the classification of micrometeorites due to their small size the mineralogical and chemical properties of micrometeorites mms are not representative of their parent bodies on the centimeter to meter scales that are used to define parent body groups through the petrological study of meteorites identifying which groups of mm are derived from the same type of parent body is problematic and requires particles to be rigorously grouped on the basis of mineralogical textural and chemical properties that reflect the fundamental genetic differences between meteorite parent bodies albeit with minimal bias towards preconceived genetic models specifically the interpretation of mms requires a rigorous and meaningful classification scheme at present the classification of mms is however at best ambiguous a unified petrological chemical classification scheme is proposed in the current study and is based on observations of several thousand mms collected from antarctic ice

the weathering of micrometeorites from the transantarctic mountains abstract micrometeorites are cosmic dust particles recovered from the earth s surface that dominate the influx of extraterrestrial material accreting to our planet this paper provides the first in depth study of the weathering of micrometeorites within the antarctic environment that will allow primary and secondary features to be distinguished it is based on the analysis of 366 particles from larkman nunatak and 25 from the transantarctic mountain collection several important morphological categories of weathering effects were identified 1 irregular and faceted cavities 2 surface etch pits 3 infilled cavities 4 replaced silicate phases and 5 hydrated and replaced metal these features indicate that congruent dissolution of silicate phases in particular olivine is important in generating new pore space within particles comparison of the preservation of glass and olivine also indicates preferential dissolution of olivine by acidic solutions during low temperature aqueous alteration precipitation of new hydrous phases within cavities in particular ferrihydrite and jarosite results in pseudomorph textures within heavily altered particles glass in contrast is altered to palagonite gels and shows a sequential replacement indicative of varying water to rock ratios metal is variably replaced by fe oxyhydroxides and results in decreases in ni fe ratio in contrast sulphides within metal are largely preserved magnetite an essential component of micrometeorites formed during atmospheric entry is least altered by interaction with the terrestrial environment the extent of weathering in the studied micrometeorites is sensitive to differences in their primary mineralogy and varies significantly with particle type despite these differences we propose a weathering scale for micrometeorites based on both their degree of terrestrial alteration and the level of encrustation by secondary phases the compositions and textures of weathering products however suggest open system behaviour and variable water to rock ratios that imply climatic variation over the lifetime of the micrometeorite deposits

identification of the parent bodies of micrometeorites with high precision oxygen isotope ratios oxygen isotopic compositions allow identification of potential parent bodies of extraterrestrial materials we measured oxygen isotope ratios of 33 large diameter 500 m silicate melted micrometeorites cosmic spherules from antarctica using ir laser fluorination coupled with mass spectrometry it is the first time that this high precision method is used on individual micrometeorites the selected micrometeorites are representative of the influx of extraterrestrial materials to the earth our results show that most micrometeorites are related to carbonaceous chondrites which is consistent with previous studies however 20 50 of them seem to be related to co cv carbonaceous chondrites whereas cm cr carbonaceous chondrites were thought to be the main source for micrometeorites furthermore 30 of measured samples have oxygen isotope ratios lying above the terrestrial fractionation line which relates them to ordinary chondrites or other as yet unsampled parent bodies

fractionation and fragmentation of glass cosmic spherules during atmospheric entry glass cosmic spherules are a sub type of s type cosmic spherules that are almost at the end phase of fractionation and volatilization during atmospheric entry a focused investigation of 36 glass spherules out of several hundred spherules reveals fractionation and fragmentation phenomena during atmospheric entry some of the glass spherules largely preserve relict pyroxene normative crystals within the spherules appear to have experienced temperatures of 1700 o c that resulted in vaporization of fe and other volatile elements such as s na and k from the silicate spherule resulting in the enrichment of sio2 mgo and cao in weight percent calculations with a chemical ablation model suggest an entry velocity of 11 16 km s to achieve the temperature required for glass spherule formation under these conditions the micrometeoroid undergoes a mass of loss of 20 any increase in entry velocity will increase the mass loss drastically and change its chemical composition most glass spherules beyond a certain threshold diameter of 300 m appear to undergo fragmentation resulting in two different spherules which could lead to an apparent enhancement of the percentage of glass spherules in unbiased collections siderophile and volatile element loss and subsequent development of a platinum group element pge nugget are observed in one of the spherules this appears to be the first reported observation of a platinum group nugget pgn in a glass spherule the nugget has a diameter of 3 m and contains all the six pge although some of the more volatile pge are depleted relative to an average chondritic composition interestingly the pge data of the nugget seem to have a trend which is similar to that of a pge nugget from a calcium aluminium rich inclusion cai the trace element data of these glass spherules suggest that their parent bodies were carbonaceous chondrites

chondrules in antarctic micrometeorites previous studies of unmelted micrometeorites 50 m recovered from antarctic ice have concluded that chondrules which are a major component of chondritic meteorites are extremely rare among micrometeorites we report the discovery of eight micrometeorites containing chondritic igneous objects which strongly suggests that at least a portion of coarse grained crystalline micrometeorites represent chondrule fragments six of the particles are identified as composite micrometeorites that contain chondritic igneous objects and fine grained matrix these particles suggest that at least some coarse grained micrometeorites cgmms may be derived from the same parent bodies as fine grained micrometeorites the new evidence indicates that contrary to previous suggestions the parent bodies of micrometeorites broadly resemble the parent asteroids of chondrulebearing carbonaceous chondrites

