a new calcium aluminate from a refractory inclusion in the leoville carbonaceous chondrite abstract the first meteoritic occurrence of caal4o7 is described from a ca al rich inclusion cai in the leoville carbonaceous chondrite this cai consists mainly of gehlenitic melilite spinel perovskite and hibonite caal4o7 is a minor component and occurs within melilite preferentially in portions rich in perovskite the cai is enveloped by a succession of three rims from inside out a hibonite melilite spinel perovskite b diopside and c olivine on the basis of mineral associations found and from the presence of moderately volatile elements fe and cr we conclude that the caal4o7 bearing cai from leoville is of residual nature caal4o7 is apparently stable in the very mg and si poor environment of this cai and is probably of igneous origin the rims are interpreted as products of partial evaporation rim a and associated re condensation rims b and c

the color of meteoritic hibonite an indicator of oxygen fugacity hibonites similar in composition to those found in ca al rich inclusions change color from blue to green to orange to nearly colorless as oxygen fugacity is increased at high temperature from below the iron wustite buffer up to air the development of the blue color is correlated with the growth of an absorption band at 715 nm in the optical spectra of the hibonites as the oxygen fugacity is reduced the growth of this band is attributed to the increasing concentration of ti 3 in these hibonites with decreasing oxygen fugacity the blue hibonites in meteorites reflect equilibration under reducing conditions we estimate based on the intensity of the 715 nm band that the hibonite in the blue angel inclusion indicates an oxygen fugacity 4 5 orders of magnitude more oxidizing than that expected in the early solar nebula this may be due to formation in an anomalously oxidizing region of the nebula or to oxidation during cooling or later alteration the orange hibonites in allende reflect oxygen fugacities approximately ten or more orders of magnitude more oxidizing than the expected primitive nebula this color probably indicates alteration of initially more reduced blue hibonites the colorless hibonite in the hal inclusion reflects highly oxidizing conditions and or its low ti content

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

refractory inclusions in the murchison meteorite mineralogical and petrographic studies of a wide variety of refractory objects from the murchison c2 chondrite have revealed for the first time melilite rich and feldspathoid bearing inclusions in this meteorite but none of these is identical to any inclusion yet found in allende blue spinel hibonite spherules have textures indicating that they were once molten and thus their sio2 poor bulk composition requires that they were exposed to higher temperatures 1550 c than those deduced so far from any allende inclusion melilite rich inclusions are similar to allende compact type a s but are more al ti rich one inclusion much 1 consists of a delicate radial aggregate of hibonite crystals surrounded by alteration products and probably originated by direct condensation of hibonite from the solar nebular vapor the sinuous nodular and layered structures of another group of inclusions spinel pyroxene aggregates suggest that these also originated by direct condensation from the solar nebular gas each type of inclusion is characterized by a different suite of alteration products and or rim layers from all the other types indicating modification of the inclusions in a wide range of different physico chemical environments after their primary crystallization all of these inclusions contain some iron free rim phases these could not have formed by reaction of the inclusions with fluids in the murchison parent body because the latter would presumably have been very rich in oxidized iron other rim phases and alteration products could have formed at relatively low temperatures in the parent body but some inclusions were not in the locations in which they were discovered when this took place some of these inclusions are too fragile to have been transported from one region to another in the parent body indicating that low temperature alteration of these may have occurred in the solar nebula

trace element abundances and magnesium calcium and titanium isotopic compositions of grossite containing inclusions from the carbonaceous chondrite acfer 182 the carbonaceous chondrite acfer 182 contains ca al rich inclusions cais that differ from most cais in other meteorites many of them contain grossite caal4o7 whose modal abundance exceeds 30 vol in most of these cais grossite rich inclusions similar inclusions have been found only in the ch chondrite alh85085 and the cr chondrite acfer 059 el djouf 001 ion microprobe analyses of trace elements were made on nineteen cais from acfer 182 and two cais from acfer 059 el djouf 001 of al mg isotopes on eighteen acfer 182 and the two acfer 059 el djouf 001 inclusions and of calcium isotopes on ten acfer 182 inclusions on six of them also of titanium isotopes and one acfer 059 el djouf 001 inclusion trace element and isotopic signatures of grossite containing inclusions from acfer 182 resemble those of some inclusions from alh85085 volatility fractionated trace element abundance patterns ranging from ultrarefractory depleted similar to group ii pattern to volatile enhanced are predominant 17 cais including both inclusions from acfer 059 el djouf 001 two inclusions have ultrarefractory patterns one has a group iii pattern and one inclusion has a group iii related pattern similar to patterns found in hal type inclusions only one cai from acfer 182 but both inclusions from acfer 059 el djouf 001 have nonlinear excesses of 26mg corresponding to the initial 26al27al ratio of 5 10 5 none of the twenty inclusions has a significant intrinsic isotopic mass fractionation of mg titanium is normal in all analyzed cais and only small 48ca excesses 4 3 and 3 8 are present in two inclusions isotopes of both ca and ti show no significant intrinsic mass fractionations grossite containing inclusions from acfer 182 occur in different petrographic contexts in many cases petrographic characteristics are correlated with trace element abundances almost all inclusions studied in this work have a condensation history but no evidence for extensive evaporation processes is present many of the cais must have formed by direct gas solid condensation while some inclusions with clearly identifiable igneous textures formed from a refractory melt grossite whose formation was the subject of controversy in the past probably condensed from a reservoir with a higher than chondritic ca al ratio and depleted in the highly refractory trace elements or crystallized from a ca al rich melt the two ultrarefractory inclusions from acfer 182 have extremely high refractory trace element abundances sometimes exceeding 105 ci the lack of isotopic fractionation indicates a formation at very high temperatures by condensation rather than evaporation the lack of 26mg excesses in almost all inclusions from acfer 182 is best explained by heterogeneous distribution of 26al in the primitive solar nebula grossite rich inclusions having volatility fractionated ultrarefractory depleted trace element abundance patterns and lacking 26mg excesses could be the complement of platy hibonites placs from murchison with group iii or ultrarefractory patterns and likewise no 26mg excesses

fassaites in compact type a ca al rich inclusions in the ningqiang carbonaceous chondrite evidence for partial melting in the nebula fassaite is a major component of ca al rich inclusions cais of types b and c that crystallized from liquids in contrast this mineral is rarely reported in type a inclusions and has been much less studied in this paper we report highly ti al enriched fassaite that occurs as rims on perovskite in two compact type a inclusions from the ningqiang meteorite in addition one of the inclusions contains an euhedral grain of sc fassaite 16 4 wt sc2o3 isolated in melilite the occurrence and mineral chemistry of the fassaite rims can be explained by a reaction of pre existing perovskite with cai melts hence such rims may serve as an indicator for partial melting of type a inclusions the sc fassaite is probably a relict grain a third spherical cai contains several euhedral grains of v fassaite 4 8 5 4 wt v2o3 enclosed in a melilite fragment the high v content of fassaite cannot be related to any fremdlinge magnetite or metallic fe ni because these phases are absent in the inclusion in the same cai other fassaites intergrow with spinel and minor perovskite filling voids inside of the melilite and space adjacent to the wark lovering rim the fassaite intergrown with spinel is almost v free the coexistence of two types of fassaite suggests that this cai has not been completely melted

distribution and isotopic composition of sulfur in lake sediments of northern ontario sediments from unpolluted and highly polluted lakes in northern ontario have been fractionated into acid volatile sulfide hcl soluble sulfur elemental sulfur pyrite sulfur ester sulfate and carbon bonded sulfur and the isotopic composition of each fraction determined in general reduced inorganic s constitutes 25 50 of the total s in the polluted surficial sediments but is 20 in the unpolluted samples with pyrite formation being a minor process of s diagenesis in lake sediment ecosystems organic s in the form of ester sulfate and carbon bonded s predominates and both the c s ratios and the isotopic data suggest that in unpolluted lakes plant detritus can be a major contributor of organic s to the sediments the depth profiles observed suggest that the more labile ester sulfate is diagenetically converted to the carbon bonded form for the polluted sediments from the sudbury basin the isotopic data suggest that a the elemental s is derived from the oxidation of acid volatile sulfide in the aerobic surficial sediments and b the isotopically light reduced s species are incorporated into the organic material s diagenesis in lake sediments generally results in the release of 34s to the overlying water the suggestion is made that sulfate concentrations over 5 mg 1 accompanied by an enrichment of surficial sediments with isotopically different s may signal significant inputs of pollutant s into the lake and its basin

actinide chemistry in allende ca al rich inclusions the microscale distribution of u and th has been studied by fission track radiography in a set of ca al rich inclusions from the allende meteorite in the type b inclusions generally believed to have been melted the major phases melilite and fassaite are important actinide host phases with similar th u and roughly three times higher concentrations in melilite than fassaite significant enrichments are also found on grain boundaries and in some regions of alteration the distribution is not completely understood in terms of igneous partitioning and may also reflect incomplete assimilation of relict materials during melting on the rims of type b inclusions and throughout all other inclusions studied perovskite is the dominant actinide host phase however perovskite does not have a characteristic th u value measured ratios range from 1 4 to 12 both above and below the accepted solar system value of 3 8 overall neither alteration nor loss or gain of an actinide rich phase appears to have been an important th u fractionation mechanism volatility differences may be the dominant factor some results e g high th u for fluffy type a inclusions can be interpreted as resulting from incomplete incorporation of the more volatile u during a primary condensation stage but more complex interpretations are required for inclusions with low th u the th u and ree abundance patterns for the spinel plus perovskite rim suggest derivation of this rim by volatilization of interior material the time scale for this heating is required to be brief 10 4 sec but within this constraint spinel perovskite rim formation by several mechanisms deceleration heating passage through nebular hot spots differential sublimation or vaporization plus recondensation is possible

compound ultrarefractory cai bearing inclusions from cv3 carbonaceous chondrites two compound calcium aluminum rich inclusions cais 3n from the oxidized cv chondrite northwest africa nwa 3118 and 33e from the reduced cv chondrite efremovka contain ultrarefractory ur inclusions 3n is a forsterite bearing type b fob cai that encloses ur inclusion 3n 24 composed of zr sc y rich oxides y rich perovskite and zr sc rich al ti diopside 33e contains a fluffy type a fta cai and ur cai 33e 1 surrounded by wark lovering rim layers of spinel al diopside and forsterite and a common forsterite rich accretionary rim 33e 1 is composed of zr sc y rich oxides y rich perovskite zr sc y rich pyroxenes al ti diopside sc rich pyroxene and gehlenite 3n 24 s ur oxides and zr sc rich al ti diopsides are 16 o poor d 17 o approximately 2 to 5 spinel in 3n 24 and spinel and al diopside in the fob cai are 16 o rich d 17 o approximately 23 2 33e 1 s ur oxides and zr sc rich al ti diopsides are 16 o depleted d 17 o approximately 2 to 5 vs al ti diopside of the fta cai and spinel d 17 o approximately 23 2 and wark lovering rim al ti diopside d 17 o approximately 7 to 19 we infer that the inclusions experienced multistage formation in nebular regions with different oxygen isotope compositions 3n 24 and 33e 1 s precursors formed by evaporation condensation above 1600 c 3n and 33e s precursors formed by condensation and melting 3n only at significantly lower temperatures 3n 24 and 3n s precursors aggregated into a compound object and experienced partial melting and thermal annealing 33e 1 and 33e avoided melting prior to and after aggregation they acquired wark lovering and common forsterite rich accretionary rims probably by condensation followed by thermal annealing we suggest 3n 24 and 33e 1 originated in a 16 o rich gaseous reservoir and subsequently experienced isotope exchange in a 16 o poor gaseous reservoir mechanism and timing of oxygen isotope exchange remain unclear

