discontinuity structure of the mantle transition zone beneath the north china craton from receiver function migration 1 a better understanding of the significant phanerozoic tectonic reactivation and destruction of the north china craton ncc demands a detailed knowledge of the deep structural features of the region we applied the wave equation based poststack migration technique to a combined receiver function data set from more than 250 broadband seismic stations to construct the structural image of the mantle transition zone beneath the ncc our imaging results reveal a relatively simple and flat 410 km discontinuity but a structurally complicated 660 km discontinuity beneath the region double discontinuities and a 30 km depression of the 660 km discontinuity are observed locally in the southern part of the eastern ncc in contrast to the smoothly varying structure to the north and in the central and western parts of the craton distinctly rapid variations in both the 660 km discontinuity structure and mantle transition zone thickness were found across the northsouth gravity lineament nsgl near the boundary between the eastern and central ncc which probably reflects different thermal and probably chemical properties on the two sides of the nsgl these differences are possibly associated with the pacific slab which is imaged tomographically as a flat lying structure in the mantle transition zone under the region east of the nsgl the structural variation in the deep upper mantle appears to coincide with the sudden changes in surface topography gravity field and crustal and lithospheric structures as well indicating that the two domains may have tectonically deformed differently throughout the whole upper mantle during the phanerozoic cratonic destruction the mantle transition zone on the eastern side of the nsgl is up to 30 40 km thicker than the global average this thickness and the complex structure of the 660 km discontinuity in this region may reflect the strong influence that the deep subduction and stagnancy of the pacific slab and its possible sporadic penetration into the lower mantle have had on mantle dynamics and lithospheric reactivation in the eastern ncc since the mesozoic time on the other hand the less variable structure and normal to thin mantle transition zone imaged beneath the central and western ncc may indicate that the indiaeurasia collision has had a relatively weak effect on the cenozoic tectonics of these regions

constraining the hydration of the subducting nazca plate beneath northern chile using subduction zone guided waves abstract guided wave dispersion is observed from earthquakes at 180 280 km depth recorded at stations in the fore arc of northern chile where the 44 ma nazca plate subducts beneath south america characteristic p wave dispersion is observed at several stations in the chilean fore arc with high frequency energy 5 hz arriving up to 3 s after low frequency

sedimentary effects of cataclysmic late pleistocene glacial outburst flooding altay mountains siberia rudoy a n and baker v r 1993 sedimentary effects of cataclysmic late pleistocene glacial outburst flooding altay mountains siberia in c r fielding editor current research in fluvial sedimentology sediment geol 85 53 62 pleistocene glacial outburst floods were released from ice dammed lakes of the altay mountains south central siberia the kuray chuja lake system yielded peak floods in excess of 1 106 m 3 s 1 and as great as 18 106 m 3 s i the phenomenally high bed shear stresses and stream powers generated in these flows produced a main channel coarse grained facies of coarse gravel in 1 foreset bedded bars as much as 200 m high and several kilometers long and 2 degradational boulder capped river terraces giant current ripples 50 to 150 m in spacing composed of pebble and cobble gravel are locally abundant the whole sedimentary assemblage is very similar to that of the channeled scabland produced by the pleistocene missoula floods of western north america

a complex 660 km discontinuity beneath northeast china abstract we present a detailed seismic study of the 660 km discontinuity beneath northeast china using the receiver function technique we use seismic data collected from 24 broadband stations in northeast china analysis of these data shows that the 660 km discontinuity is locally depressed in the region from longitude 128 0 e to 130 5 e and latitude 40 0 n to 44 0 n and then it splits into multiple discontinuities in the surrounding regions the complexity of the 660 km discontinuity beneath the subduction zones is probably attributable to the interaction between the upper mantle and subducted slab we speculate that the flattening of the subducted lithosphere near the bottom of the upper mantle causes the multiple discontinuity structure and that the slab penetrating the 660 km discontinuity into the lower mantle causes the narrow 660 km depression area

slab dehydration and mantle upwelling in the vicinity of the sumatra subduction zone evidence from receiver function imaging of mantle transition zone discontinuities

mode of cenozoic east west extension in tibet suggesting a common origin of rifts in asia during the indo asian collision cenozoic rifts in tibet were traditionally interpreted as a result of topographic collapse of the tibetan plateau reaching the maximum elevation that can be supported by its mechanical strength recent studies have emphasized possible similarities between rifting in tibet and extension in the basin and range of the western united states however when examined in detail one finds that spacing of long 100 km rifts in tibet 100 300 km is significantly greater than that in the basin and range 20 40 km from south to north rift spacing decreases systematically from 191 67 km in the himalaya south of the indus yalu suture to 146 34 km in south tibet between the indus yalu and bangong nujiang sutures and farther north to 101 31 km in central tibet between the bangong nujiang and jinsha sutures instability analysis suggests that the mantle lithosphere must have been involved in east west tibetan extension specifically the widely spaced rifts in the himalaya and tibet may have been related to the presence of a relatively light crust density 2 90 g cm 3 and a strong mantle lithosphere 40 km thick and a factor of 5 stronger than the upper crust the observed systematic decrease in rift spacing can be explained by the known decrease in the crustal thickness in tibet from 70 80 km in the himalaya in the south to 50 55 km in central tibet in the north a regional comparison of rifts in east asia suggests that both the involvement of the mantle lithosphere and the age of rift initiation are similar for tibetan rifts the baikal rift and the shanxi graben this implies that topographic collapse or a convective event in the mantle cannot be the sole cause for the development of the tibetan rifts a regional boundary condition applied throughout east asia must be required

evidence for small scale mantle convection in the upper mantle beneath the baikal rift zone 1 inversion of teleseismic p wave travel time residuals collected along a 1280 km long profile traversing the baikal rift zone brz reveals the existence of an upwarped lithosphere asthenosphere interface which causes a travel time delay of about 1 s at the rift axis central high an area with early arrivals relative to the stable siberian platform of up to 0 5 s is observed on each side of the rift about 200 km from the rift axis flank lows while the location of the central high is approximately fixed in the vicinity of the rift axis those of the flank lows vary as much as 200 km with the azimuth of the arriving rays we use three techniques to invert the travel time residuals for velocity anomalies beneath the profile two of the techniques assume an isotropic velocity structure and one of them considers a transversely isotropic velocity model with a vertical axis of symmetry we use independent geophysical observations such as gravity active source seismic exploration and crustal thickness measurements to compare the applicability of the models other types of geophysical measurements suggest that the model involving transverse isotropy is a plausible one which suggests that the central high and flank lows are caused by the combined effects of an upwarped asthenosphere with a 2 5 lateral velocity reduction and a velocity increase due to transverse isotropy with a vertical axis of symmetry we consider the anisotropy to be the result of the vertical component of a lithosphere asthenosphere small scale mantle convection system that is associated with the rifting

