dynamic sedimentary environments of an arctic glacier fed river estuary adventfjorden svalbard ii meio and macrobenthic fauna abstract the paper examines the meio and macrobenthic responses to physical disturbance and sediment instabilities in a small arctic glacier fed river estuary zajiczkowski and wlodarska kowalczuk zajiczkowski m wlodarska kowalczuk m 2007 dynamic sedimentary environments of arctic glacier fed river estuary adventfjorden svalbard i flux deposition and sediment dynamics estuarine coastal and shelf science 74 1 2 285 296 distinguished three zones in adventfjorden west spitsbergen estuary the tidal flat the slope high sedimentation frequent sediment slides the central basin low sedimentation stable sediments the numbers of individuals and species of meio and macrofauna were very low on the tidal flat the total densities of meio and macrofauna were significantly lower on the slope of the glacio fluvial delta than in the central basin only the macrofauna responded to sediment instabilities on the slope by a significant decrease in total biomass nematodes inhabiting the slope sediments were larger than those in the central basin although there was no significant difference in the size of harpacticoids in the two zones the frequently disturbed resuspended and redeposited slope sediments were colonized by the opportunistic polychaete capitella capitata agg and by the high sedimentation resistant polychaetes chaetozone setosa agg and cossura longocirrata tube dwelling sedentary or suspension feeding fauna only occurred at the central basin stations the species richness and ratio of surface dwelling to burrowing deposit feeders in the macrobenthic communities decreased towards the river mouths the differences in the taxonomic composition of communities inhabiting the sediments of the slope and the central basin were less pronounced in meiofauna studied at a higher taxonomic level than in the macrofauna identified to the species level nevertheless the differences were significant for both benthic compartments anosim test p

complex anisotropy in d beneath the eastern pacific from sks skks splitting discrepancies article i nfo although observations of seismic anisotropy in the lowermost mantle are abundant the mechanism which generates anisotropy in the d layer is not well understood most observational constraints on d anisotropy come from the splitting of shear waves that propagate nearly horizontally through the lowermost mantle however anisotropy in the d layer can also give rise to discrepancies in shear wave splitting for sks and skks phases for the same event station pair as these phases sample different regions of the lowermost mantle here i report observations of strongly discrepant sks skks splitting observed at broadband stations in western mexico and california in particular strong skks splitting with fast polarization directions near 60 and delay times up to 3 s is observed for a group of raypaths that sample a region of the d layer beneath the eastern pacific ocean a comparison of skks splitting with sks splitting observed from the same events as well as with sks splitting observed at a variety of backazimuths at each station suggests that the anomalous anisotropic structure is in the lowermost mantle my preferred model for the unusual anisotropic geometry in this region is large shear deformation in d at the edge of a region where slab material impinges upon the core mantle boundary resulting in lattice preferred orientation of lower mantle minerals

deformation in the lowermost mantle beneath australia from observations and models of seismic anisotropy observations of seismic anisotropy near the core mantle boundary may yield constraints on patterns of lowermost mantle flow we examine seismic anisotropy in the lowermost mantle beneath australia bounded by the african and pacific large low shear velocity provinces we combined measurements of differential splitting of sks skks and s scs phases sampling our study region over a range of azimuths using data from ten long running seismic stations observations reveal complex and laterally heterogeneous anisotropy in the lowermost mantle we identified two sub regions for which we have robust measurements of d associated splitting for a range of ray propagation directions and applied a forward modeling strategy to understand which anisotropic scenarios are consistent with the observations we tested a variety of elastic tensors and orientations including single crystal elasticity of lowermost mantle minerals bridgmanite post perovskite and ferropericlase tensors based on texture modeling in post perovskite aggregates elasticity predicted from deformation experiments on polycrystalline mgo aggregates and tensors that approximate the shape preferred orientation of partial melt we find that post perovskite scenarios are more consistently able to reproduce the observations beneath new zealand the observations suggest a nearly horizontal 100 axis orientation with an azimuth that agrees well with the horizontal flow direction predicted by previous mantle flow models our modeling results further suggest dominant slip on the 010 plane in post perovskite aggregates provide a good fit to the data but the solution is non unique our results have implications for the mechanisms of deformation and anisotropy in the lowermost mantle and for the patterns of mantle flow

evaluating post perovskite as a cause of d anisotropy in regions of palaeosubduction seismic anisotropy in the earth s lowermost mantle d is often attributed to the alignment of mgsio3 post perovskite ppv by the movement of dislocations in response to mantle flow however ppv s plastic yield surface is not known nor do we know if this is the main deformation mechanism we make use of a heterogeneous generally anisotropic model of elasticity in d derived from a 3 d model of mantle flow which is obtained by inversion of geophysical observables unlike previous approaches completely general 3 d flow and full anisotropy are permitted yielding more information to compare with observations than has been possible before we model observations of anisotropy in d by calculating the shear wave splitting predicted in scs waves for a series of models of ppv plasticity we find that observations in regions of the lowermost mantle beneath subduction zones are best fit by a model which accommodates slip on 010 our results show that within one standard deviation slip on 010 or a mechanism giving the same style of anisotropy explains d anisotropy beneath these regions

late quaternary sediment yield from the high arctic svalbard area late quaternary sediment yields from the isfjorden drainage area 7327 km 2 a high arctic region on svalbard characterized by an alpine landscape have been reconstructed by using seismic stratigraphy supported by sediment core analysis the sediments that accumulated in the fjord during and since deglaciation can be divided into three stratigraphic units the volumes of these units were determined and converted into sediment yield rates averaged over the drainage basin during deglaciation 13 to 10 ka the sediment yield was sim 860 tons t cdot km 2 cdot yr 1 in the early holocene it decreased to 190 t cdot km 2 cdot yr 1 and then increased to 390 t cdot km 2 cdot yr 1 during the late holocene little ice age when normalized to the approximate glacierized area these rates correspond to a sediment yield of sim 800 t cdot km 2 cdot yr 1 sediment yield from non glacierized parts of the drainage is estimated to be 35 t cdot km 2 cdot yr

laboratory and seismological observations of lower mantle isotropy we have carried out seismological and mineral physics investigations to identify the extent and origin of elastic anisotropy in the lower mantle based on observations of shear wave splitting we conclude that the lower mantle is effectively isotropic this result is surprising since the lower mantle is composed of elastically anisotropic minerals silicate perovskite mgo sio 2 that have been extensively strained by geologic processes to reconcile the seismic observations we have measured texture development during deformation and high temperature recrystallization of mantle silicates we show that these experiments provide a direct explanation for the shear wave splitting measurements the lower mantle appears isotropic because silicate perovskite maintains an isotropic texture during deformation and recrystallization

lowermost mantle anisotropy and deformation along the boundary of the african llsvp shear wave splitting of sk k s phases is often used to examine upper mantle anisotropy in specific cases however splitting of these phases may reflect anisotropy in the lowermost mantle here we present sks and skks splitting measurements for 233 event station pairs at 34 seismic stations that sample d beneath africa of these 36 pairs show significantly different splitting between the two phases which likely reflects a contribution from lowermost mantle anisotropy the vast majority of discrepant pairs sample the boundary of the african large low shear velocity province llsvp which dominates the lower mantle structure beneath this region in general we observe little or no splitting of phases that have passed through the llsvp itself and significant splitting for phases that have sampled the boundary of the llsvp we infer that the d region just outside the llsvp boundary is strongly deformed while its interior remains undeformed or weakly deformed

deformation in the lowermost mantle from polycrystal plasticity to seismic anisotropy in the deep earth deformation occurs at many scales large scale convection produces subduction of slabs and upwelling of plumes in the mantle at the high temperature high pressure conditions strain is accommodated through crystal plasticity either by diffusion or the movement of dislocations slip causes crystal rotations and thus produces a characteristic pattern of crystal preferred orientation and corresponding anisotropy of physical properties at the macroscopic scale in this study we use polycrystal plasticity with experimentally derived deformation mechanisms for perovskite post perovskite and magnesiowuestite to predict texture development along streamlines in a 2d geodynamic convection model of the lowermost mantle strong preferred orientation develops during subduction and upwelling while during spreading along the core mantle boundary the orientation pattern is relatively stable from preferred crystal orientation and single crystal elastic properties bulk elastic properties can be calculated and compared with seismic observations post perovskite with predominant 001 slip and magnesiowuestite with 110 and 111 slip produce anisotropy patterns which are consistent with observed anisotropy i e fast s waves polarized parallel to the core mantle boundary and anti correlation between p and s wave anisotropies in contrast perovskite with dominant 001 slip and two post perovskite models with dominant slip on 010 and 100 produce anisotropy patterns which are inconsistent with seismic observations

the effect of temperature on the seismic anisotropy of the perovskite and post perovskite polymorphs of mgsio3 using elastic constants determined by ab initio molecular dynamics over a range of temperatures we show that the seismic anisotropy of mgsio3 perovskite is significantly temperature dependent at 90 gpa the direction of greatest shear wave splitting changes from 001 at 0 k to 010 at 3500 k in addition there is no shear wave splitting in the 100 direction at 0 k but a significant amount of splitting is exhibited at 3500 k we have also calculated the first set of high temperature elastic constants of the new post perovskite phase by ab initio molecular dynamics methods we find that in contrast to mgsio3 perovskite temperature has little effect on the acoustic anisotropy of this phase we determine ln vs ln vp for the post perovskite phase and find it to be very low about 0 9 this may be an important parameter for mapping out the post perovskite phase in the lowermost mantle

observations of changing anisotropy across the southern margin of the african llsvp we present evidence for the presence of complex anisotropy in the lowermost mantle from 3 d waveform modelling of observed core diffracted shear waves that sample the southern edge of the african large low shear velocity province llsvp the anomalously strong amplitude of the sv component for the shear core diffracted phase at large distances indicates the presence of anisotropy we measure shear wave splitting parameters to determine which part of the elastic tensor is constrained by this particular data set the modelling is performed using the spectral element method the anisotropy is strong outside the llsvp weakens or rotates close to its boundary and appears to be absent inside the llsvp the presence of the llsvp margin may cause flow in the mantle to change direction the occurrence of strong anisotropy in the region of fast seismic velocities is compatible with lattice preferred orientation in post perovskite due to accommodation of flow through dislocation creep

