bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Torino, H6, meteorite shower
Authors: Bhandari N. , Bonino G. , Callegari E. , Castagnoli G. Cini , Mathew K. J. , Padia J. T. , Queirazza G. 
Published: June 2012

Abstract— A meteorite shower fell at Torino, Italy on 18 May 1988. Petrographic studies indicate that the stone is an H6 chondrite having features of moderate to severe shock. Chemical analyses of the meteorite are reported. Cosmic ray produced 3He, 21Ne and 126Xe yield an exposure age of about 48 Ma. The cosmic ray track densities in three fragments range between 1.8 to 5 × 105/cm2 suggesting about 99% mass ablation in the atmosphere.Twelve radioisotopes with half lives ranging between 5.6 days to 7.3 × 105 years have been measured with high precision (2 to 10%). Marginal signals were observed for several short‐lived nuclides and upper limits were obtained for the activity levels of eight radionuclides (24Na, 48Cr, 57Ni, 47Sc, 47Ca, 59Fe, 42Ar and 44Ti) some of which have not been hitherto detected in fresh falls. The data are generally consistent with the nuclide production by galactic cosmic rays when modulation due to the solar cycle is taken into consideration.The preatmospheric radius of the chondrite is estimated to be 20 cm, consistent with track densities and activity levels of 60Co, 26Al and other radionuclides.
The typical meteorite event, based on photographic records of 44 fireballs
Authors: Halliday Ian , Blackwell Alan T. , Griffin Arthur A. 
Published: June 2012

Abstract— We study the observational data relating to 44 events recorded by the Canadian fireball camera network between 1971 and 1984. Each event is believed to have dropped meteorites, with main masses in the range from 0.1 to 11 kg. Median values are given for 20 parameters describing the atmospheric behavior and orbital elements. A typical duration for a meteoritic fireball is 4 seconds, reaching an end height of 31 km and a velocity of 8 km s−1 at the end of the luminous path. The peak brightness is typically −9 magnitude but varies from −7 to −15. Meteorites may survive from relatively unspectacular fireballs.Numerous correlations among parameters are investigated. The strong correlations of brightness with initial mass and of duration with slope of the trajectory could be anticipated. Moderate correlations also exist between: (1) initial mass and end height; (2) initial mass and duration of luminosity; (3) initial velocity and beginning height; (4) initial velocity and the fraction of the mass that survives as the largest fragment; (5) initial velocity and the perihelion distance of the orbit. Ablation limits the survival of small masses while fragmentation is usually severe for masses larger than 10 kg. The fractional survival may peak for entry masses between 1 and 10 kg.
The accumulation rate of meteorite falls at the Earth's surface: The view from Roosevelt County, New Mexico
Authors: Zolensky Michael E. , Wells Gordon L. , Rendell Helen M. 
Published: June 2012

Abstract— The discovery of 154 meteorite fragments within an 11 km2 area of wind‐excavated basins in Roosevelt County, New Mexico, permits a new calculation of the accumulation rate of meteorite falls at the Earth's surface.Thermoluminescence dating of the coversand unit comprising the prime recovery surface suggests the maximum terrestrial age of the meteorites to be about 16.0 ka. The 68 meteorite fragments subjected to petrological analyses represent a minimum of 49 individual falls. Collection bias has largely excluded carbonaceous chondrites and achondrites, requiring the accumulation rate derived from the recovered samples to be increased by a factor of 1.25. Terrestrial weathering destroying ordinary chondrites can be modelled as a first‐order decay process with an estimated half‐life of 3.5 ± 1.9 ka on the semiarid American High Plains. Having accounted for the age of the recovery surface, area of field searches, pairing of finds, collection bias and weathering half‐life, we calculate an accumulation rate of 9.4 × 102 falls/a per 106 km2 for falls > 10 g total mass. This figure exceeds the best‐constrained previous estimate by more than an order of magnitude. One possible reason for this disparity may be the extraordinary length of the fall record preserved in the surficial geology of Roosevelt County. The high accumulation rate determined for the past 16 ka may point to the existence of periods when the meteorite fall rate was significantly greater than at present.
Chondrule‐like objects and brown glasses in howardites
Authors: Olsen Edward J. , Fredriksson Kurt , Rajan Sundar , Noonan Albert 
Published: June 2012

