small mammal taphonomy at la trinchera de atapuerca burgos spain a remarkable example of taphonomic criteria used for stratigraphic correlations and palaeoenvironment interpretations abstract palaeoecological and biostratigraphical interpretations have been traditionally based on the presence in the fossil record of certain species nevertheless there are many taphonomic factors controlling the species composition and their relative abundance in a fossil site that may alter spatial and temporal correlations between the site where fossils have been found and the place where past beings were living taphonomic studies have been conducted at different sites from atapuerca ibeas cave complex this cave complex in burgos spain includes several karstic sites with extensive evidence of human activity and a complete record of vertebrate remains of the middle pleistocene as well as abundant human fossils the small mammal taphonomic analysis of one of these sites penal is explained and discussed here in detail to show the taphonomic procedure stratigraphical correlation between levels at the penal site is particularly difficult and correlations have been proposed here based on taphonomic data since 1980 a working hypothesis suggested a sedimentary connection between penal and another site named dolina presently separated by an abandoned railway cutting in order to test this hypothesis the results of penal obtained from the present study are compared to previous analysis done in dolina it is also attempted here through taphonomic comparison of these two sites to obtain a better understanding of the past context where hominids inhabited

si isotope fractionation between si poor metal and silicate melt at pressure temperature conditions relevant to metal segregation in small planetary bodies abstract experimental investigations of si isotope fractionation between si bearing metal alloy and silicate phases have to date been limited to high pressure 1 7 gpa and high temperature 1800 2200 c conditions at highly reducing conditions to optimize applicability of results to early core formation processes in the earth here we assess the extent and mechanism of si isotopic fractionation at conditions relevant to metal segregation in small km scale planetary bodies using samples obtained from an industrial scale blast furnace of tata steel ijmuiden the netherlands during the low pressure high temperature process of steelmaking inhomogeneous blast furnace burden consisting of pre and untreated iron ore iron silicates and coke is reduced to oxygen fugacities near the c co buffer resulting in the segregation of a metal phase containing only 0 3 wt si seven sample sets each comprising a metal alloy and a silicate slag were taken during tapping of the blast furnace at tapping temperatures between 1400 c and 1600 c we find large isotopic mass fractionation between metal and silicate with 30sisilicate metal varying between 0 7 and 1 6 values that are as high as previously obtained in high pressure highly reduced experiments a model for metal silicate si isotope fractionation in blast furnaces can explain both the sense and magnitude of fractionation if the presence of sio bearing vapour is explicitly taken into account our data indicate that significant si isotope fractionation can occur between metal and silicate at low pressure high temperature and only mildly reducing conditions for which si solubility in molten fe rich metal is low this suggests an important role for sio at low confining pressures our data can be applied to models of aubrite meteorite formation through high temperature differentiation of an enstatite chondrite parent body our calculations suggest a far larger degree of rehomogenisation during differentiation than previously thought on the basis of metal silicate si isotopic fractionation measured in natural meteorites that re equilibrated at low temperature

experimentally determined si isotope fractionation between silicate and fe metal and implications for earth s core formation abstract stable isotope fractionation amongst phases comprising terrestrial planets and asteroids can be used to elucidate planet forming processes to date the composition of the earth s core remains largely unknown though cosmochemical and geophysical evidence indicates that elements lighter than iron and nickel must reside there silicon is often cited as a light element that could explain the seismic properties of the core the amount of silicon in the core if any can be deduced from the difference in 30 si 28 si between meteorites and terrestrial rocks if the si isotope fractionation between silicate and fe rich metal is known recent studies e g georg r b halliday a n schauble e a reynolds b c 2007 silicon in the earth s core nature 447 31 1102 1106 fitoussi c bourdon b kleine t oberli f reynolds b c 2009 si isotope systematics of meteorites and terrestrial peridotites implications for mg si fractionation in the solar nebula and for si in the earth s core earth planet sci lett 287 77 85 showing sometimes subtle differences between 30 si 28 si in meteorites and terrestrial rocks suggest that si missing from terrestrial rocks might be in the core however any conclusion based on earth meteorite comparisons depends on the veracity of the 30 si 28 si fractionation factor between silicates and metals at appropriate conditions here we present the first direct experimental evidence that silicon isotopes are not distributed uniformly between iron metal and rock when equilibrated at high temperatures high precision measurements of the silicon isotope ratios in iron silicon alloy and silicate equilibrated at 1 gpa and 1800 c show that si in silicate has higher 30 si 28 si than si in metal by at least 2 0 these findings provide an experimental foundation for using isotope ratios of silicon as indicators of terrestrial planet formation processes they imply that if si isotope equilibrium existed during segregation of earth s core forming metal and silicate mantle there should be an isotopic signature of si in the core our experiments combined with previous measurements of si isotope ratios in meteorites and rocks representing the bulk silicate earth suggest that the formation of the earth s core imparted a high 30 si 28 si signature to the bulk silicate earth due to dissolution of 6 wt si into the early core

equilibrium oxygen hydrogen and carbon isotope fractionation factors applicable to geologic systems as demonstrated by the chapters in this short course stable isotope techniques are an important tool in almost every branch of the earth sciences central to many of these applications is a quantitative understanding of equilibrium isotope partitioning between substances indeed it was harold urey s 1947 thermodynamically based estimate of the temperature dependence of 18o 16o fractionation between calcium carbonate and water and a recognition of how this information might be used to determine the temperatures of ancient oceans that launched the science of stable isotope geochemistry the approach pioneered by urey has since been used to estimate temperatures for a wide range of geological processes e g emiliani 1955 anderson et al 1971 clayton 1986 valley this volume in addition to their geothermometric applications equilibrium fractionation data are also important in the study of fluid rock interactions including those associated with diagenetic hydrothermal and metamorphic processes baumgartner and valley this volume shanks this volume finally a knowledge of equilibrium fractionation is a necessary first step in evaluating isotopic disequilibrium a widespread phenomenon that is increasingly being used to study temporal relationships in geological systems cole and chakraborty this volume in the fifty four years since the publication of urey s paper equilibrium fractionation data have been reported for many minerals and fluids of geological interest these data were derived from 1 theoretical calculations following the methods developed by urey 1947 and bigeleisen and mayer 1947 2 direct laboratory experiments 3 semi empirical bond strength models and 4 measurement of fractionations in natural samples each of these methods has its advantages and disadvantages however the availability of a variety of methods for calibrating fractionation factors has led to a plethora of calibrations not all of which are in agreement in this chapter we evaluate the major methods for determining fractionation factors

geophysical investigations in the service of mount carmel israel prehistoric research abstract geophysical investigations in el wad cave mount carmel israel enabled the mapping of the surface of the bedrock and a reconstruction of the depth of the archeological deposits seismic refraction and ground penetrating radar gpr provided similar results indicating the potential value of geophysical studies when one seeks to reconstruct site features and establish future excavation strategies results of a gpr survey later conducted in the adjacent jamal cave were supported to a high degree by subsequent archeological excavations in the course of which lower and middle paleolithic layers were unearthed a continuous vertical electrical sounding cves geoelectric survey in the collapsed misliya cave indicates a low resistivity layer at the upper central part of the cave suggesting that lithified archeological deposits of ca 4 m are preserved at the site this has been supported by a test excavation recently conducted at the site more intriguing is the case of what on the basis of the outer morphology of the cliff seemed to be another collapsed cave just to the north of el wad the cves survey at the bottom of the cliff and across the hypothesized cave or chamber shows a two layer model with a low resistivity 100 200 ohm m layer overlying a layer of high resistivity 8000 10 000 ohm m a trial trench indicates that here the bedrock is covered by shallow recent surface material with no archeological value all three methods of geophysical investigation proved applicable and resulted in the successful evaluation of sites location depth and spatial extension thus forming essential tools in future prehistoric research

high temperature elasticity of iron bearing olivines the first high temperature data on the nine adiabatic elastic moduli for iron bearing olivine are reported these measurements are on two single crystal specimens of natural olivine at ambient pressure and from room temperature to a maximum of 1500 k the two specimens contain 8 and 9 modal percent fayalite which required the oxygen fugacity be controlled at high temperature to preserve their chemical stability the rectangular parallelepiped resonance apparatus was adapted to buffer the specimens from the atmosphere with a mixture of co and co2 gas a small increase 1 2 gpa in the adiabatic bulk modulus of each specimen over that of end member forsterite was found the data are high quality to extreme temperatures with good agreement found when comparing the temperature derivatives of the elastic moduli of the two specimens neither specimen exhibits measurable nonlinear temperature dependence in the computed isotropic bulk and shear moduli which is in contrast to published forsterite data the temperature derivatives of the isotropic bulk modulus ks are 1 69 1 80 10 2 gpa k 1 for the two olivine specimens and the shear modulus g derivatives are 1 38 1 36 10 2 gpa k 1 these derivatives are only slightly larger in magnitude than ks t p 1 56 10 2 and g t p 1 30 10 2 gpa k 1 found previously for iron bearing olivine over a very small temperature range there are also no significant differences between the temperature derivatives found here and the average derivatives of end member forsterite from data retrieved over a slightly larger temperature range several dimensionless parameters have been calculated from these results and are discussed in view of systematics which bear on high pressure phases in earth s transition zone one result from these systematics related to the seismic velocities in the earth and especially the shear wave velocities is that an olivine content of less than 50 is implied at the 400 km discontinuity if earth s upper mantle is isochemical furthermore the substitution of almost 10 iron for magnesium at the forsterite end of the olivine solid solution series has little effect on the dimensionless parameters or on the temperature derivatives of the elastic moduli at high temperature

level te9c of sima del elefante sierra de atapuerca spain a comprehensive approach level te9c of the sima del elefante site sierra de atapuerca spain is one of the oldest sites with evidence of human occupation in western europe we began excavating level te9c in 2003 and the work there continues today the studies of the archaeology palaeontology and geology from this locality have provided an indispensable dataset with which to capture a picture in the scenario of the origin of humans in europe based on these data we raise and discuss several topics such as the possible origin of the lineage of the first hominins that inhabited western europe their capacity to have active hunting or scavenging abilities whether their subsistence strategies were successful and what the environment and habitats where these hominin groups settled was like the aim of this paper is to present the results and discussions obtained from the research team and to establish the primary features of early human occupations in southwestern europe tentatively we may conclude based on the events recorded at te9c that the first humans were in the iberian peninsula at around 1 2 ma they used the caves of the sierra de atapuerca as shelters probably during their hunting activities the cavities were surrounded by mediterranean forest rivers and water ponds and varied habitats as suggested by the rich and diverse assemblage of fossils of vertebrates fish amphibians and reptiles birds large and small mammals where humans possibly caught what they found in the surroundings

