bluuebunny/crossref_metadata_2025 huggingface dataset:
Multiple generations of hibonite in spinel‐hibonite inclusions from Murchison
Authors: SIMON Steven B. , GROSSMAN Lawrence , DAVIS Andrew M.
Published: February 2010

Abstract— Through freeze‐thaw disaggregation of the Murchison meteorite, we have recovered, in addition to many spinel‐hibonite spherules, several hibonite‐rich inclusion fragments in which the hibonite has wider ranges in TiO2 contents (e.g., 0.07–8.6 wt% in one inclusion and 2–10 wt% in another) than previously observed within single inclusions. In these inclusions, there are sharp contacts between texturally early, Ti‐poor hibonite and relatively late, Ti‐rich hibonite, and the two types occur in complex intergrowth textures that are not consistent with crystallization from a melt in a single‐stage cooling event. One inclusion has, in addition to relatively TiO2‐rich hibonite, some that is virtually TiO2‐free but contains ∼1 wt% MgO and ∼1.5 wt% SiO2. Instead of the common substitution of Mg + Ti for 2Al, Mg coupled with Si in this case, probably reflecting crystallization from an unusual, Ti‐free silicate liquid. Ion microprobe analyses of Ti‐rich and Ti‐poor hibonite from this inclusion yield quite similar trace‐element patterns and Mg‐isotopic compositions. The results are most consistent with formation of Ti‐rich hibonite from Ti‐poor hibonite by addition of Mg and Ti to the latter by exchange with a hot, Ti‐rich liquid. That this occurred without a resolvable change in the Mg‐isotopic composition requires that the Ti‐rich, second generation of hibonite formed <2.5 times 105 yr later than the Ti‐poor hibonite. Observations of spinel‐hibonite spherules and spherule fragments in our sample suite provide additional evidence that, despite the claims by Greenwood et al. (1994), spinel‐hibonite spherules crystallized from individual, molten droplets, as earlier suggested by Macdougall (1981) and MacPherson et al. (1983).
Manganese‐chromium systematics in sulfides of unequilibrated enstatite chondrites
Authors: WADHWA Meenakshi , ZINNER Ernst K. , CROZAZ Ghislaine
Published: February 2010

Abstract— We measured with a secondary ion mass spectrometer Mn/Cr ratios and Cr isotopes in individual grains of Mn‐bearing sulfides (i.e., sphalerites, ZnS; alabandites, MnS; and niningerites, MgS) in nine unequilibrated enstatite chondrites (UECs). The goals were to determine whether live 53Mn (half‐life ∼3.7 Ma) was incorporated in these objects at the time of their isotopic closure and to establish whether Mn‐Cr systematics in sulfides in UECs can be used as a high‐resolution chronometer to constrain formation time differences between these meteorites. Sulfide grains analysed in four of these UECs, MAC 88136 (EL3), MAC 88184 (EL3), MAC 88180 (EL3), and Indarch (EH4), have clear 53Cr excesses. These 53Cr excesses can be very large (δ53Cr/52Cr ranges up to ∼18,400%, the largest 53Cr excess measured so far) and, in some grains, are well correlated with the Mn/Cr ratios. Thus, they were most likely produced by the in situ decay of 53Mn in the meteorite samples. In the remaining five meteorites, no detectable excesses of 53Cr were found, and only upper limits on the initial 53Mn/55Mn ratios could be established. The four meteorites with 53Cr excesses show variations in the inferred 53Mn/55Mn ratios in various sulfide grains of the same meteorite. The Mn‐Cr systematics in these sulfides were disturbed (during and/or after the decay of 53Mn) by varying degrees of reequilibration. Provided 53Mn was homogeneously distributed in the region of the early solar system where these objects formed, the data suggest that the time of the last isotopic equilibration of sulfides in EL chondrites occurred at least 3 Ma after a similar episode in EH chondrites.
Fullerenes, fulleranes and polycyclic aromatic hydrocarbons in the Allende meteorite
Authors: BECKER L. , BUNCH T. E.
Published: February 2010

Abstract— In this paper, we confirm our earlier observations of fullerenes (C60 and C70) in the Allende meteorite (Becker et al., 1994a, 1995). Fullerene C60 was also detected in two separate C‐rich (∼0.5–1.0%) dark inclusions (Heymann et al., 1987) that were hand picked from the Allende sample. The amounts of C60 detected were ∼5 and ∼10 ppb, respectively, which is considerably less than what was detected in the Allende 15/21 sample (∼100 ppb; Becker et al., 1994a, 1995). This suggests that fullerenes are heterogeneously distributed in the meteorite. In addition, we present evidence for fulleranes, (C60HX), detected in separate samples by laser desorption (reflectron) time‐of‐flight (TOF) mass spectrometry (LDMS). The LDMS spectra for the Allende extracts were remarkably similar to the spectra generated for the synthetic fullerane mixtures. Several fullerane products were synthesized using a Rh catalyst (Becker et al., 1993a) and separated using high‐performance liquid chromatography (HPLC). Polycyclic aromatic hydrocarbons (PAHs) were also observed (ppm levels) that included benzofluoranthene and corannulene, a cup‐shaped molecule that has been proposed as a precursor molecule to the formation of fullerenes in the gas phase (Pope et al., 1993).
The chemical variation of moldavite tektites: Simple mixing of terrestrial sediments
Authors: MEISEL Thomas , LANGE Jan‐Michael , KRÄHENBÜHL Urs
Published: February 2010

