sediment characteristics in the north branch of the yangtze estuary based on radioisotope tracers nuclide specific activity and sediment grain size were analyzed at locations along the north branch of the yangtze changjiang estuary the spatial distributions of various radioisotopes are presented along with the sources and applications of these nuclides for studies of the aquatic environment the specific activities of sediment radionuclides in the north branch increase toward the ocean indicating that the sediment is transported from the downstream side of the estuary into the north branch the 226ra 228ra ratio agrees well with the observed results and can be used to identify trends in erosion and accretion in the north branch

multiple dating approaches applied to the recent sediments in the yangtze river changjiang subaqueous delta the accumulation rate of recent deposits in a delta environment is critical to the study of delta dynamics and their sustainable management the most commonly used dating approach for recent 100

the cr renazzo type carbonaceous chondrite group and its implications abstract a petrologic geochemical and oxygen isotopic study of eight meteorites identified as cr renazzo type chondrites reveals that they have a set of similar properties that distinguishes them from other chondrite groups and confirms cr as a carbonaceous chondrite group characteristics of the cr group include 1 1 abundant large multilayered fe ni metal rich type i chondrules 2 2 abundant matrix and dark inclusions di that contain microchondrules microfragments and magnetite framboids and platelets 3 3 unique assemblages of serpentine and chlorite rich phyllosilicates and ca carbonates 4 4 ca carbonate rims on chondrules 5 5 abundant fe ni metal with a positive ni vs co trend and a solar ni co ratio 6 6 low abundance of refractory rich inclusions 7 7 amoeboid olivine aggregates aoa with mn rich and mn poor forsterite and 8 8 oxygen isotopic compositions that form a unique mixing line the cr chondrites are breccias consisting of two major components the large layered chondrules and the matrix dark inclusions al rais is an anomalous member in having a higher abundance of the dark inclusion component 70 vol and this accounts for its having a higher volatile content than other members of the group the conditions that prevailed during aqueous alteration of the cr chondrites differed from those of other hydrated chondrite groups and may be the result of a higher temperature environment than that for the ci and cm chondrites the cr chondrite components chondrules matrix dark inclusions etc experienced aqueous alteration to differing degrees prior to assembly of the host chondrites and dark inclusions represent a lithology that was altered by water to a greater degree than the rest of the meteorite the overall degree of hydration in cr chondrites varies among meteorites with al rais being the most hydrated the oxygen isotopic variation of the whole rocks chondrules and matrices may be related to degree of hydration indicating that cr chondrites interacted with a water rich component having heavy oxygen and that was the same as ci and cm water

alteration of mesostasis in chondrules and aggregates from three c2 carbonaceous chondrites abstract microprobe analyses of mesostasis glass and phyllosilicate spinach in a variety of chondrules and aggregates from the c2 chondrites murchison essebi and renazzo suggest that a two stage alteration process acted on glass to produce the current range of spinach compositions the first stage was short but active coinciding both with a period of vigorous gardening of the c2 parent regolith and with the pervasive alteration that modified the proportion of matrix phyllosilicates in c2 meteorites during this stage mesostasis glass was hydrated and was mg enriched by limited reaction with chondrule and aggregate phenocrysts the second alteration stage involved slow but extensive reactions between mesostasis material and altered matrix resulting in a field of fe enriched spinach compositions that is distinctive for each meteorite

rock magnetic properties of the fine grained sediment on the outer shelf of the east china sea implication for provenance the rock magnetic properties of surface sediments from the fine grained depositional area on the outer shelf of the east china sea an area surrounded by sands were investigated with a view to providing information on the sediment provenance multiple magnetic parameters such as magnetic susceptibility anhysteretic remanent magnetization saturation remanent magnetization sirm coercivities of sirm and s ratios relative abundance of low coercivity magnetic minerals were measured for all 179 surface samples and partial representative samples were examined for their magnetic hysteresis parameters temperature dependence of magnetic susceptibility and x ray diffraction spectra our research indicates that the magnetic mineralogy is dominated by magnetite with a small amount of hematite and is primarily of a pseudo single domain to multidomain nature with a detrital origin the magnetic concentration in the study area generally decreases to the east or southeast accompanied by magnetic particle fining to the east or northeast the geographic pattern of magnetic properties is most reasonably explained by a major source of sediment jointly from the erosion of the old huanghe river deposit and the discharge of the changjiang river the rock magnetic data facilitate understanding of the transport mechanism of fine grained sediments in the outer shelf of the east china sea

particle dynamics of the changjiang estuary and adjacent coastal region determined by natural particle reactive radionuclides 7be 210pb and 234th 1 the timescale of transport processes in estuarine and coastal regions can be evaluated using natural radionuclides with different half lives the distribution patterns of 7be 210pb and 234th in the water column from april to july 2008 were used to calculate the removal and residence times in the changjiang estuary the results showed that the maximum particulate activities of 7be 210pb and 234th were observed approximately 150 km downstream the turbidity maximum zone of the freshwater end number the mean distribution coefficients kd cm3 g 1 of the high suspended particulate matter spm group are higher than those of the lower spm group for 7be and 210pb for 234th the reverse is true based on a material balance in two dimensional models of 7be 210pb and 234th in the changjiang river mouth the removal times of these nuclides were approximately 0 66 12 1 6 21 and 1 2 5 4 days respectively the residence times increased toward the seaward side in the coastal region the removal times of 7be 210pb and 234th calculated by material balance in one dimensional models were approximately 1 1 26 1 2 27 and 0 70 23 days respectively moreover an enhanced resuspension process not only controlled the partitioning of 7be 210pb and 234th between the particulate and dissolved phases but also this process may play a dominant role in controlling the dynamic behavior of spm in the water column compared with the advection input output fluxes of the spm in the river mouth areas the removal and the resuspension fluxes were comparable in the estuary meanwhile old composition whose deposition into the seabed for a long time is enough for 7be to decay completely occupied only a small part in the resuspended sediment during resuspension process

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

investigating enso and wpwp modulated typhoon variability in the south china sea during the mid late holocene using sedimentological evidence from southeastern hainan island china abstract the link between tropical cyclone tc activity in the south china sea scs and global climate change is commonly debated and there is a clear need for long term geological records of tc activity if we are to clarify this connection multi millennial high resolution paleo storm records from the scs are rare in the region and this causes difficulties for those exploring potential climate drivers of tc variability over centennial to millennial timescales and reduces our ability to fully assess the risks associated with future tc activity this paper presents an age constrained mud dominated sedimentary sequence from a coastal lagoon on hainan island china multiproxy analyses incorporating chronological lithological sedimentological and geochemical evidence were used to infer storm deposits preserved within the sequence and to reconstruct a time series of storm activity in the scs during the mid to late holocene this long sedimentary record shows that tcs were highly active over the periods 5500 to 3500 and 1700 to 0 cal yrs bp and these periods contrast with a relatively quiet period 3500 1700 cal yrs bp an apparent inverse correlation between tc reconstructions from the scs and those from the korean peninsula and japan implies an oscillating pattern across the scs and western north pacific wnp over centennial to millennial timescales a comparison between the sedimentary and paleoclimatic records implies that the el nino southern oscillation was not the only mechanism responsible for typhoon variability over the past 7500 cal yrs bp suggesting that other factors such as the thermal state of the western pacific warm pool likely also had a strong influence on both scs and wnp tc variability

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

organic matter and metamorphic history of co chondrites abstract the metamorphic grades of a series of eight co3 chondrites alha77307 colony kainsaz felix lance ornans warrenton and isna have been quantified the method used was based on the structural grade of the organic matter trapped in the matrix which is irreversibly transformed by thermal metamorphism the maturation of the organic matter is independent with respect to the mineralogical context and aqueous alteration this metamorphic tracer is thus valid whatever the chemical class of chondrites moreover it is sensitive to the peak metamorphic temperature the structural grade of the organic matter was used along with other metamorphic tracers such as petrography of opaque minerals fa and fs silicate composition in type i chondrules presolar grains and noble gas p3 component abundance the deduced metamorphic hierarchy and the attributed petrographic types are the following alha77307 3 03 for most metamorphosed objects the peak metamorphic temperature can be estimated using a geothermometer calibrated with terrestrial metasediments beyssac o goffe b chopin c and rouzaud j n 2002 raman spectrum of carbonaceous material in metasediments a new geothermometer j metamorph geol 20 859 871 a value of 330 c was obtained for allende cv chondrite warrenton and isna consistent with temperatures estimated from fe diffusion weinbruch s armstrong j and palme h 1994 constraints on the thermal history of the allende parent body as derive from olivine spinel thermometry and fe mg interdiffusion in olivine geochim cosmochim acta 58 2 1019 1030 from the ni content in sulfide metal assemblages zanda b bourot denise m and hewins r 1995 condensate sulfide and its metamorphic transformations in primitive chondrites meteorit planet sci 30 a605 and from the d002 interlayer spacing in poorly graphitized carbon rietmeijer f and mackinnon i 1985 poorly graphitized carbon as a new cosmothermometer for primitive extraterrestrial materials nature 315 733 736 the trapped noble gas and c content appear to be sensitive but not precise metamorphic tracers indicating that the ornans paradox does not exist major problems with the current petrologic types derived from induced thermoluminescence are pointed out

