lithospheric structure in central eurasia derived from elevation geoid anomaly and thermal analysis we present new crustal and lithospheric thickness maps for central eurasia from the combination of elevation and geoid anomaly data and thermal analysis the results are strongly constrained by numerous previous data based on seismological and seismic experiments tomographic imaging and integrated geophysical studies our results indicate that high topography regions are associated with crustal thickening that is at a maximum below the zagros himalaya tien shan and the tibetan plateau the stiffer continental blocks that remain undeformed within the continental collision areas are characterized by a slightly thickened crust and flat topography lithospheric thickness and crustal thickness show different patterns that highlight an important strain partitioning within the lithosphere the arabia eurasia collision zone is characterized by a thick lithosphere underneath the zagros belt whereas a thin to non existent lithospheric mantle is observed beneath the iranian and anatolian plateaus conversely the india eurasia collision zone is characterized by a very thick lithosphere below its southern part as a consequence of the underplating of the cold and stiff indian lithosphere our new model presents great improvements compared to previous global models available for the region and allows us to discuss major aspects related to the lithospheric structure and acting geodynamic processes in central eurasia

penetration of mid crustal low velocity zone across the kunlun fault in the ne tibetan plateau revealed by ambient noise tomography abstract the ne tibetan plateau composed of the mesozoic accretions of lhasa qiangtang and songpan ganze terranes are bounded by the east kunlun qaidam block in the north with the boundary delineated by the kunlun fault the ne tibetan plateau is at a nascent stage of plateau growth resulting from the collision between the indian and eurasian plate starting 50 million years ago and is one of the best areas to study the growth mechanism of the tibetan plateau in this study we process continuous ambient noise data collected from 280 stations during 2007 and 2010 and generate rayleigh wave phase velocity maps at 10 60 s periods with a lateral resolution of 30 50 km for most of the study region by adopting a bayesian monte carlo method we then construct a 3 d vsv model of the crust using the rayleigh wave dispersion maps our 3 d model reveals that strong lvzs exist in the middle crust across the ne tibetan plateau and the lateral distribution of lvzs exhibit significant west east variations along the kunlun fault in the west of 98 e lvzs are confined to regions of the kunlun fault and the eastern kunlun ranges but absent beneath the qaidam basin while in the east of 98 e lvzs extend and penetrate northward into the east kunlun and qinling orogens over 100 km across the kunlun fault the strong contrast of the lvzs distribution along the kunlun fault may be related to the distinct neighboring tectonic units in the north a strong crust of the qaidam basin in the west blocking the penetration of lvzs but a weak crust in the qinling orogens facilitating the extrusion of lvzs the distribution of lvzs in the ne tibetan plateau is consistent with the crustal channel flow model which predicts a branch of north eastward mid crustal channel flow our 3d model clearly delineates the north extent of the mid crustal lvzs probably reflecting the status of channel flow in the ne tibetan plateau

lateral variation of crustal structure and composition in the cathaysia block of south china and its geodynamic implications abstract in order to clarify lateral variations in the crustal structure and composition of the cathaysia block in south china which was affected by violent mesozoic and cenozoic tectono magmatic activities we studied the crustal thickness and the poisson s ratio in this region using the h stacking method of teleseismic receiver functions our results show that the poisson s ratio varies between 0 20 and 0 29 and the crustal thickness ranges from 26 to 34 km in the cathaysia block the crustal thickness and poisson s ratio show considerable variations across the lishui haifeng fault the southeast coast magmatic belt is characterized by poisson s ratios 0 25 and a crustal thickness of 28 33 km reflecting probably intermediate to mafic compositions of the crust the southwestern part of the cathaysia fold belt exhibits a crustal thickness of 27 30 km and poisson s ratios

the distribution of the mid to lower crustal low velocity zone beneath the northeastern tibetan plateau revealed from ambient noise tomography we collected continuous seismic data recorded between 2007 and 2010 by 208 broadband stations from the chinese provincial digital seismic networks a seismic collaborative experiment of northern tibet and the northeastern tibet seismic experiment cross correlations of vertical component records are computed to extract the rayleigh wave empirical green s functions group and phase velocities are then constructed from the empirical green s functions in 8 to 50 s period at periods 25 s more than 10 lower velocities are imaged beneath the qaidam basin and high velocities are observed beneath the nonbasin regions at periods 30 s up to 10 lower velocities are imaged in the qiangtang and songpan ganze terranes from these group and phase velocity maps a three dimensional 3 d vsv model of the crust is derived the model shows that the qiangtang and songpan ganze terranes have a very thick crust with a prominent low velocity zone lvz in the middle crust the lvz thins out in the vicinity of the eastern kunlun mountains providing a new constraint on the mode of deformation across the tibetan plateau the northwestern qilian orogen where receiver functions reveal a moho deeper than the surrounding areas also features a relatively weak midcrustal lvz which we interpret as an intracrustal response associated with the shortening between the north china craton and the tibetan plateau

crustal velocity structure of the northeastern tibetan plateau from ambient noise surface wave tomography and its tectonic implications abstract broadband seismic data from the regional seismic network operated by the china earthquake administration and 32 temporary seismic stations are used to image the crustal velocity structure in the northeast tibetan plateau empirical rayleigh and love wave green s functions are obtained from interstation cross correlation of continuous seismic records group velocity dispersion curves for rayleigh and love waves between 10 and 50 s are obtained using the multiple filter analysis method with phase matched processing the group velocity variations of rayleigh and love waves overall correlate well with the major geologic structures and tectonic units in the study region shear wave velocity structures were then inverted from rayleigh and love wave dispersion maps the results show that the songpan ganzi terrane is associated with a low velocity at depth greater than 20 km the northern qilian orogen with higher elevation and thicker crust compared to the southern qilian orogen is also dominated by low velocity at depth greater than 25 km however there is no clear evidence of the low velocity mid to lower crust beneath the southern qilian orogen as the crustal flow model predicts the low velocity zone lvz beneath the northern qilian orogen may suggest that the crustal thickening and surface uplift of the northern qilian orogen are related to the lvz and the lvz may be considered as an intracrustal response to bear the ongoing deformation in the northern qilian orogen online material figures of crustal topography number of group velocity measurements checkerboard tests for nets stations and 1d velocity models

plate tectonic history basin development and petroleum source rock deposition onshore china abstract china comprises a mosaic of distinct continental fragments separated by fold belts these fold belts are suture zones resulting from the accretion of various fragments formerly separated by intervening areas of oceanic crust the major sedimentary basins onshore china can be classified into four groups those in western china are flexural developing as a result of north south compression in contrast those in the east are extensional and related to development of the pacific oceanic margin in central china basins have a more problematic origin those of north central china ordos sichuan are flexural basins controlled by eastward directed thrusting along their western margin in contrast basins further south chuxiong shiwandashan are predominantly extensional and related to major strike slip movements by synthesizing basin stratigraphies across china in tectonostratigraphic terms and in particular comparing the nature and timing of unconformities it is possible to formulate a coherent model for the palaeoreconstruction of china we identify five major tectonostratigraphic breaks which equate with the collision of the following continental fragments tarim north china carboniferous permian south china block permian triassic qiantang late triassic early jurassic lhasa block late jurassic early cretaceous and india early tertiary prior to permian times the southern margin of eurasia ran approximately along the northern border of modern china the late carboniferous collision of tarim north china with eurasia resulted in the development of a flexural basin junggar and deposition of non marine clastics to the south of the suture shallow marine deposition continued in the late permian early triassic the progressive collision from east to west of the south china block with the north china block resulted in a change to fluvial lacutrine sedimentation across the entire north china tarim block open marine carbonate deposition in the north of the south china block passed southward into a deeper marine clastic sequence deposited in a backarc basin further south a subduction zone existed along the southeastern margin of the south china block in western china northward subduction throughout the triassic resulted in the development of the songban ganzi accretionary prism with retroarc thrusting resulting in flexure and the first development of the tarim basin oblique collision of the qiantang block in the late triassic along the east of the south china block resulted in east west directed thrusting which initiated the suchuan and ordos basins continued strike slip deformation along the south western margin of the south china block resulted in the development of basins with a significant extensional component such as chuxiong the collision of the qiantang block with the southern edge of the tarim basin early jurassic resulted in a renewed clastic influx in both the tarim and junggar basins along the eastern pacific margin a compressional arc and retroarc basin in the south passed northwards into an extensional arc system subduction rollback of the extensional arc initiated rifting in the late jurassic in the eren and songliao basins the late jurassic early cretaceous collision of the lhasa block in the west rejuvenated the thrust systems bordering the western basin and resulted in a renewed clastic influx in the southeast the compressional arc phase culminated in widespread thrusting and folding of early cretaceous age in the northeast extension continued with the progressive migration of the rift system southward with time the arrival of the indian block in the early tertiary rejuvenated the bounding thrust belts of all the western basins in the east the change in convergence of the pacific plate to a more westerly direction is marked by extension and widespread rifting along the entire length of eastern china throughout most of china mesozoic and cenozoic deposition occurred in predominantly non marine environments source rocks in such settings comprise principally mudstones deposited in lakes organic rich mudstones these can accumulate in both deep and shallow lakes in order to accumulate substantial volumes the lake must be significant in space and time in china lacustrine orms occur in both rift and flexural basins lacustrine orms deposited under humid climatic conditions are restricted to the period of maximum tectonic subsidence in the flexural basins of western china source rock deposition follows basin initiation by 20 30 ma in the extensional basins of eastern china source rock deposition takes place 5 15 ma after basin initiation by contrast semi arid and arid climate lacustrine orms whilst being best developed during the period of maximum tectonic subsidence occur at all stages in the basin history

