ice pumps and their rates an ice pump is a heat engine driven by the change of freezing point with pressure which will melt ice at depth in the ocean and deposit it at a shallower location it is self starting calculations of the maximum magnitude of this effect are made which show good agreement with field data available for sea and lake ice the discussion is applied to the general case of a moving pack ice sheet with a well mixed surface layer and to floating ice shelves the rate of melt from an 11 m deep pressure ridge keel due to ice pumping is estimated as 26 cm year and that from the front of the ross ice shelf at mcmurdo sound antarctica is estimated as 5 m year for the level of water movement noted in the authors field observations far from the ice front pumping between shelf areas of different thickness will still occur with tidal motion providing the necessary water exchange but its magnitude is now limited by the ability to remove the potentially stable layer of melt water out of the system it is important to realize that the pumping does not depend on the availability of sensible heat in the water column and its effects are additional to any melting caused by the advection of warmer water to the ice water interface

motion of the pacific plate relative to eurasia and its potential relation to cenozoic extension along the eastern margin of eurasia extension along the eastern margin of eurasia has been regarded commonly as a far field effect of the india eurasia collision however some aspects of the timing and location of this extension make a link between the collision and extension difficult we suggest that some extensional features commonly interpreted as effects of the collision may be related more simply to changes in plate convergence rates along the eastern plate boundary of eurasia an analysis of the motion of the pacific plate relative to eurasia suggests that the rate of pacific eurasia convergence varied significantly during the tertiary period from a late cretaceous convergence rate of 120 140 mm yr the rate declined substantially during early tertiary time and reached a minimum in eocene time of 30 40 mm yr in oligocene to earliest miocene time the average convergence rate increased moderately to 70 95 mm yr then decreased again to 65 70 mm yr during early to middle miocene time from late miocene to the present the rate of convergence increased to an average of 100 110 mm yr the paleocene through middle miocene episode of relatively slow convergence correlates with a period of widespread extension along the eastern margin of eurasia decreased convergence may have been related to a net reduction in horizontal compressional stress transmitted between the pacific and eurasian plates which resulted in widespread extension adjacent to the margin of eurasia

melting characteristics of horizontal ice surfaces in cold saline water the results of an experimental investigation of the buoyancy driven flow adjacent to and below a horizontal ice surface melting in cold water at near oceanic salinity are presented this melting configuration is characteristic of circumstances encountered by sea ice for example by new ice and also on the bottom of tabular ice floes several ambient water temperatures t are investigated from t 1 75 c to t 3 c time exposure photographs of the flow field reveal that distinctively different flow regimes occur across even that narrow range of ambient temperature at all temperature levels the flow immediately below the ice surface is found to be horizontally radially inward toward the center of the ice also another outward moving horizontal layer appeared parallel to and below the inward moving layer the downward extent of penetration of this layer motion was seen to vary with t the lower layer sinks lower into the ambient medium with increasing t measured water ice interface temperatures and ice melt rates are also presented these results are compared with earlier similar measurements for vertical surfaces melting in cold saline water and found to vary in a similar way with ambient temperature t

the response of ice shelf basal melting to variations in ocean temperature abstract a three dimensional ocean general circulation model is used to study the response of idealized ice shelves to a series of ocean warming scenarios the model predicts that the total ice shelf basal melt increases quadratically as the ocean offshore of the ice front warms this occurs because the melt rate is proportional to the product of ocean flow speed and temperature in the mixed layer directly beneath the ice shelf both of which are found to increase linearly with ocean warming the behavior of this complex primitive equation model can be described surprisingly well with recourse to an idealized reduced system of equations and it is shown that this system supports a melt rate response to warming that is generally quadratic in nature this study confirms and unifies several previous examinations of the relation between melt rate and ocean temperature but disagrees with other results particularly the claim that a single melt rate sensitivity to warming is universally valid the hypothesized

an offshore eddy in the california current system part iii chemical structure abstract from january 9 to 17 1981 detailed physical chemical and biological measurements were made through the historical surface signature berstein breaker and whritner 1977 burkov and pavlova 1980 simpson 1982 of a warm core eddy in the california current system the data show a three layer system surface layer to 75 m intermediate cold core region to about 200 m and the physically dominant subsurface warm core eddy to about 1400 m the chemical structure simultaneously possesses characteristics of both warm and cold core eddies this structure results from a complex interplay among non local eddy generation processes at the time the three layer system was formed and a continuous set of interactions within the three layer system both inshore cold and offshore warm waters of the california current and coastal and local biological processes e g this california current system eddy is not an isolated structure like some gulf stream rings the dominant biological chemical process in the euphotic zone is phytoplankton photosynthesis photosynthetic alteration of the chemical structure below 100 m is much reduced the effects of heterotrophic activity on the deeper lying chemical structure however are not as significant as those of autotrophs on the chemical structure of the euphotic zone hence below 100 m the distribution and structure of chemical properties is controlled primarily by physical processes the continuous set of interactions of the three layer system with coastal and oceanic waters of the california current make this offshore eddy in the california current system fundamentally different chemically and biologically from cold core gulf stream rings and rather similar to some of the warm core eddies found in the east australian current

