multiple indicator study of groundwater flow and chemistry and the impacts of river and paddy water on groundwater in the alluvial fan of the tedori river japan to investigate the source flow paths and chemistry of rich resources of high quality shallow groundwater in the alluvial fan between the tedori and sai rivers in central japan we analysed stable isotope ratios of h o and sr and concentrations of major dissolved ions and trace elements in groundwater river water and paddy water the sr 87 sr 86 ratios of the groundwater are related to near surface geology groundwater in sediment from the tedori river has high sr 87 sr 86 ratios 0 711 whereas that from the sai river in the north of the fan has low sr 87 sr 86 ratios 0 711 h 2 and o 18 values and sr 87 sr 86 ratios indicate that groundwater in the central and southern fans is recharged by the tedori river whereas recharge in the north is from the sai river mg2 ca2 sr2 hco3 and so42 concentrations and h 2 and o 18 values in the groundwater are high in the central fan and except for the northern area tend to increase with distance from the tedori river there are linear relationships between sr 87 sr 86 ratio and the reciprocal concentrations of sr2 mg2 and ca2 these geochemical characteristics suggest that as groundwater recharged from the tedori river flows towards the central fan it mixes with waters derived from precipitation and paddy water that have become enriched in these components during downward infiltration these results are consistent with our hydrological analysis and numerical simulation of groundwater flow thus verifying the validity of the model we used in our simulation of groundwater flow copyright c 2016 john wiley sons ltd

strontium isotopes as tracers of ecosystem processes theory and methods abstract the strontium sr isotope method can be a powerful tool in studies of chemical weathering and soil genesis cation provenance and mobility and the chronostratigraphic correlation of marine sediments it is a sensitive geochemical tracer applicable to large scale ecosystem studies as well as to centimeter scaled examination of cation mobility within a soil profile the 87sr 86sr ratios of natural materials reflect the sources of strontium available during their formation isotopically distinct inputs from precipitation dryfall soil parent material and surface or groundwater allow determination of the relative proportions of those materials entering or leaving an ecosystem the isotopic compositions of labile soil exchange complex and soil solution strontium and sr in vegetation reflect the sources of cations available to plants strontium isotopes can be used to track the biogeochemical cycling of nutrient cations such as calcium the extent of cation contributions from in situ weathering and external additions to soil from dust and rain can also be resolved with this method in this paper we review the geochemistry and isotopic systematics of strontium and discuss the use of this method as a tracer of earth surface processes

strontium isotope systematics of base flow in piedmont province watersheds georgia usa abstract 87 sr 86 sr ratio variations were analyzed in rainfall shallow ground water and base flow collected from 4 piedmont streams within the middle oconee river basin in northeastern georgia during the period between march 2003 and march 2004 they sr isotope ratio analyses were accompanied by measurements of stream discharge rainfall stable o isotope ratios and major ion and 3 h concentrations the average sr ion concentration and 87 sr 86 sr ratio for the terminal stream basin the middle oconee river were 23 6 g l and 0 7172 respectively the average 87 sr 86 sr ratios of the rainwater and shallow ground water were below 0 7125 indicating that most of the sr in this stream water is input by weathering reactions in deeper ground water rather than by ion exchange in shallow soil horizons this is consistent with the higher alkalinity concentrations 23 47 mg l and specific conductance values 60 113 s cm that characterize stream base flow piedmont streams are characterized by lower concentrations of sr and higher 87 sr 86 sr ratios than average global stream flow base flow rates decreased by a factor of 2 3 during the summer months and this is accompanied by increased alkalinity concentrations 87 sr 86 sr ratios however were temporally invariant for a given stream basin and were independent of season antecedent rainfall and discharge 87 sr 86 sr ratios were unique for each of the 4 basins and a general trend toward higher ratios with increasing basin area was apparent the inferred contribution from minerals with high rb contents such as k feldspar and muscovite may have resulted from the greater integration of flow from mineralogically diverse pathways afforded by a larger basin area the basin specificity and temporal or seasonal invariability make 87 sr 86 sr ratios an invaluable hydrological tracer that can be readily employed in mass balance studies of stream flow within the piedmont province

a seismic refraction investigation of the archaean kaapvaal craton south africa using mine tremors as the energy source summary the structure of the central kaapvaal craton of southern africa has been investigated by deep seismic sounding using mine tremors as energy sources seismometers were deployed at approximately 10 km intervals on two profiles stretching between major mine tremor source regions mine tremors are rich in shear energy enabling joint interpretation of p and s waves and produce substantial energy at frequencies as low as 1 hz record sections are presented for both p and s waves and the traveltimes and amplitudes interpreted using 2 d ray tracing techniques synthetic seismograms computed for a 1 d velocity model by the reflectivity method compare well with the observed data a generalized seismic model of the kaapvaal craton has the following features supracrustal strata 0 10 km thick upper crystalline basement with p wave velocities of 6 0 6 2 km s the boundary between upper and lower crust at a depth of 14 18 km a lower crust with a relatively uniform seismic velocity in the range 6 4 6 7 kms and the crust mantle transition over 1 3 km with the moho at a depth of about 35 km the lower crust is found to be seismically attenuating and has a poisson s ratio of about 0 28 it is also known to be electrically conductive these observations are in accord with the presence of hydrated mantle rock at the base of the crust the velocity depth model of the kaapvaal craton is similar to models derived for other archaean cratons the proterozoic provinces adjacent to the kaapvaal craton are significantly thicker and have an intermediate to high velocity layer developed at the base of the crust this is interpreted to indicate a change in the process of crustal growth with basaltic underplating becoming more important since the archaean this change is attributed to a change in the composition of the upper mantle the higher temperatures in the archaean mantle led to the eruption of komatiitic lavas resulting in an ultradepleted mantle unable to produce significant volumes of basaltic melt proterozoic crust developed above fertile mantle and subsequent partial melting resulted in basaltic underplating and crustal inflation

sulfur isotope constraint on the provenance of salinity in a confined aquifer system of the southwestern nobi plain central japan abstract a combination of 34 s values and chemical compositions of brackish groundwater were used to examine the provenance of salinity in a confined aquifer system in the southwestern nobi plain central japan a tongue of brackish confined groundwater cl 1000 mg l which extends from the shoreline of ise bay inland has somewhat lower so 4 cl ratios and higher 34 s values 79 than those of the present seawater although the cation compositions of the brackish groundwater are consistent with values calculated for a mixture of fresh recharge water and seawater the anion compositions cannot be adequately interpreted as derived from such a mixing process alone using a rayleigh distillation model we found that the groundwater chemistry could be explained by sulfate reduction in combination with the mixing of two types of seawaters the present seawater and so 4 free seawater with the fresh recharge water the so 4 free seawater may consist mainly of fossil seawater that was trapped in an aquiclude for thousands of years model calculations based on cl and so 4 2 contents and 34 s values showed that the present and fossil seawaters compose at most 10 7 and 9 4 respectively of the brackish groundwater volume and the reduced so 4 2 content is up to 353 mg l in the confined aquifer the model s discrimination of the two seawaters is also in agreement with the spatial distribution patterns of groundwater composition from the west to the east in succession the main influence on the groundwater chemistry is fresh recharge water the present seawater and the fossil seawater moreover the area of intrusion of present seawater predicted by the model agrees well with the area of seawater intrusion determined from water quality data obtained a decade ago indicating that the model calculations can be reasonably used to discriminate quantitatively between present and fossil seawaters

time dependent convection with non newtonian viscosity we have used a numerical model of bottom heated two dimensional convection in boxes of aspect ratios 2 5 and 4 0 to study the differences in time dependent convection between newtonian and stress dependent viscosity the onset of time dependence due to boundary layer instability is found at approximately the same effective rayleigh number for both rheologies however with increasing rayleigh number the temporal and spatial fluctuations in the flow field become much more pronounced with non newtonian rheology also the tendency for breakup of long cells into smaller ones is stronger the presence of stress dependent rheology can cause long wavelength lateral viscosity variations up to an order of magnitude this result could have strong implications for the interpretation of mantle viscosity from postglacial rebound

inhomogeneities near the core mantle boundary inferred from short period scattered pkp waves recorded at the global digital seismograph network we analyze short period pkp precursor wave trains recorded at global digital seismograph network stations in the distance range 120 140 to infer the nature of inhomogeneities near the core mantle boundary travel times and particle motions are consistent with predictions of single scattered waves near the cmb the dominant frequencies are around 1 hz the regions best sampled are beneath indonesia north america central africa and south america based on first order scattering theory the characteristics of the wave number spectrum of the structural inhomogeneities are obtained for two hypotheses volume inhomogeneities and topographic irregularities for the range of wavelengths sampled by these data between 10 and 70 km the spectrum of inhomogeneities is best represented by a power law of index 5 3 for volume inhomogeneities and 6 8 for topographic irregularities if the scattering is due only to volumetric inhomogeneities we estimate the strength of the structural variations to be about 0 5 in p wave velocity for a 200 km thick layer if the scattering is due only to topographic irregularities the topography has an rms height of 280 m at present we can not distinguish between these two types of inhomogeneities