an increased abundance of micrometeorites on earth owing to vesicular parachutes micrometeorites mms are extraterrestrial dust particles that survive atmospheric entry and can be recovered from sedimentary rocks fossil mms allow events beyond the earth such as the collisional breakup of asteroids to be identified here the effects of vesicle formation during melting of dust are investigated through numerical modeling and observations of antarctic mms vesicle formation is shown to cause a parachute effect that causes rapid deceleration decreasing peak temperature vesicular parachuting enhances the abundance of melted mms formed from phyllosilicate bearing c type asteroid dust on the earth surface by a factor of 2 micrometeorites recovered from the geological record therefore are biased toward breakup events involving hydrated c type asteroids whilst those involving phyllosilicate poor particles are diluted by the enhanced background flux of hydrous dust the parachute effect is also likely to increase the delivery of 3he to ocean sediments by c type asteroid dust

igneous rims on micrometeorites abstract melting of micrometeorites mms due to atmospheric entry heating causes significant changes in the textures mineralogies and compositions of particles that obscure their primary properties and greatly complicate interpretation of these extraterrestrial materials despite the abundance of melted mms the nature of melting processes in these materials is poorly constrained in this study mineralogical textural and compositional data on 77 mms with igneous rims are presented which suggest that fusion of micrometeorites during atmospheric entry occurs initially by surface melting textural and mineralogical evidence are presented that demonstrate unequivocally that igneous rims crystallized from a melt surrounding a largely unmelted core and establish melting as a gradational process the compositions of igneous rims on fine grained mms fgmms are broadly similar to those of the unmelted core except for depletions in volatile and moderately volatile elements produced by partial evaporation and suggest the formation of the rims by melting of the fine grained matrix core enrichments in fe si ni si and mn si in igneous rims compared with unmelted cores within fgmms are suggested to occur due to the migration of fe s eutectic liquids from the core of the particle into the surface melt layer the sulphide liquids are probably generated in the core of the particle under reducing conditions resulting by the pyrolysis of carbonaceous materials the presence of igneous rims on fgmms is enabled by the thermal decomposition of phyllosilicates and therefore indicates that fgmms were hydrated particles prior to atmospheric entry in contrast the compositions of igneous rims on coarse grained mms cgmms are difficult to reconcile with those of the unmelted core and instead closely resemble those of fgmms the igneous rims of cgmms are therefore suggested to form by melting of fine grained matrix that was present on the exterior of these particles prior to atmospheric entry coarse grained mms with igneous rims thus were originally composite micrometeoroids which consist of both fine grained and coarse grained materials and are thought to be samples of chondrule like objects the abundance of composite mms to cgmms allows a first estimate of the mean chondrule radius within the parent bodies of mms of 625 m to be made

shock fabrics in fine grained micrometeorites the orientations of dehydration cracks and fracture networks in fine grained unmelted micrometeorites were analyzed using rose diagrams and entropy calculations as cracks exploit pre existing anisotropies analysis of their orientation provides a mechanism with which to study the subtle petrofabrics preserved within fine grained and amorphous materials both uniaxial and biaxial fabrics are discovered often with a relatively wide spread in orientations 40 60 brittle deformation cataclasis and rotated olivine grains are reported from a single micrometeorite this paper provides the first evidence for impact induced shock deformation in fine grained micrometeorites the presence of pervasive low grade shock features in cm chondrites and cm like dust anomalously low density measurements for c type asteroids and impact experiments which suggest cm chondrites are highly prone to disruption all imply that cm parent bodies are unlikely to have remained intact and instead exist as a collection of loosely aggregated rubble pile asteroids composed of primitive shocked clasts

partitioning of transgressive deposits in the southeastern yellow sea a sequence stratigraphic interpretation abstract the last glacio eustatic sea level fluctuation in the southeastern part of the yellow sea formed a number of unconformity bounded sedimentary sequences these sequences comprise 1 regressive to transgressive incision fills unit c 2 transgressive sand ridges and swales unit b and 3 transgressive to highstand muds lower mud unit a2 upper mud unit a1 the sequence boundary between unit c and the lower unit comprises erosional surface which can be traced for the entire study area the even and sharp boundary between the incision fills unit c and the sand ridges unit b represents a transgressive surface of erosion the depositional boundary between the lower mud unit a2 and the upper mud unit a1 suggests a change in oceanographic conditions the boundary is confined landward and correlated offshore with the top of units b and c that is exposed on the seafloor these transgressive deposits show partitioning controlled by currents tides and sediment supply as well as physiography of the seafloor

numbers types and compositions of an unbiased collection of cosmic spherules abstract abstract micrometeorites collected from the bottom of the south pole water well spww may represent a complete well preserved sample of the cosmic dust that accreted on earth from 1100 1500 a d we classified 1588 cosmic spherules in the size range 50 800 pm the collection has 41 barred olivine spherules 17 glass spheres 12 cryptocrystalline spherules 11 porphyritic olivine spherules 12 relic grain bearing spherules 3 scoriaceous spherules 2 i type spherules 1 ca al ti rich cat spherules and 1 g type spherules we also found bubbly glass spherules spherules with glass caps and ones with sulfide coatings particles that are absent from other collections a classification sequence of the stony spherules scoriaceous relic grain bearing porphyritic barred olivine cryptocrystalline glass and cat is consistent with progressive heating and evaporation of fe from chondritic materials the modem day accretion rate and size distribution measured at the spww can account for the stony spherules present in deep sea collection through preferential dissolution of glass and small stony spherules however weathering alone cannot account for the high accretion rate of i type spherules determined for two deep sea collections the spww collection provides data to constrain models of atmospheric entry heating and to assess the effects of terrestrial weathering

