bluuebunny/crossref_metadata_2025 huggingface dataset:
Asteroid 6 Hebe: The probable parent body of the H‐type ordinary chondrites and the IIE iron meteorites
Authors: GAFFEY Michael J. , GILBERT Sarah L.
Published: February 2010

Abstract— The S(IV)‐type asteroid 6 Hebe is identified as the probable parent body of the H‐type ordinary chondrites and of the IIE iron meteorites. The ordinary chondrites are the most common type of meteorites falling to Earth; but prior to the present study, no large mainbelt source bodies have been confirmed. Hebe is located adjacent to both the v6 and 3:1 resonances and has been previously suggested as a major potential source of the terrestrial meteorite flux. Hebe exhibits subtle rotational spectral variations, indicating the presence of some compositional variations across its surface. The silicate portion of the surface assemblage of Hebe is consistent (both in overall average and in its range of variation) with the silicate components in the suite of H‐type chondrites. The high albedo of Hebe rules out a lunar‐style space weathering process to produce the weakened absorption features and reddish spectral slope in the S‐type spectrum of Hebe. Linear unmixing models show that a typical Ni‐Fe metal spectrum is consistent with the component that modifies an H‐chondrite spectrum to produce the S‐type spectrum of Hebe. On the basis of the association between the H chondrites and the HE iron meteorites, our model suggests that large impacts onto the relatively metal‐rich H‐chondrite target produced melt bodies (sheets or pods) that differentiated to form thin, laterally extensive near‐surface layers of Ni‐Fe metal. Fragments of the upper silicate portions of these melt bodies are apparently represented by some of the igneous inclusions in H‐chondrite breccias. Alternately, masses of metal could have been deposited on the surface of Hebe by the impact of a core or core fragment from a differentiated parent body of H‐chondrite composition. Subsequent impacts preferentially eroded and depleted the overlying silicate and regolith components, exposing and maintaining large masses of metal at the optical surface of Hebe. In this interpretation, the nonmagmatic IIE iron meteorites are samples of the Ni‐Fe metal masses on the surface of Hebe, whereas the H chondrites are samples from between and/or beneath the metal masses.
Aerial crystallization of hematite in impact bombs from the Araguainha astrobleme, Mato Grosso, central Brazil
Authors: HIPPERTT J. , LANA C.
Published: February 2010

Abstract— Optical and scanning electron microscope (SEM) observations of hematite impact bombs from the Araguainha astrobleme in central Brazil reveal an aerodynamically stable microstructure, which is interpreted to reflect the aerial crystallization of hypervelocity melt globules derived from Fe‐rich sedimentary target rocks. The bombs are composed of an aggregate of preferentially oriented conic units with different degrees of packing, giving rise to porous and massive hematite varieties. These varieties generally occupy the front and rear of the bombs, respectively. Quartz fragments with planar deformation features are common in the porous domains and represent ejected solid particles captured by the bombs during cooling. The absence of typical contorted shapes in these bombs reflects the lack of spin during their ballistic trajectory. The bombs are enriched in Rh (4×); Ru, Ir, and Pd (5×); and Pt (>30×) relative to the indigenous level of target sediments. This suggests the presence of a projectile‐derived component in their constitution. Single composition oxidic bombs (pure hematite and pure silica) predominate in this occurrence, indicating that a mechanism of segregation has operated in the ejected melt volumes.
A survey of shergottite, nakhlite and chassigny meteorites whole‐rock compositions
Authors: LODDERS K.
Published: February 2010

Abstract— Literature data on major and trace elemental abundances and water contents of the shergottite, nakhlite, and chassigny (SNC) meteorites are compiled and evaluated. The individual members of the SNC group are relatively homogeneous, and representative average compositions for each meteorite can be computed from multiple data reported in the literature. Major element abundances are used to calculate normative compositions and densities. The data survey shows that our knowledge of whole rock abundances in SNC meteorites is very limited for many elements and that more basic analytical work is needed.
Classification of four new Roosevelt County meteorites
Authors: BENEDIX G. K. , KEIL K.
Published: February 2010

Abstract— We have classified four new ordinary chondrites from Roosevelt County, New Mexico (RC 091–094) that were found in June and July of 1994 by I. Wilson. They include one H4(S2) and three L5(S4) chondrites. Degree of weathering is variable and ranges from W2–6.
The Galkiv meteorite: A new H4 chondrite from Ukraine
Authors: SEMENENKO V. P. , GIRICH A. L.
Published: February 2010

Abstract— The Galkiv chondrite is a single 5 kg stone that fell in the Chernigov region of Ukraine on 1995 January 12. The composition of olivines in the meteorite indicate that Galkiv belongs to the H group of ordinary chondrites. Although the heterogeneity of olivine corresponds to a petrologic type 5 and the heterogeneity of low‐Ca pyroxene suggests the chondrite is type 3, clearly defined chondrule boundaries, the presence of clinopyroxene, cryptocrystalline glass and rare grains of feldspatic plagioclase, structural evidences of shock metamorphism and very low level of terrestrial weathering allow us to classify the meteorite as an H4 chondrite of shock stage S3 and weathering grade WO.
The crystalline lunar spherules: Their formation and implications for the origin of meteoritic chondrules
Authors: SYMES STEVEN J. K. , SEARS DEREK W. G. , AKRIDGE D. GLEN , HUANG SHAOXIONG , BENOIT PAUL H.
Published: February 2010

