bluuebunny/crossref_metadata_2025 huggingface dataset:
The flux of meteorites on the Earth's surface
Authors: Halliday Ian , Blackwell Alan T. , Griffin Arthur A.
Published: June 2012

Abstract— We derive values for the number and size distributions of meteorites landing on Earth from a study of photographic observations of bright fireballs with the Canadian camera network. The observations cover 11 years from 1974 to 1985. This analysis is an extension of a previous study and represents a 30% increase in the data base.

The cumulative plot of numbers vs estimated mass of the largest fragment for each event shows a change in slope near 0.6 kg due to a deficiency of small meteorites surviving from the group of slow fireballs. The change can be explained by a mass dependence of the fraction of the incoming object that survives as the largest fragment. For larger falls, the main mass appears to represent a decreasing fraction of the total mass of the surviving meteorites and estimates of these effects are used to derive the final distribution of both main masses and total masses of meteoritic events. For total masses greater than 1 kg the population index is 1.82, close to previous estimates. About 9 events per year drop at least 1 kg of meteorites in an area of a million square km and the same area receives an annual influx of 54 kg from meteorite events with total masses between 0.01 and 100 kg.

There is sufficient confidence in these results that they may be used for comparison of the present flux of meteorites with values inferred for other times, in particular the long accumulation times of the Antarctic meteorite collections.
Problems of origin of asteroids and comets
Authors: Safronov V. S.
Published: June 2012

Abstract— Various hypotheses of the origin of asteroids and comets are briefly discussed. Interaction of planetesimals in the asteroid zone (AZ) with the gas, their perturbations by proto‐Jupiter, and sweeping them out by more massive Jupiter zone bodies when they penetrated the AZ are considered. If the gas was turbulent, it could prevent a settling of dust particles to the equatorial plane of the disk and formation of dust condensations due to gravitational instability. Then particles grew by sticking upon collision. Gas moved radially due to turbulent viscosity and its dissipation. Small particles moved more‐or‐less together with the gas. As a result of gas drag, larger particles and bodies moved relative to the gas in the direction of increasing gas pressure. Gas would remove much of the solid material from the AZ if most bodies larger than a few km disintegrated by collisions into fragments smaller than a few tens of meters. Most of these fragments would then move into the Martian zone, and the small mass of Mars would have no explanation.

Resonant perturbations of asteroids by Jupiter are discussed. In the model of a small mass disk they could scan through the asteroid belt due to changes in Jupiter's distance from the Sun that occurred when this planet accreted the gas and ejected the bodies from the solar system. Such a scanning considerably accelerated the removal of asteroids from the AZ. Massive Jupiter zone bodies with large orbital eccentricities that crossed the AZ were probably efficient at sweeping out bodies. Larger bodies increased the random velocities of the remaining asteroids at close encounters to the present values ∼ 5 km/s.

Restrictions on the runaway growth of giant planets, on the relative velocities of bodies and the disk surface density that follow from the consideration of the origin of the asteroid belt and the cometary cloud are considered.
A numerical model for isotopic patterns from thermal‐extraction experiments
Authors: Robert François , Halbout Jérôme
Published: June 2012

Abstract— A model based on volume diffusion is proposed to describe thermal extraction (progressive or stepped vacuum‐pyrolysis or combustion) experimental results (yield and isotopic composition), reported against time or temperature. It accounts for the common asymmetrical shape of the release patterns, with peak‐tails due to the extraction kinetics. By analogy to this model, a simulation function is introduced which allows calculation of the concentration and isotopic patterns resulting from component mixings during such experiments. In this calculation, each component's isotopic composition is assumed to be constant throughout its extraction. The simulation readily explains the shift between the isotopic composition peaks and the concentration peaks in the temperature release pattern commonly observed during pyrolysis or combustion of meteorite samples. Because of its simplicity, the principles of the simulation can be easily applied by the readers to real data. One example is taken from the meteoritic stable isotope literature: the progressive pyrolysis extraction of hydrogen from the Parnallee LL3 meteorite (Robert et al., 1987a). The simulation permits calculation of a range for the isotopic composition of a D‐depleted reservoir in this meteorite: −460 < δD < −320‰ rel. SMOW.
Isotopic Hg in an Allende carbon‐rich residue
Authors: Reed G. W. , Jovanovic S.
Published: June 2012

Abstract— A carbon‐rich residue from Allende subjected to stepwise heating yielded two isotopically resolvable types of Hg: one with a 196Hg/202Hg concentration ratio the same as terrestrial (monitor) Hg; the other enriched in 196Hg relative to 202Hg by ∼60%. Hg with the 202 isotope enriched relative to 196, as is found in bulk Allende, was not observed. Whether the result of mass fractionation or nucleosynthesis, the distinct types of Hg entered different carrier phases and were not thermally mobilized since the accretion of the Allende parent body.
A contemporary account of the Ensisheim meteorite, 1492
Authors: Rowland Ingrid D.
Published: June 2012

Abstract— A report of the 1492 fall of a large stone meteorite near Ensisheim, Alsace, reached the Italian parish priest Sigismondo Tizio, who included this report and a picture of the event in his manuscript History of Siena. The colored picture presents some variations on the woodcut illustration which accompanied Sebastian Brant's printed broadsheets issued immediately after the appearance of the “thunderstone,” while Tizio's report demonstrates how such information travelled quickly along European trade routes.
Classification of four ordinary chondrites from Spain
Authors: McCoy T. J. , Casanova I. , Keil Klaus , Wieler R.
Published: June 2012

Abstract— Based on optical microscopy and electron microprobe analysis of mafic minerals, four previously poorly described ordinary chondrites from Spain are classified. The classifications of Guareña (H6), Olmedilla de Alarcón (H5) and Reliegos (L5) are confirmed. Molina is reclassified as H5, based on new data.
Deformation and thermal histories of chondrules in the Chainpur (LL3.4) chondrite
Authors: Ruzicka Alex
Published: June 2012

Abstract— Transmission‐electron‐microscopy (TEM) and optical data suggest that chondrules in the Chainpur (LL3.4) chondrite experienced varied thermal and deformation histories prior to the final agglomeration of the meteorite. Chainpur may be regarded as an agglomerate or breccia that experienced little deformation or heating during and after the final accumulation and compaction of its constituents.