koronis asteroid dust within antarctic ice here i report the first discovery of large numbers of ordinary chondrite derived micro meteorites mms recovered from antarctic ice ordinary chondrite derived mms comprise 70 coarse grained igneous particles and are identified on the basis of their distribution of petrologic types accessory mineralogy and minor element compositions all of which are very similar to those of millimeter sized igneous objects known as chondrules from ordinary chondrites and largely distinct from those of other meteorite groups the majority of ordinary chondrite derived mms are unequilibrated materials however 15 are equilibrated indicating parent body metamorphism and have compositions consistent with both h high iron and l low iron chondrites the total abundance of ordinary chondrite derived mms of 18 is similar to predictions by numerical calculations for the abundance of dust generated by the recent breakup of the karin group asteroids of the koronis asteroid family suggesting that these asteroids are the main source of the particles these mms represent the first to be associated with a known asteroid and imply that the karin group progenitor asteroid was a rubble pile asteroid that sampled different depths within the original internally metamorphosed koronis parent body

petrology and geochemistry of antarctic micrometeorites abstract the petrology and geochemistry of twentythree chondritic dust particles with masses of 1 47 g sizes 100 400 m were recovered from blue ice near cap prudhomme antarctica and studied by inaa asem empa and optical microscopy sample selection criteria were irregular shape and for a subsample black color with the aim of studying as many unmelted micrometeorites mms as possible of thirteen unmelted mms six were phyllosilicate dominated mms and seven were coarsegrained crystalline mms consisting mainly of olivine and pyroxene the remaining ten particles were largely melted and consisted of a foamy melt with variable amounts of relic phases scoriaceous mms thus of the black particles selected an astonishing portion 40 by number consisted of largely unmelted mms although unmelted most phyllosilicate mms have been thermally metamorphosed to a degree that most of the phyllosilicates were destroyed but not melted the original preterrestrial mineralogy is occasionally preserved and consists of serpentine like phyllosilicates with variable amounts of cronstedtite tochilinite like oxides olivine and pyroxene the crystalline mms consist of olivine low ca pyroxene tochilinite like oxides and occasional ni poor metal relics in scoriaceous mms consist of the same phases mineral compositions and the coexistence of phyllosilicates with anhydrous phases are typical of cm and cr type carbonaceous chondrites however the olivine pyroxene ratio 1 and the lack of carbonates sulfates and of very fe poor refractory element rich olivines and pyroxenes sets the mms apart from cm and cr chondrites the bulk chemistry of the phyllosilicate mms is similar to that of cm chondrites however several elements are either depleted ca ni s less commonly na mg and mn or enriched k fe as br rb sb and au in mms as compared to cm chondrites similar depletions and enrichments are also found in the scoriaceous mms we suggest that the depletions are probably due to terrestrial leaching of sulfates and carbonates from unmelted mms the overabundance of some elements may also be due to processes acting during atmospheric passage such as the recondensation of meteoric vapors in the high atmosphere most mms are coated by magnetite of platy or octahedral habit which is rich in mg al si mn and ni we interpret the magnetites to be products of recondensation processes in the high 90 km atmosphere which are therefore probably the first refractory aerominerals identified

xenoliths and microxenoliths in h chondrites sampling the zodiacal cloud in the asteroid main belt abstract xenoliths are inclusions of a given meteorite group embedded in host meteorites of a different group xenoliths with dimensions between a few m and about 1 mm microxenoliths are meteorite trapped analogues of micrometeorites collected on the earth however they have the unique features of sampling the zodiacal cloud 1 at more ancient times than those sampled by micrometeorites and 2 at larger distances from the sun corresponding to the asteroid main belt than that sampled by micrometeorites 1 au herein we describe a systematic search for new xenoliths and microxenoliths in h chondrites aimed at determining their abundance in these ordinary chondrites analyzing their mineralogy and searching for possible correlations with host meteorite properties sixty six sections from 40 meteorites have been analyzed twenty four new xenoliths have been discovered about 87 of them are microxenoliths i e 1 mm in their largest dimension all the newly discovered xenoliths and microxenoliths are composed of carbonaceous chondritic material hence the zodiacal cloud was dominated by carbonaceous material even in past epochs all the new xenoliths and microxenoliths have been found in regolith breccias hydrous phase rich xenoliths and microxenoliths in h4 and h5 chondrites attest that their embedding happened after the end of the thermal metamorphism all these data suggest that xenoliths and microxenoliths were embedded when their host meteorites were part of the parent body regolith this combined with the h chondrite impact age distribution attests that the embedding may have happened as early as 3 5 gyr ago

