bluuebunny/crossref_metadata_2025 huggingface dataset:
Major element composition of stratospheric micrometeorites
Authors: Schramm L. S. , Brownlee D. E. , Wheelock M. M.
Published: June 2012

Abstract— The elemental compositions of 200 interplanetary dust particles (IDPs) collected in the stratosphere have been determined by energy dispersive X‐ray (EDX) analysis. The results reasonably define the normal compositional range of chondritic interplanetary dust particles averaging 10 micrometers in size, and constitute a database for comparison with individual IDPs, meteorites, and spacecraft data from comets and asteroids. The average elemental composition of all IDPs analyzed is most similar to that of CI chondrites, but the data show that there are small yet discernable differences between mean IDP composition and the CI norm. Individual particles were classified into broad morphological groups, and the two major groups show unambiguous compositional differences. The “porous” group is a close match to bulk CI abundances, but the “smooth” group has systematic Ca and Mg depletions, and contains stoichiometric “excess” oxygen consistent with the presence of hydrous phases. Similar depletions of Ca and Mg in CI and CM matrix have been attributed to leaching, and by analogy we suggest that particles in the smooth group have also been processed by aqueous alteration. The occurrence of carbonates, magnetite framboids, and layer silicates provides additional evidence that at least a significant number of the smooth‐class IDPs have been substantially processed by aqueous activity. The presence or absence of aqueous modification in members of a particle sub‐class is an important clue to the origin. Although it cannot be proven, we hypothesize that extensive aqueous activity only occurs in asteroids and that, accordingly, the smooth class of IDPs has an asteroidal origin. If both comets and asteroids are major sources of interplanetary dust, then by default the porous particles are inferred to be dominated by cometary material.
An olivine‐microchondrule‐bearing clast in the Krymka meteorite
Authors: Rubin Alan E.
Published: June 2012

Abstract— A small (150 × 200‐μm‐size) clast consisting of 20 vol.% olivine microchondrules (with barred and granular textures) and 80 vol.% recrystallized silicate matrix material occurs in Krymka (LL3.1). This is the fourth microchondrule‐bearing clast to be described. The chondrules are zoned in FeO with concentrations increasing toward the surface. The clast most closely resembles a previously described radial‐pyroxene‐microchondrule‐bearing clast in Piancaldoli (LL3.4).
Minor elements in forsterites of Orgueil (C1), Alais (C1) and two interplanetary dust particles compared to C2‐C3‐UOC forsterites
Authors: Steele Ian M.
Published: June 2012

Abstract— The rare Mg‐rich silicate fraction of the C1 meteorites, Orgueil and Alais, is dominated by minute (< 30 μm) forsterite. Twenty three forsterite grains of these meteorites as well as large forsterites in two chondritic porous interplanetary dust particles (IDPs) are characterized by levels of MnO generally, but not always, higher than found in forsterites of C2, C3 and unequilibrated ordinary chondrites (UOC). Forsterite in Orgueil contains 900 to 6200 ppmw MnO while Alais forsterite has less than 2000 ppmw MnO suggesting that the forsterites in the two meteorites are chemically distinct. Alais forsterite shows lower Cr and Al relative to Orgueil forsterite. The C1 forsterites do not show Fe‐poor (FeO < 0.3), refractory‐rich (Al, Ca, Ti, V) compositions which are relatively common in the C2‐C3‐UOC meteorites suggesting that the most primitive forsterite compositions are not present in these C1 meteorites. While minor elements in forsterite can not distinguish unambiguously between C1 and C2‐C3‐UOC sources, the high Mn levels in some IDP forsterites are similar to some C1 forsterites suggesting a possible relation between the forsterites of these two extraterrestrial samples.
Chemical analyses of meteorites: A compilation of stony and iron meteorite analyses
Authors: Jarosewich Eugene
Published: June 2012

Abstract— A compilation of the chemical analyses of 241 stony and 36 iron meteorites is presented; 196 analyses were published previously, 81 are new. This compilation includes analyses of new falls, new finds, previously analyzed meteorites, previously analyzed meteorites with suspect values, analyses of separates and inclusions, and analyses of 53 stony and 29 iron meteorites from Antarctica, including one of the “lunar” type. Mean compositions of chondrite falls, finds, and Antarctic chondrites are compared. References are listed for earlier published analyses and an appendix provides an outline of the sampling procedures, sample preparation, and the analytical methods.
Orbit of the Murchison meteorite
Authors: Halliday Ian , McIntosh Bruce A.
Published: June 2012

