bluuebunny/crossref_metadata_2025_split huggingface dataset:
Meteorites from the Nullarbor Region, Western Australia: I. A review of past recoveries and a procedure for naming new finds
Authors: Bevan A. W. R. , Binns R. A. 
Published: June 2012

Abstract— Currently, 44 distinct meteorites are recorded from the Nullarbor Region in Western Australia. Recovery data for the Billygoat Donga, Cardanumbi, Cocklebiddy, Forrest Lakes, Laundry East, Lookout Hill, North East Reid, North Reid, Reid, Webb, West Forrest, West Reid and Yayjinna meteorites are amended, and North Forrest is recognized as distinct from North West Forrest (H).Since 1971, the recovery of more than 500 specimens (predominantly ordinary chondrites) from the desert has made the Nullarbor Region one of the most productive areas of the world for meteorite recoveries and has caused major problems for meteorite nomenclature. To overcome a lack of geographical names, we have delineated a grid of 47 named ‘areas’ in the Nullarbor Region. Henceforth, distinct meteorites will take the name of the ‘area’ in which they are found and a number (e.g., 001) in order of discovery. In general, the names of past recoveries remain unchanged. The absence of transportation processes in the region, and accurate documentation of the distribution of finds allows ‘pairing’ of specimens to at least 90% level of confidence.
The Bencubbin chondrite breccia and its relationship to CR chondrites and the ALH85085 chondrite
Authors: Weisberg Michael K. , Prinz Martin , Nehru Cherukupalli E. 
Published: June 2012

Abstract— Bencubbin is an unclassified meteorite breccia which consists mainly of host silicate (∼40 vol.%) and host metal (∼60%) components. Rare (< 1%) ordinary chondrite clasts and a dark xenolith (formerly called a carbonaceous chondrite clast) are also found. A petrologic study of the host silicates shows that they have textures, modes, mineralogy and bulk compositions that are essentially the same as that of barred olivine (BO) chondrules, and they are considered to be BO chondritic material. Bulk compositions of individual host silicate clasts are identical and differ only in their textures which are a continuum from coarsely barred, to finely barred, to feathery microcrystalline; these result from differing cooling rates. The host silicates differ from average BO chondrules only in being angular clasts rather than fluid droplet‐shaped objects, and in being larger in size (up to 1 cm) than most chondrules; but large angular to droplet‐shaped chondrules occur in many chondrites. Bencubbin host metallic FeNi clasts have a positive Ni‐Co trend, which coincides with that of a calculated equilibrium nebular condensation path. This appears to indicate a chondritic, rather than impact, origin for this component as well. The rare ordinary chondrite clast and dark xenolith also contain FeNi metal with compositions similar to that of the host metal.Two scenarios are offered for the origin of the Bencubbin breccia. One is that the Bencubbin components are chondritic and were produced in the solar nebula. Later brecciation, reaggregation and minor melting of the chondritic material resulted in it becoming a monomict chondritic breccia. The alternative scenario is that the Bencubbin components formed as a result of major impact melting on a chondritic parent body; the silicate fragments were formed from an impact‐induced lava flow and are analogous to the spinifex‐textured rocks characteristic of terrestrial komatiites. Both scenarios have difficulties, but the petrologic, chemical and isotopic data are more consistent with Bencubbin being a brecciated chondrite.Bencubbin has a number of important chemical and isotopic characteristics in common with the major components in the CR (Renazzo‐type) chondrites and the unique ALH85085 chondrite, which suggests that their major components may be related. These include: (1) Mafic silicates that are similarly Mg‐rich and formed in similar reducing environments. (2) Similarly low volatiles; TiO2, Al2O3 and Cr2O3 contents are also similar. (3) Similar metallic FeNi compositions that sharply differ from those in other chondrites. (4) Remarkable enrichments in 15N. (5) Similar oxygen isotopic compositions that lie on the same mixing line. Thus, the major components of the Bencubbin breccia are highly similar to those of the ALH85085 and CR chondrites and they may have all formed in the same isotopic reservoir, under similar conditions, in the CR region of the solar nebula.
Temperature conditions for chondrule formation
Authors: Hewins Roger H. , Radomsky Patrick M. 
Published: June 2012