timing of formation of beta regio and its geodynamical implications 1 recent evidence suggests that the beta regio equatorial highland generally considered to be a plume related structure was emplaced over a relatively short period of time in the recent venus history 100 400 m y we perform numerical simulations which use this evidence as a new constraint on geodynamic models and find that it is difficult to satisfy simultaneously the constraint on the uplift rate and the constraints on gravity topography and rheology one possible solution is that the effective viscosity contrast between the mantle and the lithosphere does not exceed about 104 if our simple models do capture the basic dynamics of formation of beta regio this value implies that the viscosity of the lithosphere is softer than olivine at subsolidus temperatures and that the venusian lithosphere may not be much stronger than the terrestrial one

seismic signature of the lake mien impact structure southern sweden the eugeno s seismic profile iv in southern sweden crossed lake mien a confirmed heavily eroded 121 ma impact structure the lake mien structure has a pre erosion rim diameter of about 9 km it is

strontium isotopes in trees as an indicator for calcium availability summary the increasing acidification and impoverishment of soil poses a great environmental problem today and in the future and is exemplified by the decreased availability of calcium in the soil pool unfortunately budgeting the inputs and outputs of calcium in the soil vegetation ecosystem is a very laborious task some of the fluxes are internal in the ecosystem and cannot be measured explicitely like weathering of primary minerals however since strontium and calcium exhibit similar geochemical behaviour it is possible to make an estimation of the calcium content in different media in the soil vegetation eco system using natural strontium isotopes preliminary analyses of water precipitation throughfall runoff soil water soil mineral matter and biological material trees mussel shells show that the use of the strontium isotope ratio 87 sr 86 sr is a powerful tool in estimating and understanding environmental changes

three dimensional spherical models of convection in the earth s mantle three dimensional spherical models of mantle convection in the earth reveal that upwelling cylindrical plumes and downwelling planar sheets are the primary features of mantle circulation thus subduction zones and descending sheetlike slabs in the mantle are fundamental characteristics of thermal convection in a spherical shell and are not merely the consequences of the rigidity of the slabs which are cooler than the surrounding mantle cylindrical mantle plumes that cause hotspots such as hawaii are probably the only form of active upwelling and are therefore not just secondary convective currents separate from the large scale mantle circulation active sheetlike upwellings that could be associated with mid ocean ridges did not develop in the model simulations a result that is in agreement with evidence suggesting that ridges are passive phenomena resulting from the tearing of surface plates by the pull of descending slabs

provenance of the north pacific sediments and process of source material transport as derived from rb sr isotopic systematics abstract rb sr isotopic systematics of 111 samples of sediments in nine cores from the north pacific of quaternary and pliocene ages have been investigated they provide information on the provenance the process of particle transport and temporal variation in the flux of source material the rb sr isotopic systematics of the core sediments show well correlated pseudo isochrons the pseudo isochrons reflect the mixing of two types of material i e the asian continental material with high 87 rb 86 sr ratios 4 5 6 5 and high 87 sr 86 sr ratios 0 723 0 727 and the volcanic material with low 87 rb 86 sr ratios and low 87 sr 86 sr ratios from island arc volcanics such as the izu ogasawara mariana and the japanese islands and oceanic islands such as the hawaiian islands 0 0 2 0 0 703 0 708 the clearness of the pseudo isochrons implies that the rb sr isotopic composition of the weathering products derived from the asian continental crust is extremely homogenized the fine fraction a few m with a high 87 rb 86 sr ratio 5 0 6 5 is widely transported into the north pacific by the middle latitude westerlies and contributes largely to pelagic sediments the coarser fraction with a lower 87 rb 86 sr ratio

the core mantle boundary the largest compositional discontinuity within the earth is the core mantle boundary cmb at a depth of 2889 km this boundary and the adjacent transition zones in the lowermost mantle and outermost core play a critical role in the earth s thermal and chemical evolution estimates of the heat flux out of the core indicate that the 200 km thick d region at the base of the mantle is a major thermal boundary layer the d region like its counterpart boundary layer in the lithosphere is laterally heterogeneous and possibly chemically stratified this complexity obscures the exact dynamic behavior of the d region however it is clear that the large density contrast 4 3 g em 3 across the cmb provides favorable con ditions for density stratification on both sides of the boundary the d region may be the refuse pile for heavy mantle heterogeneities while the outermost core may have a concentration of light components boundary layer instabilities in d have been invoked as sources of both localized mantle plumes and major upwelling currents in whole mantle convection systems dynamically supported topography on the cmb and lateral temperature gradients in d may produce coupling between the core and mantle influencing the excitation of the geodynamo the outer most core is generally believed to be radially and laterally homogeneous although chemical stratification has not been ruled out seismological geodynamical and geomagnetic investigations are unveiling the three dimensional complexity of the deep earth in the vicinity of the cmb

a seismic q profile for the lower mantle from short period p waves a few studies of the quality factor q the ratio of peak to dissipated energies of seismic waves in the earth s mantle have used a limited data set of spectral ratios for body waves1 3 most estimates of q have come from the analysis of surface waves and free oscillations but use of such data to estimate q in the deep mantle suffers from a significant lack of resolution to improve this resolution in the lower mantle we have compiled a large data base of digital short period p wave recordings from underground nuclear explosions we have analysed p and pp waves to develop a set of t seismic travel time divided by effective path q station corrections corresponding to the upper mantle beneath each station and a t distance profile the t distance profile is inverted to determine a q depth profile for the lower mantle a thermal activation model used to interpret the q depth profile and to estimate a lower mantle geotherm enables a thermal boundary layer to be identified in the lowermost 200 km of the mantle this boundary layer is large enough to be indicative of mantle convection driven by heat flow from the earth s core

rising through earth s mantle convection in earth9s mantle is driven by temperature and density gradients and carries vast amounts of partially molten rock through earth9s mantle subducting oceanic plates have been traced from the top to the bottom of the mantle but the nature of the upward flow is still a matter of debate seismic studies by goes et al page 1928 and ritsema et al page 1925 indicate large scale upwellings of hot material in the lower mantle that extend all the way to the surface the results are interpreted as direct evidence for the deep driving forces that cause rifting and intraplate volcanism in central europe and east africa

solitary waves in mantle plumes numerical calculations in two dimensions show that solitary wave disturbances can propagate along thermal plumes in a homogeneous viscous fluid with a thermally activated rheology similar to the mantle comparison of the numerical results with analytic results from an idealized two fluid model indicates that the two fluid model can be applied to solitary waves in the thermally activated plume a two fluid model of solitary waves on cylindrical conduits is accordingly applied to mantle plumes to estimate the propagation speeds time durations and pulse lengths of solitary waves in mantle plumes as a function of background mantle viscosity plume flux plume density deficit plume viscosity and the volume of material transported by the solitary wave it is inferred that mantle plumes may be episodic via solitary waves and that these disturbances might account for observed 0 10 m y variations in the durations and spacings of episodes of enhanced hotspot volcanic activity solitary waves in mantle plumes could be generated by interactions among plumes and between plumes and the large scale time dependent mantle circulation

in situ seismic measurements in borehole lb 08a in the bosumtwi impact structure ghana preliminary interpretation in order to assist in the interpretation of previous seismic refraction and reflection surveys a vertical seismic profile was acquired in the lake bosumtwi ghana hard rock core hole lb 08a no seismic reflections are seen in the up going wave field obtained and this observation is consistent with the lack of reflectivity observed in the corresponding 2 d surface seismic profile obtained in earlier studies direct down going p waves were found both in the cased sediment column from a depth of 73 m to 239 m below the lake surface and in the open hole hard rock section from a depth of 239 m to 451 m of lb 08a analysis of the observed travel times indicates a nearly constant p wave velocity of 1520 m s through the soft lacustrine sediments in the hard rock however the p wave velocity rapidly increases by nearly 30 from 2600 m s to 3340 m s these values are in good agreement with the gross velocity structure obtained in the earlier joint inversion of seismic reflection and refraction data these values are low relative to those expected for the metasedimentary protoliths an observation that has been made at other young impact structures of similar size the low velocities together with the fact that they increase so rapidly is suggestive of a decreasing density of fractures and microcracks with depth consequently the seismic velocity trend may provide a proxy measure of damage and hence the decay of the shock pressure from the impact point validation of this requires additional detailed studies of the porosity structure in the core