continental crust composition constrained by measurements of crustal poisson s ratio deciphering the geological evolution of the earth s continental crust requires knowledge of its bulk composition and global variability the main uncertainties are associated with the composition of the lower crust seismic measurements probe the elastic properties of the crust at depth from which composition can be inferred of particular note is poisson s ratio this elastic parameter can be determined uniquely from the ratio of p to s wave seismic velocity and provides a better diagnostic of crustal composition than either p or s wave velocity alone1 previous attempts to measure have been limited by difficulties in obtaining coincident p and s wave data sampling the entire crust2 here we report 76 new estimates of crustal spanning all of the continents except antarctica we find that on average increases with the age of the crust our results strongly support the presence of a mafic lower crust beneath cratons and suggest either a uniformitarian craton formation process involving delamination of the lower crust during continental collisions followed by magmatic underplating or a model in which crust formation processes have changed since the precambrian era

the structure of the moho in the northern apennines evidence for an incipient slab tear fault abstract this study investigates the geometry of the crust mantle boundary along the northern apennines italy and its relationship to the tectonic evolution of a retreating subduction system using receiver function analysis from teleseismic records the moho depth was computed beneath 26 seismic stations located in key positions along the orogen the results show a relatively shallow 20 km moho in the tyrrhenian side as expected from an extended overriding plate and a deeper moho 40 km in the subducted adriatic plate sw dipping 15 45 beneath the chain stations deployed on the northeastern edge of the plio quaternary extensional basins provide maximum moho depth estimates thus supporting the hypothesis that these basins define the zone where the two plates separate at depth in addition an abrupt change in the moho depth is recognized along strike of the orogen attributed to a 45 km wide trench normal deformation zone that crosses the northern apennines in the proximity of the livorno sillaro lineament this zone is interpreted as an incipient lithospheric tear fault which accommodates varying rates of trench retreat along the length of the subduction zone

crustal magnetic anomaly in the ordos region and its tectonic implications abstract in this paper the ngdc 720 v3 model is utilized to investigate the distribution of crustal magnetic anomaly and curie surface in the ordos block and its surrounding areas the curie surface is compared with the regional heat flow bouguer anomalies moho and seismicity the interior block has strong wide distributed magnetic anomalies well corresponding to the basement lithofacies the surrounding areas have weak anomalies of various strikes and intensities the magnetic anomaly confirms the geological finding that the yabulai and bayanhot basins are small blocks detached from the northern ordos block the magnetic anomalies at the satellite altitude reveal that deep materials flow northward from the northeast margin of tibet plateau to the qilian fold belt the depth of curie surface ranges from 24 to 42 km and the ordos block is dominated by curie surface depth over 32 km and average heat flow value of 44 mw m2 the distribution of bouguer anomalies is consistent with that of magnetic anomalies the well correlation between the curie surface and the seismicity is also explained

halogen and ar ar age determinations of inclusions within quartz veins from porphyry copper deposits using complementary noble gas extraction techniques abstract extension of ar ar methodology has been used to determine mineralisation ages from mica inclusions and to simultaneously evaluate the noble gas and halogen composition of inclusion fluids within irradiated quartz vein samples from five porphyry copper deposits samples have been collected from the potassic and propylitic zones of bingham canyon utah and four arizonan deposits silverbell globe miami pinto valley and ray data obtained using three noble gas extraction techniques laser ablation in vacuo crushing and stepped heating are compared with each other laser ablation provides a means for the analysis of individual fluid inclusions but is limited by blank levels and detection limits stepped heating and in vacuo crushing are bulk extraction techniques that preferentially release gases from solid and fluid inclusion phases respectively and can be used in combination to obtain accurate and meaningful ages of mineralisation ages obtained for porphyry copper deposits are as follows bingham canyon 37 1 0 5 ray 65 3 1 5 globe miami 61 7 3 4 pinto valley 63 2 8 0 and silverbell 55 8 1 8 the age of mineralisation at ray is of particular interest as it enables a reported discrepancy in k ar ages to be understood halogen data for the bingham canyon samples gives insight into the partitioning of the heavy halogens br and i between solid and liquid phases

crustal structure across the ne tibetan plateau and ordos block from the joint inversion of receiver functions and rayleigh wave dispersions abstract we investigated the crustal structure at 34 stations using the h stacking method and jointly inverting receiver functions with rayleigh wave phase and group velocities these seismic stations are distributed along a profile extending across the songpan ganzi terrane qinling qilian terranes and southwestern ordos basin our results reveal the variation in crustal thickness across this profile we found thick crust beneath the songpan ganzi terrane 47 59 km that decreases to 45 47 km in the west qinling and qilian terranes and reaches its local minimum beneath the southwestern ordos block 43 51 km at an average crustal thickness of 46 7 2 5 km a low velocity zone in the upper crust was found beneath most of the stations in ne tibet which may be indicative of partial melt or a weak detachment layer our observations of low to moderate vp vs 1 67 1 79 represent a felsic to intermediate crustal composition the shear velocity models estimated from joint inversions also reveal substantial lateral variations in velocity beneath the profile which is mainly reflected in the lower crustal velocities for the ordos block the average shear wave velocities below 20 km are 3 8 km s indicating an intermediate to felsic lower crust the thick ne tibet crust is characterized by slow shear wave velocities 3 3 3 6 km s below 20 km and lacks high velocity material vs 4 0 km s in the lower crust which may be attributed to mafic lower crustal delamination or and the thickening of the upper and middle crust

crustal structure and deformation of the se tibetan plateau revealed by receiver function data we analyze a large amount of receiver function data recorded by regional seismic networks of the china earthquake administration to estimate crustal structure and deformation beneath the southeast margin of the tibetan plateau and its surrounding areas we develop a comprehensive analysis method that facilitates robust extraction of azimuthal seismic anisotropy from receiver function data the method includes an estimate of fast polarization direction and splitting time by a joint analysis of radial and transverse receiver function data and an evaluation of measurement reliability by statistical and harmonic analysis we find significant seismic anisotropy with a splitting time of 0 5 0 9 s beneath the se margin of the tibetan plateau both the splitting time and fast polarization direction are comparable to those estimated from sks skks data suggesting that crustal anisotropy is the main cause of shear wave splitting of the sks skks wave this also suggests that deformation in the upper mantle is either weak or predominantly vertical and is obviously different from the one in the crust a vertical flow in the upper mantle combined with the observation of a thin lithosphere beneath the study area leads to the inference that part of the mantle lithosphere may have been removed and is descending into deep mantle stations located in the surrounding areas on the other hand exhibit very little to no crustal anisotropy the estimated moho depth and vp vs ratio also show a distinct difference between the se tibetan plateau and the surrounding regions stations on the tibetan plateau have a vp vs ratio of 1 79 which is substantially higher than those measured at the yunnan guizhou yungui plateau 1 69 our observations here are consistent with the scenario that the se tibet has been built by lower crustal flow they also suggest that the mantle lithosphere beneath the margin may have been mechanically decoupled from the upper crust

multiscale spatial distribution of crustal seismic anisotropy beneath the northeastern margin of the tibetan plateau and tectonic implications of the haiyuan fault abstract the haiyuan fault is a large strike slip fault in the northeastern ne margin of the tibetan plateau using new data recorded by a temporary seismic array this study obtains crustal seismic anisotropy measurements in different scales across the haiyuan fault by analyzing splitting of shear waves from local earthquakes parameters of shear wave splitting sws indicate clear zoning characteristics in seismic anisotropy in the upper crust the study area is divided into two different anisotropic subzones by the haiyuan fault the dominant orientation of fast polarizations is nne or ne north of the faults and wnw to ew south of the fault this pattern of spatial variation indicates the controlling impact of haiyuan fault to observed seismic anisotropy with a zone of dozens of kilometers from the haiyuan fault the dominant orientations of fast polarizations are wnw generally coincidental with the strike of the haiyuan fault except for several stations it indicates that the influence of the fault on stress could reach to about 10 km from the fault distance spatial pattern of anisotropy indicates multiple effects by stress faults and local tectonics it suggests different anisotropic mechanisms including stress induced anisotropy and tectonic or structural anisotropy the dominant orientation of fast polarizations can indicate in situ maximum horizontal principal compressive stress although there is always influence of tectonics the normalized time delays are higher around the haiyuan fault than those away from the fault suggesting stronger crustal seismic anisotropy in a narrow belt around the strike slip fault zone the sws parameters suggest that the haiyuan fault is the actual crustal boundary of ne tibetan plateau about 200 km north of the reported boundary of the tibetan plateau block combining with other studies in the crust and the lithosphere this paper infers possible two layer crustal anisotropy beneath the yinchuan graben north of the haiyuan fault the dominant orientation of fast polarizations are nne or ne in the upper crust probably originated from crack induced anisotropy but become wnw or nw in the middle lower crust possibly originated from deformation anisotropy

