seismic structure and rheology of the crust under mainland china abstract the crust and upper mantle in mainland china were relatively densely probed with wide angle seismic profiling since 1958 and the data have provided constraints on the amalgamation and lithosphere deformation of the continent based on the collection and digitization of crustal p wave velocity models along related wide angle seismic profiles we construct several crustal transects across major tectonic units in mainland china in our study we analyzed the seismic activity and seismic energy releases during 1970 and 2010 along them we present seismogenic layer distribution and calculate the yield stress envelopes of the lithosphere along the transects yielding a better understanding of the lithosphere rheology strength beneath mainland china our results demonstrate that the crustal thicknesses of different tectonic provinces are distinctively different in mainland china the average crustal thickness is greater than 65 km beneath the tibetan plateau about 35 km beneath south china and about 36 38 km beneath north china and northeastern china for the basins the thickness is 55 km beneath qaidam 50 km beneath tarim 40 km beneath sichuan and 35 km beneath songliao our study also shows that the average seismic p wave velocity is usually slower than the global average equivalent with a more felsic composition of crust beneath the four tectonic blocks of mainland china resulting from the complex process of lithospheric evolution during triassic and cenozoic continent continent and mesozoic ocean continent collisions we identify characteristically different patterns of seismic activity distribution in different tectonic blocks with bi or even tri peak distribution of seismic concentration in south tibet which may suggest that crustal architecture and composition exert important control role in lithosphere deformation the calculated yield stress envelopes of lithosphere in mainland china can be divided into three groups the results indicate that the lithosphere rheology structure can be described by jelly sandwich model in eastern china and creme brulee models with weak and strong lower crust corresponding to lithosphere beneath the western china and kunlun orogenic belts respectively the spatial distribution of lithospheric rheology structure may provide important constraints on understanding of intra or inter plate deformation mechanism and more studies are needed to further understand the tectonic process es accompanying different lithosphere rheology structures

complex upper mantle deformation beneath the north china craton implications for lithospheric thinning summary the mechanism of lithospheric thinning of the north china craton ncc remains controversial to constrain the mechanism this study investigated the upper mantle deformation pattern of the craton by measuring shear wave splitting at the cratonic edge the results derived from data recorded at 47 stations reveal a complex pattern of mantle deformation inside the eastern craton the majority of fast direction trends se nw parallel to the tectonic extension direction accompanying with the lithospheric thinning at the cratonic edge 15 stations with only null splitting results indicate undetectable anisotropy beneath the stations this may be due to upwelling or chaotic ascension of mantle flow to the north off the craton large delay times and variation of splitting parameter with backazimuth are generated by the combination of lithospheric and asthenospheric anisotropy based on comparison of the splitting results and the predicted ones by the compelling models it is likely that lithospheric delamination dominated the lithospheric thinning at the north edge of the ncc during the mesozoic to cenozoic

electrical resistivity structure of the upper mantle beneath northeastern china implications for rheology and the mechanism of craton destruction abstract the north china craton ncc and central asian orogen belt caob in northeastern china experienced a range of tectonic events during the phanerozoic dominated by lithospheric thinning of the eastern ncc in the late mesozoic and cenozoic in order to better understand the tectonic evolution of the ncc and the caob new broadband and long period magnetotelluric data were collected along a north west to south east trending profile that extended from the caob across the yanshan belt the tanlu fault zone to the liaodong peninsula a two dimensional 2 d resistivity model was derived from inversion of the transverse electric mode transverse magnetic mode and vertical magnetic field data in the crust of the caob the resistivity model shows a northwest dipping low resistivity zone beneath the solonker suture that is identified as the suture zone formed by the collision between the siberian and north china cratons the upper mantle of the caob is characterized by moderate resistivity values 300 1000 m that are best explained by the presence of hydrogen dissolved in olivine the water concentration of the caob mantle is comparable to values reported for the asthenosphere and cratons that have been significantly hydrated the ncc upper mantle is generally lower in resistivity than the caob upper mantle and a zone of lower resistivity is observed in the upper mantle at the southeast end of the profile beneath the ncc superimposed on this southeast decrease in upper mantle resistivity three low resistivity zones were imaged 1 below the xilamulun fault 2 close to the north south gravity lineament and 3 between the northern yanshan belt and tanlu fault zone the low resistivities can be explained as regions of partial melts or fluids perhaps caused by asthenospheric upwelling together with seismic imaging results and geochemical data the resistivity model shows that the modification of the lithosphere associated with craton destruction has occurred in a spatially non uniform manner in the region of the ncc investigated in this study

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

crust structure of the north china craton from a long range seismic wide angle reflection refraction data abstract we present an interpretation of a 1530 km long wide angle seismic reflection refraction profile that extends across the north china craton ncc approximately from east to west this profile is the longest and the densest wide angle seismic reflection refraction profile in china up to now parameterizing the velocity model as layers with variable thickness we perform seismic travel time tomography to resolve the velocity variation within layers and velocity contrast across moho our model shows crustal thickness that varies from 35 km under the shandong peninsula to 30 km under the north china plain ncp and 32 40 km under central ncc to 45 km under the ordos plateau these results indicate obvious crustal thinning beneath the ncp in comparison with the 35 km crustal thicknesses typical of most cratonic regions in particular an abrupt moho step of 10 km is detected at the junction of the eastern block and western block of the ncc these crustal characteristics are consistent with studies of lithosphere asthenosphere boundary lab with the method of receiver function migration and they indicate a close correlation with lithospheric thickness and surface tectonics of the northeastern ncc these results provide robust seismological evidence that the lithosphere from ncc to the western edge of the taihang mountain might have been widely affected and thinned since its formation in the archean era

shear wave splitting in eastern and central china implications for upper mantle deformation beneath continental margin eastern china located at the east margin of the eurasia plate is an ideal place to study the deformation pattern of upper mantle beneath continental margin we investigated the upper mantle anisotropy beneath eastern china by applying teleseismic shear wave splitting measurements we examined shear wave splitting measurements at 33 permanent stations from cdsn and gsn iris networks in eastern and central china as well as splitting parameters from a previous regional study the splitting observations are characterized by apparent diversity of anisotropy pattern in adjacent tectonic domains including the southeast china orogenic belt and the yangtze craton and the eastern and central north china craton based upon the straightforward relationships between seismic anisotropy and the development of lattice preferred orientation of mineral in upper mantle rocks we interpret the splitting results in terms of tectonic fabric within the upper mantle our interpretation implies that the upper mantle anisotropy beneath eastern china remained the effects of tectonic rejuvenation occurred during the late mesozoic to cenozoic we proposed that there are possibly two kinds of mechanisms involved in the upper mantle deformation beneath eastern china depending on the roles of thick root of cratonic lithosphere one mechanism is the deflecting the asthenospheric flow by the thick root of craton and the other one is the extensional asthenospheric flow causing the craton lost part of its thick root 2007 elsevier b v all rights reserved

