growyouric a step toward a coherent model of the earth s inner core seismic structure a complex inner core structure has been well established from seismic studies showing radial and lateral heterogeneities at various length scales yet no geodynamic model is able to explain all the features observed one of the main limits for this is the lack of tools to compare seismic observations and numerical models successfully we use here a new python tool called growyouric to compare models of inner core structure we calculate properties of geodynamic models of the inner core along seismic ray paths for random or user specified datasets we test kinematic models which simulate fast lateral translation super rotation and differential growth we explore first the influence on a real inner core data set which has a sparse coverage of the inner core boundary such a data set is however able to successfully constrain the hemispherical boundaries due to a good sampling of latitudes combining translation and rotation could explain some of the features of the boundaries separating the inner core hemispheres the depth shift of the boundaries observed by some authors seems unlikely to be modelled by a fast translation but could be produced by slow translation associated to super rotation

seismic evidence for distinct anisotropy in the innermost inner core to understand the evolution of the inner core it is important to constrain the structure of its innermost part analysis of two types of seismic waves that traverse the inner core reveals seismic anisotropy of the innermost region and is consistent with the slowest direction of anisotropy being tilted away from the equatorial plane

axial high topography and partial melt in the crust and mantle beneath the western galapagos spreading center 1 the hot spot influenced western galapagos spreading center gsc has an axial topographic high that reaches heights of 700 m relative to seafloor depth 25 km from the axis we investigate the cause of the unusual size of the axial high using a model that determines the flexural response to loads resulting from the thermal and magmatic structure of the lithosphere the thermal structure simulated is appropriate for large amounts of cooling by hydrothermal circulation which tends to minimize the amount of partial melt needed to explain the axial topography nonetheless results reveal that the large axial high near 92 w requires that either the crust below the magma lens contains 35 partial melt or that 20 melt is present in the lower crust and at least 3 in the mantle within a narrow column 35 in the crust are considered unreasonable it is likely that much of the axial high region of the gsc is underlain by a narrow region of partially molten mantle of widths approaching those imaged seismically beneath the east pacific rise a narrow zone of mantle upwelling and melting driven largely by melt buoyancy is a plausible explanation

pb isotopic evidence for u th pb behaviour in a prograde amphibolite to granulite fades transition from the lewisian complex of north west scotland implications for pb pb dating abstract two end member types of u pb fractionation behaviour are recognised type i in which pb isotopic homogenisation occurs and type ii in which pb isotopic homogenisation is incomplete or absent type ii can be further subdivided into three categories depending upon the relationship of the post fractionation 3 238 u 204 pb value to prefractionation 2 in type iia 3 is unrelated to 2 in type iib 3 k 2 where k is a constant in type iic 3 values are uniform each of these types of behaviour results in a predictable effect upon observed uranogenic pb isotope systematics which may lead to an incorrect geochronological interpretation an example of the relationship between these specific types of u pb behaviour and metamorphic grade is provided from the late archaean lewisian complex of n w scotland this complex was metamorphosed during the 2660 ma badcallian event three suites of tonalitic granodioritic grey gneisses have been analysed pyroxene granulite facies from scourie hornblende granulite facies from gruinard bay and amphibolite facies from the northern region the present day pb isotopic composition of these suites can be interpreted as representing a transition from type lib behaviour in the lowest grade rocks resulting in a rotated isochron through type ha in the hornblende granulites which yield a scatter of data points to type i in the pyroxene granulites which yield an isochron corresponding to the badcallian event this transition presumably reflects increasing u depletion with metamorphic grade and ultimately at the highest grade pb mobility and or depletion in addition a consideration of the thorogenic pb isotopic data reveals a systematic variation during prograde metamorphism an attempt to test the model of 2660 ma initial ratio inhomogeneity by analysis of k feldspars from the amphibolite facies gneiss suite reveals 1700 ma laxfordian resetting of their pb isotope systematics this study has implications for pb pb geochronological data particularly in lower grade metamorphic terrains it suggests that reliable isochrons may only be generated by type i behaviour or by the imposition of high 3 values during type iia behaviour at higher grades of metamorphism

inner core structure behind the pkp core phase triplication the structure of the earth s inner core is not well known between depths of 100 200 km beneath the inner core boundary this is a result of the pkp core phase triplication and the existence of strong precursors to pkp phases which hinder the measurement of inner core compressional pkikp waves at epicentral distances between roughly 143 and 148 consequently interpretation of the detailed structure of deeper regions also remains difficult to overcome these issues we stack seismograms in slowness and time separating the pkp and pkikp phases which arrive simultaneously but with different slowness we apply this method to study the inner core s western hemisphere beneath south and central america using paths travelling in the quasi polar direction between 140 and 150 epicentral distance which enables us to measure pkikp pkikp differential traveltimes up to greater epicentral distance than has previously been done the resulting pkikp pkikp differential traveltime residuals increase with epicentral distance which indicates a marked increase in seismic velocity for polar paths at depths greater than 100 km compared to reference model ak135 assuming a homogeneous outer core these findings can be explained by either i inner core heterogeneity due to an increase in isotropic velocity or ii increase in anisotropy over the studied depth range although this study only samples a small region of the inner core and the current data cannot distinguish between the two alternatives we prefer the latter interpretation in the light of previous work

evolution of depleted mantle the lead perspective abstract isotopic data have established that compared to estimated bulk earth abundances the sources of oceanic basaltic lavas have been depleted in large ion lithophile elements for at least several billions of years various data on the tertiary mesozoic gorgona komatiite and cretaceous oka carbonatite show that those rocks also sample depleted mantle sources this information is used by analogy to compare pb isotopic data from 2 6 billion year old komatiite and carbonatite from the suomussalmi belt of eastern finland and munro township ontario that are with associated granitic rocks and ores that should contain marked crustal components within experimental error no differences are detected in the isotopic composition of initial pb in either of the rock suites these observations agree closely with sr and nd data from other laboratories showing that depleted mantle could not have originated in those areas more than a few tenths of billions of years before the rocks were emplaced on a world wide basis the pb isotope data are consistent with production of depleted mantle by continuous differentiation processes acting over approximately the past 3 billion years the data show that pb evolution is more complex than the simpler models derived from the rb sr and sm nd systems the nature of the complexity is still poorly understood

from mixed flow reactor to column experiments and modeling upscaling of calcite dissolution rate abstract the objective of this work was to assess the extent to which calcite dissolution rate rcalcite measured at controlled saturation state in mixed flow set ups could be upscaled to column experiments where the solution composition was variable in space and time the dissolution rate of the 104 calcite face was investigated in mixed flow reactor set ups at room temperature and ph 8 various saturation conditions were studied by changing the composition of the inlet solution enabling the determination of an empirical relation between rcalcite and the gibbs free energy of calcite dissolution g by measuring the surface topography with vertical scanning interferometry vsi the prevalent dissolution mode i e etch pit nucleation or homogeneous surface retreat was assessed with the same method a dramatic decrease of the dissolution rate was observed for 8

imaging the inner core under africa and europe abstract the inner core under africa is thought to be a region where the nature of inner core texture changes from the strongly anisotropic western part of the inner core to the weakly anisotropic or isotropic eastern part of the inner core additionally observations of a difference in isotropic velocity between the two hemispheres have been made a very large new dataset of simultaneous pkpdf and pkpbc observations on which differential travel times have been measured is used to examine the upper 360 km of the inner core under europe africa and the surrounding oceans inversion of the differential travel time data for laterally varying inner core anisotropy reveals that inner core anisotropy is stronger under central africa and the atlantic ocean than under the western indian ocean no hemispherical pattern is present in voigt isotropic velocities indicating that the variation in anisotropy is due to differing degrees of crystal alignment in the inner core not material differences when anisotropy is permitted to change with depth the upper east most part of the study region shows weaker anisotropy than the central and western regions when depth dependence in the inner core is neglected the hemisphere boundary is better represented as a line at 40 e than one at 10 e however it is apparent that the variation of anisotropy as a function of depth means that one line of longitude cannot truly separate the more and less anisotropic regions of the inner core the anisotropy observed in the part of the inner core under africa which lies in the western hemisphere is much weaker than that under central america showing that the western hemisphere is not uniformly anisotropic as the region of low anisotropy spans a significant depth extent it is likely that heterogeneous heat fluxes in the core which may cause variations in inner core anisotropy have persisted for several hundred million years

the use of hornblende etching clast weathering and soils to date alpine glacial and periglacial deposits a study from southwestern montana many techniques for relative dating of surficial deposits suffer from 1 the need to make judgments and 2 poor reproducibility of data furthermore many of the techniques generate data that do not permit the use of statistical analysis in contrast assessing the etching of hornblende grains yields objectively obtained reproducible data that can be subjected to statistical analysis in a study of the deposits of the bear gulch basin tobacco root range southwestern montana the hornblende etching data proved superior to the clast weathering data and the soil profile data in making interpretations of age relationships the mean etching of hornblende grains decreases as a logarithmic function of depth hornblende grains from older deposits are more etched especially near the surfaces of the profiles the collective evidence supports a record of four first order glacial and periglacial events which have been correlated with 1 the youngest pre bull lake glaciation about 280 000 yr b p 2 the bull lake glaciation about 140 000 yr b p 3 the pinedale glaciation consisting of two second order advances the first and most extensive between 26 000 and 20 000 yr b p and the second about 12 000 yr b p and 4 a mid neoglacial episode of periglacial activity in addition a major landslide blocked the valley in pre bull lake time and an episode of flood erosion along the valley floor is believed to have truncated the late pinedale terminal moraine about 1500 yr b p in a study area for which numerical ages of the deposits are available hornblende etching can be expressed mathematically as a function of the time since deposition with the resulting relationship used to date deposits wherein ages are unknown

high resolution probing of inner core structure with seismic interferometry increasing complexity of earth s inner core has been revealed in recent decades as the global distribution of seismic stations has improved the uneven distribution of earthquakes however still causes a biased geographical sampling of the inner core recent developments in seismic interferometry which allow for the retrieval of core sensitive body waves propagating between two receivers can significantly improve ray path coverage of the inner core in this study we apply such earthquake coda interferometry to 1846 usarray stations deployed across the u s from 2004 through 2013 clear inner core phases pkikp 2 and pkiikp 2 are observed across the entire array spatial analysis of the differential travel time residuals between the two phases reveals significant short wavelength variation and implies the existence of strong structural variability in the deep earth a linear n s trending anomaly across the middle of the u s may reflect an asymmetric quasi hemispherical structure deep within the inner core with boundaries of 99 w and 88 e

