ordinary chondrite related giant 800 μm cosmic spherules from the transantarctic mountains antarctica abstract in order to identify the parent bodies of cosmic spherules melted micrometeorites with porphyritic olivine po and cryptocrystalline cc textures we measured the oxygen isotopic composition of 15 giant 800 m cosmic spherules recovered in the transantarctic mountains antarctica with ir laser fluorination mass spectrometry and we conducted a characterization of their petrographic and magnetic properties samples include 6 8 and 1 spherules of po cc and barred olivine bo textural types respectively eleven spherules 70 of the total 4 6 po and 6 8 cc and the bo spherule are related to ordinary chondrites based on oxygen isotopic compositions olivines in ordinary chondrite related spherules have compositions fa 8 5 11 8 they are ni poor to ni rich 0 04 1 12 wt and tend to be richer in cao than other spherules 0 10 0 17 wt ordinary chondrite related spherules also have high magnetite contents 2 12 wt one po and one cc spherules are related to previously identified 17 o enriched cosmic spherules for which the parent body is unknown one cc spherule has an oxygen isotopic signature relating it to cm cr carbonaceous chondrites the majority of po cc cosmic spherules derive from ordinary chondrites this result exemplifies how the texture of cosmic spherules is not only controlled by atmospheric entry heating conditions but also depends on the parent body whether be it through orbital parameters entry angle and velocity or chemistry mineralogy or grain size of the precursor

oxygen isotopic compositions of individual minerals in antarctic micrometeorites further links to carbonaceous chondrites abstract we report in situ measurements of oxygen isotopic abundances in individual silicate and oxide minerals from 16 antarctic micrometeorites amms the oxygen isotopic compositions of 10 olivine and 11 pyroxene grains are enriched in 16 o relative to terrestrial minerals and on an oxygen three isotope diagram they plot on the low 18 o side of the 16 o mixing line defined by calcium aluminum rich inclusions cai from chondritic meteorites amm olivine and pyroxene 18 o values range from 9 9 to 8 0 and 17 o ranges from 11 3 to 5 5 similar to values measured in individual olivine grains and whole chondrules from carbonaceous chondrites these data indicate that the mineral grains preserve their pre terrestrial oxygen isotopic compositions and provide another link between amms and carbonaceous chondrites however no clear relationship with one single subgroup of carbonaceous chondrite can be established based on their textures crystal chemistries and oxygen isotopes some coarse grained crystalline amms could originate from chondrule fragmentation whether the remaining mineral grains were formed by igneous or condensation processes is unclear no clear correlation is observed between isotopic compositions and mineral compositions of amm olivine grains suggesting that the feo and 16 o enrichment processes are not coupled in a simple way nor are any relatively large 16 o enrichments measured in any of the olivine grains however two mg al spinels and a melilite grain are 16 o enriched at the level of 18 o 17 o 40 the discovery of an 16 o enriched melilite grain in amms supports the hypothesis that refractory minerals throughout the solar nebula formed from a relatively uniformly 16 o enriched reservoir this unique 16 o rich signature of refractory minerals in primitive solar system materials suggests that they either formed from a widespread 16 o rich reservoir in the solar nebula or that an efficient mechanism such as bipolar outflows was acting to spread them from a highly localized 16 o rich region over the early solar nebula

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

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

raman spectroscopy in heavy mineral studies abstract raman spectroscopy is an innovative tool with tremendous potential serving as a fun damental complement to a variety of provenance methods including heavy mineral analysis anddetrital geochronology because of its accuracy ef ciency and versatility the results of theraman technique are indispensable for fully reliable identi cation of heavy minerals in grainmounts or thin sections thorny long standing problems that cannot be solved con dently witha polarizing microscope alone such as the determination of opaque and altered heavy minerals of detrital grains as small as a few microns or of colourless crystals with uncertain orientationand rounded morphology can nally be addressed although the method can be highly automa tized the full ability and experience of the operator is required to combine raman data with theoptical information obtained under the microscope on the same grains which is essential for theef cient application of the method in provenance studies this article provides exemplaryramanspectrausefulforthecomparisonand determinationof over70 differentopaqueandtrans parent heavy mineral species commonly found in sediments conveying speci c information onthe genesis of their source rocks and thus is particularly useful in provenance diagnoses andpalaeotectonic reconstructions supplementary material detailed information on the lasers used and the origin of the analysedminerals is available at http www geolsoc org uk sup18615it is the scattering of light by atoms and moleculesthat gives us the light of the sky the blue colour ofthe deep sea and the delicate opalescence of largemasses of clear ice raman 1928 pp 368 369

comment on the letter on the influx of small comets into the earth s upper atmosphere a critical comment is made on the proposal by frank et al 1986 that a flux of small comets constantly impacts the earth s atmosphere the seismic amplitudes generated in the moon by such comets impacting that body are calculated and it is concluded that the proposed flux of comets is 100 000 times greater than would be supported by either the seismic impact rate of the moon or the amplitude of its steady state reverberation frank et al reply that this discrepancy may be traced to the insensitivity of the lunar seismic stations for the detection of the impacts of tenuous weakly bound comets relative to those of dense stony meteoroids

the leonard award address presented 1996 july 25 berlin germany the elemental composition of stony cosmic spherules five hundred stony cosmic spherules collected from deep sea sediments polar ice and the strato sphere have been analyzed for major and some minor element composition typical spherules are products of atmospheric melting of millimeter sized and smaller meteoroids the samples are small and modified by atmospheric entry but they are an important source of information on the composition of asteroids the spherules in this study were all analyzed in an identical manner and they provide a sampling of the solar system s asteroids that is both different and less biased than provided by studies of conventional meteorites volatile elements such as na and s are depleted due to atmospheric heating while siderophiles are depleted by less understood causes the refractory nonsiderophile elements appear not to have been significantly dis turbed during atmospheric melting and provide important clues on the elemental composition of millimeter sized meteoroids colliding with the earth typical spherules have cm like composition that is distinctively different than ordinary chondrites and most other meteorite types we assume that c type asteroids are the primary origin of spherules with this composition type s asteroids should also be an important source of the spherules and the analysis data provide constraints on their composition a minor fraction of the spher ules are melt products of precursor particles that did not have chondritic elemental compositions the most common of these are particles that are dominated by olivine the observed compositions of spherules are in consistent with the possibility that an appreciable fraction of the spherules are simply chondrules remelted during atmospheric entry

accretion rate of cosmic spherules measured at the south pole micrometeorites are terrestrially collected extraterrestrial particles smaller than about 1 mm which account for most of the mass being accreted to the earth1 2 compared with meteorites micrometeorites more completely represent the earth crossing meteoroid complex3 4 and should include fragments of asteroids comets mars and our moon as well as pre solar and interstellar grains3 6 previous measurements of the flux of micrometeoroids that survive to the earth s surface have large uncertainties owing to the destruction of particles by weathering7 8 9 inefficiencies in magnetic collection or separation techniques7 8 9 low particle counts10 11 poor age constraint7 8 9 12 13 or highly variable concentrating processes12 13 here we describe an attempt to circumvent these problems through the collection of thousands of well preserved and dated micrometeorites from the bottom of the south pole water well which supplies drinking water for the scott amundsen station using this collection we have determined precise estimates of the flux and mass distribution for 50 700 m cosmic spherules melted micrometeorites allowing for the expected abundance of unmelted micrometeorites14 in the samples our results indicate that about 90 of the incoming mass of submillimetre particles evaporates during atmospheric entry our data indicate the loss of glass rich and small stony spherules from deep sea deposits7 8 and they provide constraints for models describing the survival probability of micrometeoroids15 16