p and s wave tomography and anisotropy in northwest pacific and east asia constraints on stagnant slab and intraplate volcanism we determined three dimensional p and s wave velocities and p wave azimuthal anisotropic tomography of the northwest pacific subduction zones by inverting 1 225 086 p wave and 335 117 s wave arrival times from 13 413 earthquakes our results show some differences between p and s wave images for the stagnant pacific slab in the mantle transition zone mtz beneath northeast china the stagnant slab looks thicker in the p wave image than that in the s wave image which may reflects the effects of both hydration and lower temperature in the mtz though differences in the resolution of p and s wave tomography may also have some effects the changbai intraplate volcanism is caused by hot and wet upwelling in the big mantle wedge above the stagnant pacific slab our p wave anisotropy tomography shows that the fast velocity direction fvd in the subducting philippine sea plate beneath the ryukyu arc is ne sw trench parallel which is consistent with the spreading direction of the west philippine basin during its initial opening stage suggesting that it may reflect the fossil anisotropy a striking variation of the fvd with depth is revealed in the subducting pacific slab beneath the northeast japan arc which may be caused by slab dehydration that changed elastic properties of the slab with depth the fvd in the mantle wedge beneath the northeast japan and ryukyu arcs is trench normal which reflects subduction induced convection beneath the kuril and izu bonin arcs where oblique subduction occurs the fvd in the mantle wedge is nearly normal to the moving direction of the downgoing pacific plate suggesting that the oblique subduction together with the complex slab morphology have disturbed the mantle flow

slab temperature and thickness from seismic tomography 1 method and application to tonga delay times of compressional body wave phases from both teleseismic and local events are used to invert for a high resolution p wave velocity model in the tonga subduction zone the images obtained show a high velocity subducting slab with velocity deviations of the order of 3 4 assuming to first order that the positive velocity anomalies within the slab are caused by a temperature effect a theoretical slab temperature model based on the diffusion equation is used to explain velocity anomalies within the tomographic slab temperature differences between the interior of the slab and the ambient mantle are converted to velocity perturbations using the scaling parameter dvp dt 4 8 10 4 km s 1 c 1 for lithosphere material the optimal values for the parameters in the temperature model are found using a nonlinear optimization that compares the integrated velocity anomalies in the tomographic slab region to integral of high velocities in a synthetic slab derived from a temperature model the parameters for slab thickness and mantle potential temperature are not uniquely determined therefore a fixed value for the mantle potential temperature based on laboratory values for the temperature of the spinel to perovskite transition at 660 km is used using 1180 c as the potential temperature the theoretical temperature model gives an optimal slab thickness of 82 km for a region near 29 s in tonga the uncertainty in the thickness is dominated by the uncertainty in the mantle temperature and would be 8 km for an uncertainty of 100 in mantle temperature but nonsystematic errors are less in order to enhance the tomographic result the velocity model is biased towards the theoretical slab model however a posteriori changes made to the tomogram will most likely violate the fit to the delay time data to prevent this the difference between the tomogram and the predicted slab model is projected onto the null space of the inversion to remove components which do not satisfy the seismic data using only null space components to modify the minimum norm solution an enhanced model is obtained which has been biased toward the theoretical solution but has the same data misfit as the minimum norm solution the final image shows a very narrow and continuous slab with maximum velocity anomalies of the order of 6 7 many of the gaps within the slab as well as artifacts around the slab which were present in the minimum norm solution are absent in the biased image

seismic velocity variations beneath central mongolia evidence for upper mantle plumes abstract central mongolia is marked by wide spread recent volcanism as well as significant topographic relief even though it is far from any plate tectonic boundaries the cause of the recent magmatism and topography remains uncertain partially because little is known of the underlying mantle seismic structure due to the lack of seismic instrumentation in the region from august 2011 through august 2013 69 broadband seismic stations were deployed in central mongolia teleseismic traveltime residuals were measured using waveform correlation and were inverted to image upper mantle p and s velocity variations significant lateral variations in seismic velocity are imaged in the deep upper mantle 100 to 800 km depth most significant are two continuous slow anomalies from the deep upper mantle to near the surface one slow feature has been imaged previously and may be a zone of deep upwelling bringing warm mantle to beneath the hangay dome resulting in uplift and magmatism including the active khanuy gol and middle gobi volcanoes the second deep low velocity anomaly is seen in the east from 800 to 150 km depth the anomaly ends beneath the gobi desert that is found to have fast shallow mantle indicating a relatively thick lithosphere we interpret the second deep slow anomaly as a mantle upwelling that is deflected by the thick gobi desert lithosphere to surrounding regions such as the hentay mountains to the north the upwellings are a means of feeding warmer than normal asthenospheric mantle over a widely distributed region beneath mongolia resulting in distributed volcanic activity and uplift there is no indication that the upwellings are rooted in the deep lower mantle i e classic plumes we speculate the upwellings may be related to deep subduction of the pacific and indian plates and are thus plumes anchored in the upper mantle

correlation and paleomagnetism of glacial and loess paleosol sequences on the west siberian plain abstract a complex assemblage of geological biostratigraphical paleopedological magnetostratigraphical and radiometric techniques has been used for analysis and correlation of deposits on the west siberian plain a series of magnetostratigraphical columns has been constructed and the glacial alluvial lacustrine and loess paleosol deposits compared the data are paleomagnetic boundaries such as the brunhes matuyama boundary the base of the jaramillo subchron and the blake excursion their position in the sections is discussed a loess paleosol succession is considered in detail the number of climatostratigraphic cycles is comparable with the world s standard sections of similar genesis special attention is given to the description of the early pleistocene stages of soil formation the malinovka pedocomplex has been described here for the first time it is related to the final stage of the matuyama chron and is characterized by fauna similar to the petropavovka karai dubina fauna a scheme is proposed to correlate glacial and loess paleosol deposits on the west siberian plain and to compare them with the oxygen isotope scale