a lower mantle s wave triplication and the shear velocity structure of d summary a lower mantle s wave triplication detected with short and longperiod wwssn and csn recordings indicates a substantial shear velocity discontinuity near 280 km above the core mantle boundary the triplication can be observed in rotated sh seismograms from intermediate and deep focus events throughout the distance range from 70 to 95 three distinct source region receiver array combinations that have been investigated in detail demonstrate consistent travel time and relative amplitude behaviour of the triplication with slight systematic shifts in the triplication indicating up to 40km variations in the depth of the discontinuity modelling of the observations with synthetic seismograms produced with the cagniard de hoop and reflectivity methods constrains the shear velocity increase to be 2 75 k 0 25 per cent comparable to upper mantle discontinuities short period observations indicate that the velocity increase may be a sharp first order discontinuity or may extend over a transition zone no more than 50 km thick the shear velocity gradient below the discontinuity within the d layer is not well constrained by the sh data but slightly positive or near zero velocity gradients are consistent with the long period amplitude ratios of scsh sh

superchron cycles driven by variable core heat flow 1 a numerical dynamo with time variable core heat flow and inner core growth rate links the thermal state of the earth s core to the long term trends in the geomagnetic polarity time scale gpts increasing core heat flow over 100 myr drives the numerical dynamo from a superchron state to reversing behavior whereas a similar decrease in core heat flow produces a decrease in reversal frequency driving the dynamo back into a superchron the polarity sequence including more than 400 reversals and two superchrons compares favorably with the gpts as does the dynamo frequency spectrum we find that core heat flow is positively correlated with polarity reversal frequency dipole variability and the relative strength of the non dipole field our results imply that changes in geomagnetic reversal frequency can be attributed to long period fluctuations in core heat flow and suggest heat flow minima during superchrons and a maximum near the present day

dynamical influences from thermal chemical instabilities at the core mantle boundary two dimensional time dependent calculations show that the thermal and flow structures can be influenced by the lower mantle thermal chemical instabilities the style of the core mantle boundary cmb deformation in thermal chemical convection is different from that obtained in thermal convection the amplitude of cmb hills is reduced greatly from the depth dependence of thermal expansivity found in recent high pressure experiments

seismic refraction studies in the basement of the vredefort structure abstract the 30 mgal positive gravity anomaly in the centre of the basement of the vredefort structure has been a feature of discussion for a number of years to supply constraints on the depth and nature of this body refraction seismic measurements were made on a n s line across the basement anomaly the results support a three fold subdivision of the uppermost structure on the seismic profile granitic gneisses in the north dioritic gneisses in the central sector over the gravity anomaly and carboniferous karoo strata in the southern part of the basement throughout the central section of the refraction profile rocks with p wave velocity of 6 40 6 43 km s dominate the profile whilst to the north and south of this central section basement velocities are all less than 6 0 km s computer travel time simulations of the basic model were carried out using 2 d ray tracing

integrated geophysical modelling of a giant complex impact structure anatomy of the vredefort structure south africa abstract only three very large confirmed impact structures are known on earth the chicxulub crater mexico 65 ma ca 180 km wide the sudbury structure canada 1 85 ga 200 km in diameter and the vredefort structure in south africa 2 02 ga while extensive data on large impact structures have been obtained by remote sensing studies of such features on other planetary bodies only this small number of large terrestrial impact structures can provide data crucial to understanding these catastrophic impact processes on earth integrated modelling of gravity and magnetic data constrained by geological as well as refraction and reflection seismic data accomplished the reconstruction of the vredefort impact structure in south africa approximately 250 km wide the original vredefort impact structure covered the whole extent of the archaean witwatersrand basin distinguished by enormous gold resources as it is structurally preserved today in fact it is clear that the preservation of vast volumes of economically important witwatersrand strata is the direct result of the formation of the ring basin around the central uplift the vredefort dome of the impact structure this study is the first attempt to create an integrated and geophysically well constrained model of this very large complex impact structure

radioelement concentrations in the deep profile through precambrian basement of the vredefort structure the vredefort basement granite in south africa forms the core of an undomed and overturned sequence of precambrian strata slawson 1976 proposed that the granite core has also been overturned exposing to view a thick section through the archean crust incrasing in depth toward the center of the dome profiles across the vredefort basement provide an opportunity for studying the distribution of u th and k with depth in the upper and middle crust detailed radioelement concentration profiles across the granitic basement showed that 1 the central part of the basement core is depleted in th and u relative to the perimeter and the concentration of th and u falls off regularly from the basement margin inward 2 the distribution of the radioelements and the distribution of heat production with depth over the outer 8 km are consistent with an exponential depth function 3 the felsic rocks of the central basement are characterized by high k u and th u ratios and the ratios k u k th and th u increase from the margin inward and 4 mafic granulites which occur in the central regions of the dome have normal k u k th and th u ratios high grade metamorphic environment resulted in the depletion of bothmore u and th relative to k in the greater proportion of the felsic rocks from the central regions of the vredefort basement depletion of u was far greater than that of th the normal th u k u and k th ratios in mafic rocks in close proximity to the felsic rocks suggest that mineral assemblages have a strong control on the behavior of the radioelements during regional metamorphism in the vredefort basement less

strontium isotope constraint on the provenance of basic cations in soil water and stream water in the kawakami volcanic watershed central japan positive correlations among the concentrations of sr ca and mg in soil water and stream water in a forested volcanic watershed at kawakami central japan indicate that the sr isotope can be used as a tool to elucidate the source and transport of the essential terrestrial ecosystem nutrients ca and mg the 87sr 86sr ratio in surface soil water varied widely along a 74 m slope it was almost identical to the 87sr 86sr ratio of exchangeable soil and existing plants with different rooting zones japanese oak and bamboo grass but differed significantly from that of soil minerals in contrast the 87sr 86sr ratios of stream water at baseflow periods were uniform regardless of location and time and were indistinguishable from those of the weathered andesite bedrock the sr isotopic and elemental data indicate that sr ca and possibly other cations e g k mg in the plant cycle efficiently with exchangeable soil through soil water and without a large supply of cations from secondary soil minerals while cations in stream water are controlled mainly by exchange reactions with bedrock derived secondary minerals occurring in the lower soil horizon to water saturated zones it is calculated that about 10 of sr and mg and 20 of ca in stream water are derived from wet precipitation while the contribution of atmospherically derived sr and ca in the exchangeable soil pool increases from 22 to 72 and from 42 to 87 respectively with increasing distance from the valley this increase of sr and ca in the exchangeable soil pool coincides with rock derived low ca materials dominating in the surface soil of the upper elevation in the slope copyright 2001 john wiley sons ltd

evolution of the amphibolite granulite facies transition exposed by the vredefort impact structure kaapvaal craton south africa abstract geological mapping is integrated with high precision u pb zircon and monazite geochronology to document in detail the nature and temporal evolution of the amphibolite granulite facies boundary exposed in the vredefort impact structure of the central kaapvaal craton our study has revealed that the preimpact configuration of the amphibolite granulite facies boundary is best preserved in panels between impact related brittle faults and that past concepts of the boundary must be revised a regional lithologic transition exists between amphibolite facies outer granite gneiss 3 084 3 09 ga and a heterogeneous assemblage of granulite facies gneisses ca 3 1 3 3 ga tabular deformed quartz syenite bodies dated at documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cy

constraints from seismic anisotropy on the nature of the lowermost mantle the d layer lies at the bottom of the earth s rocky mantle and separates it from the liquid metal alloy core this region extending from the core mantle boundary to a few hundred kilometres above fig 1 is geodynamically analogous to the more easily studied lithosphere at the top of the mantle the structure of d may reflect the style of lower mantle convection the nature of core mantle interaction and perhaps even the fate of subducting lithosphere1 observations of lithospheric seismic anisotropy have provided valuable insight into the nature of the upper mantle boundary layer but discussion of lower mantle seismic anisotropy has been somewhat contentious2 5 here we present evidence from seismic waves that have traversed the lowermost mantle beneath the caribbean region for a zone of seismic anisotropy below the d discontinuity which in this region lies 250 km above the core mantle boundary the anisotropy is most probably due to horizontal layering or aligned inclusions of a material with differing shear wave velocity if d is a graveyard for subducted lithosphere a plausible explanation of the anisotropy may be the contrast between cold lithospheric mantle and material that formerly constituted the oceanic crust which may have lower shear wave velocity owing to the presence of melt

trade off in production between adjacent seamount chains near the east pacific rise bathymetric data and side scan sonar images collected near the southern east pacific rise between 15 and 19 s1 2 have revealed many seamounts on the west flank of the rise most of which are organized into chains running perpendicular to the rise axis the number of seamounts of 5 km diameter is at least twice that expected for average east pacific sea floor3 the formation of numerous small 5 myr linear seamount chains and the tendency for fresh lava flows to be found primarily at the near ridge ends of the chains suggest that there are plume like sources in the upper mantle which are relatively stationary active for extended periods and affected by adjacent sources