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

crustal structure of the northern margin of the north china craton and adjacent region from sinoprobe02 north china seismic war r experiment abstract the sinoprobe02 north china seismic experiment consisted of three seismic recording efforts along a 450 km long profile the profile extended from northwest of beijing across the northern margin of the north china craton ncc and across the southeastern portion of the central asian orogenic belt caob to the solonker suture zone we processed analyzed and modeled the data collected during a wide angle reflection and refraction effort the recording of seismic waves from 8 explosions was conducted in 4 deployments of 300 texan recorders with station spacings of 1 1 5 km the p wave field provided good quality data for most of the profile arrivals of refracted and reflected waves from sediments and basement pg intracrustal phases pcp plp and the moho pmp pn were typically observed travel time modeling was done layer by layer using the top to bottom approach and was constrained by a coincident deep reflection seismic profile the initial velocity model was altered by trial and error and the forward model was updated by damped least squares inversion in our modeling calculated travel times fit observed arrivals for all 1439 traces with an average rms error of 0 113 s the final 2 d p wave velocity model contains many features of tectonic significance 1 the velocity structure varies significantly from the ncc to the caob 2 thicker crust appears beneath the yinshan yanshan belt and was probably generated by compression in the early jurassic and modified during the craton s destabilization and extension the flat and relatively shallow moho in the caob may be attributed to the extension 3 strong velocity variations beneath the bainaimiao arc and ondor sum subduction accretion complex indicate that multiple pulses of magmatism occurred during the complex tectonic evolution of this area

crustal structure of bohai sea and adjacent area north china from two onshore offshore wide angle seismic survey lines abstract in 2010 and 2011 onshore offshore surveys along two lines in the bohai area were carried out this paper presents the deep structure from wide angle seismic data along the two lines and try to improve the reliability of deep interfaces by using of the cmp prospecting method the result is as follows 1 the environmental noise of records from obss in shallow water area is stronger than that from deep waters 2 the cmp stacking method is potential for high density obs surveys 3 the thickness of sedimentary layer in bohai sea and surrounding area is 3 5 km the velocity increases with depth from about 2 km s at the seafloor to about 4 5 km s on the sedimentary basement 4 the upper crust thins toward the sea area from the land area the middle and lower crust also vary insignificantly the middle crust is about 4 km and the lower crust is about 15 km the velocities of the middle and lower crust shows gentle variation in vertical but obvious in lateral due to the impact of fault zones 5 the velocity contours nearby the tancheng lujiang tlfz and zhangjiakou penglai zpfz fault zones are u shaped where the velocity changes laterally and the interface undulates significantly velocity disturbances exist in the crust mantle transition zone at the fault zones the tlfz and zpfz could be the upwelling channels of deep material 6 in the eastern part of north china craton ncc the moho gently ranges at the depth of about 30 km with local rises lithosphere thinning occurred predominantly at the top of upper mantle the east boundary of lithosphere thinning is inferred to be on the east of bohai sea

holocene relative mean sea level changes in the wadden sea area northern netherlands although the netherlands has a long tradition of sea level research no holocene relative sea level curve is available for the north of the netherlands previous studies hypothesised that the relative sea level reconstruction for the western netherlands is also valid for the northern part of the country however glacial isostatic adjustment gia models predict a lower and steeper relative sea level curve because of greater postglacial isostatic subsidence long term data of relative sea level change are important to inform gia models and understand postglacial vertical land motion related to the rebound of fennoscandia and neotectonic activity we compiled and evaluated a set of basal peat radiocarbon dates to reconstruct the holocene relative mean sea level rise in the dutch wadden sea area for the early holocene this reconstruction is lower than the western netherlands curve after 6400 cal a bp the curve for the wadden sea is statistically indistinguishable from that for the western netherlands a result that conflicts with gia model results it remains to be investigated whether the problem lies with the gia model predictions or with the quality of the available data additional basal peat radiocarbon dates from suitable sites should be collected to further solve this problem

late holocene land and sea level changes in the british isles implications for future sea level predictions abstract four decades of palaeosea level research in the british isles have produced a large dataset of age altitude curves of postglacial sea level changes patterns of late holocene relative sea level change reveal the persistent influence of the british irish ice sheet and the larger scandinavian ice sheet on contemporary rates of vertical land movements the shennan and horton 2002 map of late holocene relative land movements has been used in future sea level rise predictions by the united kingdom climate impact programme in their 2002 assessment ukcip02 but has been mistaken for a map of absolute land movements in this paper land motion data for britain are extracted from the shennan and horton 2002 relative sea level data and a new map of crustal land movements is presented which also includes ireland this procedure takes into account the regional 20th century sea level rise 0 14 m and the process of ocean syphoning i e a global fall in sea level of 0 3 mm yr due to gia induced ocean floor lowering and re distribution of ocean mass the calculated land motion rates also depend on the global late holocene ice equivalent sea level change given by the intergovernmental panel on climate change as 0 0 0 2 mm yr accounting for these processes reduces the misfit between geological observations of vertical land motion and those independently derived from gravity aligned global positioning system ag gps measurements and shows that ukcip02 has underestimated land subsidence in southern britain and over estimated land uplift in scotland both by 0 1 0 2 mm yr a best fit between gps and geological estimates of land movements in britain is achieved for a global long term eustatic sea level fall of ca 0 2 mm yr suggesting some global ice expansion in the late holocene rather than melt if this is correct uplift rates in scotland would be lower and subsidence rates in southern britain would be faster by 0 4 0 5 mm yr than estimated by ukcip02 more high quality late holocene relative sea level data are required to quantify vertical land motion as accurately as possible especially near large coastal population centres for input into regional scenarios of future sea level rise

