seismic evidence for sharp lithosphere asthenosphere boundaries of oceanic plates the mobility of the lithosphere over a weaker asthenosphere constitutes the essential element of plate tectonics and thus the understanding of the processes at the lithosphere asthenosphere boundary lab is fundamental to understand how our planet works it is especially so for oceanic plates because their relatively simple creation and evolution should enable easy elucidation of the lab data from borehole broadband ocean bottom seismometers show that the lab beneath the pacific and philippine sea plates is sharp and age dependent the observed large shear wave velocity reduction at the lab requires a partially molten asthenosphere consisting of horizontal melt rich layers embedded in meltless mantle which accounts for the large viscosity contrast at the lab that facilitates horizontal plate motions

evolution of the archean and paleoproterozoic lower crust beneath the trans north china orogen and the western block of the north china craton abstract we report u pb ages and hf isotopes of zircons in granulites from two continental suture zones in the north china craton ncc from granulite xenoliths entrained in the cenozoic hannuoba basalts within the trans north china orogen tnco that amalgamates the western and eastern blocks and from a mafic granulite associated with ultrahigh temperature uht granulites within the inner mongolia suture zone imsz that welds the yinshan and ordos blocks the zircons in these rocks together with the inherited zircons from mesozoic subalkalic intrusives of these regions show several distinct u pb age populations and provide constraints on the evolution of the lower crust beneath the ncc parts of the older zircons from the tnco yield discordant data that project to ages of about 2 5 to 2 7 ga these old zircons show hf tdm model ages of 2 6 2 9 ga suggesting the existence of archean lower crust beneath the tnco which is coupled with the neoarchean metamorphic basement and greenstone belt a major zircon population grew at 1 75 2 0 ga consistent with the timing of the paleoproterozoic collision between the various crustal blocks within the ncc suggesting that this event had a significant effect on the archean lower crust the older inherited zircons from the western block also yield discordant data that project to younger ages of about 1 8 to 1 9 ga this age is consistent with the timing of intrusion of the mafic magmatic protoliths of the granulites associated with the uht rocks in the khondalite belt within the imsz these older zircons yield hf tdm model ages of 2 0 2 5 ga suggesting that the lower crust beneath the western block in the ncc to be dominantly paleoproterozoic and decoupled with the archean metamorphic basement of the region yet another population of zircons from the hannuoba banded granulite xenoliths garnet bearing pyroxenite cumulate and dark pyroxenite xenoliths yield a large spread of phanerozoic concordant ages ranging from 470 ma to 40 ma with peaks at 315 ma 220 230 ma 120 ma and 46 ma the late paleozoic zircons predominantly occur in the garnet bearing pyroxenite xenoliths and yield variable ehf t values of 24 to 18 triassic cretaceous zircons mainly occur in the banded granulite xenoliths and yield highly variable ehf t values ranging from 48 to 16 the tertiary zircons occur only in the dark pyroxenite xenoliths and show a restricted ehf t with a dominant range from 0 to 18 these data suggest episodic magmatic underplating in the ancient lower crust of the ncc lasting continuously throughout phanerozoic producing zircons from the underplated magmas or providing the heat source for the recrystallization of zircons from the ancient crust our data clearly demonstrate the important events of phanerozoic magmatic underplating beneath the neoarchean paleoproterozoic crust of the ncc

