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

resistivity saturation of hcp fe si alloys in an internally heated diamond anvil cell a key to assessing the earth s core conductivity abstract electrical resistivity and thermal conductivity of iron fe light element alloys at high pressure and temperature are key parameters to constrain the dynamics and thermal evolution of the earth s core we determined the electrical resistivity of hcp fe 2 4 and 6 5 wt silicon si alloys up to 117 gpa and 3120 k using a four terminal method in an internally heated diamond anvil cell the temperature dependence of electrical resistivity of hcp fe si alloys was suppressed as both si concentration and temperature increased which indicates the resistivity saturation phenomenon the electrical resistivity of metal asymptotically approaches the saturation resistivity our results are fully reproduced by a highly resistive saturation model and the obtained saturation resistivities for hcp fe si alloys are comparable to those for hcp pure fe at around 100 gpa if si is a major light element in the earth s core the pure fe like saturation resistivity would keep the core conductivity high enough to induce active dynamics there and rapid growth of the inner core

cloud layer overlap characteristics derived from long term cloud radar data assumptions regarding the vertical overlap characteristics of horizontal cloudy layers have been shown to be important to both the radiation transfer and the cloud microphysics that are predicted in general circulation models certain reasonable assumptions regarding cloud layer overlap have been applied in models up to now where vertically continuous cloudy layers were assumed to overlap maximally leading to a minimum in cloud cover and layers separated by noncloudy layers were assumed to overlap randomly however these assumptions have not been systematically evaluated with a comprehensive dataset that can resolve simultaneously occurring cloud layers presented here is an analysis of cloud layer overlap characteristics derived from 103 months of cloud radar data collected by continuously operating millimeter wavelength instruments deployed at the atmospheric radiation measurement arm sites in the tropics middle latitudes and the arctic using an approach recently proposed by hogan and illingworth it is shown that an assumption of random overlap for layers separated by noncloudy layers is supported by observations however that the overlap characteristics of vertically continuous layers cannot be considered maximal is also shown indeed vertically continuous cloudy layers do not appear to lend themselves to a simple overlap assumption therefore to avoid significant biases in diagnosed cloud cover the overlap properties of these layers in models will need to be parameterized it is shown that the cloud layer overlap characteristics in the middle latitudes do appear to be a strong function of season suggesting that an overlap parameterization in terms of cloud system type may be possible

sharp mantle transition from cratons to cordillera in southwestern canada the western canada sedimentary basin marks the transition from the old north american continental lithosphere to young accreted terranes earlier studies in this region have suggested a large number of intricate basement domains as well as major seismic velocity gradients in the mantle to investigate the effect of the accretion and subduction on the mantle structure beneath the western margin of the north american craton we analyze p to s converted waves from upper mantle discontinuities from the canadian rockies and alberta network a regional broadband seismic array based in alberta canada the depths of the 410 and 660 km seismic discontinuities are correlated and on average are 9 km and 7 km greater than their respective global estimates the largest depression is observed beneath the rocky mountain foreland belt in southern alberta which highlights a steep southward westward structural gradient from the cratons to cordillera at lithospheric mantle depths the severity of the depressions especially in the southernmost alberta may be triggered by diffuse partial melt or increased water content above the 410 km discontinuity this result is corroborated by locally increased impedance contrast across the 410 km discontinuity and a strongly depressed 660 km discontinuity a relic mesozoic slab fragment may be partially responsible for the deep olivine phase boundary at the base of the upper mantle

sediments at the top of earth s core unusual physical properties at the core mantle boundary have been inferred from seismic and geodetic observations in recent years we show how both types of observations can be explained by a layer of silicate sediments which accumulate at the top of the core as earth cools compaction of the sediments expels most of the liquid iron but leaves behind a small amount of core material which is entrained in mantle convection and may account for the isotopic signatures of core material in some hot spot plumes extraction of light elements from the liquid core also enhances the vigor of convection in the core and may increase the power available to the geodynamo

the melting curve of ni to 1 mbar the melting curve of ni has been determined to 125 gpa using laser heated diamond anvil cell lh dac experiments in which two melting criteria were used firstly the appearance of liquid diffuse scattering lds during in situ x ray diffraction xrd and secondly plateaux in temperature vs laser power functions in both in situ and off line experiments our new melting curve defined by a simon glatzel fit to the data where t m k p m 18 78 10 20 1 1 2 42 0 66 1726 is in good agreement with the majority of the theoretical studies on ni melting and matches closely the available shock wave melting data it is however dramatically steeper than the previous off line lh dac studies in which determination of melting was based on the visual observation of motion aided by the laser speckle method we estimate the melting point t m of ni at the inner core boundary icb pressure of 330 gpa to be t m 5800 700 k 2 within error of the value for fe of t m 6230 500 k determined in a recent in situ lh dac study by similar methods to those employed here this similarity suggests that the alloying of 5 10 wt ni with the fe rich core alloy is unlikely to have any significant effect on the temperature of the icb though this is dependent on the details of the topology of the fe ni binary phase diagram at core pressures our melting temperature for ni at 330 gpa is 2500 k higher than that found in previous experimental studies employing the laser speckle method we find that those earlier melting curves coincide with the onset of rapid sub solidus recrystallization suggesting that visual observations of motion may have misinterpreted dynamic recrystallization as convective motion of a melt this finding has significant implications for our understanding of the high pressure melting behaviour of a number of other transition metals