the textures and compositions of fine grained antarctic micrometeorites implications for comparisons with meteorites abstract micrometeorites recovered from the earth s surface constitute the most abundant interplanetary dust now falling to earth we studied eighty nine fine grained antarctic micrometeorites fg amms to evaluate their state of alteration and to identify the nature of their precursor materials fine grained amms are divided into melted and unmelted groups and subdivided on the basis of textures related to atmospheric entry heating the textures of melted particles reflect crystallisation after entry heating and those of unmelted amms broadly resemble cl cm and cr chondrite matrix the matrix compositions of the fg amms closely resemble those of cm2 chondrites matrices provide a more reliable comparison to meteorites than bulk compositions because components such as chondrules and cais are not present in representative proportions within individual amms divergences from cm like matrix compositions are generally minor and probably arose during entry heating by the dissociation of volatile bearing phases at subsolidus temperatures and evaporation and loss of immiscible metallic liquids at higher temperatures depletions in ni and mg relative to cm matrix are tentatively attributed to terrestrial weathering no conclusive evidence for contamination during atmospheric residence was observed contrary to theory textural evidence suggests that bow shocks and high thermal gradients existed during deceleration of micrometeoroids in the atmosphere

chondritic micrometeorites from the transantarctic mountains abstract on the basis of morphological and petrographic characteristics eight giant unmelted micrometeorites in the 300 1100 m size range were selected from the transantarctic mountain micrometeorite collection victoria land antarctica mineralogical and geochemical data obtained by means of scanning electron microscopy electron probe microanalyses and synchrotron x ray diffraction allow their classification as chondritic micrometeorites the large size of the micrometeorites increases considerably the amount of mineralogical and geochemical information compared to micrometeorites in smaller size fractions therefore allowing a better definition of their parent material a large variety of material is observed five micrometeorites are related to unequilibrated and equilibrated ordinary chondrite one to cv chondrite one to cm chondrite and one to ci chondrite parent materials besides reporting the first occurrence of a cv like micrometeorite our study shows that the abundance of chondritic material supports observations from recent studies on cosmic spherules that a large part of the micrometeorite flux in this size range is of asteroidal origin

unmelted cosmic metal particles in the indian ocean fe ni metal is a common constituent of most meteorites and is an indicator of the thermal history of the respective meteorites it is a diagnostic tool to distinguish between groups subgroups of meteorites in spite of over a million micrometeorites collected from various domains reports of pure metallic particles among micrometeorites have been extremely rare we report here the finding of a variety of cosmic metal particles such as kamacite plessite taenite and fe ni beads from deep sea sediments of the indian ocean a majority of which have entered the earth unaffected by frictional heating during atmospheric entry such particles are known as components of meteorites but have never been found as individual entities their compositions suggest precursors from a variety of meteorite groups thus providing an insight into the metal fluxes on the earth some particles have undergone heating and oxidation to different levels during entry developing features similar to i type cosmic spherules suggesting atmospheric processing of individual kamacites taenite grains as another hitherto unknown source for the i type spherules the particles have undergone postdepositional aqueous alteration transforming finally into the serpentine mineral cronstedtite aqueous alteration products of kamacite reflect the local microenvironment therefore they have the potential to provide information on the composition of water in the solar nebula on the parent bodies or on surfaces of planetary bodies our observations suggest it would take sustained burial in water for tens of thousands of years under cold conditions for kamacites to alter to cronstedtite

mineralogy and composition of matrix and chondrule rims in carbonaceous chondrites abstract the degree of compositional variation of fine grained minerals displayed by the members within any carbonaceous chondrite group i e ci cm cv cr is a direct reflection of the range of aqueous alteration assemblages present matrix and fine grained chondrule rims within any particular carbonaceous chondrite are mineralogically nearly identical to one another but not necessarily similar in bulk elemental composition even though they have subsequently experienced post accretional secondary processing aqueous alteration under identical conditions this may indicate preferential alteration of one component brecciation exchange of components between rims and matrix and or accretion of matrix and rims from mineralogically or compositionally distinct materials we propose that co chondrites experienced parent body conditions of low f o2 low water rock ratios and temperatures below 50 c cr chondrites experienced higher water rock ratios potentially higher temperatures 150 c and a wide range of f o2 the alteration mineralogy of cv chondrites indicates water rock ratios at the high end at least of the range for cr chondrites essebi and mac 87300 cm chondrites experienced temperatures below 50 c low f o2 and low water rock ratios except eet 83334 which probably experienced relatively higher f o2 and b 7904 and y 86720 which experienced postalteration temperatures in the range 500 700 c most ci chondrites experienced temperatures between 50 and 150 c relatively high water rock ratios and variable f o2 with a late stage increase in the latter due possibly to brecciation and consequent release of methane y 82162 witnessed post alteration heating possibly as high as 400 c

modeling of cyclic tidal rhythmites based on a range of diurnal to semidiurnal tidal station data abstract where individual tides deposit appreciable accumulations of sediment cyclic tidal rhythmites can form that exhibit semimonthly tidal cyclicities a number of modern analogs and ancient counterparts indicate the importance of such features for paleoenvironmental analyses in this study predicted high low tidal station data are used to simulate current speeds which in turn are used to simulate sedimentation of tidal rhythmites this modeling has been done to depict the patterns encoded in cyclic tidal rhythmites in order to delineate the spectrum of different tidal regimes the simulations are based upon a series of macrotidal diurnal to semidiurnal tidal systems depending upon thresholds of relative tidal current speed only portions of semimonthly tidal cycles will be preserved within cyclic tidal rhythmites

