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

oxygen isotopes in r chondrite magnetite and olivine links between r chondrites and ordinary chondrites ion microprobe studies yield 17o 17o 0 52 18o values in magnetite from the rumurti chondrite rc pca91241 which is paired with pca91002 of 3 1 to 3 9 slightly higher than that in o from whole rock r samples despite 17o values in whole rock rcs that are much by ca 1 6 higher than in whole rock ll chondrites the 17o in r magnetite is much lower by ca 2 than the values 4 to 7 from ll3 semarkona and ngawi choi et al 1998 the 18o values in pca magnetite 15 to 10 are the lowest known in meteorites well below the range in semarkona 4 to 9 on a 17o 18o diagram both magnetite data sets form linear arrays with slopes of ca 0 7 indicating mixing of o from different isotopic reservoirs the slopes and intercepts of the two arrays are similar enough to permit them to be segments of a single array this suggests that in rcs and ll chondrites magnetite formed from the same raw materials by the same processes probably by aqueous alteration of metal in an asteroidal setting we observed 17o values in olivines and pyroxene from rcs ranging from 1 2 to 2 9 and 18o from 1 4 to 9 1 these compositions scatter in the same general range observed in chondrules from ordinary chondrites the similarity in the o isotopic composition of minerals that preserve a record of formation in the solar nebula supports a model in which rcs formed from nebular components similar to those in h chondrites but with a matrix chondrule ratio several times higher in the rcs and with more extensive aqueous alteration in the rcs than in known h chondrites we postulate that the matrix in r chondrites has 17o higher than whole rock values we suggest that the original 17o value of h2o in the rc body was similar to that incorporated into the ordinary chondrites previously estimated by choi et al 1998 to be ca 7 in the ll parent body

eh3 matrix mineralogy with major and trace element composition compared to chondrules abstract we investigated the matrix mineralogy in primitive eh3 chondrites sahara 97072 alh 84170 and lar 06252 with transmission electron microscopy measured the traceand major element compositions of sahara 97072 matrix and ferromagnesian chondruleswith laser ablation inductively coupled plasma mass spectrometry la icpms andanalyzed the bulk composition of sahara 97072 with la icpms solution icpms andinductively coupled plasma atomic emission spectroscopy the ne grained matrix of eh3chondrites is unlike that in other chondrite groups consisting primarily of enstatite cristobalite troilite and kamacite with a notable absence of olivine matrix and pyroxene rich chondrule compositions differ from one another and are distinct from the bulkmeteorite refractory lithophile elements are enriched by a factor of 1 5 3 in chondrulesrelative to matrix whereas the matrix is enriched in moderately volatile elements thecompositional relation between the chondrules and matrix is reminiscent of the differencebetween eh3 pyroxene rich chondrules and eh3 si rich highly sul dized chondrules similar refractory element ratios between the matrix and the pyroxene rich chondrulessuggest the ne grained material primarily consists of the shattered sul dized remains of theformerly pyroxene rich chondrules with the minor addition of metal clasts the matrix chondrule and metal sul de nodule compositions are probably complementary suggestingall the components of the eh3 chondrites came from the same nebular reservoir introductionthe origin and nature of chondrite matrix materialthat is amorphous or with grains 5 lm in diameter are debated scott et al 1988 suggestions include thatit consists mainly of chondrule fragments alexanderet al 1989 brearley 1996 ci like material with anorigin distinct from chondrules alexander 2005 reprocessed material from the parent molecular cloud ofthe solar system buseck and hua 1993 zolensky et al 1993 huss et al 2005 and products of nebularcondensation larimer and anders 1967 the enstatite chondrites ec were estimated tocontain between 2 and 15 vol matrix scott and krot2005 rubin et al 2009 material that has not beenwidely studied ec are thought to have accreted in theinner solar system shukolyukov and lugmair 2004 they are linked to earth by nearly identical isotopiccompositions of several major and minor elements javoy et al 2010 jacobsen et al 2013 kaminski andjavoy 2013 and they have been proposed as potentialsource material for earth and the moon clayton et al 1984 javoy 1995 javoy et al 2010 therefore like theec chondrules the matrix in highly unequilibrated eh3chondrites potentially provides insight into events andmaterials from the early inner solar system preliminary work showed that the eh matrixconsists primarily of enstatite cristobalite troilite andkamacite lehner and buseck 2010 lehner et al 2012b the abundant cristobalite suggests a possiblelink with sul dized chondrules which are a subset ofeh3 chondrules in which forsterite and enstatite were

phosphate minerals in ll chondrites a record of the action of fluids during metamorphism on ordinary chondrite parent bodies ordinary chondrites contain two phosphate minerals merrillite and chlorapatite both of which are secondary minerals that developed in response to metamorphism on the chondrite parent bodies we have studied the phosphate mineralogy of four ll chondrites of petrologic types 3 9 6 in order to determine the petrogenesis of the two minerals and interpret the conditions under which they formed characterization of merrillite and apatite includes textural observations mineral compositions determined by electron probe microanalysis and ion microprobe analyses of trace element and volatile anion elemental abundances initial formation of phosphate minerals during mild metamorphism to petrologic type 4 conditions resulted in oxidation of p that was originally incorporated in metal and growth of merrillite as inclusions within metal grains subsequent development of both phosphate minerals occurred in response to diffusional equilibration possible precipitation from fluids as well as replacement reactions resulting from interactions with fluids porosity and vein filling textures in both merrillite and chlorapatite as well as textures indicating replacement of merrillite by chlorapatite support a model in which fluid played a significant role and suggest an interface coupled dissolution reprecipitation mechanism during metasomatism some associations of phosphate minerals with chromite plagioclase assemblages suggest that phosphate minerals could also be related to impact processes either as precipitation from an impact melt or as a result of interactions with a fluid or vapor derived from an impact melt fluid compositions may have been water bearing initially at low temperatures of metamorphism but later evolved to become halogen rich and very dry late stage halogen rich fluids that dominated during cooling of ll chondrite material may have been derived from vaporization of partial melts in the interior of the parent body overall the ll chondrite parent body underwent a complex chemical evolution in which metasomatism played a significant role