mantle transition zone structure beneath the changbai volcano insight into deep slab dehydration and hot upwelling near the 410 km discontinuity we study the detailed mantle transition zone structure beneath the active changbai intraplate volcano in northeast china by using a receiver function method a total of 3005 teleseismic receiver functions recorded by 70 broadband stations are obtained by using a common conversion point stacking method for conducting the time to depth conversion we use a three dimensional velocity model of the study region so as to take into account the influence of structural heterogeneities our results reveal significant depth variations of the 410 520 and 660 km discontinuities a broad depression of the 410 km discontinuity and a low velocity anomaly are revealed beneath the changbai volcano which may reflect a large scale hot mantle upwelling around the 410 km discontinuity with a positive clapeyron slope the 520 km discontinuity is identified clearly and its uplift occurs above the stagnant pacific slab we also find a prominent depression of the 660 km discontinuity which is elongated along the trend of deep earthquake clusters in a range of 39 n 44 n latitude and the depression area has a lateral extent of about 400 km because the 520 and 660 km discontinuities correspond to positive and negative clapeyron slopes respectively we think that the 520 uplift and the 660 depression are caused by the cold subducting pacific slab a part of the pacific slab may have penetrated into the lower mantle and so caused the large scale 660 depression in front of the deep earthquake clusters our results also reveal a part of the upper boundary of the subducting pacific slab in the mantle transition zone

upper mantle and mantle transition zone thermal and water content anomalies beneath ne asia constraints from receiver function imaging of the 410 and 660 km discontinuities abstract the 410 and 660 km discontinuities d410 and d660 bordering the mantle transition zone mtz beneath ne asia including ne china eastern mongolia and southern siberia are imaged in successive circular bins with a radius of 1 degree by stacking a total of 274 413 p to s radial receiver functions recorded by 799 broadband seismic stations after moveout correction based on the 1 d iasp91 earth model the resulting apparent depths of the discontinuities exhibit significant and spatially systematic variations three approximately n s elongated narrow zones with significantly thickened mtz are observed which may be associated with the thermal effect and dehydration of subducted slabs the major volcanoes in ne china are underlain by a d660 that is apparently depressed by 19 km which can be interpreted by the presence of an anomalously high water concentration in the lower mtz released from the stagnated slabs low wavespeed anomalies above the d410 west of the datong volcanic fields are underlain by an mtz with normal thickness and are attributable by dehydration of the leading portion of the stagnant pacific slab in the mtz that is revealed in an n s oriented narrow zone east of this area the lateral shift of the upper mantle low wavespeed zone and the area with thickened mtz may suggest a westward drift of the upper mantle relative to the subducted slab an abnormally thin mtz is observed beneath the hangay dome in central mongolia suggesting the possible existence of thermal upwelling from the lower mantle through the mtz

quaternary stratigraphy and optical dating of loess from the east european plain russia abstract optical dating of silt sized potassium feldspar grains was found to be suitable for dating the formation of key loess units at two sites on the central east european plain loess bracketing the bryansk palaeosol yielded optical ages in agreement with the well dated radiocarbon chronology when corrected for anomalous fading optical ages from loess bracketing a significant pedogenic unit below the bryansk palaeosol support our lithostratigraphic interpretation that it is the mezin palaeosol complex and its formation during the last interglaciation oxygen isotope stage ois 5 optical ages from a stratigraphically older loess unit directly underlying a significant 10 m thick till unit in conjunction with its regional stratigraphic context suggest that the loess and the till were deposited during the dnieper glaciation which probably occurred during ois 6

a regionalized upper mantle rum seismic model seismic velocity heterogeneity in the earth s mantle is strongly concentrated near its top the shallow heterogeneity of the mantle correlates strongly with surface tectonics we use these observations as constraints of a tomographic experiment aimed at building a regionalized upper mantle rum reference model we use a select set of teleseismic travel times to minimize the mapping of mislocation into structure the data selection emphasizes the robustness of individual picks the form of the rum model is a set of velocity profiles as functions of depth through the upper mantle for each of the different tectonic provinces of earth together the profiles constitute a three dimensional model which incorporates considerable structural detail but is described by only 90 parameters and has only about 22 degrees of freedom this is achieved by irregularly sampling a detailed regionalization of the globe by detailed mapping of subducted lithosphere in the mantle as defined by seismicity and by combining these structures in an irregular grid in which bookkeeping is efficiently handled the resulting rum model includes subducting slabs as sharp fast features in the upper mantle old continents are fast young oceans are slow models have been derived for both compressional and shear velocity the rum model is designed to represent as much of upper mantle heterogeneity as seen by body wave travel times as possible with a simple model it can be useful as a reference model for individual tectonic regions travel times are efficiently generated for the rum model mislocations of explosions of known location are significantly reduced when corrections for the rum model are applied to travel time residuals for a spherically symmetrical earth model

receiver function images of the mantle transition zone beneath ne china new constraints on intraplate volcanism deep subduction and their potential link abstract in order to better understand the deep subduction geometry of the pacific plate and genesis of intraplate volcanism in northeast china ne china we computed a total of 45 505 receiver functions from 788 teleseismic events recorded by 255 stations necessarray temporal and permanent stations in ne china we used a common conversion point stacking ccp method to generate a 3d reflectivity volume beneath the study area to position the p to s conversions to the correct depths we employed 3d crustal and mantle models as references to make time to depth conversion the 3d reflectivity volume was generated in an area between 115 135 e and 40 49 n in the depth range of 300 to 800 km we found significant topographic relief on the 660 km discontinuity across the study area in particular in a westward pacific plate subduction section between 40 n and 45 5 n the 660 km discontinuity is depressed by as much as 30 40 km along the western extension of the deep seismicity the depression is elongated along the strike of the deep seismicity and is confined to a 200 300 km region in the e w direction of subduction to the west of this depression the 660 km discontinuity is uplifted by 5 10 km in a rectangular area of 100 km by 200 km centered at about 125 e and 43 n in the north the 660 km discontinuity is moderately depressed 20 km in a broad area that extends further west the high and low regions in the 660 km topographic map correlate respectively with low and high velocity anomalies in the p and s wave tomographic velocity images at the same depth our results suggest that slab stagnation might not be occurring in the southern part of the ne china where the changbaishan volcanic complex is located thus the magmatism is unlikely caused by dehydration of the flat lying pacific slab in the transition zone the low velocity mantle upwelling arising from a gap of stagnant slabs is a likely source that feeds the volcanic complex in ne china

