the kaidun chondrite breccia petrology oxygen isotopes and trace element abundances abstract oxygen isotope and trace element data for 13 samples of the kaidun chondritic breccia reaffirm the complex polymict nature of this unique meteorite bulk kaidun samples most closely resemble cr chondrites but the matrix is ci like two separated clasts are cr like but have some properties that resemble cm two clasts are enstatite chondrites one el and one eh one clast is an aubrite like metal rich impact melt and one clast is a unique layered olivine bearing pyroxenite with the isotopic composition of an aubrite yet although each clast resembles a known meteorite group all deviate in some respect from the norms for those groups collectively kaidun has sampled materials not yet represented in the world meteorite collections and which greatly extend the definitions of known meteorite groups phyllosilicates in kaidun span a very wide range in composition and vary from clast to clast suggesting that the aqueous alteration experienced by the clasts predated assembly of the kaidun parent body

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

olivine in terminal particles of stardust aerogel tracks and analogous grains in chondrite matrix abstract the dearth of both major and minor element analyses of anhydrous silicate phases in chondrite matrix has thus far hindered their comparison to the wild 2 samples we present 68 analyses of olivine fa 0 97 in the coarse grained terminal particles of stardust aerogel tracks and a comprehensive dataset 10 3 analyses of analogous olivine grains 5 30 m isolated in ci cm cr ch co cv3 oxidized cv3 reduced c3 ungrouped acfer 094 and ningqiang l ll 3 0 4 eh3 and kakangari chondrite matrix these compositions reveal that wild 2 likely accreted a diverse assortment of material that was radially transported from various carbonaceous and ordinary chondrite forming regions the wild 2 olivine includes amoeboid olivine aggregates aoas refractory forsterite type i and type ii chondrule fragments and or microchondrules and rare relict grain compositions in addition we have identified one terminal particle that has no known compositional analog in the meteorite record and may be a signature of low temperature aqueous processing in the kuiper belt the generally low cr content of feo rich olivine in the stardust samples indicates that they underwent mild thermal metamorphism akin to a petrologic grade of 3 05 3 15

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

in situ measurements of sediment settling characteristics in ﬂoodplains using a lisst st due to a lack of data on settling velocities ws and grain size distributions gsds in oodplain environments sedimentation models often use calibrated rather than measured parameters since the characteristics of suspended matter differ from those of deposited sediment it is impossible to derive the ws and gsd from the latter therefore one needs to measure in situ suspended sediment concentrations sscs settling velocities effective grain sizes and sedimentation uxes for this purpose we used the lisst st a laser particle sizer combined with a settling tube in 2002 twice and 2004 we located the lisst st with an optical backscatter sensor and sediment traps in two oodplains in the netherlands one along the unembanked ijssel river another along the embanked waal river measurements revealed that the ssc in the oodplains varied in relation to the ssc in the river channel smaller ocs dominated the ssc while larger ocs dominated the potential sedimentation uxes the in situ gsd in the ijssel oodplain was signi cantly coarser than in the waal oodplain while the dispersed median grain sizes were equal for both oodplains therefore the dispersed median grain size was two to ve times smaller than the effective one the in situ grain size exhibited a signi cant positive relationship with ws although the ws for the largest ocs showed high variability consequently the variability in sedimentation uxes was also large in the actual sedimentation uxes and hence in sedimentation models in situ grain sizes up to about 20 m can be neglected in oodplain sedimentation models the relation between settling velocity and in situ grain size can be used instead of stokes s law which is only valid for dispersed grain sizes these models should also use adequate data on ow conditions as input since these strongly in uence the suspended sediment characteristics copyright 2005 john wiley sons ltd

composition and origin of clasts and inclusions in the abee enstatite chondrite breccia abstract the concentrations of 25 major minor and trace elements have been determined in four clasts a metal rich inclusion and two dark metal poor inclusions from the abee enstatite chondrite the clasts are heterogeneous displaying 2 fold enrichments or depletions in some elements the data suggest that there are two generations of metal one with low the other with high concentrations of refractory siderophiles the other elemental patterns can be understood in terms of variations in the abundance of major minerals we infer that sc and mn are located largely in the niningerite fe mg s v in the troilite fes and rare earth elements in the oldhamite cas heterogeneities among the clasts are probably primary resulting from the accretion agglomeration process although shock processes in a regolithic setting remain a possibility provided that they were followed by a period of metamorphism sufficient to erase petrologic evidence in the dark inclusions the concentrations of the rare earths eu excepted are 4 higher than mean eh levels this infers enhanced amounts of cas the dark inclusions are low in siderophiles sc mn k na and al implying low amounts of metal niningerite and feldspar the origin of the dark inclusions is unclear they do not appear to be the result of a simple single stage process