Abstract— Because the path of the Murchison meteorite fortuitously intersected the Earth's path at an angle of only a few degrees, the visual observations establish the entry velocity to be within 2 km/s of 13 km/s and determine the nature of its orbit with a precision quite unusual for visually sighted falls.
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.
Tektite research 1936–1990*
Authors: Barnes Virgil E.
Published: June 2012

Abstract— Fifty‐odd years of tektite research are reviewed, proceeding from the discovery of the first North American tektites in 1936. This included the early recognition that tektites were terrestrial objects rather than meteorites and that the glassy particles in tektites were fused quartz (lechatelierite). Later, during National Science Foundation‐supported research, it was found that some tektites appeared to have formed as puddles of melt, that the content and character of bubbles in lechatelierite can be used as a relative temperature scale, that rayed bubbles in tektites formed from hydrous minerals, that bubbles in tektites formed chiefly from water which was absorbed into the walls of the bubbles leaving vacuums, and that “fingers” in the surficial part of some tektites may have formed by differential volatilization. Some unpublished observations and adventures are briefly reported.
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.
Compositional variations among whole‐rock fragments of the L6 chondrite Bruderheim
Authors: Haas Johnson R. , Haskin Larry A.
Published: June 2012

Abstract— Twenty ∼100‐mg random fragments of the Bruderheim chondrite were analyzed by INAA to determine extents of heterogeneity and to check earlier results that gave anomalous LREE concentrations. Considerable compositional heterogeneity was observed in both concentrations (maximum/minimum of 1.7 for Ir, 1.8 for Na, 6.8 for La, 7.4 for Co) and concentration ratios (>3 × for Ni/Co and La/Eu). Compositions could be modelled quantitatively in terms of end‐member components of constant composition representing the minerals olivine + orthopyroxene, clinopyroxene, plagioclase, kamacite, taenite, troilite, chromite, and phosphate. The model yields the proportions of minerals in each sample as well as the meteorite as a whole; accurate determination of the end members depends on high intrasample precision for many elements. No evidence of compositional heterogeneity of end members for trace elements was found. It is shown that these analyses, which used only ∼2 grams of the meteorite, are equivalent in accuracy to a single sample of several tens of grams, and that knowledge of the extent of heterogeneity is essential to knowing the quality of sampling as well as for comparing results from one analysis with another and of one meteorite with another.
Determination of sulphur‐bearing components in C1 and C2 carbonaceous chondrites by stepped combustion
Authors: Burgess R. , Wright I. P. , Pillinger C. T.
Published: June 2012

Abstract— Ten type 1 and 2 carbonaceous chondrites have been analysed by stepped combustion to determine the nature of their sulphur‐bearing components. All samples show complex release patterns which, when combined with published petrographic observations, can be interpreted in terms of sulphur derived from a mixture of at least seven components (elemental sulphur, organic sulphur, sulphide, FESON or tochilinite and sulphates: gypsum, bloedite and epsomite). Estimated concentrations of individual components show that most of the sulphur in the meteorites exists in oxidised form. The concentrations of reduced and oxidised components can be used to derive approximate oxidised/reduced sulphur ratios for the meteorites. These ratios are indicators of the extent of aqueous alteration and increase in the order CM < CI. Formation of the different alteration products by aqueous processes active on the meteorite parent body appears to be the most likely origin.
The Raghunathpura iron meteorite from Alwar, India
Authors: Bapna V. S. , Sharma P. N. , Sathe M. D. , Mathur K. N. , Dwivedi G. L.
Published: June 2012

Abstract— The Raghunathpura iron meteorite fell on 20 November 1986 around 8 p.m.; it weighed 10.2 kg. It is a group IIA hexahedrite based on metallographic, x‐ray diffraction and chemical studies. Eighteen major, minor and trace elements were determined using classical, atomic‐absorption spectrometry and semiquantitative spectrographic procedures.
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.
Degree of equilibration of eucritic pyroxenes and thermal metamorphism of the earliest planetary crust
Authors: Takeda Hiroshi , Graham A. L.
Published: June 2012