on the possible influence of extraterrestrial volatiles on earth s climate and the origin of the oceans abstract a consideration of observational and circumstantial evidence suggests that earth may be subject to high influx rates 1011 1012 kg yr of extraterrestrial sourced volatile elements carbon hydrogen oxygen nitrogen derived from comets or other primitive solar system material the total extraterrestrial influx rate may be four to five orders of magnitude greater than previously thought large enough to account for today s total near surface inventories of water and carbon the possibility of high rates of extraterrestrial volatile accretion suggests a new climatic paradigm wherein earth s surface temperature is influenced by conflicting internal and external processes a variable influx of volatile elements tends to warm the earth while terrestrial processes cool the planet by absorbing these gasses at a more uniform rate variations in extraterrestrial influx rates may explain the variation of sea level and mean global temperature over geologic time as well as some types of climate change the occurrence of the pleistocene ice ages and the asymmetry of the phanerozoic climate record sudden warmings slow coolings the extraterrestrial influx rate may also act as the pacemaker of terrestrial evolution at times leading to mass extinctions through climatic shifts induced by changes in accretion rates with concomitant disruptions of the carbon and nitrogen cycles life on earth may be balanced precariously between cosmic processes which deliver an intermittent stream of life sustaining volatiles from the outer solar system or beyond and biological and tectonic processes which remove these same volatiles from the atmosphere by sequestering water and carbon in the crust and mantle

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

carbonado like diamond from the avacha active volcano in kamchatka russia abstract in addition to a series of finds of diamond in mafic volcanic and ultramafic massive rocks in kamchatka russia a carbonado like diamond aggregate was identified in recent lavas of the active avacha volcano this aggregate differs from classic carbonado by its location within an active volcanic arc well formed diamond crystallites and cementing by si containing aggregates rather than sintering the carbonado like aggregate contains inclusions of mn ni si fe alloys native mn tungsten and boron carbides which are uncommon for both carbonado and monocrystalline diamonds mn ni si fe alloys trigonal w 2 c and trigonal b 4 c are new mineral species that were not previously found in the natural environment the formation of the carbonado like diamond aggregate started with formation at 850 1000 c of tungsten and boron carbides mn ni si fe alloys and native mn which were used as seeds for the subsequent crystallization of micro sized diamond aggregate in the final stage the diamond aggregate was cemented by amorphous silica tridymite sic and native silicon the carbonado like aggregate was most likely formed at near atmospheric pressure conditions via the cvd mechanism during the course or shortly after one of the volcanic eruption pulses of the avacha volcano volcanic gases played a great role in the formation of the carbonado like aggregate

micrometer and nanometer sized platinum group nuggets in micrometeorites from deep sea sediments of the indian ocean abstract we examined 378 micrometeorites collected from deep sea sediments of the indian ocean of which 175 180 and 23 are i type s type and g type respectively of the 175 i type spherules 13 contained platinum group element nuggets pgns the nuggets occur in two distinct sizes and have distinctly different elemental compositions micrometer m sized nuggets that are 3 m contain dominantly ir os and ru iridium platinum group element or ipge and sub m or nanometer sized 1 m nuggets which contain dominantly pt rh and pd palladium pge or ppge the m sized nuggets are found only one per spherule in the cross section observed and are usually found at the edge of the spherule by contrast there are hundreds of nanometer sized nuggets distributed dominantly in the magnetite phases of the spherules and rarely in the wustite phases both the nugget types are found as separate entities in the same spherule and apparently nugget formation is a common phenomenon among i type micrometeorites however the m sized nuggets are seen in fewer specimens 2 5 of the observed i type spherules in all we analyzed four nuggets of m size and 213 nanometer sized nuggets from 13 i type spherules for platinum group elements chemically the m sized pgns contain chondritic ratios of os ir but are depleted in the more volatile pge pt rh and pd relative to chondritic ratios on the other hand the nanometer sized nuggets contain dominantly pt and rh importantly the refractory pges are conspicuous by their absence in these nanometer nuggets palladium the most volatile pge is highly depleted 1 1 with respect to chondritic ratios in the m sized pgns and is observed in only 17 of 213 nanometer nuggets with concentrations that are just above the detection limit 0 2 distinct fractionation of the pge into ipge ir os ru and ppge seems to take place during the short span of atmospheric entry these observations suggest several implications 1 the observation of fractionated pge in an fe ni system gives rise to the possibility that earth s core could contain fractionated pge 2 the present data support the processes suggested for the fractionated pge patterns observed in the ejecta of ancient meteorite impacts 3 meteoric metals released in the troposphere could contain fractionated pgns in large numbers

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

determination of the earth s plasmapause location from the ce 3 euvc images the moon based extreme ultraviolet camera euvc aboard china s chang e 3 ce 3 mission has successfully imaged the entire earth s plasmasphere for the first time from the side views on lunar surface an euvc image on 21 april 2014 is used in this study to demonstrate the characteristics and configurations of the moon based euv imaging and to illustrate the determination algorithm of the plasmapause locations on the magnetic equator the plasmapause locations determined from all the available euvc images with the minimum l algorithm are quantitatively compared with those extracted from in situ observations defense meteorological satellite program time history of events and macroscale interactions during substorms and radiation belt storm probes excellent agreement between the determined plasmapauses seen by euvc and the extracted ones from other satellites indicates the reliability of the moon based euvc images as well as the determination algorithm this preliminary study provides an important basis for future investigation of the dynamics of the plasmasphere with the moon based euvc imaging

ionospheric response to the interplanetary magnetic field southward turning fast onset and slow reconfiguration 1 this paper presents a case study of ionospheric response to an interplanetary magnetic field imf southward turning it is based on a comprehensive set of observations including a global network of ground magnetometers global auroral images and a superdarn hf radar there is a clear evidence for a two stage ionospheric response to the imf southward turning namely fast initial onset and slow final reconfiguration the fast onset is manifested by nearly simultaneous within 2 min rise of ground magnetic perturbations at all local times corroborated by a sudden change in the direction of line of sight velocity near local midnight and by the simultaneous equatorward shift of the auroral oval the slow reconfiguration is characterized by the different rising rate of magnetic perturbations with latitudes faster at high latitude than at lower latitudes furthermore a cross correlation analysis of the magnetometer data shows that the maximum magnetic perturbation is reached first near local noon and then spread toward the nightside corresponding to a dayside to nightside propagation speed of 5 km s along the auroral oval global ionospheric convection patterns are derived based on ground magnetometer data along with auroral conductances inferred from the polar uv images using the assimilative mapping of ionospheric electrodynamics amie procedure the amie patterns especially the residual convection patterns clearly show a globally coherent development of two cell convection configuration following the imf southward turning while the foci of the convection patterns remain nearly steady the convection flow does intensify with time and the cross polar cap potential drop increases the overall changes as shown in the amie convection patterns therefore are fully consistent with the two stage ionospheric response to the imf southward turning

the plasmapause response to the southward turning of the imf derived from sequential euv images 1 we statistically examined the plasmapause response to the southward turning of the interplanetary magnetic field imf using sequential global images of the plasmasphere in order to understand how the convection electric field propagates to the inner magnetosphere the extreme ultraviolet euv imager on the imager for magnetopause to aurora global exploration satellite clearly observed inward motion of the plasmapause driven by the southward turning of the imf we surveyed the euv data in the 2000 2001 period and found 16 events using the sequential euv images we calculated the plasmapause radial velocity and then estimated the time development of the convection electric field at the plasmapause epp epp and the solar wind electric field derived from the measurement by the ace satellite had very similar variations each other but there surely was a time lag consequently our research indicates that the plasmapause response to the southward turning of the imf takes 10 30 min this timescale suggests that the convection electric field penetrates from the magnetopause to the inner magnetosphere through the ionosphere