s wave scattering by 3 d heterogeneities at the base of the mantle the hypothesis of s wave scattering by three dimensional heterogeneity in the lowermost mantle is shown to provide a plausible alternative to the spherically stratified models recently proposed by lay and helmberger to explain certain observed complexities in long period s wave data a result of central importance is that contrary to the conclusions of lay and helmberger and most recently young and lay sharp increases of s velocity with depth are not required to explain their data

effect of mantle plumes on the growth of d by reaction between the core and mantle the core mantle boundary is a fundamental compositional discontinuity in the earth where molten iron alloy from the core meets solid silicate minerals from the mantle heat flow from the core to the mantle creates a thermal boundary layer at the base of the mantle at the same time chemical reactions may create a layer of different composition and density than the overlying mantle using a finite element model of convection in a spherical shell that includes formation of dense material at the base of the shell we investigate how a layer forms at the base of the mantle development of a layer at the base of the mantle by this method depends both on the composition of the material forming at the core mantle boundary and on the rate at which the material diffuses into the mantle if the material is less than 3 6 denser than the overlying mantle assuming reasonable choices of lower mantle thermodynamic parameters the reactant material will be swept away by upwelling plumes more dense material on the other hand forms an internally convecting layer that entrains material from above the varying thickness and composition of the layer is consistent with geophysical observations of the characteristics of the deep mantle

the geographic distribution of sr isotopes from surface waters and soil extracts over the island of bornholm denmark a base for provenance studies in archaeology and agriculture abstract in this paper we report the sr isotope signatures and sr al and na concentrations of 30 surface waters lakes ponds and rivers creeks and 19 soil sample extracts from the island of bornholm denmark and present a categorized 87 sr 86 sr value distribution map that may serve as a base for provenance studies including archaeological migration and authenticity proof for particular food products the sr isotopic compositions of surface waters range from 87 sr 86 sr 0 7097 0 7281 average 0 7175 0 0049 1 whereas 0 1 m hno 3 0 05 m hno 3 and 0 01 m cacl 2 soil extracts range from 87 sr 86 sr 0 7095 0 7197 and define somewhat lower but statistically indistinguishable averages of 0 7125 0 003 1s these compositions are lower than the values expected from the precambrian granitoid basement 87 sr 86 sr 0 758 0 944 and from the overlying mainly clastic paleozoic sediments combined sr isotope composition vs sr na and al concentration relationships of soil extracts imply that lowering of the isotopic composition of leachable sr on bornholm results as a consequence of significant admixture to this fraction of sr deposited as marine salts aerosols and that rainwater only has a minor influence on the sr budget of the surface waters positively correlated al na and 1 sr vs 87 sr 86 sr relationships in soil extracts and surface waters indicate that the surface run off on bornholm is characterized by two predominant sources namely marine aerosols sea salts with high sr and low 87 sr 86 sr values and a source with lower sr delivering radiogenic sr to the surface waters which we equate with sr leached from the products of mineral weathering soils a feasibility study for using sr isotopic compositions of surface waters and soil extracts as a proxy for bioavailable sr signatures was performed with a few samples collected in the vicinity of the eleventh century ad ndr grodbygard cemetery site in sw bornholm from where sr isotope compositions of modern fauna samples and tooth enamel of humans buried in the cemetery have been reported waters and soil extracts studied herein from around this site range from 87 sr 86 sr 0 7104 0 7166 and correspond to sr compositions extracted from snail shells in this area which span a range of 87 sr 86 sr 0 7095 0 7160 some human tooth enamel is characterized by more radiogenic values 87 sr 86 sr up to 0 718 which points to a possible provenance of these humans from the granite gneiss terrain in the north of the island and or to immigration of these humans in their childhood from other places for example from mainland sweden to bornholm if the total compositional range of 87 sr 86 sr 0 709 0 718 n 44 recorded in human enamel from the ndr grodbygard site is considered representative for the variation of bioavailable sr on bornholm then our soil leachate and surface water data entirely covers this range we therefore propose that the combination of sr isotope analyses of surface waters and soil leachates are an easy fast and relatively cost efficient way to characterize a local bioavailable 87 sr 86 sr signature and consequently propose that the overall average of 87 sr 86 sr 0 7153 0 0048 1 n 50 can be taken as a band for bioavailable sr fractions suitable to discriminate between local and non local signatures in provenance studies in the field of archaeology and for food and plant authenticity control in agricultural applications

the excess temperature of plumes rising from the core mantle boundary we study the rise of conduit type thermal plumes from the core mantle boundary cmb in a simplified numerical model viscosity is a strong function of temperature and pressure assuming that all plumes start with the same excess temperature at the cmb we find that their temperature in the upper mantle is controlled by the plume flux and is insensitive to variations in viscosity or other material parameters or to the kind of flow law newtonian or non linear the reduction of excess temperature with height is stronger for weaker plumes plumes with a buoyancy flux of less than 1000 kg s should have cooled so much that they would not melt beneath old lithosphere the existence of such hot spots possibly indicates that not all plumes rise from the cmb

quantitative strontium isotope models for weathering pedogenesis and biogeochemical cycling abstract isotopes of strontium sr are a useful tracer for weathering atmospheric fluxes cation biocycling and pedogenesis we present basic models for application of strontium isotopes to the soil vegetation atmosphere system the mathematical formulations fall into the general categories of 1 steady state models in which isotopic ratios remain constant over the time scale of interest and 2 time dependent models in which isotope ratios change through time in the steady state models fluxes of sr and other elements to the system are constant steady state models can be used to infer short term weathering rates from river and stream isotope compositions to determine fluxes to a single or multiple layer soil exchange solution system and to quantify nutrient fluxes to vegetation time dependent models involve a change in isotopic ratio from some initial value to a new value over the time period of interest in some cases the change may represent a shift from one steady state situation to a new one after a shift in one or more of the fluxes feeding the system examples of applications of time dependent models include identifying the dominant cation sources to an evolving soil exchange solution system and calculating weathering rates by measuring the isotopic compositions of primary soil minerals we use time dependent models to explain differences in the isotopic ratios of labile and carbonate sr from arid sites in hawaii with a basalt parent material isotopic signature and new mexico with an atmospheric isotopic signature these models suggest that the difference is due to a combination of low atmospheric strontium fluxes and high weathering rates in the hawaiian profile compared to the new mexico calcrete profile

plume formation in the d double prime layer and the roughness of the core mantle boundary numerical simulations of the formation of thermal plumes in the d layer at the base of the earth s mantle show that plumes are initiated by coalescence of small scale convective instabilities within the low viscosity region immediately above the core mantle boundary cmb these instabilities support topographic roughness on the cmb having horizontal scales of 20 50 km and provide a source for scattered p waves seen as precursors to the phases pkikp and pkkp the calculated structure of fully developed plumes emerging from d consists of 5 50 cm yr 1 flow confined to 50 100 km thick vertical conduits with strongly temperature dependent viscosity plumes exhibit time dependent behaviour including upward propagating solitary conduit waves which may contribute to episodicity in hotspot volcanism

effects of multiple phase transitions in a three dimensional spherical model of convection in earth s mantle numerical models of mantle convection that incorporate the major mantle phase changes of the transition zone reveal an inherently three dimensional flow pattern with cylindrical features and linear features that behave differently in their ability to penetrate the 670 km discontinuity the dynamics are dominated by accumulation of cold linear downwellings into rounded pools above the endothermic phase change at 670 km depth resulting in frequent avalanches of upper mantle material into the lower mantle the effect of the exothermic phase transition at 400 km depth is to reduce the overall degree of layering by pushing material through the 670 km phase change resulting in smaller and more frequent avalanches and a wider range of morphologies large quantities of avalanched cold material accumulate above the coremantle boundary cmb resulting in a region of strongly depressed mean temperature at the base of the mantle the 670 km phase change has a strong effect on the temperature field with three distinct regions being visible 1 the upper mantle containing linear downwellings and pools of cold material in the transition zone and characterized by a high amplitude long wavelength spectrum 2 the midmantle containing quasi cylindrical avalanche conduits and characterized by a low amplitude broad spectrum and 3 the deep mantle containing large pools of cold avalanched material and characterized by a high amplitude ultra red i e long wavelength spectrum the effect on the velocity field is very different flow penetration across the 670 km phase change is strongly wavelength dependent with easy penetration at long wavelengths but strong inhibition at short wavelengths thus when comparing numerical models with long wavelength seismic tomography diagnostics based on the density field such as the radial correlation function are much more sensitive to the effects of phase transitions than those based on the velocity field the amplitude of the geoid is not significantly affected by the partial layering because the contribution from the strong heterogeneity in the transition zone is almost perfectly balanced by the contribution from deflection of the 670 km discontinuity avalanches are associated with geoid lows however a more complex viscosity structure is required to correctly match the sign of the geoid over slabs in earth