Abstract— The pyroxenes in two new monomict eucrites from Antarctica, Yamato 791186 and Yamato 792510, have been studied and compared with those of other Antarctic and non‐Antarctic eucrites. The purpose of this study is to identify compositional and textural relationships shown by these pyroxenes which may be used as indicators of the thermal history of the meteorite. An attempt is made, using petrographic and compositional criteria, to distinguish between the initial cooling history and subsequent thermal events. We suggest that it is possible to identify stages of thermal “metamorphism” which may be used to indicate the conditions on the surface and crust of the parent body. A picture of the geological setting of the HED (Howardites, Eucrites, Diogenites) parent body is proposed, for which thermal metamorphism by impact heating is an important process.
Aqueous alteration of the Nakhla meteorite
Authors: Gooding James L. , Wentworth Susan J. , Zolensky Michael E.
Published: June 2012

Abstract— Interior samples of three different Nakhla specimens contain an iron‐rich silicate “rust” (which includes a tentatively identified smectite), Ca‐carbonate (probably calcite), Ca‐sulfate (possibly gypsum or bassanite), Mg‐sulfate (possibly epsomite or kieserite), and NaCl (halite); the total abundance of these phases is estimated as <0.01 weight percent of the bulk meteorite. Rust veins are truncated and decrepitated by fusion crust and are preserved as faulted segments in partially healed olivine crystals, indicating that the rust is pre‐terrestrial in origin. Because Ca‐carbonate and Ca‐sulfate are intergrown with the rust, they are also indicated to be of pre‐terrestrial origin. Similar textural evidence regarding origins of the NaCl and Mg‐sulfate is lacking. Impure and poorly crystallized sulfates and halides on the fusion crust of the meteorite suggest leaching of interior (pre‐terrestrial) salts from the interior after Nakhla arrived on Earth but coincidental addition of these same salts by terrestrial contamination cannot be excluded. At least the clay‐like silicate “rust,” Ca‐carbonate, and Ca‐sulfate were formed by precipitation from water‐based solutions on the Nakhla parent planet although temperature and pressure conditions of aqueous precipitation are unconstrained by currently available data. It is possible that aqueous alteration on the parent body was responsible for the previously observed disturbance of the Rb‐Sr geochronometer in Nakhla at or near 1.3 Ga.
The Cerro los Calvos and La Banderia chondrites
Authors: Whitlock Randall , Lewis Charles F. , Clark James C. , Moore Carleton B.
Published: June 2012

Abstract— The Cerro los Calvos meteorite is a single stone of 68.5 g found in the Nuevo Mercurio strewn field of Zacatecas, Mexico (24°20′N, 102°8′W). It is an unusual H4 chondrite. Its olivine (Fa12.5) and orthopyroxene (Fs 11.7, Wo 0.8) are reduced relative to typical H chondrites. The La Banderia meteorite of 54.3 g from the same vicinity is an LL5 chondrite of shock classification e.
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.
Anomalous Ne enrichments in tektites
Authors: Matsubara Kayo , Matsuda Jun‐ichi
Published: June 2012

Abstract— We measured noble gases and Ne isotopic compositions of five tektites collected from three different strewn fields. The elemental abundance patterns of noble gases in all samples show anomalous Ne enrichments relative to air. Ne isotopic compositions in tektites are in good agreement with that of atmospheric Ne, suggesting that Ne has diffused in from the atmosphere. It is conceivable that the high relative Ne abundance is essentially an equilibrium effect, i.e., storage of Ne in vesicles rather than the glass itself, facilitated by the relatively high diffusion coefficient of Ne.
Ureilites: A critical review
Authors: Goodrich Cyrena Anne
Published: June 2012