fine structure of the lowermost crust beneath the kaapvaal craton and its implications for crustal formation and evolution high quality data from a dense seismic array covering an area of approximately 60 40 km2 are used to obtain tight quantitative estimates of the fine scale velocity and density structure of the lowermost crust and the crust mantle boundary moho beneath the kaapvaal craton in the vicinity of kimberley south africa results based on a modified receiver function waveform analysis of moho conversions and crustal reverberation phases show that the crust beneath the array is thin 35 4 km with an average poisson s ratio of 0 254 the minimum s wave velocity contrast across the moho is 17 3 while the contrast in density is 15 4 the density contrast across the moho is particularly diagnostic for an assumed uppermost mantle density beneath kimberley of 3 3 gm cc as determined from mantle xenoliths the density of the lowermost crust is 2 86 gm cc indicating rocks of felsic to intermediate composition analysis of waveform broadening of the crustal reverberation phases relative to that of the direct p wave shows the thickness of the moho transition zone to be less than 0 5 km and the maximum variation in crustal thickness over the region of the array to be less than 1 km the flat and almost perfectly sharp moho together with the absence of a mafic lower crust suggests large scale crustal reworking in the period between crustal formation and the time of cratonic stabilization

neotectonics of the bailongjiang and hanan faults new insights into late cenozoic deformation along the eastern margin of the tibetan plateau

channel flow extrusion model to constrain dynamic viscosity and prandtl number of the higher himalayan shear zone constraining magnitudes of mechanical and thermo mechanical parameters of rocks and shear zones are the important goals in structural geology and tectonics talbot in j struct geol 21 949 957 1999 such parameters aid dynamic scaling of analogue tectonic models ramberg in gravity deformation and the earth s crust in theory experiments and geological applications 2nd edn academic press london 1981 which are useful to unravel tectonics in further details schultz ela and walsh in j struct geol 24 247 275 2002 the channel flow extrusion of the higher himalayan shear zone hhsz higher himalaya can be explained by a top to s sw simple shear i e the d2 deformation in combination with a pressure gradient induced flow against gravity presuming its newtonian incompressible rheology with parallel inclined boundaries the viscosity of this shear zone along a part of the himalayan chain through india nepal and bhutan is estimated to vary widely between 1016 and 1023 pa s and its prandtl number pr within 1021 1028 the estimates utilized ranges of known thickness 6 58 km of the hhsz that of its top subzone of ductile shear of normal shear sense stdsu 0 35 9 4 km total rate of slip of its two boundaries 0 7 131 mm year 1 pressure gradient 0 02 6 kb km 1 density 2 2 3 1 g cm 3 and thermal diffusivity 0 5 10 6 2 1 10 6 m s 2 along the orogenic trend considering most of the parameters specifically for the sutlej section india the calculated viscosity and the prandtl number pr of the hhsz are deduced to be 1017 1023 pa s and pr 1022 1028 the upper limits of the estimated viscosity ranges are broadly in conformity with a strong tibetan mid crust from where a part of the hhsz rocks extruded on the other hand their complete ranges match with those for its constituent main rock types and partly with those for the superstructure and the infrastructure the estimated mechanical and thermo mechanical parameters of the hhsz will help to build dynamically scaled analogue models for the himalayan deformation of the d2 phase

lateral variation of crustal structure in the ordos block and surrounding regions north china and its tectonic implications abstract crustal thicknesses and poisson s ratios in the ordos block and surrounding regions were estimated by the use of the h k stacking method on teleseismic receiver functions the data came from 353 temporary and permanent seismic stations in 2006 2011 results show that the crustal thickness and poisson s ratio gently vary within the ordos block with an average of 41 3 km and 0 265 respectively consistent with a felsic composition of the crust crustal thicknesses predicted on the basis of airy isostasy are consistent with the estimated thicknesses implying that the topography is approximately compensated the reactivated portion of the north china craton that has undergone mesozoic cenzoic lithospheric thinning is also characterized by the thinning crust while the ordos block maintains normal crustal thickness and average crustal velocity inferred higher densities in the lower crust and the anti correlation between poisson s ratio and crustal thickness in the ordos block may be the result from underplating of mafic magmas in the precambrian around the ordos block the paleoproterozoic khondalite zone in the northern edge has higher poisson s ratio and thickened crust which is consistent with the lower crust being of more mafic composition the weihe shanxi graben in the southeastern edge has mid high poisson s ratio high heat flow and thinning crust which is consistent with the known transtensional tectonic setting in the liupanshan thrust belt along the southwestern edge of the ordos plateau significant variations in crustal thicknesses and poisson s ratios occur on two sides besides a thickened crust a concaved moho implies horizontal shortening of this edge of the ordos block due to its collision with the northeastern tibetan plateau the structural differences between the eastern and western edges of the ordos block reflect that the ordos block is in tectonic stress environment of the western compression and the eastern extension

three dimensional lithospheric s wave velocity model of the ne tibetan plateau and western north china craton we present a new 3 d lithospheric vs model for the ne tibetan plateau netp and the western north china craton ncc first high frequency receiver functions rfs were inverted using the neighborhood algorithm to estimate the sedimentary structure beneath each station then a 3d vs model with unprecedented resolution was constructed by jointly inverting rfs and rayleigh wave dispersions a low velocity sedimentary layer with thicknesses varying from 2 to 10 km is present in the yinchuan hetao graben ordos block and western alxa block velocities from the middle lower crust to the uppermost mantle are generally high in the ordos block and low in the alxa block indicating that the alxa block is not part of the ncc the thickened crust in southwestern ordos block and western alxa block suggests that they have been modified two crustal low velocity zones lvzs were detected beneath the kunlun fault kf zone and western qilian terrane qlt the origin of the lvz beneath the kf zone may be the combined effect of shear heating localized asthenosphere upwelling and crustal radioactivity the lvz in the western qlt representing an early stage of the lvz that has developed in the kf zone acts as a decollement to decouple the deformation between the upper and lower crust and plays a key role in seismogenesis we propose that the crustal deformation beneath the netp is accommodated by a combination of shear motion thickening of the upper middle crust and removal of lower crust

shear wave structure in the northeastern tibetan plateau from rayleigh wave tomography 1 the northeastern tibetan plateau has undergone active shortening due to the india asia collision and has been an ideal place for studying the growth of the plateau to reveal deep structure that is responsible for geological observations in ne tibet we have constructed a 3 d shear wave velocity model from rayleigh waves recorded by 36 stations in the northeast tibetan plateau seismic experiment first the two plane wave tomography method was applied to compute the average and 2 d variations of phase velocities in a period range of 20 to 100 s then 1 d and 3 d shear wave velocity models were developed from the obtained rayleigh wave dispersions the entire region is characterized by a weak upper mantle with a relatively thin lithosphere of 80 100 km thick this observation helps to explain the active deformation at the kunlun mountains and the qinling orogen in ne tibet relative low velocity anomalies appear along and to the south of the kunlun fault kf in contrast to high velocity anomalies in the north and northeast one pronounced slow anomaly centered at 120 km depth is imaged right beneath the restraining bend of the kunlun fault which might be a northern extension of the large scale slow anomaly to the south of the fault we interpret it as a local feature due to its large magnitude and coincidence with the restraining bend it is probably related to anomalously high temperature and associated partial melting resulted from localized asthenosphere upwelling after the delamination of a thick lithosphere root the formation of the thick lithosphere root would require coherent shortening in the crust and mantle lithosphere caused by local compression due to the bend of the strike slip fault indicating that the kunlun fault is probably on lithosphere scale and has played an important role in accommodating the eastward extrusion of the tibetan plateau

crustal thickness map of the chinese mainland from teleseismic receiver functions abstract we present a new crustal thickness map of the chinese mainland and adjacent areas based on a compilation of previously published data more than 1900 estimates of crustal thickness from receiver function studies were collected and the weighted averages were used to develop a contour map of crustal thickness beneath the chinese mainland the combined dataset provided good coverage especially over eastern and central china and our analysis revealed crustal thickness variations of the chinese mainland with considerably more detail than in previous models our crustal thickness map shows a large variation from a thickness of less than 30 km in the mesozoic basin of eastern china to over 80 km in the tibetan plateau the thickest crust was found in central tibet while the thinnest continental crust was observed beneath eastern china normal to slightly thick crust 38 51 km was found for the stable precambrian basins and orogenic belts comparison between our model and other models reveals that the models share similar large scale and smaller scale features over large portions of eastern china where the data coverage is good however large differences up to 25 km in crustal thickness occur in areas with complex crustal structure or poor data coverage we also evaluated the quality of previous models by comparing them with our newly compiled point observations of crustal thickness