application of field geophysics in geomorphology advances and limitations exemplified by case studies abstract during the last decade the use of geophysical techniques has become popular in many geomorphological studies however the correct handling of geophysical instruments and the subsequent processing of the data they yield are difficult tasks furthermore the description and interpretation of geomorphological settings to which they apply can significantly influence the data gathering and subsequent modelling procedure e g achieving a maximum depth of 30 m requires a certain profile length and geophone spacing or a particular frequency of antenna for more than three decades geophysical techniques have been successfully applied for example in permafrost studies however in many cases complex or more heterogeneous subsurface structures could not be adequately interpreted due to limited computer facilities and time consuming calculations as a result of recent technical improvements geophysical techniques have been applied to a wider spectrum of geomorphological and geological settings this paper aims to present some examples of geomorphological studies that demonstrate the powerful integration of geophysical techniques and highlight some of the limitations of these techniques a focus has been given to the three most frequently used techniques in geomorphology to date namely ground penetrating radar seismic refraction and dc resistivity promising applications are reported for a broad range of landforms and environments such as talus slopes block fields landslides complex valley fill deposits karst and loess covered landforms a qualitative assessment highlights suitable landforms and environments the techniques can help to answer yet unsolved questions in geomorphological research regarding for example sediment thickness and internal structures however based on case studies it can be shown that the use of a single geophysical technique or a single interpretation tool is not recommended for many geomorphological surface and subsurface conditions as this may lead to significant errors in interpretation because of changing physical properties of the subsurface material e g sediment water content in many cases only a combination of two or sometimes even three geophysical methods gives sufficient insight to avoid serious misinterpretation a good practice guide has been framed that provides recommendations to enable the successful application of three important geophysical methods in geomorphology and to help users avoid making serious mistakes

first principles calculations of equilibrium ca isotope fractionation implications for oldhamite formation and evolution of lunar magma ocean abstract calcium is a major element of the earth the moon terrestrial planets and rocky meteorites here we present equilibrium ca isotope fractionation factors of ca bearing minerals using the first principles calculations based on density functional theory dft the sequence of minerals from the isotopically heaviest to the lightest in ca is forsterite orthopyroxene opx grossular pigeonite diopside anorthite oldhamite overall the equilibrium fractionation of ca isotopes is mainly controlled by the average bond lengths although oldhamite is enriched in light ca isotopes relative to silicate minerals in equilibrium natural oldhamite of enstatite chondrites are isotopically heavier than coexisting silicate materials this implies that enstatite chondrites oldhamites should have been formed during solar nebular gas condensation instead than during parent body processing following previous models for crystallization of the lunar magma ocean lmo we simulated ca isotopic fractionation of the lmo based on our calculated equilibrium ca isotope fractionation factors it shows that the 44 40 ca of the lunar anorthositic crust should be lower than the average of the bulk moon by 0 09 0 11 considering that the lunar mantle might have overturned and mixed after solidification of the lmo we further predict that the lunar mantle should be isotopically heavier than the bulk moon by 0 17 0 26 if the mantle was fully overturned or only by 0 06 0 08 for the case of fully mixing therefore we predict that the potential offset of ca isotopic composition between the anorthositic crust and the lunar mantle can be used to test lmo evolution models

evolution of multilevel caves in the sierra de atapuerca burgos spain and its relation to human occupation abstract the evolution of the torcas cave system sierra de atapuerca is analysed in order to shed light on the formation of the atapuerca archaeological sites and human occupation in the area critical for identifying the paths of the first human dispersal into europe the geomorphological analysis of the endokarst system and the regional base levels has revealed a multilevel cave system with drainage directions from south to north where old karst springs fed the pico river using morphological and topographic evidence we have correlated the fluvial terraces situated at relative heights of 84 80 m and 78 70 m above the arlanzon river main course with the first and second cave levels respectively both of early pleistocene age the fluvial levels t4 60 67 m and t5 50 54 m are linked with the third level early middle pleistocene which contains fluvial deposits probably related to terrace t6 44 46 m progressive fluvial incision allowed humans to gain access to the cave system through several entrances from 1 22 myr until the end of the middle pleistocene when these cave entrances became filled forming the most interesting hominid bearing deposits in europe

stress distribution due to olivine spinel phase transition in descending plate and deep focus earthquakes the stress field due to olivine spinel phase transition in and around a descending plate is studied based on the calculations for an equilibrium phase transition with a constant clapeyron s slope and for a nonequilibrium transition taking a kinetic effect into consideration the material concerned is assumed to be a viscoelastic body whose physical coefficients are functions of temperature and pressures the calculated stress distribution for the equilibrium transition is characterized by a compressional stress near the upper and or lower surfaces of the plate and by a tensional stress at the central part in the depth range from 200 to 550 km the magnitude of principal stress being greater than 0 5 gpa however for the nonequilibrium transition a tensional stress predominates near the upper and lower surfaces and the central part is compressional in the depth range from 300 to 600 km unlike the case of equilibrium transition the maximum principal stress in the latter case is greater than 2 gpa which is much more than that for the equilibrium transition the principal axes in the high stressed region are oriented almost parallel to the descending direction in both cases comparison of the calculated results to the actually observed seismicity depth relation and to focal mechanisms of deep focus earthquakes in descending plates beneath island arcs shows that the nonequilibrium phase transition agrees better with the observations

transformation of silicon in a sandy beach ecosystem insights from stable silicon isotopes from fresh and saline groundwaters abstract dissolved silicon isotope compositions 30si have been analysed for the first time in groundwaters of beach sediments which represent a subterranean estuary with fresh groundwater discharge from a freshwater reservoir and mixing with recirculated seawater the fresh groundwater reservoir has high and variable dissolved silica concentrations between 136 and 736 m but homogeneous 30si of 1 0 0 15 by contrast the seawater is strongly depleted in dissolved silica with concentrations of 3 m and consequently characterised by high 30si of 3 0 the beach groundwaters are variably enriched in dissolved silica compared to seawater 23 192 m and concentrations increase with depth at all sampling sites the corresponding 30si values are highly variable 0 3 to 2 2 and decrease with depth at each site all groundwater 30si values are lower than seawater and most values are lower than dissolved 30si of freshwater discharge indicating a significant amount of lithogenic silica dissolution in beach sediments in contrast to open north sea sediments diatom dissolution or formation of authigenic silica in beach sediments is very low ca 5 mol si g 1 silica discharge from the beach to the coastal ocean is estimated as approximately 210 mol si yr 1 per meter shoreline considering the extent of coastline this is at least for the study area a significant amount of the total si budget and amounts to ca 1 of river and 3 5 of backbarrier tidal flat area si input

pleistocene sedimentary facies of the gran dolina archaeo paleoanthropological site sierra de atapuerca burgos spain abstract gran dolina is a cavity infill of the sierra de atapuerca containing three important early and middle pleistocene archaeo paleontological layers including hominid bones fauna and lithic remains due to the relevance of this site to understand human evolution in europe it is essential to define in detail the sedimentary processes and environments associated with the archaeological remains gran dolina has a 19 m thick sedimentary infill divided into 11 lithostratigraphic units in this work we describe the sedimentary facies of the early and middle pleistocene units and we update its stratigraphy for that purpose we have studied the stratigraphic excavation profiles available where we have combined field observations with laboratory sedimentary analysis sieving laser diffraction and image analysis to characterize the texture and structure of the sediments through these studies 19 sedimentary facies have been distinguished grouped as sediment gravity flow facies fluvial facies and autochthonous facies the facies associations indicate two main trends in the allochthonous sequence during the early pleistocene td4 td7 the cavity acted as a stream sink where channel and floodplain facies migrated along the sequence and were interbedded with lateral gravity sediment flows on the other hand the middle pleistocene sequence between td7 and td10 is dominated almost exclusively by gravity flows at least three main entrances have been inferred from input directions of the sediments which changed over time sediment characteristics have allowed us to preliminarily infer environmental conditions around the cavity

exploration of driving mechanisms of equilibrium boron isotope fractionation in tourmaline group minerals and fluid a density functional theory study abstract the equilibrium boron isotope fractionations 3 4 11b tur fluid between tourmaline mineral groups and fluids at 0 5 gpa 600 1000 k are investigated using density functional theory calculations the first solvent shell controls boron isotope fractionation in solution where the values of both h3bo3 and b oh 4 decrease with increasing numbers of hydrogen bonds in supercritical fluids the weakening of hydrogen bonds and the diversity in configurations of hydrated boron species both contribute to variations in the vibrational frequencies the 1000ln tur fluid value increases with increasing mg fe mg ratios in the dravite schorl solid solution series this effect together with the crystallization sequence predicted from the gibbs free energies of tourmaline formation accounts well for the association of boron isotope and chemical zonation observed in zoned tourmaline grains the dependence of boron isotope fractionation on the b o bond length in tourmaline group minerals reflects the changes in relevant molar volumes caused by differences in the mass and charge of the atoms occupying the x y and z sites of tourmalines this study suggests that the chemical composition of the tourmaline plays an important role in controlling the boron isotope composition in tourmalines crystallized from hydrothermal systems

coupled core mantle thermal evolution of early mars 1 several arguments point out that at the end of planetary accretion the core of mars was likely to be much hotter than its mantle resulting in the formation of a completely or partially molten thermal boundary layer at the base of the mantle here we address the following questions how did the superheated core cool and what role did it play in the early mantle dynamics of mars we divide the coupled core mantle evolution of early mars into two stages during the first stage vigorous convection within the molten boundary layer removes the heat from the core so that the boundary layer expands up as the boundary layer gets thicker the temperature of the layer decreases eventually the temperature of the molten boundary layer drops down to the temperature for the rheological transition melt fraction 40 within 100 years this stage is described by a parameterized convection approach the second stage is modeled in spherical shell geometry using the fully three dimensional finite element code citcoms a single plume superplume forms by the instability of the thermal boundary layer the superplume stage lasts much longer on the scale of millions to hundreds of millions of years depending on the mantle viscosity during both stages of evolution the heat flux can easily satisfy the requirements for the dynamo

thermal expansion measurements at very high pressure systematics and a case for a chemically homogeneous mantle new data on thermal expansivity of iron to over 400 kbar in laser and electrically heated diamond anvil cells and on mgo and forsterite from spectroscopic data to over 200 kbar and previously measured adiabats boehler 1982 imply that at high pressure may be described by a constant value of 1n 1nv t 5 5 0 5 this behavior is supported by previous measurements at lower pressures on a large variety of materials densities of magnesio wustite and silicate perovskite in a pyrolitic ratio calculated at lower mantle conditions using a finite strain equation and at high pressures using the above systematics match those in prem through the entire lower mantle making a strong case for a uniform mantle