equation of state and phase diagram of fe 16si alloy as a candidate component of earth s core the outer core of the earth contains several weight percent of one or more unknown light elements which may include silicon therefore it is critical to understand the high pressure temperature properties and behavior of an iron silicon alloy with a geophysically relevant composition 16 wt silicon we experimentally determined the melting curve subsolidus phase diagram and equations of state of all phases of fe 16 wt si to 140 gpa finding a conversion from the d03 crystal structure to a b2 hcp mixture at high pressures the melting curve implies that 3520 k is a minimum temperature for the earth s outer core if it consists solely of fe si alloy and that the eutectic composition in the fe si system is less than 16 wt silicon at core mantle boundary conditions comparing our new equation of state to that of iron and the density of the core we find that for an fe ni si outer core 11 3 1 5 wt silicon would be required to match the core s observed density at the core mantle boundary we have also performed first principles calculations of the equations of state of fe3si with the d03 structure hcp iron and fesi with the b2 structure using density functional theory

lithoprobe reflection studies of archean and proterozoic crust in canada abstract lithoprobe canada s national collaborative earth science research project established to develop a comprehensive understanding of the evolution of the north american continent is a multidisciplinary program spearheaded by seismic reflection studies five recently recorded seismic lines discussed in this paper are located in precambrian regions the mesoproterozoic grenville province the paleoproterozoic trans hudson orogen tho the paleoproterozoic archean basement of alberta and the archean superior province data acquired across the grenville orogen in eastern quebec show strong reflectivity throughout the crust upper crustal reflections can be correlated with exposed structural elements including extensional shear zones and packages of deformed high pressure rocks eclogites in a marine survey across the grenville orogen off southeastern labrador seismic images show variably dipping reflections and a structural high associated with a major gravity anomaly data acquired across central alberta show crustal scale thrust stacking and imbrication of the archean hearne craton to the east across the trans hudson orogen images of similar collisional features are observed geochronologic constraints indicate contemporaneity of tectonic activity between the two regions at 1 8 ga suggesting that collisional tectonic activity was coeval over a broad crustal region ca 1000 km across strike in the superior province seismic data across a collision zone involving the northern abitibi greenstone belt and the arc related opatica plutonic belt show spectacular crustal reflectivity and dipping reflections that extend 8 s 30 km into the mantle the latter feature is interpreted as representing a relict 2 69 ga old suture associated with subduction providing the first direct evidence that plate tectonics was active in the late archean these five examples supported by other lithoprobe results refute a number of generalizations about crustal reflectivity that have been made in the past and illustrate how reflection studies combined with other geoscience studies can lead to a better understanding of precambrian tectonics reflectivity persists throughout the crust there is no general separation into a poorly reflective upper crust and a reflective lower crust crustal reflectivity in archean and proterozoic regions is as pervasive as that in areas of more recent tectonism the precambrian reflection moho is generally well defined but shows a range of characteristics relative ages of reflectors can be discerned and tectonic significance can be attached to characteristic features of the crustal reflectivity

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

cloud overlap statistics the u s air force three dimensional nephanalysis 3dneph has been employed to analyze the vertical distribution of clouds and cloud overlap statistics during january 1979 over the north atlantic ocean 40 to 60 n the 3dneph integrates both satellite and conventional observations and gives what is probably the best available information on the vertical distribution of clouds this region was chosen because of the predominance of layered clouds and the high density of conventional observations the grid size of the 3dneph is 45 km and the data set was additionally averaged over three different grid sizes 90 221 and 442 km three cloud overlap assumptions that have been commonly used were tested namely the maximum minimum and random overlap assumptions for adjacent layers of the 3dneph that contained cloud the maximum overlap assumption performed the best accurately determining the total cloud cover to within the roundoff error for the layered cloud amounts in 82 of the cases for two or three cloud layers that were separated by clear interstices the random overlap assumption performed the best overall for all resolutions although there were systematic biases in the predicted cloud fraction which depend on the cloud fraction of the layers and on grid size for grid sizes 9o km random overlap resulted in a systematic underestimation of total cloud cover 5 random overlap performed worst when there were two layers with intermediate cloud fractions 30 70 the results of this study indicate that while random overlap performs reasonably well on average the systematic bias which depends on grid resolution and random discrepancies could result in significant errors when this approximation is used in general circulation modeling and cloud climatologies

crustal imprints of precambrian orogenesis in western laurentia crustal low velocity zones lvzs have been reported in active orogens such as the himalayas and the andes but rarely in stable cratonic regions in this study we provide compelling evidence for a significant midcrustal lvz beneath eastern central alberta an integral part of the precambrian canadian shield covered by thick phanerozoic sedimentary deposits this 200 km wide over 10 km thick midcrustal lvz is well resolved by shear velocity inversions using p to s receiver functions from more than 4600 earthquakes it is generally overlain by a high velocity upper crust in the depth range of 8 15 km especially in western central alberta which coincides with the previously documented winagami reflection sequence we interpret the lvz to be of granitic composition potentially in connection with the crystallization of partially molten crust during the paleoproterozoic eon in addition to the precambrian tectonic history of western laurentia which featured plate convergence conducive to crustal melting our crustal model is further supported by 1 a moderate spatial correlation between the lvz and heat flow and 2 shear velocities consistent with that of granite the well preserved winagami reflection sequence and the lvz are potential evidence of distinct episodes of magmatism and crust modification in the precambrian basement of the western canada sedimentary basin the existence of a broad crustal lvz suggests extensive subduction orogenesis and crustal melting during the precambrian assembly of the north american craton