opaque minerals in the matrix of the bishunpur ll3 1 chondrite constraints on the chondrule formation environment abstract the chemistry and mineralogy of a group of opaque mineral assemblages in the matrix of the bishunpur ll3 1 ordinary chondrite provide insight into the nebular environment in which they formed the assemblages consist of a kamacite fe ni core that is rimmed by troilite fes and fayalite fe2sio4 accessory phases in the rims include silica sio2 chromite fecr2o4 whitlockite ca3 po4 2 maricite fenapo4 magnetite fe3o4 and tetrataenite feni we suggest that the metal melted in and equilibrated with an igneous chondrule under high temperature reducing conditions in this environment the molten alloys incorporated varied amounts of si ni p cr and co depending on the oxygen fugacity and temperature of the melt some of the metal was subsequently expelled from the chondrule interiors into the surrounding nebular gas as the temperature dropped the alloy solidified and volatile elements corroded the metal the main reaction products were troilite and fayalite thermodynamic equilibrium calculations are used to constrain the conditions under which these two phases can form simultaneously in the solar nebula kinetic factors are used to place a lower limit on the formation temperature we determine that the metal corroded between 1173 and 1261 k at a total pressure in the range of 10 5 0 to 10 4 1 bars and a dust gas ratio of 302 to 355 x relative to solar composition these conditions are consistent with our model that the metal corroded in a dust rich region of the solar nebula that was cooling after a chondrule formation event

the influence of feo on the solubilities of cobalt and nickel in silicate melts abstract the effect of iron on the solubilities of co and ni in silicate melts was determined at a wide range of oxygen fugacities from 10 8 1 to 10 12 6 atm and at temperatures ranging from 1305 1600 c four different systems were studied in system a an feo free silicate of anorthite diopside eutectic composition was equilibrated with pure co or pure ni metal in system b the same silicate starting material was equilibrated with feconi alloys in systems c and d feo containing silicates basaltic komatiite were equilibrated with pure co and pure ni metal system c and with feco and feni alloys system d experiments at temperatures below 1450 c were performed by equilibrating metal loops with silicates at higher temperature well mixed metal powder and silicates were equilibrated in alumina crucibles concentrations of ni and co in the silicate and in some of the alloys were determined by neutron activation analysis most of the alloy compositions were analyzed by electron microprobe at constant temperature 1400 c but variable oxygen fugacities co ni and fe metal silicate partition coefficients calculated from metal solubilities increase with decreasing oxygen fugacities the extent of the increase suggests that all three metals are dissolved as oxides coo nio feo in the silicate melt no evidence for the presence of metallic co ni or fe as major species in silicate melt was found within the oxygen fugacity range covered by the experiments even at oxygen fugacities three log units below the fe feo equilibrium iw 3 a minor fraction of metallic ni below 20 may be present in the most reducing experiments no difference in ni and co solubility was found for feo free and feo containing silicates depending on temperature all metal silicate partition coefficients of co and ni decrease slightly with increasing temperature along the oxygen fugacity appropriate for core formation 2 3 log units below the fe feo equilibrium iw 2 3 the experiments confirm that the relatively high present day upper mantle concentrations of co ni and fe and in particular the chondritic ni co ratio cannot be explained by equilibrium between coreforming metal and silicates of the earth s mantle in a low pressure environment even at temperatures as high as 4000 c thus supporting models of inhomogeneous accretion of the earth accumulation of differentiated planetesimals i e with metal cores as major building blocks of the earth can also be excluded in these bodies metal silicate equilibration would have occurred at low pressures and equilibration of metal cores of accreting planetesimals with the earth s mantle is unlikely homogeneous accretion models may only be possible if equilibration occurred between lower mantle minerals and liquid core forming metal during differentiation of the earth and if the relevant ni and co partition coefficients are sufficiently high the ni and co partition coefficients between liquid metal and mg wustite and mg perovskite are not well known

mineralogical characterization of primitive type 3 lithologies in rumuruti chondrites rumuruti r chondrites constitute a new well established chondrite group different from the carbonaceous ordinary and enstatite chondrites many of these samples are gas rich regolith breccias showing the typical light dark structure and consist of abundant fragments of various parent body lithologies embedded in a fine grained olivine rich matrix unequilibrated type 3 lithologies among these fragments have frequently been mentioned in various publications in this study detailed mineralogical data on seven primitive fragments from the r chondrites dar al gani 013 and hughes 030 are presented the fragments range from 300 in size up to several millimeters generally the main characteristics can be summarized as follows 1 unequilibrated type 3 fragments have a well preserved chondritic texture with a chondrule to matrix ratio of 1 1 chondrules and chondrule fragments are embedded in a fine grained olivine rich matrix thus the texture is quite similar to that of type 3 carbonaceous chondrites 2 in all cases matrix olivines in type 3 fragments have a significantly higher fa content 44 57 mol than olivines in other equilibrated lithologies 38 40 mol fa 3 olivines and pyroxenes occurring within chondrules or as fragments are highly variable in composition fa0 65 and fs0 33 respectively and generally more magnesian than those found in equilibrated r chondrites agglomerated material of the r chondrite parent body or bodies was highly unequilibrated it is suggested that the material that accreted to form the parent body consisted of chondrules and chondrule fragments mainly having mg rich silicate constituents and fe rich highly oxidized fine grained materials the dominating phase of this fine grained material may have been fa rich olivine from the beginning the brecciated whole rocks the r chondrite regolith breccias were not significantly reheated subsequent to brecciation or during lithification as indicated by negligible degree of equilibration between matrix components and mg rich olivines and pyroxenes in primitive type 3 fragments