geological characterization of remote field sites using visible and infrared spectroscopy results from the 1999 marsokhod field test upcoming mars surveyor lander missions will include extensive spectroscopic capabilities designed to improve interpretations of the mineralogy and geology of landing sites on mars the 1999 marsokhod field experiment mfe was a mars rover simulation designed in part to investigate the utility of visible near infrared and thermal infrared field spectrometers to contribute to the remote geological exploration of a mars analog field site in the california mojave desert the experiment simultaneously investigated the abilities of an off site science team to effectively analyze and acquire useful imaging and spectroscopic data and to communicate efficiently with rover engineers and an on site field team to provide meaningful input to rover operations and traverse planning experiences gained during the mfe regarding effective communication between different mission operation teams will be useful to upcoming mars mission teams field spectra acquired during the mfe mission exhibited features interpreted at the time as indicative of carbonates both dolomitic and calcitic mafic rocks and associated weathering products and silicic rocks with desert varnish like coatings the visible near infrared spectra also suggested the presence of organic compounds including chlorophyll in one rock postmission laboratory petrologic and spectral analyses of returned samples confirmed that all rocks identified as carbonates using field measurements alone were calc silicates and that chlorophyll associated with endolithic organisms was present in the one rock for which it was predicted rocks classified from field spectra as silicics and weathered mafics were recognized in the laboratory as metamorphosed monzonites and diorite schists this discrepancy was likely due to rock coatings sampled by the field spectrometers compared to fresh rock interiors analyzed petrographically in addition to somewhat different surfaces analyzed by laboratory thermal spectroscopy compared to field spectra

composition and tectonic evolution of the chinese continental crust constrained by poisson s ratio article i nfo we have measured both p and s wave velocities vp and vs and poisson s ratios of 60 typical ultrahigh pressure uhp metamorphic rock samples from the chinese continental scientific drilling ccsd main and pre pilot holes and surface outcrops in the sulu dabie orogenic belt at hydrostatic confining pressures up to 850 mpa the experimental results together with those compiled in handbook of seismic properties of minerals rocks and ores ji s c wang q xia b 2002 handbook of seismic properties of minerals rocks and ores polytechnic international press montreal 630 pp reveal that except for monomineralic rocks such as quartzite serpentinite anorthosite limestone and marble the rest of the rock types have poisson s ratios falling along an upward convex curve determined from the correlations between elastic moduli and density poisson s ratios increase with density as the lithology changes from granite felsic gneiss and schist through diorite syenite intermediate gneiss and metasediment to gabbro diabase amphibolite and mafic gneiss and then decrease as the rocks become ultramafic in composition eclogite has a higher density but a lower poisson s ratio than peridotite the results were applied to constrain the crustal composition and tectonic evolution of the chinese continental crust based on crustal thickness h and poisson s ratio from 248 broadband seismic stations measured using teleseismic receiver function techniques the north china yangtze south china and northeast china blocks and songpan ganzi terrane are dominated by low b0 26 and moderate 0 26 b0 28 values n70 suggesting the dominance of felsic composition in the crust the lhasa terrane qiangtang terrane and indochina block are characterized by high proportions 33 42 of measurements with very high values 0 30 and h is found for the south china block northeast block lhasa block qiangtang terrane and indochina block indicating either tectonic thickening of the felsic upper and middle crust by folding and thrusting or the removal of mafic layers from the lower crust into the upper mantle by delamination

receiver function migration image of the deep structure in the bohai bay basin eastern china 1 we apply a receiver function poststack migration method to image the crustal and upper mantle structures beneath the bohai bay basin eastern china the thick sediments of the basin appear to have a substantial influence on the migrated image of the deep structure by using the surface reflected ppps multiples instead of the commonly used ps converted phases a curved moho is coherently imaged showing a thinned crust of 30 km in the basin area compared with the 40 km thick crust in the west mountain range by incorporating the sedimentary velocity model into migration both the 410 km and the 660 km discontinuities present a simple structural feature with relatively flat topography within the basin s interior although possible local structural complexities may exist at the base of the upper mantle around the boundary areas of the basin the mantle transition zone is on average 10 15 km thicker than the global average reflecting a cold lower upper mantle environment that is distinct from the warm shallow upper mantle of the region