tripleclouds an efficient method for representing horizontal cloud inhomogeneity in 1d radiation schemes by using three regions at each height abstract radiation schemes in general circulation models currently make a number of simplifications when accounting for clouds one of the most important being the removal of horizontal inhomogeneity a new scheme is presented that attempts to account for the neglected inhomogeneity by using two regions of cloud in each vertical level of the model as opposed to one one of these regions is used to represent the optically thinner cloud in the level and the other represents the optically thicker cloud so along with the clear sky region the scheme has three regions in each model level and is referred to as tripleclouds in addition the scheme has the capability to represent arbitrary vertical overlap between the three regions in pairs of adjacent levels this scheme is implemented in the edwards slingo radiation code and tested on 250 h of data from 12 different days the data are derived from cloud retrievals using radar lidar and a microwave radiometer at chilbolton southern united kingdom when

detection of widespread fluids in the tibetan crust by magnetotelluric studies magnetotelluric exploration has shown that the middle and lower crust is anomalously conductive across most of the north to south width of the tibetan plateau the integrated conductivity conductance of the tibetan crust ranges from 3000 to greater than 20 000 siemens in contrast stable continental regions typically exhibit conductances from 20 to 1000 siemens averaging 100 siemens such pervasively high conductance suggests that partial melt and or aqueous fluids are widespread within the tibetan crust in southern tibet the high conductivity layer is at a depth of 15 to 20 kilometers and is probably due to partial melt and aqueous fluids in the crust in northern tibet the conductive layer is at 30 to 40 kilometers and is due to partial melting zones of fluid may represent weaker areas that could accommodate deformation and lower crustal flow

ice cloud inhomogeneity quantifying bias in emissivity from radar observations in numerical models the infra red emissivity of ice clouds is generally computed from the optical depth the convex relationship between these two quantities implies that if ice clouds are inhomogeneous emissivities calculated from a grid box mean optical depth will be biased high an analogous effect in stratocumulus albedo and liquid water path is compensated for by multiplying liquid water by 0 7 to calculate albedo however it is unclear that a similar correction is valid for all cloud types in this paper profiles of radar reflectivity in mid latitude winter ice clouds are analysed to derive the variability of optical depth and quantify any biases introduced into emissivities calculated from grid box mean optical depths the bias is small for grid lengths of 10km but the average optical depth should be multiplied by a correction factor of 0 44 for calculating emissivities in a 300km box

fesi melting curve up to 70 gpa abstract the melting curve of iron monosilicide fesi has been determined in a laser heated diamond anvil cell from 6 up to 70 gpa by direct visual observation of the continuous laser speckle motion in the liquid state at 12 gpa and 1700 k a discontinuous change in the slope of the melting curve indicates the first order phase transition between the fesi b20 and the cscl type fesi structures b2 during the phase transition the coordination number of both fe and si atoms increases from 7 to 8 above this pressure the melting curve rises steeply but shows significant flattening at higher pressures a comparison with the melting curve of fe shows that both curves cross at 32 3 gpa fesi having higher melting temperatures about 100 k at high pressures

influence of sulfur on the electrical resistivity of a crystallizing core in small terrestrial bodies abstract electrical experiments were performed on core analogues in the fe s system and on fesi2 up to 8 gpa and 1850 c in the multi anvil apparatus electrical resistivity was measured using the four electrode method for all samples resistivity increases with increasing temperature the higher the s content the higher the resistivity and the resistivity increase upon melting at 4 5 gpa liquid fes is up to 10 times more resistive than fe 5 wt s and twice more resistive than fesi2 suggesting a stronger influence of s than si on liquid resistivity electrical results are used to develop crystallization resistivity paths considering both equilibrium and fractional crystallization in the fe s system at 4 5 gpa equilibrium crystallization as expected locally in thin snow zones during top down core crystallization presents electrical resistivity variations from about 300 to 190 microhm cm for a core analogue made of fe 5 wt s depending on temperature fractional crystallization which is relevant to core scale cooling leads to more important electrical resistivity variations depending on s distribution across the core temperature and pressure estimates of the lower bound of thermal resistivity are calculated using the wiedemann franz law comparison with previous works indicates that the thermal conductivity of a metallic core in small terrestrial bodies is more sensitive to the abundance of alloying agents than that of the earth s core application to ganymede using core adiabat estimates from previous studies suggests important thermal resistivity variations with depth during cooling with a lower bound value at the top of the core that can be as low as 3 w m k it is speculated that the generation and sustainability of a magnetic field in small terrestrial bodies might be favored in light element depleted cores

mercury s thermal evolution controlled by an insulating liquid outermost core abstract the weak intrinsic magnetic field of mercury is intimately tied to the structure and cooling history of its metallic core recent constraints about the planet s internal structure suggest the presence of a fes layer overlying a silicon bearing core we performed 4 electrode resistivity experiments on core analogues up to 10 gpa and over wide temperature ranges in order to investigate the insulating properties of core materials our results show that the fes layer is liquid and insulating and that the electrical resistivity of a miscible fe si s core is comparable to the one of an immiscible fe s fe si core the difference in electrical resistivity between the fes rich layer and the underlying fe si s core is at least 1 log unit at pressure and temperature conditions relevant to mercury s interior estimates of the lower bound of thermal conductivity for fes and fe si s materials are calculated using the wiedemann franz law a thick 40 km fes rich shell is expected to maintain high temperatures across the core and if temperature in this layer departs from an adiabat then this might affect the core cooling rate the presence of a liquid and insulating shell is not inconsistent with a thermally stratified core in mercury and is likely to impact the generation and sustainability of a magnetic field

granite magma formation transport and emplacement in the earth s crust the origin of granites was once a question solely for petrologists and geochemists but in recent years a consensus has emerged that recognizes the essential role of deformation in the segregation transport and emplacement of silica rich melts in the continental crust accepted petrological models are being questioned either because they require unrealistic rheological behaviours of rocks and magmas or because they do not satisfactorily explain the available structural or geophysical data provided flow is continuous mechanical considerations suggest that far from being geologically sluggish granite magmatism is a rapid dynamic process operating at timescales of or 100 000 years irrespective of tectonic setting