earthʼs inner core innermost inner core or hemispherical variations the structure of earth s deep inner core has important implications for core evolution since it is thought to be related to the early stages of core formation previous studies have suggested that there exists an innermost inner core with distinct anisotropy relative to the rest of the inner core using an extensive new data set of handpicked absolute travel time observations of the inner core phase pkikp we find that the data are best explained by variations in anisotropy between two hemispheres and do not require an innermost inner core we demonstrate that observations of an innermost inner core are an artifact from averaging over lateral anisotropy variations more significantly we show that hemispherical variations in anisotropy previously only imaged in the upper inner core continue to its centre the eastern region has 0 5 1 5 anisotropy whereas the western region has 3 5 8 8 anisotropy increasing with depth with a slow direction at 57 61 to the earth s rotation axis at all depths such anisotropy is consistent with models of aligned hcp or bcc iron aggregates

dating the oldest terrestrial rocks fact and fiction abstract this paper is a review of well documented geochronological and related isotopic evidence for the age and total crustal residence time of the oldest known terrestrial rocks mainly using rb 1bsr sm 1bnd and u 1bpb decay schemes the oldest known stable sialic crust of true continental character predominantly composed of calc alkaline orthogneisses was produced during major mantle differentiation some 3 7 3 5 ga ago and is represented on several continents enclaves of older supracrustal rocks as well as a major remnant of a volcano sedimentary sequence of greenstone belt affinity dated at 3 8 ga are preserved within the surrounding gneisses in southern west greenland recent ionmicroprobe evidence for 4 1 ga old detrital zircon grains in a younger early archaean metasedimentary sequence in western australia is also discussed several cases are reviewed where claims for early archaean 3 4 ga dates are believed to be erroneous and to result from oversimplistic and incorrect interpretation of isotopic data some of the geological and geochemical mechanisms which have given rise to claims for spuriously old sm 1bnd u 1bpb and pb pb dates are critically discussed to supplement published data we present several new sets of whole rock sm 1bnd and pb pb isotopic data from west greenland labrador zimbabwe and eastern india relevant to the overall topic of this review

can we use pyroxene weathering textures to interpret aqueous alteration conditions yes and no pyroxene minerals are a significant component of shergottite nakhlite chassignite snc meteorites e g velbel 2012 and detected across large areas of mars surface e g mustard et al 2005 these minerals are associated with chloride sulfate and perchlorate salts that may represent briny waters present in mars history previous textural analyses by velbel and losiak 2010 comparing pyroxenes and amphiboles from various natural weathering environments showed no correlation between apparent apical angles describing the morphology of denticular weathering textures and mineralogy or aqueous alteration history in relatively dilute solutions however high salinity brines preferentially dissolve surface species potentially leading to different textures dependent on the brine chemistry in this study we performed controlled pyroxene dissolution experiments in the laboratory on a well characterized diopside to determine if aqueous alteration in different high salinity brines representative of potential weathering fluids on mars produce unique textural signatures following two months of dissolution in batch reactors we observed denticles on etch pit margins and pyroxene chip boundaries in all of the solutions investigated ultrapure water 18 m cm 1 a h 2 o 1 low salinity solutions containing 0 35 m nacl a h 2 o 0 99 0 35 m na 2 so 4 a h 2 o 0 98 and 2 m naclo 4 a h 2 o 0 9 and near saturated brines containing 1 7 m na 2 so 4 a h 2 o 0 95 3 m nacl a h 2 o 0 75 and 4 5 m cacl 2 a h 2 o 0 35 no systematic change in denticle length or apical angle was observed between any of the solutions investigated even when altered in brines with significantly different salinity activity of water and anion composition based on these and previous results from natural systems apical angle measurements are not a useful proxy for determining the extent or nature of aqueous alteration however since denticles form relatively slowly during weathering at circum neutral ph denticle length may be a useful proxy for chemical weathering duration all of the experimental solutions produced median denticle lengths 1 m likely due to the brief weathering experiments however perchlorate brines produced a significantly wider range of denticle lengths than those observed in all the other experimental solutions tested since perchlorate is likely a common constituent in martian soils glotch et al 2016 denticle length measurements should be used cautiously as proxies for extent of aqueous alteration on mars particularly in samples that also contain perchlorate

the inner core hemispheric boundary near 180 w abstract the inner core ic east west hemispheric dichotomy is widely recognized but the reported position of the hemispheric boundary varies among studies due to uneven sampling coverage and the data analyzed this study investigates the sharpness of the western hemispheric boundary whb near 180 w by analyzing differential time residuals of pkikp pkpdf and pkp bc df for pkpdf phases that sample 155 e 130 w in various azimuthal directions using pkikp pkpdf observations the whb is located at 175 e 180 w in the southern hemisphere based mainly on the lateral isotropy anisotropy transition however based on the lateral isotropic velocity contrast and this isotropy anisotropy transition between the two hemispheres its location is 170 160 w in the northern hemisphere these findings indicate that the whb is sharp and exhibits a latitudinal dependence with a 10 20 kink as well as 1 75 anisotropy in the uppermost ic across the 180 155 w range of the western hemisphere as suggested by pkp bc df the whb could remain at 160 w at depth the isotropic velocity contrast near the whb 160 w between the eastern and western hemispheres is lower than previous estimates using pkpdf phases sampling the bulk part of each hemisphere

revised sm nd systematics of kambalda greenstones western australia sm nd isotope systematics in mafic ultramafic lavas from the norseman wiluna greenstone belt western australia have been reinvestigated a previous age based on mixing lavas and granites is not confirmed instead a sm nd age of 3 262 44 myr is indicated for the lavas 400 myr older than intruding granites and predating gneisses that have been proposed as basement rocks

the feasibility of thermal and compositional convection in earth s inner core inner core convection and the corresponding variations in grain size and alignment has been proposed to explain the complex seismic structure of the inner core including its anisotropy lateral variations and the f layer at the base of the outer core we develop a parametrized convection model to investigate the possibility of convection in the inner core focusing on the dominance of the plume mode of convection versus the translation mode we investigate thermal and compositional convection separately so as to study the end members of the system in the thermal case the dominant mode of convection is strongly dependent on the viscosity of the inner core the magnitude of which is poorly constrained furthermore recent estimates of a large core thermal conductivity result in stable thermal stratification hindering convection however an unstable density stratification may arise due to the pressure dependant partition coefficient of certain light elements we show that this unstable stratification leads to compositionally driven convection and that inner core translation is likely to be the dominant convective mode due to the low compositional diffusivity the style of convection resulting from a combination of both thermal and compositional effects is not easy to understand for reasonable parameter estimates the stabilizing thermal buoyancy is greater than the destabilizing compositional buoyancy however we anticipate complex double diffusive processes to occur given the very different thermal and compositional diffusivities

equatorial anisotropy in the inner part of earth s inner core from autocorrelation of earthquake coda the speed of seismic waves passing through the earth s inner core varies with direction analysis of earthquake seismic data suggests that this directional dependence differs between innermost and outer inner core

bayesian inversion of free oscillations for earth s radial an elastic structure abstract we perform a bayesian inversion of degree zero spheroidal mode splitting function measurements for radial 1 d earth structure in terms of the voigt averages of p wave v p and s wave v s velocities density bulk and shear attenuation using neural networks the method is flexible and allows us to assess the robustness of features in existing reference models such as prem the bayesian framework provides a means for quantifying uncertainties in the model parameters and for measuring the information content of the data the analysis of the information content suggests that the free oscillations constrain most parameters better than body wave travel time data our most important findings can be summarised as follows the data prefer an inner outer core boundary icb that lies in the depth range 5154 7 5165 7 km i e deeper than in existing reference models the effect on the travel time of inner core sensitive seismic phases is comparable to the estimated noise in such measurements the density contrast at the icb 0 73 g cm 3 is larger than in prem 0 60 g cm 3 and ak135f 0 56 g cm 3 but our range including uncertainties 0 52 0 94 g cm 3 encompasses all previous estimates in the literature the average v p and v s in the d region are smaller than in prem whereas the mean density is probably larger the data cannot uniquely determine whether this density excess is restricted to the d region or distributed throughout the lower most mantle the data cannot determine with certainty the presence or absence of a discontinuity at 220 km depth for v p v s and density if present the jump in both velocities is likely smaller than in prem shear attenuation parameters in the mantle deviate from prem in a similar fashion to results from more recent studies we find a non homogeneous shear attenuation in the inner core reinforcing the hypothesis that a distinct innermost inner core may exist the bulk attenuation in the mantle and the outer core is stronger than in prem we investigate the influence of radial anisotropy on the inversions and analyse possible trade offs between anisotropic parameters the largest trade offs are observed in regions that are believed to be anisotropic such as the d region this illustrates the need to constrain anisotropy in the deep mantle

crystal size distribution csd in rocks and the kinetics and dynamics of crystallization crystal size distributions csds measured in metamorphic rocks yield quantitative information about crystal nucleation and growth rates growth times and the degree of overstepping t of reactions during metamorphism csds are described through use of a population density function n dn dl where n is the cumulative number of crystals per unit volume and l is a linear crystal size plots of ln n vs l for olivine pyroxene and magnetite in high temperature 1000 c basalt hornfelses from the isle of skye define linear arrays indicating continuous nucleation and growth of crystals during metamorphism using the slope and intercept of these linear plots in conjunction with growth rate estimates we infer minimum mineral growth times of less than 100 years at t 10 c and nucleation rates between 10 4 and 10 1 cm3 s garnet and magnetite in regionally metamorphosed pelitic schists from south central maine have csds which are bell shaped we interpret this form to be the result of two processes 1 initial continuous nucleation and growth of crystals and 2 later loss of small crystals due to annealing the large crystals in regional metamorphic rocks retain the original size frequency distribution and may be used to obtain quantitative information on the original conditions of crystal nucleation and growth the extent of annealing increases with increasing metamorphic grade and could be used to estimate the duration of annealing conditions if the value of a rate constant were known finally the different forms of crystal size distributions directly reflect differences in the thermal histories of regional vs contact metamorphosed rocks because contact metamorphism involves high temperatures for short durations resulting csds are linear and unaffected by annealing similar to those produced by crystallization from a melt because regional metamorphism involves prolonged cooling from high temperatures primary linear csds are later modified by annealing to bell shapes