Abstract— To test different hypotheses of moldavite formation, a major and trace‐element study of 25 moldavite tektites and Sm‐Nd isotope measurement of three moldavite tektites was completed. The samples were selected from the classical substrewnfields and the newly described locations in Lusatia (Saxony, Germany). Samples with unusual bulk composition were also included. The results confirm earlier studies that the variation in the chemical composition can be explained by single impact and through incomplete mixing of at least three lithographical components dominated by one of the three minerals or mineral groups: dolomite, clay minerals and quartz. An additional endmember, possibly a rare Earth's mantle component, containing high Co, Cr and Ni concentrations is also needed to explain the observed variations in compatible elements of some tektites. Volatile element abundances are low but not necessarily the result of selective volatilization.
Equilibrated ordinary chondrites: Constraints for thermal history from iron‐magnesium ordering in orthopyroxene
Authors: FOLCO L. , MELLINI M. , PILLINGER C. T.
Published: February 2010

Abstract— iron‐magnesium ordering was determined in orthopyroxenes from two suites of unshocked (shock stage S1, S2), equilibrated L‐ and LL‐chondrites (10 grains from 5 meteorites and 7 grains from 4 meteorites, respectively) by means of single crystal x‐ray diffraction (SCXRD). This study, together with a previous investigation of H‐chondrites (13 grains from 8 meteorites), produces an internally consistent data set about the thermal record in equilibrated ordinary chondrites (EOCs).

The major feature outlined by cation ordering in EOC orthopyroxenes is that H‐, L‐ and LL‐chondrites share a common low‐temperature record, that is, a common range of similar cooling rates in the 340–480 °C interval for the petrographic types 4 to 6. As a consequence, the thermal evolution of EOCs consists of at least two subsolidus stages; the first stage occurred at temperatures >480 °C where petrographic types were established in distinct environments; the second stage occurred when EOCs, irrespective of chemical class and type, cooled through 340–480 °C in environments characterized by close temperature‐time conditions.

Quantitative estimates of minimal cooling rates for EOCs range from a few °C/ka to ∼102°C/ka in the 340–480 °C interval. Possibly, final ordering was attained in environments where moderate radiative heat‐loss was possible and, thus indicating shallow burial depths in the parent body.
Piplia Kalan eucrite: Fall, petrography and chemical characteristics
Authors: SHUKLA A. D. , SHUKLA P. N. , SUTHAR K. M. , BHANDARI N. , VAYA V. K. , SISODIA M. S. , ROY S. SINHA , RAO K. N. , RAJAWAT R. S.
Published: February 2010

Abstract— Two stones that fell near Piplia Kalan on 1996 June 20 are identified as Ca‐rich achondrites belonging to the eucrite group. The conditions of their fall are described. The petrographic description, texture and chemical composition, the elemental ratios, particularly K/La and Yb/Sc, and relatively flat rare‐earth‐element (REE) patterns (6–8× chondrite) of bulk samples without any significant Eu anomaly all agree with the characteristic values found in eucrites. A feldspar‐rich fraction shows a significant positive Eu anomaly. The presence of several different lithologies and clasts indicates that it is a texturally diverse breccia, and the chemical analysis suggests that it belongs to the noncumulate group of eucrites falling in the Nuevo Laredo trend.
Thoroughly anomalous chromium in Orgueil
Authors: PODOSEK F. A. , OTT U. , BRANNON J. C. , NEAL C. R. , BERNATOWICZ T. J. , SWAN P. , MAHAN S. E.
Published: February 2010

Abstract— Stepwise dissolution of bulk Orgueil reveals that all of the Cr in the whole rock is isotopically anomalous, with an anomaly pattern that is thus far unique. Most of the Cr (along with other major and minor cations) is dissolved by acetic and nitric acids; it is deficient in 54Cr by ∼5 ɛ. Subsequent treatment with hydrochloric acid dissolves a small fraction of the Cr with positive 54Cr anomalies, up to ∼210 ɛ. Mass balance indicates that whole rock Cr is isotopically normal within analytical uncertainties. The least extravagant interpretation of these results is that some mineral phase is enriched in a heavy‐Cr nucleosynthetic component, while most of the Cr is a homogenized mixture of diverse nucleosynthetic components that would be normal except for lack of the postulated heavy Cr carrier. The carrier is likely, but not necessarily, presolar interstellar grains. Its identity is unknown and constrained only circumstantially: it must be relatively rich in Cr, it is substantially soluble in hydrochloric acid, and it is not magnetite or spinel/chromite. Scanning electron microscope (SEM) examination of Orgueil reveals candidate Cr‐rich oxides, silicates, sulfides and phosphides, but none of these can be identified yet as the heavy Cr carrier. Whether presolar or not, the carrier is not chemically resistant and likely not thermally refractory, thereby differing from most other phases known to host isotopic anomalies. Its survival (or production) thus establishes constraints on a different regime of nebular history.
An experimental study of silver and palladium partitioning between solid and liquid metal, with applications to iron meteorites
Authors: CHABOT NANCY L. , DRAKE MICHAEL J.
Published: February 2010

Abstract— Solid metal/liquid metal partition coefficients for Ag and Pd were determined experimentally as a function of the S concentration of the metallic liquid. Silver is incompatible in solid metal and strongly sensitive to the S content of the metallic liquid; partition coefficients for Ag decrease more than an order of magnitude with increasing S content of the metallic liquid and can be expressed as:

where k(Ag) is the molar solid metal/liquid metal partition coefficient and XS is the molar S content of the metallic liquid. The partition coefficient of Pd is less variable but changes from modestly incompatible to modestly compatible in solid metal with increasing S content of the metallic liquid:

With these new partition coefficients for Pd and a fractional crystallization model, Pd abundance trends recorded in iron meteorite groups are modeled successfully. Measured Ag distribution between troilite‐rich nodules and adjacent metal in iron meteorites also agree well with experimental solid metal/liquid metal equilibrium values. However, observed Pd metal/nodule distributions do not agree with experimentally determined partition coefficients, which suggests a more complex history than simple solid metal/liquid metal equilibrium.
Transmission electron microscope texture and crystal chemistry of coexisting ortho‐ and clinopyroxene in the Antarctic ureilite Frontier Mountain 90054: Implications for thermal history
Authors: TRIBAUDINO M. , FIORETTI A. M. , MARTIGNAGO F. , MOLIN G.
Published: February 2010

Abstract— Frontier Mountain (FRO) 90054, from Antarctica, is a rare clino‐ and orthopyroxene‐bearing ureilite with a coarse equigranular oriented texture (grains up to 3 mm); it is classified as a low‐shock Ca‐rich type. The crystal chemistry of its clinopyroxene (Wo39.3En54.6Fs6.1), orthopyroxene (En84 2Fs11Wo4.8) and olivine (Fa12.6Fo86.9) was investigated by single‐crystal x‐ray structural refinements and transmission electron microscope (TEM) observations to obtain data on the evolutionary history of the parent body. The M1 octahedron and unit cell volumes of the orthopyroxene and clinopyroxene are consistent with low‐pressure crystallization. The closure temperatures for intracrystalline Mg‐Fe2+ ordering yielded values of 674 °C and 804 °C for opx and 596 °C for cpx, which indicate high‐temperature equilibration and fast cooling.

Trasmission electron microscope investigations were performed on clinopyroxene, orthopyroxene and pigeonite. The (100) twin lamellae in the clinopyroxene and intergrowth of clino‐ and orthoenstatite lamellae in orthopyroxene most probably originated by deformation. Exsolution was not observed in any of the phases, which suggests rapid cooling. Analysis by TEM also revealed interstitial Na‐rich glass and pigeonite with sharp h + k odd reflections and rare stacking faults parallel to (100). Textural and crystal chemical data, obtained by TEM, indicated rapid cooling that was probably due to fast radiative heat loss as a result of the disintegration of the parent body into small fragments, which subsequently reassembled into a larger body. One or more collisional events caused fine‐scale stacking faults and partial melting.
Geochemistry and neodymium‐strontium isotope signature of tektite‐like objects from Siberia (urengoites, South‐Ural glass)
Authors: DEUTSCH ALEXANDER , OSTERMANN MARKUS , MASAITIS VICTOR L.
Published: February 2010

Abstract—We report Sr‐Nd isotope parameters, rare earth element (REE), and major element data for isolated findings of tektite‐like objects from western Siberia (urengoites, South‐Ural glass), as well as for two indochinites. The latter were recovered in Vietnam and their overall geochemical characteristics equal those of other tektites from the indochinite subgroup of the Australasian strewn field.

The three urengoites (∼24 Ma) are extremely silica‐rich (89 to 96 wt% SiC2), and their REE abundances vary between 45 and 76 ppm. With LaN/YbNranging from 7.6 to 10.4 and EuN/EU* between 0.69 and 0.75, their REE distribution patterns match that of average upper crust. The urengoites have present‐day ɛSrof +155 to +174 and ɛNdranging from −18 to −23. Their model ages in million years are: TSruR = 1200 up to 4060 and TNdcHUR = 1570 up to 2070. Data points for the urengoites plot colinearly in the Rb‐Sr evolution diagram. The age corresponding to the slope is 183 ± 30 Ma (2s̀), which is indistinguishable from the intercept age of 211 Ma in the TSrURvs.l/fRbdiagram. Rubidium‐strontium and Sm‐Nd systematics of the urengoites indicate a heterogeneous precursor material, derived from Paleoproterozoic continental crust, which underwent Rb/Sr fractionation and partial Sr isotope homogenization in Jurassic times. Any relation between the urengoites and the Haughton impact crater, having within 2s̀ errors an identical age, can be excluded on the basis of isotope relationships and geochemical data.

The only known South‐Ural glass (∼6.2 Ma) is characterized by intermediate SiO2(65 wt%), high Al2O3(14 wt%) and CaO (12 wt%), and low FeOTOT(0.4 wt%) contents. This unique tektite‐like object contains 110 ppm REE displaying a steeply negative C1 normalized distribution with LaN/YbNof 17, and EuN/Eu1of 0.71. The Rb abundance (10 ppm) and Rb/Sr ratio are low, and combined with a “crustal”87Sr/86Sr ratio of 0.722, yielding an unrealistic TSruR age of 2.5 Ga. The Rb‐Sr systematics imply a rather recent parent/daughter element decoupling. The TNdCHUR age of the South‐Ural glass is ∼1690 Ma. Geochemical data suggest that urengoites and the South‐Ural glass belong to two discrete groups of tektites, whose source craters remain to be discovered.
Noble gases and nitrogen in Muong Nong tektites
Authors: MURTY S. V. S.
Published: February 2010

Abstract— Three samples of Muong Nong tektites have been studied for N and noble gases. The isotopic composition of noble gases is airlike. The noble gas amounts are much higher in Muong Nong tektites than in splash‐form tektites. As compared to air, He and Ne have been enriched, most likely due to inward diffuion from ambient air, subsequent to glass formation. Nitrogen contents range from 0.3 to 1.34 ppm, with a non‐atmospheric δ15N ranging from 8 to 17%. The release pattern of δ15N clearly shows the presence of two N components. Higher N/36Ar values than those of air, together with positive δ15N, show that a major portion of N in Muong Nong tektites is a remnant from the sedimentary source material.
Spectral characteristics of iron‐bearing phyllosilicates: Comparison to Orgueil (CI1), Murchison and Murray (CM2)
Authors: CALVIN WENDY M. , KING TRUDE V. V.
Published: February 2010