mineralogy of tagish lake an ungrouped type 2 carbonaceous chondrite in this paper we describe the recovery handling and preliminary mineralogical investigation of the tagish lake meteorite tagish lake is a type 2 carbonaceous chondrite which bears similarities to ci1 and cm chondrite groups but is distinct from both abundant phyllosilicates as well as chondrules however sparse and common olivine grains in the matrix preclude any other classification the bulk density of tagish lake 1 67 g cc which is far lower than ci or cm chondrites 2 2 2 3 and 2 6 2 9 g cc respectively or any other meteorite for that matter we have identified two lithologies a dominant carbonate poor lithology and a less abundant carbonate rich lithology the meteorite is a breccia at all scales we have noted similarities between tagish lake and some clasts within the enigmatic meteorite kaidun possibly there are genetic relationships here worth exploring in the paper we describe a clast of cm1 material within tagish lake which is very similar to a major lithology in kaidun

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

moon based euv imaging of the earth s plasmasphere model simulations the euv imager on board the chang e 3 lunar lander will image the earth s plasmasphere from a lunar perspective to focus on some of the open questions in plasmaspheric researches i e global structures erosion and refilling of plasmasphere in order to achieve the understanding of the plasmaspheric dynamics in relation to these euv images in lunar perspective the he 30 4nm emission intensities and global structures of the plasmasphere viewed from the moon are investigated using a dynamic global core plasma model embedded with ts07 magnetic field model and w05 electric field model two typical storms observed by the image euv imager are systematically simulated from the perspectives of the moon it is found from the simulations that the maximum emission intensity of the plasmasphere is similar to 12 3 r which is greater than that detected from polar orbit and the global shapes and temporal evolutions of large scale plasmaspheric structures plasmapause shoulder and plume also have different patterns in moon based simulated images it is also shown that the plasmaspheric structures extracted from moon based euv images are in agreement with those from image euv images systematic simulations demonstrate that specific latitudinal distribution of the plasmaspheric structures can only be imaged at specific positions in lunar orbit it is expected that this investigation provides us with an overall understanding on moon based euv images and helps to identify the plasmaspheric structures and evolution patterns in future moon based euv imaging

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

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

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

magnetization of polar ice a measurement of terrestrial dust and extraterrestrial fallout abstract laboratory induced remanent magnetization of polar ice constitutes a measurement of the magnetization carried by the ferromagnetic dust particles in the ice this non destructive technique provides a novel kind of information on the dust deposited on the surface of polar ice sheets measurements made on ice samples from greenland north grip ice core and antarctica vostok and epica dome c ice cores allowed the recognition of a fraction of magnetic minerals in ice whose concentration and magnetic properties are directly related to that of insoluble dust the source of this fraction of magnetic minerals thus appears closely related to terrestrial dust transport and deposition and its magnetic properties are informative of the dust provenance areas the rock magnetic properties of the dust may reflect distinct changes of dust source areas from glacial to interglacial periods in agreement with and adding further information to the isotopic 87 sr 86 sr and 143 nd 144 nd analyses a second magnetic fraction consists of particles of nanometric size which are superparamagnetic at freezer temperature and whose concentration is independent of the mass of aerosol dust found in the ice the source of these nanometric sized magnetic particles is ascribed to fallout of meteoric smoke and their concentration in ice was found to be compatible with the extraterrestrial fallout inferred from ir concentrations the diameter of the smoke particles as inferred from magnetic measurements is in the range of about 7 20 nm

atmospheric holes and small comets global images of earth s ultraviolet dayglow as gained with an imaging photometer on board dynamics explorer 1 exhibit transient decreases or atmospheric holes in the dayglow intensities over areas with diameters 50 km features of these atmospheric holes include 1 preferential motion in the east to west direction across the sunlit face of earth 2 similar diurnal variations in occurrence rates as those for radar meteors 3 correlation of the occurrence rates with the nonshower rates as determined with forward scatter radar and 4 larger angular diameters for these atmospheric holes when the spacecraft approaches earth during its perigee passes a significantly less extensive series of images of earth s ultraviolet dayglow with the viking spacecraft also provides evidence of these atmospheric holes the atmospheric holes are interpreted in terms of obscuration of the dayglow by water clouds from the disruption and subsequent vaporization of small comets at low altitudes above the atmosphere supporting evidences for the existence of these small comets are given by telescopic sighting of these objects at greater altitudes before disruption and the detection of water bursts in earth s upper atmosphere we summarize the current status of this small comet hypothesis and its relationship to conventional wisdom concerning geophysical lunar and interplanetary phenomena

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

ordinary chondritic micrometeorites from the indian ocean extraterrestrial particulate materials on the earth can originate in the form of collisional debris from the asteroid belt cometary material or as meteoroid ablation spherules signatures that link them to their parent bodies become obliterated if the frictional heating is severe during atmospheric entry we investigated 481 micrometeorites isolated from 300 kg of deepsea sediment out of which 15 spherules appear to have retained signatures of their provenance based on their textures bulk chemical compositions and relict grain compositions seven out of these 15 spherules contain chromite grains whose compositions help in distinguishing sub groups within the ordinary chondrite sources there are seven other spherules which comprise either entirely of dusty olivines or contain dusty olivines as relict grains two of these spherules appear to be chondrules from an unequilibrated ordinary chondrite in addition a pop porphyritic olivine pyroxene chondrule like spherule is also recovered the bulk chemical composition of all the spherules in combination with trace elements the chromite composition and presence of dusty olivines suggest an ordinary chondritic source these micrometeorites have undergone minimal frictional heating during their passage through the atmosphere and have retained these features these micrometeorites therefore also imply there is a significant contribution from ordinary chondritic sources to the micrometeorite flux on the earth

shock metamorphism of ordinary chondrites a revised petrographic classification of progressive stages of shock metamorphism of ordinary chondrites is proposed six stages of shock s1 to s6 are defined based on shock effects in olivine and plagioclase as recognized by thin section microscopy the characteristic shock effects of each shock stage are s1 unshocked sharp optical extinction of olivine s2 very weakly shocked undulatory extinction of olivine s3 weakly shocked planar fractures in olivine s4 moderately shocked mosaicism in olivine s5 strongly shocked isotropization of plagioclase maskelynite and planar deformation features in olivine and s6 very strongly shocked recrystallization of olivine sometimes combined with phase transformations ringwoodite and or phases produced by dissociation reactions s6 effects are always restricted to regions adjacent to melted portions of a sample which is otherwise only strongly shocked in stages s3 to s6 localized melting results from stress and temperature peaks which locally deviate from the equilibration shock pressure due to differences in shock impedance these melting effects are a opaque melt veins shock veins b melt pockets with interconnecting melt veins c melt dikes and d troilite metal deposits in fractures based on a critical evaluation of data from shock recovery experiments a shock pressure calibration for the six shock stages is proposed which defines the s1 s2 s2 s3 s3 s4 s4 s5 and s5 s6 transitions at 5 5 10 15 20 30 35 and 45 55 gpa respectively whole rock melting and formation of impact melt rocks or melt breccias occurs at about 75 90 gpa the symbol for the shock stage may be used in combination with the symbol for the petrologic type to abbreviate the complete classification of a chondrite e g h5 s3 we propose this new shock classification and pressure calibration system to replace previous systems which are out of date with respect to the pressure calibration nominally restricted to l chondrites and based on incomplete and in part illdefined sets of shock effects we have classified seventy six ordinary chondrites using the new classification system and conclude the following 1 1 shock effects and the sequence of progressively increasing degrees of shock metamorphism are very similar in h l and ll groups differences in the frequency distribution of shock stages are relatively minor e g l chondrites appear to have the largest fraction with stages s5 and s6 this suggests that the collisional histories of the h l and ll parent bodies were similar 2 2 petrologic type 3 chondrites are deficient in stages s4 to s6 and with increasing petrologic type the frequency of stages s4 to s6 increases we suggest that the more porous and volatile rich type 3 chondrites are subject to melting at a lower shock pressure than the nonporous chondrites of higher petrologic type volatiles trapped in pores cause shock induced dispersal of the shocked and melted material into small particles which are not expected to survive as meteorites 3 3 stage s3 is the most abundant in nearly all petrologic types 4 4 at shock pressures in excess of about 35 gpa s5 and s6 4he and 40ar are almost completely lost pressures below 10 gpa s1 and s2 do not cause noble gas losses