complicated crustal deformation beneath the ne margin of the tibetan plateau and its adjacent areas revealed by multi station receiver function gathering abstract we use a multi station stacking method to analyze receiver function data recorded by a large scale dense seismic array covering the northeastern ne margin of the tibetan plateau and its adjacent regions to estimate crustal thickness h vp vs ratio and crustal anisotropy fast polarization direction and splitting time for each station of the array we gathered all the receiver functions recorded by the station and its nearby stations located inside a circle with a radius of 0 5 we applied the h stacking technique and the joint inversion scheme to a total of 654 station clusters to measure the h and respectively the measured moho depth varies from a peak value of 67 km beneath the northern central plateau to 39 45 km beneath the surrounding blocks in the northeast the front of the depressed moho beneath the plateau margin exhibits a complicated geometry which suggests that when the tibetan plateau encroached upon the surrounding terranes the front expanded unevenly depending on the strength of the encountering terranes the thickened crust beneath the margin also has a very low vp vs ratio indicating that the crust is composed largely of felsic minerals more than one third of the station clusters 221 have a splitting time significantly larger than 0 2 s the average splitting times of the 221 measurements is 0 68 s which is comparable to those measured from the sks skks xks phases 0 94 s the fast directions estimated from the moho ps and xks phases recorded by the station clusters within the margin are very similar and are also approximately parallel to the strikes of major faults sutures and thrust fronts in the area the low vp vs ratio together with the observed fast polarization directions from the moho ps and xks phases suggests that shortening of the entire lithosphere orthogonal to the compressional direction is likely the main cause for the observed crustal thickening occurring at the margin we also found that the moho ps and xks recorded by stations inside the western hetao basin and the yinchuan basin present very different anisotropy which may suggest that the crust and mantle beneath the two basins have very different deformation patterns

velocity structure of the uppermost mantle beneath east asia from pn tomography and its dynamic implications 1 east asia is one of the most tectonically active regions on earth s surface due to the collision from the india plate and the suctions induced by the subduction of the pacific and philippine plates to better understand the complicated deformation and active seismicity of the area we conducted a pn traveltime tomography to estimate the compressive wave speed of the uppermost mantle beneath east asia we collected a total of 296 334 pn arrivals recorded by 1354 stations from 27 777 earthquakes in a rectangular area from 60 e to 145 e in longitude 15 n to 60 n in latitude the data set was carefully integrated from three different catalogs after examining potential systematic biases in the catalogs the inversion results revealed a large scale velocity perturbation in the study area pn velocity in the region west to 108 e is approximately 10 higher than that in the east in each region stable blocks tend to have high pn velocity while the boundary regions which show a high level of seismicity and surface deformation appear to have low pn velocity we further computed the benioff strain rate in the two regions and found it correlates negatively with the averaged pn velocity our observations here suggest that pn velocity which is predominantly determined by moho temperature is a good indicator of lithosphere strength

lithospheric architecture and deformation of ne tibet new insights on the interplay of regional tectonic processes abstract gps measurements indicate rapid lateral extrusion of the ne tibetan plateau which causes active ne directed crustal shortening and has initiated oblique shearing along the margins of ne tibet however the tibetan highlands terminate around 103 e longitude and topographic relief disappears to the northeast the exact reasons for this drop in elevation remain obscure due to widespread tertiary sediments and quaternary loess which obscure details of the lithospheric structure this study describes a new 310 km long deep seismic reflection line striking ne sw across the interior of ne tibet integrating its data with a previously described 165 km long deep seismic profile of the tibet ordos transition zone together these datasets provide a complete picture of the crustal architecture of the north easternmost tibetan plateau gravity anomaly and previous geological evidence also help constrain complex deformation pattern in the region interpretations of these patterns indicate the importance of the large scale sinistral haiyuan fault zone and inherited vertical variation in mechanical properties of the lithosphere in the overall tectonic evolution of the ne tibetan plateau the overall crustal architecture obtained in this study provides spatial context for the neotectonic evolution of ne tibet and helps constrain the interplay of geologic and geodynamic processes affecting ne tibet and adjacent regions

seismic anisotropy and implications for mantle deformation beneath the ne margin of the tibet plateau and ordos plateau the northeastern tibet and the ordos plateau connects east china and west china which are dominated by horizontal extension and compression respectively knowledge of seismic anisotropy beneath this transitional region can provide important constraints on deformation pattern of the crust and lithosphere mantle during an orogeny process we measured sks wave splitting parameters from the new installed regional networks and obtained a detailed anisotropy map for 119 broadband stations beneath the ne margin of tibet the observed wnw fast polarization direction is parallel to the surface geological features the coherence between the observed geodetic motion of the crust and fast axis direction suggests that the vertical coherent deformation of the lithosphere is the dominate source for the observed seismic anisotropy further east to the qinling orogenic belt the fast axis direction tracks change in strike of the faults with the fast direction aligning almost ew we suggest that both the lithosphere mantle and east extrusion of mantle material contribute to the observed anisotropy small value of delay time is observed interior the thick rooted ordos plateau suggesting a rigid and stable lithosphere with little deformation the deviation of fast polarization direction beneath the adjacent rifting regions might be caused by the edge flow induced by sharp changes in the thickness of lithosphere our results propose that the upper crust and mantle lithosphere beneath the northeastern tibet are at least partly coupled or subjected to the same boundary conditions which is inconsistent with the channelized lower crustal flow model

sulige field in the ordos basin geological setting field discovery and tight gas reservoirs abstract the sulige gas field in central ordos basin is one of the largest gas fields in china with about 860 7 billion cubic meters bcm of proven gas reserve this field covers an area of about 500 km 2 with largely tight clastic reservoirs the upper carboniferous lower permian deltaic sandstones and upper permian lacustrine mudstones deposited in a stable cratonic tectonic setting form an effective petroleum system that is favorable for gas accumulation in large scale stratigraphic lithologic traps based on wire line log response drilling stem test and core data a generalized classification system was developed for the gas reservoirs of the sulige field thus type i and ii rocks are capable of gas production without natural and or artificial fracturing type iii rocks are capable of gas production after artificial fracturing and type iv rocks are too tight to produce at commercial rates even with artificial fracturing the discovery of the sulige field not only adds large gas reserve in the ordos basin but strongly indicates the overlook potential of both tight sandstone reservoir rock and relatively porous and permeable sweet spots in it

large contrasts in crustal structure and composition between the ordos plateau and the ne tibetan plateau from receiver function analysis article i nfo article history we analyzed thousands of receiver function data recorded by 154 national and regional seismic stations to study the crustal structure beneath the ordos plateau and the ne margin of the tibetan plateau moho depth and average crustal vp vs ratio were measured at each station the ordos plateau and the trans north china orogen east of the ordos are underlain by a moderately thick crust of 42 km the weihe graben lying at the southern edge of the ordos plateau has a thin crust of 30 km while its southern neighbor the qinling orogenic belt shows a thick crust extending to as much as 45 km deep the moho depth beneath the ne margin of the tibetan plateau varies from 55 to 65 km we found a remarkable contrast between the tibetan and ordos plateaus in the measured poisson s ratio the ordos plateau is featured by a high poisson s ratio while the tibetan margin has a very low poisson s ratio in general mafic lower crustal rocks have a higher poisson s ratio than felsic ones the measured low poisson s ratio beneath the ne margin of the tibetan plateau thus indicates that the crustal column beneath the margin is rather felsic which seems to be inconsistent with a scenario of an inflated crust due to extrusion of lower crust material from the tibetan plateau to the margin

crustal structure beneath the weihe graben in central china evidence for the tectonic regime transformation in the cenozoic abstract in central china weihe graben wg and its adjacent area suffered intensive compressional tectonics in the paleozoic and the mesozoic then this region was dominated by extensional tectonics due to the far field effect of the india eurasia collision in the cenozoic we deployed a portable broad band seismic array in this region to investigate the crustal structure by using receiver functions integrated with regional geophysical and geological characteristics the analysis of the receiver functions reveals that the moho is 32 37 km 25 41 km and 41 km depth beneath the northern qinling terrane the wg and the southern margin of the ordos block respectively the moho depth increases beneath the southern boundary of the wg while decreases 10 15 km beneath the northern boundary of the wg the moho discontinuity beneath the wg is not a fully mirror image of the crystalline basement because the thickest sediments 10 km is in the south of the wg the crustal structure in this region reveals how the crust responds to the tectonic regime transformation the effect of the cenozoic crustal extension was top down however the cenozoic crustal extension has limited effect on the moho deformation we suggested that the compressional tectonics before the cenozoic dominated the lateral variation of the moho

continental rifting at pre existing lithospheric weaknesses continental rifting is the poorly understood thermomechanical process by which continents break up and new ocean basins form two dominant styles of continental rifting are recognized1 crevice style rifts are characterized by initial graben formation local uplift of the graben shoulders and little or no volcanism arch volcanic rifts exhibit an initial doming of the crust extensive volcanism and late stage graben formation the prevailing expla nation for the two styles is that crevice rifts form in response to regional horizontal stresses principally derived from the inter action of the lithospheric plates along their edges whereas arch volcanic rifts are thought to be the result of mantle convection currents which upwell directly beneath the rift axis2 we propose an alternative working model of continental rifting in which both styles initiate in response to regional horizontal stresses the different surface expressions of the two styles are explained in terms of differences in the mode of failure at different kinds of pre existing weaknesses in the continental lithosphere rather than differences in the nature of the driving forces involved

