crustal deformation along the altyn tagh fault system western china from gps we collected gps data from the southern tarim basin the qaidam basin and the western kunlun shan region between 1993 and 1998 to determine crustal deformation along the altyn tagh fault system at the northern margin of the tibetan plateau we conclude from these data that the altyn tagh is a left lateral strike slip fault with a current slip rate of 9 mm yr in sharp contrast with geological estimates of 20 30 mm yr this contrast poses an enigma because the gps data cover a wider region than the geologic data they might be expected to reveal somewhat more slip we also find that the tarim and qaidam basins behave as rigid blocks within the uncertainty of our measurements rotating clockwise at a rate of 11 and 4 5 nrad yr respectively with respect to the eurasia plate the rotation of the tarim basin causes convergence across the tian shan increasing progressively westward from 6 mm yr at 87 e to 18 mm yr at 77 e our data and other gps data suggest that the indo asia collision is mainly accommodated by crustal shortening along the main himalayan thrust system 53 and the tian shan contractional belt 19 eastward extrusion of the tibetan plateau along the altyn tagh and kunlun faults accommodates only 23 of the indo asia convergence

lateral extrusion of lower crust from under high topography in the isostatic limit where there is isostasy the rocks of the lower continental crust are subject to an effective lateral pressure gradient equal to the gradient of topographic load whether compensation is in crustal roots or in the mantle the result is a poiseuille flow planar channel flow in the weak lower crust which removes crust from under mountains and smooths and levels the topography assuming cubic power law creep the flux of crust is proportional to the third power of the topographic gradient to the usual arrhenius term to the tenth power of the absolute temperature of the lower crust and to the negative fifth power of the geothermal gradient the result is that any initial condition with an isolated high tends eventually toward a state where the topography is pancake shaped with a flat central plateau and steeper flanks spreading outward when adjacent pancakes merge most of the relief is eliminated flow may either roughen or smooth the moho depending on whether there are lateral density contrasts in the mantle lithosphere or not although it is difficult to find analytic solutions for this evolution it is easily simulated numerically using various published flow laws for plausible lower crustal rocks lateral extrusion is shown to be insignificant under the oceans marginally significant under shields and platforms important under elevated plains and dominant beneath high plateaus and or hot delaminated regions in particular the basin and range province of the western united states cannot maintain short wavelength 100 km moho relief of more than 1 km for times greater than 10 20 m y at most if the tibetan plateau of china has been delaminated as recently suggested then it may flatten even faster reducing 100 km wavelength topographic features to 200 m relief in no more than 0 03 0 13 m y and leaving only features with wavelengths over 400 km at the present therefore the lower crust of tibet may resemble a hydraulic reservoir as previously suggested because the flatness of the moho is self maintained in these regions information on past tectonics is continually lost and the present moho shape cannot be used to balance cross sections for times in the past the flatness of the moho today is not a constraint on the mechanisms of extension or shortening in these regions nor is it evidence for underplating by intrusions it also follows that very intense and inhomogeneous dilational strains may have occurred locally as in the metamorphic core complexes of the basin and range province

lithospheric structure in central eurasia derived from elevation geoid anomaly and thermal analysis we present new crustal and lithospheric thickness maps for central eurasia from the combination of elevation and geoid anomaly data and thermal analysis the results are strongly constrained by numerous previous data based on seismological and seismic experiments tomographic imaging and integrated geophysical studies our results indicate that high topography regions are associated with crustal thickening that is at a maximum below the zagros himalaya tien shan and the tibetan plateau the stiffer continental blocks that remain undeformed within the continental collision areas are characterized by a slightly thickened crust and flat topography lithospheric thickness and crustal thickness show different patterns that highlight an important strain partitioning within the lithosphere the arabia eurasia collision zone is characterized by a thick lithosphere underneath the zagros belt whereas a thin to non existent lithospheric mantle is observed beneath the iranian and anatolian plateaus conversely the india eurasia collision zone is characterized by a very thick lithosphere below its southern part as a consequence of the underplating of the cold and stiff indian lithosphere our new model presents great improvements compared to previous global models available for the region and allows us to discuss major aspects related to the lithospheric structure and acting geodynamic processes in central eurasia

kinematic model of active deformation in central asia the velocity field of present day deformation in central asia is modelled using a set of four rotating blocks siberia tarim tibet india on a spherical earth a best fit is inverted on the basis of estimated shortening rates across the main thrust zones himalayas tien shan and measured slip rates along the principal strike slip faults altyn tagh and karakorum separating those blocks the fit to the data implies that nearly all the present convergence between india and asia can be accounted for by slip partitioning on these four zones with as much as 50 absorbed by northeastwards extrusion of tibet this suggests that localised deformation governs the present mechanical behaviour of the central asian lithosphere

the crustal structure from the altai mountains to the altyn tagh fault northwest china 1 we present a new crustal section across northwest china based on a seismic refraction profile and geologic mapping the 1100 km long section crosses the southern margin of the chinese altai mountains junggar accretional belt and eastern junggar basin easternmost tianshan mountains and easternmost tarim basin the crustal velocity structure and poisson s ratio which provide a constraint on crustal composition were determined from p and s wave data despite the complex geology the crustal thickness along the entire profile is nearly uniform at 50 km the thickest crust 56 km occurs at the northern end of the profile beneath the altai mountains and the thinnest 46 km crust is beneath the junggar basin beneath surficial sediments the crust is found to have three layers with p wave velocities vp of 6 0 6 3 6 3 6 6 and 6 9 7 0 km s respectively the southern half of the profile including the eastern tianshan mountains and eastern margin of the tarim basin shows low p wave velocities and 0 25 to a depth of 30 km which suggests a quartz rich granitic upper crustal composition the northern half of the profile below the altai mountains and junggar accretional belt has a higher poisson s ratio of 0 26 0 27 to a depth of 30 km indicative of an intermediate crustal composition the entire 1100 km long profile is underlain by a 15 30 km thick high velocity 6 9 7 0 km s 0 26 0 28 lower crustal layer that we interpret to have a bulk composition of mafic granulite at the southern end of the profile a 5 km thick midcrustal low velocity layer vp 5 9 km s 0 25 underlies the tianshan and the region to the south and may be indicative of a near horizontal detachment interface pn velocities are 7 7 7 8 km s between the tianshan and the junggar basin and 7 9 8 0 km s below the altai mountains and eastern margin of the tarim basin we interpret the consistent three layer stratification of the crust to indicate that the crust has undergone partial melting and differentiation after paleozoic terrane accretion the thickness 50 km of the crust appears to be related to compression resulting from the indo asian collision

surface deformation and lower crustal flow in eastern tibet field observations and satellite geodesy indicate that little crustal shortening has occurred along the central to southern margin of the eastern tibetan plateau since about 4 million years ago instead central eastern tibet has been nearly stationary relative to southeastern china southeastern tibet has rotated clockwise without major crustal shortening and the crust along portions of the eastern plateau margin has been extended modeling suggests that these phenomena are the result of continental convergence where the lower crust is so weak that upper crustal deformation is decoupled from the motion of the underlying mantle this model also predicts east west extension on the high plateau without convective removal of tibetan lithosphere and without eastward movement of the crust east of the plateau

coupling and decoupling of crust and mantle in convergent orogens implications for strain partitioning in the crust topographic relief strain partitioning and crust mantle coupling within convergent orogens may be systematically related to the distribution of strength as a function of depth within continental crust this result is obtained by solving analytically for basally driven three dimensional flow within an idealized crust with a laterally invariant depth dependent newtonian viscosity two end member flow states are shown to occur in the first crustal flow is directly coupled to the underlying mantle and is controlled by stresses transmitted vertically through the crust in the second upper crustal to midcrustal flow is decoupled from the underlying mantle and is controlled by stresses transmitted horizontally through the crust this model is applied to deformation of continental crust above plate like mantle that undergoes oblique convergence across a narrow suture if no significant low viscosity zone develops within the crust crustal deformation is coupled to motion of the underlying mantle and a triangular mountain range develops surface shortening occurs at the foot of the mountains normal to the trend of the range while strike slip and extension are partitioned along the axis of the orogen if a low viscosity zone is initially absent but develops during crustal thickening a steep sided flat topped plateau forms crustal deformation is coupled to mantle motions on the plateau flanks but may be strongly decoupled beneath the plateau surface shortening normal to the plateau occurs at the foot of the plateau while surface extension normal to the plateau occurs at the plateau edge if a low viscosity zone is present in the lower crust prior to convergence a wide orogen with low topographic relief develops crustal deformation is decoupled from the mantle except at the edges of the deforming region and surface shortening is partitioned uniformly across the belt this study shows that horizontal and vertical partitioning of strain occur even in the absence of lateral strength variations and that shortening and extension may exist simultaneously in different parts of an orogen similar morphology and strain partitioning can be observed in many real orogenic belts including the eastern alps the tibetan plateau and the lachlan tasman fold belt

constraints on north anatolian fault zone width in the crust and upper mantle from s wave teleseismic tomography we present high resolution s wave teleseismic tomography images of the western segment of the north anatolian fault nafz in turkey using teleseismic data recorded during the deployment period of the dana array the array comprised 66 stations with a nominal station spacing of 7 km thus permitting a horizontal and vertical resolution of approximately 15 km we use the current s wave results with previously published p wave teleseismic tomography to produce maps of relative vp vs anomalies which we use to highlight the difference in overall composition of the three terranes separated by the northern nnaf and southern snaf branches of the nafz our results show a narrow s wave low velocity anomaly beneath the northern branch of the nafz extending from the upper crust where it has a width of 10 km to the lower crust where it widens to 30 km this low velocity zone most likely extends into the upper mantle where we constrain its width to be 50 km and interpret it as indicative of localised shear beneath the nnaf this structure is similar to what has been observed for the nafz west of 32 and therefore we propose that the structure of the nnaf is similar to that of the nafz in the east the snaf does not show a very strong signature in our images and we conclude that it is most likely rooted in the crust possibly accommodating deformation related to rotation of the armutlu almacik blocks situated between the two nafz branches

