nebular thermal evolution and the properties of primitive planetary materials models of the solar nebula are constructed to investigate the hypothesis that surviving planetary objects began to form as the nebula cooled from an early hot epoch the imprint of such an epoch might be retained in the spatial distribution of planetary material the systematic deviations of its elemental composition from that of the sun chemical indicators of primordial oxidation state and variations in oxygen and other isotopic compositions our method of investigation is to calculate the time dependent two dimensional temperature distributions within model nebulas of prescribed dynamical evolution and to deduce the consequences of the calculated thermal histories for coagulated solid material the models are defined by parameters which characterize nebular initial states mass and angular momentum mass accretion histories and coagulation rates and efficiencies it is demonstrated that coagulation during the cooling of the nebula from a hot state is expected to produce systematic heterogeneities which affect the chemical and isotopic compositions of planetary material the radial thermal gradient at the midplane results in delayed coagulation of the more volatile elements vertical thermal gradients isolate the most refractory material and concentrate evaporated heavy elements in the gas phase it is concluded that these effects could be responsible for the distribution of terrestrial planetary masses the systematic depletion patterns of the moderately volatile elements in chondritic meteorites and the earth the range of oxygen isotopic compositions exhibited by calcium aluminum rich inclusions cais and other refractory inclusions and some geochemical evidence for a moderately enhanced oxidation state however nebular fractionations on a global scale are unlikely to account for the more oxidizing conditions inferred for some cais and chondritic silicates which require dust enhancements greater than a few hundred this conclusion along with the well established evidence from studies of chondrules and cais for thermal excursions of short duration make it likely that local environments unrelated to nebular thermal evolution were also important

the cr renazzo type carbonaceous chondrite group and its implications abstract a petrologic geochemical and oxygen isotopic study of eight meteorites identified as cr renazzo type chondrites reveals that they have a set of similar properties that distinguishes them from other chondrite groups and confirms cr as a carbonaceous chondrite group characteristics of the cr group include 1 1 abundant large multilayered fe ni metal rich type i chondrules 2 2 abundant matrix and dark inclusions di that contain microchondrules microfragments and magnetite framboids and platelets 3 3 unique assemblages of serpentine and chlorite rich phyllosilicates and ca carbonates 4 4 ca carbonate rims on chondrules 5 5 abundant fe ni metal with a positive ni vs co trend and a solar ni co ratio 6 6 low abundance of refractory rich inclusions 7 7 amoeboid olivine aggregates aoa with mn rich and mn poor forsterite and 8 8 oxygen isotopic compositions that form a unique mixing line the cr chondrites are breccias consisting of two major components the large layered chondrules and the matrix dark inclusions al rais is an anomalous member in having a higher abundance of the dark inclusion component 70 vol and this accounts for its having a higher volatile content than other members of the group the conditions that prevailed during aqueous alteration of the cr chondrites differed from those of other hydrated chondrite groups and may be the result of a higher temperature environment than that for the ci and cm chondrites the cr chondrite components chondrules matrix dark inclusions etc experienced aqueous alteration to differing degrees prior to assembly of the host chondrites and dark inclusions represent a lithology that was altered by water to a greater degree than the rest of the meteorite the overall degree of hydration in cr chondrites varies among meteorites with al rais being the most hydrated the oxygen isotopic variation of the whole rocks chondrules and matrices may be related to degree of hydration indicating that cr chondrites interacted with a water rich component having heavy oxygen and that was the same as ci and cm water

on the formation of fe ni metal in renazzo like carbonaceous chondrites the fe ni metal within chondrites has been postulated to have originated either through condensation or as a byproduct of chondrule formation to test these hypotheses we studied metal in three renazzo like carbonaceous cr2 chondrites from three petrographic settings inside chondrules on chondrule rims and in the matrix abundances of fe ni co cr and p were determined in situ by electron microprobe and those of os ir pt and au were measured by a newly developed ion microprobe technique the refractory platinum group elements os ir and pt behave coherently in cr2 metal they are either all enriched all depleted or unfractionated with respect to fe and cosmic ratios metal with approximately ci os fe ir fe and pt fe occur primarily in chondrule interiors all metal grains have essentially ci values of ni fe and co fe almost all metal grains have lower than ci ratios of the volatile elements au and p we also estimated the bulk compositions via analyses of phases and modal recombination of a subset of the chondrules whose metal we analyzed the bulk compositions of chondrules are generally unfractionated relative to ci chondrites for elements more refractory than cr but are depleted in more volatile elements abundances of siderophile elements correlate strongly with the metal abundance in the chondrules which implies that siderophile depletions are due to expulsion of metal from the chondrule melts the metal most likely originated during melting via reduction of oxides by c that was part of the chondrule precursor during chondrule heating molten metal efficiently extracted siderophile elements from the silicate melt rim metal consists of two types one is like metal in chondrule interiors and was in the process of being expelled when the chondrules were quenched the other shows systematic depletions in os ir and pt relative to fe and higher concentrations of au and p than interior metal this metal is attributed to recondensation from a vapor depleted in refractory siderophiles a vapor most likely derived via evaporation from chondrules large isolated matrix metal grains comprise the same two groups as rim grains and have the same origins bulk chondrule compositions and siderophile abundance patterns in metal indicate that the precursors of cr2 chondrules had ci like abundances of refractory and moderately volatile elements but was likely depleted in the more volatile elements

a compositional classification scheme for meteoritic chondrules a taxonomic scheme is proposed for the main component of the primitive chondrite meteorites the chondrules the scheme provides insight into the variety of chondrules originally produced in the primordial solar nebula and the effects on them of secondary processes on meteorite parent bodies it may also contribute to understanding the origin of compositional diversity in the chondrites

oxygen isotope compositions of chondrule phenocrysts and matrix grains in kakangari k grouplet chondrite implication to a chondrule matrix genetic relationship abstract to investigate a possible relationship between chondrules and matrix we studied mineralogy mineral chemistry and in situ o isotope compositions of chondrules clastic matrix grains and amoeboid olivine aggregates aoas in the kakangari k grouplet chondrite most olivines and low ca pyroxenes in the kakangari chondrules matrix and aoas have similar magnesium rich compositions fo 95 97 0 3 0 5 wt mno and en 90 96 respectively these rather uniform chemical compositions of the different chondritic components are likely due to partial fe mg mn equilibration during thermal metamorphism experienced by the host meteorite oxygen isotope compositions of olivine and low ca pyroxene grains in chondrules and matrix plot along a slope 1 line on a three o isotope diagram and show a range from 16 o enriched composition similar to that of the sun to 16 o depleted composition similar to the terrestrial o isotope composition most olivines and low ca pyroxenes in chondrules are 16 o poor and plot on or close to the terrestrial mass fractionation line mean 17 o values 2 standard deviations 0 0 0 8 and 0 2 0 9 for olivine and pyroxene respectively consistent with the previously reported compositions of bulk chondrules 17 o 0 16 0 70 in addition to these 16 o poor grains a coarse grained igneous rim surrounding a porphyritic chondrule contains abundant 16 o rich relict olivines 17 o 24 oxygen isotope compositions of olivines and low ca pyroxenes in matrix show a bimodal distribution 12 out of 13 olivine and 4 out of 17 pyroxene grains measured are similarly 16 o rich 17 o 23 5 2 9 others are similarly 16 o poor 17 o 0 1 1 7 due to slow oxygen self diffusion olivines and low ca pyroxenes largely retained their original oxygen isotope compositions the nearly identical o isotope compositions between the chondrule phenocrysts and the 16 o poor matrix grains suggest both chondrules and matrix of kakangari sampled isotopically the same reservoirs in addition the presence of abundant 16 o rich grains in matrix and the chondrule igneous rim suggests both components acquired similar precursor inventories these observations imply that chondrules and matrix in kakangari are genetically related in the sense that material that formed matrix was one of the precursors of chondrules and chondrules and some fraction of matrix experienced the same thermal processing event the 16 o enriched bulk matrix value compared to the bulk chondrules reported previously is likely due to presence of abundant 16 o rich grains in the kakangari matrix

origin of chondrule rims and interchondrule matrices in unequilibrated ordinary chondrites optical microscopy electron probe microanalysis scanning electron microscopy and analytical transmission electron microscopy were used to study the interchondrule matrix and opaque chondrule rims in bishunpur krymka semarkona chainpur all ll3 tieschitz and sharps both h3 the size distribution of grains in matrix in bishunpur obeys a power law rims around chondrules tend to be finer grained than matrix and may be layered all rims and matrices studied contain clasts of forsteritic olivine and low ca pyroxene in bishunpur the clasts may be cemented by amorphous glue rich in normative albite and partly altered to smectite rims in krymka sharps chainpur and tieschitz have a densely packed olivine groundmass with a grain size of about 0 1 m in krymka groundmass olivine is fo20 30 and forms interlocking dendrites various fe oxides are present in rims and matrices grain size distribution and chemical data indicate that clastic olivines and pyroxenes are derived from chondrules from analyses matrices rims in the ll group apparently are enriched in a feldspathic component tieschitz rims are slightly enriched but here the feldspathic component is present as white matrix sharps rims are not enriched in a feldspathic component opaque interchondrule matrices and chondrule rims probably formed from the products of fragmentation of chondrules partly induced by contraction of protopyroxene on inversion to clinopyroxene fragmented silica rich chondrule mesostases reacted with fe oxides and na to form the groundmass of fayalitic olivine and feldspathic glue a low temperature nebular or pre solar component is limited to 3 vol of each meteorite so equilibrium condensate was not the carrier of volatiles such as tl and bi