One chondrule in Chainpur was impact‐shocked to high pressures (∼ 20–50 GPa), almost certainly prior to final agglomeration, either while it was an independent entity in space or while it was in the regolith of a parent body. However, most (>85%) of the chondrules in Chainpur were evidently not significantly shock‐metamorphosed subsequent to their formation. The dearth of shock effects implies that most chondrules in Chainpur did not form by shock melting, although some chondrules may have formed by this process.

Dusty‐metal‐bearing olivine grains, which are widely interpreted to have escaped melting during chondrule formation, contain moderate densities of dislocations (∼ 108 cm−2). The dislocations in these grains were introduced before or during the last episode of melting in at least one chondrule. This observation can be explained if olivine was impact‐deformed before or during chondrule formation, or if olivine was strained by reduction or thermally‐induced processes during chondrule formation.

Low‐Ca pyroxene grains in chondrules are often strained. In most cases this strain probably arose as a by‐product of polytype transformations (protoenstatite → clinoenstatite/orthoenstatite and clinoenstatite → orthoenstatite) that occurred during the igneous crystallization and static annealing of chondrules.

Droplet chondrules with glassy mesostases were minimally annealed, consistent with an origin as relatively rapidly cooled objects in an unconfined, cold environment. Some irregular chondrules and at least one droplet chondrule were thermally metamorphosed prior to final agglomeration, either as a result of moderately slow cooling (∼ 100 °C/hr) from melt temperatures (during autometamorphism) or as a result of reheating episodes. Two of the most annealed chondrules contain relatively abundant plagioclase feldspar, and one of these has a uniform olivine composition appropriate to that of an LL4 chondrite.
Alkali (Rb/K) abundances in Allende barred‐olivine chondrules: Implications for the melting conditions of chondrules
Authors: Matsuda Hitoshi , Nakamura Noboru , Noda Shinji
Published: June 2012

Abstract— In order to study abundances of alkali metals in chondrules, 25 petrographically characterized chondrules, including 18 barred olivine (BO) chondrules from the Allende (CV3) meteorite, were analyzed for alkalis (K and Rb) and alkaline earths (Sr, Ba, Ca and Mg) by mass spectrometric isotope dilution.

Most BO chondrules with higher alkalis (>CI level) have nearly CI‐chondritic Rb/K ratios, while those with lower alkalis clearly show higher Rb/K ratios than the CI‐chondritic. In general, BO chondrules with higher Rb/K exhibit more depletion of alkalis relative to Ca. The mean olivine Fa for individual chondrules positively correlates with bulk alkali concentrations in BO type but not in porphyritic type chondrules. These observations suggest that some BO chondrules formed from more reducing assemblages of precursor minerals, which experienced more intensive vaporization losses of alkalis, accompanied by Rb/K fractionation, during the chondrule‐formation melting.
Lake Machattie, a weathered H5 chondrite find from Queensland, Australia
Authors: McCoy T. J. , Keil Klaus
Published: June 2012

Abstract— Lake Machattie is an H5a chondrite find. The 2.6‐kg stone is heavily weathered; unoxidized metal occurs only as 10‐μm‐size blebs enclosed in olivine.
Salts in two chondritic porous interplanetary dust particles
Authors: Rietmeijer Frans J. M.
Published: June 2012

Abstract— Grain‐by‐grain analytical electron microscope analyses of two micrometeorites, or interplanetary dust particles (IDPs), of the chondritic porous subtype, show the presence of rare barite (BaSO4) and magnesium carbonate, probably magnesite. Salt minerals in chondritic porous (CP) IDPs give evidence for in situ aqueous alteration in their parent bodies. The uniquely high barium content of CP IDP W7029*C1 is consistent with barite precipitation from a mildly acidic (pH > ∼5) aqueous fluid at temperatures below 417 K and low oxygen fugacity. The presence of magnesite in olivine‐rich, anhydrous CP IDP W7010*A2 is evidence that carbonate minerals occur in both the chondritic porous and chondritic smooth subtypes of chondritic IDPs. Citing Schramm et al. (1989) for putative asteroidal‐type aqueous alteration in IDPs and probable sources of chondritic IDPs, salt minerals in CP IDPs could support low‐temperature aqueous activity in nuclei of active short‐period comets.
Search for solar‐type nitrogen in the gas‐rich Pesyanoe meteorite
Authors: Murty S. V. S. , Marti K.
Published: June 2012