Abstract— Ureilites are coarse‐grained ultramafic rocks whose petrography, mineral chemistry, lithophile element bulk chemistry, and Sm‐Nd isotopic systematics suggest that they are highly fractionated igneous rocks and thus are products of common planetary differentiation processes. However, they also have primitive characteristics that are difficult to reconcile with extensive igneous processing. These include high abundances of siderophile elements, planetary‐type noble gases, and the oxygen isotopic signature of unequilibrated solar system materials. The incongruity between igneous and primitive features constitutes the most important problem in understanding ureilite petrogenesis. In this review the petrographic, chemical, and isotopic characteristics of ureilites are summarized, and the petrogenetic implications of these characteristics are discussed. The most important constraints on ureilite petrogenesis are: 1) Ureilites have lost a basaltic complement; 2) Ureilites had a two‐stage cooling history; 3) Ureilites are probably residues but partly crystallized from melts; 4) Ureilites are derived from a minimum of six reservoirs which were distinct in oxygen isotopic composition and did not equilibrate with one another; 5) A correlation between oxygen isotopic composition and mg ratio was established in ureilite parent material in the solar nebula; 6) If carbon‐metal‐silicate‐CO/CO2 equilibrium was maintained then the mg ratios of ureilites were pressure/depth‐dependent; however, if the pressure was sufficiently high (> 100–200 bars) that a CO/CO2 gas phase was not present then carbon and metal could have been at equilibrium with all ureilite mg ratios at the same pressure; 7) Ureilites either lost a low‐melting temperature metal fraction or gained a refractory‐rich metal component; 8) Primordial noble gases were retained in carbon in ureilites; 9) The ultramafic ureilite assemblage formed at ∼4.55 Ga, but Sm‐Nd and Rb‐Sr isotopic systematics have been subsequently disturbed. Recently proposed models for ureilite petrogenesis are evaluated in terms of how well they satisfy these constraints; no models unequivocally satisfy all of them. Reconciling constraints 5 and 6 requires a large ureilite parent body.
Cosmogenic nuclides in core samples of the Chico L6 chondrite: Evidence for irradiation under high shielding
Authors: Garrison D. H. , Bogard D. D. , Albrecht A. A. , Vogt S. , Herzog G. F. , Klein J. , Fink D. , Dezfouly‐Arjomandy B. , Middleton R.
Published: June 2012

Abstract— Core samples were obtained from various locations of the ∼ 105‐kg Chico, NM, L6 chondrite in order to study the effects of large shielding on the production rates of cosmic‐ray‐produced nuclides. Relations between measured abundances of cosmogenic nuclides (10Be, 26Al, and stable isotopes of He, Ne, and Ar) and the cosmogenic 22Ne/21Ne ratio were determined and compared with recent model predictions of production rates. The measured 22Ne/21Ne ratios (1.06‐1.08) and significant variations observed in concentrations of cosmogenic 21Ne and 3He suggest an ∼40‐cm shielding gradient across Chico and irradiation within a large object (> 100‐cm radius). Noble gas data indicate that Chico experienced greater shielding than chondrites Knyahinya or Keyes and similar to Jilin. Values of 10Be (average = 20.7 dpm/kg) and 26Al (average = 71.1 dpm/kg) are nearly constant, however, and show no correlation with either 22Ne/21Ne or 21Ne. Activities of 10Be and 26Al suggest irradiation in a smaller object (∼40–80 cm radius). The 26Al activity and the 26Al/10Be ratio (average value = 3.42) are both significantly larger than values for most other chondrites. These results could indicate a two‐stage irradiation with t1 ∼ 104 Ma and t2 ∼ 4 Ma and a second‐stage body the size of Knyahinya. The single stage, 10Be/21Ne exposure age for Chico is 65 Ma. The 22Ne/21Ne ratio apparently becomes insensitive to shielding for objects the size of Chico. No substantial evidence exists for chondrites with 22Ne/21Ne ratios significantly less than ∼ 1.055.
An experimental evaluation of mineral‐specific comminution
Authors: Cintala Mark J. , Hörz Friedrich
Published: June 2012

