intracontinental subduction and palaeozoic inheritance of the lithosphere suggested by a teleseismic experiment across the chinese tien shan teleseismic tomography across the chinese tien shan shows that seismic wave speeds in the lithosphere beneath central tien shan are high and therefore the lithosphere is not weaker than that beneath the adjacent undeformed tarim and junggar basins there is evidence for significant velocity contrasts within the lithosphere that are presumably inherited from the palaeozoic collision history the high velocity thick yili block observed underneath the northern tien shan is a clue for shortening by a intracontinental subduction the observed geometry is consistent with a simple model of intracontinental subduction and suggests that during orogeny the lithosphere has remained heterogeneous and has deformed along existing planes of weakness rather than by homogeneous thickening of a particularly weak lithosphere

climate instability during the last interglacial period recorded in the grip ice core isotope and chemical analyses of the grip ice core from summit central greenland reveal that climate in greenland during the last interglacial period was characterized by a series of severe cold periods which began extremely rapidly and lasted from decades to centuries as the last interglacial seems to have been slightly warmer than the present one its unstable climate raises questions about the effects of future global warming

three dimensional thermo mechanical modeling of the cenozoic uplift of the tianshan mountains driven tectonically by the pamir and tarim abstract we develop a three dimensional thermo mechanical model as an approximate representation of the lithosphere of the tianshan orogenic belt and adjacent geological units for simulating the uplift mechanism of the tianshan mountains in the cenozoic we apply a velocity boundary condition approximating the northward push of the pamir and tarim against the tianshan block to derive lithospheric deformation of the model in particular we investigate systematically the influence of gravity induced creep deformation on mountain uplift our modeling results indicate that 1 the modeled topographic pattern coincides well with the actual topography implying that the tectonic push of the pamir and tarim can cause significant uplift of the tianshan mountains 2 the lithosphere of the tianshan mountains is mechanically weaker than that of the platforms to the south and north of the tianshan orogenic belt and 3 the gravity induced creep deformation has a significant influence on the process and elevation of mountain uplift therefore when subjected to the tectonic compression resulting from the northward push of the pamir and tarim the relatively weak lithosphere of the tianshan mountains would deform easily and hence absorb more shortening resulting in lithospheric thickening and consequent mountain uplift

self consistent thermodynamic description of silicate liquids with application to shock melting of mgo periclase and mgsio3 perovskite summary we develop a self consistent thermodynamic description of silicate liquids applicable across the entire mantle pressure and temperature regime the description combines the finite strain free energy expansion with an account of the temperature dependence of liquid properties into a single fundamental relation while honouring the expected limiting behaviour at large volume and high temperature we find that the fundamental relation describes well previous experimental and theoretical results for liquid mgo mgsio3 m g2sio4 and sio2 we apply the description to calculate melting curves and hugoniots of solid and liquid mgo and mgsio3 for periclase we find a melting temperature at the core mantle boundary cmb of 7810 160 k with the solid hugoniot crossing the melting curve at 375 gpa 9580 k and the liquid hugoniot crossing at 470 gpa 9870 k for complete shock melting of periclase we predict a density increase of 0 14 g cm 3 and a sound speed decrease of 2 2 km s 1 for perovskite we find a melting temperature at the cmb of 5100 100 k with the perovskite section of the enstatite hugoniot crossing the melting curve at 150 gpa 5190 k and the liquid hugoniot crossing at 220 gpa 5520 k for complete shock melting of perovskite along the enstatite principal hugoniot we predict a density increase of 0 10 g cm 3 with a sound speed decrease of 2 6 km s 1

relationship between cyclone tracks anticyclone tracks and baroclinic waveguides abstract this study presents observational results concerning the structure and evolution of high frequency fluctuations with periods shorter than 6 days in the geopotential height field the results are based on a statistical analysis of 1000 500 and 250 mb height fields derived from twice daily nmc final analyses over the northern hemisphere for the 20 winters 1964 65 through 1983 84 the disturbances assume the form of waves elongated in the meridional direction with a mean wavelength of 4000 km a westward tilt with height and a mean eastward phase propagation of 12 1 5 m s 1 these results support an interpretation in terms of finite amplitude baroclinic waves whose structure and evolution varies with geographical location over the continents and especially along the eastern slopes of the rockies and the tibetan plateau the waves show marked departures in structure and evolution from those over the oceans in particular we find evidence of a systematic influence of the terrain in steering the

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

active thrusting and folding along the northern tien shan and late cenozoic rotation of the tarim relative to dzungaria and kazakhstan we have studied geometries and rates of late cenozoic thrust faulting and folding along the northern piedmont of the tien shan mountain belt west of urumqi where the m 8 3 manas earthquake occurred on december 23 1906 the northern range of the tien shan rising above 5000 m overthrusts a flexural foredeep filled with up to 11 000 m of sediment of the dzungarian basement our fieldwork reveals that the active thrust reaches the surface 30 km north of the range front within a 200 km long zone of neogene quaternary anticlines fault scarps are clearest across inset terraces within narrow valleys incised through the anticlines by large rivers flowing down from the range in all the valleys the scarps offset vertically the highest terrace surface by the same amount 10 2 0 7 m inferring an early holocene age 10 2 kyr for this terrace which is continuous with the largest recent fans of the piedmont yields a rate of vertical throw of 1 0 0 3mm yr on the main active thrust at the surface a quantitative morphological analysis of the degradation of terrace edges that are offset by the thrust corroborates such a rate and yields a mass diffusivity of 5 5 2 5 m 2 kyr a rather fresh surface scarp 0 8 0 15 m high that is unlikely to result from shallow earthquakes with 6 m 7 in the last 230 years is visible at the extremities of the main fold zone we associate this scarp with the 1906 manas earthquake and infer that a structure comprising a deep basement ramp under the range gently dipping flats in the foreland and shallow ramps responsible for the formation of the active fault propagation anticlines could have been activated by that earthquake if so the return period of a 1906 type event would be 850 380 years the small size of the scarp for an earthquake of this magnitude suggests that a large fraction of the slip at depth 2 3 is taken up by incremental folding near the surface comparable earthquakes might activate flat detachments and ramp anticlines at a distance from the front of other rising quaternary ranges such as the san gabriel mountains in california or the mont blanc aar massifs in the alps we estimate the finite cenozoic shortening of the folded dzungarian sediments to be of the order of 30 km and the cenozoic shortening rate to have been 3 1 5 mm yr assuming comparable shortening along the tarim piedmont and minor additional active thrusting within the mountain belt we infer the rate of shortening across the tien shan to be at least 6 3 mm yr at the longitude of manas 85 5 e a total shortening of 125 30 km is estimated from crustal thickening assuming local airy isostatic equilibrium under the same assumption serial n s sections imply that cenozoic shortening across the belt increases westwards to 203 50 km at the longitude of kashgar 76 e as reflected by the westward increase of the width of the belt this strain gradient implies a clockwise rotation of tarim relative to dzungaria and kazakhstan of 7 2 5 around a pole located near the eastern extremity of the tien shan west of hami 96 e 43 5 n comparable to that revealed by paleomagnetism between tarim and dzungaria 8 6 8 7 a 6 mm yr rate of shortening at the longitude of manas would imply a rate of rotation of 0 45 m y and would be consistent with a shortening rate of 12 mm yr north of kashgar taking such values to be representative of late cenozoic rates would place the onset of reactivation of the tien shan by the india asia collision in the early to middle miocene 16 22 9 m y in accord with the existence of particularly thick late neogene and quaternary deposits such reactivation would thus have started much later than the collision roughly at the time of the great mid miocene changes in tectonic regimes denudation and sedimentation rates observed in southeast asia the himalayas and the bay of bengal and of the correlative rapid change in seawater sr isotopic ratio 20 to 15 ma like these other changes the rise of the tien shan might be a distant consequence of the end of indochina s escape

anomalous surface waves from lop nor nuclear explosions observations and numerical modeling surface waves from the chinese test site of lop nor are analyzed using long period and broadband stations located at regional and teleseismic distances and at different azimuths for most azimuths strong love waves between 0 02 and 0 045 hz are observed with an amplitude of up to 10 times that of the rayleigh waves in addition an anomalous early rayleigh wave train is observed at some stations in western europe due to a particularly favorable station and source configuration it is possible to isolate the areas where the anomalies are created the high amplitude love waves must be attributed to either source effects or path effects immediately north of lop nor the early wave train is shown to be due to a partial energy conversion between love and rayleigh waves probably at the tornquist zone to estimate the possible contribution from surface wave conversions to the observed anomalies numerical simulations are carried out with the indirect boundary element method the simulations show that a relatively small variation of crustal thickness can induce rayleigh to love wave conversions between 0 02 and 0 1 hz frequency the calculated amplitudes of the love waves are significant up to 35 of the amplitude of the incoming rayleigh waves but they are too small to fit the observed amplitude anomaly the observed converted waves and the numerical results nevertheless indicate that surface wave conversions can be significant across strong lateral crustal heterogeneities in particular the conversions due to changes in crustal thickness are located in the period interval which is routinely used for estimation of ms