refractory precursor components of semarkona chondrules and the fractionation of refractory elements among chondrites abstract chondrules from the semarkona ll3 0 chondrite show refractory and common lithophile fractionation trends similar to those observed among the chondrite groups it appears that chondrules are mixtures of a small number of pre existing solid components and we infer that chondrule precursor materials were related to the nebular components involved in the lithophile element fractionations recognized in ordinary chondrites compositional trends among the chondrules can be used to deduce the compositions of these components we use instrumental neutron activation analysis to measure many 20 of the lithophile elements in 30 chondrules the amounts of oxidized iron were calculated from other compositional parameters concentrations of si were estimated using mass balance considerations the data were corrected for the diluting effects of non lithophile constituents plots of lithophile elements versus a reference refractory element such as al show that there were two major chondrule silicate precursor components a refractory olivine rich feo free one and a non refractory sio 2 feo rich one the refractory component probably forms from olivine enriched condensates formed above the condensation temperature of enstatite the non refractory component must have formed from fine grained materials that were able to equilibrate down to lower nebular temperatures chondrite matrix may have had an origin similar to that of the non refractory material and constitutes a third lithophile bearing component that took part in chondrite fractionation processes the low abundance of refractories and mg in ordinary and enstatite chondrites was produced by the loss of materials having a higher refractory element mg ratio than that in the refractory component of chondrules

the oxygen isotopic composition of olivine and pyroxene from ci chondrites the ci chondrites are taken to represent average solar system material based on the similarity of their elemental compositions to that of the solar photosphere however their oxygen isotope geochemistry is dominated by secondary minerals that formed during aqueous alteration on the ci parent body precursors to this alteration namely olivine and pyroxene are extremely rare in ci chondrites precluding previous measurements of their oxygen isotopic composition we report ion microprobe analyses of oxygen isotopes in single olivine and pyroxene grains separated from ci chondrites orgueil and ivuna the ci chondrite olivine and pyroxene grains most likely represent liberated chondrule phenocrysts based on petrographic chemical and isotopic evidence consistent with crystallization from a melt the oxygen isotope data form an array that falls nearly along the carbonaceous chondrite 16o mixing line with 18o values ranging from 9 3 to 12 3 o and 17o from 11 3 o to 7 8 o consistent with nebular processes being the source of the oxygen isotopic compositions the degree of 16o enrichment in orgueil olivines is negatively correlated with feo content but the exact nature and timing of the process that introduced this variation remains unknown the pyroxene oxygen isotopic compositions are similar to those of olivines with 5 mol fayalite the oxygen isotopic analyses of the olivine and pyroxene in ci chondrites have been used to revise previous models for the isotopic evolution of ci materials our data require more complete gas solid equilibration in the nebula and constrain the initial aqueous fluids on the ci parent body to have lower 17o values than previously postulated the refined model indicates that the temperature of aqueous activity on the ci parent body was no higher than 50 c and the fluid rock ratio was significantly less than previously estimated even prior to alteration and formation of secondary minerals the ci chondrites were the most 16o depleted carbonaceous chondrites and thus the solids originally contained in the ci chondrites are the most equilibrated nebular materials represented in the carbonaceous chondrites the data suggest the oxygen isotopic composition of average solar system to be approximately equivalent to average terrestrial oxygen as recorded in the compositions of terrestrial and lunar basalts

compositional evidence regarding the origins of rims on semarkona chondrules abstract the compositions of the interiors and abraded surfaces of 7 chondrules from semarkona ll3 0 were measured by neutron activation analysis for nonvolatile elements the lithophile and siderophile element abundance patterns in the surfaces are generally similar to those in the corresponding interiors siderophile and chalcophile concentrations are much higher in the surfaces whereas lithophile concentrations are similar in both fractions most of the similarities in lithophile patterns and some of the similarities in siderophile patterns between surfaces and interiors may reflect incomplete separation of the fractions in the laboratory but for 3 or 4 chondrules the siderophile resemblance is inherent implying that the surface and interior metal formed from a single precursor assemblage metal and sulfide rich chondrule rims probably formed when droplets of these phases that migrated to the chondrule surface during melting were reheated and incorporated into matrix like material that had accreted onto the surface the moderately volatile to volatile elements k as and zn tend to be enriched in the surfaces compared with other elements of similar mineral affinity both enrichments and depletions are observed for other moderately volatile elements a small fraction of chondrules experienced fractional evaporation while they were molten

on the relationship between isolated and chondrule olivine grains in the carbonaceous chondrite alha77307 abstract the origin of isolated olivine grains in carbonaceous chondrites has been suggested to be either by direct condensation or by fragmentation of chondrules in an attempt to resolve this debate isolated olivine grains in the carbonaceous chondrite alha77307 have been studied in detail zoning characteristics and minor element compositions of olivines from all isolated and chondrule occurrences are described the data show that a strong relationship exists between isolated olivines and the chondrule population chondrule olivine compositions and zoning properties are consistent with olivine crystallization from the molten chondrules because properties of isolated grains are very similar to chondrule olivines an igneous origin for most if not all isolated grains is proposed large isolated forsterite grains may be derived from fragmentation of macroporphyritic type i chondrules which contain one or very few large olivine grains relic forsterite grains in type ii chondrules and complex isolated olivine grains with forsteritic cores and fayalite rich rims provide evidence that fragmentation and recycling of chondrules and their components was a common and efficient process in the chondrule forming region

thermoluminescence and compositional zoning in the mesostasis of a semarkona group a1 chondrule and new insights into the chondrule forming process a large group a1 porphyritic olivine chondrule in the semarkona ll3 0 chondrite with induced thermoluminescence tl and compositional zoning in its mesostasis has been discovered the chondrule has ca rich and fe poor olivine cao 0 36 0 40 wt fa0 3 0 5 and its mesostasis is highly anorthite normative 52 5 wt the chondrule shows an intense induced tl peak at 300 c with a half width of 180 c the induced tl in the 40 440 c range increases monotonically by a factor of 6 from center to rim while sio2 na2o and mno increase by factors of 1 1 3 6 and 6 respectively the spectrum of the induced tl over the 200 350 c range i e a dominant peak at 570 nm with a half width of about 100 nm and the mn tl correlation suggest mn activated plagioclase is an important constituent of the refractory mesostases in group a1 chondrules the zoning may reflect fractional crystallization soret diffusion transport of volatiles into the chondrule by aqueous alteration a zoned precursor reduction of precursor dust aggregate or recondensation of volatiles lost during chondrule formation the first four possibilities seem unlikely explanations for the zoning of the mesostasis but both reduction of precursor dust aggregate and recondensation of volatiles seem to have played significant roles to the formation of the zoning reducing conditions at high temperatures are suggested to have prevailed during the formation of group a1 chondrules

abundances of presolar silicon carbide grains in primitive meteorites determined by nanosims abstract it has been suggested that the matrices of all chondrites are dominated by a common material with ivuna like ci abundances of volatiles presolar grains and insoluble organic matter iom e g alexander 2005 however matrix normalized abundances of presolar silicon carbide sic grains estimated from their noble gas components show significant variations in even the most primitive chondrites huss and lewis 1995 huss et al 2003 in contradiction to there being a common chondrite matrix material here we report presolar sic abundances determined by nanosims raster ion imaging of iom extracted from primitive members of different meteorite groups we show that presolar sic abundance determinations are comparable between nanosims instruments located at three different institutes between residues prepared by different demineralization techniques and between microtomed and non microtomed samples our derived sic abundances in cr chondrites are comparable to those found in the ci chondrites 30 ppm and are much higher than previously determined by noble gas analyses the revised higher cr sic abundances are consistent with the crs being amongst the most primitive chondrites in terms of the isotopic compositions and disordered nature of their organic matter similar abundances between cr1 cr2 and cr3 chondrites indicate aqueous alteration on the cr chondrite parent body has not progressively destroyed sic grains in them a low sic abundance for the reduced cv3 rbt 04133 can be explained by parent body thermal metamorphism at an estimated temperature of 440 c minor differences between primitive members of other meteorite classes which did not experience such high temperatures may be explained by prolonged oxidation at lower temperatures under which sic grains formed outer layers of sio2 that were not thermodynamically stable leading to progressive degassing destruction of sic

trace element contents of chondrule rims and interchondrule matrix in ordinary chondrites abstract the abundances of forty elements have been measured in the rims and matrices of the unequilibrated ordinary chondrites semarkona bishunpur chainpur and krymka the rims appear to be mixtures of matrix like material and material that was volatilized during chondrule formation iron silicon manganese and copper all appear to have behaved as volatiles during chondrule formation and their enrichments are generally confined to the rims suggesting recondensation of these elements was rapid and localized this is supported by petrologic observations that show many chondrules were still partially molten or plastic when the rims accreted some rims also exhibit a decrease in both their feo content and the degree of mineral re equilibration away from the chondrule the alkali metals are enriched in both the rims and matrices the alkalis may have recondensed onto the matrix as well as the rims but their mobility is such that they have probably undergone extensive redistribution after accretion some na may even have been able to diffuse back into chondrules either during chondrule cooling or during metamorphism alteration most refractory lithophiles are depleted with respect to a1 in the rims and matrices in all four uocs these depletions are probably due to postaccretional redistribution of these elements into phosphates and other secondary minerals that form in and around metal sulfide grains the matrix is probably composed of chondrule fragments and processed nebular dust but the presence of carbonaceous presolar grains in the matrix indicates that there must be unprocessed presolar silicates present too on average the presolar silicates presumably have a ci like composition but a ci like signature is not seen in the matrix compositions simple estimates suggest that the abundances of carbonaceous presolar grains are consistent with there being at most 10 wt o presolar silicates present in uoc matrix which would be hard to detect in this study