Abstract— We report nitrogen isotopic data obtained from a stepwise gas release of two grain‐size fractions of the gas‐rich meteorite Pesyanoe. Cosmic‐ray‐produced 15Nc may be present in all temperature steps ≥600 °C, and we correct this component using spallation 21Ne data. The resulting ratios reveal the presence of more than one trapped N component. Indigenous N is released above 1000 °C with an isotopic signature of δ15N = −33‰. This is consistent with the rather uniform signatures of indigenous nitrogen in enstatite meteorites. There is no evidence for the presence of “very light” N of δ15N ≅ −200‰. On the other hand, a “heavy” nitrogen component appears in the temperature range 700–800 °C, and coincides with a major release of solar‐type noble gases. For a two‐component mixture, the isotopic shifts in this temperature range define a lower limit δ15Ncorr = −6‰ for the second component (e.g., solar‐type nitrogen). However, for the case of a solar‐type component, the calculated δ15N signature depends on the adopted elemental abundances. For example, adoption of the relative abundances of 14N and noble gases in lunar ilmenite 71501 yields δ15N ≅ +170, which is in the range of the heavier nitrogen signatures observed on the lunar surface.
The Iguaraçu H5 chondrite: a fall from Paraná State, Brazil
Authors: Brooks R. R. , Hoashi M. , de Lima E. Fernandes , dos Santos M. L. , Ryan D. E. , Holzbecher J. , Johnston J. H. , Kawachi Y. , Sipiera P. P.
Published: June 2012

Abstract— The Iguaraçu meteorite, a single stone of 1200 g, fell in Paraná State, Brazil in October 1977. It is classified as an H5 ordinary chondrite with olivine of composition Fa 18.7.
The histories of ordinary chondrite parent bodies: U,Th‐He age distributions
Authors: Wasson John T. , Wang Sichao
Published: June 2012

Abstract— Age patterns observed in meteorite groups reflect the different thermal or impact histories experienced by their parent bodies. To assess the number of ordinary chondrite (OC) parent bodies rare‐gas data in the Schultz and Kruse (1989) data base were used to calculate U,Th‐He gas‐retention ages. Most H‐ and LL‐chondrite ages are high; ∼81% are >2.2 Ga. In contrast, most L‐chondrite ages are low; ∼69% are ≤2.2 Ga, and ∼35% are ≤0.9 Ga. The latter fraction is substantially lower than the value of 44% given by Heymann (1967). The difference is attributed to the preferential inclusion of shocked L chondrites in early studies. Broad age peaks in the H and LL groups near 3.4 Ga probably reflect thermal loss during metamorphism, but in the H distribution there is a hint of minor outgassing “events” near 1 Ga. The L/LL chondrites have chemical properties intermediate between and unresolvable from L and LL chondrites. The high ages of most L/LL chondrites are evidence against these originating on the L parent body; the L/LL age distribution is consistent with an origin on the LL parent body or on an independent body.
Isotopic signatures of black tektites from the K‐T boundary on Haiti: Implications for the age and type of source material
Authors: Premo W. R. , Izett G. A.
Published: June 2012

Abstract— U‐Th‐Pb, Rb‐Sr, and Sm‐Nd isotopic signatures of corroded, but unaltered, black glassy tektites from Cretaceous‐Tertiary (K‐T) boundary rock on Haiti are not consistent with their derivation from an impact on MOR‐derived oceanic crust or continental regions involving middle Proterozoic or older crustal material. Two single‐grain and two batches of these tektites yielded present‐day ∍Nd = −3.0 to −3.4, ∍Sr = +55 to 56, 206Pb/204Pb = 18.97; 207Pb/204Pb = 15.74; 208Pb/204Pb = 38.91 values, and Pb, Rb, Sr, Sm, and Nd concentrations of ∼6, ∼45, ∼535, ∼4.7, and ∼22 ppm, respectively. Initial ∍Nd and ∍Sr values for the tektites are different from time‐integrated Nd‐Sr isotopic signatures for almost all oceanic crustal types. Age‐corrected Pb isotopic values are similar to those for pelagic sediments with distinctly higher 207Pb/204Pb values compared to MORB. However, these results do not exclude the possibility of an oceanic impact site, if the tektites were derived from fine‐grained sediments that typically overlie such regions, although other mineralogic and chemical evidence from K‐T boundary debris suggests otherwise. Moreover, the Nd average crustal residence age of ∼ 1080 Ma (TDM) for the black tektites eliminates impact sites on continental crustal regions involving middle Proterozoic or older rocks, or sedimentary rocks largely derived from them.

Previously reported major and trace element data from the black tektites suggest that the source material was possibly sedimentary with a composition similar to average shale or graywacke. If this is the case, then the Nd isotopic data suggest that the source rocks were not older than Silurian (TCHUR = 400 Ma) in age, and were composed largely of young (< 1080 Ma) crustal material. Of the suspected K‐T boundary impact sites, both the Manson (Iowa) and Chicxulub (Yucatan) structures occur in suitable lithologies to yield the Haitian black tektites, although neither structure has as yet proven to be the tektite source.
The age of the meteorite recovery surfaces of Roosevelt County, New Mexico, USA
Authors: Zolensky Michael E. , Rendell Helen M. , Wilson Ivan , Wells Gordon L.
Published: June 2012