source parameters for 11 earthquakes in the tien shan central asia determined by p and sh waveform inversion the tien shan mountain belt of central asia was formed in late paleozoic time and reactivated in tertiary time following the collision of india with eurasia more than 1500 km to the south to study the style and distribution of faulting occurring today in the tien shan we digitized long period world wide standard seismograph network p and sh waveforms of 11 of the largest tien shan earthquakes between 1965 and 1982 and then used a least squares inversion routine to constrain their fault plane solutions and depths four of the earthquakes occurred near the southern edge of the tien shan and two occurred in the intermontane fergana basin these earthquakes occurred at depths of 10 20 km and are associated with thrust faulting on east west to southwest northeast striking fault planes that dip moderately 35 55 the other five earthquakes in the northern tien shan were mostly deeper 15 44 km and the fault plane solutions of four of them are similar to the events farther south the exception an event on june 2 1973 probably occurred on a gently northward dipping east west striking fault plane all events occur within the basement at depths of 10 km or greater waveforms for earthquakes near the edges of the dzungarian fergana and kucha basins are fit best using velocity structures with thick sediment layers implying that sediments from these basins have been and are being underthrust beneath the neighboring mountains we examined only the relatively small mb 5 5 6 2 events after 1965 and did not study any of the largest events ms 8 that occurred in the tien shan earlier in this century still we can conclude that north south shortening is presently occurring in the tien shan with the formation of basement uplifts flanked by moderately dipping thrust faults the present day tectonics of the tien shan seem to be analogous to those of the rocky mountains in colorado wyoming and utah during the laramide orogeny in late cretaceous and early tertiary time

experimental constraints on melting temperatures in the mgo sio2 system at lower mantle pressures eutectic melting curves in the system mgo sio2 have been experimentally determined at lower mantle pressures using laser heated diamond anvil cell lh dac techniques we investigated eutectic melting of bridgmanite plus periclase in the mgo mgsio3 binary and melting of bridgmanite plus stishovite in the mgsio3 sio2 binary as analogues for natural peridotite and basalt respectively the melting curve of model basalt occurs at lower temperatures has a shallower dt dp slope and slightly less curvature than the model peridotitic melting curve overall melting temperatures detected in this study are in good agreement with previous experiments and ab initio simulations at 25 gpa liebske and frost 2012 de koker et al 2013 however at higher pressures the measured eutectic melting curves are systematically lower in temperature than curves extrapolated on the basis of thermodynamic modelling of low pressure experimental data and those calculated from atomistic simulations we find that our data are inconsistent with previously computed melting temperatures and melt thermodynamic properties of the sio2 endmember and indicate a maximum in short range ordering in mgo sio2 melts close to mg2sio4 composition the curvature of the model peridotite eutectic relative to an mgsio3 melt adiabat indicates that crystallization in a global magma ocean would begin at 100 gpa rather than at the bottom of the mantle allowing for an early basal melt layer the model peridotite melting curve lies 500 k above the mantle geotherm at the core mantle boundary indicating that it will not be molten unless the addition of other components reduces the solidus sufficiently the model basalt melting curve intersects the geotherm at the base of the mantle and partial melting of subducted oceanic crust is expected

solidus and liquidus profiles of chondritic mantle implication for melting of the earth across its history abstract we investigated the melting properties of a synthetic chondritic primitive mantle up to core mantle boundary cmb pressures using laser heated diamond anvil cell melting criteria are essentially based on the use of x rays provided by synchrotron radiation we report a solidus melting curve lower than previously determined using optical methods the liquidus curve is found between 300 and 600 k higher than the solidus over the entire lower mantle at cmb pressures 135 gpa the chondritic mantle solidus and liquidus reach 4150 150 k and 4725 150 k respectively we discuss that the lower mantle is unlikely to melt in the d layer except if the highest estimate of the temperature profile at the base of the mantle which is associated with a very hot core is confirmed therefore recent suggestions of partial melting in the lowermost mantle based on seismic observations of ultra low velocity zones indicate either 1 a outer core exceeding 4150 k at the cmb or 2 the presence of chemical heterogeneities with high concentration of fusible elements our observations of a high liquidus temperature as well as a large gap between solidus and liquidus temperatures have important implications for the properties of the magma ocean during accretion not only complete melting of the lower mantle would require excessively high temperatures but also below liquidus temperatures partial melting should take place over a much larger depth interval than previously thought in addition magma adiabats suggest very high surface temperatures in case of a magma ocean that would extend to more than 40 gpa as suggested by siderophile metal silicate partitioning data such high surface temperature regime where thermal blanketing is inefficient points out to a transient character of the magma ocean with a very fast cooling rate

geodynamics of the tarim basin and the tian shan in central asia the india asia collision has caused crustal thickening in tibet by at least a factor of 2 in the last 20 30 myr of this collision the tian shan mountain range has also been reactivated the tarim basin however shows little internal deformation we describe a series of numerical experiments which constrain the effective lithospheric strength parameters of the tarim basin and the tian shan in the context of a thin viscous sheet model we use a finite element representation of the thin viscous sheet model to approximate the deformation field in the india asia collision and compare model crustal thickness distributions with that inferred from a local isostatic model of topography the experiments show that a strong tarim basin while undergoing little internal deformation transfers strain to the tian shan producing significant crustal thickening in the tian shan region based only on diagnostic parameters such as the maximum thickening in the tian shan and the minimum in the tarim basin the principal features of the topography can be approximately reproduced using models in which either the tarim basin is strong or the tian shan is weak or both for a rheological model in which the stress versus strain rate exponent is n 3 the strength coefficient for the strong tarim basin model vtarim is between about 1 7 and 2 for the weak tian shan model the relative strength coefficient vtian is between about 0 65 and 0 75 if both strong tarim and weak tian shan are included there is a trade off between the required values of vtarim and vtian and the shape of the predicted crustal thickness profiles better matches the observed profiles the steep topographic slope on the southern margin of the tarim basin requires that it is anomalously strong while the rapid decrease of topographic height to the north of the tian shan requires that it is anomalously weak similar conclusions are obtained with a rheological model based on n 10 simplified rheological models of the lithosphere show that the variations in lithospheric strength may be explained by changes to the moho temperature of the order of 10 to 30 c

thermodynamics of silicate liquids in the deep earth article i nfo we discuss the geophysical implications of recent first principles molecular dynamics simulations of mgsio3 liquid in particular the findings that the gruneisen parameter increases by a factor of three on two fold compression and the predicted melting curve the predicted melting temperature of mgsio3 perovskite at 136 gpa is 5400 600 k which if lowered by freezing point depression by 1300 k yields a mantle solidus temperature of 4100 k identical to recent estimates of the temperature at the base of the mantle we argue on this basis that partial melting at the base of the mantle is plausible while mgsio3 perovskite is denser than the isochemical liquid reasonable values of iron partitioning and bulk iron contents leads to the conclusion that a melt at the base of the multi component mantle would be denser than its surroundings and therefore buoyantly stable we predict the bulk sound velocity of this melt to be 10 9 km s 1 less than that of ultra low velocity zones and consistent with the explanation of these regions as being due to partial melting the increase on compression of the gruneisen parameter in the liquid state yields isentropes that are much hotter than previously thought a potential temperature of only 2450 k is sufficient to melt the entire mantle and a magma ocean will begin crystallization at mid mantle depths rather than at the base of the mantle

lateral variations in cmb heat flux and deep mantle seismic velocity caused by a thermal chemical phase boundary layer in 3d spherical convection article i nfo numerical simulations of thermo chemical multi phase compressible mantle convection in a three dimensional spherical shell are used to investigate the relationship between lateral variations in seismic shear wave velocity vs above the core mantle boundary cmb and lateral variations in heat flux across the cmb qcmb when compositional variations and the post perovskite phase transition are included for simple thermal convection the vs qcmb relationship is reasonably but not perfectly linear the post perovskite transition introduces a non linearity that amplifies fast vs anomalies in cold regions but there is still a unique mapping between vs and qcmb lateral variations in composition such as piles of dense material introduce another non linearity that affects hot upwelling regions and introduces a non uniqueness in vs qcmb if the dense material e g morb is seismically fast compared to the surrounding material in this case dense piles are ringed by sharp low vs anomalies if the cmb is covered by a global dense layer than variations in vs and qcmb are reduced but so is the mean value of qcmb in all cases the peak to peak lateral variation in qcmb is similar to or larger than twice the mean value which might create problems for generating a dynamo according to existing numerical dynamo simulations analytical scalings are developed to explain the observed trends