nd isotopic constraints on crustal formation in the north china craton abstract recent tectonic analysis suggests that the north china craton consists of two archean continental blocks called the eastern and western blocks separated by the paleoproterozoic trans north china orogen although the published geochronological data are not sufficient to constrain the detailed tectonothermal evolution of the craton the available nd isotopic data show some important differences in nd model ages between the tectonic units the eastern block shows two main nd model age peaks one between 3 6 and 3 2 ga and the other between 3 0 and 2 6 ga limited nd isotopic data from the western block show a large range of model ages between 3 2 and 2 4 ga these differences are consistent with the recently proposed model the nd isotopic data from mantle derived mafic rocks indicate that the mantle beneath the north china craton was depleted in the archean consistent with major crustal growth during this period in the paleoproterozoic however the mantle derived mafic rocks show negative end t values implying crustal contamination this may have resulted from subduction and collision between the eastern and western block implying that the mechanisms of crustal formation and evolution may have been different between the archean and paleoproterozoic the north china craton was re activated by addition of mantle derived magma into the lower crust in the late mesozoic resulting in rejuvenation of the lower crust this indicates that underplating is also an important mechanism for continental addition although in this case it may not equate to crustal growth since it was preceded by removal of lithospheric mantle and possible some lower crust

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

joint application of surface electrical resistivity and gpr measurements for groundwater exploration on the island of spiekeroog northern germany geophysical surveys have been carried out on the east frisian island of spiekeroog at the german north sea coast in 1996 so called freshwater lenses lying on top of saltwater saturated layers because of their lower density provide most of the freshwater supply on the frisian islands the major goal of the present study is to show the possibilities of a joint application of surface electrical resistivity soundings and ground penetrating radar gpr for the hydrogeological investigation of the island it is shown that a comprehensive interpretation of large scale gpr profiling data in a sandy aquifer provides valuable hydrogeological information especially if there is not any other information available such as from boreholes or groundwater measuring points applying the techniques of surface electrical resistivity and ground penetrating radar jointly we were able to construct a groundwater contour map for the entire island of spiekeroog in addition we were able to delineate hydrogeologically important changes in grain size and stratigraphical features and to indicate temporal changes of the spatial extent of the freshwater reservoir in comparison to earlier less complete investigations finally we located an area previously unknown in the eastern part of the island where precipitation appears to be developing a substantial new freshwater lens

mantle flow pattern and geodynamic cause of the north china craton reactivation evidence from seismic anisotropy 1 we investigate the mantle flow pattern and geodynamic cause of north china craton ncc reactivation using shear wave splitting measurements from 140 broadband stations using a newly developed method for simulating wave propagation in a two dimensional anisotropic medium we first examined the influence of sedimentary structures on sks splitting measurements the simulations show that a sedimentary layer whether isotropic or anisotropic significantly influences the waveform however the shear wave splitting parameters can be retrieved with negligible errors as a result this study included new splitting measurements at stations which were deployed within basins and not used previously among 121 broadband stations that contribute valid splitting results 55 stations are newly added which were deployed within basins this significantly improved the sampling coverage on the ncc the complicated spatial patterns of the splitting parameters indicate that complex upper mantle deformation has occurred in the ncc to obtain both deep kinematic and geometric information we interpret our splitting measurements in the context of new high resolution tomographic results for the ncc by comparing our observations with three end member conceptual models upwelling wedge flow and lithospheric delamination we found that the observed anisotropy pattern beneath the ncc is not completely consistent with any of them thus we prefer a hybrid mantle flow model where the subduction of the pacific plate causes a mantle wedge flow beneath the eastern archean block and a regional upwelling beneath the central block which has been imaged as a low velocity anomaly in seismic tomography thus we speculate that the subduction of the pacific plate compared to the ncc yangtze craton amalgamation and the india eurasian collision is most likely the geodynamic cause of the reactivation of the ncc eastern block during the late mesozoic to cenozoic

tidal evolution of the northwest european shelf seas from the last glacial maximum to the present 1 two dimensional paleotidal simulations have been undertaken to investigate tidal and tide dependent changes tidal amplitudes tidal current velocities seasonal stratification peak bed stress vectors that have occurred in the nw european shelf seas during the last 20 ka the simulations test the effect of shelf wide isostatic changes of sea level by incorporating results from two different crustal rebound models and the effect of the ocean tide variability by setting open boundary values either fixed to the present state or variable according to the results of a global paleotidal model the use of the different crustal rebound models does not affect the overall changes in tidal patterns but the timing of the changes is sensitive to the local isostatic effects that differ between the models the incorporation of ocean tide changes greatly augments the amplitude of tides and tidal currents in the celtic and malin seas before 10 ka bp and has a large impact on the distribution of seasonally stratified conditions magnitude of peak bed stress vectors and tidal dissipation in the shelf seas the predictions on seasonal stratification are supported by well dated evidence on tidal mixing front migration in the celtic sea additional experiments using the global model suggest that the variability of offshore tides has been caused mainly by changes of eustatic sea level and ice sheet extent in particular a large decrease observed at 10 8 ka bp is attributed to the opening of hudson strait accompanied by the retreat of the laurentide ice sheet

constraints on the timing of uplift of the yanshan fold and thrust belt north china this paper reports in situ u pb ages and hf isotopic data on detrital zircons from paleozoic to late mesozoic strata in the xishan area near beijing that provide important constraints on the evolution and paleogeography of the northern part of the north china craton ncc zircons from carboniferous to late mesozoic sandstones are characterized by three major groups of u pb ages 2 5 2 3 ga 1 9 1 7 ga and late phanerozoic ages the neoarchean and paleoproterozoic zircons and some phanerozoic zircons have negative ehf t values similar to igneous zircons from intrusive rocks known from the ncc indicating that the source of the sandstones was locally derived however late triassic to late jurassic 205 158 ma sandstones contain a group of phanerozoic zircons with positive ehf t values distinct from known igneous zircons in the ncc suggesting an exotic source the nearest potential source is the xing meng orogenic belt xmob to the north of the ncc where considerable amounts of juvenile crustal materials exist it is concluded that there are two sudden shifts in source provenances of the xishan sediments from the ncc before the late triassic to a mixed source from the ncc and xmob during the late triassic to late jurassic and then from the ncc again during the late jurassic 158 ma the first shift in source resulted from the exhumation and denudation of rocks due to uplift of the xmob which coincided with post collisional extension in the late triassic and intraplate extension of the ncc in the middle to late jurassic the second source shift resulted from the uplift of the yanshan fold and thrust belt thus constraining the timing of this to the late jurassic

