indicators of aqueous alteration in cm carbonaceous chondrites microtextures of a layered mineral containing fe s o and ni a petrographic and transmission electron microscopy study of the mighei murchison and murray cm carbonaceous chondrites shows that much of the cm matrix material was probably produced by aqueous alteration of olivine pyroxene sulfide and metal the amount of cm matrix appears to be proportional to the degree of alteration as suggested by mcsween 1979 and microtextures of pcp poorly characterized phase provide evidence of the progressive alteration pcp is divided into two major types one occurs in chondrules and aggregates and consists largely of an fe ni s o phase type i and the other occurs in matrix and consists of the fe ni s o phase and cronstedtite in various proportions type ii microtextures of pcp suggest that it resulted from a three stage alteration process 1 1 type i was produced by alteration of kamacite in chondrules and aggregates presumably early in the parent body regolith 2 2 as the alteration advanced olivine and pyroxene were converted to serpentine type i pcp separated from chondrules and aggregates into the matrix during regolith gardening simultaneously the fe ni s o phase reacted with si released by alteration of olivine and pyroxene producing well formed platy cronstedtite and coherent intergrowths of the fe ni s o phase and cronstedtite the fe ni s o phase also recrystallized into platy and pod like crystals fe s ni cr and p were leached out of type i pcp and were deposited as small grains of fe ni sulfides magnetite chromite and a mineral unidentified containing fe ni cr and p as a result pcp came to consist primarily of the fe ni s o phase and cronstedtite i e type ii pcp 3 3 during continued alteration the well formed crystals of the fe ni s o phase cronstedtite and their intergrowths in type ii pcp were replaced by poorly formed fibers in comparison to other cm chondrites mighei murchison and murray are relatively unaltered their matrices retain abundant amounts of the fe ni s o phase and cronstedtite commonly as distinctive pcp grains which account for a large proportion of the fe in these meteorite matrices in more altered cm chondrites much of the fe ni s o phase was probably consumed to produce cronstedtite magnetite and sulfides with further alteration cronstedtite itself reacted with the serpentine to form ferroan serpentine thus the cm matrix was increasingly enriched in mg with alteration and pcp was increasingly degraded and intimately mixed with the magnesian phyllosilicates

non nebular origin of dark mantles around chondrules and inclusions in cm chondrites abstract our examination of nine cm chondrites that span the aqueous alteration sequence leads us to conclude that compact dark fine mantles surrounding chondrules and inclusions in cm chondrites are not discrete fine grained rims acquired in the solar nebula as modeled by metzler et al accretionary dust mantles in cm chondrites evidence for solar nebula processes geochim cosmochim acta 56 1992 2873 2897 nebular processes that lead to agglomeration produce materials with porosities far higher than those in the dark mantles we infer that the mantles were produced from porous nebular materials on the cm parent asteroid by impact compaction a process that produces the lowest porosity adjacent to chondrules and inclusions compaction was followed by aqueous alteration that formed tochilinite serpentine ni bearing sulfide and other secondary products in voids in the interchondrule regions metzler et al reported a correlation between mantle thickness and the radius of the enclosed object in yamato 791198 we find no correlation when all sizes of central objects and dark lumps are included but a significant correlation r2 0 44 if we limit consideration to central objects with radii 35 m a moderate correlation is also found in que 97990 we suggest that impact induced shear of a plum pudding like precursor produced the observed mantles these were shielded from comminution during impact events by the adjacent stronger chondrules and inclusions some mantles in cm chondrites with low degrees of alteration show distinct layers that may largely reflect differences in porosity typically a gray uniform inner layer is surrounded by an outer layer consisting of darker silicates with bse bright speckles the cm chondrite objects characterized as primary accretionary rocks by metzler et al did not form in the nebula but rather on the parent body the absence of solar flare particle tracks and solar wind implanted rare gases in these clasts reflect their lithified nature and low surface volume ratios during the period when they resided in the regolith and were subject to irradiation by solar particles the clasts are analogous to the light colored metamorphosed clasts in ordinary chondrite regolith breccias which also lack solar flare particle tracks and solar wind gas