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

formation of orange hibonite as inferred from some allende inclusions we studied three fluffy type a refractory inclusions from allende that contain orange hibonite the melilite in the present samples is very al rich averaging ak6 ak14 and ak12 in the three samples studied hibonite in two inclusions unlike that in murchison has low rare earth element abundances of 10 ci in the other inclusion the hibonite melilite and perovskite have group ii like patterns the hibonite and melilite in all three inclusions studied have excess 26mg consistent with 26al 27al i 5 10 5 much of the hibonite and some of the spinel in these inclusions is corroded these phases are found enclosed in melilite but based on bulk compositions and phase equilibria hibonite should not be an early crystallizing phase in these inclusions we conclude that the hibonite and probably some of the spinel is relic reversely zoned melilite rounded spinel and isotopically heavy mg in the inclusions probably reflect reheating events that involved melting and evaporation alteration of the gehlenitic melilite gave rise to some rare phases including corundum and nearly pure cats pyroxene studies have shown that blue hibonite contains ti3 while orange hibonite does not ihinger and stolper 1986 beckett et al 1988 orange hibonite formed either under oxidizing conditions such as at oxygen fugacities at least seven orders of magnitude greater than that of a solar gas at 1700 k or under conditions reducing enough e g solar that it contained ti3 which was later oxidized in situ although v and ce oxides are volatile at the temperature and range of oxygen fugacities at which orange hibonite is known to be stable we find that a the hibonite is v rich 1 wt v2o3 and b there are no negative ce anomalies in allende hibonite this indicates that the hibonite did not form by condensation under oxidizing conditions in addition there are slight excesses of ti si cations relative to mg fe cations up to 0 1 of 0 8 cations per 19 oxygen anions probably reflecting the original presence of ti3 the results of this study strongly support the suggestion ihinger and stolper 1986 that allende hibonite originally formed under reducing conditions and was later oxidized oxygen fugacities within 2 3 orders of magnitude of that of a solar gas are implied otherwise strong ce and v depletions would be observed

chronological study of oxygen isotope composition for the solar protoplanetary disk recorded in a fluffy type a cai from vigarano abstract fluffy type a ca al rich inclusions cais containing reversely zoned melilite crystals are suggested to be aggregates of direct condensates from solar nebular gas we conducted an investigation of 26 al 26 mg systematics of a fluffy type a cai from vigarano named v2 01 with known oxygen isotopic distributions of reversely zoned melilite crystals we also conducted oxygen isotope measurements of coexisting minerals two of six reversely zoned melilite crystals show continuous variations in magnesium isotopic composition with 25 mg decreasing along the inferred direction of crystal growth which supports the idea that they originated through condensation petrography suggests that the constituent minerals of v2 01 formed in the following order first spinel and fassaite enclosed by melilite then reversely zoned melilite crystals and spinel and diopside in the wark lovering rim the spinel enclosed by melilite has 16 o rich compositions 17 o 24 and on an al mg evolutionary diagram plots along model isochron with an initial value of 26 al 27 al 0 5 6 0 2 10 5 the fassaite enclosed by melilite crystals shows variable oxygen isotopic compositions 17 o 12 and 17 and plots on an isochron with 26 al 27 al 0 5 6 0 2 10 5 the oxygen isotopic compositions of reversely zoned melilite showed continuous variations in 17 o along the inferred direction of crystal growth suggesting that surrounding nebular gas during the formation of the reversely zoned melilite changed from 16 o poor 17 o values larger than 10 to 16 o rich 17 o 25 the six reversely zoned melilite crystals show indistinguishable initial 26 al 27 al values with an average 26 al 27 al 0 of 4 7 0 3 10 5 which is clearly distinguishable from the value of enclosed spinel and fassaite indicating a younger formation age than the enclosed spinel and fassaite the spinel and diopside from the wark lovering rim show 16 o rich compositions 17 o 23 with 26 al 27 al 0 4 5 0 4 10 5 the values of 26 al 27 al 0 are consistent with the formation sequence inferred from petrography the formation period for the v2 01 cai is estimated to be 0 18 0 07 myr from the difference in initial 26 al 27 al values these data suggest that the oxygen isotopic composition of solar nebular gas surrounding the cai changed from 16 o rich to 16 o poor and back to 16 o rich during the first 0 2 myr of solar system formation

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

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

bulk mg isotopic compositions of ca al rich inclusions and amoeboid olivine aggregates high precision mg isotopic compositions of ca al rich inclusions cais from both ningqiang ungrouped and allende cv3 carbonaceous chondrites and amoeboid olivine aggregations aoas from allende were analyzed by multicollector inductively coupled plasma mass spectrometry mc icp ms the cais from allende plot on a line with an inferred initial 26al 27al ratio of 4 77 0 39 10 5 close to the canonical value this indicates a relatively closed al mg system in the cais and no significant mg isotope exchange with ambient materials although two of the cais are severely altered the aoas contain excess 26mg and plot close to the cai regression line which is suggestive of their contemporary formation the cais from ningqiang define a different line with a lower inferred 26al 27al 0 ratio of 3 56 0 08 10 5 none of the cais and aoas studied in this work shows significant mass fractionation with enrichment of the heavier mg isotopes arguing against an evaporation origin

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

evidence for successive episodes of condensation at high temperature in a part of the solar nebula abstract a centimeter sized ca al rich inclusion cai 3643 in the allende meteorite has preserved a record of its multiple stages of growth by condensation at high temperature it consists of three distinct concentric layers core mantle and crust the open textured core is composed of hibonite laths interstitial melilite and voids grains of alumina and osir metal nuggets in the inner core that are complementary in composition to rupt rich nuggets in the outer core the core formed out of rapidly aggregated crystals from two episodes of condensation in the same gaseous reservoir mo and w depletions in the nuggets indicate condensation from a relatively oxidizing gas with 60 times higher h 2 oh 2 than solar gas the compact mantle of coarse melilite contains perovskite inclusions and rare nife metal and sulfide grains the compact fine grained crust consists of melilite hibonite spinel perovskite and opaques similar to those in the mantle neither mantle nor crust has been molten each grew by condensation of solids directly onto the surface of the cai the formed cai experienced some metamorphic recrystallization of melilite and volatile alteration producing grossular feldspathoids and hercynite trace element analyses of perovskites and a bulk sample show the mantle and crust to be depleted in refractory elements i e group ii and complementary to the ultra refractory core despite differences in texture and composition the core mantle and crust display a continuity in their modal mineralogical compositions their extreme al 2 o 3 enrichments 53 69 cf 25 45 for other cai s and their trace element complementarity this implies that all the layers of 3643 formed from the same cooling gaseous reservoir within a limited interval of time and space consistent with an origin in a local transient heating event in the cv chondrite formation region of the nebula

nepheline and sodalite in the matrix of the ningqiang carbonaceous chondrite implications for formation through parent body processes abstract ningqiang is an ungrouped carbonaceous chondrite that chemically and petrologically resembles cv3 chondrites the matrix of ningqiang shows much higher abundances of na k and al by factors of 4 4 2 7 and 1 6 respectively than in cv3 chondrites our scanning and transmission electron microscope observations and synchrotron radiation x ray diffraction measurements reveal that the major proportions of these elements can be attributed to the presence of nepheline and sodalite rietveld refinement of x ray diffraction data shows that the feldspathoids constitute 7 7 vol of all crystalline phases in the matrix nepheline and sodalite occur mostly as discrete equidimensional grains 2 5 m in diameter that are dispersed homogeneously in the matrix most of the grains contain inclusions of fe rich olivine and minor ca pyroxene magnetite troilite and pentlandite despite the high abundances of na k and al in the matrix of ningqiang the bulk meteorite abundances of these elements are comparable to those of the cv group e g rubin et al 1988 this means that the chondrules which constitute a major proportion of the volume other than the matrix in ningqiang are depleted in na k and al in fact our analyses and observations show that the chondrules in ningqiang overall contain very small amounts of these elements our interpretation of these findings suggests that nepheline and sodalite in the ningqiang matrix were originally formed by na metasomatism of the chondrules and ca al rich inclusions in the meteorite parent body afterward they were likely disaggregated and scattered into the matrix however it is difficult to envisage that the disaggregation and scattering occurred in situ in the present setting of the meteorite hence we suggest that the ningqiang meteorite underwent these processes before final lithification

u th pb systematics of individual perovskite grains from the allende and murchison carbonaceous chondrites ion microprobe u th pb isotopic measurements have been made of individual perovskite grains from the allende cv3 and murchison cm2 chondrites these are the first chronological data reported for murchison refractory inclusions several generations of perovskite were identified in polished thin sections of fluffy type a inclusions 3529 44 and 4691 from allende of which only the largest anhedral perovskites 20 m were analysed with the ion microprobe the allende perovskites are characterised by low u typically 3 ppm but ranging up to 12 ppm in grain 7 1 from 3529 44 and th u of around 4 in 3529 44 and 10 in 4691 the204pb concentrations in the allende perovskites range from 6 to 140 ppb a precise age measurement could be obtained on grain 7 1 only the u pb systematics of this grain are concordant with a207pb 206pb age of 4565 34 2 ma two of the murchison perovskites occurred as individual 20 m inclusions in spinel grains 7 309 7 a52 while the third perovskite bearing inclusion was a spherule dominated by perovskite with interstitial spinel 7 396 u concentrations range from 3 6 to 15 ppm with th u less than 0 5 and204pb concentrations ranging from 61 to 369 ppb all analyses of the murchison perovskites are consistent with a single formation age of 4569 26ma the ages determined by ion microprobe from these perovskites show good agreement with previous age estimates of allende refractory inclusions measured by conventional mass spectrometric techniques there is no evidence in the u pb systematics of allende and murchison refractory inclusions for material that substantially predates the formation of the solar system