ultra reduced phases in apollo 16 regolith combined field emission electron probe microanalysis and atom probe tomography of submicron fe si grains in apollo 16 sample 61500 the lunar regolith contains a variety of chemically reduced phases of interest to planetary scientists and the most common metallic iron is generally ascribed to space weathering processes lucey et al 2006 reports of silicon metal and iron silicides phases indicative of extremely reducing conditions in lunar samples are rare anand et al 2004 spicuzza et al 2011 additional examples of fe silicides have been identified in a survey of particles from apollo 16 sample 61501 22 herein is demonstrated the utility of low kev electron probe microanalysis epma using the fe ll x ray line to analyze these submicron phases and the necessity of accounting for carbon contamination we document four fe si and si0 minerals in lunar regolith return material the new fe si samples have a composition close to fe ni 3si whereas those associated with si0 are close to fesi2 and fe3si7 atom probe tomography of fe ni 3si shows trace levels of c 60 ppma and nanodomains enriched in c ni p cr and sr these reduced minerals require orders of magnitude lower oxygen fugacity and more reducing conditions than required to form fe0 documenting the similarities and differences in these samples is important to constrain their formation processes these phases potentially formed at high temperatures resulting from a meteorite impact whether carbon played a role in achieving the lower oxygen fugacities and there is evidence of nearby carbonaceous chondritic material it remains to be proven that carbon was the necessary component for the unique existence of these si0 and iron silicide minerals

moissanite sic with metal silicide and silicon inclusions from tuff of israel raman spectroscopy and electron microscope studies abstract here we present studies of natural sic that occurs in situ in tuff related to the miocene alkaline basalt formation deposited in northern part of israel raman spectroscopy sem and fib assisted tem studies revealed that sic is primarily hexagonal polytypes 4h sic and 6h sic and that the 4h sic polytype is the predominant phase both sic polytypes contain crystalline inclusions of silicon sio and inclusions of metal silicide with varying compositions e g si58v25ti12cr3fe2 si41fe24ti20ni7v5zr3 and si43fe40ni17 the silicides crystal structure parameters match si2tiv5 pm 3m space group cubic fesi2ti pbam space group orthorhombic and fesi2 cmca space group orthorhombic respectively we hypothesize that sic was formed in a local ultra reduced environment at respectively shallow depths 60 100 km through a reaction of sio2 with highly reducing fluids h2o ch4 h2 c2h6 arisen from the mantle hot spot and passing through alkaline basalt magma reservoir sio2 interacting with the fluids may originate from the walls of the crustal rocks surrounding this magmatic reservoir this process led to the formation of sic and accompanied by the reducing of metal oxides to native metals alloys and silicides the latter were trapped by sic during its growth hence interplate hot spot alkali basalt volcanism can now be included as a geological environment where sic silicon and silicides can be found

lightning induced beads fulguroids associated with kimberlite eruptions in the kalahari botswana glassy beads were found in the sand cover associated with known and suspected kimberlites on the kalahari plateau botswana morphology and chemistry were examined by esem and edax the polymetallic and quartzose beads here described for the first time and termed fulguroids formed at very high temperatures well in excess of those reached by the kimberlites they solidified in free fall we propose that they were melted in the atmosphere by lightning strikes on kalahari overburden entrained when the kimberlites erupted

discovery of moissanite in a peralkaline syenite from the azores islands abstract our discovery of moissanite grains in a peralkaline syenite from the agua de pau volcano sao miguel azores islands portugal represents the first report of this mineral in present day oceanic geodynamic settings raman spectroscopy and single crystal x ray diffraction show the presence of both the 6h and 4h polytypes with the predominance of the first one the distribution of trace elements is homogeneous except for al and v azorean moissanite often hosts rounded inclusions of metallic si and other not yet identified metallic alloys a process involving a flushing of ch4 h2 ultra reducing fluids in the alkaline melts might be considered as a possible mechanism leading to the formation of natural sic thus calling for strongly reducing conditions that were locally met in the crust mantle beneath the sao miguel island

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

enigmatic super reduced phases in corundum from natural rocks possible contamination from artificial abrasive materials or metallurgical slags abstract recently a number of reports claimed enigmatic appearance of high pressure and super reduced minerals in ophiolitic chromitite and peridotite diamond moissanite various metal alloys and native metals carbides and nitrides were found in mineral separates from bulk rock probes of chromitite and peridotite from tibet polar ural and other localities similar findings of super reduced phases were reported for pyroclastic rocks and alluvial deposits of mt carmel in israel we performed the study of microinclusions in corundum grains from abrasive materials produced industrially in an electric arc furnace and found that they are very similar to microinclusions in corundum grains from natural samples the key similar phases are ti3 4al2 zr ti4 4o11 carmeltazite ti2o3 tistarite tin1 x tic1 x fe si and fe si ti alloys hibonite grossite anorthite and residual feldspatic glass although some differences between abrasive corundum and corundum from tibet and mt carmel are obvious the morphology of melt pockets and amount of mineralogical similarities is more than critical to suggest that they can be of the same origin the additional possible source of corundum grains with super reduced inclusions is various al bearing slags after aluminothermic reactions during steelmaking moreover taking into account the spectacular similarity of diamonds from ophiolite with synthetic diamonds we claim for a thorough reconsideration of ultrahigh pressure and super reduced phases in natural rocks and argue that we need to find criteria for discrimination between natural and artificial samples one of the strongest criteria would be textural and structural features that clearly demonstrate the indigenous character of the host minerals

oxygen isotopes in cosmic spherules and the composition of the near earth interplanetary dust complex abstract a long standing controversy in the micrometeorite community regards the relative contribution of primitive asteroids or comets and of evolved asteroids to the interplanetary dust cloud we compiled and studied a large set of oxygen isotopic data from the literature on cosmic spherules from different collections covering different influx periods within the last 1 myr cosmic spherules micrometeorites melted during atmospheric entry are the most abundant micrometeorites in worldwide collections according to several models they are representative of the composition and origin of micrometeorites 50 m in size spherule statistics 136 spherules 50 2280 m in size indicate that at least 20 of the micrometeoroid complex is fed by asteroids observed in the inner asteroid belt the ordinary chondrite and secondarily the hed parent asteroids likely belonging to the s type and v type spectral classes respectively another 60 or more is related to primitive objects of the solar system with carbonaceous chondrite compositions either primitive asteroids belonging to the c d or p type spectral classes in the outer asteroid belt or comets contribution from terrestrial planets has not been identified yet oxygen isotopes also document that the composition of the micrometeoroid complex is different from that of macroscopic meteoroids since the latter is dominated by materials from evolved and differentiated asteroids rather than primitive asteroids or comets cosmic spherule statistics show that the contribution of ordinary chondrite material to the composition of the micrometeoroid complex increases with micrometeorite size thereby documenting a continuum between meteorites and micrometeorites the transition in terms of relative abundance of the two cosmic spherule populations occurs around 500 m in size