modal mineralogy of cm2 chondrites by x ray diffraction psd xrd part 1 total phyllosilicate abundance and the degree of aqueous alteration abstract cm carbonaceous chondrites are samples of incompletely serpentinized primitive asteroids using position sensitive detector x ray diffraction psd xrd and a pattern stripping technique we quantify the modal mineralogy of cm2 chondrites mighei murray murchison nogoya and cold bokkeveld there is a narrow range in the combined modal volume vol of the most abundant phases mg serpentine 25 33 and fe cronstedtite 43 50 cold bokkeveld is anomalous in containing more mg serpentine 49 59 than fe cronstedtite 19 27 even including cold bokkeveld the range in modal total phyllosilicate is 73 79 average 75 total phyllosilicate abundance provides a non ambiguous measure of the degree of aqueous alteration and indicates that these meteorites have all experienced essentially the same degree of aqueous alteration this reflects pervasive hydration of matrix across cm2 samples apparent differences in the alteration of chondrules observed in petrographic studies represent various stages in the progression towards complete hydration of all components but are not manifest in significant differences in modal mineralogy for all samples there is a limited range in olivine 6 9 and pyroxene 5 abundances modal abundances of the remaining identified phases also show a limited range calcite 0 1 3 gypsum 0 1 6 magnetite 1 1 2 4 pentlandite 0 2 1 and pyrrhotite 1 3 8 as expected we observe a strong negative correlation in the modal abundance of anhydrous fe mg silicates olivine pyroxene and total phyllosilicate mg serpentine fe cronstedtite consistent with the idea that phyllosilicate is forming by aqueous alteration of the anhydrous components the negative correlation in the modal abundance between mg serpentine and fe cronstedtite indicates a mineralogic transformation of fe cronstedtite to mg serpentine by fluid driven recrystallisation or b that these meteorites had different initial abundances of olivine and pyroxene the observed positive correlation in the relative proportion of mg serpentine with increasing total phyllosilicate abundance reflects the evolution of increasingly mg rich phyllosilicate during aqueous alteration fe cronstedtite is the dominant phyllosilicate while cm chondrule olivines are forsteritic and will form mg serpentine during aqueous alteration this implies that matrix olivine was more fe rich than chondrule olivine prior to aqueous alteration

iron rich aureoles in the cm carbonaceous chondrites murray murchison and allan hills 81002 evidence for in situ aqueous alteration iron rich aureoles in cm carbonaceous chondrites are previously unidentified domains of aqueously altered matrix material whose feo content may exceed that of the surrounding matrix by up to more than 15 wt we describe the petrography and mineralogy of these objects in the cm chondrites murray murchison and allan hills alh 81002 the size of fe rich aureoles ranges from a few hundred microns to several millimeters in diameter and appears to be a function of the degree of alteration of the host chondrite the origin of fe rich aureoles is related to the alteration of large metal grains that has resulted in the formation of characteristic pcp rich reaction products that are frequently observed at the centers of the aureoles this suggests that fe rich aureoles in cm chondrites are the result of the mobilization of fe from altering metal grains into the matrix the fact that fe rich aureoles enclose numerous chondritic components such as chondrules calcium aluminum rich inclusions cais and mineral fragments as well as their radial symmetric appearance are strong evidence that they formed in situ and that significant directional fluid flow was not involved in the alteration process this and additional constraints such as the distribution of s and other elements as well as the inferred alteration conditions are consistent with in situ parent body alteration the observations are however entirely incompatible with preaccretionary alteration models in which the individual cm chondrite components have experienced diverse alteration histories the presence of numerous intact aureoles in the brecciated cm chondrites murray and murchison further suggests that the alteration occurred largely after brecciation affected these meteorites therefore the progressive aqueous alteration of cm chondrites may not be necessarily coupled to brecciation as has been previously proposed

seismic reflection profiling of the pyhasalmi vhms deposit a complementary approach to the deep base metal exploration in finland abstractin the pyhasalmi case study the seismic data is used in direct targeting of shallowly dipping mineralized zones in a massive sulfide ore system that was deformed in complex fold interference structures under high grade metamorphic conditions the pyhasalmi volcanic hosted massive sulfide vhms deposit 50 mt is located in a proterozoic volcanic belt in central finland acoustic impedance of pyhasalmi ore 32 106 kg m2 s is distinct from the host rocks 16 19 106 kg m2s enabling its detection with seismic reflection methods drill hole logging further indicates that the seismic imaging of a contact zone between mafic and felsic volcanic rocks possibly hosting additional mineralizations is plausible six seismic profiles showed discontinuous reflectors and complicated reflectivity patterns due to the complex geology the most prominent reflective package at 1 2 km depth was produced by shallowly dipping contacts between interlayered felsic and mafic volcanic rocks the topmost of these b