crustal structure of mainland china from deep seismic sounding data abstract since 1958 about ninety seismic refraction wide angle reflection profiles with a cumulative length of more than sixty thousand kilometers have been completed in mainland china we summarize the results in the form of 1 a new contour map of crustal thickness 2 fourteen representative crustal seismic velocity depth columns for various tectonic units and 3 a pn velocity map we found a north south trending belt with a strong lateral gradient in crustal thickness in central china this belt divides china into an eastern region with a crustal thickness of 30 45 km and a western region with a thickness of 45 75 km the crust in these two regions has experienced different evolutionary processes and currently lies within distinct tectonic stress fields our compilation finds that there is a high velocity 7 1 7 4 km s layer in the lower crust of the stable tarim basin and ordos plateau however in young orogenic belts including parts of eastern china the tianshan and the tibetan plateau this layer is often absent one exception is southern tibet where the presence of a high velocity layer is related to the northward injection of the cold indian plate this high velocity layer is absent in northern tibet in orogenic belts there usually is a low velocity layer lvl in the crust but in stable regions this layer seldom exists the pn velocities in eastern china generally range from 7 9 to 8 1 km s and tend to be isotropic pn velocities in western china are more variable ranging from 7 7 to 8 2 km s and may display azimuthal anisotropy

structure of the crust and uppermost mantle of the yanshan belt and adjacent regions at the northeastern boundary of the north china craton from rayleigh wave dispersion analysis abstract we have used rayleigh wave dispersion analysis and inversion to produce a high resolution s wave velocity imaging profile of the crust and uppermost mantle structure beneath the northeastern boundary regions of the north china craton ncc using waveform data from 45 broadband ncisp stations rayleigh wave phase velocities were measured at periods from 10 to 48 s and utilized in subsequent inversions to solve for the s wave velocity structure from 15 km down to 120 km depth the inverted lower crust and uppermost mantle velocities about 3 75 km s and 4 3 km s on average are low compared with the global average the moho was constrained in the depth range of 30 40 km indicating a typical crustal thickness along the profile however a thin lithosphere of no more than 100 km was imaged under a large part of the profile decreasing to only 60 km under the inner mongolian axis ima where an abnormally slow anomaly was observed below 60 km depth the overall structural features of the study region resemble those of typical continental rift zones and are probably associated with the lithospheric reactivation and tectonic extension widespread in the eastern ncc during mesozoic cenozoic time distinctly high velocities up to 4 6 km s were found immediately to the south of the ima beneath the northern yanshan belt ysb extending down to 100 km depth the anomalous velocities are interpreted as the cratonic lithospheric lid of the region which may have not been affected by the mesozoic cenozoic deformation process as strongly as other regions in the eastern ncc based on our s wave velocity structural image and other geophysical observations we propose a possible lithosphere asthenosphere interaction scenario at the northeastern boundary of the ncc we speculate that significant undulations of the base of the lithosphere which might have resulted from the uneven mesozoic cenozoic lithospheric thinning may induce mantle flows concentrating beneath the weak ima zone the relatively thick lithospheric lid in the northern ysb may serve as a tectonic barrier separating the on craton and off craton regions into different upper mantle convection systems at the present time

a new model for the dynamic evolution of chinese lithosphere continental roots plume tectonics abstract chinese continental lithosphere comprises three tectonic domains 1 eastern china a region characterized by rifting extensional basins and voluminous basaltic volcanism 2 central china a plexus of cratonic terrains with low heat flow 40 50 mw m2 including the tarim erdos and yangtze blocks welded by pre cenozoic orogenic belts and 3 western china a region comprising the qinghai tibet himalaya orogen the relatively thin crust 35 km and lithosphere 70 km of eastern china is believed to reflect mantle upwelling while near normal crust 45 km and thickened lithosphere 200 km in central china suggest a mantle lithosphere root resembling those inferred for the kaapvaal and siberian cratons thickened crust 70 km and lithosphere 150 km in western china reflect the advanced development of an orogen root the lower density and relative buoyancy of central cratonic mantle roots appear to have contributed to the long term tectonic stability of the central chinese lithospheric blocks in contrast gravitational instability produced by thickening of the denser western chinese lithosphere and the resulting subsidence and eventual delamination of orogenic roots are believed to have led to postorogenic extensional collapse although the geological relationships suggest compressional forces caused both mountain building and orogen root development extensional stress resulting from gravitational collapse is believed to have induced lithospheric and crustal thinning with concomitant reduction of topography the term continental roots plume tectonics has been adopted to describe the configuration and dynamic condition of subcontinental lithosphere and upper mantle beneath china accordingly it is proposed that supracrustal tectonic forms represent the surface expressions of and responses to deep continental roots plume tectonics while the prevailing view is that the western orogenic belt is not genetically related to eastern continental rifting such a relationship is inherent to the continental roots plume tectonics model it is further proposed that the formation of orogenic lithosphere roots triggered eastward extrusion of the asthenosphere along the 400 km depth mantle interface and in response to subduction at the eastern margin produces plume like upwelling beneath eastern china we suggest that processes involved in continental roots plume tectonics are directly responsible for the formation and evolution of the eurasian supercontinent

