surface wave tomography of the western united states from ambient seismic noise rayleigh and love wave phase velocity maps summary we present the results of rayleigh wave and love wave phase velocity tomography in the western united states using ambient seismic noise observed at over 250 broad band stations from the earthscope usarray transportable array and regional networks all available threecomponent time series for the 12 month span between 2005 november 1 and 2006 october 31 have been cross correlated to yield estimated empirical rayleigh and love wave green s functions the love wave signals were observed with higher average signal to noise ratio snr than rayleigh wave signals and hence cannot be fully explained by the scattering of rayleigh waves phase velocity dispersion curves for both rayleigh and love waves between 5 and 40 speriod were measured for each interstation path by applying frequency time analysis the average uncertainty and systematic bias of the measurements are estimated using a method based on analysing thousands of nearly linearly aligned station triplets we find that empirical green s functions can be estimated accurately from the negative time derivative of the symmetric component ambient noise cross correlation without explicit knowledge of the source distribution the average traveltime uncertainty is less than 1 s at periods shorter than 24 s we present rayleigh and love wave phase speed maps at periods of 8 12 16 and 20 s the maps show clear correlations with major geological structures and qualitative agreement with previous results based on rayleigh wave group speeds

a 3d shear wave velocity model of the upper mantle beneath china and the surrounding areas we present a three dimensional model of shear wave velocity for the upper mantle of china and the surrounding region by analyzing 50 338 vertical component multi mode rayleigh wave seismograms recorded at 144 permanent and more than 300 temporary broadband stations in and around china the procedure involves combination of 1 d path average models obtained by modeling each rayleigh waveform up to the 4th higher mode in a tomographic inversion scheme the dense station network and the use of multi mode analysis help to achieve a lateral resolution of a few hundred kilometers down to 400 km depth the seismic lithosphere as it is defined by the crust and the high velocity mantle lid is to the first order thin in east china and thick in the west with a high velocity lid extending down to about 200 km depth beneath much of the tibet pamir plateau beneath india the thickness of the seismic lithosphere gradually increases from 100 km in south india to more than 150 km in north india where it underthrusts the tibetan plateau to approximately the jinsha river suture high velocity lid extending down to 100 150 km depth is also observed in the tarim basin sichuan basin and ordos block in the eastern part of the north china craton the seismic lithosphere is probably close to or thinner than 70 km adjacent to these areas the high velocity lid in the eastern yangtze craton and south china fold system extends down to 70 80 km depth a large scale subhorizontal high velocity body is observed at depths of 150 350 km beneath the entire east china cratonic areas this high velocity body might be the remnant of a delamination process which resulted in the decratonization of the north china and the yangtze cratons

on the structure of grain boundaries in tectonites abstract grain boundaries in several tectonites have been examined using high voltage and scanning transmission electron microscopy on a gross scale grain boundaries are observed to differ from the host crystal in exhibiting faster rates of preferential etching during ion beam thinning and faster rates of ionization damage during exposure to the electron beam grain boundary features can be grouped according to decreasing size as follows grain junction voids that can form linked networks of tubules arrays of isolated voids and inclusions along the grain boundary surface and a narrow grain boundary film of distorted crystal structure the presence of inclusions in voids and the propensity for electron damage along the boundary suggests that the former were initially fluid filled and that the latter may be hydrated initial microchemical analyses using stem indicate that no compositional difference exists between the grain boundaries and host crystals the overall complex grain boundary structure in tectonites suggests that the effective grain boundary width for intercrystalline diffusion is much greater than that proposed based on metals and that diffusion path lengths along grain boundaries are much less than the theoretical maximum the net effect is to greatly enhance deformation mechanisms dependent on intercrystalline mass transport

lithosphere structure and thickness beneath the north china craton from joint inversion of ambient noise and surface wave tomography 1 we imaged detailed 3 d crustal and uppermost mantle seismic structures in the north china craton from inversion of rayleigh wave phase velocity at periods of 6 to 143 s the phase velocities were obtained from a combination of ambient noise and teleseismic surface wave tomography and then the phase velocities were inverted to s wave velocities the results show that both the huabei basin and ordos block have markedly rapid variations in both crustal velocities and the moho depth huabei basin has a thin 31 34 km crust with low velocities while ordos block has a thick 40 km crust with high velocities we also estimated the lithospheric thickness from the inverted s wave velocities using a simple s wave velocity temperature relationship huabei basin was imaged as a low s wave velocity anomaly in the uppermost mantle with very thin lithosphere 65 km while ordos block was revealed as a high s wave velocity anomaly with rather thick lithosphere 120 km these results indicated that huabei basin and ordos block have different thermal and or chemical properties and had experienced different mantle processes and evolution histories since the cenozoic furthermore slow s wave velocities and very thin lithosphere 65 km were also found beneath hetao and weihe rifts bounding ordos block at north and south respectively however shanxi rift the boundary between huabei basin and ordos block had a much thicker and higher velocity lithosphere than hetao and weihe rifts

mid lithosphere discontinuities beneath the western and central north china craton by analyzing p reflectivity extracted from stacked autocorrelograms for teleseismic events on a dense seismic profile we obtain a detailed image of the mid lithosphere discontinuity mld beneath western and central north china craton ncc this seismic daylight imaging exploits a broad high frequency band 0 5 4 hz to reveal the fine scale component of multi scale lithospheric heterogeneity the depth of the mld beneath the western and central parts of the ncc ranges 80 120 km with a good match to the transition to negative s velocity gradient with depth from rayleigh wave tomography the mld inferred from seismic daylight imaging also has good correspondence with the transition from conductive to convective regimes estimated from heat flow data indicating likely thermal control within the seismological lithosphere

seismic imaging of the crust and upper mantle under beijing and surrounding regions abstract we determined a high resolution 3d p wave velocity model of the crust and upper mantle under beijing and surrounding regions in north china by jointly inverting 48 750 arrival times from 2973 local events and 12 249 relative residuals from 234 teleseismic events recorded by the newly built capital seismic network our results show considerable differences in the lithospheric structure down to about 200 km depth between the north china basin the taihangshan uplift and the yanshan uplift which are the three main tectonic units in the study area at depths of 50 150 km a pronounced low velocity anomaly exists under north china basin and bohai bay and right beneath it a high velocity anomaly extends down to about 200 300 km depth suggesting that this area has experienced large scale lithospheric thinning and lithospheric detachment has occurred the taihangshan front fault and the zhangjiakou penglai fault zone may have cut through the crust to lithosphere and they become flimsy tectonic boundaries and the asthenospheric materials may upwell from the two channels we consider that the deep and shallow structures beneath this region are closely related to dynamic processes that result from the deep subduction of the pacific slab and its stagnancy in the mantle transition zone under east asia