an earth moon silicon isotope model to track silicic magma origins abstract a comparison between terrestrial and lunar igneous rocks reveals that si isotope compositions become slightly though significantly enriched in heavy isotopes from basalts to granites and anorthosites as a function of the rock sio 2 concentration and or tectosilicate content this is interpreted as the result of a global igneous differentiation process that leads to an increased amount of tectosilicates in the rocks this relationship of increasing degree of melt polymerization with increasingly heavy silicon isotope composition is particularly apparent in lunar rocks the terrestrial trend however is more scattered given the sensitivity of si isotopes to water rock interactions it is likely that the more erratic terrestrial trend reveals the involvement of water that does not occur on the moon hence si isotopes appear to reflect the occurrence of low temperature water rock interaction products like clay minerals in the source of peraluminous leucogranites conversely the heavy silicon isotope composition of some andesites possibly trace the input of fluids involved in subduction zones and or interaction of the oceanic crust with isotopically heavy seawater before subduction

rheology of olivine and the strength of the lithosphere in order to throw some light on the rheological behavior of the upper mantle of the earth a detailed series of high temperature deformation experiments has been performed on olivine single crystals at 1 atm pressure under highly controlled thermodynamic conditions the effects of stress temperature oxygen fugacity and orthopyroxene activity on the deformation rate of olivine have been carefully measured for the major high temperature slip systems these experimental results have been extrapolated to the pressures and strain rates of the upper mantle to provide new insight into the mechanical behavior of the mantle and a better constrained approach to extrapolation of laboratory deformation data to the conditions present in the upper mantle the authors suggest that extrapolations in stress provide the most reliable means for extending laboratory creep data to upper mantle strain rates they also predict that in the dislocation creep field the bulk of the strain in olivine in the upper mantle is accommodated by the 010 100 slip system in addition true mantle strengths are probably most accurately modeled using the experimental data for samples oriented favoring the 010 001 slip system however the reliable prediction of mantle strengths requires highly accurate temperature versus depth relationships and good indicationsmore of the local oxygen fugacity in the mantle less

karst features interpretation using ground penetrating radar a case study from the sierra de atapuerca spain abstract we used ground penetrating radar gpr to identify a variety of karstic features in the archaeo paleontological sites of the sierra the atapuerca burgos spain the aim of this study was to discover the structure of the caves exposed in the 19th century by a railroad trench specifically their bottom part which remains covered under the railroad current surface for this purpose three gpr grids were made in the trinchera area next to the sites of the sima del elefante the galeria complex and the gran dolina the analysis of both the radar wave signatures and the radar amplitude reflections together with the existing data on the caves allowed for the definition of the location and geometry of different karstic features including air filled caves sediment filled caves and bedrock structures two mechanical boreholes drilled next to the sites also added the information on the stratigraphy of the bottom part of the caves and helped with the interpretations of the gpr survey we could distinguish between the intact geological features and the areas that were altered by the railroad construction and the later quarrying activity

si isotope systematics of meteorites and terrestrial peridotites implications for mg si fractionation in the solar nebula and for si in the earth s core abstract high precision si isotope ratios have been measured for a series of meteorites and terrestrial samples using high resolution multi collector icp ms our results differ from those reported in an earlier study georg et al 2007 si in the earth s core nature 447 1102 1106 in two important aspects first our data set reveals systematic differences in 30 si between different chondrite groups that are correlated with their mg si elemental ratio second in agreement with the previous study 30 si for the terrestrial samples are higher than values for chondrites but the difference between the bulk silicate earth bse and the carbonaceous chondrites 30 si bse c arbonaceous chondrites 0 08 0 04 1 standard deviation is about a factor of 2 smaller than previously reported the 30 si versus mg si trend defined by the chondrite groups can be explained by reaction of olivine with a sio rich vapor to form enstatite starting from a carbonaceous chondrite composition in contrast the difference between the bse and carbonaceous chondrites must reflect a different process and can be explained by incorporation of si into the earth s core during metal silicate equilibration in a deep magma ocean the observed si isotope fractionation is consistent with the temperatures and pressures of metal silicate equilibration derived from siderophile element abundances in the earth s mantle

elasticity of a grossular pyrope almandine garnet the single crystal elastic properties of a natural grossular rich garnet solid solution have been measured at ambient conditions using brillouin spectroscopy this garnet sample is unusual for a grossular in that it contains appreciable pyrope and almandine components with a composition of gr48 4py27 6alm23 4sp0 6 it is thus suitable for investigating the variation of elastic properties with composition in ca rich garnet solid solutions that are stable only at high pressure the values obtained for the bulk modulus k 170 4 6 and for the shear modulus 101 6 3 of the garnet examined in this study vary by less than 1 from those obtained from a weighted sum of the end member moduli this suggests that any composition in the grossular pyrope almandine system which comprise the majority of upper mantle garnets is accurately estimated with this simple approach more complex elasticity composition variations observed for the grossular andradite garnets may be specific to garnet solid solutions where the cation substitutions occur at six coordinated crystallographic sites

2d and 3d ert imaging for identifying karst morphologies in the archaeological sites of gran dolina and galeria complex sierra de atapuerca burgos spain abstract this work focusses on the sierra de atapuerca thinchera karst system in which gran dolina and galeria complex sites are located a total of eight ert profiles were performed over an area that covers both sites with the aim of identifying the dimensions and continuity of these passages the interpretation of the 2d and 3d profiles has allowed determining the extension of the conduits as well as the presence of a filled entrance that might be common to both sites with the aid of 2d modelling experiments it was also possible to resolve some of the hypothesis raised from the interpretation of the 2d pseudosections all these data have ultimately lead to a better understanding of the karst and sites formation process

onset of thermal chemical convection with crystallization and its geological implications 1 buoyancy forces derived from either thermal or compositional origins or both are the main driving mechanisms for dynamic instabilities within natural fluid systems crystallization can contribute to the compositional buoyancy due to density differences between the original bulk fluid and the residual fluid of crystallization depending on the density contrast the compositionally induced buoyancy force may enhance or decrease the thermal buoyancy force established by the prevailing temperature gradient of the environment the purpose of this paper is to examine the complex interactions between the compositional and the thermal buoyancy forces within a thermal chemical system incorporating the effects of crystallization like a thermal chemical system without crystallization also known as an ordinary double diffusive system our results identify a dynamic and an oscillatory instability boundary in a traditional stability diagram a dynamic instability boundary separates the stability diagram into two regimes on one side of the boundary fluid dynamic perturbations will grow indefinitely leading to rigorous convection eventually on the other side perturbations decay in time and the system will ultimately return to a static condition in the absence of crystallization the oscillatory instability boundary defines a regime where perturbations lead to oscillatory motions in the presence of crystallization however other investigators have observed the formation of convective layering despite these similarities our results show significant differences in flow characteristic when crystallization is present when crystallization is taken into consideration the slope of a dynamic instability boundary is no longer governed by the diffusion coefficient ratio between heat and composition alone the release of latent heat and the location of crystallization also play some roles in addition convective layering i e the oscillatory instability regime is no longer confined within a domain where fluid composition is stably stratified it can extend into the compositionally unstable domain as well applications of our results to the solidification of magmatic bodies the formation of columnar joints and the cooling of the outer liquid core are examined the existence of oscillatory instability within the compositionally unstable domain is significant because it suggests that the possible existence of convective layering within a cooling tholeiitic magma body cannot be ruled out in contrast to a conclusion derived from double diffusion studies in the absence of crystallization our analysis also suggests a possible criterion to test if columnar jointing has a double diffusive origin if columnar joints were thermal cracks formed along a preexisting double diffusive fingering pattern as speculated they should occur only in calc alkaline basaltic lava and they are not expected to appear in tholeiitic basalts iron nickel precipitation above the inner outer core boundary operates in a compositionally unstable domain because the residual liquid is expected to be less dense since the condition is unstable both thermally and compositionally at this boundary solidification should lead to rigorous convection above the inner core however the existence of convective layering remains a possibility if the latent heat release is sufficient to cause the solidification process to operate within the newly determined oscillatory instability regime although the averaged temperature beneath the core mantle boundary is believed to exceed the melting temperature of iron and nickel local solidification is possible resulting in the production of stabilizing convective layering that can inhibit large scale convection near the top of the liquid outer core

hydroxyl contents of accessory minerals in mantle eclogites and related rocks infrared spectra in the region 3000 to 3800 cm 1 have been measured on coesite kyanite sanidine and rutile occurring in inclusions of eclogite and on garnet and spinel in an inclusion of alkremite from south african kimberites coesite and sanidine contain virtually no h 2o or oh although one sanidine crystal was observed to contain abundant h2o apparently as fluid inclusions of molecular h2o kyanite contains significant oh consistent with previous results for similar samples corundum gives no indication of the presence of h 2o or oh rutile containing significant amounts of fe cr al and nb also contains significant amounts of structural oh garnet in alkremite contains small amounts of molecular h 2o whereas the spinel coexisting with this garnet gives no indication of h 2o or oh indicating that the spinel structure is not able to accommodate significant amounts of oh ammonium contents of all samples were less than the detection limit about 10 ppm

theoretical calculation of equilibrium mg isotope fractionations between minerals and aqueous solutions abstract there are large discrepancies existing in equilibrium mg isotope fractionation calculations and experimental investigations for cases related to mineral vs solution to clarify this confusing issue a newly designed cluster model based quantum chemistry method i e volume variable cluster model vvcm is used to provide equilibrium mg isotope fractionation factors between mg bearing carbonates calcite aragonite dolomite and magnesite amorphous calcium carbonates accs brucite and aqueous species i e mg2 aq mghco3 aq and mgoh aq we find that local configuration sampling of aqueous species is essential to provide precise fractionations between mineral and solution the phonon based periodic boundary method is also used for several minerals and it obtains very similar fractionations with vvcm results our results are very close to those of pinilla et al 2015 although via completely different approaches both of them have included the effect of local configuration disorder however both of them are significantly different from some of experimental results for cases of carbonates vs solutions the existence of various mg bearing species in fluids of experiments the direct incorporation of hydrated mg2 into the solids the mg2 concentration effect and the existence of intermediate precursors e g accs are several possible causes for the mismatches relative to coexisting aqueous mg2 we find that accs will enrich heavy mg isotopes i e 1 45 at 25 c agreeing with previous experimental estimation equilibrium mg isotope fractionation factors between brucite and solutions are also predicted besides we applied vvcm to predict the mg isotope fractionations between high temperature phases i e forsterite diopside enstatite tremolite and spinel the predicted factors are in the order of spinel tremolite diopside enstatite forsterite this study provides a base for understanding the accumulating mg isotope data

