Abstract:Abstract: Many new findings and achievements have been obtained in the special-subject study of the "3D lithospheric structure of China". They are as follows: China's first "3D lithospheric structure database" has been established; China's lithospheric structure model has been constructed; the knowledge of the behaviors and structures of the lithosphere and asthenosphere below eastern China have been deepened, it has been proved that there exists a transition zone with the "layer and block" structure between the lithosphere and asthenosphere, and a giant low-velocity anomaly belt has been found at 70～250 km depth from East Asia to the western Pacific region; an apparent age structure of being "older in the upper part and younger in the lower part" has been revealed in the lithosphere below eastern China; a petrological structure model of the lithosphere of continental China has been constructed, in which five types of lithosphere below continental China and its adjacent sea areas are distinguished; a classification scheme of lithospheric tectonic units of China is proposed, in which continental China and its adjacent areas are divided into two lithospheric domains and six lithospheric blocks; the existence of a gigantic latitudinal structure on the Qinghai-Tibet Plateau has been verified; and some new findings and knowledge have been obtained in the geological context.

Abstract:Abstract: In light of the principle of combining the Earth's surface tectonics with deep tectonics, the paper proposes six principles that should be followed in the lithospheric tectonic unit division. Based on the geological and geochemical characteristics, especially the characteristics shown by the geophysical field, with the Helan Mountains-Sichuan-Yunnan latitudinal tectonic belt as the boundary, the authors preliminarily divide continental China and its adjacent sea areas into two first-order lithospheric tectonic units: the Central Asian lithospheric tectonic domain and East Asian lithospheric tectonic domains, which are subdivided into six second-order lithospheric tectonic units: the Xiyu lithospheric block, Qinghai-Tibet lithospheric block, Songliao lithospheric block, North China lithospheric block, South China lithospheric block and South China Sea lithospheric block. Their main geological, geophysical and geochemical characteristics are described separately. Finally, some problems concerning the lithospheric tectonic unit division are discussed and some views are presented.

Abstract:Abstract: The lithosphere beneath the Qinghai-Tibet Plateau may be divided into three areas with different geophysical characteristics by the Kunlun fault and the Yarlung Zangbo suture. To the north of the Kunlun fault is the Qinghai Plateau, which is a basin and range area with contiguous gravity highs and gravity lows. To the south of the Yarlung Zangbo suture is the southern Tibetan Plateau, which belongs to the Indian plate, covered by continental-margin sediments of the Indian plate. Its crustal structure is marked by a south-vergent thrust nappe system. The Main Himalaya Thrust(MHT) found in southern Tibet by the INDEPTH reflection profile coincides with the T4 reflector obtained by wide-angle seismic reflection fanshooting. The fanshooting profile extends through the Himalaya, but the T4 reflector is not displayed there. The extension of the MHT to the Higher Himalaya is merely a deduction. Therefore, whether the MHT does exist needs new evidence. The region from south of the Kunlun Mountains to the Yarlung Zangbo suture is the northern Tibetan Plateau, where the partially melted, strongly rheological lithosphere occurs. The area of partial melting is funnel-shaped. The prevalent low-velocity layer in the upper crust at 15～20 km depth in northern Tibet is the most rheological partially melted layer. With a persistent burial depth, this layer probably contains abundant water. Immediately below the aforesaid partially melted layer, there appears netlike inhomogeneous partial melting. The depth of the base of the partially melted body increases gradually from 80 km in the Yarlung Zangbo River northward to 200 km. The bottom tube of the funnel is situated at Qiangtang-Hoh Xil. The partially melted body in northern Tibet is formed by the back-arc high heat flow in the Qiangtang-Hoh Xil area produced by high-angle subduction of the Indian plate along the Yarlung Zangbo suture beneath the Qinghai-Tibet Plateau as the northward movement of the Indian plate was hindered by the Asian plate. Satellite gravity anomalies, aeromagnetic anomalies, seismic receiver function study, geochemical data and surface geological observations all show that the subduction of the Indian Plate along the Yarlung Zangbo suture only occurred in western Tibet west of the Yadon-Tanggula line, while in eastern Tibet east of the Yadon-Tanggula line, there only occurred collision between the Indian plate and the Tibet block rather than subduction of the former. The wholesale uplift of the Qinghai-Tibet Plateau resulted from the effect of hydraulic pressure. The Qinghai-Tibet Plateau was like a hydraulic pressure machine and the various stresses produced during the subduction of the Indian plate were transferred through partially melted rocks to the partially melted layer at 15～20 km depth, forming an equi-pressure surface. Driven by this equi-pressure surface, the bottom of the not partially melted crust above the low-velocity layer was uplifted synchronously. At the end of the plateau uplift, the collapse of the plateau caused the upper crust to flow at all sides, thus forming a series of NE-directed imbricate structures on the Qinghai Plateau, a series of arcuate thrusts convex southward south of the Yarlung Zangbo. Between the Kunlun fault and Yarlung Zangbo suture the eastward flow resulted in the formation of detachments in the upper crust. Although the formation of the Qinghai-Tibet Plateau is due to the subduction of the Indian plate, its uplift is not merely a rigid dynamic problem, but more importantly we should consider the fluid processes and cannot explain the plateau uplift mechanism simply using the plate theory based on rigid bodies. The deep part of the Tibetan Plateau is a vast heat reservoir; so the exploitation and utilization of the heat reservoir are an important research subject.