Abstract— Early “regolith‐evolution” experiments using fragmental, polycrystalline gabbro targets displayed mineral‐specific comminution trends, with feldspar being significantly fractionated into the finest grain sizes. Since planetary regoliths are similar mixtures of lithic and monomineralic detritus, the comminution of monomineralic grains is important in understanding the evolution of such regoliths. Particulate targets of monomineralic feldspar, olivine, pyroxene, and quartz therefore were subjected to at least 25 impacts each to complement the previous gabbro‐based investigations. Stainless‐steel projectiles 3.18 mm in diameter were launched at the targets at nominal velocities of 1.4 km s−1, depositing an average of about 2.6 × 106 ergs per g of target per impact. The quartz and feldspar comminuted most readily, while olivine and pyroxene were the most resistant. In addition, the feldspar and quartz were virtually indistinguishable in terms of any measure of comminution used here. The behavior of the olivine differed somewhat from that of the pyroxene, but the variation between these two minerals was much less than the difference between them and the tectosilicates. The apparent energy required to create new surfaces through comminution was about a factor of two higher for the mafic minerals. Densities of pre‐existing cracks and other crystal defects depend on sample preparation techniques, among other things, and appear to play a notable role in the early evolution of these “regoliths.” It is probable that the history of a particular regolith's parent rocks will exert a comparable influence on the early stages of evolution of a planetary regolith. The trends for the individual targets in these monomineralic series duplicated those exhibited by the gabbro charges, leading to the general conclusion that mineral‐specific comminution will occur during repetitive impact of planetary surfaces, whether they comprise freshly excavated, large blocks, or highly comminuted, clastic fines containing substantial fractions of monomineralic debris. This mineral‐specific behavior will cause small grain sizes in planetary regoliths to be substantially fractionated relative to coarse regolith components, and especially relative to their source rocks.
The 1991 EUROMET micrometeorite collection at Cap‐Prudhomme, Antarctica
Authors: Maurette Michel , Pourchet Michel , Perreau Michel
Published: June 2012

Abstract— An inventory of 1991 EUROMET Antarctic micrometeorite (AMM) collection is presented. Fifty grams of sediments were collected by filtration of 260 tonnes of melted ice water. Four sieve fractions were obtained and material from these is available from the EUROMET group. The few hundred milligrams of the 50–100 μm fraction are the most productive ones, in which 10% of the grains are AMMs. Input for planning a 1994 expedition to collect AMMs is also invited.
Electrophonic sounds from large meteor fireballs
Authors: Keay Colin S. L.
Published: June 2012

Abstract Anomalous sounds from large meteor fireballs, anomalous because they are audible simultaneously with the sighting, have been a matter for debate for over two centuries. Only a minority of observers perceive them. Ten years ago a viable physical explanation was developed (Keay, 1980a) which accounts for the phenomenon in terms of ELF/VLF radiation from the fireball plasma being transduced into acoustic waves whenever appropriate objects happen to be in the vicinity of an observer. This explanation has now been verified observationally and supported by other evidence including the study of meteor fireball light curves reported here.
Mechanism of Muong Nong‐type tektite formation and speculation on the source of Australasian tektites
Authors: Schnetzler C. C.
Published: June 2012

Abstract The source crater of the youngest and largest of the tektite strewnfields, the Australasian strewnfield, has not been located. A number of lines of evidence indicate that the Muong Nong‐type tektites, primarily found in Indochina, are more primitive than the much more abundant and widespread splash‐form tektites, and are proximal to the source. In this study the spatial distribution of Muong Nong‐type tektite sites and chemical character have been used to indicate the approximate location of the source. The variation of Muong Nong‐type tektite chemical composition appears to be caused by mixing of two silicate rock end‐members and a small amount of limestone, and not by vapor fractionation. The variation in composition is not random, and does not support in‐situ melting or multiple impact theories. The distribution of both Muong Nong and splash‐form tektite sites suggest the source is in a limited area near the southern part of the Thailand‐Laos border.
Elemental abundance data for the Manitouwabing iron meteorite
Authors: Brooks R. R. , Guo X. , Hoashi M. , Reeves R. D. , Ryan D. E. , Holzbecher J. , Henderson G. S.
Published: June 2012

Abstract The Manitouwabing meteorite whose trace constituents have not been previously quantified was analysed for Au, As, Ga, Ge, Ir, Ni, Os, Pd, Pt, Rh and Ru. Our data confirm that it belongs to subgroup IIIA of the IIIAB group and on the basis of the much higher concentrations of As, Ir, Os, Pt, Rh and Ru, it is not paired with Madoc as had previously been proposed.
The Barringer Medal Address
Authors: Masaitis V. L.
Published: June 2012