presolar diamond sic and graphite in primitive chondrites abundances as a function of meteorite class and petrologic type abstract acid resistant residues were prepared for eighteen meteorites from seven chondrite classes using improved procedures designed to minimize loss of presolar grains noble gases were measured by stepped pyrolysis and the abundances of five exotic noble gas components were used to determine abundances of diamond sic and graphite diamond separates were prepared to check diamond abundances determined from noble gases diamond and sic were found in unmetamorphosed members of all seven chondrite classes and evidence for graphite was found in orgued ci and ll3 0 3 1 chondrites our data and noble gas and stable isotope data in the literature show that presolar grains were incorporated into all chondrite classes the grains are sited in the fine grained matrix and their abundances within the matrix reflect mainly the degree of metamorphism suffered by the host meteorite the pattern of metamorphic destruction differs from class to class in unequilibrated ordinary chondrites uocs graphite is most easily destroyed followed by sic and then diamond no presolar grains remain in uocs of petrologic type 3 8 whose matrices have been completely recrystallized in eh chondrites diamond and sic survive much more severe metamorphism than in uocs with sic apparently more stable than diamond presolar graphite was not detected in cv3 and c03 chondrites diamond appears to be more stable than sic and graphite again is missing inferred premetamorphic diamond abundances matrix normalized vary by a factor of 2 2 between classes with eh cv and co chondrites having higher initial abundances than orgueil similar diamond sic ratios are observed in most classes and differences in the ratio can be tied to secondary processing suggesting that all chondrite classes sampled the same solar system wide reservoir of presolar grains differences in initial abundances between classes appear to correlate with chemical and physical properties of the host meteorites these bulk properties and variations in presolar grain abundances both may be the result of thermal processing of presolar dust in the accretion disk

petrology of feo poor porphyritic pyroxene chondrules in the semarkona chondrite abstract the mineralogy and petrology of feo poor porphyritic pyroxene and olivine rich chondrules in the semarkona ll3 0 chondrite are described in detail in an extension of the textural classification scheme these chondrules are designated types iab and ib in type iab chondrules the proportion of olivine phenocrysts is between 20 80 and in type ib chondrules olivine constitutes

quantifying the error of 2d bulk chondrule analyses using a computer model to simulate chondrules simchon bulk chondrule compositions are important to many questions in cosmochemistry however the number of available bulk chondrule data sets is still small a main reason for this is the difficulties of determining bulk chondrule compositions a commonly used technique is to obtain 2d bulk chondrule compositions from meteorite sections this technique has an error that we quantify here for the first time using a mathematical model of a chondrule called simchon the theoretically calculated errors are compared to errors that we determined from serial sectioning of eight efremovka chondrules the errors obtained from both approaches are in excellent agreement proving that our mathematical model produces reliable errors that can be assigned to 2d bulk chondrule compositions these errors allow a much better interpretation of 2d bulk chondrule data we provide a table that contains typical errors for 2d bulk compositions of porphyritic chondrules the errors are in the range of 1 30 relative this should be acceptable for many problems in cosmochemistry the effect of a chemical layering inside chondrules and the occurrence of a rim around them as well as the occurrence of opaque and other accessory phases have been studied a spreadsheet is provided that enables the calculation of errors for any desired chondrule mineral composition bo chondrules have a negligible error but it is impossible to provide reasonable error estimates for bo chondrules with an igneous rim radial pyroxene chondrules have negligible errors

chondrule collisions in shock waves detailed numerical models have shown that solar nebula shock waves would be able to thermally process chondrules in a way that is consistent with experimental constraints however it has recently been argued that the high relative velocities that would be generated between chondrules of different sizes immediately behind the shock front would lead to energetic collisions that would destroy the chondrules as they were processed rather than preserving them for incorporation into meteorite parent bodies here the outcome of these collisions is quantitatively explored using a simple analytic expression for the viscous dissipation of collisional energy in a liquid layer it is shown that molten chondrules can survive collisions at velocities as high as a few hundred meters per second it is also shown that the thermal evolution of chondrules in a given shock wave varies with chondrule size which may allow chondrules of different textures to form in a given shock wave while experiments are needed to further constrain the parameters used in this work these calculations show that the expected outcomes from collisions behind shock waves are consistent with what is observed in meteorites

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

re examining the role of chondrules in producing the elemental fractionations in chondrites the matrices of all primitive chondrites contain presolar materials circumstellar grains and interstellar organics in roughly ci abundances suggesting that all chondrites accreted matrix that is dominated by a ci like component the matrix normalized abundances of the more volatile elements condensation temperatures 750800 k in carbonaceous and ordinary chondrites are also at or slightly above ci levels the modest excesses may be due to low levels of these elements in chondrules and associated metal subtraction of a ci like matrix component from a bulk ordinary chondrite composition closely matches the average composition of chondrules determined by instrumental neutron activation analysis inaa if some fe metal is added to the chondrule composition measured matrix compositions are not ci like sampling bias and secondary redistribution of elements may have played a role but the best explanation is that 1030 of refractory rich volatile depleted material was added to matrix if most of the more volatile elements are in a ci dominated matrix the major and volatile element fractionations must be largely carried by chondrules there is both direct and indirect evidence for evaporation during chondrule formation type iia and type b chondrules could have formed from a mixture of ci material and material evaporated from type ia chondrules the mg si fe fractionations in the ordinary chondrites can be reproduced with the loss of type ia chondrule material and associated metal the loss of evaporated material from the chondrules could explain the volatile element fractionations mechanisms for how these fractionations occurred are necessarily speculative but two possibilities are briefly explored

accretionary dust mantles in cm chondrites evidence for solar nebula processes abstract the texture and modal composition of fourteen carbonaceous chondrites of the cm group were studied in detail to unravel the origin of their various components and the evolution of their parent body ies the analysis and mapping of complete thin sections by scanning electron and optical microscopy revealed textural units in most samples in which all coarse grained primordial chondritic components chondrules chondrule fragments refractory inclusions particles rich in hydrous silicates pcp and various mineral fragments are coated by fine grained serpentine and tochilinite rich dust the dust mantled particles have spheroidal shapes and form a special lithology in which they are densely aggregated and compacted without any interstitial clastic material the dust mantles termed accretionary dust mantles and their host lithology called primary accretionary rock are interpreted as products of accretion processes in the solar nebula an origin by processes on the parent body is excluded for textural and mineralogical reasons most cm chondrites are affected by secondary impact induced brecciation of variable intensity except for yamato 791198 which is composed entirely of a primary accretionary rock obviously unaltered by secondary parent body processes such as aqueous alteration or brecciation the cm chondrites y74662 haripura cold bokkeveld kivesvaara mighei pollen nogoya y793321 alh 83100 murray and murchison consist of clasts of primary accretionary rock embedded in a fine grained clastic matrix derived from primary rock material the volume percentage of the clastic matrix ranges from 5 y74662 to 76 murchison bells and essebi are brecciated and affected by aqueous alteration to an extent that fragments of primary rock are not preserved the evaluation of literature data indicates that solar wind implanted noble gases are absent in the primary accretionary rock component of cm chondrites they are only present in brecciated samples it must be concluded from the relation between the content of trapped solar wind and degree of brecciation that 1 the solar noble gases are residing exclusively in the clastic matrix and 2 some cm chondrites are regolith breccias and others are fragmental or monomict breccias both types were formed on the parent body although the latter were never exposed to the solar wind based on the results of textural chemical and mineralogical investigations we conclude that a major portion of the water bearing phases in cm chondrites were produced by the hydration of refractory phases prior to the formation of dust mantles and prior to the formation of the recent cm parent body this process requires special physicochemical conditions which allow the crystallization of oh bearing silicates e g higher density of the nebula gas or special precursor planetesimals of the cm chondrite parent body

the matrices of unequilibrated ordinary chondrites implications for the origin and history of chondrites abstract the matrices of sixteen unequilibrated ordinary chondrites all witnessed falls were studied microscopically in transmitted and reflected light and analyzed by electron microprobe selected specimens were also studied by scanning electron microscopy these studies indicate that the fine grained opaque silicate matrix of type 3 unequilibrated chondrites is compositionally mineralogically and texturally distinct from the chondrules and chondrule fragments and may be the low temperature condensate proposed by larimer and anders 1967 1970 examination of the matrices of unequilibrated chondrites also shows that each meteorite has been metamorphosed with the alteration ranging in intensity from quite mild where the matrix has been only slightly altered to a more severe metamorphism that has completely recrystallized the opaque matrix most of the metamorphic changes in the matrix occurred without significant effects on the compositions or textures of the chondrules the metamorphic alteration probably resulted from a combination of processes including thermal metamorphism and the passage of shock waves the present appearance of each unequilibrated chondrite is a result of the particular temperature and pressure conditions under which it and its components formed plus the subsequent metamorphic alteration it experienced

