deformation induced crystallographic preferred orientation of hcp iron an experimental study using a deformation dia apparatus abstract shear and uniaxial deformation experiments on hexagonal close packed iron hcp fe was conducted using a deformation dia apparatus at a pressure of 13 17 gpa and a temperature of 723 k to determine its deformation induced crystallographic preferred orientation cpo development of the cpo in the deforming sample is determined in situ based on two dimensional x ray diffraction using monochromatic synchrotron x rays in the shear deformation geometry the 0001 and 11 2 0 axes gradually align to be sub parallel to the shear plane normal and shear direction respectively from the initial random texture in the uniaxial compression and tensile geometry the 0001 and 11 2 0 axes respectively gradually align along the direction of the uniaxial deformation axis these results suggest that basal slip 0001 11 2 0 is the dominant slip system in hcp fe under the studied deformation conditions the p wave anisotropy for a shear deformed sample was calculated using elastic constants at the inner core condition by recent ab initio calculations strength of the calculated anisotropy was comparable to or higher than axisymmetric anisotropy in earth s inner core

strength and water weakening of mantle minerals olivine wadsleyite and ringwoodite rheological properties of olivine and its high pressure polymorphs both dry and hydrous have been studied by monitoring x ray diffraction peak broadening as a function of pressure temperature and time the measurements were carried out up to a pressure of 10 gpa and a temperature of 600 c for olivine and wadsleyite and a pressure of 20 gpa and a temperature of 1000 c for ringwoodite the observations indicate that olivine is much weaker than the other two minerals for this range of conditions and furthermore water weakens olivine dramatically but only slightly weakens wadsleyite and ringwoodite when the temperature increases from 25 c to 400 c the yield strength in the olivine drops by 39 without water and 62 with water however there is hardly any change in strength for wet or dry wadsleyite and ringwoodite

upper and mid mantle anisotropy beneath the tonga slab measurements of source side splitting in s waves fromevents within the tonga slab reveal anisotropy in the upperand mid mantle beneath the slab we observed splitting forevents originating at both upper mantle and transition zonedepths anisotropic fast directions are trench parallel orsub parallel for both upper mantle and transition zoneevents delaytimes dt decreasewithdepthforuppermantleevents the source of anisotropy for the upper mantle eventsis likely in the sub slab mantle and is likely indicative oftrench parallel flow due to slab rollback the source ofanisotropy for the deeper earthquakes is more difficult toconstrain but the pattern of splitting measurements arguesfor an uppermost lower mantle anisotropic source and slabinduced deformation may be responsible for this anisotropyas well additional constraints from mineral physics studiesare necessary to interpret the mid mantle anisotropy signalin terms of geodynamical processes

slab stagnation in the shallow lower mantle linked to an increase in mantle viscosity subducting slabs can stagnate in the lower mantle high pressure laboratory experiments show that the viscosity of a dominant mantle phase increases dramatically at shallow lower mantle depths which could cause the slabs to halt their descent

genesis of soils from holocene tidal deposits at the north sea coast abstract the southern north sea coast has served as an exemplification to analyse and discuss the genesis of soils from holocene tidal deposits the accumulation wedge of holocene tidal deposits at the north sea coast is artificially embanked for the most part in the enclosed area hinterland a variety of different soils developed disparate models attempting to explain the genesis of these soils deduce genesis of hinterland soils from recent foreland conditions disregarding that geogenic preconditions have fundamentally changed by consolidating and reviewing established literature we show that differences in geogenic preconditions are the initiating key for a feasible model describing geogenic preconditions to infer pedogenic processes we develop a model comprising four different development pathways high settling velocities and regular flooding as present in the foreland cause high inputs of mineral sediments and carbonate moderate sulfur dynamics and thus the development of calcareous soils synsedimentary decalcification prevails in irregularly flooded areas due to enduring low sedimentation rates low carbonate inputs and moderate sulfur dynamics under alternating redox states as mainly proposed for the unobstructed landscape high contents of soil organic matter som facilitate intensive sulfur dynamics creating potential acid sulfate soils pass which become extreme acid upon oxidation actual acid sulfate soils aass a great gradient in depositional conditions occurring at unobstructed plain coasts enables the deposition of deflocculated fine grained sediments which promotes the formation of very compact soils with low water conductivities although this proposed model is based mainly on conditions known from the german north sea coast it is shown that shaping geogenic and pedogenic processes are applicable to other humid coastal regions around the world

two new eucrite breccias from northwest africa this work describes two newly discovered eucrite breccias three presumably paired meteorites all named northwest africa nwa 6105 and nwa 6106 for each meteorite major and minor element compositions of minerals were determined using the electron microprobe pyroxene fe mn co variations and bulk rock oxygen isotope compositions confirm their classification as eucrites variations in mineral compositions and textures are attributed to differences in clast types present i e basaltic or cumulate eucrite the pyroxene compositions support the hypothesis that samples nwa 6105 1 6105 2 and 6105 3 are paired polymict eucritic breccias whereas sample nwa 6106 is a monomict basaltic eucritic breccia two pyroxene geothermometry yields temperatures too low for igneous crystallization the variation in temperatures among samples suggests that metamorphism occurred prior to brecciation

eucritic crust remnants and the effect of in falling hydrous carbonaceous chondrites characterizing the composition of vesta s marcia region abstract the equatorial marcia quadrangle region is characterized by the large relatively young impact craters marcia and calpurnia and their surrounding dark ejecta field a hill with a dark rayed crater named aricia tholus and an unusual diffuse material surrounding the impact crater octavia the spectral analysis indicates that while this region is relatively uniform in the pyroxene band centers it instead shows large differences in pyroxene band depths and reflectance a large variation of reflectance is seen in the quadrangle bright and dark materials are present as diffuse material and as concentrated spots and outcrops moreover oh signature is pervasive in the quadrangle with a few exceptions the region especially the marcia ejecta field is characterized by spectra showing the 2 m band shifted at long wavelengths this is commonly associated with eucritic material believed to have crystallized as lava on vesta s surface or within relatively shallow level dikes and plutons thus suggesting that this region is a remnant of the old vestan basaltic crust however other characteristics of the spectra do not fully fit the eucritic composition indicating an alternative explanation for the band center distribution including the presence of carbonaceous chondritic material mixed with the native vestan pyroxene the detailed mineralogical analysis of the marcia quadrangle indicates that this quadrangle is the result of the mixture of the vestan endogenic minerals with the exogenic carbonaceous chondrites the stratigraphic units around marcia clearly show the bright uncontaminated material interlaced and mixed with the dark material that contains a strong oh signature only few small areas can be considered as representative of the old vestan original material