a thinned lithospheric image of the tanlu fault zone eastern china constructed from wave equation based receiver function migration 1 we apply the newly proposed wave equation based receiver function poststack migration method to the northern china interior structure project broadband data to image the lithospheric structure of the tanlu fault zone area in eastern china our migration result reveals a 60 to 80 km thick present day lithosphere beneath the study region significantly thinned from the paleozoic lithosphere of 180 km the lithosphere asthenosphere boundary lab is coherently imaged along the 300 km east west profile displaying an arc like shape with its apex roughly coincident with the transverse location of the tanlu fault zone on the surface an obvious uplift from 36 km to 32 km of the moho is also clearly detected right below this fault zone the coincidence of the imaged moho uplift and the lab apex with the surface location of the tanlu fault zone provides seismological evidence for the steep geometry and deep penetration of the fault system and indicates that the tanlu fault zone might have acted as a major channel for anthenosphere upwelling during the mesozoic cenozoic continental extension and lithospheric thinning in eastern china frequency analysis and synthetic modeling suggest that both the moho and the lab are sharp and strong the latter in particular is constrained to have a 3 7 drop in s wave velocity over a depth range of 10 km or less such a rapid velocity change at the base of the lithosphere in the study region cannot be solely explained by thermal variation but likely reflects the presence of volatiles or melt in the asthenosphere or is partially attributed to the compositional contrast between the preserved depleted and dehydrated cratonic lithospheric veneer and the uplifted hydrated and fertile asthenospheric materials

two crustal flowing channels and volcanic magma migration underneath the se margin of the tibetan plateau as revealed by surface wave tomography abstract the se margin of the tibetan plateau is an important area to develop a better understanding of the plateau uplift and the indian eurasian continental collision dynamics previous studies have reported widespread low velocity anomalies beneath this region particularly in the tengchong volcanic field tcvf however the spatial distribution and dynamic processes of these low velocity anomalies are not well constrained in this study a 3 d s wave velocity structure model of the crust and upper mantle 10 120 km in the region is constructed by the inversion of surface wave dispersion data a two step inversion procedure is adopted to generate the s wave velocity structure images the measured phase velocities and inverted s wave velocities jointly show a large scale low velocity anomaly distributed in the crust consistent with the view that the region is the passageway of the eastward migration of tibetan plateau material two crustal flowing channels are clearly observed at depths of 20 km and 30 km which connect and rotate clockwise around the eastern himalaya syntaxis beneath the tcvf there are two prominent low velocity anomaly zones at depths of 15 25 km and 50 80 km which indicate the existence of magma chambers one of the crustal flowing channels is connected with the magma chamber of the tcvf and the other has a short branch north of kunming toward the mile shizong fault at a depth of 20 km based on the distribution of the s wave velocities under the tcvf a dynamic model of the tengchong volcano magma system is proposed to explain the migration patterns of the volcanic material

teleseismic p wave tomography and mantle dynamics beneath eastern tibet we determined a new 3 d p wave velocity model of the upper mantle beneath eastern tibet using 112 613 high quality arrival time data collected from teleseismic seismograms recorded by a new portable seismic array in yunnan and permanent networks in southwestern china our results provide new insights into the mantle structure and dynamics of eastern tibet high velocity high v anomalies are revealed down to 200 km depth under the sichuan basin and the ordos and alashan blocks low velocity low v anomalies are imaged in the upper mantle under the kunlun qilian and qinling fold zones and the songpan ganzi qiangtang lhasa and chuan dian diamond blocks suggesting that eastward moving low v materials are extruded to eastern china after the obstruction by the sichuan basin and the ordos and alashan blocks furthermore the extent and thickness of these low v anomalies are correlated with the surface topography suggesting that the uplift of eastern tibet could be partially related to these low v materials having a higher temperature and strong positive buoyancy in the mantle transition zone mtz broad high v anomalies are visible from the burma arc northward to the kunlun fault and eastward to the xiaojiang fault and they are connected upward with the wadati benioff seismic zone these results suggest that the subducted indian slab has traveled horizontally for a long distance after it descended into the mtz and return corner flow and deep slab dehydration have contributed to forming the low v anomalies in the big mantle wedge our results shed new light on the dynamics of the eastern tibetan plateau

relationships between dynamically recrystallized grain size and deformation conditions in experimentally deformed olivine rocks new microstructural data on experimentally deformed wet and dry natural olivine rocks anita bay and aheim dunite together with the other reliable experimental data indicate that the experimental stress recrystallized grain size relationship in olivine rocks is largely independent of water content and temperature and is only slightly dependent on the flow properties of the material the experimental data cover a stress range of 30 300 mpa water contents from 30 ppm to 300 ppm and temperatures in the range 1100 1650 c local melt contents of up to 10 volume cannot be demonstrated to have a significant effect on the stress grain size relationship

timing of destruction of the north china craton abstract the north china craton ncc is the typical example of destruction of an ancient craton however the destruction mechanism and geodynamic controlling factors still remain enigmatic due to controversy on the timing of destruction which is the key to understanding the destruction processes based on temporal and spatial distributions of the igneous rocks and their sources and tectonic settings it is recognized that six stages of tectono magmatism occurred in the ncc during the phanerozoic i e carboniferous to early permian late permian to middle triassic late triassic jurassic early cretaceous and cenozoic among them cenozoic magmatism mainly consists of alkali basalts and is found only occasionally in the eastern ncc the first four stages of magmatism and tectonism related to the southward subduction of the paleo asian plate and the assembly of sino korean and yangtze cratons are locally distributed in limited parts of the ncc reflecting a multiple stage modification of the ncc from the late carboniferous to jurassic however the intensive development of early cretaceous magmatism extensional deformation and associated gold mineralization with significant continental crustal growth indicate that the eastern ncc was destroyed during this time period this destruction was the result of paleo pacific subduction beneath the eastern asian continent with lithospheric removal and or replacement of an ancient cratonic lithosphere by a juvenile oceanic lithosphere

rayleigh wave tomography of china and adjacent regions 1 this paper presents a tomographic study on the s wave velocity structure of china and adjacent regions group velocity dispersions of fundamental rayleigh waves along more than 4000 paths were determined with frequency time analysis the study region was divided into a 1 1 grid and velocities in between grid nodes were calculated by bilinear interpolation the occam s inversion scheme was adopted to invert for group velocity distributions this method is robust and allows us to use a fine grid in model parameterization and thus helps to restore a more realistic velocity pattern checkerboard tests were carried out and the lateral resolution was estimated to be 4 6 in china and its eastern continental shelves the resulting group velocity maps from 10 to 184 s showed good correlation with known geological and tectonic features the pure path dispersion curves at each node were inverted for shear wave velocity structures the three dimensional velocity model indicates thick lithospheres in the yangtze and tarim platforms and hot upper mantles in baikal and western mongolia coastal area and continental shelves of eastern china and indochina and south china sea regions the tibetan plateau has a very thick crust with a low velocity zone in its middle beneath the crust a north dipping high velocity zone mimicking a subducting plate reaches to 200 km in depth and reaches to the kunlun mountains northward in northern tibet a low velocity zone immediately below the moho extends eastward then turns southward along the eastern edge of the plateau until it connects to the vast low velocity area in indochina and the south china sea