early solar system processes recorded in the matrices of two highly pristine cr3 carbonaceous chondrites met 00426 and que 99177 the mineralogy and bulk compositions of the matrices of the cr chondrites met 00426 and que 99177 have been studied using a combination of sem epma and tem techniques the matrices of these two chondrites are texturally chemically and mineralogically similar and are characterized by significant feo enrichments with respect to other cr chondrite matrices nearly flat refractory lithophile patterns variable volatile element patterns and a simple mineral assemblage dominated by amorphous silicate material and fe ni sulfides fine grained crystalline silicate phases such as olivine and pyroxene appear to be extremely rare in the matrices of both meteorites instead the mineralogy of matrices and fine grained rims of both meteorites consists of abundant amorphous feo rich silicate material containing nanoparticles of fe ni sulfides troilite pyrrhotite and pentlandite secondary alteration minerals that are characteristic of other cr chondrites e g renazzo and al rais such as phyllosilicates magnetite and calcite are also rare the texture and mineralogy of the matrices of met 00426 and que 99177 share many features with matrices in the primitive carbonaceous chondrites alh a77307 co3 0 and acfer 094 unique these observations show that met 00426 and que 99177 are very low petrologic type 3 chondrites that have escaped the effects of aqueous alteration unlike other cr chondrites which are typically classified as petrologic type 2 we suggest that these meteorites represent additional samples of highly primitive but extremely rare carbonaceous chondrites of petrologic type 3 00 according to the classification scheme of grossman and brearley 2005 the highly pristine nature of met 00426 and que 99177 provides important additional insights into the origins of fine grained materials in carbonaceous chondrites based on our new observations we infer that the amorphous silicate material and nanosulfide particles that dominate the matrices of these meteorites formed in the solar nebula by rapid condensation of material following high temperature events such as those that formed chondrules

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

aqueous alteration of chondrules in the cm carbonaceous chondrite allan hills 81002 implications for parent body alteration abstract alh 81002 is a cm carbonaceous chondrite that has petrographic characteristics suggesting that it experienced a high degree of aqueous alteration but has entirely escaped parent body brecciation in this study we report the results of a systematic investigation of the alteration of more than 35 chondrules in alh 81002 that belong to specific well defined chondrule types our results show that the extent of chondrule alteration is almost exclusively controlled by the properties of the chondrule phases although these chondrules taken as a group show highly variable degrees of alteration no evidence for differences in the alteration histories of chondrules has been found instead the widely varying rates of alteration of chondrule phases such as forsteritic and fayalitic olivine clinoenstatite orthopyroxene and augite are sufficient to explain the diversity of chondrule alteration in alh 81002 chondrules with similar primary textural and mineralogical characteristics e g type ia type iia etc show remarkably similar degrees of alteration detailed studies of the alteration products of chondrules show that they retain a detailed record of the alteration history of the chondrules from the earliest to last stages and provide strong evidence for the compositional evolution of the altering fluid contrary to what might be expected the fluid composition appears to be the dominant controlling factor on the composition of serpentines that replace olivines pyroxenes and mesostasis the consistent degree of alteration observed in chondrules of the same type in alh 81002 indicates that they were altered under the same conditions for similar lengths of time such conditions are most consistent with alteration in a parent body environment in addition the compositional and textural uniformity of rim material chondrule alteration phases and vein fillings in chondrule components throughout alh 81002 also argue strongly that alteration occurred after accretion several observations on alh 81002 provide additional constraints and modifications on existing models of in situ parent body alteration for example inferences on the degree of alteration of cm chondrites based on the extent of brecciation as a parameter of the alteration degree appear to be compromised in addition models which suggest that tochilinite serpentine pcp rich objects have resulted from the break up of chondrules during brecciation are also inconsistent with our observations on alh 81002