Abstract:Abstract: Mesozoic orogens in eastern China are different from continental-margin subductional and continent-continent collisional orogens and are not the product in a particular stage of development and evolution of continental-margin and continent-continent collisional orogens either. They are a new type of orogen resulting from orogeny due to asthenospheric upwelling at depth and may be distinguished from plate-margin and continent-continent collisional orogens by their tectonic setting, tectonic framework, tectonic deformation and metamorphism, magmatism and sedimentation and tectonic evolution. We consider that such orogeny caused by asthenospheric upwelling is another orogenic mechanism that is as important as continent-continent collisional and plate-margin subductional orogenies. Therefore the process of formation of orogens by asthenospheric upwelling is termed by us asthenospheric upwelling orogeny or East Asia-type orogeny. Viewing the Da Hinggan orogen, Yanshan orogen and other orogens in eastern China from the lithospheric-asthenospheric deep process, we think that the formation of these orogens is an orogenic event caused by vertically upward dynamic processes originating by asthenospheric upwelling at depth as well as a new orogenic mechanism. The evidence is as follows: (1) the lithosphere-asthenosphere dos not show a typical horizontal layered structure but asthenospheric material commonly occurs as mushroom-shaped upwelling plumes penetrating and intruding into the lithospheric mantle, thus causing the older lithospheric mantle to be extensively dismembered and delaminated and forming a steep contact pattern with the relics of the older mantle; (2) the chronological structure of the lithosphere has the nature of uncoupling, i.e.: the mantle is younger, while the crust is older; (3) mafic-ultramafic rocks generated by underplating and ascending of Mesozoic asthenospheric material along lithospheric fractures are found; (4) magmatism of Mesozoic volcanic-plutonic rocks is different from that of classic subduction-type and continent-continent collision-type magmatic rocks but is related to upwelling of the asthenosphere; and (5) the process of asthenospheric upwelling orogeny has the unique character of evolution from the deep level to shallow level. Asthenospheric upwelling orogeny in eastern China is a global important tectonothermal event and its orogenic process is as follows: (1) before and in the initial orogenic phase in the Early Mesozoic (230-180 Ma), upwelling and underplating of asthenospheric material at depth resulted in linear fracturing and local delamination of the cold and strong continental lithosphere; (2) in the main orogenic phase in the Mid-Late Jurassic (180-140 Ma), due to large-scale upwelling of asthenospheric material and its lateral intrusion and extension along the crust～mantle boundary at the base of the lithosphere, vertical differential movement was transformed into horizontal compression, and thus extensive fold and nappe structures occurred at the crustal surface, causing the continental crust to be thickened into the crustal root and the lithospheric root to be delaminated; and (3) in the late orogenic phase in the Cretaceous (140-80 Ma), with thickening of the continental crustal root and extensive delamination of the lithospheric root, the lithosphere entered a completely new stage of transition from compression to extension and substantial thinning and the asthenosphere upwelled to form mountains.