magnitude of late quaternary left lateral displacements along the north edge of tibet images taken by the earth observation satellite spot of the quaternary morphology at 18 sites on the 2000 kilometer long altyn tagh fault at the north edge of tibet demonstrate that it is outstandingly active long term left lateral strike slip offsets of stream channels alluvial terrace edges and glacial moraines along the fault cluster between 100 and 400 meters the high elevation of the sites mostly above 4000 meters in the periglacial zone suggests that most offsets resulted from slip on the fault since the beginning of the holocene these data imply that slip rates are 2 to 3 centimeters per year along much of the fault length and support the hypothesis that the continuing penetration of india into asia forces tibet rapidly toward the east

is the north altyn fault part of a strike slip duplex along the altyn tagh fault system although the altyn tagh fault system has played an important role in the indo asian collision its geometry and tectonic evolution remain poorly known between 86 and 92 e this system is at least 100 km wide and is bounded to the north and south by the north altyn and altyn tagh faults respectively mapping along the jianglisai reach of the north altyn fault indicates that miocene to pliocene motion was predominantly left to left reverse slip with transport vectors trending n45 60 e map relationships suggest that total offset on the fault is 120 km these results are inconsistent with previous models of the altyn tagh fault system in which oblique convergence along the northern margin of the tibetan plateau is partitioned into thrusting on the north altyn fault and left slip on the altyn tagh fault an alternative hypothesis is that the north altyn fault is the northern boundary of a transpressional strike slip duplex within which the structurally elevated altyn mountains were created our model suggests that transpressional deformation may be restricted to this strike slip duplex and need not characterize the entire margin

no late quaternary strike slip motion along the northern karakoram fault abstract models that treat long term evolution of the tibetan orogen in terms of interactions between rigid blocks require the right slip karakoram fault that bounds the western margin of the tibetan plateau to be a long lived stable high slip rate feature while the southern portion of the fault clearly remains active recent work has proposed that the northern half of the karakoram fault is currently inactive new field observations and geochronologic results from the northern end of the karakoram fault system confirm this interpretation and provide the first quantitative data on the minimum age for the termination of slip in the southeast pamir gravel that yields a u series age of 198 5 ka on secondary carbonate caps a non deformed strath terrace that extends across the main strand of the karakoram fault the secondary achiehkopai fault strand is overlain by undisturbed hangdi glacial stage 24 6 ka deposits and dabudar glacial stage penultimate glacial cycle 150 ka or older deposits which lack observable lateral displacement or deformation together these observations show that the northern portion of the karakoram fault system has not accommodated any detectable strike slip deformation since at least 24 6 ka and most likely since 200 ka or more these results show that the karakoram fault system no longer forms a continuous discrete kinematic boundary at the western margin of the tibetan plateau this suggests that even long 500 km strike slip faults within orogenic belts are inherently unstable features consistent with models of continental collision zones involving relatively weak crust and distributed deformation

reversal of the 1960s to 1990s freshening trend in the northeast north atlantic and nordic seas hydrographic time series in the northeast north atlantic and nordic seas show that the freshening trend of the 1960s 1990s has completely reversed in the upper ocean since the 1990s temperature and salinity have rapidly increased in the atlantic inflow from the eastern subpolar gyre to the fram strait in 2003 2006 salinity values reached the previous maximum last observed around 1960 and temperature values exceeded records the mean properties of the atlantic inflow decrease northwards but variations seen in the eastern subpolar gyre at 57 n persist with the same amplitude and pattern along the pathways to fram strait time series correlations and extreme events suggest a time lag of 3 4 years over that distance this estimate allows predictions to be made the temperature of atlantic water in the fram strait may start to decline in 2007 or 2008 salinity a year later but both will remain high at least until 2010

tomographic inversion of pn travel times in china 1 pn travel times are useful for studying crustal and uppermost mantle structure and regional tectonics because they are affected by crustal velocity and thickness as well as uppermost mantle velocity and anisotropy we obtained 57 740 pn travel time picks from 5433 earthquakes and 307 stations from chinese national and provincial earthquake bulletins and the international seismological center bulletins to invert for pn velocity variation and anisotropy and station delays in china our inversion reveals significant features that correlate with surface geology the main results are as follows 1 the pn velocities show a mosaic of very fast and very slow anomalies mirroring the heterogeneous geology of china at the surface the pn velocities are high beneath the major basins in the west sichuan qaidam west tarim tulufan and junggar and low in areas of active volcanoes myanmar and western yunnan and quaternary volcanism in northern tibet in seismically active areas in north china and tien shan and in the southern part of south china the hainan plume 2 the pn anisotropy beneath the major basins in the west is generally weak strong anisotropy is found beneath high deformation regions the tibetan plateau southeastern margin of the tibetan plateau western tien shan and part of north china suggesting the anisotropy is likely related to recent large scale tectonic activity 3 a large area of north china shows prominent low pn velocity beneath archean basement with thin crust our observations are consistent with rifting lithospheric thinning and mantle upwelling in the region the pn anisotropy is consistent with a dextral simple shear in the nne direction in the lithosphere mantle during the last and ongoing major deformation period 4 the pn velocity in northern tibet is generally lower than that in the south southern tibet has significant e w structure low velocity anomalies can be traced from northern tibet across southwestern tibet and south central tibet to near the india plate anisotropy is absent beneath much of the himalaya block but consistent anisotropy with e w fast direction is present beneath the lhasa block and large anisotropy up to 4 is observed in low velocity regions of the northern and western tibet complex station delays in the eastern margin of the plateau suggest that the whole crust may be highly deformed the anisotropy pattern in the southeastern margin of the tibetan plateau suggests a mantle lithospheric deformation similar to the clockwise rotation of material observed at the surface 5 crustal thicknesses inferred from our station delays are consistent with previous models which correlate well with surface topography

formation and evolution of strike slip faults rifts and basins during the india asia collision an experimental approach the processes which have governed the formation and evolution of large tertiary strike slip faults during the penetration of india into eastern asia are investigated by means of plane strain indentation experiments on layered plasticine models the steady state deformation of plasticine obeys a power creep flow law e c t n the stress exponent n is between 6 and 9 at 25 c uniaxial plane strain tests on cubic specimens show that the growth of faults in layered plasticine results from strain softening a process observed for strain rates ranging from 3 5 10 5 to 3 6 10 3 s 1 fault or shear zones form after only 7 10 bulk strain subsequent deformation is controlled by the geometry of the fault pattern rather than the physical properties of the plasticine a series of nine plane strain indentation experiments shows the influence of boundary conditions as well as that of the internal structure of the plasticine model on the faulting sequence the ubiquity of strain softening in experimental deformation of a variety of rocks as well as the widespread occurrence of shear zones in nature suggest that long term deformation of the continental lithosphere may also be primarily influenced by the geometry of large faults which rapidly develop with increasing strain the deformation and faulting sequence observed in the plasticine indentation experiments may thus be compared to collision induced strikeslip faulting in asia particularly to total offsets and rates of movements on the faults the experiments simulate the evolution of the western ends of the strike slip faults which have probably been analogous to trench fault fault triple junctions the experiments also illustrate mechanisms for the formation of extensional basins such as the south china sea north china basin and andaman sea near active continental margins the basins which appear to absorb terminal offsets along major strike slip faults near such margins may result from mismatch between the sharply angular shape of the deformed continental edge and the more regularly curved trench along which the smoothly flexed oceanic lithosphere subducts the existence of distinct phases of strike slip extrusion corroborates the idea that the discontinuities in time which typify intracontinental tectonics and orogenic cycles may often result from strain localization and the ensuing discontinuous non steady state deformation of the continental lithosphere

the s velocity structure of the east asian mantle from inversion of shear and surface waveforms summary the structure of the mantle beneath east asia down to 800 km depth is investigated using full waveforms of seismic shear and surface waves epicentral distances are limited to less than 40 in contrast with previous waveform inversions we avoid ray theoretical or path integral approaches instead we use 1 exact 3 d waveform sensitivity kernels that correctly reflect off path sensitivity and the existence of fresnel zones we apply 2 an accurate 3 d forward modelling technique based on a coupled mode multiple forward scattering approach allowing us 3 to iterate the inversion procedure through several 3 d models and 4 to evaluate the true misfit between the data and the synthetics for the 3 d model average lateral resolution of the model in regions with good path coverage is 400 km throughout the upper mantle in the depth range from 100 to 250 km the lateral resolution even approaches 200 km since wave front healing is taken into account the amplitudes of velocity perturbations are larger than in other tomographic models moreover the waveform sensitivity kernels provide an intrinsic physical smoothing of the model stabilizing the inversion finally owing to the use of exact sensitivities better resolution can be achieved with a given set of seismograms major features of the model are high velocity subducting slabs along the west pacific subduction zones stagnating at the 660 km discontinuity a strong low velocity zone between 80 and 250 km depth in the west pacific backarc regions a plume like low velocity feature beneath the southern tip of the baikal rift zone extending into the transition zone a low velocity region under the tien shan with connection into the transition zone and thick crust under tibet reaching its maximum thickness of approximately 80 km close to the 35th parallel the lithospheric mantle underneath southern tibet is very fast indicating underthrusting of the indian lithosphere in contrast the upper mantle beneath northern tibet exhibits average to slow values from the moho down to the 660 km discontinuity very high s velocities are again observed beneath the tarim basin the high velocity mantle lithospheres under southern tibet and the tarim join beneath the karakorum range at the western tip of the tibet plateau

