grain growth in forsterite nickel mixtures analogues of small parent bodies during early accretion abstract we report an experimental study on the grain growth kinetics and microstructural evolution of olivine metal systems 32 experiments have been performed on four different mixtures of forsterite fo and nickel ni respectively in vol 95 5 80 20 30 70 and 10 90 all experiments were carried out at high temperature 1440 c at oxygen fugacity fo 2 3 log units below the ni nio buffer and for durations between 2 h and 21 days in aggregates containing isolated forsterite grains in a nickel matrix fo ni 10 90 forsterite did not grow and grain growth of nickel was abnormal in all other cases features of normal grain growth were observed and the data were fit to the classic grain growth law d n d 0 n kt for all these aggregates grain growth exponents are in the range 4 0 n nichols and mackwell 1991 for porous olivine aggregates both ni and pores apparently behaving as mobile minor phases extrapolation to time scales relevant to the formation of ordinary chondrite parent bodies shows that mean grain sizes reached fo and ni are of the same order of magnitude 100 m to 1 mm as those observed in several types of meteorites iron rich phases kamacite taenite and or troilite in several h chondrites are shown to present normal grain growth features and ngsd shapes similar to those in our experimental samples where nickel grains are not interconnected i e fo ni 95 5 and 80 20 the grain growth mechanism for the iron rich phases in these meteorites may thus also occur by coalescence rate limited by grain boundary migration of olivine

reduction during metamorphism of four ordinary chondrites abstract three type 3 chondrite finds willaroy suwahib buwah and moorabie and one type 4 find cerro los calvos are ordinary chondrites oc in all respects except redox state a they have oc abundances of refractory lithophiles cerro los calvos data are ambiguous zn and other taxonomic elements b they have oc matrix chondrule abundance ratios and their chondrule sizes are consistent with bulk siderophile indicators of group membership h for willaroy and cerro los calvos l for suwahib buwah and moorabie and c their oxygen isotope compositions are far closer to those of oc than to those of any other chondrite group in each of the four chondrites the range of olivine compositions is relatively narrow fayalite modes and means are distinctly below those of other members of their respective groups having similar or greater degrees of equilibration the most plausible explanation of these properties is that these four oc experienced reduction during metamorphism this is consistent with reverse zoning in olivine from one type ii chondrule in willaroy the reducing agents may have been foreign clasts incorporated during an earlier accretional history alternatively these chondrites could themselves have been foreign materials incorporated into a reduced regolith examples of reducing clasts are the c rich aggregates in sharps examples of reducing host regoliths are the host materials in bencubbin and cumberland falls confirmation of this interpretation will require identification of the reduced foreign material or their relicts in the four reduced oc initial searches have been unsuccessful

an amoeboid olivine inclusion aoi in ck3 nwa 1559 comparison to aois in cv3 allende and the origin of aois in ck and cv chondrites an amoeboid olivine inclusion in ck3 nwa 1559 0 54 1 3 mm consists of a diopside rich interior approximately 35 vol and an olivine rich rim approximately 65 vol it is the first aoi to be described in ck chondrites the apparent paucity of these inclusions is due to extensive parent body recrystallization the aoi interior contains irregular 3 15 m sized al bearing diopside grains approximately 70 vol 2 20 m sized pores approximately 30 vol and traces of approximately 2 m plagioclase grains the 75 160 m thick rim contains 20 130 m sized ferroan olivine grains some with 120o triple junctions a few coarse 25 50 m sized patches of plagioclase with 2 18 m thick diopside rinds occur in several places just beneath the rim the occurrence of olivine rims around aoi 1 and around many aois in cv3 allende suggests that ck and cv aois formed by the acquisition of porous forsteritic rims around fine grained rimless cais that consisted of diopside anorthite melilite and spinel individual aois in carbonaceous chondrites may have formed after transient heating events melted their olivine rims as well as portions of the underlying interiors in aoi 1 coarse plagioclase grains with diopside rinds crystallized immediately below the olivine rim secondary parent body alteration transformed forsterite in the rims of cv and ck aois into more ferroan olivine some of the abundant pores in the interior of aoi 1 may have formed during aqueous alteration after fine grained melilite and anorthite were leached out chondrite groups with large chondrules tend to have large aois aois that formed in dust rich nebular regions where cv and ck chondrites later accreted tend to be larger than aois from less dusty regions

chondrule precursor minerals as anhydrous phases abstract chondrules might be generated from hydrous or anhydrous precursor minerals but vesicles due to dehydration during melting are absent in natural chondrules the occurrence of vesicles in experimental charges made from serpentine rich starting material that was a flash heated and remelted several times b melted for long durations and c melted in a vacuum has been studied in order to test whether vesicles could be eliminated in chondrules made from hydrous precursors high percentages of vesicles in all experiments indicate that chondrules whether melted once multiple times for a brief or extended period at solar nebula or higher pressure were made from anhydrous phases in t r 0 duct i0 n chondrules are millimeter sized igneous textured spheres of mostly silicate composition grossman et al 1988 that were melted in the solar nebula and are found in meteorites the pervasive chondrule forming event has to a large extent obscured the meteor itic record of earlier nebular events such

crystal bearing lunar spherules impact melting of the moon s crust and implications for the origin of meteoritic chondrules crystal bearing lunar spherules clss in lunar breccia 14313 14315 14318 soil 68001 24105 and impact melt rock 62295 samples can be classified into two types feldspathic and olivine rich feldspathic clss contain equant tabular or acicular plagioclase grains set in glass or a pyroxene olivine mesostasis the less common olivine rich clss contain euhedral or skeletal olivine set in glass or possess a barred olivine texture bulk chemical and mineral chemical data strongly suggest that feldspathic clss formed by impact melting of mixtures of ferroan anorthosite and mg suite rocks that compose the feldspathic crust of the moon it is probable that olivine rich clss also formed by impact melting but some appear to have been derived from distinctively magnesian lunar materials atypical of the moon s crust some clss contain reversely zoned relic plagioclase grains that were not entirely melted during cls formation thin 5 m thick rims of troilite or phosphate and chemical gradients in glassy mesostases attributed to metasomatism in a volatile rich na k p rich environment crystal bearing lunar spherules were rimmed and metasomatized prior to brecciation compound cls objects are also present these formed by low velocity collisions in an environment probably an ejecta plume that contained numerous melt droplets factors other than composition were responsible for producing the crystallinity of the clss we agree with previous workers that relatively slow cooling rates and long ballistic travel times were critical features that enabled these impact melt droplets to partially or completely crystallize in free flight moreover incomplete melting of precursor materials formed nucleation sites that aided subsequent crystallization clearly clss do not resemble meteoritic chondrules in all ways the two types of objects had different precursors and did not experience identical rimming processes and vapor fractionation appears to have played a less important role in establishing the compositions of clss than of chondrules however the many detailed similarities between clss and chondrules indicate that it is more difficult to rule out an origin for some chondrules by impact melting than some have previously argued differences between clss chondrules and their host rocks possibly can be reconciled with an impact melt origin for some chondrules when different precursors the higher gravity of the moon compared to chondrite parent bodies and the likely presence of nebular gas during chondrule formation are taken into account

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

fine grained rims in the allan hills 81002 and lewis cliff 90500 cm2 meteorites their origin and modification antarctic cm meteorites allan hills alh 81002 and lewis cliff lew 90500 contain abundant fine grained rims fgrs that surround a variety of coarse grained objects fgrs from both meteorites have similar compositions and petrographic features independent of their enclosed objects the fgrs are chemically homogeneous at the 10 m scale for major and minor elements and at the 25 m scale for trace elements they display accretionary features and contain large amounts of volatiles presumably water they are depleted in ca mn and s but enriched in p all fgrs show a slightly fractionated rare earth element ree pattern with enrichments of gd and yb and depletion of er gd is twice as abundant as er our results indicate that those fgrs are not genetically related to their enclosed cores they were sampled from a reservoir of homogeneously mixed dust prior to accretion to their parent body the rim materials subsequently experienced aqueous alteration under identical conditions based on their mineral textural and especially chemical similarities we conclude that alh 81002 and lew 90500 likely have a similar or identical source

size frequency distributions of chondrules and chondrule fragments in ll3 chondrites implications for parent body fragmentation of chondrules we measured the sizes and textural types of 719 intact chondrules and 1322 chondrule fragments in thin sections of semarkona ll3 0 bishunpur ll3 1 krymka ll3 1 piancaldoli ll3 4 and lewis cliff 88175 ll3 8 the mean apparent diameter of chondrules in these ll3 chondrites is 0 80 units or 570 um much smaller than the previous rough estimate of 900 m chondrule fragments in the five ll3 chondrites have a mean apparent cross section of 1 60 phi units or 330 m the smallest fragments are isolated olivine and pyroxene grains these are probably phenocrysts liberated from disrupted porphyritic chondrules all five ll3 chondrites have fragment chondrule number ratios exceeding unity suggesting that substantial numbers of the chondrules in these rocks were shattered most fragmentation probably occurred on the parent asteroid porphyritic chondrules porphyritic olivine porphyritic pyroxene porphyritic olivine pyroxene are more readily broken than droplet chondrules barred olivine radial pyroxene cryptocrystalline the porphyritic fragment chondrule number ratio 2 0 appreciably exceeds that of droplet textured objects 0 9 intact droplet chondrules have a larger mean size than intact porphyritic chondrules implying that large porphyritic chondrules are fragmented preferentially this is consistent with the relatively low percentage of porphyritic chondrules within the set of the largest chondrules 57 compared to that within the set of the smallest chondrules 81 differences in mean size among chondrule textural types may be due mainly to parent body chondrule fragmentation events and not to chondrule formation processes in the solar nebula