Abstract:Abstract： Two lithospheric-scale tectonic units may be distinguished in North China： the circular North China rift and its surrounding mountain ranges in the east and the Ordos cratonic block and its surrounding elongated down-faulted basins in the west. The former consists of the main quasi-circular basins and surrounding ranges, as well as the mountain ranges in Jiangsu and Shandong in the central part of the large quasi-circular basin. The North China rift basins formed mainly by pure shearing and distributed shearing (both of which contain simple shear components) deformation mechanisms during the Paleogene and Neogene-Quaternary respectively. They originated by the combined action of the uplift of the Ordos cratonic block and NE-directed compression on the Liupan Mountains at the southern margin of Ordos from the Qinghai-Tibet Plateau collision zone. In the Cenozoic, during the rapid extensive lithospheric thinning, the rate of the E-directed extension in the eastern North China region was much higher than that in the Ordos block in the west, which implies that the eastward flow of the asthenospheric material may have actively dragged the overlying lithosphere eastward. There might be three passageways to allow the eastward flow of the asthenospheric material below the Qinghai-Tibet collision zone： (a) from the southern part of the plateau through Songpan-Garzê and Sanjiang (which refers to the Lancang, Nujiang and Jinsha rivers flowing in eastern Tibet, southwestern Sichuan and western Yunnan) to the South China Sea, (b) from the northern part of the plateau through the Liupan Mountains, peripheries of Ordos and Northeast China plain to the Sea of Japan, and (c) from Pamir through the Tianshan Mountains, western Mongolia and Baikal to the Okhotsk Sea.

Abstract:Abstract: In recent years, with the development of geosciences, there has been a growing interest in the study of electrical conductivity structure of the continental lithosphere, which is because the results of solid geophysical research show that the study of electrical conductivity structure of the continental lithosphere can provide important physical grounds for research in other areas of geosciences. Magnetotelluric(MT) sounding is an indispensable geophysical method for the study of the structures of the crust and upper mantle in the context of electrical conductivity. For a long time, great efforts have been devoted to the study of MT technologies in China. At present, with the development of science and technology, major advances have been made in instrumentation, data acquisition or processing technology and inversion technology. In China, superwide-band and high-precision MT survey techniques have been applied and data processing and inversion technologies have been improved greatly and in the main are compatible with the world's advanced technologies. Therefore, an MT profile was run along the Yingxian, Shanxi, to Shanghe, Shandong, in 2001. A 2D conductivity structure model of the profile, obtained by using the advanced MT data processing method and rapid release inversion (RRI), shows the features of the conductivity structure of the lithosphere in North China. According to the electrical features, the North China lithosphere is divided into the eastern and western parts by the frontal fault of the Taihang Mountains. The eastern part is characterized by low resistivity and the western part by high resistivity. In the eastern part, the electrical structure of the upper curst corresponds roughly to a tectonic framework of alternating uplifts and depressions in the North China rift system and the lithosphere conductance reaches a maximum of 30 000 S, being far greater than that of the Andes magma arc area with strong volcanic activities and that of the Tibetan Plateau. In the western part, the lithosphere of the Taihang and Hengshan mountains, marked by high-resistance blocks, is characterized by the conductivity structure of the stable continental lithosphere. However, a group of gently west-inclined high-conductive layers, with a conductivity of 0.04—0.25 S/m and a top depth of 20 km and a bottom depth of 40 km, were discovered under the high-resistance block of Hengshan Mountain.Study indicates that the very low-resistivity feature of the crust below the North China rift basin is probably determined by the thermal structure and regime in the curst and mantle of the rift basin. According to a discussion on continental resistivity models, it can be inferred that the “asthenosphere” character defined by predecessors might not exist in the upper mantle below the Ordos block. Although the North China rift basin is a Meso-Cenozoic tectonically active area, its activity is weaker than that of younger volcanic arcs or zones with violent tectonic movement. Therefore, the asthenosphere character of the North China rift basin is not distinct. That is one of the possible reasons why there is no "high-conductive layer of the upper mantle" in the MT profile from Yingxian to Shanghe, which images the asthenosphere electrical characters. However, according to the survey results, it can be inferred that the crust and lithosphere of western North China are thicker than those of eastern North China. In order to obtain more accurate results, more intensive and precise geophysical surveys and studies remain to be conducted.

Abstract:Abstract: There exist Meso-Cenozoic crust-mantle and lithosphere-asthenosphere interaction zones in the lower lithosphere beneath eastern China, which are also two important magma sources. The heat and material exchanges between crust and mantle and between lithosphere and asthenosphere in the interactions and their dynamic processes are the critical mechanisms for thickness readjustment in the interior of the Meso-Cenozoic lithosphere, lithospheric uneven thinning and tectono-magmatic mineralization. Three types of crust-mantle interaction can be recognized in the interior of the continent; they are the interactions between mantle-derived underplating melts and the lower crust, between the delaminated lower crust and weakening lithospheric mantle and between the deeply subducted crust and mantle wedge in the continental-continental collision zone. Although the volcanic rock associations formed by the three types of crust-mantle interaction are somewhat different, their magma sources all contain crustal components. The lithosphere-asthenosphere interaction zone is also a major component of the magma source, which consists predominantly of asthenospheric mantle and in the main contains no crustal component. Lithospheric thinning was largely coeval with large-scale asthenosphere-derived basalt eruption and also with transformation of the two types of interaction. It occurred about 100 Ma later.