mineralogic mapping of the av 9 numisia quadrangle of vesta abstract in this manuscript we present the mineralogic mapping of the av 9 numisia quadrangle of vesta using the most up to date data from the nasa dawn mission this quadrangle is located in vesta s equatorial zone 22 south to 22 north 218 to 288 east in claudia coordinate system and takes its name from the impact crater numisia the main feature which dominates the quadrangle is the vestalia terra plateau a topographic high about 10 km above the surrounding areas to the south this region fades into the rheasilvia basin while to the north it is bounded by the steep scarp of postumia basin the visible and infrared mapping spectrometer vir onboard nasa dawn provided the main data source for this work at an unprecedented level of spatial and spectral resolution in particular we are using spectral parameters to synthesize characteristics of the whole spectra into a single value pyroxene related spectral parameters allow for the detection of lower crust or mantle material diogenites and upper crust material eucrites in the study area the combined analysis of albedo from the framing camera the geologic map and the spectroscopic data offer an interesting opportunity to understand better the surface features of this region of vesta and their evolution numisia cornelia fabia teia and drusilla are the main craters in the study area rich in bright and dark material outcrops pitted terrains and oh rich materials using the spectral parameters we demonstrate that the internal composition of vestalia terra is mainly diogenite rich howardite as shown by materials excavated by cornelia and fabia and the composition of the slope north of vestalia terra this agrees with the strong positive bouguer anomaly observed in the area indicating a higher density of these features in relation to the surrounding areas besides the recently published works based on gravimetric modeling and geologic interpretation the mineralogic mapping presented herein gives an additional contribution in order to depict a more complete geologic history of the numisia quadrangle of vesta

distinction between sortable silts and aggregated particles in muddy intertidal sediments of the east frisian wadden sea southern north sea abstract in muddy sediments the distinction between sortable silt and aggregated silty clay is important for the understanding of fine particle dynamics because both have different hydraulic properties the wadden sea of the southern north sea is severely depleted in fine grained sediments mainly due to high energy levels along the diked coastline as a result muddy sediments are restricted to a narrow belt along the diked mainland shore in the present study the mechanism by which this mud is deposited and how floc deposition and break up are reflected in the size distribution has been investigated for this purpose surficial sediments from four intertidal nearshore transects were monitored and repeatedly sampled in the course of two years high resolution grain size analyses were performed by an automated settling tube and a sedigraph particle analyser for the sand and mud fractions respectively the grain size frequency distributions of the fine fractions demonstrate that the wadden sea muds are composed of two subpopulations a well sorted coarse silt and an unsorted silty clay population a depletion of grain size around 8 m 7 phi demarcates the grain size boundary between the two populations suggesting that the finer mud population

sub slab anisotropy beneath the sumatra and circum pacific subduction zones from source side shear wave splitting observations understanding the dynamics of subduction is critical to our overall understanding of plate tectonics and the solid earth system observations of seismic anisotropy can yield constraints on deformation patterns in the mantle surrounding subducting slabs providing a tool for studying subduction dynamics while many observations of seismic anisotropy have been made in subduction systems our understanding of the mantle beneath subducting slabs remains tenuous due to the difficulty of constraining anisotropy in the sub slab region recently the source side shear wave splitting technique has been refined and applied to several subduction systems worldwide making accurate and direct measurements of sub slab anisotropy feasible and offering unprecedented spatial and depth coverage in the sub slab mantle here we present source side shear wave splitting measurements for the central america alaska aleutians sumatra ryukyu and izu bonin japan kurile subduction systems we find that measured fast splitting directions in these regions generally fall into two broad categories aligning either with the strike of the trench or with the motion of the subducting slab relative to the overriding plate trench parallel fast splitting directions dominate beneath the izu bonin japan and southern kurile slabs and part of the sumatra system while fast directions that parallel the motion of the downgoing plate dominate in the ryukyu central america northern kurile western sumatra and alaska aleutian regions we find that plate motion parallel fast splitting directions in the sub slab mantle are more common than previously thought we observe a correlation between fast direction and age of the subducting lithosphere older lithosphere 95 ma is associated with trench parallel splitting while younger lithosphere 95 ma is associated with plate motion parallel fast splitting directions finally we observe source side splitting for deep earthquakes transition zone depths beneath japan and sumatra suggesting the presence of anisotropy at midmantle depths beneath these regions

grosvenor mountains 95 howardite pairing group insights into the surface regolith of asteroid 4 vesta regolithic howardites are analogs for the surface materials of asteroid 4 vesta recently mapped by the dawn spacecraft rigorously evaluating pairing of howardites recovered in 1995 in the grosvenor mountains gro 95 antarctica enables an examination of a larger more representative regolith sample previous work on two of the howardites studied here concluded that gro 95602 and gro 95535 are solar wind rich surface regolith samples and that they are not paired with each other leading to uncertainty regarding pairing relationships between the other gro 95 howardites based on petrology cosmic ray exposure history and terrestrial age four gro 95 howardites are paired the paired howardites gro 95534 95535 95574 95581 were from a meteoroid with radius of 10 15 cm a preatmospheric size comparable to that of kapoeta the largest known regolithic howardite the paired gro 95 howardites contain clasts of at least 18 separate hed lithologies providing evidence they were assembled from diverse source materials the total eucrite diogenite mixing ratio ratio of all eucrite lithologies to all diogenite lithologies in the paired gro 95 howardites is 2 1 petrographically determined basaltic eucrite cumulate eucrite ratios in regolithic howardites studied here and previously vary more widely than total eucrite diogenite ratios relative to eucritic pyroxene plagioclase is depleted in these howardites which provides evidence that plagioclase is preferentially comminuted in the vestan regolith the extent of plagioclase depletion could be an indicator of regolith maturity