mercury and trace element distribution in density separates of a south african highveld 4 coal implications for mercury reduction and preparation of export coal abstract eight density separates of permian highveld 4 coal were investigated for partitioning of hg and trace elements the separates include float fractions obtained in heavy media having densities of 1 4 1 5 1 6 1 7 1 8 1 9 and 2 0 g cm 3 and the sink fraction for 2 0 g cm 3 bulk analysis of the separates shows strong r 2 0 80 positive correlations between pyritic sulfur and mercury and between ash yield and both pyritic sulfur and mercury laser ablation la icp ms analysis of individual pyrite grains in the separates confirms association of hg and as with pyrite as indicated by bulk analysis other elements detected in pyrite by la icp ms include mn co ni tl and pb results for the separates allow prediction of hg trace elements and ash yields expected in specific south african coal products these range from 0 06 ppm hg and an ash yield of 11 5 ash for the export fraction to 0 47 ppm hg and an ash yield of 60 9 for the discard stone fraction dry basis results show pronounced differences expected between coal used for domestic power generation and coal which is exported

matrix and fine grained rims in the unequilibrated co3 chondrite alha77307 origins and evidence for diverse primitive nebular dust components abstract the mineralogical and chemical characteristics of dark matrix and fine grained rims in the unequilibrated co3 chondrite alha77307 have been investigated in detail by scanning electron microscopy electron microprobe analysis and transmission electron microscopy matrix and fine grained rims on chondrules and other objects are compositionally homogeneous on the scale of 10 m and there are no compositional differences between matrix and rims mineralogically both the matrix and rims are extremely diverse and consist of a highly unequilibrated assemblage of si and fe rich amorphous material olivine pyroxene fe ni metal magnetite pentlandite pyrrhotite anhydrite and mixed layer phyllosilicate phases several distinct components can be recognized within the matrix and rims based on their textural and compositional characteristics which appear to represent basic fine grained units of nebular dust the microstructures of these different components show that they have experienced significantly different thermal histories unlike the ordinary chondrites an origin for any significant component of the matrix or rims in alha77307 from chondrules is improbable based on compositional and microstructural evidence the matrix and rim components in alha77307 formed by disequilibrium condensation processes as fine grained amorphous dust that is represented by the abundant amorphous component in the matrix such condensation could have occurred under a variety of conditions at different times and locations within the solar nebula or possibly earlier in a circumstellar environment subsequent thermal processing of this primitive condensate material in a variety of environments in the nebula resulted in partial or complete recrystallization of the fine grained dust the intimate association of fine grained components with disparate compositions and thermal histories shows that mixing of fine grained dust within the nebula must have been extremely thorough

mineralogy of fine grained rims in the alh 81002 cm chondrite abstract the mineralogy of fine grained rims in alh 81002 a relatively primitive cm carbonaceous chondrite has been determined by using transmission electron microscopy the most abundant phase is mg rich serpentine which occurs in small 20 nm crystals with cylindrical or fibrous morphologies cronstedtite an fe rich phyllosilicate occurs as relatively large 100 to 2500 nm platy crystals some cronstedtite is coherently intergrown with tochilinite in many cases cronstedtite has been partially altered to serpentine the compositions and textures of these two phases provide a mineralogical and morphologic alteration sequence that parallels the known compositional trend for cm chondrite matrix accessory minerals embedded within the phyllosilicates include chlorite pentlandite gypsum olivine kamacite taenite and chromite regions containing only anhydrous minerals also occur the hydrated and anhydrous regions are in direct contact with each other suggesting that the rims accreted material from multiple reservoirs

why aqueous alteration in asteroids was isochemical high porosity high permeability carbonaceous chondrite meteorites are the most compositionally primitive rocks in the solar system but the most chemically pristine ci1 and cm2 chondrites have experienced pervasive aqueous alteration apparently within asteroid parent bodies unfractionated soluble elements suggest very limited flow of liquid water indicting a closed system at scales large than 100 s m consistent with data from oxygen isotopes and meteorite petrography however numerical studies persistently predict large scale 10 s km water transport in model asteroids either in convecting cells or via exhalation flow an open system at scales up to 10 s km these models have tended to use permeabilites in the range 10 13 to 10 11 m2 we show that the permeability of plausible chondritic starting materials lies in the range 10 19 to 10 17 m2 0 1 10 d around six orders of magnitude lower than previously assumed this low permeability is largely a result of the extreme fine grain size of primitive chondritic materials applying these permeability estimates in numerical models we predict very limited liquid water flow distances of 100 s m at most even in a high porosity water saturated asteroid with a high thermal gradient over millions of years isochemical alteration with flow over minimal lengthscales is not a special circumstance it is inevitable once we consider the fundamental material properties of these rocks to achieve large scale flow it would require average matrix grain sizes in primitive materials of 10 s 100 s m orders of magnitude larger than observed finally in addition to reconciling numerical modelling with meteorite data our work explains several other features of these enigmatic rocks most particularly why the most chemically primitive meteorites are also the most altered