oxygen isotopes of chondritic components we review the oxygen isotopic compositions of chondrite components refractory inclusions chondrules and matrix and their inter and intra crystalline oxygen isotopic distributions primary oxygen isotopic compositions acquired before planetesimal accretion are easily disturbed by parent body processes such as aqueous alternation and thermal metamorphism primary or original oxygen isotopic compositions of refractory inclusions ca al rich inclusions and amoeboid olivine aggregates distribute along a slope 1 line on the three oxygen isotope diagram over the range of 60 17 o 18 o 16 o rich and 17 o 18 o rich during refractory inclusion formation on the other hand primary minerals of most chondrules have small isotopic variations and are enriched in 17 o and 18 o relative to refractory inclusions suggesting that chondrule formation occurred in 17 o 18 o rich nebular gas however rare 16 o rich chondrules have been found suggesting some overlap in the timing of formation of chondrules and refractory inclusions in the solar nebula oxygen isotopic compositions of matrix grains distribute along the slope 1 line over the same range as refractory inclusions and chondrules the similarity in oxygen isotopic distributions suggests that matrix was originally a mechanical mixture of nebular dusts co generated with chondrules and refractory inclusions presolar grains with oxygen isotopic compositions that are clearly distinct from those of solar nebular materials are a trace component of chondrite matrices based on these oxygen isotopic characteristics more than 99 5 of the solid materials in the nebula formed locally in the solar nebula and the remainder formed in interstellar space the astrophysical setting of chondrite component formation in the early solar system is also discussed refractory inclusions and 16 o rich matrix dusts formed around the inner edge of the solar nebula on the other hand most chondrules and 17 o 18 o rich matrix dusts seem to have formed elsewhere in the solar nebula efficient large scale radial mixing of the solar nebular materials may have been an essential process in the formation of chondritic planetesimals

refractory inclusions in the pristine carbonaceous chondrites dom 08004 and dom 08006 the antarctic carbonaceous chondrites dom 08004 and dom 08006 have been paired and classified as co3 0s there is some uncertainty as to whether they should be paired and whether they are best classified as co chondrites but they provide an opportunity for the study of refractory inclusions that have not been modified by parent body processes in this work refractory inclusions in thin sections of dom 08004 and 08006 are studied and compared with inclusions in alha77307 co3 0 and acfer 094 c3 0 ungrouped results show that the dom samples have refractory inclusion populations that are similar to each other but not typical of co3 chondrites main differences are that the dom samples are slightly richer in inclusions in general and more specifically in the proportions of grossite bearing inclusions in dom 08004 and dom 08006 12 4 and 6 6 respectively of the inclusions are grossite bearing this is higher than the proportion found in acfer 094 5 2 whereas none were found in alha77307 like those in acfer 094 dom inclusions are small mostly 100 m across and fine grained and thin rims of aluminous diopside melilite are very common also like acfer 094 most phases in the dom inclusions have feo contents higher than expected for primary refractory phases in addition to typical inclusions some unusual ones were found in dom 08004 including a perovskite rich one with a rare recently reported sc al oxide and davisite a very grossite rich inclusion with a small hibonite rich core enclosed in a grossite mantle and a relict grossite rich inclusion enclosed in an al rich chondrule the cai populations in the dom samples are similar to each other and based on grossite abundances feo enrichments and occurrences of rims are more acfer 094 like than co3 like an earlier history on an feo rich parent was previously favored over nebular equilibria or in situ reactions to account for feo enrichments in cais in the otherwise pristine chondrite acfer 094 and a similar history is indicated for the dom cais acfer 094 dom 08004 and 08006 might best be classified as a new subgroup of co3 chondrites

anorthite spinel rich inclusions in the ningqiang carbonaceous chondrite genetic links with type a and c inclusions many ca al rich inclusions cais were molten once and the question of what their precursors consisted of is controversial in this paper we report a new type of anorthite spinel rich inclusion asi in the ningqiang carbonaceous chondrite the modal and bulk compositions of the asis are similar to those of type c inclusions but with nonmolten textures the asis are proposed to be the precursors of type c inclusions the asis show alteration textures with melilite being replaced by anorthite and ca pyroxene furthermore compositions of the melilites and the calculated modal and bulk compositions of the possible precursors of the asis are close to those of the spinel rich type a inclusions in the ningqiang meteorite which suggests that asis formed by alteration of the latter in the solar nebula petrography and mineral chemistry of one type c inclusion in ningqiang are also reported

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

petrographic studies of refractory inclusions from the murchison meteorite textural and mineral chemical data on freeze thaw disaggregated refractory inclusions from the murchison meteorite are reported the data were obtained with neutron activation analysis sem and spectroscopy the study revealed corundum bearing inclusions spinel hibonite aggregates and spherules and spinel pyroxene and elivine pyroxene inclusions one of the three spinel pyroxene forsterite rich inclusions had an amoeba shaped spinel pyroxene core implying vapor to solid condensation and therefore crystallization from a melt it is concluded that the meteorite formation encompassed diverse nebular materials and that further studies of the meteorite will enhance the data base on the planetary nebular processes

refractory inclusions in the unique carbonaceous chondrite acfer 094 abstract acfer 094 is an unshocked nearly unaltered carbonaceous chondrite with an unusual suite of refractory inclusions the refractory inclusions in a newly prepared thin section and a small aliquot of disaggregated material were studied to compare the population with previous work and to report new or unusual inclusion types a total of 289 ca al rich inclusions in the thin section and 67 among the disaggregated material having a total of 31 different mineral assemblages were found inclusions are largely free of secondary alteration products and are typically 200 m across the most common are gehlenitic melilite spinel perovskite spinel perovskite and spinel with a thin silicate rim typically melilite diopside such rims and thicker mantles are very common among acfer 094 inclusions and they exhibit a variety of zoning patterns with respect to akermanite and feo contents in the thin section about 13 of the inclusions contain hibonite and approximately 5 are grossite bearing in the disaggregated material the percentages are 14 and 9 respectively comparable to previous work among the unusual inclusions are a fine grained porous ti rich hibonite spinel perovskite melilite inclusion with a compact coarse ti poor hibonite spinel melilite clast two inclusions in which hibonite has reacted to form grossite two inclusions with feo rich spinel and a small object consisting of fassaite enclosing euhedral spinel the first fragment of a type b inclusion reported from acfer 094 inclusions similar to those found in cm or cv chondrites are rare acfer 094 contains a distinctive population of inclusions the population dominated by small melilite bearing inclusions is most similar to that of co chondrites a distinguishing feature is that in acfer 094 almost every phase in almost every refractory inclusion contains 0 5 1 5 wt feo a lack of diffusion gradients and the pristinity of the matrix imply that the inclusions experienced prolonged exposure to feo bearing fluid prior to accretion into the acfer 094 parent body there are no known nebular conditions under which the refractory phases found in the present samples could acquire feo enrichments to the observed levels the most likely setting is therefore in an earlier feo rich parent body the inclusions were ejected from this parent body mixed with typical cais chondrules amoeboid olivine aggregates and amorphous material and incorporated into the acfer 094 parent body

unusually abundant refractory inclusions from sahara 97159 eh3 a comparative study with other groups of chondrites abstract sixty eight refractory inclusions and fragments were found in two polished thin sections of the sahara 97159 eh3 chondrite indicative of the highest abundance of refractory inclusions 22 cm 2 or 0 06 vol in enstatite chondrites studied to date all of the inclusions are intensely altered mainly producing feldspathoids and albite cao depletion and minor ti rich compounds such as ti sulfides the alteration assemblages and feo poor spinel suggest that the reactions took place under reducing and sio 2 rich conditions this is consistent with the redox state of the host enstatite chondrite the presence of ti sulfides and low feo alteration phases distinguishes alteration of e chondrite refractory inclusions from that of carbonaceous and ordinary chondrites most of the inclusions are referred to as type a like 35 and spinel rich 26 respectively assuming melilite has been altered these inclusions could be analogues of individual concentrically zoned objects of fluffy melilite spinel rich type a and spinel pyroxene rich inclusions from carbonaceous chondrites such as the ningqiang cv anomalous and y 81020 co3 chondrites two inclusions consist mainly of ca pyroxene fine grained alteration products feldspathoids and albite and spinel they are probably altered fragments of ca pyroxene plagioclase rich type c inclusions assuming all plagioclase has been altered to produce the fine grained groundmass five other inclusions are hibonite and or corundum bearing similar to those reported in carbonaceous chondrites abundance ratios of various types of the inclusions from sahara 97159 are similar to those from ningqiang and y 81020 most of the observations including mineral assemblages mineral chemistry texture bulk compositions o isotopic compositions and ree patterns of the sahara inclusions suggest a common reservoir of refractory inclusions in enstatite ordinary and carbonaceous chondrites the apparent differences such as absence of melilite and anorthite rare wark lovering rim and small size can be explained by intense alteration due to large change of postformation environment of these inclusions size sorting and collision during transfer hence these differences are not inconsistent with the common reservoir model refractory inclusions in non carbonaceous chondrites may put additional constraints on origins of refractory inclusions and provide hints for a spatial relationship of their host meteorites

chemical compositions of refractory inclusions in the murchison c2 chondrite abstract samples from ten refractory inclusions in murchison some of which are splits of inclusions whose mineralogical and petrographic characteristics are known have been analysed for thirty six elements by neutron activation six inclusions have group ii or group iii patterns or variants of such patterns two inclusions bb 5 and much 1 have large negative yb anomalies unaccompanied by correspondingly large negative eu anomalies it is possible that the latter condensed originally with group iii patterns and preferentially took up eu in later exchange processes under reducing conditions one inclusion sh 2 has heavy ree enrichment factors that increase with the refractoriness of the ree indicating the presence of an extremely high temperature or ultrarefractory ree condensate but it also has a heavy ree light ree ratio that indicates mixing of that component with a lower temperature ree condensate the frequency of highly fractionated ree patterns and absence of group i patterns suggest that refractory inclusions in murchison stopped equilibrating with the nebular gas at higher temperatures than most allende coarse grained inclusions the lower ir os and ru re ratios of some murchison inclusions compared to those of allende coarse grained inclusions indicate that condensate alloys that contributed noble metals to the former also stopped equilibrating with the nebular gas at higher temperatures than those that contributed noble metals to the latter murchison inclusions tend to be lower in non refractory elements than allende coarse grained inclusions suggesting that on average the former underwent less severe secondary alteration than the latter

oxygen isotopic and chemical zoning of melilite crystals in a type a ca al rich inclusion of efremovka cv3 chondrite abstract different oxygen isotopic reservoirs have been recognized in the early solar system fluffy type a ca al rich inclusions cais are believed to be direct condensates from a solar nebular gas and therefore have acquired oxygen from the solar nebula oxygen isotopic and chemical compositions of melilite crystals in a type a cai from efremovka cv3 chondrite were measured to reveal the temporal variation in oxygen isotopic composition of surrounding nebular gas during cai formation the cai is constructed of two domains each of which has a core mantle structure reversely zoned melilite crystals were observed in both domains melilite crystals in one domain have a homogeneous 16o poor composition on the carbonaceous chondrite anhydrous mineral ccam line of 18o 5 10 which suggests that the domain was formed in a 16o poor oxygen isotope reservoir of the solar nebula in contrast melilite crystals in the other domain have continuous variations in oxygen isotopic composition from 16o rich 18o 40 to 16o poor 18o 0 along the ccam line the oxygen isotopic composition tends to be more 16o rich toward the domain rim which suggests that the domain was formed in a variable oxygen isotope reservoir of the solar nebula each domain of the type a cai has grown in distinct oxygen isotope reservoir of the solar nebula after the domain formation domains were accumulated together in the solar nebula to form a type a cai