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

fabric development in mg fe o during large strain shear deformation implications for seismic anisotropy in earth s lower mantle abstract large strain shear deformation experiments were performed on mg 1 x fe x o x 0 25 1 0 one of the important minerals in earth s lower mantle deformation experiments were made on coarse grained 15 20 m grain size hot pressed aggregates at conditions of t t m 0 46 0 65 t temperature t m melting temperature and 0 4 10 3 to 0 9 10 3 differential stress shear modulus up to the shear strain of 7 8 under these conditions deformation occurs by dislocation creep the microstructural development in mg fe o is found to be sluggish and the complete dynamic recrystallization and nearly steady state fabric lattice preferred orientation are achieved only after shear strains of 4 at nearly steady state mg fe o shows strong fabrics characterized by the 1 1 0 axes being parallel to the shear direction and the poles of the 1 0 0 planes and to a lesser extent the poles of the 1 1 1 planes normal to the shear plane the seismic anisotropy corresponding to the deformation fabrics in mg fe o was calculated the nature of anisotropy corresponding to a given flow geometry changes significantly with strain as a result of fabric evolution anisotropy changes also with depth pressure due to the large variation of elastic anisotropy of mg fe o with depth seismic anisotropy caused by the deformation fabric of mg fe o is very weak in the shallow lower mantle v sh v sv anisotropy assuming that mg fe o occupies 20 volume fraction of the lower mantle and little shear wave splitting of vertically travelling waves a result that is consistent with the seismological observations in the d layer of the circum pacific regions thus the deformation fabric of mg fe o is a vital candidate of the cause of seismic anisotropy in these regions anisotropy caused by the lattice preferred orientation of mg fe o has a distinct azimuthal anisotropy with a strong 4 term azimuth the direction of propagation of the fastest slowest sh or p wave is parallel perpendicular to the flow direction and the slowest fastest sh or p wave is at 45 from these two directions

the deformational journey of the nazca slab from seismic anisotropy s a and c m e are currently supported by australian research council grant de190100062

olivine diogenites the mantle of the eucrite parent body abstract two olivine rich antarctic diogenites alh a77256 and alh 84001 of the howardite eucritediogenite hed meteorite association have olivine pyroxene ratios similar to normative ratios in devolatilized ordinary chondrites based on chemical data and petrological analysis these meteorites represent the residuum of partial melting of the mantle in the eucrite parent body epb mineral assemblages in these olivine rich diogenites record a continuum in thermal histories from initial partial melting 1150 1200 c to subsolidus re equilibration 795 55 c the small number of olivine rich diogenites known hints that only the outer portion of the epb has been sampled

deformation of mg0 9 fe0 1 sio3 perovskite aggregates up to 32 gpa room temperature investigations on the shear stress and deformation mechanisms of mg0 9fe0 1 sio3 perovskite are performed in situ up to 32 gpa using radial x ray diffraction and the diamond anvil cell as a deformation apparatus the uniaxial stress supported by the perovskite aggregate is found to increase continuously with pressure up to 10 9 1 9 gpa at 32 1 gpa our measurements show no development of significant lattice preferred orientations in the sample which indicates that deformation by dislocation glide is not the dominant deformation mechanism under these conditions assuming that the underlying cause for seismic anisotropy in the deep earth is elastic anisotropy combined with lattice preferred orientation our results indicate that silicate perovskite deformed under the conditions of this experiment would not be the source of seismic anisotropy c 2003 elsevier science b v all rights reserved

ordinary mesostasis and not so ordinary symplectites late stage assemblages in howardites abstract two categories of symplectites have been observed in howardites three phase composed of vermicular intergrowths of ferroan augite fayalitic olivine and silica and two phase composed of vermicular intergrowths of orthopyroxene and troilite three phase symplectites have been previously shown to represent the breakdown products of metastable pyroxene in howardites they appear to be genetically related to gabbroic eucrites in some cases and under yet to be specified conditions ferroan clinopyroxene in gabbroic eucrites may undergo only localized decomposition resulting in oriented exsolution like features breakdown phases in those cases are fayalitic olivine silica and depending on the mgo content of the system orthopyroxene as opposed to three phase symplectites two phase symplectites are most likely of diogenitic origin they probably formed via impact induced localized melting of diogenitic orthopyroxene in the presence of troilite grain boundary melting three phase symplectites in howardites occasionally contain accessory amounts of ilmenite troilite and or kamacite and are exclusively associated with medium grained feo rich pyroxene silica and plagioclase all minerals involved are late stage crystallites or mesostasis phases in general highly evolved eucritic lithologies constitute only a minor fraction of howardites however considering that three phase symplectites are generated in a low pressure i e near surface environment feo and cao rich eucritic rocks may be exposed locally on vesta s surface this in turn is highly relevant to the ongoing dawn mission

in situ laser ablation icp ms analyses of dimict diogenites further evidence for harzburgitic and orthopyroxenitic lithologies trace element concentrations in pyroxene plagioclase and olivine were measured in five diogenite breccias previously identified as containing distinct harzburgitic ol opx and orthopyroxenitic opx lithologies dimict three samples show two distinct populations of pyroxene trace element abundances supporting their classification as dimict these three meteorites show increases in y yb and hree concentrations from harzburgitic to orthopyroxenitic pyroxenes supporting the hypothesis that the lithologies are related through fractional crystallization whereby harzburgite olivine and pyroxene crystallized from the magma first followed by orthopyroxenite pyroxene depletions in lree and eu concentrations in the orthopyroxenitic lithology are most likely due to equilibration with lree and eu rich phases likely plagioclase which is found primarily in that lithology two samples do not show evidence supporting a dimict classification large pyroxene trace element variation in one sample indicates that it is polymict while uniform trace element distribution in the other suggests that it may be a monomict breccia

single crystal elasticity of al fe bearing bridgmanite and seismic shear wave radial anisotropy at the topmost lower mantle abstract in this study we investigated the single crystal elasticity of al fe bearing bridgmanite bgm with chemical compositions of mg 0 95 fe 0 033 2 fe 0 027 3 al0 04si0 96o3 fe6 al4 bgm and mg 0 89 fe 0 024 2 fe 0 096 3 al0 11si0 89o3 fe12 al11 bgm using combined experimental results from brillouin light scattering bls impulsive stimulated light scattering isls and x ray diffraction xrd measurements in diamond anvil cells at 25 and 35 gpa based on experimentally measured compressional and shear wave velocities v p v s as a function of azimuthal angles within selected crystal platelets that are sensitive to derivation of nine elastic constants for each composition we reliably derived the full elastic constants of fe6 al4 bgm and fe12 al11 bgm at the two experimental pressures our results show that the combined fe and al substitution results in a reduction of both v s and v p in fe12 al11 bgm up to 2 6 0 5 and 1 5 0 3 respectively compared with those in fe6 al4 bgm at the experimental pressures in particular we observed strong combined fe and al effects on v s splitting anisotropy of al fe bearing bgm at the two experimental pressures fe6 al4 bgm exhibits the highest v s splitting anisotropy of 8 23 9 0 along the 001 direction while the direction shifts to the midway between 100 and 001 directions for fe12 al11 bgm with v s splitting anisotropy of 7 68 11 06 combining the single crystal elasticity data of fe6 al4 bgm and fe12 al11 bgm with the crystallographic preferred orientation cpo results of deformed bgm at relevant lower mantle pressure temperature p t conditions from literature we modeled the seismic v s radial anisotropy of deformed al fe bearing bgm near a subducting slab at conditions relevant to the topmost lower mantle taking into account the fe and al contents in al fe bearing bgm with depth in the earth s topmost lower mantle the results of our model show that the deformation of fe6 al4 bgm and fe12 al11 bgm crystals would produce 0 9 and 0 8 v s radial anisotropy at depths of 670 and 920 km respectively these findings provide mineral physics explanations to the distinct seismically detected v s radial anisotropies at the topmost lower mantle near subducted slabs especially in the tonga kermadec subduction region