cation deficient phlogopitic mica exsolution in diopside from garnet peridotite in sulu china article i nfo deep subduction and return to the surface of sediments and other continental rocks is now well known forming terranes of ultrahigh pressure metamorphism uhpm a common constituent of these terranes is garnet peridotite mantle rock that has been brought to the surface along with the returning subducted material microstructures of these peridotites especially precipitates within their constituent minerals offer promise of providing information not only about their depth of origin but also about the subduction environment here we report exsolution lamellae of cation deficient phlogopitic mica within diopside of a drill core from the uhpm terrane of sulu china detailed analysis by transmission electron microscopy tem shows these precipitates to be phlogopitic mica that is highly complex both structurally and compositionally with a significant component of the 10 a phase a talc like phase stable only at quite high pressures several mica polytypes are present the simplest one 1m being the most cation deficient the presence of a significant 30 10 a phase component in the mica suggests a means of expanding the 10 a phase bridge for subduction of h2o to deep mantle depths published by elsevier b v

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

the response of high latitude convection to a sudden southward imf turning we describe the response of the high latitude convection to a sudden southward turning of the imf in this event bz recorded at the wind satellite switched from 6 nt to 6 nt in 2 minutes and effects in the ionosphere were observed by the superdarn hf radars in the vicinity of noon mlt the convection switched suddenly 2 min from sunward to antisunward with the velocity change reaching magnitudes as great as 1500 m s in about 6 minutes surprisingly the responses at the other mlts distributed from noon to midnight began at virtually the same time meridional flows near 22 mlt were observed to reverse direction in about 4 minutes with the velocity change reaching magnitudes as great as 750 m s in about 8 minutes this example shows that the convection can respond to a sudden imf change practically simultaneously 2 min over the entire high latitude zone and reconfigure from a pattern characteristic of bz to one characteristic of bz in a very short 2 4 min time

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

extraterrestrial water in micrometeorites and cosmic spherules from antarctica an ion microprobe study the d h ratios and water contents were measured by ion microprobe analysis in 52 individual antarctic micrometeorites amms and 10 antarctic cosmic spherules acss containing nuggets of iron hydroxide cops phase in amms d values vary from 366 to 249 and water contents lie between 0 4 3 7 wt the cops nuggets in cosmic spherules have high water contents 2 to 8 wt and exhibit d values from 144 to 167 which is indicative of an extraterrestrial origin of their constituent water the silicate portion of acss also contain extraterrestrial h equivalent to 0 l to 1 2 wt water deuterium exchange experiments were performed with isotopically spiked water these experiments demonstrate that water in mineral phases of amms and acss is indigenous and does not result from contamination during residence in antarctic ice the frequency distribution of d h ratios in amms allows us to further narrow the relationship between amms and carbonaceous chondrites to cm and ci chondrites but contrasts with that of stratospheric interplanetary dust particles idps of similar sizes from 10 to 50 m the relatively narrow range of d h ratios measured in amms as well as in acss which are more resistant and thus less susceptible to collection biases suggests that d rich idp like particles are very rare in our amms collections this indicates that these d rich grains might constitute a minor fraction of the micrometeorite flux in the interplanetary medium and that possible collection biases in antarctica would not be responsible for their strong depletion in the amms collections

not all moissanites are created equal new constraints on moissanite from metamorphic rocks of bulgaria abstract terrestrial moissanite sic is widely reported as an ultra high pressure mineral occurring in kimberlites diamonds and ultramafic mafic rocks of mantle origin however the conditions of crystallization remain largely unknown moreover dozens of sic occurrences have been reported from continental crust sources such as granitoids andesite dacite volcanic rocks and their breccia metasomatic and metamorphic rocks and even limestones the validity of many of these reports is still debated primarily due to possible contaminations from the widespread use of synthetic sic abrasives in samples preparation indeed reports of well documented in situ occurrences of moissanite in association with co existing minerals are still scarce the only condition of moissanite formation that is agreed upon is that extremely reducing media are required e g 4 5 6 log units below the iron wustite buffer here we report the new occurrence of moissanite that was found in situ within the garnet staurolite mica schists of topolovgrad metamorphic group of triassic age in southern bulgaria the 10 300 m moissanite crystals are situated within 0 1 1 2 mm isolated clusters filled with amorphous carbon and nanocrystalline graphite most of moissanite crystals are 15r rhombohedral and 6h hexagonal polytypes and one prismatic crystal found within them exhibits unusual concentric polytypical zoning with core 15r intermediate zone 6h and rim 3c cubic experimental data show that this type of polytypical zonation is likely due to a decrease in temperature or and pressure and changes in si c ratio indeed amphibolite facies metamorphism 500 580 c garnet staurolite zone followed by a subsequent cooling during the retrograde stage of green schist facies metamorphism 400 500 c could have provided a change in temperature the sic containing clusters exhibit evidence that they are pre metamorphic and we hypothesize that their protolith was a black shale material likely rich in carbon hydrocarbon and terrigenous silica the latter served as a source of isolated chemically reduced media which is required for sic formation other concepts to explain moissanite occurrences in metasedimentary rocks are also discussed importantly our findings show that the formation conditions of moissanite are likely more variable than previously recognized

an urban collection of modern day large micrometeorites evidence for variations in the extraterrestrial dust flux through the quaternary we report the discovery of significant numbers 500 of large micrometeorites 100 m from rooftops in urban areas the identification of particles as micrometeorites is achieved on the basis of their compositions mineralogies and textures all particles are silicate dominated s type cosmic spherules with subspherical shapes that form by melting during atmospheric entry and consist of quench crystals of magnesian olivine relict crystals of forsterite and iron bearing olivine within glass four particles also contain ni rich metal sulfide beads bulk compositions are chondritic apart from depletions in the volatile moderately volatile and siderophile elements as observed in micrometeorites from other sources the reported particles are likely to have fallen on earth in the past 6 yr and thus represent the youngest large micrometeorites collected to date the relative abundance ratio of barred olivine to cryptocrystalline spherule types in the urban particles of 1 45 is shown to be higher than a quaternary average of 0 9 suggesting variations in the extraterrestrial dust flux over the past 800 k y changes in the entry velocities of dust caused by quasi periodic gravitational perturbation during transport to earth are suggested to be responsible variations in cosmic spherule abundance within the geologic column are thus unavoidable and can be a consequence of dust transport as well as major dust production events

small antarctic micrometeorites a mineralogical and in situ oxygen isotope study we have investigated the texture bulk chemistry mineralogy as well as the anhydrous minerals oxygen isotopic composition of 67 small antarctic micrometeorites amms collected at cap prudhomme antarctica and belonging to the currently poorly studied size fraction 25 50 m when compared to larger 50 400 m micrometeorites collected at the same site in antarctica with the same techniques no significant differences are found between the two populations we therefore conclude that the population of cap prudhomme amms is homogeneous over the size range 25 400 m in contrast small amms have different textures mineralogy and oxygen isotopic compositions than those of stratospheric interplanetary dust particles idps because small amms 50 m overlap in size with idps the differences between these two important sources of micrometeorites can no longer be attributed to a variation of the micrometeorite composition with size physical biases introduced by the collection procedures might account for these differences