anomalously strong observations of pkikp pcp amplitude ratios on a global scale the inner core boundary marks the phase transition between the solid inner core and the fluid outer core as the site of inner core solidification the boundary provides insight into the processes generating the seismic structures of the inner core in particular it may hold the key to understanding the previously observed hemispherical asymmetry in inner core seismic velocity anisotropy and attenuation here we use a large pkikp pcp amplitude ratio and travel time residual data set to investigate velocity and density contrast properties near the inner core boundary although hemispherical structure at the boundary has been proposed by previous inner core studies we find no evidence for hemispheres in the amplitude ratios or travel time residuals in addition we find that the amplitude ratios are much larger than can be explained by variations in density contrast at the inner core boundary or core mantle boundary this indicates that pkikp is primarily observed when it is anomalously large due to focusing along its raypath using data in which pkikp is not detected above the noise level we calculate an upper estimate for the inner core boundary icb density contrast of 1 2 kg m 3 the travel time residuals display large regional variations which differ on long and short length scales these regions may be explained by large scale velocity variations in the f layer just above the inner core boundary and or small scale topography of varying magnitude on the icb which also causes the large amplitudes such differences could arise from localized freezing and melting of the inner core

upper mantle slab under alaska contribution to anomalous core phase observations on south sandwich to alaska paths abstract observations of travel time anomalies of inner core sensitive pkpdf seismic body waves as a function of path orientation with respect to the earth s rotation axis have been interpreted as evidence of anisotropy in the inner core paths from earthquakes in the south sandwich islands to stations in alaska show strongly anomalous travel times with a large spread that is not compatible with simple models of anisotropy here we assess the impact of strong velocity heterogeneity under alaska on the travel times directions of arrival and amplitudes of pkpdf we use 3d ray tracing and 2 5d waveform modelling through a new high resolution tomography model of the upper mantle beneath alaska we find that the structure beneath alaska notably the subducting slab is reflected in the patterns of these pkpdf observations and this can be replicated by our model we also find similar patterns in observed teleseismic p waves that can likewise be explained by our slab model we conclude that at least 2 s of the travel time anomaly often attributed to inner core anisotropy is due to slab effects in the upper mantle beneath alaska

the late archaean to early proterozoic lead isotopic evolution of the northern baltic shield of norway sweden and finland abstract the late archaean rocks of the northern baltic shield comprise high grade gneiss terrains and granite greenstone terrains the high grade gneiss terrains consist mainly of older upper crustal material which became metamorphosed during the lopian orogeny ca 2 9 2 6 ga in contrast the 2 7 ga old granite greenstone terrains comprise mainly mantle derived materials at the southern and western edge the archaean craton became partially remobilized during the svecofennian orogeny 2 0 1 75 ga this orogeny represents a major crust forming event in the baltic shield during which mantle material was added to the crust and older material was remobilized whole rock galena and sulfide trace lead are used to outline lead provinces on the northern baltic shield the archaean lead from the baltic shield defines three secondary lead isochrons at 2 65 ga with different initial lead compositions which reflect average pre 2 65 ga 1 ratios of 8 0 8 1 and 8 3 respectively the variation of the initial lead composition of the high grade gneisses and tonalites lofoten and koitelainen area probably indicates 1 variable crustal residence time and or 2 different degrees of crustal contamination assimilation before the 2 65 ga metamorphic event and the lead from the eastern finland greenstone belts indicates a heterogeneous mantle with respect to u pb before 2 65 ga lead in proterozoic rocks of the different lead provinces defines sets of subparallel mixing fields which can be modelled by a 2 65 ga lead component and a 1 8 ga lead component the parallel offset of these fields reflects the pre 2 65 ga 1 ratio of these terrains i e it reveals the pre 2 65 ga 1 of the involved archaean rocks proterozoic terrains with involvement of archaean lower crustal lead show a poor correlation in the 206 pb 204 pb 208 pb 204 pb diagram whereas the other proterozoic terrains show a good correlation in the 206 pb 204 pb 208 pb 204 pb diagram

origin of granitic magma by crustal remobilisation rb sr and pb pb geochronology and isotope geochemistry of the late archaean qorqut granite complex of southern west greenland abstract rb sr and pb pb whole rock isochrons on the qorqut granite complex yield ages of 2530 30 myr initial 87 sr 86 sr 0 7081 0 0008 and 2580 80 myr respectively a model relating initial sr and pb isotopic compositions of the qorqut granites to the sr and pb isotopic compositions of the amitsoq gneisses ca 3700 myr and nuk gneisses ca 2900 myr at 2550 myr ago as well as sr and pb contents of the gneiss units suggests that between 40 and 50 of the qorqut granite magma was generated by partial melting of amitsoq gneisses and the remainder by partial melting of nuk gneisses

seismic velocity and attenuation structures in the top of the earth s inner core 1 we collect a global data set of pkikp and pkikp phases recorded by the global seismic network and many regional seismic arrays to study seismic structure in the top of the earth s inner core the pkikp and pkikp observations show different characteristics between those sampling the eastern hemisphere 40 e 180 e of the inner core and those sampling the western hemisphere 180 w 40 e pkikp phases 1 arrive about 0 4 s earlier than the theoretical arrivals based on preliminary reference earth model prem for those sampling the eastern hemisphere of the inner core and about 0 3 s later for those sampling the western hemisphere 131 141 2 bifurcate at smaller epicentral distances for those sampling the eastern hemisphere compared to those sampling the western hemisphere and 3 have smaller amplitudes for those sampling the eastern hemisphere waveform modeling of these observations suggests two different types of models for the two hemispheres of the top of the inner core with a model in the eastern hemisphere having a p velocity increase of 0 765 km s across the inner core boundary a small radial velocity gradient of 0 000055 km s km and an average q value of 250 and a model in the western hemisphere with a p velocity increase of 0 633 km s across the inner core boundary a radial velocity gradient of 0 000533 km s km and an average q value of 600 the hemispherical difference of seismic structures may be explained by different geometric inclusions of melt and or different alignments of iron crystals with anisotropic properties in both velocity and attenuation we speculate that this large scale pattern of seismic heterogeneities may be caused by a large scale heat flow anomaly at the bottom of the outer core and or different vigorousness of convection in the top of the inner core between the two hemispheres

test of the innermost inner core models using broadband pkikp travel time residuals 1 two different innermost inner core imic models have recently been proposed each with different radii and different orientation and strength of anisotropy in order to test these imic models we have systematically assembled a high quality dataset of broadband pkikp data in the epicentral distance range of 150 to 180 our new dataset consists of 1 100 individually measured absolute pkikp arrival times also pkikp bottoming points and ray paths in the inner core are well distributed in the east west and north south hemispheres we invert this dataset for two layer models of anisotropy in the inner core and compare the fits obtained with those predicted from the existing imic models our results show that if there is an imic its radius is most likely around 500 km rather than the 300 km originally proposed and is in better agreement with the layering in the inner core based on pkikp waveform modeling

partial melting of a pb sn mushy layer due to heating from above and implications for regional melting of earth s directionally solidified inner core superimposed on the radial solidification of earth s inner core may be hemispherical and or regional patches of melting at the inner outer core boundary little work has been carried out on partial melting of a dendritic mushy layer due to heating from above here we study directional solidification annealing and partial melting from above of pb rich sn alloy ingots we find that partial melting from above results in convection in the mushy layer with dense melted pb sinking and resolidifying at a lower height yielding a different density profile than for those ingots that are just directionally solidified irrespective of annealing partial melting from above causes a greater density deeper down and a corresponding steeper density decrease nearer the top there is also a change in microstructure these observations may be in accordance with inferences of east west and perhaps smaller scale variations in seismic properties near the top of the inner core

thermochemical flows couple the earth s inner core growth to mantle heterogeneity the uppermost 100 km of the earth s inner core is subject to an east west divide seismic waves travel more rapidly and are attenuated more severely in the eastern than in the western hemisphere and the west is more anisotropic that is seismic waves travel at different speeds in different directions than the eastern hemisphere the origin of this hemispherical dichotomy has remained enigmatic aubert et al now show that a model incorporating thermochemical convection and dynamo action can account for these effects by producing a large scale long term outer core flow that couples the heterogeneity of the inner core with that of the lower mantle seismic waves sampling the top 100 km of the earth s inner core have revealed that the eastern hemisphere is seismically faster more isotropic and more attenuating than the western hemisphere it is now shown that a single model of thermo chemical convection and dynamo action can account for all these effects by producing a large scale long term outer core flow that couples the heterogeneity of the inner core with that of the lower mantle seismic waves sampling the top 100 km of the earth s inner core reveal that the eastern hemisphere 40 e 180 e is seismically faster1 2 more isotropic2 3 and more attenuating4 than the western hemisphere the origin of this hemispherical dichotomy is a challenging problem for our understanding of the earth as a system of dynamically coupled layers previously laboratory experiments have established that thermal control from the lower mantle can drastically affect fluid flow in the outer core5 which in turn can induce textural heterogeneity on the inner core solidification front6 the resulting texture should be consistent with other expected manifestations of thermal mantle control on the geodynamo specifically magnetic flux concentrations7 8 in the time average palaeomagnetic field9 10 over the past 5 myr and preferred eddy locations11 in flows imaged below the core mantle boundary by the analysis of historical geomagnetic secular variation12 here we show that a single model of thermochemical convection and dynamo action can account for all these effects by producing a large scale long term outer core flow that couples the heterogeneity of the inner core with that of the lower mantle the main feature of this thermochemical wind is a cyclonic circulation below asia which concentrates magnetic field on the core mantle boundary at the observed location and locally agrees with core flow images this wind also causes anomalously high rates of light element release in the eastern hemisphere of the inner core boundary suggesting that lateral seismic anomalies at the top of the inner core result from mantle induced variations in its freezing rate