lithospheric shear wave velocity and radial anisotropy beneath the northern part of north china from surface wave dispersion analysis rayleigh and love wave phase velocities in the northern part of the north china are obtained from ambient noise tomography in the period range of 8 35 s and two plane wave earthquake tomography at periods of 20 91 s using data recorded at 222 broadband seismic stations from the temporary north china seismic array and permanent china digital seismic array the dispersion curves of rayleigh and love wave from 8 to 91 s are jointly inverted for the 3 d shear wave structure and radial anisotropy in the lithosphere to 140 km depth distinct seismic structures is observed from the fenhe graben and taihang mountain to the north china basin the north china basin from the lower crust to the depth of 140 km is characterized by high velocity anomaly reflecting mafic intrusion and residual materials after the extraction of melt and by strong radial anisotropy with vsh vsv implying horizontal layering of intrusion and alignment of minerals due to vigorous extensional deformation and subsequent thermal annealing however low velocity anomaly and positive radial anisotropy are observed in the fenhe graben and taihang mountain suggesting the presence of partial melt in the lithosphere due to the mantle upwelling and horizontal flow pull

crustal structure across the yanshan belt at the northern margin of the north china craton abstract we applied an integrated receiver function imaging technique to the teleseismic data from 54 ncisp iii broadband seismic stations to study the fine scale crustal structure beneath the eastern yanshan belt ysb and adjacent areas at the northern margin of the north china craton ncc the robustness and reliability of the resultant crustal image were noticeably improved by achieving imaging consistency between common conversion point stacking and waveform inversion of the receiver functions our imaging result revealed substantial lateral heterogeneities in the crust of the study region as displayed by the undulating intra crustal interfaces highly varying upper middle and lower crust thicknesses and interlayers of low and high velocities the crustal structure of the ysb is characterized by significant structural variations together with a sharp moho a thin to normal crust and a lower crust with lower velocity and normal thickness it differs markedly from the bohai bay basin and the taihang mountains within the interior of the ncc the distinct features and structural complexity of the ysb might be attributed to the complex tectonic history of the region especially the multiple phases of contraction and possible occurrence of crustal delamination which is in large contrast to other subregions of the ncc where tectonic extension likely dominated the crustal deformation since the late mesozoic

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

extension in the graben systems around the ordos china and its contribution to the extrusion tectonics of south china with respect to gobi mongolia the graben basins around the ordos block are major tectonic features of late cenozoic extension in north china this paper gives a synthetic view of the basic characteristics of the graben basins and of the kinematics of the graben bounding faults this view is based on the available geological data spot imagery analysis field observations and focal mechanisms of earthquakes from this region these graben basins have been grouped into two major systems the yinchuan hetao graben system along the northern and northwestern margins of the ordos and the weihe shanxi graben system along the southern and eastern margins of the ordos crustal deformation along these graben systems involves normal slip on ne sw striking graben bounding faults normal right lateral and normal left lateral slip on nne ssw and wnw ese striking faults respectively this fault pattern is consistent with nw se trending extension the amount and rate of deformation resulting from this extension have been estimated from geological data using a cross sectional area balance and the extensional factor method deduced from the tilt of faulted blocks the results of these estimates show that the uppermost pliocene quaternary extension rate in a nw se direction is in the order of 1 6 mm yr 1 across the weihe graben 0 5 mm yr 1 across the central shanxi graben on the southeastern margin of the ordos block and 3 1 mm yr 1 across the linhe graben on the northwestern margin of the ordos block the extension across these graben systems is accompanied with counterclockwise rotation of continental blocks in north china ordos taihang shan north china plain a kinematic model is proposed in which the late cenozoic extension and block rotation in north china are interpreted as the effect of the eastward termination of the left lateral slip haiyuan fault and kunlun taibai fault system the ordos block rotates counterclockwise as a result of the push of tibet through the left lateral strike slip haiyuan fault and the liupan shan thrust and fold belt the extension along the weihe shanxi graben system may represent the effect of the left lateral slip on the kunlun taibai qinling fault system the rough estimates of the extensional deformation around the ordos block indicate that this contributes to about 5 2 mm yr 1 of left lateral movement in a n125 e direction between south china and gobi mongolia this motion adds to the left lateral slip on the qinling fault zone about 7 2 mm yr 1 in a n90 e direction between the qinling shan and the hua shan north china thus the eastward motion of south china with respect to gobi mongolia is partitioned between normal faulting around the ordos and strike slip faulting in the qinling shan it is estimated to be in the order of 12 4 mm yr 1 in a n105 e direction during the quaternary