Abstract:Abstract: The focal mechanism solutions of 3130 moderate and strong earthquakes occurred in continental China and its surroundings between 1918 and 2005 have been analyzed systematically, and according to their characteristics the tectonic divisions of the lithospheric stress field have been determined. The distribution of extensional and compressive axes was studied by statistics. The results suggest that the stress field of the lithosphere and tectonic movement in and around continental China are attributable to the motions of the Eurasian plate relative to the Indian, Pacific and Philippine Sea plates and interactions among blocks within the continental plate. The strong compressive stress due to collisions between the Eurasian and Indian plates dominated the movements from the Himalayas to Tianshan mountains in western China. Azimuths of the horizontal component of compressive stress P-axes likely lie between 20° and 40°, forming a nearly NE-directed stress field in the wide region west of the North-South Seismic Belt. Thrust type strong earthquakes occurred frequently along the edges of the Qinghai-Tibet Plateau and in the Tianshan region. Most normal fault type earthquakes are concentrated in the central Qinghai-Tibet Plateau with high altitudes. The horizontal component of the fault dislocation is oriented in an E-W direction. It implies that, simultaneously with the north-south strong compression and shortening in the Qinghai-Tibet Plateau and its surroundings, a nearly E-W-directed extensional motion apparently occurred in the high-altitude area of the central part of the plateau. Focal mechanism solutions in North China show that the earthquakes occurred under the combined action of the ENE compressive stress due to the subduction of the Pacific plate beneath the Eurasian plate and the NNW extensional stress in a unifying extensional stress field with a 170°azimuth in a vast region from Baikal Lake through North China to the Ryukyu Trench. The Longitudinal Valley fault of Taiwan is the boundary of collision and compression between the Eurasian and Philippine Sea plates. The stress field due to the northwestward motion of the Philippine Sea plate controls the stress field of the lithosphere from the Longitudinal Valley of Taiwan through the South China block to the eastern part of the southern segment of the North-South Seismic Belt. The results of the focal mechanism solutions also indicate that the North-South Seismic Belt that divides continental China into the eastern and western parts is the boundary of the influence scope between the Indian plate and eastern Philippine Sea and the Pacific plate within in the interior of continental China.

Abstract:Abstract：The continent of China and its adjacent land and sea areas were formed by convergence of a number of small plates and blocks since the Late Paleozoic. In the Mesozoic, in eastern Asia the lithosphere underwent extension, breakup and thinning and the asthenosphere upwelled, forming a giant rift system; whereas in western Asia India-Eurasia collision in the Paleocene resulted in crustal shortening and uplift, forming the Qinghai-Tibet Plateau and Himalaya orogenic belt. Data of seismic and explosion seismic surveys and other geoscience data obtained from continental China and its adjacent areas have been inverted by multidisciplinary means. The changes in characteristics and thickness of the lithosphere, crust and sediment layers have been studied and a series of maps compiled to discuss the characteristics and geodynamics of the lithosphere beneath continental China and its land and sea areas.

Abstract:Abstract： This paper discusses the 3D structure features of the asthenosphere beneath China and adjacent land and sea areas based on a systematic tectonic analysis of the 3D velocity structure by using seismic surface wave tomographic imaging. Both high-velocity blocks and low-velocity anomalies were discovered in the asthenosphere of the region, indicating the existence of vertical and lateral heterogeneities in the asthenosphere. Study of the 3D geometric structure of the low-velocity anomalies in the asthenosphere suggests that the anomaly beneath the South China Sea asthenosphere is composite mushroom-shaped. According to this finding, combined with the mantle body wave tomographic image, it is concluded that a giant composite mushroom-shaped low-velocity mantle plume might occur at over 2000 km depth in the region. In addition, this paper approaches the problem related to the impact of the asthenosphere on the lithospheric structure and their interaction.