crystallization of mount st helens 1980 1986 dacite a quantitative textural approach quantitative measurements of crystal size distributions csds have been used to obtain kinetic information on crystallization of industrial compounds randolph and larson 1971 and more recently on hawaiian basalts cashman and marsh 1988 the technique is based on a population balance resulting in a differential equation relating the population densityn of crystals to crystal sizel i e at steady staten no exp l itg whereno is nucleation density g is the average crystal growth rate is the average growth time and the nucleation ratej nog csd inn vsl plots of plagioclase phenocrysts in 12 samples of mount st helens blast dacite and 14 samples of dacite from the 1980 1986 mount st helens dome are similar and averageg 9 6 1 1 10 3 cm andno 1 2 106 cm 4 reproducibility of the measurements was tested by measuring csds of 12 sections cut from a single sample in three mutually perpendicular directions precision of the size distributions is good in terms of relative but not necessarily absolute values 10 growth and nucleation rates for plagioclase have been calculated from these measurements using time brackets of 30 150 years growth ratesg are 3 10 10 12cm s and nucleation ratesj are 5 21 10 6 cm3 s g andj for fe ti oxides calculated from csd data areg 2 13 10 13 cm sec andj 7 33 10 5 cm3 s respectively the higher nucleation rate and lower growth rate of oxides resulted in a smaller average crystal size than for plagioclase sizes of plagioclase microlites 0 01 mm in the blast dacite groundmass have been measured from backscatter sem photographs nucleation of these microlites was probably triggered by intrusion of material into the cone of mount st helens in spring 1980 this residence time of 52 days gives minimum crystallization estimates ofg 1 3 10 11 cm s andj 9 16 1o3 cm3 s the skeletal form of the microlites provides evidence for nucleation and growth at high values of undercooling t relative to the phenocrysts a comparison of nucleation and growth rates for the two crystal populations phenocrysts vs microlites suggests that while growth rate seems to be only slightly affected by changes in t nucleation rate is a very strong function of undercooling a comparison of plagioclase nucleation and growth rates measured in the mount st helens dacite and in basalt from makaopuhi lava lake in hawaii suggests that plagioclase nucleation rates are not as dependent on composition groundmass textures suggest that plagioclase microphenocrysts crystallized at depth rather than in the conduit in the dome or after extrusion onto the surface most of this crystallization appears to be in the form of crystal growth coarsening of groundmass microphenocrysts at small degrees of undercooling rather than extensive nucleation of new crystals this continuous crystallization in a shallow magmatic reservoir may provide the overpressurization needed to drive the continuing periodic domebuilding extrusions which have been the pattern of activity at mount st helens since december 1980

regional variation of inner core anisotropy from seismic normal mode observations earth s solid inner core is surrounded by a convecting liquid outer core creating the geodynamo driving the planet s magnetic field seismic studies using compressional body waves suggest hemispherical variation in the anisotropic structure of the inner core but are poorly constrained because of limited earthquake and receiver distribution here using normal mode splitting function measurements from large earthquakes based on extended cross coupling theory we observe both regional variations and eastern versus western hemispherical anisotropy in the inner core the similarity of this pattern with earth s magnetic field suggests freezing in of crystal alignment during solidification or texturing by maxwell stress as origins of the anisotropy these observations limit the amount of inner core super rotation but would be consistent with oscillation

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

melting induced stratification above the earth s inner core due to convective translation several observed properties of earth s solid inner core and liquid outer core remain enigmatic including an east west seismic asymmetry and the presence of a roughly 250 kilometre thick layer of reduced seismic velocity at the base of the outer core alboussiere et al now suggest a model that can produce both of these features based on experiment and numerical modelling they propose that simultaneous crystallization and melting at opposite sides of earth s inner core surface can result in a translational mode of thermal convection within the inner core which also introduces an asymmetry between hemispheres these authors show that simultaneous crystallization and melting at the surface of the earth s inner core can result in a translational mode of thermal convection within the inner core producing the observed stratified layer of reduced seismic velocity at the base of the outer core the dynamical model they propose also introduces an asymmetry between hemispheres that may explain the enigmatic east west asymmetry in seismic properties of the inner core in addition to its global north south anisotropy1 there are two other enigmatic seismological observations related to the earth s inner core asymmetry between its eastern and western hemispheres2 3 4 5 6 and the presence of a layer of reduced seismic velocity at the base of the outer core6 7 8 9 10 11 12 this 250 km thick layer has been interpreted as a stably stratified region of reduced composition in light elements13 here we show that this layer can be generated by simultaneous crystallization and melting at the surface of the inner core and that a translational mode of thermal convection in the inner core can produce enough melting and crystallization on each hemisphere respectively for the dense layer to develop the dynamical model we propose introduces a clear asymmetry between a melting and a crystallizing hemisphere which forms a basis for also explaining the east west asymmetry the present translation rate is found to be typically 100 million years for the inner core to be entirely renewed which is one to two orders of magnitude faster than the growth rate of the inner core s radius the resulting strong asymmetry of buoyancy flux caused by light elements is anticipated to have an impact on the dynamics of the outer core and on the geodynamo

is inner core seismic anisotropy a marker for plastic flow of cubic iron this paper investigates whether observations of seismic anisotropy are compatible with a cubic structure of the inner core fe alloy we assume that anisotropy is the result of plastic deformation within a large scale flow induced by preferred growth at the inner core equator based on elastic moduli from the literature body centered cubic or face centered cubic fe produces seismic anisotropy well below seismic observations 0 4 a monte carlo approach allows us to generalize this result to any form of elastic anisotropy in a cubic system within our model inner core global anisotropy is not compatible with a cubic structure of fe alloy hence if the inner core material is indeed cubic large scale coherent anisotropic structures incompatible with plastic deformation induced by large scale flow must be present

pb isotopic compositions of archean komatiites and sulfides abstract pb isotopic compositions were measured in komatiites and other volcanic rocks from several archean greenstone belts and in magmatic and exhalative sulfides associated with these volcanics thin komatiite flows generally yielded pb pb isochron ages consistent with other geochronological or geological information but thicker basaltic flows gave ages that are too young these results suggest that the thin komatiite flows were hydrothermally altered during eruption and that this event is recorded by the pb pb age thicker basaltic flows resisted alteration during eruption but were affected by later events their pb pb ages probably correspond to the time of metamorphism and not to the time of emplacement magmatic and exhalative sulfides from the abitibi belt in canada fall on the same trend in the 207 pb 204 pb 206 pb 204 pb diagram as komatiites basalts sedimentary rocks and k feldspars from granites the calculated 1 value is 7 8 0 1 a similar suite of rocks and minerals from the kambalda area in australia has distinctly higher 207 pb 204 pb and a higher 1 of 8 3 nd isotopic data demonstrate that some kambalda rocks are highly contaminated with older continental crust the differences in initial pb isotopic compositions are attributed to the presence or absence and the age of underlying granitoid basement kambalda greenstones are underlain and contaminated by old 3 0 ga granitoid crust but significantly older granitoid basement appears absent from the abitibi belt the pb isotopic compositions of kambalda greenstones are dominated by the crustal component and do not represent the composition of the mantle source of these rocks the abitibi greenstones are not highly influenced by crustal contamination and their pb isotopic compositions may reflect those of archean mantle

waveform search for the innermost inner core abstract waveforms of the pkikp seismic phase are inconsistent with the effects of a sharp boundary at 300 km radius of an inner most inner core seismograms synthesized for the distance range 150 to 180 in models having a discontinuity at 300 km radius in the inner core exhibit focused diffractions around the innermost sphere at antipodal range that are inconsistent with observed pkikp waveforms a few examples however can be found of pkikp complexity near 165 consistent with a triplication created by a 475 km radius discontinuity a rapid change in the magnitude and variance of seismic attenuation of pkikp whose rays turn between 400 and 600 km radius is also observed consistent with an innermost sphere of low regionally uniform seismic attenuation models predicting waveforms in agreement with observed waveforms have either a transition in elastic and anelastic properties spread over a depth interval greater than 100 km or an innermost sphere of differing elastic properties that exceeds 450 km radius the weak but suggestive evidence for an innermost inner core may simply represent a transition in fabric spread over 100 km or more centered near 500 km radius this change may signify the end stage of solidification flow and re crystallization resulting in the highest ordering and largest grain sizes of intrinsically anisotropic crystals

applications of mineral surface chemistry to environmental problems environmental surface chemistry involves processes that occur at the interface between the regolith hydrosphere and atmosphere the more limited scope of the present review addresses natural and anthropogenically induced inorganic geochemical reactions between solutes in surface and ground waters and soil and aquifer substrates important surficial reactions include sorption ion exchange dissolution precipitation and heterogeneous oxidation reduction processes occurring at the solid aqueous interface recent research advances in this field have addressed both directly and indirectly societal issues related to water quality pollution biogeochemical cycling nutrient budgets and chemical weathering related to long term global climate change this review will include recent advances in the fundamental and theoretical understanding of these surficial processes breakthroughs in experimental and instrumental surface characterization and development of methodologies for field applications

constraints on inner core anisotropy using array observations of p p author s frost da romanowicz b abstract 2017 american geophysical union all rights reserved recent studies of pkpdf travel times suggest strong anisotropy 4 or more in the quasi western inner core hemisphere however the availability of paths sampling at low angles to the earth s rotation axis the fast axis is limited to augment this sampling we collected a travel time data set for the phase p p df pkppkpdf for which at least one inner core leg is quasi polar at two high latitude seismic arrays we find that the inferred anisotropy is weak on the order of 0 5 to 1 5 confirming previous results based on a much smaller p p data set while previous models of inner core anisotropy required very strong alignment of anisotropic iron grains our results are more easily explained by current dynamic models of inner core growth we observe large travel time anomalies when one leg of p p df is along the south sandwich to alaska path consistent with pkpdf observations and warranting further investigation

depth extent of hemispherical inner core from pkp df and pkp cdiff for equatorial paths abstract differential travel times and amplitude ratios of pkp df and pkp cdiff partly including pkp bc for equatorial paths at epicentral distances from 150 to 160 are examined to discuss the radial structure of the uppermost 500 km of the inner core by using seismograms with a predominant frequency of approximately 0 5 hz 649 measurements are successfully collected including 295 and 354 readings for the eastern and western hemispheres respectively forward modeling with the reflectivity method suggests that the best fit velocity structures in the eastern and western hemispheres are 0 5 faster and 0 9 slower respectively than an average structure at the inner core boundary icb and that the velocity perturbations become linearly closer to the average with depth finally coinciding with the average at 400 km and 250 km below the icb respectively if ak135 is adopted for the structure above the icb in the eastern hemisphere the q values in the uppermost 250 km of the inner core and that in the range from 300 to 450 km below the icb are approximately 180 and 1000 respectively in contrast the q value in the western hemisphere is almost constant at approximately 300 400 in the uppermost 450 km of the inner core

age and lead isotope systematics of uranium enriched cobalt mineralization in the modum complex south norway abstract in the modum complex in the precambrian kongsberg sector of south norway cobalt sulphides and arsenides chalcopyrite and pyrite occur in stratiform bands and lenses the cobalt ore minerals are intimately associated with thorian uraninite both on a regional and on a microscopic scale due to the presence of coeval inclusions and intergrowths of uraninite in the cobalt minerals hand picked separates of ore minerals show a large range of u pb ratios this has led to a very large range of present day lead isotopic composition 206 pb 204 pb 18 1 to 277 207 pb 204 pb 15 6 to 36 208 pb 204 pb 37 to 57 two groups of samples can be discerned group 1 defines an imperfectly fitted pb pb lead isochron with an age of 1434 29 ma group 2 defines a pb pb correlation line with an age of 1146 66 ma these results indicate that the uranium bearing cobalt ore was deposited during the orogenic interlude commonly thought to separate the gothian kongsbergian ca 1 5 ga and sveconorwegian 1 2 0 9 ga orogenies in the baltic shield multi stage lead modelling indicates that the initial isotopic composition of the lead in the ores is indistinguishable from that of lead in the country rock metasediments suggesting that it was extracted from such a source the group 2 leads were affected by a strongly localized hydrothermal reworking process during the sveconorwegian orogeny which led to small scale partial pb isotopic homogenization and to strong fractionation of uranium thorium and lead the 1 43 ga age for primary mineralization defines a definite lower age limit for the onset of clastic sedimentation in the kongsberg sector the crustal precursor of the sediments must have retained a high lile upper continental crust character for several hundred million years prior to sedimentation