a late quaternary loess paleosol record at kurtak southern siberia a high resolution paleoclimatic record for the last two glacial interglacial cycles has been documented at kurtak in southern siberia a unique 34 m high late quaternary loess section section 29 with a series of 32 variably developed paleosol horizons provides evidence of a strongly fluctuating but patterned climatic change mineralogical composition and grain morphology of the undifferentiated aeolian and colluviated loess indicate a local provenance and a short transport of the silt derived by glacial erosion of the granitic and metamorphic bedrock in the kuznetskiy alatau and eastern sayan mountains and subsequently subaerially redeposited from the alluvial plain in the yenisey river valley the succession of chernozemic brunisolic and gleyed regosolic soils alternating with nonweathered or weakly weathered loess events matched by parallel changes in magnetic susceptibility can be correlated with marine isotope stages 1 7 the magnetic susceptibility pattern is completely opposite to

pleistocene climate change natural environments and palaeolithic occupation of east kazakhstan abstract the territory of east kazakhstan the southern altai mountains the bukhtarma and zaisan black irtysh basins still insufficiently investigated because of its proximity to the kazakh russian chinese border zone shows a complex quaternary history and the associated environmental transformations reflected by intensive geomorphic processes related to the past global climate evolution in conjunction with the regional neotectonic activity the marked climatic changes are indicated by the preserved palaeolandscape forms in both the mountain and steppe regions as well as by the glacial and sedimentary geology palaeoecology and geoarchaeology proxy records indicating long term variations in temperature as well as humidity following the generally warmer early pleistocene climates witnessed by the distribution of deeply weathered red palaeosols the increased continentality and relief gradient during the middle and particularly the late pleistocene led to establishment of the present type forest steppe semi desert during warm stages and the periglacial arid steppe during cold stages correlated with the glaciations in the southern altai mountains and loess deposition in the foothills the mapped glacigenic and high resolution loess palaeosol sections and contextual environmental archaeology data from the pleistocene occupation sites provide new evidence of a rather pronounced natural dynamics spectacular glaciofluvial terraces in the principal mountain valleys indicate the presence of deep ice dammed last glacial lakes documented from other parts of the altai that were subjected to cataclysmic drainages during deglaciations the recently discovered localities in the bukhtarma river valley in diverse settings bear witness of a much earlier middle upper palaeolithic inhabitation of this geographically marginal area and adaptation to local mountain and steppe environments predating the holocene prehistoric cultures this paper summarizes some results of the initial multidisciplinary quaternary field studies in the southern altai region of east kazakhstan and the adjacent part of gorno altai 2003 2007

the baikal rift zone the effect of mantle plumes on older structure abstract the main chain of sw ne striking cenozoic half grabens of the baikal rift zone brz follows the frontal parts of early paleozoic thrusts which have northwestern and northern vergency most of the large rift half grabens are bounded by normal faults at the northwestern and northern sides we suggest that the rift basins were formed as a result of transformation of ancient thrusts into normal listric faults during cenozoic extension seismic velocities in the uppermost mantle beneath the whole rift zone are less than those in the mantle beneath the platform this suggests thinning of the lithosphere under the rift zone by asthenosphere upwarp the geometry of this upwarp and the southeastward spread of its material control the crustal extension in the rift zone this nw se extension cannot be blocked by sw ne compression generated by pressure from the indian lithospheric block against central asia the geochemical and isotopic data from late cenozoic volcanics suggest that the hot material in the asthenospheric upwarp is probably provided by mantle plumes to distinguish and locate these plumes we use regional isostatic gravity anomalies calculated under the assumption that topography is only partially compensated by moho depth variations variations of the lithosphere asthenosphere discontinuity depth play a significant role in isostatic compensation we construct three dimensional gravity models of the plume tails the results of this analysis of the gravity field are in agreement with the seismic data the group velocities of long period rayleigh waves are reduced in the areas where most of the recognized plumes are located and azimuthal seismic anisotropy shows that these plumes influence the flow directions in the mantle above their tails the baikal rift formation like the kenya rio grande and rhine continental rifts achauer u granet m 1997 complexity of continental rifts as revealed by seismic tomography and gravity modeling in jacob a w b delvaux d khan m a eds lithosphere structure evolution and sedimentation in continental rifts proceedings of the igcp 400 meeting dublin march 20 22 1997 institute of advanced studies dublin pp 161 171 is controlled by the three following factors i mantle plumes ii older prerift linear lithosphere structures favorably positioned relative to the plumes and iii favorable orientation of the far field forces

wet subduction versus cold subduction 1 in situ x ray diffraction study of post spinel transformation in hydrous peridotite 2 wt h2o indicates that the phase boundary is shifted to higher pressures by 0 6 gpa relative to anhydrous peridotite at 1473 k whereas it shows no obvious shift at high temperature around 1873 k a linear equation for the boundary is p gpa 0 002 t k 26 3 which is applicable for temperatures below 1800 k the present data shows that a significant part of the depressions seen in the 660 km seismic discontinuity may be affected by existence of water it is also well resolved that the olivine wadsleyite phase transformation corresponding to the 410 km seismic discontinuity is shifted to lower pressures by 1 2 gpa by the addition of water thus the topography of seismic discontinuities in the transition zone associated with slabs can be attributed not only to cold subduction but also wet subduction

upper mantle tomography and dynamics beneath the north china craton 1 a high resolution tomographic model of the upper mantle beneath the north china craton ncc is determined using a large number of precisely hand picked teleseismic p wave arrival times the results are generally consistent with previous results but high quality arrivals provide new insights into the dynamics beneath the ncc obviously north south trending low velocity low v zones are revealed down to 300 400 km depth under the shanxi rift and tanlu fault zone while a north south trending high velocity high v zone representing the remainder of detached lithosphere is visible down to 200 km depth under the western portion of eastern ncc high v anomalies representing the detached lithosphere are detected at 200 400 km depth under central and eastern ncc under the ordos block high v anomalies are visible above 400 km depth indicating intact lithosphere broad high v anomalies representing the stagnant pacific slab are imaged with a low v anomaly from datong volcano to the edge of bohai sea in the mantle transition zone beneath eastern and central ncc suggesting that the pacific slab has subducted to central ncc but with a gap a continuously y shaped low v structure is clearly imaged under datong volcano and bohai sea from the lower mantle through this gap in the mantle transition zone to the upper mantle indicating the existence of a lower mantle plume these results suggest that in addition to the subduction of the pacific plate the plume has also played an important role in lithospheric destruction by thermal erosion of the asthenosphere and detachment of the lithosphere beneath the ncc