Abstract:Abstract:The lithosphere beneath the Hingmong-Jihei (Hinggan-Mongolia-Jilin-Heilongjiang) region, northeastern China, is composed of the Ergun, Hinggan, Songneng and Jiamusi continental blocks and Mesozoic Wandashan accretionary complex. Nd isotope model ages indicate that: the Nd model age of the Jiamusi block is oldest, being 1500-2200 Ma; the age of the Ergun block comes next, being 1000-1600 Ma; and the Hinggan block and Songnen block have the same Nd model age, ranging from 500 to 1200 Ma. Geochemical tracing analysis indicates that the Nd isotope model age of Paleozoic supracrustal rocks is dominantly Mesoproterozoic, while that of Mesozoic granites is mainly Neoproterozoic. Therefore, it is concluded that the deep level of the crust is younger than the surficial level of the crust, indicating that the crust in the region has an age structure of being younger in the lower part and older in the upper part. The Os isotope analysis also indicates that the lithospheric mantle in this region also shows the younger character. The seismic (Vp) velocity structure shows that vertically the lithospheric structure in the region has the following two prominent features: (1) notably different from the traditional concept of the seismic lithosphere, the low-velocity zone of the lithospheric mantle has no persistent and continuous top interface which the low-velocity anomalous top is highly varied in depth and interlocks with the high-velocity anomalous bodies, and the low-velocity anomalies below some tectonic units may reach the Moho but the bottom interface occurring at 230-240 km depth is very persistent; and (2) the “overpass-type” velocity structure is manifested by the following: the velocity contours are generally distributed in a NE direction in the crust, in a NNW-NS direction in the lithospheric mantle and in a nearly E-W direction in the low-velocity anomaly asthenosphere.

Abstract:Abstract: Two-dimensional (2D) inversion and integrated interpretation of the gathered MT data were made by using 2D continuous automatic inversion technology and 2D electric structure cross-sections of the MT profiles were obtained in different areas. The 2D inversion cross-sections show that the eastern and western boundaries of the Songliao basin are steeper while the southern boundary is gentler and that low-resistivity objects are commonly present at 15-30 km depth in volcanic areas, which offers a basis for interpreting the existence of a magma pocket at depth of volcanic areas. In addition, the cross-section of 2D inversion of the MT data re-surveyed along Huanan-Laohe has also clearly revealed the following: the western segment of the cross-section has a high resistivity feature and a persistent lithospheric thickness (80-90 km), corresponding to the Jiamusi massif. The central segment of the cross-section obviously contains an electricity gradient zone, which furnishes a basis for the determination of the eastern boundary of the Jiamusi massif and its deep structure configuration. The eastern segment of the cross-section reveals a thrust nappe at shallow depth in an area east of the Jiamusi massif and an electric structure composed of alternate high-resistivity strips and low-resistivity strips at depth.

Abstract:Abstract: An intensive study has been conducted of the tectonic characteristics of the middle axial tectonic belt in the Lanping-Simao basin, western Yunnan, through reinterpretation of available DSS (deep seismic sounding) data and petroleum seismic reflection data and an integrated analysis of geophysical, geochemical and mineral resources data. Study indicates that the middle axial tectonic belt in the Lanping-Simao basin is a nearly N-S-trending large-scale tectonic belt integrating the fault zone, extensional structure and deep-seated uplift. The velocity structure of seismic sounding and seismic reflection profile indicate that mantle upwelling occurred at depth in the southern Simao basin of the middle axial tectonic belt. There is difference in dip direction of the fault system in the tectonic belt south and north of the basin. This tectonic belt is closely related to the distributions of mineral deposits, alkaline intrusions and regional geochemical anomalies. On the basis of the above study, combined with the tectonic analysis, the authors think that this tectonic belt is characterized by multi-stage activity and shows the extensional strike-slip characters. During the formation and evolution, the middle axial tectonic belt was dislocated by several nearly E-W-trending linear faults and has the distribution characteristics similar to those of the mid-ocean ridge in terms of the tectono-morphology. The tectonic belt has an important controlling effect on the tectonic evolution of the basin and formation of mineral deposits.

Abstract:Abstract: On the basis of the geological and geophysical characteristics of continental China, different lithospheric types in various regions are distinguished. In light of the petrological method, model of Earth's evolution and relationships between the seismic velocity and rock composition, eighteen petrological structure prisms corresponding with different lithospheric types have been set up. According to the dynamic properties, five types of lithosphere, i.e. cratonic, orogenic belt, rift, marginal oceanic crust and island―arc, are recognized in continental China. A petrological structure model of lithosphere beneath continental China is constructed and the inhomogeneous characteristics of the lithosphere beneath continental China are displayed for the first time.