crustal structure underneath central china across the tibetan plateau the north china craton the south china block and the qinling dabie orogen constrained by multifrequency receiver function and surface wave data abstract investigating the crustal structure at the juncture region of the tibetan plateau the north china craton the south china block and the qinling dabie orogen is important to understand processes of uplift of the tibetan plateau and the craton destruction and preservation in this study we dropped the h k stacking of receiver functions rfs rf nonlinear inversion and joint inversion of rf and surface wave dispersion with multiple gaussian factors successively to invert the crustal thickness h average vp vs ratio k and s wave velocity in the juncture region the imaging results and the synthetic tests of multifrequency h k stacking were further used to study the crustal structure and related tectonic evolution our results show that the h and k values generally increase and decrease respectively as the gaussian factor increases in the study region which is consistent with synthetic tests of h k stacking the cores of the ordos block and the sichuan basin exhibit a typical cratonic crust whereas the zhongtiao mountains and adjacent qinling dabie orogen to the south may have undergone delamination of the lower crust local low velocity anomalies in the middle lower crust were observed in the western qinling orogen and qilian orogen whereas high s wave velocities in the middle lower crust were observed at the juncture region between the western qinling orogen and the qinling dabie orogen our results suggest that the lower crustal flow is probably restricted to the central area in the western qinling orogen and does not flow into the qilian orogen or the qinling dabie orogen

receiver function structures beneath the deep large faults in the northeastern margin of the tibetan plateau using the teleseismic p and s wave receiver functions of the dense linear temporary seismic array the crust and uppermost mantle structures beneath the deep large faults in the northeastern margin of the tibetan plateau were imaged the images of the first converted wave and the multiples indicated that the north fault zone of west qinling nwq mountain and diebu lueyang dbl faults cut the mohorovicic moho discontinuity and cause an obvious difference feature for the moho in the two sides of the faults the higher vp vs ratio and lower velocity layer is found beneath the west portion of the array near the tibetan plateau which implies a lower crust channel flow coming from the tibetan plateau the weak moho and higher vp vs ratio beneath the eastern portion of the array near the ordos suggest the upwelling of the hot mantle material the results also indicate an obvious deformation in the upper crust with the lower vp vs ratio beneath the middle of the array such upper crust deformation is closely related to the topography of the surface therefore we deduce that the deformation of the brittle upper crust is accompanied by the formation of the local topography during the uplift of the tibetan plateau which is also the primary reason for the active seismicity in the study region the deformation of the lithosphere asthenosphere boundary lab can also be associated with the formation of the diapir caused by the upwelling hot materials in the upper mantle due to the uprising of the thrusting plate caused by the subduction of the india plate the existence of the lower crust channel flow the crust shortening and the mantle diapir in the local region simultaneously implies that the elevation and formation of the tibetan plateau cannot be explained with a single model the higher resolution results for the crust and the mantle especially beneath the block boundary region are necessary to construct the completed geodynamic model to understand the formation of the tibetan plateau

lateral growth of ne tibetan plateau restricted by the asian lithosphere results from a dense seismic profile abstract we present high resolution receiver function images along a 700 km long dense seismic array extending from northern tibetan plateau to the alxa block crossing the entire qilian thrust belt qtb the dense stations with less than 2 km station intervals allow the receiver functions to unveil unprecedented details of crustal structures across the northern frontier of the growing tibetan plateau the migration image shows a thickened and strongly deformed qtb crust with an uneven moho and complex internal structures that are indicative of pure shear shortening the alxa block in contrast has a thinner crust a flat moho and little internal crustal deformation these results suggest that the lateral growth of ne tibetan plateau is restricted by the strong asian lithosphere which shows no visible subduction beneath the tibetan plateau as previously suggested

numerical investigation of the geodynamic mechanism for the late jurassic deformation of the ordos block and surrounding orogenic belts abstract orogenic belts have developed along the edges of the stable ordos block in northern china three main geodynamic models have been proposed to explain the formation of these orogenic belts they have included the collision between the north china and south china blocks subduction of the pacific plate and stresses transmitted over long distances from the closure of the mongolia okhotsk ocean however these explanations are still controversial and not universally accepted leaving the mechanisms that formed the orogenic belts poorly understood to address these fundamental questions we developed a 3d numerical model using the finite element method to explore the geodynamic mechanism for the late jurassic deformation of the ordos block and its surrounding orogenic belts we investigated the effect of different dynamic regimes on the late jurassic deformation of this region our primary results suggest that strong and stable ordos block remains undeformed despite its location at the center of a region of deformation east west trending fold and thrust belts would have developed along the north and south edges of the ordos block during the closure of the mongolia okhotsk ocean or the collision between the north china and south china blocks north south trending fold and thrust belts would have developed along the east and west edges of the ordos block due to subduction of the pacific plate however the paleo stress field in the late jurassic indicates that the orientations of the maximum compressive principle stress were nearly perpendicular to the edge of the ordos block and the compressive deformation around it was coeval it is difficult to explain the distribution of belts of deformation with a single stress regime our numerical model reveals that multi direction convergence pattern with time during the transformation of these three regimes can be used to interpret the formation and deformation styles of ringed mountains around the ordos block during the late jurassic this proposed mechanism results in many insights into the mesozoic tectonic deformation and mountain building of this region

receiver function analysis of crustal structure beneath the eastern tibetan plateau abstract we measure the crustal structure beneath the eastern tibetan plateau by analyzing three component teleseismic data recorded at 252 stations from january 1 2008 to march 31 2011 lateral variations of the crustal thickness and poisson s ratio are obtained by using receiver function method the thinnest crust is 27 km in the south yangtze craton and the deepest moho 70 km is estimated in the eastern margin of the tibetan plateau the distribution of poisson s ratio shows the heterogeneity that high poisson s ratios 0 27 are found in the chuandian plateau intermediate values 0 24 0 27 exhibit in the ordos block the qilian orogen the qinling dabie orogen the songpan ganzi terrane and the sichuan basin and low values 0 30 in the southeastern margin of the tibetan plateau can be considered as the evidence of the dominantly mafic composition or locally partial melting in crust our observations of the crustal thickness and poisson s ratio beneath the eastern tibetan plateau not only reveal the lateral inhomogeneity of the crustal structure but also provide some constraints on the mechanism of uplift and crustal thickening of the tibetan plateau

distribution of the crustal low velocity zones beneath the central and northeastern tibetan plateau insights from joint analysis of receiver functions and surface wave dispersion observations abstract a crustal and uppermost mantle shear wave velocity model beneath the central and northeastern tibetan plateau is obtained from the joint analysis of rayleigh wave phase dispersions and teleseismic p wave receiver functions at 188 broadband seismic stations deployed in this region this newly presented model reveals wide spread low velocity zones in the middle crust and these zones are mainly confined to the region south of the kunlun fault the velocities in the low velocity zones are extremely low

the behaviour of the fronts of komatiite lavas in medial to distal settings abstract field characteristics of komatiites and observations of flow behaviour and propagation processes for subaerial basalt lavas are used to reconsider the flow behaviour of archean komatiite lavas planar conformable bases at contacts with pelitic sedimentary strata the existence of coherent to quench fragmented tops but the absence of autobreccias indicate that many komatiite lavas were emplaced passively under laminar flow conditions to determine how widely this may apply to active komatiite lavas we model flow front thicknesses noting that the preserved flow thickness is thus significantly greater than the thickness of the propagating flow front we apply the concept of inflation of basalt lava flows to komatiites application of the jeffreys equation allows lava thickness to be determined as a function of flow velocity viscosity density and slope of the terrain using the results together with estimates of flow front velocities and viscosity in the reynolds number equation indicates that at expected low flow front velocities in medial to distal settings most komatiites would have propagated in a laminar flow state we therefore envisage that komatiites were turbulent in near vent settings and capable of physical erosion and at times as previously proposed channel forming thermal erosion as flow area increased downstream and magma supply rate to the flow front and the flow front velocity decreased significantly the flow state would have transformed to laminar flow preserved flow thicknesses are often considerably greater than the calculated flow front thicknesses for such low viscosity lavas indicating that the final preserved thicknesses are either due to flow inflation ponding in topography or that some komatiites were intrusions

effects of water and melt on seismic velocities and their application to characterization of seismic reflectors the effects of a silicate melt and water on seismic velocities are compared at relatively small fluid fraction less than 20 vol on the basis of a theoretical model of composite materials to show that the two fluids are clearly characterized by the velocity ratio vp vs for a silicate melt vp vs increases with increasing fluid fraction when a significant reflection is expected vp vs becomes much larger than 2 for water vp vs decreases as the fluid fraction increases to 10 vol then it increases but it remains similar to a solid state value about 1 8 unless the amount of water exceeds 15 vol this will be a good measure to distinguish between two candidates for seismic reflectors partially molten rocks and rocks containing free water if a reflector can be treated as a thin low velocity layer the velocity ratio in it can be estimated from the frequency dependence of reflection coefficient