carbonaceous micrometeorites from antarctica over 100 000 large interplanetary dust particles in the 50 500 micrometers size range have been recovered in clean conditions from approximately 600 tons of antarctic melt ice water as both unmelted and partially melted dehydrated micrometeorites and cosmic spherules flux measurements in both the greenland and antarctica ice sheets indicate that the micrometeorites deliver to the earth s surface approximately 2000x more extraterrestrial material than brought by meteorites mineralogical and chemical studies of antarctic micrometeorites indicate that they are only related to the relatively rare cm and cr carbonaceous chondrite groups being mostly chondritic carbonaceous objects composed of highly unequilibrated assemblages of anhydrous and hydrous minerals however there are also marked differences between these two families of solar system objects including higher c o ratios and a very marked depletion of chondrules in micrometeorite matter hence they are chondrites without chondrules thus the parent meteoroids of micrometeorites represent a dominant and new population of solar system objects probably formed in the outer solar system and delivered to the inner solar system by the most appropriate vehicles comets one of the major purposes of this paper is to discuss applications of micrometeorite studies that have been previously presented to exobiologists but deal with the synthesis of prebiotic molecules on the early earth and more recently with the early history of the solar system

olivine settling in cosmic spherules during atmospheric deceleration an indicator of the orbital eccentricity of interplanetary dust a new type of cosmic spherule is reported with textures suggesting settling of olivine during atmospheric deceleration numerical simulations of entry heating reveal that relict forsterite which survives melting can settle over the 1 2 s of flight at high entry angles and entry velocities up to 16 km s 1 enhanced crystallisation of phenocrysts by heterogeneous nucleation on accumulated relict forsterites is the most likely origin of the observed cumulate textures in cosmic spherules such textures in cosmic spherules reveal interplanetary dust with higher encounter velocity with the earth that correspond to orbital eccentricities 0 3 the relative abundance of cumulate spherules suggests 14 of ordinary chondrite related s iv type asteroid dust over the last 800 kyr had relatively high orbital eccentricity owing to secular and planetary perturbations the textures of cosmic spherules collected from sediments can therefore be used to trace dust orbital variations with time which may influence terrestrial climate

the fusion crusts of stony meteorites implications for the atmospheric reprocessing of extraterrestrial materials fusion crusts develop on all meteorites during their passage through the atmosphere but have been little studied we have characterized the textures and compositions of the fusion crusts of 73 stony meteorites to identify the nature of meteorite ablation spheres mas and constrain the processes operating during the entry heating most chondrite fusion crusts are porphyritic and are dominated by olivine glass and accessory magnetite whereas those of the achondrites are mainly glassy chondrite fusion crusts contain sulphide droplets with high ni contents 55 wt the partially melted substrate of ordinary chondrites underlying the outer melted crusts are dominated by silicate glass and composite metal sulphide and cr bearing fe oxide droplets that form as coexisting immiscible liquids enstatite chondrite substrates contain cr and mn bearing sulphides the substrates of the carbonaceous chondrites comprise a sulphide enriched layer of matrix the compositions of melted crusts are similar to those of the bulk meteorite however differences from whole rock suggest that three main processes control their chemical evolution 1 the loss and reaction of immiscible fe rich liquids 2 mixing between substrate partial melts and bulk melts of the melted crust and 3 the loss of volatile components by evaporation and degassing data from fusion crusts suggest that mas produced at low altitude have compositions within the range of those of silicate dominated cosmic spherules that are formed by the melting dust particles meteorite ablation spheres produced at high altitude probably have compositions very different from bulk meteorite and will resemble cosmic spherules derived from coarse grained precursors

crystalline micrometeorites from greenland blue lakes their chemical composition mineralogy and possible origin among the different populations of cosmic particles found in the greenland cryoconites the irregular shaped population is probably the most interesting one because it provides direct information about the nature of small meteoroids that impact the earth petrographic and trace element analyses of this material reveal two main families labelled as coarse grained cg and fine grained fg which have respectively compact and porous structures we have restricted our study to the coarse grained particles which contain large relic minerals and thus are well adapted to the sem and microprobe analysis techniques we compare the mineralogical associations of 49 coarse grained particles to that of meteorites and find that a majority of them belong to the same population of mineral grains previously found in cm chondrites and a minority of ordinary chondrites

a new variant of saponite rich micrometeorites recovered from recent antarctic snowfall abstract eight saponite rich micrometeorites with very similar mineralogy were found from the recent surface snow in antarctica they might have come to earth as a larger meteoroid and broke up into pieces on earth because they were recovered from the same layer and the same location of the snow synchrotron x ray diffraction xrd analysis indicates that saponite mg fe carbonate and pyrrhotite are major phases and serpentine magnetite and pentlandite are minor phases anhydrous silicates are entirely absent from all micrometeorites suggesting that their parental object has undergone heavy aqueous alteration saponite serpentine ratios are higher than in the orgueil ci chondrite and are similar to the tagish lake carbonaceous chondrite transmission electron microscope tem observation indicates that serpentine occupies core regions of fine grained saponite pyrrhotite has a low ni concentration and mg fe carbonate shows unique concentric ring structures and has a mean molar mg mg fe ratio of 0 7 comparison of the mineralogy to hydrated chondrites and interplanetary dust particles idps suggests that the micrometeorites are most similar to the carbonate poor lithology of the tagish lake carbonaceous chondrite and some hydrous idps but they show a carbonate mineralogy dissimilar to any primitive chondritic materials therefore they are a new variant of saponite rich micrometeorite extracted from a primitive hydrous asteroid and recently accreted to antarctica