Abstract— Terrestrial impact craters are important geological and geomorphological objects that are significant not only for scientific research but for industrial and commercial purposes. The structures may contain commercial minerals produced directly by thermodynamic transformation of target rocks (including primary forming ores) controlled by some morphological, structural or lithological factors and exposed in the crater. Iron and uranium ores, nonferrous metals, diamonds, coals, oil shales, hydrocarbons, mineral waters and other raw materials occur in impact craters. Impact morphostructures may be used for underground storage of gases or liquid waste material. Surface craters may serve as reservoirs for hydropower. These ring structures may be of value to society in other ways. Scientific investigation of them is especially important in comparative planetology, terrestrial geology and in other divisions of the natural sciences.
The meteorite of Ensisheim: 1492 to 1992
Authors: Marvin Ursula B.
Published: June 2012

Abstract— On November 7, 1492, a 127‐kg stony meteorite fell at Ensisheim in Alsace after a fireball explosion that was heard for a distance of 150 km over the upper Rhineland. Today, a 56‐kg specimen of the stone, an LL6 chondrite with large patches of fusion crust, remains on display in the Hotel de Ville at Ensisheim. This was the earliest witnessed meteorite fall in the West from which pieces are preserved. Initially, the stone's survival depended on the presence of a magistrate at Ensisheim who forbade the removal of pieces, which had begun apace as soon as a crowd gathered and pulled the stone out of a 1‐m hole in a wheat field. He ordered the stone brought into the city to await the arrival of King Maximilian, son of the Holy Roman Emperor Friedrich III, who was approaching with his army. In nearby Basel, broadsheets were printed within weeks bearing the story in Latin and German verses by the eminent poet, Sebastian Brant, who turned the sheets into propaganda tracts by claiming the stone as a portent of victory and admonishing Maximilian to make war on the French without delay. Maximilian declared the stone to be a sign of divine favor and ordered it to be preserved in the Ensisheim parish church. The stone grew in fame when Maximilian won his impending battle with the French, but strange new elements entered the story as it was repeated over the years in books and chronicles. Through centuries of battle and political changes, the stone remained in the church until 1793 when French revolutionaries transferred it to a new National Museum in Colmar. There, many pieces were taken for chemical analyses during the birth of the meteoritics at the turn of the 19th century. In 1803 the stone was returned to the Ensisheim church where it outlasted the structure itself which collapsed in 1854. This paper traces the history of the stone itself and people's responses to it through the 500 years since the fall at Ensisheim.
Mineral compositions in Antarctic and Greenland micrometeorites
Authors: Michel‐Levy Mireille Christophe , Bourot‐Denise Michèle
Published: June 2012

Abstract— The mineral compositions of 250 micrometeorites have been studied and olivines and low‐calcium pyroxenes with crystals larger than 5 μm have been analyzed. While magnesium‐rich grains dominate, the Fa content of olivine may reach 50% and the Fs content of pyroxene may reach 26%. The Ca and Mn of the olivine show no consistent trends with increasing Fe, but Cr shows a negative correlation. For low‐Ca pyroxene, Al and Cr contents are generally higher than in pyroxenes of equilibrated chondrites but similar to those of highly unequilibrated chondrites. Calcium‐bearing pyroxene, feldspar and chromite are rare in the micrometeorites which were selected because of their high Mg, Si, Fe and their low Ca and Al content. All these minerals are found as coarse‐grained particles often with adhering iron‐rich scoria or as clasts in fine‐grained or scoriaceous micrometeorites. Apart from a few particles which could be the debris of ordinary chondrites, most micrometeorites probably come from a common source similar, but not identical to carbonaceous chondrites, as shown by their lower Ni and S content and their different oxygen isotopic composition assuming two measurements performed on olivine grains prove to be typical.
Canadian Arctic Meteorite Project (CAMP): 1990
Authors: Cresswell Richard G. , Herd Richard K.
Published: June 2012