plagioclase rich chondrules in the reduced cv chondrites evidence for complex formation history and genetic links between calcium aluminum rich inclusions and ferromagnesian chondrules plagioclase rich chondrules prcs in the reduced cv chondrites efremovka leoville vigarano and grosvenor mountains gro 94329 consist of magnesian low ca pyroxene al ti cr rich pigeonite and augite forsterite anorthitic plagioclase feni metal sulfide nodules and crystalline mesostasis composed of silica anorthitic plagioclase and al ti cr rich augite the silica grains in the mesostases of the cv prcs are typically replaced by hedenbergitic pyroxenes whereas anorthitic plagioclase is replaced by feldspathoids nepheline and minor sodalite some of the prcs contain regions that are texturally and mineralogically similar to type i chondrules and consist of forsterite low ca pyroxene and abundant feni metal nodules several prcs are surrounded by igneous rims or form independent compound objects twelve prcs contain relic calcium aluminum rich inclusions cais composed of anorthite spinel high ca pyroxene forsterite and al rich low ca pyroxene anorthite of these cais is generally more heavily replaced by feldspathoids than anorthitic plagioclase of the host chondrules this suggests that either the alteration predated formation of the prcs or that anorthite of the relic cais was more susceptible to the alteration than anorthitic plagioclase of the host chondrules these observations and the presence of igneous rims around prcs and independent compound prcs suggest that the cv prcs may have had a complex multistage formation history compared to a more simple formation history of the cr prcs relatively high abundances of moderately volatile elements such as cr mn and si in the prcs suggests that these chondrules could not have been produced by volatilization of ferromagnesian chondrule precursors or by melting of refractory materials only we infer instead that prcs in carbonaceous chondrites formed by melting of the reduced chondrule precursors magnesian olivine and pyroxene feni metal mixed with refractory materials relic cais composed of anorthite spinel high ca pyroxene and forsterite the mineralogical chemical and textural similarities of the prcs in several carbonaceous chondrite groups cv co ch cr and common presence of relic cais in these chondrules suggest that prcs may have formed in the region s intermediate between the regions where cais and ferromagnesian chondrules originated

mineralogy and petrology of chondrules and inclusions in the mokoia cv3 chondrite all objects 100 m in apparent diameter in five polished thin sections of the mokoia cv3 chondrite were studied and classified number and volume percentages and mean apparent size of each type of chondrule and inclusion were determined three major types of olivine chondrules were observed igneous chondrules recrystallized chondrules and chondrules that appear to be accretional aggregates coarse grained cai s have igneous textures and mineral parageneses while fine grained cai s are aggregates containing varying proportions of al rich concentric objects ca rich chaotic material and inclusion matrix chondrules and refractory inclusions in mokoia and allende are broadly similar in texture and mineral chemistry but mokoia refractory inclusions contain phyllosilicates rather than feldspathoids and melilite rich cai s are more abundant in allende we think that most cai s formed during the metamorphism partial melting and incomplete distillation of primitive dust aggregates when they were heated in the solar nebula in the process ca rich melt appears to have been physically separated from al rich residues producing the observed fractionation of ca from al into distinct constituents of cai s some cai s may be aggregates of devitrified amorphous metastable condensates inclusion matrix may have condensed from silicate rich vapors produced during distillation mokoia inclusion matrix contains phyllosilicates that are probably primitive nebular material

relict and other anomalous grains in chondrules implications for chondrule formation we have identified relict olivine and pyroxene grains in chondrules from ordinary and carbonaceous chondrites that probably did not crystallize in situ some of these olivines are clear but others contain fine grained fe ni dusty olivines and resemble previously described occurrences in ordinary chondrites there are also chondrules in which all olivine is dusty we conclude 1 not all relict olivines are dusty 2 not all dusty olivines crystallized outside the chondrule in which they occur and 3 some dusty olivines were produced during chondrule formation by a reduction process that affected the whole chondrule the occurrence of dusty olivines and relict pyroxenes and olivines in chondrules from carbonaceous as well as ordinary chondrites supports the argument that chondrules from all chondrites had similar origins and histories we propose that chondrules and mineral fragments were transported across f o2 gradients in the solar nebula while they were hot or were reheated in an environment different from the one in which they formed partially molten chondrules sometimes incorporated mineral grains or chondrules with different redox states producing compound chondrules and chondrules containing anomalous grains dusty olivines may also have formed when hot chondrules were transported to regions of lower oxygen fugacity

compositions and taxonomy of 15 unusual carbonaceous chondrites abstract we used instrumental neutron activation analysis and petrography to determine bulk and phase compositions and textural characteristics of 15 carbonaceous chondrites of uncertain classification acfer 094 type 3 0 ungrouped cm related belgica 7904 mildly metamorphosed anomalous cm like chondrite possibly a member of a new grouplet that includes wisconsin range wis 91600 dhofar 225 and yamato 86720 dar al gani dag 055 and its paired specimen dag 056 anomalous reduced cv3 like dag 978 type 3 ungrouped dominion range 03238 anomalous magnetite rich co3 1 elephant moraine 90043 anomalous magnetite bearing co3 graves nunataks 98025 type 2 or type 3 ungrouped grosvenor mountains gro 95566 anomalous cm2 with a low degree of aqueous alteration hammadah al hamra hah 073 type 4 ungrouped possibly related to the coolidge loongana c l 001 grouplet lewis cliff lew 85311 anomalous cm2 with a low degree of aqueous alteration northwest africa 1152 anomalous cv3 pecora escarpment pca 91008 anomalous metamorphosed cm queen alexandra range 99038 type 2 ungrouped sahara 00182 type 3 ungrouped possibly related to hah 073 and or to c l 001 and wis 91600 mildly metamorphosed anomalous cm like chondrite possibly a member of a new grouplet that includes belgica 7904 dhofar 225 and y 86720 many of these meteorites show fractionated abundance patterns especially among the volatile elements impact volatilization and dehydration as well as elemental transport caused by terrestrial weathering are probably responsible for most of these compositional anomalies the metamorphosed cm chondrites comprise two distinct clusters on the basis of their 17o values approximately 4 for pca 91008 gro 95566 dag 978 and lew 85311 and approximately 0 for belgica 7904 and wis 91600 these six meteorites must have been derived from different asteroidal regions

petrology trace element abundances and oxygen isotopic compositions of a compound cai chondrule object from allende abstract we report the petrology trace element abundances and oxygen isotopic characteristics of a compound cai chondrule object wi 025 found in the allende cv3 chondrite the wi 025 is an irregularly shaped inclusion consisting of three texturally and chemically distinct portions the interior portion the igneous rim and the intermediate zone located between these two portions the interior portion consists of anorthite spinel olivine and al bearing low ca pyroxene the major element chemistry of the interior portion corresponds to that of al rich chondrules and is of intermediate character between fine grained spinel rich cais and ferromagnesian chondrules the interior portion has abundant 16 o rich spinel 17 o 14 2 to 24 7 and displays a group ii cai like ree composition these observations indicate that the interior portion contains a cai component formed by fractional condensation the major and trace element chemistry of the interior portion indicate that the cai had subsequently assimilated chondrule materials through partial melting the maximum heating temperature of the partial melting is estimated at approximately 1400 c similar to the maximum heating temperature of type b cais the oxygen isotopic compositions of the olivine and low ca pyroxene 17 o 6 3 in the interior portion indicate that the partial melting and chondrule assimilation took place under a moderately 16 o poor nebular gas the igneous rim is texturally and chemically similar to ferromagnesian chondrules and entirely surrounds the interior portion the oxygen isotopic compositions of the olivine and low ca pyroxene in the igneous rim are indistinguishable from those of the interior olivine and al bearing low ca pyroxenes these observations indicate that a chondrule material which was melted in the same nebular gas as the interior portion was accreted to the interior portion the intermediate zone represents a reaction zone accompanying the igneous rim formation the formation history of wi 025 can be summarized by the following processes 1 original cai formation 2 partial melting and chondrule assimilation 3 igneous rim formation and 4 secondary alteration on the parent body

chondrules in the lew85332 ungrouped carbonaceous chondrite fractionation processes in the solar nebula abstract we studied 14 chondrules separated from lew85332 an ungrouped type 3 carbonaceous chondrite related to cr chondrites 23 elements were determined by neutron activation and the chondrules were characterized petrographically oxygen isotopic compositions were determined by r n clayton and t k mayeda for seven chondrules chondrule abundance ratios tend to form one of two distinct patterns in low feo chondrules refractory lithophile patterns are flat i e unfractionated siderophile abundances are high and show a small decrease with increasing volatility although high feo chondrules also have flat refractory lithophile abundance patterns siderophile abundances are highly fractionated refractory ir is very low and fe is very high relative to other siderophiles we suggest that the low feo chondrules in lew85332 formed early in nebular history when metal was intimately mixed with silicates in the chondrule precursors and that the viscosity of the liquid solid mix was too high to permit expulsion of the metal by centrifugal action their porphyritic structures are consistent with incomplete melting which would result in relatively high viscosities when the high feo chondrules formed somewhat later much of the fe was oxidized and the melting of precursors was more extensive feo and other oxidized siderophiles were retained in the silicate liquid and metal was lost possibly expelled from low viscosity chondrule melts the o isotopic compositions of the chondrules form a linear array of slope 0 93 0 05 on a three isotope diagram parallel to the carbonaceous chondrite anhydrous minerals ccam line and a cr chondrule array but offset from the latter by 1 in 18 o some or all of this offset may reflect incorporation of o from antarctic water during weathering chondrule 17 o values correlate positively with feo possibly indicating that the 17 o of the nebular gas composition increased with time the chemical and o isotopic data suggest a temporal sequence extending from early low feo to late high feo chondrules

dark inclusions in allende leoville and vigarano evidence for nebular oxidation of cv3 constituents dark lithic inclusions are known to occur in several cv3 chondrites we report petrologic chemical and oxygen isotopic data on examples from allende leoville and vigarano the allende inclusions comprise a petrographic sequence ranging from a type which contains chondrules and refractory inclusions and resembles cv3 or co3 chondrites to a type which contains porous aggregates of iron rich olivine oxygen isotopic compositions correlate with the sequence chondrule rich inclusions have compositions similar to the host meteorite bulk values whereas olivine aggregate rich inclusions have more 16o depleted compositions chemical compositions on the other hand do not correlate with the petrographic sequence the dark inclusions are all systematically enriched in iron and depleted in potassium and sodium relative to their host meteorites the inclusions appear to be fragments of cv3 parent bodies which were processed to different degrees prior to their incorporation as clasts into allende leoville and vigarano the processing homogenized olivine compositions presumably through heating and also involved oxygen exchange with 16o poorer surroundings either parent body metamorphism or nebular heating might have produced the petrographic and isotopic sequences however the most 16o depleted inclusions also have layered silicate rims surrounding them which are better attributed to gas solid reactions than parent body processes in particular andradite is abundant in the rims which implies that the rims grew under conditions significantly more oxidizing than those likely to have occurred on a cv3 parent body at least part of the processing therefore appears to have taken place prior to final accumulation of the material when the fragments were dispersed in the nebula the evidence for coupled oxidation and 16o depletion in the nebula suggests that other features of the cv3 group such as the oxidized and reduced subgroups ferrous rims on forsteritic olivines and coarse grained rims on chondrules may have been established by similar gas solid reactions prior to the final assembly of the meteorites