Abstract— The liquidus temperatures of chondrules range from about 1200 °C to almost 1900 °C, based on the calculation of Herzberg (1979). Dynamic melting and crystallization experiments with no external seeding suggest that some chondrule textures formed with initial temperatures below the liquidus (e.g., porphyritic, granular) and some were completely melted (e.g., excentroradial, glassy). Type I and III chondrules in carbonaceous chondrites in this interpretation consist of incompletely melted magnesian chondrules, completely melted silica‐rich chondrules and intermediate composition chondrules with both porphyritic and nonporphyritic textures. A similar pattern for ordinary chondrites, with data also for Type II porphyritic and barred olivine chondrules, suggests that few chondrules with liquidus temperatures over 1750 °C were completely melted and few with under 1400 °C were incompletely melted. The range of liquidus temperatures for barred olivine chondrules, for which initial temperatures appear to have been essentially at the liquidus, is similar. Most chondrules may therefore have been heated to temperatures of 1400–1750 °C and, because of a peak in the distribution of barred olivine chondrule temperatures at 1500–1550 °C, the temperatures appear normally distributed within this range. Given a narrow range of temperatures, bulk composition is at least as important as initial temperature in controlling chondrule textures.Truly granular (not microporphyritic) Type I and truly glassy Type II and III chondrules appear under‐represented in nature according to this model, based on internal nucleation experiments. External heterogeneous nucleation, or seeding due to droplet‐dust collisions, is likely to occur in a dusty nebula and has been shown to reproduce chondrule textures experimentally. Generally high initial temperatures (1600–1800 °C), coupled with dust‐seeding of superheated droplets of less refractory composition is an alternative explanation of chondrule textures. Cooling rates of 100–1000 °C/hr are required for chondrules, which must have been mass produced in clouds with sufficient particle density to buffer cooling rate and perhaps also initial temperature. Melting precursor particles in a thick clump and/or the nebular mid‐plane would provide evaporation and thus explain the high oxidation state and volatile content of chondrules, relative to the bulk hydrogen‐rich nebula, as well as the nature of the cooling.
Evidence for the existence of groups of meteorite‐producing asteroidal fragments
Authors: Halliday Ian , Blackwell Alan T. , Griffin Arthur A. 
Published: June 2012

Abstract— The MORP camera network in western Canada observed 56 events which we associate with meteorites larger than 0.1 kg. An additional 33 Prairie Network (central USA) fireballs with published orbits were previously identified as the sources of meteorites of at least 0.25 kg. A comparison of the MORP orbits with each other and with the PN orbits, using the D′ criterion of orbital similarity, exhibits a surprising number of small values. This suggests there are groups of related objects among the 89 events. We evaluate the probability of small values of D′ arising by chance from a group of random orbits that has the distribution of orbital elements expected for meteorites. There is an excess of small values of D′ among the 89 meteoritic objects over the expectation for random orbits and a marked excess of very small values. Four groups comprising a total of 16 objects account for this excess. These groups exhibit a preference for the larger masses of the population and a very strong concentration of perihelia just slightly inside the Earth's orbit.Although it has been shown by others that gravitational perturbations will disperse Earth‐crossing streams in times that are much less than cosmic‐ray exposure ages, the properties of the four groups suggest they may be streams of fragments that crossed the Earth's orbit only recently. Such streams may include a considerable fraction of meteorites falling at a given time. Orbital evolution of these streams could alter the sample of meteorites arriving on Earth over time intervals that are less than the accumulation time of the Antarctic collections.
The Bencubbin stony‐iron meteorite breccia: Electron petrography, shock‐history and affinities of a “carbonaceous chondrite” clast
Authors: Barber D. J. , Hutchison R. 
Published: June 2012