geochemical alteration of pyrochlore group minerals pyrochlore subgroup primary alteration of uranpyrochlore from granitic pegmatites is characterized by the substitutions adyd acayo anayf acayo and anayoi i acayo alteration occurred at 450 650 c and 2 4 kbar with fluid phase compositions characterized by relatively low ana high aeah and high ph in contrast primary alteration of pyrochlore from nepheline syenites and carbonatites follows a different tre nd represented by the substitutions anayf adydand acayo adyd in carbonatites primary alteration of pyrochlore probably took place during and after replacement of diopside forsterite calcite by tremolite dolomite t ankerite at 300 550 c and 0 2 kbar under conditions of relatively low ahf low ana low aeah low ph and elevated activities of fe and sr microscopic observations suggest that some altered pyrochlor1es are transitional between primary and secondary alteration alteration paths for these specimens scatter around the trend anayf adyd alteration probably occurred at 200 350 c in the presence of a fluid phase similar in composition to the fluid present during primary alteration but with elevated activities of ba and rees mineral reactions in the system na ca fe nb o h indicate that replacement of pyrochlore by fersmite and columbite occurred at similar conditions with fluid conpositions having relatively low ana moderate aeah and moderate to high afeh secondary alteration 150 c is charactlerizedby the substitutions anayf adyd acayo adyd and acaxo adxdtogether with moderate to extreme hydration 10 15 wt h20 or 2 3 molecules per formula unit minor variations in the amounts of mg ai k mn fe sr ba and rees are commonly observed as a result of secondary alteration major cation exchange for k sr and ba is a feature of samples from laterite horizons overlying carbonatites in most cases u th and b site cations remain relatively constant radiogenic pb is typically lost via long te rm diffusion but in some grains of uranpyrochlore 25 90 of the pb is lost as a result of alteration

the influence of hyperpycnal flows on the salinity of deep marine environments and implications for the interpretation of marine facies abstract interpretation of the continental or marine character of sediments on the basis of the paleosalinity is increasingly based on the concentration of some trace elements the paleosalinity can be affected however also in deep marine environments by discharge peaks of major sediment laden rivers these induce hyperpycnal flows that run down the basin slope the huge volume of fresh water gradually mixes with the ambient saline seawater diminishing the paleosalinity the temporary lowered paleosalinity may be preserved in the sedimentary record in the form of diverging concentrations of trace elements and trace element ratios this is exemplified for the early cretaceous lingshandao formation on lingshan island western yellow sea it was found during field work and geochemical analysis that hyperpycnal currents may not only lower the salinity of a deep marine environmental setting but may also carry along continental plant fragments and other biological remains which may obscure the marine character of the sediments it is deduced that detailed facies analysis in the field is consequently required to reveal the true character of a marine environment

pyrochlores from the lueshe carbonatite complex democratic republic of congo a geochemical record of different alteration stages abstract magmatic pyrochlores from the lueshe syenite carbonatite complex from the northeastern part of democratic republic of congo ex zaire are characterized by ta nb ratios in an increasing order from pyroxenite calcite carbonatite sovite silicate xenoliths nodules to syenite substitutions involving nb ta ti and ree have been precisely described hydrothermal alteration of lueshe pyrochlore involves the substitution of na f va vy and ca o va vy va a site vacancy and vy y site vacancy in calcite carbonatite hydrothermal alteration of pyrochlore took place during and after the precipitation of ancylite ce strontianite celestite baryte and fayalite according to a fluid composition of relatively low ph a na a ca 2 and a hf and high a sr 2 and a lree 3 the supergene alteration is characterized by complete leaching of na ca and f and partial incorporation of k ba sr and ce resulting in the formation of kali bario strontio and ceriopyrochlore respectively the na poor pyrochlore may be an intermediate variety corresponding to an alteration stage between the hydrothermal and weathered pyrochlores the ir spectroscopic study has indicated that the weathered pyrochlore is a hydrated variety containing two bands of oh vibration modes at 3413 and 1630 cm 1 during hydrothermal and supergene alterations the cations at b site remain relatively constant the variable chemical compositions of the pyrochlores from the lueshe complex represent geochemical memories of the different alteration conditions including the variation in the oxidation reduction environment

behavior of a glacier derived suspended sediment plume in a small arctic inlet the changing configuration of a glacier derived turbid surface meltwater plume was observed over a 40 hr period in a small marine inlet in spitsbergen factors controlling plume position tides winds and melt stream discharge were also monitored tidal forcing was the dominant control on plume behavior over the study period when winds were calm or light the plume spread over much of the inlet on the flood and around high tide and was restricted to the north side on the ebb and at low water winds were generally 5 kts and only influenced plume position when reaching over 12 kts coriolis effects were unimportant sediments on the inlet floor fined progressively with distance from glacier fed stream effluxes short cores showed that deposition was mainly in the form of structureless sands and silts

petrological constraints on seismic anisotropy the purpose of this paper is to investigate the correlations between anisotropic parameters for different orientations and mineralogies for realistic mineralogical and petrological models of the upper mantle such correlations make it possible to reduce the number of independent parameters required in seismic modelling of the upper mantle the variation with depth and with degree of random orientation is also investigated it is shown that the anisotropic combinations involved in an equivalent transversely isotropic medium azumithally averaged velocities with a vertical symmetry axis are strongly correlated but the combinations involved in azimuthal anisotropy are more weakly correlated comparison with available seismic data does not yet allow discrimination based on anisotropy between different petrological models it is shown that even if a proportion of random orientation is introduced it should be possible to achieve petrological discrimination from seismic data for some orientation configurations if the inverse problem is well posed i e takes account of the correlations between anisotropic parameters these correlations are incorporated in an inversion process to show that it is possible to explain the dataset used to derive the prem by alternative anisotropic models for the uppermost 220 km

hyperpycnal plume formation from riverine outflows with small sediment concentrations a series of laboratory experiments has been conducted in order to elucidate the sediment induced mixing processes accompanying riverine outflows specifically the discharge of a warm fresh particle laden fluid over a relatively dense cool brine in a parameter regime analogous to recently acquired field measurements hypopycnal surface plumes were subject to a convective instability driven by some combination of heat diffusing out of the warm fresh sediment laden plume and particle settling within it convection was robust in the presence or absence of intense turbulence at sediment concentrations as low as 1 kg m 3 and took the form of millimetre scale sediment laden fingers descending from the base of the surface plume a consequence of the convective instability of the original hypopycnal plume is the generation of a hyperpycnal bottom riding flow the experiments presented here indicate that natural river outflows may thus generate hyperpycnal plumes when sediment concentrations are 40 times less than those required to render the outflow heavy relative to the oceanic ambient the resulting hyperpycnal plumes may play an important role in transporting substantial quantities of sediment to the continental slope and beyond

suspended sediment fluxes in a high arctic glacierised catchment implications for fluvial sediment storage suspended sediment fluxes from the 68 km2 finsterwalderbreen catchment in svalbard were monitored intensively during the 1999 and 2000 melt seasons at proximal and distal ends of a 4 2 km2 proglacial area which has been deglacierised during the twentieth century measured distal sediment fluxes correspond to total catchment denudation rates of 2700 710 t km 2 year 1 1999 and 1800 350 t km 2 year 1 2000 hourly net sediment flux time series distal flux minus proximal flux isolating change within the proglacial area itself reveal that the proglacial area serves as both a source and a sink of sediment during different periods of the melt season and that the majority of sediment evacuation from the area occurs during discrete episodes of enhanced meltwater discharge the mean net flux from the proglacial area itself was 690 230 t km 2 year 1 1999 and 3800 1700 t km 2 year 1 2000 therefore in 1999 there was a net increase in sediment storage in the proglacial area aggradation and in 2000 there was a net decrease denudation the pattern of sediment storage change appears to be driven by the runoff regime with net storage occurring during a year of relatively episodic sediment transport in which relative supply exhaustion occurs and net release in a year of more sustained sediment transport when relative supply exhaustion is absent many more years monitoring would be required for any trend to emerge from the large interannual variability in sediment yield

seismic evidence links the subducted mongol okhotsk slab to deformation in d near the northeastern margin of the perm anomaly abstract numerical simulations have indicated that the large low shear velocity provinces llsvps dynamically interact with subducted slabs in d and slabs in turn play an important role in influencing the shape and location of the llsvps in this study we find evidence for the existence of the d discontinuity near the northeastern margin of the perm anomaly a smaller llsvp beneath eurasia by analyzing the scd the lower mantle triplication phases generated from two deep events occurring in the northwestern pacific subduction zone and recorded at stations in europe and turkey the d discontinuity in the north is characterized with a 2 velocity increase occurring at a height of 300 km above the core mantle boundary cmb whereas the discontinuity in the south is characterized with a 3 velocity increase occurring at a height of 260 km above the cmb the d discontinuity is most likely attributed to a phase transition from perovskite to post perovskite in conjunction with the presence of relic slab materials likely related to the subducted mongol okhotsk slab our observations along with previous seismic anisotropic detections provide a clue to dynamically link the subducted slab to deformation taking place near the edges of the llsvp

anisotropy in the deep earth abstract seismic anisotropy has been found in many regions of the earth s interior its presence in the earth s crust has been known since the 19th century and is due in part to the alignment of anisotropic crystals in rocks and in part to patterns in the distribution of fractures and pores in the upper mantle seismic anisotropy was discovered 50 years ago and can be attributed for the most part to the alignment of intrinsically anisotropic olivine crystals during large scale deformation associated with convection there is some indication for anisotropy in the transition zone particularly in the vicinity of subducted slabs here we focus on the deep earth the lower mantle and core where anisotropy is not yet mapped in detail nor is there consensus on its origin most of the lower mantle appears largely isotropic except in the last 200 300 km in the d region where evidence for seismic anisotropy has been accumulating since the late 1980s mostly from shear wave splitting measurements recently a picture has been emerging where strong anisotropy is associated with high shear velocities at the edges of the large low shear velocity provinces llsvps in the central pacific and under africa these observations are consistent with being due to the presence of highly anisotropic mgsio 3 post perovskite crystals aligned during the deformation of slabs impinging on the core mantle boundary and upwelling flow within the llsvps we also discuss mineral physics aspects such as ultrahigh pressure deformation experiments first principles calculations to obtain information about elastic properties and derivation of dislocation activity based on bonding characteristics polycrystal plasticity simulations can predict anisotropy but models are still highly idealized and neglect the complex microstructure of polyphase aggregates with strong and weak components a promising direction for future progress in understanding the origin of seismic anisotropy in the deep mantle and its relation to global mantle circulation is to link macroscopic information from seismology and microscopic information mineral physics through geodynamics modeling anisotropy in the inner core was proposed 30 years ago to explain faster p wave propagation along the direction of the earth s axis of rotation as well as anomalous splitting of core sensitive free oscillations there is still uncertainty about the origin of this anisotropy in particular it is difficult to explain its strength based on known elastic properties of iron as it would require almost perfect alignment of iron crystals indeed the strongly anomalous p travel times observed on paths from the south sandwich islands to alaska may or may not be due to inner core anisotropy and will need to be explained before consensus can be reached on the strength of anisotropy in the inner core and its origin