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

collisional facilitation of aqueous alteration of cm and cv carbonaceous chondrites abstract cm chondrites exhibit a strong correlation between the degree of alteration and the extent of particle alignment i e the strength of the petrofabric it seems likely that the s1 shock stage of essentially every cm and the high matrix abundance 70 vol of these samples ensured that the shock waves that produced cm petrofabrics by collapsing matrix pores and squeezing chondrules into pore spaces were significantly attenuated and were too weak to damage olivine crystal lattices random collisions on the cm body produced petrofabrics and created fractures in the target rocks subsequent impact mobilization of water caused hydrated phases to form preferentially in the more fractured regions those with the strongest petrofabrics the less deformed less fractured cm regions experienced lower degrees of aqueous alteration many cv3 chondrites also have petrofabrics roughly half are from the oxidized bali like subgroup cv3 oxb roughly half are from the reduced subgroup cv3 r and none is from the oxidized allende like subgroup cv3 oxa which is less altered than cv3 oxb nearly all cvs with petrofabrics are s3 s4 and nearly all cvs that lack petrofabrics are s1 oxidized cvs have much higher porosities typically 20 28 than reduced cvs 0 6 8 facilitating more extensive aqueous alteration the cv3 r chondrites formed from low porosity material that inhibited oxidation during alteration the oxidized cv subgroups formed from higher porosity materials the cv3 oxb samples were shocked became extensively fractured and developed petrofabrics the cv3 oxa samples were not shocked and never developed petrofabrics when water was mobilized both sets of porous cv chondrites became oxidized the more fractured cv3 oxb subgroup was more severely altered

coarse grained chondrule rims in type 3 chondrites abstract relatively coarse grained rims occur around all types of chondrules in type 3 carbonaceous and ordinary chondrites those in h l ll3 chondrites are composed primarily of olivine and low ca pyroxene those in cv3 chondrites contain much less low ca pyroxene average grain sizes range from 4 m in h l ll3 chondrites to 10 m in cv3 chondrites such rims surround 50 10 and 1 of chondrules in cv3 h l ll3 and co3 chondrites respectively but are rare 1 around cv3 ca al rich inclusions rim thicknesses average 150 m in h l ll3 chondrites and 400 m in cv3 chondrites the rims in h l ll3 chondrites are composed of material very similar to that which comprises darkzoned chondrules and recrysiallized matrix dark zoned chondrules and coarse grained rims probably formed in the solar nebula from clumps of opaque matrix material heated to sub solidus to sub liquidus temperatures during chondrule formation mechanisms capable of completely melting some material while only sintering other material require steep thermal gradients suitable processes are lightning reconnecting magnetic field lines and possibly aerodynamic drag heating cv chondrites may have formed in a region where the chondrule formation mechanism was less efficient probably at greater solar distances than the ordinary chondrites the lesser efficiency of heating could be responsible for the greater abundance of coarse grained rims around cv chondrules alternatively cv chondrules may have suffered fewer particle collisions prior to agglomeration

chondrules in the murray cm2 meteorite and compositional differences between cm co and ordinary chondrite chondrules abstract bulk compositions were determined by broad beam electron microprobe analysis for thirteen of the least aqueously altered chondrules in murray cm2 these and literature data reveal compositional differences between cm co and ordinary chondrite oc chondrules 1 a co chondrules are richer in refractory lithophiles and poorer in cr mn and volatile lithophiles than oc chondrules much lower refractory lithophile abundances in cm chondrules resulted from aqueous alteration 2 b in cm co chondrites abundances of refractory lithophiles are higher in nonporphyritic than porphyritic chondrules whereas in h l ll3 chondrites the converse is true 3 c cr ranges are greater and cr and mn correlate more strongly in chondrules in cm co than in h l ll3 chondrites we find evidence for two important lithophile precursor components of cm co chondrite chondrules 1 1 pyroxene and refractory rich feo poor 2 2 olivine rich refractory and feo poor the occurrence of a few feo rich chondrules attests to a third component similar to matrix olivine and feo rich refractories not characterized the first two components differ from those inferred for oc chondrules consistent with formation at different locations the pyroxene and refractory rich feo poor lithophile precursor component probably formed by an incomplete evaporation of presolar silicates that brought these materials into the enstatite stability field

accretionary rims on inclusions in the allende meteorite abstract many inclusions in allende particularly those with irregular shapes are surrounded by a sequence of thin layers which differ from one another in texture mineralogy and mineral chemistry the layer underlying all others contains either ia pyroxene needles olivine clumps of hedenbergite and andradite ib olivine doughnuts or ic rectangular olivine crystals the next layer outward ii contains tiny

grain size distribution of the matrix in the allende chondrite abstract hrtem atem and sem studies of the allende chondrite reveal that the matrix is composed of very fine grained iron rich olivine ca poor and iron rich clinopyroxene iron rich spinel and ni bearing troilite there are two types of very fine grained aggregates one is not sintered and the other is slightly sintered most 1 10 m olivine aggregates show the sintered microstructure but ultrafine grained aggregates 1 10 nm display little evidence of sintering this means that coarse grained olivine aggregates experienced a heating event but ultrafine grained aggregates underwent no heating event the size distribution of matrix grains were measured by sem and tem at magnifications of 570 000 to 2000 corresponding to grain sizes ranging from 1 nm to 10 m the frequency distribution shows a log normal pattern having a peak at 5 nm in the range from 1 to 10 nm and it has a long term tail with power law this distribution means that the fine grained matrix seems to be formed at conditions far from equilibrium in the protosolar cloud

matrix material in type 3 chondrites occurrence heterogeneity and relationship with chondrules abstract matrix material in type 3 chondrites forms rims on chondrules metal sulfide aggregates ca al rich inclusions and chondritic clasts it also forms lumps up to a millimeter in size which may contain coarser silicates chondrules of all types were found with internal matrix lumps that appear to have entered the chondrules before the latter had crystallized mean concentrations of mg na al and ca in matrix occurrences show up to fivefold variations in a single chondrite variations between mean matrix compositions of individual type 3 ordinary chondrites are almost as large and partly reflect systematic differences between h l and ll matrices such variations are probably a result of nebular separation of feldspathic material and ferromagnesian silicates compositions of chondrules and their matrix rims are normally unrelated although rim compositions are correlated with those of matrix lumps inside chondrules a single chondrule was found with a composition nearly identical to that of its internal matrix lump suggesting that some chondrules may have formed from matrix material matrix lumps are as heterogeneous as chondrules but mean chondrule and matrix compositions differ even allowing for possible loss of metallic fe ni during chondrule formation since bulk compositions of matrix lumps and rims have probably not changed significantly since their formation except for fe mg exchange our matrix samples cannot represent typical chondrule precursor materials

quantified whole section trace element mapping of carbonaceous chondrites by synchrotron x ray fluorescence microscopy 1 cv meteorites abstract we present the application of a new synchrotron based technique for rapid mapping of trace element distributions across large areas of the cv3 meteorites allende and vigarano this technique utilizes the australian synchrotron x ray fluorescence microscopy xfm beam line with its custom designed and built x ray detector array called maia xfm with maia allows data to be collected using a 2 m spot size at very low dwell times 0 1 0 5 ms resulting in maps of entire thin sections in 5 h maia is an energy dispersive detector system with a large collection solid angle which allows full spectral acquisition and high sensitivity hence there is no need to constrain the elements of interest a priori we collected whole section maps 2 cm 1 cm from 3 thick sections of allende and a single map 2 cm 1 5 cm from a thick section of vigarano our experimental conditions provide data for elements with 20 z 40 k shell ca through zr and the l emissions of os ir pt au and pb we illustrate the unique capabilities of this technique by presenting observations across myriad length scales from the centimeter scale down to the detection of sub micrometer particles within these objects our initial results show the potential of this technique to help decipher spatial and textural variations in trace element chemistry between cais chondrules matrix and other chondritic components we also illustrate how these datasets can be applied to understanding both nebular and parent body processes within meteorites

forsterite rich accretionary rims around calcium aluminum rich inclusions from the reduced cv3 chondrite efremovka it was suggested that multilayered accretionary rims composed of ferrous olivine andradite wollastonite salite hedenbergitic pyroxenes nepheline and ni rich sulfides around allende calcium aluminum rich inclusions cais are aggregates of gas solid condensates which reflect significant fluctuations in physico chemical conditions in the slowly cooling solar nebula and grain gas separation processes in order to test this model we studied the mineralogy of accretionary rims around one type a cai e104 and one type b cai e48 from the reduced cv3 chondrite efremovka which is less altered than allende in contrast to the allende accretionary rims those in efremovka consist of coarse grained 20 40 mum anhedral forsterite fa 1 8 fe ni metal nodules amoeboid olivine aggregates aoas and fine grained cais composed of al diopside anorthite and spinel forsterite although the fine grained cais aoas and host cais are virtually unaltered a hibonite spinel perovskite cai in the e48 accretionary rim experienced extensive alteration which resulted in the formation of fe rich zn bearing spinel and a ca al si hydrous mineral forsterites in the accretionary rims typically show an aggregational nature and consist of small olivine grains with numerous pores and tiny inclusions of al rich minerals no evidence for the replacement of forsterite by enstatite was found no chondrule fragments were identified in the accretionary rims

fine grained aggregates in l3 chondrites abstract the textures and chemical compositions of the constituent minerals of the fine grained aggregates fga s of l3 chondrites were studied by the backscattered electron image technique electron probe microanalysis and transmission electron microscopy plagioclase and glass in the interstices between fine grains of olivine and pyroxene indicate that the fga s once partly melted compositional zoning and decomposition texture of pyroxenes are similar to those observed in chondrules indicating a common cooling history of the fga s and chondrules therefore the mechanism that caused melting of the fga s is considered to be the same as for chondrules bulk compositions of the fga s are within the range of those of chondrules so some chondrules probably were produced by complete melting of the same precursor materials as those of the fga s the precursor materials must have included fine olivine and other grains that probably are condensates