formation of unequilibrated r chondrite chondrules and opaque phases abstract sulfide assemblages are commonly found in chondritic meteorites as small inclusions in the matrix or in association with chondrules these assemblages are widely hypothesized to form through pre accretionary corrosion of metal by h2s gas or through parent body processes we report here on two unequilibrated r chondrite samples that contain large chondrule sized sulfide nodules in the matrix both samples are from mount prestrud pre 95404 chemical maps and spot and broad beam electron microprobe analyses empa were used to assess the distribution stoichiometry and bulk composition of sulfide nodules and silicate chondrules in the clasts oxygen isotope data were collected via secondary ion mass spectrometry sims to assess the relationship of chondrules to other chondrite groups scanning electron microscopy sem focused ion beam fib and transmission electron microscopy tem analyses were used to assess fine scale features and identify crystal structures in sulfide assemblages thermodynamic models were used to assess the temperature sulfur fugacity fs2 total pressure dust to gas ratio and oxygen fugacity fo2 conditions during sulfide nodule and chondrule formation the unequilibrated clasts include a mixture of type i and type ii chondrules as well as non porphyritic chondrules chondrule oxygen isotopes overlap with ordinary chondrite chondrules sulfide nodules average 200 m in diameter have rounded shapes and are primarily composed of pyrrhotite pentlandite and magnetite some are deformed around chondrules in a petrologic relationship similar in appearance to compound chondrules both nodules and sulfides in chondrules include phosphate inclusions and cu rich lamellae which suggests a genetic relationship between sulfides in chondrules and in the matrix ni co ratios for matrix and chondrule sulfides are solar while fe and ni are non solar and inversely related we hypothesize that sulfide nodules formed via pre accretionary melt processes during chondrule formation precursors composed of a mixture of silicate and sulfide material were heated to form immiscible melt droplets which separated and cooled to form si rich chondrules and s rich nodules sulfide melt was stabilized by a high total pressure 1 atm in a dust or ice enriched environment heating of this material contributed to a high fs2 2 10 3 atm at 1138 c and high fo2 iw 1 to iw 4 in an environment with peak temperatures between 1539 c and 1750 c oxygen isotopic compositions in this region were similar to those recorded by the ll chondrite chondrules

clues to the origin of metal in almahata sitta el and eh chondrites and implications for primitive e chondrite thermal histories abstract enstatite e chondrites are a group of texturally highly variable meteorites formed under strongly reducing conditions giving rise to unique mineral and chemical characteristics e g high abundances of various sulfides and si bearing metal in particular the abundant metal comprises a range of textures in e chondrites of different petrologic type but available in situ siderophile trace element data on metal are limited nine samples of e chondrites from the recent almahata sitta fall one eh3 two el3 4 two el6 two el impact melt rocks imr two eh imr were investigated in this study in addition to st mark s eh5 and grein 002 el4 5 with a focus on the nature of their metal constituents special attention was given to metal silicate intergrowths mssi that occur in many primitive e chondrites which have been interpreted as post accretionary asteroidal impact melts or primitive nebular condensates this study shows that siderophile trace element systematics in e chondrite metal are independent of petrologic type of the host rock and distinct from condensation signatures three basic types of siderophile trace element signatures can be distinguished indicating crystallization from a melt thermal equilibration upon metamorphism complete melting and exsolution of schreibersite perryite sulfide textural and mineral chemical constraints from el3 4s are used to evaluate previously proposed formation processes of mssi impact melting vs nebular condensation and elucidate which other formation scenarios are feasible it is shown that post accretionary in situ impact melting or metallic melt injection forming mssi on the thin section scale and nebular condensation are unlikely formation processes this leads to the conclusion that mssis are pre accretionary melt objects that were formed during melting processes prior to the accretion of the primitive e chondrites the same can be concluded for metal nodules in the eh3 chondrite examined the pre accretionary origin of mssis in e chondrites is consistent with a growing body of evidence for early differentiation followed by impact disruption of early formed planetesimals in all major chondrite types

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

partitioning of moderately siderophile elements among olivine silicate melt and sulfide melt constraints on core formation in the earth and mars abstract this study investigates the effects of variations in the fugacities of oxygen and sulfur on the partitioning of first series transition metals v cr mn fe co ni and cu and w among coexisting sulfide melt silicate melt and olivine experiments were performed at 1 atm pressure 1350 c with the fugacities of oxygen and sulfur controlled by mixing co2 co and so2 gases starting compositions consisted of a cao mgo al2o3 sio2 feo na2o analog for a barred olivine chondrule from an ordinary chondrite and a synthetic komatiite the f o 2 f s 2 conditions ranged from log f o 2 7 9 to 10 6 wi log f s 2 values ranging from 1 0 to 2 5 our experimental results demonstrate that the f o 2 f s 2 dependencies of sulfide melt silicate melt partition coefficients for the first series transition metals are proportional to their valence states the f o 2 f s 2 dependencies for the partitioning of fe co ni and cu are weaker than predicted on the basis of their valence states variations in f o 2 f s 2 conditions have no significant effect on olivine melt partitioning other than those resulting from f o 2 induced changes in the valence state of a given element the strong f o 2 f s 2 dependence for the olivine silicate melt partitioning of v is attributable to a change of valence state from 4 to 3 with decreasing f o 2 our experimentally determined partition coefficients are used to develop models for the segregation of sulfide and metal from the silicate portion of the early earth and the shergottite parent body mars we find that the influence of s is not sufficient to explain the overabundance of siderophile and chalcophile elements that remained in the mantle of the earth following core formation important constraints on core formation in mars are provided by our experimental determination of the partitioning of cu between silicate and sulfide melts when combined with existing estimates for siderophile element abundances in the martian mantle and a mass balance constraint from fe the experiments allow a determination of the mass of the martian core 17 to 22 wt of the planet and its s content 0 4 wt these modeling results indicate that mars is depleted in s and that its core is solid

the formation of chondrules petrologic tests of the shock wave model chondrules are millimeter sized rounded igneous rocks within chondritic meteorites their textures and fractionated mineral chemistries suggest that they formed by repeated localized brief minutes to hours melting of cold aggregates of mineral dust in the protoplanetary nebula astrophysical models of chondrule formation have been unable to explain the petrologically diverse nature of chondrites however a nebular shock wave model for chondrule formation agrees with many of the observed petrologic and geochemical properties of chondrules and shows how particles within the nebula are sorted by size and how rims around chondrules are formed it also explains the volatile rich nature of chondrule rims and the chondrite matrix