a new record of silica rich coating on carbonate substrates in southeast central iran constraints on geochemical signatures abstract there exist few data on the geochemical signatures and occurrence of silica rich coatings developed on siliceous carbonate substrates the rock coatings in the maran e galu area in southeast central iran are composed of four layers a lower thick layer 1 mm of silica a lower thin film of fe mn oxide an upper thick 1 mm silica rich layer and an upper thin film of fe mn oxide energy dispersive x ray spectrometer eds x ray diffraction and bulk coating geochemistry data obtained by xrf and icp ms highlight that the 1 3 mm thick silica rich coatings occur as a silica glaze of opal composition on the siliceous carbonate substrate the coatings were probably formed by the interaction of rainfall water vapor or dew with silicate and carbonate rich detrital atmospheric dust releasing h4sio4with a ph of 5 10 in this semiarid arid desert environment this led to the formation of silica gels as well as minor fe mn oxide gels by evaporation and supersaturation and finally changed to the black brown silica glaze probably at ambient temperatures of 40 c major and minor element signatures are consistent with the known silica glazes displaying enrichment in ba sr p and lrees with little to no eu and ce anomalies and a weak tm anomaly however the very low content of aluminum oxide is well correlated with the known classified silica glaze of genetic type 1 reflecting the absence of detrital clay minerals the low fe and mn contents in bulk coatings 3 6 and 10 magnitudes lower than crustal abundance respectively and lack of biochemical processes in the atmospheric dust highlight the semiarid arid climate setting we thereby conclude that a new variant of silica glaze of 1 3 mm thickness could form on siliceous carbonate substrates under an alkaline ph in semiarid arid regions

a wave equation migration method for receiver function imaging 2 application to the japan subduction zone 1 the newly developed wave equation poststack depth migration method for receiver function imaging is applied to study the subsurface structures of the japan subduction zone using the fundamental research on earthquakes and earth s interior anomalies freesia broadband data three profiles are chosen in the subsurface imaging two in northeast ne japan to study the subducting pacific plate and one in southwest sw japan to study the philippine sea plate the descending pacific plate in ne japan is well imaged within a depth range of 50 150 km the slab image exhibits a little more steeply dipping angle 32 in the south than in the north 27 although the general characteristics between the two profiles in ne japan are similar the imaged philippine sea plate in eastern sw japan in contrast exhibits a much shallower subduction angle 19 and is only identifiable at the uppermost depths of no more than 60 km synthetic tests indicate that the top 150 km of the migrated images of the pacific plate is well resolved by our seismic data but the resolution of deep part of the slab images becomes poor due to the limited data coverage synthetic tests also suggest that the breakdown of the philippine sea plate at shallow depths reflects the real structural features of the subduction zone rather than caused by insufficient coverage of data comparative studies on both synthetics and real data images show the possibility of retrieval of fine scale structures from high frequency contributions if high frequency noise can be effectively suppressed and a small bin size can be used in future studies the derived slab geometry and image feature also appear to have relatively weak dependence on overlying velocity structure the observed seismicity in the region confirms the geometries inferred from the migrated images for both subducting plates moreover the deep extent of the pacific plate image and the shallow breakdown of the philippine sea plate image are observed to correlate well with the depth extent of the seismicity beneath ne and sw japan such a correlation supports the inference that the specific appearance of slabs and intermediate depth earthquakes are a consequence of temperature dependent dehydration induced metamorphism occurring in the hydrated descending oceanic crust