an offshore eddy in the california current system part ii surface manifestation abstract ship and satellite observations taken over the last thirty years show that mesoscale patterns of sea surface temperature sst in the california current system are consistently found throughout the year and usually occur in approximately the same geographical locations typically these patterns are more pronounced in fall winter than in spring summer the temporal and spatial characteristics of these persistent feature were examined with satellite infrared ir measurements during winter 1980 1981 in january 1981 a ship surveyed the vertical structure of several physical chemical and biological parameters beneath one of these sst features centered near 32 n 124 w the surface ir pattern had a length scale of 200 km and a time scale of about 100 days it disintegrated following the first two storms of the winter season motion studies of the pattern in late october indicated an anticyclonic rotation with maximum velocities of 50 cm s 1 at 50 km from the axis of rotation as a unit the pattern advected southward with an average speed of 1 cm s 1 thermal fronts determined from the satellite imagery were strongest 0 4 c km 1 along the rim of the pattern and were advected anticyclonically with the pattern their length scales were 20 30 km in the along front direction and less than 10 km wide the hydrographic data revealed a three layer structure beneath the surface pattern a 75 m deep surface layer a cold core region from 75 to 200 m depth and a warm core eddy extending from 250 to 1450 m the anticyclonic motion of the surface layer was caused by a geostrophic adjustment to the surface dynamic height anomaly produced by the subsurface warm core eddy the ir pattern observed from space reflects the horizontal structure of the surface layer and is consistent with a theoretical model of a mean horizontal sst gradient perturbed by a subsurface density anomaly ship of opportunity sst observations collected by the national marine fisheries are shown to resolve mesoscale patterns for december 1980 the sst pattern near 32 n 124 w represented a 2 c warm anomaly compared with the 20 year mean monthly sst pattern

an offshore study in the california current system preface l etude d un tourbillon de mesoechelle quasi permanent et quasi stationnaire dans le systeme du courant de californie comprend quatre parties dynamique au sein du systeme manifestations a la surface structure chimique et distribution du plancton

meroplanktonic distribution and circulation in a coastal retention zone of the northern california upwelling system previous studies have shown that settlement of several crab species along the coast north of point reyes 38 00 n 123 00 w occurs primarily during relaxation from upwelling when warm water flows poleward from the gulf of the farallones during 1994 and 1995 we sampled planktonic larval distributions and hydrography both south and north of point reyes during upwelling to test whether high concentrations of crab and rockfish larvae were concentrated in the source of the relaxation flow to the south of point reyes an upwelling plume off point reyes and an upwelling shadow indicated by warmer less saline water in the northern gulf were evident in both years as were frontal regions that marked the boundaries between water types of three different types 1 newly upwelled 2 oceanic and 3 san francisco bay outflow in addition there was a fourth type termed gulf water that was a mixture of these three types concentrations of larvae of cancrid pinnotherid and coastal crabs and rockfishes were high south of point reyes but were low or absent in the newly upwelled water north of the point within the upwelling shadow these meroplankton taxa were associated with different water masses several intertidal crab species and early stage cancrid crabs were concentrated in san francisco bay outflow water and coastal gulf water late stage cancrid crabs early and late stage pinnotherid crabs and rockfishes were concentrated at the frontal region between newly upwelled and gulf water of the taxa examined only rockfishes were found offshore in oceanic water the high concentrations of meroplankton observed suggest that the gulf of the farallones is an important retention area for larvae that settle into coastal populations in the gulf and to the north via poleward transport during upwelling relaxation

wintertime heat flux to the underside of east antarctic pack ice in the sea ice zone there is a delicate balance between the heat loss from the surface of the snow covered sea ice and the heat supplied to the underside of the ice by the deep ocean the difference between these two heat fluxes determines the amount of ice growth or melt in global atmospheric models the ocean heat flux is often prescribed and has been shown to be an important parameter in determining how thick sea ice will grow thermodynamically although this ocean heat flux is a critical component in climate models there are relatively few direct measurements in the antarctic sea ice region in this study we use measurements of the temperature gradient through the sea ice and of ice growth during a field experiment to estimate the ocean heat flux in the east antarctic region around 140 e 65 s during august 1995 we find an average ocean heat flux of 13 0 14 5 w m 2 this is more than twice the winter values reported in the western weddell sea under multiyear sea ice but similar to the 19 w m 2 that has been estimated for the entire weddell gyre during august 1995 the air temperature showed large variations ranging from near freezing to 30 c this resulted in the thicker ice floes 50 60 cm alternating between a no growth or melting condition and an active ice growth at the base however it is likely that the thicker 60 cm ridged portions of the floes were continually melting