decline of subpolar north atlantic circulation during the 1990s observations of sea surface height reveal that substantial changes have occurred over the past decade in the mid to high latitude north atlantic ocean topex poseidon altimeter data show that subpolar sea surface height increased during the 1990s and the geostrophic velocity derived from altimeter data exhibits declining subpolar gyre circulation combining the data from earlier satellites we find that subpolar circulation may have been weaker in the late 1990s than in the late 1970s and 1980s direct current meter observations in the boundary current of the labrador sea support the weakening circulation trend of the 1990s and together with hydrographic data show that the mid to late 1990s decline extends deep in the water column analysis of the local surface forcing suggests that the 1990s buoyancy forcing has a dynamic effect consistent with altimetric and hydrographic observations a weak thermohaline forcing allows the decay of the domed structure of subpolar isopycnals and weakening of circulation

north atlantic nordic seas exchanges abstract the northeastern part of the north atlantic is unique in the sense that it is much warmer in the surface than other ocean areas at similar latitudes the main reason for this is the large northward transport of heat that extends to high latitudes and crosses the greenland scotland ridge to enter the nordic seas and the arctic there the warm atlantic water is converted to colder water masses that return southwards over the ridge partly as surface outflows and partly as overflows through the deep passages across the ridge in this paper the state of knowledge on the exchanges especially across the eastern part of the greenland scotland ridge is reviewed based on results from the ices nansen north atlantic norwegian sea exchanges project from the nordic woce project and from other sources the accumulated evidence allows us to describe the exchanges in fair detail the origins of the waters the patterns of their flow towards and over the ridge and their ultimate fate there is also increasing information on temporal variations of the exchanges although dynamical changes are still not well understood quantitative estimates for the volume transport of most of the overflow branches seem reasonably well established and transport measurements of the atlantic inflows to the nordic seas are approaching acceptable levels of confidence which allows preliminary budgets to be presented the deep overflows are driven by pressure gradients set up by the formation of deep and intermediate water the dominance of deep overflows over surface outflows in the water budget argues that this thermohaline forcing also dominates over direct wind stress and estuarine forcing in driving the atlantic water inflow across the greenland scotland ridge while wind stress seems to influence the characteristics and distribution of the atlantic water north of the ridge

geodetic evidence for a low slip rate in the altyn tagh fault system the collision between india and asia has been simulated with a variety of computational models that describe or predict the motions of the main faults of east asia geological slip rate estimates of 20 30 mm yr 1 suggest that the largest of these faults the 2 000 km long altyn tagh fault system on the northern edge of the tibetan plateau absorbs as much of the indo asian convergence signal as do the himalayas partly by oblique slip and partly by contraction and mountain growth however the predictions of dynamic models for asian deformation and the lower bounds of some geological slip rates estimates 3 9 mm yr 1 refs 7 8 suggest that the altyn tagh system is less active here we report geodetic data from 89 91 degrees e that indicate left lateral shear of 9 5 mm yr 1 and contraction of 3 1 mm yr 1 across the altyn tagh system this result combined with our finding that at 90 degrees e tibet contracts north south at 9 1 mm yr 1 supports the predictions of dynamic models of asian deformation

observed sources and variability of nordic seas overflow the overflows from the nordic seas maintain the deep branch of the north atlantic circulation that is an important part of the global climate system an analysis of observed ocean temperatures and salinities between 1950 and 2005 shows that the atlantic water circulating in the nordic seas is the main source for change in the overflow waters

structure of the central altyn tagh fault revealed by magnetotelluric data new insights into the structure of the northern margin of the india asia collision abstract the altyn tagh fault atf is a left lateral strike slip fault that forms the northern margin of the tibetan plateau and plays a significant role in accommodating the convergence between the colliding indian and eurasian plates as a part of the fourth phase of the indepth project magnetotelluric mt data were collected across the central segment of the atf to determine the lithospheric scale structure of the fault system dimensionality analyses demonstrated that the mt data can be interpreted using two dimensional approaches but some localized 3 d effects are seen consequently both 2 d and 3 d inversions were carried out and a joint interpretation was made on the basis of these two types of models inversion models revealed two major conductors beneath the qaidam basin qb and altyn tagh range atr respectively the conductive region beneath the qb was interpreted as a ductile layer in the lower crust to upper mantle that might represent flow beneath the western margin of the qb whereas the large scale south dipping conductor beneath the atr is interpreted as a region with high fluid content formed by metamorphism associated with the oblique underthrusting of the tarim block beneath the northern tibetan plateau these fluids migrate upwards through the fault system and have formed serpentinized zones in the crust combining these interpretations a structural model compatible with diverse geophysical observations is proposed in which we suggest the competing end member rigid block model and continuum model are reconcilable with the continuum model locally dominant for the study region as evidenced by a thickened crust

lithospheric deformation beneath the altyn tagh and west kunlun faults from recent gravity surveys 1 new gravity and topographic elevation data crossing the altyn tagh and west kunlun faults in northern tibet are used to test key features of a recently proposed tectonic model for the northern boundary of the tibetan plateau the observations collected in 1997 and 1998 at 468 stations along three profiles were converted to bouguer gravity anomalies to constrain flexural models for isostatic compensation of the large relief associated with these faults initially we failed to reproduce the main features of the gravity anomalies with any isostatic model that assumes that the main contribution to the observed gravity anomalies is from the flexure of the moho by integrating sedimentary information derived from exploration seismology in the tarim and qaidam basins we obtained satisfactory fits to the data using simple models of isostasy no elastic strength across the altyn tagh is required to fit the gravity data suggesting that the fault breaks the entire lithosphere beneath it and has negligible thrust component currently or in the past this result is consistent with tectonic models that create the thickened crust of northern tibet through thick skinned thrust sheets progressively overriding asia to the northeast as the altyn tagh behaving as a classic transform fault propagates in that direction farther west the gravity observations across the west kunlun are best explained by significant underthrusting of the high topography by an elastic plate with effective thickness between 30 and 40 km in agreement with geologic interpretation and modeling of earlier but very sparse gravity observations

moho undulations beneath tibet from grace integrated gravity data summary knowledge of the variation of crustal thickness is essential in many applications such as forward dynamic modelling numerical heat flow calculations seismologic applications and geohistory reconstructions we present a 3 d model of the moho undulations over the entire tibetan plateau derived from gravity inversion the gravity field has been obtained by using the gravity recovery and climate experiment grace potential field development which has been integrated with terrestrial data and is presently the best available in the studied area for the effective use of the global geopotential model that has no height information of observation stations upward continuation is applied the moho model is characterized by a sequence of troughs and ridges with a semi regular pattern which could reflect the continent continent collision between the indian and eurasian plates the three deep moho belts troughs and shallow moho belts ridges between them are clearly found to have an e w directional trend parallel to the border of the plateau and tectonic lines while variation of the directionality is observed in central to southeast tibet to describe the distinctive shape of the moho troughs beneath tibet we introduce the term moho ranges the most interesting aspects of the moho ranges are 1 that they run in parallel with the border and tectonic sutures of the plateau 2 that the distances between ranges are found at regular distances of about 330 km except in northeast tibet and 3 that the splitting of the ranges into two branches is found as the distance between them is increasing from our study we conclude that the distinctive undulations of the tibetan moho have been formed by buckling in a compressional environment superimposed on the regional increase in crustal thickness according to our analysis the grace satelliteonly data turns out to have good enough resolution for being used to determine the very deep moho beneath tibet our moho model is the first one that covers the entire plateau

an overview of the earth crust under china abstract we assess the results of a number of deep seismic soundings performed in china over the last few decades and study the variations in crustal structure in 18 tectonic units comprised of three platforms and 15 fold systems thickness data on 344 mesozoic cenozoic sedimentary basins as well as data on moho depth are collected in order to discuss the relationship between the thickness of the basins and the average thickness of the consolidated crust in each tectonic unit the degree of mirror image symmetry between mesozoic cenozoic sedimentary basins and the uplifting topmost parts of the mantle is herein analyzed using deep geophysical data on sedimentary basins by applying standard methods of least squares analysis to both datasets we have obtained both the average thickness of the consolidated crust and the mirror image symmetry factor for every platform and tectonic fold system thereby allowing us to explore the correlation between the depths of the bottom of the sedimentary basins and the top of the uplifting mantle the thickness of the consolidated crust in china is found to be between 20 and 63 km following a pattern of gradual thickening from east to west expressed in terms of spatial seismicity and the concentration of seismic energy and according to the sharing out of earthquake hypocenters in the top 80 km of the earth the rheology of the area does not appear to suit the widely accepted jelly sandwich model for the continents which does not seem to be entirely valid in china the findings on the mirror image symmetry factor show that this parameter varies mainly in the range 0 5 to 1 8 compared with each other tectonic unit most of the tectonic systems in china appear to be isostatically compensated tibet is an exception in that the symmetry factor is positive for the gangdise nyainqentanglha 1 0 and himalayan 0 1 fold systems implying that these tectonic zones are far from being in the isostatic equilibrium of the other regions we have also analyzed the zoning characteristics through the logarithmic relationship ln r ln h a using the average thickness of the consolidated crust and the absolute value of the symmetry factor the key finding is that regardless of geographical location all the values of r h a for those sedimentary basins in which oil gas reservoirs have to date been found fall into the narrow range of values between 19 38 and 37 40 there is some appeal in a possible relationship involving the ratio of crustal thickness to symmetry factor more so when the results obtained appear to suggest a prognostic tool for exploratory practice in relation to oil gas reservoirs