constraints on s wave velocity structures of the lithosphere in mainland china from broadband ambient noise tomography abstract in this study a 3 d s wave velocity model of the lithosphere in mainland china down to 150 km depth was determined from ambient noise data first we collected 2 year continuous waveforms recorded by 1031 broadband stations of the china regional seismic network and necessarray then by applying the procedures of noise cross correlation and time frequency domain phase weighted stacking we obtained the interstation empirical green s functions of rayleigh waves we measured the group and phase velocity dispersions at periods of 5 125 s from the egfs and inverted both group and phase velocities for the s wave velocity model our model revealed that the lithospheric thickness in the northern songliao basin is 70 110 km a weak high velocity anomaly that is discontinuous in the vertical direction was detected beneath the southern songliao basin which may indicate that the lithosphere is delaminated in this area the model also revealed that deep 150 km high velocity lithospheric roots exist beneath the ordos and sichuan basins the lithospheric thicknesses in eastern parts of the northeast china block the north china craton and the south china block are only 60 100 km which may be the result of a series of deep processes caused by the subduction of the pacific plate to the eurasian plate that produced strong lithospheric thinning in eastern china the lithospheric thickness within the tanlu fault belt is generally thinner than that in the adjacent areas of the fault belt and the s wave velocity of the mantle lithosphere beneath the fault belt is also lower than that beneath the adjacent areas indicating that the tanlu fault belt is a deep fault belt cutting through the lithosphere

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

the recrystallized grain size piezometer for quartz an ebsd based calibration we have re analyzed samples previously used for a quartz recrystallized grain size paleopiezometer using electron backscatter diffraction ebsd recrystallized and relict grains are separated using their grain orientation spread gos which acts as a measure of intragranular lattice distortion and a proxy for dislocation density for ebsd maps made with a 1 m step size the piezometer relationship is d 103 91 0 41 1 41 0 21 for rms mean diameter values we also present a sliding resolution piezometer relationship d 104 22 0 51 1 59 0 26 that combines 1 m step size data at coarser grain sizes with 200 nm step size data at finer grain sizes the sliding resolution piezometer more accurately estimates stress in fine grained 10 m samples the two calibrations give results within 10 of each other for recrystallized grain sizes between 10 m and 100 m both piezometers match the original light optical microscopy quartz piezometer within error

anisotropic rayleigh wave tomography of northeast china using ambient seismic noise abstract the ambient noise data recorded by 249 seismic stations in the permanent and temporary networks in northeast china are used to invert for the isotropic phase velocity and azimuthal anisotropy of rayleigh waves in the period band 5 50 s the inversion results reflect the structure from the shallow crust to upper mantle up to approximately 120 km depth beneath the songliao basin both the fast direction in shallow crust and strike of a low velocity anomaly in the middle crust are nne ssw which is coincident with the main tectonic trend of the paleo pacific tectonic domain this indicates that the rifting of the songliao basin is influenced by the subduction of paleo pacific plate the upper mantle of songliao block except the central area of songliao basin to the west of mudanjiang fault and the east of the north south gravity lineament is characterized by high velocity and weak anisotropy up to approximately 120 km depth we infer that there is delamination of lithospheric mantle beneath the songliao block obvious n s ne sw and e w trending fast directions are found in the lithospheric mantles of the east west and south sides of songliao block respectively which coincide with the strikes of the paleozoic tectonic in these areas this suggests that the frozen in anisotropic fabric in the lithospheric mantle can be used to indicate the historical deformation of the lithosphere in the northern margin of the north china craton the spatial variations of phase velocity and azimuthal anisotropy are more dramatic than those in northeast china blocks which indicates that the lithosphere of the north china craton has experienced more complicated tectonic evolution than that of the northeast china blocks

mapping the moho with seismic surface waves a review resolution analysis and recommended inversion strategies abstract the strong sensitivity of seismic surface waves to the moho is evident from a mere visual inspection of their dispersion curves or waveforms rayleigh and love waves have been used to study the earth s crust since the early days of modern seismology yet strong trade offs between the moho depth and crustal and mantle structure in surface wave inversions prompted doubts regarding their capacity to resolve the moho here we review surface wave studies of the moho with a focus on early work and then use model space mapping to establish the waves sensitivity to the moho depth and the resolution of their inversion for it if seismic wavespeeds within the crust and upper mantle are known then moho depth variations of a few kilometres produce large 1 perturbations in phase velocities however in inversions of surface wave data with no a priori information wavespeeds not known strong moho depth shear speed trade offs will mask 90 of the moho depth signal with remaining phase velocity perturbations 0 1 only in order to resolve the moho with surface waves alone errors in the data must thus be small up to 0 2 for resolving continental moho with larger errors moho depth resolution is not warranted and depends on error distribution with period an effective strategy for the inversion of surface wave data alone for the moho depth is to first constrain the crustal and upper mantle structure by inversion in a broad period range and then determine the moho depth in inversion in a narrow period range most sensitive to it with the first step results used as reference prior information on crustal and mantle structure reduces the trade offs and thus enables resolving the moho depth with noisier data such information should be used whenever available joint analysis or inversion of surface wave and other data receiver functions topography gravity can reduce uncertainties further and facilitate moho mapping

surface wave array tomography in se tibet from ambient seismic noise and two station analysis i phase velocity maps summary empirical green s functions egfs between pairs of seismographs can be estimated from the time derivative of the long time cross correlation of ambient seismic noise these egfs reveal velocity dispersion at relatively short periods which can be used to resolve structures in the crust and uppermost mantle better than with traditional surface wave tomography we combine rayleigh wave dispersion estimates from egfs and from traditional two station ts analysis into a new approach to surface wave array tomography with data from dense receiver arrays we illustrate the methodology with continuous broad band recordings from a temporary seismographic network on the southeastern part of the tibetan plateau in sichuan and yunnan provinces sw china the egfs are robust under temporal changes in regional seismicity and the use of either ambient noise approximated by records without signal from events with magnitude mb 5 or 4 or surface wave coda produces similar results the egfs do not strongly depend on the presence of large earthquakes but they are not reciprocal for stations aligned in the n s direction this directionality reflects the paucity of seismicity to the north of the array using a far field representation of the surface wave green s function and an image transformation technique we infer from the egfs the rayleigh wave phase velocity dispersion in the period band from 10 30 s a classical ts approach is used to determine rayleigh wave phase velocity dispersion between 20 120 s together they constrain phase velocity variations for t 10 120 s which can be used to study the structure from the crust to the upper mantle beneath se tibet short and intermediate period 10 80 s phase velocities are prominently low suggesting that the crust and upper mantle beneath se tibet is characterized by slow shear wave propagation

