origin of fayalitic olivine rims and lath shaped matrix olivine in the cv3 chondrite allende and its dark inclusions we have studied an allende dark inclusion by optical microscopy scanning electron microscopy electron microprobe analysis and transmission electron microscopy the inclusion consists of chondrules isolated olivines and matrix which as in the allende host is mainly composed of 5 20 m long lath shaped fayalitic grains with a narrow compositional range fa42 2 and nepheline olivine phenocrysts in chondrules and isolated olivine grains show various degrees of replacement by 5 10 m wide fayalitic rims fa39 2 and 100 1000 m wide translucent zones which consist of 5 20 m long lath shaped fayalitic grains fa41 1 intergrown with nepheline these fayalitic olivines like those in the matrix of the dark inclusion contain 10 20 nm sized inclusions of chromite hercynite and fe ni sulfides the fayalitic rims around remnant olivines are texturally and compositionally identical to those in allende host suggesting that they have similar origins chondrules are surrounded by opaque rims consisting of tiny lath shaped fayalitic olivines 1 3 m long intergrown with nepheline as in the allende host fayalitic olivine veins may crosscut altered chondrules fine grained chondrule rims and extend into the matrix indicating that alteration occurred after accretion we infer that fayalitic olivine rims and lath shaped fayalites in allende and its dark inclusions formed from phyllosilicate intermediate phases this explanation accounts for 1 the similarity of the replacement textures observed in the dark inclusion and allende host to aqueous alteration textures in cm chondrites 2 the anomalously high abundances of al and cr and the presence of tiny inclusions of spinels and sulfides in fayalitic olivines in allende and allende dark inclusions 3 abundant voids and defects in lath shaped fayalites in the allende dark inclusion which may be analogous to those in partly dehydrated phyllosilicates in metamorphosed cm ci chondrites we conclude that the matrix and chondrule rims in allende were largely converted to phyllosilicates and then completely dehydrated the allende dark inclusions experienced diverse degrees of aqueous hydrothermal alteration prior to complete dehydration the absence of low ca pyroxene in the dark inclusion and its significant replacement by fayalitic olivine in allende is consistent with the lower resistance of low ca pyroxene to aqueous alteration relative to forsteritic olivine hydro thermal processing of allende probably also accounts for the low abundance of planetary noble gases and interstellar grains and the formation of nepheline sodalite salite hedenbergite pyroxenes wollastonite kirschsteinite and andradite in chondrules and ca al rich inclusions

oxygen isotopic compositions and origins of calcium aluminum rich inclusions and chondrules primary minerals in calcium aluminum rich inclusions cais al rich and ferromagnesian chondrules in each chondrite group have 18o values that typically range from 50 to 5 0 neglecting effects due to minor mass fractionations the oxygen isotopic data for each chondrite group and for micrometeorites define lines on the three isotope plot with slopes of 1 01 0 06 and intercepts of 2 1 this suggests that the same kind of nebular process produced the 16o variations among chondrules and cais in all groups chemical and isotopic properties of some cais and chondrules strongly suggest that they formed from solar nebula condensates this is incompatible with the existing two component model for oxygen isotopes in which chondrules and cais were derived from heated and melted 16o rich presolar dust that exchanged oxygen with 16o poor nebular gas some fun cais inclusions with isotope anomalies due to fractionation and unknown nuclear effects have chemical and isotopic compositions indicating they are evaporative residues of presolar material which is incompatible with 16o fractionation during mass independent gas phase reactions in the solar nebula there is only one plausible reason why solar nebula condensates and evaporative residues of presolar materials are both enriched in 16o condensation must have occurred in a nebular region where the oxygen was largely derived from evaporated 16o rich dust a simple model suggests that dust was enriched or gas was depleted relative to cosmic proportions by factors of 10 to 50 prior to condensation for most cais and factors of 1 5 for chondrule precursor material we infer that dust gas fractionation prior to evaporation and condensation was more important in establishing the oxygen isotopic composition of cais and chondrules than any subsequent exchange with nebular gases dust gas fractionation may have occurred near the inner edge of the disk where nebular gases accreted into the protosun and shu and colleagues suggest that cais formed

al rich objects in ordinary chondrites related origin of carbonaceous and ordinary chondrites and their constituents ca al rich inclusions cais common constituents of carbonaceous chondrites have been studied extensively because they contain refractory high temperature minerals suggesting that they formed at high temperatures during the early history of the solar system few cais have previously been discovered in ordinary chondrites here we describe 169 al rich objects arbitrarily defined as having 10 wt al2o3 from 24 types 3 and 4 ordinary chondrites five regolith breccias containing unequilibrated material the unique meteorite kakangari and a few types 5 and 6 ordinary chondrites based on shape and texture we divide al rich objects into chondrules round with igneous textures irregularly shaped inclusions similar to type f and spinel rich complex cais and fragments probably fragments of al rich chondrules and inclusions for descriptive purposes we further subdivide al rich chondrules into compositional subgroups although they are entirely transitional conclusions 1 a al rich chondrules and irregularly shaped inclusions and fragments are wide spread albeit rare constituents of ordinary chondrites and are similar to cais except the coarse grained ones in carbonaceous chondrites thus providing strong support for a related origin of ordinary and carbonaceous chondrites and their constituents 2 b al rich chondrules formed as independent freely floating molten droplets and cooled rather rapidly 3 c al rich chondrules like the common mg fe rich chondrules formed by melting of millimeter to submillimeter sized dust balls in the case of al rich chondrules the dust balls consisted largely of mixtures of variable amounts of at least two solid precursor materials one refractory rich and the other volatile rich phases which we interpret as unmelted relicts in some of these objects support this model 4 d the wide ranges in bulk compositions of al rich chondrules from refractory rich to volatile rich ones yet complete transition between them and the existence of chondrules transitional in composition between the al rich and common mg fe rich chondrules of ordinary chondrites suggest that all chondrules formed by related processes differences in bulk composition result from mixing of different proportions of refractory volatile and mg fe rich and other solid precursor materials into dust balls which were then melted 5 e most irregularly shaped inclusions show no indication of a once molten origin secondary alteration has probably changed the original mineral assemblage mainly volatile rich materials entered the refractory objects as a gas reacted with the constituents and produced secondary phases rims probably formed both by decomposition and reaction with solar gas as well as by accretion 6 f coarse grained inclusions as found in allende were not observed in ordinary chondrites

formation conditions of plagioclase bearing type i chondrules in co chondrites a study of natural samples and experimental analogs abstract about ten percent of type i feo poor chondrules in unequilibrated co chondrites contain plagioclase that appears to be igneous in origin crystallizing at a late stage of solidification of host chondrule melts we have studied plagioclase bearing chondrules in detail and compared them with plagioclase free chondrules in order to determine the formation conditions of plagioclase and the constraints that the presence of plagioclase places on the conditions of chondrule formation plagioclase bearing chondrules have similar textures mineral compositions and bulk compositions to plagioclase free chondrules the only possible chemical difference that might control the presence or absence of plagioclase in a given chondrule is that most plagioclase bearing chondrules have a slightly higher bulk al ca ratio than plagioclase free chondrules we carried out dynamic cooling experiments on a type iab chondrule analog in order to investigate chondrule formation conditions our experiments at slow cooling rates

26al in plagioclase rich chondrules in carbonaceous chondrites evidence for an extended duration of chondrule formation abstract the 26al 26mg isotope systematics in 33 petrographically and mineralogically characterized plagioclase rich chondrules prcs from 13 carbonaceous chondrites ccs one ungrouped acfer 094 six cr five cv and one co reveal large variations in the initial 26al 27al ratio 26al 27al 0 well resolved 26mg excesses 26mg from the in situ decay of the short lived nuclide 26al t1 2 0 72 ma were found in nine chondrules two from acfer 094 five from the cv chondrites allende and efremovka and one each from the paired cr chondrites eet 92147 and eet 92042 with 26al 27al 0 values ranging from 3 10 6 to 1 5 10 5 data for seven additional chondrules from three cv and two cr chondrites show evidence suggestive of the presence of 26al but do not yield well defined values for 26al 27al 0 while the remaining chondrules do not contain excess radiogenic 26mg and yield corresponding upper limits of 11 2 10 6 for 26al 27al 0 the observed range of 26al 27al 0 in prcs from ccs is similar to the range seen in chondrules from unequilibrated ordinary chondrites uocs of low metamorphic grade 3 0 3 4 however unlike the uoc chondrules there is no clear trend between the 26al 27al 0 values in prcs from ccs and the degree of thermal metamorphism experienced by the host meteorites high and low values of 26al 27al 0 are found equally in prcs from both ccs lacking evidence for thermal metamorphism e g crs and ccs where such evidence is abundant e g cvs the lower 26al 27al 0 values in prcs from ccs relative to most cais are consistent with a model in which 26al was distributed uniformly in the nebula when chondrule formation began approximately a million years after the formation of the majority of cais the observed range of 26al 27al 0 values in prcs from ccs is most plausibly explained in terms of an extended duration of 2 3 ma for the formation of cc chondrules this interval is in sharp contrast to most cais from ccs whose formation appears to be restricted to a narrow time interval of less than 105 years the active solar nebula appears to have persisted for a period approaching 4 ma encompassing the formation of both cais and chondrules present in ccs and raising important issues related to the storage assimilation and mixing of chondrules and cais in the early solar system

two forsterite bearing fun inclusions in the allende meteorite we have discovered two fun inclusions cg 14 and te among a group of five forsterite rich inclusions in allende two of which are described for the first time herein all five consist of euhedral forsterite and spinel crystals poikilitically enclosed by fassaite forsterite and spinel are usually segregated from one another sometimes into a spinel rich mantle and a forsterite rich core some inclusions contain vesicles indicating that they were once molten the crystallization sequence inferred from textures is spinel forsterite fassaite and finally mg rich melilite one concentrically zoned inclusion contains melilite in its mantle whose composition lies on the opposite side of the liquidus minimum in the melilite binary from that in its core this suggests that segregation of forsterite from spinel in all of these inclusions could be due to volatilization of mgo and sio2 relative to al2o3 and cao from the outsides of droplets cg 14 is relatively uniformly enriched in refractory elements relative to cl chondrites by a factor similar to that for ca al rich coarse grained inclusions except for ca al and hf which are unusually low no ce anomaly such as found in fun inclusions cl and hal is present in cg 14 whole rock samples of cg 14 and te are more strongly mass fractionated in oxygen relative to normal allende inclusions than the fun inclusion ek 1 4 1 and less so than cl relative to bulk allende both inclusions have strongly massfractionated magnesium and silicon and 25mg excesses or deficits of 24mg or 26mg cg 14 has a 29si excess or a deficit of 28si or 30si volatilization loss cannot be responsible for the magnesium and silicon isotope fractionations as this would require prohibitively large mass loss from these magnesium rich inclusions the remarkable similarity in textures between fun and non fun inclusions implies similar thermal histories arguing against different rates of evaporative loss of major elements sputtering alone may be insufficient to account for the magnitude and direction of oxygen isotope fractionation in fun inclusions

formation conditions of aluminum rich chondrules abstract we have studied the formation conditions of al rich chondrules by doing isothermal and dynamic crystallization experiments at one atmosphere on four different chondrule analogue compositions within the pure cao mgo al2o3 sio2 system for the dynamic crystallization experiments we cooled from both liquidus and subliquidus peak temperatures tmax at cooling rates from 5 1000 c h the starting compositions include two with anorthite and two with forsterite as the dominant liquidus phases all at or near spinel saturation one of each pair evolves towards diopside crystallization and the others cordierite or enstatite crystallization giving a total of four completely different crystallization sequences analogous to the four basic varieties of al rich chondrule recently proposed bulk composition is the main controlling factor both in terms of mineralogy and texture the textures of the anorthite rich compositions are more sensitive to tmax than they are to cooling rate whereas the textures of the forsterite rich compositions are more sensitive to cooling rate comparisons of natural al rich chondrules having similar compositions to our synthetic analogues indicate that the natural objects reflect a range of peak heating temperatures 1400 1500 c and cooling rates of 10 500 c h for porphyritic chondrules and possibly higher 1000 c h for barred chondrules these conditions are consistent with the conditions inferred for ferromagnesian chondrules but differ from those inferred for some calcium aluminum rich inclusions