in situ observations of floc settling velocities in glacier bay alaska abstract in situ floc settling velocities and diameters of particles ranging in size from 0 63 to 5 05 mm equivalent circular diameter were measured under a buoyant discharge plume by deploying a bottom tripod mounted floc camera assembly fca in tarr inlet glacier bay alaska these observations were used to estimate floc effective densities three results emerge from this work first fits of settling velocity and effective density to diameter are consistent with expressions published for other environments suggesting that common controls on floc size and settling velocity operate across diverse marine environments second the raw data show considerable scatter with upper and lower 95 prediction intervals on settling velocity and excess density differing by about a factor of 7 analysis of sources of error suggests that the variability is caused by differences in component grain composition among flocs and turbulent stirring within the stilling box third bin averaged effective densities and settling velocities are highly correlated with diameter thus while it is not possible based on diameter to predict accurately the settling velocity of a single floc it is possible to estimate the mean settling velocity of a population of like sized flocs

complex seismic anisotropy at the border of a very low velocity province at the base of the earth s mantle 1 we constrain the anisotropy associated with a very low velocity province vlvp at the base of the earth s mantle using the sks and skks waves sampling the region our selected high quality data sets consist of 415 sks and 111 skks waveforms for 127 deep earthquakes recorded at distances between 90 and 150 by the seismic stations in three temporary broadband passcal seismic arrays the kaapvaal seismic array 1997 1999 the tanzania seismic array 1994 1995 and the ethiopia kenya seismic array 1999 2001 as well as the permanent stations in the global seismographic network these seismic data provide good sampling coverage for some portion of the vlvp and its surrounding areas our results show when the sks or skks phases sample the regions away from the border of the vlvp inside or outside the vlvp the apparent splitting parameters inferred from the sks phases are consistent with those inferred from the skks phases and their variations strongly correlate with seismic stations but not with the exit points at the core mantle boundary of these seismic phases however when the sks or skks phases sample near the border of the vlvp the apparent splitting parameters inferred from the sks phases and skks phases are different and their variations no longer correlate with seismic stations these features indicate that part of the shear wave splitting for the seismic data sampling the border of the vlvp has to originate from deep mantle most likely near the border of the vlvp we assume that the anisotropy in the shallow mantle beneath seismic stations has a horizontal hexagonal symmetry axis and infer the splitting parameters associated with the shallow anisotropy beneath the seismic stations using the sks and skks waveforms for the seismic data sampling the regions away from the border of the vlvp we then obtain the splitting parameters associated with the lowermost mantle anisotropy using the sks and skks waveforms corrected for the inferred shallow anisotropy beneath seismic stations assuming that the medium in the lowermost mantle also has a horizontal hexagonal symmetry axis our results reveal a complex anisotropy pattern near the border of the vlvp such a complex anisotropy pattern may be explained by lattice preferred orientation of anisotropic mantle aggregates aligned by a complex mantle flow near the vlvp margins the complex flow pattern near the vlvp margins may indicate strong interactions between the vlvp a compositional anomaly and the surrounding normal mantle and may provide an explanation to the concentration of some hot spots geographically near the borders of the vlvps in the lowermost mantle

a three dimensional radially anisotropic model of shear velocity in the whole mantle summary we present a 3 d radially anisotropic s velocity model of the whole mantle saw642an obtained using a large three component surface and body waveform data set and an iterative inversion for structure and source parameters based on non linear asymptotic coupling theory nact the model is parametrized in level 4 spherical splines which have a spacing of 8 the model shows a link between mantle flow and anisotropy in a variety of depth ranges in the uppermost mantle we confirm observations of regions with vsh vsv starting at 80 km under oceanic regions and 200 km under stable continental lithosphere suggesting horizontal flow beneath the lithosphere we also observe a vsv vsh signature at 150 300 km depth beneath major ridge systems with amplitude correlated with spreading rate for fast spreading segments in the transition zone 400 700 km depth regions of subducted slab material are associated with vsv vsh while the ridge signal decreases whilethemid mantlehasloweramplitudeanisotropy vsv in the lowermost 300 km which appears to be a robust conclusion despite an error in our previous paper which has been corrected here the 3 d deviations from this signature are associated with the large scale low velocity superplumes underthecentralpacificandafrica suggestingthatvsh vsv isgeneratedinthepredominant horizontal flow of a mechanical boundary layer with a change in signature related to transition to upwelling at the superplumes

the limits of ray theory when measuring shear wave splitting in the lowermost mantle with scs waves observations of shear wave splitting provide unambiguous evidence of the presence of anisotropy in the earth s lowermost mantle a region known as d much recent work has attempted to use these observations to place constraints on strain above the core mantle boundary cmb as this may help map flow throughout the mantle previously this interpretation has relied on the assumption that waves can be modelled as infinite frequency rays or that the earth is radially symmetric due to computational constraints it has not been possible to test these approximations until now we use fully three dimensional generally anisotropic simulations of scs waves at the frequencies of the observations to show that ray methods are sometimes inadequate to interpret the signals seen we test simple uniform models and for a d layer as thin as 50 km significant splitting may be produced and we find that recovered fast orientations usually reflect the imposed fast orientation above the cmb ray theory in these cases provides useful results though there are occasional notable differences between forward methods isotropic models do not generate apparent splitting we also test more complex models including ones based on our current understanding of mineral plasticity and elasticity in d the results show that variations of anisotropy over even several hundred kilometres cause the ray theoretical and finite frequency calculations to differ greatly importantly models with extreme mineral alignment in d yield splitting times not dissimilar to observations t 3 s suggesting that anisotropy in the lowermost mantle is probably much stronger than previously thought potentially 10 shear wave anisotropy or more we show that if the base of the mantle is as complicated as we believe future studies of lowermost mantle anisotropy will have to incorporate finite frequency effects to fully interpret observations of shear wave splitting

bebedourite from its type area salitre i complex a key petrogenetic series in the late cretaceous alto paranaiba kamafugite carbonatite phoscorite association central brazil abstract bebedourite is a cumulate rock composed of variable but roughly equant amounts of diopside apatite magnetite phlogopite and a ca ti phase mostly perovskite more rarely titanite and or ti garnet other minerals may be modally important such as olivine and k feldspar in the least and most evolved members of the bebedourite series respectively the magmatic evolution in bebedourites is accompanied by a progressive increase in sio2 activity which results in the transformation of perovskite into titanite and titanite into ti garnet although the sio2 increase may in some cases result from crustal contamination it seems to be a localized effect and cannot account for the evolution of the whole bebedourite series crystal fractionation is supported by the chemical variation of key mineral phases such as pyroxene and phlogopite the salitre complex is an ultrapotassic carbonatite and phoscorite bearing plutonic complex belonging to the late cretaceous alto paranaiba igneous province apip and consisting of three main bodies salitre i ii and iii the complex is composed mainly of bebedourite with lesser amounts of carbonatite and phoscorite in its central north portion a particular type of bebedourite where the main ca ti phase is ti garnet dominates the southern part of salitre i and also occurs as dikes crosscutting older bebedourites suggesting that ti garnet bebedourites form an independent intrusion sr and nd isotopic data indicate that the parental magmas to the bebedourites in the salitre complex originated in a metasomatized sub continental lithospheric mantle similar to that involved in the origin of the rest of the apip

rainstorm induced event sedimentation at the tidewater front of a temperate glacier runoff from a late summer storm drained rapidly to a subglacial stream of mcbride glacier southeast alaska the stream transported large volumes of sediment that discharged from the glacier s tidewater front directly into fjord water at 40 m depth measurements of salinity temperature and suspended sediment concentration indicate that the sediment was transported by interflows within brackish fjord water sedimentation rates were exceptionally high up to five times normal laminated fine sand accumulated in proximal sediment traps and silty mud accumulated in distal traps the low frequency of large storms late in the melt season indicates that the sedimentary products would be rare but significant marker horizons in temperate glaciomarine sequences

micromorphological changes as an indicator of the transition from glacial to glaciofluvial quartz grains evidence from svalbard abstract the micromorphology of quartz grains in a sedimentary environment is determined by the transport mechanism and the nature of weathering both these aspects change during the transport history of grains thus important questions include how are quartz grains affected by possible changes in the transport medium and how quickly do the different micromorphological features develop or disappear the main goal of this study was to characterize the changes in the micromorphological features of quartz grains during the transition from a glacial to a glaciofluvial environment and to identify a set of diagnostic microtextures that can be used to distinguish between glacial and glaciofluvial quartz grains the samples came from the moraines of the bertilbreen and horbyebreen glaciers svalbard and from the sediments of glacier fed rivers in the forelands of these glaciers a total of 30 different micromorphological features was observed on 800 different quartz grains from 13 samples of glaciofluvial sediment and 3 samples of glacial sediment it was found that the frequency of rounded grains v shaped pits meandering ridges and cemented microblocks on glaciofluvial grains increased significantly with increasing length of fluvial transport whereas the frequency of angular grains straight steps straight and curved grooves adhering particles pitting and oriented etch pits decreased significantly different types of micromorphological features of quartz grains change with fluvial transport at different rates adhering particles after the first kilometer of fluvial transport straight steps and meandering ridges after the second kilometer of fluvial transport and v shape pits angular shape and straight grooves after the third kilometer of fluvial transport are reliable mechanical micromorphological features for distinguishing between glacial and glaciofluvial quartz grains

geomorphic tectonic control of sediment discharge to the ocean the importance of small mountainous rivers analysis of data from 280 rivers discharging to the ocean indicates that sediment loads yields are a log linear function of basin area and maximum elevation of the river basin other factors controlling sediment discharge e g climate runoff appear to have secondary importance a notable exception is the influence of human activity climate and geology on the rivers draining southern asia and oceania sediment fluxes from small mountainous rivers many of which discharge directly onto active margins e g western south and north america and most high standing oceanic islands have been greatly underestimated in previous global sediment budgets perhaps by as much as a factor of three in contrast sediment fluxes to the ocean from large rivers nearly all of which discharge onto passive margins or marginal seas have been overestimated as some of the sediment load is subaerially sequestered in subsiding deltas before the proliferation of dam construction in the latter half of this century rivers