Abstract— Phyllosilicate alteration minerals are commonly found in low petrologic types of carbonaceous chondrites. Previous spectral studies have examined Mg‐bearing phyllosilicates with limited success in matching the spectral properties of CM and CI chondrites. Transmission electron microscope and other analytical techniques suggest that Fe‐bearing clays are more abundant in CI and CM chondrites than magnesian varieties. Here, we present the results of an examination of the reflectance spectra of Fe‐phyllosilicates, including serpentines and berthierines, of which the latter were formerly known as septechlorites. We have measured the diffuse reflectance spectra of powdered samples from 0.3 to 25 μn. We find that these minerals provide a better spectral match to many of the features seen in CI and CM chondrites, and simple linear combinations of the spectra of both Fe‐ and Mg‐phyllosilicates closely approximate the spectra of CM and CI chondrites.
The nature of silicon carbide: Astronomical observations versus meteoritic evidence
Authors: SPECK A. K. , BARLOW M. J. , SKINNER C. J.
Published: February 2010

Abstract— We have investigated the 7.5–13.5 μm spectra of 30 definite or candidate carbon stars. We discuss the discrepancies between properties of SiC grains found in meteorites and the spectral properties of dust emitting in red giant winds, where most of the meteoritic grains are believed to have formed. We have investigated the nature of carbon star SiC and its relationship to meteoritic SiC dust, by using a X2‐minimisation routine to fit the observed SiC features with laboratory optical constants that have been published for a variety of SiC samples. All but one of the observed astronomical SiC features are best fitted by α‐SiC grains. All but one of the sources with 8–13 μm colour temperatures >1200 K (corresponding to mass‐loss rates at the bottom end of the range) are best fitted by α‐SiC in pure emission; whereas, all but one of the sources with 8–13 μm colour temperatures <1200 K (corresponding to higher mass‐loss rates) are best fitted using self‐absorbed α‐SiC emission. The four sources whose SiC features are in net absorption (and which have the lowest 8–13 μm colour temperatures and, therefore, presumably the highest mass‐loss rates) are also well fitted by self‐absorbed α‐SiC emission but with higher optical depths. Given that β‐SiC is the form most commonly found in meteorites, we have searched for evidence of β‐SiC in the circumstellar shells of all these stars. However, our observations provide no unequivocal evidence for the presence of β‐SiC around these stars. Other discrepancies between meteoritic SiC grains and astronomical spectra are discussed. The self‐absorption that we find in the observed SiC emission features has not previously been taken into account in radiative transfer modeling and so the amount of SiC present in the outflows may have been underestimated in the past.
Infrared spectroscopy of interstellar nanodiamonds from the Orgueil meteorite
Authors: HILL H. G. M. , D'HENDECOURT L. B. , PERRON C. , JONES A. P.
Published: February 2010

Abstract— We present results from an ongoing study of the infrared (IR) and optical properties of nanodiamonds, an objective of which is to identify spectral features in the laboratory that could also be used telescopically to trace the presence of these particles in the interstellar medium (ISM). Fourier transform mid‐and far‐infrared spectra of nanodiamond residue extracted from the Orgueil (CI) chondrite were acquired. All of the mid‐IR bands initially present were found to diminish, with the exception of a band at ∼1100 cm−1, following additional oxidation of the diamonds. The ∼1100 cm−1 band can be predominantly attributed to adsorbed species, especially an ether‐type linkage, while the “oxidisable” features seem to be associated with less stable, surface‐bonded species and residual carbonaceous material. We obtained three far‐IR features but are uncertain about the origin of those at 475 and 188 cm−1. We did not obtain a feature at ∼120 cm−1 reported by another group but do not discount the possibility that the band at 188 cm−1 could be related to it. The weak absorption band at 475 cm−1 (21 μm) is especially interesting because it may be strong in emission from hot nanodiamonds and, therefore, related to the unidentified infrared feature (UIF) observed at this wavelength in the spectra of some C‐rich protoplanetary nebulae.
Mineralogy of meteorite groups: An update
Authors: RUBIN ALAN E.
Published: February 2010

Abstract— Twenty minerals that were not included in the most recent list of meteoritic minerals have been reported as occurring in meteorites. Extraterrestrial anhydrous Ca phosphate should be called merrillite, not whitlockite.
Magnetic properties of Martian meteorites: Implications for an ancient Martian magnetic field
Authors: COLLINSON D. W.
Published: February 2010

Abstract—The magnetic properties of samples of seven Martian meteorites (EET 79001, Zagami, Nakhla, Lafayette, Governador Valadares, Chassigny and ALH 84001) have been investigated. All possess a weak, very stable primary natural remanent magnetization (NRM), and some have less stable secondary components. In some cases, the latter are associated with magnetic contamination of the samples, imparted since their recovery, and with viscous magnetization, acquired during exposure of the meteorites to the geomagnetic field since they fell. The magnetic properties are carried by a small content (<1%) of titanomagnetite and, in ALH 84001, possibly by magnetite as well. The most likely source of the primary NRM is a thermoremanent magnetization acquired when the meteorite material last cooled from a high temperature in the presence of a magnetic field. Current evidence is that this was 1.3 Ga ago for the nakhlites and Chassigny and 180 Ma for shergottites: the time of the last relevant cooling of ALH 84001 is not presently known. Preliminary estimates of the strength of the magnetizing field are in the range 0.5–5 üT, which is at least an order of magnitude greater than the present field. It is tentatively concluded that the magnetic field was generated by a dynamo process in a Martian core with appropriate structure and properties.
Impact origin of the Vesta family
Authors: ASPHAUG ERIK
Published: February 2010