global plasmasphere evolution 22 23 april 2001 1 the evolution of the plasmasphere during the moderate 22 23 april 2001 storm is studied by comparing observed plasmasphere behavior to the predictions of a simulation the plasmasphere observations include global images from image euv and density and flow measurements from lanl mpa the subjective uncertainty in the euv plasmapause was found to be 0 2l inward plasmapause motion was correlated with southward interplanetary magnetic field imf with a 27 min delay the electric e field at the plasmapause was approximately 13 of the solar wind e field the observations support the idea that plasmaspheric erosion begins with a partial plasmapause indentation which then gradually widens in magnetic local time mlt to encompass the entire nightside in situ measurements confirm a dayside plume of sunward flowing plasma and images show that the plume subsequently experienced phases of mlt narrowing and rotation wrapping to simulate the event we employed a test particle representation of the plasmapause using a parametric e field model that includes corotation and convection from two sources dayside magnetopause reconnection dmr and the subauroral polarization stream saps the model captures the phases of plume evolution and it reproduces the observed plasmapause with maximum mean error 0 7l 0 24l the model fails to reproduce important subglobal features e g a predawn plasmaspheric shoulder and grossly misplaces the inner edge of the rotating and wrapping plume saps contributes significantly to the duskside flows but the simulated flows are about 50 smaller than those seen by lanl mpa the simulated plasmapause e field is about 70 of the euv inferred value

melted micrometeorites from antarctic ice with evidence for the separation of immiscible fe ni s liquids during entry heating we report the discovery of four large 50 m cosmic spherules css and a single scoriaceous micrometeorite smm that contain evidence for the separation of immiscible fe ni s liquids during atmospheric entry heating the particles contain segregated fe rich regions dominated by either ni s bearing fe oxides or iron sulphides and have textural relations that suggest these separated from the silicate portions of the particles as metallic liquids the oxides which may be hydrous are thought to result from alteration of metal and sulphide the compositions of the silicate portions of the css are equivalent to spherules without fe rich regions implying that metallic liquids are exsolved during the heating of most spherules but completely separate the single smm has a very different composition from other scoriaceous particles and the occurrence of an exsolved metallic liquid probably indicates extreme reduction during entry heating the pyrolysis of carbonaceous materials is the most likely explanation for reduction and suggests that the precursor material of this particle was unusually c rich this smm might be therefore an appropriate candidate for a large melted anhydrous or smectite interplanetary dust particle idp the exsolution of immiscible fe ni s liquids during entry heating will result in systematic changes in the compositions of the remaining silicate melt

micrometeorites and extraterrestrial he in a ferromanganese crust from the pacific ocean abstract extraterrestrial helium he et in ferromanganese crusts from the deep oceans is presumed to originate in micrometeorites the carrier phase of the he et has so far not been identified to address this issue we have recovered and examined several metallic micrometeorites from crust 237kd from the deep pacific ocean and have performed he isotope determinations on powdered samples of the crust a peak of release of extraterrestrial helium he et at 600 800 c is observed that is similar to the release peak of micrometeorite bearing deep ocean sediments the he et content of acid leached ferromanganese crust is approximately 70 less than that in unleached crust implying that the bulk of the extraterrestrial 3 he is hosted by a metallic phase rather than the refractory phases that host primordial he in meteorites these observations support a micrometeoritic source for the he et in 237kd the time integrated flux of extraterrestrial he measured in the ferromanganese crust is a small fraction of that determined from pacific ocean sediments implying that the crust has trapped only a small fraction of the extraterrestrial dust that has fallen to earth the presence of metallic micrometeorites provides qualitative support to the contention that the 60 fe previously measured in crust 237kd may be meteoritic in origin

an american on paris extent of aqueous alteration of a cm chondrite and the petrography of its refractory and amoeboid olivine inclusions paris is the least aqueously altered cm chondrite identified to date classified as subtype 2 7 however literature data indicate that some regions of this apparently brecciated meteorite may be subtype 2 9 the suite of cais in paris includes 19 spinel pyroxene inclusions 19 spinel inclusions 8 spinel pyroxene olivine inclusions 43 pyroxene inclusions 8 pyroxene olivine inclusions and 3 hibonite bearing inclusions both simple and complex inclusions are present some have nodular banded or distended structures no melilite was identified in any of the inclusions in the present suite but other recent studies have found a few rare occurrences of melilite in paris cais because melilite is highly susceptible to aqueous alteration it is likely that it was mostly destroyed during early stage parent body alteration two of the cais in this study are part of compound cai chondrule objects their presence suggests that there were transient heating events probably associated with chondrule formation in the nebula after chondrules and cais were admixed also present in paris are a few amoeboid olivine inclusions aoi consisting of relatively coarse forsterite rims surrounding fine grained porous zones containing diopside and anorthite the interior regions of the aois may represent fine grained rimless cais that were incorporated into highly porous forsterite rich dustballs these assemblages were heated by an energy pulse that collapsed and coarsened their rims but failed to melt their interiors

correlated si isotope anomalies and large 13c enrichments in a family of exotic sic grains a suite of morphologically distinctive silicon carbide sic grains from the orgueil and murchison carbonaceous chondrite meteorites contains si and c of highly anomalous isotopic composition all of the sic grains in this suite are characterized by a distinctive platy morphology and roughly developed hexagonal crystal forms that allow them to be distinguished from other types of sic found in the host meteorites the 29 si and 30 si values of individual sic crystals deviate from those of normal solar material by more than 100 while the 13 c values range from 150 to 5200 isotopically normal c and si are not found in any of these sic crystals the sic grains belonging to this morphological suite are isotopically distinct from fine grained sic aggregates and other morphological types of sic in unequilibrated meteorites the 29 si 28 si and 30 si 28 si ratios of these platy grains are well correlated and define a linear array that does not pass through the composition of normal solar si this behavior contrasts sharply with the diverse and poorly correlated si isotopic compositions shown by the total sic population we suggest that the distinctive morphological characteristics and comparatively simple si isotope systematics identify the platy sic crystals as a genetically related family formed around a single isotopically heterogeneous presolar star or an association of related stars the enrichments in 13 c and the si isotope systematics of the platy sic are broadly consistent with theoretical models of nucleosynthesis in low mass carbon stars on the asymptotic giant branch the si isotope array most plausibly reflects mixing between 28 si rich material inherited from a previous generation of stars and material enriched in 29 si and 30 si produced in intershell regions by neutron capture during he burning 13 c is also produced in intershell regions by proton reactions on 12 c seed nuclei and is carried withs process nuclei to the stellar envelope by convection which penetrates down to the he shell the absence of a correlation between the si and c isotopic compositions of the sic suggests either episodic condensation of sic extending over several thermal pulses in the atmosphere of a single star or derivation of the sic from several stars characterized by different rates of 13 c production in the multiple star scenario the linear correlation of the 29 si 28 si and 30 si 28 si ratios among the platy sic indicates that these stars evolved from a common si seed composition under similar conditions of neutron capture nucleosynthesis the 29 si 30 si ratio of the sic inferred by us to be produced by neutron capture in the stellar interior is distinct from values calculated from models of nucleosynthesis in agb stars

apollo lunar seismic experiment final summary processing and initial analysis of the entire set of apollo lunar seismic data collected continuously from 1969 through 1977 have now been completed recent results include 1 better defined deep moonquake locations which appear to be bounded rather sharply between about 800 km and 1000 km depths with concentrations near both boundaries and 2 middle mantle 500 to 1000 km depth seismic velocities of vp 8 3 0 4 km sec and vs 4 6 0 2 km sec which are significantly higher than previous estimates and represent an increase of velocities from the upper mantle as opposed to a decrease in previous estimates