an upper mantle s wave velocity model for east asia from rayleigh wave tomography abstract we present a new shear velocity model of the upper mantle beneath the east asia region derived by inverting rayleigh wave group velocity measurements between 10 and 145 s combined with previously published rayleigh wave phase velocity measurements between 150 and 250 s rayleigh wave group velocity dispersion curves along more than 9500 paths were measured and combined to produce 2d dispersion maps for 10 145 s periods the group velocity maps benefit from the inclusion of new data recorded by the china national seismic network and surrounding global stations the increase in available data has resulted in enhanced resolution compared with previously published group velocity maps the horizontal resolution across the region is about 3 for the periods used in this study the new shear wave velocity models indicate varying velocity structure beneath eastern china which yields estimates of a lithosphere asthenosphere boundary depth from around 160 km beneath the yangtze block to approximately 140 km beneath the western part of the north china craton ncc up to depths of 70 100 km beneath the eastern ncc northeast china and the cathaysia block the models reveal the subduction of two opposite facing continental plates under the southern and northern margin of tibet an obvious low velocity anomaly appears in the top 200 km of the upper mantle beneath northern tibet which is inconsistent with the presence of subducted asian or indian mantle lithosphere beneath northern tibet the cenozoic volcanism fields in the mongolian plateau are characterized by an obvious upper mantle negative anomaly but no signature of deep seated plume was observed

high resolution mantle tomography of china and surrounding regions 1 a high resolution p wave tomographic model of the crust and mantle down to 1100 km depth under china and surrounding regions is determined by using about one million arrival times of p pp pp and pcp waves from 19 361 earthquakes recorded by 1012 seismic stations the subducting pacific slab is imaged clearly as a high velocity zone from the oceanic trenches down to about 600 km depth and intermediate depth and deep earthquakes are located within the slab the pacific slab becomes stagnant in the mantle transition zone under east china the western edge of the stagnant slab is roughly coincident with a surface topographic boundary in east china the active changbai and wudalianchi intraplate volcanoes in northeast china are underlain by significant slow anomalies in the upper mantle above the stagnant pacific slab these results suggest that the active intraplate volcanoes in ne china are not hot spots but a kind of back arc volcano associated with the deep subduction of the pacific slab and its stagnancy in the transition zone under the mariana arc however the pacific slab penetrates directly down to the lower mantle the active tengchong volcano in southwest china is related to the eastward subduction of the burma microplate the subducting indian and philippine sea plates are also imaged clearly the indian plate has subducted down to 200 300 km depth under the tibetan plateau with a horizontal moving distance of about 500 km high velocity anomalies are revealed in the upper mantle under the tarim basin ordos and sichuan basin which are three stable blocks in china

destruction of lithosphere within the north china craton inferred from surface wave tomography 1 the north china craton ncc is one of the oldest cratons in the world however the lithosphere of the craton was destructed during phanerozoic tectonism and then became tectonically and seismically active because the lithospheric structure of this complex craton has not been well studied the mechanism behind the thinning transformation and destruction of the lithosphere remains debated using an efficient and scalable 3 d surface wave tomography method we obtain a high resolution regional s wave velocity model that shows the three dimensional lithospheric structure of the ncc in addition we convert the s wave structure to an estimated thermal structure using accepted relationships between s wave velocity and temperature the model images a large upper mantle low velocity body beneath the eastern ncc especially beneath the seismically active zone from tangshan to xingtai this body is interpreted to represent hot material or volatiles escaping from the slab edge in the transition zone between the upper and lower mantle the low velocity body is a key piece of evidence in demonstrating thermochemical bottom up erosion transformation of the overlying cratonic lithosphere thereby leading to destruction of the lithosphere which may have occurred during the cenozoic this erosion mechanism appears to have had less influence in the western ncc ordos block however our results reveal a 130 km thick lithosphere beneath the present cratonic ordos block which is thinner than the 200 km thickness of the ncc lithosphere during the paleozoic as determined from analyses of xenoliths

intraplate volcanism controlled by back arc and continental structures in ne asia inferred from transdimensional bayesian ambient noise tomography intraplate volcanism adjacent to active continental margins is not simply explained by plate tectonics or plume interaction recent volcanoes in northeast ne asia including ne china and the korean peninsula are characterized by heterogeneous tectonic structures and geochemical compositions here we apply a transdimensional bayesian tomography to estimate high resolution images of group and phase velocity variations with periods between 8 and 70 s the method provides robust estimations of velocity maps and the reliability of results is tested through carefully designed synthetic recovery experiments our maps reveal two sublithospheric low velocity anomalies that connect back arc regions in japan and ryukyu trench with current margins of continental lithosphere where the volcanoes are distributed combined with evidences from previous geochemical and geophysical studies we argue that the volcanoes are related to the low velocity structures associated with back arc processes and preexisting continental lithosphere

experimental study of the influence of stress temperature and strain on the dynamic recrystallization of carrara marble carrara marble has been deformed experimentally at temperatures ranging between 500 and 1000 c at confining pressures of 200 and 300 mpa and up to very large strains in extension and compression in order to study the microstructural and mechanical property changes associated with dynamic recrystallization microstructural studies were made by optical microscopy on ultrathin sections and automatic grain size measurement techniques were used when the temperature is sufficiently high 600 c and the stresses are high enough for deformation twinning to occur twin boundary migration is a powerful recrystallization mechanism that does not modify the grain size at stress levels too low to activate twinning recrystallization occurs in two stages the formation of nuclei by grain boundary bulging and subgrain rotation recrystallization in the grain boundary regions followed by a second stage of grain boundary migration recrystallization to a larger grain size that eventually overprints the entire rock volume the recrystallization process requires larger prestrains at the lower temperatures the size to which migration recrystallized grains grow seems to be limited by the stress and grain size dependent twinning field boundary or by the boundary between the dislocation creep and grain size sensitive flow mechanisms within the range of experimental observations dynamically recrystallized grain size does not depend on strain rate or temperature separate empirical stress versus grain size relations are presented for rotation and migration recrystallization that may be used for palaeopiezometry no unequivocal experimental evidence of weakening resulting from recrystallization to finer grain sizes at laboratory strain rates was found however extrapolation of the experimental data to low natural strain rates suggests that weakening following recrystallization may occur in nature

structural model of the lithosphere asthenosphere system beneath the qinghai tibet plateau and its adjacent areas abstract the deep structure of the lithosphere asthenosphere system as imaged from geophysical data of the qinghai tibet plateau the highest on the earth provides important clues in understanding its orogenic processes here we reconstruct the main features of the structure of the crust and upper mantle from surface wave tomography in the qinghai tibet plateau and its adjacent areas in order to understand the modality of the convergence and collision process between the indian and eurasian plates based on rayleigh waves dispersion theory we collected long period and broad band seismic data from the global and regional seismic networks surrounding the study area 20 n 50 n 70 e 110 e after applying instrument response calibration and filtering group velocities of the fundamental mode of rayleigh waves are measured using the frequency time analysis ftan combining the published dispersion data a 2 d surface wave tomography method is applied to calculate the lateral variations of group velocity distribution at different periods in the range from 8 s to 150 s the hedgehog non linear inversion method is performed to obtain shear wave velocity vs versus depth models of the crust and upper mantle for 181 cells with size 2 2 in order to identify the cellular representative models we applied the local smoothness optimization method lso fairly detailed structural models of the lithosphere asthenosphere system have been defined the vs models demonstrate the lateral variation of the thickness of the metasomatic lid between the south and north of the bangong nujiang suture bns and the west and east of tibet the variation in thickness of the metasomatic lid may suggest that the leading edge of the subducting indian slab reaches up to bns