variation in sedimentary 210pb over the last 60 years in the yangtze river estuary new insight to the sedimentary processes abstract anthropogenic activities have decreased the sediment transport from catchment to the river dominated continental margin mainly through river damming that controlled the estuarine and associated shelf modern sedimentation in this study radioisotopes 210pb 210pbex and 226ra and 137cs grain size and x radiograph were combined to evaluate the modern sedimentary processes in the yangtze river estuary yre we found that seabed cores collected on the estuary and associated shelf show a direct temporal correlation between decreases in initial activity and burial flux of 210pbex and suspended sediment load in relation to river damming and soil conservation from 1950 to 2016 most of sediment cores are characterized by low uniform and reverse 210pb patterns at surface and negligible sediment accumulation rates sars indicating that due to the limited sediment supply following the construction of the three gorges dam in 2003 erosion and remobilization of fine grained sediments by energetic tidal currents and biological mixing tends to have become determinant forces in controlling the fate of modern sediment burial in the yre moreover these results indicated that decline in sediment load and additional input of eroded materials will largely violate the basic assumption of constant 210pb flux raising a substantial challenge for 210pb chronology in the river dominated continental margins however we suggest that radiotracer 210pb could provide critical information for understanding the complex the sedimentary processes e g terrestrial sediment supply and redistribution by tidal currents and assessing past environmental status on the river and or tidal dominated estuaries subject to human modification

provenance discrimination of siliciclastic sediments in the middle okinawa trough since 30 ka constraints from rare earth element compositions the late quaternary paleoceanography and paleoenvironment in the okinawa trough east china sea have been well reconstructed over the last decade while in contrast the provenance of terrigenous sediments that have accumulated there remains enigmatic in this study rare earth elements ree were used to investigate provenance changes in sediments from core dgks9604 taken from the middle okinawa trough discrimination plots based on ree fractionation parameters suggest that the cored sediments have variable provenances over the last 30 ka with the lower part ca 31 8 2 ka ultimately originating mostly from the changjiang yangtze river and the upper part 7 1 0 ka primarily from taiwan during the last glacial maximum and early deglacial period sea level was low and the main stream of the kuroshio current was deflected to the east of the ryukyu islands as a result the changjiang derived sediments might have dominated sedimentation of the middle okinawa trough however since about 7 ka the main stream of the kuroshio current strengthened in the area of the trough as sea level approximated the modern position this caused near bottom transport of fine grained sediments from the continental margin to the trough to become weak and instead taiwan derived terrigenous sediments dominated in the middle trough the changing provenances of terrigenous sediments into the middle okinawa trough are closely related to the evolution of oceanic circulation and sea level in the east china sea two tephra layers in the core have distinct ree compositions and correlate well with two volcanic eruptions at 7 6 and 25 8 ka in southern japan

crustal structure beneath ne china imaged by necessarray receiver function data abstract we analyzed tens of thousands of receiver function data recorded by 185 broadband seismic stations to study the crustal structure beneath the northeast china moho depth and average crustal v p v s ratio were measured at each station using the h grid searching technique for stations located above unconsolidated sediments we applied the h method to remove strong shallow reverberations and generate subsurface receiver functions that allow for effective h analysis the measurements show that the songliao basin has a relatively thin crust 31 km and the moho depth increases significantly from southeast 27 km to northwest 35 km the northwestward tilting of the songliao basin may suggest that it was initiated by lithospheric flexure due to the load of the great xing an range in the jurassic before the large scale extension in the cretaceous moho depth varies from 26 7 km to 42 3 km across the study area with the shallowest and deepest moho being located at the eastern flank of the songliao basin and the great xing an range respectively the moho depth correlates well with the surface topography in the western part but not the central and eastern parts of the study area the residual topography computed based on the airy s isostasy model indicates that the high topography at the eastern flank of the songliao basin the changbaishan volcanic center and the southern end of the great xing an range is likely dynamically supported by the upper mantle

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

paired renazzo type cr carbonaceous chondrites from the sahara ten chondrites with chemical and mineralogical similarities to the carbonaceous chondrite renazzo were recovered at two locations of the sahara acfer 059 087 097 114 139 186 187 209 270 and el djouf 001 although the el djouf location is more than 500 km away from the acfer location all samples appear to result from a single fall based on chemical and petrographic similarities and supported by light element stable isotope geochemistry noble gas record and similar 26al contents the acfer el djouf meteorite is classified as a cr renazzo type carbonaceous chondrite this group presently comprises three non antarctic members al rais renazzo acfer el djouf and five antarctic meteorites the major lithological components of the acfer el djouf meteorite are large chondrules up to 1 cm in size mean diameter 1 0 0 6 mm chondrule and mineral fragments ca al rich inclusions feni metal about 8 10 vol and dark inclusions embedded in a fine grained fragment bearing groundmass mineral compositions of the ten acfer el djouf samples are similar to those of other cr chondrites most of the ca al rich inclusions are below 300 m in size and rich in melilite and spinel in some cais the rare phase caal4o7 is dominant fo rich cr bearing olivine fa0 4 and enstatite fs0 4 are the major phases of the chondrite the meteorite is mildly shocked with a shock stage of s2 indicating a peak shock pressure of 5 10 gpa for the bulk meteorite the oxygen isotopic compositions and carbon and nitrogen stable isotope geochemistry of the acfer el djouf samples are very similar to those of the other cr type chondrites the major element composition of the acfer el djouf meteorite is indistinguishable from cr chondrites when compared to renazzo the acfer el djouf samples however have systematically lower contents of the moderately volatile elements zn ga as au sb and se and the highly volatile elements br c and n this is thought to reflect primary differences between renazzo and the acfer el djouf meteorite

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

p wave velocity structure under the changbaishan volcanic region ne china from wide angle reflection and refraction data abstract we present velocity models determined by inverting refracted and reflected arrivals along two active source lines in the changbaishan volcanic region ne china we resolve a prominent low velocity zone lvz in the crust with velocities as low as 5 4 km s away from the lvz the velocity gradients in the crust are relatively smooth with average p wave velocities of about 6 0 6 5 km s the moho is at about 35 km depth thickening to about 40 km under the tianchi volcano and thinning to about 30 km under the lvz the lvz is located about 30 60 km to the north of the summit of the tianchi volcano the most recently active volcano in the region is about 30 75 km in north south extent is at most 35 km in east west extent and is in the depth range of about 10 25 km below the surface we use these results to constrain receiver function inversions and show that the receiver functions in the region are compatible with our findings with these data alone the significance of the lvz in non unique although we do not see any evidence to support the presence of partial melt in the crust and favor the interpretation that the lvz indicates a residual crustal magma chamber

early solar system processes recorded in the matrices of two highly pristine cr3 carbonaceous chondrites met 00426 and que 99177 the mineralogy and bulk compositions of the matrices of the cr chondrites met 00426 and que 99177 have been studied using a combination of sem epma and tem techniques the matrices of these two chondrites are texturally chemically and mineralogically similar and are characterized by significant feo enrichments with respect to other cr chondrite matrices nearly flat refractory lithophile patterns variable volatile element patterns and a simple mineral assemblage dominated by amorphous silicate material and fe ni sulfides fine grained crystalline silicate phases such as olivine and pyroxene appear to be extremely rare in the matrices of both meteorites instead the mineralogy of matrices and fine grained rims of both meteorites consists of abundant amorphous feo rich silicate material containing nanoparticles of fe ni sulfides troilite pyrrhotite and pentlandite secondary alteration minerals that are characteristic of other cr chondrites e g renazzo and al rais such as phyllosilicates magnetite and calcite are also rare the texture and mineralogy of the matrices of met 00426 and que 99177 share many features with matrices in the primitive carbonaceous chondrites alh a77307 co3 0 and acfer 094 unique these observations show that met 00426 and que 99177 are very low petrologic type 3 chondrites that have escaped the effects of aqueous alteration unlike other cr chondrites which are typically classified as petrologic type 2 we suggest that these meteorites represent additional samples of highly primitive but extremely rare carbonaceous chondrites of petrologic type 3 00 according to the classification scheme of grossman and brearley 2005 the highly pristine nature of met 00426 and que 99177 provides important additional insights into the origins of fine grained materials in carbonaceous chondrites based on our new observations we infer that the amorphous silicate material and nanosulfide particles that dominate the matrices of these meteorites formed in the solar nebula by rapid condensation of material following high temperature events such as those that formed chondrules

transport of fallout plutonium to the ocean by the mississippi river mississippi river suspended sediment shows a continual decrease of239 240pu content over a seven year time period an exponential curve best fit through the data predicts a half time of decrease equal to 4 3 years however unsupported210pb a naturally occurring nuclide at steady state in the environment maintains constant concentration over the same time period the decrease in pu content of river sediment results from several factors cessation of atmospheric weapons testing transport of pu to deeper levels of soil profiles storage of sediment in floodplains and behind dams and dilution by erosion of older prebomb soil material most of the fallout pu in the mississippi drainage basin will remain on the continent unless there are major changes in erosion and sediment transport patterns in the basin itself

morphodynamic impacts of large scale engineering projects in the yangtze river delta morphodynamics of world s river deltas are increasingly affected by human activities which are of great ecological economic and social implications however impacts of human interventions in deltaic regions are insufficiently understood especially superimposed upon diminishing sediment supplies this study uses the heavily interfered yangtze river delta as an example to address this issue the morphodynamic impacts of the deepwater navigation channel project dncp during 1997 2013 are investigated through process based modeling approach delft3d and bathymetric data analysis the dncp was implemented in the mouth bar area of the yangtze river delta including the twin dikes and 19 groynes with the total length of 132 0 km hydrodynamic simulations indicate that the training walls resulted in weaker tidal flow and longer slack period at the east hengsha shoal ehs and stronger tidal flow at the subaqueous delta thus the ehs is characterized as a sediment accumulation zone after the completion of the training walls subsequently morphological modeling shows enhanced accretion at the ehs and enhanced erosion at the subaqueous delta when the training walls are taken into account numerical experiments further demonstrate that the above changes are mainly attributed to the seaward half of the northern training walls constructed in 2002 2005 this is probably the reason for the observed accretion peak of the ehs in 2002 2007 and the gradual increase in the erosion rate of the subaqueous delta after 2002 the schematized paths of sediment transport after the dncp indicate that sediment eroded from the subaqueous delta serves as an important source for accretion of the mouth bar area it is suggested that siltation promoting projects within the mouth bar area increased shallow shoal accretion and aggravated erosion at the subaqueous delta with the overall erosion of the yangtze river delta due to river sediment reduction large scale estuarine engineering projects substantially increase the complicacy of its morphodynamic pattern which merits close attention for sustainable delta management