recipes for making synthetic cais refractory residues and minerals for rim forming experiments recipes are presented for synthesizing various type a and type b ca al rich inclusions cais refractory volatilization residues and the minerals forsterite and melilite that are required for experiments these experiments described in other works aim to make two determinations 1 the conditions under which the surfaces of cais were either flash heated or volatilized subsolidus to form a temporary ultra refractory residue and 2 the conditions under which the residue was then metasomatized to form the mineral layers making up wark lovering wl rims on cais

the occurrence of grossite caal4o7 in chondrites the mineral grossite caal4o7 ca dialuminate also termed ca2 is a rare phase in terrestrial and extraterrestrial rocks in meteorites grossite was found in ca al rich inclusions cais from allende cv3 vigarano cv3 leoville cv3 efremovka cv3 colony co3 murchison cm2 alh 85085 ch acfer 182 ch acfer 059 e1 djouf 001 cr2 and the anomalous c chondrite adelaide in ca al rich inclusions from most of these meteorites grossite is an accessory phase however in many cais from alh 85085 acfer 182 and acfer 059 e1 djouf 001 it is a major phase in this paper we summarize the results of literature reports on grossite bearing inclusions and focus in detail on the occurrence mineralogy and chemistry of caal4o7 containing ca al rich inclusions in acfer 182 and acfer 059 e1 djouf 001 in these carbonaceous chondrites abundant cais with high modal abundances of grossite 30 vol often 60 vol were discovered to classify ca al rich inclusions with such high modal abundances of caal4o7 we suggest to introduce a new type of ca al rich inclusion grossite rich inclusions in acfer 059 e1 djouf 001 and acfer 182 grossite containing inclusions occur with different petrographic characteristics the most common type consists of a core of grossite rimmed by melilite ca pyroxene spinel hibonite in an other type anhedral polycrystalline grossite complexes of irregular shape are enclosed in melilite in some spherical ca2 inclusions abundant euhedral to subhedral grossite and or hibonite crystals are embedded in melilite in two inclusions a core of hibonite is mantled by grossite additionally some grossite bearing inclusions with unique texture and or mineralogy were found one of these inclusions is rich in zr y rich perovskite and contains phases rich in the ultrarefractory elements sc and or zr almost all of the grossite containing inclusions are rich in al2o3 50 wt even if grossite is only a minor phase based on textural appearance and or on ree contents in some inclusions core minerals with group ii patterns a condensation history for most inclusions is suggested a single inclusion rich in perovskite and other phases containing high concentrations of ultrarefractory elements appears to have formed as an early condensate from the solar nebula

high time resolution by use of the 26al chronometer in the multistage formation of a cai the allende calcium rich inclusion cai 5241 has been found to contain distinct initial 26 al 27 al in the three consecutive igneous zones that have been identified by extensive petrogenetic studies to have formed in three distinct crystallization events the zones in order of sequence of formation from the petrologic observations are 1 spinel free islands sfi included in 2 a pyroxene spinel rich core src which in turn is included in 3 a melilite mantle mm the initial 26 al 27 al values of these zones are respectively 4 6 5 0 10 5 4 3 10 5 and 3 3 10 5 it is argued that these distinct 26 al 27 al 0 values are not the result of metamorphism but reflect the relative times of formation by crystallization from melts relative to the canonical value of 26 al 27 al 0 5 10 5 we find the following chronology t sfi 0 t src 10 5 yr and t mm 4 10 5 yr the three layer cai is inferred to have sampled a reservoir with an initial uniform 26 al 27 al ratio that decreased in value due to radioactive decay from these observations we conclude that we have resolved time differences of a few hundred thousand years at the very early stages of formation of the solar system the sfi src and mm zones reflect sequential addition of molten cai material which crystallized rapidly without seriously metamorphosing the previously formed material these additions took place over a time of about 400 000 years we believe that these sequential events are not compatible with condensation in a hot region of the solar nebula it is proposed that a scenario involving stages of protoplanetary accretion and of melt generation in protoplanetary sites heated by 26 al might provide a possible source for cais and chondrules

an oxygen isotope study of wark lovering rims on type a cais in primitive carbonaceous chondrites calcium aluminium rich inclusions cais and the thin wark lovering wl rims of minerals surrounding them offer a record of the nature of changing conditions during the earliest stages of solar system formation considerable heterogeneity in the gas composition in the immediate vicinity of the proto sun had previously been inferred from oxygen isotopic variations in the wl rim of a cai from allende simon et al 2011 however high precision and high spatial resolution oxygen isotope measurements presented in this study show that wl rim and pristine core minerals of individual cais from meteorites that had experienced only low degrees of alteration or low grade metamorphism one from leoville reduced cv3 two in que 99177 cr3 0 and two in alha 77307 co3 0 are uniformly 16o rich this indicates that the previously observed variations are the result of secondary processes most likely on the asteroid parent body and that there were no temporal or spatial variations in oxygen isotopic composition during cai and wl rim formation such homogeneity across three groups of carbonaceous chondrites lends further support for a common origin for the cais in all chondrites 16o poor oxygen reservoirs such as those associated with chondrule formation were probably generated by uv photo dissociation involving self shielding mechanisms and must have occurred elsewhere in outer regions of the solar accretion disk

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

extinct 10be in type a calcium aluminum rich inclusions from cv chondrites we have found clear evidence of live 10be in five normal type a calcium aluminum rich inclusions cais one normal type b cai and one fun type a cai all from cv3 chondrites the 10be 9be 0 ratios range from 0 36 10 3 to 0 77 10 3 and are similar to those found by previous workers the 10be 9be 0 ratios do not correlate in a temporal fashion with 26al 27al 0 suggesting that 10be and 26al were produced by different mechanisms an examination of possible sources for the short lived radionuclides indicates that production of 10be was almost certainly by particle irradiation possibly within the solar system and was probably accompanied by significant production of 41ca and 53mn in contrast all of the 60fe most of the 26al and some of the 53mn were probably produced in stars and were imported into the solar system within presolar dust grains

the interstellar dust as a precursor of ca al rich inclusions in carbonaceous chondrites abstract 1 the observed anomalies in meteoritic oxygen isotope compositions are not due to an incomplete mixing of several dust or gas plus dust components in the solar nebula if they were other elements would display similar anomalies the fun inclusions in allende appear to be exceptions to this premise 2 the anomalies must therefore stem from differing degrees of incomplete exchange of oxygen isotopes between the primordial gas and dust components of the nebula the dust is more likely to have been the 16 o enriched component 3 since the isotopic difference between dust and gas probably could not have been preserved if the dust was ever completely vaporized in the nebula the ca al rich inclusions cai s in carbonaceous chondrites are unlikely to be condensates but instead are distillation residues 4 if so the observed depletion of super refractory elements in the group ii cai s cannot have been accomplished by fractional condensation in the solar nebula 5 then this depletion and a number of other properties of the components of primitive meteoritic material must be relics of pre solar system fractionations among different populations of interstellar dust grains

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

physicochemical isotope anomalies isotopic composition of refractory elements can be modified by physical processes such as distillation and sputtering in unexpected patterns distillation enriches the heavy isotopes in the residue and the light isotopes in the vapor however current models appear to be inadequate to describe the detailed mass dependence in particular for large fractionations coarse and fine grained inclusions from the allende meteorite exhibit correlated isotope effects in mg both as mass dependent fractionation and residual anomalies this isotope pattern can be duplicated by high temperature distillation in the laboratory a ubiquitous property of meteoritic inclusions for mg as well as for most of the other elements where measurements exist is mass dependent fractionation in contrast terrestrial materials such as microtektites tektite buttons as well as lunar orange and green glass spheres have normal mg isotopic composition a subset of interplanetary dust particles labelled as chondritic aggregates exhibit excesses in sup 26 mg and deuterium anomalies sputtering is expected to be a dominant mechanism in the destruction of grains within interstellar dust clouds an active proto sun as well as the present solar wind and solar flare flux are of sufficient intensity to sputter significant amounts of material laboratory experiments in mg show widespread isotope effects including residual supmore 26 mg excesses and mass dependent fractionation it is possible that the sup 26 mg excesses in interplanetary dust is related to sputtering by energetic solar wind particles the implication if the laboratory distillation and sputtering effects are discussed and contrasted with the anomalies in meteoritic inclusions the other extraterrestrial materials the authors have access to less

fluffy type a ca al rich inclusions in the allende meteorite abstract allende fluffy type a s fta s are a distinct sub group of ca al rich inclusions whose primary mineral assemblage consists of al rich melilite ak 0 33 spinel that is commonly very v rich perovskite and frequently hibonite some contain relatively coarse grained melilite up to 1 5 mm that is intensely kink banded and commonly reversely zoned hibonite and v rich spinel others contain much finer grained and strain free melilite 50 m and have not been found to contain hibonite or v rich spinel some fta s contain both coarser and finer grained melilite and textural relationships indicate that the latter is replacing the former fta s are characterized by extremely irregular shapes and 60 75 volume per cent of fine grained secondary alteration products many are aggregates of innumerable nodules each of which is surrounded by a wark lovering type rim sequence these nodules are frequently separated from one another by matrix like clastic rim material other fta s do not have nodular structure structural and mineralogical characteristics of their wark lovering rims suggest that fta s did not achieve their shapes by deformation of a liquid or a hot plastic solid in contrast to those in type b inclusions formation of reverse zoning in the coarser grained melilite crystals in fta s cannot be understood in terms of crystallization from a liquid but are readily explainable by condensation from a solar nebular gas during a period of falling pressure further evidence against a liquid origin is the wide range of spinel compositions within individual coarser grained fta s the fact that the reversely zoned melilite crystals cannot have been produced in any kind of sublimation or distillation process precludes formation of these inclusions as volatilization residues fta s are aggregates in some of which are preserved vapor solid condensate grains that formed at high temperature in the solar nebula