geochronology and isotopic variation of the early archaean amitsoq gneisses of the isukasia area southern west greenland abstract relatively unaltered samples of the amitsoq gneiss complex in the isukasia area were identified and analysed despite the effects of metamorphism and local proterozoic hydrothermal alteration and contamination the parents of the three lithologies that make up the amitsoq gneisses of the area were emplaced over about 320 ma taking a weighted average of dates from u pb on zircons rb sr on wr sm nd on wr and pb pb on wr the most probable ages of intrusion are grey gneisses at 3690 50 ma white gneisses at 3590 40 ma and pegmatitic gneisses at 3370 60 ma the rb sr isochron initial 87 sr 86 sr ratios for the grey white and pegmatitic gneisses are 0 7006 1 0 7016 1 and 0 8248 3 respectively the corresponding average nd t values are 1 0 0 7 and 0 2 since the ree chemistry of the rocks that were the direct parents of the grey gneisses is not known the 1 0 average nd t of the grey gneisses need not imply generation from a depleted mantle the sr initial ratio and nd t values for the white and pegmatitic gneisses are compatible with consecutive derivation at two discrete intervals by partial melting of crust mainly comprised of rocks similar to the grey gneisses the progressive evolution of nd with t for the amitsoq gneisses in the early archaean shows that values of nd t near zero in granitoids do not necessarily indicate derivation from the undepleted mantle chur

in situ nanoscale observations of gypsum dissolution by digital holographic microscopy abstract recent topography measurements of gypsum dissolution have not reported the absolute dissolution rates but instead focus on the rates of formation and growth of etch pits in this study the in situ absolute retreat rates of gypsum 010 cleavage surfaces at etch pits at cleavage steps and at apparently defect free portions of the surface are measured in flowing water by reflection digital holographic microscopy observations made on randomly sampled fields of view on seven different cleavage surfaces reveal a range of local dissolution rates the local rate being determined by the topographical features at which material is removed four characteristic types of topographical activity are observed 1 smooth regions free of etch pits or other noticeable defects where dissolution rates are relatively low 2 shallow wide etch pits bounded by faceted walls which grow gradually at rates somewhat greater than in smooth regions 3 narrow deep etch pits which form and grow throughout the observation period at rates that exceed those at the shallow etch pits and 4 relatively few submicrometer cleavage steps which move in a wave like manner and yield local dissolution fluxes that are about five times greater than at etch pits molar dissolution rates at all topographical features except submicrometer steps can be aggregated into a continuous mildly bimodal distribution with a mean of 3 0 mol m 2 s 1 and a standard deviation of 0 7 mol m 2 s 1

atomic scale imaging of calcite growth and dissolution in real time we present a new experimental technique for real time observation of aqueous mineral growth and dissolution at the atomic scale using an atomic force microscope afm equipped with a flow through fluid cell we applied this technique to observe changes in surface topography on the 10 batchmode documentclass fleqn 10pt legalpaper article usepackage amssymb usepackage amsfonts usepackage amsmath pagestyle empty begin document overline 1 end document 4 cleavage plane of calcite during alternating episodes of growth and dissolution growth occurred in a layer by layer fashion by the forward motion of monomolecular steps 0 3 0 1 nm high lying parallel to the edges of the cleavage face under all conditions studied the velocities of positive 48 batchmode documentclass fleqn 10pt legalpaper article usepackage amssymb usepackage amsfonts usepackage amsmath pagestyle empty begin document overline 1 end document and batchmode documentclass fleqn 10pt legalpaper article usepackage amssymb usepackage amsfonts usepackage amsmath pagestyle empty begin document overline 4 end document 41 steps were the same velocities of negative batchmode documentclass fleqn 10pt legalpaper article usepackage amssymb usepackage amsfonts usepackage amsmath pagestyle empty begin document overline 4 end document 81 and batchmode documentclass fleqn 10pt legalpaper article usepackage amssymb usepackage amsfonts usepackage amsmath pagestyle empty begin document overline 4 end document 41 steps were undetectably small less than 0 1 not s 1 steps were straight passing above perfect crystalline material but roughened into two dimensional dendrites above defective material dissolution nucleated shallow 90 nm deep rhombic etch cores growth into these etch cores was impeded so that steps moved around them afm images of the surface atomic structure revealed rows of atoms along 010 spaced by 0 39 0 05 nm with a periodicity along the rows of 0 43 0 05 run

grain growth of e iron implications to grain size and its evolution in the earth s inner core abstract knowledge of grain growth rate of e iron can put constraint on estimation of the grain size in the inner core we determined grain growth rate of e iron at 55 gpa and 1200 1500 k by means of in situ x ray diffraction observation to be g n g 0 n k t where g m is the grain size at time t s g 0 m is the initial grain size n is growth exponent fixed to 2 and k is the growth constant expressed as k k 0 exp h r t with log k 0 m n s 5 8 2 4 and activation enthalpy h 221 61 kj mol and r is the gas constant and t is the absolute temperature extrapolation of the grain growth law of e iron to the inner core conditions suggests that the grain size in the inner core is in a range from several hundred meters to several kilometers which is intermediate among the previous estimations and hence the dominant deformation mechanism is considered to be harper dorn creep rather than diffusion creep as pointed out by the previous work this indicates the relatively uniform viscosity in the entire inner core

seasonal speedup of a greenland marine terminating outlet glacier forced by surface melt induced changes in subglacial hydrology we present subdaily ice flow measurements at four gps sites between 36 and 72 km from the margin of a marine terminating greenland outlet glacier spanning the 2009 melt season our data show that 35 km from the margin seasonal and shorter time scale ice flow variations are controlled by surface melt induced changes in subglacial hydrology following the onset of melting at each site ice motion increased above background for up to 2 months with resultant up glacier migration of both the onset and peak of acceleration later in our survey ice flow at all sites decreased to below background multiple 1 to 15 day speedups increased ice motion by up to 40 above background these events were typically accompanied by uplift and coincided with enhanced surface melt or lake drainage our results indicate that the subglacial drainage system evolved through the season with efficient drainage extending to at least 48 km inland during the melt season while we can explain our observations with reference to evolution of the glacier drainage system the net effect of the summer speed variations on annual motion is small 1 this in part is because the speedups are compensated for by slowdowns beneath background associated with the establishment of an efficient subglacial drainage system in addition the speedups are less pronounced in comparison to land terminating systems our results reveal similarities between the inland ice flow response of greenland marine and land terminating outlet glaciers

the innermost inner core of the earth evidence for a change in anisotropic behavior at the radius of about 300 km since the discovery of the inner core in 1936 no additional spherical subshell of the earth has been observed based on an extensive seismic data set we propose the existence of an innermost inner core with a radius of 300 km that exhibits a distinct transverse isotropy relative to the bulk inner core specifically within the innermost inner core the slowest direction of wave propagation is 45 from the east west direction in contrast the direction of the slowest wave propagation in the overlying inner core is east west the distinct anisotropy at the center of the earth may represent fossil evidence of a unique early history of inner core evolution

the effects of boundary topography on convection in earth s core summary we present the first investigation that explores the effects of an isolated topographic ridge on thermal convection in a planetary core like geometry and using core like fluid properties i e using a liquid metal like low prandtl number fluid the model s mean azimuthal flow resonates with the ridge and results in the excitation of a stationary topographic rossby wave this wave generates recirculating regions that remain fixed to the mantle reference frame associated with these regions is a strong longitudinally dependent heat flow along the inner core boundary this effect may control the location of melting and solidification on the inner core boundary theoretical considerations and the results of our simulations suggest that the wavenumber of the resonant wave lr scales as ro 1 2 where ro is the rossby number this scaling indicates that small scale flow structures wavenumber in the core can be excited by a topographic feature on the core mantle boundary the effects of strong magnetic diffusion in the core must then be invoked to generate a stationary magnetic signature that is comparable to the scale of observed geomagnetic structures

effect of surface orientation on dissolution rates and topography of caf2 this paper reports how during dissolution differences in surface chemistry affect the evolution of topography of caf2 pellets with a microstructure similar to uo2 spent nuclear fuel 3d confocal pr

microtextural controls of weathering of perthitic alkali feldspars the relationship between the microtexture and dissolution behaviour of fresh hf acid etched and naturally weathered alkali feldspar phenocrysts from the lower devonian shap granite has been investigated by sem and tem a novel resin impregnation technique has revealed the three dimensional shape and interconnectivity of etch pits beneath the weathered crystal surface further electron microscope work suggests that shap phenocrysts are representative of the alkali feldspar in the protolith of many soils fresh and unweathered shap feldspars have a complex microtexture comprising areas of pristine cryptoperthite and lamellar microperthite cross cut by volumes of microporous altered feldspar or patch perthites cryptoperthites are made up of 75 nm wide albite films the platelets are coherent but albite films have numerous edge dislocations along their interface with orthoclase 001 and 010 cleavage surfaces intersect 2 3 edge dislocations m2 in three dimensions these edge dislocations form an orthogonal net in the murchison plane of easy fracture close to 601 patch perthites are irregular semicoherent to incoherent intergrowths of albite and irregular microcline subgrains with 0 65 0 70 sub m to m sized pores m2 microporous patch perthites form by dissolution reprecipitation reactions with magmatic or hydrothermal fluids and pores are present before the alkali feldspars enter the weathering regime dissolution of shap feldspars during natural weathering and laboratory acid etching is controlled by their microtexture especially by dislocations and exsolution lamellae the core and strain energy associated with dislocation outcrops on 001 and 010 cleavage surfaces promotes rapid dissolution at those sites and formation of nn sized etch pits after 30 s of laboratory etching with hf acid vapour with progressive hf etching crystallographically controlled differences in the reactivity of etch pit walls cause them to expand more rapidly into orthoclase than albite naturally weathered feldspars were collected from the glacial erratic boulders fine gravels surrounding exposed granite surfaces and from peat soil overlying the granite during natural weathering etch pits on microperthites enlarge almost exclusively by dissolution of albite and resin casts demonstrate that they can penetrate 15 m below the cleavage surface forming an interconnecting ladder like grid of submicrometer wide channels in the murchison plane coherent albite platelets and volumes of albite between dislocations in films dissolve uniformly but faster than orthoclase this is probably because the albite lamellae have significant elastic coherency strain but this is much less per unit volume of albite than the core and strain energy associated with edge dislocations patch perthites etch in hf vapour and weather rapidly in nature to produce a honeycomb like texture of interconnecting nanometer to micrometer sized pits which nucleate at preexisting micropores or incoherent subgrain boundaries the size and density of etch pits on microperthite surfaces which is determined by rates of growth and coalescence may be a useful progress variable for natural and experimental dissolution all alkali feldspars are highly heterogeneous materials whose chemical composition and microtexture can vary on a submicrometer scale these microtextures are critical variables with regard to the origin of surface roughness of fresh and weathered grains the controls on absolute dissolution rates and why they commonly change over time the nonlinear variation of dissolution rate with grain size the ratio of alkali ions released into solution and disparities between laboratory dissolution rates and those observed in the field