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

the cr chondrite clan implications for early solar system processes in this paper we review the mineralogy and chemistry of calcium aluminum rich inclusions cais chondrules feni metal and fine grained materials of the cr chondrite clan including cr ch and the metal rich cb chondrites queen alexandra range 94411 hammadah al hamra 237 bencubbin gujba and weatherford the members of the cr chondrite clan are among the most pristine early solar system materials which largely escaped thermal processing in an asteroidal setting bencubbin weatherford and gujba may be exceptions and provide important constraints on the solar nebula models these constraints include 1 multiplicity of cai formation 2 formation of cals and chondrules in spatially separated nebular regions 3 formation of cais in gaseous reservoir s having o 16 rich isotopic compositions chondrules appear to have formed in the presence of o 16 poor nebular gas 4 isolation of cais and chondrules from nebular gas at various ambient temperatures 5 heterogeneous distribution of al 26 in the solar nebula and 6 absence of matrix material in the regions of cai and chondrule formation

nanosims isotopic investigation of xenolithic carbonaceous clasts from the kapoeta howardite abstract we report on the investigation of presolar grains and organic matter om in 14 xenolithic carbonaceous clasts c clasts identified in the kapoeta howardite based on high resolution nanosims hydrogen carbon nitrogen and oxygen isotopic imaging data the 14 c clasts are 50 200 m in size and consist of one cm like and 13 ci like clasts which are classified based on their mineralogies the clasts from this study are likely sourced from an ice bearing parent body either an icy asteroid or a comet originating from the outer solar system according to the following mineralogical observations 1 in two ci like clasts embayments of magnetite grains between the c clast and the host howardite point to aqueous alteration occurring on vesta as a result of melting the ice embedded in the c clasts 2 all of the c clasts especially the 13 ci like clasts likely originated from the same parent body because i the 14 c clasts are clustered in the thin section and ii the clasts show a much higher ratio of ci like to cm like clasts with respect to those reported in the literature four presolar silicon carbide sic and two presolar silicate grains were identified in the c clasts in addition all the c clasts contain moderate bulk d and 15n enrichments with the presence of sub micron to micron sized d and 15n hotspots indicating the presence of primitive organic material comparison of the abundances and isotopic compositions of presolar grains and om in these c clasts with literature data for different samples of primitive extraterrestrial material provides support for 1 the genetic linkage of xenolithic c clasts to highly aqueously altered but minimally heated carbonaceous chondritic materials and 2 a homogeneous distribution of circumstellar and interstellar materials in the protoplanetary disk the low amounts of heat experienced by the c clasts suggest that they arrived at vesta and or vestoids at low speeds after the late heavy bombardment in the inner solar system 3 5 4 0 gyr ago

the origin of volatile element depletion in early solar system material clues from zn isotopes in chondrules abstract volatile lithophile elements are depleted in the different planetary materials to various degrees but the origin of these depletions is still debated stable isotopes of moderately volatile elements such as zn can be used to understand the origin of volatile element depletions samples with significant volatile element depletions including the moon and terrestrial tektites display heavy zn isotope compositions i e enrichment of 66zn vs 64zn consistent with kinetic zn isotope fractionation during evaporation however luck et al 2005 found a negative correlation between 66 zn and 1 zn between ci cm co and cv chondrites opposite to what would be expected if evaporation caused the zn abundance variations among chondrite groups we have analyzed the zn isotope composition of multiple samples of the major carbonaceous chondrite classes ci 1 cm 4 cv 2 co 4 cb 2 ch 2 ck 4 and ck cr 1 the bulk chondrites define a negative correlation in a plot of 66 zn vs 1 zn confirming earlier results that zn abundance variations among carbonaceous chondrites cannot be explained by evaporation exceptions are cb and ch chondrites which display zn systematics consistent with a collisional formation mechanism that created enrichment in heavy zn isotopes relative to the trend defined by ci ck we further report zn isotope analyses of chondrite components including chondrules from allende cv3 and mokoia cv3 as well as an aliquot of allende matrix all chondrules are enriched in light zn isotopes 500 ppm on 66zn 64zn relative to the bulk contrary to what would be expected if zn were depleted during evaporation on the other hand the matrix has a complementary heavy isotope composition we report sequential leaching experiments in un equilibrated ordinary chondrites which show sulfides are isotopically heavy compared to silicates and the bulk meteorite by ca 0 65 per mil on 66zn 64zn we suggest isotopically heavy sulfides were removed from either chondrules or their precursors thereby producing the light zn isotope enrichments in chondrules

progressive alteration in cv3 chondrites more evidence for asteroidal alteration abstract the oxidized cv3 chondrites can be divided into two major subgroups or lithologies bali like cv3oxb and allende like cv3oxa in which chondrules calcium aluminum rich inclusions cais and matrices show characteristic alteration features weisberg et al 1997 krot et al 1997d kimura and ikeda 1997 the cv3oxb lithology is present in bali kaba parts of the mokoia breccia and possibly in grosnaja and allan hills alh 85006 it is characterized by the presence of the secondary low ca phyllosilicates saponite and sodium phlogopite magnetite ni rich sulfides fayalite fa 90 ca fe rich pyroxenes fs10 50wo45 50 and andradite phyllosilicates replace primary ca rich minerals in chondrules and cais which suggests mobilization of ca during aqueous alteration magnetite nodules are replaced to various degrees by fayalite ca fe rich pyroxenes and minor andradite fayalite veins crosscut fine grained rims around chondrules and extend into the matrix thermodynamic analysis of the observed reactions indicates that they could have occurred at relatively low temperatures 300 c in the presence of aqueous solutions oxygen isotopic compositions of the coexisting magnetite and fayalite plot close to the terrestrial fractionation line with large 18ofayalite magnetite fractionation 20 we infer that phyllosilicates magnetite fayalite ca fe rich pyroxenes and andradite formed at relatively low temperatures 300 c by fluid rock interaction in an asteroidal environment secondary fayalite and phyllosilicates are virtually absent in chondrules and cais in the cv3oxa lithology which is present in allende and its dark inclusions axtell alha81258 alh 84028 lewis cliff lew 86006 and parts of the mokoia and vigarano breccias instead secondary nepheline sodalite and fayalitic olivine are common fayalitic olivine in chondrules replaces low ca pyroxenes and rims and veins forsterite grains it also forms coarse lath shaped grains in matrix secondary ca fe rich pyroxenes are abundant we infer that the cv3oxa lithology experienced alteration at higher temperatures than the cv3oxb lithology the presence of the reduced and cv3oxa lithologies in the vigarano breccia and cv3oxa and cv3oxb lithologies in the mokoia breccia indicates that all cv3 chondrites came from one heterogeneously altered asteroid the metamorphosed clasts in mokoia krot and hutcheon 1997 may be rare samples of the hotter interior of the cv asteroid we conclude that the alteration features observed in the oxidized cv3 chondrites resulted from the fluid rock interaction in an asteroid during progressive metamorphism of a heterogeneous mixture of ices and anhydrous materials mineralogically similar to the reduced cv3 chondrites

mineralogy and petrography of amoeboid olivine aggregates from the reduced cv3 chondrites efremovka leoville and vigarano products of nebular condensation accretion and annealing amoeboid olivine aggregates aoas from the reduced cv chondrites efremovka leoville and vigarano are irregularly shaped objects up to 5 mm in size composed of forsteritic olivine fa 50 melting we infer that aoas are aggregates of high temperature nebular condensates which formed in cai forming regions and that they were absent from chondrule forming regions at the time of chondrule formation the absence of low ca pyroxene and depletion in moderately volatile elements mn cr na k suggest that aoas were either removed from cai forming regions prior to condensation of these elements and low ca pyroxene or gas solid condensation of low ca pyroxene was kinetically inhibited

trace elements in rims and interiors of chainpur chondrules trace elements were measured in the rims and interiors of nine chondrules separated from the chainpur ll 3 chondrite whole rock samples of chainpur and samples of separated rims were also measured chondrule rims are moderately enriched in siderophile and volatile elements relative to the chondrule interiors the enriched volatile elements include the lithophilic volatile element zn the moderate enrichment of volatiles in chondrule rims and the lack of severe depletion in chondrules can account for the complete volatile inventory in chainpur these results support a three component model of chondrite formation in which metal plus sulfide chondrules plus rims and matrix silicates are mixed to form chondrites

the building blocks of planets within the terrestrial region of protoplanetary disks our solar system was formed from a cloud of gas and dust most of the dust mass is contained in amorphous silicates yet crystalline silicates are abundant throughout the solar system reflecting the thermal and chemical alteration of solids during planet formation even primitive bodies such as comets contain crystalline silicates little is known about the evolution of the dust that forms earth like planets here we report spatially resolved detections and compositional analyses of these building blocks in the innermost two astronomical units of three proto planetary disks we find the dust in these regions to be highly crystallized more so than any other dust observed in young stars until now in addition the outer region of one star has equal amounts of pyroxene and olivine whereas the inner regions are dominated by olivine the spectral shape of the inner disk spectra shows surprising similarity with solar system comets radial mixing models naturally explain this resemblance as well as the gradient in chemical composition our observations imply that silicates crystallize before any terrestrial planets are formed consistent with the composition of meteorites in the solar system

chondrules and matrix in the ornans co3 meteorite possible precursor components abstract bulk compositions of 17 chondrules and one sample of matrix from co3 omans were determined by instrumental neutron activation analysis chondrule precursor components deduced from chondrule compositions are characterized by 1 1 common and slightly volatile siderophiles cr and chalcophiles 2 2 refractory lithophiles and na 3 3 mn si and modal pyroxene and 4 4 feo and olivine component 4 may be closely related to matrix material precursor components have now been inferred for oc eh cv cm and co chondrules a mn and si rich component occurs exclusively among carbonaceous chondrite chondrules although there are significant intergroup differences common to chondrules in all chondrite groups are refractory lithophile rich common siderophile rich and with the exception of eh common lithophile rich components this indicates that the siderophile lithophile and refractory lithophile common lithophile fractionations recorded in chondrite whole rocks were established prior to chondrule formation at all nebular locations