detailed crustal structure of the north china and its implication for seismicity abstract since the mesozoic cenozoic era the north china craton has experienced an important tectonic transition and it has given rise to complicated crustal structure and strong earthquake activity based on the large scale surface gravity data we studied the detailed crustal structure and seismogenic mechanism of the north china the results indicate that the north china presents typical characteristics of adjoining depression and uplift alternating basins and hills inhomogeneous density and also great differences in crustal structure and moho topography the upper and middle crustal structures are dominated by the nne striking tectonic units with many faults cut down to the middle crust the lower crust is characterized by the folding structure with high and low density placed alternately from west to east presenting lateral heterogeneous feature adjusted by the gravity isostasy moho topography of the north china fluctuates greatly compared with the north china basin crustal thickness in the western taihang northern yanshan and luzhong areas are much thicker while those densities are lower than the north china basin the dominating tectonic direction of the moho topography strikes ne to nne and undulates alternately from west to east the epicenters are mostly concentrated in the upper and middle crust especially the transitional areas between the high and low gravity anomalies the tancheng earthquake in 1668 sanhe earthquake in 1673 tangshan earthquake in 1976 and all other seismic tectonic zones of the north china are all distributed in area where magma moves strongly beneath the crust which is considered to be related to the movement of the high density unstable and heat flows along the deep passage from the uppermost and asthenosphere due to the subduction of the pacific slab towards the eurasian plate

sea level change glacial rebound and mantle viscosity fornorthern europe northwestern europe remains a key region for testing models of glacial isostasy because of the good geological record of crustal response to the glacial unloading since the time of the last glacial maximum models for this rebound and associated sea level change require a detailed knowledge of the ice sheet geometry including the ice thickness through time existing ice sheet reconstructions are strongly model dependent and inversions of sea level data for the mantle response may be a function of the model assumptions thus inverse solutions for the sea level data are sought that include both ice and earth model parameters as unknowns sea level data from fennoscandia the north sea the british isles and the atlantic and english channel coasts have been evaluated and incorporated into the solutions the starting ice sheet for fennoscandia is based on a reconstruction of a model by denton hughes 1981 that is characterized by quasi parabolic cross sections and symmetry about the load centre both global northwestern europe as a whole and regional subsets of the data solutions have been made for earth model parameters and ice height scaling parameters the key results are as follows 1 the response of the upper mantle to the changing ice and water loads is spatially relatively homogenous across scandinavia the north sea and the british isles 2 this response can be adequately modelled by an effective elastic lithosphere of thickness 65 85 km and by an effective upper mantle viscosity from the base of the lithosphere to the 670 km depth seismic discontinuity of about 3 4 1020 pa s the effective lower mantle viscosity is at least an order of magnitude greater 3 the ice thickness over scandinavia at the time of maximum glaciation was only about 2000 m much less than the 3400 m assumed in the denton hughes model 4 the ice profiles are asymmetric about the centre of the ice sheet with those over the western part being consistent with quasi parabolic functions whereas the ice heights over the eastern and southern regions increase much more slowly with distance inwards from the ice margin

geophysical constraints on the link between cratonization and orogeny evidence from the tibetan plateau and the north china craton abstract understanding the geodynamic process of orogeny and cratonization and their transition is among the key topics of research in evaluating the link between plate tectonics and continental dynamics the tibetan plateau and the north china craton ncc two key areas in mainland china offer excellent laboratories to understand continental tectonics over a broad span of earth history particularly the deep structure of the lithosphere as imaged from geophysical data on the tibetan plateau and the ncc provide important clues in understanding orogeny and cratonization the tibetan plateau is the largest and highest plateau on earth in terms of mean altitude and is an important region for understanding the mechanisms of continent continent collision and cenozoic plateau uplift the ncc is an archean craton that underwent lithospheric disruption during the mesozoic here we reconstruct the main features of the structure of the crust and upper mantle from surface wave tomography and gravity modeling in tibet and its neighboring regions in order to understand the modality of the convergence and collision process between the indian and eurasian plates and the influence of this process on the uplift of the plateau in the ncc geological geochemical geophysical and tectonic investigations demonstrate that lithospheric destruction mainly occurred in the eastern block the crustal structure of the ncc is reconstructed from ambient noise surface wave tomography and the different possible disruption mechanisms are evaluated the vs shear wave velocity tomography results and the density structure of the crust and upper mantle to about 350 km depth 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 which suggest that the leading edge of the subducting indian slab reaches the bns the subduction angle of indian plate indicates a transition from steep to shallow from the west to east tibet sections depicting the gravitational potential energy suggest that mantle flow contributes to the subduction of the indian plate as far as the bns and the transition from the asthenospheric layer to the metasomatic lid overlaps with the transition from north south shortening in south tibet to eastward tectonic escape in north tibet qiangtang and songpan ganzi blocks both vs and models suggest the following 1 north southward lower crust flow beneath the eastern ncc and interaction between the westward mantle flow and eastward escape flow beneath the central ncc in addition to the earlier proposed mechanisms of delamination and thermal erosion played important roles in the lithospheric disruption of the archean craton 2 mantle flow plays an important role in the continental tectonic transition between neighboring tectonic blocks and within the cycle between orogeny and cratonization

composition model of the crust beneath the ordos basin and the yinshan mountains in china based on seismic velocity heat flow and gravity data abstract in this paper we have constructed a composition model of the crust beneath the ordos basin and the yinshan mountains in north china with reference to the seismic velocity heat flow and gravity data measured along the 650 km geophysical profile in the direction of n s from yanchuan county in the ordos basin to mandula town on the north side of the yinshan mountains in order to get this model we have corrected the crustal physical parameters measured along the profile into the data under the pressure of 600 mpa and room temperature 20 c which we can use to compare with the data measured in laboratory under the same pressure and temperature conditions inversion of the geophysical data set to rock compositions indicates that the composition of the crust along the yanchuan mandula profile reveals difference in the ordos basin and the yinshan mountains respectively in general the composition model of the crust beneath the yanchuan mandula profile generally varies significantly in vertical direction but slightly in lateral direction the heterogeneity of the distribution of lithologic composition exists mainly in the coupling zone between the ordos basin and the yinshan mountains