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

a short duration of chondrule formation in the solar nebula evidence from 26al in semarkona ferromagnesian chondrules abstract the 26 al 26 mg systems of five ferromagnesian chondrules from the least metamorphosed ordinary chondrite semarkona ll3 0 were studied using a secondary ion mass spectrometer their glass or plagioclase portions contain excesses of 26 mg and in two chondrules the 26 mg excesses are well correlated with 27 al 24 mg which demonstrates the in situ decay of 26 al the initial 26 al 27 al ratios in these chondrules obtained from the slope of isochrons show a narrow range of between 6 10 6 and 9 10 6 indicating their short formation duration of less than 1 my if the solar nebula was initially homogeneous in al isotopes the chondrule formation ages are 2 my younger than those of cais our results based on the study of the least metamorphosed uoc are consistent with the previous studies on al rich chondrules that the chondrule formation started at least 2 my after cais alternatively the older records before 2 my were erased by chondrule recycling process it further suggests that the young apparent ages 3 to 5 my after cais for chondrules in type 3 4 uocs are due to the disturbance of the 26 al 26 mg system possibly during parent body metamorphism the result is not consistent with the extended nebular time scale of 5 my and the chondrule formation by planetary processes the ni isotopic analysis of the feo rich olivines in a type ii chondrule in semarkona did not show any detectable excess 60 ni in spite of their high fe ni ratios the upper limit of the initial 60 fe 56 fe ratio of the solar system was estimated to be 3 4 10 7 which is consistent with the previous estimate 0 2 1 9 10 7 from eucrites this result confirms that the 60 ni excess previously observed from cais was not due to the decay of the short lived nuclide 60 fe but a ni isotopic anomaly of nucleosynthetic origin

microstructural analysis of wark lovering rims in the allende and axtell cv3 chondrites implications for high temperature nebular processes a coordinated electron backscatter diffraction ebsd and transmission electron microscope tem study was undertaken to obtain information on the origin of rims on refractory inclusions in the allende and axtell cv3 chondrites these measurements were supported by theoretical modeling using density functional theory crystal orientation analysis of wark lovering rims via ebsd revealed pyroxene grains with similar crystallographic orientations to one another in both inclusions an epitaxial relationship between grains within the diopside and anorthite rim layers was observed in allende tem examination of the rims of both samples also revealed oriented crystals at depth the microstructural data on the rims suggest that grain clusters grew in the form of three dimensional islands density functional theory calculations confirm that formation of oriented grain islands is the result of energy minimization at high temperature the results point toward condensation as the mode of origin for the rims studied here

an unusual clast in lunar meteorite macalpine hills 88105 a unique lunar sample or projectile debris lunar meteorite macalpine hills mac 88105 is a well studied feldspathic regolith breccia dominated by rock and mineral fragments from the lunar highlands thin section mac 88105 159 contains a small rock fragment 400 350 m in size which is compositionally anomalous compared with other mac 88105 lithic components the clast is composed of olivine and plagioclase with minor pyroxene and interstitial devitrified glass component it is magnesian akin to samples in the lunar high mg suite and also alkali rich akin to samples in the lunar high alkali suite it could represent a small fragment of late stage interstitial melt from an mg suite parent lithology however olivine and pyroxene in the clast have fe mn ratios and minor element concentrations that are different from known types of lunar lithologies as fe mn ratios are notably indicative of planetary origin the clast could either 1 have a unique lunar magmatic source or 2 have a nonlunar origin i e consist of achondritic meteorite debris that survived delivery to the lunar surface both hypotheses are considered and discussed the meteoritical society 2014

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

relationship among o mg isotopes and the petrography of two spinel bearing compound chondrules the petrological properties and o and al mg isotopic compositions of two spinel bearing chondrules from the allende cv chondrite were investigated using scanning electron microscopy and secondary ion mass spectrometry a coarse spinel grain in a barred olivine bo chondrule is less enriched in 16o 17o 5 17o 17o 0 52 18o whereas smaller spinel grains in a plagioclase rich chondrule member of a compound chondrule are extremely 16o rich 17o 17 and the spinels have a strongly serrated character the petrological features and 16o enrichments of the spinels in the plagioclase rich chondrule indicate that spinels originating in coarse grained ca al rich inclusions cais were incorporated into chondrule precursors and survived the chondrule forming event the degree of 16o excesses among minerals within each chondrule is correlated to the crystallization sequences this evidence suggests that the o isotopic variation among minerals may have resulted from incomplete exchange of o isotopes between 16o rich chondrule melt and 16o poor nebular gas aqueous alteration also has changed the o isotope compositions in the mesostasis the feldspathic mesostasis in the bo chondrule shows a disturbed mg al isochron indicating that the bo chondrule experienced secondary alteration while plagioclase in the plagioclase rich chondrule member of the compound chondrule shows slight 26mg excesses corresponding to 26al 27al 0 4 6 4 0 2 10 6 nepheline formed by secondary alteration shows no detectable excess the al mg isotopic system of these chondrules was disturbed by aqueous alteration and thermal metamorphism on the allende parent body

nepheline formation in chondrite parent bodies verification through experiments abstract nepheline is present as fine grains mainly in refractory inclusions and chondrules in cv and co carbonaceous chondrites the nepheline has been formed primarily by replacement of melilite and plagioclase in refractory inclusions and plagioclase and glass in chondrules the nepheline formation is thought to have occurred during aqueous alteration and thermal metamorphism in the meteorite parent bodies to verify this hypothesis we performed the following experiments hydrothermal experiments of gehlenite al rich melilite and plagioclase an48 were carried out at 200 c and 15 bar for 168 h using solutions of ph 0 7 13 and 14 with a uniform na concentration in the gehlenite experiments various amounts of sio2 were added the results revealed that a na zeolite analcime was produced from 10 3 and 10 6 mixtures of gehlenite sio2 at ph 7 13 and 14 and from a 10 10 mixture of gehlenite sio2 and plagioclase at ph 13 and 14 in particular at ph 14 in addition to analcime significant amounts of two other zeolites fabriesite and hydroxycancrinite were produced from the 10 6 mixture of gehlenite sio2 and fabriesite from plagioclase isothermal heating experiments for 24 h showed that fabriesite hydroxycancrinite and analcime transform to nepheline at 600 650 550 600 and 750 800 c respectively differential thermal analysis of these zeolites revealed that fabriesite and hydroxycancrinite exhibit exothermic peaks which correspond to transformation to nepheline and that the temperatures of those peaks decrease steadily with decreasing heating rate kinetic analysis using these data revealed that fabriesite transforms to nepheline at 102 yr and hydroxycancrinite transforms to nepheline at 1 yr analcime heated non isothermally at a rate of 1 c min transformed to nepheline at temperature higher than that determined by the isothermal experiments suggesting that its transformation temperature also decreases if it is heated for a much longer duration from these experiments and analyses we conclude that fabriesite hydroxycancrinite and possibly analcime are capable of transforming to nepheline by heating in meteorite parent bodies from our results we propose that the nepheline in refractory inclusions and chondrules in meteorites formed by a two stage alteration process 1 formation of the na zeolites from melilite plagioclase and glass by hydrothermal alteration at low temperature probably

oxygen isotope compositions of chondrules in cr chondrites abstract we report in situ ion microprobe analyses of oxygen isotopic compositions of olivine low ca pyroxene high ca pyroxene anorthitic plagioclase glassy mesostasis and spinel in five aluminum rich chondrules and nine ferromagnesian chondrules from the cr carbonaceous chondrites eet92042 gra95229 and mac87320 ferromagnesian chondrules are isotopically homogeneous within 2 in 17 o the interchondrule variations in 17 o range from 0 to 5 small oxygen isotopic heterogeneities found in two ferromagnesian chondrules are due to the presence of relict olivine grains in contrast two out of five aluminum rich chondrules are isotopically heterogeneous with 17 o values ranging from 6 to 15 and from 2 to 11 respectively this isotopic heterogeneity is due to the presence of 16 o enriched spinel and anorthite 17 o 10 to 15 which are relict phases of ca al rich inclusions cais incorporated into chondrule precursors and incompletely melted during chondrule formation these observations and the high abundance of relict cais in the aluminum rich chondrules suggest a close genetic relationship between these objects aluminum rich chondrules formed by melting of spinel anorthite pyroxene cais mixed with ferromagnesian precursors compositionally similar to magnesium rich type i chondrules the aluminum rich chondrules without relict cais have oxygen isotopic compositions 17 o 2 to 8 similar to those of ferromagnesian chondrules in contrast to the aluminum rich chondrules from ordinary chondrites those from crs plot on a three oxygen isotope diagram along the carbonaceous chondrite anhydrous mineral line and form a continuum with amoeboid olivine aggregates and cais from crs we conclude that oxygen isotope compositions of chondrules resulted from two processes homogenization of isotopically heterogeneous materials during chondrule melting and oxygen isotopic exchange between chondrule melt and 16 o poor nebular gas

refractory calcium aluminum rich inclusions and aluminum diopside rich chondrules in the metal rich chondrites hammadah al hamra 237 and queen alexandra range 94411 the metal rich chondrites hammadah al hamra hh 237 and queen alexandra range que 94411 paired with que 94627 contain relatively rare 1 vol calcium aluminum rich inclusions cais and al diopside rich chondrules forty cais and cai fragments and seven al diopside rich chondrules were identified in hh 237 and que 94411 94627 the cais 50 400 mum in apparent diameter include a 22 56 pyroxene spinel melilite forsterite rim b 11 28 forsterite bearing pyroxene spinel melilite anorthite forsterite rim c 2 5 grossite rich spinel melilite pyroxene rim d 2 5 hibonite melilite spinel pyroxene forsterite rim e 1 2 hibonite bearing spinel perovskite melilite pyroxene rim f 1 2 spinel melilite pyroxene anorthite and g 1 2 amoeboid olivine aggregate each type of cai is known to exist in other chondrite groups but the high abundance of pyroxene spinel melilite cais with igneous textures and surrounded by a forsterite rim are unique features of hh 237 and que 94411 94627 additionally oxygen isotopes consistently show relatively heavy compositions with delta o 17 ranging from 6 parts per thousand to 10 parts per thousand 1 sigma 1 3 parts per thousand for all analyzed cai minerals grossite hibonite melilite pyroxene spinel this suggests that the cais formed in a reservoir isotopically distinct from the reservoir s where normal o 16 rich delta o 17 20 cais in most other chondritic meteorites formed

a petrologic and ion microprobe study of a vigarano type b refractory inclusion evolution by multiple stages of alteration and melting abstract usnm 1623 8 is a type b vigarano inclusion 6 mm in diameter consisting of melilite ak12 72 fassaite 17 23 a12o3 5 17 tio2 anorthite and spinel secondary alteration is negligible and consists of diopside and sparse nepheline melilite is normally zoned and contains up to 0 35 wt na2o higher than generally seen in melilite from other refractory inclusions a strong correlation between akermanite content and na2o in 1623 8 melilite suggests that the na was present during igneous crystallization rather than introduced later by diffusion anorthite in 1623 8 is coarse grained but commonly has an irregular border with neighboring melilite crystals many spinel grains enclosed within anorthite have selvages of melilite around them which in places are continuous with melilite exterior to the anorthite the anorthite appears to be replacing melilite ion microprobe analyses of anorthite in 1623 8 show that there is no detectable excess 26mg in nine anorthite crystals that have 27 al 24 mg as high as 970 implying an upper limit of 26 al 27 al 0 7 one crystal was found that has excess 26mg consistent with 26 al 27 al 0 3 10 6 melilite in the outer portion of the inclusion 27 al 24 mg 2 7 11 5 contains excess 26mg that considered together with spinel and pyroxene defines an isochron consistent with the canonical early solar system value of 26 al 27 al 0 4 5 10 5 melilite near an anorthite 27 al 24 mg 1 6 5 9 has 26mg values in excess of those predicted from 26 al 27 al 0 4 5 10 5 presumably caused by redistribution of radiogenic 26mg from adjacent anorthite the high na2o inferred to have been present in the melt suggests that the precursor solids were na bearing such as for example refractory material having an allende like overprint of feldspathoid bearing secondary alteration the melting event must have been brief in order that not all of the na was vaporized during melting the isotopic composition of the anorthite relative to melilite indicates a subsequent much later after the decay of most or all 26a1 episode of partial melting or solidstate recrystallization that did not affect the al rich melilite but reset most of the anorthite and some mg rich melilite near anorthite because the inclusion is both rimmed and slightly altered this late resetting event appears to have been a nebular one an assumption of homogeneously distributed 26a1 in the regions of the nebula where the inclusion formed and was later modified implies a several millionyear interval between condensation of the precursors and final melting of 1623 8