seismic images of crust and upper mantle beneath tibet evidence for eurasian plate subduction seismic data from central tibet have been combined to image the subsurface structure and understand the evolution of the collision of india and eurasia the 410 and 660 kilometer mantle discontinuities are sharply defined implying a lack of a subducting slab beneath the plateau the discontinuities appear slightly deeper beneath northern tibet implying that the average temperature of the mantle above the transition zone is about 300 c hotter in the north than in the south there is a prominent south dipping converter in the uppermost mantle beneath northern tibet that might represent the top of the eurasian mantle lithosphere underthrusting the northern margin of the plateau

reconstruction of the altyn tagh fault based on u pb geochronology role of back thrusts mantle sutures and heterogeneous crustal strength in forming the tibetan plateau 1 reconstructing deformation along the northwestern margin of the tibetan plateau is critical for evaluating the relative importance of microplate versus continuum models of the indo asian collision questions regarding this margin s evolution are as follows 1 what is the total offset along the sinistral altyn tagh strike slip system 2 how has that offset been absorbed in the western kunlun shan 3 why does the n s width of the plateau vary along strike ion microprobe u pb zircon apparent ages of 17 plutons from nw tibet together with regional geologic observations define a discrete e w trending boundary between two tectonic belts that has been offset along the altyn tagh system by 475 70 km kinematic arguments indicate that this offset cannot be the result of north directed thrusting in the western kunlun shan therefore we propose that south directed faulting in the tianshuihai thrust belt both offset the tectonic boundary and produced the asymmetry in the plateau shortening appears to have been absorbed in the upper crust by thin skinned thrusting in the middle lower crust by east directed ductile flow and or subduction and in the mantle by north dipping subduction factors controlling the formation of the south directed thrust system appear to be the contrast between the rigid tarim and the weaker songpan ganzi flysch belt and a mantle suture inherited from late paleozoic subduction the evolution of western tibet leads to a view of continental deformation that integrates elements of the microplate model e g plate like mantle and crust mantle decoupling with aspects of the continuum model weak crustal flow beneath the plateau

density and magnetic intensity of the crust and uppermost mantle across the northern margin of the tibetan plateau abstract recently we have processed the gravitational and geomagnetic data from a geophysical survey along a profile baicheng to da qaidam which crosses the northern and eastern tarim basin the altyn tagh mountains and the qaidam basin respectively based on the p and s wave velocities zhao et al 2006 both the density and magnetic intensity of the crust and uppermost mantle were determined by using a joint inversion of gravity versus geomagnetism our new results at the northern margin of the tibetan plateau reflect different crustal structures beneath tarim basin and qaidam basin and these two basins may be produced by different terranes in addition strong deformation has occurred in the basement and interior of the qaidam basin during the tectonic evolution

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

a thin viscous sheet model for continental deformation summary for the purposes of describing its large scale and long term deformation the continental lithosphere is regarded as a continuum obeying a newtonian or a power law rheology the flow of a thin sheet of power law material overlying an inviscid substrate is studied under the assumption that vertical gradients of the horizontal velocity are negligible a numerical model is used to investigate the deformation of such a sheet under conditions approximating those of continent continent collision the material flows in response to forces applied to its boundaries for example the indenting of one continent by another and to forces in its interior arising from gradients in crustal thickness the horizontal divergence of the flow produces changes in the crustal thickness and hence a time dependent form to the flow itself for a given set of boundary conditions the flow depends on the stress exponent in the power law rheology n and on the argand number which is a measure of the ratio between the stress arising from crustal thickness contrasts and the stress required to deform the material at the ambient strain rates when the effective viscosity of the medium is very high ar o crustal thickness variations do not influence the flow if the material is newtonian n l the deformation associated with an influx of material approximating an indenter is of much greater lateral dimension than the width of the indenter whereas when material has a power law rheology n 3 5 are used the deformation is confined to a region of lateral extent comparable to that of the indenter as ar increases the forces arising from crustal thickness contrasts exert more influence on the flow and the maximum crustal thickness that can be sustained by a given influx of material is related by a simple expression to the effective viscosity of the medium at the ambient strain rates in the limit of a very weak medium ar 10 the lithosphere is unable to sustain appreciable crustal elevation contrasts the results of these numerical experiments show that systems in which the effective viscosities are such that the maximum deviatoric stresses are between 1 kbar

on the flow of atlantic water and temperature anomalies in the nordic seas toward the arctic ocean the climatic conditions over the arctic ocean are strongly influenced by the inflow of warm atlantic water conveyed by the norwegian atlantic slope current nwasc based on sea surface height ssh data from altimetry we develop a simple dynamical measure of the nwasc transport to diagnose its spatio temporal variability this supports a dynamical division of the nwasc into two flow regimes the svinoy branch svb in the southern norwegian sea and the fram strait branch fsb west of spitsbergen the svb transport is well correlated with the ssh and atmospheric variability within the nordic seas factors that also affect the inflow to the barents sea in contrast the fsb is influenced by regional atmospheric conditions around svalbard and northern barents sea using a composite analysis we further relate anomalous strong svb flow events to temperature fluctuations along the core of atlantic water a warm composite anomaly is found to propagate northward with a tendency to amplify enroute after these events a roughly 12 months delayed temperature signal is identified in the fsb however also in the lofoten basin interior a delayed temperature signal is found which appears to originate from the nwasc this study suggests that hydrographic anomalies both upstream from the north atlantic and locally generated in the norwegian sea are important for the oceanic heat and salt transport that eventually enters into the arctic

numerical modeling of intraplate deformation simple mechanical models of continental collision we study a model of continental collision in which one of the continents acts as a rigid die indenting the other plate which flows as an incompressible viscoplastic medium we consider two extreme cases of plane deformation 1 plane strain which corresponds to an infinitely thick lithospheric plate and 2 plane stress corresponding to a very thin plate deformation of the lithosphere a thick plate should be intermediate between those extremes we found that the flow in the plane strain case is quite similar to that obtained by slip line theory the plane stress results are quite different since in this case most of the plate shortening is taken up by the thickening of the lithosphere we also explored the role of boundary conditions on the flow in particular the role of the side walls containing the flow of the lithosphere in the case of a free lateral boundary the main feature is a flow of matter toward this free wall and a s like pattern for the horizontal stress field for a rigid wall on the other hand the plane strain and the plane stress results are quite different in the first case there is a large return flow on the sides of the punch the material being extruded along the only free surface available in the plane stress case the return flow disappears and the material displaced by the penetration of the die tends to thicken the plate the role of a nonlinear constitutive relation is studied for power law creep as the power of the flow limit increases the flow retains its general features but the deformation localizes creating sharper contrasts between high and low strain rate areas in plane stress the effect of nonlinearity is to increase the contrasts in vertical motion available data for asia are discussed in the light of the new results

crustal structure of the northeastern tibetan plateau from the southern tarim basin to the sichuan basin china abstract we present a new crustal cross section of the northeastern tibetan plateau based on active source seismic data recorded along a 1600 km long profile crossing the southern tarim basin the western flank of the south qilian shan the northeastern margin of qaidam basin east kunlun shan songpan ganzi terrane and sichuan basin the crustal p and s wave velocity structure and poisson s ratio outline the seismic characteristics of the crust and provide constraints on the crustal composition the derived crustal cross section shows several significant features 1 the crustal thickness varies considerably along this profile from 48 km to 70 km 2 north of the kunlun fault variations in total crustal thickness are mainly caused by variations in lower crustal thickness whereas south of the kunlun fault they are caused by thickness variations throughout the crust 3 north of the kunlun fault we detect a mid crustal low velocity zone that is not apparent south of the fault 4 the kunlun fault seems to act as a compositional boundary for the lower crust with a poisson s ratio of 0 29 north of the fault kunlun qaidam terrane and 0 26 south of the fault songpan ganzi terrane measured poisson s ratio and p wave velocity values suggest that the lower crust throughout the tibetan plateau south qilian shan margins of the qaidam basin east kunlun shan songpan ganzi terrane is of intermediate composition thus the ne tibetan plateau along our profile is missing a mafic lower crustal layer

moho offset across the northern margin of the tibetan plateau anomalous double pulse teleseismic p wave arrivals were observed at one station near the northern margin of the tibetan plateau the azimuthal dependence of the waveform distortion and its absence at nearby stations indicated that the distortion was produced by receiver side crustal heterogeneity modeling of the three component data revealed a 15 to 20 kilometer moho offset that occurs over a narrow lateral range of less than 5 kilometers this east west striking offset separates the thick tibetan plateau crust from the qaidam basin crust such a sharp crustal thickness change implies a weak tibetan plateau crust that thickens vertically in response to penetration by india from the south and to blockage caused by a strong qaidam basin crust to the north

tomographic evidence for localized lithospheric shear along the altyn tagh fault seismic tomography across the altyn tagh fault at the north edge of the tibetan plateau reveals a low p wave velocity anomaly below the fault down to 140 kilometers this anomaly probably reflects strike slip shear in the lithosphere slip partitioning may also induce a wedge of crust from the tarim basin to plunge into the mantle

tectonic history of the altyn tagh fault system in northern tibet inferred from cenozoic sedimentation the active left slip altyn tagh fault defines the northern edge of the tibetan plateau to determine its deformation history we conducted integrated research on cenozoic stratigraphic sections in the southern part of the tarim basin fission track ages of detrital apatites existing biostratigraphic data and magnetostratigraphic analysis were used to establish chronostratigraphy whereas composition of sandstone and coarse clastic sedimentary rocks was used to determine the unroofing history of the source region much of the detrital grains in our measured sections can be correlated with uplifted sides of major thrusts or transpressional faults implying a temporal link between sedimentation and deformation the results of our studies together with existing stratigraphic data from the qaidam basin and the hexi corridor suggest that crustal thickening in northern tibet began prior to 46 ma for the western kunlun shan thrust belt at ca 49 ma for the qimen tagh and north qaidam thrust systems bounding the north and south margins of the qaidam basin and prior to ca 33 ma for the nan shan thrust belt these ages suggest that deformation front reached northern tibet only 10 5 m y after the initial collision of india with asia at 65 55 ma because the aforementioned thrust systems are either termination structures or branching faults of the altyn tagh left slip system the altyn tagh fault must have been active since ca 49 ma the altyn tagh range between the tarim basin and the altyn tagh fault has been a long lived topographic high since at least the early oligocene or possibly late eocene this range has shed sediments into both the tarim and qaidam basins while being offset by the altyn tagh fault its continuous motion has made the range act as a sliding door which eventually closed the outlets of westward flowing drainages in the qaidam basin this process has caused large amounts of oligocene miocene sediments to be trapped in the qaidam basin the estimated total slip of 470 70 km and the initiation age of 49 ma yield an average slip rate along the altyn tagh fault of 9 2 mm yr remarkably similar to the rates determined by gps global positioning system surveys this result implies that geologic deformation rates are steady state over millions of years during continental collision