the origins of i type spherules and the atmospheric entry of iron micrometeoroids the earth s extraterrestrial dust flux includes a wide variety of dust particles that include feni metallic grains during their atmospheric entry iron micrometeoroids melt and oxidize to form cosmic spherules termed i type spherules these particles are chemically resistant and readily collected by magnetic separation and are thus the most likely micrometeorites to be recovered from modern and ancient sediments understanding their behavior during atmospheric entry is crucial in constraining their abundance relative to other particle types and the nature of the zodiacal dust population at 1 au this article presents numerical simulations of the atmospheric entry heating of iron meteoroids to investigate the abundance and nature of these materials the results indicate that iron micrometeoroids experience peak temperatures 300 800 k higher than silicate particles explaining the rarity of unmelted iron particles which can only be present at sizes of 50 m the lower evaporation rates of liquid iron oxide leads to greater survival of iron particles compared with silicates which enhances their abundance among micrometeorites by a factor of 2 the abundance of i types is shown to be broadly consistent with the abundance and size of metal in ordinary chondrites and the current day flux of ordinary chondrite derived mms arriving at earth furthermore carbonaceous asteroids and cometary dust are suggested to make negligible contributions to the i type spherule flux events involving such objects therefore cannot be recognized from i type spherule abundances in the geological record

evidence for an asteroid comet continuum from simulations of carbonaceous microxenolith dynamical evolution abstract micrometeoroids with 100 and 200 m size dominate the zodiacal cloud dust such samples can be studied as micrometeorites after their passage through the earth atmosphere or as microxenoliths i e submillimetric meteorite inclusions microxenoliths are samples of the zodiacal cloud dust present in the asteroid main belt hundreds of millions years ago carbonaceous microxenoliths represent the majority of observed microxenoliths they have been studied in detail in howardites and h chondrites we investigate the role of carbonaceous asteroids and jupiter family comets as carbonaceous microxenolith parent bodies the probability of low velocity collisions of asteroidal and cometary micrometeoroids with selected asteroids is computed starting from the micrometeoroid steady state orbital distributions obtained by dynamical simulations we selected possible parent bodies of howardites vesta and h chondrites hebe flora eunomia koronis maria as target asteroids estimates of the asteroidal and cometary micrometeoroid mass between 2 and 4 au from the sun are used to compute the micrometeoroid mass influx on each target the results show that all the target asteroids except koronis receive the same amount within the uncertainties of asteroidal and cometary micrometeoroids therefore both these populations should be observed among howardite and h chondrite carbonaceous microxenoliths however this is not the case carbonaceous microxenoliths show differences similar to those existing among different groups of carbonaceous chondrites e g ci cm cr but two sharply distinct populations are not observed our results and the observations can be reconciled assuming the existence of a continuum of mineralogical and chemical properties between carbonaceous asteroids and comets

major and trace element geochemistry of s type cosmic spherules micrometeorites that pass through the earth s atmosphere undergo changes in their chemical compositions thereby making it difficult to understand if they are sourced from the matrix chondrules or calcium aluminum rich inclusions cais these components have the potential to provide evidence toward the understanding of the early solar nebular evolution the variations in the major element and trace element compositions of 155 different type scoriaceous relict bearing porphyritic barred cryptocrystalline and glass of s type cosmic spherules are investigated with the intent to decipher the parent sources using electron microprobe and laser ablation inductively coupled plasma mass spectrometry the s type cosmic spherules appear to show a systematic depletion in volatile element contents but have preserved their refractory trace elements the trends in their chemical compositions suggest that the s type spherules comprise of components from similar parent bodies that is carbonaceous chondrites large fosteritic relict grains observed in this investigation appear to be related to the fragments of chondrules from carbonaceous chondrites furthermore four spherules two of these spherules enclose spinels and one comprised entirely of a ca al rich plagioclase show enhanced trace element enrichment patterns that are drastically different from all the other 151 cosmic spherules the information on the chemical composition and rare earth elements rees on cosmic spherules suggest that the partially to fully melted ones can preserve evidences related to their parent bodies the ce eu and tm anomalies found in the cosmic spherules have similar behavior as that of chondrites distinct correlations observed between different rees and types of cosmic spherules reflect the inherited properties of the precursors

the entry heating and abundances of basaltic micrometeorites basaltic micrometeorites mms derived from hed like parent bodies have been found among particles collected from the antarctic and from arctic glaciers and are to date the only achondritic particles reported among cosmic dust the majority of antarctic basaltic particles are completely melted cosmic spherules with only one unmelted particle recognized from the region this paper investigates the entry heating of basaltic mms in order to predict the relative abundances of unmelted to melted basaltic particles and to evaluate how mineralogical differences in precursor materials influence the final products of atmospheric entry collected on the earth s surface thermodynamic modeling is used to simulate the melting behavior of particles with compositions corresponding to eucrites diogenites and ordinary chondrites in order to evaluate degree of partial melting and to make a comparison between the behavior of chondritic particles that dominate the terrestrial dust flux and basaltic micrometeroids the results of 120 000 simulations were compiled to predict relative abundances and indicate that the phase relations of precursor materials are crucial in determining the relative abundances of particle types diogenite and ordinary chondrite materials exhibit similar behavior although diogenite precursors are more likely to form cosmic spherules under similar entry parameters eucrite particles however are much more likely to melt due to their lower liquidus temperatures and small temperature interval of partial melting eucrite mms therefore usually form completely molten cosmic spherules except at particle diameters 100 m the low abundance of unmelted basaltic mms compared with spherules if statistically valid is also shown to be inconsistent with a low velocity population 12 km s 1 and is more compatible with higher velocities which may suggest a near earth asteroid source dominates the current dust production of basaltic mms