Abstract— The Devon Ice Cap, Northwest Territories, has been targeted for searches for extra‐terrestrial material in the Canadian Arctic. Of three expeditions (1981, 1986, 1990), only the last met with weather conditions favourable for meteorite reconnaissance. Surveys were carried out on the ice cap margin, along boulder trains brought to the surface along ice layers, supra‐glacial stream and lake sediments, and the ubiquitous cryoconite that covers the ice surface. In addition, outwash streams and plains were covered, in the hope of discerning meteoritic material lying on the Lower Palaeozoic bedrock. No meteorites were recovered, though a number of pseudotaks were identified as potential searching grounds for future expeditions. Samples of cryoconite, supra‐glacial lake sediments and outwash silts were collected, and some of these have been given a preliminary examination. SEM analysis indicates that this material represents a new source for micro‐meteoritic material, analogous to the deposits found in Greenland.
Fall days of the SNC meteorites: Evidence for an SNC meteoroid stream, and a common site of origin
Authors: Treiman Allan H.
Published: June 2012

Abstract— Four of the SNC meteorites of putative Martian origin are falls. Two of these fell on October 3: Chassigny in 1815 and Zagami in 1962. The probability of this coincidence arising from random fall days is approximately 1 in 60. If this coincidence is not the result of chance, it suggests that some of the SNC meteorites are derived from a meteoroid stream. In that Chassigny and Zagami span nearly the full range of SNC lithologies and histories, the coincidence of fall days is consistent with suggestions that all of the SNCs came from a single site (impact crater) on their parent planet.
Trapping of noble gases in proton‐irradiated silicate smokes
Authors: Nichols R. H. , Nuth J. A. , Hohenberg C. M. , Olinger C. T. , Moore M. H.
Published: June 2012

Abstract— We have measured Ne, Ar, Kr and Xe in Si2O3 “smokes” that were condensed on Al substrates, vapor‐deposited with various mixtures of CH4, NH3, H2O and noble gases at 10 K and subsequently irradiated with 1 MeV protons to simulate conditions during grain mantle formation in interstellar clouds. The noble gases were analyzed using conventional stepwise heating and static noble gas mass spectrometry. Neither Ne nor Ar is retained by the samples upon warming to room temperature, but Xe is very efficiently trapped and retained. Kr is somewhat less effectively retained, typically depleted by factors of about 10–20 relative to Xe. Isotopic fractionation favoring the heavy isotopes of Xe and Kr of about 5–10‰/amu is observed. Correlations between the specific chemistry of the vapor deposition and heavy noble gas retention are most likely the result of competition by the various species for irradiation‐produced trapping sites. The concentration of Xe retained by some of these smokes exceeds that observed in phase Q of meteorites and, like phase Q, they do not seem to be carriers of the light noble gases. Such artificially prepared material may, therefore, offer clues concerning the incorporation of the heavy planetary noble gases in meteoritic material and the nature of phase Q.
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.
Mineralogy, petrology and geochemistry of carbonaceous chondritic clasts in the LEW 85300 polymict eucrite
Authors: Zolensky M. E. , Hewins R. H. , Mittlefehldt D. W. , Lindstrom M. M. , Xiao X. , Lipschutz M. E.
Published: June 2012

Abstract— We have performed a detailed petrologic and mineralogic study of two chondritic clasts from the polymict eucrite Lewis Cliff (LEW) 85300, and performed chemical analyses by INAA and RNAA on one of these. Petrologically, the clasts are identical and are composed of dispersed aggregates, chondrules and chondrule fragments supported by matrix. The aggregates and chondrules are composed of olivine (Fo100–45), orthopyroxene (Wo1–2En98–60), plus some diopside. The matrix consists of fine‐grained olivine (Fo60–53), and lesser orthopyroxene and augite. Fine‐grained saponite is common in the matrix. The bulk major element composition of the matrix is identical in both clasts and similar to that of CM, CO and CV chondrites. The bulk composition of the clast studied by INAA and RNAA shows unusual abundance patterns for lithophile, siderophile and chalcophile elements but is basically chondritic. The INAA/RNAA data preclude assignment of the LEW 85300,15 clast to any commonly accepted group of carbonaceous chondrite. The unusual rare earth element abundance pattern may, in part, be due to terrestrial alteration.
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.