in situ measurement of texture development rate in cairo3 post perovskite the rate of crystallographic preferred orientation cpo development during deformation of post perovskite is crucial in interpreting seismic anisotropy in the lowermost mantle but the stability field of mgsio3 post perovskite prevents high strain deformation experiments being performed on it therefore to constrain the rate of cpo development in post perovskite we deformed cairo3 a low pressure analogue of mgsio3 post perovskite in simple shear at 3 2 gpa and 400 c to a shear strain of 0 81 from x ray diffraction patterns acquired during deformation we invert for cpo as a function of strain by comparing the cpo that develops with visco plastic self consistent vpsc models we constrain the critical resolved shear stresses crss of the non primary slip systems in cairo3 to be of order 6 times stronger than the primary 100 010 slip system this value is significantly less than has been assumed by previous studies and if applicable to mgsio3 implies that seismic anisotropy in the d layer develops slower than has previously been assumed

complex polarization analysis of particle motion knowledge of particle motion polarization aids in identifying phases on three component seismograms the scheme of montalbetti and kanasewich 1970 is extended to analytic three component seismograms where the imaginary part of the signal is the hilbert transform of the real part this scheme has only one free parameter the length of the time window over which the polarization parameters are estimated so it can be applied in a routine way to three component data the azimuth and dip of the direction of maximum polarization and the degree of elliptical polarization as a function of time for the seismograms are obtained polarization analysis of strong motion data from the 1971 san fernando earthquake aids in the discrimination between wave types which is important for the understanding of the complicated earthquake induced shaking observed in basins most arrivals are incident on the receivers in the direction of the back azimuth to the epicenter which suggests that despite the complicated motions two dimensional finite difference methods are sufficient to understand the effect on seismic waves of the los angeles and san fernando basins vidale and helmberger 1986b

elastic anisotropy of d predicted from global models of mantle flow in order to test the hypothesis that seismic anisotropy in the lowermost mantle is caused by the development of a post perovskite lattice preferred orientation and that anisotropy can thus be used as a probe of the dynamics of the mantle s lower boundary layer an integrated model of texture generation in d is developed this is used to predict the elastic anisotropy of the lowermost mantle as probed by global anisotropic tomographic inversions the model combines the current 3d mantle flow field with simulations of the deformation of post perovskite polycrystalline aggregates different descriptions of single crystal plasticity can lead to model results which are anti correlated to each other in models where post perovskite deformation is accommodated by dislocations moving on 010 or 100 patterns of anisotropy are approximately correlated with the results of tomographic inversions on the other hand in models where dislocations move on 001 patterns of anisotropy are nearly anti correlated with tomographic inversions if all the seismic anisotropy in d extracted from global anisotropic inversions is due to the presence of a lattice preferred orientation in post perovskite in the lowermost mantle and if the results of the tomographic inversions are not strongly biased by the sampling geometries these results suggest that in contrast to ideas based on the 1d anisotropic signal deformation of post perovskite in the lowermost mantle may be accommodated by dislocations moving on 010 or 100 alternatively a significant portion of the anisotropic signal may be caused by mechanisms other than the alignment of post perovskite crystals

fine grained sediment flocculation below the hubbard glacier meltwater plume disenchantment bay alaska a study in disenchantment bay alaska demonstrates that fine sediment beneath a meltwater plume is flocculated and that floc sizes and fraction of mass bound within flocs exhibit a pronounced increase with depth rather than down fjord this spatial pattern of variability likely is due to the longer depositional timescale of flocs compared to their horizontal advection timescale within the meltwater plume the flux of mass within flocs also increases with depth these observations have implications for sedimentation models as sedimentation rates estimated from surface waters underestimate those at depth and could result in the inaccurate prediction of the position of suspension depocenters the results also may explain the behavior of fine sediment in more complex environments where floc properties are difficult to observe

primary and secondary niobium mineral deposits associated with carbonatites abstract this work reviews the character and origin of primary and supergene economic deposits of niobium associated with carbonatites the brazilian supergene deposits account for about 92 of the total worldwide production of nb with the primary st honore carbonatite and other sources accounting for only for 7 and 1 respectively the emphasis of the review is upon the styles of nb mineralization and the geological factors which lead to economic concentrations of nb bearing minerals primary economic deposits of nb are associated principally with carbonatites found in diverse types of plutonic alkaline rock complexes primary magmas are principally those of the melilitite nephelinite and aillikite clans although many primary niobium deposits are associated with carbonatites ijolites and syenites in the same alkaline complexes can also contain significant nb mineralization in the form of niobian titanite and diverse nb zr silicates marianoite wohlerite these potential sources of nb have not as yet been explored or exploited primary nb deposits can be regarded as large tonnage low grade typically

columbitization of fluorcalciopyrochlore by hydrothermalism at the saint honore alkaline complex quebec canada new insights on halite in carbonatites abstract niobium nb in carbonatite is mainly hosted in fluorcalciopyrochlore and columbite fe information related to nb petrogenesis is useful for understanding the processes related to nb mineralization and carbonatite evolution the saint honore quebec alkaline complex offers a rare opportunity for studying these processes as the complex is not affected by post emplacement deformation metamorphism nor weathering columbite fe is shown to be an alteration product of fluorcalciopyrochlore columbitization columbitization is characterized by the leaching of na and f from the a and y sites of the pyrochlore crystal structure as alteration increases fe and mn are slowly introduced while ca is simultaneously leached leached ca and f then crystallize as inclusions of calcite and fluorite within the columbite fe a site cations and vacancies in the crystal structure of fresh and altered pyrochlores demonstrate that pyrochlore alteration is hydrothermal in origin moreover halite is a ubiquitous mineral in the saint honore alkaline complex petrographic evidence shows that halite forms in weakly altered pyrochlores suggesting halite has a secondary origin as alteration increases halite is expelled by the hydrothermal fluid and is carried farther into the complex filling factures throughout the carbonatite the hydrothermal hypothesis is strengthened by significant enrichments in cl and hrees in columbite fe chlorine is most likely introduced by a hydrothermal fluid that increases the solubility of rees

lowermost mantle anisotropy beneath the north pacific from differential s scs splitting summary seismic anisotropy is an important tool for studying the nature origin and dynamics of the lowermost mantle d we introduce differential s scs splitting as a tool for removing the effect of near source and near receiver anisotropy to estimate splitting accrued in the d region this is applicable to events recorded at epicentral distances between 60 and 85 near source anisotropy has often been ignored in previous studies of lowermost mantle anisotropy we apply differential s scs splitting to records from canadian national seismic network stations of western pacific earthquakes these sample the lowermost mantle beneath the north pacific the residual splitting in scs which we attribute to d shows lag times between 1 0 and 3 9 s given the near horizontal ray path of scs in d we interpret the recovered fast directions as the orientation of the fast shear wave in the plane defined by the vertical and transverse directions and observe a clearly non vti transverse isotropy with a vertical axis of symmetry style of anisotropy the largest population of results shows an approximately southeasterly dipping symmetry axis which we speculate might be explained by descending palaeoslab material being swept horizontally across the core mantle boundary towards an upwelling region beneath the central pacific non vti symmetry and the many possible contributions to d anisotropy from lower mantle minerals melt and subducted materials suggest that our understanding of the lowermost mantle could be greatly improved by trying to resolve a more general style of anisotropy

gypsum a joint tomographic model of mantle density and seismic wave speeds 1 gypsum is a 3 d model of mantle shear wave s speeds compressional wave p speeds and density the model is developed through simultaneous inversion of seismic body wave travel times p and s and geodynamic observations while using realistic mineral physics parameters linking wave speeds and density geodynamic observations include the global free air gravity field divergence of the tectonic plates dynamic topography of the free surface and the flow induced excess ellipticity of the core mantle boundary gypsum is built with the philosophy that heterogeneity that most closely resembles thermal variations is the simplest possible solution models of the density field from earth s free oscillations have provided great insight into the density configuration of the mantle but are limited to very long wavelength solutions alternatively scaling higher resolution seismic images to obtain density anomalies generates density fields that do not satisfy geodynamic observations the current study provides a 3 d density model for the mantle that directly satisfies geodynamic and seismic observations through a joint seismic geodynamic inversion process notable density field observations include high density piles at the base of superplume structures supporting the general results of past normal mode studies however we find that these features are more localized and have lower amplitude than past studies would suggest when we consider both fast and slow seismic anomalies in gypsum we find that p and s wave speeds are strongly correlated throughout the mantle however we find a low correlation of fast s wave zones in the deep mantle 1500 km depth with the corresponding p wave anomalies suggesting a systematic divergence from simplified thermal effects in ancient subducted slab anomalies the cratonic lithosphere and d regions are shown to have strong compositional signatures however we argue that temperature variations are the primary cause of p wave speed s wave speed and density anomalies throughout most of the mantle

seismic anisotropy in the lower mantle a comparison of waveform splitting of sks and skks 1 we have carried out a global investigation on seismic anisotropy in the lower mantle by comparing the waveform splitting of sks and skks found at the same seismogram the two shear waves have very similar ray paths in the upper mantle but different ones in the lower mantle we collected a total of 104 sks skks waveform data recorded at 76 stations the sks skks data are first matched with a single anisotropic model 2 parameters the fast polarization direction and delay time t and two independent anisotropic models 4 parameters we then applied an f test to examine whether the 4 parameter models are better than the 2 parameter ones based on error improvement we found that the data from most of the stations can be explained by the simple 2 parameter models while this observation provides compelling evidence that the vast part of the lower mantle below 1000 km including the d region is transversely isotropic it is still arguable that the uppermost lower mantle and the transition may partly contribute the sks skks splittings we also found that the 4 parameter models provide a better fitting to the sks and skks splitting at 8 stations suggesting the existence of transverse anisotropy or anomalous dipping structures in some part of the lower mantle

seismic anisotropy in the lowermost mantle near the perm anomaly the lower mantle is dominated by two large structures with anomalously low shear wave velocities known as large low shear velocity provinces llsvps several studies have documented evidence for strong seismic anisotropy at the base of the mantle near the edges of the african llsvp recent work has identified a smaller structure with similar low shear wave velocities beneath eurasia dubbed the perm anomaly here we probe lowermost mantle anisotropy near the perm anomaly using the differential splitting of sks and skks phases measured at stations in europe we find evidence for lowermost mantle anisotropy in the vicinity of the perm anomaly with geographic trends hinting at lateral variations in anisotropy across the boundaries of the perm anomaly as well as across a previously unsampled portion of the african llsvp border our observations suggest that deformation is concentrated at the boundaries of both the perm anomaly and the african llsvp