a three dimensional moho depth model for the tien shan from egm2008 gravity data 1 the tien shan in central asia is the largest intracontinental mountain range in the world but it is 1500 km away from the collision zone between the indian and eurasian plates this region has been and still is the focus of numerous geoscientific studies mainly because of its evolutionary history and its unique position in the eurasian lithosphere plate so far mainly seismological data have been used to explore the origin of and ongoing seismic activity in this region but only one study has investigated terrestrial gravity data in this study a new gravity data set egm2008 is used to determine the crust mantle boundary mohorovicic discontinuity moho of the tien shan using inversion of gravity data in addition an isostatic moho is calculated from topographic data which by comparison to the results of the gravity inversion illuminates the effects of isostatic compensation the results of the gravity inversion generally agree with results of previous seismic studies and indicate that the tien shan has a mountain root with a thickness of about 75 km furthermore the moho is shallow under the basins e g in the tarim and ili basins the comparison with the isostatic moho indicates an over compensation of the orogen and an under compensation of the basins the over compensation results from the former subduction of the tarim basin terrane in the south the under compensation of the tarim basin is generated by support of the terrane between the tien shan in the north and the pamir mountains tibet and himalayas in the south

gravity anomalies the deep structure and dynamic processes beneath the tien shan bouguer gravity anomalies over the tien shan and pamir are large and negative and therefore consistent with crustal thickening beneath both mountain ranges gravity anomalies over the western tien shan are within about 10 mgal of those expected for local airy isostatic equilibrium but those over the eastern tien shan are up to 50 mgal too large and negative thus they require static or dynamic support of an uncompensated mass deficit these gravity anomalies cannot be matched using regional compensation of the weight of the range on a continuous elastic plate a simple model of two separate elastic plates extending north and south from the axis of the tien shan can allow an adequate fit of observed and calculated anomalies the flexural rigidity of the northern plate must be quite small d 1023 n m corresponding to an equivalent effective elastic thicknesste 25 km but that of the southern plate must be larger d 1024 n m te 50 60 km the data for the eastern tien shan cannot be fit without a force per unit length of roughly 1 4 1012 n or by a bending moment applied to the end of the southern plate thus either a deep mass per unit length of about 1 4 1011 kg m must underlie the eastern part of the range or dynamic deviatoric tensional normal stresses of up to about 5 mpa due to flow in the asthenosphere must pull the tien shan down probably a combination of them resulting from the formation and sinking of a thickened lithospheric root causes the deflection of the moho and the deviations from local isostatic equilibrium

experimental evidence for perovskite and post perovskite coexistence throughout the whole d region article i nfo since the phase diagram for fe al bearing mgsio3 compositions at the p t conditions of the core mantle boundary remains ambiguous we investigated the fe distribution among the silicate perovskite pv and post perovskite ppv polymorphs using tandem synchrotron analyses of x ray diffraction and x ray absorption spectroscopy we performed measurements at the fe k edge of the partitioning of iron between pv and ppv up to more than 150 gpa after annealing at about 3300 k we obtain a unique solution for kfe pv ppv of 4 2 0 5 our results evidence that the two silicates should coexist over the whole d region with the main post perovskite phase being largely depleted in fe compared to the perovskite as fe and al have a dominant effect on the phase diagram these new results challenge recent determinations of the temperature profile in the lowermost mantle based on the clapeyron slope of the pv to ppv transition for pure mgsio3 composition also it appears clear that variations in the molar fractions of perovskite and post perovskite phases should be expected radially or laterally in the d region in relation with thermal or compositional heterogeneities this can help explaining the seismological anomalies observed for this mantle region finally we predict a significant increase of the feo activity in the d region which should greatly affect the chemical exchange between mantle and core

crustal and upper mantle structure under the tien shan from surface wave dispersion long period seismograms of nuclear explosions and natural earthquakes in central asia recorded at three digital stations of the laboratoire de detection geophysique ldg network in france attest to a significant propagation effect in the tien shan area this allows for an investigation of the deep structures under the range which has been the site of particularly intense intracontinental deformation since about the middle miocene group velocity curves have been obtained by regionalization for pure paths across either the central or eastern tien shan they indicate a crust of approximately 50 55 km in thickness and particularly low shear wave velocities under the central tien shan our study suggests lateral variation of the deep structures under the range which could be related to a westward increase along the range of cumulative amount and rate of shortening

the melting curve of ni to 1 mbar the melting curve of ni has been determined to 125 gpa using laser heated diamond anvil cell lh dac experiments in which two melting criteria were used firstly the appearance of liquid diffuse scattering lds during in situ x ray diffraction xrd and secondly plateaux in temperature vs laser power functions in both in situ and off line experiments our new melting curve defined by a simon glatzel fit to the data where t m k p m 18 78 10 20 1 1 2 42 0 66 1726 is in good agreement with the majority of the theoretical studies on ni melting and matches closely the available shock wave melting data it is however dramatically steeper than the previous off line lh dac studies in which determination of melting was based on the visual observation of motion aided by the laser speckle method we estimate the melting point t m of ni at the inner core boundary icb pressure of 330 gpa to be t m 5800 700 k 2 within error of the value for fe of t m 6230 500 k determined in a recent in situ lh dac study by similar methods to those employed here this similarity suggests that the alloying of 5 10 wt ni with the fe rich core alloy is unlikely to have any significant effect on the temperature of the icb though this is dependent on the details of the topology of the fe ni binary phase diagram at core pressures our melting temperature for ni at 330 gpa is 2500 k higher than that found in previous experimental studies employing the laser speckle method we find that those earlier melting curves coincide with the onset of rapid sub solidus recrystallization suggesting that visual observations of motion may have misinterpreted dynamic recrystallization as convective motion of a melt this finding has significant implications for our understanding of the high pressure melting behaviour of a number of other transition metals

the flickering switch of late pleistocene climate change polar ice contains a unique record of past climate variations previous greenland ice cores have documented relatively warm interstadial periods during the last glaciation and short centuryscale returns to colder conditions during the glacial to interglacial warming see for example ref 1 these climate features have also been observed to varying degrees in ocean sediment cores2 4 and terrestrial pollen and insect records5 7 here we report electrical conductivity measurements from a new greenland ice core which confirm these previous observations and also reveal a hitherto unrecognized mode of rapid climate variation fluctuations in ice conductivity on the scales of 5 20 years reflect rapid oscillations in the dust content of the atmosphere this flickering between two preferred states would seem to require extremely rapid reorganizations in atmospheric circulation

tropospheric rivers a one year record and a possible application to ice core data the morphology of tropospheric rivers has been examined for the period june 1991 may 1992 from atmospheric specific humidity and wind velocity data vertically integrated water vapor flux vectors are subjected to harmonic analysis and the high frequency components periods less than 3 days show large amplitude values in the north atlantic north pacific south atlantic south indian ocean and south pacific plus small amplitude occurrences in the red sea arabian sea region in the december february season in june august the latter is replaced with a large amplitude monsoon related region over south east asia maximum intensities increase slightly in altitude with latitude the correspondence between rivers frontal boundaries and storm tracks is noted sometimes rivers originating over the north pacific cross north america and reach greenland while at other times they pass polewards over the north atlantic raising the possibility that water vapor involved in ice core formation may have evaporated from surface water bodies with different temperature and salinity characteristics changes in oxygen isotope variations at a point may therefore reflect changes in the dynamics of tropospheric rivers in addition to local temperature changes

analysis of meteorological precursors to ordinary and explosive cyclogenesis in the western north pacific abstract thirty five cases of cyclogenesis that occurred during the cold seasons from 1975 to 1995 in the western north pacific ocean are studied to determine common and disparate dynamic and thermodynamic structures in both the ordinary and rapid developments an analysis of 1000 hpa height and 1000 500 hpa thickness anomalies with respect to the 20 yr climatology reveals the following results though each sample of cyclogenesis is characterized by a favorable appearing thickness trough ridge structure important differences are found both the upstream surface anticyclone and the downstream precedent cyclone are preferentially stronger at the beginning of the most rapid cyclogenesis in the strong sample because of the consequently stronger equatorward flow the 1000 500 hpa thickness anomaly in the strong sample is colder by approximately 40 m 2 c in the region of incipient cyclogenesis and eastward by 1500 km a harmonic time series analysis of ncep gridded fields partitions the geopotential height

crustal thickness variations across the northern tien shan from teleseismic receiver functions variations in crustal thickness from the kazakh shield to the north central tien shan are determined by receiver function analysis of broadband teleseismic p waveforms recorded on the kyrgyzstan seismic telemetry network knet the receiver functions are calculated using a time domain deconvolution approach and are interpreted in terms of a single crustal layer with thickness determined by a grid search comparison of observed receiver functions with synthetics crustal thicknesses average 42 km in the southern kazakh shield and increase to approximately 60 km in the tien shan together with mass balance calculations these results are consistent with the hypothesis that the compensation of the central tien shan relative to the kazakh shield are accommodated by an airy type crustal root with a modest 300 kg m density contrast across the moho