crustal structure of the eastern qinling orogenic belt and implication for reactivation since the cretaceous a high resolution crustal model of the eastern qinling belt and central north china craton central ncc is obtained along a n s trending profile corridor by joint inversion of surface wave and receiver function the ncc is one of the oldest cratons on earth and the qinling belt is the suture zone between the ncc and south china block scb the qinling belt is characterized by low crustal velocity 1 8 the forward gravity modeling supports the presence of a high density layer 3 05 g cm3 at the base of the crust beneath the central ncc we propose that the high velocity in the lowermost crust beneath the central ncc is most likely due to the repeated mafic underplating which also results in high crustal vp vs ratio and is responsible for the rapid crustal uplift during the late mesozoic

oblique stepwise rise and growth of the tibet plateau two end member models of how the high elevations in tibet formed are i continuous thickening and widespread viscous flow of the crust and mantle of the entire plateau and ii time dependent localized shear between coherent lithospheric blocks recent studies of cenozoic deformation magmatism and seismic structure lend support to the latter since india collided with asia 55 million years ago the rise of the high tibetan plateau likely occurred in three main steps by successive growth and uplift of 300 to 500 kilometer wide crustal thrust wedges the crust thickened while the mantle decoupled beneath gently dipping shear zones did not sediment infilling bathtub like of dammed intermontane basins formed flat high plains at each step the existence of magmatic belts younging northward implies that slabs of asian mantle subducted one after another under ranges north of the himalayas subduction was oblique and accompanied by extrusion along the left lateral strike slip faults that slice tibet s east side these mechanisms akin to plate tectonics hidden by thickening crust with slip partitioning account for the dominant growth of the tibet plateau toward the east and northeast

poisson s ratio behaviour in various crystalline rocks application to the study of the earth s interior the study of poisson s ratio behaviour in various crystalline rocks under different temperatures and pressures shows this parameter to depend upon the rock composition rather than upon p t conditions the results of this study are presented in the form of a comparison of z distributions within the consolidated crust and continental upper mantle and the specific variations of in crust and mantle rocks underlying the voronezh crystalline massif vcm these investigations which are based upon seismic and seismological data as well as high pressure experiments should clarify in particular the composition and petrology of the earth s interior

receiver function study of the crustal structure of the southeastern caribbean plate boundary and venezuela 1 we have investigated crustal thickness and composition across the southeastern caribbean plate boundary with the receiver function technique we used teleseismic data recorded by a temporary broadband array deployed under the bolivar project and the permanent national seismic network of venezuela we used the primary p to s conversion and crustal reverberations to estimate crustal thickness and average crustal vp vs ratio over the region we observe large variations in crustal thickness and poisson s ratio estimated moho depth ranges from 16 km beneath the southeastern caribbean sea to 52 km beneath northeastern venezuela and the venezuelan andes there is a good correlation between crustal structure and tectonic terranes data from the precambrian guayana shield suggest that the underlying crustal structure is relatively uniform with a moderate thickness 37 km and an intermediate composition a thick crust is found below the foreland basins the two mountain systems in northern venezuela the serrania del interior and the serrania del falcon have a thin crust with arc composition and are likely dynamically supported by elastic rebound or underthrusting of the oceanic plateau that characterizes the southern caribbean on the other hand the venezuelan andes and perija range on the western side of the country are probably isostatically balanced by thick crustal roots

crustal structure beneath china from receiver function analysis 1 we collected and processed a large amount of high quality broadband teleseismic waveform data recorded by the 48 chinese national digital seismic network stations to estimate large scale lateral variations of crustal thickness and vp vs ratio hence poisson s ratio beneath china a statistical method was used to select mutually coherent receiver functions at each station which yielded over 200 traces for most of the stations with the conventional h the crustal thickness and vp vs ratio approach there is a large trade off between h and consequently multiple maxima are frequently observed in the h domain we introduced a weight function that measures the coherence between the p to s conversion and the reverberation phases at each h grid to reduce the trade off a 4th root stacking method was further applied to reduce uncorrelated noise relative to the linear stack these modifications turned out to be very effective in reducing the h trade off and yielded reliable estimates of crustal thickness and vp vs ratio the crust beneath eastern china is as thin as 31 33 km and the underlying moho is relatively flat and sharp in the western part of china the crust is considerably thicker and shows large variations the moho is observed at about 51 km depth along the tian shan fold system and about 84 km deep beneath the central part of the tibetan plateau the transition occurs at the so called n s belt between about 100 and 110 e which is featured by unusually high seismicity and large gravity anomalies the average vp vs ratio over the mainland china crust is about 1 730 0 249 significantly lower than the global average 1 78 0 27 of the continental crust this lower vp vs ratio may suggest a general absence of mafic lowermost crustal layer beneath china

regional variation in moho depth and poisson s ratio beneath eastern china and its tectonic implications abstract eastern china comprises a complex amalgamation of geotectonic blocks of different ages and undergone significant modification of lithosphere during the meso cenozoic time to better characterize its deep structure we conducted h stacking of receiver functions using teleseismic data collected from 1143 broadband stations and produced a unified and detailed map of moho depth and average poisson s ratio of eastern china a coexistence of modified and preserved crust with generally in airy type isostatic equilibrium was revealed in eastern china which correlates well with regional geological and tectonic features crust is obviously thicker to the west of the north south gravity lineament but exhibits complex variations in with an overall felsic to intermediate bulk crustal composition moho depth and values show striking differences as compared to the surrounding areas in the rifts and tectonic boundary zones where earthquakes usually occur systematic comparison of moho depth and values demonstrated that there are both similarities and differences in the crustal structure among the northeast china north china craton south china and the qinling dabie orogen as well as different areas within these blocks which may result from their different evolutionary histories and strong tectonic magma events since the mesozoic using new data from dense temporary arrays we observed a change of moho depth by 3 km and of by 0 04 beneath the tanlu fault zone and an alteration of moho depth by 5 km and of by 0 05 beneath the xuefeng mountains in addition striking e w difference in crustal structure occur across the xuefeng mountains to the east the moho depth is overall has values of 40 km and shows complex and large range variation with values between 0 22 and 0 32 these together with waveform inversion of receiver functions and sks shear wave splitting measurements suggest that the tanlu fault zone is at least a crustal scale fault and the xuefeng mountains may be a deep tectonic boundary between the eastern yangtze craton and western cathaysia block

cenozoic shortening budget for the northeastern edge of the tibetan plateau is lower crustal flow necessary 1 two of the most popular mechanisms for thickening the crust beneath the tibetan plateau are 1 pure shear with faulting and folding in the upper crust and horizontal shortening below and 2 flow of lower or middle crust without significant shortening of the upper crust to help discriminate between the relative contributions of these two mechanisms well constrained estimates of upper crustal shortening are needed here we document the cenozoic shortening budget across the northeastern tibetan plateau margin with several balanced cross sections that exploit thermochronological and magnetostratigraphic constraints these sections indicate 11 2 1 east west shortening since middle miocene time and 9 2 3 nne ssw shortening between middle eocene and middle miocene times with little subsequent shortening of this orientation shortening rates accelerate fivefold after middle miocene time given the present day crustal thickness of 56 4 km in northeastern tibet crustal restorations that remove cenozoic shortening suggest that the northeastern tibetan crust was 45 5 km thick prior to the india asia continental collision this precollision thickness estimate is equivalent to average continental crustal thicknesses both adjacent to the tibetan plateau 44 4 km and globally 41 6 km and suggests that pure shear alone may account for cenozoic crustal thickening in northeastern tibet in contrast to eastern tibet where in the absence of significant shortening structures crustal flow has been invoked to explain the addition of crustal material since middle miocene time our results may obviate lower crustal flow as a necessary crustal thickening agent in northeastern tibet

growth of the lower continental crust via the relamination of arc magma abstract how does continental crust transition from basaltic mantle derived magmas into an andesitic composition the relamination hypothesis has been presented as an alternative dynamical mechanism to classical delamination theory to explain new crust generation and has been supported by petrological and geochemical studies as well as by thermomechanical numerical modeling however direct evidence of this process from detailed seismic velocity structures is lacking here we imaged the three dimensional 3d velocity structures of the crust and uppermost mantle beneath the geologically stable ordos terrane of the north china craton ncc we identify a region of continental crust that exhibits extreme growth using teleseismic data and an imaging technique that models the common conversion point ccp stacking profiles our results show an approximately 400 400 km2 wide growth zone that underlies the primitive crust at depths of 30 50 km and exhibits a gradual increase of velocity with depth the upper layer of the growth zone has a shear wave velocity of 3 6 3 9 km s vp 6 2 6 8 km s indicating felsic material and the lower layer has a shear wave velocity of 4 1 4 3 km s vp 7 2 7 5 km s which corresponds to mafic material we suggest that this vertical evolution of the layered structure could be created by relamination and that the keel structure formed by relamination may be the root of the supernormal stability of the ancient ordos terrane