diopside bearing el6 eet 90102 insights from rare earth element distributions abstract eet 90102 is the first known diopside bearing el6 chondrite diopside occurs in most aubrites and is occasionally found as rare small grains in unequilibrated enstatite chondrites but is unknown from equilibrated enstatite chondrites we have carried out a study of the rare earth element ree distributions in eet 90102 with a specific emphasis on diopside in order to better understand its origin in this meteorite we also present data for ca rich pyroxenes from two unequilibrated eh3 enstatite chondrites for comparison our data show that diopside and other silicates in eet 90102 exhibit volatility related anomalies indicative of formation under highly reducing conditions such anomalies have not previously been observed in el6 chondrites although they are common in unequilibrated enstatite chondrites diopside in eet 90102 probably formed by metamorphic equilibration of enstatite and oldhamite the ree compositions of some grains in particular the presence of positive yb anomalies indicate that they inherited their ree characteristics largely from cas other grains have ree patterns that are more consistent with a derivation of diopside primarily from enstatite in contrast to other el6 chondrites which experienced slow cooling eet 90102 was quenched from high metamorphic temperatures thus there may have been insufficient time to completely homogenize diopside ree compositions the presence of diopside in eet 90102 simplifies one outstanding problem of aubrite formation melting of a diopside bearing enstatite chondrite protolith provides a source for the abundant diopside in aubrites without requiring the oxidation of oldhamite as suggested by previous research

chemical and physical studies of type 3 chondrites i metamorphism related studies of antarctic and other type 3 ordinary chondrites abstract thermoluminescence sensitivity measurements have been made on 18 unequilibrated ordinary chondrites 12 finds from antarctica 5 non antarctic finds and 1 fall the tl sensitivities of these meteorites normalized to dhajala range from 0 034 st mary s county to 2 3 allan hills a78084 and based primarily on these data petrologic type assignments range from 3 3 st mary s county to 3 9 allan hills a78084 although the very low levels of metamorphism experienced by types 3 0 to 3 4 evidently cause large changes in tl sensitivity the new data demonstrate that they are unable to cause any appreciable homogenization of silicate compositions we have therefore slightly revised the silicate heterogeneity ranges corresponding to the lower petrologic types we have discovered that the temperature of maximum tl emission and the broadness of the major tl peak vary systematically with tl sensitivity as tl increases these parameters first decrease and then increase several mechanisms which could account partially or completely for the relationship between tl sensitivity and metamorphism are discussed those which involve the formation of feldspar the tl phosphor in equilibrated meteorites seem to be consistent with the trends in peak temperature and peak width since experiments on terrestrial albite show that the tl peak broadens and moves to higher temperatures as the stable form changes from the low ordered state to the high disordered state the post metamorphism equilibration temperature of type 3 5 meteorites would then correspond to the transformation temperature for the high to low form of meteorite feldspar other factors which may be involved are obscuration of the tl by carbonaceous material changes in the composition of the phosphor and changes in the identity of the phosphor