water ice phases ii iii and v plastic deformation and phase relationships several of the high pressure crystalline forms of ice exist in the interiors of the larger icy moons of the outer planets guided by the phase relations established by bridgman 75 years ago we have transformed ordinary water ice i to ices ii iii v and perhaps vi we subsequently deformed those phases in a gas deformation apparatus designed for these experiments we found ice ii to be the strongest of the high pressure phases having a strength roughly comparable to that of ice i ice ii is very weak at fixed levels of stress ice iii flows 10 sup 2 10 sup 3 times faster than ice ii we confirm bridgman s 1912 findings that ices iii and v can exist metastably within the ice ii field and in addition find that these phases may be deformed plastically within much of the metastable region without reverting to ice ii the most persistent metastable existence of ice iii occurs in the warmer portions of the ice ii field through which historical and present day temperature pressure profiles in the icy moons pass thus although the stability field of ice iii is small the weakness of this phase may have profoundly influenced the evolution and present day behavior of themore icy moons less

ground penetrating radar soil suitability map of the conterminous united states abstract the performance of ground penetrating radar gpr in soils strongly depends on soil electrical conductivity soils having high electrical conductivity rapidly attenuate radar energy which restricts penetration depths and severely limits the effectiveness of gpr factors influencing the electrical conductivity of soils include the amount and type of salts in solution and the clay content the ground penetrating radar soil suitability map of the conterminous united states is a thematic map showing the relative suitability of soils for gpr applications within comparatively large areas of the united states this map is based on over twenty five years of field observations made throughout the united states and soil attribute data contained in the state soil geographic statsgo database attribute data used to determine the suitability of soils include taxonomic criteria clay content salinity sodium absorption ratio and calcium carbonate content based on additional testing several gpr specific adjustments have been made this paper describes these revisions and outlines the procedures used to develop the revised map the revised map limits areas that are rated as being unsuited for gpr to saline and sodic soils reassesses calcareous and gypsiferous soils and provides a mineralogy override for soils with low activity clays this map can be used to assess the relative appropriateness of gpr for soil investigations within comparatively large areas of the conterminous united states

micro scale silicon isotope heterogeneity observed in hydrothermal quartz precipitates from the 3 7 ga isua greenstone belt sw greenland pillow basalt and chert form integral lithologies comprising many archean greenstone belt packages to investigate details of these lithologies in the 3 7 ga isua greenstone belt sw greenland we measured silicon isotope compositions of quartz crystals by secondary ion mass spectrometry from a quartz cemented quartz amygdaloidal basaltic pillow breccia recrystallized chert and chert clasts thought to represent silica precipitation under hydrothermal conditions the recrystallized chert chert clasts and quartz cement have overlapping 30si values while the 30si values of the quartz amygdules span nearly the entire range of previously published values for quartz precipitates of any age despite amphibolite facies metamorphism we suggest that the heterogeneity is derived from kinetic isotope fractionation during quartz precipitation under disequilibrium conditions in a hydrothermal setting consistent with the pillow breccia origin on the basis of the present data we conclude that the geological context of each sample must be carefully evaluated when interpreting 30si values of quartz

the strength of mantle silicates at high pressures and room temperature implications for the viscosity of the mantle the rheological properties of the upper mantle important in convective and tectonic processes have long been studied through low pressure creep experiments on olivine1 5 in comparison our understanding of deformation in the deep earth is incomplete because there are few experimental constraints on the rheology of the transition zone 400 670 km depth and the lower mantle estimates of the viscosity at these depths have had to rely on geophysical models of for example post glacial uplift the geoid and changes in the earth s rate of rotation6 13 recently we developed techniques for measuring solid state creep at mantle pressures14 and here we use these methods to make direct laboratory measurements of the strength of key mantle minerals we study mg fe 2sio4 olivine representative of about 60 of the upper mantle mg fe 2sio4 spinel which constitutes a large fraction of the transition zone and mg fe sio3 perovskite and perovskite mg fe o magnesiowiistite assemblages which comprise most of the lower mantle all at room temperature and pressures of up to 60 gpa our results suggest that the transition zone may form a layer of relatively high viscosity or strength between the upper and lower mantle a simple theological model shows that this behaviour may be compatible with current geophysical observations

first principles calculations of equilibrium fractionation of o and si isotopes in quartz albite anorthite and zircon in this study we used first principles calculations based on density functional theory to investigate silicon and oxygen isotope fractionation factors among the most abundant major silicate minerals in granites i e quartz and plagioclase including albite and anorthite and an important accessory mineral zircon combined with previous results of minerals commonly occurring in the crust and upper mantle orthoenstatite clinoenstatite garnet and olivine our study reveals that the si isotope fractionations in minerals are strongly correlated with sio4 tetrahedron volume or average si o bond length the 30si enrichment order follows the sequence of quartz albite anorthite olivine zircon enstatite diopside and the 18o enrichment follows the order of quartz albite anorthite enstatite zircon olivine our calculation predicts that measurable fractionation of si isotopes can occur among crustal silicate minerals during high temperature geochemical processes this work also allows us to evaluate si isotope fractionation between minerals and silicate melts with variable compositions trajectory for 30si variation during fractional crystallization of silicate minerals was simulated with our calculated si isotope fractionation factors between minerals and melts suggesting the important roles of fractional crystallization to cause si isotopic variations during magmatic differentiation our study also predicts that 30si data of ferroan anorthosites of the moon can be explained by crystallization and aggregation of anorthite during lunar magma ocean processes finally o and si isotope fractionation factors between zircon and melts were estimated based on our calculation which can be used to quantitatively account for o and si isotope composition of zircons crystallized during magma differentiation

abiologic silicon isotope fractionation between aqueous si and fe iii si gel in simulated archean seawater implications for si isotope records in precambrian sedimentary rocks abstract precambrian si rich sedimentary rocks including cherts and banded iron formations bifs record a 7 spread in 30si 28si ratios 30si values yet interpretation of this large variability has been hindered by the paucity of data on si isotope exchange kinetics and equilibrium fractionation factors in systems that are pertinent to precambrian marine conditions using the three isotope method and an enriched 29si tracer a series of experiments were conducted to constrain si isotope exchange kinetics and fractionation factors between amorphous fe iii si gel a likely precursor to precambrian jaspers and bifs and aqueous si in artificial archean seawater under anoxic conditions experiments were conducted at room temperature and in the presence and absence of aqueous fe ii fe ii aq results of this study demonstrate that si solubility is significantly lower for fe si gel than that of amorphous si indicating that seawater si concentrations in the precambrian may have been lower than previous estimates the experiments reached 70 90 si isotope exchange after a period of 53 126 days and the highest extents of exchange were obtained where fe ii aq was present suggesting that fe ii fe iii electron transfer and atom exchange reactions catalyze si isotope exchange through breakage of fe si bonds all experiments except one showed little change in the instantaneous solid aqueous si isotope fractionation factor with time allowing extraction of equilibrium si isotope fractionation factors through extrapolation to 100 isotope exchange the equilibrium 30si 28si fractionation between fe iii si gel and aqueous si 30sigel aqueous is 2 30 0 25 2 in the absence of fe ii aq in the case where fe ii aq was present which resulted in addition of 10 fe ii in the final solid creating a mixed fe ii fe iii si gel the equilibrium fractionation between fe ii fe iii si gel and aqueous si 30sigel aqueous is 3 23 0 37 2 equilibrium si isotope fractionation for fe si gel systems is significantly larger in magnitude than estimates of a near zero solid aqueous fractionation factor between pure si gel and aqueous si indicating a major influence of fe atoms on si o bonds and hence the isotopic properties of fe si gel larger si isotope fractionation in the fe ii bearing systems may be caused by incorporation of fe ii into the solid structure which may further weaken fe si bonds and thus change the si isotope fractionation factor the relatively large si isotope fractionation for fe si gel relative to pure si gel provides a new explanation for the observed contrast in 30si values in the precambrian bifs and cherts as well as an explanation for the relatively negative 30si values in bifs in contrast to previous proposals that the more negative 30si values in bifs reflect hydrothermal sources of si or sorption to fe oxides hydroxides

mineral physics of iron and of the core mineral physics is a field of materials physics and materials chemistry confined to the study of materials pertinent to the earth and planetary interiors in the last two decades emphasis has been given to research on the values of physical properties in materials appropriate to the earth s mantle and core braginsky and roberts 1995 listed the physical properties that play a key role in their analysis of convection of the earth s core and the dynamo these connect mineral physics to geomagnetism of the core this review will be concerned primarily with progress made in the last four years in refining values of these properties

desilication in archean weathering processes traced by silicon isotopes and ge si ratios abstract the influence of continental weathering on oceanic seawater compositions in the precambrian is poorly understood here we combine si isotopes and ge si ratios of a mesoarchean paleosol 2 95 ga and overlying shales as proxies for weathering processes and si mass transfer at the early earth s surface results show that as with modern soils neoformation of secondary clay minerals in the paleosol was associated with the fractionation of si isotopes and ge si ratios in response to chemical weathering and soil desilication furthermore the loss of fe bearing minerals most likely fe bearing smectites produced additional controls on si and ge mobility through the coupled dissolution and re precipitation of clay minerals under reductive conditions opposite fractionation behaviors are observed neoformed secondary clay minerals acted as a 28 si and ge sink whereas the leaching of fe bearing minerals released 28 si and ge into soil solutions an attempt to estimate 30 si and ge si signatures of released dissolved elements into soil solution provided 30 si and ge si signatures of about 0 1 and 1 4 mol mol respectively furthermore shales deposited shortly after paleosol formation display 30 si and ge si compositions that may be explained as mixtures of the recognized paleosol components the shale record suggests that weathering induced desilication and leaching of fe bearing minerals to a lesser extent might have been widely effective during the mesoarchean for the transfer of si from the continents to the hydrosphere comparison of si isotopes recorded in detrital sediments and chemical precipitates over time might thus provide a useful supplementary tool to decipher the impact of putative increases in continental weathering and desilication relative to changes in hydrothermal and continent derived solute inputs to ocean and ocean cooling