micrometeorite precursors clues from the mineralogy and petrology of their relict minerals abstract we analyzed 91 relict grain bearing micrometeorites mms from two antarctic collections tottuki icefield and the south pole water well to determine if the mms are related to specific meteorite groups we analyzed their relict olivines and low ca pyroxenes and compared them with olivines and pyroxenes we analyzed in various meteorites an enstatite chondrite eh3 a suite of carbonaceous chondrites cm2 cr2 cv3 2 co3 0 and co3 2 an ungrouped carbonaceous chondrite tagish lake various unequilibrated ordinary chondrites h3 2 l3 7 ll3 0 ll3 2 ll3 3 and a rumuruti chondrite r3 5 5 breccia mg rich olivines are the most common relict mineral in the mms studied 42 followed by fe rich olivines 16 mg rich low ca pyroxenes 15 and mms containing both mg rich olivine and low ca pyroxene 13 if one corrects for the effects of atmospheric heating on the proportion of olivines and pyroxenes then 59 of mms are related to carbonaceous chondrites 22 to ordinary chondrites mostly unequilibrated uocs and 19 to a high mn group results of textural observations suggest that four mms resemble chondrules from co3 carbonaceous chondrites and one is a shock melted h chondrite mms from the high mn group appear to have crystallized from a melt and might be fragments of chondrule like objects similar to those found in comet 81p wild 2

multiple precursors of secondary mineralogical assemblages in cm chondrites we report a petrographic and mineralogical survey of tochilinite cronstedtite intergrowths tcis in paris a new cm chondrite considered to be the least altered cm identified to date our results indicate that type i tcis consist of compact tochilinite cronstedtite rims surrounding fe ni metal beads thus confirming kamacite as the precursor of type i tcis in contrast type ii tcis are characterized by complex compositional zoning composed of three different fe bearing secondary minerals from the outside inwards tochilinite cronstedtite and amakinite type ii tcis present well developed faces that allow a detailed morphological analysis to be performed in order to identify the precursors the results demonstrate that type ii tcis formed by pseudomorphism of the anhydrous silicates olivine and pyroxene hence there is no apparent genetic relationship between type i and type ii tcis in addition the complex chemical zoning observed within type ii tcis suggests that the alteration conditions evolved dramatically over time at least three stages of alteration can be proposed characterized by alteration fluids with varying compositions 1 fe and s rich fluids 2 s poor and fe and si rich fluids and 3 s and si poor fe rich fluids the presence of unaltered silicates in close association with euhedral type ii tcis suggests the existence of microenvironments during the first alteration stages of cm chondrites in addition the absence of mg bearing secondary minerals in paris tcis suggests that the mg content increases during the course of alteration

the mineralogy and petrology of i type cosmic spherules implications for their sources origins and identification in sedimentary rocks abstract i type cosmic spherules are micrometeorites that formed by melting during atmospheric entry and consist mainly of iron oxides and feni metal i types are important because they can readily be recovered from sedimentary rocks allowing study of solar system events over geological time we report the results of a study of the mineralogy and petrology of 88 i type cosmic spherules recovered from antarctica in order to evaluate how they formed and evolved during atmospheric entry to constrain the nature of their precursors and to establish rigorous criteria by which they may be conclusively identified within sediments and sedimentary rocks two textural types of i type cosmic spherule are recognised 1 metal bead bearing met spherules dominated by ni poor 100 and suggest that metal from h group ordinary cm cr and iron meteorites may form the majority of particles oxidation during entry heating increases in the series met 80 wt ni comprising a particle mass fraction of

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

oxygen isotopes in deep sea spherules oxygen isotopic compositions have been measured on several size fractions of deep sea spherules of extraterrestrial origin the silicate spherules have an isotopic composition unlike that of any known macrometeorite their pre terrestrial compositions may have been similar to those of c3 chondrites or the anhydrous component of c2 chondrites the latter being preferred on chemical grounds metallic particles oxidize in the upper atmosphere and sample a region for which no previous oxygen isotope data exist this part of the atmosphere above about 100 km is apparently strongly enriched in the heavy isotopes of oxygen

meteoritic event recorded in antarctic ice during systematic sampling of volcanic ash tephra layers at a well known antarctic meteorite collection site the allan hills main ice field a band of unusually dark and rounded many spheroidal particles was discovered this debris layer bit 58 extends parallel to the stratigraphy of the ice established from the tephra bands apparently marking a single depositional event the shapes internal texture major element composition and levels of cosmogenic nuclides of particles from within bit 58 all strongly suggest that this material represents ablation debris from the passage of a large h group ordinary chondrite preliminary cosmogenic isotope dating suggests an age of 2 8 ma implying that the east antarctic ice sheet has been stable since that time the relationship of the bit 58 layer to known impact events is not clear

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

global response of the plasmasphere to a geomagnetic disturbance 1 global images of the plasmasphere obtained by the extreme ultraviolet euv imager on the image satellite are used to study the evolving structure of the plasmasphere during two geomagnetic disturbances by tracking the location of the plasmapause as a function of l shell and magnetic local time quantitative measurements of radial and azimuthal motions of the boundary are made for intervals 7 hours in duration with a time resolution of 10 min the two cases presented are 26 27 june 2001 a relatively weak but isolated geomagnetic disturbance and 9 10 june 2001 a moderate event with a multistaged onset and recurring substorm activity after the main disturbance in both cases the onset of the disturbance correlated with a southward turning of the imf is characterized by inward motion or erosion of the plasmapause and a smoothing of any existing azimuthal variations across the nightside over a period of many hours a plasmaspheric plume forms in the afternoon sector as a result of sunward flows from dusk and corotational flows across the dayside azimuthal variations in the plasmapause radius tend to form in the local time sector from dawn to the western edge of the plume including mesoscale 0 5 in l and 2 hours in local time crenulations and larger scale shoulder features while the nightside boundary remains featureless in the 26 27 june 2001 case the magnetosphere entered a period of deep quiet after the main disturbance and the plasmaspheric plume began to corotate with the main plasmasphere from the afternoon sector across the nightside in contrast the plume in the 9 10 june 2001 event became wrapped around the main plasmasphere and a second plume formed in the afternoon sector perhaps due to continued substorm activity in situ density data for these events show highly irregular density structure within the plumes as measured at geosynchronous orbit whereas a measurement by image rpi suggests that there may be less structure near the base of the plume closer to the main plasmasphere

diagenetically altered fossil micrometeorites suggest cosmic dust is common in the geological record abstract we report the discovery of fossil micrometeorites from late cretaceous chalk seventy six cosmic spherules were recovered from coniacian 87 1 ma sediments of the white chalk supergroup particles vary from pristine silicate and iron type spherules to pseudomorphic spherules consisting of either single phase recrystallized magnetite or fe silicide pristine spherules are readily identified as micrometeorites on the basis of their characteristic mineralogies textures and compositions both magnetite and silicide spherules contain dendritic crystals and spherical morphologies testifying to rapid crystallisation of high temperature iron rich metallic and oxide liquids these particles also contain spherical cavities representing weathering and removal of metal beads and irregular cavities representing vesicles formed by trapped gas during crystallization both features commonly found among modern antarctic iron type i type cosmic spherules on the basis of textural analysis the magnetite and fe silicide spherules are shown to be i type cosmic spherules that have experienced complete secondary replacement during diagenesis fossilization our results demonstrate that micrometeorites preserved in sedimentary rocks are affected by a suite of complex diagenetic processes which can result in disparate replacement minerals even within the same sequence of sedimentary beds as a result the identification of fossil micrometeorites requires careful observation of particle textures and comparisons with modern antarctic collections replaced micrometeorites imply that geochemical signatures the extraterrestrial dust are subject to diagenetic remobilisation that limits their stratigraphic resolution however this study demonstrates that fossil pseudomorphic micrometeorites can be recognised and are likely common within the geological record