age and origin of early proterozoic dolerite dykes in south west greenland samples of three dolerite dykes from south west greenland give a pooled weighted mean rb sr whole rock isochron age of 2 130 65 ma initial 87sr 86sr ratios are 0 70155 0 00018 for one of the dykes naujat and 0 70277 0 00012 for the other two torssut and akinaq a fourth dyke qaqarssuaq did not yield an isochron torssut samples have significantly lower initial 207pb 204pb ratios than samples from the naujat dyke indicating that the torssut dyke has been affected by crustal contamination

the inner inner core of the earth texturing of iron crystals from three dimensional seismic anisotropy abstract we present a three dimensional model of the seismic anisotropy and texturing of iron crystals in the inner core the form of the anisotropy changes suddenly at slightly less than half of the inner core radius the outer part is composed of iron crystals of a single phase with different degrees of preferred alignment along the spin axis of the earth the inner part may be composed of a different phase of crystalline iron or have a different pattern of alignment

the sm nd age of kambalda volcanics is 500 ma too old although sm nd isotopic analyses of volcanics from kambalda western australia form a 3 2 ga linear array pb pb analyses of the same suite give an isochron age of 2 73 0 03 ga and a 2 7 ga model age for the associated sulphides we suggest that the 3 2 ga age is incorrect and that the sm nd array results from mixing between depleted mantle and either older continental crust or enriched mantle

frequency dependent seismic attenuation in the inner core 1 a viscoelastic interpretation 1 using reference source time functions broadband velocity waveforms of pkikp in the distance range 150 180 are inverted for a viscoelastic model of inner core attenuation a mean q at 1 hz of 307 90 is determined from 345 available pkikp ray paths both global and regional results find a depth dependent attenuation in the deep inner core with anisotropic attenuation resolved in regional results attenuation is much stronger in the upper 300 km of the inner core the preferred model of viscoelastic attenuation is frequency dependent with very weak velocity dispersion our data do not resolve any hemispherical differences of attenuation in the deep inner core

the age of the kambalda greenstones resolved by ion microprobe implications for archaean dating methods abstract a chert horizon within the archaean basalt pile at kambalda western australia contains zircons from air fall tuffs erupted as the sediment was laid down ion microprobe analyses of these magmatic zircons constrain the long sought age of the kambalda lavas to 2692 4ma 2 and show that regional metamorphism and deformation of the greenstone pile occurred within 30 ma of deposition rare zircon xenocrysts are evidence of pre greenstone crust as old as 3450 ma exposed remnants of which are yet to be identified subsets of both the magmatic and xenocryst zircons show evidence of hitherto unsuspected low temperature u and or pb mobility in the proterozoic long after stabilisation of the craton the ion microprobe data unravel complexities of isotopic inheritance and alteration illustrating the hazards of using bulk or whole rock samples in archaean isotopic investigations identification of interflow cherts as a precisely dateable rock type opens the way to direct ion probe dating of mafic ultramafic piles and close numerical age control of the complex but ill exposed stratigraphic and structural relations in this richly mineralised greenstone belt

crystal size distribution csd in rocks and the kinetics and dynamics of crystallization ii makaopuhi lava lake crystal size distribution csd theory has been applied to drill core samples from makaopuhi lava lake kilauea volcano hawaii plagioclase and fe ti oxide size distribution spectra were measured and population densities n were calculated and analyzed using a steady state crystal population balance equation n n0 exp l g slopes on ln n versus crystal size l plots determine the parameter g a product of average crystal growth rate g and average crystal growth time the intercept is j g where j is nucleation rate known temperature depth distributions for the lava lake provide an estimate of effective growth time allowing nucleation and growth rates to be determined that are independent of any kinetic model plagioclase growth rates decrease with increasing crystallinity 9 9 5 4 10 11 cm s as do plagioclase nucleation rates 33 9 1 6 10 3 cm3 s ilmenite growth and nucleation rates also decrease with increasing crystallinity 4 9 3 4 10 10 cm s and 15 2 2 10 3 cm3 s respectively magnetite growth and nucleation rates are also estimated from the one sample collected below the magnetite liquidus g 2 9 10 10 cm s j 7 6 10 2 cm3 s moments of the population density function were used to examine the change in crystallization rates with time preliminary results suggest that total crystal volume increases approximately linearly with time after 50 crystallization a more complete set of samples is needed for material with 50 crystals to define the entire crystallization history comparisons of calculated crystallization rates with experimental data suggests that crystallization in the lava lake occurred at very small values of undercooling this interpretation is consistent with proposed thermal models of magmatic cooling where heat loss is balanced by latent heat production to maintain equilibrium cooling

ab initio calculations of the elasticity of hcp fe as a function of temperature at inner core pressure ab initio finite temperature molecular dynamics simulations have been used to calculate the elastic constants of hexagonal close packed hcp fe as a function of temperature at similar to 300 gpa the longitudinal modulus c 1 1 decreases with temperature in stark contrast to previous calculations but in agreement with experimental observations on other transition metals at ambient pressures c 33 and c 44 also decrease with temperature while c 12 and c 23 slightly increase when these moduli are used to calculate p wave velocities through the crystal the sense of the anisotropy is such that v p is fastest along the c axis up to 5000 k however by 5500 k the anisotropy reverses with v p becoming faster in the a b plane this suggests that for an inner core dominated by crystals of hcp fe aligned with the c axis in the polar direction the observed isotropic outer inner core could result from the hcp fe being at a temperature close to melting where the axial wave velocities parallel and perpendicular to the c axis become similar while at greater depths in the inner inner core where iron is further from melting stronger anisotropy is achieved with the faster p wave velocities parallel to the polar axis no other mechanisms such as changes in composition or crystal alignment are therefore required to account for the observed change in seismic anisotropy of the earth s inner core with depth c 2009 elsevier b v all rights reserved

geochronologic significance of lead lines from old cratons abstract lead isotope data from geologically mixed suites of archaean gneisses often yield secondary isochrons that have statistically better fits than might be expected from the geological constraints on the range of samples used accepted as true isochrons these pb pb lines are commonly used both to determine the age of the rock suite and as evidence that all the rocks that yield data points within error of the isochron were formed at the same time from the same source using within geologically reasonable limits random data for initial lead and secondary lead growth we demonstrate that heterogeneous sample sets may yield statistically valid secondary isochrons this implies that the fit to a common secondary isochron does not necessarily mean that the samples used have the same age or an isotopically similar source numerical modelling of artificial data sets suggests that high correlation between 1 and 2 values is the single most important factor that enhances the statistical fit of the samples about a lead line and smoothes the initial scatter in contrast initial scatter will be preserved in data sets with a random relation between 1 and 2 values the 1 value estimated from the lead line will be biased towards the sample with the lowest 2 value

influences of dolomite precipitation on quartz surface textures abstract scanning electron microscopic examination of surface textures of quartz grains digested from dolomite cemented sandstones and sandy dolostones revealed that dolomite precipitation can affect quartz surfaces by 1 impeding syntaxial quartz overgrowth precipitation and 2 causing detrital quartz dissolution both of these processes resulted in the formation of dolomite rhombohedron shaped molds on quartz grain surfaces which are diagnostic for the recognition of secondary porosity formed by cement dissolution precipitation controlled dolomite replacement of quartz along euhedral dolomite crystal faces is consistent with the force of crystallization controlled replacement model some dolomite cement precipitation occurs without noticeable alteration of quartz grain surfaces dolomite c mentation is also associated with surface reaction controlled dissolution textures that may have formed by either 1 host grain controlled replacement of quartz by dolomite or 2 void filling dolomite precipitation into etch pits formed by earlier quartz dissolution in undersaturated bulk pore waters

sm nd and pb isotopic study of mafic rocks associated with early proterozoic continental rifting the peropohja schist belt in northern finland the perapohja schist belt in northern finland rests unconformably on archaean granitoids and marks the early stages of proterozoic crustal evolution in the fennoscandian baltic shield 2440 ma old layered mafic intrusions predate the supracrustal and ca 2200 ma old sills of the gabbro wehrlite association intrude the lowest quartzites and volcanics runkaus of the sequence the sm nd mineral isochron of the penikat layered intrusion gives an age of 2410 64 ma the initial nd values of the penikat intrusion nd 2440 1 6 and the runkausvaara sill nd 2200 0 suggest that these mafic magmas were contaminated by older crustal material the sm nd and pb isotopic results on the 2 44 2 2 ga old runkaus volcanics indicate mobility of pb fractionation of sm nd during late greenschist facies metamorphism and crustal contamination the pb pb data provide an age of 1972 80 ma with a high initial 207pb 204pb ratio 1 8 49 while scattered sm nd data result in an imprecise age of 2330 180 ma with an initial nd value of about zero secondary titanite gives an u pb age of ca 2250 ma the jouttiaapa basalts in contrast ascended from the mantle without interaction with older crust these lree depleted tholeiites mark a break in continental sedimentation and yield a sm nd age of 2090 70 ma their initial nd 4 2 0 5 implies that the subcontinental early proterozoic mantle had been depleted in lree for a long period of time the first lava flows are strongly depleted in lree suggesting that their source was significantly more depleted than the source of mid ocean ridge basalts today