Abstract— We have obtained minimum age estimates for the sand units underlying the two largest meteorite deflation surfaces in Roosevelt County, New Mexico, USA, using thermoluminescence dating techniques. The dates obtained ranged from 53.5 (±5.4) to 95.2 (±9.5) ka, and must be considered lower limits for the terrestrial ages of the meteorites found within these specific deflation surfaces. These ages greatly exceed previous measurements from adjacent meteorite‐producing deflation basins. We find that Roosevelt County meteorites are probably terrestrial contemporaries of the meteorites found at most accumulation zones in Antarctica. The apparent high meteorite accumulation rate reported for Roosevelt County by Zolensky et al. (1990) is incorrect, as it used an age of 16 ka for all Roosevelt County recovery surfaces. We conclude that the extreme variability of terrestrial ages of the Roosevelt County deflation surfaces effectively precludes their use for calculations of the meteorite accumulation rate at the Earth's surface.
Na‐bearing Ca‐Al‐rich inclusions in the Yamato‐791717 CO carbonaceous chondrite
Authors: Tomeoka Kazushige , Nomura Koji , Takeda Hiroshi
Published: June 2012

Abstract Ca‐Al‐rich inclusions (CAIs) in the Yamato‐791717 CO carbonaceous chondrite contain 5 to 80 vol% of nepheline, along with minor sodalite, and thus are among the most nepheline‐rich CAIs known. The primary phases in inclusions are mainly spinel, fassaite, aluminous diopside, perovskite, and hibonite. In contrast to many CO chondrites, melilite is rare. Spinel contains variable amounts of Fe (0 to 57 mol% FeAl2O4) and is commonly zoned. Texture suggests that nepheline is a secondary alteration product formed by replacing mainly melilite, fassaite, and spinel; melilite is the most susceptible to alteration of the primary phases, so most of it was probably already consumed to form nepheline. The majority of inclusions are single concentric objects or aggregates of concentric objects. Lightly altered inclusions have cores of spinel surrounded by bands of nepheline (replacing fassaite), fassaite, and diopside. In moderately altered inclusions, spinel cores are replaced by nepheline. In heavily altered inclusions, the major part of internal areas (50 to 80% in volume) are replaced by nepheline. In some moderately and heavily altered inclusions, only diopside rims remain unaltered. Textural relationships indicate that the resistance of primary phases to alteration increases in the order melilite, fassaite, spinel, diopside. The alteration probably proceeded with reaction of the primary phases with the low‐temperature (≤ 1000 K) nebular gas rich in Na, Fe and CI. The degree of alteration in Y791717 CAIs appears to be much higher than those in CAIs in other reported meteorites.
The Melnikovo LL6 chondrite: A new find from Ukraine
Authors: Krot A. N. , Zaslavskaya N. I. , Petaev M. I. , Kononkova N. N. , Barsukova L. D. , Kolesov G. M.
Published: June 2012

Abstract Melnikovo is a relatively unweathered 545.6‐g LL6 chondrite that was found in 1983. Only a few poorly defined chondrules are discernable in the examined sections; two of these are enriched in chromite. The meteorite contains olivine (Fa27,8), low‐Ca pyroxene (Fs24,4), plagioclase, rare clinopyroxene, chlorapatite, merrillite and opaque minerals, which have a modal abundance (in wt%) of troilite (3.9%), kamacite (0.4%), taenite plus tetrataenite (0.7%), chromite (0.8%), and trace amounts of ilmenite and Mn‐ilmenite. The meteorite appears unbrecciated on a centimeter scale.
A survey of Rb‐Sr systematics of eucrites
Authors: Smoliar M. I.
Published: June 2012

Abstract— This paper surveys the experimental material on the Rb‐Sr systematics of eucrites accumulated in the literature for the last two decades. Among the meteorites studied, those representatives have been chosen for which the absence of disturbances of isotope systems seems reliably fixed (according to evidence from Rb‐Sr, Sm‐Nd, and U‐Pb isotope data). These data have been subjected to joint statistical treatment. For ordinary eucrites the age has been estimated as T = 4.548 ± 0.058 Ga, and initial Sr isotope ratio, Iord = 0.698925 ± 14. For cumulate eucrites, the initial Sr isotope ratio has been estimated as Icum = 0.698872 ± 14. The substantial difference in initial Sr isotope composition suggests that those two eucrite groups originate from distinct parent bodies.

Joint treatment of the available Rb‐Sr data for angrites has been carried out for comparison, and the angrites initial Sr ratio has been estimated. On the basis of the estimates obtained formation intervals for the corresponding parent bodies have been calculated.
Classification of five new ordinary chondrites (RC 073, 074, 076–078) from Roosevelt County, New Mexico
Authors: McCoy Timothy J. , Keil Klaus , Wilson Ivan E.
Published: June 2012

Abstract— Five new ordinary chondrites from Roosevelt County, New Mexico, USA, have been assigned to a chemical group, petrologic type and shock stage. All five are moderately to heavily weathered. They are: RC 073, H5(S2); RC 074, L5(S3); RC 076, L4(S3); RC 077, L4(S2); RC 078, L4(S2).
The Julesburg (L3) meteorite
Authors: Graham A. L.
Published: June 2012

Abstract— The Julesburg chondrite, a single stone weighing 57.9 kg, was found in 1983 in Sedgewick County, Colorado, USA. It contains abundant chondrules and chondrule fragments but little fine‐grained matrix. The olivine composition ranges from Fa1 to Fa25 but a frequency plot of olivine compositions is strongly peaked at Fa23. The low‐Ca pyroxenes range from Fs3 to Fs28 and show no dominant composition. The abundance of clearly defined chondrules, the heterogeneity of the silicates and the presence of glass within chondrules indicate a type 3 chondrite, refined by thermoluminescence data to 3.6. The total iron content of 20.46% is indicative of an L‐group stone. The low noble gas retention ages indicate that this meteorite was outgassed late in its history. This is supported by petrographic evidence of brecciation and shock. Aluminum‐rich spinels within chondrules and inclusions contain up to 2.6% ZnO which suggests that they formed in a volatile‐rich environment.
Magombedze: A new H‐chondrite with light‐dark structure
Authors: MacPherson Glenn J. , Jarosewich Eugene , Lowenstein Peter
Published: June 2012