Abstract— The compelling petrographic link (Consolmagno and Drake, 1977; Gaffey, 1983) between basaltic achondrite meteorites and the ∼530 km diameter asteroid 4 Vesta has been tempered by a perceived difficulty in launching rocks from this asteroid's surface at speeds sufficient to bring them to Earth (Wasson and Wetherill, 1979) without obliterating Vesta's signature crust. I address this impasse in response to recent imaging (Zellner et al, 1996; Dumas and Hainaut, 1996) of a ∼450 km impact basin across Vesta's southern hemisphere (Thomas et al., 1997) and model the basin‐forming collision using a detailed two‐dimensional hydrocode with brittle fracture including self‐gravitational compression (cf., Asphaug and Melosh, 1993). A ∼42 km diameter asteroid striking Vesta's basaltic crust (atop a denser mantle and iron core) at 5.4 km/s launches multikilometer fragments up to ∼600 m/s without inverting distal stratigraphy, according to the code. This modeling, together with collisional, dynamical, rheological and exposure‐age timescales (Marzari et al., 1996; Welten et al., 1996), and observations of V‐type asteroids (Binzel and Xu, 1993) suggests a recent (<∼1 Ga) impact origin for the Vesta family and a possible Vesta origin for Earth‐approaching V‐type asteroids (Cruik‐shank et al., 1991).
Rumanová H5 chondrite, Slovaki
Authors: Rojkoviĉ Igor , Siman Pavol , PorubĉAn Vladimír
Published: February 2010

Abstract— An H5 chondrite was found near the village of Rumanová, Slovakia. dominant minerals of the meteorite are enstatite, olivine, kamacite, taenite and troilite. The minor minerals are oligoclase, augite, pigeonite, accessory chromite, whitlockite and chlorapatite. The composition of olivine (Fa19.0) and low‐Ca orthopyroxene (Fs17.0), and the density and chemical composition of the meteorite correspond to those of an H chondrite. Normal zoning of Ni in metal grains and parallel planar fractures in olivine suggest weak shock metamorphism of stage S3. Due to moderate oxidation of metal, iron hydroxides were formed corresponding to weathering stage W2.
Monnig collection meteorites from Forestburg, Davy, Harrison Township and Gurram Kond
Authors: Mccoy T. j. , Ehlmann A. j.
Published: February 2010

Abstract— We report the histories and classifications of poorly known meteorites from the Oscar Monnig meteorite collection. Forestburg (a), Texas, is an L4(S2) ordinary chondrite. Forestburg (b), Texas, is a shock‐blackened L5(S5) ordinary chondrite containing an impact‐melt clast. Davy (a), Texas, L4(S2), is represented by several highly weathered stones. Davy (b), Texas, is a single stone classified as H4(S2). Harrison Township, Kansas, (L6(S4)) was found in the vicinity of several meteorites grouped as Ladder Creek but appears distinct. We have identified the second and largest fragment of the 1814 October Gurram Konda, India, L6(S3) meteorite fall and uncovered details of its early history.
Expected characteristics of cometary meteorites
Authors: CAMPINS Humberto , SWINDLE Timothy D.
Published: February 2010

Abstract— Recent developments in our understanding of comets provide insights into the topic of cometary meteorites. These developments include the identification of comet‐asteroid transition objects (such as 4015 Wilson‐Harrington and 3200 Phaethon), information on the composition of cometary solids, and new ideas on the collisional history of Jupiter‐family comets. In this work, we revisit this question, and we conclude that comets do indeed yield macroscopic meteorites, which either have not been found or have not been recognized. We also consider the expected characteristics of cometary meteorites, with an emphasis on those that may help identify and differentiate them from other types of meteorites. If cometary meteorites have preserved the main characteristics of cometary dust, the mineralogy would be dominated by highly unequilibrated anhydrous silicates, and the chemistry would be nearly chondritic but with a high abundance of C and N. On the other hand, if an unknown process produced extensive aqueous alteration in the material that formed cometary meteorites, they would resemble (or could even be) CI carbonaceous chondrites. We do not expect cometary meteorites to have chondrules. So far, no single meteorite looks unequivocally cometary. However, we have identified xenoliths in ordinary chondrite regolith breccias that meet most of our criteria for a cometary origin and deserve further study.
Meteoritic iron from the Libyan glass area, southwestern Egypt
Authors: BARAKAT Aly A.
Published: February 2010

Abstract— A fragment of a weathered iron meteorite was collected from the Libyan Desert glass area of southwestern Egypt in 1991 May. The specimen is of irregular shape, measuring 5 × 3.5 × 2 cm and weighing 110 g. It is covered by a shiny black layer of magnetite ∼1 mm thick.

The interior is brownish‐black in color owing to terrestrial oxidation. An unetched polished surface shows some areas still having remnants of kamacite and taenite. Remnants of the lamellar octahedral structure have been detected. The kamacite bandwidth ranges from 0.2 mm to 0.8 mm.

Chemical analysis shows that the meteorite contains 3.4% Ni, 0.24% Co, 85 ppm Cu, 4 ppm As, 132 ppm Au and 2530 ppm Ir.