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

53 mn 53 cr chronology of ca fe silicates in cv3 chondrites abstract high precision secondary ion mass spectrometry sims analyses of kirschsteinite cafesio4 in the reduced cv3 chondrites vigarano and efremovka yield well resolved 53cr excesses that correlate with 55mn 52cr demonstrating in situ decay of the extinct short lived radionuclide 53mn to ensure proper correction for relative sensitivities between 55mn and 52cr ions we synthesized kirschsteinite doped with mn and cr to measure the relative sensitivity factor the inferred initial ratio 53mn 55mn 0 in chondritic kirschsteinite is 3 71 0 50 10 6 when anchored to 53mn 53cr relative and u corrected 207pb 206pb absolute ages of the d orbigny angrite this ratio corresponds to kirschsteinite formation 3 2 0 7 08 ma after cv ca al rich inclusions the kirschsteinite data are consistent within error with the data for aqueously formed fayalite from the asuka 881317 cv3 chondrite as reported by doyle et al 2015 supporting the idea that ca fe silicates in cv3 chondrites are cogenetic with fayalite and magnetite and formed during metasomatic alteration on the cv3 parent body concentrically zoned crystals of kirschsteinite and hedenbergite indicate that they initially formed as near end member compositions that became more mg rich with time possibly as a result of an increase in temperature

correlated study of initial sr 87 sr 86 and al mg isotopic systematics and petrologic properties in a suite of refractory inclusions from the allende meteorite we have studied a suite of six coarse grained ca al rich inclusions cais from the allende meteorite applying in concert detailed petrographic and chemical characterization ion probe mass spectrometric analyses of the al mg isotopic system to determine the abundance and distribution of 26a1 and thermal emission mass spectrometric analyses of the rb sr system to determine initial 87sr86sr ratios the simplest inclusion is a type bl usnm 3529 z that shows evidence of minor alteration and recrystallization since solidification from a melt droplet e g some of the coarse grained anorthite in the inclusion especially near the inclusion rim apparently formed by recrystallization or melting of fine grained secondary anorthite that had replaced melilite four other type bs contain evidence of more widespread recrystallization in addition to evidence of local replacement of melilite by coarse anorthite e g melilite zoning is complex and not igneous in origin and in one inclusion usnm 3529 21 melilite and pyroxene crystals enclose relicts of an earlier generation of the same phases the sixth inclusion usnm 3898 is a type a whose properties appear to be largely metamorphic in origin all six inclusions show variations in mg isotopic compositions indicating that they incorporated 26a1 in 3529 z the relative abundance of 26a1 26al27al 4 0 0 1 10 5 is close to the canonical value 26al27al 5 10 5 for cais but both anorthite and melilite show minor departures from a strict isochron relationship between mg and al in particular the coarse anorthite near the inclusion rim has initial 26al27al ratios of 1 2 10 5 implying formation at least 1 5 million years after the first generation anorthite the other four type bs exhibit larger disturbances of the al mg system that can be understood in terms of local recrystallization and isotopic exchange primarily between anorthite and melilite only 3898 is consistent with a strict al mg isochron relationship but this cai lacks primary anorthite and the small range of al mg among the phases analyzed may preclude resolution of any small isotopic disturbances the rb sr isotopic system also typically indicates some level of disturbance some of which must have been relatively recent nevertheless phases characterized by very low rb sr permit precise identification of initial 87sr86sr our al mg and sr data are largely consistent with a simple chronological interpretation of both systems i e the 26al results suggest that all the initial 87sr86sr ratios should have the same value and with one exception our initial 87sr86sr ratios are consistent with a single value this value is somewhat higher than the primitive value all reported by gray et al 1973 however also with one exception the very low rb sr cai data reported by gray et al 1973 are consistent with the same value the exception is the same inclusion in both studies our analysis of usnm 3898 yields an initial 87sr86srhigher than that of the other cais while gray et al 1973 obtained an initial 87sr86srlower than that of the other cais for the same inclusion labeled as d7 on which all is based neither result can be readily explained as a chronological aberration since 3898 has nearly canonical 26al27al the present data are the first which establish a firm association between primitive 26al27al and primitive 87sr86sr by analysis of both isotopic systems in the same inclusions the comparison of both isotopic systems interpreted as simple nebular chronometers does not reveal any chronological inconsistencies that demand resolution in terms of a grossly heterogeneous distribution of 26al

plagioclase rich inclusions in carbonaceous chondrite meteorites liquid condensates plagioclase rich inclusions in carbonaceous chondrites are of two types 1 mm cm sized ca al rich inclusions cais with 30 60 vol anorthite and up to 35 vol each of ti al pyroxene tpx melilite and spinel and 2 smaller 3 mm ca chondrules similar to those found in ordinary chondrites containing more sodic plagioclase pyroxene olivine and spinel the cais which were formerly named type i and thought to be intermediate between type a and type b cais are shown to be an independent type renamed type c with distinctive chemical and mineralogical compositions type c cais have group i or group ii trace element patterns low initial 26al27al ratios of 5 10 6 typical ak 35 55 melilite tpx with 2 12 tio2 and opaque grains osirrumopt alloy nuggets and fremdlinge smaller than 10 m the textures sequence of crystallization and concentric zonation indicate that they crystallized from melt droplets the texture of the anorthite ranges from coarse laths to a fine grained groundmass reflecting increasing retardation of its nucleation the few cais with the coarse laths cooled slowly 2 5 h from below the liquidus but the majority cooled faster from completely molten material as the elemental abundances in type c s are dominated by volatility the melts were not formed by planetary magmatic processes evaporative residues and remelted solid condensates are also ruled out because the compositions of naturally occurring experimentally produced and thermodynamically calculated residues and solid condensates differ from those of type c cais type c cais have compositions similar to those calculated for liquid condensates under high solar gas pressure 1 atm or in dust rich environments and are probably liquid condensates the few type c cais that crystallized from incompletely molten materials may have been reheated liquid condensates or mixed liquidsolid condensates

search for extinct 36cl vigarano cais the pink angel from allende and a ningqiang chondrule abstract we have searched for excesses of 36 s derived from the decay of extinct 36 cl in sodalite a secondary cl rich mineral in ca al rich inclusions cais from the vigarano and allende cv3 chondrites and in a chondrule from the ningqiang carbonaceous chondrite the presence of sodalite in two cais from vigarano and its absence from surrounding cai fragments suggests sodalite formation after cai fragmentation as for sodalite in the allende pink angel cai oxygen isotopic compositions have been interpreted as indicative of high temperature interactions thus suggesting formation prior to accretion to the parent body probably in a nebular setting sodalite in the ningqiang chondrule is considered to have formed via alkali ca exchange which is believed to have occurred before accretion to the parent body sodalites in the vigarano cais and in the ningqiang chondrule show no clear evidence for the presence of radiogenic 36 s the inferred 2 upper limits for 36 cl 35 cl at the time of sodalite formation are 1 6 10 6 vigarano cais and 3 3 10 6 ningqiang chondrule respectively in the pink angel cai sodalite exhibits small 36 s excesses which weakly correlate with 35 cl 34 s ratios the inferred 36 cl 35 cl ratio of 1 8 2 2 10 6 2 error is lower than that found by hsu et al hsu w guan y leshin l a ushikubo t and wasserburg g j 2006 a late episode of irradiation in the early solar system evidence from extinct 36 cl and 26 al in meteorites astrophys j 640 525 529 thus indicative of heterogeneous distribution of 36 cl in this cai spallation reactions induced by energetic particles from the young sun are suggested for the origin of 36 cl similar to the case of 10 be while 10 be appears to be present in roughly equal abundance in all studied cais our study indicates the level of 36 cl abundances to be variable so that there seems to be no simple relationship between 10 be and 36 cl this would be expected if trapped cosmic rays rather than early solar system spallation were the dominant source of 10 be in the early solar system since their contribution to 36 cl would have been tiny if the variability of 36 cl abundances is caused by temporal differences in the alteration that formed sodalite sodalite in the vigarano cais and in the ningqiang chondrule may have formed 0 5 and 0 2 ma after formation of the sodalite in the ningqiang cai analyzed by lin et al lin y guan y leshin l a ouyang z and wang d 2005 short lived chlorine 36 in a ca and al rich inclusion from the ningqiang carbonaceous chondrite proc natl acad sci usa 102 1306 1311 the pink angel sodalite that we analyzed may have formed 0 3 ma after formation of the sodalite in the pink angel analyzed by hsu et al hsu w guan y leshin l a ushikubo t and wasserburg g j 2006 a late episode of irradiation in the early solar system evidence from extinct 36 cl and 26 al in meteorites astrophys j 640 525 529 the estimated temporal differences suggest that alteration extended over at least 0 5 ma if previous works showing very low initial 36 cl 35 cl in the allende cais and a h3 chondrite cai are also considered then alteration processes may have been more than 1 7 ma

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

a refractory inclusion returned by stardust from comet 81p wild 2 among the samples returned from comet 81p wild 2 by the stardust spacecraft is a suite of particles from one impact track track 25 that are ca al rich and feo free we studied three particles from this track that range in size from 5 3 x 3 2 m to 15 x 10 m scanning and transmission electron microscopy show that they consist of very fine grained typically from 0 5 to 2 m al rich ti bearing and ti free clinopyroxene mg al spinel and anorthite with trace amounts of fine perovskite feni metal and osbornite tin grains in addition to these phases the terminal particle named inti also contains melilite all of these phases with the exception of osbornite are common in refractory inclusions and are predicted to condense at high temperature from a gas of solar composition osbornite though very rare has also been found in meteoritic refractory inclusions and could have formed in a region of the nebula where carbon became enriched relative to oxygen compared to solar composition compositions of ti pyroxene in inti are similar but not identical to those of fassaite from allende inclusions electron energy loss spectroscopy shows that ti rich pyroxene in inti has ti3 ti4 within the range of typical meteoritic fassaite consistent with formation under reducing conditions comparable to those of a system of solar composition inti is 16o rich with 18o 17o 40 like unaltered phases in refractory inclusions and refractory idps with grain sizes mineralogy mineral chemistry and an oxygen isotopic composition like those of refractory inclusions we conclude that inti is a refractory inclusion that formed in the inner solar nebula identification of a particle that formed in the inner solar system among the comet samples demonstrates that there was transport of materials from the inner to the outer nebula probably either in a bipolar outflow or by turbulence

genetic relationship between na rich chondrules and ca al rich inclusions formation of na rich chondrules by melting of refractory and volatile precursors in the solar nebula abstract al rich objects ca al rich inclusions cais al rich chondrules al rich fragments occur in all chondrite classes these objects can be centimeter sized in cv3 carbonaceous chondrites but they are generally much smaller in other chondrite groups and classes within the ordinary chondrites most al rich objects are chondrules that vary from ca to na rich here we have investigated the mineralogy and major element chemistry of 32 na rich chondrules and 3 na rich fragments from 15 different chondrites most objects chondrules and chondrule fragments are from ordinary chondrites petrologic types 3 2 3 8 but two of the chondrules are from two co3 chondrites and three of the chondrules are from one rumuruti r chondrite we found that these na rich objects have bulk na 2 o concentrations between 4 3 and 15 2 wt texturally they typically consist of euhedral to subhedral often skeletal mafic minerals olivine and pyroxenes embedded within a nepheline normative glassy mesostasis which is brownish in transmitted light in addition some chondrules contain euhedral to subhedral spinel bulk chondrule compositions show group ii group iii and ultrarefractory rare earth element ree patterns similar to those found in cais these results clearly demonstrate that the na rich chondrules must have been formed by melting of precursors containing an ultra refractory element rich component and na rich constituents the na rich chondrules showed sm and eu anomalies indicating that they must have formed at low oxygen fugacities based on the chemical composition of the na rich objects we can rule out that they were formed as a result of planetary formation due to metasomatic processes or processes related to collisions between molten planetesimals