a lagrangian based analysis of extratropical cyclones ii a detailed case study a detailed case study analysis is undertaken of the occurrence of significant coherent ensembles of trajectories cets that accompany atlantic cyclogenesis the approach is based upon the lagrangian based analysis scheme introduced in part i the analysis reveals the existence of several distinct moist ascending and dry descending cets two types of moist ascending cets associated with strong condensational processes ascend from the boundary layer of the warm sector either in the close vicinity of the cyclone centre or in the trailing cold frontal region the latter is the main contributor to the precipitation along the cold front during the early phase of the development another type of moist cets distinguished by maximum water vapour flux travels at low levels through the warm sector and ascends to mid tropospheric levels in the warm frontal region where it produces strong precipitation around the time of maximum storm intensity cets with an upper level origin are linked to the classical dry intrusion different cets correspond to strong descent of upper level tropospheric air that penetrated to the lower troposphere the movement of stratospheric air toward the centre of the maturing cyclone and an event of stratosphere to troposphere exchange upstream of the upper level trough two different visualizations of time sequences of the moist ascending cets indicate that they represent well defined flexible tubes or airstreams that exist over a time period comparable with the duration of the main cyclone intensification they provide a translating flexible but coherent river bed for the quasi continuous ascent of moist boundary layer air to the upper troposphere these tubes are akin to the concept of warm conveyor belts and the present analysis method objectively diagnoses their geometrical and physical characteristics and potential vorticity pattern some consideration is also given to the relationship of cets and tropospheric rivers and to possible shortcomings of the approach

thermodynamics of the mgo sio2 liquid system in earth s lowermost mantle from first principles abstract knowledge of the multi component thermodynamics and phase equilibria of silicate melts in earth s deep interior are key to understanding the thermal and chemical evolution of the planet yet the melting phase diagram of the lower mantle remains poorly constrained with large uncertainties in both eutectic composition and temperature we use results from first principles molecular dynamics of nine compositions along the mgo sio 2 binary to investigate the compositional dependence of liquid state thermodynamics applying our results to describe incongruent melting for the system at deep lower mantle pressures our phase diagram is bi eutectic throughout the lower mantle with no liquid immiscibility accounting for solid liquid partitioning of fe we find partial melts of basaltic and peridotitic lithologies to be gravitationally stable at the core mantle boundary while liquidus density contrasts predict that perovskite will sink and periclase will float in a crystallizing pyrolytic magma ocean

multiyear accumulation and temperature history near the north greenland ice core project site north central greenland this paper presents a comparison of two independent methods of estimating subseasonal accumulation across the interior of greenland these methods high resolution snow pit studies and atmospheric modeling have differing spatial and temporal resolution but both can estimate net accumulation for subseasonal and shorter periods the snow pit approach is based on a documented relationship between high resolution snow pit profiles of oxygen stable isotope ratio 18o and multiyear special sensor microwave imager ssm i 37 ghz brightness temperature records comparison of ssm i data to profiles obtained during the 1995 alfred wegener institut north greenland traverse field season shows that 18o data from snow in north central greenland are a reliable high resolution temperature proxy this enables determination of accumulation amount rate and timing from approximately july 1991 through june 1995 across this 220 km long transect of the ice sheet precipitation estimates derived from early modeling based on european centre for medium range weather forecasts data show a similar average seasonal pattern but a diminished magnitude of accumulation 56 for these sites the slope of the multiyear t versus correlation was evaluated for each site on the basis of the observed and calculated temperature history from the nearby north greenland ice core project ngrip site automatic weather station these data should assist interpretation of the paleoclimatic record in the ngrip deep core

the inland penetration of atmospheric rivers over western north america a lagrangian analysis abstractalthough atmospheric rivers ars typically weaken following landfall those that penetrate inland can contribute to heavy precipitation and high impact weather within the interior of western north america in this paper the authors examine the evolution of ars over western north america using trajectories released at 950 and 700 hpa within cool season ars along the pacific coast these trajectories are classified as coastal decaying inland penetrating or interior penetrating based on whether they remain within an ar upon reaching selected transects over western north america interior penetrating ar trajectories most frequently make landfall along the oregon coast but the greatest fraction of landfalling ar trajectories that eventually penetrate into the interior within an ar is found along the baja peninsula in contrast interior penetrating ar trajectories rarely traverse the southern high sierra at landfall interior penetrating ar trajectories are associated with a more amplified flow

upper mantle heterogeneities in africa deduced from rayleigh wave dispersion abstract rayleigh wave group velocities have been measured along 11 paths on the african continent north of the equator the results lead to a division of this part of the continent into three regions cratonic areas non cratonic areas mobile zones and a region located to the east of the meridian 31 e red sea neighbourhood ethiopia djibouti the highest velocities are found beneath the cratonic areas at 200 km depth 5 at greater depths the mobile zones exhibit higher velocities than the cratonic regions but the difference is not as marked 2 and the resolution is poor velocities in the eastern region are similar to those found under young oceanic regions

shear wave splitting at central tien shan evidence for rapid variation of anisotropic patterns at active collisional belts the fast polarization axis of shear wave splitting is generally aligned parallel to the strike of the belt which has been proposed to indicate mantle strain that is coherent with crustal deformation a notable exception is central tien shan where anomalous patterns of splitting have previously been observed we here analyze shear wave splitting of sks phases across north central tien shan using digital data from the kyrgyzstan broadband seismic network knet we find a pattern of short wavelength anisotropic heterogeneity that supports complex mantle flow due to small scale convection the along strike variations in mantle structure contrast with the coherent pattern of crustal shortening and indicate that mantle flow is not directly coupled to crustal deformation in this region

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

a perovskitic lower mantle inferred from high pressure high temperature sound velocity data determination of the shear wave velocities for silicate perovskite and ferropericlase under the pressure and temperature conditions of the deep lower mantle indicates that perovskite constitutes much more of the lower mantle than predicted by the conventional mantle model and is consistent with the chondritic earth model earth s upper mantle is apparently depleted of silicon when compared with meteorites which are thought to represent the material from which the earth formed this missing silicon problem has provoked intense debate it suggests that the deficit might be balanced by silicon in the core or that the upper mantle is not representative of the entire mantle and that the lower mantle is enriched in silicon murakami et al provide evidence to support the latter case they made laboratory measurements of sound wave transmission through silicate perovskite and ferropericlase minerals at pressures and temperatures matching those of the lower mantle and compared the resulting shear wave values with seismic data that sample the lower mantle they conclude that the mineralogical model that provides the best fit is one in which perovskite constitutes greater than 93 of the lower mantle this suggests that the lower mantle is enriched in silicon in comparison with the upper mantle consistent with the chondritic earth model and that there is limited mass transport between the upper and lower mantle the determination of the chemical composition of earth s lower mantle is a long standing challenge in earth science accurate knowledge of sound velocities in the lower mantle minerals under relevant high pressure high temperature conditions is essential in constraining the mineralogy and chemical composition using seismological observations1 but previous acoustic measurements were limited to a range of low pressures and temperatures here we determine the shear wave velocities for silicate perovskite and ferropericlase under the pressure and temperature conditions of the deep lower mantle using brillouin scattering spectroscopy2 the mineralogical model that provides the best fit to a global seismic velocity profile1 indicates that perovskite constitutes more than 93 per cent by volume of the lower mantle which is a much higher proportion than that predicted by the conventional peridotitic mantle model it suggests that the lower mantle is enriched in silicon relative to the upper mantle which is consistent with the chondritic earth model such chemical stratification implies layered mantle convection with limited mass transport between the upper and the lower mantle

altitudinal variation of the stable isotopes of snow in regions of high relief a major discontinuity in the variation of 18 o d with altitude in high mountains was first seen in data from mount logan yukon territory canada holdsworth and others 1991 the profile of vs altitude revealed three well defined regions 1 a lower monotonic fractionation sequence below 3 km 2 a middle layer typically 1 2 km thick within which values are nearly constant or stepped with altitude and 3 part of another fractionation sequence in the quasi geostrophic flow region above 5 3 km the middle region was inferred to be a mixed layer combining moisture from regions 1 and 3 this type of structure is now seen to occur on other high altitude mountains including cerro aconcagua argentina where observations reach almost 7 km the new observations confirm the general occurrence of a multi layered atmosphere during precipitation at high altitude glacier sites this structure is linked to synoptic scale polar cyclones where the middle layer is identified as being the signature of the warm front zone these results have implications for the common practice of using a specific spatially derived isotopic thermometer in the time domain for the paleoclimatic interpretation of high altitude ice core records

melting of morb at core mantle boundary abstract we investigated the melting properties of natural mid ocean ridge basalt morb up to core mantle boundary cmb pressures using laser heated diamond anvil cell textural and chemical characterizations of quenched samples were performed by analytical transmission electron microscopy we used in situ x ray diffraction primarily for phase identification whereas our melting criterion based on laser power versus temperature plateau combined with textural analysis of recovered solidus and subsolidus samples is accurate and unambiguous at cmb pressure 135 gpa the morb solidus temperature is 3970 150 k quenched melt textures observed in recovered samples indicate that casio3 perovskite capv is the liquidus phase in the entire pressure range up to cmb the partial melt composition derived from the central melt pool is enriched in feo which suggests that such melt pockets may be gravitationally stable at the core mantle boundary