deuterium enrichments in chondritic macromolecular material implications for the origin and evolution of organics water and asteroids here we report the elemental and isotopic compositions of the insoluble organic material iom isolated from several previously unanalyzed meteorites as well as the reanalyses of h isotopic compositions of some previously measured samples alexander et al 2007 the iom in ordinary chondrites ocs has very large d enrichments that increase with increasing metamorphism and decreasing h c the most extreme d value measured being almost 12 000 we propose that such large isotopic fractionations could be produced in the oc parent bodies through the loss of isotopically very light h2 generated when fe was oxidized by water at low temperatures 200 c we suggest that similar isotopic fractionations were not generated in the iom of cv and co chondrites with similar metamorphic grades and iom h c ratios because proportionately less water was consumed during metamorphism and the remaining water buffered the h isotopic composition of the iom even a h was being lost from it hydrogen would also have been generated during the alteration of ci cm and cr carbonaceous chondrites the iom in these meteorites exhibit a considerable range in isotopic compositions but all are enriched in d as well as 15n relative to terrestrial values we explore whether these enrichments could also have been produced by the loss of h2 but conclude that the most isotopically anomalous iom compositions in meteorites from these groups are probably closest to their primordial values the less isotopically anomalous iom has probably been modified by parent body processes the response of iom to these processes was complex and varied presumably reflecting differences in conditions within and between parent bodies the d enrichments associated with h2 generation along with exchange between d rich iom and water in the parent bodies means that it is unlikely that any chondrites retain the primordial h isotopic composition of the water ice that they accreted the h isotopic compositions of the most water rich chondrites the cms and cis are probably the least modified and their compositions d 25 suggest that their water did not form at large radial distances from the sun where ice is predicted to be very d rich yet models to explain the o isotopic composition of inner solar system bodies require that large amounts of ice were transported from the outer to the inner solar system

replacement of olivine by serpentine in the queen alexandra range 93005 carbonaceous chondrite cm2 reactant product compositional relations and isovolumetric constraints on reaction stoichiometry and elemental mobility during aqueous alteration abstract isovolumetric replacement of euhedral and anhedral olivine by serpentine produced both centripetal and meshwork textures in the cm2 chondrites alh 81002 and nogoya the compositions of these textural varieties of serpentine are uniform within narrow limits within each previously studied meteorite independent of the composition of olivine being replaced and different between the two meteorites in que 93005 cm2 coarse olivines of widely varying compositions fo are replaced in a texturally similar manner by compositionally uniform serpentine mg 0 73 0 05 fe 0 27 0 05 3 si 2 o 5 oh 4 the narrow compositional range of serpentine replacing coarse olivine indicates that the aqueous solution from which the serpentine formed was compositionally uniform on scales at least as large as the meteorite 2 5 cm in longest dimension isovolumetric textures and compositional observations constrain elemental redistribution from coarse olivine to serpentine and to surrounding phases during serpentinization regardless of olivine s composition isovolumetric replacement of coarse olivines by serpentine of the observed composition released more mg and si from olivine than was required to form the serpentine excess mg and si released by olivine destruction and not retained in serpentine were exported from the replaced volume olivines with different fa fo proportions contributed different amounts of fe and mg to the serpentine ferroan olivines released more fe than required to form the serpentines replacing them so some of the fe released from ferroan olivine was exported from the replaced volumes forsteritic olivines released less fe than required to form the serpentines replacing them so some fe was imported into the replaced volumes augmenting the small amount of fe released from forsteritic olivine in que 93005 fo 83 8 is the threshold composition between fe exporting and fe importing behavior in individual olivine serpentine pairs which released exactly the amount of fe required to form serpentine of the observed uniform composition compositions of serpentines isovolumetrically replacing olivines and threshold olivine compositions in que 93005 differ from the corresponding values in nogoya solvent and solute species diffused through the serpentine between the olivine serpentine interface and the aqueous solution outside the isovolumetrically replaced volume in que 93005 some of the fe released from ferroan olivine in excess of the amount required to form serpentine reacted with s sourced from outside the pseudomorphs to form fe sulfide decorating the margins of the pseudomorphs of serpentine after fayalitic olivine such fe sulfide decorated outlines after fayalitic olivine do not occur in alh 81002 or nogoya indicating different fe and s mass transfer regimes in different cm2 chondrites mg fe si and s in the aqueous solution including the excess mg and si exported from all serpentine pseudomorphs after olivine of any composition were available to be incorporated into other phases spatially separate from the pseudomorphs after olivine including regularly interstratified serpentine tochilinite serpentines that replaced coarse olivines in que 93005 and alh 81002 are less magnesian than those in nogoya indicating that the nogoya aqueous alteration environment was more evolved toward mg rich solutions this easily located and characterized phase assemblage may be potentially useful for characterizing clasts of varying degrees of alteration in brecciated and heterogeneous cm chondrites and future returned samples from mineralogically similar asteroids