Abstract— Crystalline lunar spherules (CLS) from three thin sections of Apollo 14 regolith breccias (14318,6; 14318,48 and 14315,20) have been examined. The objects have been classified and their abundances, size distributions, bulk compositions, and (where possible) plagioclase compositions determined. By number, 64% consist predominantly of very fine‐grained equant plagioclase grains but can also contain larger (∼50 μm) feldspar crystals (type X), while 22% contain plagioclase lathes in a fine‐grained mafic mesostasis (type Y). Plagioclase in both spherule types displays bright yellow cathodoluminescence that is conspicuous among the blue CL of the normal feldspar of the breccias. Type Z spherules (5%) contain feldspar with blue CL and minor amounts of olivine and pyroxene. Type Q spherules (4%) contain feldspar with yellow CL but in a luminescent mesostasis (of quartz or feldspar?). A few spherules are mixtures of type Y and type X textures. Most type X spherules, and a few type Y spherules, have fine‐grained opaque rims. Compound objects were also found and consist of two or more CLS that appear to have collided while still plastic or molten. The CLS are thought to be impact spherules that crystallized in free flight, their coarse textures suggesting fairly slow cooling rates (∼ <1 °C/s). The abundance of the CLS resembles that of chondrules in the CM chondrite Murchison, and their cumulative size‐frequency distributions are very similar to those of the chondrules in several meteorite classes. The bulk compositions of the CLS do not resemble regoliths at any of the Apollo sites, including Apollo 14, or any of the common impact glasses, but they do resemble the bulk compositions of several lunar meteorites and the impact glasses they contain. The Apollo 14 site is located on a region containing Imbrium ejecta, and we suggest that the CLS derive from the Imbrium impact. Ballistic calculations indicate that only impact events of this size on the Moon are capable of producing melt spherules with the required free flight times and slow cooling rates. Smaller impacts produce glassy spherules and agglutinates. As has been pointed out many times, the CLS have many properties in common with meteoritic chondrules. While much remains unclear, difficulties with a nebular origin and new developments in chondrule chronology, studies of asteroid surfaces and impact ejecta behavior, and the present observations indicate that meteoritic chondrules could have formed by impact.
Noble gases, bulk chemistry, and petrography of olivine‐rich achondrites Eagles Nest and Lewis Cliff 88763: Comparison to brachinites
Authors: SWINDLE T. D. , KRING D. A. , BURKLAND M. K. , HILL D. H. , BOYNTON W. V.
Published: February 2010

Abstract— Eagles Nest and Lewis Cliff (LEW) 88763 are olivine‐rich achondrites that have been suggested to be related to Brachina and ALH 84025. Both are ultramafic, although LEW 88763 has ∼10% plagioclase, which Eagles Nest lacks. Olivine in Eagles Nest (Fo68) is virtually identical in composition to that in Brachina (Fo68–70), and that in LEW 88763 is only slightly different (Fo63–64). The meteorites' cosmic‐ray exposure ages differ from each other and from Brachina and ALH 84025. Like Brachina, Eagles Nest has a substantial amount of radiogenic 129Xe and an apparent K‐Ar age of <4.5 Ga. Lewis Cliff 88763, on the other hand, has no detectable radiogenic 129Xe, an apparent K‐Ar age of ∼4.5 Ga, and a substantial amount of trapped Xe. The chemical composition of LEW 88763 is within a factor of two of chondritic for virtually every element analyzed, including siderophiles, which suggests that it was melted (or at least heated and recrystallized) in a closed system. Analyses of the chemical composition of Eagles Nest are hampered by extensive terrestrial weathering; but it appears to be broadly chondritic also, although it, like Brachina, is depleted in siderophiles. Our data suggest that Eagles Nest is genetically related to Brachina but that LEW 88763 is not, which is a conclusion that is consistent with the O isotopic data of Clayton and Mayeda (1996).
On the lower limit of chondrule cooling rates: The significance of iron loss in dynamic crystallization experiments
Authors: WEINBRUCH STEPHAN , BÜTTNER HEINZ , HOLZHEID ASTRID , ROSENHAUER MATTHIAS , HEWINS ROGER H.
Published: February 2010

Abstract— Dynamic crystallization experiments performed with different container materials (Fe crucible, pure Pt wire loop, presaturated Pt wire loop) demonstrate the strong influence of Fe loss on texture, mineralogy and chemical zoning in olivine. The use of pure Pt wire loops results in severe Fe loss and prevents the development of strong Fe/Mg zoning in olivine in slower cooled runs (≤ 100 °C/h). Presaturated Pt wire loops reduce Fe loss to some extent but not completely. If severe Fe loss from the melt is avoided by the use of Fe crucibles, then cooling rates between 2000 and 1.2 °C/h yield textures, modal mineral abundances and Fe/Mg zoning in olivine comparable to natural porphyritic olivine chondrules. However, Fe gain from the crucible may possibly enhance Fe/Mg zoning in olivine for cooling rates < 10 °C/h. Therefore, it is concluded that the lower limit of cooling rates of porphyritic olivine chondrules derived from dynamic crystallization experiments is 10 °C/h, perhaps it is even lower, on the order of a few degrees Celsius per hour. This value is not significantly different from estimates for subsolidus temperatures based on the microstructure of chondrule minerals (Weinbruch and Müller, 1995). The lower limit of chondrule cooling rates of 100 °C/h advocated by Hewins (1988) and Radomsky and Hewins (1990) seems to be an artifact of the experimental technique, as their samples were crystallized in pure Pt wire loops.
Inversion of crater morphometric data to gain insight on the cratering process
Authors: HERRICK ROBERT R. , LYONS SUZANNE N.
Published: February 2010