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

origin of lamprophyres by the mixing of basic and alkaline melts in magma chamber in beiya area western yunnan china abstract lamprophyres consisting mainly of diopside phlogopite and k feldspar formed in the early tertiary around 60 ma in the beiya area and are characterized by low sio 2 46 50 wt rb 31 45 ppm and sr 225 262 ppm high al 2 o 3 11 2 13 1 wt cao 8 0 8 7 wt mgo 11 5 12 1 wt k 2 o 4 9 5 5 wt tio 2 2 9 3 3 wt and ree 174 177 ppm and compatible elements e g sc cr and ni and hsf elements e g th u zr nb ta ti and y and low 143 nd 144 nd 0 512372 0 512536 middle 87 sr 86 sr 0 707322 0 707395 middle 206 pb 204 pb 18 50 18 59 207 pb 204 pb 15 60 15 65 and 208 pb 204 pb 38 75 38 8 these rocks developed peculiar quartz megacrysts with poly layer reaction zones melt inclusions and partial melted k feldspar and plagioclase inclusions and plastic shapes important features of these rocks include 1 hybrid composition of elements 2 abrupt increase of sio 2 content of the melt recorded by zoned diopside 3 development of sanidine and aegirine augite reaction zones 4 alkaline melt and partial melted k feldspar and plagioclase inclusions 5 deformed quartz inclusions associated with quartz megacrysts 6 the presence of quartz megacrysts in plastic shape with their parent melts 7 the occurrence of olivine high mgo ilmenite and spinel inclusions within earlier formed diopside phlogopite and magnetite median 87 sr 86 sr values between tertiary alkaline porphyries in the beiya area and the western yunnan and tertiary basalt in the western yunnan indicate that the beiya lamprophyre melts were derivative and resulted from the mixing between basic melts that were related to the partial melting of phenocrysts of spinel iherzolite from a mantle source the alkaline melts originated from partial melting along the jinshajiang subduction ductile shear zone at the contact between the buried palaeo tethyan oceanic lithosphere and the upper mantle lithosphere the alkaline melts are composed of 65 sanidine or 70 ab 28 an 2 and 35 sio 2 the melt mixing occurred in magma chambers in the middle shallow crust at 8 10 km before the derivative lamprophyre melts intruded into the shallow cover in beiya area this mixing of basic and alkaline melts might represent a general process for the formation of lamprophyre in the western yunnan

non spherical lobate chondrules in co3 0 y 81020 general implications for the formation of low feo porphyritic chondrules in co chondrites non spherical chondrules arbitrarily defined as having aspect ratios 1 20 in co3 0 chondrites comprise multi lobate distended and highly irregular objects with rounded margins they constitute 70 of the type i low feo porphyritic chondrules in y 81020 75 of such chondrules in alha77307 and 60 of those in colony although the proportion of non spherical type i chondrules in ll3 0 semarkona is comparable 60 multi lobate oc porphyritic chondrules with lobe heights equivalent to a significant fraction of the mean chondrule diameter are rare if the non spherical type i chondrules in co chondrites had formed from totally molten droplets calculations indicate that they would have collapsed into spheres within 10 3 s too little time for their 20 m size olivine phenocrysts to have grown from the melt these olivine grains must therefore be relicts from an earlier chondrule generation the final heating episode experienced by the non spherical chondrules involved only minor amounts of melting and crystallization the immediate precursors of the individual non spherical chondrules may have been irregularly shaped chondrule fragments whose fracture surfaces were rounded during melting because non spherical chondrules and circular chondrules form a continuum in shape and have similar grain sizes mineral and mesostasis compositions and modal abundances of non opaque phases they must have formed by related processes we conclude that a large majority of low feo chondrules in co3 chondrites experienced a late low degree melting event previous studies have shown that essentially all type ii high feo porphyritic chondrules in y 81020 formed by repeated episodes of low degree melting it thus appears that the type i and type ii porphyritic chondrules in y 81020 and presumably all co3 chondrites experienced analogous formation histories because these two types constitute 95 of all co chondrules it is clear that chondrule recycling was the rule in the co chondrule formation region and that most melting events produced only low degrees of melting the rarity of significantly non spherical multi lobate chondrules in semarkona may reflect more intense heating of chondrule precursors in the ordinary chondrite region of the solar nebula

physical properties of chondrules in different chondrite groups implications for multiple melting events in dusty environments chondrite groups cv ck cr with large average chondrule sizes have low proportions of rp plus c chondrules high proportions of enveloping compound chondrules high proportions of chondrules with thick igneous rims and relatively low proportions of type i chondrules containing sulfide in contrast chondrite groups cm co oc r eh el with smaller average chondrule sizes have the opposite properties equilibrated ck chondrites have plagioclase with relatively low na equilibrated oc r eh and el chondrites have more sodic plagioclase enveloping compound chondrules and chondrules with igneous rims formed during a remelting event after the primary chondrule was incorporated into a dustball repeated episodes of remelting after chondrules were surrounded by dust would tend to produce large chondrules rp and c chondrules formed by complete melting of their precursor assemblages remelting of rp and c chondrules surrounded by dust would tend to produce porphyritic chondrules as small dust particles mixed with the melt providing nuclei for crystallizing phenocrysts this process would tend to diminish the numbers of rp and c chondrules correlations among these chondrule physical properties suggest that chondrite groups with large chondrules were typically surrounded by thick dust rich mantles that formed in locally dusty nebular environments chondrules that were surrounded by thick dust mantles tended to cool more slowly because heat could not quickly radiate away slow cooling led to enhanced migration of sulfide to chondrule surfaces and more extensive sulfide evaporation these chondrules also lost na the plagioclase that formed from equilibrated ck chondrites was thus depleted in na

accretion dispersal and reaccumulation of the bishunpur ll3 1 brecciated chondrite evidence from troilite silicate metal inclusions and chondrule rims abstract a set of troilite silicate metal tsm inclusions and chondrule rims in the bishunpur ll3 1 chondrite provide information regarding impact brecciation of small bodies in the early solar system the tsm inclusions and chondrule rims consist of numerous angular to subrounded silicate grains that are individually enclosed by fine networks of troilite feni metal also occurs in the troilite matrix the silicates include olivine fo55 98 low ca pyroxene en78 98 and high ca pyroxene en48 68wo11 32 al and si rich glass coexists with the silicates relatively coarse silicate grains are apparently fragments of chondrules typical of petrologic type 3 chondrites troilite fills all available cracks and pores in the silicate grains some of the tsm inclusions and rims are themselves surrounded by fine grained silicate rich rims fgr the tsm inclusions and rims texturally resemble the troilite rich regions in the smyer h chondrite breccia they probably formed by shock induced mobilization of troilite during an impact event on a primitive asteroidal body because silicates in the tsm inclusions and rims have highly unequilibrated compositions their precursor was presumably type 3 chondritic material like bishunpur itself the tsm inclusions and the chondrules with the tsm rims were fragmented and dispersed after the impact induced compaction then reaccreted onto the bishunpur parent body fgr probably formed around the tsm inclusions and rims as well as around some chondrules during the reaccumulation process components of most type 2 and 3 chondrites probably experienced similar processing i e dispersal of unconsolidated materials and subsequent reaccumulation

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

earliest rock fabric formed in the solar system preserved in a chondrule rim rock fabrics record the formation compaction and deformation history of that rock high resolution mapping of tiny grains in the allende cv meteorite reveals preservation of a spherical fabric that may have formed in the solar nebula and could be the oldest rock fabric to have formed in the solar system

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

chondrules matrix and coarse grained chondrule rims in the allende meteorite origin interrelationships and possible precursor components bulk compositions of 20 chondrules 13 coarse grained chondrule rims and two composite samples of matrix material from cv3 allende were determined by instrumental neutron activation analysis three rare nonporphyritic cv chondrules from allende leoville and vigarano were analyzed by broad beam electron microprobe analysis chondrule precursor components deduced from chondrule compositions are characterized by 1 refractory and semi refractory lithophiles with low feo 2 common siderophiles and chalcophiles 3 common to slightly volatile lithophiles si cr mn and modal pyroxene with moderately high feo feo mgo 4 moderately volatile siderophiles and 5 alkalies these precursor components can be explained by plausible processes occurring in the solar nebula the precursor components of coarsegrained rims are apparently the same as those of chondrules these components differ from those inferred previously for oc eh or cm co chondrules in general the compositions of coarse grained rims are more similar to the mean chondrule composition than to those of the chondrules they enclose rim siderophile contents are generally 2 5x greater than those in the chondrules and 0 5 to 2x those in bulk allende rims as a group are more homogeneous than chondrules suggesting that rims formed from finer grained precursors several chondrules and rims have fractionated rare earth patterns and may have been affected by metamorphism the enclosure of some coarse grained rims by fine grained matrix like rims that are almost certainly of nebular origin indicates that coarse grained rims were also formed in the nebula two matrix samples are similar in composition to some coarse grained rims suggesting that matrix was derived from similar compositional reservoirs of nebular dust chondrules with coarse grained rims were reheated in space following the accretion of dusty coatings this restricts plausible chondrule forming mechanisms to those that allow multiple nebular heating events

petrography and classification of ca al rich and olivine rich inclusions in the allende cv3 chondrite a detailed systematic petrographic survey of all 189 ca al rich and olivine rich inclusions larger than 0 2 mm in diameter in 17 thin sections of allende was performed by optical and scanning electron microscopy most of these inclusions are aggregates containing varying proportions of three distinct constituents termed concentric objects chaotic material and inclusion matrix a new classification system for allende inclusions is proposed olivine rich inclusions occur in two textural varieties unrimmed olivine aggregates type 1a inclusions and rimmed olivine aggregates type 1b inclusions we classify ca al rich inclusions cai s on the basis of the size and abundance of their constituent concentric objects rather than their grain size into unrimmed complex cai s type 2 inclusions rimmed complex cai s type 3 inclusions and simple cai s type 4 inclusions several of the inclusion classes grade into each other some fundamental relationships among various types of allende inclusions are discussed we suggest that the term coarse grained even if used only in a relative sense is too restrictive for some members of one class of inclusion simple cai s and is inappropriate for most members of another class melilite rich complex cai s

oxygen isotope studies of ordinary chondrites several stages in the evolution of ordinary chondritic meteorites are recorded in the oxygen isotopic composition of the meteorites and their separable components chondrules fragments clasts and matrix the whole rock isotopic compositions reflect the iron group of the meteorite h l or ll isotopic uniformity of h3 to h6 and l3 to l6 are consistent with closed system metamorphism within each parent body ll3 chondrites differ slightly from ll4 to ll6 implying a small degree of opensystem aqueous alteration and carbon reduction on the scale of individual chondrules the meteorites are isotopically heterogeneous allowing recognition of the solar nebular processes of chondrule formation chondrules for all classes of ordinary chondrites are derived from a common population which was separate from the population of chondrules in carbonaceous or enstatite chondrites chondrules define an isotopic mixing line dominated by exchange between 16o rich and 16o poor reservoirs the oxygen isotopic compositions of chondrites serve as fingerprints for identification of genetic association with other meteorite types achondrites and iron and for recognition of source materials in meteoritic breccias