anorthite rich chondrules in cr and ch carbonaceous chondrites genetic link between ca al rich inclusions and ferromagnesian chondrules anorthite rich chondrules in cr and ch carbonaceous chondrites consist of magnesian low ca pyroxene and forsterite phenocrysts feni metal nodules interstitial anorthite al ti cr rich low ca and high ca pyroxenes and crystalline mesostasis composed of silica anorthite and high ca pyroxene three anorthite rich chondrules contain relic ca al rich inclusions composed of anorthite spinel al diopside and forsterite a few chondrules contain regions which are texturally and mineralogically similar to magnesian type i chondrules and consist of forsterite low ca pyroxene and abundant feni metal nodules anorthite rich chondrules in cr and ch chondrites are mineralogically similar to those in cv and co carbonaceous chondrites but contain no secondary nepheline sodalite or ferrosilite relatively high abundances of moderately volatile elements such as cr mn and si in the anorthite rich chondrules suggest that these chondrules could not have been produced by volatilization of the ferromagnesian chondrule precursors or by melting of the refractory materials only we infer instead that anorthite rich chondrules in carbonaceous chondrites formed by melting of the reduced chondrule precursors olivine pyroxenes feni metal mixed with the refractory materials including relic cais composed of anorthite spinel high ca pyroxene and forsterite the observed mineralogical and textural similarities of the anorthite rich chondrules in several carbonaceous chondrite groups cv co ch cr may indicate that these chondrules formed in the region s intermediate between the regions where cais and ferromagnesian chondrules originated this may explain the relative enrichment of anorthite rich chondrules in 16o compared to typical ferromagnesian chondrules russell et al 2000

fayalite rich rims veins and halos around and in forsteritic olivines in cais and chondrules in carbonaceous chondrites types compositional profiles and constraints of their formation abstract fayalite rich rims veins and halos around and in forsteritic olivines are a wide spread phenomenon in chondrules ca al rich inclusions cais and single grains in carbonaceous chondrites the presence of fayalite rod like crystals and laths in rims veins in wall of pores and as fluffy network bridging neighbouring olivines pyroxenes feldspars etc is strongly suggestive that the fayalitic olivine was formed by condensation presumably from the solar nebula gas the formation of the fayalitic olivine was probably caused by an increase in the h 2 o h 2 ratio to a ratio between 0 1 1 subsequent to condensation of forsterite at that stage feni inclusions in olivine were also oxidized and fayalitic halos around the metal were then formed by fe diffusion along with addition of sio 2 from the solar gas or loss of mgo to the solar gas the fa rich olivine rims and veins display a narrow compositional variation between fa 34 and fa 46 subsequent to condensation of fa rich olivine and oxidation of feni metal fe diffused in forsterite this diffusion was probably enhanced due to the presence of point defects in olivine or the formation of a nonstoichiometric phase analogous to laihunite enriched in al 2 o 3 and cr 2 o 3 however the presence of al 2 o 3 and cr 2 o 3 rich discrete domains cannot be excluded cooling rates calculated by modelling of the diffusion profiles are indicative of rapid cooling subsequent to the condensation of fayalitic olivines we obtain cooling rates ranging from 2000 c day and 10 c day at an initial temperature of 1200 c and 900 c respectively

origin of plagioclase olivine inclusions in carbonaceous chondrites plagioclase olivine inclusions pois are an abundant group of chondrule like objects with igneous textures found in carbonaceous chondrites pois consist of plagioclase olivine pyroxene and spinel and cover a wide range of compositions between type c ca al rich inclusions cais and ferromagnesian chondrules pois are distinguished from cais by the absence of melilite lack of refractory siderophile rich opaque assemblages more sodic plagioclase and abundance of olivine and aluminousenstatite rare accessory minerals including armalcolite zirconolite rutile and sapphirine are found in several pois the petrographie and chemical properties of pois indicate that they are not condensates or evaporative residues but formed by melting or partial melting of pre existing solids seven of fourteen pois contain isotopically fractionated mg and despite their textures these pois are not isotopically homogeneous spinel is the major carrier of fractionated mg in six pois the magnitude of mg isotopic fractionation fmg of spinel ranges from 8 to 11 amu among the pois but f mg is always either positive or negative within an individual pol within a single inclusion f mg of coexisting spinel is not constant but varies by up to 7 amu isotopic fractionation of mg in silicates is less common and always positive f mg 0 pyroxenes in two pois and plagioclase in a third contain isotopically heavy mg radiogenic 26 mg is rare in pois as only two inclusions show evidence of excess 26 mg with 26 mg 27 al 4 10 6 the preservation of isotopic heterogeneity in objects whose igneous textures suggest crystallization from a homogeneous melt implies that melting was incomplete allowing survival of relict phases a comparison of the essential characteristics of pois and cais suggests that the major processes leading to formation of pois including condensation dust gas fractionation aggregation of chemically and isotopically disparate materials and partial melting are common to most cais and chondrules we present a scenario for the formation of these objects and conclude that the homogeneity of the final assemblage cai poi or chondrule is primarily a reflection of the thermal history rather than the nature of precursor materials

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

principal modes of atmospheric circulation anomalies associated with global angular momentum fluctuations abstract this paper provides a description of the variability of global atmospheric angular momentum gam and its relationship with principal modes of three dimensional atmospheric circulation anomalies the data used are 5 day mean global wind fields from the european centre for medium range weather forecasts initialized dataset for 1980 1989 significant seasonal variation of gam is observed with maxima in april and november and a minimum during late july the amplitude of the annual cycle is largest in the upper troposphere and decreases toward the surface although the lower tropospheric contribution to the total angular momentum is relatively small its annual cycle is out of phase with those of the upper atmosphere and gam also identified is a distinct semiannual component with double peaks appearing in april and november this signal is most noticeable in the upper troposphere above the 300 mb level the principal modes of zonal mean angular momentum and meridional circulation anomalies and thei

a clast of bali like oxidized cv material in the reduced cv chondrite breccia vigarano the cv vigarano type chondrites are a petrologically diverse group of meteorites that are divided into the reduced and the ball like and allende like oxidized subgroups largely based on secondary mineralogy weisberg et al 1997 krot et al 1998b some chondrules and calcium aluminum rich inclusions cais in the reduced cv chondrite vigarano show alteration features similar to those in allende metal is oxidized to magnetite low ca pyroxene forsterite and magnetite are rimmed and veined by ferrous olivine fs 40 50 and plagioclase mesostases and melilite are replaced by nepheline and sodalite sylvester et al 1993 kimura and ikeda 1996 1997 1998

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

origin and chronology of chondritic components a review abstract mineralogical observations chemical and oxygen isotope compositions absolute 207pb 206pb ages and short lived isotope systematics 7be 7li 10be 10b 26al 26mg 36cl 36s 41ca 41k 53mn 53cr 60fe 60ni 182hf 182w of refractory inclusions ca al rich inclusions cais and amoeboid olivine aggregates aoas chondrules and matrices from primitive unmetamorphosed chondrites are reviewed in an attempt to test i the x wind model vs the shock wave model of the origin of chondritic components and ii irradiation vs stellar origin of short lived radionuclides the data reviewed are consistent with an external stellar origin for most short lived radionuclides 7be 10be and 36cl are important exceptions and a shock wave model for chondrule formation and provide a sound basis for early solar system chronology they are inconsistent with the x wind model for the origin of chondritic components and a local irradiation origin of 26al 41ca and 53mn 10be is heterogeneously distributed among cais indicating its formation by local irradiation and precluding its use for the early solar system chronology 41ca 41k and 60fe 60ni systematics are important for understanding the astrophysical setting of solar system formation and origin of short lived radionuclides but so far have limited implications for the chronology of chondritic components the chronological significance of oxygen isotope compositions of chondritic components is limited the following general picture of formation of chondritic components is inferred cais and aoas were the first solids formed in the solar nebula 4567 4568 myr ago possibly within a period of 10 and have 26al 27al 0 similar to those in chondrules 5 nebular gas the majority of chondrules within a chondrite group may have formed over a much shorter period of time

ca al rich inclusions amoeboid olivine aggregates and al rich chondrules from the unique carbonaceous chondrite acfer 094 i mineralogy and petrology based on their mineralogy and petrography 200 refractory inclusions studied in the unique carbonaceous chondrite acfer 094 can be divided into corundum rich 0 5 hibonite rich 1 1 grossite rich 8 5 compact and fluffy type a spinel melilite rich 50 3 pyroxene anorthite rich 7 4 and type c pyroxene anorthite rich with igneous textures 1 6 ca al rich inclusions cais pyroxene hibonite spherules 0 5 and amoeboid olivine aggregates aoas 30 2 melilite in some cais is replaced by spinel and al diopside and or by anorthite whereas spinel pyroxene assemblages in cais and aoas appear to be replaced by anorthite forsterite grains in several aoas are replaced by low ca pyroxene none of the cais or aoas show evidence for fe alkali metasomatic or aqueous alteration the mineralogy textures and bulk chemistry of most acfer 094 refractory inclusions are consistent with their origin by gas solid condensation and may reflect continuous interaction with sio and mg of the cooling nebula gas it appears that only a few cais experienced subsequent melting the al rich chondrules arcs 10 wt bulk al2o3 consist of forsteritic olivine and low ca pyroxene phenocrysts pigeonite augite anorthitic plagioclase spinel feni metal and crystalline mesostasis composed of plagioclase augite and a silica phase most arcs are spherical and mineralogically uniform but some are irregular in shape and heterogeneous in mineralogy with distinct ferromagnesian and aluminous domains the ferromagnesian domains tend to form chondrule mantles and are dominated by low ca pyroxene and forsteritic olivine anorthitic mesostasis and fe ni metal nodules the aluminous domains are dominated by anorthite high ca pyroxene and spinel occasionally with inclusions of perovskite have no or little feni metal and tend to form cores of the heterogeneous chondrules the cores are enriched in bulk ca and al and apparently formed from melting of cai like precursor material that did not mix completely with adjacent ferromagnesian melt the inferred presence of cai like material among precursors for al rich chondrules is in apparent conflict with lack of evidence for melting of cais that occur outside chondrules suggesting that these cais were largely absent from chondrule forming region s at the time of chondrule formation this may imply that there are several populations of cais in acfer 094 and that mixing of normal cais that occur outside chondrules and chondrules that accreted into the acfer 094 parent asteroid took place after chondrule formation alternatively there may have been an overlap in the cai and chondrule forming regions where the least refractory cais were mixed with fe mg chondrule precursors this hypothesis is difficult to reconcile with the lack of evidence of melting of aoas which represent aggregates of the least refractory cais and forsterite grains

exploring the efficiency of stepwise dissolution in removal of stubborn non radiogenic pb in chondrule u pb dating abstract chondrules in chondritic meteorites are unique witnesses of nebular and asteroidal processes that preceded large scale planetary accretion together with refractory calcium aluminium rich inclusions cais they are the sources of our knowledge of the initial evolution of the early solar system we have investigated a single very large 10 mm in longer dimension chondrule hereafter the mega chondrule a25 2 extracted from the allende cv3 chondrite we characterised texture mineralogy and mineral chemistry of this chondrule and studied its al mg u pb and u isotope systematics we also studied the distribution of u th and pb and measured pb isotopic composition in individual minerals of a25 2 by secondary ion mass spectrometry sims the main difficulty in absolute age determination was the presence of pervasive and resilient non radiogenic pb in the search for the best way to separate radiogenic pb from non radiogenic pb components of terrestrial and asteroidal origins we used various protocols of multi step leaching and assessed their efficiency in generating data suitable for the construction of an isochron testing the data filtering procedure led us to explore the behaviour of the stepwise leaching method in the presence of pervasive and resilient non radiogenic pb the model age patterns observed in the final hf partial dissolution steps were probably induced by isotopic fractionation although step leaching did not yield fractions with highly radiogenic pb a pb pb isochron age corrected for measured 238u 235u was obtained by 1 data filtering process based on strict analytical and geochemical criteria to include in the pb pb isochron only leaching steps free from terrestrial contamination and 2 arithmetically recombined analyses to cancel the effects of leaching induced isotopic fractionation this extensive data processing yielded the age of 4568 5 3 0 ma which we consider reliable within its uncertainty limits although it is not as precise as and more model dependent than the age that could have been obtained if pb isotopic compositions were more radiogenic the 238u 235u ratio of the mega chondrule is 137 764 0 016 which is similar to the ratios obtained from single chondrules yet slightly different from small pooled allende chondrules the initial 27al 26al ratio inferred from internal isochron obtained from sims al mg isotope measurements is 5 4 6 5 10 6 which corresponds to 4565 0 0 8 ma assuming homogeneous distribution of 26al throughout the protoplanetary disk at the canonical level 5 2 10 5 this age is 3 5 3 1 ma younger than the pb isotopic age calculation of 26al 26mg age assuming initial 27al 26al 0 of 1 36 0 72 10 5 in the cv chondrule forming region yields the age of 4566 4 0 8 which is consistent with the pb isotopic age