surface wave array tomography in se tibet from ambient seismic noise and two station analysis i phase velocity maps summary empirical green s functions egfs between pairs of seismographs can be estimated from the time derivative of the long time cross correlation of ambient seismic noise these egfs reveal velocity dispersion at relatively short periods which can be used to resolve structures in the crust and uppermost mantle better than with traditional surface wave tomography we combine rayleigh wave dispersion estimates from egfs and from traditional two station ts analysis into a new approach to surface wave array tomography with data from dense receiver arrays we illustrate the methodology with continuous broad band recordings from a temporary seismographic network on the southeastern part of the tibetan plateau in sichuan and yunnan provinces sw china the egfs are robust under temporal changes in regional seismicity and the use of either ambient noise approximated by records without signal from events with magnitude mb 5 or 4 or surface wave coda produces similar results the egfs do not strongly depend on the presence of large earthquakes but they are not reciprocal for stations aligned in the n s direction this directionality reflects the paucity of seismicity to the north of the array using a far field representation of the surface wave green s function and an image transformation technique we infer from the egfs the rayleigh wave phase velocity dispersion in the period band from 10 30 s a classical ts approach is used to determine rayleigh wave phase velocity dispersion between 20 120 s together they constrain phase velocity variations for t 10 120 s which can be used to study the structure from the crust to the upper mantle beneath se tibet short and intermediate period 10 80 s phase velocities are prominently low suggesting that the crust and upper mantle beneath se tibet is characterized by slow shear wave propagation

transmission electron microscopy of subsolidus oxidation and weathering of olivine olivine crystals in basaltic andesites which crop out in the abert rim south central oregon have been studied by high resolution and analytical transmission electron microscopy the observations reveal three distinct assemblages of alteration products that seem to correspond to three episodes of olivine oxidation the olivine crystals contain rare dense arrays of coherently intergrown ti free magnetite and inclusions of a phase inferred to be amorphous silica we interpret this first assemblage to be the product of an early subsolidus oxidation event in the lava the second olivine alteration assemblage contains complex ordered intergrowths on 001 of forsterite rich olivine and laihunite distorted olivine structure with fe3 charge balanced by vacancies based on experimental results for laihunite synthesis kondoh et al 1985 these intergrowths probably formed by olivine oxidation between 400 and 800 c the third episode of alteration involves the destruction of olivine by low temperature hydrothermal alteration and weathering elongate etch pits and channels in the margins of fresh olivine crystals contain semi oriented bands of smectite olivine weathers to smectite and hematite and subsequently to arrays of oriented hematite crystals the textures resemble those reported by eggleton 1984 and smith et al 1987 we find no evidence for a metastable phase intermediate between olivine and smectite m eggleton 1984 the presence of laihunite exerts a strong control on the geometry of olivine weathering single laihunite layers and laihunite forsteritic olivine intergrowths increase the resistance of crystals to weathering preferential development of channels between laihunite layers occurs where growth of laihunite produced compositional variations in olivine rather than where coherency strain is associated with laihunite olivine interfaces

accumulation of anthropogenic and natural radionuclides in bottom sediments of the northwest pacific ocean abstract activities of anthropogenic radionuclides in bottom sediments of the northwest central and west caroline basins of the northwest pacific ocean are reported down core distributions of natural radionuclides were also investigated in order to elucidate the sedimentation processes of anthropogenic radionuclides in the seafloor in the northwest central basin the inventories of 239 240pu and 241am decrease from south to north while the opposite trend is observed for 137cs and 90sr this latitudinal gradient in the inventories of artificial radionuclides reflects higher fluxes of 239 240pu and 241am near the weapons test sites and transport of 137cs and 90sr over longer distances as well as the regional differences in sediment mixing and accumulation rates in the west caroline basin relatively low inventories of 239 240pu and 241am were observed due to the topographic isolation of deep water sediment mixing rates were calculated using down core distributions of 239 240pu 241am 137cs and 90sr based on two distinct models continuous and constant of tracer input and with a third model with pulsed input during the peak fallout period the continuous input model yielded mixing coefficients comparable to those derived from excess 210pb profiles within an order of magnitude

210pb 137cs and 239 240pu in east china sea sediments sources pathways and budgets of sediments and radionuclides profiles of 210 pb 137 cs and 239 240 pu measured in 83 sediment cores collected from various sedimentary regimes in the east china sea were analyzed to elucidate the sources routes and budgets ofsediments as well as these radionuclides distributions ofsedimentation rates and nuclide inventories reveal alongshore transport ofsediments 137 cs and 239 240 pu from the mouth of the yangtze river toward the south largely confined to the inner shelf area water depth 6 70 m mass balance calculations suggest that the east china sea is a sink for the particle reactive 210 pb and 239 240 pu with about one sixth oftheir sedimentary budgets supplied via boundary scavenging in contrast due to lower affinity of 137 cs for particles and rapid turnover of the shelf water the east china sea serves as a source for 137 cs about two thirds ofthe cumulative input of 137 cs have been transported out ofthe east china sea leaving the remaining one third stored in the bottom sediments and the overlying water column as for the sediment budget mass balance cannot be established due to a shortfall in sediment supply of more than 30 based on a comparison between input terms documented thus far and the sedimentation flux derived from this study it is very likely that we have overestimated the sediment burial flux or that long distance transport from the yellow river s dispersal system to the east china sea is underestimated alternatively the imbalance could be explained by the discrepancy between sediment input and output on decadal to centennial timescales 7 2002 elsevier science b v all rights reserved

magnetic properties of east china sea shelf sediments off the yangtze estuary influence of provenance and particle size abstract the east china sea continental shelf offshore from the yangtze river estuary is a sedimentary system characterized by complicated hydrodynamic conditions and large variability in sediment texture granulometric geochemical and environmental magnetic analyses were carried out on surface sediments from this area to investigate the spatial variations of sediment composition and their underlying mechanisms magnetic properties of three particle size fractions 63 m were further analyzed to assist data interpretation our results reveal four distinct units subaqueous yangtze delta and inner shelf mud deposits unit a relict sands on the middle shelf unit b the transitional environment between unit a and b unit c and the area northern to unit a unit d the distributions of organic carbon iron manganese and their ratios mn fe suggest minor effects of reductive diagenesis on the surface sediment magnetic properties because of differences in sediment source and hydrodynamic conditions sediments in unit a have the highest ferrimagnetic and antiferromagnetic mineral concentrations as well as the finest ferrimagnetic grain size the significant variations of magnetic properties within unit a indicate the effect of particle size sorting during sediment transportation and deposition sediments in unit b have the coarsest ferrimagnetic grain size and the highest proportion of ferrimagnetic versus antiferromagentic minerals unit c which has a bimodal size distribution can be subdivided into a southern and northern part magnetically reflecting the influence of provenance and particle size the distinct magnetic characteristics of unit d are probably due to the strong influence of materials from the yellow river our results provide a new method for characterizing east china sea shelf sediments offshore of the yangtze river mouth against which the extent of the influence of the yangtze river on the east china sea can be examined furthermore it may provide a baseline for future long term monitoring in this sensitive continental margin environment that is influenced by the yangtze river

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

p wave tomography of northeast asia constraints on the western pacific plate subduction and mantle dynamics abstract a high resolution model of 3 d p wave velocity structure beneath northeast asia and adjacent regions is determined by using 244 180 arrival times of 14 163 local and regional earthquakes and 319 857 relative travel time residuals of 9988 teleseismic events recorded at 2100 seismic stations in the study region our tomographic results reveal the subducting pacific slab clearly as a prominent high velocity anomaly from the japan trench to the north south gravity lineament nsgl in east china the nsgl is roughly coincident with the western edge of the stagnant pacific slab in the mantle transition zone mtz the subducting pacific slab has partly sunk into the lower mantle beneath northeast china but under the sino korean craton the slab lies horizontally in the mtz the nsgl as an important tectonic line in mainland china is marked by sharp differences in the surface topography gravity anomaly crustal and lithospheric thickness and mantle seismic velocity from the east to the west these features of the nsgl and large scale hot and wet upwelling in the big mantle wedge bmw in the east of the nsgl are all related to the subduction processes of the western pacific plate the changbai intraplate volcanic group is underlain by a striking low velocity anomaly from the upper mtz and the bmw up to the surface and deep earthquakes 410 650 km depths occur actively in the subducting pacific slab to the east of the changbai volcano we propose that the changbai volcanic group is caused by upwelling of hot and wet asthenospheric materials and active convection in the bmw the formation of other volcanic groups in the east of the nsgl is also associated with the subduction driven corner flow in the bmw

high resolution 3 d crustal structure beneath ne china from joint inversion of ambient noise and receiver functions using necessarray data abstract we used ambient noise data recorded by the necessarray a portable seismic array deployed in northeast china to construct rayleigh wave phase velocity dispersion curves and obtain phase velocity maps for periods from 6 to 40 s s wave velocity structure beneath ne china is obtained by joint inversion of the phase velocities and receiver functions our results show good correlation between crustal velocity structure and geological features at shallow depths the songliao basin is separated into two small sub basins by a fast velocity anomaly corresponding to a southwest uplifted horst and the southern sub basin is associated with the kailu depression a low velocity anomaly extending from the lower crust to uppermost mantle beneath the changbaishan mountain range is consistent with p and s wave tomography models the mantle low velocity has been interpreted as a local mantle upwelling attributed to the subducting pacific slab induced return flow finally the s wave velocity in the mid and lower crust is lower beneath the xing an mongolia orogenic belt xmob than beneath the changbaishan mountain range this was not expected since the changbaishan mountain range has experienced more extensive volcanic activity in the cenozoic including the currently active changbaishan and jingpohu volcanoes than the xmob we infer that the mid and lower crust of the xmob is mainly felsic in composition and propose that the low shear wave velocity of the mid and lower crust beneath the xmob could be the consequence of removal of deep mafic crust through a continental accretion and subsequent delamination event in the paleozoic or via convection removal induced by the rollback of the flat subducted paleo pacific slab during the middle mesozoic