a continuous late glacial and holocene record of vegetation changes in kazakhstan the late glacial and holocene vegetation history of northern kazakhstan is reconstructed using a well dated continuous pollen record from ozerki swamp 50 degrees 24 n 80 degrees 28 e altitude 210 m near semipalatinsk a montane steppe taiga community chenopodiaceae artemisia picea larix and betula dominated in this area between 13 000 and 10 100 yr b p at the beginning of the holocene poaceae and artemisia dominated the steppe and picea and larix disappeared from 7800 to 7250 yr b p a sharp increase in betula pollen percentages suggests afforestation after 5800 yr b p pinus sylvestris spread through the steppe zone of kazakhstan these changes in vegetation distribution are interpreted in terms of changing absolute winter temperatures due to orbitally induced insolation changes the absence of boreal conifers during the early holocene can be explained by absolute minimum temperatures below 60 degrees c or 8 degrees c colder than today c 1997 elsevier science b v

water transport into the deep mantle and formation of a hydrous transition zone abstract the phase relations in the peridotite water system to the top of the lower mantle reveal that a certain amount of water can be transported and stored in the transition zone by various hydrous minerals resulting in formation of a hydrous transition zone results of preliminary experiments to clarify the effect of water on kinetics of the olivine wadsleyite transformation are given and show that water enhances the transformation kinetics significantly there are potential dehydration sites in the deep mantle four sites along the descending slabs depending on their temperature profiles i e the mantle wedge of the subduction zone mantle transition zone top of the lower mantle where hydrous ringwoodite and superhydrous phase b decompose and deep in the lower mantle around 1200 1500 km depth where decomposition of phase d g occurs we also expect one site of dehydration melting at the base of the upper mantle where the hot mantle plume hydrated in the transition zone can be dehydrated the transition zone can serve as a water absorber for the mantle scale water circulation system some of the recent seismic works including the p wave tomography images reveal the existence of low velocity anomalies in the transition zone suggesting possibly a wet transition zone elevation of the 410 km discontinuity and lack of clear evidence for a metastable olivine wedge in cold slabs may be consistent with the equilibrium phase transformation from olivine to wadsleyite in cold and wet slabs on the basis of our kinetic study of the transformation under wet conditions

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

mantle transition zone discontinuities beneath the baikal rift and adjacent areas like most other major continental rifts the baikal rift zone brz in siberia ispresumably underlain by a hot and partially molten mantle which has a reduced seismicvelocity relative to surrounding areas recent seismic tomography studies however gaveconflicting results about the depth extent and even the existence of the low velocityanomaly beneath the brz suggesting that additional constraints are needed here wepresent results from stacking of about 1700 radial p to s receiver functions from asingle long running seismic station tly located at the sw tip of lake baikal a clearuplift of the 410 km discontinuity d410 with a magnitude of about 47 km relative tothe south margin of the siberian platform is observed beneath the rift currently availableseismic results suggest that the uplift is unlikely to be caused by addition of water tomantle transition zone mtz silicates but is the result of a 550 c reduction in temperaturein the vicinity of the d410 in addition the 660 km discontinuity d660 shows adownward trend toward the rift from the south suggesting that the entire mtz might havea low temperature beneath the rift the thickening of the mtz suggests a high velocityanomaly of about 2 in the mtz and rules out the possibility that the rifting is caused bya mantle plume originated in or beneath the mantle transition zone

a high resolution late quaternary climatostratigraphic record from iskitim priobie loess plateau sw siberia abstract the siberian loess being a part of the eurasian loess belt has provided the most complete terrestrial record of past climate change in the north central asia the continuous high resolution sections of aeolian dust deposits inter bedded with fossil soils from the priobie loess plateau and the northern altai plains mapped as a part of the 2000 km w e siberian palaeoclimate transect have produced extraordinary evidence of the late quaternary climate evolution and landscape development in the parkland steppe north of the altai sayan mountains a complete stratigraphic loess palaeosol record was studied at the iskitim reference section spanning the last c 250 ka mis 7 1 the climate indicative proxy data magnetic susceptibility grain size caco3 toc and thin section studies show marked and cyclic climatic variations particularly pronounced during the last interglacial glacial cycle equivalent to the loess reference sites from the yenisei and katun altai plain areas the kurtak and krasnogorskoye sections the iskitim loess palaeosol record illustrates a rapid onset of the last interglacial in agreement with the marine oxygen isotope records with a strongly continental warm climate culminating around the peak of the last interglacial mis 5e this was succeeded by a dramatic cooling mis 5d defined by a major cryogenic event that resulted in deformation of the mis 5e chernozem followed by loess deposition in congruence with the lake baikal detrital stratigraphic sequence cooler climate conditions during the subsequent interglacial sub stages mis 5c and 5a correspond to shifts in the bioclimatic zonal development with a gradual replacement of parkland steppe and mixed southern taiga by boreal forest and by cold arid periglacial tundra steppe during the stadial sub stages mis 5d and 5b following the most intensive loess sedimentation during the early last glacial mis 4 a new cycle with warm and very cold climate variations characterises the mid last glacial interstadial interval mis 3 with most favourable surface stabilisation phases represented by cryogenically distorted parkland chernozem soils the iskitim loess palaeosol sequence characterised by intensive syndepositional pedogenic processes provides unique evidence of a dynamic climate change during the late quaternary in the continental north central asia and a linkage site for transcontinental eurasian correlations of high resolution loess records

magnetic investigation of late quaternary loess deposition ili area china abstract a late quaternary loess section in ili river valley xinjiang northwest china has been studied magnetically samples from two sections exhibit variations in magnetic susceptibility which displays a positive relationship with pedogenesis intensity in s 0 and negative in s 1 and l 1 the detailed magnetic properties investigation reveals that concentration of initial magnetite and maghemite fm varies and may be dominated by wind intensity and source mineralogy furthermore this is the most important magnetic component influencing magnetic properties of loess paleosol sequences and controls magnetic properties of loess deposition in contrast concentration of pedogenic fm is low and has little influence on magnetic properties of loess however it is an ideal magnetic parameter to assess paleoclimate the magnetic minerals in s 1 soil units might be linked to reducing environments reflected by the enhancement of the coercive force of remanence