quantitative reconstruction of late cenozoic landscapes a case study in the sierra de atapuerca burgos spain we have developed a method to reconstruct palaeorelief by means of detailed geomorphological and geological studies geostatistical tools gis and a dem this method has been applied to the sierra de atapuerca ne duero basin burgos spain allowing us to model a three dimensional reconstruction of the relief evolution from the middle miocene to the present the modelling procedure is based on geostatistical recovery of the palaeosurfaces characteristic of each geomorphological evolution stage using polynomial regressions trend surfaces and kriging the modelling of morphology trends has been useful in establishing new geological and geomorphological relationships in the geodynamic evolution of this basin such as uplift quantification correlation of erosion surfaces and sedimentary units and the evolution of fluvial base levels the palaeosurface reconstruction together with an analysis of the slope retreat have allowed us to reconstruct the palaeoreliefs that define the late cenozoic landscape evolution of this area where the lower and middle pleistocene archaeopalaeontological sites of the sierra de atapuerca are located copyright 2007 john wiley sons ltd

shear modulus and internal friction of calcite rocks at seismic frequencies pressure frequency and grain size dependence abstract the shear modulus g and associated internal friction q 1 have been measured at seismic frequencies for a suite of four essentially monomineralic calcite rocks with grain sizes ranging from 4 to 1000 m the measurements are based on a previously described technique for the observation of forced torsional oscillations of a series combination of a rock cylinder and a steel standard under high confining pressure at room temperature the behaviour of each rock has been studied as a function of strain amplitude 10 8 10 6 maximum at surface pressure 0 300 mpa and oscillation period 1 300 s no evidence is found of any departure from linearity in the range of strain amplitudes studied corrections which are significant only at the shortest periods 1 3 s have been applied to the raw data to account for the influence of torques exerted on the specimen assembly by the gas pressure medium up to about 100 mpa increase in pressure results in a marked increase in g and decrease in q 1 attributable to the closure of crack porosity except in the fine grained solnhofen limestone in which both g and q 1 are insensitive to change in pressure indicative of the virtual absence of crack porosity at higher pressures g is much less pressure sensitive and q 1 is essentially pressure independent with values less than 0 001 in all four rocks since the rock specimens were jacketted under conditions of normal humidity these relatively low values of q 1 indicate a diminished role for adsorbed water in the anelasticity of rocks at high effective pressures within the pressure independent regime q 1 is essentially independent of frequency for periods of 3 100 s and increases by only 30 as the grain size decreases from 1000 to 4 m thus within this regime it is concluded that the observed value of q 1 results to a large degree from an intracrystalline mechanism with a broad range of relaxation times the possibility of significant dislocation damping will be discussed

silicon isotope fractionation during magmatic differentiation abstract the si isotopic composition of earth s mantle is thought to be homogeneous 30 si 0 29 0 08 2 s d and not greatly affected by partial melting and recycling previous analyses of evolved igneous material indicate that such rocks are isotopically heavy relative to the mantle to understand this variation it is necessary to investigate the degree of si isotopic fractionation that takes place during magmatic differentiation here we report si isotopic compositions of lavas from hekla volcano iceland which has formed in a region devoid of old geochemically diverse crust we show that si isotopic composition varies linearly as a function of silica content with more differentiated rocks possessing heavier isotopic compositions data for samples from the afar rift zone as well as various igneous usgs standards are collinear with the hekla trend providing evidence of a fundamental relationship between magmatic differentiation and si isotopes the effect of fractionation has been tested by studying cumulates from the skaergaard complex which show that olivine and pyroxene are isotopically light and plagioclase heavy relative to the si isotopic composition of the earth s mantle therefore si isotopes can be utilised to model the competing effects of mafic and felsic mineral fractionation in evolving silicate liquids and cumulates at an average sio 2 content of 60 wt the predicted 30 si value of the continental crust that should result from magmatic fractionation alone is 0 23 0 05 2 s e barely heavier than the mantle this is at most a maximum estimate as this does not take into account weathered material whose formation drives the products toward lighter 30 si values mass balance calculations suggest that removal of continental crust of this composition from the upper mantle will not affect the si isotopic composition of the mantle

phase transformations in a harzburgite composition to 26 gpa implications for dynamical behaviour of the subducting slab abstract the mineralogy adopted by a depleted harzburgite composition has been studied over the pressure interval 5 26 gpa at temperatures of 1300 1400 c the pyroxene garnet component of the harzburgite composition harzburgite minus 82 wt olivine transforms to majorite garnet by 18 19 gpa and further disproportionates to the assemblage of garnet stishovite mg 2 sio 4 spinel above 20 gpa at still higher pressures first ilmenite 22 24 gpa and then perovskite mgsio 3 24 26 gpa are found to coexist with garnet garnet disappears at 26 gpa and almost complete transition to perovskite is achieved at this pressure the mineral proportions and density profiles in the subducting oceanic lithosphere modelled by a combination of 80 harzburgite 20 primitive morb compositions are calculated as a function of depth under conditions isothermal with surrounding pyrolite mantle and also for a temperature distribution in which the slab is substantially cooler than surrounding mantle to below 700 km under isothermal conditions the slab has a density similar to surrounding mantle to a depth of 600 km however between 600 and 700 km the slab is up to 0 08 g cm 3 denser than surrounding mantle this is caused primarily by the higher alumina content in pyrolite as compared to harzburgite which causes the transition to perovskite in pyrolite to occur at substantially higher pressures than in harzburgite the presence of alumina also smears out the garnet perovskite transition in pyrolite over a depth interval of 50 km whereas this transformation is much sharper in the harzburgite composition calculations based on the observed phase equilibria also show that a subducted cool slab remains much denser by 0 1 0 3 g cm 3 than surrounding mantle to a depth of 700 km but possesses a density similar to surrounding mantle below this depth these results have important implications for the dynamical behaviour of slabs possessing different thermal regimes when they encounter the 670 km discontinuity and also for the nature of this discontinuity

early transient superplumes and the origin of the martian crustal dichotomy 1 the large temperature difference between the core and mantle of mars at the end of planetary accretion creates a hot internally convecting thermal boundary layer at the base of the mantle whose viscosity is several orders of magnitude lower than the viscosity of the mantle above it theoretical analysis and numerical simulations of the instability of this thermal boundary layer show that it is likely that only one large plume forms this superplume may play a role in the formation of crustal dichotomy and generation of the magnetic field in the early history of mars

redox state during core formation on asteroid 4 vesta abstract core formation is the main differentiation event in the history of a planet however the chemical composition of planetary cores and the physicochemical conditions prevailing during core formation remain poorly understood the asteroid 4 vesta is the smallest extant planetary body known to have differentiated a metallic core howardite eucrite diogenite hed meteorites which are thought to sample 4 vesta provide us with an opportunity to study core formation in planetary embryos partitioning of elements between the core and mantle of a planet fractionates their isotopes according to formation conditions one such element silicon shows large isotopic fractionation between metal and silicate and its partitioning into a metallic core is only possible under very distinctive conditions of pressure oxygen fugacity and temperature therefore the silicon isotope system is a powerful tracer with which to study core formation in planetary bodies here we show through high precision measurement of si stable isotopes that hed meteorites are significantly enriched in the heavier isotopes compared to chondrites this is consistent with the core of 4 vesta containing at least 1 wt of si which in turn suggests that 4 vesta s differentiation occurred under more reducing conditions iw 4 than those previously suggested from analysis of the distribution of moderately siderophile elements in heds

palaeogeographical reconstruction of the sierra de atapuerca pleistocene sites burgos spain abstract the sierra de atapuerca is an anticlinal ridge of mesozoic carbonate rocks on the nw edge of the iberian chain northern spain burgos surrounded by subhorizontal continental sediments of the ne duero cenozoic basin under endorheic conditions the shift to exorheic conditions in the duero basin lead to the onset of an episodic downcutting phase and the development of the atapuerca multilevel cave system containing several sites from the early and middle pleistocene in this work we have reconstructed the pleistocene palaeogeographical evolution of the sw flank of the sierra de atapuerca where these archaeological sites are located the study is based on a detailed geomorphological and geological analysis combined with global navigation satellite system gnss and 3d lidar data and gis modeling these techniques have been applied to analyse the small valleys and the interfluve on the sw flank of the sw sierra de atapuerca the results were combined with the regional base levels recorded by fluvial terraces and the chronostratigraphic sequences of the sierra de atapuerca sites these reconstructions have allowed us to model the palaeogeographical evolution in the nearby area of the cave sites during the early middle pleistocene coupling the main formation phases of the sites with the local physical landscape changes that occurred outside the caves surface processes are defined by incision phases entailing mitigate knickpoint recession and slope retreatment and local aggradational phases associated with caves opened and captured by fluvial incision this reconstruction provides the local physical palaeogeographical habitats developed during the pleistocene hominid occupation of the sierra de atapuerca

silicon in the earth s core the earth and moon have iron isotopic abundances that are slightly heavy compared with mars the asteroid vesta and primitive meteorites the reason for this has been unclear one suggestion is that there was a large scale isotopic equilibration during the giant impact the collision between the early earth and a mars sized body that created the moon but this has seemed unlikely given that most other elements do not show the effect an analysis of 44 meteorite and terrestrial samples now shows that the silicon isotopic compositions of basaltic rocks from the earth and moon are also distinctly heavy the finding is consistent with the isotopic equilibration model and it suggests that silicon was already partitioned into the earth s core as a light element before the moon formed the silicon isotopic compositions of basaltic rocks from the earth and moon are distinctly heavy the similar isotopic composition of the bulk silicate earth and the moon are consistent with large scale isotopic equilibration during the giant impact indicating that si was already a light element in the earth s core before the moon formed small isotopic differences between the silicate minerals in planets may have developed as a result of processes associated with core formation or from evaporative losses during accretion as the planets were built up basalts from the earth and the moon do indeed appear to have iron isotopic compositions that are slightly heavy relative to those from mars vesta and primitive undifferentiated meteorites1 2 3 4 chondrites explanations for these differences have included evaporation during the giant impact that created the moon when a mars sized body collided with the young earth however lithium5 and magnesium6 lighter elements with comparable volatility7 8 9 reveal no such differences rendering evaporation unlikely as an explanation here we show that the silicon isotopic compositions of basaltic rocks from the earth and the moon are also distinctly heavy a likely cause is that silicon is one of the light elements in the earth s core we show that both the direction and magnitude of the silicon isotopic effect are in accord with current theory10 based on the stiffness of bonding in metal and silicate the similar isotopic composition of the bulk silicate earth and the moon is consistent with the recent proposal11 that there was large scale isotopic equilibration during the giant impact we conclude that si was already incorporated as a light element in the earth s core before the moon formed