Abstract— In recent years, morphometric data for Venus and several outer planet satellites have been collected, so we now have observational data of complex craters formed in a large range of target properties. We present general inversion techniques that can utilize the morphometric data to quantitatively test various models of complex crater formation. The morphometric data we use in this paper are depth of a complex crater, the diameter at which the depth‐diameter ratio changes, and onset diameters for central peaks, terraces, and peak rings. We tested the roles of impactor velocities and hydrostatic pressure vs. crustal strength, and we tested the specific models of acoustic fluidization (Melosh, 1982) and nonproportional growth (Schultz, 1988). Neither the acoustic fluidization model nor the nonproportional growth in their published formulations are able to successfully reproduce the data. No dependence on impactor velocity is evident from our inversions. Most of the morphometric data is consistent with a linear dependence on the ratio of crustal strength to hydrostatic pressure on a planet, or the factor c/p g.
New Chilean iron meteorites: Medium octahedrites from Northern Chile are unique
Authors: WASSON JOHN T. , DE BON CLAUDIO CANUT
Published: February 2010

Abstract— We report data on three new iron meteorites from Northern Chile and propose names. All are unnamed iron meteorites from the meteorite collection at the Universidad de La Serena. For two, the provenance is unknown; for the third, the presumed discovery site is in the countryside east of Iquique. The three meteorites have been analyzed by instrumental neutron activation analysis (INAA) and their structures examined with a binocular microscope. La Serena is a complete 663 g iron, a new member of group IIICD; it is not paired with any other iron. Elqui has a mass of 260 g; two faces are fractures, possibly produced by human actions, but fusion crust appears to be present on some of the remaining surface. It is a hexahedrite and a member of group IIAB, but its composition differs from that of all other Chilean hexahedrites. The third iron, Pozo Almonte, is a medium octahedrite member of group IIIAB, one of the most common meteorite groups. To find out whether it is paired, we assembled a full set of IIIAB iron meteorites from Northern Chile. Our compositional data show that Pozo Almonte is not paired with any other IIIAB iron, and that there are no pairings within the full set with the possible exception of Joel's Iron and Sierra Sandon, which differ only in their contents of Ir, 0.39 and 0.34 μg/g, respectively. However, Buchwald's (1975) structural observations rule out this possible pairing. We find appreciable differences in Cu, As and Au between the previously paired IIIAB irons Chañaral and Ilimaës and conclude that these should not be paired.
Effects of liquid immiscibility on trace element fractionation in magmatic iron meteorites: A case study of group IIIAB
Authors: ULFF‐MØLLER FINN
Published: February 2010

Abstract— Magmatic iron meteorites are generally agreed to represent metal that crystallized in asteroidal cores from a large pool of liquid. Estimates suggest that the metallic liquid contained significant amounts of S and P, both of which are incompatible and exert a strong effect on trace element partitioning. In tandem, S and P are also prone to cause immiscibility between sulfide liquid and P‐rich metal liquid. The liquid immiscibility field occupies ∼70% of the portion of the Fe‐Ni‐S‐P system in which Fe is the first phase to crystallize. In spite of this, previous fractional crystallization models have taken into account only one liquid phase and have encountered significant discrepancies between the meteorite data and model values for the key elements Ni, Ir, Ga, Ge and Au at even moderate degrees of fractionation.

For the first time, a model for trace element partitioning between immiscible liquids in the Fe‐Ni‐S‐P system is presented in order to assess the effects on fractionation in magmatic iron meteorite groups. The onset of liquid immiscibility causes a significant change in the enrichment patterns of S and P in both liquids; so elements with contrasting partitioning behavior will show trends deviating clearly from one‐liquid trends. A trend recorded in the solid metal will either be a smooth curve as long as equilibrium is maintained between the two liquids or the trend may diverge into a field limited by two extreme curves depending on the degree of disequilibrium. Bulk initial liquids for most magmatic groups have S/P (wt%) ratios well below 25. In these cases and due to the constitution of the Fe‐Ni‐S‐P system, most of the metal will crystallize from the rapidly decreasing volume of metal liquid and only a subordinate amount from the sulfide liquid. Because of the strong extraction of P into the metal liquid, P will have a much larger influence on trace element partitioning than a low initial P content might suggest.

My model calculations suggest that liquid immiscibility played a significant role during the solidification of the IIIAB parent body's core. The two‐liquid model reproduces the IIIAB trends more closely than previous one‐liquid models and can account for: (a) the general widening of the IIIAB trend with increasing Ni and decreasing Ir contents, (b) the occurrence of high‐Ni members that are not strongly depleted in Ir, Ga and Ge; and (c) an upper limit at ∼11 wt% Ni where the metal liquid was almost consumed.
Paucity of sulfide in a large slab of Esquel: New perspectives on pallasite formation
Authors: ULFF‐MØLLER FINN , CHOI BYEON‐GAK , RUBIN ALAN E. , TRAN JACQUELYN , WASSON JOHN T.
Published: February 2010