terrestrial heat flow in the south of east siberia abstract we summarize the results of heat flow studies in the paleozoic southern parts of the siberian platform mesozoic zabaikalye and cenozoic baikal rift activity areas it is established that regional heat flow values are greatly influenced by the latest tectonic activity rather than by the age of crust formation

mantle driven uplift of hangai dome new seismic constraints from adjoint tomography the origin of hangai dome an unusual large scale high elevation low relief landform in central mongolia remains enigmatic partly due to lack of constraints on its underlying seismic structure using adjoint tomography a full waveform tomographic technique and a large seismic waveform data set in east asia we discover beneath the dome a deep low shear wave speed low v conduit indicating a slightly warmer 54 k to 127 k upwelling from the transition zone this upwelling is spatially linked to a broader uppermost mantle low v region underlying the dome further observations of high compressional to shear wave speed ratios and positive radial anisotropy in the low v region suggest partial melting and horizontal melt transport we propose that the mantle upwelling induced decompression melting in the uppermost mantle and that excess heat associated with melt transport modified the lithosphere that isostatically compensates the surface uplift at upper mantle depths 80 km

pleistocene climate change natural environments and palaeolithic occupation of the upper yenisei area south central siberia abstract the upper yenisei river area near the geographical centre of asia is of major importance for mapping the pleistocene climate evolution over siberia an extensive loess cover with a suite of buried palaeosols from the northern minusinsk basin has provided one of the most complete high resolution late quaternary palaeoclimatic archives currently described in north central asia coupled with the pollen evidence the loess palaeosol records indicate establishment of periglacial steppe tundra during cold stadial intervals replaced by parkland steppe and boreal forest during warm interstadial intervals zonal transformations of the pleistocene environments due to marked climatic variations are reflected by the diversity of fossil faunal species including non analogue communities geoarchaeological records incorporated in the loess palaeosol formations represent important palaeoenvironmental multi proxy data complementing the fossil biotic and palaeopedological evidence abundant pebble tool assemblages provide explicit evidence of human occupation of the upper yenisei area prior to the last interglacial 130 ka bp the morphological and technological variability of the palaeolithic industries displaying a differential degree of patination and aeolian abrasion attest to several stages of the initial peopling of the southern siberian territory the cultural finds associated with the middle pleistocene cold adapted fossil fauna indicate that early humans were able to survive in local periglacial environments favourable climatic conditions during the last interglacial promoted expansion of the more advanced mousterian levallois tradition that persisted until the early last glacial stage ois 4 warming during the mid last glacial stage ois 3 accelerated formation of the late palaeolithic cultures dominated by developed blade reduction techniques intervals of significant climatic deterioration and onset of full glacial conditions are manifested by the absence of any archaeological record the main focus of the current quaternary investigations is to refine the established chronological framework and detail contextual settings of the cultural records within the larger study area

constraining the timing of the most recent cataclysmic flood event from ice dammed lakes in the russian altai mountains siberia using cosmogenic in situ 10be ice dammed lakes were repeatedly formed in intermontane basins in the russian altai mountains throughout the pleistocene these cataclysmic outburst floods caused by ice dam failures were documented as earth9s largest flood waves by other geoscientists using in situ 10 be we successfully dated surfaces of flood associated boulders located in a former lake basin and downvalley from a former ice dam our precise surface exposure ages suggest that all boulders were associated with the most recent out of a number of cataclysmic floods that occurred at 15 8 1 8 ka the field location of the boulders implies that they were deposited by the largest late pleistocene flood that drained the chuya katun lake completely following initial dam failure a published reconstruction of the late glacial paleoenvironment in the vicinity of the former ice dam indicates that dam failure was likely a result of climatically induced downwasting of glaciers the failure of the ice dam provides more evidence for the timing of widespread warming during the late glacial in southern russia this flooding event in the headwaters of the ob river coincides with a freshwater peak as recorded in isotopic records of the kara sea and the arctic ocean

magnetoclimatology teleconnection between the siberian loess record and north atlantic heinrich events new environmental magnetic data from loess and paleosol successions in outcrops in the upper reaches of the ob river drainage southern siberia track the major climatic variations over the last glacial interglacial cycle profiles of magnetic susceptibility and alternating deposition of loess and soil formation events correspond to oxygen isotope stages 1 5 the magnetic susceptibility data in association with the stratigraphic succession confirm that the wind vigor magnetoclimatological model is a viable alternative to the classic pedogenic model interpretation of magnetic susceptibility data from loess paleosol successions must therefore consider eolian dynamics available source materials and transport directions in addition to pedogenic processes rapid magnetic fluctuations are also observed these are identified for the first time in siberian records as the signature of the abrupt cold pulses responsible for the heinrich layers in north atlantic marine sediments the data thus form a component of climatic teleconnections across the northern hemisphere allowing correlations to be made among 1 siberian magnetic susceptibility stratigraphy 2 data recorded from other loess paleosol successions in china european russia europe and north america 3 north atlantic ice rafted detritus and 4 sea surface temperatures derived from molecular stratigraphy of marine sediments off the northwest coast of africa

evaluation of ground penetrating radar gpr and geology survey for slope stability study in mantled karst region engineering geological problems such as slope failure may be a result of the karst process slope stability evaluation is an effective way to minimize the losses caused by slope failure in this study a methodology is developed to evaluate the slope stability first a ground penetrating radar gpr survey is conducted along the survey lines which have a mixed orthogonal distribution in the study area detailed information of the stratum structure and karst feature is presented through gpr profiles interpretation concurrently punctual data are obtained through surface geology investigations borehole surveying and laboratory tests subsequently a series of two dimensional geological cross sections in the horizontal direction and along the topographic dip direction are generated based on the spatial database in the coordinate system relative to the geological map finally numerical simulation is performed utilizing the finite element method the horizontal deformation and distribution of the plastic zone are used to evaluate the cross sectional stability along the topographic dip direction whereas the vertical deformation is chosen as the criterion to evaluate the same in the horizontal direction slope stability analysis is conducted in terms of the above comprehensive analysis to verify the validity of the method an application is performed in nan an district in chongqing city the results of the numerical simulation indicate that a sliding surface is not formed and regional collapse does not occur the results prove that the slope is stable in the study site which is consistent with the actual conditions