silicon isotopes in meteorites and planetary core formation the silicon si isotope compositions of 42 meteorite and terrestrial samples have been determined using mc icpms with the aim of resolving the current debate over their compositions and the implications for core formation no systematic 30si differences are resolved between chondrites 30si 0 49 0 15 2 sd and achondrites 30si 0 47 0 11 2 sd although enstatite chondrites are consistently lighter 30si 0 63 0 07 2 sd in comparison to other meteorite groups the data reported here for meteorites and terrestrial samples display an average difference 30sibse meteorite 0 15 0 10 which is consistent within uncertainty with previous studies no effect from sample heterogeneity preparation chemistry or mass spectrometry can be identified as responsible for the reported differences between current datasets the heavier composition of the bulk silicate earth is consistent with previous conclusions that si partitioned into the metal phase during metal silicate equilibration at the time of core formation fixing the temperature of core formation to the peridotite liquidus and using an appropriate metal silicate fractionation factor e 0 89 the 30sibse meteorite value from this study indicates that the earth core contains at least 2 5 and possibly up to 16 8 wt si

assessing automated image analysis of sand grain shape to identify sedimentary facies gran dolina archaeological site burgos spain abstract gran dolina is a cave sierra de atapuerca spain infilled by a 25 m thick sedimentary record divided into 12 lithostratigraphic units that have been separated into 19 sedimentary facies containing early and middle pleistocene hominin remains in this paper an automated image analysis method has been used to study the shape of the sedimentary particles since particle shape is interpreted as the result of sedimentary transport and sediment source this study can provide valuable data about the sedimentological mechanism of sequence formation the shape of the sand fraction in 73 samples from gran dolina site and sierra de atapuerca was analyzed using the malvern morphologi g3 an advanced particle characterization tool in this first complete test we used this method to the published sequence of gran dolina defined previously through field work observations and geochemical and textural analysis the results indicate that this image analysis method allows differentiation of the sedimentary facies providing objective tools to identify weathered layers and measure the textural maturity of the sediments channel facies have the highest values of circularity and convexity showing the highest textural maturity of particles on the other hand terra rossa and debris flow samples show similar values with the lowest particle maturity

thermodynamics and lattice vibrations of minerals 5 applications to phase equilibria isotopic fractionation and high pressure thermodynamic properties in previous papers in this series a model that uses available elastic structural and spectroscopic data on minerals has been used to predict the thermodynamic functions cv heat capacity s entropy e internal energy and f helmholtz free energy in this paper four applications to problems of current geochemical and geophysical interest are presented 1 interpretation of complex trends of calorimetric data 2 calculation of phase equilibria 3 calculation of oxygen isotopic fractionation factors and 4 estimation of the effect of pressure on thermodynamic functions the model demonstrates that trends in high temperature thermodynamic properties of silicates are determined by the position and relative numbers of high frequency modes generally antisymmetric si al o stretching modes the position of these modes varies systematically with degree of polymerization of tetrahedra and therefore high temperature calorimetric behavior is relatively systematic as a function of crystal structure and mineral composition trends at low frequency are much more complex because the low frequency optic modes that most strongly influence the low temperature thermodynamic functions depend in a complex way on the size coordination and mass of cations and various polyhedra in the minerals the heat capacity curves of kyanite andalusite and sillimanite and of quartz coesite and stishovite show crossovers that cannot be explained by debye theory which accounts only for acoustic mode behavior but can be explained by the model spectra proposed because proper account is taken of the changing low and high frequency optic modes upon polymorphic transformations the proposed model is sufficiently accurate that phase equilibrium problems can be addressed the quartz coesite stishovite equilibrium curves the kyanite andalusite sillimanite triple point and the breakdown of albite to jadeite plus quartz are cited as specific examples for each example predicted slopes of equilibrium curves agree moderately well to excellently with slopes determined experimentally the calculated slopes are sensitive to spectroscopic parameters particularly to the distribution of optic modes in the far infrared this sensitivity is discussed in detail for the albite breakdown reaction the model can be used for prediction of isotopic fractionation factors if spectra of the isotopic forms of the mineral are known or postulated a simple set of rules for generating hypothetical spectra of 18o minerals from measured spectra of the 16o forms is given reduced partition functions are calculated for 13 minerals at 298 k the model values of reduced partition function 1000 ln of these minerals decrease in the order quartz calcite albite muscovite clinoenstatite anorthite diopside pyrope grossular zircon forsterite andradite rutile in good agreement with experimental data at 1000 k the first six minerals show small crossovers so that the order becomes calcite muscovite albite quartz anorthite and clinoenstatite the differences in 1000 ln at high temperature for these minerals are so small that the model probably cannot address the deviations from experimental trends the model clearly defines the region in which the fractionation factors do not follow a 1 t trend and should be useful for extrapolation of experimental data to low temperatures finally a modified gruneisen parameter model is proposed for shift of the lattice vibrational frequencies under compression and thermodynamic properties to 1000 kbar 1000 k are given for nine minerals at 1 mbar the predicted decrease in entropy at 298 k ranges from 54 of the 1 bar value for periclase to 25 for stishovite

an experimental investigation of the pyroxene garnet transformation in a pyrolite composition and its bearing on the constitution of the mantle abstract the pyroxene garnet transformation in a model pyrolite composition has been investigated over the pressure interval 4 0 to 17 5 gpa at temperatures of 1200 1400 c the transformation is largely completed in the pressure interval 14 16 gpa and a single phase aluminum deficient garnet majorite becomes stable above 16 gpa the mineral assemblages and the density and seismic velocity distributions for pyrolite are calculated as a function of depth on the basis of this and other recent experimental data density and seismic velocity profiles calculated for pyrolite are consistent with models based on seismic observations to a depth of 550 km if the existence of a high density velocity gradient between 550 km and 650 km is confirmed the presence of further phase transformations in majorite and or some degree of chemical heterogeneity in this depth interval would be indicated

melting of the fefeo and the fefes systems at high pressure constraints on core temperatures melting temperatures of feo fes and fes2 have been accurately determined in a hydrostatic inert pressure environment up to about 0 5 mbar using a new yttrium lithium fluoride ylf heating laser the melting curve for feo is in perfect agreement with data obtained from multi anvil experiments at 160 kbar 1 but is in stark disagreement with previous laser heating experiments 2 preliminary measurements show strong melting depression on mixtures of fe and fes whereas mixtures of fe and feo were observed to melt close to the melting curve of iron the kraut kennedy melting relationship 3 in which the melting temperature is a linear function of volume is successfully tested in this study for li na k fe fes fes2 and feo to compressions up to 30 at 1 36 mbar core mantle boundary cmb feo fe and fes are estimated to melt at 3670 3260 and 3060 100 k respectively assuming outer core compositions with about 60 fe and about 40 feo or fes and a solid solution system the melting temperature at the cmb on the core side would be 3300 k 200 k compared to a temperature at the bottom of the mantle of 2650 100 k if these systems exhibit eutectic behaviour the melting gradient through the outer core would have to be substantially higher than the adiabatic gradient in order to maintain a thermal boundary at the cmb the present melting data and experimental constraints on the adiabatic gradient in the outer core suggest a temperature at the inner core outer core boundary of nearly 4200 k

constraints on lower mantle composition and temperature from density and bulk sound velocity profiles recent studies comparing density from the seismological model prem to that predicted for various perovskite and magnesiowustite phase assemblages under lower mantle conditions suggest that the lower mantle is a few percent denser than reasonable candidates for upper mantle composition such as pyrolite this has been interpreted as evidence for an iron enriched lower mantle in addition to density bulk sound velocity provides an important constraint upon proposed lower mantle compositions being independent of the shear modulus has several desirable characteristics experimentally it can be determined in the laboratory by density measurements under static compression seismologically it is not affected by attenuative dispersion and is expected to be much less laterally heterogeneous than p or s wave velocities we have calculated and along lower mantle adiabats as functions of iron magnesium content xmg and silica content xpv and compared them to values obtained from prem for a reasonable temperature estimate at the top of the lower mantle tlm of 2000 k we find that the data are most compatible with a lower mantle enriched in fe in agreement with previous studies in addition the data require that silica enrichment accompany this fe enrichment furthermore increasing tlm increases both the required fe and si content with a high assumed tlm 2700 k the data can be satisfied by low xmg values but even a pure perovskite lower mantle is too slow compared to thus assuming no free sio2 in the lower mantle this provides an upper bound on tlm of approximately 2700 k finally conclusions regarding the composition and temperature of the lower mantle are strongly dependent upon uncertainties in estimated thermoelastic parameters and upon choice of a seismological model most importantly neither fe nor si enrichment is required if the zero pressure volume coefficient of thermal expansion of perovskite is about 2 5 10 5k 1 rather than 4 0 10 5k 1 at high temperatures alternatively but less probably fe and si enrichment are not required if the average of the lower mantle is 1 0 less than given by prem the si enrichment is not required if the average of the lower mantle is 0 5 slower than pkem closer to the value given by the body wave model derived from the jeffreys bullen tables or if the lower mantle is anomalously cold with tlm 1700 k

the dynamics of si cycling during weathering in two small catchments in the black forest germany traced by si isotopes abstract silicon stable isotopes have emerged as a powerful proxy to investigate weathering because si uptake from solution by secondary minerals or by the vegetation causes significant shifts in the isotope composition in this study we determined the si isotope compositions of the principle si pools within two small catchments located on sandstone and paragneiss respectively in the temperate black forest germany at both settings clay formation is dominated by mineral transformation preserving largely the signature of parental minerals with 30si values of around 0 7 bulk soils rich in primary minerals are similar to bulk parental material with 30si values close to 0 4 topsoils are partly different because organic matter degradation has promoted intense weathering leading to 30si values as low as 1 0 water samples expose highly dynamic weathering processes in the soil zone 1 after spring snowmelt increased release of doc and high water fluxes trigger clay mineral dissolution which leads to 30si values down to 0 7 and 2 in course of the summer si uptake by the vegetation and secondary mineral formation drives dissolved si to typical positive 30si values up to 1 1 groundwater with 30si values of around 0 4 records steady processes in bedrock reflecting plagioclase weathering together with kaolinite precipitation an isotope mass balance approach reveals incongruent weathering conditions where denudation of si is largely driven by physical erosion erosion of phytoliths contributes 3 to 21 to the total si export flux which is in the same order as the dissolved si flux these results elucidate the si dynamics during weathering on catchments underlain of sedimentary origin prevailing on the earth surface and provide therefore valuable information to interpret the isotope signature of large river systems