heterogeneous distribution of 26al at the birth of the solar system evidence from refractory grains and inclusions we review recent results on o and mg isotope compositions of refractory grains corundum hibonite and calcium aluminum rich inclusions cais from unequilibrated ordinary and carbonaceous chondrites we show that these refractory objects originated in the presence of nebular gas enriched in 16o to varying degrees relative to the standard mean ocean water value the 17osmow value ranges from approximately 16 to 35 and recorded heterogeneous distribution of 26al in their formation region the inferred 26al 27al 0 ranges from approximately 6 5 10 5 to 2 10 6 there is no correlation between o and mg isotope compositions of the refractory objects 26al rich and 26al poor refractory objects have similar o isotope compositions we suggest that 26al was injected into the 26al poor collapsing protosolar molecular cloud core possibly by a wind from a neighboring massive star and was later homogenized in the protoplanetary disk by radial mixing possibly at the canonical value of 26al 27al ratio approximately 5 10 5 the 26al rich and 26al poor refractory grains and inclusions represent different generations of refractory objects which formed prior to and during the injection and homogenization of 26al thus the duration of formation of refractory grains and cais cannot be inferred from their 26al 26mg systematics and the canonical 26al 27al 0 does not represent the initial abundance of 26al in the solar system instead it may or may not represent the average abundance of 26al in the fully formed disk the latter depends on the formation time of cais with the canonical 26al 27al ratio relative to the timing of complete delivery of stellar 26al to the solar system and the degree of its subsequent homogenization in the disk the injection of material containing 26al resulted in no observable changes in o isotope composition of the solar system instead the variations in o isotope compositions between individual cais indicate that o isotope composition of the cai forming region varied because of coexisting of 16o rich and 16o poor nebular reservoirs gaseous and or solid at the birth of the solar system or because of rapid changes in the o isotope compositions of these reservoirs with time e g due to co self shielding in the disk

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

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

terminal particle from stardust track 130 probable al rich chondrule fragment from comet wild 2 abstract a 4 6 m terminal particle from stardust track 130 named bidi is composed of a refractory assemblage of fo 97 olivine al and ti bearing clinopyroxene and anorthite feldspar an 97 mineralogically bidi resembles a number of components found in primitive chondritic meteorites including al rich chondrules plagioclase bearing type i ferromagnesian chondrules and amoeboid olivine aggregates aoas measured widths of augite pigeonite lamellae in the clinopyroxene indicate fast cooling rates suggesting that bidi is more likely to be a chondrule fragment than an aoa bulk element concentrations including an al 2 o 3 content of 10 2 wt further suggests that bidi is more akin to al rich rather than ferromagnesian chondrules this is supported by high anorthite content of the plagioclase feldspar overall bulk composition and petrogenetic analysis using a cosmochemical al 2 o 3 ca 2 sio 4 mg 2 sio 4 phase diagram measured minor element abundances of individual minerals in bidi generally support an al rich chondrule origin but are not definitive between any of the object types oxygen isotope ratios obtained from olivine minor high ca pyroxene fall between the tf and ccam lines and overlap similar minerals from chondrules in primitive chondrites but are generally distinct from pristine aoa minerals oxygen isotope ratios are similar to some minerals from both al rich and type i ferromagnesian chondrules in unequilibrated carbonaceous enstatite and ordinary chondrites although no single piece of evidence uniquely identifies bidi as a particular object type the preponderance of data including mineral assemblage bulk composition mineral chemistry inferred cooling rates and oxygen isotope ratios suggest that bidi is more closely matched to al rich chondrules than aoas or plagioclase bearing type i ferromagnesian chondrules and likely originated in a chondrule forming region in the inner solar system

calcium aluminum rich inclusions in enstatite chondrites i mineralogy and textures abstract like calcium aluminum rich inclusions cais from carbonaceous and ordinary chondrites enstatite chondrite cais are composed of refractory minerals such as spinel perovskite al ti diopside melilite hibonite and anorthitic plagioclase which may be partially to completely surrounded by halos of na cl rich minerals porous aggregate and compact textures of the refractory cores in enstatite chondrite cais and rare wark lovering rims are also similar to cais from other chondrite groups however the small size 100 m low abundance 1 by mode in thin section occurrence of only spinel or hibonite rich types and presence of primary ti v oxides and secondary geikelite and ti fe sulfides distinguish the assemblage of enstatite chondrite cais from other groups the primary mineral assemblage in enstatite chondrite cais is devoid of indicators e g oldhamite osbornite of low o fugacities thus high temperature processing of the cais did not occur under the reducing conditions characteristic of enstatite chondrites implying that either 1 the cais are foreign to enstatite chondrite forming regions or 2 o fugacities fluctuated within the enstatite chondrite forming region in contrast secondary geikelite and ti fe sulfide which replace perovskite indicate that alteration of perovskite occurred under reducing conditions distinct from cais in the other chondrite groups we have not ascertained whether the reduced alteration of enstatite chondrite cais occurred in a nebular or parent body setting we conclude that each chondrite group is correlated with a unique assemblage of cais indicating spatial or temporal variations in physical conditions during production or dispersal of cais

ion microprobe studies of efremovka cais i magnesium isotope composition five coarse grained ca al rich refractory inclusions cais from the efremovka cv3 chondrite are analysed for their magnesium isotopic composition using an ion microprobe the analysed inclusions represent the three common cai types a b1 and b2 data for magnesium isotopic composition of the major mineral phases melilite spinel fassaite and anorthite in these inclusions are used to determine intrinsic magnesium isotopic fractionations and to identify nonlinear effect in 26mg due to the decay of extinct 26al the magnesium isotopic mass fractionation f mg generally favours the heavier isotopes as is expected in the case of coarse grained cais the f mg data for two of the inclusions however show contrasting trends sympathetic behaviour found in both isotopic and petrographic data in one type b1 inclusion suggests that the parent melt of this inclusion experienced a short duration volatilization event prior to crystallization the isotopic data also suggest possible presence of relict spinel in this inclusion that constrains the cooling rate of the parent melt to 70 c h during crystallization hot and dense nebular settings that allow for such fast cooling can only be localized in nature the pristine nature of the efremovka cais as evident from the lack of secondary alteration products in them is well supported by the isotopic data three of the five inclusions yield well behaved mg al isochrons with 26al27al 0 close to the canonical value of 5 10 5 the anorthite data for another inclusion suggest minor disturbance in the isotopic systematics and yield a nearly well behaved isochron with a slightly lower value of 26al27al 0 data for melilite and anorthite in the fifth inclusion define apparent isochrons that suggest partial re equilibration and exchange of magnesium isotopes between these two phases the efremovka data are suggestive of a relatively homogeneous distribution of 26al in the solar nebula

zonal contributions to global momentum variations on intraseasonal through interannual time scales the authors separate the variability in a 13 year time series of daily values of the relative angular momentum of the atmosphere m into three frequency bands intraseasonal seasonal and interannual two methods are used to achieve this separation and the amount of variance attributable to intraseasonal fluctuations in particular is sensitive to the choice made seasonal time scales clearly dominate the global momentum series included in this frequency band is a notable dip in the series early in almost every calendar year to localize the sources of the frequency band dependent fluctuations in m they decompose the data into series of angular momentum values within each of 46 equal area zonal belts over the globe and form covariances between these belt series and m seasonal variations in m represent the residual of opposing contributions from the subtropical jets of the northern and southern hemispheres both intraseasonal and interannual variations in m result mostly from behavior in the tropics

a lithic clast of oxidized cv3 material in the reduced cv3 chondrite breccia vigarano reference epfl conf 177129view record in web of science record created on 2012 05 15 modified on 2016 08 09

calcium aluminum rich inclusions in enstatite chondrites ii oxygen isotopes abstract ln situ ion microprobe analyses of spinel in refractory calcium aluminium rich inclusions cais from type 3 eh chondrites yield 160 rich compositions dl80 and 6170 about 40 0 spinel and feldspar in a cai from an el3 chondrite have significantly heavier isotopic compositions dl80 and 6170 about 5 0 a regression through the data results in a line with slope 1 o on a three isotope plot similar to isotopic results from unaltered minerals in cais from carbonaceous chondrites the existence of cais with 160 rich and 16o poor compositions in carbonaceous as well as enstatite chondrites indicates that cais formed in at least two temporally or spatially distinct oxygen reservoirs general similarities in oxygen isotopic compositions of cais from enstatite carbonaceous and ordinary chondrites indicate a common nebular mechanism or locale for the production of most cais introduction refractory calcium aluminium rich inclusions cais in chondritic meteorites preserve a record of high temperature processing in the early solar nebula including condensation evaporation and melting macpherson

refractory materials in comet samples transmission electron microscope examination of more than 250 fragments 1 m from comet wild 2 and a giant cluster interplanetary dust particle gcp of probable cometary origin has revealed four new calcium aluminum rich inclusions cais an amoeboid olivine aggregate aoa and an additional aoa or al rich chondrule arc object all of the cais have concentric mineral structures and are composed of spinel anorthite cores surrounded by al ti clinopyroxenes and are similar to two previous cais discovered in wild 2 all of the cometary refractory objects are of moderate refractory character the mineral assemblages textures and bulk compositions of the comet cais are similar to nodules in fine grained spinel rich inclusions fgis found in primitive chondrites and like the nodules may be nebular condensates that were altered via solid gas reactions in the solar nebula oxygen isotopes collected on one wild 2 cai also match fgis the lack of the most refractory inclusions in the comet samples may reflect the higher abundances of small moderately refractory cai nodules that were produced in the nebula and the small sample sizes collected in the comet samples approximately 2 3 of all fragments larger than 1 m by number are cais and nearly 50 of all bulbous stardust tracks contain at least one cai we estimate that 0 5 volume of wild 2 material and 1 volume of gcp is in the form of cais arcs and aoas account for 1 of the wild 2 and gcp grains by number

type c ca al rich inclusions from allende evidence for multistage formation abstract the coarse grained igneous anorthite rich type c cais from allende studied 100 160 6 1 72 3529 40 cg5 abc ts26 and 93 have diverse textures and mineralogies suggesting complex nebular and asteroidal formation histories cais 100 160 6 1 72 and 3529 40 consist of al ti diopside fassaite 13 23 wt al 2 o 3 2 14 wt tio 2 na bearing akermanitic melilite 0 1 0 4 wt na 2 o ak 30 75 spinel and fine grained 5 10 m anorthite groundmass most of the fassaite and melilite grains have lacy textures characterized by the presence of abundant rounded and prismatic inclusions of anorthite 5 10 m in size lacy melilite is pseudomorphed to varying degrees by grossular monticellite and pure forsterite or wollastonite cai 6 1 72 contains a relict type b cai like portion composed of polycrystalline gehlenitic melilite ak 10 40 fassaite spinel perovskite and platinum group element nuggets the type b like material is overgrown by lacy melilite and fassaite some melilite and fassaite grains in cais 100 and 160 are texturally similar to those in the type b portion of 6 1 72 cais abc and ts26 contain relict chondrule fragments composed of forsteritic olivine and low ca pyroxene cai 93 is overgrown by a coarse grained igneous rim of pigeonite augite and anorthitic plagioclase these three cais contain very sodium rich akermanitic melilite 0 4 0 6 wt na 2 o ak 63 74 and cr bearing al ti diopside up to 1 6 wt cr 2 o 3 1 23 wt al 2 o 0 5 7 wt tio 2 melilite and anorthite in the allende type c cai peripheries are replaced by nepheline and sodalite which are crosscut by andradite bearing veins spinel is enriched in feo the cai fragment cg5 is texturally and mineralogically distinct from other allende type cs it is anorthite poor and very rich in spinel poikilitically enclosed by na free gehlenitic melilite ak 20 30 fassaite and anorthite neither melilite nor pyroxene have lacy textures secondary minerals are absent the al rich chondrules 3655b 2 and 3510 7 contain aluminum rich and ferromagnesian portions the al rich portions consist of anorthitic plagioclase al rich low ca pyroxene and cr bearing spinel the ferromagnesium portions consist of fosteritic olivine low ca pyroxene and opaque nodules we conclude that type c cais 100 160 6 1 72 and 3529 40 formed by melting of coarse grained type b like cais which experienced either extensive replacement of melilite and spinel mainly by anorthite and diopside traces of secondary na bearing minerals e g nepheline or sodalite might have formed as well or addition of silica and sodium during the melting event cg5 could have formed by melting of fine grained spinel melilite cai with melilite and spinel partially replaced anorthite and diopside cais abc 93 and ts 26 experienced melting in the chondrule forming regions with addition of chondrule like material such as forsteritic olivine low ca pyroxene and high ca pyroxene anorthite rich chondrules formed by melting of the al rich type c cai like precursors mixed with ferromagnesian type i chondrule like precursors the allende type c cais and al rich chondrules experienced fluid assisted thermal metamorphism which resulted in pseudomorphic replacement of melilite and anorthite by grossular monticellite and forsterite 100 160 6 1 72 3592 40 or by grossular monticellite and wollastonite abc 93 ts 26 the pseudomorphic replacement was followed or accompanied by iron alkali metasomatic alteration resulting in replacement of melilite and anorthite by nepheline and sodalite enrichment of spinel in feo and precipitation of salite hedenbergite pyroxenes wollastonite and andradite in fractures and pores in and around cais