a no lid zone in the central chang thang platform of tibet evidence from pure path phase velocity measurements of long period rayleigh waves pure path phase velocities of fundamental mode rayleigh waves in the period range 30 80s are obtained for different paths across the tibet plateau using a two event method with events located in tibet and aligned with world wide standard seismograph network stations at teleseismic distance evidence is found for significant lateral variations of structure of the crust and uppermost mantle in tibet in particular phase velocities obtained on paths contained in the chang thang platform are higher than average in tibet at periods shorter than 60s while remaining very low at longer periods when interpreting these phase velocities in terms of simple layered s velocity models it is found that contrary to other areas in tibet they are incompatible with the existence of a high velocity lid s velocities of 4 4 4 5 km s are found immediately beneath the moho and the crust is somewhat thinner 50 60 km than average in tibet this indicates a possible upwelling of hot asthenospheric material compatible with landsat evidence for subrecent basaltic volcanism and independent seismic evidence such as inefficient transmission of sn waves on the other hand a 70 km thick crust and very high upper mantle s velocities are found on the western border of tibet karakorum hindu kush compatible with previous finer scale results concerning the associated zone of intermediate depth seismicity

influence of station topography and moho depth on the mislocation vectors for the kyrgyz broadband seismic network knet deviations of slowness and backazimuth from theoretically calculated values the so called mislocation vectors are measured for the kyrgyz broadband seismic network knet in the tien shan region 870 events have been analysed for arrivals of p and pkp waves from all azimuths the deviations of slowness and backazimuth show a strong trend with values up to 1 s deg 1 for slowness values for waves arriving from the north and south and backazimuth deviations of in some cases more than 10 degrees for waves arriving from the east and west calculating the traveltime deviations of the stations for topography of the tien shan region and moho depth values appropriate for this area shows that most slowness and backazimuth deviations can be reduced to very small values the remaining mislocation vectors show no strong trends and are on average smaller than 0 2 s deg 1 for slowness and 2 degrees for backazimuth values which is within the error bars of these measurements results from array methods that rely on the knowledge of the backazimuth values show much improved resolution after the correction of the mislocation vectors which shows the importance of knowing and correcting for structures directly beneath arrays

three dimensional elastic wave velocity structure of the western and central tien shan arrival times of compressional p and shear s waves generated by earthquakes at local and teleseismic distances and recorded by seismographs located in the western and central tien shan are used to determine one and three dimensional elastic wave velocity structures of the crust and upper mantle beneath the mountain belt the best fit one dimensional structures suggest that the average depth of the mohorovicic discontinuity in this area is 50 km the three dimensional structure of the upper crust reveals thick sediments within each of the major depressions in the region a 7 km thick wedge of sediment beneath the chu depression is outlined at depth by a south dipping plane of seismic activity suggesting the presence of an active decollemont these low velocities extend continuously to the southeast toward issyk kul suggesting a structural relationship between the two however rather than being consumed it appears that issyk kul is overthrusting the surrounding ranges the low velocity sediments in the fergana basin reach depths of 10 km and are bounded on three sides by amorphous bands of seismicity velocities at midcrustal depths generally are lower beneath the central tien shan than beneath the western tien shan this pattern becomes more evident in the uppermost mantle with p velocity contrasts of as much as 10 across a boundary that corresponds roughly to the geographical position of the talasso fergana fault the low velocities beneath the central tien shan exceed 150 km depth but do not appear to be deeper than 300 km depth there is no evidence for a lithospheric root beneath this part of the range rather the low velocities imply the presence of a positive buoyancy force uplifting the mountains evidence that this low velocity region existed before the collision suggests that the tien shan may not owe its rejuvenation simply to its location at the northern edge of a strong tarim basin but rather to an anomalous upper mantle that was easier to deform than the surrounding lithosphere

north pacific cold season surface cyclone activity 1975 1983 abstract an eight year sample of cold season 1 october through 31 march extratropical cyclones in the pacific ocean basin is used to study central pressure changes and life cycle characteristics we find that over 90 of the cyclones passing through the area of the kuroshio current intensify in this region corresponding percentages in excess of 60 extend from the kuroshio south of 45 n eastward to 130 w mean 24 h central pressure falls of all cyclones exceed 9 mb through the entire basin west of 140 w in the latitude band 30 to 50 n a statistical analysis of 24 h central pressure changes is performed on all cyclones within our domain a frequency distribution of 1996 cases of 24 h maximum deepening reveals statistically significant departures from a gaussian distribution with the coefficient of skewness substantially negative we also find similarly significant departures from normal in a frequency distribution of all 24 h central pressure changes in spite of the fact that this distribution wo

recording of el nino in ice core δ18o records from nevado huascaran peru the 68 year monthly resolved time series of 18 o from ice cores retrieved from the glaciated col of nevado huascaran peru 9 s 77 w 6050 m reflects climate variability over amazonia and the western tropical atlantic over the 25 year period 1968 1993 of midtroposphere observations the interannual variations in huascaran 18 o relate closely with the zonal wind variations over tropical south america at the 500 hpa level additionally there is some evidence that the spatial distribution of temperature anomalies in the western tropical atlantic has influence on the 500 hpa circulation and hence the isotopic fractionation of moisture advected across amazonia during el nino warming the moisture convergence axis over the atlantic ocean is commonly diverted northward leading to unusual warm and dry conditions over northeast brazil and 18 o enriched snowfall at huascaran this enrichment phase is enhanced when the peak pacific warming occurs during the first half of the calendar year coincident with the wet season over amazonia approximately 12 months later the el nino demise is affiliated with a reprisal of strong trade wind circulation and the resultant cool pluvial environment over amazonia triggers a reversal to strongly depleted isotope anomalies

thermochemical structures beneath africa and the pacific ocean large low velocity seismic anomalies have been detected in the earth s lower mantle beneath africa and the pacific ocean that are not easily explained by temperature variations alone the african anomaly has been interpreted to be a northwest southeast trending structure with a sharp edged linear ridge like morphology the pacific anomaly on the other hand appears to be more rounded in shape mantle models with heterogeneous composition have related these structures to dense thermochemical piles or superplumes it has not been shown however that such models can lead to thermochemical structures that satisfy the geometrical constraints as inferred from seismological observations here we present numerical models of thermochemical convection in a three dimensional spherical geometry using plate velocities inferred for the past 119 million years we show that earth s subduction history can lead to thermochemical structures similar in shape to the observed large lower mantle velocity anomalies we find that subduction history tends to focus dense material into a ridge like pile beneath africa and a relatively more rounded pile under the pacific ocean consistent with seismic observations

intraplate volcanism originating from upwelling hydrous mantle transition zone most magmatism occurring on earth is conventionally attributed to passive mantle upwelling at mid ocean ridges to slab devolatilization at subduction zones or to mantle plumes however the widespread cenozoic intraplate volcanism in northeast china1 3 and the young petit spot volcanoes4 7 offshore of the japan trench cannot readily be associated with any of these mechanisms in addition the mantle beneath these types of volcanism is characterized by zones of anomalously low seismic velocity above and below the transition zone8 12 a mantle level located at depths between 410 and 660 kilometres a comprehensive interpretation of these phenomena is lacking here we show that most or possibly all of the intraplate and petit spot volcanism and low velocity zones around the japanese subduction zone can be explained by the cenozoic interaction of the subducting pacific slab with a hydrous mantle transition zone numerical modelling indicates that 0 2 to 0 3 weight per cent of water dissolved in mantle minerals that are driven out from the transition zone in response to subduction and retreat of a tectonic plate is sufficient to reproduce the observations this suggests that a critical amount of water may have accumulated in the transition zone around this subduction zone as well as in others of the tethyan tectonic belt13 that are characterized by intraplate or petit spot volcanism and low velocity zones in the underlying mantle the widespread intraplate volcanism in northeast china and the unusual petit spot volcanoes offshore japan could have resulted from the interaction of the subducting pacific slab with a hydrous mantle transition zone

velocity variations in the crust and upper mantle beneath the tien shan inferred from rayleigh wave dispersion implications for tectonic and dynamic processes we used data from nuclear explosions and earthquakes recorded by the kyrgyzstan telemetered broadband seismic network to examine crustal structure in the tien shan region of central asia seventy nine measurements of fundamental and first higher mode rayleigh waves were analyzed using the single station multiple filtering technique to determine group velocity dispersions we found that there was a distinct difference in rayleigh wave group velocity values between different regions but the data could be combined in three groups 1 paths from the west and south across the turan platform and western tarim basin 2 paths across the eastern tarim basin and 3 nuclear explosions from the lop nor test site group velocity values were inverted to derive one dimensional shear wave velocity models for the tien shan region results reveal crustal thickness varying from 50 to 60 km with thickness increasing toward the eastern tien shan region in agreement with published crustal thickness maps for the region array analysis indicates that paths along the eastern tien shan and tarim tien shan are affected by lateral refractions and multipathing but we argue that these have a small effect on the measured dispersion curves our results indicate that upper mantle velocities in the eastern tarim and tien shan are significantly lower than those beneath the western tien shan and turan platform our results suggest that the boundary between these two regimes lies somewhere west of the depocenter of the tarim basin and east of kashgar china