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

temperature plant pigment optical relations in a recurrent offshore mesoscale eddy near point conception california the temperature plant pigment optical structure of a mesoscale anticyclonic eddy consistently found in shipboard surveys and satellite sensed data several hundred kilometers southwest of point conception california is described on three different time scales 100 day mesoscale annual and several year the satellite coastal zone color scanner czcs ocean color imagery detected the near surface chlorophyll structure of the eddy but in situ optical and plant pigment data suggest that such imagery does not provide a good estimate of the integrated chlorophyll field of the eddy the temperature and plant pigment boundaries of the eddy as determined from two dimensional gradients of advanced very high resolution radiometer avhrr and czcs imagery do not coincide spatially this and in situ temperature plant pigment and optical structure provide additional evidence that some eddy systems in the california current are not isolated vortex systems but rather continuously entrain waters of nonlocal origin laterally into their upper layers within the california current a ratio of avhrr czcs data is useful for separating inshore from oceanic water masses and following their surface entrainment by offshore vortices the historical 28 year california cooperative oceanic fisheries investigations data for the point conception region of the california current and remotely sensed data over this region show that the point conception eddy is a recurrent feature in the offshore california current moreover the available data provide evidence that a large number of warm core mesoscale eddies occur simultaneously in a transition zone between coastal and oceanic regimes that these features recur at preferred locations within the transition zone and that this family of eddies should impose a significant offshore boundary condition on the flow of the california current

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

an offshore eddy in the california current system part i interior dynamics abstract from january 9 to 17 1981 detailed observations of the horizontal and vertical structure beneath one of the quasi permanent semi stationary mesoscale offshore eddy signatures in the california current system ccs discussed by bernstein breaker and whritner 1977 burkov and pavlova 1980 and simpson 1982 were made the vertical sections of temperature and density show the presence of three layer system a subsurface warm core eddy whose diameter is about 150 km at the 7 c isotherm is the dominant feature a warm surface layer which extends to a depth of 75 m lies over the eddy between the warm surface layer and the subsurface warm core eddy there is a cold core region which extends to a depth of about 200 m there is a high degree of symmetry about the vertical axis of rotation vertical sections of salinity and dissolved oxygen are entirely different from sections of temperature and density diagrams of water mass characteristics confirm that the core of the eddy found between 250 600 m consists of inshore water from the california undercurrent cu below about 700 m local waters from the deep poleward flow dpf have been incorporated into the eddy the observed distributions of properties t s o 2 are inconsistent with a single local generation process for the eddy system radial distributions of angular velocity normalized gradient velocity and relative vorticity support the use of a gaussian radial height field as an initial condition in eddy models possible reasons why ccs eddies may differ dynamically from gulf stream rings are given in the text at the time the observations were made the system as a whole was in near geostrophic balance local geostrophic balance however cannot explain the observed distribution of properties and structure the observed symmetry in the structure of the eddy system chemical evidence simpson 1984 biological distributions haury 1984 and satellite images of the cc koblinsky simpson and dickey 1984 suggest that lateral entrainment of warm oceanic and cold coastal water into the upper two layers of the three layer system by the subsurface eddy is a likely generation mechanism for the cold core region the coastal origin of the frontal structure along the northeastern quadrant and the oceanic origin of the frontal structure along the southwestern quadrant of the eddy system further support lateral entrainment as a generation mechanism for the cold core this entrainment makes the ccs eddy system different from cold core rings in the gulf stream and rather similar to some warm core eddies found in the east australian current the presence of cu water in the core of this eddy raises the question of how cu water was transported from the continental slope eddy generation mechanisms other than baroclinic instability of the cc may be required to explain the distribution persistence and core composition of offshore mesoscale eddies in the ccs there is evidence that barotropic in addition to baroclinic processes may be important