The meteorite was discovered after the discovery of two different chondritic meteorites in the same area; so, it will be named Great Sand Sea 003.
The Juancheng chondrite: A new meteorite fall from China
Authors: CHEN Yongheng , WANG Daode , WANG Ruitian
Published: February 2010

Abstract— A new meteorite, the Juancheng chondrite, fell recently in Juancheng County, Shandong Province, China. It is classified as an H5 (S2) chondrite on the basis of the compositions of olivine (Fa 19.2, σFa 0.46), low‐Ca pyroxene (Fs 16.9, σFs 0.4) and Co contents of kamacite (0.36–0.47 wt%). Plagioclase is compositionally heterogeneous.
Transmission electron microscope study of compact Type A calcium‐aluminum‐rich inclusions from CV3 chondrites: Clues to their origin
Authors: GRESHAKE ANSGAR , BISCHOFF ADDI , PUTNIS ANDREW
Published: February 2010

Abstract— A transmission electron microscope (TEM) study of three coarse‐grained Type A Ca, Al‐rich inclusions (CAIs) from Allende, Acfer 082 and Acfer 086 (all CV3 chondrites) was performed in order to decipher their origin and effects of possible metamorphism. The constituent minerals of the CAIs are found to exhibit very similar microstructural characteristics in each of the inclusions studied. In general, the minerals show a well‐developed equilibrium texture with typical 120° triple junctions. Melilites are clearly considerably strained and characterized by high dislocation densities up to 3 × 1011 cm−2. The dislocations have Burgers vectors of [001], [110] or [011] and often form subgrain boundaries subparallel {100}. Melilite in the Allende CAI additionally contains thin amorphous lamellae mostly oriented parallel to {001}. Fassaite (Al‐Ti‐diopside) is almost featureless even on the TEM scale. Only a few subplanar dislocation walls composed of dislocations with Burgers vectors [001] and 1/2 [110] were detected. Although enclosed within the highly strained melilites, the euhedral spinels contain only low dislocation densities (<2 × 104 cm−2). In the Allende CAI, spinels were found twinned on {111}. Perovskite is also characterized by a low number of linear lattice defects. All grains possess orthorhombic symmetry and are commonly twinned according to a 90° rotation around [101]. Many crystals exhibit typical domain structures as well as curved twin walls where two orthogonal sets intersect. In addition to the mineral phases described above, tiny inclusions of the simple oxides CaO and TiO2 were found within melilite (CaO), spinel (CaO, TiO2) and perovskite (CaO, TiO2). Based on these observations, it is assumed that at the beginning of the formation of the CAIs a condensed solid precursor was present. Euhedral spinels poikilitically enclosed within melilites suggest that this solid aggregate was then molten. If the pure oxides represent relict condensates, their presence proves that this melting was incomplete. While still plastic, the CAIs were shocked by microimpacts causing the high dislocation densities in melilite as well as diaplectic melilite glass and twinned spinels in the Allende CAI. In Acfer 082 and 086, the deformation took place at elevated temperatures, preventing the solid phase transition and mechanical twinning. The absence of linear lattice defects in spinel, fassaite and perovskite most probably reflects inhomogeneous pressure distribution in the polycrystalline CAI as well as the different strengths of the minerals. According to cooling‐rate experiments on perovskite by Keller and Buseck (1994), the dominating (101) twins in the CAI perovskites point to cooling rates ≤50 °C/min. Finally, after crystallization of the CAI was complete, mild thermal metamorphism caused the formation of subgrain boundaries, 120° triple junctions and chemical homogenization of the melilites.
An acid‐etch study of the Kapoeta achondrite: Implications for the argon‐36/argon‐38 ratio in the solar wind
Authors: BECKER R. H. , SCHLUTTER D. J. , RIDER P. E. , PEPIN R. O.
Published: February 2010

Abstract— Noble gases were measured in the Kapoeta achondrite by means of step‐wise closed‐system acid‐etching with H2SO3. Isotopic ratios indicate that He, Ne and Ar are primarily solar in origin, although elemental abundance ratios indicate that the He and Ne have been significantly depleted relative to the Ar. Xenon is dominated by a typical trapped meteoritic component, and the same is probably true for Kr. The initial 11% of the Ar released from the sample by acid etching has a cumulative 36Ar/38Ar ratio of 5.58 ± 0.03, which indicates that the solar wind at some time in the past had a 36Ar/38Ar ratio significantly above previous values suggested for this ratio.
Upper Eocene tektite and impact ejecta layer on the continental slope off New Jersey
Authors: GLASS B. P. , KOEBERL C. , BLUM J. D. , MCHUGH C. M. G.
Published: February 2010

Abstract— During Leg 150 of the Ocean Drilling Project (ODP), two sites (903C and 904A) were cored that have sediments of the same biostratigraphic age as the upper Eocene tektite‐bearing ejecta layer at Deep Sea Drilling Project (DSDP) Site 612. Core 45X from ODP Site 904A (∼4 km north of Site 612) contains a 5 cm thick tektite‐bearing ejecta layer, and Core 56 from Site 903C (∼8 km north‐northwest of Site 904) contains a 2 cm thick layer of impact ejecta without any tektite or impact glass. Shocked quartz and feldspar grains, with multiple sets of planar deformation features (PDFs), and abundant coesite‐bearing grains are present at both sites.

The major oxide contents, trace element compositions, and rare earth element (REE) patterns of the Site 904 tektites are similar to those of the Site 612 tektites and to North American tektites (especially bediasites). The ɛSr and ɛNd values for one composite tektite sample from Site 904 fall within the range previously obtained for the Site 612 tektites, which defines a linear trend that, if extrapolated, would intersect the values obtained for North American tektites. The water contents of eight tektite fragments from Site 904 range from 0.017 to 0.098 wt%, and, thus, are somewhat higher than is typical for tektites. The heavy mineral assemblages of the 63–125 μm size fractions from the ejecta layers at Sites 612, 903, and 904 are all similar. Therefore, we conclude that the ejecta layer at all three sites is from the same impact event and that the tektites at Sites 904 and 612 belong to the North American tektite strewn field.