equilibrium isotopic fractionation between aqueous zn and minerals from first principles calculations abstract theoretical mineral solution equilibrium isotopic fractionation can contribute to the interpretation of zn isotopic compositions in this study we investigate equilibrium isotopic fractionation properties of hexaaquo zinc complex a major zn aqueous species using first principles molecular dynamics fpmd based on density functional theory dft pentaaquo and tetraaquo zinc complexes which can be relevant for specific mechanisms such as adsorption on mineral surfaces are also considered this approach takes into account both configurational and solvation effects that are less easily accounted for in molecular cluster models the logarithmic value of the reduced partition function ratio of aqueous zn ln 66zn 64zn is 2 86 0 04 at 295 k while the same computational approach gave ln 66zn 64zn in the range 2 2 4 1 for various zn bearing minerals for example calculations predict at 295 k equilibrium fractionations between mineral and aqueous zn of 0 46 for primary zinc sulfide sphalerite and of 0 20 and 0 34 for secondary phases gunningite and hydrozincite respectively molecular clusters are also modelled predicting isotopically heavier zn with respect to related fpmd models ln increases by 0 09 to 0 23 these values are small but significant in the zn isotopic system and supports the idea that a proper description of the dynamics of the system and the solvation effect are required for a reliable prediction of the isotopic properties of solvated ions

evaluating the suitability of extended range luminescence dating techniques over early and middle pleistocene timescales published datasets and case studies from atapuerca spain the emergence of alternative luminescence dating techniques such as thermally transferred optically stimulated luminescence tt osl post infrared infrared stimulated luminescence pir irsl and osl dating of individual quartz supergrains has opened up new possibilities for establishing numerical age control on sedimentary deposits that exceed the traditional upper age limits of quartz osl dating in this study we evaluate the reliability of these extended range luminescence dating techniques over middle and early pleistocene timescales using two approaches i a broad scale synthesis of extended range luminescence chronologies published so far as part of known age comparison studies ii a series of new tt osl and pir irsl case studies at the palaeoanthropological sites of galeria sima del elefante and gran dolina atapuerca spain the published known age tt osl datasets n 82 and supergrain osl datasets n 3 display good correspondence i e suitably linear and proportion relationships with associated age control the known age pir irsl datasets n 228 display more inter sample scatter though there is general support for the reliability of more stringent pir irsl protocols and multiple elevated temperature pir irsl approaches over late and middle pleistocene timescales while these reliability assessments are encouraging there remains a clear need for more widespread known age empirical assessments of extended range luminescence techniques beyond 300 400 ka the ages obtained at atapuerca using single grain tt osl and pir irsl measurement temperatures of 225 c pir ir225 are in agreement with independent age control over an age range spanning 240 930 ka in contrast the pir irsl chronologies obtained using a more stringent measurement temperature of 290 c pir ir290 consistently overestimate the expected ages of the atapuerca sequences the single grain tt osl ages obtained at gran dolina permit calculation of a new weighted mean age of 846 57 ka for the homo antecessor palaeoanthropological horizon unit td6 the known age atapuerca case studies highlight the feasibility and advantages of applying tt osl dating at the single grain scale of analysis and demonstrate that the suitability of pir irsl dating protocols can vary significantly at a site or regional scale together our analyses show that no single extended range luminescence dating technique is likely to be universally applicable to all samples collectively however these approaches offer good potential for obtaining reliable chronologies and they are likely to offer the greatest benefits when applied in tandem to individual samples

raman spectroscopy of diamond in ureilite and implication for the origin of diamond most ureilite meteorites contain diamonds that are generally thought to have been formed by shock induced high pressure that converted carbonaceous material to diamond we measured raman spectra of ureilite diamond in order to investigate the origin of such diamonds the fwhm full width at half maximum of the raman line at 1330 cm 1 from diamond in the alh 77257 ureilite is about 10 cm 1 which is narrower than those of artificially shock produced diamonds 20 cm 1 but within the range of vapor growth diamonds measured previously this result suggests that the vapor growth origin of ureilite diamond in an interstellar environment should be considered seriously although further studies are necessary to characterize vapor growth diamonds by measuring the raman line of diamonds synthesized by various methods

mutual interactions of redox couples via electron exchange in silicate melts models for geochemical melt systems the mutual interactions via electron exchange of redox couples in glass forming melts were investigated from both theoretical and experimental points of view a thermodynamic approach for considering the mutual interactions leads to the conclusion that the degree of mutual interaction in the melt should be proportional in part to the difference in relative reduction potentials em of the interacting redox couples experimental studies verify this conclusion for numerous redox couples in several composition temperature oxygen fugacity regimes geochemical systems simultaneously possess many potentially multivalent elements the stabilized redox states in the resulting magmas can be explained in part by mutual interactions and by redox buffering through the central fe iii fe ii couple in the melts

silicon isotope evidence against an enstatite chondrite earth the compositions of earth materials are strikingly similar to those of enstatite chondrite meteorites in many isotope systems although this suggests that earth largely accreted from enstatite chondrites definitive proof of this model has been lacking by comparing the silicon si isotope signatures of several extraterrestrial materials with terrestrial samples we show that they cannot be explained by core formation scenarios involving a bulk earth of enstatite chondrite composition si isotope similarities between the bulk silicate earth and the moon preclude the existence of a hidden reservoir in the lower mantle a necessary condition of the enstatite chondrite model and require an equilibrium process after the moon forming impact a three end member chondritic mixing model for earth reconciles the si isotope similarities between enstatite chondrites and earth

seismic anisotropy and mantle flow seismic anisotropy in the mantle is primarily due to deformation induced lattice preferred orientation lpo of olivine crystals the aim of this paper is to better understand how such lpo is produced by flow and to learn whether observations of seismic anisotropy can be used to infer the local direction of flow within the mantle the basis of the work is a two dimensional theory which describes how lpo evolves during an arbitrary time dependent deformation ribe 1989 i investigate the evolution of lpo beneath ocean ridges above subducted slabs and in thermal convective flows the ocean ridge model predicts that the seismic anisotropy produced at a fast spreading ridge should be greater in magnitude than that produced at a slow spreading ridge and that the fast axis should be more nearly horizontal the subduction zone model predicts that strong seismic anisotropy should be produced above subducted slabs with the fast axis aligned with the slab regardless of the subduction angle the evolution of lpo in typical convective flows is extremely complex and depends strongly on such factors as the mode of heating and the surface boundary conditions in general there is no simple relation between the lpo and the local flow direction in any of the models considered the attempt to use seismic anisotropy to map flow patterns on a global scale is therefore probably unwarranted however the lpo does become aligned with the flow direction when the flow is a progressive simple shear such a flow occurs in limited portions of the mantle beneath the lithosphere at a fast spreading ridge above subducted slabs and in boundary layers beneath rigid surfaces such as continents observations of seismic anisotropy may therefore indicate the sense of shear at shallow depths in the mantle

solubilities of mantle oxides in molten iron at high pressures and temperatures implications for the composition and formation of earth s core the solubilities of several oxide components of the mantle in molten iron have been measured at 16 gpa and 1700 2000 c their relative solubilities are as follows feo cr2o3 mno v2o3 tio2 sio2 mgo al2o3 oxide contents reach significant levels varying from 10 wt feo to 1 wt sio2 at the respective metal oxide eutectics but are very small for mgo and al2o3 the solubilities of these oxides are expected to increase substantially at temperatures above 2000 c and at pressures above 16 gpa and are relevant to the core formation process in the earth individual oxide species dissolve quasi congruently under conditions which maintain oxygen fugacities near the iron wustite buffer however the dissolution of mantle mineral phases is highly incongruent if a mixture of metallic iron and mantle silicates were subjected to increasing pressures and temperatures above 16 gpa and 2000 c the most soluble species feo would first be extracted into the metallic liquid when the feo activity had been lowered sufficiently significant amounts of sio2 would then enter this melt at extremely high temperatures and pressures appreciable amounts of mgo could even dissolve these results provide a background for interpreting recent diamond anvil experiments in which molten iron was observed to react with mantle silicates at temperatures of 2700 3700 c and pressures of 20 70 gpa they also elucidate the nature of chemical reactions between the core and mantle which may occur in the d layer of the lower mantle the differing solubilities of mantle oxides in molten iron place constraints on models of accretion of the earth and of accompanying core formation processes the observation that tio2 is undepleted in the earth s mantle relative to ci chondrites makes it improbable that the core contains a substantial amount of dissolved si or sio2 it therefore seems likely that oxygen as dissolved feo is the principal light element component of the core this conclusion is reconciled more readily with a modified version of homogeneous accretion of the earth than with some current models of heterogeneous accretion accretion of the earth from a population of giant planetesimals would have led to complete melting of the mantle and core at very high temperatures under these conditions nearly all feo and other transition metal oxides would have been extracted from the mantle into the core together with a significant amount of sio2 it is difficult to reconcile the geochemical consequences of this accretion scenario with the present composition of the mantle

extreme silicon isotope fractionation due to si organic complexation implications for silica biomineralization abstract a combination of theoretical predictions and isotopic equilibration experiments using the three isotope method have been performed to assess si isotope fractionation among minerals and aqueous species in the presence of dissolved catechol aqueous si in abiotic ambient temperature aqueous solutions is dominated by the iv coordinated h4sio 4 0 species but the presence of aqueous catechol provokes the formation of a vi fold si catechol complex results show an equilibrium si fractionation factor of 19 between the vi fold coordinated si catechol complex and the iv fold coordinated aqueous silicic acid an amplitude never previously observed for silicon the fractionation between v fold si organo complexes with diolate glyconate or methyllactate groups and silicic acid has also been estimated through theoretical predictions to be about 10 these extreme fractionations can be used to improve our ability to interpret the si isotope compositions of natural solids and in particular those associated with marine silica biomineralization processes e g sponge spicules

the silicon isotopic composition of fine grained river sediments and its relation to climate and lithology abstract the 30si stable isotopic composition of silicon in soils and fine grained sediments can provide insights into weathering processes on continents with important implications on the si budget of modern and past oceans to further constrain the factors controlling the distribution of si isotopes in sediments we have analysed a large number n 50 of separate size fractions of sediments and suspended particulate materials collected near the mouth of rivers worldwide this includes some of the world s largest rivers e g amazon congo mackenzie mississippi murray darling nile yangtze and rivers from the case study areas of the congo river basin and northern ireland silt size fractions exhibit a mean si isotopic composition 30si 0 21 0 19 2 s d similar to that previously inferred for the upper continental crust in contrast clay size fractions display a much larger range of 30si values from 0 11 to 2 16 which yield a global 30siclay of 0 57 0 60 2 s d representative of the mean composition of the average weathered continental crust overall these new data show that the si isotopic signature transported by river clays is controlled by the degree of chemical weathering as inferred from strong relationships with al si ratios at a global scale the clay bound si isotopic composition of the world s largest river systems demonstrates a link with climate defining a general correlation with mean annual temperature mat in corresponding drainage basins while the distribution of si isotopes in river sediments also appears to be influenced by the tectonic setting lithological effects and sediment recycling from former sedimentary cycles our results pave the way for their use as paleo weathering and paleo climate proxies in the sedimentary record