effect of water in depleted mantle on post spinel transition and implication for 660 km seismic discontinuity abstract we have determined the post spinel transition boundary in anhydrous and hydrous mg2sio4 in a temperature range from 1173 to 2023 k at 19 3 25 4 gpa using synchrotron in situ x ray diffraction measurements the phase boundary in mg2sio4 is located at 22 gpa and 1800 k and 22 1 gpa and 1500 k which is slightly lower 0 3 0 5 gpa than that determined in the previous in situ measurements using the same pressure scale e g katsura et al 2003 post spinel transition in mg2sio4 determined by high p t in situ x ray diffractometry phys earth planet inter 136 11 24 the clapeyron slope of mg2sio4 was found to be gentle i e between 0 4 and 0 7 mpa k which is also consistent with previous in situ measurements but inconsistent with diamond anvil cell experiments and theoretical estimations the phase boundary in mg2sio4 2 wt h2o which is relevant to fe free depleted harzburgitic composition is located between 23 4 and 23 6 gpa and 1500 k which shifts the hydrous boundary to the higher pressures relative to anhydrous mg2sio4 from 1 3 to 1 0 gpa the result for hydrous mg2sio4 shows steeper clapeyron slope between 3 2 and 3 1 mpa k compared with anhydrous mg2sio4 and hydrous pyrolite system the present data suggest that water has a strong influence on 660 km discontinuity and the depressions observed at this boundary in several regions especially related to subduction zones can be explained by the presence of water in depleted harzburgite component

mantle transition zone stagnant slab and intraplate volcanism in northeast asia 3 d p and s wave velocity structures of the mantle down to a depth of 800 km beneath ne asia are investigated using similar to 981 000 high quality arrival time data of local earthquakes and teleseismic events recorded at 2388 stations of permanent and portable seismic networks deployed in ne china japan and south korea our results do not support the existence of a gap or a hole in the stagnant slab under the changbai volcano which was proposed by a previous study of teleseismic tomography in this work we conducted joint inversions of both local earthquake arrival times and teleseismic relative traveltime residuals leading to a robust tomography of the upper mantle and the mantle transition zone mtz beneath ne asia our joint inversion results reveal clearly the subducting pacific slab beneath the japan islands and the japan sea as well as the stagnant slab in the mtz beneath the korean peninsula and ne china a big mantle wedge bmw has formed in the upper mantle and the upper part of the mtz above the stagnant slab localized low velocity anomalies are revealed clearly in the crust and the bmw directly beneath the active changbai and ulleung volcanoes indicating that the intraplate volcanism is caused by hot and wet upwelling in the bmw associated with corner flows in the bmw and deep slab dehydration as well

absence of thermal influence from the african superswell and cratonic keels on the mantle transition zone beneath southern africa evidence from receiver function imaging abstract the depths of the 410 km d410 and 660 km d660 discontinuities beneath southern africa which is presumably underlain by the lower mantle african superswell are imaged in 1 radius consecutive circular bins using over 6400 p to s receiver functions rfs recorded by 130 seismic stations over a 27 yr period when the iasp91 standard earth model is utilized for moveout correction and time depth conversion a normal mantle transition zone mtz thickness of 246 7 km is observed suggesting that the superswell has no discernible effect on mantle transition zone temperature based on the negligible disparity of the mean mtz thicknesses between on 246 6 km and off 246 8 km cratonic regions we conclude that the deep archean cratonic keels possess limited influence on mtz thermal structure the apparently shallower than normal mtz discontinuities and the parallelism between the d410 and d660 are mostly the results of upper mantle high wave speed anomalies probably corresponding to a thick lithosphere with a mean thickness of about 245 km beneath the kaapvaal and 215 km beneath the zimbabwe cratons in contradiction to conclusions from some of the previous studies the resulting spatial distribution of the stacking amplitudes of the p to s converted phases at the discontinuities is inconsistent with the presence of an excessive amount of water in the mtz and atop the d410

significant crustal thinning beneath the baikal rift zone new constraints from receiver function analysis 1 thinning of the crust of more than 10 km is a major feature of typical continental rifts such as the east african ear and rio grande rgr rifts however numerous previous studies across the baikal rift zone brz which has similar surface expressions and tectonic history and more active seismicity relative to ear and rgr have resulted in contradicting amount of thinning ranging from almost none to more than 10 km we measure crustal thickness by stacking teleseismic receiver functions beneath 51 sites on the southern and central parts of the brz and adjacent siberian platform and sayan baikal mongolian foldbelt our measurements reveal that beneath the southern part of the platform the average crustal thickness is about 38 km which is about 7 km thinner than that beneath the foldbelt and the un rifted part of the brz the thinnest crust 35 km is found beneath the central part of the rift and represents a significant thinning of about 10 km relative to the un rifted parts of the brz index terms 7200 seismology 7203 seismology body wave propagation 7205 seismology continental crust 1242 citation gao s s k h liu and c chen 2004 significant crustal thinning beneath the baikal rift zone new constraints from receiver function analysis geophys res lett 31 l20610 doi 10 1029 2004gl020813

the siberian loess record and its significance for reconstruction of pleistocene climate change in north central asia abstract the siberian loess represents the most significant terrestrial proxy record of quaternary climatic history in northern asia loess is extensive in southern siberia between the irtysh basin in the west and the angara basin in the east palaeoenvironmental multi proxy data magnetic susceptibility ms grain size caco 3 toc pollen etc from high resolution loess palaeosol sections provide evidence for a strongly fluctuating climatic sequence in north central asia during the late quaternary displaying the globally diagnostic sequences found in the deep sea oxygen isotope records ms provides the most continuous and detailed record encompassing the last two interglacial glacial cycles in loess sections in the minusinsk basin yenisei area and on the northern altai plains evidence for periodic atmospheric shifts is provided by gradual changes in the main vegetation zones with parkland steppe and mixed taiga during warm interglacial interstadial stages being replaced by boreal tundra forest and arid periglacial tundra steppe during stadials climatic pulses from warm intervals to cold are recorded by incipient forest steppe tundra gleysols the occurrence of the highest sediment accumulation rates in glacial stages ois 4 and ois 2 in the southern plains and depressions indicates that the most intensive aeolian dust deposition followed the glacial maxima with the most recent interval dated to ca 19 15 ka bp because of its zonal distribution and pronounced climatic continentality the siberian loess region represents an important data source for reconstructing past climates in the northern hemisphere it provides a key to the correlation of other loess regions within the west east eurasian continental zone