evolved mare basalt magmatism high mg fe feldspathic crust chondritic impactors and the petrogenesis of antarctic lunar breccia meteorites meteorite hills 01210 and pecora escarpment 02007 antarctic lunar meteorites meteorite hills 01210 and pecora escarpment 02007 are breccias that come from different regolith lithologies on the moon met 01210 is composed predominantly of fractionated low ti basaltic material and is classified as an immature predominantly basaltic glassy matrix regolith breccia pca 02007 is a predominantly feldspathic regolith breccia consisting of metamorphosed feldspathic noritic troctolitic and noritic anorthosite clasts agglutinate and impact glasses as well as a number of basaltic clasts with mare and possible non mare affinities the basalt clasts in met 01210 have undergone fenner trend enrichments in iron and may also have witnessed late stage crystallization of zircon or a zirconium rich mineral some of the features of met 01210 are similar to other basaltic lunar breccia meteorites e g northwest africa 773 elephant moraine 87521 96008 yamato 793274 981031 but it is not paired with them the presence of metamorphic anorthositic clasts as well as agglutinates indicates a small regolith component similarities with previously discovered evolved e g lapaz icefield 02205 northwest africa 032 and ferroan e g asuka 881757 yamato 793169 basaltic lunar meteorites suggest a similar mare source region for met 01210 despite lack of evidence for pairing pca 02007 shares many features with other feldspathic regolith breccias e g yamato 791197 queen alexandra range 94281 including a high mg fe whole rock composition glass spherules agglutinate fragments and a diverse clast inventory spanning the range of ferroan anorthosite and high magnesium suite rocks some of the basalt fragments in this sample are fractionated and have an igneous origin however the majority of the basalt fragments are impact melt clasts pca 02007 supports previous studies of feldspathic lunar meteorites that have suggested an aluminous crust for the moon with compositions more similar to magnesium granulite breccias than ferroan anorthosites a chondrule like fragment found in pca 02007 and unlike any previously described lunar material is described and tentatively identified as the remnants of a chondritic lunar impactor this clast is porphyritic with equant olivines that have forsterite rich cores fo 98 extreme normal zonation to more fayalitic rims fo 44 and a mineral assemblage with rare earth element abundances distinct from described lunar material and more similar to chondrules found in ordinary or carbonaceous chondrites its discovery and description is significant for understanding the composition of lunar impactors previously the main evidence for chondritic lunar impactors was from chondritic relative abundances and near chondritic ratios of highly siderophile elements in lunar impact melt breccias however the presence of this clast along with two other chondritic clasts from apollo soils 12037 and 15602 provides clues to the identity of ancient meteorite impactors on the moon

a unique omphacite amphibole and graphite bearing clast in queen alexandra range que 99177 a metamorphosed xenolith in a pristine cr3 chondrite abstract a metamorphosed unshocked chondritic clast containing approximately equal volumes of matrix and chondrules has been identified in the primitive cr3 chondrite que 99177 the most striking features of this clast are the presence of ferroan omphacitic pyroxenes amphiboles pargasite and pargasitic hornblende and coarse grained up to 70 m graphite laths the clast also contains relatively equilibrated feo rich olivine low ca pyroxene and sulfides pentlandite and troilite the clast s matrix contains coarse interlocking crystals the chondrules are extensively recrystallized contain no mesostasis or metal and present poorly defined boundaries based on its compositional and crystallographic features omphacite appears to have formed at high pressures 6 gpa amphibole formation probably postdated graphite formation and occurred by reaction of olivine clinopyroxene and omphacite in the presence of an oxidizing na rich fluid at high temperatures 700 c the absence of metal suggests that this fluid was also rich in s

aluminum 26 in calcium aluminum rich inclusions and chondrules from unequilibrated ordinary chondrites in order to investigate the distribution of 26 a1 in chondrites we measured aluminum magnesium systematics in four calcium aluminum rich inclusions cais and eleven aluminum rich chondrules from unequilibrated ordinary chondrites uocs all four cais were found to contain radiogenic 26 mg 26 mg from the decay of 26 a1 the inferred initial 26 al 27 al ratios for these objects 26 al 27 al 0 5 10 5 are indistinguishable from the 26 al 27 al 0 ratios found in most cais from carbonaceous chondrites these observations together with the similarities in mineralogy and oxygen isotopic compositions of the two sets of cais imply that cais in uocs and carbonaceous chondrites formed by similar processes from similar or the same isotopic reservoirs or perhaps in a single location in the solar system we also found 26 mg in two of eleven aluminum rich chondrules the 26 al 27 al 0 ratio inferred for both of these chondrules is 1 10 5 clearly distinct from most cais but consistent with the values found in chondrules from type 3 0 3 1 uocs and for aluminum rich chondrules from lightly metamorphosed carbonaceous chondrites 0 5 10 5 to 2 10 5 the consistency of the 26 al 27 al 0 ratios for cais and chondrules in primitive chondrites independent of meteorite class implies broad scale nebular homogeneity with respect to 26 al and indicates that the differences in initial ratios can be interpreted in terms of formation time a timeline based on 26 al indicates that chondrules began to form 1 to 2 ma after most cais formed that accretion of meteorite parent bodies was essentially complete by 4 ma after cais and that metamorphism was essentially over in type 4 chondrite parent bodies by 5 to 6 ma after cais formed type 6 chondrites apparently did not cool until more than 7 ma after cais formed this timeline is consistent with 26 al as a principal heat source for melting and metamorphism

the annual cycle of the axial angular momentum of the atmosphere earlier analyses of the annual cycle of the axial angular momentum aam are extended to include mass flows and vertical transports as observed and to establish angular momentum budgets for various control volumes using the european centre for medium range forecasts ecmwf re analyses era for the years 1979 92 transformed to height coordinates in particular the role of the torques is examined the annual cycle of the zonally averaged angular momentum is large in the latitude belt 20 45 with little attenuation in the vertical up to a height of 12 km the oscillation of the mass term aam due to the earth s rotation dominates in the lower troposphere but that of the wind term relative aam is more important elsewhere the cycle of the friction torque as related to the trade winds prevails in the tropics mountain torque and friction torque are equally important in the extratropical latitudes of the northern hemisphere the annual and the semiannual cycle of the global angular momentum are in good balance with the global mountain and friction torques the addition of the global gravity wave torque destroys this agreement the transports must be adjusted if budgets of domains of less than global extent are to be considered both a streamfunction representing the nondivergent part of the fluxes and a flux potential describing the divergences convergences are determined the streamfunction pattern mainly reflects the seasonal shift of the hadley cell the flux potential links the annual oscillations of the angular momentum with the torques it is concluded that the interaction of the torques with the angular momentum is restricted to the lower troposphere in particular in the tropics the range of influence is deeper in the northern hemisphere than in the southern hemisphere presumably because of the mountains the angular momentum cycle in the upper troposphere and stratosphere is not affected by the torques and reflects interhemispheric flux patterns budgets for the polar as well as for the midlatitude domains show that fluxes in the stratosphere are important

an isotopic and petrologic study of calcium aluminum rich inclusions from co3 meteorites we have studied the mineralogy and petrology of 229 calcium aluminum rich inclusions cais from ten co3 meteorites of petrologic types 3 0 3 7 subsets of these inclusions were measured by ion probe for magnesium calcium and titanium isotopes and ree abundances most cais from co3 meteorites fall into three major types 1 melilite rich inclusions which also contain spinel hercynite perovskite and occasionally hibonite 2 spinel pyroxene inclusions and 3 hibonite hercynite inclusions in addition several isolated hibonite grains two grossite caal 4o 7 bearing cais two hibonite fassaite microspherules and one anorthite spinel pyroxene inclusion were found cais from co3 meteorites exhibit all of the ree patterns commonly seen in inclusions from cv3 and cm2 chondrites most exhibit evidence of 26 ai and many have inferred 26 ai 27 ai o 5 10 5 the relative abundances of different types of cais in co3 chondrites differ from those in cv3 and cm2 chondrites cais in co3 chondrites have experienced considerable secondary alteration both before and after accretion signatures of nebular alteration include wark lovering rims and the high fe contents in spinels from all hibonite hercynite inclusions occasionally melilite and anorthite show evidence of nebular alteration to feldspathoids and pyroxene the magnesium aluminum systematics of some melilite rich inclusions were apparently disturbed prior to final accretion of the parent body parent body alteration is indicated by correlations between cai characteristics and the petrologic type of the host meteorite spinel in melilite rich and coarse grained spinel pyroxene inclusions becomes more fe rich with the development of relatively homogeneous hercynitic spinel 50 60 mol in cais from metamorphic grades 3 4 perovskite has been converted to ilmenite in types 3 4 melilite rich inclusions are abundant in co3 0 3 3 meteorites rare in 3 4 meteorites and absent meteorites of types 3 5 3 7 melilite rich cais are probably replaced by inclusions rich in feldspathoids pyroxene and fe rich spinel isotopic disturbance of the magnesium aluminum systematics may be more severe in higher petrologic types hibonite seems to be unaffected by this level of metamorphism three isotopically unusual inclusions were found one single crystal hibonite isna sp16 has a ree pattern strongly depleted in ce and y 26 ai 27 ai o 2 4 0 3 10 5 and mass fractionated calcium f ca 12 2 amu but no resolvable nuclear anomalies in neutron rich calcium isotopes the ree pattern which is thought to reflect nebular conditions and mass fractionated calcium indicative of evaporation are similar to those of the fun inclusion hal and related hibonites indicating similar formation conditions the absence in isna sp16 of the nuclear anomalies observed in hal and the difference in 26 ai 27 ai o between hal and isna sp16 indicate that the processes that produced hal type hibonites operated on diverse materials two hibonite bearing microspherules colony sp1 and alh82101 sp15 exhibit nearly flat ree patterns with negative europium anomalies and slightly negative 26 mg alh82101 sp15 has resolved excesses of 48 ca and 50 ti these characteristics are similar to those of previously described microspherules from murchison and lance implying that the microspherules formed via a single process from related but not identical source materials

spinel group minerals in ll3 00 6 chondrites indicators of nebular and parent body processes we carried out a systematic study of spinel group minerals in ll3 00 3 9 and ll4 6 chondrites with increasing petrologic type the size and abundance of spinel increase the compositions of spinel group minerals in type 3 chondrites depend on the occurrence mg al rich spinel occurs mainly in chondrules some chromite occurs in chondrules and matrix and nearly pure chromite is exclusively encountered in the matrix the occurrence of nearly pure chromite and the wide compositional variations distinguish spinel group minerals in types 3 00 3 3 from those in the other types spinel group minerals in types 3 5 3 9 show a narrower range of compositions and those in types 4 6 are homogeneous the changes in composition and abundance of spinel in type 3 chondrites are most likely due to thermal metamorphism therefore the chemistry of spinel group minerals could be used as a sensitive indicator of metamorphic conditions not only for type 3 6 but also 3 00 3 9 they can be applied to identify the most primitive least metamorphosed chondrites the bulk compositions of spinel bearing chondrules and the textural setting of the spinel indicate that most spinel group minerals crystallized directly from chondrule melts however some spinel grains especially those enclosed in olivine phenocrysts can not be explained by in situ crystallization in the chondrule we interpret these spinel grains to be relic phases that survived chondrule melting this is supported by the oxygen isotopic composition of a spinel grain which has significantly lighter oxygen than the coexisting olivine the oxygen isotopic composition of this spinel is similar to those of al rich chondrules our discovery of relic spinel in chondrules is an indication of the complexities in the early solar nebular processes that ranged from formation of refractory inclusion through al rich chondrule to ferromagnesian chondrules and attests to the recycling of earlier formed materials into the precursors of later formed materials the characteristic features of spinel group minerals are not only sensitive to thermal metamorphism but also shed light on chondrule formation processes