age of the subducting pacific slab beneath east asia and its geodynamic implications abstract we study the age of the subducting pacific slab beneath east asia using a high resolution model of p wave tomography and paleo age data of ancient seafloor our results show that the lithosphere age of the subducting slab becomes younger from the japan trench 130 ma to the slab s western edge 90 ma beneath east china and the flat stagnant slab in the mantle transition zone mtz is the subducted pacific plate rather than the proposed izanagi plate which should have already collapsed into the lower mantle the flat pacific slab has been in the mtz for no more than 10 20 million years considerably less than the age of the big mantle wedge beneath east asia 110 million years hence the present flat pacific slab in the mtz has contributed to the cenozoic destruction of the east asian continental lithosphere with extensive intraplate volcanism and back arc spreading whereas the destruction of the north china craton during the early cretaceous 140 110 ma was caused by the subduction of the izanagi or the paleo pacific plate

matrix and fine grained rims in the unequilibrated co3 chondrite alha77307 origins and evidence for diverse primitive nebular dust components abstract the mineralogical and chemical characteristics of dark matrix and fine grained rims in the unequilibrated co3 chondrite alha77307 have been investigated in detail by scanning electron microscopy electron microprobe analysis and transmission electron microscopy matrix and fine grained rims on chondrules and other objects are compositionally homogeneous on the scale of 10 m and there are no compositional differences between matrix and rims mineralogically both the matrix and rims are extremely diverse and consist of a highly unequilibrated assemblage of si and fe rich amorphous material olivine pyroxene fe ni metal magnetite pentlandite pyrrhotite anhydrite and mixed layer phyllosilicate phases several distinct components can be recognized within the matrix and rims based on their textural and compositional characteristics which appear to represent basic fine grained units of nebular dust the microstructures of these different components show that they have experienced significantly different thermal histories unlike the ordinary chondrites an origin for any significant component of the matrix or rims in alha77307 from chondrules is improbable based on compositional and microstructural evidence the matrix and rim components in alha77307 formed by disequilibrium condensation processes as fine grained amorphous dust that is represented by the abundant amorphous component in the matrix such condensation could have occurred under a variety of conditions at different times and locations within the solar nebula or possibly earlier in a circumstellar environment subsequent thermal processing of this primitive condensate material in a variety of environments in the nebula resulted in partial or complete recrystallization of the fine grained dust the intimate association of fine grained components with disparate compositions and thermal histories shows that mixing of fine grained dust within the nebula must have been extremely thorough

three dimensional density modeling of the egm2008 gravity field over the mount paekdu volcanic area here we use the global gravity field data set egm2008 for 3 d crustal density modeling of the mount paekdu stratovolcano and surrounding area located on the border between north korea and china curvature analysis and euler deconvolution are used to assist interpretation and the 3 d model is constrained by multiple geological and geophysical data sets mount paekdu is characterized by a low bouguer anomaly of 110 10 5 m s2 which is caused by the combined gravity effects of 1 a depth to the moho of about 40 km 2 a zone with lower p wave velocity and density than the surrounding 3 low density volcanic rocks on the surface and 4 the presence of a magma chamber that has not previously been identified the modeled magma chamber has a mean thickness of 5 km and a density of about 2350 kg m3 and is located 10 km from the surface magma chambers are also modeled beneath mount wangtian and mount nampotae however the results of the 3 d density modeling do not confirm the existence of a previously proposed midcrustal low velocity zone in the area 70 km to the north of mount paekdu since the pliocene volcanic activity in the mount paekdu region has migrated from the east coast of north korea to the northwest following the path of nw se trending faults

crustal structure in the changbaishan volcanic area china determined by modeling receiver functions abstract during 1998 1999 we installed a temporary broadband seismic network in the changbaishan volcanic region ne china we estimated crustal structure using teleseismic seismograms collected at the network we detected a near surface region of strong anisotropy directly under the main volcanic edifice of the volcanic area we modeled 109 receiver functions from 19 broadband stations using three techniques first we used a slant stacking method to model the principal crustal p reverberation phases to estimate crustal thickness and the average crustal p to s speed ratio vp vs assuming an average p wave velocity in the crust we then estimated crustal s wave velocity vs and vp vs profiles by modeling stacked receiver functions using a direct search finally we inverted several receiver functions recorded at stations closest to the main volcanic edifice using least squares to estimate vs velocity profiles assuming a vp vs value the results from the three estimation techniques were consistent and generally we found that the receiver functions constrained estimates of changes in wave speeds better than absolute values we resolved that the crust is 30 39 km thick under the volcanic region and 28 32 km thick away from the volcanic region with a midcrust velocity transition at about 10 15 km depth we estimated that the average crust p wave velocity is about 6 0 6 2 km s surrounding the main volcanic region while it is slightly lower in the vicinity of the main volcanic edifice the estimates of vp vs were more ambiguous but we inferred that the bulk crustal poisson s ratio which is related to vp vs ranges between 0 20 and 0 30 with a suggestion that the poisson s ratio is lower under the central volcanic region compared to the surrounding areas we resolved low s wave velocities down to about 3 km s in the middle crust in the region of the main volcanic edifice the low velocity anomaly extends from about 5 10 to 15 25 km below the surface probably indicating a region of elevated temperatures we were unable to determine if partial melt is present with the data we considered in this paper

sources of plutonium to the tropical northwest pacific ocean 1943 1999 identified using a natural coral archive abstract the pu isotopes 239pu and 240pu were determined in annually banded skeletons of an accurately dated 1943 1999 modern coral porites lobata from guam island to identify historical pu sources to the tropical northwest pacific ocean activity concentrations of 239 240pu and 240pu 239pu atom ratios were determined in the dated coral bands using multi collector inductively coupled plasma mass spectrometry mc icp ms close in fallout from the former us pacific proving grounds ppg in the marshall islands and global fallout were identified as the two main sources the guam site was dominated by ppg close in fallout in the 1950s with an average 240pu 239pu atom ratio of 0 315 0 005 in addition a higher 240pu 239pu atom ratio 0 456 0 020 was observed that could be attributed to fallout from the ivy mike thermonuclear detonation in 1952 the atom ratio decreased in the 1960s and 1970s due to increase in the global fallout with a low 240pu 239pu atom ratio 0 18 recent coral bands 1981 1999 are dominated by the transport of remobilised pu with high 240pu 239pu atom ratios from the marshall islands to guam island along the north equatorial current nec this remobilised pu was estimated to comprise 69 of the total pu in the recent coral bands although its contribution was variable over time

origin of intraplate volcanism in northeast china from love wave constraints the tectonic source for widespread volcanism in northeast china has not been completely understood we develop a 3 d sh velocity model in ne china that provides new constraints to the origin of the volcanism the 3 d model is constructed from fundamental mode love waves at the periods of 20 125 s recorded at 269 broadband seismic stations the changbai mountain is characterized by a significant low velocity in the lower crust and uppermost mantle which probably results from mantle upwelling due to the subduction of the pacific plate a fast and thin mantle lid of 75 km is present beneath the songliao basin indicating lithosphere extension from back arc rifting the slow velocity in the middle and fast velocities in the south and north at 75 115 km depths in the songliao basin suggest complex mantle flow with upwelling and downwelling unlike the other volcanic fields changbaishan volcano jingpohu volcano and abaga volcano the halaha volcano has high velocity in the lower crust and upper mantle implying a limited melt supply from mantle source recently the subduction induced upwelling leads to complicated small scale mantle convection which is responsible for the intraplate magmatism in northeast china

the microstructure of semarkona and bishunpur abstract the ordinary chondrites semarkona and bishunpur appear to have experienced in situ hydrous alteration here we report the results of the first detailed tem examination of them which supports this conclusion in semarkona all but the most magnesian mafic minerals have been destroyed and primary sulphides most likely troilite have been partially altered to phyllosilicates and ni rich pyrrhotite in bishunpur alteration is confined to the production of smectite from an amorphous feldspathic material in the chondrule rims and interchondrule matrix during hydrous alteration of both meteorites the temperature probably did not exceed 260 c the equilibrium composition of the gas present during the alteration of semarkona was not solar but was dominated by h2o the formation of smectite does not require the presence of liquid water however evidence for the redistribution of elements such as ca zn and si over tens of microns or more implies that there was at least some transient grain boundary fluid present the alteration in semarkona and bishunpur is far from complete thermodynamic modelling suggests that more altered ordinary chondrites would be mineralogically similar to the cm and ci carbonaceous chondrites superficially the mineralogy mineral chemistry and bulk chemistry of semarkona matrix rims resemble those of some chondritic interplanetary dust particles cidps the ordinary chondrite parent bodies may therefore be a source of some cidps

recent unrest of changbaishan volcano northeast china a precursor of a future eruption 1 over 12 years of continuous monitoring of changbaishan volcano in the border region of china and north korea by means of volcanic seismicity ground deformation and volcanic gas geochemistry yields new evidence for magmatic unrest of the volcano between 2002 and 2006 in this so called active period the frequency of volcanic earthquakes increased by about 2 orders of magnitude compared to that of the background inactive periods the active period was also accompanied by ground inflation high values of co2 he h2 and high ratios of n2 o2 and 3he 4he in volcanic gases released from three hot springs near the caldera rim the monitoring evidence implies pressurization of the magma chamber possibly caused by incremental magma recharge the ground deformation data from both gps and precise leveling are modeled to suggest the corresponding deformation source is at 2 60 km depth beneath the volcano s summit where earthquake swarms were detected in 2002 and 2003 our findings suggest that the magma chamber beneath changbaishan volcano has awakened and resumed activity after remaining dormant since ad 1903 there is an urgent need to keep close watch on this active and very hazardous volcano in northeast china