oxygen isotope fractionation in quartz albite anorthite and calcite laboratory measurements of equilibrium oxygen isotope fractionation in quartz albite anorthite and calcite have been carried out by anhydrous exchange between silicates and calcite at temperatures of 600 c and above exchange in these systems is as rapid as exchange between silicates and water fractionation factors can be summarized in the following equations qc 0 38 106t 2 abc 0 57 106t 2 anc 1 59 106t 2 from which the silicate pair fractionations are readily obtained these results are compared with published theoretical estimates as well as data derived from hydrothermal experiments some significant differences are found in particular it is difficult to reconcile all of the hydrothermal data either with theoretical calculations or with the present experimental data the new experiments provide an internally consistent set of fractionation factors suitable for isotopic thermometry and for test of disequilibrium in natural systems

orientation of olivine in dunite from elastic wave velocity measurements there is a strong correlation between the measured elastic anisotropy of dunite and the preferred orientation of its main component olivine olivine is a major constituent of the mantle and dunite is considered representative of upper mantle materials in this report the measured elastic wave velocities for a dunite from hidaka horoman are used to determine the coefficients w1mn of a series expansion of the crystallite orientation distribution function in generalised legendre functions this function gives the probability of a crystallite having a given orientation with respect to a set of axes fixed in the rock the solution to this problem allows construction of crystallographic pole figures which indicate a strong alignment of olivine a axes in agreement with the conclusions of petrofabric examination seismic studies of the crystallite orientation distribution function are therefore feasible and these should lead to a better understanding of the deformation processes associated with flow in the upper mantle

on cooling of the earth s core abstract we have constructed a self consistent model for cooling of the earth s core in which the thermal history of the core is computed as a function of the time evolution of the heat flux delivered to the mantle across the core mantle boundary the temperature profile in the convecting core is first assumed to be adiabatic and its evolution in time is calculated with the only constraint that energy be globally conserved when the temperature at the centre drops below the freezing point of the core alloy the inner core starts growing and cools by conduction it is found that it cannot have reached its present size in more than 1 7 billion years if the heat flux delivered to the mantle becomes less than that conducted down the adiabat the temperature profile becomes subadiabatic in a shell at the top of the core through which heat is evacuated by conduction although it is stable against thermal convection this shell is not necessarily stagnant and may be the seat of motions owing to compositional convection

condensation evaporation melting and crystallization in the primitive solar nebula experimental data in the system mgo sio 2 h 2 to 1 0x10 super 9 bar and 1870 degrees c with variable oxygen fugacity

experimental calibration of silicon and oxygen isotope fractionations between quartz and water at 250 c by in situ microanalysis of experimental products and application to zoned low δ30si quartz overgrowths abstract the interpretation of silicon isotope data for quartz is hampered by the lack of experimentally determined fractionation factors between quartz and fluid further there is a large spread in published oxygen isotope fractionation factors at low temperatures primarily due to extrapolation from experimental calibrations at high temperature we present the first measurements of silicon isotope ratios from experimentally precipitated quartz and estimate the equilibrium fractionation vs dissolved silica using a novel in situ analysis technique applying secondary ion mass spectrometry to directly analyze experimental products these experiments also yield a new value for oxygen isotope fractionation quartz overgrowths up to 235 m thick were precipitated in silica h2o naoh nacl fluids at ph 12 13 and 250 c at this temperature 1000ln 30si qtz fluid 0 55 0 10 and 1000ln 18o qtz fluid 10 62 0 13 yielding the relations 1000ln 30si qtz fluid 0 15 0 03 106 t2 and 1000ln 18o qtz fluid 2 91 0 04 106 t2 when extended to zero fractionation at infinite temperature values of 30si qtz from diagenetic cement in sandstones from the basal cambrian mt simon formation in central north america range from 0 to 5 4 paired 18o and 30si values from individual overgrowths preserve a record of precambrian weathering and fluid transport the application of the experimental quartz growth results to observations from natural sandstone samples suggests that precipitation of quartz at low temperatures in nature is dominated by kinetic rather than equilibrium processes

convection and anisotropy of the inner core estimation of the rayleigh number of the inner core suggests that this region is convecting the flow pattern is likely to produce crystallographic preferred orientation of the elastically anisotropic hexagonal closest packed phase of iron such that compressional wave velocities would be greater in the axial relative to the equatorial direction by roughly 1 percent this result is in agreement with seismological evidence that the inner core is elastically anisotropic

erosion surfaces and neogene landscape evolution in the ne duero basin north central spain abstract we present a chronological model of erosion surface development in the iberian and cantabrian ranges of north central spain we map four erosion surfaces and interpret these to be related to duero basin continental sediments and tectonic activity from upper oligocene to plio pleistocene the oldest erosion surface se1 formed across upper oligocene lower miocene synorogenic deposits while surface se2 was contemporaneous with the middle miocene alluvial systems ending with an uplift stage in the astaracian the two most recent erosion surfaces se3 and se4 developed during extensional tectonic episodes and are associated with the deposition of upper paramo sedimentary units at the end of the miocene upper turolian and alluvial fan deposits known as ranas plio pleistocene with the exception of se1 which seems to be associated with a relatively wet climate the surfaces formed during periods of marked aridity and generally warm temperatures through geostatistical reconstruction of the best preserved surface se2 applying ordinary kriging method to the topography dem of the erosion surface and its correlating sedimentary plains we identify the deformation processes which occurred on this surface after its formation

fine scale heterogeneity in the earth s inner core the seismological properties of the earth s inner core have become of particular interest as we understand more about its composition and thermal state1 2 observations of anisotropy and velocity heterogeneity in the inner core are beginning to reveal how it has grown and whether it convects3 4 the attenuation of seismic waves in the inner core is strong and studies of seismic body waves5 6 have found that this high attenuation is consistent with either scattering or intrinsic attenuation5 the outermost portion of the inner core has been inferred to possess layering and to be less anisotropic than at greater depths7 8 9 10 here we present observations of seismic waves scattered in the inner core which follow the expected arrival time of the body wave reflection from the inner core boundary the amplitude of these scattered waves can be explained by stiffness variations of 1 2 with a scale length of 2 kilometres across the outermost 300 km of the inner core these variations might be caused by variations in composition by pods of partial melt in a mostly solid matrix or by variations in the orientation or strength of seismic anisotropy

static compression and olivine flotation in ultrabasic silicate liquid piston cylinder techniques have been used to observe static compressions of ultrabasic silicate liquids to 6 gpa and 2000 c compressions are measured by bracketing sinking and floating of olivine crystals of known density at run conditions komatiite peridotite and their liquid mixtures with fe2sio4 all show constant density changes with pressure of 0 07 g cm3 gpa along their liquidi these results confirm shock wave studies and ultrasonic studies which show weak compositional effects on compressibility of basic to ultrabasic silicate liquid the techniques converge in supporting the conjecture of stolper et al 1981 that ultrabasic silicate liquids may be denser than their equilibrium coexisting olivines and pyroxenes at high compressions the pressure of this density inversion is 7 8 gpa for the compositions studied olivine flotation provides an important constraint upon earth evolution models that include extensive melting during early differentiation it also provides a mechanism for concentrating high mg si olivine in the upper mantle without unduly perturbing other geochemical parameters a full evaluation of the physical and geochemical consequences is required at an early date

hemispherical variations in seismic velocity at the top of the earth s inner core knowledge of the seismic velocity structure at the top of the earth s inner core is important for deciphering the physical processes responsible for inner core growth1 2 3 previous global seismic studies4 5 6 7 8 9 have focused on structures found 100 km or deeper within the inner core with results for the uppermost 100 km available for only isolated regions10 11 12 here we present constraints on seismic velocity variations just beneath the inner core boundary determined from the difference in travel time between waves reflected at the inner core boundary and those transmitted through the inner core we found that these travel time residuals observed on both global seismograph stations and several regional seismic networks are systematically larger by about 0 8 s for waves that sample the eastern hemisphere of the inner core 40 e to 180 e compared to those that sample the western hemisphere 180 w to 40 e these residuals show no correlation with the angle at which the waves traverse the inner core this indicates that seismic anisotropy is not strong in this region and that the isotropic seismic velocity of the eastern hemisphere is about 0 8 higher than that of the western hemisphere

the nature of the earth s core the properties of the earth s core are overviewed with emphasis on seismologically determined regions and pressures and seismologically measured density elastic wave velocities and gravitational acceleration attention is given to solid state convection of the inner core and it is noted that though seismological results do not conclusively prove that the inner core is convective the occurrence and magnitude of seismic anisotropy are explained by the effects of solid state convection igneous petrology and geochemistry of the inner core a layer at the base of the mantle and contact metasomatism at the core mantle boundary and evolution of the core mantle system are discussed it is pointed out that high pressure melting experiments indicate that the temperature of the core is ranging from 4500 to 6500 k and a major implication of such high temperature is that the tectonics and convection of the mantle as well as the resulting geological processes observed at the surface are powered by heat from the core as a result of the high temperatures along with the compositional contrast between silicates and iron alloy the core mantle boundary is considered to be most chemically active region of the earth

silicon isotope fractionation in silicate minerals insights from first principles models of phyllosilicates albite and pyrope abstract isotopic fractionation factors for oxygen and silicon in phyllosilicates pyrophyllite talc albite and pyrope have been calculated using first principles methods based on density functional theory based on exhaustive analysis of numerical convergence we also update our previous calculations on enstatite and forsterite silicon fractionation properties calculated oxygen isotope fractionations agree well with existing estimates for talc and albite in the case of silicon qualitative agreement is found with natural data for phyllosilicates kaolinite lizardite pyrophyllite talc si isotope fractionation properties appear to be correlated with stoichiometry 1 1000 ln 30 si phyllosilicate quartz a mg t mg eq a al t al eq si eq where si eq si al eq 3 4 al and mg eq 1 2 mg cation equivalents are the charge weighed stoichiometric coefficients of each cation normalized to the charge of the silicon atom and a x t are proportionality coefficients depending on temperature it is suggested that the effect of cation x on si isotope fractionation i e a x t will increase with decreasing electronegativity of x si isotope fractionation is further correlated with si o distances suggesting a crystal chemical explanation for relation 1 in terms of electron donation effects this relationship appears valid for quartz pyrope and enstatite r 2 0 99 n 7 but forsterite is strongly anomalous error of 0 7 at 600 c these models indicate that attention should be given to chemical compositions in si isotope studies relation 1 would explain the enrichment in heavy silicon isotopes accompanying magmatic differentiation