an improved method to extract very broadband empirical green s functions from ambient seismic noise the extraction of green s functions by cross correlation of continuous seismic records at station pairs is best achieved in a diffuse wave field where energies radiated by random sources have equal power to partially satisfy the diffuse wave field condition original seismic records must be normalized as they are highly nonstationary and may have amplitude variations of orders of magnitude within the cross correlation time window we adapt a frequency time normalization method to obtain seismograms with an even spectrum at all times within the data processing unit compared with the commonly used one bit normalization the new method improves the signal to noise ratio of empirical green s functions by a factor of 2 and increases the effective data recording duration by a factor of 4 assuming random local and instrument noise it yields useful rayleigh waves at periods up to 300 s for program for array seismic studies of the continental lithosphere passcal type deployments and 600 s for permanent stations with very broadband sensors thus the new method makes it possible to extend surface wave signals to frequencies beyond those in traditional earthquake based surface wave tomography at both the high and low frequency ends

3 d velocity model beneath the middle lower yangtze river and its implication to the deep geodynamics abstract a mineralization zone exists in the middle and lower yangtze river mlyr region previous studies have shown that this zone might be caused by the rich ejection of magma in the mesozoic we have applied the teleseismic tomography method to determine a 3 d p wave velocity structure of the mantle down to 500 km depth beneath this region by using 14 740 p wave arrival times collected from 519 teleseismic events recorded by 46 portable and 47 static seismic stations located in this region the relative residual times used for the tomography are calculated by the modified multi channel cross correlation method which increases not only the efficiency but also the data precisions up to 0 01 s the grid space is set as 1 1 horizontally and 50 100 km vertically our tomographic results show that the lithosphere with high velocity anomalies is separated into two parts one locates above the depth of 100 km and the other at the depths between 250 km and 400 km and the asthenosphere with low velocity anomalies locates between these two parts of lithosphere which indicates that the lithosphere delaminated together with the asthenosphere upwelling the detachment of lithosphere might relate to the subduction of the western pacific slab therefore our study provides clear evidence to geoscientists for understanding the deep dynamic process beneath this region and a three stage geodynamic process is developed based on the new evidence

high resolution lithospheric structure beneath mainland china from ambient noise and earthquake surface wave tomography abstract we present a new high resolution shear velocity model of the lithosphere down to about 160 km beneath china using rayleigh wave tomography we combined ambient noise and earthquake data recorded at 1316 seismic stations the largest number used for the region to date more than 700 000 dispersion curves were measured to generate group and phase velocity maps at periods of 10 140 s the resolution of our model is significantly improved over previous models with about 1 2 in eastern china and 2 3 in western china we also derived models of the study region for crustal thickness and averaged s velocities for upper and mid lower crust and uppermost mantle these models reveal important lithospheric features beneath china and provide a fundamental data set for understanding continental dynamics and evolution different geological units show distinct features in the moho depth lithospheric thickness and shear velocity in particular the north china craton ncc lithosphere shows strong east west structural variations with thin and low velocity lithosphere in eastern ncc and thick and high velocity lithosphere beneath western ncc and the lithosphere of the ordos block seems to have undergone strong erosion the results support the progressive destruction of the ncc lithosphere from east to west at least partly caused by the thermal chemical erosion of the cratonic lithosphere from the asthenosphere another pronounced feature of our model is the strong lateral variations of the mantle lithosphere beneath the tibetan plateau tp the indian lithosphere beneath the tp shows variable northward advancement with nearly flat subduction in western and eastern tp and steep subduction in central tp with evidence for the tearing of indian lithosphere beneath central tp which may be important for the riftings at the surface in himalayas and southern tp the low velocity zone in northern tp shows strong correlation with the region of the mid miocene to quaternary potassic magmatism suggesting that delamination of lithosphere may have played an important role in the rise of the tp

stress development in heterogeneous lithosphere insights into earthquake initiation in the tan lu fault zone abstract the tan lu fault zone tlfz east china is the site of several historical m 6 5 8 0 earthquakes and remains seismically active today although differential kinematic and geomorphic features in the upper crust can well divide the tlfz into several segments many questions remain regarding the spatial distribution of the middle large earthquakes along the active faults and what triggers earthquakes in the seismic zone namely what is the relationship if any between the observed seismicity and the fault segmentation along the tlfz here we present a three dimensional viscoelastic finite element model to simulate the stress distribution along the tlfz and better understand the relationship between the regional stress field and observed seismicity with a particular emphasis on how the heterogeneous lithosphere influences earthquake initiation at different depths and along the various segments of the tlfz the global crustal model crust 1 0 and structural information from regional and areal studies are utilized to infer the lithospheric viscosity structure and provide an important input to the numerical model the model results are well supported by the geological evidence in terms of both the observed stress field and distribution our results suggest ene oriented maximum principal compressive stress in east china which are consistent with the local fault plane solutions the calculated maximum shear strain and rupture values at different crustal depths are consistent with the distribution of the large earthquakes which suggest that these larger earthquakes are initiated by stress localization in the heterogeneous lithosphere along the tlfz cross sections of our calculated maximum shear strain and rupture values along the tlfz support the initiation of large earthquakes in the middle crust particularly along the bohai bozhong and yishu segments furthermore the soft low velocity zone fluid system in the lower crust along the tlfz provides the potential for earthquake stratification and initiation in the middle crust along the tlfz our results provide strong evidence that the stress localization of the heterogeneous lithosphere in different segments of the tlfz and the lower crustal fluid system initiate different magnitude of earthquakes in each seismic zone

broadband ambient noise surface wave tomography across the united states 1 this study presents surface wave dispersion maps across the contiguous united states determined using seismic ambient noise two years of ambient noise data are used from march 2003 through february 2005 observed at 203 broadband seismic stations in the us southern canada and northern mexico cross correlations are computed between all station pairs to produce empirical green functions at most azimuths across the us coherent rayleigh wave signals exist in the empirical green functions implying that ambient noise in the frequency band of this study 5 100 s period is sufficiently isotropically distributed in azimuth to yield largely unbiased dispersion measurements rayleigh and love wave group and phase velocity curves are measured together with associated uncertainties determined from the temporal variability of the measurements a sufficient number of measurements 2000 is obtained between 8 and 25 s period for love waves and 8 and 70 s period for rayleigh waves to produce tomographic dispersion maps both phase and group velocity maps are presented in these period bands resolution is estimated to be better than 100 km across much of the us from 8 40 s period for rayleigh waves and 8 20 s period for love waves which is unprecedented in a study at this spatial scale at longer and shorter periods resolution degrades as the number of coherent signals diminishes the dispersion maps agree well with each other and with known geological and tectonic features and in addition provide new information about structures in the crust and uppermost mantle beneath much of the us