the origin and evolution of chondrites recorded in the elemental and isotopic compositions of their macromolecular organic matter extraterrestrial organic matter in meteorites potentially retains a unique record of synthesis and chemical thermal modification by parent body nebular and even presolar processes in a survey of the elemental and isotopic compositions of insoluble organic matter iom from 75 carbonaceous ordinary and enstatite chondrites we find dramatic variations within and between chondrite classes there is no evidence that these variations correlate with the time and or location of chondrite formation or with any primary petrologic or bulk compositional features that are associated with nebular processes e g chondrule and volatile trace element abundances nor is there evidence for the formation of the iom by fischer tropsch type synthesis in the nebula or in the parent bodies the elemental variations are consistent with thermal maturation and or oxidation of a common precursor for reasons that are unclear there are large variations in isotopic composition within and between chondrite classes that do not correlate in a simple way with elemental composition or petrologic type nevertheless because of the pattern of elemental variations with petrologic type and the lack of any correlation with the primary features of the chondrite classes at present the most likely explanation is that all iom compositional variations are the result of parent body processing of a common precursor if correct the range of isotopic compositions within and between chondrite classes implies that the iom is composed of several isotopically distinct components whose relative stability varied with parent body conditions the most primitive iom is found in the cr chondrites and bells cm2 isotopically the iom from these meteorites resembles the iom in interplanetary dust particles chemically their iom resembles the chon particles of comet halley despite the large isotopic anomalies in the iom from these meteorites it is uncertain whether the iom formed in the interstellar medium or the outer solar system although the former is preferred here

impacts of large dams on downstream fluvial sedimentation an example of the three gorges dam tgd on the changjiang yangtze river summary under the influence of climate and human activities fluvial systems have natural ability to make adjustments so that the river hydrology sediment movement and channel morphology are in dynamic equilibrium taking the changjiang yangtze river for example in the early stages after the three gorges dam tgd began operational ten years ago the suspended sediment content ssc and fluxes in the middle and lower reaches of the river decreased noticeably at present they appear to be in a stable state on the decadal scale although the river runoff has not shown any trends the water level in the river decreased appreciably in time in the meantime channel down cutting along the thalweg almost existed throughout the river course the riverbed has turned from depositional before the dam construction to erosional afterwards in other words the riverbed had turned from being sediment sinks to sediment sources in the main channel of the changjiang between yichang and nanjing a distance of 1300 km the riverbed sedimentation mode displays strong intermediate and weak erosion depending on the closeness to the tgd

plutonium activities and 240pu 239pu atom ratios in sediment cores from the east china sea and okinawa trough sources and inventories abstract plutonium concentrations and 240 pu 239 pu atom ratios in the east china sea and okinawa trough sediment cores were determined by isotope dilution inductively coupled plasma mass spectrometry after separation using ion exchange chromatography the results showed that 240 pu 239 pu atom ratios in the east china sea and okinawa trough sediments ranging from 0 21 to 0 33 were much higher than the reported value of global fallout 0 18 the highest 240 pu 239 pu ratios 0 32 0 33 were observed in the deepest okinawa trough sediment samples these ratios suggested the us nuclear weapons tests in the early 1950s at the pacific proving grounds in the marshall islands were a major source of plutonium in the east china sea and okinawa trough sediments in addition to the global fallout source it was proposed that close in fallout plutonium was delivered from the pacific proving grounds test sites via early direct tropospheric fallout and transportation by the north pacific equatorial circulation system and kuroshio current into the okinawa trough and east china sea the total 239 240 pu inventories in the cores were about 150 200 of that expected from direct global fallout about 46 67 of the total inventories were delivered from the pacific proving grounds much higher 239 240 pu inventories were observed in the east china sea sediments than in sediments of the okinawa trough because in the open oceans part of the 239 240 pu was still retained in the water column and continued pu scavenging was higher over the margin than the trough according to the vertical distributions of 239 240 pu activities and 240 pu 239 pu atom ratios in these cores it was concluded that sediment mixing was the dominant process in controlling profiles of plutonium in this area faster mixing in the coastal samples has homogenized the entire 240 pu 239 pu ratio record today slightly slower mixing and less scavenging in the okinawa trough have left the surface sediment ratios closer to the modern north pacific water end member and higher ratios 0 30 0 34 at the bottom of the cores

recent sediment accumulation and carbon burial in the east china sea 1 sediment and carbon budgets were constructed for the east china sea ecs shelf based on up to date data the total annual sediment flux in the ecs shelf is approximately 96 of the terrestrial input there is high retention of sediment on the ecs shelf owing to the broad nature of the shelf edge i e 500 600 km and because of an along shore sediment dispersal path driven by the east china sea coastal current ecscc and the taiwan warm current twc organic carbon oc burial was also observed based on the results for sediment accumulation and the oc proportion in surface sediment a total of 7 4 106 t of oc is preserved in shelf sediments source discrimination of sedimentary oc revealed that the percentage of oc burial for both terrigenous and marine oc sources was higher than the global mean value at 10 and 5 5 respectively presumably owing to high sediment accumulation high oc flux to sediment in the estuary and shelf break suggests that riverine discharge and upwelling of the kuroshio intrusion are key factors regulating oc burial over the shelf estimated using a mass balance model 15 20 of the carbon inventory is buried in the shelf sediment while 80 of the carbon inventory must be transported out of shelf area in the form of dissolved carbon organic and inorganic the accumulation of carbon in sediments and the outflow of dissolved carbon sustain a high carbon sink in the ecs

reversible ion exchange fixation of cesium 137 leading to mobilization from reservoir sediments abstract the radioactive fission product 137cs has been observed to mobilize from bottom sediments of two south carolina reservoirs during summer thermal stratification and hypolimnetic anoxia mobilization is attributed to ion exchange displacement of 137cs from sediments by cations such as nh 4 fe 2 and mn 2 released under anaerobic conditions three types of 137cs binding sites to sediment clay minerals are identified 1 surface and planar sites from which 137cs is generally exchangeable by all cations studied na nh 4 h cs ca 2 mg 2 fe 2 and mn 2 2 wedge sites where 137cs exchange is sterically limited to cations of similar size and charge nh 4 cs k and perhaps h3o 3 interlayer sites from which 137cs is not readily exchanged more than 15 years after final 137cs inputs the reservoir sediments we studied showed the following percentage distribution of sites 2 to 9 surface sites 6 to 13 wedge sites and 78 to 85 interlayer sites in contrast lake and stream sediments near oak ridge tennessee receiving 137cs inputs more than 20 years earlier had greater than 99 of their 137cs associated with non exchangeable interlayer sites the difference is attributed to the paucity in the south carolina sediments of weathered micaceous clay minerals with their abundant interlayer sites such interlayer deficient clays are dominant in the atlantic and gulf coastal plains of the united states and elsewhere this suggests that 137cs will be physically and chemically more mobile in such areas as well as more biologically available mobility will be enhanced in regimes where cation inputs favoring 137cs exchange occur subsurface waste disposal sites where anaerobic conditions develop with nh 4 production and fe 2 and mn 2 release might be such a regime

pu 137cs and excess 210pb in russian arctic sediments the activity ratios of pu and radiocesium isotopes have been used to delineate the major sources such as global and close in debris fallout nuclear fuel reprocessing and fabrication plant effluents in the environment we have measured 238pu 239 240pu 137cs and excess 210pb concentrations in 107 surficial sediments as well as in 5 sediment cores collected in the summer months of 1993 and 1994 from the ob and yenisey rivers russia and the kara sea a comparison of the sediment core inventories of 239 240pu and 137cs along with the 238pu 239 240pu activity ratios with those expected from global fallout allows us to estimate the relative amounts if any of reactor derived 238pu and 239 240pu from the dumped reactor sites in the study area in surficial sediment samples collected in 1993 and 1994 the 239 240pu concentrations varied between 4 2 and 856 mbq kg 1 with a mean of 239 mbq kg 1 in samples with a measurable 238pu the 238pu 239 240pu activity ratios varied between 0 010 and 0 069 with an average value of 0 035 0 014 this range can be compared to the average 238pu 239 240pu activity ratio of 0 030 for the year 1993 from nuclear weapons testing and snap fallout obtained from soil studies indicating very little 5 additional sources of 238pu to the sediments in the study area the inventories of pu in the 5 sediment cores from the study area varied between 2 67 0 67 and 24 5 2 2 bq m 2 with a mean value of 8 83 bq m 2 the 137cs concentrations in the upper 3 cm of the sediments varied between below detection limit to 71 4 bq kg 1 with a mean of 14 9 bq kg 1 the 137cs inventories in the 5 sediment cores varied between 156 7 28 3 and 1600 153 3 bq m 2 with a mean value of 583 3 bq m 2 the mean ratio of inventories of pu to that of 137cs 0 015 is comparable to the values in other places in the arctic region there is a significant correlation between total organic carbon and concentrations of 137cs 239 240pu and 210pb suggesting that organic matter enriched fine particles are a likely carrier phase for these nuclides the ratio of 137cs 239 240pu also suggests that most of these nuclides are derived from global fallout