gems like material in the matrix of the paris meteorite and the early stages of alteration of cm chondrites abstract the paris meteorite is a weakly altered cm chondrite that has been discovered recently hewins et al 2014 its matrix offers the opportunity to search for well preserved pristine pre accretional material as well as to study the earliest stages of aqueous alteration in the cm parent body the study of the matrix of paris has been conducted by analytical transmission electron microscopy on focused ion beam sections extracted from matrix areas showing different degrees of aqueous alteration the least altered matrix sample consists of amorphous silicate grains a few hundreds of nm in size separated from one another by an abundant porosity the amorphous silicates enclose numerous fe sulfide nanograins and their average composition is close to the chondritic composition they share many similarities with gems glass with embedded metal and sulfides grains present in chondritic porous interplanetary dust particles and with primitive type 3 0 carbonaceous chondrites this first discovery of gems like texture in a cm chondrite suggests that gems grains could have been the building blocks of the cm matrices in more aqueously altered samples pronounced microstructural heterogeneities were detected at the micrometer scale the matrix consists mostly of a mixture of amorphous material and fe rich spongy to fine fibrous poorly crystalline phyllosilicates the porosity fraction is significantly reduced and the mixed amorphous fibrous material frequently forms a continuous groundmass the close association between these two material types suggests a replacement mechanism due to aqueous alteration chemical compositions correlate strongly with the microstructure the amorphous material has a composition close to the chondritic value while the fine fibrous phyllosilicate material is fe enriched this fe enrichment is found to be continuous from weakly to more heavily altered areas in which the fibrous morphology is coarser and better crystalline cronstedtite with intercalated tochilinite is also found but in pore spaces this chemical evolution concomitant with the maturation of the phyllosilicates demonstrates that the early aqueous fluids that interacted with silicates in the matrix were enriched in fe this composition is probably the consequence of the preferential dissolution of metal and iron sulfides during the first stages of alteration the enrichment of phyllosilicates in mg seen in more altered cm chondrites is not observed in paris

the paris cm chondrite secondary minerals and asteroidal processing abstract we report a petrographic and mineralogical survey of paris a new cm chondrite considered to be the least altered cm identified so far hewins et al 2014 compared to other cms paris exhibits 1 a higher concentration of fe ni metal beads with nickel contents in the range 4 1 8 1 wt 2 the systematic presence of thin lamellae and tiny blebs of pentlandite in pyrrhotite grains and 3 ubiquitous tochilinite cronstedtite associations with higher feo sio2 and s sio2 ratios in addition paris shows the highest concentration of trapped 36ar reported so far for a cm chondrite hewins et al 2014 in combination with the findings of previous studies our data confirm the reliability of 1 the alteration sequence based on the chemical composition of tochilinite cronstedtite associations to quantify the fluid alteration processes and 2 the use of cr content variability in type ii ferroan chondrule olivine as a proxy of thermal metamorphism in contrast the scales based on 1 the fe3 content of serpentine in the matrix to estimate the degree of aqueous alteration and 2 the chemical composition of fe ni metal beads for quantifying the intensity of the thermal metamorphism are not supported by the characteristics of paris it also appears that the amount of trapped 36ar is a sensitive indicator of the secondary alteration modifications experienced by chondrites for both aqueous alteration and thermal metamorphism considering paris our data suggest that this chondrite should be classified as type 2 7 as it suffered limited but significant fluid alteration and only mild thermal metamorphism these results point out that two separated scales should be used to quantify the degree of the respective role of aqueous alteration and thermal metamorphism in establishing the characteristics of cm chondrites