evidence for 100 slip in ferropericlase in earth s lower mantle from high pressure high temperature experiments abstract seismic anisotropy in earth s lowermost mantle resulting from crystallographic preferred orientation cpo of elastically anisotropic minerals is among the most promising observables to map mantle flow patterns a quantitative interpretation however is hampered by the limited understanding of cpo development in lower mantle minerals at simultaneously high pressures and temperatures here we experimentally determine cpo formation in ferropericlase one of the elastically most anisotropic deep mantle phases at pressures of the lower mantle and temperatures of up to 1400 k using a novel experimental setup our data reveal a significant contribution of slip on 100 to ferropericlase cpo in the deep lower mantle contradicting previous inferences based on experimental work at lower mantle pressures but room temperature we use our results along with a geodynamic model to show that deformed ferropericlase produces strong shear wave anisotropy in the lowermost mantle where horizontally polarized shear waves are faster than vertically polarized shear waves consistent with seismic observations we find that ferropericlase alone can produce the observed seismic shear wave splitting in d in regions of downwelling which may be further enhanced by post perovskite our model further shows that the interplay between ferropericlase causing vsh vsv and bridgmanite causing vsv vsh cpo can produce a more complex anisotropy patterns as observed in regions of upwelling at the margin of the african large low shear velocity province

mid mantle anisotropy in subduction zones and deep water transport the earth s transition zone has until recently been assumed to be seismically isotropic increasingly however evidence suggests that ordering of material over seismic wavelengths occurs there but it is unclear what causes this we use the method of source side shear wave splitting to examine the anisotropy surrounding earthquakes deeper than 200 km in slabs around the globe we find significant amounts of splitting 2 4 s confirming that the transition zone is anisotropic here however there is no decrease in the amount of splitting with depth as would be the case for a metastable tongue of olivine which thins with depth suggesting this is not the cause the amount of splitting does not appear to be consistent with processes in the ambient mantle such as lattice preferred orientation development in wadsleyite ringwoodite or mgsio3 perovskite we invert for the orientation of several mechanisms subject to uncertainties in mineralogy and deformation and the best fit is given by updip flattening in a style of anisotropy common to hydrous phases and layered inclusions we suggest that highly anisotropic hydrous phases or hydrated layering is a likely cause of anisotropy within the slab implying significant water transport from the surface down to at least 660 km depth

in situ observation of crystallographic preferred orientation of deforming olivine at high pressure and high temperature abstract simple shear deformation experiments on polycrystalline olivine and olivine single crystal were conducted at pressures of 1 3 3 8 gpa and temperatures of 1223 1573 k to understand the achievement of steady state fabric strength and the process of dynamic recrystallization development of crystallographic preferred orientation cpo of olivine was evaluated from two dimensional x ray diffraction patterns and shear strain was measured from x ray radiographs the steady state fabric strength of the a type fabric was achieved within total shear strain of 2 at strains higher than 1 an increase in concentration of the 0 1 0 axes mainly contributes to an increase in fabric strength at strains higher than 2 the magnitude of v sh v sv i e ratio of horizontally and vertically polarized shear wave velocities scarcely increased in most of the runs the v sh v sv of peridotite 70 vol olivine 30 vol minor phases having the steady state a type olivine fabric coincides with that of recent global one dimensional models under the assumption of horizontal flow suggesting that the seismic anisotropy observed in the shallow upper mantle is mostly explained by the development of a type olivine fabric experimental results on the deformation of single crystal olivine showed that the cpo of olivine is influenced by the initial orientation of the starting single crystal because strain is concentrated in the recrystallized areas and the relic of the starting single crystal remains in the upper mantle the old cpo of olivine developed in the past may affect the olivine cpo developed in the present

water distribution in the lower mantle implications for hydrolytic weakening abstract the presence of water in lower mantle minerals is thought to have substantial effects on the rheological properties of the earth s lower mantle in what is generally known as hydrolytic weakening this weakening will have profound effects on global convection but hydrolytic weakening in lower mantle minerals has not been observed experimentally and thus the effect of water on global dynamics remains speculative in order to constrain the likelihood of hydrolytic weakening being important in the lower mantle we use first principles methods to calculate the partitioning of water strictly protons between mineral phases of the lower mantle under lower mantle conditions we show that throughout the lower mantle water is primarily found either in the minor ca perovskite phase or in bridgmanite as an al3 h pair ferropericlase remains dry however neither of these methods of water absorption creates additional vacancies in bridgmanite and thus the effect of hydrolytic weakening is likely to be small we find that water creates significant number of vacancies in bridgmanite only at the deepest part of the lower mantle and only for very high water contents 1000 ppm we conclude that water is thus likely to have only a limited effect on the rheological properties of the lower mantle

stress relaxation experiments of olivine under conditions of subducted slab in earth s deep upper mantle abstract stress relaxation experiments of olivine were conducted under high pressure and high temperature conditions up to 10 gpa and 1273 k using a kawai type multi anvil apparatus a pre sintered san carlos olivine sample rod was inserted between two dense al 2 o 3 pistons to yield high stress at high pressure within an octahedral pressure medium stress was determined from the two dimensional diffraction pattern taken using monochromatic x rays and an imaging plate and sample length was determined from an x ray radiograph in these experiments pressure was first increased at room temperature and then the temperature was increased and kept at 673 873 1073 and 1273 k four relaxation cycles in total were carried out in two experimental runs the magnitude of deviatoric stress was calculated from five diffraction peaks with the following hkl s 0 2 1 1 0 1 1 3 0 1 3 1 and 1 1 2 the calculated deviatoric stress was significantly different depending on which diffraction peak was used up to a factor of 2 due to plastic deformation within the polycrystalline sample the deviatoric stress decreased with increasing temperature in all of relaxation cycles at given temperatures the final state value of deviatoric stress increased with increasing pressure the upper bound for the plastic strain rate in the final state was determined to be 10 7 s 1 based on a comparison between the total sample length determined from the radiograph and the d spacings along the piston direction determined from x ray diffraction present results suggest a positive activation volume for the low temperature rheology of olivine