Abstract— Chondrule‐like objects and brown glasses were analyzed in the howardites, Bununu, Malvern, Monticello, Pavlovka, and Yamato 7308. The objects are very similar to chondrules in ordinary and carbonaceous chondrites. Like the brown glasses the chondrule‐like objects could have been produced by impact melting that left some crystalline nuclei, followed by a slower cooling rate than for the glasses. Alternatively, these objects are chondrules implanted from chondrite impactors. They are, however, without rims or any adhering matrix. The brown glasses appear to represent melting of average regolithic surface material, except for Monticello and Y7308, both of which have some siliceous glasses. The siliceous glasses could not have been produced by vapor fractionation but by melting of differentiated lithologies such as fayalitic granites.Impact mechanics indicates that howardites with abundant brown glasses came from an asteroid larger than Vesta (>400 km radius), upon which impacts occurred at relative velocities of up to 5 km/s. Howardites with little or no brown glasses came from a smaller parent body. We conclude that at least two parent bodies are likely sources for the basaltic achondrites.
Magnetic properties of the Estherville mesosiderite
Authors: Collinson D. W. 
Published: June 2012

Abstract— Evolutionary processes in meteorites and magnetic fields in the early solar system, both spatial and localised in planetary bodies, can leave their imprint in meteorites through the natural remanent magnetization (NRM) and other magnetic properties they impart to them. In the present investigation the Estherville mesosiderite has been studied to enquire whether its magnetic properties can help to resolve any of the uncertainties associated with mesosiderite history and evolution, and to examine evidence for any magnetic fields to which it or its constituent fragments have been subjected.The Estherville sample as received is strongly magnetized, with an initial NRM intensity of 1.4 × 10−3 Am2 kg−1. The NRM of individual fragments broken from the main mass, when referred to common reference axes, is scattered in direction on a scale which ranges from ∼ 1 cm down to ∼ 1 mm. Alternating field and thermal demagnetization show a range of magnetic stability among the samples and also some secondary NRM, indicating a variety of magnetic histories. Thermomagnetic analyses of matrix and iron‐nickel separates show that the dominant magnetic carriers are kamacite and tetrataenite.The non‐coherent directions of NRM within the matrix imply the acquisition of an initial NRM by kamacite in the fragments prior to their final accumulation into the mesosiderite material, and the presence of an ambient magnetic field when the fragment material cooled after its formation. If the tetrataenite carrying the primary NRM was formed from the previously magnetized kamacite/taenite during slow cooling after later metamorphic heating, the maximum temperature during the latter event could not have been higher than ∼700 °C or the kamacite would have been remagnetized uniformly or demagnetized, according to whether or nor there was an ambient magnetic field present.Susceptibility anisotropy observations indicate the acquisition of anisotropic properties occurred before final accumulation of the meteorite. Shock and flow processes were probably important in producing foliation and lineation respectively in the fragments resulting from brecciation, and there could also be a contribution from larger metal fragments and/or veins. The scattered NRM of the iron‐nickel fragments also indicates magnetization prior to emplacement, therefore favouring introduction in the solid rather than the molten form.
The structure and composition of metal particles in two type 6 ordinary chondrites
Authors: Holland‐Duffield C. E. , Williams D. B. , Goldstein J. I. 
Published: June 2012