evidence for impact induced pressure gradients on the allende cv3 parent body consequences for fluid and volatile transport carbonaceous chondrites such as those associated with the vigarano cv parent body exhibit a diverse range of oxidative reduced alteration mineralogy mcsween 1977 although fluids are often cited as the medium by which this occurs rubin 2012 a mechanism to explain how this fluid migrates and why some meteorite subtypes from the same planetary body are more oxidized than others remains elusive in our study we examined a slab of the well known allende cv3oxa meteorite using several petrological techniques e g fry s and flinn and computerized tomography ct we discover it exhibits a strong penetrative planar fabric resulting from strain partitioning among its major components calcium aluminum rich inclusions cais 64 5 ct matrix 21 5 fry chondrules 17 6 ct in addition to the planar fabric we found a strong lineation defined by the alignment of the maximum elongation of flattened particles interpreted to have developed by an impact event the existence of a lineation could either be non coaxial deformation or the result of a mechanically heterogeneous target material in the later case it could have formed due to discontinuous patches of sub surface ice and or fabrics developed through prior impact compaction macpherson and krot 2014 which would have encouraged preferential flow within the target material immediately following the impact compacting pore spaces we suggest that structurally controlled movement of alteration fluids in the asteroid parent body along pressure gradients contributed to the formation of secondary minerals which may have ultimately lead to the different oxidized subtypes

the formation of rims on calcium aluminum rich inclusions step i flash heating abstract wark lovering rims of six calcium aluminum rich inclusions cais representing the main cai types and groups in allende efremovka and vigarano were microsurgically separated and analysed by neutron activation analysis naa all the rims have similar 4x enrichments relative to the interiors of highly refractory lithophile and siderophile elements the naa results are confirmed by ion microprobe and scanning electron microscope sem analyses of rim perovskites and rim metal grains less refractory eu yb v sr ca and ni are less enriched in the rims the refractory element patterns in the rims parallel the patterns in the outer parts of the cais in particular the rims on type b1 cais have the igneously fractionated rare earth element ree pattern of the melilite mantle below the rim and not the ree pattern of the bulk cai proving that the refractory elements in the rims were derived from the outer mantle and were not condensates onto the cais the refractory elements were enriched in an al2o3 rich residue 50 m thick after the most volatile 80 of the outermost 200 m of each cai had been volatilized including much mg si and ca some volatilization occurred below the rim and created refractory partial melts that crystallized hibonite and gehlenitic melilite the required flash heating probably exceeded 2000 c but for only a few seconds in order to melt only the outer cai and to unselectively volatilize slow diffusing o isotopes which show no mass fractionation in the rim the volatilization did however produce heavy mass fractionated mg in rims in some cais this was later obscured when normal mg diffused in from accreted olivine grains at relatively high temperature not the lower temperature meteorite metamorphism and created the 50 m set of monomineralic rim layers of pyroxene melilite and spinel

alteration of al rich inclusions inside amoeboid olivine aggregates in the allende meteorite lightly altered al rich inclusions in amoeboid olivine aggregates have cores containing primary melilite fassaite spinel perovskite and no secondary alteration products in moderately altered inclusions whose cores now contain only fassaite spinel perovskite melilite was replaced by a fine grained mixture of grossular anorthite feldspathoids and perovskite was partially replaced by ilmenite in heavily altered inclusions fassaite has been replaced by a mixture of phyllosilicates ilmenite and the remaining primary phases are spinel perovskite in very heavily altered inclusions no primary phases remain the spinel having reacted to form either phyllosilicates or a mixture of olivine feldspathoids this sequence of alteration reactions may reflect successively lower solar nebular equilibration temperatures during alteration sio2 na2o k2o feo cr2o3 h2o and cl were introduced into the inclusions and cao was lost mgo may have been lost during the melilite reaction and added during formation of phyllosilicates electron microprobe analyses indicate that the phyllosilicates are a mixture of na rich phlogopite and chlorite or alrich serpentine thermodynamic calculations suggest that at a solar nebular water fugacity of 10 6 na rich phlogopite could have formed from fassaite at 470 k and chlorite from na rich phlogopite at 328 k olivine mantling al rich inclusions is not serpentinized suggesting that these objects stopped equilibrating with the nebular gas above 274 k

evaporites marine or non marine division of evaporites into those types that retain information about primary mineralogy textures and structures primary evaporites and those types so extensively altered that few or no primary features remain secondary evaporites only primary evaporites can give unequivocal data bout their marine or non marine origin to help evaluate such primary deposits they have been further divided using the following attributes 1 whether the depositional setting was marine or non marine 2 whether the source water was a seawater b meteoric c hydrothermal d diagenetic e volcanogenic or f mixed specific criteria for making distinctions are 1 kinds of fossils 2 sedimentology of the associated non saline facies 3 kinds of primary saline minerals 4 association of such saline minerals both in qualitative and quantitative terms 5 trace element isotope and fluid inclusion geochemistry of such saline minerals modified journal abstract

mineral chemistry and origin of spinel rich inclusions in the allende cv3 chondrite the mineral chemistry of 20 spinel rich inclusions and spinel rich nodules in 16 olivine rich inclusions in allende was studied by electron probe microanalysis variations in the chemistry of hibonite are explained by a coupled substitution among al ti mg si fe and v two types of perovskite occur 1 1 a variety enriched in the super refractory trace elements zr and y 2 2 zr y poor perovskite spinel typically contains a significant amount of fe 5 wt feo and small amounts of cr v zn ca and ti there are positive crfe and znfe correlations in fe rich spinel mg rich clinopyroxenes that rim spinel generally contain 11 wt a12o3 3 wt tio2 and 2 wt feo the chemistry of many accessory minerals in the inclusions was also studied the mineralogy of spinel rich allende inclusions is similar to the mineralogy of fine grained ca al rich inclusions cai s in alh 77003 and rims on coarse grained cai s in allende spinel rich inclusions in mokoia kaba and murchison differ in that they contain fe poor spinel and lack feldspathoid rims the mineralogy mineral chemistry and bulk chemistry of spinel rich allende inclusions indicate that they are not primitive aggregates of crystalline nebular condensates the inclusions are aggregates of tiny concentric objects each of which we interpret to be a fractionated distillation residue that lost ca si rich partial melt we believe that the mineral chemistry of spinel rich allende inclusions rims on coarse grained cai s and olivine rich allende inclusions and chondrules was largely established in the solar nebula at high temperatures under moderately oxidizing conditions and later modified to some degree by mild thermal metamorphism in the allende parent body we suggest that interstellar dust aggregates were melted or distilled into allende inclusions by aerodynamic drag heating in regions of the nebula where the dust gas ratio was so enhanced that the local oxygen fugacity was raised by several orders of magnitude and liquids became thermodynamically stable

oxygen isotopic zoning of reversely zoned melilite crystals in a fluffy type a ca al rich inclusions from the vigarano meteorite the oxygen isotopic microdistributions within melilite measured using in situ secondary ion mass spectrometry correspond to the chemical zoning profiles in single melilite crystals of a fluffy type a ca al rich inclusions cais of reduced cv3 vigarano meteorite the melilite crystals show chemical reverse zoning within an individual single crystal from the akermanite rich core to the akermanite poor rim the composition changes continuously with the crystal growth the zoning structures suggest that the melilite grew in a hot nebular gas by condensation with decreasing pressure the oxygen isotopic composition of melilite also changes continuously from 16o poor to 16o rich with the crystal growth these observations suggest that the melilite condensation proceeded with change consistent with an astrophysical setting around the inner edge of a protoplanetary disk where both 16o rich solar coronal gas and 16o poor dense protoplanetary disk gas could coexist fluffy type a cais could have been formed around the inner edge of the protoplanetary disk surrounding the early sun

a refractory inclusion in the kaba cv3 chondrite some implications for the origin of spinel rich objects in chondrites abstract the first detailed petrographic and mineralogical study of a ca al rich inclusion cai from the kaba cv3 chondrite is reported this fine grained cai contains abundant small rounded rimmed spinel rich objects which have important features in common with the spinel rich objects in other carbonaceous and ordinary chondrites these nodules are interpreted as fractionated distillation residues of primitive dust however the available data do not unambiguously rule out a condensation origin for at least some of these objects finally the preservation of distinct diopside hedenbergite rims on the spinel rich bodies and the small grain size of many minerals in the cai matrix material both suggest that the cai accreted cool and had a relatively cool thermal history in the kaba parent body

al mg isotopic evidence for episodic alteration of ca al rich inclusions from allende textures mineral assemblages and al mg isotope systematics indicate a protracted episodic secondary mineralization history for allende ca al rich inclusions cais detailed observations from one type b1 cai one b2 one compact type a cta and one fluffy type a fta indicate that these diverse types of cais are characterized by two distinct textural and mineralogic types of secondary mineralization 1 grossular rich domains concentrated along melilite grain boundaries in cai interiors and 2 feldspathoid bearing domains confined mostly to cai margins just interior to the wark lovering rim sequence the al mg isotopic compositions of most secondary minerals in the type b1 cai and some secondary minerals in the other cais show no resolvable excesses of 26mg whereas the primary cai phases mostly yield correlated excesses of 26mg with increasing al mg corresponding to canonical initial 26al 27al 4 55 10 5 these secondary minerals formed at least 3 ma after the primary cai minerals all but two analyses of secondary minerals from the fluffy type a cai define a correlated increase in 26mg 24mg with increasing al mg yielding 26al 27al 0 4 9 2 8 10 6 the secondary minerals in this cai formed 1 8 3 2 ma after the primary cai minerals in both cases the timing of secondary alteration is consistent with but does not necessarily require alteration in an asteroidal setting one grossular from the type b2 cai and several grossular and secondary feldspar analyses from the compact type a cai have excesses of 26mg consistent with initial 26al 27al 4 5 10 5 especially in the compact type a cai where 26mg 24mg in grossular correlates with increasing al mg these 26mg excesses are almost certainly due to in situ decay of 26al they indicate a nebular setting for formation of the grossular the preservation of these diverse isotopic patterns indicates that heating on the allende parent body was not pervasive enough to reset isotopic systematics of fine grained secondary minerals secondary mineralization clearly was not restricted to a short time interval and at least some alteration occurred coincident with cai formation and melting events chondrule formation in the nebula this observation supports the possibility that alteration followed by melting affected the compositional evolution of cais