Abstract— A “carbonaceous chondrite” clast from Bencubbin was studied by analytical transmission electron microscopy and other electron beam techniques. In section, the clast consists of oval augen, with a preferred orientation, set in fine‐grained matrix. The augen comprise olivine microphenocrysts in fine‐grained to glassy mesostases. The olivines are heavily deformed, giving rise to mosaicism. Many sub‐grains have high densities of dislocations with [001] Burgers vectors. In some regions the dislocation configurations are recovered, causing a reduced dislocation density; recrystallization is rarer. Severe cataclasis is absent; there are few open fractures and little intergranular porosity except where a second phase occurs. Such porosity in olivine mainly occurs as finescale negative crystals, which appear to be healed cracks. Some mesostases consist of small amounts of microporous oxides and feldspathic glass but glassy veins are absent. Pyrhottite and Fe/Ni sulfides are major mesostasis constituents that rarely form tongues between the olivines, which commonly include smaller sulfide blebs.The matrix of the clast has abundant sulfides and fine‐grained, poorly crystalline Fe‐ and Fe/Ni‐oxides, with more sparse ferrihydrite. The oxides mostly occur in contact with, or within, aluminous and siliceous glassy material in which crystals of melilite, spinel, Ca‐pyroxene, feldspar, and other minor silicate phases have grown. Small patches of fibrous and/or sheet‐like Mg/Fe silicates with layer morphologies also occur. They are microporous, poorly crystalline and lack the layer spacings of phyllosilicates, of which they may be relics. Grains of anhydrite and calcite are interlaced with fibrous silicates.There is evidence that one, or more, intense shock‐heating event(s) produced local melting. A later shock event(s) involved less severe shock‐heating, to about 900 °C. The mineralogy indicates that the clast may have originated from a CM2 precursor or from material like Allan Hills 85085, although it is just possible that terrestrial weathering produced some of the diagnostic minerals.
Transmission electron microscopy of a refractory inclusion from the Allende meteorite: Anatomy of a pyroxene
Authors: Doukhan N. , Doukhan J. C. , Poirier J. P. 
Published: June 2012

Abstract— A crystal of clinopyroxene from the coarse‐grained refractory inclusion Egg 6 of the Allende meteorite has been studied in detail by transmission electron microscopy.The pyroxene crystal contains euhedral, dislocation‐free inclusions of pure spinel MgAl2O4, without any topotactic relation to the host. Extensive dislocation walls at equilibrium, characteristic of high‐temperature anneal, are present in the crystal. Alteration products are occasionally observed at the spinel‐pyroxene interface close to regions where dislocation walls decorated with bubbles (or voids) are present. The bubbles, often in the shape of tubes along the dislocation lines, are thought to be due to the precipitation of a fluid migrating along the dislocations.The observations are compatible with crystallization of the refractory inclusions from the melt and with the existence of a later stage of metasomatism.
The Hashima, Japan H4 chondrite: A newly reported meteorite
Authors: Hoshino Mitsuo , Suwa Kanenori 
Published: June 2012

Abstract We report a new chondrite that fell in Hashima City in central Japan sometime during the period 1868–1912. The chondrite weighs 1110.64 g and exhibits distinct chondritic structure. Chondrules occupy 24 vol% of the stone and consist of olivine (average Fa17,8), low‐Ca pyroxene (average Fs15,8 Wo0.9), devitrified glass and lesser amounts of oligoclase (ca. Ab80Or4), kamacite, taenite, troilite and chromian spinel. Matrix occupying 76 vol% of the stone consists of olivine, low‐Ca pyroxene, kamacite, taenite, troilite, cryptocrystalline minerals and lesser amounts of chromian spinel and chlorapatite. Matrix minerals have the same compositions as those in chondrules.Mineral chemistry, bulk chemistry and magnetic properties indicate that Hashima is an H‐group chondrite. Well‐defined chondrules, scarcely recrystallized oligoclase and relatively small variations of olivine and low‐Ca pyroxene compositions indicate that Hashima is of petrologic type 4.
The Divnoe meteorite: Petrology, chemistry, oxygen isotopes and origin
Authors: Petaev M. I. , Barsukova L. D. , Lipschutz M. E. , Wang M.‐S. , Ariskin A. A. , Clayton R. N. , Mayeda T. K. 
Published: June 2012