spatial variations of current tectonic stress field and its relationship to the structure and rheology of lithosphere around the bohai sea north china abstract the tectonic stress field in the middle upper crust is closely related to the structure and rheology of the lithosphere to determine the stress field in the deep crust we inversed the focal mechanism solutions fmss of 62 earthquakes that occurred between 2009 and 2015 in the bohai sea and its surrounding areas using broadband seismic waveforms collected from 140 stations we then derived the tectonic stress field using the software satsi spatial and temporal stress inversion based on the damped linear inversion method the inversion results show that both the maximum 1 and minimum 3 principle stress axes throughout the entire region are nearly horizontal except in the tangshan and haicheng areas suggesting that the study area is predominantly under a strike slip faulting stress regime the 1 and 3 axes are found to be oriented in the nee sww or nearly e w and nnw sse or nearly s n directions respectively these results indicate that the stress field in the north china craton is controlled by the combined effects of the pacific plate westward subduction and the india eurasia plate collision however localized normal faulting stress regimes where the vertical stress v 1 are observed in the tangshan and haicheng areas where low viscosity bodies lvbs were identified using geophysical data based on the analysis of focal mechanism solutions active faults and lithosphere rheology characteristics in the tangshan and haicheng areas we speculate that the anomalous stress regime is caused by the local extension resulting from the movement of strike slip faults under the action of the regional stress field the existence of lvb may indicate weakness in the crust that favors the accumulation of tectonic stress and triggers large earthquakes

the mesozoic cenozoic east china rift system abstract the mesozoic cenozoic rift system of eastern china extends in a n s direction over a distance of some 4000 km and has a width of 600 1000 km to the east it reaches into the coastal areas of the east and south china sea and extends onto the continental shelf this very large rift system evolved on a heterogenous basement consisting of a number of terranes which were amalgamated during the indosinian orogeny a first rifting phase spanned late jurassic early cretaceous times it was followed by a period of relative tectonic quiescence and thermal relaxation a latest cretaceous phase of compressional tectonics giving rise to partial basin inversion was followed by a renewed rifting cycle spanning eocene early neogene times development of the east china rift system involving vertical as well as lateral crustal movements was probably induced by physico chemical changes within the earth s mantle that can be related to activity along the pacific subduction zones the mesozoic cenozoic east china rifts contain some important hydrocarbon provinces which rely to a large extent on syn rift sediments for source and reservoir rocks

craton destruction and related resources craton destruction is a dynamic event that plays an important role in earth s evolution based on comprehensive observations of many studies on the north china craton ncc and correlations with the evolution histories of other cratons around the world craton destruction has be defined as a geological process that results in the total loss of craton stability due to changes in the physical and chemical properties of the involved craton the mechanisms responsible for craton destruction would be as the follows 1 oceanic plate subduction 2 rollback and retreat of a subducting oceanic plate 3 stagnation and dehydration of a subducting plate in the mantle transition zone 4 melting of the mantle above the mantle transition zone caused by dehydration of a stagnant slab 5 non steady flow in the upper mantle induced by melting and or 6 changes in the nature of the lithospheric mantle and consequent craton destruction caused by non steady flow oceanic plate subduction itself does not result in craton destruction for the ncc it is documented that westward subduction of the paleo pacific plate should have initiated at the transition from the middle to late jurassic and resulted in the change of tectonic regime of eastern china we propose that subduction rollback and retreat of oceanic plates and dehydration of stagnant slabs are the main dynamic factors responsible for both craton destruction and concentration of mineral deposits such as gold in the overriding continental plate based on global distribution of gold deposits we suggest that convergent plate margins are the most important setting for large gold concentrations therefore decratonic gold deposits appear to occur preferentially in regions with oceanic subduction and overlying continental lithospheric destruction modification growth

the cretaceous duimiangou adakite like intrusion from the chifeng region northern north china craton crustal contamination of basaltic magma in an intracontinental extensional environment abstract zircon u pb ages major and trace element and sr nd and pb isotope compositions of the duimiangou dmg quartz monzonite from the chifeng region on the northern north china craton ncc were studied to investigate its derivation evolution and geodynamic significance laser ablation inductively coupled plasma mass spectrometry la icp ms zircon u pb dating yields an emplacement age of 128 1 ma for this intrusion with numerous mesozoic inherited zircons clustering at 219 12 ma and 161 3 ma along with some ancient zircons with ages of 2 5 ga 1 77 ga and 324 ma bulk rock analyses show that this intrusion is characterized by variable sio 2 63 4 69 4 wt al 2 o 3 14 5 16 3 wt na 2 o k 2 o 8 01 8 95 wt and mg 41 3 48 0 they are enriched in large ion lithophile elements and light rare earth elements without significant eu anomalies mostly between 0 89 1 10 and depleted in heavy rare earth elements and high field strength elements with high sr y 63 7 101 7 and la yb n 20 5 31 0 ratios the dmg intrusion formed in an intracontinental extensional setting contemporaneous with the formation of pull apart basins metamorphic core complexes and intense magmatism rather than in a convergent margin it has homogeneous sr 87 sr 86 sr i 0 7059 0 7066 nd e nd t 6 2 to 7 2 and pb 206 pb 204 pb i 17 289 17 375 207 pb 204 pb i 15 359 15 463 208 pb 204 pb i 37 130 37 472 isotope compositions sr nd isotope modeling results plus relatively young nd model ages 1522 1618 ma and the presence of relict zircons suggest that this intrusion could have originated from crustal contamination of newly formed basaltic melts derived from asthenospheric mantle accompanied by fractional crystallization of k feldspar biotite apatite fe ti oxides and minor hornblende and plagioclase thus the dmg adakite like intrusion may record the magmatic event associated with underplating of asthenospheric magma in an intracontinental extensional environment and both asthenospheric magma underplating and lithospheric delamination may have played important roles in the lithospheric thinning of the northern ncc