Abstract— Magombedze is a light‐dark structured H‐chondrite breccia that fell in Zimbabwe on 1990 July 2 at 15:30 GMT. White clasts are moderately shocked and have equilibrated mafic silicates (pyroxene Fs16–18, olivine Fa18–19) together with clear optically‐recognizable plagioclase of variable composition (An9–13 found); chondrules are distinct but contain no trace of preserved glass. The darker surrounding material contains a higher proportion of fine‐grained metal and sulfide than the white clasts, and many of its constituent grains show little evidence of shock. Mafic silicates in the dark lithology are distinctly less‐equilibrated (pyroxene Fs5–21, olivine Fa11–20) than those in the white clasts, and many chondrules preserve brown devitrified glass; some metamorphic plagioclase of variable composition (An11–22, found) is present. Some monoclinic pyroxene occurs in both fractions, but it is relatively common in the dark fraction. The white clasts are classified as H5, and the enclosing dark material is H3–5.
The Meteoritical Bulletin, No. 74, 1993 March.*
Authors: Wlotzka Frank
Published: June 2012

Abstract— The Meteoritical Bulletin, Number 74, contains listings for 190 meteorites, including 112 from North Africa, 63 from Antarctica and eight from Australia and six from the U.S. Among the meteorites described are 15 type 3 ordinary chondrites, most notably Roosevelt County 075 which is the lowest petrologic type H chondrite known to date, two very similar ureilites (Nova 1 and Nullarbor 010), a howardite (Old Homestead 001), a CK3 chondrite (Camel Donga 003), a CV3 chondrite (Denman 002) and a major new CR chondrite (Acfer 311 and 10 meteorites with which it is paired).
The age of the Roter Kamm impact crater, Namibia: Constraints from 40Ar‐39Ar, K‐Ar, Rb‐Sr, fission track, and 10Be‐26Al studies
Authors: Koeberl Christian , Hartung Jack B. , Kunk Michael J. , Klein Jeffrey , Matsuda Jun‐Ichi , Nagao Keisuke , Reimold Wolf Uwe , Storzer Dieter
Published: June 2012

Abstract The well‐preserved 2.5 km diameter Roter Kamm impact crater is located in the Namib desert in Namibia. The impact has occurred in Precambrian granitic and granodioritic orthogneisses of the 1200–900 Ma old Namaqualand Metamorphic Complex which were partly covered by Gariep metasediments; the granites are invaded by quartz veins and quartz‐feldspar‐pegmatites. Previous geological field evidence suggested a crater age of about 5–10 Ma. In order to constrain this age, we selected a set of basement rocks (granites, granodiorites) exposed at the crater rim and studied the Rb‐Sr, K‐Ar, 40Ar‐39Ar, and 10Be‐26Al isotopic systems as well as apatite fission track ages of these samples. The Rb‐Sr isotopic systematics confirm the derivation of these samples from the Namaqualand basement (age about 1.29 Ga), which underwent Damaran orogenesis at about 650 Ma. No basement rocks with Rb‐Sr ages younger than about 410 Ma were identified. The K‐Ar ages of pseudotachylite and melt breccia samples show that these samples are dominated by incompletely degassed fragments of basement rocks, with some retaining their original metamorphic ages of about 470 Ma. The apatite fission track ages range from 20–28 Ma, which may be interpreted as an extension of the 25 Ma Burdigalian peneplanation event, or as incomplete resetting of the apatite fission tracks during the impact event. The 10Be and 26Al exposure age of a quartz sample isolated from a quartz‐pegmatite was found to be 150 ka; it is likely that the exposure of the sample began after material covering it had been removed by erosion 150 ka ago. Two glassy fractions extracted from a rim granite were dated by 40Ar‐39Ar analysis. One sample gives practically a plateau age of 3.7 ± 0.3 Ma, while the other gives a minimum age of 3.6 Ma. The best available age estimate for the Roter Kamm crater is therefore 3.7 ± 0.3 Ma.
Fall and recovery of the Noblesville (Indiana, U.S.A.) H chondrite
Authors: Lipschutz Michael E. , Spaulding Brodie , Kinzie Brian D. , Gartenhaus Solomon
Published: June 2012

Abstract We describe the circumstances of fall of a 0.5‐kg meteorite that landed in Noblesville, Indiana, USA, 3.6 m in front of two witnesses on 1991 August 31. Provisional assessment of Noblesville as an H chondrite is confirmed by data reported elsewhere which demonstrate that it is a regolith breccia with unusual properties.
Geophysical signature of the Pretoria Saltpan impact structure and a possible satellite crater
Authors: Brandt Dion , Reimold Wolf Uwe , Durrheim Raymond J.
Published: June 2012

Abstract— The genesis of the 1.13‐km‐diameter Pretoria Saltpan crater has long been the focus of a controversy. Its origin has been explained by either meteorite impact or “cryptoexplosive” volcanic activity, but it was recently confirmed, through detailed petrographic and chemical analysis of a breccia layer forming part of the crater fill, that the crater was formed by impact. As the limited previous geophysical work failed to support an impact origin, a more detailed gravity and magnetic study was conducted. A possible 400‐m‐diameter circular crater located 3 km to the southwest of the main crater was also investigated with geophysical methods, including resistivity, seismics and ground‐probing radar. The gravity signature of the main crater is compatible with that of a simple impact crater and the magnetic signature (no magnetic anomaly could be detected) rules out the possibility of a central magnetic volcanic body below the crater‐fill sediments. The results for the possible twin or satellite crater are inconclusive. As it is the only such feature in the entire region, it should not be overlooked. A drilling program may reveal interesting results.
Fractional crystallization of iron meteorites: Constant versus changing partition coefficients
Authors: Jones J. H.
Published: June 2012