wintertime convection in warm core rings thermocline ventilation and the formation of mesoscale lenses large heat losses from warm core ring 82b during february march and april 1982 formed a 400 m thick thermostad in the center of the ring two different models were constructed to simulate the formation of the thermostad water mass properties a one dimensional vertical model forced with a meteorological time series and a volumetric mixing model with climatological input both models indicate that a flux of slope water into the ring is necessary to yield the observed thermostad salinities the subsequent slow decay of the ring core in the slope water suggests that such winter convected rings can easily maintain the warm band water identified by wright and parker 1976 the large loss of core water during interactions with the gulf stream suggests that the reabsorption of such winter cooled warm rings is an important source of high salinity high oxygen anomalies in the main thermocline of the sargasso sea the volume of water in a typical ring reabsorption is sufficient to generate many 20 intrathermocline eddies with t s properties close to those of recently reported lenses this suggests that many of these small eddies are much more local in origin and may be more highly dissipative than has previously been suggested an estimate of the flux of high salinity high oxygen water into the main thermocline by this mechanism leads to ventilation at a rate that is a significant fraction of the ekman pumping at these density levels thus the reabsorption of winter cooled warm core rings by the gulf stream is an important eddy ventilation mechanism for the sargasso sea

gulf stream warm core ring collection an introduction the collection of papers that follows evolved out of presentations given at a warm core rings workshop at the alton jones conference center university of rhode island in august 1984 at that time it became clear that a number of investigators in the warm core rings program had reached a stage where they were completing the analysis of their individual data sets and models some of these studies were interrelated and others were not our aim in collecting these investigations is not to present an integrated synthesis of gulf stream warm core rings but rather to provide a forum where some of our initial results can be focused

an offshore eddy in the california current system part iv plankton distributions abstract the distribution of plankton across a warm core eddy system in the california current 400 km off point conception california was studied in january 1981 the eddy system about 150 km in diameter at the 7 c isotherm was made up of a 75 m thick surface layer a cold core region extending from 75 m to about 200 m and a warm core eddy below 200 m extending to at least 1450 m casts for the vertical distribution of chlorophyll phaeophytin and integrating zooplankton net tows were taken at 37 stations located about 20 km apart on two orthogonal transects across the eddy system vertical distributions of microplankton were determined on one section from the eddy center to beyond the eastern edge integrated chlorophyll phaeophytin values were highest to the north and east of the eddy system across the system itself there was only a small increase of values near the center asymmetrical distributions of maximum concen current water was being entrained into the center of the eddy system from the northeast dinoflagellates were numerically the most important member of the microplankton especially in the deep chlorophyll maximum zooplankton distributions indicated the intermingling of warm and cool water species throughout at least the upper 200 m of the eddy system some cold water species were as abundant inside the system as outside to the north and east their numbers were much reduced in a band surrounding the system where warm water species were most abundant the presence of species characteristic of different water types throughout the region of the eddy system provides an indication of the mixing that had occurred since the system originally formed the biological data together with the physical and chemical results indicate the importance of frontal boundary processes and lateral entrainment of surrounding water into the eddy system in determining the character and productivity of such systems

the effects of a headland eddy on surface macro zooplankton assemblages north of otago peninsula new zealand abstract the seasonal near surface distribution of macro zooplankton within an eddy in the northern lee of otago peninsula was determined by four grid surveys sampled at three monthly intervals the distribution of multi species assemblages derived from hierarchical multivariate techniques were compared directly with patterns in the hydrographic data despite seasonal differences in species composition three zooplankton assemblages strongly affiliated with specific aspects of the coastal hydrography were consistently identified in the surveys a mixed assemblage comprising holoplanktonic species with sub tropical or sub antarctic affinities was assoiated with the waters over the outer shelf characteristic of the southland current the assemblage identified within neritic waters that flow south over the inner shelf in blueskin bay was dominated by meroplanktonic zooplankton mainly benthic crustacean larvae the zooplankton assemblage associated with the low salinity neritic waters originating south of otago peninsula and present over the mid shelf region and within northern blueskin bay contained relatively low numbers of oceanic species and was dominated by coastal species the assemblages within neritic waters appeared to be related to the flow patterns in the topographic eddy north of the peninsula this eddy appears not only to entrain oceanic species within inshore coastal waters but also to retain larvae of benthic crustaceans and the eggs of inshore spawning fish species and to recruit larvae of mid outer shelf benthic crustaceans to the nearshore zone the importance of physical rather than biological processes as the proximal determinant of the spatial structure of the local zooplankton community is discussed