oxygen isotopes in chondrule olivine and isolated olivine grains from the co3 chondrite allan hills a77307 we have measured o isotopic ratios in a variety of olivine grains in the co3 chondrite allan hills alh a77307 using secondary ion mass spectrometry in order to study the chondrule formation process and the origin of isolated olivine grains in unequilibrated chondrites oxygen isotopic ratios of olivines in this chondrite are variable from delta 17 o 15 5 to 4 5 parts per thousand and delta 18 o 11 5 to 3 9 parts per thousand with delta 17 o varying from 10 4 to 3 5 parts per thousand forsteritic olivines fa 1 are enriched in o 16 relative to the bulk chondrite whereas more feo rich olivines are more depleted in o 16 most ratios lie close to the carbonaceous chondrite anhydrous minerals ccam line with negative values of delta 17 o although one grain of composition fa 4 has a mean delta 17 o of 1 6 parts per thousand marked o isotopic heterogeneity within one feo rich chondrule is the result of incorporation of relic o 16 rich mg rich grains into a more o 16 depleted host isolated olivine grains including isolated forsterites have similar o isotopic ratios to olivine in chondrules of corresponding chemical composition this is consistent with derivation of isolated olivine from chondrules as well as the possibility that isolated grains are chondrule precursors the high o 16 in forsteritic olivine is similar to that observed in forsterite in cv and ci chondrites and the ordinary chondrite julesburg and suggests nebula wide processes for the origin of forsterite that appears to be a primitive nebular component

trace element distributions within ordinary chondrite chondrules implications for chondrule formation conditions and precursors the concentrations of thirty six lithophile elements in the major silicate phases of chondrules have been determined by ion microprobe two types of porphyritic chondrule olivines normal and incompatible rich have been identified the incompatible rich olivines which have forsterite contents that are greater than fo98 appear to have formed under highly reducing conditions the olivine and low ca pyroxene grains in porphyritic chondrules have relatively unfractionated l chondrite normalized ree abundances compared to expectations from equilibrium distribution coefficients this is consistent with porphyritic chondrules having formed at cooling rates of the order of 1000 c h or faster the alkali metal na k rb and cs to al ratios in chondrule glasses vary by two orders of magnitude the lower values possibly being the result of volatile loss from chondrules no correlation was found between alkali metal depletions in chondrule glasses and enrichments in the surrounding rims but any such correlation may have been destroyed by the diffusive redistribution of these elements in rims that is likely to occur even under mild metamorphic conditions the refractory lithophiles with the exception of mg are all highly incompatible in silicate melts and are as a result concentrated in the chondrule glasses the refractory lithophiles in the glass are in most cases unfractionated from one another suggesting that neither vapor phase nor crystal liquid fractionation played a major role in the formation of chondrules or their precursors based largely on the observation that the refractory lithophiles are concentrated in the chondrule glasses it is suggested that previously reported correlations between these elements in bulk chondrule analyses are due to chondrules themselves as opposed to refractory condensates having been their own immediate precursors a simple monte carlo simulation using the compositions of the major chondrule silicate phases reported here supports this hypothesis it is argued that the upper limit of about one observed in the atomic na al ratios of chondule glasses is not due to an albitic precursor but simply reflects that for na to be incorporated into the structure of the melt it must take part in the coupled substitution naalo2 sio2

compositional and genetic relationship between chondrules chondrule rims metal and matrix in the renazzo chondrite individual chondrules coarse and fine grained metal chondrule rims and matrix samples were separated from the renazzo chondrite cr2 and studied by instrumental neutron activation analysis both renazzo chondrule and matrix fractions have ci cr mg concentration ratios unlike chondrules from other classes of chondrites which have fractionated cr mg ratios this and other arguments suggest that renazzo chondrules and matrix formed in the same nebular region in renazzo fine grained metal the dominant metal component is mostly located inside chondrules or in chondrule rims matrix contains few coarse metal grains both types of metal fine and coarse exhibit similar chemical signatures comparatively high in cr and low in ni suggesting a genetic relationship although metal is mostly contained in chondrules chondrules and matrix of renazzo have similar common siderophile lithophile abundance ratios this may imply that renazzo chondrules and metal were formed by reduction of oxidized precursors compositionally similar to ci chondrites the ci like concentrations of sc mg se and zn in renazzo matrix are consistent with this inference the differences in siderophile element pattern between chondrules chondrule metal and matrix indicate evaporation and recondensation of volatile elements during chondrule formation recondensation of evaporated elements was incomplete and the degree of recondensation correlates with element volatility the higher than ci k mg na mg and ga fe ratios of renazzo matrix may reflect recondensation of k na and ga into the matrix the ci se sc and zn sc concentration ratios of the matrix however reflect very limited degrees of recondensation of se and zn into matrix the presence of abundant phyllosilicates and organic material in renazzo matrix requires a low background temperature 200 k during formation of the renazzo meteorite partial recondensation of volatile elements in a cold nebular environment implies instantaneous agglomeration of the renazzo chondrite following chondrule formation

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

iodine xenon chemical and petrographie studies of semarkona chondrules evidence for the timing of aqueous alteration we have performed inaa petrographie and noble gas analyses on seventeen chondrules from the semarkona meteorite ll3 0 primarily to study the relationship of the i xe system to other measured properties we observe a range of 10 ma in apparent i xe ages the three latest apparent ages fall in a cluster suggesting the possibility of a common event the initial 129i 127i ratio r0 is apparently related to chondrule type and or mineralogy with nonporphyritic and pyroxene rich chondrules showing evidence for lower r0 s later apparent i xe ages than porphyritic and olivine rich chondrules in addition chondrules with sulfides on or near the surface have lower r0s than other chondrules the 129xe 132xe ratio in the trapped xe component anticorrelates with r0 consistent with evolution of a chronometer in a closed system or in multiple similar systems on the basis of these correlations we conclude that the variations in r0 represent variations in ages and that later event s possibly aqueous alteration preferentially affected chondrules with nonporphyritic textures and or sulfide rich exteriors about 10 ma after the formation of the chondrules

petrographic and oxygen isotopic study of refractory forsterites from r chondrite dar al gani 013 r3 5 6 unequilibrated ordinary and carbonaceous chondrites we have conducted petrographic chemical and in situ oxygen isotopic studies of refractory forsterites from unequilibrated ordinary and carbonaceous chondrites as well as an unequilibrated r chondrite refractory forsterites occur in all types of unequilibrated chondrites and all have very similar chemical composition with low feo and high refractory lithophile element rle contents refractory forsterites are typically enriched in 16o relative to normal olivine independent of the bulk o isotope ratios of the parent meteorites analyses of refractory forsterites spread along a 17o mixing line with 17o ranging from 2 to 10 due to similarities in oxygen isotopes and chemical compositions we conclude that refractory forsterites of various types of chondrites come from a single common reservoir implications of this hypothesis for the chemical and o isotope evolution of silicates in the early solar nebular are discussed

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

the origin and evolution of chondrites recorded in the elemental and isotopic compositions of their macromolecular organic matter extraterrestrial organic matter in meteorites potentially retains a unique record of synthesis and chemical thermal modification by parent body nebular and even presolar processes in a survey of the elemental and isotopic compositions of insoluble organic matter iom from 75 carbonaceous ordinary and enstatite chondrites we find dramatic variations within and between chondrite classes there is no evidence that these variations correlate with the time and or location of chondrite formation or with any primary petrologic or bulk compositional features that are associated with nebular processes e g chondrule and volatile trace element abundances nor is there evidence for the formation of the iom by fischer tropsch type synthesis in the nebula or in the parent bodies the elemental variations are consistent with thermal maturation and or oxidation of a common precursor for reasons that are unclear there are large variations in isotopic composition within and between chondrite classes that do not correlate in a simple way with elemental composition or petrologic type nevertheless because of the pattern of elemental variations with petrologic type and the lack of any correlation with the primary features of the chondrite classes at present the most likely explanation is that all iom compositional variations are the result of parent body processing of a common precursor if correct the range of isotopic compositions within and between chondrite classes implies that the iom is composed of several isotopically distinct components whose relative stability varied with parent body conditions the most primitive iom is found in the cr chondrites and bells cm2 isotopically the iom from these meteorites resembles the iom in interplanetary dust particles chemically their iom resembles the chon particles of comet halley despite the large isotopic anomalies in the iom from these meteorites it is uncertain whether the iom formed in the interstellar medium or the outer solar system although the former is preferred here

carbon abundance and silicate mineralogy of anhydrous interplanetary dust particles we have studied nineteen anhydrous chondritic interplanetary dust particles idps using analytical electron microscopy we have determined a method for quantitative light element edx analysis of small particles and have applied these techniques to a group of idps our results show that some idps have significantly higher bulk carbon abundances than do carbonaceous chondrites we have also identified a relationship between carbon abundance and silicate mineralogy in our set of anhydrous idps in general these particles are dominated by pyroxene olivine or a subequal mixture of olivine and pyroxene the pyroxene dominated idps have a higher carbon abundance than those dominated by olivines members of the mixed mineralogy idps can be grouped with either the pyroxene or olivine dominated particles based on their carbon abundance the high carbon pyroxene dominated particles have primitive mineralogies and bulk compositions which show strong similarities to cometary dust particles we believe that the lower carbon olivine dominated idps are probably derived from asteroids based on carbon abundances the mixed mineralogy group represents particles derived from either comets or asteroids we believe that the high carbon pyroxene rich anhydrous idps are the best candidates for cometary dust