a weathering index for ck and r chondrites we present a new weathering index wi for the metallic fe ni poor chondrite groups ck and r based mainly on transmitted light observations of the modal abundance of crystalline material that is stained brown in thin sections wi 0 95 vol wi 6 significant replacement of mafic silicates by phyllosilicates brown staining reflects mobilization of oxidized iron derived mainly from terrestrial weathering of ni bearing sulfide with increasing degrees of terrestrial weathering of ck and r chondrites the sulfide modal abundance decreases and s se and ni become increasingly depleted in addition bulk cl increases in antarctic ck chondrites probably due to contamination from airborne sea mist

the origin of sulfide rimmed metal grains in ordinary chondrites abstract we report results from an experimental study of sulfide chemistry during metamorphism on ordinary chondrite parent bodies artificial ll chondrite material composed of silicate iron metal and sulfide grains was placed in sealed evacuated silica tubes and heated to either 500 c or 900 c these temperatures are representative peak metamorphic temperatures experienced by type 3 and type 6 ordinary chondrites respectively rapid sulfur mobilization occurs during heating and results in the formation of sulfide rims around the metal grains and sulfur loss from the original sulfide crystals the newly formed sulfide rims have two distinct layers that incorporate nearby silicate grains we also observe narrow sulfide trails that follow silicate grain boundaries and connect separate sulfide rimmed metal grains the morphologies of the sulfide rims suggest that vapor transport is the main mechanism for sulfur mobilization sulfur loss is observed along cracks and crystal boundaries of the initial sulfide grains after extensive reaction patches of iron metal appear at the outer edges of the sulfide crystals and large pore spaces form throughout the original sulfides the experimental metal sulfide assemblages resemble those found in low metamorphic grade ordinary chondrites this suggests metamorphism is mainly responsible for the observed metal sulfide textures in these chondrites

diffusion in silicate minerals and glasses a data digest and guide to the literature the rates of diffusion of cations oxygen and hydrogen in silicates are of fundamental importance to a wide range of petrological and geochronological problems in order that the earth scientist may readily apply the available experimentally determined diffusion rates to such problems a compilation of data for diffusion in silicate minerals and glasses is presented along with a working guide for its use published data and experimental conditions are listed in tables and these are preceded by an outline of diffusion mechanisms terminology equations and units diffusion regimes factors controlling diffusion rates measurement techniques and diffusional behaviour

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

high precision sims oxygen three isotope study of chondrules in ll3 chondrites role of ambient gas during chondrule formation we report high precision sims oxygen three isotope analyses of 36 chondrules from some of the least equilibrated ll3 chondrites and find systematic variations in oxygen isotope ratios with chondrule types feo poor type i chondrules generally plot along a mass dependent fractionation line d 17 o 0 7 with d 18 o values lower in olivine rich ia than pyroxenerich ib chondrules data from feo rich type ii chondrules show a limited range of d 18 o and d 17 o values at d 18 o 4 5 d 17 o 2 9 and d 17 o 0 5 which is slightly 16 o enriched relative to bulk ll chondrites d 17 o 1 3 data from four chondrules show 16 o rich oxygen isotope ratios that plot near the ccam carbonaceous chondrite anhydrous mineral line glass analyses in selected chondrules are systematically higher than co existing minerals in both d 18 o and d 17 o values whereas high ca pyroxene data in the same chondrule are similar to those in olivine and pyroxene phenocrysts our results suggest that the ll chondrite chondrule forming region contained two kinds of solid precursors 1 16 o poor precursors with d 17 o 1 6 and 2 16 o rich solid precursors derived from the same oxygen isotope reservoir as carbonaceous chondrites oxygen isotopes exhibited open system behavior during chondrule formation and the interaction between the solid and ambient gas might occur as described in the following model significant evaporation and recondensation of solid precursors caused a large mass dependent fractionation due to either kinetic or equilibrium isotope exchange between gas and solid to form type ia chondrules with higher bulk mg si ratios type ii chondrules formed under elevated dust gas ratios and with water ice in the precursors in which the ambient h2o gas homogenized chondrule melts by isotope exchange low temperature oxygen isotope exchange may have occurred between chondrule glasses and aqueous fluids with high d 17 o 5 in ll the parent body according to our model oxygen isotope ratios of chondrules were strongly influenced by the local solid precursors in the proto planetary disk and the ambient gas during chondrule melting events 2010 elsevier ltd all rights reserved

spatial attenuation the most sensitive ultrasonic parameter for detecting petrographic features and decay processes in carbonate rocks abstract the evaluation of stone quality by means of non destructive tests is of vital importance especially when rock is used as a building material usually however only vp p wave velocity is considered when rock properties such as strength durability or decay level are assessed in this paper we propose a novel ultrasonic estimator based on wave energy spatial attenuation s the benefits of this estimator were evaluated by comparison with five other ultrasonic parameters compressional v p and shear v s wave velocities velocity ratio v p v s waveform energy and temporal attenuation the sensitivity of each ultrasonic parameter was compared by measuring 300 samples from ten different types of rock each type was selected according to its mineralogy calcite and or dolomite rock and structural complexity homogeneous fractured brecciated foliated or laminated samples were subjected to weathering tests thermal shock and salt crystallisation tests in order to study the sensitivity of both ultrasonic parameters during fracture initiation fracture growth and rock fabric disintegration results show that although vp is the most widely used parameter the information it yields is extremely imprecise however the new parameter s is highly sensitive to the petrographic characteristics of rocks as well as to the presence of individual defects fractures vugs or disintegrated areas moreover the most significant aspect of s is that its values fall between two fixed limits 0 db cm and 20 db cm a rock with a s value close to 0 db cm is an unweathered homogeneous and good quality rock whilst a s value higher than 12 db cm indicates extreme decay i e open fractures developed vugs and or disintegrated areas