using helicopter electromagnetic hem surveys to identify potential hazards at coal waste impoundments examples from west virginia we have used 14 multifrequency helicopter borne electromagnetic hem surveys to determine the internal structure and integrity of mine impoundment structures in west virginia u s a the first time such technology has been applied in this way and apparently well suited for such activities the hem surveys identified areas of concern in each of the impoundments investigated in most cases these were areas where filtrate was emerging high on the downstream embankment and represented an erosion risk of greater concern the hem survey identified thick bodies of slurry that remained unconsolidated and were buried deep beneath the embankment s crest of some impoundments ground confirmation activities indicated that hem survey interpretations provided an accurate representation of the conductivity distribution within coal waste impoundments we then interpreted the conductivity depth images from the hem surveys to provide a snapshot of hydrologic conditions that existed within the impoundment at the time of the survey resistivity profiles were obtained at the inactive impoundment along segments of flight lines from the hem survey hem and resistivity surveys detected a conductive layer at a depth of about 7 m that was interpreted to be unconsolidated coal slurry the methods also detected conductive bodies at a depth of about 26 m that were interpreted to be flooded mine works resistivity surveys from these segments corroborated hem data thereby providing independent confirmation of the hem data and its processing the resistivity and hem surveys indicated a resistive surface layer where the coarse coal refuse was placed beneath the resistive surface layer is a conductive layer of unconsolidated or partially consolidated coal slurry these highly loaded bodies of unconsolidated slurry are susceptible to solifluction which can threaten embankment stability underground mine workings were identified in the hem data from one impoundment

formation of spinels in cosmic objects during atmospheric entry a clue to the cretaceous tertiary boundary event abstract magnetic spinels produced by oxidation of extraterrestrial objects in the atmosphere have a composition distinct from terrestrial spinels they are characterized by a high iron oxidation state arising from crystallization under high oxygen fugacities and a high nickel concentration due to the relatively high abundance of this element in extraterrestrial material the iron oxidation state increases from micrometeorites to meteoroid ablation material and to impact generated products this reflects a progressive increase of the oxygen fugacity corresponding to decreasing altitudes of crystallization spinels found at the cretaceous tertiary boundary are similar to those that crystallized from meteoroid ablation material and impact generated products supporting the view that a collisional event did occur at the end of the cretaceous

bulk mineralogy of individual micrometeorites determined by x ray diffraction analysis and transmission electron microscopy abstract bulk mineralogy of individual fine grained micrometeorites from 50 to 200 m in diameter was determined on the basis of the powder x ray diffraction patterns and the observation of internal textures by a transmission electron microscope tem x ray diffraction analysis of 56 micrometeorites indicated that 42 11 and 3 samples are olivine rich pyroxene rich and phyllosilicate rich micrometeorites respectively among the phyllosilicate rich micrometeorites one contains saponite and other two contain serpentine no samples contain both saponite and serpentine we found that saponite rich micrometeorite was weakly heated which results in shrinkage of 001 basal spacing of saponite down to 9 7 a and that cronstedtite which is commonly contained in cm chondrites occurs in serpentine rich micrometeorites micrometeorites that consist entirely of anhydrous minerals and amorphous phases are predominant in the samples studied the major phases of such micrometeorites are olivine low ca pyroxene magnetite and fe sulfide and the average abundances are 65 17 11 and 7 wt respectively when the total abundance of the four minerals are normalized to 100 wt the relative mineral abundance varies greatly between samples low ca pyroxene olivine ratios range from 0 to 3 5 with a mean of 0 3 tem observations of inner portions of some micrometeorites revealed that they are aggregates of very small equigranular grains 100 nm of olivine magnetite or low ca pyroxene olivine magnesiowustite the textures are very similar to those of hydrous carbonaceous chondrite that was experimentally heated to temperature below melting point thus suggesting that the micrometeorites had been hydrous particles but were decomposed by the brief heating upon atmospheric entry it is newly found that magnesiowustite was formed in micrometeorites instead of magnetite as a product of phyllosilicate decomposition under low oxygen fugacity the decomposed hydrous micrometeorites gave two types of characteristic x ray diffraction patterns 1 broad olivine and magnetite reflections or 2 variable intensities of magnesiowustite reflections together with magnetite low ca pyroxene and olivine reflections twenty nine olivine or pyroxene rich micrometeorites showed such diffraction patterns thus suggesting that more than half of micrometeorites investigated must be decomposed hydrous particles the results confirmed that hydrous dust particles are much more abundant in the interplanetary space than in the micrometeorites recovered on the earth

