respectively.The relevant extensive stress field in three phases is suggested and their directions are NS, NE-SW and SE-NW.

The mantle xenoliths from 6 localities along and eastward of the active Tanlu fault zone are mostly spinel lherzolite, with few exception of wehrlite. The textures are variable from initial porphyroclastic through granuloblaslic to mylonitic. The analysis of mineral equilibria has revealed that these xenoliths attained to a good state of equilibrium.The equilibrium temperatures determined by using 3 different methods are 700-1000℃, while the pressures have been estimated to be in a range of 0.9-2.5 GPa. The constructed geotherms have shown that most of the points lie above the theorectical continental geotherm, indicating the existence of an upper mantle diapir associated with tectonic extension known to occur in thus region. The low temperature of mylonitic xenoliths indicates the existence of an active shear zone just below the crust. It might control the development of seismically active zone in this region.

Mylonite,cataclasite and especially fault rocks subjected to both mylonitization and cata-clasis widely developed along the Kangding-Moxi fault zone.A mylonite zone has formed as a result of ductile shearing in early stage.In later stage brittle fracturing has occurred along this mylonite zone,accompanied by the formation of the present Kangding-Moxi fault zone.Later on,ductile shearing and multiperiods of brittle fracturing occurred along the fault zone.Differential stress magnitude during the early faulting process was 50 MPa,as determined by using microstructural piezometer,while that for the late stage was 30 MPa.The activity of the fault zone tends to be weaker,i.e.from high to low stress level.

The neotectonic activity of a minor fault zone on the Southwest margin of Yangzi platform has been studied based on analysis and comparison of the microstructural features of deformed rocks within and outside the fault zone.According to thermoluminesccne dating it is proposed that after Pleistocene there would be more than one active period of the fault.The strees of the main period was up to 700 bars.The strain and stress of the rocks within the fault during the faulting process were significantly greater than those in the rocks outside the fault.

The neotectonic activity of a minor fault zone on the Southwest margin of Yangzi platform has been studied based on the analysis and comparison of the microstructural features of deformed rocks within and outside the fault zone.The fault developed in Permian Emei basalt,striking NE40—50°,dipping toward Southeast at an angle of 70—80°,with a total length of 250m and horizontal displacement of 1.5m.Within the fault developed a zone 3—30cm in width consisting of fault gouge and fractured lenticular rock fragments,which along with the country rocks were cut by the late calcite veins.The samples were collected from the veins within the fault and the veins within the country rocks of different distance from the fault.The optical microscopic observation has shown that almost all of the calcite posseses twin lamellae,while U-stage measurement has shown that the space index of twin lamellae varies with the increasing distance from the fault.The space index is highest in the fault (50/mm),and decreases rapidly with the increasing distance from the fault (10/mm in the sample 20m away from the fault).The differential stress during the deformation process has been estimated from the developement degree of twin lamellae by using Jamison and Spang's method.The Result is in good agreement with that estimated from dynamically recrystallized grain-size.It is shown that the stress within the fault(700 bars) is much higher than that outside the fault(300 bars).According to thermoluminenscence dating the calcite veins were formed in Pleisto-cence.It is proposed that after Pleistocene there would be more than one active period of the fault.The stress of the main period was up to 700 bars.The strain and stress of the rocks within the fault during the faulting process were significantly greater than those in the rocks outside the fault.

The Beishicheng and Hefangkou fault zones in Miyun and Huairou area have been studied.A mylonite belt tens to hundreds meters in width was developed on the foot wall of the former fault and a fracture belt 300—500 meters in width on the hanging wall.A mylonitized granite belt occurred on the foot wall of the latter fault and cataclasites or cataclastic granite on the hanging wall.Microscopically quartz and mica ,within mylonites exhibit their features of strong plastic deformation indicated by apparent flow structure and grain size reduction due to dynamic recrystallization.All minerals in the cataclastic rocks,however,display brittle behaviour.It is clear that the two kinds of rocks were formed under different physical conditions.Based on the distribution pattern of the fault rocks and dynamic analysis of twin lamellae of dolomite,it can be inferred that there were two phases during the developement of the fault zones: a ductile shearing occurred at the deeper level of the crust leading to the formation of mylonite belts,and then the mylonite belts gradually were uplifted along the south-eastern sides of the fault zones onto the higher level.According to the mineralogical assemblage and the characteristic of the mylonites,it is deduced that the ductile shearing occurred at temperature of 450—500°,and confining pressure of about 4 kb,corresponding to the depth of 15 km.A differential stress value of 0.5—1 kb and a strain rate of 1.6×10^-9—10^-10 sec^-1 have been estimated from rescrytallized grain size,subgrain size,dislocation density and the spacing of deformation lamellae of quartz revealed in chemically etched mylonite samples.Finally,the possible relationship between ductile shear belt,the elastic-plastic transition zone within the crust and the layer feasible to shake in continent has been discussed.

According to the principle proposed by A. B. Spencer, a computer program for pe-trofabric data processing has been compiled. The program presented in this paper consists of plofing fabric diagram and diagram of kinetic orientation of carbonate minerals which is very useful not only to common petrofabric analysis, but also to petrofabric stress analysis. An example of its application is illustrated herein.