Abstract— Analyses of magmatic iron meteorites, plotted on LogCi vs. LogCNi diagrams, often form linear arrays. Traditionally, this linearity has been ascribed to fractional crystallization under the assumption of constant partition coefficients (i.e., Rayleigh fractionation). Paradoxically, however, partition coefficients in the Fe‐Ni‐S‐P system are decidedly not constant. This contribution provides a rationale for understanding how trends on LogCi vs. LogCNi diagrams can be linear, even when partition coefficients are changing rapidly.
The Cretaceous‐Tertiary fireball layer, ejecta layer and coal seam: Platinum‐group element content and mineralogy of size fractions
Authors: Evans Noreen Joyce , Gregoire D. Conrad , Goodfellow Wayne D. , Miles Norman , Veizer Ján
Published: June 2012

Abstract— Grain size separates of the Cretaceous‐Tertiary (K‐T) fireball layer at marine sites and the entire K‐T boundary interval at nonmarine sites (fireball layer, ejecta layer, coal seam) were analysed for platinum‐group elements (PGE: Ru, Ir, Ft, Pd, Rh) and Au using inductively coupled plasma mass‐spectrometry. X‐ray diffractometry and scanning electron microscopy were performed on each fraction to establish the mineralogy. It was determined that the most abundant minerals in the finest fraction were a smectite‐group mineral at marine K‐T sites and illite‐smectite mixed layer clay at nonmarine K‐T sites. Positive correlation of PGE content and mineralogy indicates that the PGE are presently associated with these clay minerals which were likely formed by alteration of a condensed mafic phase (e.g., olivine or pyroxene). The correlation of clay mineral abundance with PGE content is imperfect because not all of the clay minerals in the fireball layer are derived by alteration of the original condensed ejecta. In addition, undetected PGE host(s), present in trace amounts, are likely also present.
The Bison LL6 breccia
Authors: Dominik B. , Bussy F.
Published: June 2012

Abstract— Bison LL6 chondrite is an impact breccia. The meteorite consists of unmolten clasts and accessory melt‐breccia clasts incorporated into a host of the same parentage.
Pecora Escarpment 91002: A member of the new Rumuruti (R) chondrite group
Authors: Rubin Alan E. , Kallemeyn Gregory W.
Published: June 2012

Abstract— Pecora Escarpment (PCA)91002 is a light/dark‐structured chondrite breccia related to Carlisle Lakes and Rumuruti; the meteorite contains ∼10–20 vol% equilibrated (type −5 and −6) clasts within a clastic groundmass, much of which was metamorphosed to type‐3.8 levels. The olivine compositional distribution forms a tight cluster that peaks at Fa38–40; by contrast, low‐Ca pyroxene compositions are highly variable. Opaque phases identified in PCA91002 and its paired specimen, PCA91241, include pyrrhotite, pentlandite, pyrite, chromite, ilmenite, metallic Cu and magnetite. The majority of the rock is of shock stage S3‐S4; there are numerous sulfide‐rich shock veins and 50‐μm plagioclase melt pockets. Instrumental neutron activation analysis shows that, unlike Carlisle Lakes and ALH85151, PCA91002 exhibits no Ca enrichment or Au depletion; because PCA91002 is relatively unweathered, it seems probable that the Ca and Au fractionations in Carlisle Lakes and ALH85151 were caused by terrestrial alteration.

The Rumuruti‐like (formerly Carlisle‐Lakes‐like) chondrites now include eight separate meteorites. Their geochemical and petrographic similarities suggest that they constitute a distinct chondrite group characterized by unfractionated refractory lithophile abundances (0.95 ± 0.05x CI), high bulk Δ17O, a low chondrule/groundmass modal abundance ratio, mean chondrule diameters in the 400 ± 100 μm range, abundant NiO‐bearing ferroan olivine, sodic plagioclase, titanian chromite, abundant pyrrhotite and pentlandite and negligible metallic Fe‐Ni. We propose that this group be called R chondrites after Rumuruti, the only fall.

The abundant NiO‐bearing ferroan olivine grains, the occurrence of Cu‐bearing sulfide, and the paucity of metallic Fe‐Ni indicate that R chondrites are highly oxidized. It is unlikely that appreciable oxidation took place on the parent body because of the essential lack of plausible oxidizing agents (e.g., magnetite or hydrated silicates). Therefore, oxidation of R chondrite material must have occurred in the nebula. A few type‐I porphyritic olivine chondrules containing olivine grains with cores of Fa3–4 composition occur in PCA91002; these chondrules probably formed initially as metallic‐Fe‐Ni‐bearing objects at high nebular temperatures. As temperatures decreased and more metallic Fe was oxidized, these chondrules accreted small amounts of oxidized material and were remelted. The ferroan compositions of the >5‐μm olivine grains in the R chondrites reflect equilibration with fine‐grained FeO‐rich matrix material during parent body metatnorphism.
On unfractionated solar noble gases in the H3–6 meteorite Acfer 111
Authors: Pedroni A. , Begemann F.
Published: June 2012