the adhi kot breccia and implications for the origin of chondrules and silica rich clasts in enstatite chondrites abstract the adhi kot eh4 enstatite chondrite breccia consists of silica rich clasts 12 mn 5 vol chondrule rich clasts 55 mn 10 vol and matrix 35 mn 10 vol the silica rich clasts are a new kind of enstatite chondritic material which contains more cristobalite 18 28 wt than enstatite 12 14 wt as well as abundant niningerite and troilite the bulk atomic mg si ratios of the clasts 0 22 0 40 are much lower than the average for enstatite chondrites 0 79 kamacite and martensite with 8 11 wt ni and a martensitic structure occur in all three breccia components the clasts have kamacite rich rims and kamacite rich aggregates occur in the matrix a unidirectional change in the ambient ps2 po2 ratio in the region of the solar nebula where adhi kot agglomerated can explain many of the breccia s petrologic features if this region initially had a very high ps2 po2 ratio in a gas of non cosmic composition sulfurization of enstatite and metallic fe e g mgsio3 2fe c 3h2s mgs sio2 2fes h2o ch4 may have occurred producing abundant niningerite free silica and troilite at the expense of enstatite and metallic fe the ni content of the residual metal would have increased perhaps to 8 10 wt the silica rich clasts agglomerated under these conditions a significant fraction of the originally produced niningerite was lost perhaps by aerodynamic size sorting processes lowering the clasts bulk mg si ratios the ps2 po2 ratio then decreased perhaps because of infusion of additional h2o and sulfurization of metallic fe and enstatite ceased the chondrule rich clasts agglomerated under these conditions acquiring little free silica and niningerite an episode of chondrule formation occurred at this time by melting millimeter sized agglomerates of this relatively silica poor enstatite chondrite material and concomitant fractionation of an immiscible liquid of metallic fe ni and sulfide the chondrule rich clasts agglomerated many such chondrules subsequently the matrix agglomerated acquiring the few remaining chondrules kamacite rich aggregates formed after the cessation of metal sulfurization and agglomerated with the matrix the kamacite rich clast rims were acquired at this time the components of adhi kot accreted to the eh chondrite parent body where the breccia was assembled buried beneath additional accreting material and metamorphosed at temperatures of 700 c impact excavation of the breccia and deposition onto the surface caused the formation of martensite from taenite inside the clasts and the matrix at the surface impact melting produced an albite glass spherule which was incorporated into the matrix however the absence of solar wind implanted rare gases in bulk adhi kot indicates that the breccia spent little time in a regolith

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

the blithfield meteorite and the origin of sulfide rich metal poor clasts and inclusions in brecciated enstatite chondrites abstract blithfield el6 is one of five known enstatite chondrite breccias it consists of troilite rich clasts 35 5vol embedded in an extremely metallic fe ni rich matrix 65 5 vol that contains metal nodules up to 17 mm in size clasts and matrix agglomerated independently in the solar nebula under conditions of high and low ps 2 po 2 ratios respectively the matrix accreted to an el chondrite planetesimal and was metamorphosed to 1000 c above the fe ni s eutectic chondrule textures were obliterated the s rich eutectic melt was lost from the matrix the matrix material was buried to a depth of at least 3 km accreting troilite rich material was incorporated into the matrix as clasts the breccia cooled through 500 c at 1000 10 000 c myr after cooling below 500 c blithfield was quenched possibly by impact excavation from depth and deposition onto the surface clasts or inclusions that are enriched in sulfide and depleted in metallic fe ni are common in brecciated enstatite chondrites variations in the ps 2 po 2 ratio in the nebular regions where these materials formed may explain many of their petrologic properties the silica rich clasts in adhi kot eh4 formed at very high ps 2 po 2 ratios 10 27 niningerite free silica and troilite were produced from the sulfurization of enstatite and metallic fe the troilite rich clasts in blithfield and atlanta el6 as well as the troilite rich regions of the hvittis el6 matrix formed at somewhat lower ps 2 po 2 ratios where sulfurization of metalic fe produced troilite the ni content of the residual metal increased forming some metal of martensitic composition the dark inclusions in abee eh 4 which contain up to 9 wt oldhamite formed at high ps 2 po 2 ratios in the presence of an additional ca rich component

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

chondrules in the qingzhen type 3 enstatite chondrite possible precursor components and comparison to ordinary chondrite chondrules abstract the qingzhen eh3 fall appears to be the least equilibrated enstatite chondrite mineral compositions vary widely from chondrule to chondrule and in some cases from grain to grain within individual chondrules as in ordinary chondrite oc chondrules most elements show appreciable ranges in concentration porphyritic olivine pyroxene pop chondrules are richer than porphyritic pyroxene pp and radial pyroxene rp chondrules in refractory lithophiles and siderophiles unlike oc chondrules qingzhen s rp and pp chondrules have similar bulk compositions elements in each of the following sets intercorrelate significantly probably because these elements were present in the same nebular components 1 1 fe co ni ir au 2 2 ca eu se 3 3 al sc hf 4 4 na ree 5 5 cl br several additional elements show no correlations set 1 elements were probably derived from a metal component as in oc chondrules set 3 elements which occur in higher concentrations in olivine bearing pop chondrules suggest the existence of a refractory lithophile rich olivine rich component similar to the one previously inferred for oc chondrules set 2 elements suggest a precursor component rich in oldhamite and set 4 elements suggest another refractory bearing component components 2 and 4 were not precursors of oc chondrules for some chondrules interelement ratios of refractory lithophiles such as ca al ti sc and ree are similar to ci ratios this indicates that these elements were probably derived from silicates we suggest that the earliest solid phases were refractory silicates that were sulfurized before chondrule formation some of these sulfurized components e g one rich in oldhamite were abundant in the region where the qingzhen chondrules formed