the lithosphere of north china craton from surface wave tomography abstract fundamental mode rayleigh wave group velocity dispersion data were used in a tomographic study to reconstruct the crust and upper mantle shear velocity structure in east asia this article expounds the features of lithosphere structure in different sub regions of north china and discusses their implications for the tectonic evolution and present tectonics of north china craton ncc the study revealed that strong earthquakes took place in the low velocity zones and along the boundaries between high and low velocities in the middle and lower crust the active nw trending zhangjiakou bohai seismic belt corresponds to a prominent low velocity zone in the crust and upper mantle lid in addition to the well known structural difference between western and eastern ncc we are able to resolve clearly the lithospheric features of sub regions in eastern ncc the southern north china basin and north yellow sea are characterized by a high velocity crust and upper mantle lid down to 70 80 km depth while the northern north china basin has a low velocity crust and the velocity below moho to about 130 km is rather uniform and low there is also a general trend of velocity decrease in the upper mantle from west to east the velocity images bear the imprints of subduction and collision that took place in the periphery of ncc since mesozoic and shed some light on the mechanism of mesozoic lithospheric thinning of eastern ncc

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

what drove late mesozoic extension of the northern china mongolia tract the northern china mongolia tract exhibited a tectonic transition from contractional to extensional deformation in late mesozoic time late middle to early late jurassic crustal shortening is widely thought to have resulted from collision of an amalgamated north china mongolia block and the siberian plate but widespread late late jurassic early cretaceous extension has not been satisfactorily explained by existing models some prominent features of the extensional tectonics of the northern china mongolia tract are 1 late jurassic voluminous volcanism prior to early cretaceous large magnitude rapid extension 2 overlapping in time of contractional deformation in the yinshan yanshan belt with development of extensionrelated basins in the interior of the northern china mongolia tract and 3 widespread occurrence of alkali granitic plutonism extensional basins and metamorphic core complexes in the early cretaceous a new explanation is advanced in this study for this sequence of events the collision of amalgamated north china mongolia with siberia led to crustal overthickening of the northern china mongolia tract and formation of a high standing plateau subsequent breakoff at depth of the north dipping mongol okhotsk oceanic slab is suggested as the main trigger for late mesozoic lithospheric extension of that tract slab breakoff resulted in mantle lithospheric stretching of the adjacent northern china mongolia tract with subsequent ascent of hot asthenosphere and magmatic underplating at the base of the crust collectively these phenomena triggered gravitational collapse of the previously thickened crust leading to late late jurassic early cretaceous crustal extension and importantly coeval contraction along the southern margin of the plateau in the yinshan yanshan belt the proposed model provides a framework for interpreting the spatial and temporal relationships of distinct processes and reconciling some seemingly contradictory phenomena such as the synchronous extension of northerly terranes during major contraction in the neighboring yanshan yinshan belt d 2003 elsevier b v all rights reserved