sulfur isotope composition of putative primary troilite in chondrules from bishunpur and semarkona the sulfur isotopic compositions of putative primary troilite grains within 15 ferromagnesian chondrules 10 feo poor and 5 feo rich chondrules in the least metamorphosed ordinary chondrites bishunpur and semarkona have been measured by ion microprobe some troilite grains are located inside metal spherules within chondrules since such an occurrence is unlikely to be formed by secondary sulfidization processes in the solar nebula or on parent bodies those troilites are most likely primary having survived chondrule forming high temperature events if they are primary they may be the residues of evaporation at high temperatures during chondrule formation and may have recorded mass dependent isotopic fractionations however the supposed primary troilites measured in this study do not show any significant sulfur isotopic fractionations 104 106 k h would be required to avoid a large degree of sulfur isotopic fractionation in the chondrule precursors this heating rate may provide a new constraint on the chondrule formation processes

oxygen isotopic constraints on the origin of mg rich olivines from chondritic meteorites chondrules are the major high temperature components of chondritic meteorites which accreted a few millions years after the oldest solids of the solar system the calcium aluminum rich inclusions were condensed from the nebula gas chondrules formed during brief heating events by incomplete melting of solid dust precursors in the protoplanetary disk petrographic compositional and isotopic arguments allowed the identification of metal bearing mg rich olivine aggregates among the precursors of magnesian type i chondrules two very different settings can be considered for the formation of these mg rich olivines either a nebular setting corresponding mostly to condensation evaporation processes in the nebular gas or a planetary setting corresponding mostly to differentiation processes in a planetesimal an ion microprobe survey of mg rich olivines of a set of type i chondrules and isolated olivines from unequilibrated ordinary chondrites and carbonaceous chondrites revealed the existence of several modes in the distribution of the 17o values and the presence of a large range of mass fractionation several within each mode the chemistry and the oxygen isotopic compositions indicate that mg rich olivines are unlikely to be of nebular origin i e solar nebula condensates but are more likely debris of broken differentiated planetesimals each of them being characterized by a given 17o mg rich olivines could have crystallized from magma ocean like environments on partially molten planetesimals undergoing metal silicate differentiation processes considering the very old age of chondrules mg rich olivine grains or aggregates might be considered as millimeter sized fragments from disrupted first generation differentiated planetesimals finally the finding of only a small number of discrete 17o modes for mg rich olivines grains or aggregates in a given chondrite suggests that these shattered fragments have not been efficiently mixed in the disk and or that chondrite formation occurred in the first vicinity of the breakup of these planetary bodies

formation of niningerite by silicate sulfidation in eh3 enstatite chondrites unequilibrated eh chondrites contain silica bearing chondrules with abundant niningerite mg fe mn s and troilite fes distinguishing them from the silica bearing chondrules in ordinary and carbonaceous chondrites the conventional explanation for the origin of niningerite and oldhamite cas is that they are condensates from c rich nebular gas however models of condensation from a solar gas with an elevated c o ratio predict mineralogy that is inconsistent with petrographic observations we report petrographic and chemical evidence from 45 silica bearing chondrules from the eh3 chondrites sahara 97072 and alan hills 84170 for formation of niningerite and oldhamite by sulfidation of ferromagnesian silicates the results indicate extensive thermal processing of the chondrules including melting before during and after sulfidation bulk compositions of chondrules exhibiting varied degrees of sulfidation suggest that depletion of mg and enrichment of fe mn and na accompany the reactions sulfidation of feo bearing silicates which formed at oxidizing conditions at least iw 3 can occur with exposure to a h poor c and s rich gaseous reservoir 6 8 fo2 log units below the iw buffer at temperatures high enough for partial melting of silicates physicochemical analysis of mineral reactions inferred from sulfidized chondrules suggests a melted metal sulfide assemblage in a h poor environment is capable of generating sufficient s vapor to drive sulfidation the reaction of silicates with the s gas will result in progressive extraction of fe ca and mg into sulfides with the stoichiometric amounts of silica either reacting with olivine to form enstatite or when olivine is exhausted precipitating as free silica the sulfidation environment drastically increases mg volatility resulting in evaporative loss until saturation in the ambient gas is reached the newly formed mg rich niningerite will tend to reach equilibrium composition by losing mg and gaining fe plus mn from the ambient gas consistent with the observed chemical fractionation in the sulfidized chondrules therefore sulfidation of ferromagnesian silicates can also explain the low bulk mg si ratios of the enstatite chondrites if the sulfidizing gas was lost before accretion of the enstatite chondrite parent body

metal and associated phases in bishunpur a highly unequilibrated ordinary chondrite it appears that the highly unequilibrated bishunpur ordinary chondrite preserves phase relations acquired during solar nebular processes to a relatively high degree metamorphic temperatures may not have exceeded 300 350 c the major categories of metal are 3 kinds of metal in the metal matrix three kinds in chondrule interiors and 2 kinds in chondrule rims the fine grained matrix metal is highly variable in composition the kamacite co content 7 8 2 0 mg g is within the l group range 6 7 8 2 mg g but extends well above and below its ni content 38 5 mg g is considerably lower than in more equilibrated chondrites and taenite is ni rich 450 mg g and unzoned these compositions imply equilibration at very low temperatures of about 300 350 c it seems unlikely that volume diffusion could account for the observed relatively unzoned phases a better model involves mass transport by grain boundary diffusion and grain growth at the indicated temperatures we find no evidence that the matrix was ever at higher temperatures large 50 650 m polycrystalline metal aggregates consisting of individually zoned crystals are also found in the matrix they probably represent clusters formed in the solar nebula a few large 50 250 m round monocrystalline grains are also present in the matrix metal bearing chondrules tend to be highly reduced they contain low ni metal that occasionally contains si and or cr silicates in these chondrules tend to have low feo feo mgo ratios the si rich metal grains are never in contact with silicates and are always surrounded by troilite with a poorly characterized ca cr sulfide at the metal troilite interface they appear to be high temperature nebular condensates that avoided oxidation even during the chondrule forming process silicon contents drop below our detection limit when the sulfide coating is absent much more common in chondrule interiors are si free spheroidal metal grains not associated with sulfides these have ni and co contents very similar to the si bearing grains and appear to be oxidized variants of the same material the third class of chondrule metal is fine 1 m dusty grains inside individual olivine grains these seem to reflect high temperature in situ reduction of feo from the olivine the composition of kamacite is different in sulfide rich and sulfide poor chondrule rims and in both cases it is dissimilar to the compositions in the chondrule interiors and matrix this indicates that chondrule rims could not have resulted from reactions with the matrix but are primary features acquired prior to accretton