various influences on plumes and dynamics in time dependent compressible mantle convection in 3 d spherical shell the effects on the dynamics of compressible mantle convection from increasing rayleigh number viscosity stratification and internal heating are investigated in a time dependent 3 d spherical shell model resolution of up to spherical harmonics of degree 192 and 150 higher order finite difference grid points unevenly distributed in the radial direction have been employed surface rayleigh number varies from 5 104 to o 107 the viscosity profiles used range from constant to a depth dependent viscosity profile the adams williamson adiabatic assumption is adopted for describing the equation of state both depth dependences of thermal expansivity and thermal conductivity are included we have focused on the viscosity stratification in the lower mantle the mean temperature profiles are very sensitive to the input parameters such as the amount of internal heating and the dissipation number in the isoviscous model the number of hot plumes decreases for low rayleigh number 5 104 and increases dramatically with higher rayleigh number 106 in the model with a high viscosity zone in the lower mantle the number of plumes is small and does not change too much when the rayleigh number varies from 3 106 to 8 106 in the purely base heated viscously stratified models well organized triple junctions of the downwelling sheets are developed near the surface and interconnected cold walls of downwellings are produced around upwelling plumes the presence of internal heating increases the number of upwelling plumes and breaks up the interconnection of downwelling sheets strong viscous heating in the compressible solutions is found near the top and bottom at the higher values of rayleigh number the laterally averaged value of viscous dissipation is comparable with the chondritic strength of internal heating whether the maximum viscous heating is found in upwelling plumes or downwelling flows depends on the presence of internal heating and the mechanical boundary conditions the effects of compressibility on local structures and plume morphologies can be significant however these compressible effects are moderate on the global patterns

the terrestrial impact cratering record approximately 130 terrestrial hypervelocity impact craters are currently known due to variations in preservation and in geologic knowledge this sample is biased towards young x 20 km craters on the cratons of australia europe including the former u s s r and north america the rate of discovery of new craters is 3 5 craters per year although modified by erosion terrestrial impact craters exhibit the range of morphologies observed for craters on other terrestrial planetary bodies such as the moon terrestrial craters provide essential ground truth data on the geologic effects of impact and the subsurface structure of impact craters which can be used to constrain interpretations of lunar samples and models of crater formation due to erosion and its effects on form terrestrial craters are recognized primarily by the occurrence of shock metamorphic effects these include shatter cones microscopic planar deformation features solid state and fusion glasses high pressure polymorphs and whole rock melting and vaporization shock recovery experiments indicate that these features occur over shock pressures of 5 gpa to x 100 gpa terrestrial craters have a set of geophysical characteristics which are largely the result of the passage of a shock wave and impact induced fracturing they include gravity and magnetic lows and reductions in seismic velocity the gravity anomalies are seldom greater than 30 mgal due to the limiting effects of lithostatic pressure on fracturing at large complex craters the gravity signature may include a central relative gravity high due to uplift and short wavelength central magnetic anomalies due to a variety of processes much current work is focused on the effects of impact on earth evolution previous work on shock metamorphism and the contamination of impact melt rocks by meteoritic siderophile elements provides a basis for the interpretation of the physical and chemical evidence from cretaceous tertiary boundary sites as resulting from a major impact suggestions that other biological boundaries in the stratigraphie record are due to periodic impacts are not supported by time series analysis of the terrestrial cratering record by analogy with the lunar record and modelling of the effects of very large impacts it has been proposed that biological and atmospheric evolution of the earth could not stabilize before the end of the late heavy bombardment 3 8 ga ago the present terrestrial cratering rate is 5 4 2 7 10 15 km 2a 1 for a diameter 20 km this represents a local threat on historic time scales on a global scale a major impact sufficient to cripple human civilization severely will occur on time scales of 106 a

a thermal balancing act heat is constantly transported from earth9s core through the mantle to the crust where it results for example in volcanic eruptions the heat transport depends on the thermal conductivity of the different materials in the core and the mantle but for many years the numbers did not add up and the power could not be balanced between the core and the mantle anderson now shows that a reevaluation of the thermal conductivity of the mantle by hofmeister may balance the power

geoid anomalies and dynamic topography from convection in cylindrical geometry applications to mantle plumes on earth and venus summary a variety of evidence suggests that at least some hotspots are formed by quasi cylindrical mantle plumes upwelling from deep in the mantle we model such plumes in cylindrical axisymmetric geometry with depth dependent newtonian viscosity cylindrical and sheet like cartesian upwellings have significantly different geoid and topography signatures however rayleigh number nusselt number systematics in the two geometries are quite similar the geoid anomaly and topographic uplift over a plume are insensitive to the viscosity of the surface layer provided that it is at least 1000 times the interior viscosity increasing the rayleigh number or including a low viscosity asthenosphere decreases the geoid anomaly and the topographic uplift associated with an upwelling plume increasing the aspect ratio increases both the geoid anomaly and the topographic uplift of a plume the nusselt number is a weak function of the aspect ratio with its maximum value occurring at an aspect ratio of slightly less than 1

the non linear initiation of diapirs and plume heads abstract a simple theory is devised to describe the non linear feedback mechanisms involved in the initial growth of a single diapir or plume head from a low viscosity channel overlain by a much more viscous layer such feedbacks arise primarily from the relation between the growth of a proto diapir i e an undulation on the upper boundary of the low viscosity channel and the draining of the low viscosity channel in the period of time between its initial exponential growth characterized by linear stability analysis and its separation from the low viscosity channel as a fully formed diapir the proto diapir can undergo a significant cessation in its development due to deflation of the low viscosity channel i e the proto diapir s growth can essentially stall for a long period of time before it separates and begins its ascent through the overlying medium the theory is used to determine a criterion for separation of the diapir from the low viscosity channel that is in terms of the geometrical and mechanical properties of the channel instead of the ad hoc volume flux widely used in many models of mantle plumes and plume heads e g whitehead and luther 1975 richards et al 1989 olson 1990 sleep 1990 bercovici and mahoney 1994 from this separation criterion self consistent scaling laws can be formulated to relate the size of the fully developed diapir and its trailing conduit to the properties of the initial channel instead of to the ad hoc volume flux basic laboratory experiments involving highly viscous fluids are presented and demonstrate that the so called stalling period between initial growth and separation does indeed occur these results suggest that nascent mantle plume heads may stall for extended periods at the base of the mantle and thereby contribute to variations in thickness of the d layer

thermal evolution of two textural types of mafic granulites in the north china craton evidence for both mantle plume and collisional tectonics mafic granulites from the north china craton can be divided into two textural types referred to as a and b types a type mafic granulites display garnet quartz symplectic coronas and outcrop in the eastern and western zones of the craton whereas b type mafic granulites exhibit orthopyroxene plagioclase clinopyroxene symplectites or coronas and are mainly exposed in the central zone of the craton most a type mafic granulites preserve the prograde m 1 peak m 2 and post peak near isobaric cooling m 3 assemblages which are represented respectively by inclusions of hornblende plagioclase quartz a peak mineralogy of orthopyroxene clinopyroxene plagio clase quartz garnet and overprinted by garnet quartz symplectic coronas these mineral assem blages and their p t pressure temperature estimates define anticlockwise p t evolutionary paths the b type mafic granulites preserve the peak m 1 post peak near isothermal decompression m 2 and cooling m 3 assemblages which are represented by the peak assemblage of orthopyroxene clinopyroxene plagioclase quartz garnet hornblende post peak orthopyroxene plagioclase clinopyroxene symplectites or coronas and later hornblende plagioclase magnetite symplectites respectively these mineral assemblages and their p t estimates define clockwise p t paths the anticlockwise p t paths of the a type mafic granulites in the eastern and western zones of the north china craton are consistent with a model of underplating and intrusion of mantle derived magmas in combination with lithological structural and geochronological data the eastern and west ern zones of the north china craton are considered to represent two continental blocks that devel oped through the interaction of mantle plumes with the lithosphere from the palaeoarchaean to the neoarchaean era the b type mafic granulites and associated rocks in the central zone represent a magmatic arc that was metamorphosed and deformed during amalgamation of the eastern and west ern continental blocks in the late palaeoproterozoic era the mineral reaction relations and clockwise p t paths of the b type mafic granulites from the central zone record the tectonothermal history of the collision that resulted in the final assembly of the north china craton at c 1800 ma