upper cenozoic bio magnetic stratigraphy of central asian mammalian localities abstract this research is focused on biostratigraphic and palaeomagnetic correlations of upper cenozoic mammalian localities of central asia in the territory of tadjikistan uzbekistan kyrgyzstan and southern kazakhstan the absence of the lithological markers and absolute dates emphasizes the true importance of using bio magnetic evidence for stratigraphy of terrestrial molasse late turolian villafranchian and middle pleistocene faunal assemblages are recorded in central asian localities providing a good basis for a broad interregional stratigraphic correlation

changbaishan volcanism in northeast china linked to subduction induced mantle upwelling the changbaishan volcanic complex in china cannot be easily explained as the consequence of a mantle plume seismic images from the region identify buoyant mantle material that may have been entrained and dragged downwards by the subducting pacific plate but is now escaping upwards through a gap in the plate and producing the intraplate volcanism

receiver functions in northeast china implications for slab penetration into the lower mantle in northwest pacific subduction zone abstract seismic studies of the subducting lithosphere and the upper mantle discontinuities in the northwest pacific subduction zone beneath japan and northeast china have suggested contrary subduction scenarios there was little consensus on the issue whether the subducting slab penetrates the upper mantle discontinuities into the lower mantle or it is deflected atop of the 660 km discontinuity over several hundred kilometers we calculate receiver functions from a recent seismic broadband station network located in northeast china and find topographic variations of the upper mantle discontinuities a deeper than normal 660 km discontinuity is observed over an area of 400 km and it coincides with the stagnant slab imaged by seismic tomography the 660 km discontinuity is locally depressed by more than 35 km and the transition zone is thickened by more than 20 km in the east of the region where it encounters the slab these observations provide evidence of the slab accumulating in the mantle transition zone and locally penetrating into the lower mantle

first assessment of recent tectonics and paleoearthquakes along the irtysh fault eastern kazakhstan abstract the asian plate interiors are known to have host strong earthquakes with magnitudes up to m 8 in recent history especially around the border area between mongolia kazakhstan china and russia e g m7 3 chuya earthquake 2003 their recurrence times seem to be long because of the relative low slip rates in this study we focus on a large inherited fault zone namely the irtysh fault zone with no historical earthquakes larger than m6 to test whether this structure could have generated surface rupturing events during the last thousands of years like some other historically silent similar faults of cratonic southern kazakhstan did in pre historic times to do so we use tectonic morphological analyses of satellite images and trenching across several fault portions to detect potential paleoearthquakes the irtysh fault zone ifz is a 250 km long basement set of faults that marks a major tectonic block boundary between different units with paleozoic magmatic rocks and thick deposits of late paleozoic age the formation of the ifz dates back into the late paleozoic times during collision between siberia kazakh cratons and it was repeatedly reactivated in later times e g oligo miocene the quaternary activity of the irtysh fault zone has never been addressed in modern studies and in this study we document for the first time that the ifz is an active fault and is a potential source of large earthquakes in easternmost kazakhstan our analyses actually revealed at different spots along the ifz the occurrence of a set of lineaments offsetting lithologies or deflecting streams and other landscape features trenching sites across those lineaments eventually confirmed that they were active fault strands and in some trenches 14c dated holocene late pleistocene deposits are clearly faulted those recent deposits include organic soils loess layers and colluvium directly overlying the paleozoic rocks our findings lead to the conclusions that the ifz is clearly active along several strands of its trace in bedrock during the holocene it hosted earthquakes with surface rupture individual displacements of up to 1 5 m suggesting events with a magnitude around m 7 however our investigations do not allow to confident estimation of slip rates we propose for one fault section parallel to the main fault a preliminary estimation of 0 22 mm y vertical displacement rate based on a single trench based on regional morphoclimatic arguments and landscape features offsets we also propose a first assessment of the lateral slip rate along the major fault between 0 3 and 0 5 mm y additional investigations should be undertaken to refine surface fault mapping the paleoearthquake calendar the slip rate and potential along strike evolution in order to constrain future seismic hazard analyses with fault models in this region of eastern kazakhstan

imaging mantle discontinuities using multiply reflected p to s conversions abstract improving the reliability and accuracy in the determination of the depth to velocity discontinuities in the earth s mantle is essential for a better understanding of mantle dynamics as well as for addressing such fundamental questions as the origin of mantle plumes and fate of subducted slabs most existing techniques that utilize receiver function stacking which is perhaps the most commonly used method to image mantle discontinuities suffer from strong trade offs between the depth and velocity anomalies above the discontinuities here we propose and test a procedure that utilizes both the p to s converted phase pds and the multiply reflected and converted phase ppds at the discontinuities to simultaneously determine the depth of mantle discontinuities and velocity anomalies in the overlying layer the procedure includes masking the strong pp arrivals prior to computing receiver functions computing non plane wave travel times for pds and ppds for accurate moveout corrections and utilizing the discrepancies in the apparent discontinuity depths from pds and ppds to simultaneously estimate velocity anomalies and discontinuity depths that are independent of velocity anomalies application of the procedure to data recorded by stations in seven radius 1 5 circles along a 780 km n s profile centered at the yellowstone hotspot reveals lower than normal upper mantle and mtz velocities beneath yellowstone a positive temperature anomaly of 40 190 c in the vicinity of the 410 km discontinuity d410 and a lower than normal temperature in the vicinity of the 660 km discontinuity d660 the perceived hotspot is not associated with a localized depression of the d410 or an uplift of the d660 suggesting that the proposed mantle plume does not traverse the mtz beneath the profile

upwelling mantle plume and lithospheric delamination beneath the north china craton abstract various models have been proposed for the destruction of the eastern north china craton ncc however it is still a highly controversial scientific issue in this study abundant teleseismic data recorded by permanent and temporary stations in the ncc were collected and p wave tomography and common conversion point ccp stacking of receiver functions were performed the results from this study reveal an upwelling mantle plume and a shallow lehmann discontinuity or the lower boundary of a low velocity zone beneath the eastern ncc additionally a large scale plate like high velocity anomaly is defined under the eastern ncc that might be related to the delamination of a lithospheric keel based on the above results and assessment ncc destruction might include two causes lithospheric keel removal or delamination and mantle plume upwelling