a new inference of mantle viscosity based upon joint inversion of convection and glacial isostatic adjustment data we present new profiles of mantle viscosity derived on the basis of non linear occam style joint inversions of an extensive set of data associated with mantle convection and glacial isostatic adjustment gia the convection related observables include satellite derived free air gravity harmonics the geodetically inferred excess ellipticity of the cmb and tectonic plate motions the gia constraints involve two classes of observables previously shown to be relatively insensitive to errors in the late pleistocene ice history the so called fennoscandian relaxation spectrum frs and a set of site specific decay times determined from the postglacial sea level history in hudson bay and sweden the inverted viscosity profiles show a significant three orders of magnitude increase from the upper mantle mean value of f4 10 20 pa s to a high viscosity 10 23 pa s peak at

the catalao i niobium deposit central brazil resources geology and pyrochlore chemistry abstract the catalao i alkaline carbonatite phoscorite complex contains both fresh rock and residual weathering related niobium mineralization the fresh rock niobium deposit consists of two plug shaped orebodies named mine ii and east area respectively emplaced in carbonatite and phlogopitite together these orebodies contain 29 mt at 1 22 wt nb2o5 measured and indicated in closer detail the orebodies consist of dike swarms of pyrochlore bearing olivine free phoscorite series rocks nelsonite that can be either apatite rich p2 unit or magnetite rich p3 unit dolomite carbonatite dc is intimately related with nelsonite natropyrochlore and calciopyrochlore are the most abundant niobium phases in the fresh rock deposit pyrochlore supergroup chemistry shows a compositional trend from ca na dominant pyrochlores toward ba enriched kenopyrochlore in fresh rock and the dominance of ba rich kenopyrochlore in the residual deposit carbonates associated with ba sr enriched pyrochlore show higher 18osmow than expected for carbonates crystallizing from mantle derived magmas we interpret both the 18osmow and pyrochlore chemistry variations from the original composition as evidence of interaction with low temperature fluids which albeit not responsible for the mineralization modified its magmatic isotopic features the origin of the catalao i niobium deposit is related to carbonatite magmatism but the process that generated such niobium rich rocks is still undetermined and might be related to crystal accumulation and or emplacement of a phosphate iron oxide magma

mineralogical effects on the detectability of the postperovskite boundary the discovery of a phase transition in mg silicate perovskite pv to postperovskite ppv at lowermost mantle pressure temperature p t conditions may provide an explanation for the discontinuous increase in shear wave velocity found in some regions at a depth range of 200 to 400 km above the core mantle boundary hereafter the d discontinuity however recent studies on binary and ternary systems showed that reasonable contents of fe2 and al for pyrolite increase the thickness width of the mixed phase region of the pv ppv boundary 400 600 km to much larger than the d discontinuity 70 km these results challenge the assignment of the d discontinuity to the pv ppv boundary in pyrolite homogenized mantle composition furthermore the mineralogy and composition of rocks that can host a detectable pv ppv boundary are still unknown here we report in situ measurements of the depths and thicknesses of the pv ppv transition in multiphase systems san carlos olivine pyrolitic and midocean ridge basaltic compositions at the p t conditions of the lowermost mantle searching for candidate rocks with a sharp pv ppv discontinuity whereas the pyrolitic mantle may not have a seismologically detectable pv ppv transition due to the effect of al harzburgitic compositions have detectable transitions due to low al content in contrast al rich basaltic compositions may have a detectable pv ppv boundary due to their distinct mineralogy therefore the observation of the d discontinuity may be related to the pv ppv transition in the differentiated oceanic lithosphere materials transported to the lowermost mantle by subducting slabs

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

geophysical analysis of catalao i alkaline carbonatite complex in goias brazil the catalao i alkaline carbonatite complex which is located in central brazil is one of the main producers of niobium and phosphates in the world it has been intensely studied geologically and geochemically for its economic potential this work presents a geophysical analysis over this complex identifying its behaviour in the subsurface and in portions that have not been explored yet different geophysical methods and techniques were applied to achieve the most reliable results possible at the surface through radiometric geological and topographic data and at depth by geological magnetic and gravimetric data the analysis was successfully completed with inversions of gravity and magnetic data that resulted in quite similar models both in volume and shape their density and magnetic susceptibility contrasts were consistent with the expected dunite pyroxenite lithology from the original mafic intrusion and indicated by exclusion the volume of the carbonatite body which along with the known contents of phosphates and niobium allowed an indirect estimate of the reserves and resources of the complex

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

full wave effects on shear wave splitting in this chapter we develop an approach to the inversion of 3d anisotropy structure using the sensitivity frechet kernels calculated by an efficient and flexible full wave algorithm based on the normal mode theory

on the likelihood of post perovskite near the core mantle boundary a statistical interpretation of seismic observations abstract recent experimental studies indicate that perovskite the dominant lower mantle mineral undergoes a phase change to post perovskite at high pressures however it has been unclear whether this transition occurs within the earth s mantle due to uncertainties in both the thermochemical state of the lowermost mantle and the pressure temperature conditions of the phase boundary in this study we compare the relative fit to global seismic data of mantle models which do and do not contain post perovskite following a statistical approach our data comprise more than 10 000 pdiff and sdiff travel times global in coverage from which we extract the global distributions of dln vs and dln vp near the core mantle boundary cmb these distributions are sensitive to the underlying lateral variations in mineralogy and temperature even after seismic uncertainties are taken into account and are ideally suited for investigating the likelihood of the presence of post perovskite a post perovskite bearing cmb region provides a significantly closer fit to the seismic data than a post perovskite free cmb region on both a global and regional scale these results complement previous local seismic reflection studies which have shown a consistency between seismic observations and the physical properties of post perovskite inside the deep earth

the anisotropic signal of topotaxy during phase transitions in d abstract while observations and modelling of seismic anisotropy in the lowermost mantle offers the possibility of imaging mantle flow close to the core mantle boundary current models do not explain all observations here we seek to explain a long wavelength pattern of shear wave anisotropy observed in anisotropic tomography where vertically polarised shear waves travel faster than horizontally polarised shear waves in the central pacific and under africa but this pattern is reversed elsewhere in particular we test an explanation derived from experiments on analogues which suggest that texture may be inherited during phase transitions between bridgmanite perovskite structured mgsio3 and post perovskite and that such texture inheritance may yield the long wavelength pattern of anisotropy we find that models that include this effect correlate better with tomographic models than those that assume deformation due to a single phase in the lowermost mantle supporting the idea that texture inheritance is an important factor in understanding lowermost mantle anisotropy it is possible that anisotropy could be used to map the post perovskite stability field in the lowermost mantle and thus place constraints on the temperature structure above the core mantle boundary

joint seismic geodynamic and mineral physical constraints on three dimensional mantle heterogeneity implications for the relative importance of thermal versus compositional heterogeneity summary the joint interpretation of seismic and geodynamic data requires mineral physical parameters linking seismic velocity to density perturbations in the earth s mantle the most common approach is to link velocity and density through relative scaling or conversion factors r s dln dlnv s however the range of possible r s values remains large even when only considering thermal effects we directly test the validity of several proposed depthdependent conversion profiles developed from mineral physics studies for thermally varying properties of mantle materials the tests are conducted by simultaneously inverting shear wave traveltime data and a diverse suite of convection related constraints interpreted with viscous flow response functions of the mantle these geodynamic constraints are represented by surface spherical harmonic basis functions up to harmonic degree 16 and they consist of the global free air gravity field tectonic plate divergences dynamic surface topography and the excess ellipticity of the core mantle boundary cmb the tests yield an optimum 1 d thermal r s profile that is generally compatible with all considered data with the exception of the dynamic surface topography that is most sensitive to the shallow upper mantle this result is not surprising given that cratonic roots are known to be compositionally distinct from the surrounding ambient mantle moreover it is expected that the temperature dependence of the thermal r s in the upper mantle is significant due to the temperature dependence of seismic attenuation or q therefore a simple 1 d density velocity relationship is insufficient to address this problem we obtained independent estimates of the first order correction factors to the selected r s profile within the cratonic roots and in the ambient thermal upper mantle these correction factors defined as r s lnv s are highly negative within the cratons signifying considerable compositional buoyancy this result confirms that the negative buoyancy associated with the low temperatures in the cratons is significantly counteracted by the composition induced positive buoyancy resulting in near neutral buoyancy of the cratonic roots within the ambient upper mantle the correction factors are found to be positive which is consistent with the expected behaviour of the r s relationship in thermally varying upper mantle material we obtain a significantly greater reconciliation of the global gravity anomalies and dynamic surface topography when applying these laterally varying corrections compared to a simple 1 d r s relationship inversion for a fully 3 d r s relationship reveals secondary effects including additional compositional variation within the cratonic roots and the deep mantle superplume structures we estimate the relative magnitude of the thermal and compositional non thermal contributions to mantle density anomalies and conclude that thermal effects dominate shear wave and density heterogeneity throughout the non cratonic mantle we also demonstrate the potential pitfalls of scaling a purely seismically derived model to obtain density rather than performing a true joint inversion to obtain velocity and density simultaneously

transport of salt and suspended sediments in a curving channel of a coastal plain estuary satilla river ga abstract this study describes the transport of salt and suspended sediment in a curving reach of a shallow mesotidal coastal plain estuary circulation data revealed a subtidal upstream bottom flow during neap tide indicating the presence of a gravitational circulation mode throughout the channel during spring tide landward bottom flow weakened considerably at the upstream end of the channel and changed to seaward in the middle and downstream areas of the reach suggesting the importance of tidal pumping salt flux near bottom was landward at both ends of the channel during neap tide at spring however the salt flux diverged along the bottom of the thalweg suggesting that tidal pumping caused a transfer of salt vertically and laterally into the intertidal zone thus landward flux of salt is maintained even in the presence of subtidal seaward flow along the bottom at the downstream end of the channel landward bottom stress is greater than seaward stress preferentially transporting suspended sediments upstream compared with salt however the weight of the suspended sediments causes less upward transfer of sediments into the intertidal zone flood flow carried more suspended sediments landward at the upstream end compared with the downstream end we speculate that secondary flow in the curving channel picks up increasing amounts of suspended sediments along the sides during flood and adds them to the axial flow in the thalweg since the landward flow along the bottom of the thalweg weakens and even reverses during spring tide there appears to be a complex re circulation system for sediments re suspended in curving channels that complicates the picture of a net transport of sediments landward