ca al rich inclusions from the ningqiang meteorite continuous assemblages of nebular condensates and genetic link to type b inclusions the petrography and mineral chemistry of 110 ca al rich inclusions cais and 9 ca and or al rich amoeboid olivine aggregates aoas from the ningqiang carbonaceous chondrite are reported these cais are referred to as hibonite bearing and hibonite free melilite spinel rich type a and spinel pyroxene inclusions melilite is more gehlenitic in the hibonite bearing type as than in the other two types and all of them vary within a range of ak0 30 modal compositions of the three types of cais overlap with each other and make up a continuum with wide ranges of melilite spinel diopside the diopside occurs as rims on the cais or their individual concentric objects the 9 aoas contain spinel diopside anorthite in the centers of the aggregates the spinel grains rimmed by diopside in the centers are similar to the spinel pyroxene inclusions bulk compositions of these cais vary along the condensation trajectory with the hibonite bearing type as plotting at the beginning followed by hibonite free type as then by spinel pyroxene inclusions as temperature decreases bulk compositions of the aoas are close to the lowest temperature condensation trajectory except for a few with compact textures most of the type as and spinel pyroxene inclusions are fluffy aggregates probably pristine vapor solid condensates of the nebula the bulk compositions of the type as appear to overlap with the range of most melilite ti al clinopyroxene rich type b inclusions hence crystallization of liquids produced by melting the type as can form type b inclusions without significant evaporative loss of mgo or sio2 a few type bs have bulk compositions deviating from the range of their proposed precursors and may have suffered significant evaporation as suggested in previous studies

origin of compact type a refractory inclusions from cv3 carbonaceous chondrites compact type a cta inclusions are one of the major types of coarse grained refractory inclusions found in carbonaceous chondrites they have not been studied in a systematic fashion leading to some uncertainties and unproven assumptions about their origin to address this situation we studied a total of eight ctas from allende efremovka and axtell by scanning electron microscopic and electron and ion microprobe techniques these inclusions are very melilite rich ranging from 60 vol to nearly monomineralic also present are mg al spinel 5 20 perovskite trace 3 and in some samples ti rich 17 wt tio2tot fassaite trace 20 and rhonite 1 melilite compositions are mostly between ak15 and ak40 chondrite normalized ree abundance patterns for melilite flat at 10 ci with positive eu anomalies and fassaite slight hree enrichment relative to lree and negative eu anomalies are like those for their counterparts in once molten type b inclusions the patterns for rhonite have positive slopes from la through lu and abundances 10 ci for la and 35 60 ci for lu features of ctas that suggest that they were once molten include rounded inclusion shapes positively correlated sc and v abundances in fassaite radially oriented melilite laths at inclusion rims and the distribution of trace elements among the phases fractional crystallization models show that with one exception the ree contents of perovskite and fassaite arose by crystallization of these phases from late residual liquids that would have resulted from prior crystallization of the observed proportions of melilite and spinel from liquids having the bulk compositions of the inclusions one allende cta ts32 however has several features irregular shape reversely zoned melilite fassaite ree contents that are not readily explained by crystallization from a melt this inclusion may have undergone little melting and may be dominated by relict grains

sodium metasomatism in chondrules in co3 chondrites relationship to parent body thermal metamorphism we have studied the mineralogy and petrology of mesostases of 783 type i chondrules in seven co3 chondrites that range in petrologic subtype from 3 0 to 3 7 chondrule mesostases in the co chondrite of subtype 3 0 consist mainly of primary glass and plagioclase while chondrule mesostases in the co chondrites of higher subtypes 3 2 3 7 contain various amounts of nepheline in addition to glass and plagioclase nepheline has replaced glass and plagioclase forming finegrained aggregates and thin parallel lamellar intergrowths with plagioclase the nephelinization has proceeded preferentially from the outer margins of chondrules toward the inside although the degree of nephelinization differs widely among chondrules in each of the metamorphosed chondrites our modal analyses and bulk chemical analyses of individual mesostases indicate that the amounts of nepheline in chondrules systematically increase with the increasing petrologic subtype of the host chondrites nepheline also has a tendency to increase in grain size with increasing petrologic subtype we conclude that nepheline in chondrules in the co3 chondrites has formed largely as a result of effects related to heating on the meteorite parent body we suggest that nepheline initially formed as hydrous nepheline under the presence of aqueous fluids and subsequently was dehydrated after exhaustion of aqueous fluids the degree of hydrothermal activity must have increased with increasing degree of heating and thus chondrules in more thermally metamorphosed chondrites produced larger amounts of nepheline the results imply that co3 chondrites have gone through lowgrade aqueous alteration and subsequent dehydration at the early stage of heating on the meteorite parent body

the rifting to spreading transition in the red sea highlights the red sea rift rsr comprises the typical terrain of slow mor axes seen elsewhere submarine salt glaciers occur extensively along the rsr and blanket parts of the rsr inter trough zones are not continental but oceanic crust covered by evaporite flows we see a global mechanism for spreading initiation and no need for a multi node model we see prospects for large mineral deposits at passive margins that host evaporites abstract the transition from continental rifting to seafloor spreading is presently occurring at only a few places on earth such as the red sea or the woodlark basin competing theories for how spreading begins either by quasi instantaneous formation of a whole spreading segment or by initiation of spreading at multiple discrete nodes separated by thinned continental lithosphere have been put forward the major evidence for the nodes theory comes from the red sea and geophysical surveys carried out there in the multi deeps region during the 1970 s and 1980 s we present new high resolution multibeam bathymetric information over the same region which when combined with acoustic backscatter data seafloor sampling and magmatic geochemical information appears to provide no support for the nodes model we show that although the discrete deeps undoubtedly exist they are not separated from one another by tectonic boundaries but rather represent windows onto a continuous spreading axis which is locally inundated and masked by massive slumping of sediments and evaporites from the rift flanks the geophysical data that was previously used to support the presence of continental crust between the nodes can be equally well explained by processes related to the sedimentary blanketing and sub sedimentary hydrothermal alteration a single quasi instantaneous segment formation model would appear to be all that is required to explain observations from present day rifting spreading transitions globally

petrographic comparison of refractory inclusions from different chemical groups of chondrites twenty four refractory inclusions 40 230 m with average of 86 40 m were found by x ray mapping of 18 ordinary chondrites all inclusions are heavily altered consisting of finegrained feldspathoids spinel and ca pyroxene with minor ilmenite the presence of feldspathoids and lack of melilite are due to alteration that took place under oxidizing conditions as indicated by feo zno rich spinel and ilmenite the pre altered mineral assemblages are dominated by two types one rich in melilite referred to as type a like and the other rich in spinel referred to as spinel pyroxene inclusions this study and previous data show similar type and size distributions of refractory inclusions in ordinary and enstatite chondrites a survey of refractory inclusions was also conducted on allende and murchison in order to make unbiased comparison with their counterparts in other chondrites the predominant inclusions are type a and spinel pyroxene with average sizes of 170 130 m except for two mm sized inclusions in allende and 150 100 m in murchison the relatively larger sizes are partially due to common conglomerating of smaller nodules in both chondrites the survey reveals closely similar type and size distributions of refractory inclusions in various chondrites consistent with our previous data of other carbonaceous chondrites the petrographic observations suggest that refractory inclusions in various groups of chondrites had primarily formed under similar processes and conditions and were transported to different chondrite accreting regions heterogeneous abundance and distinct alteration assemblages of refractory inclusions from various chondrites could be contributed to transporting processes and secondary reactions under different conditions

lime silicates in amoeboid olivine aggregates in carbonaceous chondrites indicator of nebular and asteroidal processes mno feo ratios in olivine from amoeboid olivine aggregates aoas reflect conditions of nebular condensation and can be used in concert with matrix textures to compare metamorphic conditions in carbonaceous chondrites lime low iron mn enriched olivine was identified in aoas from y 81020 co3 05 kaba cv 3 1 and in y 86009 cv3 y 86751 cv3 nwa 1152 cr cv3 but was not identified in aoas from efremovka cv3 1 3 4 or allende cv 3 6 according to thermodynamic models of nebular condensation lime olivine is stable at lower temperatures than mn poor olivine and at low oxygen fugacities dust enrichment 95 in our study whereas efremovka aoas are slightly fe rich fo 92 aoa olivines from kaba are mostly forsteritic but rare fe rich olivine precipitated from an aqueous fluid a combination of precipitation of fe rich olivine and diffusion of fe into primary olivine grains resulted in iron rich compositions fo97 59 in allende aoas variations from fine grained nonporous matrix toward higher porosity and coarser lath like matrix olivine can be divided into six stages represented by 1 y 81020 efremovka nwa 1152 2 y 86751 lithology b 3 y 86009 4 kaba 5 y 86751 lithology a 6 allende these stages are inferred to represent general degree of metamorphism although the specific roles of thermally driven grain growth and diffusion versus aqueous dissolution and precipitation remain uncertain

refractory inclusions with unusual chemical compositions from the vigarano carbonaceous chondrite abstract ten inclusions nine from vigarano and one from leoville both members of the reduced subgroup of c3v chondrites were analyzed for major and trace elements by neutron activation most have some refractory element characteristics that are common in refractory inclusions from allende a member of the oxidized subgroup of c3v chondrites for instance three leo 3537 2 vig 1623 8 vig 1623 11 are type b inclusions with group i or modified group i ree patterns three vig 1623 5 vig 1623 10 vig 1623 13 are olivine rich inclusions each of which is rather uniformly diluted in most refractory elements compared to group i inclusions and two vig 1623 14 vig 1623 16 are fine grained inclusions with group ii ree patterns six of the vigarano inclusions however have refractory element fractionations that are unusual in allende inclusions vig 1623 11 has cl chondrite normalized enrichment factors for th and refractory siderophiles that are lower than those for ree by 60 or more a positive mo anomaly mo ir 1 92 0 02 relative to cl chondrites and an unusually low zr hf ratio 0 67 0 06 relative to cl relative to cl chondrites the ir enrichment factor is 1 7 times greater than the mean enrichment factor for re os and ru in vig 1623 10 vig 1623 13 has one of the lowest ir sm ratios 0 00044 0 00007 relative to cl ever measured in an olivine chondrule vig 1623 16 has a modified group ii ree pattern which reflects removal of refractory rees from the nebular gas at unusually low temperatures vig 477 5 has a ree pattern with a small negative ce anomaly ce la 0 79 0 01 relative to cl a large negative yb anomaly yb lu 0 57 0 02 relative to cl and no eu anomaly this inclusion also has a positive mo anomaly mo ir 2 25 0 03 relative to cl and enrichment factors for zr and th that are lower than those for lu by about 65 vig 477 b has a ree pattern that may be a mixture of five parts of a component with an ultrarefractory ree pattern and ninety five parts of another with a modified group ii ree pattern vigarano apparently sampled a different population of refractory inclusions from allende presumably because refractory nebular materials were not well mixed where and when c3v chondrites accreted the vigarano and leoville coarse grained inclusions studied here like others analyzed previously tend to have lower concentrations of na and au than allende coarse grained inclusions but the two vigarano fine grained inclusions of this study have concentrations of these elements that are comparable to those of allende fine grained inclusions thus although coarse grained inclusions in the reduced subgroup of c3v chondrites were altered under different conditions from those in the oxidized subgroup some fine grained inclusions in the reduced subgroup were altered under similar conditions as some in the oxidized subgroup