complexity of holocene climate as reconstructed from a greenland ice core glaciochemical time series developed from summit greenland indicate that the chemical composition of the atmosphere was dynamic during the holocene epoch concentrations of sea salt and terrestrial dusts increased in summit snow during the periods 0 to 600 2400 to 3100 5000 to 6100 7800 to 8800 and more than 11 300 years ago the most recent increase and also the most abrupt coincides with the little ice age these changes imply that either the north polar vortex expanded or the meridional air flow intensified during these periods and that temperatures in the mid to high northern latitudes were potentially the coldest since the younger dryas event

path specific velocity structure of western china from surface wave dispersion we develop one dimensional 1 d path specific velocity models in western china using new rayleigh and love wave group and phase velocity dispersion measurements for 20 events in the region the earthquakes were grouped into three geographic clusters from which we compute the average phase and group velocity dispersion we invert the average dispersion curves simultaneously for 1 d shear velocity models appropriate for the three central asian paths using three previous shear velocity models as initial models the models are validated by forward modeling waveforms of recent events the crustal thickness beneath western china in the vicinity of the lop nor test site is 50 60 km and our velocity models are consistent with major geologic features e g basins and mountain ranges and previous structural models for this region

tectonic setting of the taltson magmatic zone at 1 92 0 ga a granitoid based perspective the paleoproterozoic taltson magmatic zone is one of the key tectonic features of western laurentia the existing tectonic model for the belt envisions its formation by subduction of oceanic crust beneath a continental margin followed by direct collision between formerly separate crustal blocks we tested this model by comparing the large geochemical and isotopic database available for taltson magmatic zone granitoids with similar databases for phanerozoic granitoid suites from different tectonic environments the comparison reveals that the early granitoid suite of the taltson magmatic zone which had been ascribed to the subduction phase of orogenesis lacks the mantle signature apparent in granitoids of phanerozoic continental margin arc settings instead both early and late suites appear to have an intracrustal origin similar to mesozoic and cenozoic granitoids of the cordilleran interior of western north america which formed in the distant hinterland of a convergent plate margin in light of thes

crust and upper mantle structure beneath western china from p wave travel time tomography 1 three dimensional velocity images of the crust and upper mantle beneath western china are obtained through seismic tomography by using p wave arrival times of local regional and teleseismic events recorded in chinese and kyrgyzstan seismic networks at shallow depths most mountain belts and tectonically elevated areas are imaged as higher velocities relative to adjacent sediment filled basins and foreland depressions with lower velocities at mid lower crust depths the kyrgyz tian shan is underlain by lower velocity material and a distinct low velocity zone in the south north direction is observed between the eastern and western parts of the chinese tian shan the moho of the southern tarim basin has a greater depth over 50 km in front of the western kun lun compared to the northern and western tarim basin lateral heterogeneity within the upper mantle is apparent at depths from 71 to 571 km the uppermost mantle beneath the kyrgyz tian shan altay qi lian and eastern kun lun is characterized by low velocity material that is probably related to the upwelling of hot mantle the lithospheric thickness varies from 120 to 170 km beneath the chinese tian shan and northern tibetan plateau to 200 250 km beneath the tarim basin deep coupling pattern of the chinese tian shan with adjacent provinces can be classified into the embedding detaching and sinking and underthrusting of lithospheric roots in addition the lithosphere of the northern edge of the tibetan plateau seems to be thickened in contrast to the central part of the northern plateau north dipping low velocities exist in the upper mantle between the tibetan plateau and provinces to its north which might indicate mantle flow from the tibetan plateau toward surrounding areas but it has been blocked by the thick tarim lithosphere

constraints on the structure of the tibet plateau from pure path phase velocities of love and rayleigh waves pure path phase velocities of love and rayleigh waves across the tibet plateau are determined for the period range 30 90 s and for two opposite directions of propagation along the length of the plateau the method used is a two event method similar in principle to the classical two station method where the roles of stations and events are interchanged the success of this method is due to a favorable geometry whereby events located at each end of the plateau align to within 1 of a great circle path with one wwssn station at teleseismic distance to the east and one to the west body wave modeling is used to constrain depth and source mechanism of the events in order to calculate the corresponding source phases for surface waves phase velocities are determined to within 0 02 km s or better for rayleigh waves and 0 007 km s for love waves the constraints added by these data to the crust and upper mantle structure beneath tibet are discussed in the light of previous studies the best fitting model has a 65 km thick crust with low average crustal velocities and an sn velocity of 4 65 km s the low velocity zone is limited to the depth range 100 150 km the interesting result of this study is that both love and rayleigh wave data can be matched to within 1 in phase velocity by a unique isotropic model this points to a similarity with a stable region upper mantle structure such as that of the canadian shield finally additional rayleigh wave phase velocity data are used to compare propagation on different paths in the vicinity of tibet the tarim basin to the north of tibet stands out as having a distinct crustal structure more similar to an average tectonic region structure moreover evidence is presented for the existence of a very low velocity region at the western end of tibet which correlates well with a pronounced gravity low observed in that area

phase relations in the transition zone phase relations in the systems mgo al2o3 sio2 and cao mgo sio2 have been investigated experimentally at 166 226 kbar pressures and 1350 2500 c temperatures with a split sphere anvil apparatus ussa 2000 mgsio3 ilmenite is stable to lower pressures 175 kbar than found previously casio3 perovskite forms at p bar 15t c 151 000 three new high pressure phases are reported a phase with the diopsidic composition the cm phase a high pressure polymorph of al2o3 and superphase b with the tentative composition mg10si3o14 oh f 4 the invariant point for coexisting majorite mg4si4o12 perovskite mgsio3 beta phase mg2sio4 and liquid has been located at 224 kbar 2430 c with the eutectic melt composition on the enstatite forsterite join at 40 44 wt of forsterite the melting temperature of mgsio3 perovskite at 225 kbar is predicted to be 2600 c the new data made possible the calculation of a temperature pressure phase diagram for the system cao mgo al2o3 sio2 cmas in the pressure range 0 280 kbar the mineralogy of the earth s mantle and the possible mechanisms for producing large seismic velocity gradients in the transition zone are discussed on the basis of the derived phase relations

winter depression tracks and climatological jet streams in the southern hemisphere during the fgge year a band pass filter transparent to fluctuations in the 2 5 6 day period range is applied to a set of twice daily analyses covering the 1979 fgge year winter of the southern hemisphere fields analysed include msl pressure 500mb height 300mb wind and the meridional heat flux due to transient eddies at 850mb variance maxima in these filtered fields indicate regions of high cyclonic activity with favoured cyclolysis areas in the vicinity of the antarctic coastline also showing up in the msl pressure statistics using these results supplemented by data on the distribution of cyclogenesis we are able to identify the major depression tracks in this analysis extensive use is made of studies relating satellite observed cloud vortices to the various stages of cyclonic development in general it appears there was significantly more activity in the eastern hemisphere than in the western during the 1979 winter by evaluating the terms in the time averaged zonal momentum equation using the unfiltered data set it is possible to assess the role of transient eddies in the maintenance of the time mean zonal flow this analysis shows that coriolis acceleration associated with poleward time mean ageostrophic flow at the tropopause level dominates the forcing of the jet centred around 25 s but that convergence of eddy momentum flux maintains the higher latitude jet around 50 s however a significant contribution to the latter jet comes from poleward ageostrophic flow south of africa

greenland antarctic phase relations and millennial time scale climate fluctuations in the greenland ice cores abstract the greenland grip gisp2 and antarctic byrd ice cores are examined in the frequency domain with the data synchronized using common methane variations using conventional time series analysis a simple picture emerges there is low frequency periods longer than about 10 kyr coherence between the two records consistent with a simple time delay antarctica leading by 1 2 kyr two geographical data points are however inadequate to infer causality from the south to north time lag at higher frequencies in the millennial band there is no measurable average relationship between the records and they appear to represent different processes with a regional character a serious question concerns the extent to which the greenland cores reflect tracer concentration change without corresponding abrupt climate change the large abrupt shifts in ice 18 o can be rationalized as owing to wind trajectory shifts perhaps of rather modest size many different physical phenomena probably do however contribute to the record as a function of time and time scale