using isotopes to determine the contribution of volcanic ash to sr and ca in stream waters and plants in a granite watershed mt tsukuba central japan strontium sr isotope ratios of soils stream water plants and atmospheric precipitation were used to trace calcium ca and to determine the influence of volcanic ash in soils on ca cycling in forest ecosystems in a small forested watershed on mt tsukuba central japan the 87sr 86sr ratios of soils on steep slopes and the valley floor ranged from 0 7110 to 0 7139 which indicates that the major source of sr was the granite substrate 87sr 86sr ratio 0 7120 0 7131 soils on a ridge had lower 87sr 86sr ratios 0 7068 0 7072 indicating that they were mainly composed of volcanic ash materials released around 30 000 years ago from mt akagi 0 7069 the 87sr 86sr ratio decreased and the concentrations of sr and ca increased in stream water with increased elevation from the valley bottom to the ridge indicating that volcanic ash was the dominant source of both cations in the upstream area the contributions of volcanic ash derived sr to upstream and downstream water were 50 and 0 1 respectively the 87sr 86sr ratios of plants were between those of the soils in which the plants were growing and those of atmospheric precipitation 0 7100 more than 74 of the sr in plants on the ridge but 17 in plants in the valley bottom was volcanic ash derived the origin of sr and thus ca in stream waters and plants varied depending on the volcanic ash content in soils which was significantly influenced by the site elevation

small scale lateral shear velocity and anisotropy heterogeneity near the core mantle boundary beneath the central pacific imaged using broadband scs waves core reflected scs waves from 49 large m 5 1 deep tonga fiji events recorded in western north america are used to study a localized region of the core mantle boundary cmb under the central pacific ocean a total of 248 observations from the berkeley digital seismic network bdsn caltech united states geological survey usgs terrascope and the incorporated research institutions for seismology iris broadband arrays span epicentral distances of 73 85 scs reflection points sample a cmb patch southeast of the hawaiian islands at latitude 4 to 16 n and longitude 156 to 144 w near the proposed source location of the hawaiian plume highly variable scs travel times amplitudes waveforms and shearwave splitting indicate that the lowermost mantle in this region is heterogeneous both laterally and radially scsh sh differential travel times are on average 4 s larger than predicted by the preliminary reference earth model prem this is due to delayed scs arrivals and is largely accounted for by a model with a strong velocity decrease in d the scsh sh residuals also show a spatial trend not accounted for by a radial model indicating a lateral decrease in lower mantle shear velocity to the northeast this lateral velocity gradient appears to cause focusing of scs energy scsh sh amplitude ratios are larger than predicted by prem or by a model with a strong negative gradient with depth in d which enhances scs scs splitting corrected for lithospheric anisotropy beneath the receivers indicates spatial variations in d anisotropy with a systematic change in the orientation of the fast polarization direction from transverse to the ray path fast scsh to parallel to the ray path fast scsv along a northeast traverse these spatial trends suggest lateral gradients in the boundary layer shear flow on scale lengths of a few hundred kilometers which may be related to dynamical flow near the near the root of the large hawaiian plume

significance of stemflow in groundwater recharge 1 evaluation of the stemflow contribution to recharge using a mass balance approach stemflow was evaluated in a water balance and its contribution to groundwater recharge determined gross precipitation throughfall and stemflow were measured for one year in a pine forest tsukuba japan to determine each component of the water balance in the forest groundwater recharge rates by stemflow and throughfall were calculated from a mass balance method using chloride in subsurface waters the stemflow in the water balance was relatively small when estimated as a value per canopy projected area of the tree in the forest however the results for the mass balance of chloride in subsurface waters indicated that it was impossible to disregard the stemflow in determining groundwater recharge although the ratio of stemflow to the net precipitation was small in the water balance the effect of stemflow on groundwater recharge was relatively large

south african seismicity april 1997 to april 1999 and regional variations in the crust and uppermost mantle of the kaapvaal craton abstract events induced by deep gold mining activity on the edge of the witwatersrand basin dominate the seismicity of south africa the deployment of 54 broad band seismic stations at 84 separate locations across southern africa between april 1997 and april 1999 kaapvaal network enabled the seismicity of south africa to be better defined over a 2 year period seismic events located by the south african national network and by localized seismic networks deployed in mines or across gold mining areas were used to evaluate earthquake location procedures and to show that the kaapvaal network locates mining induced tremors with an average error of 1 56 0 10 km compared with 9 50 0 36 km for the south african network travel times of seismic events from the mines recorded at the kaapvaal network indicate regional variations in the thickness of the crust but no clearly resolved variations in seismic wavespeeds in the uppermost mantle greater average crustal thicknesses 48 50 km compared with 41 43 km are observed in the northern parts of the kaapvaal craton that were affected by the bushveld magmatism at 2 05 ga estimates of average crustal thickness for the southern part of the kaapvaal craton from receiver functions 38 km agree well with those from refracted arrivals from mining induced earthquakes if the crustal thicknesses below the sources are assumed to be 40 43 km in contrast the average crustal thickness inferred from refracted arrivals for the northern part of the kaapvaal craton is larger by about 7 km 51 km than that inferred from receiver functions 44 km suggesting a thick mafic lower crust of variable seismic properties due to variations in composition and metamorphic grade pn wavespeeds are high 8 3 8 4 km s indicating the presence of highly depleted magnesium rich peridotite throughout the uppermost mantle of the craton seismic pg and sg phases indicate that the upper crust around the witwatersrand basin is comparatively uniform in composition when averaged over several kilometres

the geographic distribution of strontium isotopes in danish surface waters a base for provenance studies in archaeology hydrology and agriculture abstract in this paper sr isotope signatures are reported for 192 surface water lakes ponds and rivers creeks samples from within denmark and an isotope distribution map is presented that may serve as a base for provenance applications including archaeological migration studies ground water surface water seawater interaction contamination monitoring and potentially for agricultural applications including cases of authenticity proof for particular food products the sr isotopic compositions of surface waters range from 87sr 86sr 0 7078 to 0 7125 average 0 7096 0 0016 2 this average value lies above the range of 87sr 86sr values between 0 7078 and 0 7082 expected from late cretaceous to early tertiary oligocene limestones which form the dominant bedrock type in a nw se trending belt in denmark the elevated 87sr 86sr signatures 0 7095 are explained by additions to the surface waters of radiogenic sr predominantly derived from the near surface weathering and wash out of quarternary glaciogenic tills and soils deposited and formed during and after the last two ice age stages saale and weichsel the sr isotopic compositions and concentrations of the surface waters can therefore best be modeled by a two component mixing involving carbonaceous bedrock and glaciogenic cover sediments as the two predominant sr sources a feasibility study for using sr isotopic compositions of surface waters as a proxy for bio available sr signatures was conducted in a representative test area on zealand land of legends lejre where there is no use and application of commercial fertilizers it is demonstrated that the sr isotopic signatures of lake waters from within this area are slightly higher but statistically still indistinguishable from the average value defined by snail shells and soil leachates considered to characterize the true bio available sr in combination with results from other studies this is interpreted to reflect the wash out of sr with a higher 87sr 86sr signature released by weathering in the topsoils into the saturated water tables a component which is consequently not readily transferred into the shallow rooting plants and into small herbivores feeding on them since drinking water is a likely important source of sr uptake of humans and larger animals the contention is that a surface water isotopic composition can potentially characterize the bio available component relevant for human and carnivorous large animals spline functions and ordinary linear kriging were used for modeling the geographic distribution of bio available sr isotopes over territorial denmark as expected based on the two source mixing scenario the water 87sr 86sr ratio contour maps with some notable exceptions neither mirror the pre quarternary bedrock geology nor a pleistocene soil type distribution map of denmark as a conservative suggestion the use of the average 87sr 86sr ratio of 0 7096 0 0015 2 is recommended as an average for bio available sr from within denmark bornholm excluded for human and larger animals and as a confidence band for distinguishing local from non local signatures in archaeological provenance studies the study also reveals that the average 87sr 86sr ratio of 0 7088 defined from soil extracts and small herbivores lies approximately 0 15 lower than that defined by the surface waters the authors recommend using this lower value as a local non local discriminator for food and plant authenticity control in agricultural applications

hydrogeochemical evolution of confined groundwater in northeastern osaka basin japan estimation of confined groundwater flux based on a cation exchange mass balance method abstract a confined aquifer system has developed in argillaceous marine and freshwater sediments of pliocene holocene age in the northeastern osaka basin neob in central japan the shallow groundwater 3 type water which changes as it flows toward the sw to mg hco 3 type and then to na hco 3 type water comparison of the chemical and sr isotopic compositions of the groundwater with those of the bulk and exchangeable components of the underground sediments indicates that elements leached from the sediments contribute negligibly to the neob aquifer system moreover model calculations show that contributions of paleo seawater in the deep horizon and of river water at the surface are not major factors of chemical change of the groundwater instead the zonal pattern of the hco 3 dominant groundwater is caused by the loss of ca 2 from the water as it is exchanged for mg 2 in clays followed by loss of mg ca as they are exchanged for na k in clays between the ca hco 3 type recharge water and the exchangeable cations in the clay layers which were initially enriched in na part of this process was reproduced in a chromatographic experiment in which na type water with high 87 sr 86 sr was obtained from mg type water with low 87 sr 86 sr by passing it through marine clay packed in a column the flux of recharge water into the confined aquifer system according to this chromatographic model is estimated to be 0 99 mm day which is compatible with the average recharge flux to unconfined groundwater in japan 1 mm day