geochronology of sediments in the sabine neches estuary texas u s a the accumulation rate of sediments in the sabine neches estuary near beaumont texas was studied in four sediment cores using radioisotopes 210pb and 239 240pu due to very low and variable activities of unsupported 210pb in the sediments the sedimentation rates could not be reliably established using the 210pb dating method however 239 240pu profiles showed distinct peaks corresponding to the maximum fallout in 1963 and using these pu peaks the average sedimentation rates were estimated at 4 5 mm yr 1 in the upper and lower estuary various assumptions that are commonly used in the 210pb dating method were tested it was found that the 226ra activities were in equilibrium with 238u and the possible loss of 222rn was judged to be insignificant the lack of an exponential profile of excess 210pb with depth did not appear to be a direct result of sediment mixing as the post depositional mixing rates estimated using a numerical mixing model were low compared to other coastal areas a significant positive correlation between the amount of 63 m fraction sediments and the total 210pb activity was observed in the surface sediments while the hydraulic residence time was relativelt short in this estuary 10 days the average total residence time of 210pb was 10 days between 50 and 94 of the total 210pb in the water column was found in the 0 5 m fraction resulting in low kd values the measured inventories of excess 210pb and 239 240pu in estuarine sediments were only 10 34 and 19 50 respectively of the total expected inventories it appears that the estuarine retention and sediment inventory of these radionuclides and by analogy other particle reactive metals are a function of the hydraulic residence time grain size and possibly complexation of these nuclides with doc

mechanisms of weathering of meteorites recovered from hot and cold deserts and the formation of phyllosilicates abstract petrographic mineralogical and chemical analysis of naturally weathered equilibrated ordinary chondrites collected from hot deserts and antarctica has revealed striking similarities and also pronounced differences in weathering between the two environments terrestrial weathering in all meteorites studied is dominated by oxidation and hydration of fe ni metal producing fe oxides and oxyhydroxides that have partially replaced the metal grains and have also occluded primary intergranular pores to form veins troilite weathers readily in hot desert environments but undergoes very little alteration under antarctic conditions most of the primary porosity of ordinary chondrites has been occluded by the time that 15 to 25 of the initial fe 0 and fe 2 has been oxidised to fe 3 in both environments results from modelling the volume changes upon alteration of primary minerals to a range of weathering products demonstrates that the primary porosity of most meteorites is sufficient to accommodate weathering products dilation of primary pores and brecciation which has been observed in parts of some meteorites will only occur if the meteorite is especially metal rich or has a low primary porosity these weathering products are absent from recent falls but have formed in a fall after 100 yr of museum storage cl bearing akaganeite and hibbingite are common weathering products in antarctic finds but occur in abundance in only one hot desert meteorite daraj 014 the majority of fe rich weathering products in meteorites from both environments contain low but variable concentrations of si mg and ca in most meteorites a proportion of these elements are inferred to be present as a very finely crystalline mineral with a 1 0 nm lattice fringe spacing where seen within intragranular fractures this mineral has a topotactic relationship with olivine and orthopyroxene in the heavily weathered antarctic finds alha 78045 and 77002 si is concentrated in cronstedtite a fe rich phyllosilicate an unidentified hydrous si fe ni mg mineral or gel has also partially replaced taenite in alha 78045 in addition to fe rich weathering products hot desert meteorites contain sulphates ca carbonate and silica whereas such minerals are largely absent from antarctic finds the abundance of silicate weathering products in antarctic meteorites is unexpected and indicates that olivine and pyroxene undergo significant chemical weathering in these environments as preterrestrial cronstedtite is abundant in cm2 carbonaceous chondrites the antarctic environment may be a powerful analog for aqueous alteration in the asteroidal parent bodies of primitive meteorites

auger nanoprobe analysis of presolar ferromagnesian silicate grains from primitive cr chondrites que 99177 and met 00426 abstract we have investigated the presolar grain inventories of two cr chondrites que 99177 and met 00426 which are less altered than most members of this meteorite group both meteorites contain high abundances of o anomalous presolar grains with concentrations of 220 40 and 160 30 ppm for que 99177 and met 00426 respectively the presolar grain inventories are dominated by ferromagnesian silicates with group 1 oxygen isotopic compositions indicative of origins in low mass red giant or asymptotic giant branch stars grains with pyroxene like compositions are somewhat more common than those with olivine like compositions but most grains are non stoichiometric with compositions intermediate between these two phases consistent with recent work suggesting that amorphous interstellar silicates have stoichiometries between olivine and pyroxene type silicates although structural data are not available one grain contains only si and o and has a stoichiometry consistent with sio 2 our presolar grains are much more fe rich than predicted by astronomical observations although secondary alteration may play a role in enhancing the fe contents of presolar grains it seems unlikely that the large and ubiquitous fe enrichments observed in the grains from this study can be due only to secondary processing particularly given the highly primitive nature of these two meteorites grain condensation in the stellar outflows where these grains formed likely proceeded under rapidly changing kinetic conditions that may have enhanced the incorporation of fe into the grains over that expected based on equilibrium condensation theory both que 99177 and met 00426 appear to contain unusually low abundances of oxide grains and have higher silicate oxide ratios than other primitive meteorites analyzed to date we explore various possibilities for this discrepancy but note that most scenarios are not likely to result in the preferential destruction of oxides relative to silicates thus the highest silicate oxide ratios such as those observed in the cr chondrites should reflect the true initial proportions of presolar silicate and oxide grains in the parent molecular cloud from which the solar nebula evolved

concepts of sediment deposition and accumulation applied to the continental shelf near the mouth of the yangtze river a fundamental understanding of how sedimentary strata form requires distinction between deposition and accumulation of particles deposition refers to the temporary emplacement of particles on the seabed accumulation is the net sum of many episodes of sediment deposition and removal the difference between rates of deposition and accumulation affects the ability of an environment to record sedimentary events radionuclide profiles of 234 th and 210 pb within the seabed can be used to determine 100 day deposition rates and 100 yr accumulation rates respectively on the continental shelf near the mouth of the yangtze river short term deposition rates are about 4 4 cm month whereas accumulation rates integrated over a century are an order of magnitude less about 5 4 cm yr

combined receiver function and surface wave phase velocity inversion using a niching genetic algorithm application to patagonia a combined inversion of body wave receiver functions and rayleigh wave phase velocities using a niching genetic algorithm nga increases the unique ness of the solution over separate inversions and also facilitates explicit parameteri zation of layer thickness in the model space this parameterization requires fewer layers and a priori constraints for modeling more complex structures than traditional linearized inversion ngas solve for a suite of locally optimal solutions in addition to isolating the globally optimal solution by using an evolutionary paradigm this nonlinear examination of the error space provides an opportunity to examine trade off within the model space the method when applied to synthetic data locates interfaces within 2 km of the test structure and identifies appropriate structure and velocity applying this method to data from a deployment of five broadband stations in chilean patagonia yields a regional model of crustal structure that is consistent with the geological history of the region sediment thickness is inversely proportional to crustal thickness with sediment thicknesses reaching more than 4 km where the crustal thickness thins to 28 km this is consistent with previous geological studies which suggests that the rocas verdes basin in western patagonia formed by crustal thinning isostatic compensation and subsequent sedimentation

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

accumulation rates and mixing processes in near surface north atlantic sediments evidence from c 14 and pu 239 240 downcore profiles abstract the vertical distributions of c 14 and pu 239 240 activities and c 14 ages of sediments collected in n atlantic areas are analyzed in ne atlantic sediments radiocarbon mixed layer ages and depths range from 2500 to 5500 years and from 6 5 to 7 3 cm respectively while the vertical profiles of pu 239 240 indicate for the nw atlantic sites mixing depths of only 1 2cm in the ne atlantic sites accumulation rates over a period of 10 kyr range from 1 4 to 3 7 cm kyr 1 and fluxes of material from 9 2 to 24 1 g m 2 yr 1 with a marked difference between samples collected from plain highest values and hill lowest values sites related to downslope transport of sediment the inventories of pu range from 9 0 to 25 2 bq m 2 for ne atlantic sites and from 0 3 to 1 1 bq m 2 for nw atlantic sites probably reflecting different primary production rates in the two areas numerical simulations of the mixing processes of plutonium have been performed by using both a continuous and a pulse input flux the estimated values of d b range from 0 1 to 1 0 cm 2 yr 1 for the ne atlantic sites while they are in the order of 0 01 cm 2 yr 1 for the nw atlantic sites

a persistent localized microseismic source near the kyushu island japan 1 very strong signals with apparent velocity higher than rayleigh wave velocity are observed on noise correlation functions ncfs between seismic stations in east asia these signals are present on one month ncfs in ten years period with stable arrival times indicating their persistent and localized nature the signals are strong in the frequency band of 0 07 0 12hz and their amplitudes show inter annual but not seasonal variation location obtained from two algorithms with gsn and fnet data indicates that the source is situated in kyushu island japan after an earthquake is used to account for heterogeneity effects the location is closer to the ariake bay but still in the island the non seasonal amplitude variation and the peak frequency of 0 1hz suggest the signals are probably not generated by oceanic sources this persistent localized microseismic source needs to be taken into consideration in ambient noise tomography studies in east asia