Abstract— The Divnoe meteorite is an olivine‐rich primitive achondrite with subchondritic chemistry and mineralogy. It has a granoblastic, coarse‐grained, olivine groundmass (CGL: coarse‐grained lithology) with relatively large pyroxene‐plagioclase poikilitic patches (PP) and small fine‐grained domains of an opaque‐rich lithology (ORL). Both PP and ORL are inhomogeneously distributed and display reaction boundaries with the groundmass. Major silicates, olivine (Fa20–28) and orthopyroxene (Fs20–28 Wo0.5–2.5), display systematic differences in composition between CGL and ORL as well as a complicated pattern of variations within CGL. Accessory plagioclase has low K content and displays regular igneous zoning with core compositions An40–45 and rims An32–37. The bulk chemical composition of Divnoe is similar to that of olivine‐rich primitive achondrites, except for a depletion of incompatible elements and minor enrichment of refractory siderophiles. Oxygen isotope compositions for whole‐rock and separated minerals from Divnoe fall in a narrow range, with mean δ18O = +4.91, δ17O = +2.24, and Δ17O = −0.26 ± 0.11. The isotopic composition is not within the range of any previously recognized group but is very close to that of the brachinites. To understand the origin of Divnoe lithologies, partial melting and crystallization were modelled using starting compositions equal to that of Divnoe and some chondritic meteorites. It was found that the Divnoe composition could be derived from a chondritic source region by ∼20 wt% partial melting at T ∼ 1300 °C and log(fO2) = IW‐1.8, followed by ∼60 wt% crystallization of the partial melt formed, and removal of the still‐liquid portion of the partial melt. Removal of the last partial melt resulted in depletion of the Divnoe plagioclase in Na and K. In this scenario, CGL represents the residue of partial melting, and PP is a portion of the partial melt that crystallized in situ. The ORL was formed during the final stages of partial melting by reaction between gaseous sulfur and residual olivine in the source region.A prominent feature of Divnoe is fine μm‐scale chemical variations within olivine grains, related to lamellar structures the olivines display. The origin of these structures is not known.
The Mbale meteorite shower
Authors: Jenniskens Peter , Betlem Hans , Betlem Jan , Barifaijo Erasmus , Schlüter Thomas , Hampton Craig , Laubenstein Matthias , Kunz Joachim , Heusser Gerd 
Published: June 2012

Abstract— On 1992 August 14 at 12:40 UTC, an ordinary chondrite of type L5/6 entered the atmosphere over Mbale, Uganda, broke up, and caused a strewn field of size 3 × 7 km. Shortly after the fall, an expedition gathered eye witness accounts and located the position of 48 impacts of masses between 0.1 g and 27.4 kg. Short‐lived radionuclide data were measured for two specimens, one of which was only 12 days after the fall. Subsequent recoveries of fragements has resulted in a total of 863 mass estimates by 1993 October. The surfaces of all fragments contain fusion crust. The meteorite shower caused some minor inconveniences. Most remarkably, a young boy was hit on the head by a small specimen.The data are interpreted as to indicate that the meteorite had an initial mass between 400–1000 kg (most likely ∼1000 kg) and approached Mbale from Az = 185 ± 15, H = 55 ± 15, and V∞ = 13.5 ± 1.5/s. Orbital elements are given. Fragmentation of the initial mass started probably above 25 km altitude, but the final catastrophic breakup occurred at an altitude of 10–14 km. An estimated 190 ± 40 kg reached the Earth's surface minutes after the final breakup of which 150 kg of material has been recovered.
Equilibration temperatures of EL chondrites: A major downward revision in the ferrosilite contents of enstatite
Authors: Wasson John T. , Kallemeyn Gregory W. , Rubin Alan E. 
Published: June 2012

Abstract A study of enstatite grains separated from EL6 chondrites shows ferrosilite contents to be ∼0.02–0.04 mol%, about an order of magnitude lower than reported in the literature. The higher values reported earlier can probably be attributed to the excitation of Fe atoms in Fe‐Ni and FeS, in part from μm‐sized blebs of FeS and Fe‐Ni commonly present in enstatite grains but mainly from large neighboring opaque grains excited by bremsstrahlung or by doubly backscattered electrons. Our EL6 ferrosilite contents are similar to those observed in coarse enstatite grains in some aubrites.The equilibrium between ferrosilite and Si‐bearing kamacite is highly temperature dependent. At constant Si concentration in kamacite, the equilibrium ferrosilite mole fraction drops by a factor of roughly 2.5 for each 100 K decrease in the equilibrium temperature. As a result, the compositions of these two most common EL6 phases can be used to estimate metamorphic equilibration temperatures. The inferred temperatures are near 1200 K.
Lunar soil evolution processes and Apollo 16 core 60013/60014
Authors: Basu Abhijit , McKay David S. 
Published: June 2012