geophysical evidence on segmentation of the tancheng lujiang fault and its implications on the lithosphere evolution in east china abstract the north south trending tancheng lujiang tanlu fault belt extends from northeast china to the dabie sulu orogenic belt for a length of more than 3000 km this fault belt probably has close links with the lithosphere evolution seismic activity and mineral resource concentration in east china surface geological mapping and studies on sedimentation and basin formation have indicated segmentation at the southern middle and northern domains of the fault here we employ geophysical constraints to evaluate these fault segments unlike previous geophysical studies focused on laterally varying crust mantle seismic velocity structure across the fault in this study we have integrated a variety of geophysical data sets such as crustal p wave velocity earthquake occurrence and released seismic energy seismogenic layer thickness surface heat flow and geothermal field to understand the deep structure and strength of the lithosphere along the tanlu segmented fault belt the results demonstrate remarkable crustal scale north to south segmentation this major fault the geophysical evidence and some geochemical constraints suggest that the tanlu fault belt probably served as a channel for melt and fluid percolation and exerted a significant control on the lithosphere evolution in east china

shallow crustal structure of the tanlu fault zone near chao lake in eastern china by direct surface wave tomography from local dense array ambient noise analysis ambient noise tomography ant has been used successfully to image shallow earth structure here we perform ant on a local dense seismic array around the tanlu fault zone tfz to the southeast of hefei city anhui province in eastern china the array consists of 53 stations with average spacing close to 5 km cross correlations of vertical component ambient noise data of different station pairs are computed in 1 h segments and stacked over 1 month from 17 march to 26 april 2017 clear fundamental mode rayleigh waves are observed between 0 2 and 5 s period we then use the direct surface wave tomographic method with period dependent ray tracing to invert group and phase dispersion travel time data simultaneously for three dimensional 3d shear wave velocity vs structure the vs model shows clear correlation with the known geologic features the tfz is associated with a high velocity anomaly zone in the shallow crust corresponding to metamorphic rocks due to magma intrusion low velocity anomaly zones are mainly located to the west of the tfz caused by thick sedimentary layers in the hefei basin our study shows that with ambient noise data recorded on a dense array and an advanced surface wave inversion method we can image detailed structure around the fault zone

upper mantle beneath southeast asia from s velocity tomography 1 we present a three dimensional s velocity model of the se asian western pacific upper mantle with 400 km lateral resolution using the novel automated multimode inversion technique we processed 4038 vertical component seismograms and extracted 22 708 linear equations with uncorrelated uncertainties that constrain upper mantle structure we used time frequency windows to select signal with negligible proportion of scattered energy the windows included the fundamental rayleigh mode and s and multiple s waves the observed range of s velocity variations is the widest 17 18 in the upper 150 km of the mantle high velocity continental roots can reach beyond the present extent of the overlying archean proterozoic crust by 500 km beneath some precambrian units the roots are absent which can be attributed to deformation and gradual destruction of the ancient lithosphere at 120 150 km s velocity beneath some cratons reaches 4 8 km s this can be accounted for by thermal and compositional effects beneath the hainan island area a low velocity anomaly is observed from near the surface to the bottom of our model the hot spot type volcanism here may be caused by the deep mantle hainan plume a low velocity mantle domain underlies the south central sea of japan surrounded on the surface by intraplate volcanoes a deep seismicity gap is present near 40 n in the pacific slab subducting below and may result from a plume slab interaction a high velocity anomaly is present in the transition zone beneath the northern boundary of the yangtze craton we propose that the anomaly corresponds to subducted continental lithosphere stagnant atop the 660 km discontinuity

s wave velocity structure of northeastern china from joint inversion of rayleigh wave phase and group velocities summary we imaged the crust and uppermost mantle structure beneath northeastern ne china with fundamental mode rayleigh waves recorded by 125 broad band stations deployed in the region rayleigh wave phase and group velocities along more than 700 interstation paths were estimated using the wavelet transformation method and then these data were utilized to construct 2 d phase and group velocity maps in the period range of 15 60 s owing to the dense ray coverage and short ray path our results provide better lateral resolution in the ne china region compared with previous phase and group velocity studies the regularized rayleigh wave phase and group velocity dispersions at each cell were jointly inverted to determine 1 d shear wave velocity structure using the linear inversion method and then assembled into a 3 d model our results show that obvious low velocities exist in the uppermost mantle beneath the changbaishan volcanic region which may be due to asthenospheric upwelling the thin lithosphere with fast s wave velocity in the lower crust of the songliao basin implies that the lithospheric mantle beneath ne china is partly removed

an overview of the crustal structure of the tibetan plateau after 35 years of deep seismic soundings abstract since the pioneer wide angle seismic profile along the yadong gulu rift acquired in 1974 by the ex institute of geophysics chinese academy of sciences cas several research programs aimed to deep geophysics performed thanks to the participation of chinese national and international institutions have been developed during last 35 years including 23 wide angle seismic profiles with total length of about 6000 km these profiles are unevenly distributed most of them in eastern tibet and few profiles in western tibet in this paper we make a summarized presentation of all these wide angle seismic profiles and provide an overall view of the seismic velocity structure of the crust beneath the broad tibetan plateau which is the product of the continuous convergence and collision of the indian and eurasian plates since about 50 ma ago different patterns of crustal thickness variation related to the tectonic blocks and along suture zones of the region are displayed the crust thickness is confirmed to be about 70 75 km under southern tibet and 60 65 km under northern northeastern and southeastern tibet the leading edge of the subducted lithosphere reaches the northern margin of the plateau and directly contacts with tarim basin westward of the 90 e boundary the indian crust is moving towards the northern edge of the plateau and collides with tarim basin at 80 e while reach the bangong nujiang suture belt at 88 e eastward of the 90 e boundary the northern edge of the crust should be at 50 100 km south of bangong nujiang suture the results supply helpful constrains to understand the mechanism of the continent continent collision and its consequences in the plateau and neighbouring areas

cenozoic episodic volcanism and continental rifting in northeast china and possible link to japan sea development as revealed from k ar geochronology abstract cenozoic volcanic rocks in northeast china comprise part of the volcanic belt of the western circum pacific rim and represent one of the presently active tectono magmatic regions of the world over 590 volcanoes with erupted basalts covering an area of 50 000 km 2 are exposed in the songliao graben and particularly on its flanks k ar dating of the volcanic rocks sampled from a selection of eruption sites over the region reveals that the volcanism occurred episodically through the entire cenozoic corresponding to the tectono magmatic interactions particularly between the india eurasia and pacific plates the volcanism initiated in the songliao graben in late cretaceous 86 ma and migrated flankward since 28 ma the magmatic propagation shows three major stages intimately associated with the evolution of japan sea and related to the geodynamic forcing of the india eurasia collision prior to japan sea rifting volcanic eruptions were restricted to the songliao basin during japan sea opening volcanism migrated into the lateral belts after cessation of japan sea opening at 15 ma volcanism with greatest intensity occurred on both flanks particularly along the yi yi fault system around 14 13 ma and subsequently the fu mi fault between 11 and 7 ma continuing this trend of migration eruptions scattered further away from the songliao basin in the last 4 5 ma we suggest that the cenozoic volcanic belt in northeast china and the japan sea backarc basin are competitive parts in the eastern marginal magmatic system of the eurasian plate the early stage of the volcanism in the songliao basin may have resulted from mantle upwelling beneath the songliao bohai basin belt rifting of the ne faults and relatively weak intensity of volcanism in northeast china during japan sea opening could be attributable to the lithospheric breakup in the japan sea and spreading of japan sea the subsequent strong volcanism in northeast china after cessation of the japan sea opening implicates the easiest pathway for the melts of the magmatic system in the plate margin the diversified volcanism in scattered localities during the quaternary may indicate localized melting processes or notable modifications in smaller sized individual domains and possibly a magmatically waning phase of the limited source in eastern china