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

natural and anthropogenic radionuclide distributions in the nansen basin artic ocean scavenging rates and circulation timescales abstract determination of the naturally occurring radionuclides 232 th 230 th 228 th and 210 pb and the anthropogenic radionuclides 241 am 239 240 pu 134 cs and 137 cs in water samples collected across the nansen basin from the barents sea slope to the gakkel ridge provides tracers with which to characterize both scavenging rates and circulation timescales in this portion of the arctic ocean large volume water samples 15001 were filtered in situ to separate particulate 0 5 m and dissolved th isotopes and 241 am thorium 230 displays increases in both particulate and dissolved activities with depth with dissolved 230 th greater and particulate 230 th lower in the deep central nansen basin than at the barents sea slope dissolved 228 th activities also are greater relative to 228 ra in the central basin residence times for th relative to removal from solution onto particles are 1 year in surface water 10 years in deep water adjacent to the barents sea slope and 20 years in the eurasian basin deep water lead 210 in the central basin deep water also has a residence time of 20 years with respect to its removal from the water column this texture of scavenging is reflected in distributions of the particle reactive anthropogenic radionuclide 241 am which shows higher activities relative to pu in the central nansen basin than at the barents sea slope distributions of 137 cs show more rapid mixing at the basin margins barents sea slope in the south gakkel ridge in the north than in the basin interior cesium 137 is mixed throughout the water column adjacent to the barents sea slope and is present in low but detectable activities in the eurasian basin deep water in the central basin at the time of sampling 1987 the surface water at all stations had been labeled with 134 cs released in the 1986 accident at the chernobyl nuclear power station in the 1 year since the introduction of chernobyl 134 cs to the nansen basin it had been mixed to depths of 800 m at the barents sea slope and to 300 m in the central basin prechernobyl inventories of 137 cs as well as 239 240 pu are 10 times those expected from global atmospheric fallout from nuclear weapons testing and are derived principally from releases from the sellafield u k nuclear fuel reprocessing facility on the irish sea based on the sources of 137 cs to the nansen basin mixing time scales are 9 18 years for the upper water column to 1500 m and 40 years for the deep water these mixing time scales combined with more rapid scavenging at the basin margin relative to the central basin produce residence times of particle reactive radionuclides in the nansen basin comparable to other open ocean areas e g north west atlantic despite the presence of permanent ice cover and long periods of low light levels that limit productivity in the arctic

historical changes in 239pu and 240pu sources in sedimentary records in the east china sea implications for provenance and transportation abstract concentrations and isotopic compositions of plutonium pu are widely used for its source identification and to determine transport processes of pu associated particulate matter and water we investigated the concentrations of 239pu and 240pu and their ratios in a number of sediment samples from the east china sea ecs collected in the summer of 2013 august 6 28 the 239 240pu activity concentrations in surface sediment samples were found to range between 0 048 and 0 492 bq kg 1 and the 240pu 239pu atom ratios showed a similar trend as that of the 239 240pu activities the pu atom ratios ranged from 0 158 to 0 297 and were mostly higher than the mean global fallout value of 0 18 the 239 240pu inventories in the ecs varied widely from 2 to 807 bq m 2 with the highest values commonly found in the coastal areas in the yangtze estuary the mean 239 240pu activity concentration is close to the estimated value of the suspended material from the yangtze river catchment 0 18 bq kg 1 and the 240pu 239pu atom ratio was found to be 0 18 which indicates that the yangtze river input is the dominant source of pu for this area the total annual yangtze river input of 239 240pu was estimated to be 2 4 10 10 bq which is small compared to the total amount of 239 240pu buried 3 1 10 13 bq in the whole ecs the pacific proving ground input appears to be the dominant source of pu to the ecs accounting for 45 52 of the total inventory the fractional amount of 239 240pu scavenged from the total 239 240pu transported by the kuroshio current kc and taiwan warm current twc into ecs sediments is estimated to be 10 our study shows that the 240pu 239pu atom ratio is useful not only to obtain a better insight of the biogeochemistry influenced by the kc but also to trace the long range transport of other particle reactive species besides the sedimentation rates obtained based on the penetration depths of 239 240pu and vertical profiles of excess 210pb agree within uncertainties which suggests that 239 240pu can potentially be used as a chronostratigraphic time marker in the marine environment

distribution of 137cs and other radioactive tracers in the eastern mediterranean relationship ot the deepwater transient 1 the time evolution of 137cs distribution in the eastern mediterranean in the period 1977 1999 is discussed in relation to water circulation and in particular to the eastern mediterranean transient emt tritium data are used to reconstruct the spatial distribution of 137cs before the emt and the chernobyl accident relatively high concentrations characterized the surface and intermediate waters of the whole basin and the levels gradually decreased toward the bottom tracer concentrations in the deep waters decreased from west to east reflecting the spreading of the core of the eastern mediterranean deep water formed in the adriatic sea in the 1990s a significant change was induced by the intrusion of new deep water of aegean origin in the bottom layers of the ionian and levantine basins marked by a relatively high 137cs concentration around 2 5 bq m 3 as a result in 1999 the levels were almost homogeneous in the whole deep ionian sea in the past the oldest waters of the eastern mediterranean were found around 1500 m characterized by a tracer minimum layer during the emt this layer was displaced upward to 750 1500 m and was also much thinner than previous the analysis of vertical profiles and ratios of 137cs and 90sr shows that a chernobyl contribution is present in the surface intermediate and deep waters of the ionian sea but not in the tracer minimum layer and in the deep adriatic sea the analysis of tritium helium ages in this area indicates a decreased convective renewal of basin waters in the period 1987 1999 that also explains the absence of a chernobyl signal

crust and uppermost mantle beneath the north china craton northeastern china and the sea of japan from ambient noise tomography 1 a 3 d shear velocity model of the crust and uppermost mantle to a depth of 100 km is presented beneath the north china craton ncc northeastern china the korean peninsula and the sea of japan ambient noise rayleigh wave tomography is applied to data from more than 300 broadband seismic stations from chinese provincial networks cearray the japanese f net and the iris global seismic network continuous data from 2007 to 2009 are used to produce group and phase velocity maps from 8 s to 45 s periods the model is motivated to constrain the distributed intraplate volcanism crustal extension cratonic rejuvenation and lithospheric thinning that are hypothesized for the study region numerous robust features are observed that impose new constraints on the geometry of these processes but discussion concentrates only on four 1 the north south gravity lineament follows the 40 km contour in crustal thickness and crustal thickness is anticorrelated with water depth beneath the sea of japan consistent with crustal isostasy for a crust with laterally variable composition 2 the lithosphere is thin 70 km beneath the songliao bohai graben but seismically fast 3 even thinner more attenuated lithosphere bounds three sides of the eastern ncc in a horseshoe shape identifying a region of particularly intense tectonothermal modification where lithospheric rejuvenation may have reached nearly to the base of the crust 4 low velocity anomalies reach upward in a y shape in the mantle beneath the eastern and western borders of the sea of japan extending well into continental east asia in the west and are separated by a 60 km thick lithosphere beneath the central sea of japan this anomaly may reflect relatively shallow slab dehydration in the east and in the west may reflect deeper dehydration and convective circulation in the mantle wedge overlying the stagnant slab

subducting slabs stagnant in the mantle transition zone the p wave velocity structure beneath the western pacific is found from the international seismological center first arrival data special attention was paid to the deep structure beneath the wadati benioff zone we discretized the whole mantle into blocks with finer blocks in the region of interest to obtain the velocities of all the blocks this way of discretization minimizes a problem with tomographic studies of regional scale difficulty in making corrections for the effects outside the region of interest our solution is iterative with the alternate step of the relocation of earthquakes using the whole mantle model of inoue et al 1990 as a starting model a first order smoothness constraint was imposed to suppress the possible fluctuation of the solution around the initial model the essential result depends little on whether the reference spherical model is smooth or discontinuous near 400 and 670 km depths we examined the resolution by calculating the resolving kernels for selected blocks and by reconstructing the checkerboard test patterns of velocity perturbation and the test structures of subducting lithosphere the resolution is depth dependent but in general good enough to see the slab configuration beneath the southern kurile japan izu bonin arcs and the java arc it is relatively poor beneath the northern kurile and mariana arcs the seismic image of subducting slab beneath the southern kurile to bonin arcs bends to subhorizontal near the leading edge of the wadati benioff zone and extends continentward over a distance of more than 1000 km the subhorizontal portion of the slab connects a high velocity blob to the bottom that reaches a depth of at least 800 km across the 670 km discontinuity under the japan arc although the image of the java slab directly penetrates the 670 km discontinuity it then bends to a shallow dip with a considerable spread reaching a depth of about 1200 km these results suggest that descending slabs of lithosphere in the western pacific tend to be stagnant in the transition zone under a subtle control of the 670 km discontinuity although stagnant slab materials eventually descend into the lower mantle they no longer maintain their original configuration below the 670 km discontinuity

seismic image and origin of the changbai intraplate volcano in east asia role of big mantle wedge above the stagnant pacific slab abstract we determined p wave tomography of the crust and upper mantle under the changbai volcanic area in northeast asia by using 289 318 arrival time data from 4802 local earthquakes and 9599 teleseismic events a prominent low velocity anomaly is clearly imaged in the crust and upper mantle down to about 410 km depth beneath the changbai volcano a broad high velocity anomaly is revealed in the mantle transition zone and deep earthquakes occurred actively there suggesting that the subducting pacific slab is stagnating in the mantle transition zone under east asia our results suggest that the formation of the changbai and other intraplate volcanoes in northeast asia is related to the upwelling of hot and wet asthenospheric materials in the big mantle wedge above the stagnant pacific slab hence the active intraplate volcanoes in northeast asia are not hotspots related to deep mantle plumes but are caused by plate tectonic processes in the upper mantle

sedimentation dynamics in the east china sea elucidated from and sedimentation dynamics in the east china sea was investigated based on profiles and inventories of 210 pb 137 cs and ex 239 240 pu in sediment cores collected from various settings in this marginal sea the derived sedimentation rates vary by two orders of magnitude from 2 to 0 02 cm yr y1 and generally decrease southward along the inner shelf and eastward offshore this pattern is consistent with the dispersal of yangtze river derived sediments by the current and tidal systems y2 y1 the weighted mean sedimentation rate over the shelf ca 0 3 g cm yr appears to be higher than fluvial inputs from the y2 y1 yangtze river and taiwan 0 14 g cm yr the discrepancy can be reduced by considering the effect of sediment mixing which renders sedimentation rates overestimated and the possibility of additional sediment input from the yellow river s dispersal system spatial variations of the observed nuclide inventories in sediments suggest extensive sediment redistribution boundary scavenging of 210 pb and large inputs of 137 cs and 239 240 pu from yangtze river s drainage basin