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

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

the dynamic topography of eastern china since the latest jurassic period x c and s l were supported by the national key research and development program of china 2017yfc0601401 and 2016yfc0601002 national science and technology major project 2016zx05004001 003 qingdao national laboratory for marine science and techonlogy 2016askj 3 and national programme on global change and air sea interaction soa gasi geoge 01 x c was also supported by the china scholarship council for 1 year of study at the university of sydney n f was supported by arc de160101020 and r d m was supported by arc ih130200012 and dp130101946 figures were prepared using the generic mapping tools and matplotlib we thank two anonymous reviewers for constructive comments that improved the manuscript dynamic topography results are available from http portal gplates org dynamic topography list

archean blocks and their boundaries in the north china craton lithological geochemical structural and p t path constraints and tectonic evolution an examination of lithological geochemical geochronological structural and metamorphic p t path data suggests that the basement of the north china craton can be divided into eastern and western blocks separated by major crustal boundaries that roughly correspond with the limits of a 300 km wide zone called the trans north china orogen the eastern block consists predominantly of late archean domiform tonalitic trondhjemitic granodioritic ttg batholiths surrounded by anastomosing networks and linear belts of open to tight synforms of minor volcanic and sedimentary rocks metamorphosed from greenschist to granulite facies at 2 5 ga with anticlockwise p t paths some early to middle archean rocks are locally present in the eastern block but their tectonic history is unclear due to reworking by the 2 5 ga tectonothermal event the western block has a late archean assemblage structural style and metamorphic history similar to that of the eastern block but it differs in the absence of early to middle archean assemblages and in being overlain by and interleaved with paleoproterozoic khondalites which were affected by a 1 8 ga metamorphic event involving clockwise p t paths a mantle plume model is proposed for the formation and evolution of late archean basement rocks in the eastern and western blocks based on a combination of extensive exposure of ttg gneisses affinities of mafic rocks to continental tholeiitic basalts presence of voluminous komatiitic rocks dominant diaprism related domiform structures anticlockwise p t paths and a short time span from the primary emplacement of ttg and ultramafic to mafic rocks until the onset of regional metamorphism between the two blocks is the trans north china orogen which is bounded by two major fault systems and is composed of late archean to paleoproterozoic ttg gneisses and granitoids interleaved with abundant sedimentary and volcanic rocks that are geochemically interpreted as having developed in magmatic arc and intra arc basin environments these rocks underwent multiple phases of compressional deformation and peak high pressure metamorphism followed by rapid exhumation during the late paleoproterozoic at 1 8 ga as a result of collision between the eastern and western blocks resulting in the amalgamation of the north china craton

timing and magnitude of the sea level jump preluding the 8200 yr event evidence from terrestrial glacial and global climate model reconstructions suggests that a sea level jump caused by meltwater release was associated with the triggering of the 8 2 ka cooling event however there has been no direct measurement of this jump using precise sea level data in addition the chronology of the meltwater pulse is based on marine data with limited dating accuracy the most plausible mechanism for triggering the cooling event is the sudden possibly multistaged drainage of the laurentide proglacial lakes agassiz and ojibway through the hudson strait into the north atlantic ca 8470 300 yr ago here we show with detailed sea level data from rotterdam netherlands that the sea level rise commenced 8450 44 yr ago our timing considerably narrows the existing age of this drainage event and provides support for the hypothesis of a double staged lake drainage the jump in sea level reached a local magnitude of 2 11 0 89 m within 200 yr in addition to the ongoing background relative sea level rise 1 95 0 74 m this magnitude observed at considerable distance from the release site points to a global averaged eustatic sea level jump that is double the size of previous estimates 3 0 1 2 m versus 0 4 1 4 m the discrepancy suggests either a coeval antarctic contribution or more likely a previous underestimate of the total american lake drainage

holocene relative sea level change isostatic subsidence and the radial viscosity structure of the mantle of northwest europe belgium the netherlands germany southern north sea abstract a comprehensive observational database of holocene relative sea level rsl index points from northwest europe belgium the netherlands northwest germany southern north sea has been compiled in order to compare and reassess the data collected from the different countries regions and by different workers on a common time depth scale rsl rise varies in magnitude and form between these regions revealing a complex pattern of differential crustal movement which cannot be solely attributed to tectonic activity it clearly contains a non linear glacio and or hydro isostatic subsidence component which is only small on the belgian coastal plain but increases significantly to a value of ca 7 5 m relative to belgium since 8 cal ka bp along the northwest german coast the subsidence is at least in part related to the post glacial collapse of the so called peripheral forebulge which developed around the fennoscandian centre of ice loading during the last glacial maximum the rsl data have been compared to geodynamic earth models in order to infer the radial viscosity structure of the earth s mantle underneath nw europe lithosphere thickness upper and lower mantle viscosity and conversely to predict rsl in regions where we have only few observational data e g in the southern north sea a very broad range of earth parameters fit the belgian rsl data suggesting that glacial isostatic adjustment gia only had a minor effect on belgian crustal dynamics during and after the last ice age in contrast a narrow range of earth parameters define the southern north sea region reflecting the greater influence of gia on these deeper older samples modelled rsl data suggest that the zone of maximum forebulge subsidence runs in a relatively narrow wnw ese trending band connecting the german federal state of lower saxony with the dogger bank area in the southern north sea identification of the effects of local scale factors such as past changes in tidal range or tectonic activity on the spatial and temporal variations of sea level index points based on model data comparisons is possible but is still complicated by the relatively large range of earth model parameters fitting each rsl curve emphasising the need for more high quality observational data

intralithospheric mantle structures recorded continental subduction 1 we investigated the intralithospheric mantle ilm structures beneath the north china craton ncc by the seismic imaging with over 16 000 high quality receiver functions from 255 broadband stations these images were created for six profiles spanning different tectonic units in the ncc initially we inferred the crustal velocity model using an integrated receiver function imaging technique subsequently we performed a series of synthetic tests of common conversion point ccp stacking images to distinguish between the multiple waves generated by the crustal structure and the velocity discontinuities in the ilm the ilm structures were constructed by waveform inversion on the basis of these analyses our imaging results reveal 1 a homogenous lithospheric mantle in the western ncc 2 intermittent and juxtaposed velocity interfaces in the ilm beneath the southern ncc and 3 local high velocity and lower velocity volumes in the ilm beneath the eastern ncc in addition the lower crust beneath the southern ncc is thin and the moho dips northward which present evidence of the yangtze craton subduction beneath the ncc the imaged high velocity volumes in the ilm beneath the southern ncc were interpreted as a subduction remnant in the uppermost mantle which reveal a flat subduction channel resulting from the continent continent collision between the ncc and the yangtze craton the homogeneous ilm beneath a paleoproterozoic amalgamation zone in the ncc implies that the remnants of the lithosphere that were subducted before 1 8 ga might have sunk into the deeper mantle