Abstract— The 0.7 ton Esquel meteorite, found in Patagonia before 1951, is a typical main‐group pallasite in most respects. We examined petrographically a slab ∼1 m long having an area of 3000 cm2 that shows the typical pallasitic texture with fragmental olivine. Phase abundances (in vol%) are olivine (66%), metal (32%), schreibersite (0.76%), troilite (0.46%) and chromite (0.31%). Esquel can be divided into four lithologies: (1) “pallasitic” matrix consisting of olivine fragments embedded in metal (81%); (2) large (>5 cm) olivine nodules having low metal contents (18%); (3) massive metal (0.3%); and (4) zones dominated by FeS and fine olivine (0.7%). Main‐group pallasites appear to have formed by the intrusion of a highly evolved (low Ir, high Ni, Au and S) metallic magma into fragmented olivine. This model implies that FeS should be abundant in main‐group pallasites, and we had speculated that examination of an exceptionally large slab might reveal a high troilite content. We found instead an exceptionally low FeS content. New compositional data confirm that Esquel has a lower Au content than other main‐group pallasites having similar Ir contents. Literature data (based, however, on relatively small sections) suggest that high‐Au pallasites have higher S contents than Esquel but have lower S contents than expected from a trapped‐melt model. We conclude that a relatively complex model is required to explain the origin of main‐group pallasites. After intrusion, the degree of crystallization of the metallic magma varied from location to location but, in almost all cases, an FeS‐rich liquid either escaped or formed FeS‐rich pallasitic rocks that are underrepresented in the meteorite inventory.
Noble gases in twenty‐one Saharan LL‐chondrites: Exposure ages and possible pairings
Authors: SCHERER P. , HERRMANN S. , SCHULTZ L.
Published: February 2010

Abstract— Nineteen LL‐chondrites and two L/LL‐chondrites (Adrar 003 and Tanezrouft 010) from the Saharan desert of Algeria and Libya have been analysed for their He, Ne and Ar composition as well as for their abundance of 84Kr and 132Xe. Calculated 21Ne cosmic‐ray exposure ages vary between 2 and 35 Ma. The age distribution is consistent with that of modern LL‐chondrite falls except that no dominant peaks can be observed, especially not the one related to a 15 Ma collisional event. However, the lack of young exposure ages of <8 Ma is obvious. This is a characteristic feature of LL‐chondrites. Only one of the 21 LL‐chondrites, namely Acfer 066, contains solar gases and is thus considered a regolith breccia. Three specimens reveal considerable loss of 3He, probably due to periods of elevated temperatures in orbits with small perihelion distances. Furthermore, severe loss of 4He and 40Ar is found in two samples. Considering possible pairings, we suggest 14 individual falls basically on the basis of the noble gas data, the petrographic sub‐classification and by taking the find location into consideration. However, there are constraints on confirming pairings solely on the basis of our studies. Thus, we can only exclude individual samples with a unique noble gas fingerprint from paired specimens.
Heating experiments simulating atmospheric entry heating of micrometeorites: Clues to their parent body sources
Authors: GRESHAKE ANSGAR , KLÖCK WOLFGANG , ARNDT PETER , MAETZ MISCHA , FLYNN GEORGE J. , BAJT SASA , BISCHOFF ADDI
Published: February 2010

Abstract— Depending on their velocity, entry angle and mass, extraterrestrial dust particles suffer certain degrees of heating during entry into Earth's atmosphere, and the mineralogy and chemical composition of these dust particles are significantly changed. In the present study, pulse‐heating experiments simulating the atmospheric entry heating of micrometeoroids were carried out in order to understand the mineralogical and chemical changes quantitatively as well as to estimate the peak temperature experienced by the particles during entry heating. Fragments of the CI chondrites Orgueil and Alais as well as pyrrhotites from Orgueil were used as analogue material. The experiments show that the volatile elements S, Zn, Ga, Ge, and Se can be lost from 50 to 100 μm sized CI meteorite fragments at temperatures and heating times applicable to the entry heating of similar sized cosmic dust particles. It is concluded that depletions of these elements relative to CI as observed in micrometeorites are mainly caused by atmospheric entry heating. Besides explaining the element abundances in micrometeorites, the experimentally obtained release patterns can also be used as indicators to estimate the peak heating of dust particles during entry. Using the abundances of Zn and Ge and assuming their original concentrations close to CI, a maximum heating of 1100–1200 °C is obtained for previously analyzed Antarctic micrometeroites. Thermal alteration also strongly influenced the mineralogy of the meteorite fragments. While the unheated samples mainly consisted of phyllosilicates, these phases almost completely transformed into olivine and pyroxene in the fragments heated to ≥800 °C. Therefore, dust particles that still contain hydrous minerals were probably never heated to temperatures ≥800 °C in the atmosphere. During continued heating, the grain size of the newly formed silicates increased and the composition of the olivines equilibrated. Applying these results quantitatively to Antarctic micrometeorites, typical peak temperatures in the range of 1100–1200 °C during atmospheric entry heating are deduced. This temperature range corresponds to the one obtained from the volatile element concentrations measured in these micrometeorites and points to an asteroidal origin of the particles.
Anorthite‐spinel‐rich inclusions in the Ningqiang carbonaceous chondrite: Genetic links with Type A and C inclusions
Authors: LIN Y. , KIMURA M.
Published: February 2010