relationships between organics water and early stages of aqueous alteration in the pristine cr3 0 chondrite met 00426 abstract in order to investigate the nature of organics at the time of their accretion into chondrite parent bodies as well as their subsequent evolution with aqueous alteration we have conducted a study of the morphologies spatial distribution and relationships between organic particles and the surrounding matrix phases in one of the most pristine carbonaceous chondrites currently known met 00426 cr which is therefore likely to contain the best preserved record of pre accretion features focused ion beam sections were extracted for transmission electron microscope observations from its matrix organic matter om shows a heterogeneous population of grains most of them smaller than 1 m diverse morphologies are observed such as compact rounded aggregates individual and aggregated nanoglobules and micron to nanometer sized veins a common feature is the systematic presence of cracks connected to the grains and filled with om the surrounding matrix groundmass consists of amorphous iron rich silicate particles intimately mixed with phyllosilicates sulfides and occasional tochilinite with sizes ranging from several hundreds of nanometers to below 10 nm a close spatial relationship is commonly observed between some of the organic matter particles and alteration phases such as tochilinite and phyllosilicates phyllosilicates sometimes occur intimately intercalated with organic matter at a scale below 10 nm we used tem eds techniques to quantify the water concentration in the matrix amorphous silicate material and the phyllosilicates the water contents of both materials are identical at 10 6 wt h 2 o and demonstrate that the amorphous silicate material in this meteorite is hydrated therefore even though these cr3 0 chondrites are the least altered objects from a mineralogical point of view their matrices contain significant amounts of water in the amorphous silicate this coupled in situ study of organics and aqueous alteration suggests that a significant population of the om accreted as a mixture of soluble and insoluble molecules together with water ice grains and that the om was mobile at the micrometer scale the spatial distribution of the om grains can therefore in part be attributed to parent body processes we suggest that as accreted ice melted hydration of the amorphous silicates and formation of tochilinite and phyllosilicates occurred in the immediate vicinity of the composite water ice organic matter grains the water soluble component of the organics was likely transported and redistributed in the surrounding porosity cracks grain boundaries as water circulated the textural settings suggest that some of the om material could have been polymerized during aqueous alteration and transformed into insoluble molecules perhaps during the last stages of alteration as water was consumed by silicate hydration reactions

the onset of metamorphism in ordinary and carbonaceous chondrites ordinary and carbonaceous chondrites of the lowest petrologic types were surveyed by xray mapping techniques a variety of metamorphic effects were noted and subjected to detailed analysis using electron microprobe scanning electron microscopy sem transmission electron microscopy tem and cathodoluminescence cl methods the distribution of cr in feo rich olivine systematically changes as metamorphism increases between type 3 0 and type 3 2 igneous zoning patterns are replaced by complex ones and cr rich coatings develop on all grains cr distributions in olivine are controlled by the exsolution of a cr rich phase probably chromite cr in olivine may have been partly present as tetrahedrally coordinated cr3 separation of chromite is nearly complete by petrologic type 3 2 the abundance of chondrules showing an inhomogeneous distribution of alkalis in mesostasis also increases with petrologic type tem shows this to be the result of crystallization of albite residual glass compositions systematically change during metamorphism becoming increasingly rich in k glass in type i chondrules also gains alkalis during metamorphism both types of chondrules were open to an exchange of alkalis with opaque matrix and other chondrules the matrix in the least metamorphosed chondrites is rich in s and na the s is lost from the matrix at the earliest stages of metamorphism due to coalescence of minute grains progressive heating also results in the loss of sulfides from chondrule rims and increases sulfide abundances in coarse matrix assemblages as well as inside chondrules alkalis initially leave the matrix and enter chondrules during early metamorphism feldspar subsequently nucleates in the matrix and na re enters from chondrules these metamorphic trends can be used to refine classification schemes for chondrites cr distributions in olivine are a highly effective tool for assigning petrologic types to the most primitive meteorites and can be used to subdivide types 3 0 and 3 1 into types 3 00 through 3 15 on this basis the most primitive ordinary chondrite known is semarkona although even this meteorite has experienced a small amount of metamorphism allan hills alh a77307 is the least metamorphosed co chondrite and shares many properties with the ungrouped carbonaceous chondrite acfer 094 analytical problems are significant for glasses in type ii chondrules as na is easily lost during microprobe analysis as a result existing schemes for chondrule classification that are based on the alkali content of glasses need to be revised