lowermost mantle anisotropy beneath the northwestern pacific evidence from pcs scs sks and skks phases 1 in this study we utilize data from broadband seismic stations of the japanese f net network to investigate anisotropic structure in the lowermost mantle beneath the northwestern pacific the comparison of shear wave splitting from phases that have similar paths in the upper mantle but different paths in the lowermost mantle such as pcs scs or sks skks can yield constraints on anisotropy in the d region we measured splitting for sks skks pcs and scs phases at f net stations and compared the measured splitting parameters to previously published estimates of upper mantle anisotropy beneath the region we observed many examples of discrepant sks skks splitting and splitting of scs pcs sks and skks phases that does not agree well with the known upper mantle anisotropy beneath individual stations the most likely explanation for these discrepancies is a contribution to splitting from anisotropy in the lowermost mantle in particular for sks skks phases that sample the lowermost mantle just to the south and east of the kamchatka peninsula we observed generally n s fast directions with delay times between 0 5 and 1 5 s these data suggest the presence of a fairly large coherent region of deformation in the lowermost mantle beneath the northwestern pacific our preferred model for these observations is that solid state flow at the base of the mantle induces a lattice preferred orientation of lowermost mantle minerals generating a seismically anisotropic fabric

modeling lower mantle anisotropy development in a subducting slab a model is presented that simulates anisotropy development in a subducting slab from the upper lower mantle boundary 661 km to the core mantle boundary 2891 km two phases are considered orthorhombic mgsio3 perovskite and cubic magnesiowuestite mg fe o single crystal elastic properties at mantle conditions are obtained from existing density functional theory calculations and quasiharmonic approximation it is assumed that deformation is accommodated by slip a polycrystal plasticity model predicts strong texture development for perovskite and weaker texture for magnesiowuestite when averaging single crystal elastic properties with the orientation distribution this results for both phases in weak p wave anisotropy and shear wave splitting in the upper part of the lower mantle but pronounced anisotropy near the core mantle boundary up to 4 for vp and 7 for vs the anisotropy pattern is complex and asymmetric and local heterogeneity is expected these predictions are consistent with seismic observations

do foraminifera mirror diversity and distribution patterns of macrobenthic fauna in an arctic glacial fjord abstract this paper compares the distribution and diversity patterns of benthic foraminifera all taxa and only calcareous forms and macrozoobenthos in an arctic glacial fjord the samples were collected at 22 stations located in hornsund west spitsbergen the activity of tidal glaciers located in the inner basins causes steep environmental gradients of turbidity organic matter supply and sediment stability clear differences in density diversity and species composition were documented for both foraminifera and macrofauna between the groups of stations located in three zones along a gradient of increasing tidal glacier impact the assemblages of both benthic compartments in the glacial bay were dominated by small opportunistic infaunal species i e cassidulina reinforme for foraminifera and cirratulid polychaetes for macrofauna which occurred throughout the fjord but showed an increase in density and or dominance when approaching the glaciers a parallel decreasing pattern from the central basin to the inner glacial bay was noted with regard to species richness and faunal density of both groups macrofaunal evenness decreased close to glaciers but this was not observed in the foraminiferal assemblages the distribution patterns of calcareous foraminifera were correlated p 0 001 both with those of all foraminifera agglutinated and calcareous taxa and with macrofauna with the spearman s rank correlation between the respective bray curtis similarity matrices ranging from 0 94 to 0 99 total foraminifera and from 0 37 to 0 67 macrofauna respectively species richness expressed as the number of species per sample and diversity expressed by the shannon wienner index of foraminifera and macrofauna were also significantly correlated pearson correlation r 0 79 r2 0 62 p

seismic anisotropy in the lowermost mantle beneath north america from sks skks splitting intensity discrepancies abstract we examined sks skks splitting intensity discrepancies for phases that sample the lowermost mantle beneath north america which has previously been shown to exhibit seismic anisotropy using other analysis techniques we examined data from 25 long running seismic stations along with 244 stations of the temporary usarray transportable array located in the eastern southeastern and western u s we identified 279 high quality sks skks wave pairs that yielded well constrained splitting intensity measurements for both phases of the 279 pairs a relatively small number 15 exhibited discrepancies in splitting intensity of 0 4 s or greater suggesting a contribution to the splitting of one or both phases from anisotropy in the lowermost mantle because only a small minority of sk k s phases examined in this study show evidence of being affected by lowermost mantle anisotropy the traditional interpretation that splitting of these phases primarily reflects anisotropy in the upper mantle directly beneath the stations is appropriate the discrepant pairs exhibited a striking geographic trend sampling the lowermost mantle beneath the southern u s and northern mexico while other regions were dominated by non discrepant pairs we carried out ray theoretical modeling of simple anisotropy scenarios that have previously been suggested for the lowermost mantle beneath north america invoking the alignment of post perovskite due to flow induced by the impingement of the remnant farallon slab on the core mantle boundary we found that our measurements are generally consistent with this model and with the idea of slab driven flow but relatively small scale lateral variations in the strength and or geometry of lowermost mantle anisotropy beneath north america are also likely present

stable isotope composition of minerals in the belaya zima plutonic complex russia implications for the sources of the parental magma and metasomatizing fluids abstract the belaya zima alkaline carbonatite complex in the east sayan mountains russia is a multiphase concentric intrusion which comprises diverse alkaline silicate rocks and carbonatites melteigites are the earliest products of crystallization and they are followed by ijolites urtites nepheline syenites and finally calcite calcite dolomite and ankerite carbonatites in this paper we present new geochronological data ar ar method chemical and stable isotope h c and o compositions of the main rock forming minerals in carbonatites and the silicate rocks of the complex the ar ar dating of phlogopite from ankerite carbonatites is consistent with the age of syenite emplacement and implies that the silicate rocks and carbonatites are likely to be comagmatic the evolutionary trends of pyroxene fluorapatite amphibole and phlogopite are consistent with fractional crystallization from a single parental magma primary nb mineralization is represented by pyrochlore whereas columbite fe is a replacement product of pyrochlore at the post magmatic hydrothermal stage at that stage interaction of calcite carbonatites with hydrothermal fluids resulted in the formation of hydrothermal paragenesis comprising dolomite ankerite monazite ce ancylite ce minerals of burbankite group and ca ree fluorcarbonates the hydrothermal processes were also responsible for cation leaching from pyrochlore the replacements of phlogopite by tetraferriphlogopite and early ca rich pyroxene by aegirine the stable isotope data suggest that the rocks crystallized from a 18o depleted magma shifts toward higher 18o values relative to the primary compositions are commonly observed in minerals from carbonatites which is attributed to hydrothermal processes

seafloor morphology and sedimentary processes knight inlet british columbia seafloor morphology and sediment distribution in knight inlet are discussed as they relate to turbidity currents and associated gravity resedimentation phenomena the study is based on acoustic imagery high resolution seismic profiling echosounding sediment sampling and seabed monitoring seafloor morphology shows that while the upper part of knight inlet resembles other british columbia fjords it differs in that a great many channels emanate from fjord head deltas to coalesce ultimately into a few and finally one channel farther down inlet this is in contrast to the adjacent fjord buteinlet where only one channel emerges opposite each of the two fjord head rivers joining a short distance downslope to form a single incised channel in both fjords sand transporting turbidity currents are responsible for creating these extensive channel systems in knight inlet these channels are up to 40 m deep and up to 300 m wide continuing 41 km down fjord the upper fjord can be divided into four morphological zones which reflect not only the seabed character but also the flow characteristics of turbidity currents using a variety of theoretical techniques based on channel morphology coarsest grain sizes and bedform characteristics turbidity current dynamics were modelled for the seabed morphological zones turbidity current densities are estimated to range from about 1 024 g cm 3 in distal areas to a maximum of 1 048 g cm 3 in the proximal region of greatest erosion and highest velocities average flow velocities are as high as 7 00 m s 1 diminishing to less than 0 50 m s 1 at the terminus of the channel based on estimates of velocity and turbidity current density sediment fluxes were computed for various channel segments changes in flux rates clearly delineated areas of erosion and deposition and were well correlated with the morphological character of the channel and nearby seafloor estimates of turbidity current velocity based on bedform characteristics tend to be lower than those calculated from coarsest grain sizes and channel morphology preserved bedforms may reflect later waning phases of turbidity current flow whereas channel wall heights and coarsest grain size reflect maximum velocities a close relationship was found between turbidity current events as monitored by turbidity event detectors and river discharge peaks on the klinaklini river at the head of the inlet fluvial suspended matter concentrations associated with such floods are not believed to be sufficient to produce turbidity currents directly rather it is postulated that river mouth bars which accumulate during periods of low river flow are destroyed by floods and the coarse sediments along with flood related bedload are swept onto the steep delta front where they accumulate as temporary unstable sediment masses failing occasionally or continue directly downslope as debris flows turbidity currents

synthetic seismic anisotropy models within a slab impinging on the core mantle boundary the lowermost few hundreds of kilometres of the earth s mantle are elastically anisotropic seismic velocities vary with direction of propagation and polarization observations of strong seismic anisotropy correlate with regions where subducted slab material is expected in this study we evaluate the hypothesis that crystal preferred orientation cpo in a slab as it impinges on the core mantle boundary is the cause of the observed anisotropy next we determine if fast polarization directions seen by shear waves can be mapped to directions of geodynamic flow this approach is similar to our previous study performed for a 2 d geodynamic model in this study we employ a 3 d geodynamic model with temperature dependent viscosity and kinematic velocity boundary conditions defined at the surface of the earth to create a broad downwelling slab tracers track the deformation that we assume to be accommodated by dislocation creep we evaluate the models for the presence of perovskite or post perovskite and for different main slip systems along which dislocation creep may occur in post perovskite 100 010 and 001 resulting in four different mineralogical models of cpo combining the crystal pole orientations with single crystal elastic constants results in seismically distinguishable models of seismic anisotropy the models are evaluated against published seismic observations by analysing different anisotropic components the radial anisotropy the splitting for sub vertical phases i e azimuthal anisotropy and the splitting for subhorizontal phases the patterns in radial anisotropy confirm our earlier results in 2 d observations of radial anisotropy and splitting in subhorizontal phases are mostly consistent with our models of post perovskite with 010 slip and 001 slip our model of 001 slip predicts stronger splitting than for 010 slip for horizontally propagating phases in all directions the strongest seismic anisotropy in this model occurs where the slab impinges on the core mantle boundary the azimuthal anisotropy pattern for 001 slip shows fast axis directions at the edges of the slab sub parallel to flow directions suggesting horizontal flows may be mapped out in the lowermost mantle using seismic observations

migrating cretaceous eocene magmatismin the serra do mar alkaline province se brazil melts from the deflected trindade mantle plume department of geological sciences university of durham south road durham dh1 3le uk department of earth sciences university of cambridge downing street cambridge cb2 3eq uk department of physics the university newcastle upon tyne ne1 7ru uk department of geology mcmaster university 1280 main street west hamilton ont canada l8s 4m1 departmento de geoquimica e recursos minerais instituto de geociencias universidade de brasilia