distinct lateral variation of lithospheric thickness in the northeastern north china craton abstract a detailed knowledge of the thickness of the lithosphere in the northeastern north china craton ncc is important for understanding the significant tectonic reactivation of the craton in the mesozoic and cenozoic time we achieve this goal by applying the newly proposed wave equation based migration technique to the s receiver functions recently collected in the region distinct negative signals are identified below the moho in all the s receiver function migrated images and stacks which we interpret as representing the s to p conversions from the lithosphere asthenosphere boundary lab the imaged lab is as shallow as 60 70 km in the southeast basin and coastal areas and deepens to no more than 140 km in the northwest mountain ranges and continental interior these observations indicate widespread lithospheric thinning in the study region in comparison with the 180 km lithospheric thicknesses typical of most cratonic regions the revealed topography of the lab generally agrees with the lateral variation in upper mantle seismic anisotropy previously measured through sks splitting analysis in particular a sharp lab step of 40 km is detected at the triple junction of the basin and mountains at almost the same place where an abrupt change from nw se to ne sw in fast polarization direction of shear waves was found these findings suggest a close correlation between the seismic anisotropy and hence deformation of the upper mantle the lithospheric thickness and the surface tectonics of the northeastern ncc while the thinned lithosphere and the nw se fast shear wave polarizations in the east areas probably are related to the dominant nw se tectonic extension in the late mesozoic cenozoic time the thicker lithosphere and the ne sw fast polarization direction in the west mountain ranges may reflect earlier contractional deformations of the region synthetic tests indicate that the lab beneath the northeastern ncc is a well defined zone 10 20 km thick combined with seismic tomography results and geochemical and petrological data this suggests that complex modification of the lithosphere probably accompanied significant lithospheric thinning during the tectonic reactivation of the old craton

moho depth variations from receiver function imaging in the northeastern north china craton and its tectonic implications a detailed knowledge of the crustal thickness in the northeastern north china craton ncc is important for understanding the unusual phanerozoic destruction of the craton we achieve this goal by employing a 2 d wave equation based migration method to p receiver functions from 198 broadband seismic stations using ps conversions and surface reflected multiples by combining receiver function images along 19 profiles we constructed a high resolution moho depth model for the northeastern ncc the results present dominant e w moho depth variations similar to previous observations and new regional n s variations beneath both sides of the north south gravity lineament to the west while a deeper moho approximate to 42km appears in the interior of the trans north china orogen a relatively shallow moho approximate to 38km exists in the northern margin of the trans north china orogen to western ncc to the east the crust beneath the yan mountains in the marginal area is thicker approximate to 32 40km than that approximate to 26 32km beneath the bohai bay basin in the craton interior and the moho further shallows from ne approximate to 32km to sw approximate to 26km within the basin along with other observations we conclude that the dominant e w difference may have been associated with the paleo pacific plate subduction under eastern asia since the mesozoic the newly observed complex n s variations may have reflected the structural heterogeneity of the cratonic lithosphere inherited since the formation of the ncc in the paleoproterozoic or spatially uneven effects on the cratonic lithosphere of subsequent thermotectonic events during the long term evolution of the craton or both

crustal structure and tectonic study of north china craton from a long deep seismic sounding profile abstract in this paper we present the results of modeling refracted and reflected waves employing 2d ray tracing for a 1600 km long refraction reflection profile that extends e w across the entire north china craton ncc the resulting p wave velocity models reveal substantial structural variations among different geological units of the ncc the taihangshan mountains are the geographical and geological demarcation lines of the ncc in the eastern part of the ncc bohai bay basin the craton appears to be destructed as evidenced from the widespread of crust thinning 30 km development of large sedimentary basins and weaken of crust mantle boundary coupling these features indicated that cenozoic tectonic reactivation succeeded mesozoic destruction in the eastern part of ncc in the western part of ncc the craton remains high crustal p wave velocity stable cold and strongly crust mantle boundary coupling crust the tanlu faults and the taihangshan faults are the tectonic boundaries in the ncc and play important roles in the process of cratonic destruction the structural feature of the east secondary tectonic differential settlement in the process of basin extension is that the most faults in bohai bay basin are the boundaries between the depression basin and uplift area comprehensive study found an apparent difference between the north and south part in eastern ncc destruction in that the large scale cenozoic stretching mainly occurred in the bohai bay basin and the weakly existed only in the local area and in hehuai basin we discussed the crust and upper mantle tectonic evolution of ncc under the action of the convergence of regional tectonic stress field in different geological periods since the mesozoic era the plate movement around ncc affects the lithospheric and crustal modification of the eastern north china and controls the deep structural background of seismicity and metallogenesis