Abstract Solar noble gases He, Ne, Ar and Kr implanted in the H3–6 meteorite regolith breccia Acfer 111 agree in their elemental composition with that in present‐day solar wind and, except for a 25% deficit of 4He, also with adopted solar abundances. The presence of such unfractionated solar gases makes Acfer 111 unique (until now). Closed system stepped etching releases noble gases that can be explained as mixtures of two distinct types of He, Ne, and Kr of isotopic compositions as they have been derived previously from meteorites and lunar samples that contain heavily fractionated solar gases. Since the same putative end members, ascribed to the solar wind (SW) and supra‐thermal solar energetic particles (SEP), are also present in Acfer 111, we argue that these end members represent two truly independent components. We discount the possibility that one isotopic composition derived from the other by diffusion of the gases within, or upon their release from, their host phases. The isotopic signatures of noble gases in Acfer 111 agree with those in a lunar ilmenite of young antiquity ≅100 Ma) but are in disagreement with the noble gases in lunar ilmenite 79035 of 1–2 Ga antiquity. Systematic changes are discussed of the nuclide abundance ratios as etching proceeds; they are ascribed to differences in trapping efficiency and in penetration depth of the different noble gas ion species upon their implantation.
Fractionation of nitrogen isotopes in solar energetic particles
Authors: Bochsler Peter , Kallenbach Reinald
Published: June 2012

Abstract In a further step to assess processes leading to the complicated secular trend of the isotopic composition of N implanted in lunar regolith, we investigate mechanisms fractionating solar energetic particles (SEPs). We conclude that such mechanisms are likely to occur, most probably producing an enrichment of 15N over 14N in SEPs over the photospheric abundance ratio. Simultaneously, 22Ne is enriched over 20Ne but to a lesser extent. An enrichment of the heavy Ne isotope is observed in the suprathermal solar particles, implanted in the lunar regolith. Hence, the now well‐established difference between the isotopic composition of suprathermal Ne and solar wind Ne in the lunar regolith might be taken as evidence for the validity of this model. The present‐day fluxes of energetic particles produced in impulsive flare events, capable to produce such isotopic fractionations are, however, orders of magnitude below the required amounts to explain the lunar observations. The details of the secular variation of the N isotopic composition remain an enigma.
Alteration of calcium‐ and aluminium‐rich inclusions in the Murray (CM2) carbonaceous chondrite
Authors: Lee Martin R. , Greenwood Richard C.
Published: June 2012

Abstract— Four different types of calcium‐ and aluminium‐rich inclusions (CAIs) have been identified in the CM2 chondrite Murray, three of which contain alteration products. Two types of altered CAIs, spinel inclusions and spinel‐pyroxene inclusions, contain primary spinel (± perovskite ± hibonite ± diopside) and secondary Fe‐rich serpentine phyllosilicates (± tochilinite ± calcite). Original melilite in these CAIs is inferred to have been altered during aqueous activity in the parent body and Fe‐rich serpentines, tochilinite and calcite were formed in its place.

The other type of altered CAI is represented by one inclusion, here called MCA‐1. This CAI contains primary spinel, perovskite, fassaite and diopside with secondary calcite, paragonite, Mg‐Al‐Fe phyllosilicates and a Mg‐Al‐Fe sulphate. Importantly, MCA‐1 is similar in both primary and secondary mineralogy to a small number of altered CAIs described from other CM2 meteorites including Essebi, Murchison and a CM2 clast from Plainview. Features that these CAIs have in common include an unusually large size, a CV3‐like primary mineralogy and the presence of secondary aluminosilicates and calcite. The Al‐rich alteration products in MCA‐1 are also reminiscent of secondary minerals in refractory inclusions from CV3 meteorites, which have previously been interpreted to form by interaction of the inclusions with solar nebula gases. In common with the other types of altered CAIs in Murray, MCA‐1 is inferred to have experienced its main phase of alteration in a parent body environment. The Mg‐Al‐Fe phyllosilicates, calcite and the Mg‐Al‐Fe sulphate formed following aqueous alteration of an Al‐rich precursor, possibly Ca dialuminate. This episode of parent body alteration may have overprinted an earlier phase of alteration in a solar nebula environment from which only paragonite remains.
Noble gases in presolar diamonds I: Three distinct components and their implications for diamond origins
Authors: Huss Gary R. , Lewis Roy S.
Published: June 2012

Abstract— High‐purity separates of presolar diamond were prepared from 14 primitive chondrites from 7 compositional groups. Their noble gases were measured using stepped pyrolysis. Three distinct noble gas components are present in diamonds, HL, P3, and P6, each of which is found to consist of five noble gases. P3, released between 200 °C and 900 °C, has a “planetary” elemental abundance pattern and roughly “normal” isotopic ratios. HL, consisting of isotopically anomalous Xe‐HL and Kr‐H, Ar with high 38Ar/36Ar, and most of the gas making up Ne‐A2 and He‐A, is released between 1100 °C and 1600 °C. HL has “planetary” elemental ratios, except that it has much more He and Ne than other known “planetary” components. HL gases are carried in the bulk diamonds, not in some trace phase. P6 has a slightly higher median release temperature than HL and is not cleanly separated from HL by stepped pyrolysis. Our data suggest that P6 has roughly “normal” isotopic compositions and “planetary” elemental ratios. Both P3 and P6 seem to be isotopically distinct from P1, the dominant “planetary” noble‐gas component in primitive chondrites. Release characteristics suggest that HL and P6 are sited in different carriers within the diamond fractions, while P3 may be sited near the surfaces of the diamonds.