crustal structure across the altyn tagh range at the northern margin of the tibetan plateau and tectonic implications wepresentnewseismicrefraction wide angle reflection dataacrossthealtyntaghrangeanditsadjacentbasins wefindthatthe crustal velocity structure and by inference the composition of the crust changes abruptly beneath the cherchen fault i e 100 km north of the northern margin of the tibetan plateau north of the cherchen fault beneath the tarim basin a platform type crust is evident in contrast south the cherchen fault the crust is characterized by a missing high velocity lower crustal layer our seismic model indicates that the high topography 3 km of the altyn tagh range is supported by a wedge shaped region with a seismic velocity of 7 6 7 8 km s that we interpret as a zone of crust mantle mix we infer that the altyn tagh range formed by crustal scale strike slip motion along the north altyn tagh fault and northeast southwest contraction over the range the contraction is accommodated by 1 crustal thickening via upper crustal thrusting and lower crustal flow i e creep and 2 slip parallel swdirected underthrusting of only the lower crust and mantle of the eastern tarim basin beneath the altyn tagh range d 2005 elsevier b v all rights reserved

rate of left lateral movement along the easternmost segment of the altyn tagh fault east of 96 e china summary field work carried out in gansu province and complemented with analysis of spot panchromatic scenes allows us to characterize the deformations along the eastern segment of the altyn tagh fault and to place bounds on its holocene left slip rate east of 96 e the long term left lateral offset of stream channels alluvial fans and terrace edges is about 50 m these offsets are most probably of holocene age 12 2 ka and imply that the corresponding derived slip rate is 4 2 mm yr 1 this observation is consistent with a north eastward along strike decreasing slip rate on the altyn fault due to partitioning of slip on multiple more easterly trending splays

a model of the crust and mantle structure down to 700 km depth beneath the lhasa to golmud transect across the tibetan plateau as derived from seismological data abstract a 700 km deep seismic velocity cross section beneath the lhasa to golmud transect across the tibetan plateau is presented in contrast to the first version of this cross section which comprised an 800 km wide swath centred on the lhasa to golmud transect due to the recent proliferation of publications concerning the mantle structure beneath tibet this study is based only on seismic profiles which either run along or cross the transect and arrays or studies which at least partly cover the transect the results from the recent indepth iv project indicate that the crustal thickness change from 70 km beneath the songpan ganzi terrane and kunlun mountains to 54 km beneath the qaidam basin is located about 100 km north of the kunlun fault and almost 45 km north of the north kunlun thrust the qaidam basin moho is underlain by crustal velocity material for almost 45 km and the apparently overlapping crustal material may represent songpan ganzi lower crust underthrusting or flowing northward beneath the qaidam basin moho thus the high tibetan plateau may be thickening northward into south qaidam as its weak thickened lower crust is injected beneath the stronger qaidam crust beneath the crust high velocity dense cold indian lithospheric mantle extends northwards until about the banggong nujiang suture northwards asian lithospheric mantle is overlain by a low velocity less dense warm tibetan plate consisting of an upper lithospheric and a lower asthenospheric part the apparent northwards deepening of the 410 and 660 km discontinuities by about 20 km implies that the upper mantle beneath north tibet is slower less dense and warmer than under south tibet in agreement with the observed uppermost mantle velocities this in turn could provide some of the isostatic support for the high elevations in the north where the crust is somewhat thinner than in the southern plateau

subduction and accretionary tectonics of the east kunlun orogen western segment of the central china orogenic system abstract the kunlun orogen is generally divided into the east kunlun orogenic belt e kob and the west kunlun orogenic belt w kob by the altyn tagh fault the e kob forms part of the western segment of the central china orogenic system ccos and is considered to have formed by the collision between the qaidam block and qiangtang or bayanhar terrane as a consequence of the closure of the kunlun ocean branch of the paleo tethyan ocean based on a compilation recently published high quality data this contribution provides an overview of the composition nature and ages of the principal tectonic elements including ophiolitic melanges and related volcanic rocks intrusive plutons and sedimentary cover sequences in the e kob according to multiple lines of evidence from these tectonic elements we proposed herewith a paleozoic triassic subduction and accretionary tectonic model to interpret the spatiotemporal tectonic framework plate subduction polarity and tectonic processes from accretion to collision of the e kob three main ophiolitic melange zones are identified in the e kob from north to south they are the qimantagh xiangride ophiolitic melange zone qxm the aqikekulehu kunzhong ophiolitic melange zone akm and the muztagh buqingshan anemaqen ophiolitic melange zone mbam according to these ophiolitic melange zones the e kob is divided into four major tectonic units the north qimantagh belt the central kunlun belt the south kunlun belt and the bayanhar terrane based on several lines of evidence from geology geochemistry and geochronology the south kunlun belt is interpreted as a paleozoic to triassic fore arc and accretionary complex related to northward subduction of the kunlun ocean during the ordovician triassic time the akm mabm and the south kunlun belt constitute a wide accretionary complex along the kunlun suture zone that marks final closure of the major paleo tethyan ocean while the qxm represents the best expression of another suture that records final closure of the qimantagh back arc basin the central kunlun belt as a long lived island arc terrane from ordovician to triassic times rifted from the qaidam block due to the spreading of the qimantagh back arc basin during the period of ca 485 425 ma taken into all the geological geochemical and geochronological lines of evidence together a trench arc back arc basin tectonic system in the e kob was built up and evolved into a protracted and long lived northward subduction and accretion along the kunlun suture during paleozoic and triassic time

tectono magmatic rejuvenation of the qaidam craton northern tibet abstract ascertaining the enigmatic characteristics of the crystalline basement of the qaidam basin the deepest intracontinental basin yet located in the highest orogenic plateau with the thickest continental crust has broad implications for the cenozoic basin evolution in particular and intracontinental tectonics of asia in general we carried out a comprehensive investigation on the ages and geochemical isotopic characteristics of the qaidam and suganhu basement rocks obtained from drill cores petrological observations and u pb zircon dating la icp ms of granitoid samples from drill cores indicate that early neoproterozoic early paleozoic and late paleozoic mesozoic intrusions are largely represented suggesting that the qaidam and suganhu blocks were involved into three tectono magmatic episodes similar whole rock geochemistry and sr nd isotopic characteristics between the early neoproterozoic granitoids beneath the qaidam basin and the contemporaneous basement rocks in the surrounding orogenic belts confirm the existence of pervasive early neoproterozoic metamorphism and magmatism along the present day northern tibetan plateau by comparing the trace and rare earth elements patterns as well as the sr nd compositions of the ordovician arc related granitoids and silurian devonian post collisional granitoids beneath the qaidam and suganhu basins with the corresponding granitoids from the surrounding orogenic belts we assert that the proto tethys subduction events that were recorded within the eastern kunlun altyn tagh and the qilian shan orogenic belts were different they generated distinctive subduction related arc magmas whereas the closure of the oceanic basins resulted in the amalgamation of the orogenic belts inducing subsequent extensive post collisional magmatism within the qaidam block the widespread permian and triassic granitoids beneath the northwestern northern qaidam basin mainly involved a lower crust or a crust mantle source including mesoproterozoic crust they demonstrate that the influence of the paleo tethys evolution penetrated the qaidam block northwards reaching to the northern edges of the block we conclude that the qaidam block is not a craton as typical as the rigid tarim block but pertains to a tectono magmatic rejuvenated craton which is not mechanically stronger than its surrounding regions however trapped between the lithospheric left lateral strike slip altyn tagh fault system to the northwest and the qilian shan transpressional system to the northeast the qaidam block forms a relatively stable domain that escaped from significant cenozoic deformation

a twenty year reversal in water mass trends in the subtropical north atlantic temperature and salinity changes have been compared along three repeat sections at 36 n in the north atlantic the principal changes cooling of the upper waters and warming of the intermediate waters observed between 1959 and 1981 were reversed between 1981 and 2005 the controlling mechanisms for the changes over the two time periods differed through the water column neutral density surfaces over the upper 800 m were firstly uplifted and secondly depressed by typically 50 m which is broadly consistent with the changes in thermocline thickness implied by the temporal changes in ekman pumping in contrast the intermediate waters 800 2500 m firstly became warmer and saltier and secondly became cooler and fresher this change in the intermediate waters was controlled by water mass changes along neutral density surfaces suggesting a change in the source waters principally labrador sea water and mediterranean outflow water

seismic evidence for stepwise thickening of the crust across the ne tibetan plateau we performed a receiver function analysis on teleseismic data recorded along two 550 km long profiles crossing the northeastern tibetan plateau results from time to depth migration grid search vp vs determination and simulated annealing inversion of waveforms reveal that the crust thickens from 50 km near the northern edge of the plateau to 80 km south of the jinsha suture in the qiang tang block crustal thickening occurs in staircase fashion with steps located beneath the main reactivated sutures the vp vs ratio close to the global continental average does not suggest widespread partial melting but rather a more usual separation between an upper felsic and a lower mafic part within the northeastern tibetan crust