strontium 87 strontium 86 as a tracer of mineral weathering reactions and calcium sources in an alpine subalpine watershed loch vale colorado sr isotopic ratios of atmospheric deposition surface and subsurface water and geologic materials were measured in an alpine subalpine watershed to characterize weathering reactions and identify sources of dissolved ca in stream water previous studies have noted an excess of ca in stream water above that expected from stoichiometric weathering of the dominant bedrock minerals mixing calculations based on 87 sr 86 sr indicate that on an annual basis 26 67 of ca export in streams is atmospherically derived 23 61 is from weathering of plagioclase and the remainder is from weathering of calcite present in trace amounts in the bedrock a potential source of error when applying sr isotopes in catchment studies is determination of the 87 sr 86 sr of sr released by mineral weathering which is complicated by the wide range of mineral isotopic compositions particularly in older rocks and the variable rates at which the minerals weather in this study base flow stream chemistry was used to represent the 87 sr 86 sr of sr derived from mineral weathering because it effectively integrates the potentially variable isotopic composition of sr released by weathering in the alpine environment

effect of a global plume distribution on earth normal modes we show that a global distribution of small scale heterogeneities in the lower mantle induces both frequency splitting and amplitude scatter of low angular order modes these effects can be used in order to map the global distribution of small scale structures in the mantle such as plumes two independent datasets consisting respectively of lower mantle modes interaction coefficients and of observed amplitudes of core modes can then be used to constrain the low angular degrees of the spatial distribution and the mean size of heterogeneities allowing us to constrain the mantle structure at different scales if these heterogeneities are assumed to be plumes associated with hotspot activity the mean size of plumes obtained using the two datasets is then in good agreement with that obtained from geodetical or numerical convection studies

evidence against a discontinuity at the top of d summary we investigate a recent suggestion of lay helmberger that there is a world wide discontinuity in 5 wave velocity about 250 300 km above the core mantle boundary with an increase of 2 5 3 per cent from above to below their model predicts pronounced pulse form changes of long period sh body waves in the epicentral distance range 95 120 a range which has not been studied by them similar pulse form changes are expected in p wave seismograms under the reasonable assumption of a similar increase in p velocity nine long period seismogram sections of sh and p waves from deepfocus earthquakes below fiji west brazil the sea of japan the sea of okhotsk and the banda sea are presented with practically no indication of the complications expected also the decay constants of pdiff as predicted by the new model differ strongly from observed values thus there is clear evidence against this model the pulse form peculiarities between mantle s and scs in transverse component seismograms at distances from 70 to 80 which lay helmberger interpreted as reflections from the discontinuity of their model must have a different cause

multiple volcanic episodes of flood basalts caused by thermochemical mantle plumes the hypothesis that a single mushroom like mantle plume head can generate a large igneous province within a few million years has been widely accepted the siberian traps at the permian triassic boundary and the deccan traps at the cretaceous tertiary boundary were probably erupted within one million years these large eruptions have been linked to mass extinctions but recent geochronological data reveal more than one pulse of major eruptions with diverse magma flux within several flood basalts extending over tens of million years this observation indicates that the processes leading to large igneous provinces are more complicated than the purely thermal single stage plume model suggests here we present numerical experiments to demonstrate that the entrainment of a dense eclogite derived material at the base of the mantle by thermal plumes can develop secondary instabilities due to the interaction between thermal and compositional buoyancy forces the characteristic timescales of the development of the secondary instabilities and the variation of the plume strength are compatible with the observations such a process may contribute to multiple episodes of large igneous provinces

the effects of adiabatic and viscous heatings on plumes we have assessed the influence of viscous and adiabatic heatings on the transient development of plumes by employing the time dependent convection equations in the extended boussinesq limit both temperature dependent and temperature and pressure dependent viscosities are employed for constant thermal expansion of coefficient we find the vigor of plume flows is diminished with larger magnitudes of the thermal expansivity this effects is caused by the local domination of adiabatic decompression over viscous heating inside the developing plume for both the cartesian and axisymmetric domains for deep mantle flows a thermal expansivity decreasing with depth is required for thin plume structures to exist values of the thermal expansivity contrast which can promote plume growth are in accord with estimates from recent studies in seismic equation of state copyright american geophysical union 1987

mapping the lower mantle determination of lateral heterogeneity in p velocity up to degree and order 6 the data from the international seismological centre bulletins for the years 1964 1979 are used to derive a three dimensional model of lateral variations of the p velocity in the lower mantle unlike previous studies in which such perturbations were represented by a blocklike parameterization we seek the solution in the form r k 0k l 0l m 0l k r kalm cos m kblm sin m plm cos some 500 000 travel time residuals for teleseismic distances from 5000 earthquakes are used in an iterative procedure to derive the coefficients a and b the maximum k and l used are 4 and 6 respectively in each iteration in addition to solving for the three dimensional structure we also relocate all the earthquakes perturb the average travel time curve and determine station corrections for over 1000 stations particular attention is given to the problem of weighting the individual observations in order to avoid as much as possible the bias due to the uneven distribution of sources and receivers the resulting model shows a high level of perturbations just below the 670 km discontinuity and just above the core mantle boundary where the maximum perturbations reach 1 1 5 of the average velocity even for this highly smoothed model at a depth of 2000 km the rms perturbations are some 3 to 4 times lower than at either of the two boundaries the model predicts well the large scale pattern of observed travel time residuals for various source regions except for the distinct effects of the subduction zones the most striking large scale three dimensional feature of the model is a ring of high velocities circumscribing the pacific basin within a depth range from 1000 km to the core mantle boundary if the proportionality between perturbations in the velocity and temperature is assumed the derived pattern of anomalies could be consistent with a two boundary layer model of convection in the lower mantle some caution however should be exercised in interpreting the results near the 670 km discontinuity where the resolving power of our data set is limited by the lack of adequate control of the upper mantle structure at the same time a significant global increase in the level of perturbations in the lowermost mantle is established beyond question the results of dziewonski et al 1977 on the correlation between the equivalent geoid and the observed geoid for the angular order numbers 2 and 3 is confirmed but there is no significant correlation for degrees from 4 to 6 these calculations are made for the rigid earth richards and hager this issue show that introduction of finite viscosity can change the sign of a geoid anomaly in addition recent studies of lateral variations in the shear velocity reveal the presence of large scale anomalies in the upper mantle thus while the inferences made here with respect to the origin of the gravest orders of the geopotential field are not conclusive they point the way in which results from seismology can be used to address some of the basic questions of geodynamics

temperature distribution in the crust and mantle in an attempt to understand the temperature distribution in the earth experimental constraints on the geotherm in the crust and mantle are considered the basic form of the geotherm is interpreted on the basis of two dominant mechanisms by which heat is transported in the earth 1 conduction through the rock and 2 advection by thermal flow data reveal that 1 the temperature distributions through continental lithosphere and through oceanic lithosphere more than 60 million years old are practically indistinguishable 2 crustal uplift is instrumental in modifying continental geotherms and 3 the average temperature through the archean crust and mantle was similar to that at present it is noted that current limitations in understanding the constitution of the lower mantle can lead to significant uncertainties in the thermal response time of the planetary interior

plate dynamics caribbean map corrections and hotspot push summary in 1986 the author s previous paper describing a simple mathematical model for the forces driving the plates had an rms error of 1 62 per cent in its best case the model included slab pull and its global and local reactions proportional to speed times age 3 2 viscous drag due to shear under moving plates and in the flow towards mantle sinks at midocean ridges and sources at subduction zones ridge push proportional to plate age and friction at continental collision zones strengths of the various forces were found by least squares fitting three different improvements now reduce the error to 1 14 per cent they are 1 revision of the n s american plate boundary east of the caribbean sea to run along the 15 20 fracture zone ii removal of a transform segment from the caribbean subduction zone and iii allowing for hotspot push hotspots cause upward flow in the mantle which spreads outwards under the lithosphere above and pushes two plates apart if their boundary runs nearby in a way which is calculated the results and their statistical significance are estimated by a method given by backus park garbasz 1981 modified slightly because three of the equations in the model are linearly dependent on the remainder all the physical mechanisms envisaged in this work as driving plates turn out to be significant except local reaction to slab pull the effect of which is very small anyway