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

gravity data inversion for the lithospheric density structure beneath north china craton from egm 2008 model abstract the density structures of the crust and upper mantle beneath the north china craton ncc are reconstructed in this paper by using the bouguer gravity anomaly derived from egm08 model the occam s inversion method and preconditioned conjugate gradient pcg are adopted in our paper for solving the 3d density inversion problems then the depth weighted function is incorporated into model parameters to avoid the skin effects in inversion in our study the bouguer gravity anomaly derived from egm08 model is used to study the crust and upper mantle structures beneath the ncc for reducing the non uniqueness of our inversion problem we use the inverted density distribution from 0 5 0 5 p wave tomographic results as our initial model finally the high resolution 3d density model is established down to 250 km depth for the first time in this region the density images at eight representative layers 10 25 40 60 80 120 160 200 km and eight vertical cross sections linear profiles along latitude 35 36 37 38 39 40 longitude 108 119 are displayed and compared with the p wave velocity tomographic images the 3d dimensional density model indicates that lateral heterogeneities are widely distributed in different units within the ncc while their density patterns and depth extensions are significantly different for three main units of ncc suggesting different tectonic mechanisms that have dominated the evolution of these regions in the phanerozoic in particular our inverted density images demonstrate that the phanerozoic lithospheric reactivation and thinning may not have influenced the central and western ncc to the same extent as the eastern ncc most of which preserves relatively thick cratonic lithosphere today however localized lithospheric thinning may exist in the circular ordos rift systems whose ancient tectonic belts around the ordos plateau may have been affected by multi phase tectonic events in its long evolution history

transverse variability of flow on both sides of a sill contraction combination in a fjord like inlet of southern chile abstract water velocity and density profiles were obtained over a semidiurnal tidal cycle to describe the transverse variability of flow in either side of galvarino pass a sill contraction combination in a fjord like inlet in southern chile 44 4 s velocity profiles were obtained with a 614 4 khz acoustic doppler current profiler adcp during eight repetitions of a circuit that consisted of along fjord transects along the pass and cross fjord transects at either side of the pass the geomorphology in galvarino pass represents a coastline contraction of about 90 decreasing from 2000 m to 200 m in just 1500 m in the along channel direction depth varies from 40 m on the landward side of the pass to 10 m at the shallowest portion of the sill to 80 m south of the pass the mean flow in the northern side of the pass showed a tendency of the flow to rotate anticlockwise throughout the water column this feature should result in a sluggish flushing of the northern side south of the pass mean surface outflow and mean bottom inflow at 20 m developed near the western side of the fjord within the pass the shallowest and narrowest section represented a boundary between inflows and outflows the strongest net inflows 15 cm s were observed in the sill region and the strongest outflows 10 cm s were seen to the south of the pass the magnitude of the tidal flows increased inside the pass reaching a maximum over the sill and then decreased northward owing to conservation of mass in the across channel momentum balance the advective terms seemed to be greater than the rest of the terms in the northern end of the pass and over the sill magnitudes of the terms in the along channel momentum balance were comparable to those in the across channel direction highlighting the importance of the transverse dimension under strong geometric constraints

crustal structure across the san andreas fault southern california from teleseismic converted waves crustal structure along a 140 km long profile across the san andreas fault saf in southern california was imaged by stacking teleseismic p s converted phases recorded by a dense short period seismic array the crust mantle discontinuity moho is visible as a continuous feature at a depth around 30 km but is offset 6 to 8 km beneath the saf a small moho disruption can also be seen under the eastern california shear zone ecsz these results suggest that the saf and ecsz extend through the entire crust the moho upwarp under the san gabriel mountains indicates that the mountain ranges were lifted en masse as a result of crustal buckling under horizontal compression

curie point depths in north china craton based on spectral analysis of magnetic anomalies magnetic anomaly analysis is an important method to study the structure of deep crust with the assumption of random magnetization sources the structure of a magnetic layer can be inverted via spectral analysis curie point depth cpd the depth at which rocks lose their ferromagnetic properties is the bottom of a magnetic layer in this study we estimate from the magnetic anomaly data of emag2 dataset the cpd and the top of the magnetic layer in north china with a moving window of 180 km 180 km we calculate the average top and centroid depth of the magnetic layer in each window and determine the regional cpd distribution across north china the cpd of north china varies from 18 to 32 km in addition the cpd in the western part of the north china craton is deeper than that in the eastern part the shallowest cpd is located near the bohai sea when compared to available heat flow data the estimated cpd values are consistent with thermal conductivity of 1 8 3 2 wm 1 k 1 and on heat production value of 0 4 1 3 wm 3

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

holocene evolution of relative sea level and local mean high water spring tides in belgium a first assessment abstract holocene age depth data from the belgian coastal plain basal peat data particularly are assessed in terms of local water and tide levels basal peat formation was generally induced by sea level rise effects of local seepage were limited and significant river gradient effects were absent no relation was found between the timing of basal peat inception and substrate permeability in general edaphic moisture conditions were unfavourable for organic accumulation prior to sea level related rise of the groundwater table error envelopes for the minimum level of local mean high water spring tides and for upper and extreme lower relative mean sea level limits during the last 9400 solar years 8400 yrs b p are presented these indicate that the rate of relative sea level rise showed marked retardations at ca 7500 7000 yrs cal b p 6650 6100 yrs b p and ca 5500 5000 yrs cal b p 4400 yrs b p a eustatic explanation appears to be plausible particularly for the former prior to ca 4000 yrs cal b p ca 3600 yrs b p the relative sea level rise in belgium differs noticeably from that established for the western netherlands with both diverging progressively back in time this implies that considerable differential crustal movement occurred between the two areas in the early holocene

crust mantle structure difference across the gravity gradient zone in north china craton seismic image of the thinned continental crust the archean north china craton ncc has been tectonically modified and lost its thick lithospheric keel during the mesozoic and cenozoic the processes and mechanisms of the lithospheric modification and its appearance in and the relation between different subregions of the ncc are still poorly understood seismic data from 45 stations along a 470 km long profile cross the bohai bay basin bbb and the taihangshan mountain range tmr in the ncc were employed to construct a coherent structural image of the crust and uppermost mantle an integrated receiver function imaging technique combining the common conversion point stacking approach with waveform inversion and forward modeling was proposed to extract the structural information beneath the study region modeling of bouguer gravity anomalies was also applied to constrain the density distribution the imaging result reveals distinct structural features between the mountain range and the basin area and presents a picture of uneven crust thinning within the study region in the east bbb the crust is significantly thinned due mainly to the reduction in the thickness of the lower crust including the crust mantle transition zone by up to 12 km the west tmr in contrast is characterized by a relatively thick lower crust of 20 km the teleseismic waveform data and the gravity observation suggest a thicker crust and a buoyant mantle lithosphere beneath the tmr compared with the bbb the contrasting crustal structural features appear coupled with the lithospheric processes and possibly reflect that different tectonic mechanisms and deformation regimes dominated the evolution of the two regions the north south gravity lineament lying between the tmr and bbb might represent a deep intra continental boundary separating the ncc into topographically and tectonically different regions