crustal structure of the northeastern margin of the tibetan plateau from the songpan ganzi terrane to the ordos basin abstract the 1000 km long darlag lanzhou jingbian seismic refraction profile is located in the ne margin of the tibetan plateau this profile crosses the northern songpan ganzi terrane the qinling qilian fold system the haiyuan arcuate tectonic region and the stable ordos basin the p wave and s wave velocity structure and poisson s ratios reveal many significant characteristics in the profile the crustal thickness increases from northeast to southwest the average crustal thickness observed increases from 42 km in the ordos basin to 63 km in the songpan ganzi terrane the crust becomes obviously thicker south of the haiyuan fault and beneath the west qinlin shan the crustal velocities have significant variations along the profile the average p wave velocities for the crystalline crust vary between 6 3 and 6 4 km s beneath the songpan ganzi terrane west qinling shan and haiyuan arcuate tectonic region p wave velocities of 6 3 km s are 0 15 km s lower than the worldwide average of 6 45 km s north of the kunlun fault with exclusion of the haiyuan arcuate tectonic region the average p wave velocity is 6 4 km s and only 0 5 km s lower than the worldwide average a combination of the p wave velocity and poisson s ratio suggests that the crust is dominantly felsic in composition with an intermediate composition at the base a mafic lower crust is absent in the ne margin of the tibetan plateau from the songpan ganzi terrane to the ordos basin there are low velocity zones in the west qinling shan and the haiyuan arcuate tectonic region the low velocity zones have low s wave velocities and high poisson s ratios so it is possible these zones are due to partial melting the crust is divided into two layers the upper and the lower crust with crustal thickening mainly in the lower crust as the ne tibetan plateau is approached the results in the study show that the thickness of the lower crust increases from 22 to 38 km as the crustal thickness increases from 42 km in the ordos basin to 63 km in the songpan ganzi terrane south of the kunlun fault both the conrad discontinuity and moho in the west qinling shan and in the haiyuan arcuate tectonic region are laminated interfaces implying intense tectonic activity the arcuate faults and large earthquakes in the haiyuan arcuate tectonic region are the result of interaction between the tibetan plateau and the sino korean and gobi ala shan platforms

crustal structure and composition beneath the northeastern tibetan plateau from receiver function analysis abstract we analyzed hundreds of p wave receiver function data recorded by 53 portable seismic stations to investigate the crustal structure beneath the ne tibetan plateau the moho depths identified by this study reveal that the crustal thickness decreases laterally from the qilian orogen 63 km to east kunlun fault eklf area 44 km the moho depth becomes obviously deeper northeast of songpan ganzi terrane and beneath the qilian orogen a remarkable contrast is observed in the measured poisson s ratio between the qilian orogen and eklf area the qilian orogen is characterized by lower poisson s ratio in general the higher poisson s ratios 0 30 in the eklf area can be considered as the evidence for dominantly mafic rocks in the crust the measured low poisson s ratio and the negative correlations between vp vs and the crustal thickness beneath the qilian orogen suggest dominantly felsic crust beneath the qilian orogen which is in contrast with the mid to lower low velocity crustal model beneath the ne margin of the tibetan plateau indicating that the low velocity zone terminates beneath the east kunlun area the seismic evidence suggests that the thickened crust is probably resulted from superposition of the successive intracrustal thrusts our results reveal the lateral inhomogeneity of crustal structure in this area and are inconsistent with the scenario of an inflated crust due to extrusion of lower crust material from the central tibetan plateau

crustal structure in the junction of qinling orogen yangtze craton and tibetan plateau implications for the formation of the dabashan orocline and the growth of tibetan plateau

new images of the crustal structure beneath eastern tibet from a high density seismic array abstract an east west trending high density seismic array was deployed along the eastern margin of the tibetan plateau to investigate its eastward expansion the 160 km long array spans the ruoergai basin minjiang fault minshan mountains tazang fault and west qinling the array included 330 short period seismographs spaced at 500 m intervals which recorded teleseismic 3 component waveforms over a one month period p wave receiver functions calculated from 35 teleseismic events provided an image of crustal structure the results show a massive thrust nappe structure around the minshan mountains and beneath the minjiang fault we suggest that this nappe formed after the closure of the paleo tethyan ocean the resultant triassic thrusting contributed to partial uplift of the eastern ruoergai basin and the minshan mountains in middle to late miocene time receiver function images show that the tazang fault is a crustal scale rupture cutting across the moho the western tazang fault appears as a nearly vertical strike slip fault accommodating left lateral shear at the terminus of the eastern kunlun fault after clockwise rotation from an approximate east west orientation to a nearly north south orientation the eastern tazang fault became a west dipping thrust fault which caused crustal thickening beneath the minshan mountains and the west qinling our results suggest that late cenozoic uplift of the eastern margin of the plateau is produced by eastward overthrusting and crustal shortening processes that absorbed slip along the tazang and kunlun faults

three dimensional density structure of the lithosphere beneath the north china craton and the mechanisms of its destruction abstract the lithosphere beneath the north china craton ncc has been thinning since the phanerozoic previous geophysical studies on ncc structures have mainly focused on the results of seismic wave propagation in this study we obtained 3d density structures of the ncc lithosphere by using the sequential inversion of observed gravity data and p wave travel times analyses of the resulting density model and discussions of the destruction of the ncc are provided our density model shows that distinct horizontal and vertical density heterogeneities exist throughout the lithosphere beneath the ncc in the west of the craton the ordos block is characterised by a relatively uniform high density lithospheric mantle while laterally heterogeneous densities are observed at shallower than 100 km depth distinct low density anomalies are imaged in the cenozoic yinchuan hetao and shaanxi shanxi rifts surrounding the ordos block comparing with the thinned lithosphere and high poisson s ratio the low density in the rifts may indicate partial melting induced by thermo mechanical erosion predominantly low density anomalies which represent an upwelling of the asthenosphere are revealed in the south of the taihang orogen as well as at the junction of the yinshan yanshan orogen near datong volcano and the taihangshan orogen from 100 to 200 km depth this supports the hypothesis of thermo mechanical erosion in these regions high density anomalies are visible at the base of the lithosphere or in the upper mantle beneath the central north china basin combined with high velocities at 300 km depth indicated by seismic tomography these high densities suggest that the lithospheric destruction of this region may not be explained by thermo mechanical erosion as there is no evidence of deep hot upwelling that could support thermo mechanical erosion

mountain building at northeastern boundary of tibetan plateau and craton reworking at ordos block from joint inversion of ambient noise tomography and receiver functions abstract we have obtained a high resolution 3 d crustal and uppermost mantle velocity model of the ordos block and its surrounding areas by joint inversion of ambient noise tomography and receiver functions using seismic recordings from 320 stations the resulting model shows wide spread low velocity zone vs 3 4 km s in the mid to lower crust beneath northeastern tibet plateau which may favor crustal ductile flow within the plateau however our model argues against the eastward crustal ductile flow beneath the qinling belt from the tibetan plateau we find high velocities in the middle part of qinling belt which separate the low velocities in the mid to lower crust of the eastern qinling belt from the low velocity zone in eastern tibetan plateau more importantly we observe significant low velocities and thickened lower crust at the liupanshan thrust belt as the evidence for strong crustal shortening at this boundary between the northeastern tibetan plateau and ordos block the most important finding of our model is the upper mantle low velocity anomalies surrounding the ordos block particularly the one beneath the trans north china craton tnco that is penetrating into the southern margin of the ordos block for 100 km horizontally in the depth range of 70 km and at least 100 km we propose an on going lithospheric mantle reworking at the southernmost boundary of the ordos block due to complicated mantle flow surrounding the ordos block that is the eastward asthenospheric flow from the tibet plateau proposed by recent sks study and mantle upwelling beneath the tnco from mantle transition zone induced by the stagnant slabs of the subducted pacific plate

crustal thicknesses and poisson s ratios in china by joint analysis of teleseismic receiver functions and rayleigh wave dispersion 1 a new grid search scheme which extends the stacking h algorithm to multi layered crustal models and fits observed dispersion of surface wave group velocity simultaneously is proposed to estimate the thickness poisson s ratio and average p wave speed of the crust we first apply it to a synthetic data of a 2 layered crustal model then we show the results analyzing records from 45 permanent broadband seismic stations in china the estimates at six stations agree well with results from deep seismic sounding profiles the crustal thicknesses agree in general with the crust 2 0 model we find that the poisson s ratio in the yangtze platform is rather low compared with the other two platforms the stations along the southeast coast of china have higher poisson s ratios the poisson s ratio of the whole region tends to increase as the average p wave velocity

crustal structure of china and surrounding regions from p wave traveltime tomography 1 a three dimensional 3 d p wave velocity model is developed for the crust and uppermost mantle of china and the surrounding area by applying the tomography method of zhao et al using 500 000 high quality p wave first arrivals extracted from the annual bulletin of chinese earthquakes abce this tomographic method can accommodate velocity discontinuities such as the moho in addition to smooth velocity variations the spatial resolution is 1 1 in the horizontal direction and 10 km in depth the velocity images of the upper crust correspond well with the surface geologic features such as basins and the tibetan plateau high velocity anomalies are found in the lower crust beneath the precambrian regions tarim basin ordos basin sichuan basin and western half of songliao basin the highest velocity anomaly is beneath the sichuan basin high and low velocity anomalies imaged beneath the bohai gulf are associated with the presence of a major cenozoic rift system in the lower crust beneath the south china block p wave velocities are lower in the north than in the south the indochina block shows low velocities both in the crust and in the uppermost mantle due to volcanism the pn velocities in the tibet area are higher than those in other areas largely due to thicker crust tomographic model significantly reduces the traveltime residuals tests conducted by relocating large explosions and earthquakes validate the 3 d velocity model