Abstract— Soils of the 62‐cm deep Apollo 16 double drive tube 60013/14 are mature at the top and submature at the bottom. Modal analyses of 5529 grains from the 90–150 μm and the 500–1000 μm. fractions from 12 levels of the core show that, in general, agglutinate abundance increases somewhat monotonically to the top and mimics the Is/FeO profile. There is a general decrease in the modal abundance of monomineralic fragments towards the top, suggesting that agglutinates were formed in part at the expense of monomineralic grains, especially feldspars, which are by far the most abundant mineral in these soils. In detail, the top 27 cm of the core differs from the bottom 21 cm, and the middle 14 cm is intermediate in its properties. In the upper segment, variations in the abundances of feldspars correspond with those of feldspathic fragmental breccias and cataclastic anorthosites; in the bottom segment, a similar but weak correspondence between feldspars and crystalline matrix breccias is observed. Mixing of the comminuted products of these three rock types likely produced the bulk of the core material. Many single feldspars in all size fractions are remarkably fresh, show no damage from shock, and are similar in appearance to the large feldspars in anorthosites and feldspathic fragmental breccias, which we consider to be the primary sources of single feldspars in this core. Major (Na, Al, Si, K, Ca) and minor (Fe, Ba) element analyses of 198 single feldspar grains indicate the presence of only one population of feldspars, which is consistent with our interpretation of feldspar provenance. Classification of 890 monomineralic feldspar, olivine, pyroxene, and glass spherules on the basis of the presence or absence of thin brownish coating—related to reworking at the surface—shows that coated grains are much more abundant in the top segment than in the bottom segment.A comparison with the mixing and maturation model (McKay et al., 1977) of soils in the core 60009/10, some 60 m away from 60013/14, shows that mixtures of an immature, nearly pure plagioclase soil (dominant in 60009/10) and another immature, crystalline breccia‐rich soil (dominant in 60013/14) may have matured through in situ reworking to produce the soils under investigation.We conclude that the soils in this core are products of mixing along soil evolution Path 2 of McKay et al. (1974). Superimposed on that soil column is the reworking of the upper part, which has evolved more recently along Path 1. This core thus represents a consanguineous column of the lunar regolith with an upper reworked segment.
Interstellar graphite in meteorites: Isotopic compositions and structural properties of single graphite grains from Murchison
Authors: Zinner Ernst , Amari Sachiko , Wopenka Brigitte , Lewis Roy S. 
Published: June 2012

Abstract— One hundred forty‐three carbon grains, ranging in size from 2 to 8 μm, from two chemical and physical separates from the Murchison CM2 chondrite, were analyzed by ion microprobe mass spectrometry for their C‐ and N‐isotopic compositions. Both separates are enriched in the exotic noble gas component Ne‐E(L). Ninety grains were also analyzed for their H and O contents and 118, for Si. Thirteen grains were analyzed by micro‐sampling laser Raman spectroscopy.Round grains have large C‐isotopic anomalies with 12C/13C ratios ranging from 7 to 4500 (terrestrial ratio = 89). Nitrogen in these grains is also anomalous but shows much smaller deviations from the terrestrial composition, 14N/15N ratios ranging from 193 to 680 (terrestrial ratio = 272). Spherulitic aggregates and non‐round compact grains have normal C‐isotopic ratios but 15N excesses (up to 35%). Raman spectra of the analyzed grains indicate varying degrees of crystalline disorder of graphite with estimated in‐plane crystallite dimensions varying from 18 Å (highly disordered, similar to terrestrial kerogen) to ∼750 Å (well‐crystallized graphite). Element contents of H, O, and Si are correlated with one another, and H and O are probably present in the form of organic molecules. On the basis of morphology, the round grains fall into two groups: grains with smooth, shell‐like surfaces (“onions”) and grains that appear to be dense aggregates of small scales (“cauliflowers”). “Onions” tend to have lower trace element contents, isotopically light C (12C/13C > 89) and a high degree of crystalline order, whereas “cauliflowers” have a larger spread in trace element contents and C‐isotopic ratios (they range from isotopically light to heavy) but tend to have a low degree of crystalline order. However, these differences exist only on average, and no clear distinction can be made for individual grains.A few limited conclusions can be drawn about the astrophysical origin of the carbon grains of this study. The 15N excesses in spherulitic aggregates and non‐round grains can be explained as the result of ion‐molecule reactions in molecular clouds. The round grains, on the other hand, must have formed in stellar atmospheres (circumstellar grains). Grains with isotopically light C must have formed in stellar environments characterized by He‐burning, either in the atmosphere of Wolf‐Rayet stars during the WC phase or in the He‐burning, 12C‐rich zone of a massive star, ejected by a supernova explosion. Isotopically heavy C is produced by H‐burning in the CNO cycle. Possible sources for grains with heavy C are carbon stars (AGB stars during the thermally pulsing phase) or novae, but the detailed distribution of 12C/13C ratios agree neither with the distribution observed in carbon stars nor with theoretical predictions for these two types of stellar sources.