Abstract— Many Ca‐Al‐rich inclusions (CAIs) were molten once, and the question of what their precursors consisted of is controversial. In this paper, we report a new type of anorthite‐spinel‐rich inclusion (ASI) in the Ningqiang carbonaceous chondrite. The modal and bulk compositions of the ASIs are similar to those of Type C inclusions but with nonmolten textures. The ASIs are proposed to be the precursors of Type C inclusions. The ASIs show alteration textures, with melilite being replaced by anorthite and Ca‐pyroxene. Furthermore, compositions of the melilites and the calculated modal and bulk compositions of the possible precursors of the ASIs are close to those of the spinel‐rich Type A inclusions in the Ningqiang meteorite, which suggests that ASIs formed by alteration of the latter in the solar nebula. Petrography and mineral chemistry of one Type C inclusion in Ningqiang are also reported.
Geophysical profile of the Roter Kamm impact crater, Namibia
Authors: BRANDT DION , REMOLD WOLF UWE , FRANZSEN ALAN J. , KOEBERL CHRISTIAN , WENDORFF LUTZ
Published: February 2010

Abstract— New gravity and magnetic data were obtained along ground profiles across the Roter Kamm impact crater in the southern Namib desert of Namibia. As the traverses of previous studies did not extend sufficiently beyond the crater rim, it had not been possible to adequately determine the regional background values. The gravity results of this study are similar to those obtained by Fudali in 1973, in that a negative, near‐symmetrical anomaly was obtained over the crater center. This anomaly conforms to the results expected for a sediment and impact breccia‐filled, simple bowl‐shaped crater. The magnetic results of this study, however, are different to those previously reported, which is most probably as a result of the longer profiles used in this new study. A slight positive magnetic anomaly was obtained over the crater interior. Short‐wavelength, high‐amplitude anomalies observed in the vicinity of the crater rim reflect magnetization contrasts that are probably related to brecciation and block rotation. Modelling of the positive magnetic anomaly indicates the possibility of a small magnetic body or lining at the crater floor‐breccia interface in the interior of the crater. Also presented is a 10 m contour digital elevation model of the crater and its environs.
Arcuate band texture in a dark inclusion from the Vigarano CV3 chondrite: Possible evidence for early sedimentary processes
Authors: TOMEOKA KAZUSHIGE , KOJIMA TOMOKO
Published: February 2010

Abstract— A dark inclusion in the Vigarano CV3 carbonaceous chondrite consists almost exclusively of small (<5 μm in diameter) grains of Fe‐rich olivine and is devoid of chondrules, Ca‐Al‐rich inclusions (CAIs) and their pseudomorphs. In backscattered electron images, this dark inclusion shows an unusual texture comprising a network of arcuate bands. Two or more bands occur roughly parallel, forming a set of succesive parallel bands, some crosscutting one another. The bands contain slightly higher amounts of relatively small (<1 μm) olivine grains and so are more densely packed than other areas. The olivine grains in the bands are slightly more Fe‐rich than those in other areas. The bands commonly show gradation on the concave side due to a decrease in the abundance of the small Fe‐rich olivine grains. Texturally, the arcuate bands closely resemble “dish structures” that are commonly observed in siltstones and sandstones on Earth. Dish structures are characterized by thin, dark‐colored, subhorizontal to concave‐upward laminations that are rich in relatively fine‐grained material. On Earth, dish structures form during compaction and dewatering of unconsolidated fine‐grained sediments; they are one of the characteristic sedimentary structures formed through fluidization of fine grains. The dark inclusion in Vigarano, therefore, provides the first evidence that sedimentary processes due to water migration may have taken place within planetesimals and further suggests that fluidization may have played a significant role in the formation of the carbonaceous chondrites.
The origin of chondritic macromolecular organic matter: A carbon and nitrogen isotope study
Authors: ALEXANDER C. M. O'D. , RUSSELL S. S. , ARDEN J. W. , ASH R. D. , GRADY M. M. , PILLINGER C. T.
Published: February 2010

Abstract— The N and C abundances and isotopic compositions of acid‐insoluble carbonaceous material in thirteen primitive chondrites (five unequilibrated ordinary chondrites, three CM chondrites, three enstatite chondrites, a CI chondrite and a CR chondrite) have been measured by stepped combustion. While the range of C isotopic compositions observed is only ∼δ13C = 30%, the N isotopes range from δ15N ' ‐40 to 260%. After correction for metamorphism, presolar nanodiamonds appear to have made up a fairly constant 3–4 wt% of the insoluble C in all the chondrites studied. The apparently similar initial presolar nanodiamond to organic C ratios, and the correlations of elemental and isotopic compositions with metamorphic indicators in the ordinary and enstatite chondrites, suggest that the chondrites all accreted similar organic material. This original material probably most closely resembles that now found in Renazzo and Semarkona. These two meteorites have almost M‐shaped N isotope release profiles that can be explained most simply by the superposition of two components, one with a composition between δ15N = ‐20 and ‐40% and a narrow combustion interval, the other having a broader release profile and a composition of δ15N ∼ 260%. Although isotopically more subdued, the CI and the three CM chondrites all appear to show vestiges of this M‐shaped profile. How and where the components in the acid‐insoluble organics formed remains poorly constrained. The small variation in nanodiamond to organic C ratio between the chondrite groups limits the local synthesis of organic matter in the various chondrite formation regions to at most 30%. The most 15N‐rich material probably formed in the interstellar medium, and the fraction of organic N in Renazzo in this material ranges from 40 to 70%. The isotopically light component may have formed in the solar system, but the limited range in nanodiamond to total organic C ratios in the chondrite groups is consistent with most of the organic material being presolar.
Martian meteorites: Volatile trace elements and cluster analysis
Authors: WANG MING‐SHENG , MOKOS JENNIFER A. , LIPSCHUTZ MICHAEL E.
Published: February 2010