the vertical slip rate of the sertengshan piedmont fault inner mongolia china abstract the vertical slip rate of a normal fault is one of the most important parameters for evaluating its level of activity the sertengshan piedmont fault has been studied since the 1980s but its absolute vertical slip rate has not been determined in this paper we calculate the displacements of the fault by measuring the heights of piedmont terraces on the footwall and the stratigraphic depths of marker strata in the hanging wall we then calculate the vertical slip rate of the fault based on the displacements and ages of the marker strata we selected nine sites uniformly along the fault to study the vertical slip rates of the fault the results show that the elevations of terraces t3 and t1 are approximately 1060 m and 1043 m respectively the geological boreholes in the basin adjacent to the nine study sites reveal that the elevation of the bottom of the holocene series is between 1017 and 1035 m and that the elevation of the top of the lacustrine strata is between 925 and 1009 m the data from the terraces and boreholes also show that the top of the lacustrine strata is approximately 65 ka old the vertical slip rates are calculated at 0 74 1 81 mm a since 65 ka and 0 86 2 28 mm a since the holocene the slip rate is the highest along the wujiahe segment and is lower to the west and east based on the findings of a previous study on the fault system along the northern margin of the hetao graben basin the vertical slip rates of the daqingshan and langshan faults are higher than those of the sertengshan and wulashan faults and the strike slip rates of these four northern hetao graben basin faults are low these results agree with the vertical slip components of the principal stress field on the faults the results of our analysis indicate that the langshankou wujiahe and wubulangkou areas and the eastern end of the sertengshan fault are at high risk of experiencing earthquakes in the future

biological consequences of a recurrent eddy off point conception california the biological effects on three different time scales 100 day mesoscale annual and several year of a mesoscale anticyclonic eddy consistently found in shipboard surveys and satellite sensed data several hundred kilometers southwest of point conception california are described a detailed shipboard study of the eddy in january 1981 found a complex system of fronts in surface chlorophyll at the northern edge of the eddy microplankton and zooplankton distributions were strongly affected by entrainment processes at the surface and apparently at depth concurrent satellite coastal zone color scanner ocean color images show agreement with the general surface characteristics of the eddy chlorophyll field but do not reflect features deeper than about 25 m including the contribution of the deep chlorophyll maximum to the integrated chlorophyll values satellite data for the period october 1980 through october 1981 and shipboard data from california cooperative oceanic fisheries investigations calcofi for december 1980 to july 1981 show the continued presence of the eddy in the sea surface temperature and color field and in the distributions of surface chlorophyll and zooplankton displacement volume a review of the calcofi survey results from 1949 to the present time demonstrates the recurrent nature of the eddy system on a year to year basis the eddy system appears to have a significant effect on the distribution of both oceanic and nearshore organisms offshore transport of coastal species occurs in the form of large entrained plumes or filaments

on supercooling and ice formation in turbulent sea water les resultats des experiences en laboratoire sur la surfusion et la formation de frasil dans l eau de mer sont analyses a l aide d un modele de couche limite

a new osl chronology for dust accumulation in the last 130 000 yr for the chinese loess plateau abstract a sensitivity corrected multiple aliquot regenerative dose protocol has been developed for fine grained quartz osl dating of chinese loess its reliability has been assessed on the basis of the methodology and by dating reference samples of known age close to the transition from the last interglacial paleosol s 1 to the last glacial loess l 1 which corresponds to the marine oxygen isotope stage mis 5 4 transition on the basis of the fine grained quartz osl age estimates for 33 loess samples from the upper part of the luochuan profile a detailed chronostratigraphy of continuous dust accumulation in the past 130 ka has been proposed changes in the accumulation rate occurred during the last glacial period mis 4 to mis 2 unexpectedly high accumulation rates were found in the weakly developed l 1 2 s paleosol of the last interstadial mis 3 rather than in the classic l 1 1 and l 1 3 loess of the cold dry glacial condition mis 2 and 4 the osl ages show some disagreement with the previous numerical chronology for the loess paleosol sequence based on correlation of variations in grain size with sedimentation rate the latter method resulted in an almost constant accumulation rate from 72 to 12 ka

neogene and quaternary faulting in and along the qinling shan the structure of the qinling shan mountain range shaanxi china involves major east south east strike slip faults field observations made during two expeditions in 1983 and 1984 show that the faults are active and may have undergone several tens of kilometres of post eocene left lateral displacement the faults cut the morphology sharply and offset left laterally small channels their trace is marked by cataclastic to mylonitic non coaxial deformation zones at least 50 100 m wide the qinling faults allow the eastward extrusion of south china and may be considered the easternmost continuation of the altyn tagh fault system they link extensional tectonics in northeastern china to the himalayan collision

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