observations of water mass transformation and eddies in the lofoten basin of the nordic seas abstractthe lofoten basin of the nordic seas is recognized as a crucial component of the meridional overturning circulation in the north atlantic because of the large horizontal extent of atlantic water and winter surface buoyancy loss in this study hydrographic and current measurements collected from a mooring deployed in the lofoten basin from july 2010 to september 2012 are used to describe water mass transformation and the mesoscale eddy field winter mixed layer depths mlds are observed to reach approximately 400 m with larger mlds and denser properties resulting from the colder 2010 winter a heat budget of the upper water column requires lateral input which balances the net annual heat loss of 80 w m 2 the lateral flux is a result of mesoscale eddies which dominate the velocity variability eddy velocities are enhanced in the upper 1000 m with a barotropic component that reaches the bottom detailed examination of two eddies from april and august 2012 highlights the variability of the e

dilution of the northern north atlantic ocean in recent decades declining salinities signify that large amounts of fresh water have been added to the northern north atlantic ocean since the mid 1960s we estimate that the nordic seas and subpolar basins were diluted by an extra 19 000 5000 cubic kilometers of freshwater input between 1965 and 1995 fully half of that additional fresh water about 10 000 cubic kilometers infiltrated the system in the late 1960s at an approximate rate of 2000 cubic kilometers per year patterns of freshwater accumulation observed in the nordic seas suggest a century time scale to reach freshening thresholds critical to that portion of the atlantic meridional overturning circulation

oblique stepwise rise and growth of the tibet plateau two end member models of how the high elevations in tibet formed are i continuous thickening and widespread viscous flow of the crust and mantle of the entire plateau and ii time dependent localized shear between coherent lithospheric blocks recent studies of cenozoic deformation magmatism and seismic structure lend support to the latter since india collided with asia 55 million years ago the rise of the high tibetan plateau likely occurred in three main steps by successive growth and uplift of 300 to 500 kilometer wide crustal thrust wedges the crust thickened while the mantle decoupled beneath gently dipping shear zones did not sediment infilling bathtub like of dammed intermontane basins formed flat high plains at each step the existence of magmatic belts younging northward implies that slabs of asian mantle subducted one after another under ranges north of the himalayas subduction was oblique and accompanied by extrusion along the left lateral strike slip faults that slice tibet s east side these mechanisms akin to plate tectonics hidden by thickening crust with slip partitioning account for the dominant growth of the tibet plateau toward the east and northeast

continental transforms a view from the alpine fault abstract continental transform faults are dominantly highly localized strike slip shear zones hundreds of kilometers long that accumulate tens to hundreds of kilometers of displacement from work on the alpine fault we pose the questions what is the deep structure of a continental transform and how does the displacement become localized we review research on the alpine fault and propose a model in which the fault partitions at depth into a steep zone extending into the mantle with largely fault parallel motion and a flat ductile decollement in the lower crust the fault localizes around two thirds of the plate motion within a 100 km wide zone of distributed deformation a review of other active continental fault systems suggests that variation between them may reflect their tectonic origins the nature of the crust in which they develop the presence of a significant oblique component of motion and the displacement rate all however have evidence for the development of a single principal fault zone that carries 50 of the total displacement and extends as a localized zone of shear into the upper mantle we review mechanisms of strain weakening and suggest that localization of a principal fault may be initiated in the seismogenic crust and through a series of positive feedbacks eventually extend through the lower crust into the upper mantle

on the spatial coherence of the atlantic water inflow across the nordic seas the co variability of the atlantic water aw branches in the nordic seas is investigated over the period 1979 2012 using an eddy permitting model a noticeable circulation change is found in the mid 1990s prior to the mid 1990s the leading mode of variability defines a large scale pattern with concomitant variations in the atlantic water aw inflow in the faroe shetland channel fsc the norwegian atlantic slope current nwasc the aw inflow to the barents sea and the west spitsbergen current wsc after the mid 1990s the co variability between the nwasc and the aw inflow in both the fsc and the wsc is lost consequently the northern barents sea circulation anomaly pattern which is present throughout the full period becomes the leading mode of circulation in the northern nordic seas after the mid 1990s the circulation change of the mid 1990s appears to be linked to a weakening of the southwesterly wind anomalies in norwegian sea as the northern center of action of the first mode of sea level pressure nao weakens passive tracer experiments suggest that this circulation change may be accompanied by increased heat transfer from the aw current to the interior nordic seas this in turn may have limited the influence of the recently observed aw warming in the iceland scotland passage on the nwasc downstream

crustal structure beneath china from receiver function analysis 1 we collected and processed a large amount of high quality broadband teleseismic waveform data recorded by the 48 chinese national digital seismic network stations to estimate large scale lateral variations of crustal thickness and vp vs ratio hence poisson s ratio beneath china a statistical method was used to select mutually coherent receiver functions at each station which yielded over 200 traces for most of the stations with the conventional h the crustal thickness and vp vs ratio approach there is a large trade off between h and consequently multiple maxima are frequently observed in the h domain we introduced a weight function that measures the coherence between the p to s conversion and the reverberation phases at each h grid to reduce the trade off a 4th root stacking method was further applied to reduce uncorrelated noise relative to the linear stack these modifications turned out to be very effective in reducing the h trade off and yielded reliable estimates of crustal thickness and vp vs ratio the crust beneath eastern china is as thin as 31 33 km and the underlying moho is relatively flat and sharp in the western part of china the crust is considerably thicker and shows large variations the moho is observed at about 51 km depth along the tian shan fold system and about 84 km deep beneath the central part of the tibetan plateau the transition occurs at the so called n s belt between about 100 and 110 e which is featured by unusually high seismicity and large gravity anomalies the average vp vs ratio over the mainland china crust is about 1 730 0 249 significantly lower than the global average 1 78 0 27 of the continental crust this lower vp vs ratio may suggest a general absence of mafic lowermost crustal layer beneath china

geologic evolution of northern tibet results of an expedition to ulugh muztagh a reconnaissance expedition across the northern margin of the tibetan plateau revealed evidence of a late cenozoic northward progression of the locus of crustal shortening and therefore of a northward growth of the area encompassed by the plateau active reverse faults crop out at the foot of the altyn tagh on the northern edge of the plateau and at the bases of several ranges within the altyn tagh and kunlun where the elevations of the neighboring basins are less than 4000 meters farther south where elevations are higher there was no evidence of recent faulting but late cenozoic rock in the ayak kum kol basin has been strongly folded south of this basin ulugh muztagh apparently the highest mountain in the eastern kunlun is underlain by late miocene tourmaline bearing and two mica granite these rocks suggest that thickening of continental crust had begun in this area by late miocene time overlying quartz sanidine welded tuffs of pliocene age imply that uplift and erosion occurred between miocene and pliocene time but with little subsequent erosion in addition we found an east west trending belt of mafic and ultramafic rock that probably marks a suture of a crustal fragment with southern asia in triassic or more recent time

receiver function imaging of the lithosphere at the kunlun qaidam boundary northeast tibet abstract we studied the crustal structure and tectonics in the north tibetan plateau from the songpan ganzi terrane to the qaidam basin using teleseismic receiver function imaging across a major lithospheric boundary the kunlun qaidam boundary where previous studies suggest a 15 20 km change in crustal thickness from thicker crust in the kunlun mountains to thinner crust in the qaidam basin we report p receiver functions for 70 stations largely the international deep profiling of tibet and the himalaya indepth phase iv experiment our most dense station coverage is located along the roughly north south indepth iv active source seismic profile at approximately 95 e longitude azimuthal and geographical changes in the receiver functions reveal significant changes in crustal structure and vp vs from across the study area receiver functions show strong converters that we interpret as the moho at 70 km depth beneath the qiangtang songpan ganzi terranes and kunlun mountains and at 50 km depth beneath the central qaidam basin this large change in crustal thickness occurs 50 km north of the north kunlun strike slip fault on which the 2001 m8 1 kunlun earthquake occurred receiver functions for some of the stations north of the thickness change at the kunlun qaidam boundary also show a deeper 70 km bright converter in addition to the 50 km converter the two converters appear to overlap by up to 30 km in some locations along the south qaidam basin we combine previous results with these new results to discuss implications for mechanisms for crustal thickening in the north tibetan plateau including crustal flow and crustal injection at depths imaged here shallower than 100 km we see no evidence of southward subduction of eurasian lithosphere

cenozoic shortening budget for the northeastern edge of the tibetan plateau is lower crustal flow necessary 1 two of the most popular mechanisms for thickening the crust beneath the tibetan plateau are 1 pure shear with faulting and folding in the upper crust and horizontal shortening below and 2 flow of lower or middle crust without significant shortening of the upper crust to help discriminate between the relative contributions of these two mechanisms well constrained estimates of upper crustal shortening are needed here we document the cenozoic shortening budget across the northeastern tibetan plateau margin with several balanced cross sections that exploit thermochronological and magnetostratigraphic constraints these sections indicate 11 2 1 east west shortening since middle miocene time and 9 2 3 nne ssw shortening between middle eocene and middle miocene times with little subsequent shortening of this orientation shortening rates accelerate fivefold after middle miocene time given the present day crustal thickness of 56 4 km in northeastern tibet crustal restorations that remove cenozoic shortening suggest that the northeastern tibetan crust was 45 5 km thick prior to the india asia continental collision this precollision thickness estimate is equivalent to average continental crustal thicknesses both adjacent to the tibetan plateau 44 4 km and globally 41 6 km and suggests that pure shear alone may account for cenozoic crustal thickening in northeastern tibet in contrast to eastern tibet where in the absence of significant shortening structures crustal flow has been invoked to explain the addition of crustal material since middle miocene time our results may obviate lower crustal flow as a necessary crustal thickening agent in northeastern tibet