Abstract:Abstract: Continental China consists of five types of lithospheres, namely, cratonic, orogenic, rift, oceanic, marginal sea crust and island-arc. As different types of lithospheres have different dynamic mechanisms and effects, the junction zones between the different types of lithospheres are bound to be discontinuity zones and have close relationship with continental metallogenesis. The greater majority of known metallic mineral deposits in continental China are distributed along the lithospheric discontinuities or reactivated discontinuities, indicating that the lithospheric discontinuities provide favorable spaces for migration and accumulation of large ore deposits (deposit clusters). A comparison of the sequences of the tectono-magmato-metallogenic events in the northwestern, eastern and southwestern regions of continental China indicates that the lithospheric crust-mantle petrological structures and large-scale metallogenesis depend on the latest and strongest magmatism, and that large-scale metallogenesis was initiated in the period of instability and de-rooting of the orogenic lithosphere and large-scale upwelling of the asthenospheric material. The occurrence of C-type adakite may be regarded as one of their indications. The Yangtze, Ordos, Tarim and Junggar basins distributed in China inland, which are called "cold basins" due to their low surface heat flow values, belong to the setting of the cratonic type lithosphere and tectonically are usually foreland basins of orogenic belts. The tectonic stability of the cratonic type lithosphere determined that these basins were swallowed, buried and modified continuously by their surrounding orogenic belts. Although many oil-gas fields have been found in these basins now, the areas outside these basins which are now covered by the front thrust sheets of orogenic belts should also be favorable areas for occurrence of oil-gas fields, i.e., those areas under granites of orogenic belts outside the basins are still important potential areas for oil-gas field finding. The plains and epicontinental seas such as the Yellow Sea, East China sea and South China sea in eastern China, which are called "hot basins" due to their high surface heat flow values, correspond with the rift- or oceanic-type lithosphere. They were formed when the coastal areas of eastern China entered a new tectonic evolution stage—the continental rifting stage—during the Cenozoic, which is marked by extensive eruption of basalt. The input of convective mantle material and heat resulted in the increase of terrestrial heat flow values in basins and thus the basins became "hot basins" with the corresponding rift-type lithosphere and even oceanic-type lithosphere (e.g. the Central basin of the South China Sea). The large-scale eruption of mantle-derived basaltic magma occurring concomitantly with rifting and tectonic extension and rapid deposition and burial of abundant sediments are favorable for the formation of oil-gas fields, in which some components, such as CO2 in CO2 fields, might be mainly derived from the mantle. It is suggested that the plains and epicontinental sea areas in eastern China are one of the most potential oil-gas fields.

Abstract:Abstract: A model of basic structure of the tectosphere and uniform layer in the study area is preliminarily constructed by using 3D VP (km/s) values with a grid of 1°×1°to the 400 km depth in Northeast China and selecting two representative sections perpendicular to each other and a structure model spectrum to the depth of the transition layer in the study area is depicted by using eight VP value sections along different longitudes and latitudes. Through further integration of the data, a 3D lithospheric structure model is obtained. Layer B″in Northeast China likely consists of three parts, the low-velocity zone in the lower part, alternating medium-velocity and low-velocity zone in the middle-upper part and accelerated velocity zone in the upper part. The lower boundary of layer B″is a stable indicator for distinguishing between B″and B″′. The velocity value of the accelerated zone in layer B″is close to the velocity value in the lower part in layer B′. According to the conventional view, the place near the zone is the position of the basal interface of the lithosphere. From the shape of the top interface, it is inferred that there probably exist loci of discontinuous or abrupt changes in layer B″in Northeast China. The wide boundary form and its change in the upper and middle parts of layer B″may reflect the corrosion and assimilation of Earth's material in the surroundings by the asthenosphere. The upwelling of the asthenospheric material provides the source for solid mineral resources and also accelerates the formation of petroleum resources. The lithospheric structure is the result of dynamic balance reached by crust-mantle interaction, which involves the effect of the asthenosphere on the overlying Earth's material and has a dynamic controlling effect on petroleum and solid mineral resources.