the chemical dissolution and physical migration of minerals induced during co2 laboratory experiments their relevance for reservoir quality the characterization of the quality and storage capacity of geological underground reservoirs is one of the most important and challenging tasks for the realization of carbon capture and storage ccs projects one approach for such an evaluation is the upscaling of data sets achieved by laboratory co2 batch experiments to field scale sub microscopic petrophysical tomographic and chemical analytical methods were applied to reservoir sandstone samples from the altmark gas field before and after static autoclave batch experiments at reservoir specific conditions to study the relevance of injected co2 on reservoir quality these investigations confirmed that the chemical dissolution of pore filling mineral phases carbonate anhydrite associated with an increased exposure of clay mineral surfaces and the physical detachment and mobilization of such clay fines illite chlorite are most appropriate to modify the quality of storage sites thereby the complex interplay of both processes will affect the porosity and permeability in opposite ways mineral dissolution will enhance the rock porosity and permeability but fine migration can deteriorate the permeability these reactions are realized down to m scale and will affect the fluid rock reactivity of the reservoirs their injectivity and recovery rates during co2 storage operations

hemispherical structure in inner core velocity anisotropy 1 we investigate the hemispherical pattern in inner core velocity anisotropy using a new and independent high quality data set of pkpbc pkpdf and pkpab pkpdf body wave observations our data show no evidence for a tilted anisotropy axis with respect to the earth s rotation axis and is significantly better fit by a model with 4 4 anisotropy in the western hemisphere and only 1 0 in the eastern hemisphere than by a model of uniform anisotropy we carry out variance minimization and find the boundaries between the hemispheres at lines of constant longitude at 14 e and 151 w variance minimization enables us to extract the imprint of hemispherical structure from all of the data and not just polar paths resulting in boundaries which are nearly 30 from the results of previous studies the high quality of the data allows us to provide robust evidence that the isotropic velocity in the eastern hemisphere is 0 2 lower than in the western hemisphere in the top 660 km of the inner core our data set also suggests an increase in inner core anisotropy in the eastern hemisphere from 1 to around 6 at depths deeper than 660 km indicating that the hemispherical pattern in anisotropy may disappear at greater depths the presence of hemispherical structure rules out mechanisms for creating anisotropy which are unable to sustain longitudinal variations in the inner core furthermore steady inner core superrotation of the order of 0 1 year would eradicate the hemispherical differences though inner core oscillation would still be permissible

inner core anisotropy in three dimensions the purpose of this paper is the investigation of cylindrical anisotropy in the inner core based on the travel time anomalies of the pkikp phase we use the arrival times reported in the international seismological centre bulletins for years 1964 1990 we select only earthquakes which have a good azimuthal coverage and a sufficiently large number of reporting stations the earthquakes are relocated using corrections for lateral heterogeneity computed for our most recent three dimensional mantle model we use a total of 313 422 observations of the df branch of pkp travel time anomalies within the epicentral distance ranges of 120 140 and 150 180 reported by 2335 stations for 26 377 earthquakes we process the data using an averaging procedure which we call cylindrical anisotropy stacking that enhances the effects of anisotropy but is expected to suppress those due to lateral heterogeneity and random errors the processed residuals show a remarkably consistent pattern this confirms the dominance of the cylindrical elastic anisotropy in the inner core with approximately a constant axis of symmetry this axis of symmetry is found to be tilted 10 5 1 from the earth s rotation axis in the direction 160 e 5 in the northern hemisphere in this new coordinate system we determine a four layer axisymmetric model of transverse anisotropy with each layer approximately 300 km thick the model shows that the anisotropy is strongest 3 within the innermost part of the core the travel time anomalies show significant 1 5 s longitudinal variations even when the tilt of the axis of symmetry is considered there is a substantial increase in the amplitude of the longitudinal variations which are dominated by the second and fourth harmonics for rays with bottoming depths exceeding 400 km below the inner core boundary the measurable tilt of the axis of symmetry and the presence of significant nonaxisymmetric signal may provide important clues with respect to the possible causes of anisotropy the increase in the anisotropy in the innermost part of the core departs from earlier inferences that anisotropy may be limited to the outermost 200 300 km of the earth s inner core

isotopically heterogeneous initial pb and continuous 222 rn loss in fossils the u pb systematics of brachiosaurus brancai abstract diagenetic incorporation of uranium into bone material establishes a u pb system that provides a minimum age for the fossil loss of rn and ra from the 238u decay series recent mobility of u and pb and incorporation of radiogenic pb from an old basement which was available during diagenesis disturbed the u pb system all data fall in a 206pb 238u 207pb 235u concordia diagram to the right of the concordia while samples that do not experience redistribution of u pb 222rn and 226ra should define a linear array that intersects the concordia curve at the age of diagenesis and at the age of the source of inherited radiogenic pb loss of 222rn and 226ra has led to displacement of the present data set to lower 206pb 238u and therefore to younger intercept ages and to older 207pb 206pb ages the 207pb 204pb 208pb 204pb systematics demonstrates that 1 three out of 19 samples experienced significant postdiagenetic fractionation of u and pb and that 2 the diagenetic pb addition was isotopically heterogeneous the 235u 207pb 206pb 207pb and 206pb 238u 207pb 235u systematics combined demonstrate that 3 the samples experienced 5 to 18 222rn loss for a 1 9 ga old source of the diagenetically introduced pb and correspondingly more for a younger pb source and that 4 there is no unique solution for the age of the source of diagenetic pb since pb from a younger source appears in the 235u 207pb 206pb 207pb diagram in the same way as higher 222rn loss no precise age can be determined from the data although the most consistent solution falls in the range of 140 to 150 ma addition of radiogenic pb to the fossil bone is obvious only through its anomalous highly radiogenic character and the isotopic heterogeneity in 208pb 204pb no th i e no in situ 208pb growth the effect of unrecognized diagenetic additions of radiogenic pb is an overestimation of the age whereas unrecognized 222rn loss results in a too young discordant age since fossil material formed at times for which the discordia only shows a small curvature anomalies originating from diagenetic pb additions and 222rn loss may not always be recognized

dating of subduction and differential exhumation of uhp rocks from the central dabie complex e china constraints from microfabrics rb sr and u pb isotope systems abstract the correlation of deformation fabrics and metamorphic reactions with geochronologic data of uhp metamorphic rocks demonstrate that the multistage subduction and exhumation history of the central dabie complex requires rapid subduction and rapid initial exhumation moreover these data show that volume diffusion is not the major resetting mechanism of radiogenic isotope systems thus our age data do not simply reflect a thermal cooling history in the investigated section the maximum age for uhp is given by the 244 3 ma 2 u pb age of a pre uhp titanite phenocryst that survived uhp metamorphism and subsequent tectonometamorphic events a minimum age for uhp is set by the 238 1 ma 2 238 u 206 pb mineral isochron age of titanite and cogenetic epidote these minerals formed from local partial melts during ascent and their age suggests fast exhumation and emplacement in the middle crust in the period of ca 238 218 ma the uhp terrain records ht metamorphism local partial melting and extensive pervasive strain below the eclogite jd grt stability field exhumation was polyphase with a first phase of fast exhumation succeeded by episodes of ht metamorphism and concomitant deformation at deep mid crustal level between 238 and 218 ma slow exhumation related to the final emplacement of tectonic units along greenschist facies shear zones did not cease before ca 209 204 ma the resetting and homogenization of radiogenic isotope systems were aided by dissolution precipitation creep which was the dominant deformation mechanism in quartz feldspar rocks in combination with fluid influx

phase shift interference microscope study of dissolution precipitation processes of nonhydrostatically stressed halite crystals in solution halite single crystals in saturated solution were used to study dissolution precipitation creep dpc at conditions where plastic deformation is negligible specifically the free unloaded surfaces of these crystals were investigated by a novel linnik based phase shift interference microscope the method allows observations of the crystal surface in situ and with an axial resolution in the nanometer scale transport phenomena in open systems temperature gradients and gradients in strain energy density were found to cause morphological changes on the free crystal surface by dissolution reprecipitation we did not find evidence for dpc by applying a homogeneous stress field to the crystal as long as plastic deformation was avoided these findings suggest that deformation of rocks by dpc in situations where dislocation creep is not activated but is rather promoted by fluid transport through the rock or by episodic changes of extensive parameters affecting solubility than by homogeneous stress alone

development of etch pit size distributions on dissolving minerals we have applied the theory of crystal size distributions to the evolution of etch pit size distributions psd s on dissolving minerals population balance equations are derived based on nucleation growth and annihilation of etch pits psd plots of log n number of pits per size per area vs w etch pit width are used to compare etch pit populations we have used psd analysis to study the development of etch pits on calcite dissolved in a rotating disk experiment far from equilibrium 25 c initial ph 8 6 0 7 m kcl a maximum is present on the psd plot in the early stages of dissolution and appears to result from nucleation of pits at all available sites on the initial cleaved surface over a finite time interval as pits grow larger become flat bottomed and annihilate the peak moves to larger sizes and decreases in magnitude to become insignificant after 17 5 hr after 0 5 hr the psd plots become linear at small pit widths marking a population balance as new pits nucleate within flat pits grow larger become flat bottomed and finally annihilate this population of short lived small 100 m etch pits possibly results from nucleation at point defect or impurity clusters a linear psd for long lived larger pits appears at 17 5 hr possibly reflecting etch pits at dislocations the overall psd plot at 17 5 hr is kinked due to these two populations calcite dissolution rates calculated from the coefficients of the psd are within a factor of two of the dissolution rate measured from solution chemistry such estimates will be more accurate if the duration of dissolution does not greatly exceed the mean lifetime of etch pits psd plots for hornblende and microcline grains from a loess soil that has weathered for 12 500 yr show similarities to the psd s from our calcite experiments the hornblende psd shows a peak and the microcline psd is linear or possibly kinked bulk dissolution rates for the grains calculated from the psd s are slower than rates measured for these minerals in the laboratory dissolution rates estimated from the psd coefficients for the hornblende and microcline soil grains are 3 4 and 1 2 orders of magnitude slower respectively than the corresponding laboratory rates

influence of etch pit development on the surface area and dissolution kinetics of the orthoclase 001 surface abstract the 001 orthoclase surface was dissolved at 180 c and at far from equilibrium conditions with an alkaline solution ph180 c 9 in a titanium open flow reactor vertical scanning interferometer vsi and atomic force microscope afm surface monitoring were periodically used during the reaction process in order to quantify the surface topography evolution the dissolution of the 001 orthoclase face occurs with the formation of diamond shape etch pits diamond pit diagonals are parallel to the 100 and 010 axes and the pit walls are parallel to 6 5 6 6 5 6 6 5 11 and 6 5 11 planes the etch pit size and global surface retreat of the 001 surface were found to increase linearly with time based on statistical treatments of etch pit development monitoring by afm we designed a numerical model aimed at reproducing and quantifying the total surface evolution numerical results show that the stabilization of etch pits doubles the calculated dissolution rate partly due to the intrinsically higher reactivity of pit walls consistent with a dissolution process in line with the periodic bond chain pbc theory in addition normalizing the dissolution rate by the initial surface area of the 001 orthoclase surface induces a 20 overestimation of the calculated dissolution rate while the total surface area of the dissolving face reaches a steady state after a few days of reaction additional simulations conducted to assess the impact of defect parameters revealed a weak dependence of the dissolution rate on dislocation density consistent with previous experimental observations overall the combined effect of the various defect parameters does not affect the dissolution rate by more than an order of magnitude and probably contributes to a moderate extent to the dispersion of mineral dissolution rate data reported in the literature