condensation of major elements during chondrule formation and its implication to the origin of chondrules abstract two glassy refractory al rich chondrules in semarkona ll3 0 the most primitive unequilibrated ordinary chondrite provide direct evidence for condensation of si and mg on melt droplets during cooling the chondrules are completely rounded rich in ca and al and poor in fe and alkalis they have extraordinarily abundant glass 70 80 vol with a subordinate amount of forsterite as the only crystalline phase that occurs mostly rimming the chondrule edge the groundmass glass is concentrically zoned in terms of si with an outward increase which is overlapped with local heterogeneity of mg and al induced by crystallization of forsterite the outward increase of si mostly compensated by al cannot be formed solely by crystallization of forsterite from a homogeneous melt in a closed system combined with skeletal or dendritic morphology and sector zoning of forsterite it is suggested that si condensed onto totally molten droplets initial melts accompanied by nucleation and rapid growth of forsterite with lowering temperature the initial melts the compositions of which were estimated from the ca contents of the first crystallized forsterite are very similar to type c cai but are notably poorer in mg and si than the bulk chondrules indicating condensation of mg in addition to si with an atomic ratio of mg si 3 2 the condensation after the nucleation of forsterite took place below 1300 c under cooling at 70 c h and amounted to 30 wt of the current chondrule this study suggests a model that a short time and local shock heating event induced melting of type c cai and concomitant evaporation of dusts ferromagnesian chondrules of earlier generation and their fragments to generate mg and si rich gas which condensed onto the melt droplets upon cooling accompanying condensation of type i chondrules

high temperature condensation of iron rich olivine in the solar nebula abstract olivine is the most abundant mineral in many chondritic meteorites it is also the first major mg silicate to condense from a solar gas upon cooling the composition of olivine provides important information concerning its origin results of calculations are presented for the fe mn and ni contents of olivine condensing from a gas with solar composition but variable oxygen fugacity a basic computational method is described that takes into account the depletion of the gas in mg and si during condensation the first olivine that condenses from a solar gas has less than 10 2 mol feo independent of the oxygen fugacity of the otherwise solar gas at lower temperatures when most of the mg is condensed more feo can be incorporated in forsterite by condensation if the oxygen fugacity is sufficiently high the feo mno ratio of the first condensing olivine is above 1000 decreasing with decreasing temperature and increasing oxygen fugacity to values of around 100 which are actually observed in fayalitic olivine rims in allende the ni content of condensed olivine is below 10 7 mol even at high oxygen fugacities indicating that condensation of nio in olivine is a very unlikely process any ni in olivine in the ppm range is therefore indicative of metal olivine equilibration under increasingly oxidizing conditions h 2 o h 2 ratios of 0 01 0 1 chromite is an early phase to condense forming before forsterite isolated olivine grains in allende and olivine on the outside of chondrules have feo rich rims texture composition and morphology of these rims indicate that they formed by condensation from a gas our calculations suggest that the gas was enriched by a factor of 100 in oxygen relative to solar composition gas and that mg was almost completely condensed when rim formation occurred the sharp boundary between forsteritic and fayalitic olivine suggests an increase in oxygen fugacity and rapid formation of fayalitic olivine by condensation cr enrichment at the rim interface with the underlying forsterite probably reflects stability of chromite under oxidizing conditions conventional models of feo bearing silicate formation require oxidation of metal silicate assemblages at temperatures as low as 400 k it is shown here that diffusion at this temperature is so slow that the time needed for formation of the observed feo bearing phases would exceed the lifetime of the solar nebula other oxygen fugacity indicators reflect similar conditions for example the hercynite component of spinel in fine grained al rich inclusions indicates equilibration with a gas of similar composition as that responsible for condensation of fayalitic olivine suggesting formation of feo rich spinel by gas solid reactions mechanisms for producing oxidizing conditions in the solar nebula are briefly discussed

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

the conditions of chondrule formation part i closed system abstract mixing was an important process in the early solar nebula and is often used as an argument to explain the compositional scatter among chondrules mm sized once molten silicate spherules in chondritic meteorites if it is hypothesized that chondrules only acted as closed systems and the scatter in chondrule bulk chemical compositions is only the result of mixing heterogeneous precursor grains the basic components of chondrules it is in turn possible to determine the sizes of the precursor grains using statistical calculations in order to reproduce the observed compositional scatter in chondrules not more than 10 precursor grains should contribute to a single chondrule each with a diameter of several 100 m this finding has important implications for the conditions of chondrule formation and replaces the so far widely accepted model that chondrules formed from fine grained dust balls chondrules rather formed from coarse grained precursor aggregates with variable amounts of m fine matrix material as a consequence only chondrite matrix or interstellar material winnows as precursor material large grains of variable composition serving as precursor grains must have been formed prior to chondrule formation chondrules probably have not been their immediate precursors as only 1 2 chondrule recycling steps would have homogenized bulk chondrule compositions chondrule recycling can therefore only have occurred to a limited extent chondrule formation needed at least three steps 1 production of large and heterogeneous chondrule precursor grains 2 agglomeration of large precursor grains and fine grained precursors into aggregates 3 formation of chondrules during transient heating events al rich chondrules can in this context be explained by the admixture of cais to either chondrule precursors or a population of existing chondrules

refractory inclusions and aluminum rich chondrules in sayh al uhaymir 290 ch chondrite petrography and mineralogy here we report the petrography mineralogy and bulk compositions of ca al rich inclusions cals amoeboid olivine aggregate aoa and al rich chondrules arcs in sayh al uhaymir sau 290 ch chondrite eighty two cals 0 1 of the section surface area were found they are hibonite rich 9 grossite rich 18 melilite spinel rich 48 fassaite spinel rich 15 and fassaite rich 10 refractory inclusions most cals are rounded in shape and small in size average 40 mu m they are more refractory than those of other groups of chondrites cals in sau 290 might have experienced higher peak heating temperatures which could be due to the formation region closer to the center of protoplanetary disk or have formed earlier than those of other groups of chondrites in sau 290 refractory inclusions with a layered texture could have formed by gas solid condensation from the solar nebula and those with an igneous texture could have crystallized from melt droplets or experienced subsequent melting of pre existing condensates from the solar nebula one refractory inclusion represents an evaporation product of pre existing refractory solid on the basis of its layered texture and melting temperature of constituting minerals only one aoa is observed 75 mu m across it consists of olivine al diopside anorthite and minor spinel with a layered texture cals and aoa show no significant low temperature aqueous alteration arcs in sau 290 consist of diopside forsterite anorthite al enstatite spinel and mesostasis or glass they can be divided into diposide rich al enstatite rich glass rich and anorthite rich chondrules bulk compositions of most arcs are consistent with a mixture origin of cals and ferromagnesian chondrules anorthite and al enstatite do not coexist in a given arc implying a kinetic effect on their formation

refractory inclusions in the ch cb like carbonaceous chondrite isheyevo i mineralogy and petrography the ch cb like chondrite isheyevo consists of metal rich 7090 vol fe ni metal and metal poor 720 vol fe ni metal lithologies which differ in size and relative abundance of fe nimetal and chondrules as well as proportions of porphyritic versus non porphyritic chondrules here we describe the mineralogy and petrography of ca al rich inclusions cais and amoeboid olivine aggregates aoas in these lithologies based on mineralogy refractory inclusions can be divided into hibonite rich 39 grossite rich 16 melilite rich 19 spinel rich 14 pyroxeneanorthite rich 8 fine grained spinel rich cais 1 and aoas 4 there are no systematic differences in the inclusion types or their relative abundances between the lithologies about 55 of the isheyevo cais are very refractory hibonite rich and grossite rich objects 20 240 m in size which appear to have crystallized from rapidly cooling melts these inclusions are texturally and mineralogically similar to the majority of cais in ch and cb chondrites they are distinctly different from cais in other carbonaceous chondrite groups dominated by the spinel pyroxene melilite cais and aoas the remaining 45 of inclusions are less refractory objects melilite spinel and pyroxene rich cais and aoas 40 300 m in size which are texturally and mineralogically similar to those in other chondrite groups both types of cais are found as relict objects inside porphyritic chondrules indicating recycling during chondrule formation we infer that there are at least two populations of cais in isheyevo which appear to have experienced different thermal histories all of the isheyevo cais apparently formed at an early stage prior to chondrule formation and prior to a hypothesized planetary impact that produced magnesian cryptocrystalline and skeletal chondrules and metal grains in cb and possibly ch chondrites however some of the cais appear to have undergone melting during chondrule formation and possibly during a major impact event we suggest that isheyevo as well as ch and cb chondrites consist of variable proportions of materials produced by different processes in different settings 1 by evaporation condensation and melting of dust in the protoplanetary disk porphyritic chondrules and refractory inclusions 2 by melting evaporation and condensation in an impact generated plume magnesian cryptocrystalline and skeletal chondrules and metal grains some igneous cais could have been melted during this event and 3 by aqueous alteration of pre existing planetesimals heavily hydrated lithic clasts the isheyevo lithologies formed by size sorting of similar components during accretion in the isheyevo parent body they do not represent fragments of ch and cb chondrites

origin of low ca pyroxene in amoeboid olivine aggregates evidence from oxygen isotopic compositions amoeboid olivine aggregates aoas in primitive carbonaceous chondrites consist of forsterite fa 50 objects is texturally and mineralogically intermediate between aoas and al rich chondrules it consists of euhedral forsterite grains pigeonite augite anorthitic mesostasis abundant anhedral spinel grains and minor fe ni metal it is surrounded by a coarse grained igneous rim largely composed of low ca pyroxene with abundant fe ni metal sulfide nodules the mineralogical observations suggest that only spinel grains in this igneous object were not melted the spinel is 16o rich 17o 22 whereas the neighboring plagioclase mesostasis is 16o depleted 17o 11 we conclude that aoas are aggregates of solar nebular condensates forsterite fe ni metal and cais composed of al diopside anorthite spinel and melilite formed in an 16o rich gaseous reservoir probably cai forming region s solid or incipiently melted forsterite in some aoas reacted with gaseous sio in the same nebular region to form low ca pyroxene some other aoas appear to have accreted 16o poor pyroxene normative dust and experienced varying degrees of melting most likely in chondrule forming region s the most extensively melted aoas experienced oxygen isotope exchange with 16o poor nebular gas and may have been transformed into chondrules the original 16o rich signature of the precursor materials of such chondrules is preserved only in incompletely melted grains

aluminian low ca pyroxene in a ca al rich chondrule from the semarkona meteorite a ca al rich chondrule labeled g7 from the semarkona ll3 0 ordinary chondrite oc consists of 73 vol glassy mesostasis 22 vol skeletal forsterite 3 vol fassaite i e al ti diopside and 2 vol al rich low ca pyroxene the latter phase which contains up to 16 3 wt al 2 o 3 is among the most al rich low ca pyroxene grains ever reported it is inferred that 20 of the tetrahedral sites and 13 of the octahedral sites in this grain are occupied by al approximately parallel optical extinction implies that the al rich low ca pyroxene grains are probably orthorhombic consistent with literature data that show that al 2 o 3 stabilizes the orthoenstatite structure relative to protoenstatite at low pressure the order of crystallization in the chondrule was forsterite al rich low ca pyroxene and fassaite the residual liquid vitrified during chondrule quenching phase relationships indicate that for a g7 composition liquid at equilibrium spinel and anorthite should crystallize early and orthopyroxene should not crystallize at all the presence of al rich orthopyroxene in g7 is due mainly to the kinetic failure of anorthite to crystallize this failure was caused by quenching of the g7 precursor droplet aluminum preferentially enters the relatively large b tetrahedra of orthopyroxene because only one tetrahedral size occurs in fassaite this phase contains higher mean concentrations of al 2 o 3 than the al rich orthopyroxene 17 8 and 14 7 wt respectively chondrule g7 may have formed by remelting an amoeboid olivine inclusion that entered the oc region of the solar nebula during an episode of chondrule formation