seismic evidence for an ancient rift beneath the cumberland plateau tennessee a detailed analysis of broadband teleseismic p waveforms broadband receiver functions developed from teleseismic p waveforms recorded on the midperiod passband of regional seismic test network station rscp are inverted for vertical velocity structure beneath the cumberland plateau tennessee the detailed broadband receiver functions are obtained by stacking source equalizd horizontal components of teleseismic p waveforms the resulting receiver functions are most sensitive to the shear velocity structure near the station a time domain inversion routine utilizes the radial receiver function to determine this structure assuming a crustal model parameterized by many thin flat lying homogeneous layers lateral changes in structure are identified by examining azimuthal variations in the vertical structure the results reveal significant rapid lateral changes in the midcrustal structure beneath the station that are interpreted in relation to the origin of the east continent gravity high located northeast of rscp the results from events arriving from the northeast show a high velocity midcrustal layer not present in results from the southeast azimuth this velocity structure can be shown to support the idea that this feature is part of a keweenawan rift system another interesting feature of the derived velocity models is the indication that the crust mantle boundary beneath the cumberland plateau is a thick probably laminated transition zonemore between the depths of 40 and 55 km a result consistent with interpretations of early refraction work in the area less

crustal structures across the western weihe graben north china implications for extrusion tectonics at the northeast margin of tibetan plateau the stable ordos plateau extensional weihe graben and qinling orogenic belt are located at the northeast margin of the tibetan plateau they have been thought to play different roles in the eastward expanding of the tibetan plateau peking university deployed a linear seismic array across the western end of the weihe graben to investigate the crustal structures of the tectonic provinces of this structure receiver function analyses revealed low to moderate poisson s ratios and anticorrelations between poisson s ratios and topography beneath the qinling orogen these features may indicate a tectonic thickening of the felsic upper crust by folding and thrusting within the qinling orogen we observed a strong horizontal negative signal at the midcrust beneath the ordos plateau which may indicate a low velocity zone this observation would suggest the stable cratonic ordos plateau had been modified due to the compression between the tibetan plateau and the ordos plateau we also observed an abrupt 4 km moho offset across the weihe fault changing from 44 km beneath the ordos plateau to 40 km beneath the qinling orogen we conclude that the weihe fault is a lithosphere scale fault shear zone which extends into the upper mantle beneath the weihe graben it acts as the major boundary separating the stable ordos plateau and the active qinling orogen

electrical resistivity structures northeast of the eastern kunlun fault in the northeastern tibet tectonic implications abstract only sparse deep geophysical data have been obtained in the region to the north of the eastern kunlun fault eklf in the tibetan plateau which leads to inconsistent and ambiguous descriptions of the area in various geodynamic models the detailed geophysical issues in the region including the northeast boundary of the plateau and the crust mantle coupling mode northeast of the eklf are under dispute to resolve these disputes we have collected magnetotelluric mt data along five profiles in the region to the north of the eklf since 2009 the interpretation of data from the latest profile labeled l5 which starts from the eastern margin of the qaidam basin crosses the qilian mountain and the hexi corridor and finally reaches the southern alashan block is the focus of this paper these new results are comparable with our previously determined structures the two dimensional 2d resistivity model supports three divisions of the qilian mountain a complex northern qilian a relatively simple sandwiched southern qilian and a transitional central qilian in between them our data indicate a relatively low resistivity layer at the middle lower crust below the eastern margin of the qaidam basin and the southern qilian mountain this result indicates a weak crustal zone wcz existing northeast of the eklf and is interpreted as a large north dipping thrust at this depth the presumed imbricated thrust in the crust in the northeastern plateau resulting from the indenting of the mantle wedge from the south is the primary process in the crustal thickening in the region the mt results indicate that the northeastern boundary of the tibetan plateau is not below the eklf instead we suggest that the northeastern boundary of the outgrowth of the tibetan plateau is along and below the northern rim of the hexi corridor

crust and upper mantle structure of the north china craton and the ne tibetan plateau and its tectonic implications abstract understanding the mesozoic cenozoic tectonic evolution of the north china craton ncc and the ne tibetan plateau tp requires detailed knowledge of the lithospheric structure using dense regional networks and temporary deployments as well as updated reference models we obtain the crust and upper mantle structure to 120 km depth our tomographic results show several major features which have particular implications for the weihe shanxi rift system wsrs deformation of the ne tp and lithospheric evolution of the ncc beneath the wsrs the crust gradually thickens from south to north the lithospheric mantle gradually becomes slower and the mid lower crustal velocities are lower in the weihe rift where rifting of the wsrs initiated we suggest that along strike variations of the lithospheric structures of the wsrs have played an important role in its multistage evolution a low velocity zone lvz in the mid crust beneath the qilian orogen is characterized by relatively higher velocities compared to lvzs in other parts of the tp thus coherent lithospheric deformation may occur due to the high viscosity of the lvz during early plateau growth causing strong anisotropy to develop the western ncc including the ordos block and part of the alashan block shows a high velocity cratonic root extending to the base of our model in contrast the lithosphere of the eastern ncc appears to have been completely modified during the mesozoic through cenozoic and presents a thin lithosphere of relatively low velocities underlain by hot asthenosphere we observed significant upper mantle heterogeneities in the ncc which may reflect its diachronous lithospheric modification

variations in crustal and uppermost mantle structures across eastern tibet and adjacent regions implications of crustal flow and asthenospheric upwelling combined for expansions of the tibetan plateau

how does crustal shortening contribute to the uplift of the eastern margin of the tibetan plateau the eastern margin of the tibetan plateau the longmen shan has triggered a vigorous debate to explain the uplift and maintaining of its steep and high topography several mechanical and kinematic models have been previously developed in order to investigate the tectonic and erosional control on the formation mechanism of the longmen shan but the contribution of crustal shortening has never been taken into account due to the lack of significant surface convergence rate about 3 mm a across the longmen shan range we investigate this question through 2d finite element modelling assuming visco elasticity rheology the numerical results are constrained with geological and geophysical observations across the longmen shan range we find that even low rate of crustal shortening contributes significantly to the uplift of the longmen shan this contribution has been greatly underestimated in previous studies the viscosity contrast between the tibetan plateau lower crust and the yangtze crust crucially controls the uplift of the longmen shan due to crustal shortening the ductile tibetan lower crust thickens to accommodate most of crust shortening as the eastward movement of the tibetan plateau is obstructed by the mechanical strong and stable yangtze craton the uplift rate contrast between the tibetan plateau and the sichuan causes a steep uplift rate gradient to produce and maintain the longmen shan steep and high topography in the time scale of several million years our results support a possible explanation for the paradox of the high topography and low convergence rate at the longmen shan range

lithospheric velocity structure of the northeast margin of the tibetan plateau relevance to continental geodynamics and seismicity abstract we provide teleseismic constraints on the continental collision zone along the sw ne profile from the tibetan plateau to the alxa block traversing lenglong ling a topographic boundary of the northeastern tibetan plateau our seismic profile crosses the qilian shan thrust belt a zone of intense earthquake activity that includes a pair of mw 5 9 earthquakes in 1986 and 2016 with a 30 year time interval occurring at the city of menyuan near lenglong ling a high degree of similarity between the two waveforms and their similar hypocenters indicate that the two events are repeating earthquakes both p and s wave receiver functions show contrasting lithospheric structure and crustal seismic properties across the repeating earthquake region suggesting that lenglong ling can be the crustal boundary between the tibetan plateau and the alxa block high frequency p receiver functions clearly show a sw dipping underthrusted upper crust beneath the foreland of the qilian shan thrust belt a strong low velocity feature above the intracrustal underthrust beneath southwest lenglong ling indicates a mechanically weak zone developed coeval with the main compressional deformation during the last major tectonic event our observed localized upper crustal deformation beneath lenglong ling can be direct evidence of the lateral growth of the northeastern tibetan plateau and can control the seismicity of the qilian shan thrust belt including the menyuan repeating earthquakes

crustal rheological strength heterogeneities control the formation of continental plateau margins the margins bordering the tibetan plateau show two end member morphologies in topographic gradient steep margins and low gradient margins to investigate the formation mechanism of convergent intracontinental plateau margins we conduct 2d numerical experiments to simulate crustal deformation process across plateau margins our numerical experiments demonstrate that heterogeneities in crustal rheological strength control significantly the formation of plateau margins when subjected to crustal convergence a very steep margin is the result of crustal convergence between plateau with weak lower crust and foreland basin with strong lower crust by contrast a low gradient margin could result from crustal convergence between plateau and foreland with less strength contrast this finding suggests that the diversity in topographic gradient along the tibetan plateau borders reflects heterogeneities in crustal rheological strength across the plateau margins steep gradient at the margins indicate large crustal rheological strength contrasts between the weak ductile lower crust of the tibetan plateau and its strong surrounding foreland basins like the sichuan basin the tarim basin and the qaidam basin beneath these steep margins the horizontal flow of the tibetan ductile lower crust is inhibited and forced to extrude to support escarpments low gradient at the margins indicate less crustal strength variations between the plateau and outer forelands like at the northeastern and southeastern margins where they might be outlets for the weak ductile tibetan lower crust to flow away from the plateau