petrology and oxygen isotope compositions of chondrules in e3 chondrites chondrules in e3 chondrites differ from those in other chondrite groups many contain near pure endmember enstatite fs 1 some contain si bearing feni metal cr bearing troilite and in some cases mg mn and ca sulfides olivine and more feo rich pyroxene grains are present but much less common than in ordinary or carbonaceous chondrite chondrules in some cases the feo rich grains contain dusty inclusions of metal the oxygen three isotope ratios 18o 17o of olivine and pyroxene in chondrules from e3 chondrites which are measured using a multi collection sims show a wide range of values most enstatite data plots on the terrestrial fractionation tf line near whole rock values and some plot near the ordinary chondrite region on the 3 isotope diagram pyroxene with higher feo contents 2 10 wt feo generally plots on the tf line similar to enstatite suggesting it formed locally in the ec enstatite chondrite region and that oxidation reduction conditions varied within the e3 chondrite chondrule forming region olivine shows a wide range of correlated 18o and 17o values and data from two olivine bearing chondrules form a slope 1 mixing line which is approximately parallel to but distinct from the ccam carbonaceous chondrite anhydrous mixing line we refer to this as the ecm enstatite chondrite mixing line but it also may coincide with a line defined by chondrules from acfer 094 referred to as the pcm primitive chondrite mineral line ushikubo et al 2011 the range of o isotope compositions and mixing behavior in e3 chondrules is similar to that in o and c chondrite groups indicating similar chondrule forming processes solid gas mixing and possibly similar 16o rich precursors solids however e3 chondrules formed in a distinct oxygen reservoir internal oxygen isotope heterogeneity was found among minerals from some of the chondrules in e3 chondrites suggesting incomplete melting of the chondrules survival of minerals from previous generations of chondrules and chondrule recycling olivine possibly a relict grain in one chondrule has an r chondrite like oxygen isotope composition and may indicate limited mixing of materials from other reservoirs calcium aluminum rich inclusions cais in e3 chondrites have petrologic characteristics and oxygen isotope ratios similar to those in other chondrite groups however chondrules from e3 chondrites differ markedly from those in other chondrite groups from this we conclude that chondrule formation was a local event but cais may have all formed in one distinct place and time and were later redistributed to the various chondrule forming and parent body accretion regions this also implies that transport mechanisms were less active at the time of and following chondrule formation

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

lithium isotope behaviour during partial melting of metapelites from the jiangnan orogen south china implications for the origin of ree tetrad effect of f rich granite and associated rare metal mineralization abstract we carried out combined nd and li isotopic studies on the neoproterozoic biotite granites late mesozoic evolved two mica muscovite granites and associated the shuangqiaoshan group metapelites from the jiangnan orogen south china which along with petrological and geochemical data were used to constrain the lithium isotopic behavior during partial melting of metapelites the origin of the ree tetrad effect in evolved granites and implications for related rare metal mineralization the neoproterozoic biotite granites show features typical of s types e g high a cnk ratios and have end 6 9 to 10 and 7li 2 2 4 comparable to the shuangqiaoshan group metapelites with end 6 to 11 and 7li 2 3 7 respectively suggesting that the biotite granites were derived from melting of the metapelites and the li isotopic fractionation during the melting process appears negligible the two late mesozoic shimensi and zengjialong granites occur as small stocks showing high silica peraluminous low cao and sr contents variably enrichment in volatiles f b and are accompanied by w cu and sn mineralization the shimensi granites have end t values of 7 0 8 6 and 7li 2 7 3 9 similar to the shuangqiaoshan group metapelites whereas the zengjialong granites have relatively high end t values 5 1 7 3 and heavy li isotopic features mostly 7li 0 18 1 53 and particularly ree tetrad effect is seen in the latter we argue that the late mesozoic evolved granites formed as a result of re melting of the granulitic residues left in the lower crust after extraction of the neoproterozoic biotite granites from the metapelites such re melting of the residues was triggered by underplating of basaltic magma with more mantle input and f b as well in the source of the zengjialong granites the elevated 7li values of the zengjialong granites were probably caused by intense interaction between melt and external fluids during magma emplacement which in turn resulted in the formation of the ree tetrad effect in the granites isotopic modeling suggests that fluid exsolution from evolved granites is minor and is less likely to have been responsible for the extensive rare metal mineralization as traditionally thought

sulfur and sulfides in chondrules abstract the nature and distribution of sulfides within type i po pop and pp chondrules of the carbonaceous chondrite vigarano cv3 have been studied by secondary electron microscopy and electron microprobe they occur predominantly as spheroidal blebs composed entirely of low ni iron sulfide troilite fes or troilite magnetite but in less abundance in association with metallic fe ni beads in opaque assemblages troilites are mainly located within the low ca pyroxene outer zone and their amounts increase with the abundance of low ca pyroxene within chondrules suggesting co crystallization of troilite and low ca pyroxene during high temperature events we show that sulfur concentration and sulfide occurrence in chondrules obey high temperature sulfur solubility and saturation laws depending on the f s 2 and f o 2 of the surrounding gas and on the melt composition mainly the feo content sulfur dissolved in chondrule melts may eventually reach a concentration limit the sulfur content at sulfide saturation scss at which an immiscible iron sulfide liquid separates from the silicate melt the occurrence of both a silicate melt and an immiscible iron sulfide liquid is further supported by the non wetting behavior of sulfides on silicate phases in chondrules due to the high interfacial tension between their precursor iron sulfide liquid droplets and the surrounding silicate melt during the high temperature chondrule forming event the evolution of chondrule melts from po to pp towards more silicic compositions very likely due to high p sio g of the surrounding nebular gas induces saturation of fes at much lower s content in pp than in po chondrules leading to the co crystallization of iron sulfides and low ca pyroxenes conditions of co saturation of low ca pyroxene and fes are only achieved in non canonical environments characterized by high partial pressures of sulfur and sio and redox conditions more oxidizing than iw 3 fe and s mass balance calculations also suggest the occurrence of an external source of iron very likely gaseous during chondrule formation we therefore propose that enrichments in sulfur and other volatile and moderately volatile elements from po to pp type i bulk chondrule compositions towards chondritic values result from progressive reaction between partially depleted olivine bearing precursors and a volatile rich gas phase