paleomagnetic study of mesozoic continental sediments along the northern tien shan china and heterogeneous strain in central asia a paleomagnetic study of rocks from the northern foot of the tien shan and the southern border of the dzungar basin east of urumqi 44 2 n 86 0 e spanning ages from middle jurassic to early tertiary was carried out to constrain the tectonic evolution in central asia since mesozoic time five middle jurassic sites reveal a remagnetized direction close to the present earth field in geographic coordinates d 6 6 i 72 6 95 7 4 thirteen out of 17 upper jurassic and lower cretaceous sites yield a characteristic direction stratigraphic coordinates of d 12 7 i 48 6 95 5 5 nine of 16 upper cretaceous and lower tertiary sites provide a characteristic direction of d 12 5 i 51 3 95 6 9 the latter two directions pass fold and reversal tests the pole positions are close to each other and to the besse and courtillot 1989 1990 eurasian apparent polar wander path for ages ranging from 130 to 70 ma however the difference in paleolatitudes amounts to about 5 9 3 7 which could indicate significant continental shortening in the altai mountains and perhaps further north subsequent to india asia collision the pole positions from the dzungar basin are close to those found for the tarim li et al 1988a leading to an insignificant paleolatitude difference 3 0 6 9 but showing a larger difference in declination 8 6 8 7 these paleomagnetic results are compatible with a model of heterogeneous deformation in the western part of the collision zone between india and siberia a significant shortening in the altai a slight counterclockwise rotation of the dzungar block the westward increasing shortening in the tien shan with attendant clockwise rotation of the tarim block are all consistent with this model in which tibet the tien shan and the altai undergo differential strain along strike in a relay fashion with the total india siberia convergence remaining approximately constant

high resolution model based investigation of moisture transport into the pacific northwest during a strong atmospheric river event abstracta series of precipitation events impacted the pacific northwest during the first two weeks of november 2006 this sequence was punctuated by a particularly potent inland penetrating atmospheric river ar that produced record breaking precipitation across the region during 5 7 november the precipitation caused destructive flooding as far inland as montana s glacier national park 800 km from the pacific ocean this study investigates the inland penetration of moisture during the event using a 4 1 33 km grid spacing configuration of the weather research and forecasting wrf modeling system a high resolution simulation allowed an analysis of interactions between the strong ar and terrain features such as the cascade mountains and the columbia river gorge cr gorge moisture transport in the vicinity of the cascades is assessed using various metrics the most efficient pathway for moisture penetration was through the gap i e cr gap between mt adams and mt hood which includes the cr gorge w

earthquake depth estimation using the f trace and associated probability determining the depths of seismic disturbances is of great importance when monitoring compliance with the comprehensive nuclear test ban treaty ctbt in plate tectonic studies and in seismic hazard assessments we have developed a semiautomated method that uses the output from the f detector a processing technique that detects correlated signals crossing a seismometer array as a tool for identifying candidate depth phases and hence estimating hypocenter depth the f trace can be interpreted approximately in terms of probability this can be used to help interpret signals and identify candidate depth phases here a method of calculating f probability traces that optimally highlight candidate depth phases is presented the values of the probability trace at the predicted times for pp and sp for a given depth are then weighted and summed over several high quality medium aperture array stations a clear maximum in the trace sum function with depth is interpreted as the probable hypocenter depth results for earthquakes from the lop nor and hindu kush regions indicate that this method of depth estimation is effective for many earthquakes with magnitude greater than about m b 4 0 and depths greater than around 10 km the method is best suited as a tool to be used by analysts to estimate the depths of individual seismic disturbances of special interest or groups of earthquakes in regions where there is a good azimuthal distribution of medium aperture array stations

three dimensional velocity structure and earthquake locations beneath the northern tien shan of kyrgyzstan central asia we used the arrival times of local earthquakes and quarry blasts recorded by the kyrgyzstan broadband network knet to obtain three dimensional 3 d p and s wave velocity models of the upper crust beneath an actively deforming mountain front and its associated foreland in the kyrgyz tien shan the continuous velocity models described by cubic b spline interpolation of the squared slowness over a regular 3 d grid were computed by simultaneous inversion of hypocenter and medium parameters exact ray tracing was done in the smooth 3 d medium by shooting rays from the sources to the stations by an analytical perturbation method based on the paraxial ray theory the deduced large sparse linear system was solved using the damped iterative least squares algorithm lsqr the stability and resolution of the result was qualitatively tested by two synthetic tests the spike test and the checkerboard resolution test we found that the models are well resolved up to a depth of 27 km for most parts of our image domain the p and s wave velocity models are consistent with each other and provide evidence for marked heterogeneity in the upper crustal structure beneath the northern tien shan at shallower depths 7 km the sediment filled foreland is imaged as a relatively lower velocity feature compared to the mountains which are cored by crystalline basement rocks in contrast at midcrustal depths the mountains are underlain by relatively lower velocity materials compared to the foreland a distinct contrast in velocity structure is also observed between the eastern and western parts of the kyrgyz range at midcrustal depths with the presence of relatively higher velocities toward the east the seismicity is concentrated near the traces of major active faults and extends deeper beneath the foreland compared to the mountains the regional compression in the tien shan is accommodated along a series of high angle reverse faults distributed throughout the orogenic system that extend from the surface down to midcrustal depths the range bounding fault zone can be identified by a sharp lateral gradient in seismic velocities with a pronounced southward dip combined with a zone of seismicity that also deepens to the south and reverse fault source mechanisms from moderate sized events a pronounced low velocity zone lvz is imaged in the p wave field at midcrustal depths beneath the western part of the kyrgyz range this lvz is presumably correlatable with reported high conductivity zones in this region that have been proposed to mark active fault zones along which fluid migration occurs the location of the lvz which is closely coincident with the depth of maximum earthquake generation might imply that it is a crustal decoupling zone at the brittle ductile transition

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

temperature history and accumulation timing for the snowpack at gisp2 central greenland previous research has documented a close association between high resolution snow pit profiles of hydrogen and oxygen stable isotope ratios and multi year special sensor microwave imager ssm i 37 ghz brightness temperature data in central greenland comparison of the ssm i data to profiles obtained during the 1989 91 field seasons indicated that d and 18 o data from the near surface snow at the greenland summit are a reliable high resolution temperature proxy to test this new technique further additional stable isotope data were obtained from a 2 m snow pit constructed during late june 1995 near the gisp2 site this new profile supported by pit stratigraphy and chemistry data confirms the utility ofcomparing stable isotope records with ssm i brightness temperatures the sub annual variation of the d record at the gisp2 site was determined using 15 match points from approximately december 1991 through june 1995 and was guided in part by time constrained hoar layers the close association of these temperature proxies supports the assertion that snow accumulation occurs frequently through the year and that the isotope record initially contains temperature information from many times of the year this is also independently confirmed by analysis of h 2 o 2 data the slope of the multi year t vs 6 correlation was evaluated along with the sub annual variation in the amount rate and timing of accumulation these new results are consistent with those from the previous study and they also demonstrate that the snow in this area initially contains temperature and chemical records with sub annual resolution this encourages confident interpretation of the paleoclimatic signal variations in the gisp2 and grip deep cores

observation of atmospheric and climate dynamics from a high resolution ice core record of a passive tracer over the last glaciation here we present a temporal analysis of diluted calcium from the greenland ice core project summit ice core over a length corresponding to the duration of the last glacial period 92 8 ka our analysis suggests that this signal can be split into two distinct temporal components whose dynamics are characterized by respective timescale regimes timescales longer than approximately 200 years show a strong negative correlation with the temperature proxy 18 o signal this we interpret as a result of the temperature dependence of processes governing source area efficiency at faster timescales 200 years correlation with the temperature proxy is significantly weakened while its variability or mean absolute deviation is negatively correlated with the 18 o this we believe is a sign of the turbulent nature or storminess of the atmosphere during the glacial climate furthermore this component of the signal displays intermittency and multifractality supporting our interpretation of an observation of atmospheric dynamics this then provides a signal of atmospheric and climate dynamics back to 92 ka

thermodynamics of the mgo feo sio2 system up to 140 gpa application to the crystallization of earth s magma ocean at the end of earth s accretion and after the core mantle segregation the existence of a basal magma ocean at the top of the core mantle boundary cmb depends on the physical properties of mantle materials at relevant pressure and temperature present day deep mantle structures such as ultralow velocity zones and low shear velocity provinces might be directly linked to the still ongoing crystallization of a primordial magma ocean we provide the first steps toward a self consistent thermodynamic model of magma ocean crystallization at high pressure we build a solid liquid thermodynamic database for silicates in the mgo feo sio2 system from 20 gpa to 140 gpa we use already published chemical potentials for solids liquid mgo and sio2 we derive standard state chemical potential for liquid feo and mixing relations from various indirect observations using this database we compute the ternary phase diagram in the mgo feo sio2 system as a function of temperature and pressure we confirm that the melt is lighter than the solid of same composition for all mantle conditions but at thermodynamic equilibrium the iron rich liquid is denser than the solid in the deep mantle we compute a whole fractional crystallization sequence of the mantle and show that an iron rich and fusible layer should be left above the cmb at the end of the crystallization