a world perspective on acid sulphate soils abstract generalizations about the morphology and genesis of acid sulphate soils at a regional scale are derived from a review of extensive though patchy soil survey data a general sequence of sedimentation accumulation of sulphides and burial of sulphitic material by peat or alluvium of low sulphide content and a parallel sequence of soil profile development are illustrated by examples of unripe sulphitic soils under a natural tidal regime artificially drained raw acid sulphate soils and ripe acid sulphate soils at various stages of development the world pattern has been driven mainly by postglacial sea level change but each regional pattern is determined by its unique sedimentary and geomorphological history distinctive patterns occur in deltas and estuaries and in humid and seasonally dry climates very extensive areas of ripe acid sulphate soils in areas that are not known to have experienced falls in relative sea level are ascribed to human activity forest clearance and soil erosion in catchments causing lower dry season river flows and piecemeal clearance of peat over the floodplains permitting the dry season water table to fall the implications for further agricultural development in other comparable areas include the absolute necessity to know the extent of potential acid sulphate soils and to maintain their water table above the sulphide datum most effective systems of management have been developed by farmers themselves but the sustainability of these systems is often doubtful due to their detrimental effects on the aquatic ecosystem

mantle dynamics inferred from the crystallographic preferred orientation of bridgmanite seismic shear wave anisotropy is observed in earth s uppermost lower mantle around several subducted slabs the anisotropy caused by the deformation induced crystallographic preferred orientation cpo of bridgmanite perovskite structured mg fe sio3 is the most plausible explanation for these seismic observations however the rheological properties of bridgmanite are largely unknown uniaxial deformation experiments have been carried out to determine the deformation texture of bridgmanite but the dominant slip system the slip direction and plane has not been determined here we report the cpo pattern and dominant slip system of bridgmanite under conditions that correspond to the uppermost lower mantle 25 gigapascals and 1 873 kelvin obtained through simple shear deformation experiments using the kawai type deformation dia apparatus the fabrics obtained are characterized by 100 perpendicular to the shear plane and 001 parallel to the shear direction implying that the dominant slip system of bridgmanite is 001 100 the observed seismic shear wave anisotropies near several subducted slabs tonga kermadec kurile peru and java can be explained in terms of the cpo of bridgmanite as induced by mantle flow parallel to the direction of subduction

midmantle deformation between the australian continent and the fiji tonga subduction zone 1 shear wave splitting measurements are performed at temporary stations deployed across the australian continent for direct s waves from events occurring in the neighboring subduction zones especially fiji tonga unlike core refracted shear waves direct s waves are not polarized at the core mantle boundary and are therefore subject to influences on the source side on the receiver side and along the ray path in between source side contamination due to the development of lattice preferred orientation of olivine can be minimized by considering deep events with an epicentral location below 410 km depth the olivine spinel phase transition depth anisotropic contributions from the transition zone or lower mantle can only be reliably inferred in the case of high delays that cannot be generated solely by the upper mantle structure underneath a station the analysis of a comprehensive data set for direct s waves from deep events leads to an average delay time of 0 9 s at stations deployed across the continent despite the limitations of such an arithmetic average the result highlights the lack of evidence for midmantle deformation between the fiji tonga subduction zone and the australian continent unlike previously suggested in studies dealing with the permanent seismological stations only a striking consistency between measurements performed across several stations belonging to an array in western australia suggests a very coherent lithospheric structure underneath the yilgarn craton

characterization by scanning precession electron diffraction of an aggregate of bridgmanite and ferropericlase deformed at hp ht scanning precession electron diffraction is an emerging promising technique for mapping phases and crystal orientations with short acquisition times 10 20 ms pixel in a transmission electron microscope similarly to the electron backscattered diffraction ebsd or transmission kikuchi diffraction tkd techniques in a scanning electron microscope in this study we apply this technique to the characterization of deformation microstructures in an aggregate of bridgmanite and ferropericlase deformed at 27 gpa and 2 130 k such a sample is challenging for microstructural characterization for two reasons i the bridgmanite is very unstable under electron irradiation ii under high stress conditions the dislocation density is so large that standard characterization by diffraction contrast are limited or impossible here we show that detailed analysis of intracrystalline misorientations sheds some light on the deformation mechanisms of both phases in bridgmanite deformation is accommodated by localized amorphous shear deformation lamellae whereas ferropericlase undergoes large strains leading to grain elongation in response to intense dislocation activity with no evidence for recrystallization plastic strain in ferropericlase can be semiquantitatively assessed by following kernel average misorientation distributions

evidence of midmantle anisotropy from shear wave splitting and the influence of shear coupled p waves 1 until recently the midmantle region of the earth the transition zone and the uppermost lower mantle has been considered isotropic recent work by wookey et al 2002 presented evidence of anisotropy in the midmantle region near the tonga kermadec subduction zone inferred from shear wave splitting in teleseismic s phases at australian seismic stations this data set is revisited to examine the possibility of contamination by shear coupled p waves using reflectivity modeling we explore the effects of these phases on the measurement of shear wave splitting contamination of such measurements is demonstrated for short epicentral distances 30 wave field decomposition is a simple technique which can be used to separate these phases from the main s wave arrival the tonga australia data set is reprocessed after wave field decomposition shear wave splitting ranging between 0 7 and 6 2 s is observed a range comparable to that observed by wookey et al 2002 as before the polarization of the fast shear wave is observed to be predominantly horizontal however the magnitudes of splitting for several events at short epicentral distances are significantly reduced suggesting some influence of shear coupled p waves in the original analysis the results are compared with possible models of mantle anisotropy and the results can be best explained by significant anisotropy in the midmantle region the best candidate location for this anisotropy is in the uppermost lower mantle and scenarios involving the alignment of lower mantle or subducted materials by regional dynamic processes are suggested to account for this