present seismic evidence for a boundary layer at the base of the mantle to improve the global coverage needed in investigating the observational consequences of boundary layer models the existing data set has been extended with long period diffracted p and sh from the sro network and short period diffracted p from the norsar array it was found that on average the amplitude decay of diffracted sh is relatively small in accordance with the majority of previously published wwssn data and consistent with the observed weakness in dispersion of this phase these results in combination with the apparent absence of anomalously high dt d can be explained by a relatively thin 100 km low velocity zone at the base of the mantle long period diffracted p wave data probably lack the required resolution for detecting a relatively thin transition zone such a zone with relatively low velocity is allowed by an average of travel time and amplitude data across the core shadow boundary and appears to be required by the norsar observations of short period diffraction far into the shadow however recent results of individual short period p wave studies pertaining to geographically limited regions only including also the norsar observations are partly conflicting unless lateral variations exist on balance current thermal models appear to be consistent with but not required by the present seismic evidence

the interaction of plume heads with compositional discontinuities in the earth s mantle the effects of compositional discontinuities of density and viscosity in the earth s mantle on the ascent of mantle plume heads is studied using a boundary integral numerical technique three specific problems are considered 1 a plume head rising away from a deformable interface 2 a plume head passing through an interface and 3 a plume head approaching the surface of the earth for the case of a plume attached to a free surface the calculated time dependent plume shapes are compared with experimental results two principal modes of plume head deformation are observed plume head elongation or the formation of a cavity inside the plume head the inferred structure of mantle plumes namely a large plume head with a long tail is characteristic of plumes attached to their source region and also of buoyant material moving away from an interface and of buoyant material moving through an interface from a high to low viscosity region as a rising plume head approaches the upper mantle most of the lower mantle will quickly drain from the gap between the plume head and the upper mantle if the plume head enters the upper mantle if the plume head moves from a high to low viscosity region the plume head becomes significantly elongated and for the viscosity contrasts thought to exist in the earth could extend from the 670 km discontinuity to the surface plume heads that are extended owing to a viscosity decrease in the upper mantle have a cylindrical geometry the dynamic surface topography induced by plume heads is bell shaped when the top of the plume head is at depths greater than about 0 1 plume head radii as the plume head approaches the surface and spreads the dynamic topography becomes plateau shaped the largest stresses are produced in the early stages of plume spreading when the plume head is still nearly spherical and the surface expression of these stresses is likely to be dominated by radial extension as the plume spreads compressional stresses on the surface are produced beyond the edges of the plume consequently extensional features will be produced above the plume head and may be surrounded by a ring of compressional features

reflection properties of phase transition and compositional change models of the 670 km discontinuity seismic observations of the amplitude ratio amplitude p 670p amplitude p p suggest a reflection coefficient r 7 13 for reflections from the underside of the 670 km discontinuity this can be compared with calculated reflection coefficients to constrain the nature of the mantle transition region velocity and density profiles through the transition region were calculated for olivine pyroxene garnet and olivine garnet model mineral assemblages for models with identical upper and lower mantle compositions the computed reflection coefficients from the phase transitions pertinent to the 670 km discontinuity are less than 0 5 these phase transitions produce their maximum r if they are effectively discontinuous which gives r 2 3 except for the garnet to perovskite transformation which gives r 8 in general given realistic impedance contrasts across a phase transition the change in material properties must occur over a region less than 3 km thick for r to be of the order of 5 a discontinuous change in chemical composition at 670 km depth coupled with a change in phase can also produce a reflection coefficient of the observed magnitude r 2 3 for a first order change in phase at 670 km with different iron concentrations on each side of the discontinuity and r 4 6 for cases with a discontinuous increase in silica content based on our analysis the thermal and chemical boundary layers which would occur across such a chemical discontinuity would probably have negligible effects on the reflection coefficient thus although limited by considerable uncertainties the mineralogical and seismic data suggest a two layered model of the mantle with a discontinuous change in both phase and composition at 670 km

the dynamical structures of d and deep plumes in a non newtonian mantle the dynamical structures of the d layer and deep mantle plumes have been determined for a mantle with a power law creep rheology generalising recent newtonian analyses the lateral scales of d and plumes are determined by a balance between thermal diffusive thickening and lateral inflow the non newtonian effect of concentrating shear in regions of high stress acts to thicken the region of rapid flow in both d and plumes this effect is nearly counterbalanced by the increased lateral inflow in the non newtonian case resulting in a modest broadening of the lateral scales of the regions of rapid flow these changes are structurally unimportant and the essential physics of core cooling via convective flow in a thin d layer and narrow plumes is remarkably independent of mantle rheology

changing sources of base cations during ecosystem development hawaiian islands 87 sr 86 sr evidence from a soil chronosequence in the hawaiian islands demonstrates that the atmosphere supplies 85 of putatively rock derived sr in older sites initially bedrock is the dominant source for sr and other lithophile elements such as ca but high rates of weathering and leaching of the substrate by 20 ka lead to a shift to atmospheric sources the loss of weathering inputs coincides with other physio chemical changes in the soil and results in a steep decline of base cations in the soil pool while these patterns imply the potential for limitation of biological productivity by low base cation supply the atmosphere provides a supply of base cations in excess of nutritional needs even after nearly all rock derived base cations have been leached from the soil this raises the possibility that p limitation in terrestrial ecosystems may develop at least as much because of low rates of atmospheric deposition of p relative to ca k and other rock derived elements as because of its chemical interaction in soil

thermal perturbations caused by large impacts and consequences for mantle convection united states national aeronautics and space administration planetary geology and geophysics program

a mantle plume model for the equatorial highlands of venus the equatorial highlands of venus consist of four main structures atla beta ovda and thetis regiones each has a circular to oval shaped planform and rises 4 5 km above the mean planetary radius these highlands are associated with long wavelength geoid highs with amplitudes ranging from 35 m at ovda to 120 m at atla they also contain topographic valleys interpreted as extensional rift zones and beta is known to contain shield volcanoes these characteristics are all consistent with the equatorial highlands being formed by mantle plumes an alternative model in which ovda and thetis are interpreted as spreading centers analogous to terrestrial mid ocean ridges fails to explain most of the observed geoid anomalies and topography in these regions some smaller highlands such as bell regio eistla regio and the hathor innini ushas region may also be plume related but most coronae are unlikely to be the direct result of plume activity we have modeled plumes using a cylindrical axisymmetric finite element code and a depth dependent newtonian rheology we compare our model results with profiles of geoid and topography across atla beta ovda and thetis our best model fits are for beta and atla assuming whole mantle convection and that earth and venus have similar mantle heat flows venus must lack an earth like low viscosity zone in its upper mantle in order satisfy the observed geoid and topography for these features this conclusion is consistent with the long wavelength admittance spectrum of venus and with the observed differences in the slopes of the geoid spectra for the two planets one explanation for the different viscosity structures of the two planets could be that the mantle of venus is drier than earth s mantle

constraining soil mineral weathering 87sr 86sr for calcium apportionment studies of a deciduous forest growing on soils developed from granitoid igneous rocks abstracts we used 87 sr 86 sr as a proxy for ca to apportion the contribution of atmospheric deposition and soil mineral weathering sources to the ca pools in trees in a small forested watershed of southern quebec the effects of topography and forest stand composition were assessed by dividing the watershed into three study zones representing two elevations and differences in tree species apportionment calculations show that all tree species studied contained ca that is dominantly sourced from soil mineral weathering averaging 85 due to the presence in the soils of easily weathered ca bearing minerals such as calcite and apatite as well as the relatively deep rooting habits reaching the mineral soil of the tree species calcium pools in trees are shifted towards the atmospheric component on hilltops due to the filtering of dry aerosols of the tree canopies which are more exposed to atmospheric circulation than trees at the bottom of the slopes although some variability in soil bulk chemistry and mineralogy in the watershed obscures the full extent of this phenomenon the buildup and recycling of ca in the soil vegetation system with the forest floor acting as the major accessible ca pool for the tree roots must be considered when interpreting apportionment calculations this work supports other ca cycling models in forests suggesting that topography can influence the balance of ca captured from atmospheric sources by trees even in cases where mineral weathering is the dominant source of ca nutrition in trees

the 13 million year cenozoic pulse of the earth abstract the geomagnetic polarity reversal rate changes radically from very low to extremely high such process indicates fundamental changes in the earth s core reorganization and core mantle boundary heat flow fluctuations however we still do not know how critical such changes are to surface geology and climate processes our analysis of the geomagnetic reversal frequency oxygen isotope record and tectonic plate subduction rate which are indicators of the changes in the heat flux at the core mantle boundary climate and plate tectonic activity shows that all these changes indicate similar rhythms on million years timescale in the cenozoic era occurring with the common fundamental periodicity of 13 myr during most of the time the periodicity is disrupted only during the last 20 myr such periodic behavior suggests that large scale climate and tectonic changes at the earth s surface are closely connected with the million year timescale cyclical reorganization of the earth s interior