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

the importance of experiments constraints on chondrule formation models abstract we review a number of constraints that have been placed on the formation of chondrules and show how these can be used to test chondrule formation models four models in particular are examined the x wind model sudden exposure to sunlight 0 1 au from the proto sun with subsequent launching in a magnetocentrifugal outflow solar nebula lightning nebular shocks driven by eccentric planetesimals and nebular shocks driven by diskwide gravitational instabilities we show that constraints on the thermal histories of chondrules during their melting and crystallization are the most powerful constraints and provide the least ambiguous tests of the chondrule formation models such constraints strongly favor melting of chondrules in nebular shocks shocks driven by gravitational instabilities are somewhat favored over planetesimal bow shocks

a comparative study of opaque phases in qingzhen eh3 and macalpine hills 88136 el3 representatives of eh and el parent bodies opaque minerals in the qingzhen eh3 and macalpine hills mac 88136 el3 enstatite chondrites were studied and compared with other eh and el chondrites all opaque minerals usually occur in multi sulfide metal clasts and nodules in the matrix between chondrules el goresy et al 1988 the higher abundance of opaque minerals the occurrence of niningerite and various alkali sulfides e g caswellsilverite phases a and b djerfisherite are diagnostic criteria for eh chondrites while alabandite is characteristic for el chondrites in addition eh chondrites are characterized by enrichments of si in both kamacite and perryite and alkali elements in sphalerite and chalcopyrite the mn contents of daubreelite and sphalerite are lower in eh than in el chondrites these are consistent with lower oxygen fugacity and higher h2s fugacity of eh than el chondrites in contrast the discovery of sphalerite and zn rich daubreelite in mac 88136 indicates that their absence in el6 chondrites is probably related to thermal metamorphism in the parent body schreibersite microspherules are commonly enclosed in most sulfides in qingzhen but are absent in mac 88136 they were once molten and probably predated all sulfide host phases the petrographic setting and chemical compositions of the sulfide hosts of the schreibersite microspherules in eh3 chondrites are consistent with formation by condensation the earliest sulfide condensates oldhamite and niningerite occupy the interiors of the clasts and nodules whereas the rims consist of troilite and djerfisherite in addition in qingzhen some other troilite djerfisherite and sphalerite assemblages coexist with perryite they were produced by sulfurization of metallic fe ni in the nebula in mac 88136 sulfurization of si bearing fe ni metal is less pronounced and it produced troilite schreibersite and less abundant perryite two kinds of normal zoning and a reverse zoning trends of niningerite and both normal and reverse zoning of sphalerite were found in clasts and nodules in qingzhen the coexistence of normal and reverse zoning profiles in niningerite grains in the same meteorite strongly suggests that they formed before accretion in the parent body because an asteroidal metamorphic or an impact event in the parent body would have erased these contrasting profiles and destroyed the textural settings in contrast alabandite in mac 88136 shows only normal zoning with the fes content decreasing to 9 3 mol toward troilite indicating very slow cooling at low temperature

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

the origin and history of the metal and sulfide components of chondrules abstract fourteen siderophile and other non lithophile elements determined in 31 semarkona ll3 0 chondrules by neutron activation analysis are severely fractionated relative to lithophile elements their chondrule whole rock abundance ratios vary by factors of up to 1000 the mean ratio is 0 2 non refractory siderophile abundance patterns in ni rich chondrules are smooth functions of volatility and in ni poor chondrules patterns are more irregular refractory siderophile elements are often fractionated from ni they covary confirming the presence of a refractory metal component the chalcophile element se correlates with br and siderophile elements zinc is uniformly low and uncorrelated with other elements most metal and sulfide in chondrules was probably present in the solar nebula before chondrule formation most siderophile and chalcophile elements were in these materials some fe was also in silicates as were minor amounts of ni co au ge and possibly se the amount of metal formed by reduction during chondrule melting was minor the common metal component in chondrules is similar to and may be the same as the common component involved in the metal silicate fractionation of the ordinary chondrite groups chondrules are depleted in metal chiefly because they sampled metal poor precursor assemblages metal segregation during the molten period and subsequent loss was a minor process that may be responsible for most surface craters on chondrules

the fountain hills unique cb chondrite insights into thermal processes on the cb parent body we report the results of an extensive study of the fountain hills chondritic meteorite this meteorite is closely related to the cba class mineral compositions and o isotopic ratios are indistinguishable from other members of this group however many features of fountain hills are distinct from the other cb chondrites fountain hills contains 23 volume percent metal significantly lower than other members of this class in addition fountain hills contains porphyritic chondrules which are extremely rare in other cba chondrites fountain hills does not appear to have experienced the extensive shock seen in other cb chondrites the chondrule textures and lack of fine grained matrix suggests that fountain hills formed in a dust poor region of the early solar system by melting of solid precursors refractory siderophiles and lithophile elements are present in near ci abundances within a factor of two related to the enhancement of metal moderately volatile and highly volatile elements are significantly depleted in fountain hills the abundances of refractory siderophile trace elements in metal grains are consistent with condensation from a gas that is reduced relative to solar composition and at relatively high pressures 10 3 bars fountain hills experienced significant thermal metamorphism on its parent asteroid combining results from the chemical gradients in an isolated spinel grain with olivine spinel geothermometry suggests a peak temperature of metamorphism between 535 c and 878 c similar to type 4 ordinary chondrites