holocene glacimarine sedimentation inner scoresby sund east greenland the influence of fast flowing ice sheet outlet glaciers abstract holocene glacimarine sedimentation associated with fast flowing outlet glaciers draining the greenland ice sheet is investigated using sedimentary and acoustic data from inner scoresby sund east greenland sedimentation in inner scoresby sund is dominated by three processes which are influenced by differences in proximity to fast flowing outlet glaciers extent of glacier ice cover and fjord bathymetry 1 sediment gravity flow principally in the form of turbidity currents and debris flows 2 suspension sedimentation from turbid meltwater plumes and 3 iceberg rafting these processes result in texturally and sedimentologically heterogeneous lithofacies proportionally fine grained muds laminated stratified and massive facies dominate cores recovered from inner scoresby sund accounting for 80 of the total whereas diamict facies account for only 15 abundant fine grained muds demonstrate that meltwater flux and sedimentation is significant in this high arctic glacimarine environment in settings proximal to fast flowing outlet glaciers with increasing distance from these glacier termini muds are replaced progressively by iceberg rafted coarse grained sediment the dominance of this iceberg rafted sediment in outer scoresby sund reflects both its more distal location from fast flowing glacier termini and the high calving flux associated with these ice masses laminated muds deposited by turbidity currents and suspension settling from overflow plumes in inner scoresby sund are similar to lithofacies produced in temperate and subpolar glacimarine systems this implies a similarity in sedimentation processes and resulting facies across a wide spectrum of climatically glaciologically fast flowing and non fast flowing ice masses and oceanographically variable glacimarine settings recognition of laminated fine grained facies in the geological record therefore does not necessarily indicate a temperate palaeo glacial setting however the predominance of iceberg rafted diamict facies in ice distal sedimentary records suggests the former presence of relatively cold environmental conditions in which iceberg sedimentation played a dominant role

fe ti p oxide melts generated through magma mixing in the antauta subvolcanic center peru implications for the origin of nelsonite and iron oxide dominated hydrothermal deposits commingling and mixing of k rich basaltic absarokitic and partially crystallized strongly peraluminous s type monzogranitic rhyodacitic magmas have been documented in the 23 8 ma antauta hypabyssal complex of the picotani group puno southeastern peru magma mixing generated intermediate andesitic rocks hosting small volumes of sio2 poor 8 4 wt fe oxide rich melt with tio2 30 wt and p2o5 23 wt contents corresponding to those of the genetically problematic nelsonite ore type microscopic spheres of this composition are embedded in rhyolitic glass surrounding both extensively melted sieve textured plagioclase xenocrysts derived from the rhyodacitic magma and cognate orthopyroxene phenocrysts exhibiting replacive fe rich mantles the andesites also contain up to 15 modal percent of strongly resorbed granite derived quartz xenocrysts with glass orthopyroxene clinopyroxene coronas intense quasipervasive silicification of the fractionating mafic magma is inferred to have displaced the hybridized melt composition into the stable liquid immiscibility region of the na2o k2o mgo al2o3 feo tio2 mno cao p2o5 sio2 h2o system some fe ti p rich bodies have 30 to ca 55 wt percent sio2 and exhibit broadly linear trends of major oxides versus sio2 but the more sio2 deficient spheres exhibit extreme compositional scatter implying the existence of complex immiscibility fields within the parental protonelsonitic melt domain in contrast the predominant apparently conjugate silicate glass 70 78 wt sio2 is relatively consistent in composition and equivalent to a syenogranite and or rhyolite the extreme local variability in the composition of the oxide rich melt bodies may directly reflect their formation in a magma mixing environment in which temperature varied over at least 200 to 300 c such a compositional range also apparent in large scale nelsonite occurrences indicates that strong fractionation of mafic melts under conditions precluding ferroan spinel crystallization may not be a prerequisite for oxide silicate immiscibility and hence nelsonite formation specular hematite is widely disseminated in the glassy andesites commonly clustered around resorbed quartz xenocrysts and microscopic bodies of illite montmorillonite chlorite occur in contact with unaltered glass in unveined andesites implying endogenous sources of respectively iron and hydrothermal fluid moreover the upper paleozoic clastic sedimentary envelope of the antauta center at pucacancha hosts hydrothermal breccias and veins rich in hematite barite quartz chalcedony and epidote with lesser anhydrite and traces of u th ree rich allanite chalcopyrite and molybdenian scheelite this unambiguously hydrothermal mineralization is analogous to that of the iron oxide copper gold clan and we propose that the development of some deposits of this type may have been triggered by the formation and subsequent vesiculation of immiscible fe rich oxide melt during the mixing of mafic and felsic magmas

phlogopite and tetra ferriphlogopite from brazilian carbonatite complexes petrogenetic constraints and implications for mineral chemistry systematics abstract the results of a mineral chemistry study of phlogopite and tetra ferriphlogopite in carbonatites and associated alkaline silicate rocks from the brazilian carbonatite complexes of jacupiranga tapira and catalao are presented a wide textural variety of mica is found ranging from primary magmatic crystals to late stage metasomatic phases primary micas from the carbonatites and from the associated plutonic silicate rocks follow distinct evolution paths with magma differentiation in all three complexes micas from the silicate rocks evolve from phlogopite towards annite although in jacupiranga they are more al rich among the micas crystallising from carbonatite liquids those from jacupiranga are typically al and mg rich while in tapira and catalao they are extremely al poor metasomatic micas bridge the gap between primary micas from silicate rocks and from carbonatites the complete phlogopite tetra ferriphlogopite series is reported from the catalao and tapira complexes this study shows that micas from carbonatite complexes may span a wide compositional range largely overlapping the fields of micas from several types of alkaline ultrapotassic rocks especially regarding ti and al contents the use of phlogopite composition and evolution to discriminate between different types of alkaline rocks should be undertaken with caution

dynamic sedimentary environments of an arctic glacier fed river estuary adventfjorden svalbard i flux deposition and sediment dynamics abstract the spatial patterns of the transport settling and deposition of sediments were studied in a small arctic glacier fed river estuary adventfjorden west spitsbergen svalbard salinity and temperature suspended solids concentration and particle fluxes in the water column were measured at seven stations situated on the tidal flat formed at the river mouth the delta slope and along the fjord axis down to the fjord mouth turbidity currents were measured in situ using a current meter combined with a turbidity meter the sediments collected with a niemisto gravity corer were x rayed and analyzed for granulometric composition the results of the major sampling campaign undertaken in july 2002 were supplemented with winter hydrological data from january 1996 since the river is frozen in winter no fresh water or fluvial sediment supply is observed in the fjord water column a hypopycnal plume of brackish water 1 5 m thick extends in summer as far as 0 8 km from the river mouth the highest concentration 826 mg l 1 and vertical flux over 1000 g m 2 day 1 of suspended solids were noted at the edge of the tidal flat and over the upper slope of the delta both concentrations and the solid particle flux decreased as distance from the river mouth increased local peaks of turbidity in the intermediate and deep water layers in the central fjord indicated the presence of hyperpycnal plumes tidal flat sediments are rhythmically laminated by the tidally controlled resuspension redeposition cycles and occasionally eroded by catastrophic events such as intense storms or winter ice cover scouring the steep inclination of the bottom of the slope 15 19 promotes the gravity driven processes of sediment transport debris flows frequent resuspension and redeposition events can be traced on x radiographs and in the granulometric composition of the sediment cores collected on the slope turbidity currents are observed throughout the fjord although their intensity and frequency of occurrence change as distance from the river mouth increases the near bottom hyperpycnal flows transport the finest sediment over the slope and into the low energy environment of the central basin of adventfjorden the current study shows that the patterns of sediment storage and sedimentary dynamics in a glacier fed river estuary are driven by gravity flows and turbidity currents rather than by the patterns of the vertical sedimentation of suspensions in the water column

seismostratigraphy and thermal structure of earth s core mantle boundary region we used three dimensional inverse scattering of core reflected shear waves for large scale high resolution exploration of earth9s deep interior d and detected multiple piecewise continuous interfaces in the lowermost layer d beneath central and north america with thermodynamic properties of phase transitions in mantle silicates we interpret the images and estimate in situ temperatures a widespread wave speed increase at 150 to 300 kilometers above the coremantle boundary is consistent with a transition from perovskite to postperovskite internal d stratification may be due to multiple phase boundary crossings and a deep wave speed reduction may mark the base of a postperovskite lens about 2300 kilometers wide and 250 kilometers thick the core mantle boundary temperature is estimated at 3950 200 kelvin beneath central america a site of deep subduction the d is relatively cold t 700 100 kelvin accounting for a factor of two uncertainty in thermal conductivity core heat flux is 80 to 160 milliwatts per square meter mw m 2 into the coldest d region and 35 to 70 mw m 2 away from it combined with estimates from the central pacific this suggests a global average of 50 to 100 mw m 2 and a total heat loss of 7 5 to 15 terawatts

lowermost mantle flow at the eastern edge of the african large low shear velocity province abstract observations of seismic anisotropy in the lowermost mantle are plentiful but their interpretation in terms of mantle flow remains challenging here we interrogate the anisotropic structure of the lowermost mantle beneath the afar region just outside the edge of the african large low shear velocity province using a combination of shear wave splitting techniques applied to phases propagating at five distinct raypath orientations we then model the resulting data set by testing various candidate mechanisms for anisotropy the observations are best fit by a model that invokes the lattice preferred orientation lpo of post perovskite with the 100 crystallographic axis oriented either nearly vertically or highly obliquely to the horizontal plane plausible corresponding mantle flow scenarios involve a significant vertical flow component which suggests that the african large low shear velocity province edge may deflect ambient mantle flow upwards or may be associated with a sheet like upwelling

seismic imaging the d region beneath the central atlantic abstract the lowermost mantle beneath the central atlantic is bounded by the western edge of african large low shear wave province llsvp and a high velocity region beneath the eastern americas which is attributed to the accumulated subducted slab material at the core mantle boundary cmb data recorded at broadband seismic arrays in western europe and morocco allow us to investigate the detailed structure beneath the central atlantic which provides an important constraint on how remnant slab material and llsvp interact and reshape the d layer here we exploit lower mantle triplicated s waveform data from deep earthquakes beneath south america our modelling results show that the d discontinuity is constantly observed from north to south beneath the central atlantic but at varied depths and with varied shear velocities in the lowermost mantle beneath east of caribbean our results indicate a sharp 2 1 shear velocity increase at 340 km above the cmb representing a possible bridgmanite dominant normal mantle d layer whereas the models of northern and southern portions of central atlantic indicate a gradual velocity increase of 4 2 across 200 km starting from 360 km above the cmb downwards we also find a distinct low velocity zone on top of the velocity jump which can be interpreted as an upwelling produced by the dynamic response of ancient slab material reaching the cmb