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

raman study of diamond based abrasives and possible artefacts in detecting uhp microdiamond abstract raman spectral characteristics of a range of diamond based abrasives powders and sprays and drilling and cutting tools originating from preparation laboratories worldwide are presented some abrasives show strong broadening of the main diamond band fwhm full width at half band maximum 5 cm 1 accompanied by strong band downshift 1316 1330 cm 1 others are characterised by moderate band broadening fwhm 1 8 5 cm 1 at rather regular band position 1331 1333 cm 1 in addition we found that a fresh abrasive and its used analogue may in some cases show vast differences in their raman spectra the raman parameters of diamond based abrasives overlap widely with raman parameters of uhp ultra high pressure microdiamond it is hence impossible to assign diamond detected in a geological specimen to either an introduced artefact or a genuine uhp relict from the raman spectrum alone raman is an excellent technique for the detection of minute amounts of diamond however it does not provide conclusive evidence for the identification of uhp microdiamond the latter requires thorough verification for instance by optical microscopy or if doubts cannot be dispelled transmission electron microscopy

magnetite spherules in pyroclastic iron ore at el laco chile the el laco iron deposits in northern chile consist of magnetite or martite and minor hematite pyroxene and apatite the orebodies are situated on a volcanic complex and resemble lavas and pyroclastic deposits but a magmatic origin is rejected by some geologists who regard the ores as products of hydrothermal replacement of volcanic rocks this study describes spherules of magnetite in the ore at laco sur and outlines a previously unrecognized crystallization process for the formation of spherical magnetite crystal aggregates during volcanic eruption mining at laco sur the second largest deposit at el laco shows that most of the ore is friable and resembles pyroclastic material hard ore with vesicle like cavities occurs subordinately the friable ore is a porous aggregate of 0 01 0 2 mm magnetite octahedra with only a local stratification defined by millimeter thin strata of apatite films of iron phosphate are common on magnetite crystals and vertical pipes called gas escape tubes are abundant in the ore a sem study reveals that magnetite spherules in the range 0 05 0 2 mm occur in most samples of friable ore from the central lower part of the deposit the proportion of spherules in a sample varies from high to nil but overall the spherule content is low in the ore the spherules are aggregates of octahedral crystals or single octahedra that have been rounded by stepwise subparallel growth of magnetite with a systematic slight shift in orientation of successive steps the shape of the spherules demonstrates that they formed unattached to any surface growth from hot magmatic gas saturated in iron in a volcanic plume and deposition as ash fall can account for the features of the spherule bearing friable ore

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

mineralogy and oxygen isotope systematics of magnetite grains and a magnetite dolomite assemblage in hydrated fine grained antarctic micrometeorites

tektites and microtektites key facts and inferences abstract tektites are generally small black rounded silicate glass bodies found scattered over several widely separated areas of the earth s surface called strewn fields four major tektite strewn fields are known 1 australasian 2 ivory coast 3 czechoslovakian and 4 north american tektites from these four strewn fields have been dated at 0 7 1 15 and 34 ma respectively most tektites are splash forms i e spheres teardrops dumbbells etc but some have undergone a second period of melting to produce ablated forms tektites with a blocky layered appearance are called muong nong types microtektites microscopic tektites belonging to the australasian ivory coast and north american strewn fields have been found in deep sea sediments the geographic occurrence and abundance of microtektites at each site have been used to determine the size and mass of each strewn field the australasian ivory coast and north american strewn fields contain 100 million 20 million and 1 billion tonnes of glass respectively although tektites resemble obsidian they can be distinguished from terrestrial volcanic glasses by their composition and petrography tektites for example are drier than volcanic glasses and have higher feo fe 2 o 3 ratios in addition tektites unlike volcanic glasses contain lechatelierite particles sio 2 glass and are devoid of primary crystallites although some authors favor a lunar volcanic origin most of the compositional and petrographic data indicate a terrestrial impact origin the major trace and isotopic compositions of tektites indicate that the parent material was a terrestrial sedimentary deposit and the presence of lechatelierite coesite and shocked relict inclusions favors an impact origin furthermore two tektite strewn fields have been associated with known impact craters and tektites from one strewn field have been found associated with impact ejecta unlike the cretaceous tertiary boundary layer microtektite layers are not associated with mass extinctions or iridium anomalies

rock forming moissanite natural α silicon carbide we report the first occurrence of moissanite sic as a rock forming mineral 8 4 vol in one unique specimen of a terrestrial rock the sample has a homogeneous porphyritic texture and was found as a beach pebble thought to be derived from a tertiary volcanic province of the aegean sea region the matrix is bluish colored and consists of very fine grained brucite calcite and magnesite in which macrocrysts of quartz 25 3 vol and moissanite are found other accessory phases are phlogopite 3t magnesiochromite an fe rich phase cl bearing brucite al rich orthopyroxene and unidentified mgfe silicates 4 vol the bulk rock composition shows a kimberlitic chemistry 55 8 wt sio 2 28 5 wt mgo 1 4 wt cao 18 1 wt loi colorless gemmy and blue or black moissanite crystals are subhedral and display characteristic hexagonal symmetry 6h polytype most moissanite grains contain metallic si and fe silicide fe 3 si 7 inclusions and more rarely other fe silicides with varying amounts of al 24 5 wt ca 8 0 wt mn 6 8 wt ti 16 3 wt and ni 2 6 wt the 13 c value of the moissanite is 28 1 according to available data the f s o2 stability field of sic is five to six log units below the iron wustite iw buffer curve therefore the observed fe bearing silicates cannot have been equilibrated with sic under ambient pressure instead our finding indicates that the rock most likely formed at the ultrahigh pressure conditions of the upper mantle or transition zone

empirical evidence for the fractionation of carbon isotopes between diamond and iron carbide from the earth s mantle we have studied two samples of mantle diamond containing iron carbide inclusions from jagersfontein kimberlite south africa syngenetic crystal growth is inferred using morphological characteristics these samples provide an opportunity to investigate the isotopic partitioning of 13c in a terrestrial natural high pressure and high temperature hpht system the difference for the 13c values between the diamond and coexisting iron carbide averaged 7 2 1 3 these data are consistent with available data from the literature showing iron carbide to be 13c depleted relative to elemental carbon i e diamond we infer that the minerals formed by crystallization of diamond and iron carbide at hpht in the mantle beneath the kaapvaal craton it is unclear whether crystallization occurred in subcratonic or sublithospheric mantle in addition the source of the iron is also enigmatic nonetheless textural coherence between diamond and iron carbide resulted in isotopic partitioning of 13c between these two phases these data suggest that significant isotopic fractionation of 13c 12c 13c up to 7 can occur at hpht in the terrestrial diamond stability field we note that under reducing conditions at or below the iron iron wustite redox buffer in a cratonic or deep mantle environment in earth the cogenesis of carbide and diamond may produce reservoirs of 13c depleted carbon that have conventionally been interpreted as crustal in origin finally the large 13c for diamond iron carbide shown here demonstrates 13c for silicate metallic melts is a parameter that needs to be constrained to better determine the abundance of carbon within the earth s metallic core