Clinopyroxene‐bearing (cpx) spherules occur below, or in the lower part of, the main ejecta layer at all three sites. At all three sites, the cpx spherules have been partly or completely replaced with pyrite that preserved the original crystalline textures. Site 612, 903, and 904 cpx spherules are similar to those found in the Caribbean Sea, Gulf of Mexico, central equatorial Pacific, western equatorial Pacific, and eastern Indian Ocean. The cpx event appears to have preceded the North American tektite event by 10–15 ka or less.

The fining‐upward sequence at all three sites and concentration of the denser, unmelted impact ejecta at the top of the tektite layer at Sites 612 and 904 suggest that the tektite‐bearing ejecta layers are not the result of downslope redeposition and that the unmelted ejecta landed after the glass. Geographic variations in thickness of the tektite‐bearing ejecta layer, the lack of carbonate clasts in the ejecta layer, and the low CaO content of the tektite glass suggest that the ejecta (including the tektite glass) were derived from the Chesapeake Bay structure rather than from the Toms Canyon structure.

A sharp decline in microfossil abundances suggests that local environmental changes caused by the impact may have had adverse effects on benthic foraminifera, radiolaria, sponges, and fish as well as the planktic foraminifera.
Constraints on the size of the Vredefort impact crater from numerical modeling
Authors: TURTLE E. P. , PIERAZZO E.
Published: February 2010

Abstract— The Vredefort structure in South Africa was created by a meteorite impact about two billion years ago. Since that time, the crater has been deeply eroded; so to estimate its original size, researchers have had to rely heavily upon comparison to other terrestrial impact structures. Recent estimates of the original crater diameter range from 160 km to as much as 400 km. In this study, we combined the capabilities of both hydrocode and finite‐element modeling, using the former to predict where the pressure of an impact‐generated shock wave would have been high enough to form planar deformation features (PDFs) and shatter cones and the latter to follow the subsequent displacement of these shock isobars during the collapse of the crater. We established constraints on the sizes of the projectile and the transient crater (and, thus, on the size of the final crater) by comparing the observed locations of PDFs around Vredefort to the results of our simulations of impacts by projectiles of various sizes. These simulations indicate that a rocky projectile with a diameter of ∼10 km, impacting vertically at a velocity of 20 km/s generates shock pressures that are consistent with the distribution of PDFs around Vredefort. These projectile parameters correspond to a transient crater ∼80 km in diameter or a final crater ∼120–160 km in diameter. Allowing for uncertainties in our modeling procedures, we consider final craters 120 to 200 km in diameter to be consistent with the observed locations of PDFs at Vredefort. The shock pressure contour corresponding to the formation of shatter cones is almost horizontal near the surface, making the locations of these features less useful constraints on the crater size. However, they may provide a constraint on the amount of erosion that has occurred since the impact.
A genetic algorithm scheme for pairing meteorite finds
Authors: CONWAY A. J. , BLAND P. A.
Published: February 2010

Abstract— A genetic algorithm is employed to perform the pairing of meteorite fragments based on various characteristics measured from thin sections using an image analysis program and from analyses routinely carried out during classification. The genetic algorithm searches for best group pairings by generating a population of trial pairs, linking them together to form groups, and evolving the population, so that only pairs that are members of likely pairing groups survive to the next generation of the population. In this way, meaningful pairing groups will emerge from the population, as long as characteristics from within real pairing groups have variance sufficiently small compared to the variance between groups. What constitutes “sufficiently small” is discussed and investigated by testing the genetic algorithm method on artificial data, which shows that, in principle, the method can achieve a 100% success rate. The method is then tested on real data whose pairing groups are definitely known. This is achieved by gathering data from the image processing of several scenes of the same meteorite thin section, treating each scene as a separate fragment. Using thin sections from the Reg el Acfer meteorite population, we find that the genetic algorithm identifies almost all of the main pairing groups, with about half the groups being found in their entirety; the pairwise success rate being 76%. Although this methodology requires some refinement before it could be applied to a population of meteorite fragments, these preliminary results are encouraging. The potential benefit of an automated approach lies in the tremendous savings in time and effort, allowing meaningful and reproducible pairings to be made from data sets that are prohibitively large for a human being.
In situ determination of iodine content and iodine‐xenon systematics in silicates and troilite phases in chondrules from the LL3 chondrite Semarkona
Authors: GOSWAMI J. N. , SAHIJPAL S. , KEHM K. , HOHENBERG C. M. , SWINDLE T. , GROSSMAN J. N.
Published: February 2010

Abstract— Iodine concentrations in small domains (∼10 μm) of silicates and troilite (FeS) phases in three chondrules from the Semarkona (LL3) meteorite were determined by an ion microprobe. Independent determination of I content in some of these phases was accomplished by in situ laser probe mass spectrometric analysis of I‐derived 128Xe in one of these neutron‐irradiated chondrules. The ion microprobe data suggest low I content for olivines (20–45 ppb) and relatively higher values for pyroxene and glass (mesostasis) (40–160 ppb). The broad similarity in the measured I contents in pyroxenes in a porphyritic pyroxene chondrule by ion microprobe (42–138 ppb) and by laser probe (37–76 ppb) demonstrate the feasibility of in situ determination of I content in silicate phases via ion microprobe. The I contents in troilite measured by ion microprobe, however, are prone to uncertainty because of the lack of a sulfide standard. The ion microprobe data suggest I content of > 1 ppm in troilite, if the calibration from our silicate standard is used. However, the noble gas data suggest that the I content in troilite is comparable to that in silicates. We attribute this apparent discrepancy to an enhanced sputter ion yield of I from sulfides. Iodine‐derived 129Xe excesses were observed in both pyroxene and troilite within this chondrule. The I‐Xe model ages of these selected phases are consistent with the I‐Xe studies of the bulk chondrule. The individual data points fall on or near the isochron obtained from the bulk chondrule, although all except the most radiogenic data point contain evidence of low‐temperature uncorrelated iodine.
Trends in the study of presolar dust grains from primitive meteorites
Authors: ZINNER ERNST
Published: February 2010