etch pit size and shape distribution on orthoclase and pyriboles in a loess catena abstract etch pits on 50 100 m orthoclase and pyribole grains from the e b and c horizons of a catena or drainage sequence of well drained somewhat poorly drained and poorly drained loessal soils were analyzed using sem and digital image analysis the objective was to determine the influence of soil drainage conditions and the associated geochemical environments on dissolution of primary silicates as determined from the distribution of etch pits on the grain surfaces etch pit size frequency distributions indicated that the poorly drained soil contained the smallest and most numerous etch pits for both minerals this indicated low growth rates for etch pits in the poorly drained soil analysis of etch pit shapes indicated that etch pits on pyriboles were more elongated and irregular in the poorly drained soil possibly resulting from a greater growth rate whereas etch pits on orthoclase grains were more elongated and irregular in the well drained soil the larger more elongated and irregularly shaped etch pits on orthoclase from the well drained soil indicative of a greater pit growth rate is consistent with a flushing model of mineral weathering in soils the etch pit size distribution on pyriboles is consistent with the flushing concept but the shape data indicates that other mechanisms of weathering may be involved

seismic structures in the earth s inner core below southeastern asia documenting seismic heterogeneities in the earth s inner core ic is important in terms of getting an insight into its history and dynamics a valuable means for studying properties and spatial structure of such heterogeneities is provided by measurements of body waves refracted in the vicinity of the inner core boundary icb here we investigate eastern hemisphere of the solid core by means of pkpbc pkpdf differential travel times that sample depths from 140 to 360 km below its boundary we study 292 polar and 133 equatorial residuals measured over the traces that probe roughly the same volume of the ic in both planes equatorial residuals show slight spatial variations in the sampled ic volume mostly below the level of 0 5 whereas polar residuals are up to three times as big direction dependent and can exhibit higher local variations the measurements reveal fast changes in seismic velocity within a restricted volume of the ic we interpret the observations in terms of anisotropy and check against several anisotropy models few of which have been found capable of fitting the residuals scatter we particularly quantify the model where a dipping discontinuity separates fully isotropic roof of the ic from its anisotropic body whereas the depth of isotropy anisotropy transition increases in southeast direction from 190 km below southeastern asia off the coast of china to 350 km beneath australia another acceptable model cast in terms of localized anisotropic heterogeneities is valid if 33 largest polar measurements over the rays sampling a small volume below southeastern asia and the rest of polar data are treated separately this model envisages almost isotropic eastern hemisphere of the ic at least down to the depth of 360 km below the icb and constrains the anisotropic volume only to the ranges of north latitudes from 18 to 23 east longitudes from 125 to 135 and depths exceeding 170 km the anisotropy strength in either model is about 2 further effective pursuit of the models presents challenges in terms of resolution and coverage and basically requires a significant dataset extension

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

constraints on upper inner core structure from waveform inversion of core phases summary the determination of the inner core boundary structure is key to understanding the mechanisms of inner core growth iron solidification and anisotropy formation in the inner core a waveform inversion of a worldwide data set of pkikp and pkikp core phases is performed to investigate the velocity and the attenuation structure of this region the data set is chosen to sample the top 50 km of the inner core two inversion methods combining time and frequency domain observations are presented synthetic tests are performed in order to evaluate the resolution and the confidence intervals of the model parameters the attenuation of p waves in the uppermost inner core is poorly resolved but appears to be high q 100 the uppermost inner core interface is divided into two regions a region extending from 180 w to 60 e and characterized by negative p wave velocity perturbations dv v 0 per cent and a region extending from 60 e to 180 e and characterized by positive p wave velocity perturbations dv v 1 per cent the results of the inversion do not favour the presence of transverse isotropy aligned along the spin axis of the earth in the uppermost inner core for these two regions however these regions are correlated with those where large scale variations of the inner core anisotropy have been determined previously in the deeper inner core 100 km beneath the inner core boundary

reconciling the hemispherical structure of earth s inner core with its super rotation earth s solid inner core grows through solidification of material from the fluid outer core onto its surface at rates of about 1 mm per year1 freezing in core properties over time and generating an age depth relation for the inner core a hemispherical structure of the inner core is well documented an isotropic eastern hemisphere with fast seismic velocities contrasts with a slower anisotropic western hemisphere2 3 4 independently the inner core is reported to super rotate at rates of up to 1 per year5 6 7 considering the slow growth steady rotation rates of this magnitude would erase frozen in regional variation and cannot coexist with hemispherical structure here we exploit the age depth relation using the largest available pkikp pkikp seismic travel time data set to confirm hemispherical structure in the uppermost inner core and to constrain the locations of the hemisphere boundaries we find consistent eastward displacement of these boundaries with depth from which we infer extremely slow steady inner core super rotation of 0 1 1 per million years our estimate of long term super rotation reconciles inner core rotation with hemispherical structure two properties previously thought incompatible it is in excellent agreement with geodynamo simulations8 9 while not excluding the possibility that the much larger rotation rates inferred earlier5 6 7 correspond to fluctuations in inner core rotation on shorter timescales10

the dissolution kinetics of major sedimentary carbonate minerals abstract among the most important set of chemical reactions occurring under near earth surface conditions are those involved in the dissolution of sedimentary carbonate minerals these minerals comprise about 20 of phanerozoic sedimentary rocks calcite and to a significantly lesser extent dolomite are the major carbonate minerals in sedimentary rocks in modern sediments aragonite and high magnesian calcites dominate in shallow water environments however calcite is by far the most abundant carbonate mineral in deep sea sediments an understanding of the factors that control their dissolution rates is important for modeling of geochemical cycles and the impact of fossil fuel co 2 on climate diagenesis of sediments and sedimentary rocks it also has practical application for areas such as the behavior of carbonates in petroleum and natural gas reservoirs and the preservation of buildings and monuments constructed from limestone and marble in this paper we summarize important findings from the hundreds of papers constituting the large literature on this topic that has steadily evolved over the last half century our primary focus is the chemical kinetics controlling the rates of reaction between sedimentary carbonate minerals and solutions we will not attempt to address the many applications of these results to such topics as mass transport of carbonate components in the subsurface or the accumulation of calcium carbonate in deep sea sediments such complex topics are clearly worthy of review papers on their own merits calcite has been by far the most studied mineral over a wide range of conditions and solution compositions in recent years there has been a substantial shift in emphasis from measuring changes in solution composition to determine batch reaction rates to the direct observation of processes occurring on mineral surfaces using techniques such as atomic force microscopy afm however there remain major challenges in integrating these two very different approaches a general theory of surface dissolution mechanisms currently lacking although see lasaga and luttge science 291 2001 2400 is required to satisfactorily relate observations of mineral surfaces and the concentration of dissolved components studies of aragonite high magnesian calcites magnesite and dolomite dissolution kinetics are much more limited in number and scope than those for calcite and provide at best a rather rudimentary understanding of how these minerals are likely to behave in natural systems although the influences of a limited number of reaction inhibitors have been studied probably the greatest weakness in application of experimental results to natural systems is understanding the often profound influences of foreign ions and organic matter on the near equilibrium dissolution kinetics of carbonate minerals

heterogeneity and anisotropy of earth s inner core seismic observations provide strong evidence that earth s inner core is anisotropic with larger velocity in the polar than in the equatorial direction the top 60 80 km of the inner core is isotropic evidence for an innermost inner core is less compelling the anisotropy is most likely due to alignment of hcp hexagonal close packed iron crystals aligned either during solidification or by deformation afterward the existence of hemispherical variations used to be controversial but there is now strong evidence from both seismic body wave and normal mode observations showing stronger anisotropy less attenuation and a lower isotropic velocity in the western hemisphere two mechanisms have been proposed to explain the hemispherical pattern either a inner core translation wherein one hemisphere is melting and the other is solidifying or b thermochemical convection in the outer core leading to different solidification conditions at the inner core boundary neither is yet able to explain all se

the effect of nickel on the properties of iron at the conditions of earth s inner core ab initio calculations of seismic wave velocities of fe ni alloys abstract we have performed athermal periodic plane wave density functional calculations within the generalised gradient approximation on the bcc fcc and hcp structures of fe 1 x ni x alloys x 0 0 0625 0 125 0 25 and 1 in order to obtain their relative stability and elastic properties at 360 gpa and 0 k for the hcp structure using ab initio molecular dynamics we have also calculated the elastic properties and wave velocities for x 0 0 0625 and 0 125 at 360 gpa and 5500 k with further calculations for x 0 and 0 125 at 360 gpa and 2000 k at 0 k the hcp structure is the most stable for x 0 0 0625 0 125 and 0 25 with the fcc structure becoming the most stable above x 0 45 the bcc structure is not the most stable phase for any composition at 0 k compressional and shear wave velocities are structure dependent in the case of fcc the velocities are very similar to pure fe but for the hcp structure the addition of ni strongly reduces v s ni also reduced velocities in fcc iron but to a lesser extent however at 5500 k and 360 gpa ni has little effect on the wave velocities of the hcp structure which remain similar to those of pure iron throughout the range of compositions studied and in the case of v s 30 greater than that from seismological models the effect of temperature on fe ni alloys is therefore very significant indicating that conclusions based on the extrapolation of results obtained at much lower temperatures must be treated with great caution the significance of temperature is confirmed by the additional simulation at 2000 k for x 0 and 0 125 which reveals a remarkably linear temperature dependence of the change in v s relative to that of pure iron at 0 k the maximum anisotropy in v p is found to be only very weakly dependent on nickel content but dependent on structure being 15 for fcc and 8 for hcp for the hcp structure at 2000 and 5500 k the maximum anisotropy in v p is also 8 and almost independent of the ni content we conclude that ni can safely be ignored when considering its effect on the seismic properties of hcp fe under core pressures and temperatures and that the negligible effect of nickel on the physical properties of iron in the core arises not because of the chemical similarities between iron and nickel but because of the high temperature of the system