efficacy of the post perovskite phase as an explanation for lowermost mantle seismic properties constraining the chemical rheological and electromagnetic properties of the lowermost mantle d is important to understand the formation and dynamics of the earth s mantle and core to explain the origin of the variety of characteristics of this layer observed with seismology a number of theories have been proposed including core mantle interaction the presence of remnants of subducted material and that d is the site of a mineral phase transformation this final possibility has been rejuvenated by recent evidence for a phase change in mgsio3 perovskite thought to be the most prevalent phase in the lower mantle at near core mantle boundary temperature and pressure conditions here we explore the efficacy of this post perovskite phase to explain the seismic properties of the lowermost mantle through coupled ab initio and seismic modelling of perovskite and post perovskite polymorphs of mgsio3 performed at lowermost mantle temperatures and pressures we show that a post perovskite model can explain the topography and location of the d discontinuity apparent differences in compressional and shear wave models and the observation of a deeper weaker discontinuity furthermore our calculations show that the regional variations in lower mantle shear wave anisotropy are consistent with the proposed phase change in mgsio3 perovskite

mgsio3 postperovskite at d conditions the postperovskite transition in mgsio3 at conditions similar to those expected at the d discontinuity of earth s lower mantle offers a paradigm for interpreting the properties of this region despite consistent experimental and theoretical predictions of this phase transformation the complexity of the d region raises questions about its geophysical significance here we report the thermoelastic properties of cmcm postperovskite at appropriate conditions and evidences of its presence in the lowermost mantle these are i the jumps in shear and longitudinal velocities similar to those observed in certain places of the d discontinuity and ii the anticorrelation between shear and bulk velocity anomalies as detected within the d region in addition the increase in shear modulus across the phase transition provides a possible explanation for the reported discrepancy between the calculated shear modulus of postperovskite free aggregates and the seismological counterpart in the lowermost mantle

glacimarine sedimentation in kangerdluk disko fjord west greenland in response to a surging glacier abstract beginning in 1995 a large outlet glacier of the sermersauq ice cap on disko island surged 10 5 km downvalley to within 10 km of the head of the fjord kuannersuit sulluat reaching its maximum extent in summer 1999 before beginning to retreat sediment discharge to the fjord increased from 13 10 3 t day 1 in 1997 to 38 10 3 t day 1 in 1999 ctd results sediment traps and cores from the 2000 melt season document the impact of the surge on the glacimarine environment of the fjord within 4 km of the inflow sedimentation rates increased by 30 times over those before the surge reaching an estimated maximum value of 29 cm a 1 up to 4 2 mm day 1 between 24 july and 9 september 2000 fine grained deposits from suspension in the water column displayed diurnal laminations in response to the interaction of tidal cycles with the sediment plume these are not found in the sediments deposited before surging thin beds of sandy turbidites from turbidity currents originating from slope failures on the delta front occurred at about 20 day intervals during the melt season each of these effects was limited to within several kilometres of the point of inflow but provide a unique signal significantly different from those generated by normal hydroclimatically induced events

sub slab seismic anisotropy and mantle flow beneath the caribbean and scotia subduction zones effects of slab morphology and kinematics subduction systems are vitally important to plate tectonics and mantle convection but questions remain about many aspects of subduction dynamics particularly the nature of sub slab mantle flow observations of seismic anisotropy can shed light on the pattern of mantle flow in subduction systems but major uncertainties remain regarding the interpretation of sub slab anisotropy here we present measurements of shear wave splitting due to anisotropy in the sub slab mantle beneath the caribbean and scotia subduction zones these subduction systems are morphologically similar with high arc curvature and short arc length but there are differences between them in terms of their kinematic and tectonic settings we apply the source side shear wave splitting technique to direct teleseismic s phases originating from slab earthquakes we restrict our analysis to seismic stations at which we have examined the receiver side splitting in detail to ensure accurate corrections for anisotropy in the upper mantle beneath the station we observe a well defined pattern of trench parallel fast directions f i n the northern half of the caribbean subduction zone with a transition to dominantly trenchperpendicular f at the southern end there is more scatter in the measurements for scotia but we observe generally trench parallel f in the northern portion of the subduction system with a mix of trench parallel perpendicular and oblique fast directions to the south our preferred interpretation of these splitting patterns is that they reflect 3 d return flow of the sub slab mantle due to trench rollback in both systems we infer that sub slab flow is being driven from south to north beneath scotia this is likely driven by differential migration of the scotia trench along strike beneath the caribbean we hypothesize that mantle flow around the southern edge of the slab is inhibited by the presence of the south american continental keel enabling trench perpendicular stretching in the subslab mantle and forcing mantle flow to escape to the north the similarities and differences we observe between the two systems yield insight into the relative contributions of slab morphology and plate kinematics in controlling mantle flow beneath subducting slabs

cyclic sedimentation produced by fluctuations in meltwater discharge tides and marine productivity in an alaskan fjord glacimarine sediment deposited in the fjord adjacent to muir glacier in south eastern alaska consists of rhythmically laminated muds stratified sandy mud sand and gravelly mud facies cyclicity is recorded by gravelly mud facies deposited during winter by ice rafting black mud laminae formed by spring plankton blooms and variations in tidal rhythmite thickness and texture produced by the interaction of meltwater discharges and tidal currents in the macrotidal fjord regular cyclicity in laminae thickness is tested statistically by fourier transform and can be attributed to a lunar tidal cycle control in the five cores collected up to 6 km from the sediment source cores close to the source can have additional laminae as a result of discharge fluctuations and distal cores may lack full cycles because of variability in the plume path and attenuation with distance cyclic variations in sediment texture are recorded in magnetic susceptibility ms profiles of the cores high ms values are produced by turbidite sand beds or by stratified sandy mud deposited by overflow plumes during peak summer meltwater discharge low values reflect muddy intervals deposited during periods of low meltwater discharge such as during autumn and winter sediment accumulation rates measured by 210pb dating range from 82 cm year 1 2 km from the sediment source at the head of the fjord to 16 cm year 1 6 km away these rates are within the same range as average sediment accumulation rates determined from cyclic seasonal markers within the cores these data show that with careful documentation annual cycles of glacimarine sediment accumulation can be detected within marine cores cores collected from the distal portion of the basin were deposited during the transition of muir glacier from a tidewater terminus ending in deep water to a terrestrial glacier with an ice contact delta deposited in front of the terminus this transition is recorded by a coarsening upward sedimentary sequence formed by turbidite sands originating from the prograding delta above fine grained laminated basin fill deposited by turbid overflow plumes

phoscorites of the salitre i complex origin and petrogenetic implications abstract the salitre i complex is a kidney shaped alkaline carbonatite phoscorite complex part of the late cretaceous alto paranaiba igneous province central brazil this complex is a key example where the phoscorite carbonatite association was preserved from metasomatism by late stage fluids and thus provides an opportunity to address the genesis of phoscorites salitre i is composed of two main coalescing intrusions a a northern one dominantly containing perovskite bebedourites b1 with swarms of ring dykes of carbonatites and phoscorites and b a southern one containing melanite bebedourites b2 salitre i phoscorites can be subdivided into p1 and p2 based on modal abundance mineral texture chemistry and mode of emplacement p1 phoscorites contain essential olivine phlogopite and apatite with accessory magnetite and traces of perovskite whereas p2 phoscorites are composed of the same essential phases but also contain carbonate rich pockets accessory pyrochlore and rare phlogopite carbonate c o isotopes and whole rock sr nd show that salitre i phoscorites crystallized from mantle derived parental magmas similar to other apip carbonatite complexes however chemical and textural discrepancies between p1 and p2 suggest derivation from different magma sources and through distinct processes for instance p1 al and ti rich phlogopite accessory perovskite and general trace element geochemical behaviour can be associated with the evolution of b1 perovskite bebedourites i e genesis through fractional crystallization from a bebedourite magma p2 phoscorites on the other hand have their evolution linked to a magmatic phase that underwent melt immiscibility as suggested by trace element fractionation additionally p2 contains pyrochlore which is generally lacking in bebedourites therefore whereas p1 phoscorites might have derived from a bebedourite magma p2 phoscorites were generated from a carbonated magma enriched in phosphate and iron oxides

the key role of mica during igneous concentration of tantalum igneous rocks with high ta concentrations share a number of similarities such as high ta nb low ti lree and zr concentrations and granitic compositions these features can be traced through fractionated granitic series formation of ta rich melts begins with anatexis in the presence of residual biotite followed by magmatic crystallization of biotite and muscovite crystallization of biotite and muscovite increases ta nb and reduces the ti content of the melt titanium bearing oxides such as rutile and titanite are enriched in ta and have the potential to deplete ta at early stages of fractionation however mica crystallization suppresses their saturation and allows ta to increase in the melt saturation with respect to ta and nb minerals occurs at the latest stages of magmatic crystallization and columbite can originate from recrystallization of mica we propose a model for prediction of intrusion fertility for ta

laminated sediments in glacimarine environments diagnostic criteria for their interpretation abstract fine grained laminated deposits are often reported from contemporary and ancient glacimarine sedimentary sequences laminated glacimarine sediments form by a variety of processes including suspension settling from turbid overflow plumes turbidity current deposition and contour current activity subglacial deformation of pre existing sediments may also produce laminated deposits in the form of glacitectonite and deformation till the development of diagnostic criteria for genetic discrimination of laminated glacimarine sediments is important both for their correct interpretation in sedimentary sequences and also for the accurate reconstruction of former glacier extent and geometry as laminated sediments may form in subglacial ice proximal and ice distal environments this paper reviews the processes by which laminated glacimarine sediments form and their resulting sedimentology the aim is to provide a synthesis of diagnostic sedimentological criteria for laminated glacimarine deposits that will assist in the interpretation of such sediments in the geological record laminated sediments are genetically differentiated on the basis of sedimentary structures bedding contacts stratigraphic relationships and macrofaunal content bioturbation these attributes also facilitate discrimination between glacimarine and glacilacustrine rhythmites the paper concludes by discussing the glaciological significance of laminated glacimarine sediments in terms of glacier hydrology reconstructions of former ice dynamics and basal thermal regime