Abstract— A series of trends can be discerned in the study of presolar dust grains from primitive meteorites, and these trends might give us hints in which direction this new field of astronomy is developing. They include: (1) a focus on ever smaller components of meteorites; (2) a shift from the study of the elemental abundances in the solar system to the study of isotopic abundances; (3) a shift of emphasis from averages of the isotopic abundances as represented by the whole solar system to individual isotopic components preserved in circumstellar dust grains; (4) the preferential study of rare types of presolar dust grains; (5) the emergence of new technical capabilities for the study of individual presolar dust grains; examples include isotopic imaging and resonance ionization mass spectrometry (RIMS); and (6) a shift from a situation in which grain data confirm previously held theoretical ideas to a situation in which the experimental data impose new constraints on theoretical models of nucleosynthesis, stellar mixing and grain formation in stellar outflows. In other words, the data do not confirm but drive the theory. An example is the distribution of Si isotopic ratios in individual mainstream SiC grains for which many different theoretical explanations have been offered.

There are still many unsolved problems posed by the grain data, the most difficult being the interpretation of the isotopic ratios of grains with a supernova signature (evidence for 44Ti and excesses in 28Si) in terms of theoretical models of nucleosynthesis and the mixing of supernova ejecta. Future progress is expected to come from the analysis of larger numbers of grains, the search for new types of presolar grains, the analysis of smaller grains and of more elements in a given grain, both made possible by the increase in sensitivity of ion microprobes and the extended application of RIMS, from multi‐dimensional models of stellar evolution with enlarged nuclear networks, and from new measurements of nuclear cross sections.
Martian atmospheric and indigenous components of xenon and nitrogen in the Shergotty, Nakhla, and Chassigny group meteorites
Authors: MATHEW K. J. , KIM J. S. , MARTI K.
Published: February 2010

Abstract— In a study of the isotopic signatures of trapped Xe in shock‐produced glass of shergottites and in ALH 84001, we observe three components: (1) modern Martian atmospheric Xe that is isotopically mass fractionated relative to solar Xe, favoring the heavy isotopes, (2) solar‐like Xe, as previously observed in Chassigny, and (3) an isotopically fractionated (possibly ancient) component with little or no radiogenic 129Xerad. In situ‐produced fission and spallation components are observed predominantly in the high‐temperature steps. Heavy N signatures in ALH 84001, EET 79001 and Zagami reveal Martian atmospheric components. The low‐temperature release of ALH 84001 shows evidence for the presence of a light N component (δ15N ≤ ‐21%), which is consistent with the component observed in the other Shergotty, Nakhla and Chassigny (SNC) group meteorites. The highest observed 129Xe/130Xe ratio of 15.60 in Zagami and EET 79001 is used here to represent the present Martian atmospheric component, and the isotopic composition of this component is compared with other solar system Xe signatures. The 129Xe/130Xe ratios in ALH 84001 are lower but appear to reflect varying mixing ratios with other components. The consistently high 129Xe/130Xe ratios in rocks of different radiometric ages suggest that Martian atmospheric Xe evolved early on. As already concluded in earlier work, only a small fission component is observed in the Martian atmospheric component. Assuming that a chondritic 244Pu/129I initial ratio applies to Mars, this implies that either Pu‐derived fission Xe is retained in the solid planet (in fact, in situ‐produced fission Xe is observed in ALH 84001) or may reflect a very particular degassing history of the planet.
Noble gases and chemical composition of Shergotty mineral fractions, Chassigny, and Yamato 793605: The trapped argon‐40/argon‐36 ratio and ejection times of Martian meteorites
Authors: TERRIBILINI DARIO , EUGSTER OTTO , BURGER MARIO , JAKOB ALFRED , KräHENBÜHL URS
Published: February 2010

Abstract— We report the elemental and isotopic composition of the noble gases as well as the chemical abundances in pyroxene, maskelynite/mesostasis glass, and bulk material of Shergotty and of bulk samples from Chassigny and Yamato 793605. The 40K‐40Ar isochron for the Shergotty minerals yields a gas retention age of 196 Ma, which is, within errors, in agreement with previously determined Rb‐Sr internal isochron ages. Argon that was trapped at this time has a 40Ar/36Ar ratio of 1100. For Chassigny and Y‐793605, we obtain trapped 40Ar/36Ar ratios of 1380 and 950, respectively. Using these results and literature data, we show that the three shergottites, Shergotty, Zagami, and QUE 94001; the lherzolites ALH 77005, LEW 88516, and Y‐793605; as well as Chassigny and ALH 84001 contain a mixture of Martian mantle and atmospheric Ar; whereas, the trapped 40Ar/36Ar ratio of the nakhlites, Nakhla, Lafayette, and Governador Valadares cannot be determined with the present data. We show that Martian atmospheric trapped Ar in Martian meteorites is correlated with the shock pressure that they experienced. Hence, we conclude that the Martian atmospheric gases were introduced by shock into the meteoritic material. For the Shergotty minerals, we obtain 3He‐, 21Ne‐, and 38Ar‐based cosmic‐ray exposure ages of 3.0 Ma, and for the lherzolite Y‐793605, 4.0 Ma, which confirms our earlier conclusion that the lherzolites were ejected from Mars ∼1 Ma before the shergottites. Chassigny yields the previously known ejection age of 11.6 Ma.