surface wave dispersion measurements from ambient seismic noise analysis in italy summary we present the surface wave dispersion results of the application of the ambient noise method to broad band data recorded at 114 stations from the istituto nazionale di geofisica e vulcanologia ingv national broad band network some stations of the mediterranean very broadband seismographic network mednet and of the austrian central institute for meteorology and geodynamics zamg vertical component ambient noise data from 2005 october to 2007 march have been cross correlated for station pairs to estimate fundamental mode rayleigh wave green s functions cross correlations are calculated in 1 hr segments stacked over periods varying between 3 months and 1 5 yr rayleigh wave group dispersion curves at periods from 8 to 44 s were determined using the multiple filter analysis technique the study region was divided into a 0 2 0 2 grid to invert for group velocity distributions checkerboard tests were first carried out and the lateral resolution was estimated to be about 0 6 the resulting group velocity maps from 8 to 36 s show the significant difference of the crustal structure and good correlations with known geological and tectonic features in the study region the po plain and the southern alps evidence lower group velocities due to soft alluvial deposits and thick terrigenous sediments our results also clearly showed that the tyrrhenian sea is characterized with much higher velocities below 8 km than the italian peninsula and the adriatic sea which indicates a thin oceanic crust beneath the tyrrhenian sea

the recrystallized grain size piezometer for quartz d 1 0 3 56 0 27 s 1 26 0 13 with no change in slope at the regime 2 3 transition and no effect of temperature or a b stability field another experimental piezometer relation for regime 1 of hirth and tullis 1992 differs in slope suggesting that different recrystallization mechanisms require different piezometer calibrations index terms 3902 mineral physics creep and deformation 5120 physical properties of rocks plasticity diffusion and creep 8030 structural geology microstructures 8159 tectonophysics rheology crust and lithosphere 8164 tectonophysics stresses crust and lithosphere citation stipp m and j tullis the recrystallized grain size piezometer for quartz geophys res lett 30 21 2088 doi 10 1029 2003gl018444 2003

lithospheric structure of the chinese mainland determined from joint inversion of regional and teleseismic rayleigh wave group velocities 1 we processed a large number of vertical component seismograms recorded by broadband seismic stations in and around china and ultimately retrieved 33 140 regional and 10 360 teleseismic fundamental mode group velocity measurements at 40 s periods with fewer measurements for shorter and longer periods we directly inverted the processed group velocity measurements for a three dimensional lithospheric s velocity model of the chinese mainland synthetic test results and data fit or misfit analysis demonstrated the reliability of our surface wave tomographic inversion the imaged upper crustal low velocities are consistent with variations in sediment thickness for example the tarim basin which contains a great thickness of sediments is characterized by a strong shallow low velocity anomaly high lithospheric velocities are observed to varying depths in the north china craton yangtze craton and tarim craton indicating varying thicknesses of the lithosphere beneath these cratonic areas low asthenospheric velocities are widely imaged in eastern and southern china around the tarim basin and along a roughly north south belt in central china the low asthenospheric velocities in eastern and southern china are attributed to partial melting of a subducted slab associated with the westward subduction of an oceanic plate while those in central china and around the tarim basin are attributed to indian eurasian collision

crustal heterogeneity and seismotectonics of the region around beijing china abstract a detailed three dimensional 3 d p wave velocity model of the crust and uppermost mantle under the chinese capital beijing region is determined with a spatial resolution of 25 km in the horizontal direction and 4 17 km in depth we used 48 750 precise p wave arrival times from 2973 events of local crustal earthquakes controlled seismic explosions and quarry blasts these events were recorded by a new digital seismic network consisting of 101 seismic stations equipped with high sensitivity seismometers the data are analyzed by using a 3 d seismic tomography method our tomographic model provides new insights into the geological structure and tectonics of the region such as the lithological variations and large fault zones across the major geological terranes like the north china basin the taihangshan and the yanshan mountainous areas the velocity images of the upper crust reflect well the surface geological and topographic features in the north china basin the depression and uplift areas are imaged as slow and fast velocities respectively the taihangshan and yanshan mountainous regions are generally imaged as broad high velocity zones while the quaternary intermountain basins show up as small low velocity anomalies velocity changes are visible across some of the large fault zones large crustal earthquakes such as the 1976 tangshan earthquake m 7 8 and the 1679 sanhe earthquake m 8 0 generally occurred in high velocity areas in the upper to middle crust in the lower crust to the uppermost mantle under the source zones of the large earthquakes however low velocity and high conductivity anomalies exist which are considered to be associated with fluids the fluids in the lower crust may cause the weakening of the seismogenic layer in the upper and middle crust and thus contribute to the initiation of the large crustal earthquakes

buried soil organic inclusions in non sorted circles fields in northern sweden age and paleoclimatic context although burial of surface organic soil horizons into deeper mineral soil layers helps drive the long term buildup of carbon in arctic soils when and why buried horizons formed as result of cryotu