chemical and oxygen isotopic compositions of accretionary rim and matrix olivine in cv chondrites constraints on the evolution of nebular dust abstract a correlation of petrography mineral chemistry and in situ oxygen isotopic compositions of fine grained olivine from the matrix and of fine and coarse grained olivine from accretionary rims around ca al rich inclusions cais and chondrules in cv chondrites is used here to constrain the processes that occurred in the solar nebula and on the cv parent asteroid the accretionary rims around leoville vigarano and allende cais exhibit a layered structure the inner layer consists of coarse grained forsteritic and 16o rich olivine fa1 40 and 17o 24 to 5 the higher values are always found in the outer part of the layer and only in the most porous meteorites whereas the middle and the outer layers contain finer grained olivines that are more fayalitic and 16o depleted fa15 50 and 17o 18 to 1 the cv matrices and accretionary rims around chondrules have olivine grains of textures chemical and isotopic compositions similar to those in the outer layers of accretionary rims around cais there is a correlation between local sample porosity and olivine chemical and isotopic compositions the more compact regions the inner accretionary rim layer have the most mgo and 16o rich compositions whereas the more porous regions outer rim layers around cais accretionary rims around chondrules and matrices have the most mgo and 16o poor compositions in addition there is a negative correlation of olivine grain size with fayalite contents and 17o values however not all fine grained olivines are feo rich and 16o poor some small 20 olivine grains in the outer layers of the cai accretionary rims and in the matrix show significant enrichments in 16o 17o 20 to 10 we infer that the inner layer of the accretionary rims around cais and at least some olivine grains in the finer portions of accretionary rims and cv matrices formed in an 16o rich gaseous reservoir probably in the cai forming region grains in the outer layers of the cai accretionary rims and in the rims around chondrules as well as matrix may have also originated as 16o rich olivine however these olivines must have exchanged o isotopes to variable extents in the presence of an 16o poor reservoir possibly the nebular gas in the chondrule forming region s and or fluids in the parent body the observed trend in isotopic compositions may arise from mixtures of 16o rich forsterites with grain overgrowths or newly formed grains of 16o poor fayalitic olivines formed during parent body metamorphism however the observed correlations of chemical and isotopic compositions of olivine with grain size and local porosity of the host meteorite suggest that olivine accreted as a single population of 16o rich forsterite and subsequently exchanged fe mg and o isotopes in situ in the presence of aqueous solutions i e fluid assisted thermal metamorphism

phyllosilicate rich chondrule rims in the vigarano cv3 chondrite evidence for parent body processes abstract a petrographic and scanning electron microscopic study of the vigarano cv3 carbonaceous chondrite reveals that a small proportion 5 of the fine grained rims surrounding chondrules consist mainly of phyllosilicates saponite and serpentine and minor but variable amounts of ferrihydrite most of the rims consist mainly of fe rich olivine the phyllosilicate rich rims and the chondrules that they enclose show abundant evidence of aqueous alteration low ca pyroxene and olivine at chondrule margins have been partially replaced by phyllosilicate rich materials producing embayments on chondrule surfaces fe ni metal fe sulfide and magnetite in the chondrules have also been partially replaced by fe hydroxide due to preferential replacement of low ca pyroxene and olivine sulfide magnetite and fe hydroxide remain exposed at chondrule margins we discovered a clast 0 7 0 9 mm in size containing several chondrules embedded in a phyllosilicate rich matrix that is almost identical in mineralogy texture and composition to the rims we also found numerous small clasts 20 400 m in size consisting of a similar phyllosilicate rich material in the host vigarano meteorite many of the clasts include fragments of chondrules amoeboid olivine aggregates and ca al rich inclusions these clasts also show abundant evidence of aqueous alteration which is similar to that observed in the rims and their host chondrules from these observations we conclude that the chondrule rim assemblages and the clasts are a part of the same precursor chondrite which was fragmented during brecciation on the meteorite parent body we interpret that a portion or portions of the vigarano parent body was aqueously altered and the interchondrule matrix was largely converted to phyllosilicates and ferrihydrite this hydrated portion was later fragmented and brecciated by impacts as fragmentation occurred preferentially along the phyllosilicate rich porous matrix most of the ejected clasts consisted of a chondrule rimmed by remnant matrix the clasts were rounded by abrasion during brecciation and transportation and finally mixed into an anhydrous portion in the regolith from which the vigarano meteorite was derived some of the phyllosilicate rich rims show evidence for partial dehydration during heating before final incorporation into the regolith these results taken together suggest that the vigarano parent body was spatially heterogeneous in degree of aqueous alteration and thermal metamorphism and the host vigarano meteorite is a breccia consisting of numerous clasts from many different locations

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

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

chondrules as products of dust collisions with totally molten droplets within a dust rich nebular environment an experimental investigation abstract chondrules are usually interpreted as the products of incomplete melting of mineral aggregates in the solar nebula and have textures controlled by the number of residual nuclei present after melting if barred olivine bo chondrules formed by nearly total melting at their respective liquidi i e over a wide temperature range it is surprising that there are so few totally glassy chondrules the occurrence of fine grained accretionary rims on chondrules suggests mineral dust in the chondrule forming environment which might have collided with totally molten droplets to produce chondrule textures we have therefore conducted experiments in which mineral dusts encounter molten droplets during their cooling at 500 c h and cause nucleation our experiments reproduce the majority of common chondrule textures the production of textures in our experiments is a function of the temperature at which dust is encountered the number of dust grains encountered and to a lesser extent the mineralogy of the encountered mineral grains crystal growth rates increase with lower dust encounter temperatures giving a textural range with increasingly skeletal or elongated crystals for lower temperature encounters we have produced some less commonly discussed types of chondrule textures e g barred olivine porphyritic olivine pyroxene bo pop by dust seeding that have not been reproduced by the incomplete melting of starting materials the reproduction of bo pop and excentroradial textures by dust collisions and the scarcity of natural totally glassy chondrules suggest that formation by seeding of total melts was common for chondrules with the lowest liquidus temperatures e g feo rich chondrules from these seeding experiments we suggest that the maximum melting temperature chondrules experienced is limited only to the temperature at which evaporation of chondrule liquid occurs however we have reproduced the very fine grained microporphyritic textures characteristic of type ia chondrules only by incomplete melting such chondrules could not have reached average internal temperatures above their liquidus temperatures the conclusion that at least some chondrules formed from total melts that collided with mineral dust during cooling indicates that chondrule formation occurred within a region of the nebula rich in mineral dust

chemical structure of migrabitumens from silurian crinoidea prague basin barrandian bohemia abstract the chemical structure of migrabitumens epi impsonite glance pitch grahamite ozocerite and weathered impsonite from the crinoidea genus scyphocrinites from the silurian of the prague basin barrandian bohemia has been studied by diffuse reflectance infrared fourier transform spectroscopy and solid state nuclear magnetic resonance oxidation of the samples in air at 150 c has been carried out in order to model structural changes of migrabitumens during weather we suggest that the structural differences h c atomic ratios content of oxygen groups aromaticities between the migrabitumens of the same parent material are the consequence of gradually decreasing temperatures during their evolution and of oxidation caused by weathering

origin of metallic fe ni in renazzo and related chondrites abstract the anomalous positive co ni correlation among metal grains from the renazzo and al rais chondrites reported in previous studies has two components 1 1 a chondrule trend that extends up to 120 145 mg g ni probably reflects the mixing of fe rich and fe poor nebular metal and 2 2 a weak extrachondrule trend that spans a ni range from 40 70 mg g reflects fe introduction during mild metamorphism to assess the formation of this metal we determined ni and co zoning profiles in metallic fe ni from different petrographic sites chondrule interiors chondrule margins chondrule rims and matrix in renazzo al rais and the related chondrite macalpine hills 87320 metal from chondrule interiors shows flat ni and co concentrations and profiles moderately large grain to grain compositional variations even within chondrules and generally high ni and co nickel concentrations extend above the kamacite stability limit etching such martensite shows high ni domains in some cases but observed ni concentrations do not exceed 190 mg g metal from chondrule margins adjacent to matrix shows convex inverted u shaped ni and co zoning profiles the highest ni and co concentrations are at grain centers although the mean central ni and co concentrations in margin grains are much lower than those in metal from chondrule interiors about half of the matrix metal shows flat co and ni profiles like those from chondrule interiors the remainder are convex the differences in mean co and ni contents between chondrules and extrachondrule materials may reflect differential sampling of nebular metal grains having compositions that varied with particle size we interpret the low co and ni contents at the edges of grains in chondrule margins to reflect dilution by fe produced by feo reduction the reduction seems not to have occurred in the nebula but rather during a brief period of parent body metamorphism reduction of fine grained feo produced metallic fe that plated onto nearby metal grains although diffusive exchange between pentlandite and metal could produce the observed ni gradient it is doubtful that it could produce the similar gradient of co metal from chondrule interiors was inaccessible during the reduction event and retained the flat profiles established during chondrule formation

trace element geochemistry of ordinary chondrite chondrules the type i type ii chondrule dichotomy we report trace element concentrations of silicate phases in chondrules from ll3 ordinary chondrites bishunpur and semarkona results are similar to previously reported data for carbonaceous chondrites with rare earth element ree concentrations increasing in the sequence olivine 10 k h than type i chondrules appreciable na concentrations 3 221 ppm are measured in olivine from both chondrule types type ii chondrules seem to have behaved as closed systems which may require chondrule formation in the vicinity of protoplanets or planetesimals at any rate higher solid concentrations in type ii chondrule forming regions may explain the higher oxygen fugacities they record compared to type i chondrules type i and type ii chondrules formed in different environments and the correlation between high solid concentrations and or oxygen fugacities with rapid cooling rates is a key constraint that chondrule formation models must account for