Abstract— The purpose of this study is to examine, using light optical and electron optical techniques, the microstructure and composition of metal particles in ordinary chondritic meteorites. This examination will lead to the understanding of the low temperature thermal history of metal particles in their host chondrites. Two type 6 falls were chosen for study: Kernouvé (H6) and Saint Severin (LL6).In both meteorites, the taenite particles consisted of a narrow rim of high Ni taenite and a central region of cloudy zone similar to the phases observed in iron meteorites. The cloudy zone microstructure was coarser in Saint Severin than in Kernouvé due to the higher bulk Ni content of the taenite and the slower cooling rate, 3 K Ma−1 vs. 17 K Ma−1. Three microstructural zones were observed within the high Ni taenite region in both meteorites. The origin of the multiple zones is unknown but is most likely due to the high Ni taenite cooling into the two phase γ″ (FeNi) + γ′ (FeNi3) region of the low temperature Fe‐Ni phase diagram. Another explanation may be the presence of uniform size antiphase boundaries within the high Ni taenite. Finally, abnormally wide high Ni taenite regions are observed bordering troilite. The wide zones are probably caused by the diffusion of Ni from troilite into the high Ni taenite borders at low cooling temperatures.
Terrestrial impact: The record in the rocks*
Authors: Grieve Richard A. F. 
Published: June 2012

Abstract— Approximately 130 terrestrial craters are currently known. They range up to 140 km, and perhaps as much as 200 km, in diameter and from Recent to ∼2 billion years in age. The known sample, however, is highly biased to geologically young craters on the better known cratonic areas. The sample is also deficient in small (D < 20 km) craters compared to other planetary bodies. These biases are largely the result of active terrestrial geologic processes and their effects have to be considered when interpreting the record. The strength of the terrestrial cratering record lies in the availability of ground truth data, particularly on the structural and lithological nature of craters, which can be interpreted to understand and constrain large‐scale impact processes. Some contributions include the definition of the concept of transient cavity formation and structural uplift during cratering events. Depths of excavation are poorly constrained, as very few terrestrial craters have preserved ejecta.Unlike their planetary counterparts, terrestrial impact craters are mostly recognized not by morphology but by the occurrence of characteristic shock metamorphic effects. Their study has led to models of shock wave attenuation and an understanding of the character and formation of various impact‐lithologies, including impact melt rocks. They, in turn, aid in interpreting the nature of extraterrestrial samples, particularly samples from the lunar highlands. The recognition of diagnostic shock metamorphic effects and the signature of projectile contamination through geochemical anomalies in impact lithologies provide the basis for recognizing the impact signature in K/T boundary samples. The record also provides a basis for testing hypotheses of periodic cometary showers. Although inherently not suitable to define short wavelength periods in time due to relatively large uncertainties associated with crater ages, the current record shows no evidence of periodicity. Future directions in terrestrial impact studies will likely continue to focus on the K/T and related problems, including the recognition of other impact signatures in the stratigraphic record. Some emphasis will likely be given to the economic potential of craters and individual large structures, such as Sudbury, will provide an increasingly better understood context for interpreting planetary impact craters. To live up to the full potential of the record to constrain impact processes, however, more basic characterization studies are required, in addition to emphasis on topical areas of study.
Rhenium and osmium systematics on iron and stony iron meteorites
Authors: Hirata Takafumi , Masuda Akimasa 
Published: June 2012

Abstract— Re and Os abundances and 187Os/186Os isotopic ratios in 12 iron meteorites of various groups and five stony iron meteorites have been determined by an inductively coupled plasma mass spectrometry (ICP‐MS). The series of iron meteorites studied have Re and Os concentrations ranging from 0.004 to 3.3 ppm and 0.03 to 41 ppm, respectively. The 187Re/186Os ratios in these meteorites fall between 3.0 and 6.1 and the 187Os/186Os between 1.0 and 1.2, giving an initial 187Os/186Os isotopic ratio of 0.790 and a Re‐Os age of iron meteorites of 4.30 ± 0.28 Ga when employing the decay constant of 1.64 × 10−11 yr−1. The observed Re‐Os age for iron meteorites appears somewhat younger than that for chondrites. The resultant younger age might be due either to a very slow cooling of the parental planetesimals or due to a secondary “shock” event. However, for definite conclusions about the Re‐Os age, higher precisions of the Re and Os isotopic measurements and of the decay constant of 187Re are required. Furthermore, the clear elucidation of the mechanisms for the fractionation of the Re/Os abundance ratios are related to the understanding of the meaning of the Re‐Os age.The Re and Os abundances in pallasite stony iron meteorites are extremely low compared with those for most iron meteorites. On the other hand, the Re and Os abundances in mesosiderite stony iron meteorites show values comparable with those observed in most iron meteorites. The difference in Re and Os abundances in pallasite and mesosiderite stony iron meteorites strongly suggests that these stony iron meteorites are different in origin or history of chemical evolution.Re and Os abundances in the series of iron and stony iron meteorites were found to have a wide variation covering nearly four orders of magnitude, with a very high correlation coefficient (0.996), and a slope very slightly less than unity. The regression line observed here covers various groups of iron meteorites, stony iron meteorites and also chondrites. Masuda and Hirata (1991) suggested the possible direct mixing process of particles of most refractory metallic elements with gaseous clouds of less refractory matrix elements, since the Re and Os were predicted theoretically to be the first elements to condense as a solid phase from the high temperature solar nebula. The aims of this paper are to present a reliable technique for the Re‐Os chronology and to study the cosmochemical sequences of the meteoritic metals.
Constraints on chondrule origins
Authors: Wasson John T. 
Published: June 2012