Abstract:Abstract: The South China Sea is one of the four major marine petroleum accumulation centers in the world and also China's only marginal sea where oceanic crust is developed. Petroleum exploration shows that petroleum fields in the South China Sea are distributed in the northern, western and southern continental-margin sedimentary basins and that large- and medium-sized petroleum fields are concentrated in basins of the western sea area. These basins are from north to south the Yinggehai-Qiongdongnan basin, Wan'an basin, Meigong basin, Zengmu basin and Brunei-Sabah basin. They contain mainly gas and subordinately oil. Moreover, there are several large potential petroleum-bearing basins in deep-water areas of the region. Further studies indicate that the petroleum distribution of the South China Sea has close relationship with the deep lithospheric structure. Tectonically, the petroleum-bearing basins in the South China Sea are located on or at the edges of the lithospheric blocks, controlled by the development and evolution of large lithospheric faults. The Moho surfaces in these basins are uplifted remarkably and form mirror images of the basin basements. The crust of the basins is only several kilometers thick at the thinnest site, where the heat flow values are notably higher than those in their surrounding areas. The thickness of the thermal lithosphere is reduced greatly. Seismic topographic imaging shows that at depths of these basins an enormous NW-trending uplift zone of the upper mantle extends from the Red River Mouth southeastward through the southwest sub-basin of the South China Sea to the northeast of Borneo, which macroscopically controls the petroleum distribution and accumulation of the South China Sea.

Abstract:Abstract: The extension-thinning mechanism of the eastern North China rift and the tectonic stress field at its peripheries during the Cenozoic and the mechanism of the uplift of the Ordos craton and formation of its peripheral down-faulted basins in the west are the hot topics of the current research, but they are seldom approached from the angle of numerical simulation. The authors used the finite element program FEVPLIB to perform numerical simulations of five sections in this region and present the following views according to the results. (1) The extension-thinning of the lithosphere near the Pacific subduction zone are strong, which coincides with pulling-apart of the Okinawa trough that the section passes through, while the effect of the Pacific subduction on the extension-thinning of the North China basin that is relatively far away from the subduction zone is weak. (2) Upwelling of asthenospheric material beneath the North China basin during volcanic eruptions resulted in the extension-thinning of the North China rift, which conforms to the mechanism of pure shear. At present the lithosphere beneath the North China region has tended to be in isostatic balance and the dynamic system tends to be in a steady state. (3) The Liupan Mountains were thrust over the Ordos block, indicating the compression on the northeastern margin of the Qinghai-Tibet Plateau, which was a great force of pushing North China and might induce the uplift of the Ordos block, while the movement of the Ordos block to the northeast provided the background of extension of the peripheral basins. (4) The extension-thinning of the lithosphere beneath the North China region is the combined effect of the compression from the Liupan Mountains and the subduction of the Pacific plate in the east. The simulation results are in agreement with the GPS data, gravity anomalies and 3D lithospheric structure in the study region.

Abstract:Abstract: Based on the high-resolution body wave tomographic images and relevant geophysical data the authors calculated the form and vertical and tangential velocities of mantle flow. Mantle flow in East Asia and the Western Pacific may fall into three patterns: (1) in the East-Asia marginal rift system and western Pacific marginal seas the mantle flow is marked by an upwelling mantle flow, characterized by flow convergence in the lower mantle and divergence in the upper mantle, especially for the South China Sea, where the structure of the upwelling mantle flow may be roughly outlined as a “工” shape in the upper mantle, a column shape in the middle and a divergent shape at the bottom; (2) in Siberia there is a “人”-shaped downwelling mantle flow, characterized by mantle material convergence in the upper mantle and divergence in the lower mantle; and (3) in the Qinghai-Tibet Plateau-Burma-Indonesia Tethys subduction zone, there is a “人”-shaped downwelling mantle flow, which is also characterized by flow convergence in the upper mantle and divergence in the lower mantle. The three regions of mantle convection beneath East Asia and the Western Pacific are in agreement with Western Pacific, Paleo-Asiatic and Tethyan tectonic domains. The material in the central part of East Asia shows no trend of flow in the deep interior of the mantle. The upwelling mantle flow originates from the core-mantle boundary and is mainly manifested in the lower mantle and lower part of the upper mantle. At the top of the upper mantle and at the surface, its location coincides with that of modern hot spots. The rate of vertical mantle flow is about 1 to 4 cm per year and the tangential rate is 1 to 10 cm per year.

Abstract:Abstract: Three nearly N-S-trending magnetotelluric (MT) sounding profiles (Yadong-Xuegula, Dagzê-Bam Co, Nagqu-Golmud) were deployed across the Qinghai-Tibet Plateau to detect and study the electrical conductivity structure of the crust and upper mantle using the superwide band MT method. The main characters of the electrical conductivity structure along the three profiles are as follows: (1) in the segment south of Nagqu, the electrical layer is thin, and the low-resistivity bodies are mostly distributed discontinuously in the form of a string of beads and apparently dip north at 20°～ 30°; (2) in the segment between Nagqu and Yanshiping, the thickness of the electrical layer is increased, and the low- or high-resistivity bodies occur as subhorizontal thin sheets; (3) in the segment north of Yanshiping, the electrical layer is thicker, and the low-resistivity bodies occur as big lenses dipping south relatively continuously at ~40°; and(4) the features of the electrical layers in the three segments are markedly different and closely related to the regional tectonic setting and magmatic activity. These important electrical characters provide important geophysical evidence for studying the mechanism of India-Eurasia collision.