distinct velocity variations around the base of the upper mantle beneath northeast asia abstract both the global and regional p wave tomographic studies have revealed significant deep structural heterogeneities in subduction zone regions in particular low velocity anomalies have been observed beneath the descending high velocity slabs in a number of subduction zones the limited resolution at large depths and possible trade off between the high and low velocities however make it difficult to substantiate this feature and evaluate the vertical extent of the low velocity structure from broadband waveform modeling of triplicated phases near the 660 km discontinuity for three deep events we constrained both the p and sh wave velocity structures around the base of the upper mantle in northeast asia for the two events beneath the southern kurile the rays traveled through the lowermost transition zone and uppermost lower mantle under the descending pacific slab our preferred models consistently suggest normal to lower p and significantly low sh velocities above and below the 660 km discontinuity extending to about 760 km depth compared with the global iasp91 model corroborating previous observations for a slow structure underneath the slab in contrast both high p and sh velocity anomalies are shown in our preferred models for the japan subduction zone region likely reflecting the structural feature of a slab stagnant above the 660 km discontinuity the velocity jumps across the 660 km discontinuity were found to be on average 4 5 and 7 for p and s waves under the south kurile and 3 and 6 under the japan subduction zone the respective velocity contrasts in the two regions are consistent with mineralogical models for colder slab interior and hotter under slab areas based on mineral physics data the depth averaged 1 5 p and 2 5 sh velocity differences in the depth range of 560 760 km between the two regions could be primarily explained by a 350 450 k temperature variation although the presence of about 0 5 1 wt water might also contribute to the subtle velocity variations near the base of the transition zone in the southern kurile from our modeling results we speculate that the slow structure in the southern kurile may be correlated to the low velocity zone observed previously around the 410 km discontinuity under northern honshu if this is the case both may be associated with a thermal anomaly rooted in the lower mantle beneath the subduction zone in northeast asia

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

insight into the geodynamics of cratonic reactivation from seismic analysis of the crust mantle boundary 1 the reactivation of craton is a crucial issue for the understanding of continent lithosphere although the partial loss of the thick lithospheric root of the north china craton ncc was documented its mechanism remains a contentious topic in the study of cratonic evolution in this paper we imaged the crust mantle structures by using the data from 36 permanent stations with fine spatial coverage in the yanshan tectonic belt ystb and the taihangshan region tsr in the northern ncc two tectonic units with distinct crust mantle structures were recognized and their junction zone was identified the results reveal distinct features of the crust mantle boundaries of the ystb and the tsr which are characterized by a sharp interface and a thick transition zone respectively based on the analysis of the seismic structures of the crust mantle boundary and the upper mantle we propose that the ncc reactivation was possibly derived by a slow secular ascension of hydrated asthenospheric material atop the stagnant pacific slab which influenced the formation of crust mantle transition zone in the eastern ncc on the other hand regional delamination of the deep crust after orogenic thickened and or magmatic underplating beneath the ystb caused the spatial variation of the crust mantle boundary both of the mantle processes possibly changed the nature of the lithospheric mantle

a detailed receiver function image of the sedimentary structure in the bohai bay basin abstract if the site at which receiver functions are constructed is filled by sediments then the waveforms from these receiver functions are dominantly controlled by the sedimentary structures within the first few seconds after the direct p arrival based on this observation waveform data collected at 44 temporary seismic stations have been used to image the sedimentary structure of the bohai bay basin a major continental petroliferous basin in eastern china an adapted hybrid global waveform inversion method was applied to the receiver functions to extract structural information beneath each of the stations the derived s velocity structure provides for the first time a basin scale seismic image of detailed sedimentary stratification the sedimentary cover of the basin is about 2 12 km thick consisting of cenozoic mesozoic and paleozoic strata from top to bottom the structural features presented in the s velocity image coincide quite well with the depression uplift type of tectonic system in the bohai bay basin the reconstructed morphology of the sedimentary layers provides seismological evidence for the two stage evolution of the intracontinental basin that were caused by an intensive tectonic regime transition in late mesozoic immediately following the lithospheric reforming of the eastern china continent

post cratonization deformation processes and tectonic evolution of the north china craton abstract the timing of events during the tectonic evolution of the north china craton ncc and the east china region is debated extension compression transpression and shearing occurred throughout the ncc since 320 ma these main structural stages and the temporal evolution of the structural framework and kinematics are summarized we present here data from multiple structural and magmatic stages related to temporally varying kinematics and deformation mechanisms during the evolution of the post cratonization of the ncc the timing of each stage is constrained using isotopic dating along with the timing of magmatic intrusion dyke intrusion and basin formation associated with tectonic transformation of the ncc age data indicate distinct structural and magmatic stages at 1600 1500 1300 1100 445 315 270 200 170 155 130 110 75 65 and 25 20 ma relating to basin formation and continental uplift or collapse these stages define the tectonic evolution and structural transformation of the ncc and associated de rooting reactivation reworking and orogenic growth the tectonic setting and movement direction of adjacent plates changed multiple times during the various stages the stages are as follows separation of the ncc from the gondwana supercontinent and northwards drift formation of the central asian orogenic belt caob and northwards subduction of the yangtze plate resulting in closure of the qinling ocean the rapid initial formation of the western pacific plate and subsequent subduction and final closure of the mongol okhotsk ocean combined with closure of the bangong nujiang suture zone and southwards movement of the siberian continent as well as thinning of the north china cratonic lithosphere moreover temporal and spatial changes in deformation magmatism and basin formation as well as kinematic and mechanical transformations occurred in response to the changing tectonic setting and movement direction of surrounding plates these various factors resulted in a complex structural evolution of the ncc since 1 8 ga