Abstract— Research on chondrules during the past decade and a half has produced a number of constraints on the processes that formed these enigmatic objects. Although some chondrules may have formed in exceptional ways, it now seems clear that the vast majority did not form by condensation or by any other process that resulted in an extended (>100 s) period of heating; viable models of chondrule formation must generate brief (1–10 s) “flash” heating events. Many chondrules were incompletely melted, indicating that the heat source was marginal; coarse‐grained rims are probably the result of heating by the same source that heated chondrules. Although some chondrules are enriched in refractories and poor in volatiles, most chondrules contain FeS in their interiors, implying that the last generation of chondrules formed after the local nebula had cooled below 650 K. The very small weight fraction of chondrules haying small (<50 μm in ordinary chondrites) radii requires either that (a) the formational process destroyed small chondrules by volatilizing them or efficiently recycling them into larger chondrules, or (b) that nebular size‐sorting occurred and the fine fraction is not well represented in our known set of chondrites.Our recent studies of compound chondrules show that about 60% are siblings that formed together in the same heating event, and about 40% are independents that originated in different events. Independent compound chondrules tend to have similar FeO/(FeO + MgO) ratios, a possible indication of a high degree of compositional homogeneity in nebular subrogions defined by location or time. About 8% of barred olivine chondrules are the primaries of independently formed compound chondrules, and have thus been subjected to at least two flash‐heating events. Allowance for observational biases suggests that a sizable fraction of chondrules have experienced two thermal events strong enough to produce major melting as well as many additional events that could produce minor melting, sintering, and crystal growth.
The petrography, mineralogy and origins of calcium sulphate within the Cold Bokkeveld CM carbonaceous chondrite
Authors: Lee Martin R. 
Published: June 2012

Abstract— A detailed scanning and transmission electron microscopy study of Cold Bokkeveld has shown that calcium sulphate is widespread, occluding ∼30 μm wide matrix‐cutting fractures in addition to μm‐sized veins and irregular dissolution pores within calcitized chondrules, matrix calcite grains and Ca‐ and Al‐rich inclusions (CAI). The majority of calcium sulphate crystals have fibrous habits, especially those which have grown within straight‐sided fractures and veins. Mineralogically, the calcium sulphate is composed of a fine‐scale mixture of hemihydrate and anhydrite which have probably formed by the dehydration of primary gypsum during sample preparation.In all contexts, calcium sulphate precipitation was the last identifiable diagenetic event in the pre‐terrestrial history of Cold Bokkeveld and followed pervasive aqueous alteration of the meteorite matrix to phyllosilicates. The fibrous fracture‐ and vein‐filling calcium sulphates are morphologically similar to a terrestrial form of gypsum termed “satinspar” and so may have formed in a similar manner by precipitation from supersaturated aqueous solutions during fracture and vein dilation. The aqueous solutions were most probably generated by melting of water ice due to internal heating and/or post‐accretional impact heating of the parent body. Although impact‐produced fractures and veins may have provided conduits for fluid advection, the dissolution of calcite, alteration of metal sulphides and precipitation of gypsum probably took place when aqueous solutions were more‐or‐less static. Despite their similarity to late‐stage mineralized fractures in CI meteorites, the calcium sulphate‐filled fractures in Cold Bokkeveld probably do not have any significance regarding a shared CM‐CI parent body.
On the Bur Gheluai H5 chondrite and other meteorites with complex exposure histories
Authors: Vogt S. K. , Aylmer D. , Herzog G. F. , Wieler R. , Signer P. , Pellas P. , Fiéni C. , Tuniz C. , Jull A. J. T. , Fink D. , Klein J. , Middleton R. 
Published: June 2012