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

predicted glide systems and crystal preferred orientations of polycrystalline silicate mg perovskite at high pressure implications for the seismic anisotropy in the lower mantle abstract we use first first principle methods and the peierls nabarro model to evaluate the resistance to glide characterized by the peierls stress of glide systems for end member mgsio 3 perovskite at mantle pressures 010 100 is the easiest glide system in mg perovskite at all pressures peierls stresses increase systematically with pressure for all systems except 001 010 indicating the importance of lattice friction at lower mantle pressures the ratio of the maximum peierls stress for each system relative to the 010 100 value defines their critical resolved shear stress crss these crss are used in a visco plastic self consistent homogenization model to predict the evolution of crystal preferred orientations cpo during deformation of polycrystalline mg perovskite in axial compression 100 tends to align with the compression direction in agreement with in situ observations in axial compression experiments in simple shear 010 concentrates near the shear direction and 100 although more dispersed tends to align near the shear plane consistent with the dominant activity of the easier 010 100 system the calculated seismic anisotropy for a 100 mg perovskite aggregate using the cpo in simple shear and the elastic constants of mgsio 3 perovskite at lower mantle pressures and temperatures is weak 3 for p waves with and 2 for s waves and decreases with increasing temperature and pressure p waves show the fastest propagation parallel to the lineation and s waves fast polarization is in the foliation at 38 gpa and normal to the lineation at 88 gpa this weak anisotropy is consistent with global seismological observations of a nearly isotropic lower mantle there are however two regions where strain induced mg perovskite cpo could contribute to anisotropy a low temperature regions in the uppermost lower mantle where the predicted s wave polarization anisotropy may attain 1 6 with a fast polarization parallel to the foliation b in high high temperature domains in the d layer where mg perovskite may be the major stable phase leading to polarization of fast s waves normal to the lineation for propagation directions at high angle to the lineation and an apparent isotropy for all other propagation directions

characteristics of a marshland soil built up from marine and peat material abstract the marine marshland area seawards of the sehestedter ausendeichsmoor is built up from marine and moor peat material the humic fluvisol investigated in this area is characterized 1 by sulfate depletion leading to intensive methanogenesis 2 by carbonate depleted soil sections and reduced ph values and 3 by high amounts of reduced sulfur compounds with respect to further development a quick acidification leading to soil properties which are characteristic of older but not currently seawater influenced humic fluvisols can be expected is seems likely that these older humic fluvisols initially developed under marine conditions

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

sulphur and iron geochemistry of holocene coastal peats nw germany a tool for palaeoenvironmental reconstruction abstract a drill core from the marshlands of nw germany covering the entire holocene was analysed at high resolution by geochemical xrf cirm ms and microfacies methods diatoms thin sections sem in order to provide information about the palaeoenvironmental development in addition microbial experiments were carried out with sulphate reducing bacteria srb and cellulose fermenting fungi in seawater using peat as substrate the core contains an intercalated reed peat layer 2 73 3 02 m and a basal peat 5 78 6 42 m the basal peat consists in the lowest part of fen woodland and raised bog peat while the upper part is formed by a reed peat bed the peat layers are characterised by a distinct enrichment of pyrite with negative bulk sediment 34 s values av 11 5 range 2 6 to 26 7 reflecting microbial sulphate reduction in some peat intervals under almost open system conditions with respect to the input of seawater sulphate pyrite occurs exclusively with framboidal texture in close vicinity to the organic matter which indicates localised pyrite formation at the decay site in microenvironments with high concentrations of dissolved fe microbial experiments reveal that peat does not represent an appropriate substrate for srb and that srb have to rely on the preceding decomposition of peat by other microorganisms in microenvironments the total sulphur content of the peat layers averages to 7 8 wt with a maximum value of 28 2 wt unusually found within the basal peat at the transition of fen woodland and raised bog peat the pyrite enrichments can be explained by two different scenarios which are related to the intensity of the sea level rise the first scenario applies to a moderate sea level rise and is decisive for the reed peats where pyrite formation coincides with peat growth a brackish zone is assumed for the peat forming environment which is influenced by iron rich freshwater and sulphate rich seawater as the freshwater forms the major fe source the amounts of pyrite increase to a certain degree with decreasing salinity in this environment the palaeosalinity is estimated by the investigation of littoral and pelagic diatoms the second scenario applies to the extensive pyrite formation within the basal peat at the transition of fen and bog peat this pyrite was likely formed after peat growth favoured by a steep sea level rise thin sections of this peat interval reveal clastic layers 1 3 mm with completely pyritised interfaces as these clastic layers contain marine pelagic diatoms e g paralia sulcata we propose that they are caused by tidal channel activities during a phase of a steep sea level rise the marine incursion led to a partial buoyancy of the basal peat at weak transition zones i e the transition from fen to bog peat as a result of the bouyancy marine suspended particulate matter can be introduced laterally in between the peat sections when the peat settles down a clastic layer remains whose interface with the peat may have favoured the inflow of waters of higher salinity therefore an enhanced formation of pyrite was possible due to the combination of sulphate rich ground water and iron rich peatland waters

using hed meteorites to interpret neutron and gamma ray data from asteroid 4 vesta here we construct a comprehensive howardite eucrite and diogenite hed bulk chemistry data set to compare with dawn data using the bulk chemistry data set we determine four gamma ray neutron parameters in the heds 1 relative fast neutron counts fast counts 2 macroscopic thermal neutron absorption cross section absorption 3 a high energy gamma ray compositional parameter cp and 4 fe abundance these correspond to the four measurements of vesta made by dawn s gamma ray and neutron detector grand that can be used to discern hed lithologic variability on the vestan surface we investigate covariance between fast counts and average atomic mass in the meteorite data set where a strong correlation r2 0 99 is observed and we demonstrate that systematic offsets from the fast count trend are linked to changes in fe and ni concentrations to compare the meteorite and grand data we investigate and report covariance among fast counts absorption cp and fe abundance in the hed meteorite data set we identify several grand measurement spaces where the yamato type b diogenites are distinct from all other hed lithologies including polymict mixtures the type b s are diogenites that are enriched in fe pigeonite diopside plagioclase relative to typical orthopyroxenitic diogenites we then compare these results to grand data and demonstrate that regions north of 70 n latitude on vesta including the north pole are consistent with type b diogenites we propose two models to explain type b diogenite compositions in the north 1 deposition as rheasilvia ejecta or 2 type b plutons that were emplaced at shallow depths in the north polar region and sampled by local impacts lastly using principal component pc analysis we identify unique pc spaces for all hed lithologies indicating that the corresponding grand measurables may be used to produce comprehensive lithologic maps for vesta