Abstract— We report data for 15 mainly volatile trace elements (Ag, Au, Bi, Cd, Co, Cs, Ga, In, Rb, Sb, Se, Te, Tl, U, Zn) by radiochemical neutron activation analysis (RNAA) in whole‐rock samples of five Martian meteorites that, with seven others studied earlier, complete the 12 member Martian meteorite suite. Nearly all of these elements exhibit highly variable compositional continua and are richer in the Martian suite compared with other basaltic meteorites. From cluster analysis, we find that the clustering of subtypes based on these elements is virtually identical to that based on contents of major refractory elements and mineralogic/petrographic character istics, which implies that each source region on Mars was closed to volatile transport. Martian meteorite data can be used to infer volatile element contents in that planet.
Isotopic composition of trapped and cosmogenic noble gases in several Martian meteorites
Authors: GARRISON DANIEL H. , BOGARD DONALD D.
Published: February 2010

Abstract—Isotopic abundances of the noble gases were measured in the following Martian meteorites: two shock glass inclusions from Elephant Moraine (EET) 79001, shock vein glass from Shergotty and Yamato (Y) 793605, and whole‐rock samples of Allan Hills (ALH) 84001 and Queen Alexandra Range (QUE) 94201. These glass samples, when combined with literature data on a separate single glass inclusion from EET 79001 and a glass vein from Zagami, permit examination in greater detail of the isotopic composition of Ne, Ar, Kr, and Xe trapped from the Martian atmosphere. The isotopic composition of Martian Ne, if actually present in these glasses, remains poorly defined. The40Ar/36Ar ratio of trapped Martian atmospheric Ar is probably considerably lower than the nominal ratio of 3000 measured byViking, and data on impact glasses suggest a value of ∼1900. The atmospheric36Ar/38Ar ratio is ≤4.0. Martian atmospheric Kr may be enriched in lighter isotopes by ∼0.5%/amu compared to both solar‐wind Kr and to the Martian composition previously reported. The isotopic composition of Xe in these glasses agrees with that previously reported in the literature. The Martian atmospheric36Ar/132Xe and84Kr/132Xe elemental ratios are higher than those reported byVikingby factors of ∼2.5–1.6 (depending on the40Ar/36Ar ratio adopted) and ∼1.8, respectively, and are discussed in a separate paper. Cosmogenic gases indicate space exposure ages of 2.7 ± 0.6 Ma for QUE 94201 and Shergotty and 14 ± 1 Ma for ALH 84001. Small amounts of21Ne produced by energetic solar protons may be present in QUE 94201 but are not present in ALH 84001 or Y‐793605. The space exposure age for Y‐793605 is 4.9 ± 0.6 Ma and appears to be distinctly older than the ages for basaltic shergottites. However, uncertainties in cosmogenic production rates still makes somewhat uncertain the number of Martian impact events required to produce the exposure ages of Martian meteorites.
Lepidocrocite to maghemite to hematite: A pathway to magnetic and hematitic Martian soil
Authors: MORRIS RICHARD V. , GOLDEN D. C. , SHELFER TAD D. , LAUER H. V.
Published: February 2010

Abstract— We examined decomposition products of lepidocrocite, which were produced by heating the phase in air at temperatures up to 525 °C for 3 and 300 h, by x‐ray diffraction (XRD), transmission electron microscopy (TEM), magnetic methods, and reflectance spectroscopy (visible and near‐infrared (IR)). Single‐crystal lepidocrocite particles dehydroxylated to polycrystalline particles of disordered maghemite that subsequently transformed to polycrystalline particles of hematite. Essentially pure maghemite was obtained at 265 and 223 °C for the 3 and 300 h heating experiments, respectively. Its saturation magnetization (Js) and mass specific susceptibility are ∼50 Am2/kg and ∼400 × 10−6 m3/kg, respectively. Because hematite is spectrally dominant, spectrally hematitic samples (i.e., a minimum near 860 nm and a maximum near 750 nm) also could be strongly magnetic (Js up to ∼30 Am2/kg) from the masked maghemite component. Analyses by TEM showed that individual particles are polycrystalline with respect to both maghemite and hematite. The spectrally hematitic and magnetic Mh + Hm particles can satisfy the spectral and magnetic constraints for Martian surface materials over a wide range of values of Mh/(Mh + Hm) either as pure oxide powders or (within limits) as components of multiphase particles. These experiments are consistent with lepidocrocite as the precursor of Mh + Hm assemblages on Mars, but other phases (e.g., magnetite) that decompose to Mh and Hm are also possible precursors. Simulations done with a copy of the Mars Pathfinder magnet array showed that spectrally hematitic Mh + Hm powders having Js equal to 20.6 Am2/kg adhered to all five magnets.
Petrology of magmatic silicate inclusions in the Allan Hills 77005 lherzolitic shergottite
Authors: IKEDA YUKIO
Published: February 2010