trans hudson orogen of north america and himalaya karakoram tibetan orogen of asia structural and thermal characteristics of the lower and upper plates 1 the trans hudson orogen tho of north america and the himalaya karakoram tibetan orogen hkto of asia preserve a paleoproterozoic and cenozoic record respectively of continent continent collision that is notably similar in scale duration and character in tho the tectonothermal evolution of the lower plate involves 1 early thin skinned thrusting and barrovian metamorphism 2 out of sequence thrusting and high t metamorphism and 3 fluid localized reequilibration anatexis and leucogranite formation the crustal evolution of the indian lower plate in hkto involves 1 early subduction of continental crust to ultrahigh pressure uhp eclogite depths 2 regional barrovian metamorphism and 3 widespread high t metamorphism anatexis and leucogranite formation the shallow depths of the high t metamorphism in hkto are consistent with early to mid miocene ductile flow of an indian lower plate midcrustal channel from beneath the southern tibetan plateau to the greater himalaya melt weakening of the lower plate in tho is not observed at a similar scale probably due to the paucity of pelitic lithologies tectonothermal events in the upper plate of both orogens include precollisional accretion of crustal blocks emplacement of andean type plutonic suites and high t metamorphism syncollisional to postcollisional events include emplacement of garnet biotite muscovite leucogranites anatectic granites and sporadic metamorphism up to 90 myr following the onset of collision in tho comparing the type and duration of tectonothermal events for tho and hkto supports the notion of tectonic uniformitarianism for at least the later half of dated earth history and highlights the complementary nature of the rock record in an older exhumed orogen compared to one undergoing present day orogenesis

seismic anisotropy in the earth s innermost inner core testing structural models against mineral physics predictions using an updated data set of ballistic pkikp travel time data at antipodal distances we test different models of anisotropy in the earth s innermost inner core imic and obtain significantly better fits for a fast axis aligned with earth s rotation axis rather than a quasi equatorial direction as proposed recently reviewing recent results on the single crystal structure and elasticity of iron at core conditions we find that an hcp structure with the fast c axis parallel to earth s rotation is more likely but a body centered cubic structure with the 111 axis aligned in that direction results in very similar predictions for seismic anisotropy these models are therefore not distinguishable based on current seismological data in addition to match the seismological observations the inferred strength of anisotropy in the imic 6 7 implies almost perfect alignment of iron crystals an intriguing albeit unlikely situation especially in the presence of heterogeneity which calls for further studies

high pressure melting experiments on fe si alloys and implications for silicon as a light element in the core abstract we carried out melting experiments on fe si alloys to 127 gpa in a laser heated diamond anvil cell dac on the basis of textural and chemical characterizations of samples recovered from a dac a change in eutectic liquid composition in the fe fesi binary system was examined with increasing pressure the chemical compositions of coexisting liquid and solid phases were quantitatively determined with field emission type electron microprobes the results demonstrate that silicon content in the eutectic liquid decreases with increasing pressure to less than 1 5 0 1 wt si at 127 gpa if silicon is a single light element in the core 4 5 to 12 wt si is required in the outer core in order to account for its density deficit from pure iron however such a liquid core whose composition is on the si rich side of the eutectic point crystallizes less dense solid cscl b2 type phase at the inner core boundary icb our data also show that the difference in silicon concentration between coexisting solid and liquid is too small to account for the observed density contrast across the icb these indicate that silicon cannot be the sole light element in the core previous geochemical and cosmochemical arguments however strongly require 6 wt si in the core it is possible that the earth s core originally included 6 wt si but then became depleted in silicon by crystallizing sio2 or mgsio3

the elastic properties of hcp fe1 xsix at earth s inner core conditions the density of the earth s inner core is less than that of pure iron and the p wave velocities and particularly the s wave velocities in the inner core observed from seismology are lower than those generally obtained from mineral physics on the basis of measurements of compressional sound velocities to 100 gpa in diamond anvil cells extrapolated to inner core pressures it has been suggested that both the inner core density and p wave velocity can be matched simultaneously by the properties of a hexagonal close packed hcp fe si or fe ni si alloy in this paper we present the results of ab initio molecular dynamics simulations of hcp fe si alloys at 360 gpa and at temperatures up to melting we find that although the inner core density can be readily matched by an fe si alloy the same is not true for the wave velocities at inner core temperatures the p wave velocity in hcp fe si remains equal to or slightly above that of hcp fe and shows little change with silicon content the s wave velocity is reduced with respect to that of pure hcp iron except for temperatures immediately prior to melting where the velocities are almost equal this is a consequence of the fact that the strong temperature dependence of the shear modulus that was seen in similar simulations of hcp fe just prior to melting was not found in hcp fe si and so in this temperature range the reduced s wave velocity of pure iron closely matches that of the alloy our results show that for an hcp fe si alloy matching the inner core density both the p wave and the s wave velocities will be higher than those observed by seismology and we conclude therefore that our calculations indicate that inner core velocities cannot be explained by an hcp fe si alloy the opposite conclusion obtained previously from experimental data measured at lower pressures is a consequence of i the necessarily large extrapolation in pressure and temperature required to extend the experimental results to inner core conditions and ii the use of a velocity density relationship for pure hcp iron that is now considered to be incorrect