structural deformation of the leoville chondrite foliations defined by alignment of elongated chondrules have been noted previously in chondrites but none displays this effect so well as leoville cv3 the shapes of leoville chondrules were produced by deformation in situ as indicated by inclusions and clasts with similar shapes and preferred orientations to those of chondrules similarities in the aspect ratios of apparent strain ellipses measured for chondrules alone 1 9 and 2 0 by several methods and for the whole meteorite 2 0 indicate either that leoville deformed homogeneously or that it deformed as a framework of touching chondrules this amount of strain corresponds to approximately 33 uniaxial shortening assuming constant volume because the strain ellipse was measured in only one orientation this strain value is a minimum estimate for the meteorite lack of correlation between foliation and either shock or thermal effects argues that impact or metamorphism are unlikely to have produced this deformation compaction due to overburden from progressive accretion on the chondrite parent body is suggested to have been its cause estimates of maximum deviatoric stresses in the interiors of asteroid sized bodies and constraints on maximum temperatures for cv3 chondrites are consistent with diffusional flow as the deformation mechanism for olivine in these chondrules diffusional flow is also suggested by the scarcity of observed lattice dislocations deformation of leoville olivines by this mechanism at geologically reasonable strain rates appears to require higher temperatures than those believed to have been experienced by this meteorite 600 c however differences in olivine grain size the presence of water or a more complex deformation history might explain this discrepancy

the semarkona meteorite first recorded occurrence of smectite in an ordinary chondrite and its implications abstract semarkona is an unshocked unequilibrated ordinary chondrite much of the interchondrule matrix and the mesostases of some chondrules and clasts have been hydrothermally altered analyses of altered materials and opaque matrix are presented ca and fe have been redistributed from primary anhydrous phases into calcite and na fe smectite respectively in semarkona the process possibly requires open system behavior inconsistent with the conventional view of metamorphism of the ordinary chondrites the low petrologic type previously assigned to semarkona is the result of retrograde metamorphism under aqueous conditions of a higher temperature mineral assemblage semarkona and possibly bishunpur should be assigned to petrologic type 2

abundance major element composition and size of components and matrix in cv co and acfer 094 chondrites abstract the relative abundances and chemical compositions of the macroscopic components or inclusions chondrules and refractory inclusions and fine grained mineral matrix in chondritic meteorites provide constraints on astrophysical theories of inclusion formation and chondrite accretion we present new techniques for analysis of low count pixel si mg ca al ti and fe x ray intensity maps of rock sections and apply them to large areas of co and cv chondrites and the ungrouped acfer 094 chondrite for many thousands of manually segmented and type identified inclusions we are able to assess pixel by pixel the major element content of each inclusion we quantify the total fraction of refractory elements accounted for by various types of inclusion and matrix among co chondrites both matrix and inclusion mg si ratios approach the solar and bulk co ratio with increasing petrologic grade but si remains enriched in inclusions relative to matrix the oxidized cv chondrites with higher matrix inclusion ratios exhibit more severe aqueous alteration oxidation and their excess matrix accounts for their higher porosity relative to reduced cv chondrites porosity could accommodate an original ice component of matrix as the direct cause of local alteration of oxidized cv chondrites we confirm that major element abundances among inclusions differ greatly across a wide range of co and cv chondrites these abundances in all cases add up to near chondritic solar bulk abundance ratios in these chondrites despite wide variations in matrix inclusion ratios and inclusion sizes chondrite components are complementary this complementarity provides a robust meteoritic constraint for astrophysical disk models

the isotope composition of selenium in chondrites constrains the depletion mechanism of volatile elements in solar system materials abstract solar nebula processes led to a depletion of volatile elements in different chondrite groups when compared to the bulk chemical composition of the solar system deduced from the sun s photosphere for moderately volatile elements this depletion primarily correlates with the element condensation temperature and is possibly caused by incomplete condensation from a hot solar nebula evaporative loss from the precursor dust and or inherited from the interstellar medium element concentrations and interelement ratios of volatile elements do not provide a clear picture about responsible mechanisms here the abundance and stable isotope composition of the moderately to highly volatile element se are investigated in carbonaceous ordinary and enstatite chondrites to constrain the mechanism responsible for the depletion of volatile elements in planetary bodies of the inner solar system and to define a 82 78 se value for the bulk solar system the 82 78 se of the studied chondrite falls are identical within their measurement uncertainties with a mean of 0 20 0 26 2 s d n 14 relative to nist srm 3149 despite se abundance depletions of up to a factor of 2 5 with respect to the ci group the absence of resolvable se isotope fractionation rules out a kinetic rayleigh type incomplete condensation of se from the hot solar nebula or partial kinetic evaporative loss on the precursor material and or the parent bodies the se depletion if acquired during partial condensation or evaporative loss therefore must have occurred under near equilibrium conditions to prevent measurable isotope fractionation alternatively the depletion and cooling of the nebula could have occurred simultaneously due to the continuous removal of gas and fine particles by the solar wind accompanied by the quantitative condensation of elements from the pre depleted gas in this scenario the condensation of elements does not require equilibrium conditions to avoid isotope fractionation the results further suggest that the processes causing the high variability of se concentrations and depletions in ordinary and enstatite chondrites did not involve any measurable isotope fractionation different degrees of element depletions and isotope fractionations of the moderately volatile elements zn s and se in ordinary and enstatite chondrites indicate that their volatility is controlled by the thermal stabilities of their host phases and not by the condensation temperature under canonical nebular conditions

chemical isotopic and mineralogical evidence for the origin of matrix in ordinary chondrites abstract we report the first combined chemical isotopic and mineralogical study of fine grained opaque matrix material from a type 3 ordinary chondrite allan hills a77299 h3 7 electron microprobe and instrumental neutron activation analysis of a large matrix lump show that it has a major element composition typical of matrix material in type 3 chondrites unlike chondrules it shows no siderophile element depletions and is remarkably unfractionated relative to ci chondrites suggesting that it is primitive solar system material the matrix lump has an unique oxygen isotopic composition which lies below the terrestrial fractionation line and differs markedly from the composition of fine grained matrix lumps and chondrule rims from semarkona grossman et al 1987 transmission electron microscope tem studies of microtomed samples of the fine grained fraction m of the matrix lump show that it consists of rare angular clastic grains 1 m of pyroxene and olivine embedded within a groundmass of rounded fine grained m olivines the mineralogy and textures of the matrix lump are typical of other occurrences of fine grained matrix studied by tem in other type 3 ordinary chondrites we conclude that the matrix lump in alha 77299 consists largely of material that formed by annealing of amorphous presolar dust or nebular condensates and could not have been derived from chondrules by any reasonable mechanism however the observed compositional differences between the matrix lump and chondrules in ordinary chondrites are consistent with the idea that some chondrules formed by melting of matrix like material accompanied by loss of siderophile and volatile elements

distribution of moderately volatile trace elements in fine grained chondrule rims in the unequilibrated co3 chondrite alh a77307 abstract the concentrations of ni cu zn ga ge and se in five fine grained chondrule rims in the highly unequilibrated co3 chondrite alh a77307 3 0 have been determined for the first time by synchrotron x ray fluorescence sxrf microprobe at brookhaven national laboratory these elements are especially useful for tracing the role of condensation and evaporation processes which occurred at moderate temperatures in the solar nebula understanding the distribution of moderately volatile elements between matrix and chondrules is extremely important for evaluating the different models for the volatile depletions in chondritic meteorites the data show that the trace element chemistry of rims on different chondrules is remarkably similar consistent with data obtained for the major and minor elements by electron microprobe these results support the idea that rims are not genetically related to individual chondrules but all sampled the same reservoir of homogeneously mixed dust of the trace elements analyzed zn and ga show depletions relative to ci chondrite values but in comparison with bulk co chondrites all the elements are enriched by 1 5 to 3 5 co the abundance patterns for moderately volatile elements in alh a77307 chondrule rims closely mimic those observed in the bulk chondrite indicating that matrix is the major reservoir for these elements the close matching of the patterns for the volatile depleted bulk chondrite and enriched matrix is especially striking for na which is anomalously depleted in alh a77307 in comparison with average co chondrite abundances the depletion in na is probably attributable to the effects of leaching in antarctica with the exception of na the volatile elements show a relatively smooth decrease in abundance as a function of condensation temperature indicating that their behavior is largely controlled by their volatility

can vertical migrations of dinoflagellates explain observed bioluminescence patterns during an upwelling event in monterey bay california 1 extensive auvs surveys showed that during the development of upwelling bioluminescent dinoflagellates from the northern part of the monterey bay california called the upwelling shadow area were able to avoid advection by southward flowing currents along the entrance to the bay while non bioluminescent phytoplankton were advected by currents it is known that vertical swimming of dinoflagellates to deeper layers helps them avoid losses due to advection in the present paper we investigate if modeling dinoflagellates vertical swimming can explain the observed dinoflagellates ability to avoid advection during the upwelling development the dynamics of a dinoflagellate population is modeled with the tracer model with introduced vertical swimming velocity three swimming behaviors are considered sinking swimming to the target depth and diel vertical migration velocities in all swimming cases are considered in the ranges of documented velocities for the observed dinoflagellates species during the upwelling development in the monterey bay our modeling confirmed that observed bioluminescent dinoflagellates avoidance of advection during the upwelling development can be explained by their vertical swimming ability in the case of swimming with 20 m day which is half of observed maximum swimming velocity around 40 of dinoflagellates population from the northern part of the bay were advected along the entrance to the bay in comparison to the case without swimming this is in agreement with the ratio of around 45 of observed mean bioluminescence intensity at the entrance to the bay to the observed mean intensity in the northern part of the bay this mechanism also helps explain the general persistence of dinoflagellates in this part of the coastline