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

trace element and petrologic clues to the formation of forsterite bearing ca al rich inclusions in the allende meteorite this work presents new trace element and petrographic data for three forsterite bearing ca alrich inclusions from the allende meteorite te 818a and 110 a such inclusions form a continuum with type b1 and b2 ca al rich inclusions cais and we refer to them as type b3 cais textures mineral chemistries crystal chemically fractionated ree patterns and other properties suggest that type b3 crystallized from partly molten evaporative residues the concentrations of refractory lithophile elements are lower than in type b1 and type b2 in approximately inverse proportion to the higher concentrations of mg and si in the type b3 s the refractory trace element abundances of the forsterite bearing isotopically anomalous fun cais te and cg14 suggest that they formed at higher temperatures and under more oxidizing conditions than other type b cais thus strengthening the previously observed link between relatively oxidized cai compositions and fun properties we also present evidence that 818a was strongly re heated and modified in the nebula after its initial crystallization it consists of a core of coarse grained ti al pyroxene tpx forsterite spinel and metal grains and a thick surrounding mantle of melilite that has been almost totally converted to fine grained alteration products in the core the mean concentrations of refractory lithophiles and siderophiles are similar both 14 ci but in the mantle the refractory siderophiles are a factor of 2 lower 9 ci than the refractory lithophiles 18 ci because the core and mantle display similar mineralogically fractionated ree patterns both sloping up from la to lu the pre alteration mantle could not have formed during fractional crystallization of the primary cai nor as a later condensate over the core a 3 stage formation process is required for 818a 1 crystallization of the primary cai rich in tpx throughout 2 re heating and partial volatilization of mg and si from the outer portion of the cai causing an increase in the concentration of refractory lithophiles a loss of siderophiles and converting tpx to melilite 3 metasomatic alteration of the melilite rich mantle

indicators of aqueous alteration and thermal metamorphism on the cv parent body microtextures of a dark inclusion from allende abstract an unusual dark clast in the allende cv3 chondrite termed allende af which was previously interpreted as a primary aggregate formed in the solar nebula kurat et al 1989 palme et al 1989 was re examined our study reveals abundant evidence suggesting that it probably experienced extensive aqueous alteration and subsequent thermal metamorphism on the meteorite parent body allende af contains numerous rounded to oval shaped inclusions embedded in a dark matrix the inclusions consisting predominantly of fine grains of fe rich olivine have internal textures suggesting that they are pseudomorphs after chondrules several inclusions appear to be replaced cais veins filled with fibrous olivine grains occur abundantly in both inclusions and matrix some veins up to 4 mm in length penetrate several inclusions providing strong evidence that aqueous alteration occurred after accretion the fibrous morphology of olivine in veins and inclusions suggests that the olivine was produced by dehydration and thermal transformation of phyllosilicate that had been formed by aqueous alteration olivine grains in the matrix contain numerous micro inclusions of fe ni sulfide which were probably incorporated during transformation from phyllosilicate allende af is probably related to the fine grained variety of dark inclusions reported from cv3 chondrites that has been described as the type containing abundant porous aggregates of fe rich olivine by johnson et al 1990 many dark inclusions previously described appear to be similar in texture and mineralogy to allende af and probably experienced similar secondary process on the meteorite parent body the wide variation in texture of dark inclusions can be explained by different degrees of aqueous alteration that preceded thermal metamorphism the size distribution of chondrule pseudomorphs and the abundance of cai pseudomorphs suggest that the precursor of allende af is a cv type chondrite probably allende itself oxygen isotopic and chemical compositions are consistent with this interpretation the cv parent body has been commonly thought to have escaped major secondary processing however allende af provides evidence that extensive aqueous alteration and thermal metamorphism have occurred locally on the cv parent body

meteorite 3 d synchrotron microtomography methods and applications methods of synchrotron x ray computed microtomography xrcmt are described which allow nondestructive high spatial and contrast resolution imaging of the density structures of meteorites and their components in three dimensions images of bulk chondrites to one cubic centimeter in size reveal compound chondrules chondrule matrix volumetric ratios metal and sulfide distribution petrofabrics and 3 d chondrule and calcium aluminum inclusion cai sizes and shapes images of separated chondrules and cais reveal void spaces mineral intergrowth textures and the true locations of crystal rims and cores at resolutions to 8 cubic micron volume element images of achondrites reveal mineral fabrics and crystal zoning lunar glass spherules can be searched for phenocrysts bearing deeply sourced melt inclusions a companion dvd and url contain images for classroom and research use numerical techniques for quantification of x ray computed microtomography xrcmt data and its potential applications are discussed three dimensional x ray images of meteorites provide a way to discover components of interest and to precisely slice samples to expose these components with minimal damage and loss of material three dimensional studies of petrographic features size shape texture and modal abundance of chondrites and their components as well as other meteorites have definite advantages over standard 2 d studies using randomly sliced thin sections

amoeboid olivine aggregates with low ca pyroxenes a genetic link between refractory inclusions and chondrules amoeboid olivine aggregates aoas in primitive unmetamorphosed and unaltered carbona ceous chondrites are uniformly 16 o enriched 17 o 20 and consist of forsterite fa2 feni metal and a refractory component individual cais and fine grained minerals interspersed with forsterite grains composed of al diopside anorthite spinel and exceptionally rare melilite a u k15 some cais in aoas have compact igneous textures melilite in aoas is replaced by a fine grained mixture of spinel al diopside and anorthite spinel is corroded by anorthite or by al diopside in 10 of 500 aoas studied in the cr cv cm co ch cb and ungrouped carbonaceous chondrites acfer 094 adelaide and lew85332 forsterite is replaced to a various degree by low ca pyroxene there are three major textural occurrences of low ca pyroxene in aoas i thin 10 m discontinuous layers around forsterite grains or along forsterite grain boundaries in aoa peripheries ii haloes and subhedral grains around feni metal nodules in aoa peripheries and iii thick up to 70 m continuous layers with abundant tiny inclusions of feni metal grains around aoas aoas with low ca pyroxene appear to have experienced melting of various degrees in the most extensively melted aoa in the cv chondrite leoville only spinel grains are relict forsterite anorthite and al diopside were melted this aoa has an igneous rim of low ca pyroxene with abundant feni metal nodules and is texturally similar to type i chondrules based on these observations and thermodynamic analysis we conclude that aoas are aggregates of relatively low temperature solar nebular condensates originated in 16 o rich gaseous reservoir s probably cai forming region s some of the cais were melted before aggregation into aoas many aoas must have also experienced melting but of a much smaller degree than chondrules before and possibly after aggregation melilite and spinel reacted with the gaseous sio and mg to form ca tschermakite caal2sio6 diopside camgsi2o6 solid solution and anorthite solid or incipiently melted olivine in some aoas reacted with gaseous sio in the cai or chondrule forming regions to form low ca pyroxene mg2sio4 sio g h2o g mg2si2o6 h2 g some low ca pyroxenes in aoas may have formed by oxidation of si bearing feni metal mg2sio4 si in feni 2h2o g mg2si2o6 2h2 g and by direct gas solid condensation mg g sio g h2o g mg2si2o6 s h2 g from fractionated mg si ratio solar nebular gas although bulk compositions of aoas are rather similar to those of type i chondrules on the projection from spinel onto the plane ca2sio4 mg2sio4 al2o3 these objects plot on different sides of the anorthite forsterite thermal divide suggesting that type i chondrules cannot be produced from aoas by an igneous fractionation formation of low ca pyroxene by reaction of aoas with gaseous sio and by melting of silica rich dust accreted around aoas moves bulk compositions of the aoas towards chondrules and provide possible mechanisms of transformation of refractory materials into chondrules or chondrule precursors the rare occurrences of low ca pyroxene in aoas may indicate that either aoas were isolated from the hot nebular gas before condensation of low ca pyroxene or that condensation of low ca pyroxene by reaction between forsterite and gaseous sio was kinetically inhibited if the latter is correct then the common occurrences of pyroxene rich type i chondrules may require either direct condensation of low ca pyroxenes or sio2 from fractionated nebular gas or condensation of gaseous sio into chondrule melts copyright 2004 elsevier ltd

origins of al rich chondrules clues from a compound al rich chondrule in the dar al gani 978 carbonaceous chondrite abstract aluminum rich chondrules are one of the most interesting components of primitive chondrites because they have characteristics that are similar to both ca al rich inclusions cais and ferromagnesian chondrules however their precursor and formation history remain poorly constrained especially with respect to their oxygen isotopic distributions in this study we report on the petrography mineralogy oxygen isotope ratios and rare earth element compositions of a sapphirine bearing al rich chondrule sarc in the ungrouped chondrite dar al gani dag 978 the sarc has a complex core mantle rim texture while both the core and the mantle are mainly composed of al rich enstatite and anorthite with minor amounts of mesostasis these regions are distinguished by the presence of fe rich spinel and sapphirine in the core and their absence in the mantle the rim of the sarc consists mainly of fe rich olivine enstatite and fe ni metal spinel and some olivine grains in the sarc are 16o rich with 17o values down to 20 and 23 respectively enstatite sapphirine and most olivine grains have similar 17o values 7 which are lower than those of anorthite and the mesostasis including augite therein 17o 3 mesostasis from both the core and mantle have group ii rare earth element ree patterns however the core mesostasis has higher ree concentrations than the mantle mesostasis these observations provide a strong indication that the sarc formed by the melting and crystallization of a mixture of materials from group ii cais and ferromagnesian chondrules both spinel and olivine with 16o rich features could be of relict origin the 16o poor isotopic compositions of most components in al rich chondrules can be explained by oxygen isotopic exchange between the melt and 16o poor nebular gas 17o 7 during melting in chondrule forming regions whereas the anorthite and mesostasis could have experienced further oxygen isotopic exchange with a relatively 16o poor reservoir 17o 3 on the parent body likely during fluid assisted thermal metamorphism during the same thermal metamorphism event spinel olivine some enstatite and the mesostasis experienced mg fe exchange to various extents

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

ca al rich inclusions in rumuruti r chondrites rumuruti chondrites r chondrites constitute a well characterized chondrite group different from carbonaceous ordinary and enstatite chondrites many of these meteorites are breccias containing primitive type 3 fragments as well as fragments of higher petrologic type ca al rich inclusions cais occur within all lithologies here we present the results of our search for and analysis of al rich objects in rumuruti chondrites we studied 20 r chondrites and found 126 ca al rich objects 101 cais 19 al rich chondrules and 6 spinel rich fragments based on mineralogical characterization and analysis by sem and electron microprobe the inclusions can be grouped into six different types 1 simple concentric spinel rich inclusions 42 2 fassaite rich spherules 3 complex spinel rich cais 53 4 complex diopside rich inclusions 5 al rich chondrules and 6 al rich spinel rich fragments the simple concentric and complex spinel rich cais have abundant spinel and based on the presence or absence of different major phases fassaite hibonite na al cl rich alteration products can be subdivided into several subgroups although there are some similarities between cais from r chondrites and inclusions from other chondrite groups with respect to their mineral assemblages abundance and size the overall assemblage of cais is distinct to the r chondrite group some ca al rich inclusions appear to be primitive e g low feo contents in spinel low abundances of na al cl rich alteration products abundant perovskite whereas others were highly altered by nebular and or parent body processes e g high concentrations of feo and zno in spinel ilmenite instead of perovskite abundant na al cl rich alteration products there is complete absence of grossite and melilite which are common in cais from most other groups cais from equilibrated r chondrite lithologies have abundant secondary ab rich plagioclase oligoclase and differ from those in unequilibrated type 3 lithologies which have nepheline and sodalite instead

formation processes of compound chondrules in cv3 carbonaceous chondrites constraints from oxygen isotope ratios and major element concentrations abstract we found thirty compound chondrules in two cv3 carbonaceous chondrites the abundance in each meteorite relative to single chondrules is 29 1846 1 6 in allende and 1 230 0 4 in axtell we examined petrologic features major element concentrations and oxygen isotopic compositions textural compositional and isotopic evidence suggests that multiple different mechanisms are responsible for the formation of compound chondrules seven compound chondrules are composed of two conjoined porphyritic chondrules with a blurred boundary at the boundary region of this type of compounds a poikilitic texture is commonly observed this suggests that the two chondrules were melted when they came to be in contact on the other hand seventeen compound chondrules consist of two conjoined chondrules with a discrete boundary the preservation of spherical boundary planes of an earlier formed chondrule of this type implies that it already solidified before fusing with a later formed chondrule that was still melted six samples out of 17 compound chondrules of this type are composed of two bo chondrules the bo bo compound chondrules have a unique textural feature in common the directions of the barred olivines are mostly parallel between two chondrules this cannot be explained by a simple collision process and forces another mechanism to be taken into consideration the remaining six compound chondrules differ from the others they consist of an earlier formed chondrule enclosed by a later formed chondrule a large feo enrichment was observed in the later formed chondrules and the enrichment was much greater than that in the later formed chondrules of other types of compounds this is consistent with the relict chondrule model which envisages that the later formed chondrule was made by a flash melting of a porous feo rich dust clump on an earlier formed chondrule the textural evidence of this type of compound shows that the earlier formed chondrule has melted again to varying degrees at the second heating event this implies that feo concentrations in bulk chondrules increases during the second heating event if an earlier formed chondrule was totally melted together with the feo rich dust aggregates silicate minerals such as olivine and low ca pyroxene in compound chondrules have oxygen isotope compositions similar to those in single chondrules from cv3 chondrites the oxygen isotope composition of each part of the compound chondrule is basically similar to their chondrule pair but silicates in some chondrules show varying degrees of 16 o enrichment down to 15 in 18 o while those in their partners have 16 o poor invariable compositions near 0 in 18 o this implies that the two chondrules in individual compounds formed in the same environments before they became conjoined and the heterogeneous oxygen isotope compositions in some chondrules resulted from incomplete exchange of oxygen atoms between 16 o rich chondrule melts and 16 o poor nebular gas