winagami reflection sequence seismic evidence for postcollisional magmatism in the proterozoic of western canada a recent lithoprobe seismic reflection transect in the peace river arch region of the western canada sedimentary basin traverses continental crust that was assembled in a series of magmatic and collisional events during the interval 2 0 1 9 ga the seismic data reveal panels of dipping reflectivity at tectonic domain boundaries but they are otherwise dominated by prominent subhorizontal reflections that occur between 3 5 and 18 5 km depth over an area of at least 120 000 km 2 these reflections here named the winagami reflection sequence overlap several tectonic domains and are comparable in geometry depth and areal distribution to sills and discordant intrusive sheets imaged by previous seismic profiling in the baltic shield and the basin and range province of the western united states as many as five distinct reflections are present some of which can be traced for more than 100 km contrasting reflection character in adjacent tectonic domains suggests an intrusive geometry controlled partly by the mechanical properties of the host rocks seismic modeling indicates that observed waveforms are consistent with reflections from tabular mafic bodies 70 m thick the winagami reflection sequence crosscuts the collisional fabric ca 1890 ma but the sequence is offset by a brittle fault with an estimated age of 1760 ma these timing constraints suggest that the winagami reflection sequence is a previously unknown component of a regional magmatic event emplaced during a period of brittle indentation of the western canadian shield by the slave province

constraints on magnetic energy and mantle conductivity from the forced nutations of the earth observations of the earth s nutations are used to explore the possible presence of a conducting layer at the base of the mantle the existence of such a layer is suggested by recent experiments on iron and silicate mixtures at high pressures and temperatures knittle and jeanloz 1986 1989 which indicate that iron may react with silicate minerals to produce metallic compounds nutations provide an ideal tool for investigating the existence of such a layer because they are sensitive to the electrical properties within a thin magnetic boundary layer along the core mantle boundary cmb evidence in favor of a conducting layer is found in the effects of ohmic dissipation which cause the amplitude of the earth s nutation to be out of phase with tidal forcings although out of phase components in the earth s nutations are conventionally attributed to the dissipative influences of ocean tides and mantle anelasticity these effects appear incapable of explaining nutation amplitudes determined from very long baseline interferometry vlbi observations the additional effects of ohmic dissipation enhanced by the presence of a thin conducting layer at the cmb are sufficient to reconcile theory and observation the largest mismatch between observations and theory taking account of ocean tides and mantle anelasticity is a discrepancy of 0 39 0 04 milliarcseconds in the out of phase component of the retrograde annual nutation this discrepancy can be eliminated if the lowermost 200 m of the mantle has a conductivity of 5 105s m 1 and the magnetic energy in the spherical harmonic components of the field at the cmb in degrees l 12 is approximately 4 times greater than the energy inferred in degrees l 12 from surface observations unfortunately the vlbi observations do not uniquely resolve the mantle conductivity and magnetic energy so that trade offs exist between these two parameters nevertheless a high mantle conductivity is favored on the grounds that the alternative involving high levels of magnetic energy yields an excessive amount of ohmic heating other interpretations of the vlbi discrepancy are also discussed one such alternative involves viscous dissipation at the cmb requiring a kinematic viscosity of 0 1m2s 1

composition of the earth s inner core from high pressure sound velocity measurements in fe ni si alloys article i nfo we performed room temperature sound velocity and density measurements on a polycrystalline alloy fe0 89ni0 04si0 07 in the hexagonal close packed hcp phase up to 108 gpa over the investigated pressure range the aggregate compressional sound velocity is 9 higher than in pure iron at the same density the measured aggregate compressional vp and shear vs sound velocities extrapolated to core densities and corrected for anharmonic temperature effects are compared with seismic profiles our results provide constraints on the silicon abundance in the core suggesting a model that simultaneously matches the primary seismic observables density p wave and s wave velocities for an inner core containing 4 to 5 wt of ni and 1 to 2 wt of si

phase relations in the fe fesi system at high pressures and temperatures the earth s core is comprised mostly of iron and nickel but it also contains several weight percent of one or more unknown light elements which may include silicon therefore it is important to understand the high pressure high temperature properties and behavior of alloys in the fe fesi system such as their phase diagrams we determined melting temperatures and subsolidus phase relations of fe 9 wt si and stoichiometric fesi using synchrotron x ray diffraction at high pressures and temperatures up to 200 gpa and 145 gpa respectively combining this data with that of previous studies we generated phase diagrams in pressure temperature temperature composition and pressure composition space we find the b2 crystal structure in fe 9si where previous studies reported the less ordered bcc structure and a shallower slope for the hcp b2 to fcc b2 boundary than previously reported in stoichiometric fesi we report a wide b2 b20 two phase field with complete conversion to the b2 structure at 42 gpa the minimum temperature of an fe si outer core is 4380 k based on the eutectic melting point of fe 9si and silicon is shown to be less efficient at depressing the melting point of iron at core conditions than oxygen or sulfur at the highest pressures reached onlymore the hcp and b2 structures are seen in the fe fesi system we predict that alloys containing more than 4 8 wt silicon will convert to an hcp b2 mixture and later to the hcp structure with increasing pressure and that an iron silicon alloy in the earth s inner core would most likely be a mixture of hcp and b2 phases less

parameterizing ice cloud inhomogeneity and the overlap of inhomogeneities using cloud radar data abstract cloud variability on scales smaller than the gridbox size of numerical forecast and climate models is believed to be important in determining the radiative effects of clouds and increasingly attempts are being made to parameterize these fluctuations in the radiation schemes of current models in order to calculate the radiative effects of an inhomogeneous cloud a model needs to know not only the degree of variability within a gridbox but also the degree to which the inhomogeneities in vertically adjacent levels are overlapped in this paper these two parameters are derived for ice clouds from an 18 month midlatitude 94 ghz cloud radar dataset and parameterized in terms of horizontal gridbox size d the vertical shear of the horizontal wind s and the vertical position in the cloud the vertical decorrelation length z0 i e the depth over which the correlation coefficient of either ice water content or optical extinction coefficient in separate vertical levels falls to e 1 is found to be