tidal marsh sedimentation and resilience to environmental change exploratory modelling of tidal sea level and sediment supply forcing in predominantly allochthonous systems abstract the existence and function of tidally dominated and predominantly allochthonous marshes are ultimately contingent upon the operation of hydrodynamic and sedimentary processes within constraints imposed by the available accommodation space and sediment supply this paper re interprets published data relating to contemporary vertical marsh growth and sea level rise in the context of the conceptual model relating elevation sedimentation sea level rise sediment supply and tidal range this analysis is supported by numerical mass balance modelling of the equivalent parameter space and of the sensitivity of marsh hydroperiod and sedimentation to sea level and sediment supply forcing the effect of autocompaction on the translation of sedimentation into elevation change is also considered parameter space modelling provides a framework for the interpretation of field data and affords indicative insights into marsh resilience to change it is argued that the assessment of marsh response to external environmental forcing should be based not on empirical comparisons of sedimentation versus sea level rise but on the estimation of sediment supply and the efficiency with which this is depleted by deposition as metrics of marsh resilience this implies a shift towards more intensive process studies aimed at elucidating more fully the linkages between tidal marshes and adjacent estuarine and coastal systems model results also indicate significant variability in marsh sedimentation associated with 18 6 yr tidal modulation and meteorological processes at short term scales such variability further complicates the interpretation of sedimentation or elevation change data obtained from monitoring programmes of short duration longer term monitoring is of value however as a means of identifying important mechanisms of climate and sediment supply forcing that may contribute to the formation and maintenance of marsh sedimentary sequences

diogenites as polymict breccias composed of orthopyroxenite and harzburgite abstract a few relatively unbrecciated olivine rich diogenites consist of an equilibrium assemblage of olivine and magnesian orthopyroxene harzburgite more common diogenites with smaller amounts of olivine are breccias containing two distinct orthopyroxenes one magnesian and one ferroan these diogenites are mixtures of a harzburgite lithology that is more magnesian with the normal orthopyroxenite lithology that is ferroan and may contain small amounts of plagioclase both lithologies likely formed by fractional crystallization in multiple plutons emplaced within the crust of asteroid 4 vesta minor element trends in orthopyroxenes indicate that these plutons exhibited a range of compositions we propose a revised taxonomy for the hed howardites eucrites and diogenites suite where all ultramafic samples are referred to as diogenites within this group the prefixes dunitic harzburgitic and orthopyroxenitic are used to distinguish diogenites consisting of more than or equal to 90 olivine olivine orthopyroxene and more than or equal to 90 orthopyroxene respectively the prefix polymict is used to describe brecciated mixtures of any of these rock types the recognition that olivine is a significant phase in some diogenites is consistent with spectral interpretations of olivine in a deeply excavated crater on vesta and has important implications for the bulk composition and petrogenesis of that body

seismic anisotropy and mantle flow below subducting slabs abstract subduction is integral to mantle convection and plate tectonics yet the role of the subslab mantle in this process is poorly understood some propose that decoupling from the slab permits widespread trench parallel flow in the subslab mantle although the geodynamical feasibility of this has been questioned here we use the source side shear wave splitting technique to probe anisotropy beneath subducting slabs enabling us to test petrofabric models and constrain the geometry of mantle fow our global dataset contains 6369 high quality measurements spanning 40 000 km of subduction zone trenches over the complete range of available source depths 4 to 687 km and a large range of angles in the slab reference frame we find that anisotropy in the subslab mantle is well characterised by tilted transverse isotropy with a slow symmetry axis pointing normal to the plane of the slab this appears incompatible with purely trench parallel flow models on the other hand it is compatible with the idea that the asthenosphere is tilted and entrained during subduction trench parallel measurements are most commonly associated with shallow events source depth 50 km suggesting a separate region of anisotropy in the lithospheric slab this may correspond to the shape preferred orientation of cracks fractures and faults opened by slab bending meanwhile the deepest events probe the upper lower mantle where splitting is found to be consistent with deformed bridgmanite

mechanisms of land sea interactions the distribution of metals and sedimentary organic matter in sediments of a river dominated mediterranean karstic estuary this paper examines disposal of metals and the origin characteristics and distribution of sedimentary organic matter som in a mediterranean karstic estuary in the north eastern adriatic this environment offers a real time small model system for studies of geochemical processes in microtidal mediterranean estuaries that are infilling with sediments and classified as river dominated disequilibrium estuaries the results have shown that the longitudinal distribution of heavy metals in sediments follows the sedimentation dynamics and deposition pattern of river borne clay mineral particles the highest concentration of metals was found in the restricted upper part of the estuary characterized by rapid deposition of clay particles and terrestrial sedimentary organic matter and decreases toward the open sea the vertical distribution of metals in sediment cores depends on the prevailing ph and eh conditions significant increases of the concentrations of metals in the uppermost strata are the result of recent anthropogenic inputs the share of the terrestrial component in

spatial patterns in accretion on barrier island salt marshes abstract on minerogenic barrier island salt marshes sedimentation is spatially heterogeneous although the main forcing factors for sedimentation are known much less is known about the characteristic sizes of this spatial patterning such patterning gives information on the spatial component of salt marsh formation and on the uncertainty in measured accretion rates we used variograms geostatistics to study the size of spatial patterns in the thickness of salt marsh deposits based on a database of over 10 000 soil cores these were taken at various spatial scales ranging from metres to kilometres along a chronosequence representing 10 150 years of salt marsh formation at three barrier islands in the wadden sea south eastern north sea the general complexity of salt marsh accretion was reflected in the observed patterns of the thickness of the marsh deposits the patterns were nested and ranged in horizontal size from 3 m on sites with micro topography to 900 m at the scale of the entire marsh their structure and size changed with salt marsh age and there was no characteristic pattern size although the pre marsh topography is an important large scale control during salt marsh development independent spatial patterns are superimposed when scaling up data on salt marsh sedimentation the presence of spatial patterning adds uncertainty to the prediction the consequence of the complexity of these patterns is that the spatial uncertainty is a not necessarily linear function of the area under consideration which can only be quantified if it is explicitly measured our findings therefore pose a cautionary note to studies of salt marsh resilience to sea level rise reliable estimates can only be derived if they are based on measurements that take into account the entire salt marsh