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

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

chondrules in ck carbonaceous chondrites and thermal history of the cv ck parent body ck chondrites are the only group of carbonaceous chondrites with petrologic types ranging from 3 to 6 it is commonly reported than 15 vol of ck4 6 samples are composed of chondrules the modal abundance of chondrules estimated here for 18 ck3 6 including 5 ck3s ranges from zero totally recrystallized to 50 5 although almost all chemically re equilibrated with the host matrix we recognized in ck3s and tanezrouft tnz 057 ck4 up to 85 of chondrules as former type i chondrules mean diameters of chondrules range from 0 22 to 1 05 mm for karoonda ck4 and tnz 057 ck4 respectively up to 60 of chondrules in ck3 4 are surrounded by igneous rims from 20 m to 2 mm width zoned olivines were found in unequilibrated chondrules from dag 431 ck3 an nwa 4724 ck3 8 nwa 4423 ck3 9 and tnz 057 ck4 we modeled fe mg interdiffusion profiles measured in zoned olivines to evaluate the peak metamorphic temperatures and time scales of the ck parent body metamorphism and proposed a two stage diffusion process in order to account for the position of inflection points situated within chondrules time scales inferred from fe mg interdiffusion in olivine from unequilibrated chondrules are on the order of tens to a hundred of thousand years from 50 to 70 000 years for peak metamorphic temperatures of 1140 and 920 k respectively these durations are longer than what is commonly accepted for shock metamorphism and shorter than what is required for nuclide decay using the concept of a continuous cv ck metamorphic series which is reinforced by this study we estimated peak metamorphic temperatures 850 k for cv 850 920 k for ck3 and 920 1140 k for ck4 6 chondrites considering a duration of 70 000 years

petrology and mineralogy of the ningqiang carbonaceous chondrite we report detailed chemical petrological and mineralogical studies on the ningqiang carbonaceous chondrite ningqiang is a unique ungrouped type 3 carbonaceous chondrite its bulk composition is similar to that of cv and ck chondrites but refractory lithophile elements 1 01 x ci are distinctly depleted relative to cv 1 29 x ci and ck 1 20 x ci chondrites ningqiang consists of 47 5 vol chondrules 2 0 vol ca al rich inclusions cals 4 5 vol amoeboid olivine aggregates aoas and 46 0 vol matrix most chondrules 95 in ningqiang are mg rich the abundances of fe rich and al rich chondrules are very low al rich chondrules arcs in ningqiang are composed mainly of olivine plagioclase spinel and pyroxenes in arcs spinel and plagioclase are enriched in moderately volatile elements cr mn and na and low ca pyroxenes are enriched in refractory elements al and ti the petrology and mineralogy of arcs in ningqiang indicate that they were formed from hybrid precursors of ferromagnesian chondrules mixed with refractory materials during chondrule formation processes we found 294 cals 55 0 type a 39 5 spinel pyroxene rich 4 4 hibonite rich and several type c and anorthite spinel rich inclusions and 73 aoas in 15 ningqiang sections equivalent to 20 cm 2 surface area this is the first report of hibonite rich inclusions in ningqiang they are texturally similar to those in cm ch and cb chondrites and exhibit three textural forms aggregates of euhedral hibonite single crystals fine grained aggregates of subhedral hibonite with minor spinel and hibonite al ti diopside spinel spherules evidence of secondary alteration is ubiquitous in ningqiang opaque assemblages formed by secondary alteration of pre existing alloys on the parent body are widespread in chondrules and matrix on the other hand nepheline and socialite existing in all chondritic components formed by alkali halogen metasomatism in the solar nebula

the relationship between ck and cv chondrites ck chondrites are highly oxidized meteorites containing abundant magnetite and trace amounts of fe ni metal although the group is predominately composed of equilibrated meteorites types 4 6 in recent years a significant number of new samples have been classified as being either ck3 or ck3 anomalous these unequilibrated cks often display a close affinity with members of the cv oxidized subgroup cks and cvs oxidized subgroup may therefore form a continuum and by implication could be derived from a single common parent body to investigate the relationship between these two groups a detailed study of the oxygen isotope composition opaque mineralogy and major and trace element geochemistry of a suite of cv and ck chondrites has been undertaken the results of oxygen isotope analysis confirm the close affinity between cv and ck chondrites while excluding the possibility of a linkage between the co and ck groups magnetites in both cv and ck chondrites show significant compositional similarities but high ti contents are a diagnostic feature of the latter group the results of major and trace element analysis demonstrate that both cv and ck chondrites show overlapping variation supporting evidence for a single common source for both groups comes from their similar cosmic ray exposure age distributions recent reflectance spectral analysis is consistent with both the cvs and cks being derived from eos family asteroids which are believed to have formed by the catastrophic disruption of a single large asteroid thus a range of evidence appears to be consistent with cv and ck chondrites representing samples from a single thermally stratified parent body in view of the close similarity between cv and ck chondrites some modification of the present classification scheme may be warranted possibly involving integration of the two groups one means of achieving this would be to reassigned ck chondrites to a subgroup of the oxidized cvs it is recognized that a full evaluation of this proposal may require further study of the still poorly understood ck3 chondrites

compositional and petrographic similarities of cv and ck chondrites a single group with variations in textures and volatile concentrations attributable to impact heating crushing and oxidation abstract greenwood et al 2010 gathered data on o isotopic and elemental compositions and reevaluated literature data for cv and ck chondrites they concluded that these two chondrite groups originated on the same parent asteroid with ck chondrites being metamorphosed cv chondrites which are otherwise missing types 4 through 6 to test this interpretation we have gathered new instrumental neutron activation analysis inaa data for cv and ck chondrites and reexamined their petrographic features the new inaa data like the older data show scatter attributable to weathering effects but we conclude that the refractory lithophile abundances are the same in cv and ck in agreement with the greenwood et al interpretation several volatile elements are significantly lower in ck than in cv chondrites among the elements we determine the greatest difference between cv and ck is found for br for which the cv ck ratio is 4 as and sb are about 20 lower in ck than cv and smaller differences are observed for zn ga and se it seems likely that volatiles were lost during impact heating events that also provided the heat responsible for metamorphic recrystallization within statistical uncertainty chondrules in cv and ck chondrites are the same size and have similar textural distributions a significant petrographic difference between ck and cv chondrites cited by kallemeyn et al 1991 was the much higher percentage of igneous rims around cv chondrules however we now recognize that many chondrules in ck3 8 nwa 1559 have igneous rims and in ck4 chondrites igneous rims are recognizable by their associated sulfide rich rings there are no quantifiable cv ck differences in igneous rim abundances we used ca and al maps to show that ck chondrites have cai abundances similar to those of cv chondrites it thus appears that there are no resolvable pre metamorphic petrographic differences between cv and ck chondrites we recommend that the ck designation be abandoned and that the cv group be acknowledged as spanning the range of petrologic types 3 6 we suggest that ck3 chondrites be designated cv3oxk most ck4 chondrites are highly fragmental collisional crushing appears to be much more common than in cv chondrites it seems likely that ck chondrites formed from reduced cv3 materials after the latter was impacted buried aqueously altered and annealed

cv chondrites more than one parent body abstract cv chondrites are one of the most studied group of carbonaceous chondrites based on a number of mineralogical features they have been divided into three sub groups cvoxa cvoxb and cvred these sub groups are classically interpreted as coming from a single parent body with a common protolith affected by significant parent body fluid assisted metasomatism occurring at different temperatures and or redox conditions in this work we studied a set of 53 cv chondrites we classified them into the three sub groups measured their apparent chondrule sizes and their matrix modal abundance we measured the triple oxygen isotopic composition for 17 of them the distributions of chondrule size and matrix abundances in cvoxa and cvoxb cannot be statistically distinguished conversely cvred and cvox have distinct distributions these two robust and simple petrographic indicators combined with the previous knowledge of the peak metamorphic temperatures experienced by these meteorites show that cvox and cvred originate from two distinct parent bodies on the other hand cvoxa and cvoxb likely originate from the same parent body with cvoxa representing deeper more metamorphosed levels for clarification of the chondrite classification scheme in which one group should ultimately represent a single parent body we propose to divide the cv group into two proper groups and not subgroups as in the current scheme keeping the names cvred and cvox these two groups can be readily separated by estimating the average nickel content of their sulfides

matrices of type 3 ordinary chondrites primitive nebular records petrologic studies were made on the fine grained matrices of type 3 ordinary chondrites of the lowest petrologic subtype the matrix minerals in order of abundance are olivine fo99 to fo9 enstatite or bronzite augite or subcalcic augite albite fe ni metal troilite magnetite spinel mgal2o4 chromite and calcite fe and mg rich fluffy particles and albite like particles are also major constituents the chemical compositions of olivine and pyroxenes vary within and among the chondrites and are in gross disequilibrium showing that the matrix materials were hardly heated after their formation textural relationships indicate that magnesian olivine was formed after ca pyroxene followed by intermediate to iron rich olivine intermediate olivine was formed from enstatite and metallic iron under relatively oxidizing conditions the observations indicate that matrices of chondrites are neither the fragments of chondrules nor the precursors of chondrules they were mostly the products of condensation and reaction among solids and or between solids and the ambient gas mostly at low temperatures and thus they contain records of primitive processes in the nebula in order to explain the presence of olivines more iron rich than fo50 the presence of free sio2 or a high activity of sio2 in the gas is necessary which was not shown in previous thermochemical calculations mineral assemblages of matrix minerals of chondrites of different chemical groups differ systematically according to oxidation state of the parental meteorites indicating that they were formed at different oxygen fugacities the rims of chondrules and surrounding matrix materials must have accreted onto chondrules during turbulent movements of the nebula

microchondrules in two unequilibrated ordinary chondrites evidence for formation by splattering from chondrules during stochastic collisions in the solar nebula the diversity of silicate glassy spherules analogous to chondrules called microchondrules and the implications for their presence in unequilibrated ordinary chondrites uocs were investigated using different electron microscope techniques our observations show that the abundance of microchondrules in uocs is much larger than the values proposed by previous studies we identified two different types of microchondrules porous and nonporous embedded within fine grained matrices and type i chondrule rims the porous microchondrules are characterized by distinctive textures and chemical compositions that have not been recognized previously additionally we show detailed textures and chemical compositions of protuberances of silicate materials connected to the chondrules and ending with microchondrules we suggest that microchondrules and protuberances formed from materials splattered from the chondrules during stochastic collisions when they were still either completely or partially molten the occurrence and distinct morphologies of microchondrules and protuberances suggest that rather than just a passive flash melting of chondrules an additional event perturbed the molten chondrules before they underwent cooling the bulk chemical compositions suggest that 1 nonporous microchondrules and protuberances were formed by splattering of materials that are compositionally similar to the bulk silicate composition of type i chondrules and 2 the porous microchondrules could represent the splattered melt products of a less evolved fine grained dust composition the preservation of protuberances and microchondrules in the rims suggests that the cooling and accretion rates were exceptionally fast and that they represent the last objects that were formed before the accretion of the parent bodies of ocs

