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 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.

Based on the study of the genetic features of mineral associations and metamorphic facies in Miyun metamorphic rocks,the characters of repeated-seismic layers have been proposed in this paper.It is suggested that the differential deformation has a close relation to the generation of strong seisms.Taking the principal elements of flow cleavage and fracture cleavage as well as their dynamic implications into account,a generation process of strong earthquakes has been proposed: the mechanism of differential deformation causes an initiation of strong earthquakes.Briefly speaking,distinct rock types in a dynamically forced system are deformed asynchronously,so there should be a mutually-restricted force in the system.When the increase of the force has attained the critical limit,the initial steady state of the system is not maintained,leading to a change of the distance in the relating moment of force.During this process,the potential energy is transformed into kinetic energy,forming a shear-compressive thrust that will cause an initiation of strong earthquakes.Therefore,the force of differential deformation is a driving force of strong-seismic event.This mechanism is proposed in a qualitative consideration without any scale restriction.It is also considered that the equilibrium of distinct energies has been involved in this process.Based on the proposed mechanism,the relationship between slow deformation and quick earthquake generation,seismostructures and petrology have been demonstrated in this paper as well.

It has been found from field observation and laboratory study that the fault rocks on the Beishicheng fault zone in Miyun region, Beijing can be classified into four main types: cataclasite series, mylonite series, pseudotachylite and fault gouge. They have distinct features in mineralogy, deformation and microfabric, representing the different mechanisms of their origin. It is shown by the features and occurrences of the fault rocks in this region that the fault zone had experinced two stage of movement of different mechanical behavior: the ductile shearing in the early stage and the brittle fracturing in the late stage accompanied by seismic events.The existences of pseudotachylite and cataclasite types of fault rocks can be regarded as the potential evidences for seismic events. The former is produced by preferred melting of minerals in country rocks due to the frictional heating on the fault plane during seismic faulting, while the later is a product of brittle fracturing due to rapid release of strain energy. During rapid frictional heating process of seismic faulting, the mafic minerals are the first to be melted, but the felsic minerals are melted at the temperature much higher than the mafic ones, so that the SiO2 contents in the pseudotachylite are much lower than that in the country rocks. That is why the crush breccia and breccia in pseudotachylite consist mainly of felsic materials, and this characteristics are completely different from that of magmatic origin.

The ultramafic nodules widely distributed in Cainozoic basalt in eastern China are regarded as fragments of upper mantle that were brought up to the ground surface by basaltic magma. It is suggested that the study of this kind of nodules would offer some direct information about upper mantle. The textures of some spinel lherzolite nodules collected from some regions in eastern China were discussed in this paper. Three main types of texture can be distinguished, such as coarse granular, porpbyroclastic and granuloblastic. Their fabrics were also analysed. And the preferred orientation of minerals indicates that the coarse granular type is lacking in orientation, whereas the porphyroclastic type has distinct orientation, and the lalter’s fabric feature is followed by the granuloblastic type with some variation. Thus, the coarse granular-porphyroclastic-granulobla-stic transitional sequence has been established. Moreover, the textures and fabrics of Alpine type of peridotite from a suite of ophiolite formed by emplacement are comparable with these kinds of nodules, it enables us thus to further infer their mantle origin.

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.