the carbonate evaporite lagoon of al dakhirah qatar an example of a modern depositional model controlled by longshore transport the southern coast of the arabian gulf is considered a good example of an arid carbonate depositional system the objective of this field investigation is to better elucidate the dynamic controls on the character and pattern of the depositional belts in a carbonate evaporite lagoonal setting the interpretation of this lagoon is based on combined field examination and laboratory analyses of surface samples and this has resulted in an updated depositional model for carbonate evaporite lagoonal settings this study highlights the effects of sediment transport by longshore currents with the formation of sand spits that gradually closed the lagoon during their southwards migration the associated narrow and elongated back barrier settings consist of tidal dominated muddy sediments affected by a network of tidal channels this wave dominated high energy system has generated several carbonate barrier and back barrier units that migrated southwards and seawards during the last few thousands of years this updated depositional model significantly differs from shoreline parallel facies tracts of the classical trucial coast model where the dominant wind is orientated perpendicular to the coastline conversely to the sediment belts of the trucial coast the al dakhirah lagoon displays a strongly asymmetrical pattern of the sediment belts marked by a southwards and seawards migration

interconnection of ferro periclase controls subducted slab morphology at the top of the lower mantle abstract the electrical conductivity of mantle rocks during phase transformation from ringwoodite to silicate perovskite and ferro periclase was measured at 25 gpa and various temperatures ranging from 1300 to 1900 k the electrical conductivity was high at the initial stage of annealing suggesting that ferro periclase forms interconnected layers in aggregates of silicate perovskite and ferro periclase that are representative of lower mantle rock at 1900 k the electrical conductivity quickly decreased and reached that of silicate perovskite suggesting the cut off of the interconnected ferro periclase because of rounding of crystals below 1700 k the high conductivity values were maintained for experimental duration the interconnection of ferro periclase which has a lower viscosity than silicate perovskite can be maintained in a cold descending slab over geological time scales 1 my indicating that a colder slab is less viscous than the warmer mantle surrounding it the low viscosity slab can be prevented from penetrating into the deeper part of the lower mantle by the high viscosities encountered at a depth of 1000 km referred to as the viscosity hill that cause stagnation at this depth as observed by seismic tomography

sand in the salt marsh contribution of high energy conditions to salt marsh accretion abstract the environmental dynamics at barrier island salt marshes are reflected in lateral and vertical textural patterns of the marsh sediment during normal conditions fine grained sediment is deposited whereas during high energy conditions also sand accretion can occur this paper describes the occurrence and importance of sand deposits for the building of salt marshes the study was carried out in the wadden sea on the islands of schiermonnikoog nl terschelling nl and the peninsula of skallingen dk firstly we recorded the presence of sand in the sediment representing initial salt marsh formation the results indicate that part of the salt marsh developed under conditions that were dynamically enough for sand to be transported the spatial distribution of these conditions depends on soil elevation and location on the marsh modified by the presence of artificial sand dikes further we recorded the presence and thickness of sand layers within the salt marsh sediment sand layers are found on twenty percent of the marsh area and are partly associated with the local sources of the sand i e marsh creeks the salt marsh edge and washovers in total sand layers contribute less than ten percent to the volume of marsh deposits on schiermonnikoog we dated the layers using the thickness of the deposits and known marsh age the ages of the layers indicate that for the decadal occurrence of storms capable of depositing sand in the salt marsh the local hydrodynamics and availability of sand determine whether a site receives sand or not

water partitioning between nominally anhydrous minerals in the mgo sio2 h2o system up to 24 gpa implications for the distribution of water in the earth s mantle multi anvil experiments have been conducted in the mgo sio2 h2o system at pressures of 15 24 gpa and temperatures of 1200 1600 c to investigate the partitioning of water between mantle phases the water contents were obtained from fourier transform infrared spectroscopy on doubly polished and clear crystals most of the mineral phases coexisted with a hydrous melt the results show that among all magnesium silicate phases 1 mgsio3 perovskite is the only phase which does not dissolve a detectable amount of water and 2 the high pressure polymorphs of mg2sio4 wadsleyite and ringwoodite dissolve about one order of magnitude more water than the polymorphs of mgsio3 clinoenstatite majorite and akimotoite the following partition coefficients of water were measured dwadsleyite clinoenstatite 3 8 at 15 gpa and 1300 c dringwoodite akimotoite 21 at 19 gpa and 1300 c dakimotoite perovskite 1 at 24 gpa and 1600 c and dpericlase perovskite 1 at 24 gpa and 1500 c these results suggest that most of the water in the earth s mantle is partitioned in the transition zone

petrologic and textural diversity among the pca 02 howardite group one of the largest pieces of the vestan surface abstract nine howardites and two diogenites were recovered from the pecora escarpment icefield pca in 2002 cosmogenic radionuclide abundances indicate that the samples are paired and that they constituted an approximately 1 m diameter meteoroid prior to atmospheric entry at about 1 m in diameter the pca 02 hed group represents one of the largest single pre atmospheric pieces of the vestan surface yet described mineral and textural variations were measured in six of the pca 02 howardites to investigate meter scale diversity of the vestan surface mineral compositions span the range of known eucrite and diogenite compositions additional non diogenitic groups of mg and fe rich olivine are observed and are interpreted to have been formed by exogenic contamination and impact melting respectively these howardites contain olivine rich impact melts that likely formed from dunite and harzburgite rich target rocks containing the first recognized olivine rich hed impact melts these samples provide meteoritic evidence that olivine rich lithologies have been exposed on the surface of vesta finally we present a new method for mapping distributions of lithologies in howardites using 8 elemental x ray maps proportions of diogenite and eucrite vary considerably among the pca 02 howardites suggesting they originated from a heterogeneous portion of the vestan surface while whole sample modes are dominated by diogenite the finer grain size fractions are consistently more eucritic this discrepancy has implications for near infrared spectral observations of portions of vesta s surface that are similar to the pca 02 howardites as the finer grained eucritic material will disproportionately dominate the spectra

ubiquitous lower mantle anisotropy beneath subduction zones seismic anisotropy provides key information to map the trajectories of mantle flow and understand the evolution of our planet while the presence of anisotropy in the uppermost mantle is well established the existence and nature of anisotropy in the transition zone and uppermost lower mantle are still debated here we use three dimensional global seismic tomography images based on a large dataset that is sensitive to this region to show the ubiquitous presence of anisotropy in the lower mantle beneath subduction zones whereas above the 660 km seismic discontinuity slabs are associated with fast sv anomalies up to about 3 in the lower mantle fast sh anomalies of about 2 persist near slabs down to about 1 000 1 200 km these observations are consistent with 3d numerical models of deformation from subducting slabs and the associated lattice preferred orientation of bridgmanite produced in the dislocation creep regime in areas subjected to high stresses this study provides evidence that dislocation creep may be active in the earth s lower mantle providing new constraints on the debated nature of deformation in this key but inaccessible component of the deep earth lower mantle anisotropy is present beneath all subduction zones indicating that dislocation creep is active in the lower mantle according to analysis of 3d global seismic tomography images