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

high temperature rims around chondrules in primitive chondrites evidence for fluctuating conditions in the solar nebula abstract rims or rim sequences surrouding chondrules have been identified in carbonaceous and unequilibrated ordinary chondrites these chondrule rims include three chemical subtypes fe ca rich and fe ni metal rich rims which occur predominantly in kainsaz co3 and ferromagnesian rims which occur in kainsaz co3 allende cv3 renazzo cr2 chainpur ll3 semarkona ll3 krymaka l3 and tieschitz h3 the compositions of minerals in these rims are often drastically different from those in the underlying chondrule cores indicating that the solar nebula was chemically heterogeneous in many cases the compositions of the rims require an environment that was much more oxidizing than a solar composition gas particularly interesting is that some of the fe ca rich chondrule rims are remarkably similar to some of the rims around refractory inclusions suggesting that chondrules and refractory inclusions experienced late coeval processing the textures of the chondrule rims suggest they formed at high temperatures and that they accreted onto chondrules that had already solidified the lengthscale of the thermal heterogeneities necessary to make available hot material that could accrete to cold chondrules has been calculated to be less than 10 km implying there were localized heat sources in the solar nebula

microchondrules in ordinary chondrites implications for chondrule formation abstract previous studies of ordinary chondrites oc reported isolated microchondrules within the fine grained or clastic matrix of many type 3 samples larger sets of microchondrules have also been found as rare clasts in type 3 oc we report here another major setting for microchondrules large numbers n 100 of microchondrules 40 m in apparent diameter occur together with irregularly shaped fragments in fine grained rims around four low feo porphyritic olivine chondrules and one barred olivine chondrule these chondrules are from ll3 1 bishunpur l3 4 eet90161 l3 4 eet90261 ll3 4 piancaldoli and ll3 0 semarkona the two kinds of microchondrules observed are 1 numerous low feo radial and cryptocrystalline microchondrules consisting of low ca pyroxene and 2 relatively rare high feo olivine microchondrules both types of microchondrules are embedded in high feo fine grained matrix materials they are typically accompanied by irregularly shaped pyroxene fragments that form a continuum in composition and shape with the low feo microchondrules the pyroxene rich surfaces of the host chondrules project into the surrounding rims as peninsulas with rounded embayments consistent with remelting although on average less ferroan the peninsulas overlap the fragments and low feo microchondrules in composition and appear to have been the main source of these objects the occurrence of numerous low feo pyroxene rich microchondrules with similar textures and compositions within high feo fine grained matrix rims around normal size chondrules and the apparent remelting of the surfaces of the host chondrules indicate that the microchondrules formed after solidification of the host chondrules mainly by remelting of their pyroxene rich surfaces or possibly igneous rims the remnants of these pyroxene rich rims are preserved as peninsulas extending outward from the chondrule surface and as irregularly shaped pyroxene fragments coexisting with the microchondrules because a newly formed microchondrule cloud in the nebula would dissipate quickly due to random motions of the individual microchondrules it seems inescapable that the fine grained material which now surrounds the microchondrules was in their immediate vicinity when they formed and served as a trapping matrix the material probably occurred as a highly porous aerogel like aggregate of feo rich nebular dust the rare high feo olivine microchondrules probably formed at the same time as the low feo pyroxene microchondrules by melting adjacent portions of the porous dust

oxygen isotope heterogeneity in chondrules from the mokoia cv3 carbonaceous chondrite we report a study of the oxygen isotope ratios of chondrules and their constituent mineral grains from the mokoia oxidized cv3 chondrite bulk oxygen isotope ratios of 23 individual chondrules were determined by laser ablation fluorination and oxygen isotope ratios of individual grains mostly olivine were obtained in situ on polished mounts using secondary ion mass spectrometry sims our results can be compared with data obtained previously for the oxidized cv3 chondrite allende bulk oxygen isotope ratios of mokoia chondrules form an array on an oxygen three isotope plot that is subparallel to and slightly displaced from the ccam carbonaceous chondrite anhydrous minerals line the best fit line for all cv3 chondrite chondrules has a slope of 0 99 and is displaced significantly by 17o 2 5 from the young and russell slope one line for unaltered calcium aluminum rich inclusion cai minerals oxygen isotope ratios of many bulk cais also lie on the cv chondrule line which is the most relevant oxygen isotope array for most cv chondrite components bulk oxygen isotope ratios of most chondrules in mokoia have 18o values around 0 and olivine grains in these chondrules have similar oxygen isotope ratios to their bulk values in general it appears that chondrule mesostases have higher 18o values than olivines in the same chondrules our bulk chondrule data spread to lower 18o values than any ferromagnesian chondrules that have been measured previously two chondrules with the lowest bulk 18o values 7 5 and 11 7 contain olivine grains that display an extremely wide range of oxygen isotope ratios down to 17o 18o around 50 in one chondrule in these chondrules there are no apparent relict grains and essentially no relationships between olivine compositions which are homogeneous and oxygen isotopic compositions of individual grains heterogeneity of oxygen isotope ratios within these chondrules may be the result of incorporation of relict grains from objects such as amoeboid olivine aggregates followed by solid state chemical diffusion without concomitant oxygen equilibration alternatively oxygen isotope exchange between an 16o rich precursor and an 16o poor gas may have taken place during chondrule formation and these chondrules may represent partially equilibrated systems in which isotopic heterogeneities became frozen into the crystallizing olivine grains if this is the case we can infer that the earliest nebular solids from which chondrules formed had 17o and 18o values around 50 similar to those observed in refractory inclusions

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

heavily metamorphosed clasts from the cv chondrite breccias mokoia and yamato 86009 metamorphosed clasts in the cv carbonaceous chondrite breccias mokoia and yamato 86009 y 86009 are coarse grained granular polymineralic rocks composed of ca bearing up to 0 6 wt cao ferroan olivine fa34 39 ferroan al diopside fs9 13wo47 50 approximately 2 7 wt al2o3 plagioclase an37 84ab63 17 cr spinel cr cr al 0 19 0 45 fe fe mg 0 60 0 79 nepheline pyrrhotite pentlandite ca phosphate and rare grains of ni rich taenite low ca pyroxene is absent most clasts have triple junctions between silicate grains indicative of prolonged thermal annealing based on the olivine spinel and pyroxene thermometry the estimated metamorphic temperature recorded by the clasts is approximately 1100 k few clasts experienced thermal metamorphism to a lower degree and preserved chondrule like textures the mokoia and y 86009 clasts are mineralogically unique and different from metamorphosed chondrites of known groups h l ll r eh el co ck and primitive achondrites acapulcoites brachinites lodranites on a three isotope oxygen diagram compositions of olivine in the clasts plot along carbonaceous chondrite anhydrous mineral line and the allende mass fractionation line and overlap with those of the cv chondrule olivines the 17o values of the clasts range from about 4 3 to 3 0 we suggest that the clasts represent fragments of the cv like material that experienced metasomatic alteration high temperature metamorphism and possibly melting in the interior of the cv parent asteroid the lack of low ca pyroxene in the clasts could be due to its replacement by ferroan olivine during iron alkali metasomatic alteration or by high ca ferroan pyroxene during melting under oxidizing conditions

igneous rims on low feo and high feo chondrules in ordinary chondrites abstract many ordinary chondrite oc chondrules are surrounded by rims that show evidence of appreciable melting and can be called igneous these rims formed after the melting and solidification of the host chondrule we studied thirteen igneous rims on low feo chondrules fa or fs 10 mol in ordinary chondrites of petrographic type 3 5 by electron microprobe analysis and scanning electron microscopy in both sets olivine and pyroxene compositions of the rims are similar to or moderately higher in feo than those in the host igneous rims around low feo chondrules show evidence of large degree 80 melting including 1 resorbed chondrule surfaces 2 rounded metal troilite nodules and feldspathic mesostasis 3 euhedral and subhedral morphology of olivine and pyroxene and limited ranges in grain sizes and 4 a rarity of relict grains most low feo chondrules have olivine as their major phase but pyroxene is commonly the predominant phase in their rims rims on high feo chondrules generally have smaller grain sizes and exhibit lower degrees of melting than rims around low feo chondrules mg rich relict grains are observed in high feo rims most low feo chondrules have matrix like rims around the igneous rims but matrix like rims are rare around rims on high feo chondrules there is a continuum between igneous rims and enveloping secondaries of compound chondrules the existence of both sets of objects supports the view that in the oc region most mm size grain assemblages experienced more than one melting event the precursors melted to produce the igneous rims on low feo chondrules differ from those that comprise the rims on high feo chondrules a sizeable fraction of the precursors of low feo rims are from the host chondrule most high feo rims appear to consist largely of melted matrix like materials if the rim precursors are mainly independent the similar fa and fs contents in mafic minerals of rims and host chondrules indicate that 1 oc nebular subregions bounded in space and or in time were dominated by well mixed solids 2 many chondrules experienced multiple heating events during a short period and were then withdrawn from the chondrule forming region and 3 chondrules formed at different times were mixed before agglomeration to form chondrites if the host chondrules were the main source of the low feo rim materials the fact that pyroxene is generally more abundant than in the host suggests that sio 2 normative matrix was also an important ingredient and or that kinetics favored pyroxene crystallization in the rim rims around high feo chondrules were heated to lower temperatures than rims around low feo chondrules the rarity of matrix like rims around high feo igneous rims may indicate that the dust chondrule ratio was lower where they formed

petrologic geochemical and experimental constraints on models of chondrule formation abstract the petrologic and geochemical properties of chondrules as well as results of experimental studies provide strong constraints on chondrule formation models nebular formation is indicated by the non mass fractionated oxygen isotopic compositions of bulk chondrules chondrule formation from a melt is required by the prototypical spheroidal shapes and the presence of euhedral phenocrysts and glassy mesostases incomplete melting is indicated by the abundance of porphyritic chondrules which experiments demonstrate require relict nuclei and coarse relict grains the length of time that chondrules were hot is constrained by their retention of relict grains and moderately volatile elements rapid cooling of chondrules after formation is supported by the presence of zoned phenocrysts isotopic anomalies and dynamic crystallization experiments it is clear from the presence of relict grains enveloping compound chondrules and igneous rims that many chondrules were heated again after cooling the heating mechanism responsible for chondrule formation seems to have operated at varying intensities over large regions of the inner solar nebula for at least the time it took ambient nebular temperatures to cool from above 900 to below 600 k the chondrule formation mechanism provided a repeatable source of energy capable of highly localized melting characteristic of flash heating the occurrence of ferroan microchondrules with low melting temperatures within some chondrule rims indicates that chondrule formation did not occur exclusively in high temperature regions near the sun as required in bipolar outflow models mechanisms for forming chondrules that are consistent with the constraints include various flash heating models nebular lightning magnetic reconnection flares gas dynamic shock waves and radiative heating

multiple melting in a four layered barred olivine chondrule with compositionally heterogeneous glass from ll3 0 semarkona chondrule k7p from ll3 0 semarkona consists of four nested barred olivine bo chondrules the innermost bo chondrule chondrule 1 formed by complete melting of an olivine rich dustball after formation the chondrule was incorporated into another olivine rich dustball a second heating event caused this second dustball to melt the mesostasis and some of the olivine in chondrule 1 were probably also melted at this time but the chondrule 1 structure remained largely intact at this stage the object was an enveloping compound bo chondrule this two step process of melting and dustball enshrouding repeated two more times the different proportions of olivine and glass in chondrules 1 4 suggest that the individual precursor dustballs differed in the amounts of chondrule fragments they contained and the mineral proportions in those fragments the final dustball which ultimately formed chondrule 4 was somewhat more ferroan after melting crystallizing and quenching chondrule 4 contained olivine and glass with higher feo and mno contents than those of the earlier formed chondrules subsequent aqueous alteration on the ll parent body transformed the abundant metal blebs and stringers at the chondrule surface into carbide iron oxide and minor ni rich metal portions of the mesostasis underwent dissolution producing holes and adjacent blades of more resistant material much of the glass in the chondrule remained isotropic even after minor hydration and leaching the sharp moderately lobate boundary between the extensively altered mesostasis and the isotropic glass represents the reaction front beyond which there was little or no glass dissolution