Abstract— Magmatic inclusions occur in both chadacrystic olivine and oikocrystic pigeonite in ALH 77005 but are different from each other. Magmatic inclusions in olivine consist mainly of aluminous pyroxenes, intergrowths of plagioclase and silica, silica‐predominant glass, and rhyodacitic glass, with minor amounts of chromite, spinel, pyrrhotite, and whitlockite. Those in pigeonite consist mainly of aluminous pyroxenes, nonaluminous ferroan pyroxenes, kaersutite, spinel, and K‐rich trachytic glass, with minor amounts of pyrrhotite and whitlockite. The magmatic inclusions in chadacrystic olivine formed from trapped melts that were basaltic, apparently dry and crystallized additional olivine metastably. The basaltic magma, with entrained olivine, experienced magma mixing with K‐rich and wet magmas, or assimilation of such crustal rocks, in the early to middle stages of the crystallization sequence of ALH 77005 during crystallization of chadacrystic olivine prior to precipitation of oikocrystic pigeonite. However the amount of mixed magmas or assimilated rocks was minor in comparison to the basaltic magma. Crystallization of pigeonite, augite, and plagioclase in the host lithologies took place in a shallow magma reservoir under an open‐system condition, and the pigeonite trapped basaltic andesite to trachyandesitic melts, which resulted in magmatic inclusions in oikocrystic pigeonite. The magmatic inclusions in both olivine and pigeonite were formed under a rapid‐cooling condition, resulting in a variety of inclusions. Kaersutite in magmatic inclusions in oikocrystic pigeonite crystallized under a closed‐system wet condition during the late‐stage crystallization of the inclusions.
Kamacite sulfurization in the solar nebula
Authors: LAURETTA D. S. , LODDERS K. , FEGLEY B.
Published: February 2010

Abstract— The kinetics and mechanisms of kamacite sulfurization were studied experimentally at temperatures and H2S/H2 ratios relevant to the solar nebula. Pieces of the Canyon Diablo meteorite were heated at 558 K, 613 K, and 643 K in 50 parts per million by volume (ppmv) H2S‐H2 gas mixtures for up to one month. Optical microscopy and x‐ray diffraction analyses show that the morphology and crystal orientation of the resulting sulfide layers vary with both time and temperature. Electron microprobe analyses reveal three distinct phases in the reaction products: monosulfide solid solution (mss), (Fe, Ni, Co)1‐xS, pentlandite (Fe, Ni, Co)9‐xS8, and a P‐rich phase. The bulk composition of the remnant metal was not significantly changed by sulfurization. Kamacite sulfurization at 558 K followed parabolic kinetics for the entire duration of the experiments. Sulfide layers that formed at 613 K grew linearly with time, while those that formed at 643 K initially grew linearly with time then switched to parabolic kinetics upon reaching a critical thickness. The experimental results suggest that a variety of thermodynamic, kinetic, and physical processes control the final composition and morphology of the sulfide layers. We combine morphological, x‐ray diffraction, electron microprobe, and kinetic data to produce a comprehensive model of sulfide formation in the solar nebula. Then, we present a set of criteria to assist in the identification of solar nebula condensate sulfides in primitive meteorites.
Scaling impact melting and crater dimensions: Implications for the lunar cratering record
Authors: CINTALA MARK J. , GRIEVE RICHARD A. F.
Published: February 2010

Abstract— The dimensions of large craters formed by impact are controlled to a large extent by gravity, whereas the volume of impact melt created during the same event is essentially independent of gravity. This “differential scaling” fosters size‐dependent changes in the dynamics of impact‐crater and basin formation as well as in the final morphologies of the resulting structures. A variety of such effects can be observed in the lunar cratering record, and some predictions can be made on the basis of calculations of impact melting and crater dimensions. Among them are the following: (1) as event magnitude increases, the volume of melt created relative to that of the crater will grow, and more will be retained inside the rim of the crater or basin. (2) The depth of melting will exceed the depth of excavation at diameters that essentially coincide with both the inflection in the depth‐diameter trend and the simple‐to‐complex transition. (3) The volume of melt will exceed that of the transient cavity at a cavity diameter on the order of the diameter of the Moon; this would arguably correspond to a Moon‐melting event. (4) Small lunar craters only rarely display exterior flows of impact melt because the relatively small volumes of melt created can become choked with clasts, increasing the melt's viscosity and chilling it rapidly. Larger craters and basins should suffer little from such a process. (5) Deep melting near the projectile's axis of penetration during larger events will yield a progression in central‐structure morphology; with growing event magnitude, this sequence should range from single peaks through multiple peaks to peak rings. (6) The minimum depth of origin of central‐peak material should coincide with the maximum depth of melting; the main central peak in a crater the size of Tycho should have had a preimpact depth of close to 15 km.
Compositional variation and mixing of impact melts on microscopic scales
Authors: SEE T. H. , WAGSTAFF J. , YANG V. , HÖRZ F. , MCKAY G. A.
Published: February 2010

Abstract— We investigated the compositional characteristics of schlieren‐rich, holohyaline impact glasses from Ries, Wabar, and Meteor Crater using a Cameca SX 100 scanning electron microprobe. This instrument is capable of producing detailed maps of major elements at spatial resolutions of <10 μm. The objective was to characterize the composition of an unusually large number of individual schlieren and to evaluate details of the process that causes melts of lithologically diverse target rocks to mix on scales of micrometers. The Ries and Meteor Crater impacts involved lithologically heterogeneous targets; whereas, Wabar Crater formed in relatively uniform dune sand.