16 o enrichments in aluminum rich chondrules from ordinary chondrites the oxygen isotopic compositions of seven al rich chondrules from four unequilibrated ordinary chondrites were measured in situ using an ion microprobe on an oxygen three isotope plot the data are continuous with the ordinary chondrite ferromagnesian chondrule field but extend it to more 16o enriched values along a mixing line of slope 0 83 0 09 with the lightest value recorded at 18o 15 7 1 8 and 17o 13 5 2 6 if al rich chondrules were mixtures of ferromagnesian chondrules and cai material their bulk chemical compositions would require them to exhibit larger 16o enrichments than we observe therefore al rich chondrules are not simple mixtures of these two components three chondrules exhibit significant internal isotopic heterogeneity indicative of partial exchange with a gaseous reservoir porphyritic al rich chondrules are consistently 16o rich relative to nonporphyritic ones suggesting that degree of melting is a key factor and pointing to a nebular setting for the isotopic exchange process because al rich chondrules are closely related to ferromagnesian chondrules their radiogenic mg isotopic abundances can plausibly be applied to help constrain the timing or location of chondrule formation

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

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

secondary calcium iron rich minerals in the bali like and allende like oxidized cv3 chondrites and allende dark inclusions we have characterized ca fe rich silicates salite hedenbergite pyroxenes fs10 50wo45 50 andradite ca3fe2si3o12 kirschsteinite cafesio4 and wollastonite ca3si3o9 in the type i chondrules and matrices in the bali like and allende like oxidized cv3 chondrites and allende dark inclusions in type i chondrules in the bali like cv3 chondrites metal is oxidized to magnetite magnetite sulfide nodules are replaced by ca fe rich pyroxenes with minor andradite and pure fayalite we infer that ca fe rich pyroxenes andradite fayalite magnetite and phyllosilicates which occur in mesostases formed at relatively low temperatures 300 c in the presence of aqueous solutions thermodynamic analysis of phase relations in the si fe ca o h system and large o isotopic fractionation of the coexisting magnetite and fayalite 20 krot et al 1998 are consistent with this interpretation in type i chondrules in the allende like cv3 chondrites and dark inclusions magnetite sulfide nodules are replaced by ca fe rich pyroxenes and ferrous olivine low ca pyroxene and forsterite phenocrysts are rimmed and veined by ferrous olivine it appear that the ca fe rich pyroxenes predate formation of ferrous olivine the latter postdates formation of talc and biopyriboles brearley 1997 the allende dark inclusions are crosscut by ca fe pyroxene andradite veins and surrounded by ca rich rims that consist of ca fe rich pyroxenes andradite wollastonite and kirschsteinite calcium rich veins and rims formed after aggregation and lithification of the dark inclusions the rimmed dark inclusions show zoned depletion in ca which is due to a lower abundance of ca fe rich pyroxenes close to the rim calcium was probably leached from the inclusions and redeposited along their edges we infer that the allende like chondrites and dark inclusions experienced similar aqueous alteration to the bali like chondrites and were metamorphosed subsequently which resulted in loss of aqueous solutions and dehydration of phyllosilicates we conclude that ca fe rich silicates in the oxidized cv3 chondrites and allende dark inclusions are secondary and resulted from aqueous fluid rock interactions during progressive metamorphism of a heterogeneous mixture of hydrous ices and anhydrous materials the latter were possibly mineralogically similar to the reduced cv3 chondrites

petrology mineralogy and oxygen isotope compositions of aluminum rich chondrules from cv3 chondrites bulk major element composition petrography mineralogy and oxygen isotope compositions of twenty al rich chondrules arcs from five cv3 chondrites northwest africa nwa 989 nwa 2086 nwa 2140 nwa 2697 nwa 3118 and the ningqiang carbonaceous chondrite were studied and compared with those of ferromagnesian chondrules and refractory inclusions most arcs are marginally al richer than ferromagnesian chondrules with bulk al2o3 of 10 15 wt arcs are texturally similar to ferromagnesian chondrules composed primarily of olivine pyroxene plagioclase spinel al rich glass and metallic phases minerals in arcs have intermediate compositions low ca pyroxene fs0 6 8 8wo0 7 9 3 has much higher al2o3 and tio2 contents up to 12 5 and 2 3 wt respectively than that in ferromagnesian chondrules high ca pyroxene fs0 3 2 0wo33 54 contains less al2o3 and tio2 than that in ca al rich inclusions cais plagioclase an77 99ab1 23 is much more sodic than that in cais spinel is enriched in moderately volatile element cr up to 6 7 wt compared to that in cais al rich enstatite coexists with anorthite and spinel in a glass free chondrule implying that the formation of al enstatite was not due to kinetic reasons but is likely due to the high al2o3 cao ratio 7 4 of the bulk chondrule three arcs contain relict cais oxygen isotope compositions of arcs are also intermediate between those of ferromagnesian chondrules and cais they vary from 39 4 to 13 9 in 18o and yield a best fit line slope 0 88 close to the carbonaceous chondrite anhydrous mineral ccam line chondrules with 5 10 wt bulk al2o3 have a slightly more narrow range in 18o 32 5 to 5 9 along the ccam line except for the arcs with relict phases however most arcs have oxygen isotope compositions 20 in 18o similar to those of typical ferromagnesian chondrules arcs are genetically related to both ferromagnesian chondrules and cais but the relationship between arcs and ferromagnesian chondrules is closer most arcs were formed during flash heating and rapid cooling processes like normal chondrules only from chemically evolved precursors arcs extremely enriched in al and those with relict phases could have had a hybrid origin krot et al 2002 which incorporated refractory inclusions as part of the precursors in addition to ferromagnesian materials the occurrence of melilite in arcs indicates that melilite rich cais might be present in the precursor materials of arcs the absence of melilite in most arcs is possibly due to high temperature interactions between a chondrule melt and the solar nebula

the influence of antarctica on the momentum budget of the southern extratropics the antarctic plateau acts as a strong heat sink for the global climate cooling the atmosphere and radiating energy to space a cold dense atmospheric boundary layer is formed strong surface winds are formed as the boundary layer drains off the plateau these drainage winds and the eddy fluxes necessary to maintain them are analysed in a general circulation model gcm the drainage flow is well represented in the gcm the associated mean meridional circulation is analysed in isentropic coordinates the momentum budget over antarctica reveals a balance between the eliassen palm flux convergence and the coriolis torque exerted by the mean meridional mass flux both vertical and horizontal components of the eliassen palm flux contribute the vertical component being the greater

remelting of refractory inclusions in the chondrule forming regions evidence from chondrule bearing type c calcium aluminum rich inclusions from allende we describe the mineralogy petrology oxygen and magnesium isotope compositions of three coarse grained igneous anorthite rich type c ca al rich inclusions cais abc ts26 and 93 that are associated with ferromagnesian chondrule like silicate materials from the cv carbonaceous chondrite allende the cais consist of lath shaped anorthite an99 cr bearing al ti diopside al and ti contents are highly variable spinel and highly akermanitic and na rich melilite ak63 74 0 4 0 6 wt na2o ts26 and 93 lack wark lovering rim layers abc is a cai fragment missing the outermost part the peripheral portions of ts26 and abc are enriched in sio2 and depleted in tio2 and al2o3 compared to their cores and contain relict ferromagnesian chondrule fragments composed of forsteritic olivine fa6 8 and low ca pyroxene pigeonite fs1wo 1 9 the relict grains are corroded by al ti diopside of the host cais and surrounded by haloes of augite fs0 5wo 30 42 the outer portion of cai 93 enriched in spinel is overgrown by coarse grained pigeonite fs0 5 2wo 5 17 augite fs0 5wo 38 42 and anorthitic plagioclase an84 relict olivine and low ca pyroxene pigeonite in abc and ts26 and the pigeonite augite rim around 93 are 16 o poor 17 o 1 to 8 spinel and al ti diopside in cores of cais abc ts26 and 93 are 16 o enriched 17 o down to 20 whereas al ti diopside in the outer zones as well as melilite and anorthite are 16 o depleted to various degrees 17 o 11 to 2 in contrast to typical allende cais that have the canonical initial 26 al 27 al ratio of 5 10 5 abc 93 and ts26 are 26 al poor with 26 al 27 al 0 ratios of 4 7 1 4 10 6 1 5 1 8 10 6 and 1 2 10 6 respectively we conclude that abc ts26 and 93 experienced remelting with addition of ferromagnesian chondrule silicates and incomplete oxygen isotopic exchange in an 16 o poor gaseous reservoir probably in the chondrule forming region this melting episode could have reset the 26 al 26 mg systematics of the host cais suggesting it occurred 2 myr after formation of most cais these observations and the common presence of relict cais inside chondrules suggest that cais predated formation of chondrules

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

petrogenesis of al rich chondrules evidence from bulk compositions and phase equilibria we measured major minor and trace element compositions for eleven al rich chondrules from unequilibrated ordinary chondrites to investigate the relationships between al rich chondrules ferromagnesian chondrules ca al rich inclusions cais and amoeboid olivine aggregates aoas phase equilibrium considerations show that for the most part mineral assemblages in al rich chondrules are those expected from melts of the observed compositions the diversity of mineral assemblages and al rich chondrule types arises mainly from the fact that the array of compositions spans both the spinel saturated anorthite forsterite reaction curve and a thermal divide defined by where the anorthite forsterite join crosses the reaction curve the reaction curve accounts for the two principal varieties of al rich chondrule plagioclase phyric and olivine phyric with or without aluminous spinel the thermal divide influences the subsequent evolution of each variety a third variety of al rich chondrule contains abundant sodium rich glass trace element fractionation patterns suggest that these glassy al rich chondrules could have been derived from the other two by extensive alteration of plagioclase to nepheline followed by remelting the bulk compositions of al rich chondrules except sodium rich ones are intermediate in a volatility sense between ferromagnesian chondrules and type c cais the combined trend of bulk compositions for cais al rich chondrules and ferromagnesian chondrules mirrors but does not exactly match the trend predicted from equilibrium condensation at pt 10 3 atm the observed trend does not match the trend found for evaporation from a liquid of chondritic composition we thus infer that the bulk compositions of the precursors to cais al rich chondrules were ferromagnesian chondrules were controlled primarily by vapor solid reactions condensation or sublimation in the solar nebula some al rich chondrules are consistent with an origin by melting of a compound cai ferromagnesian chondrule hybrid others cannot be so explained any hybrid model is restricted by the constraint that the cai precursor consisted dominantly of pyroxene plagioclase spinel melilite cannot have been a significant component amoeboid olivine aggregates also have the inferred mineralogical characteristics of al rich chondrule precursors they are mixtures of olivine with plagioclase spinel pyroxene rich cais but the few measured bulk compositions are more olivine rich than those of al rich chondrules