nanometer scale mineralogy and petrography of fine grained aggregates in anhydrous interplanetary dust particles abstract fine grained matrices in seven solar flare track rich anhydrous interplanetary dust particles idps were studied using 200 kev analytical electron microscopy the idps are u222b42 u220a19 u222b28 u230a3 w7027a11 w7027h14 u219 c2 and u219 c11 the matrices are composed of aggregates of glass disordered carbonaceous material and crystalline mineral grains with diameters between 1 and 150 nm the mineral grains were characterized using lattice fringe imaging electron microdiffraction and quantitative energy dispersive x ray spectroscopy eds the glasses were studied using eds and electron energy loss near edge structure analysis elnes three types of aggregates were observed unequilibrated equilibrated and reduced aggregates unequilibrated aggregates uas are 0 1 0 3 m diameter objects with bulk major element compositions that are approximately chondritic solar except for carbon they contain feni metal and fe rich sulfide crystals between 1 and 20 nm diameter embedded in silicate glass equilibrated aggregates eas are 0 1 to 1 m diameter objects that exhibit melt textures and mineralogy they contain fe bearing olivine and pyroxene grains with equilibrated fe mg ratios and fe sulfides embedded in feldspathic alumino silicate glass reduced aggregates ras are 0 1 to 1 0 m objects with feni metal feni carbides and fe rich sulfides embedded in a carbonaceous matrix the aggregates in the seven anhydrous idps appear to have formed in diverse physiochemical environments

transmission electron microscopy of concordia ultracarbonaceous antarctic micrometeorites ucamms mineralogical properties we performed mineralogical and petrographic studies of three ultracarbonaceous antarctic micrometeorites ucamms by analytical transmission electron microscopy tem the ucamms were identified in the concordia micrometeorite collection 2002 and 2006 recovered from central antarctic snow and are of probable cometary origin ucamms are dominated by disordered carbonaceous matter that extends over surfaces of up to 90 of the particle embedded in this carbonaceous matter we observed small and complex assemblages of fine grained mineral phases isolated minerals glassy phases that resemble glass with embedded metal and sulfides gems that were first found in interplanetary dust particles idps and rounded objects containing both glass and crystalline materials the mineral assemblages are chondritic in composition within a factor of 2 crystalline materials represent at least 25 of mineral phases this value is much larger than the upper limit of crystallinity measured in the diffuse interstellar medium 2 2 wt crystalline phases are dominated by low ca mg rich pyroxenes mg rich olivine and low ni fe sulfides exotic phases such as mn zn rich sulfide and perryite have also been found as accessory minerals the variety of high temperature mineral phases observed in ucamms is similar to that reported in chondritic porous idps and 81p wild 2 samples the close association of high temperature crystalline phases with the low temperature carbonaceous matter in ucamms supports the hypothesis of a large scale radial mixing in the early solar nebula this new type of carbon rich micrometeorites containing crystalline material provides the opportunity to analyze in situ without any chemical processing the association of materials formed at both low and high temperatures in the protoplanetary disk a better knowledge of these samples is also important to prepare for future cometary missions like rosetta in 2014

cometary dust in antarctic ice and snow past and present chondritic porous micrometeorites preserved on the earth s surface abstract chondritic porous interplanetary dust particles cp idps collected in the stratosphere are regarded as possibly being cometary dust and are therefore the most primitive solar system material that is currently available for analysis in laboratories in this paper we report the discovery of more than 40 chondritic porous micrometeorites cp mms in the surface snow and blue ice of antarctica which are indistinguishable from cp idps the cp mms are botryoidal aggregates composed mainly of sub micrometer sized constituents they contain two components that characterize them as cp idps enstatite whiskers and gems glass with embedded metal and sulfides enstatite whiskers appear as 2 o 6 rich high ca pyroxene roedderite k na 2 mg 5 si 12 o 30 and carbonaceous nanoglobules these components have previously been discovered in primitive solar system materials such as the cp idps matrices of primitive chondrites phyllosilicate rich mms ultracarbonaceous mms and cometary particles recovered from the 81p wild 2 comet the most outstanding feature of these cp mms is the presence of kosmochlor rich high ca pyroxene and roedderite which suggest that they have building blocks in common with cp idps and cometary dust particles and therefore suggest a possible cometary origin of both cp mms and cp idps it is therefore considered that cp mms are cp idps that have fallen to earth and have survived the terrestrial environment