determining chondrule size distributions from thin section measurements a method is described for correcting thin section derived chondrule sizes for three common sources of bias 1 the non equatorial sectioning of chondrules 2 the non zero thickness of thin sections and 3 the unequal probability of sectioning different size chondrules application of the correction procedure to chondrule data from co chondrites results in a reduction of mean and median chondrule diameters an increase in minimum diameters and transforms nearly log normal distributions to distributions that conform to a weibull probability function the weibull function form of co chondrule size distributions is similar to the form of chondrule distributions in ordinary chondrites obtained by disaggregation analyses

i xe studies of individual allende chondrules abstract iodine xenon studies have been performed on nine allende chondrules and a sample of oxidized allende matrix material the chondrules are all very rich in radiogenic xenon relative to trapped xenon making it possible to determine a relatively precise model initial iodine composition for each temperature extraction these model compositions show a total range in variation of about 20 percent spanning the compositions seen in bjurbole chondrules one of the chondrules chondrule 6 gives a well defined isochron with an apparent age 53 15 m y later than bjurbole whole rock the rest of the chondrules show a pattern of increasing apparent antiquity with increasing extraction temperature which could be interpreted as relatively slow cooling 100 200 c m y alternatively poorly defined plateaus in composition can be seen perhaps indicative of a few phases with distinct initial iodine compositions but also temperature ordered as has been previously suggested for allende inclusions possible consequences of these interpretations are discussed elemental abundances were determined for some elements several months after the irradiation by inaa and suggest that all the chondrules except chondrule 6 might be pyroxene or mesostasis rich the oxidized matrix sample gives a well defined isochron with an initial 129 i 127 i ratio higher than any plateaus seen in the chondrules suggesting that if this sample is representative of matrix the matrix pre dates the chondrules the initial 244 pu 238 u ratios of the allende chondrules and 10 bjurbole chondrules irradiated earlier appear to be consistent with 004 007 values quoted for unfractionated material in the early solar nebula

oxygen isotopes in chondrules and coarse grained chondrule rims from the allende meteorite abstract the oxygen isotopic compositions of porphyritic chondrules and coarse grained chondrule rims from the allende cv chondrite form a 16 o mixing trend situated near the carbonaceous chondrite anhydrous minerals ccam mixing line lying 0 1 0 7 higher in 17 o coarse grained rims are depleted in 16 o relative to their enclosed chondrules chondrules and rims exhibit significant correlations between their oxygen isotopic and chemical compositions objects rich in 16 o tend to have higher contents of refractory lithophiles and alkalies objects poor in 16 o tend to have higher contents of feo and volatile siderophiles cv chondrite matrix material is chemically and isotopically similar to some coarse grained chondrule rims previous work showed that o isotope data for cv barred olivine bo chondrules plot just below the terrestrial fractionation tf line near 18 o 4 well off the ccam line the allende data suggest that three solid precursor components are required to account for the o isotopic compositions of cv chondrules and rims 1 a high temperature refractory alkali and 16 o rich component perhaps near 18 o 40 17 o 42 relative to smow 2 a low temperature feo rich refractory and 16 o poor component lying near the ccam line perhaps near its intersection with the tf line at 18 o 10 and 3 an additional component required to explain the composition of bo chondrules

a relict grain bearing porphyritic olivine compound chondrule from ll3 0 semarkona that experienced limited remelting chondrule d8n in ll3 0 semarkona is a porphyritic olivine po chondrule 1300 1900 m in size with a complicated thermal history the oldest recognizable portion of d8n is a moderately high feo po chondrule that is modeled as having become enmeshed in a dust ball containing a small intact low feo porphyritic chondrule and fine grained material consisting of forsterite kamacite troilite and possibly reduced c the final chondrule melting event may have been a heat pulse that preferentially melted the low feo material and produced a low feo opaquerich exterior region 45 140 m in thickness around the original chondrule at one end of the exterior region a kamacite and troilite rich lump 960 m in length formed during the final melting event the coarse moderately ferroan olivine phenocrysts within the original chondrule appear to have been partly resorbed these relict phenocrysts have the highest concentrations of feo mno and cr2o3 7 5 0 20 and 0 61 wt respectively in d8n narrow olivine overgrowths crystallized around the phenocrysts following final chondrule melting their compositions seem to reflect mixing between melt derived from the exterior region and the resorbed margins of the phenocrysts during the melting event feo in the relict phenocrysts was reduced producing numerous small blebs of ni poor metallic fe along preexisting curvilinear fractures the reduced olivine flanking the trails of metal blebs has lower feo than the phenocrysts but virtually identical mno and cr2o3 contents subsequent parent body aqueous alteration in the exterior region of the chondrule formed pentlandite and abundant magnetite

fine grained dust rims in the tagish lake carbonaceous chondrite evidence for parent body alteration the tagish lake carbonaceous chondrite consists of heavily aqueously altered chondrules cais and larger mineral fragments in a fine grained phyllosilicate dominated matrix the vast majority of the coarse grained components in this meteorite are surrounded by continuous 1 5 to 200 m wide fine grained accretionary rims which are well known from meteorites belonging to petrological types 2 and 3 and whose origin and modification is still a matter of debate texturally the fine grained rims in tagish lake are very similar throughout the entire meteorite and independent of the nature of the enclosed object they typically display sharp boundaries to the core object and more gradational contacts to the meteorite matrix compared to the matrix the rims are much more finegrained and characterized by a significantly lower porosity the rims consist of an unequilibrated assemblage of phyllosilicates fe ni sulfides magnetites low ca pyroxenes and forsteritic olivines and are except for a much lower abundance of carbonates very similar to the tagish lake matrix electron microprobe and synchrotron x ray microprobe analyses show that matrix and rims are also very similar in composition and that the rims differ significantly from matrix and bulk meteorite only by being depleted in ca x ray elemental mapping and mineralogical observations indicate that ca was lost during aqueous alteration from the enclosed objects and preferentially crystallized as carbonates in the porous matrix the analyses also show that ca is strongly fractionated from al in the rims whereas there is no fractionation of the ti al ratios our data suggest that the fine grained rims in tagish lake initially formed by accretion in the solar nebula and were subsequently modified by in situ alteration on the parent body this pervasive alteration removed any potential evidence for preaccretionary alteration but did not change the overall texture of the tagish lake meteorite

petrographic constraints on the diversity of chondrule reservoirs in the protoplanetary disk abstract chondrules from different chondrite groups show characteristic properties including abundances of different chondrule textural types chondrule sizes oxygen isotope compositions chondrule bulk compositions and petrographic properties of type i and type ii chondrules including abundances of relict grains overall it can be argued that each chondrite group sampled a unique chondrule reservoir and that chondrite groups may represent fractions of larger reservoirs that are represented by chondrite classes these observations provide constraints for models of the early solar system in which it is necessary to establish multiple separate chondrule reservoirs and maintain them over extended time periods models for accretion of chondrite parent bodies must be able to account for localized accretion of chondrules that were formed in spatially or temporally separated reservoirs

a new model for the origin of type b and fluffy type a cais analogies to remelted compound chondrules abstract in the scenario developed here most types of calcium aluminum rich inclusions cais formed near the sun where they developed wark lovering rims before being transported by aerodynamic forces throughout the nebula the amount of ambient dust in the nebula varied with heliocentric distance peaking in the cv ck formation location literature data show that accretionary rims which occur outside the wark lovering rims around cais contain substantial 16o rich forsterite suggesting that at this time the ambient dust in the nebula consisted largely of 16o rich forsterite individual sub millimeter size compact type a cais each surrounded by a wark lovering rim collided in the cv ck region and stuck together in a manner similar to that of sibling compound chondrules the ctas were mixed with small amounts of 16o rich mafic dust and formed centimeter size compound objects large fluffy type a cais after experiencing minor melting in contrast to other types of cais centimeter size type b cais formed directly in the cv ck region after gehlenite rich compact type a cais collided and stuck together incorporated significant amounts of 16o rich forsteritic dust on the order of 10 15 and probably some anorthite and experienced extensive melting and partial evaporation enveloping compound chondrules formed in an analogous manner in those cases where appreciably higher amounts of 16o rich forsterite on the order of 25 and perhaps minor anorthite and pyroxene were incorporated into compound type a objects prior to melting centimeter size forsterite bearing type b cais b3 inclusions were produced type b1 inclusions formed from b2 inclusions that collided with and stuck to melilite rich compact type a cais and experienced high temperature processing

recent advances in coalification studies and their application to geology abstract recent advances in coalification studies since 1970 are reported concerning microscopic methods causes of coalification the coalification process as such and application to geology the degree of coalification rank is mostly determined on the basis of vitrinite reflectance measured on finely dispersed material in rocks for rocks bare of vitrinite other microscopic methods are used such as fluorescence properties of liptinites and graptolite reflectance under incident light or coloration of microfossils like palynomorphs and conodonts in transmitted light the validity of the various methods is discussed maximum rock temperature and its duration are the main causes of chemical coalification reactions heating rates during subsidence influence the attainment of rank equilibrium contact metamorphic coals and natural cokes formed from bituminous coals are characterized by a relatively high reflectance and anisotropy strong frictional heat may cause local increase of rank adjacent to thrust planes graphitization is thermodynamically not possible in nature without pressure and shearing confining pressure retards the chemical coalification reactions tectonic stress especially shearing promotes the increase of maximum reflectance and of anisotropy it commonly leads to bi axial optical properties instead of the more typical uni axial negative geometry of vitrinite in undisturbed coal seams bi axial optical properties are common for vitrinite inclusions in clastic rocks on the basis of combined fluorescence microscopical and geochemical studies bituminization has been recognized as the characteristic part of coalification in the range between sub bituminous and bituminous coal it is characterized by the generation of petroleum like substances which enable the coal to soften and to agglomerate during carbonization hydrogenation properties are favoured by the bituminization process the different liptinite macerals behave differently during coalification and pass coalification jumps at different rank stages a considerable part of total inertinites is formed during early coalification brown coal to sub bituminous coal stage as rank inertinite this new knowledge appears to become important in relation to hydrocarbon exploration diagenetic methane some examples for the application of coalification studies to geology refer to vitrinite reflectance as an indicator of rock diagenesis and metamorphism palaeogeographical and structural history palaeogeothermics and hydrocarbon exploration large scale areal coalification studies in foredeeps and backdeeps of ancient and recent orogens suggest estimations of crustal thicknesses and relations to plate tectonics