structure and dynamics of earth s inner core abstract the seismological exploration of the earth s inner core has revealed unexpected and puzzling structural complexities its elastic anisotropy is now well established and has been shown to vary spatially there is a well defined hemispherical dichotomy in anisotropy and attenuation and significant variations in the radial direction with weaker anisotropy in the uppermost regions and possibly different properties in an innermost inner core of radius 300 600 km perhaps even more puzzling is the observation of a stably stratified layer at the base of the outer core which has recently been proposed to result from melting of inner core material if confirmed the presence of this layer has major implications for our understanding of convection in the outer core inner core differential rotation with respect to the mantle remains controversial we will review here recent progress in understanding the dynamics of the inner core a number of different models have been proposed for the development of the inner core s structure and formation of the stable layer at the base of the outer core and particular care will be taken to clarify under which conditions the proposed mechanisms can be active

effect of improving representation of horizontal and vertical cloud structure on the earth s global radiation budget part ii the global effects reliably representing both horizontal cloud inhomogeneity and vertical cloud overlap is fundamentally important for the radiationbudget of a general circulation model here we build on the work of part i of this two part paper by applying a pair of parametrizations that account for horizontal inhomogeneity and vertical overlap to global re analysis data these are applied both together and separately in an attempt to quantify the effects of poor representation of the two components on radiation budget horizontalinhomogeneityisaccountedforusingthe tripleclouds scheme which uses two regions of cloud in each layer of a gridbox as opposed to one vertical overlapisaccounted for using exponential random overlap whichalignsvertically continuous cloud according to a decorrelation height these are applied to a sample of scenes from a year of era 40 data the largest radiative effect of horizontal inhomogeneity is found to be in areas of marine stratocumulus the effect of vertical overlap is found to be fairly uniform but with larger individual short wave and long wave effects in areas of deep tropical convection the combined effect of the twoparametrizationsisfoundtoreducethemagnitudeofthenettop of atmosphere toa cloud radiativeforcing by2 25wm 2 withshiftsofupto10wm 2 inareas of marine stratocumulus the effects on radiation budget of the uncertainty in our parametrizations is also investigated it is found that the uncertainty in the impact of horizontal inhomogeneity is of order 60 while the uncertainty in the impact of vertical overlap is much smaller this suggests an insensitivity of the radiation budget to the exact nature of the global decorrelation height distribution derived in part i copyright c

geology and thermotectonic evolution of the western margin of the trans hudson orogen evidence from the eastern sub athabasca basement saskatchewan in the cree lake zone of northern saskatchewan reworked archean orthogneisses are overlain by a highly deformed supracrustal sequence the paleoproterozoic wollaston group this package of rocks was deformed and metamorphosed during the ca 1 8 ga continent continent collision of the trans hudson orogen tho forming the wollaston fold thrust belt that underlies the eastern athabasca basin the hudsonian structural metamorphic and magmatic evolution of the wollaston fold thrust belt in the eastern athabasca area involved six major stages 1 early collisional stage dp1 at 1860 1835 ma involved burial of wollaston group metasediments from surface to depths equivalent to 3 5vkbar 1 kbar 100 mpa by thrust pile stacking or imbrication tectonics prograde metamorphism with garnet growth and development of early leucosomes and emplacement of ca 1840 ma grey granite suite 2 collisional stage dp2a at 1835 1820 ma involved continued deeper burial of wollaston group metasediments along a prograde

melting experiments on the fe c binary system up to 255 gpa constraints on the carbon content in the earth s core abstract phase relations including the eutectic liquid composition in the fe c binary system remain unclear under the core pressure range which makes estimating the carbon budget in the earth s core difficult to explore this issue we have conducted melting and subsolidus experiments on fe c alloys in a diamond anvil cell up to 255 gpa textural and compositional characterizations of quenched samples show that carbon concentration in the eutectic liquid slightly decreases with increasing pressure and is about 3 wt at the inner core boundary icb pressure the solubility of carbon in solid fe is found to be almost constant at 1 0 wt in situ x ray diffraction data indicate that fe forms eutectic melting with fe3c to 203 gpa and with fe7c3 at 255 gpa previous studies on liquid fe c alloys suggested that the density of the outer core is explained by liquid fe containing 1 8 to 4 2 wt c if the liquid core includes

fe feo and fe fe 3 c melting relations at earth s core mantle boundary conditions implications for a volatile rich or oxygen rich core eutectic melting temperatures in the fe feo and fe fe3c systems have been determined up to 150 gpa melting criteria include observation of a diffuse scattering signal by in situ x ray diffraction and textural characterisation of recovered samples in addition compositions of eutectic liquids have been established by combining in situ rietveld analyses with ex situ chemical analyses gathering these new results together with previous reports on fe s and fe si systems allow us to discuss the specific effect of each light element si s o c on the melting properties of the outer core crystallization temperatures of si rich core compositional models are too high to be compatible with the absence of extensive mantle melting at the core mantle boundary cmb and significant amounts of volatile elements such as s and or c 5 at corresponding to 2 wt or a large amount of o 15 at corresponding to 5 wt are required to reduce the crystallisation temperature of the core material below that of a peridotitic lower mantle