a once molten coarse grained ca rich inclusion in allende a compact spheroidal type b inclusion in allende contains melilite laths that project radially inward from the inclusion edge which show interference growth textures the combined textural and chemical features of this object cannot be explained by independent vapor solid condensation of grains in space followed by random aggregation of these grains into an inclusion rather it probably formed from a once molten droplet that crystallized in response to radiative cooling from its outer surface the crystallization sequence in this and another similar inclusion in which oxygen isotopes have been measured is melilite spinel anorthite fassaite this sequence supports the idea that oxygen isotopic heterogeneities in coarse grained inclusions were formed after complete solidification of these objects by partial exchange with a less16o rich gas and not during or before a melting event

the origin of type c inclusions from carbonaceous chondrites type c inclusions are plagioclase rich ca al rich inclusions found in carbonaceous chondrites they formed as solid condensates which were later melted in an event that destroyed the original condensate grains neither the melting event nor secondary alteration had a significant effect on bulk composition two stages in the condensation history can be discerned on the basis of major element bulk compositions as in type a inclusions the condensate phase assemblage originally consisted of melilite spinel perovskite hibonite type c s were however significantly enriched in spinel relative to unaltered portions of most type a s in contrast to type a s condensate grains of spinel and melilite in type c s reacted partially with a coexisting gas to produce anorthite diopside one half to two thirds of the silica now in type c inclusions was introduced by this process the reactions involving melilite and spinel that are predicted by equilibrium condensation calculations for a cooling gas of solar composition did not occur probably due to kinetic constraints type c s may be related to al rich chondrules in ordinary chondrites by the addition of olivine and albite bulk compositions of al rich chondrules in enstatite chondrites are consistent with the addition of orthopyroxene and albite to type c inclusions thus types a and c inclusions and al rich chondrules could represent sequences of condensates removed from interaction with the primitive solar nebula at progressively lower temperatures if al rich chondrules represent the high temperature component in chondritic material then type c inclusions rather than the more common subgroups of cais could be the true parents of chondrites

refractory spherules in the murchison meteorite are they condrules the textural and mineralogical features of refractory spherules found in the murchison meteorite are examined in relation to their probable origin based on a study of 12 samples it is found that the refractory spherules with hibonite bearing or spinel or spinel perovskite cores surrounded by an iron rich silicate layer have compositions similar to those of coexisting irregular inclusions the shape and internal textures of the spherules however suggest formation from a liquid it is proposed that the spherules may be melted equivalents of the irregular inclusions and thus may be properly termed chondrules it is noted that such melting would have involved very high temperatures

formation of spinel hibonite rich inclusions found in cm2 carbonaceous chondrites we report petrography mineral chemistry bulk chemistry and bulk isotopic compositions of a suite of 40 spinel rich inclusions from the murchison cm2 carbonaceous chondrite seven types of inclusions have been identified based on mineral assemblage spinel hibonite perovskite spinel perovskite pyroxene spinel perovskite melilite spinel hibonite perovskite melilite spinel hibonite spinel pyroxene and spinel melilite anorthite hibonite bearing inclusions have ti poor spinel compared to the hibonite free ones and spinel hibonite perovskite inclusions have the highest average bulk tio 2 contents 7 8 wt the bulk cao al 2 o 3 ratios of the inclusions range from 0 005 to 0 21 well below the solar value of 0 79 hibonite spinel rich inclusions consist of phases that are not predicted by condensation calculations to coexist in the equilibrium sequence hibonite is followed by melilite which is followed by spinel therefore hibonite melilite or melilite spinel inclusions should be dominant instead one explanation for the missing melilite is that it condensed as expected but was lost due to evaporation of mg and ca during heating and melting of spherule precursors if this theory were correct melilite poor spherules would have isotopically heavy mg and ca assuming rayleigh fractionation accompanied evaporation except for one inclusion with f mg 4 3 2 6 amu and another with isotopically light ca f ca 3 4 2 0 amu however all the inclusions we analyzed have normal isotopic compositions within their 2 uncertainties thus we found no evidence for significant mass dependent fractionation conditions necessary for non rayleigh evaporation are unlikely if not unrealistic and our preferred explanation for the general lack of melilite among hibonite spinel bearing inclusions is kinetic inhibition of melilite condensation relative to spinel because of similarities between the crystal structures of hibonite and spinel it should be easier for spinel than for melilite to form from hibonite

refractory inclusions in the prototypical cm chondrite mighei abstract refractory inclusions in the mighei cm2 meteorite are very abundant 35 being found in three thin sections of the meteorite the most common are pyroxene rimmed spinel rich inclusions that occur in a range of structural and textural types some inclusions are simple aggregates of crystals or rimmed crystals ranging from loose clusters of spinel grains to distended chains of pyroxene rimmed spinel knots others are more compact and may have experienced recrystallization or melting these include nodular spinel inclusions with polygonal granular textured spinel interiors and pyroxene rims ribbons of spinel in some cases with hibonite and or perovskite that are again rimmed by pyroxene and refractory spherules four inclusions are complex aggregates of several texturally distinct objects each collectively mighei inclusions are similar to those in murchison but appear to be somewhat more altered volatility fractionated and unfractionated trace element patterns similar to those found in refractory inclusions in other carbonaceous chondrites are represented in mighei inclusions and in addition some mighei inclusions have volatility fractionated pattern types not previously found in refractory inclusions in three of the complex aggregates fundamentally different trace element patterns are present within different portions of each inclusion meaning that these objects accreted from genetically different components that never equilibrated with one another subsequent to accretion bulk inclusion magnesium isotopic compositions show minor mass fractionation effects fmg values range from 2 3 to 7 5 but the average fmg value is indistinguishable from normal 1 8 1 2 there are no correlations between magnesium isotopic composition and textural type or trace element pattern type the diverse inclusion types in mighei represent a variety of origins and histories textures suggest that the nodular and banded inclusions may have experienced solid state recrystallization whereas the porous and chain like varieties and complex aggregates have not magnesium isotopic compositions and trace element abundances suggest that the mighei inclusions are unlikely to be evaporation residues and are more likely to be the products of condensation or recondensation processes

nepheline and sodalite in chondrules of the ningqiang carbonaceous chondrite implications for a genetic relationship with those in the matrix abstract ningqiang is an ungrouped carbonaceous chondrite that has a chemical and mineralogical affinity to cv3 chondrites the ningqiang matrix has distinctly higher abundances of na k and al than cv3 matrices a recent study by matsumoto et al 2014 revealed that the major proportions of these elements can be attributed to the presence of nepheline and sodalite scanning electron microscopy revealed that all of the ningqiang chondrules studied show abundant evidence of extensive na fe metasomatism only a small proportion of the chondrules contain primary mesostases in their cores but the mesostases in their mantles were replaced by fine grains of nepheline sodalite fe rich olivine and hedenbergite the mesostases in the majority of the chondrules were completely replaced by fine grains of the same secondary minerals most opaque nodules were also largely replaced by various fine grained secondary minerals nepheline sodalite form veins penetrating the primary mesostases providing evidence that aqueous fluids were involved in the alteration reactions the nepheline sodalite in the mesostases contain various amounts of inclusions of fe rich olivine diopside hedenbergite fe sulfides and magnetite the mineralogical features of the nepheline sodalite in the mesostases are almost identical to those in the meteorite matrix these results suggest that a significant fraction of the nepheline sodalite grains in the ningqiang matrix originated from the nepheline sodalite produced in chondrules and refractory inclusions and that they were disaggregated and mixed into the matrix these processes can be explained consistently by the model of the dynamic formation of chondrite lithology in a parent body proposed by tomeoka and ohnishi 2015 we suggest that after a ningqiang precursor with a cv3 like lithology was metasomatized it was fragmented causing the disaggregation of the fine grained host matrix and the fine grained altered mesostases including nepheline sodalite and opaque nodules in the chondrules the chondrules were thereby separated into multiple fragments subsequently during transportation in a fluidized state all these materials were homogenously mixed together and later underwent accumulation and lithification

a unique ultrarefractory inclusion from the murchison meteorite through freeze thaw disaggregation of the murchison meteorite we have recovered a refractory inclusion hib 11 that is unique in terms of its texture mineral compositions and bulk composition it consists of anhedral y rich 1 6 wt y2o3 perovskite and lathlike spinel grains enclosed in a matrix of fine grained sc rich 10 5 wt sc2o3 avg ti rich 12 6 wt tio2 avg reporting all ti as tio2 clinopyroxene the chondrite normalized rare earth element ree pattern is complex with light ree lree at 10 c1 abundances increasing from gd through ho the latter at 104 c1 decreasing through yb at 200 c1 and lu at 400 c1 the pattern reflects several stages of high temperature volatility fractionation removal of lu and er from the source gas in the first condensation event was followed by partial to complete removal of the somewhat less refractory heavy ree gd through ho in the hib 11 precursors by condensation from the fractionated residual gas in a second event both of these events probably reflect condensation of ree into zro2 or a mixed zr sc ti y oxide at temperatures too high for hibonite stability a second lower temperature component which was subsequently added had fractionated nd poor ce rich lree abundances that resulted from condensation from a gas that had undergone prior removal of the more refractory lree resulting in enrichment in ce and the most volatile ree eu and yb the aggregate was then melted and quickly cooled forming a fine grained spherule this is the first reported inclusion in which the two most refractory ree lu and er are strongly fractionated from the other ree an absence of mass fractionation among the ti isotopes indicates that hib 11 is not an evaporative residue implying that volatility fractionation of trace elements took place during condensation the fact that the two most refractory heavy ree could be separated from the other only slightly less refractory heavy ree suggests that a wide variety of ree patterns is possible and that ultrarefractory inclusions with other unusual ree patterns important recorders of nebular condensation may yet be discovered

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

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

variations in initial 26al 27al ratios among fluffy type a ca al rich inclusions from reduced cv chondrites abstract al mg mineral isochrons of three ca al rich inclusions cais that formed primarily by condensation one fine grained spinel rich inclusion and two fluffy type a cais from the reduced cv chondrites efremovka and vigarano were obtained by in situ al mg isotope measurements using secondary ion mass spectrometry the slope of the isochron obtained for the fine grained spinel rich inclusion gives an initial 26al 27al value 26al 27al 0 of 5 19 0 17 10 5 this is essentially identical to the solar system initial 26al 27al determined by whole rock al mg isochron studies for cais in cv chondrites in contrast the isochron slopes for the two fluffy type a cais from their al mg mineral isochrons 4 703 0 082 10 5 and 4 393 0 084 10 5 are significantly lower than the solar system initial value the range of 26al 27al 0 values of the three cais from 5 19 0 17 to 4 393 0 084 10 5 corresponds to a formation age spread of 0 17 0 04 myr this formation age spread is similar to that of igneous cais from cv chondrites the data suggest that condensation and melting of minerals occurred in the hot nebular gas contemporaneously for 0 2 myr at the very beginning of our solar system if 26al was distributed homogeneously in the cai forming region alternatively the observed variations in 26al 27al 0 among fluffy type a cais would also raise a possibility of heterogeneous distributions of 26al in the forming region