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

zoned chondrules in semarkona evidence for high and low temperature processing at least 15 of the 10w feo chondrules in semarkona ll3 0 have mesostases that are concentrically zoned in na with enrichments near the outer margins we have studied zoned chondrules using electron microprobe methods x ray mapping plus quantitative analysis ion microprobe analysis for trace elements and hydrogen isotopes cathodoluminescence imaging and transmission electron microscopy in order to determine what these objects can tell us about the environment in which chondrules formed and evolved mesostases in these chondrules are strongly zoned in all moderately volatile elements and h interpreted as water calcium is depleted in areas ofvolatile enrichment titanium and cr generally decrease toward the chondrule surfaces whereas al and si may either increase or decrease generally in opposite directions to one another mn follows na in some chondru1es but not in others fe and mg are unzoned d h ratios increase in the water rich areas of zoned chondrules mesostasis shows cathodoluminescence zoning in most zoned chondrules with the brightest yellow color near the outside mesostasis in zoned chondrules appears to be glassy with no evidence for devitrification systematic variations in zoning patterns among pyroxene and olivine rich chondrules may indicate that fractionation oflow and high ca pyroxene played some role in ti cr mn si ai and some ca zoning but direct condensation ofelements into hot chondrules secondary melting oflate condensates into the outer portions of chondrules and subsolidus diffusion of elements into warm chondrules cannot account for the sub parallel zoning profiles ofmany elements the presence ofh20 or elemental abundance patterns zoning ofmoderately volatile elements and ca may have been produced by hydration ofchondrule glass without devitrification during aqueous alteration on the parent asteroid this could have induced structural changes in the glass allowing rapid diffusion and exchange of elements between altered glass and surrounding matrix and rim material calcium was mainly lost during this process and other nonvolatile elements may have been mobile as well some unzoned 10w feo chondrules appear to have fully altered mesostasis

evidence for primitive nebular components in chondrules from the chainpur chondrite abstract the least equilibrated ordinary chrondrites contain chondrules which have experienced little change since the time of their formation in the early solar system these chondrules are excellent indicators of the physical and chemical nature of the solar nebula we separated 36 chondrules from the chainpur ll3 4 chondrite and analyzed each for 20 elements and petrographic properties sampling biases were minimized as far as possible chondrules seem to have formed through the melting of random mixtures of grains comprising a limited number of nebular components the identity of these components can be deduced from chondrule compositions the dominant components appear to be 1 a mixture of metal and sulfide with composition similar to whole rock metal and sulfide 2 refractory ir rich metal 3 refractory olivine rich silicates 4 low temperature pyroxene rich silicates and possibly 5 a component containing the more volatile lithophiles most of the textural types of chondrules formed from the same set of precursor components in some cases chondrules having different textures are almost identical in composition a few unusual chondrule types seem to mainly consist of uncommon nebular components possibly indicating different modes of formation etching experiments confirm that chondrule rims are enriched in metal troilite and moderately volatile elements relative to the bulk chondrules however a large fraction of the volatiles remains in the unetched interior

the lack of potassium isotopic fractionation in bishunpur chondrules in a search for evidence of evaporation during chondrule formation the mesostases of 11 bishunpur chondrules and melt inclusions in olivine phenocrysts in 7 of them have been analyzed for their alkali element abundances and k isotopic compositions except for six points all areas of the chondrules that were analyzed had 41k compositions that were normal within error typically 3 2s the six anomalous points are probably all artifacts experiments have shown that free evaporation of k leads to large 41k enrichments in the evaporation residues consistent with rayleigh fractionation under rayleigh conditions a 3 enrichment in 41k is produced by 12 loss of k the range of l chondrite normalized k al ratios a measure of the k elemental fractionation in the areas analyzed vary by almost three orders of magnitude if all chondrules started out with l chondrite like k abundances and the k loss occurred via rayleigh fractionation the most k depleted chondrules would have had compositions of up to 41k 200 clearly k fractionation did not occur by evaporation under rayleigh conditions yet experiments and modeling indicate that k should have been lost during chondrule formation under currently accepted formation conditions peak temperature cooling rate etc invoking precursors with variable alkali abundances to produce the range of k al fractionation in chondrules does not explain the k isotopic data because any k that was present should still have experienced sufficient loss during melting for there to have been a measurable isotopic fractionation if k loss and isotopic fractionation was inevitable during chondrule formation the absence of k isotopic fractionation in bishunpur chondrules requires that they exchanged k with an isotopically normal reservoir during or after formation there is evidence for alkali exchange between chondrules and rim matrix in all unequilibrated ordinary chondrites however melt inclusions can have alkali abundances that are much lower than the mesostases of the host chondrules which suggests that they at least remained closed since formation if it is correct that some or all melt inclusions remained closed since formation the absence of k isotopic fractionation in them requires that the k isotopic exchange took place during chondrule formation which would probably require gas chondrule exchange potassium evaporated from fine grained dust and chondrules during chondrule formation may have produced sufficient k vapor pressure for gas chondrule isotopic exchange to be complete on the timescales of chondrule formation alternatively our understanding of chondrule formation conditions based on synthesis experiments needs some reevaluation

petrology and mineralogy of type ii feo rich chondrules in semarkona ll3 0 origin by closed system fractional crystallization with evidence for supercooling abstract the petrology of type ii porphyritic olivine chondrules in semarkona ll3 0 has been studied in detail olivines in these chondrules are euhedral fe richand are strongly zoned from cores to rims of grains in feo fa10 30 cr2o3 0 2 0 6 wt mno 0 2 0 7 wt and cao 0 1 0 4 wt interstitial mesostasis is rich in si aland ca and is glassy with abundant microcrystallites minor minerals include troilite fe ni metaland chromite some olivine grains contain euhedral fayalite rich cores that are probably produced during initial supercooling of the chondrule melt rare relict grains of forsteritic olivine have compositions very similar to olivines in type ia chondrules in semarkona and may result from disaggregation of such chondrules apart from these relics all properties of type ii chondrules can be described by closed system fractional crystallization of droplets which were essentially entirely molten the chondrules did not originate as aggregates of large olivine grains and are unlikely to be fragments of precursor igneous rocks cooling rates of the order of 1000 c h are indicated from peak temperatures of around 1600 c the chondrules show considerable evidence for supercooling and large departures from equilibrium during crystallization there is no evidence for chondrule nebula exchange either during or after crystallization or any secondary processes such as aqueous alteration or thermal metamorphism bulk composition data suggest that precursor material included a refractory ca al ti rich component similar to one of the precursor components of type ia chondrulesand a non refractory fe and si rich component type ia chondrules may have formed from type ii chondrules by loss of fe and volatiles alternatively the two chondrule types may have formed in regions of considerable diversity in the solar nebula from precursor materials with different fe mg ratios

feo rich porphyritic pyroxene chondrules in unequilibrated ordinary chondrites abstract a suite of feo rich type ii porphyritic olivine pyroxene pop chondrules has been studied in detail data for ten chondrules from semarkona ll3 0 are emphasized and one chondrule from chainpur ll3 4 and two from parnallee ll3 6 are included as further examples of certain properties the chondrules contain phenocrysts of pyroxene and olivine in varying proportions and have fe fe mg 10 mol in the silicate minerals four pyroxene minerals are present clinoenstatite orthorhombic enstatite pigeonite and augite pyroxene phenocrysts may consist of all four minerals with progressive overgrowths in order of increasing wo content enstatite may occur independently of clinoenstatite but ca rich pyroxenes pigeonite and augite always nucleate on low ca pyroxene phenocrysts pyroxene and olivine phenocrysts may be independent of each other or may be intergrown and commonly show hopper morphologies indicative of rapid growth pyroxenes and olivines are commonly strongly zoned as a result of fractional crystallization of the chondrules in addition low ca pyroxene may contain ghost regions of slightly more feo and minor element rich material in the cores of grains these regions are partially resorbed and appear to be derived from previous crystallization of essentially the same chondrule oscillatory zoning is observed in enstatite in two chondrules and is believed to be the result of disquilibrium kinetic effects relict grains including a forsterite relict and a partially reduced feo rich relict in the same chondrule and clinoenstatite cores of pyroxene phenocrysts in another chondrule are evidence for recycling and mixing of chondrule material all of the chondrules are highly disequilibrium assemblages they appear to have cooled from essentially molten droplets with little volatile loss or recondensation occurring during the heating event peak temperatures were probably close to liquidus temperatures 1500 1700 c and cooling rates were probably of the order of hundreds of degrees per hour this description will serve as a basis for future interpretation of the effects of metamorphism on porphyritic pyroxene rich chondrules

mineral equilibrium in fractionated nebular systems we investigated the equilibrium mineral assemblages in chemically fractionated nebular systems using a computer routine that finds the set of minerals and gases which minimizes the gibbs free energy of a system with stipulated elemental abundances diagrams are presented showing the equilibrium mineralogy as a function of temperature 400 2300 k for unfractionated solar material and five fractionated systems the fractionated systems were defined by mixing in various proportions the following four volatility components that solar material can be divided into refractory dust carbonaceous matter ices and h2 gas dust enrichment is seen to increase temperatures of condensation evaporation and the fe2 content of mafic minerals and to permit existence of stable melt phases enrichment of dust and organic matter produces mineral assemblages that are similar in many ways to those of enstatite chondrites but with mafic minerals that are far more reduced fe2 poor than those in primitive enstatite chondrites enrichment of dust organics and ices leads to highly ferrous mineralogies even at the highest temperatures but does not predict the stability of hydrous phases above 450 k