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

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

mineralogy and texture of fe ni sulfides in ci1 chondrites clues to the extent of aqueous alteration on the ci1 parent body to better understand the role of aqueous alteration on the ci1 parent body we have analyzed the texture composition and mineral associations of iron nickel sulfides in four of the five known ci1 chondrites the most commonly occurring sulfide present in the ci1 chondrites is the iron deficient fe ni sulfide pyrrhotite fe ni 1 xs that has a composition close to that of stoichiometric troilite fes three of the ci1s alais ivuna and tonk also contain pentlandite fe ni 9s8 although pentlandite is a rare phase in ivuna cubanite cufe2s3 was found in both alais and ivuna in this study although it has also been reported in orgueil macdougall and kerridge 1977 the pyrrhotite grains in all four chondrites form hexagonal rectangular or irregular shapes and show no evidence of ni or co zoning the pyrrhotite grains in orgueil and ivuna are in general smaller and show more corrosions or embayments than those in alais or tonk we suggest that the precursor sulfide present in the ci1 chondrites was troilite which during brecciation and oxidation on the parent body at a temperature of 100 c or less converted the troilite to magnetite and pyrrhotite with pentlandite inclusions subsequently continued alteration on the parent body removed pentlandite partially from alais tonk and ivuna completely from orgueil leaving behind pyrrhotite with spaces corrosions where the pentlandite had been ni derived from the pentlandite was incorporated into ferrihydrite onto the surface of which the ni na sulfate ni bloedite formed based on the size and abundant corrosions within pyrrhotite grains combined with observations from other authors we conclude that orgueil and ivuna have undergone a greater degree of alteration than alais and tonk further work is needed to assess the conditions under which pentlandite would be dissolved preferentially to pyrrhotite as the study of terrestrial literature indicates that the latter mineral is preferentially removed

oxygen isotope ratios of feo poor chondrules in cr3 chondrites influence of dust enrichment and h2o during chondrule formation abstract we present detailed electron microprobe analyses and oxygen three isotope measurements by high precision secondary ion mass spectrometry on 45 type i feo poor chondrules fragments and 3 type ii feo rich chondrule fragments from meteorite hills 00426 and queen alexandra range 99177 two of the most primitive cr3 chondrites type i chondrules fragments have mg s defined as the mg of constituent olivine and or low ca pyroxene ranging from 94 2 to 99 2 type ii chondrule fragments have mg s of 53 63 oxygen three isotope measurements plot on the slope 1 primitive chondrule mineral pcm line within chondrules 17 o 17 o 0 52 18 o values of coexisting olivine pyroxene and plagioclase are homogeneous with propagated uncertainties of 0 3 this indicates each phase crystallized from the final chondrule melt and that efficient oxygen isotope exchange occurred between ambient gas and chondrule melt among type i chondrules there is a well defined increase in 17 o from 5 9 to 1 as mg s decrease from 99 2 to 96 type ii chondrule fragments are comparatively 16 o poor 17 o 0 2 0 6 the relationship between mg and 17 o among type i chondrules confirms that addition of a 16 o poor oxidizing agent to the highest mg chondrule precursors resulted in forming lower mg cr chondrules using aspects of existing equilibrium condensation models and a mass balance we estimate that type i cr chondrules formed at dust enrichments of 100 200 from dusts with 0 0 8 times the atomic abundance of ice relative to ci dust the type ii chondrule fragments are predicted to have formed at ci dust enrichments near 2500

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

troilite in the chondrules of type 3 ordinary chondrites implications for chondrule formation abstract the presence of primary troilite in chondrules requires that nebular temperatures were 1170 k but much less ni at lower temperatures because this is far higher than the metamorphic temperature inferred for semarkona 670 k the troilite must be primary primary troilite fitting the three criteria occurs in a smaller fraction of low feo feo feo mgo in olivine and or low ca pyroxene not greater than 0 075 than high feo porphyritic chondrules in semarkona 9 vs 33 coarse grained low feo porphyritic chondrules appear to contain somewhat more troilite on average than those of medium grain size we found a few troilite free metallic fe ni bearing low feo chondrules that contain na2o bearing augite and na2o and k2o rich mesostasis these chondrules were probably formed after ambient nebular temperatures cooled below 910 k the 50 condensation temperature of na and before they reached 650 k literature reports of rare fayalitic microchondrules in the rims around a few normal size chondrules suggest that chondrule formation persisted until nebular temperatures cooled below 500 k secondary troilite occurs in a few percent of semarkona chondrules as thin veins mobilized by shock troilite or pyrrhotite in the outer portions of some chondrules occur within opaque assemblages containing magnetite carbide ni rich sulfide awaruite and co rich kamacite produced by parent body hydrothermal alteration

the carlisle lakes type chondrites a new grouplet with high δ17o and evidence for nebular oxidation abstract carlisle lakes alh85151 and y75302 are similar ungrouped chondrites which have petrologic and bulk compositional similarities to the ordinary chondrites but are more oxidized and their oxygen isotopic compositions differ they represent a new grouplet which we call the carlisle lakes type chondrites they have the highest 17o values up to 2 91 measured to date the whole chondrites and most of their chondrules plot on the same mass fractionation line on an oxygen 3 isotope diagram they are olivine rich 70 vol essentially metal free and most olivine is feo rich equilibrated at fa38 rare olivine and pyroxene grains in chondrules and fragments are zoned and these are important in discerning the history of these chondrites the zoning does not appear to have formed during crystallization from a melt droplet chondrule but post dated chondrule formation two hypotheses are postulated to explain the zoning 1 1 parent body thermal metamorphism 2 2 nebular gas solid exchange reactions accompanied by condensation of new feo rich olivine utilizing existing olivine surfaces as nucleation sites the occurrence of steep fe mg compositional gradients of core to rim profiles oscillatory zoning in olivine fayalitic rims of fa45 that exceed instead of approach the equilibrium composition of the matrix fa38 and olivine filled veins in zoned pyroxenes are more compatible with the nebular hypothesis the carlisle lakes type chondrites may have originally been derived from an ordinary chondrite like precursor which was later oxidized prior to its final lithification however the oxygen isotopic compositions of the whole chondrites and most of their chondrules suggest that the precursor probably formed in an oxygen isotopically distinct environment