Abstract— We present the 14C, 26Al, 10Be, 3He, 4He, 20Ne, 21Ne, 22Ne, 36Ar, 38Ar, and 40Ar concentrations and the track densities measured in up to 13 samples of the Bur Gheluai (H5) meteorite fall. Only a multi‐stage exposure history can explain the data in a self‐consistent way. Parameters for a model two‐stage history obtained by simultaneous, least‐squares fitting of the concentrations of 14C, 26Al, 10Be, and 21Ne were: first stage duration ∼10 Ma and radius >2 m; second stage duration ∼0.6 Ma and radius 40–100 cm.Nominal one‐stage 21Ne production rates (P21) inferred from 26Al in Bur Gheluai samples exceed those inferred from 10Be as expected for a meteorite with a complex history. Nonetheless, data for other meteorites indicate that multi‐stage irradiations alone do not account for all the high reported values of P21 based on 26A***l: The equations describing the production of cosmogenic nuclides show that uncorrected shielding effects may also play a role.A compilation of ordinary, solar‐gas‐poor chondrites for which two‐stage histories have been proposed includes many with short second stages but none with unambiguously long first stages (>0.2 Ga).
Boron cosmochemistry. Part I: Boron in meteorites
Authors: Zhai Mingzhe , Shaw Denis M. 
Published: June 2012

Abstract Thirty‐six fragments of meteorite falls, never touched by water or other possible sources of B contamination, were analyzed for B by prompt gamma‐ray neutron activation analysis at McMaster University and at the U.S. National Institute of Standards and Technology. Boron concentrations are close to the sensitivity limit in both laboratories. Results between the two laboratories agree well but with slight systematic differences attributable to blank and background correction factors.The mean B concentrations in different meteorites are similar, from 0.5 to 1.1 ppm. The ranges in different CC, OC and ACH classes overlap, mostly from 0.4 to 1.4 ppm, which is similar to previous measurements on falls. The H, L and LL meteorites overlap in B content with Antarctic chondrites.The solar system abundance, taken as the mean B content of the matrix in all CC, was calculated from seven samples and is 0.69 ± 0.09 ppm. When normalized, this abundance is 16.9 ± 2.2 (atoms/106Si).Normalized B and S concentrations show a linear relationship in the CC; the average OC lies on the same line, but individual OCs are dispersed.
Helium and neon in lunar ilmenites of different antiquities
Authors: Nier A. O. , Schlutter D. J. 
Published: June 2012

Abstract Helium and neon were extracted from individual lunar ilmenite grains, approximately 100 μm in diameter, using a pulsed step‐heating technique. Grains from lunar samples 71501 and 79035, believed to have been exposed to solar corpuscular radiation at greatly different times, were studied. The results found were consistent with the hypothesis that in addition to solar‐wind‐implanted gas, a second more deeply implanted component was present in both species of grains.Average isotopic ratios were determined giving equal weight to each of the particles. As found in depth studies employing chemical etching, both the 3He/4He and 20He/22Ne ratios were lower in the more deeply implanted gas than in the solar wind component. The 3He/4He ratio in the solar wind component of the more ancient grains was lower than that in the more recently exposed ones, whereas no difference was found for the more deeply embedded He. In the deeply embedded component of the ancient grains, the 4He/20Ne ratio was ∼2×that found in the more recently exposed grains. In the shallowly implanted component, the ratio varied greatly from grain to grain, preventing comparison with the solar wind elemental composition.