the compositional classification of chondrites vii the r chondrite group bulk compositional and petrographic data clearly define the new r rumuruti group of chondrites consisting of rumuruti the only fall alh85151 acfer 217 carlisle lakes dar al gani 013 pca91002 pca91241 y 75302 y 793575 and y 82002 compositional petrographic rare gas and 0 isotopic data strongly suggest that pca91002 and pca91241 are paired the yamato specimens are probably not paired the matrices of the known r chondrites have experienced similar minor degrees of metamorphism petrographic types are 3 8 3 9 with the exception of alh85151 3 6 all except carlisle lakes contain equilibrated r5 r6 clasts petrographically the r chondrites are characterized by a low chondrule matrix modal abundance ratio high states of oxidation reflected by abundant nio bearing olivine with fa37 40 relatively small chondrules mean apparent diameters of 400 abundant up to 11 wt sulfides mainly pyrrhotite and pentlandite and negligible amounts of metallic fe ni refractory lithophile abundances are 0 95 x cl intermediate between those in ordinary chondrites oc and ci chondrites abundances of the volatile elements se and zn are greatly enhanced relative to oc the r chondrites are clearly distinguished from other chondrite groups on the basis of al mn and zn mn abundance ratios the oxygen isotopic data plot roughly along a slope 12 line with whole rock 17o values higher than for any other chondrite group rumuruti acfer 217 alh85151 pca91002 and pca91241 have light dark structures and solar wind implanted rare gases indicating that they are regolith breccias the yamato specimens also have light dark structures and are inferred to be regolith breccias carlisle lakes lacks solar rare gases and is unbrecciated based on similarities in refractory lithophile abundances 00 95 x ci oxygen isotope compositions 17o 0 and refractory inclusion abundances 0 1 vol none have been reported the r chondrites probably belong to a noncarbonaceous superclan of chondrites that also includes ordinary and enstatite chondrites the high oxidation state high matrix chondrule modal abundance ratio relatively low abundance of droplet chondrules and high 17o composition suggest that the r chondrites formed at greater heliocentric distances than the oc

the relative formation ages of ferromagnesian chondrules inferred from their initial aluminum 26 aluminum 27 ratios we performed a systematic high precision sims 26al 26mg isotopic study for 11 ferromagnesian chondrules from the highly unequilibrated ordinary chondrite bishunpur ll3 1 the chondrules are porphyritic and contain various amounts of olivine and pyroxene and interstitial plagioclase and or glass the chemical compositions of the chondrules vary from feo poor to feo rich eight chondrules show resolvable 26mg excesses with a maximum 26mg of 1 in two chondrules the initial 26al 27al ratios inferred for these chondrules range between 2 28 0 73 x 10 5 to 0 45 0 21 x 10 5 assuming a homogeneous distribution of al isotopes in the early solar system this range corresponds to ages relative to cais between 0 7 0 2 my and 2 4 0 4 0 7 my the inferred total span of the chondrule formation ages is at least 1 my which is too long to form chondrules by the x wind the initial 26al 27al ratios of the chondrules are found to correlate with the proportion of olivine to pyroxene suggesting that olivine rich chondrules formed earlier than pyroxene rich chondrules though we do not have a completely satisfactory explanation of this correlation we tentatively interpret it as a result of evaporative loss of si from earlier generations of chondrules followed by addition of si to the precursors of later generation chondrules

correlation between relative ages inferred from 26al and bulk compositions of ferromagnesian chondrules in least equilibrated ordinary chondrites we have studied the relationship between bulk chemical compositions and relative formation ages inferred from the initial 26al 27al ratios for sixteen ferromagnesian chondrules in least equilibrated ordinary chondrites semarkona ll3 0 and bishunpur ll3 1 the initial 26al 27al ratios of these chondrules were obtained by kita et al 2000 and mostefaoui et al 2002 corresponding to relative ages from 0 7 0 2 to 2 4 0 4 0 7 myr after calcium aluminum rich inclusions cais by assuming a homogeneous distribution of 26al in the early solar system the measured bulk compositions of the chondrules cover the compositional range of ferromagnesian chondrules reported in the literature and thus the chondrules in this study are regarded as representatives of ferromagnesian chondrules the relative ages of the chondrules appear to correlate with bulk abundances of si and the volatile elements na k mn and cr but there seems to exist no correlation of relative ages neither with fe nor with refractory elements younger chondrules tend to be richer in si and volatile elements our result supports the result of mostefaoui et al 2002 who suggested that pyroxene rich chondrules are younger than olivine rich ones the correlation provides an important constraint on chondrule formation in the early solar system it is explained by chondrule formation in an open system where silicon and volatile elements evaporated from chondrule melts during chondrule formation and recondensed as chondrule precursors of the next generation

modal mineralogy of carbonaceous chondrites by x ray diffraction and mossbauer spectroscopy carbonaceous chondrites are among the most analyzed geological materials on earth however despite this attention and unlike most terrestrial rocks little is known on the abundance of individual phases within them here we show how a combination of several novel x ray diffraction xrd techniques including a high brightness x ray microsource and mssbauer spectroscopy allows a complete modal mineralogy to be ascertained from even the most highly unequilibrated fine grained chondrites for all minerals of abundance 1 wt knowledge of the modal mineralogy of a sample also allows us to calculate grain density we analyzed allende murchison tagish lake and orgueil based on our modal data the grain density estimates for allende murchison and orgueil are close to literature values in the case of tagish lake there is no published grain density although a bulk density measurement does exist taking our estimate of grain density and the measured bulk density we calculate an exceptionally high porosity of 41 for this meteorite similar to some chondritic idps and in line with a porosity calculated from an entry model for the tagish lake fireball although it is an oxidized cv magnetite is present in allende at a level of 0 5 wt or 0 3 vol a result that is substantiated by several other instrumental studies this may be an oxidized meteorite but that oxidation is not manifested in abundant magnetite in addition we note appreciable fayalitic olivine in orgueil detected by both xrd and mossbauer we employed microsource xrd to look at heterogeneity in mineral abundance in orgueil and found substantial variation with phyllosilicates varying inversely with olivine the data suggest that orgueil was initially composed primarily of anhydrous materials which have been partially but not completely altered although the data are preliminary comparison between our xrd modal assessment bulk chemistry grain density and mossbauer data suggests that our estimates of mineral abundance are robust the advent of microsource xrd allows similar modal data to be acquired from samples as small as a few hundred micrograms

isotopic composition of carbonaceous chondrite kerogen evidence for an interstellar origin of organic matter in meteorites abstract stepwise combustion has revealed systematic patterns of isotopic heterogeneity for c h and n in the insoluble organic fraction m kerogen from the orgueil and murray carbonaceous chondrites those patterns are essentially identical for both meteorites indicating a common source of m kerogen the data cannot be reconciled with a single mass fractionation process acting upon a single precursor composition this indicates either a multi path history of mass dependent processing or a significant nucleogenetic contribution or both if mass fractionation were the dominant process the magnitude of the observed isotopic variability strongly suggests that ion molecule reactions at very low temperatures probably in interstellar clouds were responsible in any case an interstellar rather than solar nebular origin for at least some of the meteoritic organic matter is indicated this has interesting implications for the origin of prebiotic molecules temperatures in the early solar system and the isotopic compositions of volatiles accreted by the terrestrial planets

the origin and significance of reverse zoning in melilite from allende type b inclusions in many type b allende inclusions melilite is reversely zoned over restricted portions of each crystal textural relationships and the results of dynamic crystallization experiments suggest that the reverselyzoned intervals in these type melilites result from the co precipitation of melilite with clinopyroxene from a melt prior to the onset of anorthite precipitation when clinopyroxene begins to precipitate the al mg ratio of the melt rises causing the crystallizing melilite to become more gehlenitic an effect which is negated by crystallization of anorthite because the equilibrium crystallization sequence in these liquids is anorthite before pyroxene melilite reverse zoning can occur only when anorthite nucleation is suppressed relative to pyroxene this has been achieved in our experiments at cooling rates as low as 0 5 c hour our experiments further indicate however that reverse zoning does not form at cooling rates 50 c hour probably because the clinopyroxene becomes too al rich to drive up the al mg ratio of the liquid type inclusions with reversely zoned melilites must have cooled at rates greater than those at which anorthite begins to crystallize before clinopyroxene but 50 c hour such rates are far too slow for the type droplets to have cooled by radiation into a nebular gas but are much faster than the cooling rate of the solar nebula itself one possibility is that type b s formed in local hot regions within the nebula where their cooling rate was equal to that of their surrounding gas other possibilities are that their cooling rates reflect their movement along nebular temperature gradients or the influence of a heat source the sun or viscous drag on inclusions as they moved through the nebular gas are potential candidates for such heat sources

the origin of chondritic macromolecular organic matter a carbon and nitrogen isotope study the n and c abundances and isotopic compositions of acid insoluble carbonaceous material in thirteen primitive chondrites five unequilibrated ordinary chondrites three cm chondrites three enstatite chondrites a ci chondrite and a cr chondrite have been measured by stepped combustion while the range of c isotopic compositions observed is only delta 13c 30 the n isotopes range from delta 15n approximately 40 to 260 after correction for metamorphism presolar nanodiamonds appear to have made up a fairly constant 3 4 wt of the insoluble c in all the chondrites studied the apparently similar initial presolar nanodiamond to organic c ratios and the correlations of elemental and isotopic compositions with metamorphic indicators in the ordinary and enstatite chondrites suggest that the chondrites all accreted similar organic material this original material probably most closely resembles that now found in renazzo and semarkona these two meteorites have almost m shaped n isotope release profiles that can be explained most simply by the super position of two components one with a composition between delta 15n 20 and 40 and a narrow combustion interval the other having a broader release profile and a composition of delta 15n approximately 260 although isotopically more subdued the ci and the three cm chondrites all appear to show vestiges of this m shaped profile how and where the components in the acid insoluble organics formed remains poorly constrained the small variation in nanodiamond to organic c ratio between the chondrite groups limits the local synthesis of organic matter in the various chondrite formation regions to at most 30 the most 15n rich material probably formed in the interstellar medium and the fraction of organic n in renazzo in this material ranges from 40 to 70 the isotopically light component may have formed in the solar system but the limited range in nanodiamond to total organic c ratios in the chondrite groups is consistent with most of the organic material being presolar