oxygen isotopic compositions of enstatite chondrites and aubrites oxygen isotopic compositions have been measured for ten eh chondrites eight el chondrites and nine aubrites the mean 18o and 17o values are 5 31 and 2 74 5 57 and 2 96 5 24 and 2 70 respectively within the eh group more equilibrated meteorites are fractionated toward higher heavy isotope abundances than the less equilibrated meteorites small departures of individual meteorites from a common mass fractionation occur for some of the eh samples the aubrites may be genetically related to either the eh or el group or to both almost all of the measured isotopic compositions are indistinguishable from the terrestrial oxygen isotope fractionation line suggesting a genetic relationship among the earth the moon and the enstatite the meteorites

microbial colonization and weathering of silicates in a petroleum contaminated groundwater abstract the influence of native microorganisms on mineral dissolution and precipitation was examined in a petroleum contaminated aquifer near bemidji minnesota in situ microcosms containing clean silicate fragments were established in the contaminated microbially active groundwater over one year periods the recovered minerals were then examined by sem and esem for microbial colonization patterns and weathering features these experiments reveal distinct patterns of colonization and weathering associated with microbial attachment and growth microcline anorthoclase and oligoclase were widely colonized and the colonized surfaces deeply weathered with secondary clays precipitated on some uncolonized surfaces other feldspars in contrast were uncolonized and unweathered specific mineral removal rate was estimated from etch pit depth while bulk weathering rate was estimated from the rate of change of silica concentration in the groundwater in this system the primary control of silicate dissolution is apparently microbial colonization and metabolic activity

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

geochemical and petrographic studies of oldhamite diopside and roedderite in enstatite meteorites in qingzhen eh3 oldhamite contains numerous types of inclusions and intergrows with other phases but in equilibrated enstatite chondrites and aubrites it usually occurs as individual grains i suggest that oldhamite in unequilibrated enstatite chondrites uecs crystallized from a melt probably during chondrule formation subsequent thermal metamorphism on the parent bodies further modified the oldhamite occurrences in enstatite chondrites this suggestion is consistent with the results of melting experiments on uecs and aubrites and with the volatile element enrichments in this mineral i analyzed minor and trace element abundances in diopside from two aubrites these data and petrographic observations suggest that diopside formed by igneous crystallization i report the first known occurrence of roedderite in an aubrite and its major minor and trace element concentrations this mineral is rich in alkalis but is depleted in siderophile and refractory lithophile elements a negative sm anomaly was noted in albite from equilibrated enstatite chondrites and aubrites

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

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

composition and origin of enstatite in e chondrites our petrologic and electron probe study of enstatite in six eh3 4 and 5 chondrites including the previously undescribed allan hills a77156 provides no support for leitch and smith s 1982 model in which crystals and liquids from two chemically distinct partially molten planetesimals are mixed we find that cr and mn concentrations in enstatite grains in matrix and chondrules are not uniquely defined by their cathodoluminescence color wide variations in enstatite compositions among chondrules may partly reflect heterogeneities in the precursor material however correlated variations of cr mn and fe concentrations in enstatite are probably largely due to fractionation during chondrule crystallization the inverse correlation of petrologic type with minor element concentrations in enstatite appears to be a metamorphic effect

evidence for relict grains in chondrules of qingzhen an e3 type enstatite chondrite abstract petrographic and chemical studies of the qingzhen chondrite strongly suggest that it is the most highly unequilibrated type 3 enstatite chondrite recognized so far qingzhen contains abundant well defined chondrules some of which were incompletely molten during the chondrule formation process the relict olivine grains within these chondrules contain dusty inclusions of almost pure metallic fe which appear to be the in situ reduction product of the fayalitic component of the olivine the reduction process presumably took place at the time of chondrule formation and the chondrule precursor material must have been more oxidized than average enstatite chondrite material we believe that this oxidized material may have formed at the enstatite chondrite formation location in the solar nebula provided fluctuations in the degree of oxidation of the nebular gas existed at such locations reheating of this material under more reducing conditions would lead to the observed reduction of the olivine igneous olivines within chondrules always contain detectable amounts of cao while relict olivines are essentially cao free this seems to suggest that the relict olivines did not originate during a previous igneous process of chondrule formation and might represent condensation products from the early solar nebula

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

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