effect of improving representation of horizontal and vertical cloud structure on the earth s global radiation budget part i review and parametrization a poor representation of cloud structure in a general circulation model gcm is widely recognised as a potential source of error in the radiation budget here we develop a new way of representing both horizontal and vertical cloud structure in a radiation scheme this combines the tripleclouds parametrization which introduces inhomogeneity by using two cloudy regions in each layer as opposed to one each with different water content values with exponential random overlap in which clouds in adjacent layers are not overlapped maximally but according to a vertical decorrelation scale this paper part i of two aims to parametrize the two effects such that they can be used in a gcm to achieve this we first review a number of studies for a globally applicable value of fractional standard deviation of water content for use in tripleclouds we obtain a value of 0 75 0 18 from a variety of different types of observations with no apparent dependence on cloud type or gridbox size then through a second short review we create a parametrization of decorrelation scale for use in exponential random overlap which varies the scale linearly with latitude from 2 9 km at the equator to 0 4 km at the poles when applied to radar data both components are found to have radiative impacts capable of offsetting biases caused by cloud misrepresentation part ii of this paper implements tripleclouds and exponential random overlap into a radiation code and examines both their individual and combined impacts on the global radiation budget using re analysis data copyright c

the structure of fe si alloy in earth s inner core abstract phase relations of iron silicon alloy fe 6 5 wt si and fe 9 wt si were investigated up to 407 gpa and 5960 k in a laser heated diamond anvil cell which likely covers the entire pressure and temperature conditions of the earth s inner core synchrotron x ray diffraction measurements show that fe 9 wt si with a hexagonal close packed hcp structure is stable to 4800 k at 330 gpa corresponding to the pressure at the inner outer core boundary and decomposes into a mixture of si poor hcp and si rich cscl type b2 phases at higher temperatures we also found that the solubility of silicon in solid iron is relatively insensitive to temperature decreasing from 9 to 6 5 wt over a range of 1500 k at 70 gpa these suggest that the inner core is composed solely of the hcp phase when the silicon content is up to 7 wt that likely accounts for the inner core density deficit as well as for the mg si ratio and the si isotopic composition of the mantle additionally the present experiments demonstrate that the incorporation of silicon in iron expands the stability of hcp with respect to that of fcc

in situ determination of fe fe3s phase diagram and liquid structural properties up to 65 gpa abstract lighter elements than iron such as sulphur are required in the earth s core to account of the core density deficit accurate determination of the evolution of the fe fes phase diagram at high pressure is essential to determine sulphur amount in the earth s core ab initio calculations predict extensive solubility of s in solid fe at core pressures of 330 gpa whereas multi anvil quench analysis exhibits deep eutectic system at moderate pressure of 21 gpa in this study we investigated the fe rich part of fe fes phase diagram up to 65 gpa and 2200 k using in situ angle dispersive x ray diffraction we report a uniform increase with pressure of the eutectic temperatures t eut of about 15 k gpa above 50 gpa we evidence a decrease of s content in eutectic liquid with increasing pressure extrapolating this trend to inner core boundary pressures suggests that s cannot account for the 10 wt outer core density deficit and that other light elements such as si and o are needed diffraction pattern recorded at 42 gpa and 2150 k was selected for structural investigations of the fe s liquid by applying liquid structure simulation based on gaussian distribution of atoms around crystalline positions a good agreement has been found with hcp fe model structure rather than with fe 3 s structure it suggests that s acts as an interstitial impurity in the liquid state therefore s could have a relatively minor effect on sound velocities in liquid outer core

eutectic melting of fe 3 at si 4 at c up to 200 gpa and implications for the earth s core abstract properties of the fe si and fe c binary systems have been shown unable to satisfy the geophysical and petrological constraints of the earth s core i e velocities densities melting temperature if only si or c were to be incorporated as light element recent ab initio calculations suggest on the contrary that density compressional and shear sound velocities as well as the poisson s ratio of the inner core could be matched by an hcp fe alloy containing si and c the combined effect of the two elements in a ternary fe si c system has never been experimentally investigated under high pressure we thus studied the melting curve and the phase relations of the ternary iron silicon carbon system by in situ x ray diffraction at high pressures and high temperatures starting with a low light element content 4 at c 3 at si a stable assemblage made of hcp fe si c and fe3c is observed up to 200 gpa fe can incorporate both si and c in its hexagonal structure with the latter strongly affecting the volume and the melting temperature while the presence of a third light element is likely necessary we here document that the effect of c in lowering the melting temperature of fe si is large enough to possibly keep the core mantle boundary temperature below the solidus of the mantle silicates

phase relations in the system fe ni si to 200 gpa and 3900 k and implications for earth s core abstract phase relations in fe 5 wt ni 4 wt si alloy was examined in an internally resistive heated diamond anvil cell under high pressure p and temperature t conditions to about 200 gpa and 3900 k by in situ synchrotron x ray diffraction the hexagonal close packed hcp structure was observed to the highest p t condition supporting the idea that the stable iron alloy structure in earth s inner core is hcp the p t locations of the phase transition between the face centred cubic fcc and hcp structures were also constrained to 106 gpa the transition occurs at 15 gpa and 1000 k similar to for pure fe the clausius clapeyron slope is however 0 0480 gpa k which is larger than reported slopes for fe 0 0394 gpa k fe 9 7 wt ni 0 0426 gpa k and fe 4 wt si 0 0394 gpa k stabilising the fcc structure towards high pressure thus the simultaneous addition of ni and si to fe increases the d p d t slope of the fcc hcp transition this is associated with a small volume change upon transition in fe ni si the triple point where the fcc hcp and liquid phases coexist in fe 5 wt ni 4 wt si is placed at 145 gpa and 3750 k the resulting melting temperature of the hcp phase at the inner core outer core boundary lies at 550 k lower than in pure fe