the meteoritical bulletin no 86 2002 july abstract meteoritical bulletin no 86 lists information for 1154 newly classified meteorites comprising 661 from antarctica 218 from africa 207 from asia 203 of which are from oman 62 from north america 3 from south america and 3 from europe information is provided for 5 falls el idrissia undulung dashoguz el tigre and yafa noteworthy specimens include 7 martian meteorites dhofar 378 grove mountains 99027 northwest africa 856 1068 and 1110 and sayh al uhaymir 060 and 090 4 lunar meteorites dhofar 301 302 303 and 489 9 new iron meteorites a mesosiderite northwest africa 1242 an ungrouped stony iron meteorite dar al gani 962 and a wide variety of other interesting stony meteorites including ch ck cm cr cv r enstatite unequilibrated ordinary and ungrouped chondrites primitive achondrites howardite eucrite diogenite hed achondrites and ureilites

mineralogy and texture of fe ni sulfides in ci1 chondrites clues to the extent of aqueous alteration on the ci1 parent body to better understand the role of aqueous alteration on the ci1 parent body we have analyzed the texture composition and mineral associations of iron nickel sulfides in four of the five known ci1 chondrites the most commonly occurring sulfide present in the ci1 chondrites is the iron deficient fe ni sulfide pyrrhotite fe ni 1 xs that has a composition close to that of stoichiometric troilite fes three of the ci1s alais ivuna and tonk also contain pentlandite fe ni 9s8 although pentlandite is a rare phase in ivuna cubanite cufe2s3 was found in both alais and ivuna in this study although it has also been reported in orgueil macdougall and kerridge 1977 the pyrrhotite grains in all four chondrites form hexagonal rectangular or irregular shapes and show no evidence of ni or co zoning the pyrrhotite grains in orgueil and ivuna are in general smaller and show more corrosions or embayments than those in alais or tonk we suggest that the precursor sulfide present in the ci1 chondrites was troilite which during brecciation and oxidation on the parent body at a temperature of 100 c or less converted the troilite to magnetite and pyrrhotite with pentlandite inclusions subsequently continued alteration on the parent body removed pentlandite partially from alais tonk and ivuna completely from orgueil leaving behind pyrrhotite with spaces corrosions where the pentlandite had been ni derived from the pentlandite was incorporated into ferrihydrite onto the surface of which the ni na sulfate ni bloedite formed based on the size and abundant corrosions within pyrrhotite grains combined with observations from other authors we conclude that orgueil and ivuna have undergone a greater degree of alteration than alais and tonk further work is needed to assess the conditions under which pentlandite would be dissolved preferentially to pyrrhotite as the study of terrestrial literature indicates that the latter mineral is preferentially removed

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

time dependent modeling of fallout radionuclide transport in a drainage basin significance of slow erosional and fast hydrological components abstract the sediment depth distributions of 238pu 239 240pu 241am and 137cs have been measured in a sediment core from the saguenay fjord quebec canada which has been dated to better than 1 yr resolution over the past 100 yr using 210pb the historical record of fallout radionuclide fluxes to the sediments has been estimated using a 210pb constant flux model and variations in the flux distributions have been directly related to changes in the atmospheric input function rates of radionuclide transport through the drainage basin have been predicted using a two component time dependent model composed of terrestrial soil and water phases the latter including catchment basins upstream of the fjord the residence times of 137cs and 239 240pu in the soil component are 1000 and 3000 yr respectively while both radionuclides have equivalent residence times of 1 yr in the water column component the atmospheric burn up of a nuclear powered snap 9a satellite in 1964 has resulted in a well defined 238 pu 239 240 pu horizon appearing in the sediments at the 1967 1968 level the magnitude and timing of the snap 9a derived 238pu distribution are in agreement with the drainage basin model predictions and confirm the absence of post depositional remobilization of pu in these anoxic sediment regimes theoretical estimates of the change in the 241 am 239 240 pu activity ratio in sediments deposited since the 1950 s determined using the drainage basin model are in agreement with the experimental results and indicate that the initial 241 pu 239 240 pu activity ratio for the 1950 s weapons tests was 15 or more while the later weapons tests were characterized by an activity ratio closer to 12

mobile mud dynamics in the east china sea elucidated using 210pb 137cs 7be and 234th as tracers mobile mud mm which has fine grain size distribution 90 clay silt and 2 5 in south inshore indicates that the sediment focusing resulted in the increased mass flux the residence time of mm is estimated as 3 6 years both by mass balance of mm and 210pbex in mm

mantle dynamics of western pacific and east asia insight from seismic tomography and mineral physics abstract recent results of high resolution seismic tomography and mineral physics experiments are used to study mantle dynamics of western pacific and east asia the most important processes in subduction zones are the shallow and deep slab dehydration and the convective circulation corner flow processes in the mantle wedge the combination of the two processes may have caused the back arc spreading in the lau basin affected the morphology of the subducting philippine sea slab and its seismicity under southwest japan and contributed to the formation of the continental rift system and intraplate volcanism in northeast asia which are clearly visible in our tomographic images slow anomalies are also found in the mantle under the subducting pacific slab which may represent a small mantle plumes b upwellings associated with the slab collapsing down to the lower mantle or c sub slab dehydration associated with deep earthquakes caused by the reactivation of large faults preserved in the slab combining tomographic images and earthquake hypocenters with phase diagrams in the systems of peridotite water we proposed a petrologic model for arc volcanism arc magmas are caused by the dehydration reactions of hydrated slab peridotite that supply water rich fluids to the mantle wedge and cause partial melting of the convecting mantle wedge a large amount of fluids can be released from hydrated morb at depths shallower than 55 km which move upwards to hydrate the wedge corner under the fore arc and never drag down to the deeper mantle along the slab surface slab dehydration reactions at 120 km depth are the antigorite related 5 reactions which supply water rich fluids for forming the volcanic front phase a and mg surssasite breakdown reactions at 200 and 300 km depths below 700 c cause the second and third arcs respectively moreover the dehydration reactions of super hydrous phase b phases d and e at 500 660 km depths cause the fluid transportation to the mantle boundary layer mbl 410 660 km depth the stagnant slabs extend from japan to beijing china for over 1000 km long indicating that the arc trench system covers the entire region from the japan trench to east asia we propose a big mantle wedge bmw model herein where hydrous plumes originating from 410 km depth cause a series of intra continental hot regions fluids derived from mbl accumulated by the double sided subduction zones rather than the india asia collision and the subsequent indentation into asia are the major cause for the active tectonics and mantle dynamics in this broad region

p wave tomography and origin of the changbai intraplate volcano in northeast asia abstract we present the first seismic image of the upper mantle beneath the active intraplate changbai volcano in northeast asia determined by teleseismic travel time tomography the data are measured at a new seismic network consisting of 19 portable stations and 3 permanent stations our results show a columnar low velocity anomaly extending to 400 km depth with a p wave velocity reduction of up to 3 high velocity anomalies are visible in the mantle transition zone and deep focus earthquakes occur at depths of 500 600 km under the region suggesting that the subducting pacific slab is stagnant in the transition zone as imaged clearly by global tomography these results suggest that the intraplate changbai volcano is not a hotspot like hawaii but a kind of back arc volcano related to the deep subduction and stagnancy of the pacific slab under northeast asia

joint inversion of surface wave dispersions and receiver functions with p velocity constraints application to southeastern tibet we introduced a p velocity model into the traditional joint inversion of p receiver function rf and surface wave dispersions to reduce model ambiguity the method was implemented using a global search based algorithm and a flexible parameterization of a sedimentary layer and spline based parameterization that can represent sharp discontinuities we applied the method to a dense array in se tibet longitude 97 5 e to 107 e latitude 25 3 n extensive tests using synthetic and real data suggest that the method is suitable and robust for a variety of velocity structures and moho discontinuities and can simultaneously provide the crustal vp vs profile and better constrained moho depth the flexibility of the parameterization and the inclusion of the vp constraint are crucial in the improved model recovery artifacts may be created without including the sedimentary layer even when it is less perfect a reasonable vp model is valuable in such a joint inversion we showed that crustal multiples in rfs may bias the traditional h k results when the crust structure is complex and should be avoided in a joint inversion before appropriate corrections can be made the results from the joint inversion show two low velocity zones lvzs reported previously and were identified as channels of crustal flow a prominent isolated lvz is observed in the mid lower crust under the xiaojiang fault area which correlates with anomalously high vp vs ratios indicating possible partial melting however the other lvz is imaged to be in the brittle shallow upper crust without very high vp vs ratios which is likely associated with crustal fault zones rather than partial melting we observe clear low velocity structures in the mantle beneath the two crustal lvzs which also correlate with zones of low resistivity the crust mantle correlation may suggest influence of mantle processes on crustal deformation

transport of the environmental radionuclides in an alpine watershed abstract the radionuclides137cs 210pb and7be have been examined in the alpine rho ne watershed switzerland during a period of two years in order to evaluate their usefulness as tracers of the removal and transport rate of top soil particles and particle reactive contaminants of atmospheric origin the specific activities of the radionuclides in fluvial suspension show a distinct seasonal pattern which depends on the hydrologic regime of the stream and the sources of the suspended matter input output budgets based on the atmospheric deposition and fluvial removal of three radionuclides in the alpine rho ne watershed are used to estimate their erosional residence times the simplest one box model yields mean residence times of about 800 and 1400 years for137cs and210pb respectively the removal rate of short lived7be suggests that a part of the watershed 0 6 2 3 of the total surface is exposed to a rapid erosion in which the mean residence time of the radionuclides is in the range of 1 220 days this has little influence on the calculated residence time of137cs but increases the estimated residence time of210pb in soil to over 1800 years the use of210pb 7be pair in fluvial output may be very helpful in the assessment of the impact of atmospheric pollutants on the water quality in rivers and lakes