We find no evidence of separability of Xe‐H and Xe‐L or other isotopic variations in the HL component. However, because ∼1010 diamonds are required to measure a Xe composition, a lack of isotopic variability does not constrain diamonds to come from a single source. In fact, the high abundance of diamonds in primitive chondrites and the presence of at least three distinct noble‐gas components strongly suggest that diamonds originated in many sources. Relative abundances of noble‐gas components in diamonds correlate with degree of thermal processing (see companion paper), indicating that all meteorites sampled essentially the same mixture of diamonds. That mixture was probably inherited from the Sun's parent molecular cloud.
Mineralogy of new Antarctic achondrites with affinity to Lodran and a model of their evolution in an asteroid
Authors: Takeda Hiroshi , Mori Hiroshi , Hiroi Takahiro , Saito Jun
Published: June 2012

Abstract—We studied five new Antarctic achondrites, MacAlpine Hills (MAC) 88177, Yamato (Y)74357, Y75274, Y791491 and Elephant Moraine (EET)84302 by mineralogical techniques to gain a better understanding of the mineral assemblages of a group of meteorites with an affinity to Lodran (stony‐iron meteorite) and their formation processes. This group is being called lodranites. These meteorites contain major coarse‐grained orthopyroxene (Opx) and olivine as in Lodran and variable amounts of FeNi metal and troilite etc. MAC88177 has more augite and less FeNi than Lodran; Y74357 has more olivine and contains minor augite; Y791491 contains in addition plagioclase. EET84302 has an Acapulco‐like chondritic mineral assembladge and is enriched in FeNi metal and plagioclase, but one part is enriched in Opx and chromite. The EET84302 and MAC88177 Opx crystals have dusty cores as in Acapulco. EET84302 and Y75274 are more Mg‐rich than other members of the lodranite group, and Y74357 is intermediate. Since these meteorites all have coarse‐grained textures, similar major mineral assemblages, variable amounts of augite, plagioclase, FeNi metal, chromite and olivine, we suggest that they are related and are linked to a parent body with modified chondritic compositions. The variability of the abundances of these minerals are in line with a proposed model of the surface mineral assemblages of the S asteroids. The mineral assemblages can best be explained by differing degrees of loss or movements of lower temperature partial melts and recrystallization, and reduction. A portion of EET84302 rich in metal and plagioclase may represent a type of component removed from the lodranite group meteorites. Y791058 and Caddo County, which were studied for comparison, are plagioclase‐rich silicate inclusions in IAB iron meteorites and may have been derived by a similar process but in a different body.
Infrared diffuse reflectance spectra of carbonaceous chondrites: Amount of hydrous minerals
Authors: Miyamoto M. , Zolensky M. E.
Published: June 2012

Abstract— Infrared diffuse reflectance spectra (2.53–25 μm) of some carbonaceous (C) chondrites were measured. The integrated intensity of the absorption bands near 3 μm caused by hydrous minerals were compared with the modal content of hydrous minerals for the meteorites. The CM and CI chondrites show larger values of the integrated intensity than those of the unique C chondrites Y82162, Y86720 and B7904, suggesting that the amount of hydrous minerals in the CM and CI chondrites is larger, which supports the contention that hydrous minerals were dehydrated by thermal metamorphism in the unique chondrites. Orgueil (CI) has the largest value of the integrated intensity among the C chondrites we measured and shows a sharp absorption band at 3685 cm−1 (2.71 μm) that is not seen in the spectra of the CM chondrites. There is an excellent correlation between the observed hydrogen content in C chondrites and the integrated intensity. The CM chondrites show a wide variation in the strength of absorption bands at 1470 cm−1 (6.8 μm), despite the similarity in absorption features near 3 μm for all CM chondrites. The 1470 cm−1 band could be due to the presence of some hydrocarbons but may also be a result of terrestrial alteration processes.
Comment on “Fractional crystallization of iron meteorites: Constant versus changing partition coefficients” by J. H. Jones
Authors: Morgan John W.
Published: June 2012

Abstract— Jones (1994) demonstrated that fractional crystallization of IIIAB iron meteorites may result in a log Au vs. log Ni plot of constant slope even though kAu and kNi change. Jones' example is a special case, however, and does not necessarily describe behavior by other elements or in other metallic magmas.
The distribution of aluminum‐26 in the early Solar System—A reappraisal
Authors: MacPherson Glenn J. , Davis Andrew M. , Zinner Ernst K.
Published: June 2012

Abstract— A compilation of over 1500 Mg‐isotopic analyses of Al‐rich material from primitive solar system matter (meteorites) shows clearly that 26Al existed live in the early Solar System. Excesses of 26Mg observed in refractory inclusions are not the result of mixing of “fossil” interstellar 26Mg with normal solar system Mg. Some material was present that contained little or no 26Al, but it was a minor component of solar system matter in the region where CV3 and CO3 carbonaceous chondrites accreted and probably was a minor component in the accretion regions of CM chondrites as well. Data for other chondrite groups are too scanty to make similar statements. The implied long individual nebular histories of CAIs and the apparent gap of one or more million years between the start of CAI formation and the start of chondrule formation require the action of some nebular mechanism that prevented the CAIs from drifting into the Sun. Deciding whether 26Al was or was not the agent of heating that caused melting in the achondrite parent bodies hinges less on its widespread abundance in the nebula than it does on the timing of planetesimal accretion relative to the formation of the CAIs.