spatial temporal relationships of mesozoic volcanic rocks in ne china constraints on tectonic overprinting and transformations between multiple tectonic regimes abstract la icp ms zircon u pb ages and geochemical data are presented for the mesozoic volcanic rocks in northeast china with the aim of determining the tectonic settings of the volcanism and constraining the timing of the overprinting and transformations between the paleo asian ocean mongol okhotsk and circum pacific tectonic regimes the new ages together with other available age data from the literature indicate that mesozoic volcanism in ne china can be subdivided into six episodes late triassic 228 201 ma early middle jurassic 190 173 ma middle late jurassic 166 155 ma early early cretaceous 145 138 ma late early cretaceous 133 106 ma and late cretaceous 97 88 ma the late triassic volcanic rocks occur in the lesser xing an zhangguangcai ranges where the volcanic rocks are bimodal and in the eastern heilongjiang jilin provinces where the volcanics are a type rhyolites implying that they formed in an extensional environment after the final closure of the paleo asian ocean the early middle jurassic 190 173 ma volcanic rocks both in the erguna massif and the eastern heilongjiang jilin provinces belong chemically to the calc alkaline series implying an active continental margin setting the volcanics in the erguna massif are related to the subduction of the mongol okhotsk oceanic plate beneath the massif and those in the eastern jilin heilongjiang provinces are related to the subduction of the paleo pacific plate beneath the eurasian continent the coeval bimodal volcanic rocks in the lesser xing an zhangguangcai ranges were probably formed under an extensional environment similar to a backarc setting of double direction subduction volcanic rocks of middle late jurassic 155 166 ma and early early cretaceous 145 138 ma age only occur in the great xing an range and the northern hebei and western liaoning provinces limited to the west of the songliao basin and they belong chemically to high k calc alkaline series and a type rhyolites respectively combined with the regional unconformity and thrust structures in the northern hebei and western liaoning provinces we conclude that these volcanics formed during a collapse or delamination of a thickened continental crust related to the evolution of the mongol okhotsk suture belt the late early cretaceous volcanic rocks widely distributed in ne china belong chemically to a low to medium k calc alkaline series in the eastern heilongjiang jilin provinces i e the eurasian continental margin and to a bimodal volcanic rock association within both the songliao basin and the great xing an range the volcanics in the eastern heilongjiang jilin provinces formed in an active continental margin setting related to the subduction of the paleo pacific plate beneath the eurasian continent and the bimodal volcanics formed under an extensional environment related either to a backarc setting or to delamination of a thickened crust or both late cretaceous volcanics limited to the eastern heilongjiang jilin provinces and the eastern north china craton ncc consist of calc alkaline rocks in the eastern heilongjiang jilin provinces and alkaline basalts in the eastern ncc suggesting that the former originated during subduction of the paleo pacific plate beneath the eurasian continent whereas the latter formed in an extensional environment similar to a backarc setting taking all this into account we conclude that 1 the transformation from the paleo asian ocean regime to the circum pacific tectonic regime happened during the late triassic to early jurassic 2 the effect of the mongol okhotsk suture belt on ne china was mainly in the early jurassic middle late jurassic and early early cretaceous and 3 the late early cretaceous and late cretaceous volcanics can be attributed to the subduction of the paleo pacific plate beneath the eurasian continent

the structure of the crust and uppermost mantle beneath south china from ambient noise and earthquake tomography summary two years of continuous recordings of ambient seismic noise observed at 354 stations in south china from 2009 to 2010 are used to estimate rayleigh wave group and phase velocity maps from 6 to 40 s period these results are merged with rayleigh wave phase velocity maps from 25 to 70 s period derived from earthquakes in the same time frame eikonal tomography generates the dispersion maps which by monte carlo inversion are used to estimate a 3 d vsv model of the crust and upper mantle down to a depth of 150 km across all of south china with attendant uncertainties a clear image emerges of the west yangtze block a region of the western yangtze craton characterized by relatively thick crust 40 km overlying a seismic mantle lithosphere that extends to at least 150 km that may have been the nucleus for the formation of the yangtze craton in the archean and may present a present day obstacle to the eastward expansion of tibet the west yangtze block contrasts with the thinner crust 30 km and mantle lithosphere 70 80 km beneath the eastern yangtze craton and south china foldbelt these observed differences are consistent with processes associated with flat slab subduction in the mesozoic that may have eroded the lithosphere of the eastern yangtze craton and the south china foldbelt

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

lithospheric thickness thinning subduction and interaction with the asthenosphere beneath china from the joint inversion of seismic s wave train fits and rayleigh wave dispersion curves abstract a joint inversion method of simultaneously inverting regional multimode surface waveforms and fundamental mode surface wave dispersion curves is used to better constrain a 3 d s wave velocity model for the upper mantle beneath china thousands of broadband vertical component seismograms were processed and 16 500 rayleigh wave group velocity measurements were retrieved at a period of 20 s with fewer measurements at shorter and longer periods in addition 4947 regional rayleigh waveforms were obtained for paths passing mainly through the chinese mainland the joint inversion of this dataset provides new s wave velocity structures at upper mantle depths down to 400 km in particular the new model is resolved to greater depths than the approximately 200 km depth obtainable in most fundamental mode surface wave tomographic studies and is better resolved at shallow lithospheric depths than that possible in teleseismic body wave tomographic studies because the upper mantle s wave velocity is controlled mainly by temperature rather than by composition thermal structures estimated from the tomographic s wave velocity model are used to estimate the thickness of the lithosphere beneath china the results indicate that in eastern china the north china craton and the yangtze craton are characterized by pronounced variations in lithospheric thickness with the lithosphere thinning from west to east the underlying low velocity layer and deeper level high velocities provide important evidence in support of the idea that lithospheric thinning beneath eastern china is related to the westward subduction of oceanic lithosphere to the east and related thermal and dehydration processes beneath western china thickened lithosphere is imaged beneath the qinghai tibetan plateau except for beneath qiangtang in the northern part of the plateau which is underlain by low velocities the present model generally supports the interpretation of low velocities beneath qiangtang as mantle material squeezed out by convergence between the indian and asian lithospheres moreover two separate segments of the subducting indian lithosphere are imaged indicating that the deeper portion of the subducting slab may have started to break off from the shallower portion as early as 20 ma

a synoptic view of the distribution and connectivity of the mid crustal low velocity zone beneath tibet 1 based on 1 2 years of continuous observations of seismic ambient noise data obtained at more than 600 stations in and around tibet rayleigh wave phase velocity maps are constructed from 10 s to 60 s period a 3 d vsv model of the crust and uppermost mantle is derived from these maps the 3 d model exhibits significant apparently inter connected low shear velocity features across most of the tibetan middle crust at depths between 20 and 40 km these low velocity zones lvzs do not conform to surface faults and significantly are most prominent near the periphery of tibet the observations support the internal deformation model in which strain is dispersed in the deeper crust into broad ductile shear zones rather than being localized horizontally near the edges of rigid blocks the prominent lvzs are coincident with strong mid crustal radial anisotropy in western and central tibet and probably result at least partially from anisotropic minerals aligned by deformation which mitigates the need to invoke partial melt to explain the observations irrespective of their cause in partial melt or mineral alignment mid crustal lvzs reflect deformation and their amplification near the periphery of tibet provides new information about the mode of deformation across tibet

a low velocity belt beneath northern and eastern tibetan plateau from pn tomography 1 new pn tomography on tibetan plateau tp and neighboring region is conducted with data assembled from various sources the improved pn tomographic image delineates several distinct geophysical regimes that are approximately separated by geological boundaries at surface dense distribution of the stations in the eastern half of the plateau allows us to infer a 3d view of crustal thickness variation of the region the most striking feature is the bended low velocity belt lvb which extends from west to east beneath qiangtang block and songpan ganzi fold belt sgfb in northern tp and then turns consistently southward with sgfb beneath eastern tp and further south to indo china the consistency between geological boundaries on surface and sharp velocity contrast boundaries in uppermost mantle may suggest strong deformation coupling between crust and at least uppermost mantle if not whole lithosphere a north south striking lvb is also observed cutting through the southern tp coinciding with the yadong gulu rift at surface our tomographic results are generally consistent with dynamic models that involve with underthrusting in the southern tp shortening in the northern tp and extrusion to the east and the southeast furthermore our results suggest significant east west variations in the structure and dynamics