heating experiments simulating atmospheric entry heating of micrometeorites clues to their parent body sources depending on their velocity entry angle and mass extraterrestrial dust particles suffer certain degrees of heating during entry into earth s atmosphere and the mineralogy and chemical composition of these dust particles are significantly changed in the present study pulse heating experiments simulating the atmospheric entry heating of micrometeoroids were carried out in order to understand the mineralogical and chemical changes quantitatively as well as to estimate the peak temperature experienced by the particles during entry heating fragments of the ci chondrites orgueil and alais as well as pyrrhotites from orgueil were used as analogue material the experiments show that the volatile elements s zn ga ge and se can be lost from 50 to 100 m sized ci meteorite fragments at temperatures and heating times applicable to the entry heating of similar sized cosmic dust particles it is concluded that depletions of these elements relative to ci as observed in micrometeorites are mainly caused by atmospheric entry heating besides explaining the element abundances in micrometeorites the experimentally obtained release patterns can also be used as indicators to estimate the peak heating of dust particles during entry using the abundances of zn and ge and assuming their original concentrations close to ci a maximum heating of 1100 1200 c is obtained for previously analyzed antarctic micrometeroites thermal alteration also strongly influenced the mineralogy of the meteorite fragments while the unheated samples mainly consisted of phyllosilicates these phases almost completely transformed into olivine and pyroxene in the fragments heated to 800 c therefore dust particles that still contain hydrous minerals were probably never heated to temperatures 800 c in the atmosphere during continued heating the grain size of the newly formed silicates increased and the composition of the olivines equilibrated applying these results quantitatively to antarctic micrometeorites typical peak temperatures in the range of 1100 1200 c during atmospheric entry heating are deduced this temperature range corresponds to the one obtained from the volatile element concentrations measured in these micrometeorites and points to an asteroidal origin of the particles

the parent body controls on cosmic spherule texture evidence from the oxygen isotopic compositions of large micrometeorites high precision oxygen isotopic compositions of eighteen large cosmic spherules 500 mu m diameter from the atacama desert chile were determined using ir laser fluorination isotope ratio mass spectrometry the four discrete isotopic groups defined in a previous study on cosmic spherules from the transantarctic mountains suavet et al 2010 were identified confirming their global distribution approximately 50 of the studied cosmic spherules are related to carbonaceous chondrites 38 to ordinary chondrites and 12 to unknown parent bodies approximately 90 of barred olivine bo cosmic spherules show oxygen isotopic compositions suggesting they are related to carbonaceous chondrites similarly similar to 90 porphyritic olivine po cosmic spherules are related to ordinary chondrites and none can be unambiguously related to carbonaceous chondrites other textures are related to all potential parent bodies the data suggests that the textures of cosmic spherules are mainly controlled by the nature of the precursor rather than by the atmospheric entry parameters we propose that the po texture may essentially be formed from a coarse grained precursor having an ordinary chondritic mineralogy and chemistry coarse grained precursors related to carbonaceous chondrites i e chondrules are likely to either survive atmospheric entry heating or form v type cosmic spherules due to the limited number of submicron nucleation sites after total melting ordinary chondrite related coarse grained precursors that suffer higher peak temperatures will preferentially form cryptocrystalline cc textures instead of bo textures conversely the bo textures would be mostly related to the fine grained matrices of carbonaceous chondrites due to the wide range of melting temperatures of their constituent mineral phases allowing the preservation of submicron nucleation sites independently of the nature of the precursors increasing peak temperatures form glassy textures

experimental simulation of atmospheric entry of micrometeorites depending on their velocity entry angle and mass micrometeorites suffer different degrees of heating during their deceleration in the earth s atmosphere leading in most cases to significant textural mineralogical and chemical modifications one of these modifications is the formation of a magnetite shell around most micrometeorites which until now could not be reproduced neither theoretically nor experimentally the present study was designed to better understand the entry heating effects on micrometeorites and especially the formation of the magnetite shell fragments of the murchison and orgueil meteorites were used as analogue material in flash heating experiments performed in a high temperature furnace effects of temperature heating duration and oxygen fugacity were investigated these experiments were able to reproduce most of the micrometeorites textures from the vesicular fine grained micrometeorites to the totally melted cosmic spherules for the first time the formation of a magnetite shell could be observed on micrometeorite analogues we suggest that the most plausible mechanism for the formation of this shell is a peripheral partial melting with subsequent magnetite crystallization at the surface of the micrometeorite furthermore with this study it is possible to estimate the atmospheric entry conditions of micrometeorites such as the peak temperature and the duration of flash heating

mineralogy of phyllosilicate rich micrometeorites and comparison with tagish lake and sayama meteorites abstract four phyllosilicate rich micrometeorites mms were investigated by a synchrotron radiation x ray diffraction technique and transmission electron microscopy three are saponite rich mms and one is a serpentine rich one in the saponite rich mms we could not find serpentine and vice versa in the serpentine rich mm in the saponite rich mms major constituent minerals are saponite fe and ni bearing sulfides and magnetite two saponite rich mms contain fine grained magnesiowustite rich aggregates the aggregates consist of

factors controlling compositions of cosmic spinels application to atmospheric entry conditions of meteoritic materials abstract during their deceleration through the earth s atmosphere meteoritic materials i e interplanetary dust particles micrometeorites and meteorites experience thermal shocks which may alter their pristine mineralogy texture or chemical characteristics among these changes one of the most ubiquitous is the formation of spinels resulting from partial melting and subsequent crystallization of the meteoritic material these cosmic spinels differ from terrestrial spinels by their high ni and fe3 contents and show large variations in composition in order to better understand the factors controlling their chemistry pulse heating experiments simulating atmospheric entry of extraterrestrial objects were carried out using orgueil samples as proxies of meteoritic material covering a large range of experimental conditions temperature 500 c we also show that due to their fast crystallization kinetics cosmic spinels can record through their composition i e al2o3 contents and feo fe2o3 ratio the diverse conditions of the atmosphere crossed by the extraterrestrial object during its fall towards the earth s surface chemistry of cosmic spinels is thus a powerful tool for constraining the entry conditions in the earth s atmosphere of any extraterrestrial object including altitude of deceleration entry angle and incident velocity these in turn may provide valuable information on the origin of the extraterrestrial material