denudation outpaced by crustal thickening in the eastern tianshan the modern high topography of the tianshan resulted from the reactivation of a paleozoic orogenic belt by the india asia collision today the range exhibits tectonically active forelands and intermontane basins based on quantitative morphotectonic observations and age constraints derived from cosmogenic 10be dating single grain post infrared infrared stimulated luminescence p ir irsl dating and modeling of fault scarp degradation we quantify the deformation in the nalati and bayanbulak intermontane basins in the central eastern tianshan our results indicate that at least 1 4 mm yr of horizontal crustal shortening is accommodated within these two basins this shortening represents over 15 of the 8 5 0 5 mm yr total shortening rate across the entire range at this longitude this shortening rate implies that the eastern central tianshan is thickening at a mean rate of 1 4 mm yr a rate that is significantly higher than the average denudation rate of 0 14 mm yr derived from our cosmogenic analysis this discrepancy suggests that the tianshan range has not yet reached a steady state topography and remains in a transient state of topographic growth most likely due to limited denudation rates driven by the arid climate of central asia

melting of forsterite mg2sio4 from 9 7 to 16 5 gpa a multianvil apparatus has been used to determine the pressure temperature melting curve of forsterite from 9 7 to 16 5 gpa at 10 1 gpa a singular point occurs that marks the change from congruent melting at lower pressures to incongruent melting forsterite periclase liquid at higher pressures the melting curve also passes through two invariant points at one 15 6 gpa 2310 c the phases forsterite periclase anhydrous b and liquid coexist and the melting reaction changes from forsterite periclase liquid at lower pressures to forsterite anhydrous b liquid at higher pressures at the other 16 7 gpa 2315 c the phases forsterite modified spinel anhydrous b and liquid coexist and the melting reaction changes from forsterite anhydrous b liquid at lower pressures to modified spinel anhydrous b liquid at higher pressures the simon equation p gpa 2 44 t k 2171 11 4 1 fits both our melting curve data and the lower pressure data of davis and england 1964 at low pressures the melting curve of forsterite lies at higher temperatures than that of enstatite but the two curves cross at 13 3 gpa because of the lower dt dp slope of the forsterite melting curve this causes the forsterite enstatite eutectic to shift toward forsterite as pressure increases but our data are consistent with earlier findings that the shift is not sufficient to support an origin for the mantle by eutectic like melting at high pressures

is the greenland ice sheet bistable ice core work on greenland has produced dramatic evidence for an instability of the climate system in the north atlantic sector in this paper we provide climate modeling results indicating another possible example of a multiple equilibrium climate state where such behavior might apply to the ice sheet itself baseline sensitivity experiments in which the greenland ice sheet was removed simulate summer temperatures on greenland of about 10 c this number varied between about 6 and 14 c depending on specification of vegetation type elevation of greenland and orbital forcing the implied hysteresis indicates that the present geographic configuration may have been sufficient to maintain an ice free state prior to formation of the ice cap explanations for formation of the ice sheet therefore present a dilemma four possibilities involve undocumented miocene pliocene co2 excursions to values lower than present a high sensitivity of the climate system a variable sensitivity of the climate system or significant problems with the climate model a variable sensitivity is consistent with our results indicating a multiple steady state climate for greenland although most co2 scenarios do not predict a collapse of the greenland ice sheet in the future our results suggest that if it did present boundary conditions may be sufficient to maintain greenland in an ice free environment even after the greenhouse effect has dissipated

shear wave splitting and small scale convection in the continental upper mantle the deformation of the upper mantle beneath a collisional belt is key to the dynamics of the belt but this deformation is difficult to observe seismic azimuthal anisotropy manifested by shear wave splitting provides the best geophysical evidence of deformation in the upper mantle here we use observations of shear wave splitting to investigate deformation in the upper mantle beneath the tien shan in central asia we find that underneath most of the tien shan the fast direction of azimuthal anisotropy is roughly parallel to the axis of the belt but it deviates by nearly 90 where the upper mantle is anomalously hot the former relationship previously observed in other collisional belts seems to be usual for this environment the anomalous directions however provide evidence of a rising plume beneath the range suggesting more generally that the along strike flow of the mantle beneath collisional belts is a reflection of thermally driven convection

melting of subducted basalt at the core mantle boundary the geological materials in earth9s lowermost mantle control the characteristics and interpretation of seismic ultra low velocity zones at the base of the core mantle boundary partial melting of the bulk lower mantle is often advocated as the cause but this does not explain the nonubiquitous character of these regional seismic features we explored the melting properties of mid oceanic ridge basalt morb which can reach the lowermost mantle after subduction of oceanic crust at a pressure representative of the core mantle boundary 135 gigapascals the onset of melting occurs at 3800 kelvin which is 350 kelvin below the mantle solidus the sio2 rich liquid generated either remains trapped in the morb material or solidifies after reacting with the surrounding mgo rich mantle remixing subducted morb with the lowermost mantle

short period rayleigh wave group velocity tomography through ambient noise cross correlation in xinjiang northwest china abstract high quality short period rayleigh wave group velocity tomography is conducted through ambient noise cross correlation among 54 stations in the newly upgraded xinjiang provincial digital seismic network in northwest china the velocity maps obtained in this study give more details in most parts of xinjiang than previous surface wave studies that mostly focused on large scale patterns in eurasia asia or the whole of china the tomography results have a high correlation with the major tectonic and geological features in the study area in general low velocities are associated with the two basins and high velocities are associated with the two mountain belts in the xinjiang area the southernmost part of the tianshan mountains has the same velocity structure as that of the neighboring part of the tarim basin implying that they may have the same crustal composition the velocity in the tarim basin is spatially inhomogeneous due to the fact that it comprises several sub blocks that have different thickness of sediments and crustal layers in the dzungaria basin as the period becomes longer the low velocity zone shrinks toward the south reflecting the fact that the sediments and the upper crust in the southern part of the dzungaria basin are thicker than in the northern part

receiver functions for the tien shan analog broadband network contrasts in the evolution of structures across the talasso fergana fault we determined the structure of the crust beneath the central and western tien shan by analyzing broadband 1 20 s analog seismograms of converted p sv phases generated by earthquakes at teleseismic distances and recorded by 14 seismograph stations the one dimensional structures that best explain the waveforms reveal pronounced differences in crustal velocities east and west of the talasso fergana fault specifically the transition zone between the crust and the mantle east of the fault is about 2 times broader than that west of the fault also velocities at depths between 10 and 35 km are about 10 lower in the east although the depth range of these lower velocities is not well resolved the talasso fergana fault is an important boundary for other observables in addition to the structural discontinuities observed at the surface the areas east of the talasso fergana fault are associated with abnormally low mantle velocities outcrops of basalt low q and short wavelength variations in anisotropy integrating these observations we interpret the broad mantle gradient as being due to vertical intrusions of mantle material into the lower crust likewise the low velocities in the midcrust could be thermally induced or due to the introduction of magmatically derived fluids the gross contrast in structure east and west of the talasso fergana fault could reflect a contrast in the dynamics of mountain building in these two regions we postulate that while crustal shortening is the dominant mechanism controlling topography west of the talasso fergana fault vertical uplift caused by a mass deficiency in the upper mantle may contribute significantly to the generation and maintenance of the high elevations east of the fault

thermal control on post orogenic extension in collision belts abstract intracontinental extension develops in two different ways in the rhine graben the baikal or the east african rifts it is localized in a long and narrow zone along a few normal faults which often delineate a single graben in contrast in the basin and range province or the tibetan plateau it is distributed over a much broader area up to more than 1000 km across this difference arises from differences in rheology and applied forces widespread extension probably reflects the thinning of a previously thickened crust geological observations indicate that only wide orogenic belts undergo late or post orogenic thinning a related fact is that anatectic granites seem to be most abundant in wide orogenic belts the general correlation between belt width and occurrence of both extension and anatectic granites suggest that it reflects in part the characteristics of horizontal heat transfer between thickened crust and surroundings in wide orogenic plateaux the large amount of heat produced in the crust by radioactive decay and lack of erosion leads to high temperatures in narrow mountain belts horizontal heat transfer and high erosion rates concur to prevent temperatures from rising to values at which the crust may yield in extension we have tested this hypothesis using transient two dimensional numerical models of orogenic belts focussing on the effects of the shortening rate the final width of the belt and the rate of crustal radiogenic heat production in the range of geological values the shortening rate has little influence on the results crustal temperatures increase as a function of belt width we find that the sensitivity of crustal temperatures to belt width is most pronounced in the 100 300 km width range and for large values of crustal heat generation the pressure temperature paths followed by geological formations depend on the belt width which is consistent with available data the integrated shear strength of the lithosphere decreases with time as the belt is being built and then eroded this evolution is sensitive to belt width if extension occurs when the integrated shear strength drops below a critical value our results yield a framework for comparing different orogenic belts we predict that extension starts late in the history of wide belts and never occurs in narrow belts a final implication of this study is that the average rate of crustal heat production is probably close to 1 1 10 6 w m 3 which is in the upper range of possible values we present a simple and convenient diagram summarizing the thermal characteristics of orogenic belts as a function of width and shortening rate