present day kinematics of asia derived from geologic fault rates active fault geometry available quaternary rates on major faults and the far field plate motion are used to determine crustal kinematics in the collision zone between india and asia using a finite element formalism to construct a spherical shell model of the asian continent with embedded faults we seek a velocity solution approaching the motion of rigid blocks by minimizing the elastic strain energy in the fault bounded blocks by doing so we test the assumption that long term deformation within continents is mostly localized into major faults in the solution fault motion accounts for more than 80 of the deformation allowing us to describe our velocity model in terms of quasi rigid block rotations on the sphere south china is rotating clockwise about a pole located southwest of borneo implying an e ese velocity vector of 11 mm yr for a point at shanghai in agreement with the velocity vector determined by very long baseline interferometry heki et al 1995 the eastward movement of south china is accommodated by oblique extension along the red river fault at a rate of 10 5 mm yr in the south and by the combination of left lateral strike slip motion on the qinling dabie shan fault and the counterclockwise rotation of the ordos and adjacent blocks in the north the tarim rotates clockwise with respect to dzungaria about a pole located at 44 n 92 e consistent with increasing crustal shortening toward the west throughout the tien shan assuming incompressibility a crustal volume budget over a domain encompassing the tertiary mountain ranges in asia shows that over the last 10 000 years 73 4 of the north south shortening between india and asia has been absorbed by thickening of the lithosphere and 27 has been accommodated by lateral extrusion of continental blocks the present day predominance of thickening in asia results from the relatively slow eastward motion of south china controlled by strike slip faulting in the qinling shan and oblique extension in northeastern china

large scale crustal deformation of the tibetan plateau the topography velocity and strain fields calculated from a three dimensional newtonian viscous model for large scale crustal deformation are generally in good agreement with results from geological geodetic and earthquake studies in and around the tibetan plateau provided that the model rheology incorporates a weak zone within the deep crust beneath the plateau equivalent to a viscosity of 1012 pa s within a 250 m thick channel or 1018 pa s within a 15 km thick channel model studies and observations show a plateau at 5 km elevation with steep topographic gradients across the southern and northern plateau margins and more gentle gradients across the southeastern and northeastern margins rapid shortening strain is concentrated along the lower portions of the northern and southern plateau margins at rates 20 mm yr model results show north south shortening 10 mm yr in reasonable agreement with gps data 5 8 mm yr of north south shortening across the northern two thirds of the plateau and east west stretching 10 15 mm yr across the eastern half of the high plateau in reasonable agreement with seismic geologic and gps data upper crustal material moves eastward from the plateau proper into a lobe of elevated topography that extends to the south and east clockwise rotation of material around the east himalayan syntaxis at rates up to 10 mm yr occurs partly as a result of dextral shear between indian and asian mantle at depth and partly as a result of gravitational spreading from the high plateau to the south and east there is little difference in model surface deformation for assumptions of moderately weak or extremely weak lower crust except in southern and northern tibet where margin perpendicular extension occurs only for the case of an extremely weak lower crust our results suggest that the tibetan plateau is likely to have gone through a two stage development the first stage produced a long narrow high orogen whose height may have been comparable to the modern plateau the second stage produced a plateau that grew progressively to the north and east east west stretching eastward plateau growth and dextral rotation around the east himalayan syntaxis probably did not begin until well into the second stage of plateau growth perhaps becoming significant after 20 m y of convergence

teleseismic imaging of subducting lithosphere and moho offsets beneath western tibet teleseismic images suggest that the tarim plate plunges 45 s down to 300 km depth beneath nw tibet the 410 km discontinuity shallows by 10 km under the plateau implying 100 c cooler upper mantle the deepest moho on record 90 km lies under w qiangtang it rises abruptly by 20 and 10 km beneath the altyn tagh fault and bangong suture respectively vp vs ratios are normal except in the yecheng flexural basin and deep under the south karakax volcanics 1 92 w kunlun s neogene tectonics are simply accounted for by oblique subduction of lithospheric mantle beneath an upward extruding thrust wedge of the tarim crust

the freshening of surface waters in high latitudes effects on the thermohaline and wind driven circulations abstract the impacts of a freshening of surface waters in high latitudes on the deep slow thermohaline circulation have received enormous attention especially the possibility of a shutdown in the meridional overturning that involves sinking of surface waters in the northern atlantic ocean a recent study by fedorov et al has drawn attention to the effects of a freshening on the other main component of the oceanic circulation the swift shallow wind driven circulation that varies on decadal time scales and is closely associated with the ventilated thermocline that circulation too involves meridional overturning but its variations and critical transitions affect mainly the tropics a surface freshening in mid to high latitudes can deepen the equatorial thermocline to such a degree that temperatures along the equator become as warm in the eastern part of the basin as they are in the west the tropical zonal sea surface temperature gradient virtually disappears and permanently warm conditions prevail

the great salinity anomaly in the northern north atlantic 1968 1982 the widespread freshening of the upper 500 800m layer of the northern north atlantic which this paper describes represents one of the most persistent and extreme variations in global ocean climate yet observed in this century though a range of explanations have been advanced to explain this event including in situ changes in the surface moisture flux this paper describes the great salinity anomaly as largely though not entirely an advective event traceable around the atlantic subpolar gyre for over 14 years from its origins north of iceland in the mid to late 1960s until its return to the greenland sea in 1981 1982 the overall propagation speed around this subpolar gyre is estimated at about 3cm s 1 of the total salt deficit associated with the anomaly as it passed south along the labrador coast in 1971 1973 about 72 109 tonnes a deficit equivalent to about two thirds of this figure 47 109 tonnes ultimately passed through the faroe shetland channel to the barents sea arctic ocean and greenland sea during the mid 1970s possible effects on deep water formation and on the representativeness of historical section data are discussed

decadal spinup of the south pacific subtropical gyre abstract an increase in the circulation of the south pacific ocean subtropical gyre extending from the sea surface to middepth is observed over 12 years datasets used to quantify the decadal gyre spinup include satellite altimetric height the world ocean circulation experiment woce hydrographic and float survey of the south pacific a repeated hydrographic transect along 170 w and profiling float data from the global argo array the signal in sea surface height is a 12 cm increase between 1993 and 2004 on large spatial scale centered at about 40 s 170 w the subsurface datasets show that this signal is predominantly due to density variations in the water column that is to deepening of isopycnal surfaces extending to depths of at least 1800 m the maximum increase in dynamic height is collocated with the deep center of the subtropical gyre and the signal represents an increase in the total counterclockwise geostrophic circulation of the gyre by at least 20 at 1000 m a comparison of woce and

new paleomagnetic constraints on middle miocene strike slip faulting along the middle altyn tagh fault knowledge of the evolution of the altyn tagh fault atf has significant implications for our understanding of the tectonic deformation of the tibetan plateau controversy exists regarding the formation of the orocline like arcuate structures or curved thrust faults south of the atf in this paper we conducted a paleomagnetic rotation study of the akatengnengshan ak and youshashan yss anticlines to determine whether the changes in the anticlines axes were caused by frictional drag associated with sinistral strike slip faulting along the atf no significant paleomagnetic rotations during the last 20ma were observed at the xichagou and laomangai localities which are situated along the yss anticline whereas significant counterclockwise ccw rotations of similar to 50 degrees that occurred between similar to 16 2 and 11 1ma were noted at the yitunbulake locality which lies along the western edge of the ak anticline this amount of ccw rotation is consistent with the difference in axes between the ak and yss anticlines combined with other geological evidence we believe that the middle atf was active between similar to 16 and 11ma frictional drag associated with sinistral strike slip motion likely resulted in the similar to 50 degrees ccw rotation of the ak anticline which was originally straight or parallel to the yss anticline there was concentrated or insignificant strike slip faulting along the middle atf before similar to 16ma but rapid and distributed 40km strike slip faulting occurred between similar to 16 and 11ma at a rate of 10mm yr and the minimum displacement was similar to 50km

influence of the atlantic subpolar gyre on the thermohaline circulation during the past decade record high salinities have been observed in the atlantic inflow to the nordic seas and the arctic ocean which feeds the north atlantic thermohaline circulation thc this may counteract the observed long term increase in freshwater supply to the area and tend to stabilize the north atlantic thc here we show that the salinity of the atlantic inflow is tightly linked to the dynamics of the north atlantic subpolar gyre circulation therefore when assessing the future of the north atlantic thc it is essential that the dynamics of the subpolar gyre and its influence on the salinity are taken into account

teleseismic shear wave splitting and lithospheric anisotropy beneath and across the altyn tagh fault sixteen 3 component 5 sec stations along a profile crossing the altyn tagh fault atf at 90 e were used to measure shear wave splitting beneath tibet s northern edge splitting delay times t of 0 3 to 1 3 sec show a marked increase in a narrow zone centered on the fault implying anisotropy in the lithospheric mantle fast polarization directions fpd swing counterclockwise from a mean azimuth of 110 e in the qaidam basin south of the fault to a mean azimuth of 60 e in the altyn mountains this swing occurs in less than 40 km both the t increase and fpd swing are consistent with ductile sinistral shear along the 40 km wide low p wave velocity anomaly 6 8 imaged to a depth of 140 km beneath the fault by teleseismic tomography this confirms that the atf guides the northeastwards extrusion of the tibet qaidam s lithosphere relative to the tarim s