Texturally heterogeneous, schlieren‐rich glasses from the Ries Crater illustrate that schlieren of highly variable color can be surprisingly similar in composition, as first detailed by Stähle (1972). Consistent with these earlier findings, most schlieren represent mixtures of diverse rock melts; their compositions deviate only subtly from the average melt and do not resemble monomineralic melts nor binary mixtures of major rock‐forming minerals. A specific population of schlieren is enriched in mafic elements (Mg, Fe, and Ca), which suggests incomplete homogenization of an amphibolite progenitor. In the case of Wabar Crater, a compositionally simple melt of dune sand mixed with projectile (IIIA iron meteorite) materials, and specific schlieren are variable mixtures of these two progenitors. The optically homogeneous glass from Meteor Crater is compositionally homogeneous as well, which suggests ideal mixing of such diverse lithologies as platform carbonates, sandstone, and a class IIIA iron meteorite.

The mixing of projectile and target melts at Wabar and Meteor Crater unambiguously demonstrates that melts initially produced in distinctly different stratigraphic/structural locations will undergo wholesale mixing, if not homogenization. Also, the projectile melts unquestionably formed relatively early in the cratering process, and their dissemination throughout the prospective melt volume, albeit at variable concentration levels, suggests that the entire mixing process may be an early cratering feature. This also follows from the fact that we investigated ballistic melt ejecta, which thereby eliminates all of those mixing processes that may additionally operate during the pooling and generation of massive melt‐ponds following gravitational collapse of large, structurally complex craters. Substantial turbulence ranging from field dimensions to microscopic scales seems inescapable to accomplish the observed degree of mixing, yet this is not readily inferred from current models of macroscopic material motions during hypervelocity impact.
Oxygen isotopes in forsterite grains from Julesburg and Allende: Oxygen‐16‐rich material in an ordinary chondrite
Authors: SAXTON J. M. , LYON I. C. , TURNER G.
Published: February 2010

Abstract— We have used the Manchester ISOLAB 54 ion microprobe to make in situ measurements of the 17O/16O and 18O/16O ratios of olivine grains in the Julesburg (L3.6) and Allende (CV3) chondrites. We have discovered a population of olivines in Julesburg characterised by (1) the most 16O‐rich compositions yet reported for olivine from an ordinary chondrite; (2) cores of low‐Fa olivine, which frequently shows blue cathodoluminesce; (3) thick coats of more Fa‐rich (Fa ∼20) olivine, which is also 16O‐enriched. In an O isotopic plot, the Julesburg 16O‐rich grains form a roughly linear array that is offset from the Allende mixing line. The presence of very low Fa olivine and, sometimes, well‐defined Fa‐rich coats indicates that these grains experienced significantly less thermal metamorphism than most of the olivine in the meteorite. Some 16O‐rich Julesburg grains are associated with minor feldspar or pyroxene and are probably chondrule fragments. They are isotopically indistinguishable from forsterite in Allende; however, Allende forsterite grains do not have the thick Fa20 coats typical of those in Julesburg. These 16O‐rich forsterite grains appear to be related to the “blue olivine” of Steele (1986). Both cores and coats of 16O‐rich grains in Julesburg are isotopically distinct from olivine in Semarkona group A and group B chondrules.
Aqueous alteration of carbonaceous chondrites: Evidence for preaccretionary alteration—A review
Authors: BISCHOFF A.
Published: February 2010

Abstract— In most groups of carbonaceous chondrites, minerals occur that are formed due to aqueous alteration in the nebula and/or within meteorite parent bodies. For determining the evolution of materials in the early solar system, it is of significant importance to clearly identify evidence for either nebular or planetary aqueous alteration. Therefore, results from the study of chondrites have fundamental implications for ideas concerning nebular dynamics, gas‐solid interactions in the nebula, and accretionary processes.

Considering the topic of this review, it is important to define nebular and parent body processes. The solar nebula activity should include condensation processes of high‐ and low‐temperature components as well as processes of chemical fractionation and grain‐size sorting, mixing of solids and gas, and interactions between early formed solids with the remaining gas; but it should exclude processes that occurred in small uncompacted protoplanetary objects that may have been totally destroyed again before accretion of the final meteorite parent bodies. Therefore, the term “preaccretionary” instead of “nebula” is used in this paper to include all these processes that may have occurred in small precursor planetesimals.

Currently, there is no doubt that parent body aqueous alteration is a fundamental process in the evolution of several groups of carbonaceous chondrites. However, due to textural and mineralogical observations and chemical analyses, strong arguments have been found also indicating preaccretionary aqueous alteration of distinct components in carbonaceous chondrites. In this paper, evidence for preaccretionary aqueous alteration in carbonaceous chondrites and their components taken from previous studies is discussed in detail.

The strongest evidence for preaccretionary alteration comes from studies of CM chondrites. The survival of highly unequilibrated mineral assemblages in accretionary rims, and sharp contacts between chondrule glass and surrounding phyllosilicates, are only two important arguments for preaccretionary alteration features among many others discussed in the paper. Similar observations were also made in CR, CH and related chondrites. Due to the small abundance of water‐bearing phases in CO and CV chondrites, the origin of phyllosilicates in these groups is less clear. A preaccretionary origin of hydrous phases in Ca‐Al‐rich inclusions (CAIs) has also been suggested by several scientists. In CI chondrites, no strong indications for such processes have been found, mainly due to heavy brecciation and severe parent body alteration.