the thermal evolution of mercury s fe si core abstract we have studied the thermal and magnetic field evolution of planet mercury with a core of fe si alloy to assess whether an fe si core matches its present day partially molten state mercury s magnetic field strength and the observed ancient crustal magnetization the main advantages of an fe si core opposed to a previously assumed fe s core are that a si bearing core is consistent with the highly reduced nature of mercury and that no compositional convection is generated upon core solidification in agreement with magnetic field indications of a stable layer at the top of mercury s core this study also present the first implementation of a conductive temperature profile in the core where heat fluxes are sub adiabatic in a global thermal evolution model we show that heat migrates from the deep core to the outer part of the core as soon as heat fluxes at the outer core become sub adiabatic as a result the deep core cools throughout mercury s evolution independent of the temperature evolution at the core mantle boundary causing an early start of inner core solidification and magnetic field generation the conductive layer at the outer core suppresses the rate of core growth after temperature differences between the deep and shallow core are relaxed such that a magnetic field can be generated until the present also the outer core and mantle operate at higher temperatures than previously thought which prolongs mantle melting and mantle convection the results indicate that s is not a necessary ingredient of mercury s core bringing bulk compositional models of mercury more in line with reduced meteorite analogues

striding athabasca mylonite zone implications for the archean and early proterozoic tectonics of the western canadian shield study of the northern saskatchewan district of mackenzie segment of the snowbird tectonic zone suggests that fragments of relatively stiff mid archean crust possibly arc related have controlled the localization shape and complex kinematics of the multistage striding athabasca mylonite zone during the archean as well as the geometry of the early proterozoic rifted margin of the western churchill continent by the late archean the striding athabasca mylonite zone was located in the interior of the western churchill continent well removed from the contemporaneous plate margins except for the alberta segment the snowbird tectonic zone was not the site of an early proterozoic plate margin we suggest that the geometry of the archean early proterozoic boundary in the western canadian shield represents a jagged continental margin composed of a pair of reentrants defined by rifted and transform segments these segments were inherited from early proterozoic breakup and controlled by the archean structure

deriving cloud overlap statistics from radar the predictions of general circulation models gcms are sensitive to the assumed cloud overlap within a vertical column of model grid boxes but until now no reliable observations of the degree of cloud overlap have been available in this note we derive the overlap characteristics of clouds from 71 days of high vertical resolution 94 ghz cloud radar data in the uk it is found that contrary to the assumption made in most models vertically continuous clouds tend not to be maximally overlapped rather the overlap of clouds at two levels tends to fall rapidly as their vertical separation is increased and for levels more than 4 km apart overlap is essentially random a simple inverse exponential expression for the degree of overlap as a function of level separation is proposed that could once results become available from a variety of other locations and seasons be implemented in current gcms with relatively little difficulty

seismic gravity and petrological evidence for partial melt beneath the thickened central andean crust 21 23 s on the basis of seismic refraction investigations and gravimetric data we have modelled the crustal structure of the southern central andes 21 23 s a pronounced variation in crustal parameters is seen in n s and w e crossing seismic profiles over the entire andean orogene characterized by a crustal thickness of up to 70 km under the magmatic arc and backarc strongly reduced seismic velocities and a bouguer minimum of 450 mgal anomalously low velocities of 5 9 6 0 km s in the deeper crust of the western cordillera and altiplano regions lead to an over compensation of the bouguer minima resulting in values of crustal densities higher than estimates based purely on seismic velocity measurements in an attempt to reconcile these differences the behavior of crystalline rocks based on published laboratory data was studied under varying pressure and temperature conditions up to the range of partial melting if the temperature is increased above the melting point a rapid decrease in seismic velocity is accompanied by a slow decrease in density for the central andes a good fit of the observed and calculated bouguer anomalies is obtained if the densities of the rocks from the low velocity zone lvz beneath the western cordillera and the altiplano are varied model calculations lead to a velocity density relation for partial molten rocks that allows the melt proportions of rocks to be estimated model calculations indicate that 15 20 vol of basaltic to andesitic melt at depth is necessary to explain the lvz and bouguer anomaly beneath the arc and parts of the backarc high heat flow values 100 mw m2 support the idea that large areas of the deeper andean crust are strongly weakened by the presence of partially molten rocks resulting in reduced seismic velocities with the western cordillera the active volcanic arc of the andean mountain range acting as a ductile buffer between the two more rigid crustal blocks of the forearc and backarc regions

an interpretation of cloud overlap statistics abstractobservational studies have shown that the vertical overlap of cloudy layers separated by clear sky can exceed that of the random overlap assumption suggesting a tendency toward minimum overlap in addition the rate of decorrelation of vertically continuous clouds with increasing layer separation is sensitive to the horizontal scale of the cloud scenes used the authors give a heuristic argument that these phenomena result from data truncation where overcast or single cloud layers are removed from the analysis this occurs more frequently as the cloud sampling scale falls progressively below the typical cloud system scale the postulate is supported by sampling artificial cyclic and subsequently more realistic fractal cloud scenes at various length scales the fractal clouds indicate that the degree of minimal overlap diagnosed in previous studies for discontinuous clouds could result from sampling randomly overlapped clouds at spatial scales that are 30 80 of the cloud system scale removing

phase relations of iron and iron nickel alloys up to 300 gpa implications for composition and structure of the earth s inner core abstract we have investigated the phase relations of iron and iron nickel alloys with 18 to 50 wt ni up to over 300 gpa using a laser heated diamond anvil cell the synchrotron x ray diffraction measurements show the wide stability of hcp iron up to 301 gpa and 2000 k and 319 gpa and 300 k without phase transition to dhcp orthorhombic or bcc phases on the other hand the incorporation of nickel has a remarkable effect on expanding the stability field of fcc phase the geometry of the temperature composition phase diagram of iron nickel alloys suggests that the hcp fcc liquid triple point is located at 10 to 20 wt ni at the pressure of the inner core boundary the fcc phase could crystallize depending on the nickel and silicon contents in the earth s core both of which are fcc stabilizer