seismic image of the tarim basin and its collision with tibet a broadband seismic deployment in 1998 1999 in southwestern tarim provided data for imaging the crust and upper mantle across the contact between the tarim block and the tibetan plateau a profile composed of migrated teleseismic receiver functions clearly shows lateral structural changes the crust under the tarim basin is relatively simple the moho discontinuity is mapped at a depth of 42 km near the northern end of the array and dips gently toward the south to 50 km under the kunlun foreland the tarim basin appears to be rigid with little shortening farther to the south the imaging reveals a complex of reflectors in the lower crust and the upper mantle there are both north and south dipping upper mantle structures under the kunlun foreland and kunlun shan region we found the observations to be more consistent with a model of lithospheric collision in which the crust and the upper mantle on both sides interpenetrate and deform

formation and re orientation of the suerkuli basin within the altyn tagh in northeastern tibetan plateau since late miocene abstract the altyn tagh fault atf had formed in eocene time however the temporal evolution of slip along the fault remains elusive despite its important role in governing growth of the tibetan plateau tp and evaluating models of continental lithosphere deformation here we perform a high resolution magnetostratigraphic study on neogene sediments from the suerkuli basin a small basin located between two active strands of the atf results show that both depositional environment and the sedimentation rate changed at about 5 4 and 6 ma respectively lithofacies shift from conglomerates and sandstones with parallel and cross beddings to mudstones with horizontal bedding suggesting a sedimentary fluvial to lacustrine depositional environment shift even aridification increased over northern china from the tarim basin to the qaidam basin during late miocene to early pliocene times lacustrine deposition had started in the suerkuli basin still we argue that an increase in slip rate along the atf triggered concurrently forming of the intermontane basin the inferred timing of increased slip rate on the atf coincides with a variation in movement of the indian plate relative to eurasian plate since late miocene early pliocene time our work suggests that a re orientation of crustal shortening and deformation in the northern tp began since late miocene and supports the idea that the modern boundary of the tp orogen had rejuvenated to adjust deformation in plate boundary conditions

northward growth of the qimen tagh range a new model accounting for the late neogene strike slip deformation of the sw qaidam basin abstract situated along the western termination of the eastern kunlun mountains the qimen tagh range represents a key area to understand the cenozoic basin range interactions between the northeastern tibetan plateau and the qaidam basin within that region several huge bow like fault systems such as the kunbei and qimen tagh fault systems accommodate the transpressive deformation but their kinematic evolution is still highly debated newly acquired seismic profiles and isopach maps of the late eocene sediments strongly suggest that the kunbei fault system consisting of the kunbei arlar and hongliuquan faults in the southwestern qadaim basin was initially a left lateral strike slip fault system rather than a thrusting system growth strata indicate an early miocene onset age for this strike slip deformation however earthquake focal mechanisms show that the present day tectonic pattern of this fault system is dominated by ne sw transpression as for the qimen tagh fault system numerous linear geomorphic features and fault scarps indicate that it was again a strike slip fault system deformed sediments within the adatan valley prove that strike slip motion prevailed during the pleistocene yet the present day deformation is marked by ne sw transpression collectively the kunbei and qimen tagh fault systems were initially left lateral strike slip fault systems that formed during early miocene and pleistocene respectively colligating with these southward younging left lateral strike slip faulting ages and the fact that these convex northward structures converge to the center segment of active kunlun fault in the east we thus considered the kunbei and qimen tagh fault systems as former western segments of the kunlun fault once located further south in the present day location of that fault these faults gradually migrated northward since the early miocene while their kinematics changed from left lateral strike slip motion to ne sw transpression

phase velocity structure from rayleigh and love waves in tibet and its neighboring regions deep geodynamic processes involved in the continental collision between india and asia are still controversial to address this issue phase velocities of 619 rayleigh waves and 254 love waves have been inverted by using an anisotropic tomographic technique such a technique enables us not only to retrieve phase velocity distributions but also to map azimuthal anisotropy on a large scale only phase velocity anomalies in the period range 50 200 s are dealt with here but the azimuthal anisotropy has been taken into account in the inversion process moreover because of the important influence of shallow layers on the inversion results an inversion of phase velocities corrected for shallow layers has been performed to correct raw phase velocities the 3smac crust heterogeneous reference earth model has been used the comparison of phase velocity distributions for love and rayleigh waves with and without corrections of surficial layers implies that much of the low velocity zone visible at short periods in central tibet can be explained by unusually thick crust at periods longer than 100 s tibet is overall characterized by high velocity anomalies such anomalies seem to converge toward the center of the plateau as period increases we conclude that the phase velocity structure beneath tibet results at short periods from thick crust and possible partial melting in the uppermost lithosphere and at long periods from the inward plunge of the cold lithospheric mantle surrounding the high plateau

generation and stability of a quasi permanent vortex in the lofoten basin abstract in the nordic seas the lofoten basin is a region of high mesoscale activity the generation mechanism and the conditions for the stability of a quasi permanent vortex in the center of the lofoten basin are studied with a high resolution ocean circulation model and altimeter data the vortex and its generation mechanism manifest themselves by a pronounced sea surface height ssh signature and variability which are found to be in agreement with altimeter data the vortex results primarily from anticyclonic eddies shed from the eastern branch of the norwegian atlantic current which propagate southwestward the large scale bottom depression of the lofoten basin plays a crucial role for attracting anticyclones into the trough and for enabling the dynamical stability of the vortex the water mass characteristics of the anticyclone lead to enhanced atmospheric interaction heat loss during wintertime the cold water trapped in the upper part of the vortex preconditions convection in the following wi

intracrustal detachment within zones of continental deformation geologic mapping of active to recently active geologic structures in panamint valley western united states and in the haiyuan region and northern tibetan plateau china suggests detachment in the middle and lower crust on a scale of tens of kilometres to at least several hundred kilometres detachment occurs similarly in predominantly extensional panamint valley and in predominantly compressional china environments it involves structures with displacements of more than 10 km and displacement rates of more than 3 mm yr perhaps more than 10 mm yr the steeply dipping strike slip faults present in all three areas hunter mountain fault haiyuan fault and altyn tagh fault zone terminate in zones of extension or compression and geometric relations indicate that all structures including strike slip faults are thin skinned and restricted to the upper crust in panamint valley and in the haiyuan region deformation within these systems can be reconstructed in three dimensions displacement on the strike slip faults is absorbed by extension or compression occurring at the termination of the faults so strike slip displacement is roughly equal to and in the same direction as shortening or extension we propose that left slip on the altyn tagh fault zone in northern tibet is similarly absorbed by shortening southeast of the fault zone within the qaidam basin and the nan shan

advective and atmospheric forced changes in heat and fresh water content in the norwegian sea 1951 2010 climate variability in the norwegian sea was investigated in terms of ocean heat and fresh water contents of atlantic water above a reference surface using hydrographic data during spring 1951 2010 the main processes acting on this variability were examined and then quantified the area averaged water mass cooled and freshened but a deepening of the reference surface resulted in a positive trend in the heat content of 0 3 w m 2 air sea heat fluxes explained about half of the interannual variability in heat content the effect of the advection of atlantic and arctic waters on the variability varied with time apparently due to large scale changes in the ocean circulation the data are consistent with the explanation that changing wind patterns caused buffering and then release of arctic water in the iceland sea during the late 1960s to early 1970s and this caused large hydrographic changes in the norwegian sea

wind driven variability of the large scale recirculating flow in the nordic seas and arctic ocean the varying depth integrated currents in the nordic seas and arctic ocean are modeled using an integral equation derived from the shallow water equations this equation assumes that mass divergence in the surface ekman layer is balanced by convergence in the bottom ekman layer the primary flow component follows contours of f h the model employs observed winds and realistic bottom topography and has one free parameter the coefficient of the linear bottom drag the data used for comparison are derived from in situ current meters satellite altimetry and a primitive equation model the current meter data come from a 4 yr record at 75 8 ni n the greenland sea the currents here are primarily barotropic and the model does well at simulating the variability the best bottom friction parameter corresponds to a spindown time of 30 60 days a further comparison with bottom currents from a mooring on the norwegian continental slope deployed over one winter period also shows reasonable correspondence the principal empirical orthogonal function obtained from satellite altimetry data in the nordic seas has a spatial structure that closely resembles f h a direct comparison of this mode s fluctuations with those predicted by the theoretical model yields linear correlation coefficients in the range 0 75 0 85 the primitive equation model is a coupled ocean ice version of the princeton ocean model for the north atlantic and arctic monthly mean depth averaged velocities are calculated from a 42 yr integration and then compared with velocities predicted from an idealized model driven by the same reanalyzed atmospheric winds in the largely ice free norwegian sea the coherences between the primitive equation and idealized model velocities are as high as 0 9 on timescales of a few months to a few years they are lower in the remaining partially or fully ice covered basins of the greenland sea and the arctic ocean presumably because ice alters the momentum transferred to the ocean by the wind the coherence in the canadian basin of the arctic can be increased substantially by forcing the idealized model with ice velocities rather than the wind estimates of the depth integrated vorticity budget in the primitive equation model suggest that bottom friction is important but that lateral diffusion is of equal or greater importance in compensating surface ekman pumping

subduction of asian lithospheric mantle beneath tibet inferred from models of continental collision the relative northward motion of the indian subcontinent that followed the onset of continental collision with asia has produced extensive deformation of the earth s crust giving rise to the world s highest mountains in the himalayan chain and the world s largest high elevation region the tibetan plateau the formation of the broad mountain belt implies that contrary to the original tenets of plate tectonics the lithospheric plates have experienced widespread deformation far from the plate boundary1 several models have been proposed2 6 to explain the manner in which this post collisional deformation is distributed within the continental lithosphere of the indian and asian plates here we propose an alternative model in which subduction of the asian lithospheric mantle develops following the collision of india our model is supported by numerical calculations of crustal deformation and thickening and is consistent with available geological and geophysical data7 9 this picture suggests that lithospheric mantle is not deformed along with the crust and would imply that continental collision zones are more analogous to oceanic subduction zones than was previously believed