Abstract:Abstract: The Qinghai-Tibet Plateau as an integral unit has continued to be affected by northward subduction of the Indian plate since the assembling of the continent; so certainly the structures of various original terranes have been constantly reworked. As a result, the differences of the plateau as a whole in the E-W direction have been formed. These differences are not in agreement with the constitutions, structures and east-west extensions of the various original terranes. This is not only manifested in the appearance of the N-S-trending fault structure across various individual terranes, but also in the gradual division in the E-W direction. This division is highlighted by the features of the regional gravity and magnetic fields, which is not only the result of the sectional rock magnetism and density variations but also the result of the variations in crustal composition and thickness of various areas and segments in the east and west parts of the plateau caused by different compressions undergone by different parts of the leading edges of the northward subduction of the Indian plate and the differences in block uplift and expansion. Based on the above, the paper analyzes the cause for the E-W division of the Qinghai-Tibet Plateau.The N-S-trending fault structure on the Qinghai-Tibet Plateau is not a local fault in the upper crust but is of deep origin. In the course of northward pushing, the various parts of the Indian plate did not keep abreast of each other. There were differences in pushing speed and subduction depth within the limits of the Qinghai-Tibet Plateau east of the Pamir Plateau. Due to the acceleration of the uplift of the Qinghai-Tibet Plateau, faults appeared on the Qinghai-Tibet Plateau itself. Because the differences have existed since the Miocene, more N-S-trending faults are found at the earth's surface and they extend to greater depths. The Moho depth and crustal thickness are both controlled by these faults, causing the variation in the regional gravity and magnetic fields. At the same time, the E-W extension of the plateau also affects the N-S-trending fault belt.

Abstract:Abstract: Based on the law of conservation of energy and heat flow data in continental China, the upper limit of heat production for the crust beneath continental China is determined as 1.3μWm-3. Then, using the data of the heat flow and helium isotopic composition of underground fluids, the heat productions of various tectonic units in the crust of continental China are estimated to be in the range of 0.58-1.12μWm-3 with a median of 0.85μWm-3, and the corresponding U, Th and K abundances are in the ranges of 0.83-1.76μg/g, 3.16-6.69μg/g and 1.0%-2.12% respectively. These data indicate that the abundances of the radioactive elements U, Th and K in continental crust of China are notably higher than those in the Archean crust, suggesting that the components of continental crust of China are highly evolved. In addition, the crustal composition of continental China exhibits significant lateral heterogeneity. The crust beneath eastern China is enriched in highly incompatible elements such as U, Th and K relative to that beneath western China, and the crust beneath fold belts is enriched in U, Th and K relative to that beneath cratonic areas. It is inferred on the basis of a positive correlation between the SiO2 content and heat production of continental crust that the crust beneath eastern China and fold belts are more felsic than beneath western China and cratons. This regional variation is consistent with the results of inference from the seismic wave velocity data in China. According to the fact that the seismic wave velocity and heat production range of the crust of continental China are lower than the global average values, combined with a comparison with the global crustal composition models published by previous studies, it is deduced that the abundances of highly incompatible elements such as U, Th and K in continental crust are overestimated in the average composition models of global continent crust constructed by Rudnick and Fountain (1995), Rudnick and Gao (2003), Weaver and Tarney (1984), Shaw et al. (1986) and Wedepohl (1995).

Abstract:Abstract:The management system of the 3D lithospheric structure database of China is the management and service center of the 3D lithospheric structure database of China. The total system design was completed and all kinds of technical specifications were worked out based on an analysis of the requirements of the 3D lithospheric structure database of China. A metadata editor and browser that can be used for different metadata formats, such as FGDC, ESRI and XML, were developed by using the Component Object Model (COM) technique. The Geodatabase data model of ESRI, an object oriented data model, was adopted to design the 3D lithospheric structure database of China by using the Computer-Aided Software Engineering (CASE) tool. The object oriented Universal Modeling Language (UML) was used to design and optimize the database structure. Based on MapObjects (MO) and ArcObjects (AO) under Arcinfo 8.x, two different types of COM management systems, which are simple to operate, have a complete range of functions and are suitable to professional GIS experts and other users respectively to do any query and process, were established.