bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
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.
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.
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.
Carbonates in fractures of Martian meteorite Allan Hills 84001: Petrologic evidence for impact origin
Authors: SCOTT EDWARD R. D. , KROT ALEXANDER N. , YAMAGUCHI AKIRA 
Published: February 2010

Abstract— Carbonates in Martian meteorite Allan Hills 84001 occur as grains on pyroxene grain boundaries, in crushed zones, and as disks, veins, and irregularly shaped grains in healed pyroxene fractures. Some carbonate disks have tapered Mg‐rich edges and are accompanied by smaller, thinner and relatively homogeneous, magnesite microdisks. Except for the microdisks, all types of carbonate grains show the same unique chemical zoning pattern on MgCO3‐FeCO3‐CaCO3 plots. This chemical characteristic and the close spatial association of diverse carbonate types show that all carbonates formed by a similar process. The heterogeneous distribution of carbonates in fractures, tapered shapes of some disks, and the localized occurrence of Mg‐rich microdisks appear to be incompatible with growth from an externally derived CO2‐rich fluid that changed in composition over time. These features suggest instead that the fractures were closed as carbonates grew from an internally derived fluid and that the microdisks formed from a residual Mg‐rich fluid that was squeezed along fractures.Carbonate in pyroxene fractures is most abundant near grains of plagioclase glass that are located on pyroxene grain boundaries and commonly contain major or minor amounts of carbonate. We infer that carbonates in fractures formed from grain boundary carbonates associated with plagioclase that were melted by impact and dispersed into the surrounding fractured pyroxene. Carbonates in fractures, which include those studied by McKay et al. (1996), could not have formed at low temperatures and preserved mineralogical evidence for Martian organisms.
Oxygen isotopic record of silicate alteration in the Shergotty—Nakhla—Chassigny meteorite Lafayette
Authors: ROMANEK CHRISTOPHER S. , PERRY EUGENE C. , TREIMAN ALLAN H. , SOCKI RICHARD A. , JONES JOHN H. , GIBSON EVERETT K. 
Published: February 2010

Abstract—Samples from a suite of Shergotty—Nakhla—Chassigny (SNC) meteorites were analyzed for their O isotopic ratios by a modified version of the laser fluorination technique. Measured isotopic ratios (17O/16O and18O/16O) from bulk samples of the Shergottites, EETA79001, Shergotty and Zagami; the Nakhlite Lafayette; and Chassigny are similar to those reported in the literature, as are those from olivine and pyroxene mineral separates from Lafayette.Iddingsite, a preterrestrial alteration product of Lafayette, was measured for the first time as a separate phase. Oxygen isotopic ratios increase with the percentage of iddingsite in a sample to a maximum δ18O of 14.4% for a ∼90% separate. Based on these measurements, end‐member iddingsite has a δ18O of 15.6%, which places it among other18O‐enriched secondary phases (carbonate and silica) observed in SNC meteorites. The relatively large difference in δ18O between iddingsite and the olivine and pyroxene it replaces (∼11%) is typical of low‐temperature alteration products.A range of crustal fluid δ18O values can be interpreted from the δ18O for end‐member iddingsite, assuming isotopic equilibrium was achieved during low‐temperature hydrous alteration (<100 °C; Treimanet al., 1993). The calculated range of values, −15 to 5%, depends on many factors including: (1) the modal mineralogy of iddingsite, (2) potential isotopic exchange among other O‐bearing phases such as host silicate and carbonate, and (3) exchange with evolved or exotic O reservoirs on Mars. Despite the lack of constraints, the calculated range is consistent with isotopic exchange, and possibly equilibria, among components of the CO2‐carbonate‐iddingsite‐H2O system at low temperature.The SNC meteorite samples in this study have Δ17O values that are indistinguishable from bulk Mars (0.30%), except for a single, small sample of iddingsite that has an anomalous Δ17O of ∼1.4%. While analytical difficulties make isotopic measurements for this sample problematic, the Δ17O is similar in direction to Δ17O reported for waters extracted from bulk samples of Lafayette (Karlssonet al., 1992). If the Δ17O for iddingsite is confirmed, it can be concluded that evolved or exotic fluids on Mars have contributed volatiles to the O reservoir from which iddingsite formed 130 to 700 Ma ago.
The cooling history of the Lewis Cliff 86010 angrite as inferred from kirschsteinite lamellae in olivine
Authors: MCKAY G. A. , MIYAMOTO M. , MIKOUCHI T. , OGAWA T. 
Published: February 2010

Abstract— Olivine in the angritic meteorite Lewis Cliff (LEW) 86010 contains abundant exsolution lamellae of kirschsteinite. Compositional gradients adjacent to the interface in both host and lamellae were formed by diffusion of chemical components into and out of the lamellae during cooling and growth. We have compared these gradients with compositional profiles calculated from diffusion and heat flow equations to estimate the cooling rate and burial depth of the sample. The resulting values for cooling rate and burial depth depend on which values are used for the diffusion rate of Ca in olivine, and how measured diffusivities are extrapolated to the lower temperatures at which the lamellae grew.If the highest diffusion coefficients are used, the cooling rates obtained from seven different lamellae range from 30 to 52 °C/year, with an average of 42 °C/year, and burial depths (assuming an overburden with a thermal diffusivity typical of solid rock) range from 14 to 17 m, with an average of 15 m. If the lowest reasonable diffusion coefficients are used, the cooling rates range from 1.4 to 2.2 °C/year, with an average of 1.7 °C/year, and the depths range from 68 to 83 m, with an average of 75 m.For the highest Ca diffusivities, details of the compositional profiles near the olivine/kirschsteinite interface suggest that continuous cooling was greatly accelerated at a temperature near 600–700 °C. The simplest physical explanation for such an acceleration is excavation of the sample from its original burial depth by an impact event. If Ca diffusivities are lower, a two‐stage cooling history is not required.
The ubiquitous presence of silica‐rich glass inclusions in mafic minerals: Examples from Earth, Mars, Moon and the aubrite parent body
Authors: VARELA M. E. , KURAT G. , CLOCCHIATTI R. , SCHIANO P. 
Published: February 2010

Abstract— Highly silicic glass inclusions are commonly present in mafic minerals of xenolithic terrestrial upper mantle rocks (Schiano and Clocchiatti, 1994). They are believed to be the products of volatile‐rich silicic melts for which several sources have been proposed (Francis, 1976; Frey and Green, 1974; Schiano et al, 1995), but their origin(s) and, consequently, that of the glasses, remains unknown. However, in situ formation by very low‐degree partial melting seems to be possible as has been shown by experiments (e.g., Baker et al, 1995; Draper and Green, 1997).Glass inclusions of silicic chemical composition are also present in some mafic minerals of achondritic meteorites (e.g., Fuchs, 1974; Okada et al, 1988; Johnson et al, 1991). The enstatite achondrites (aubrites) Aubres and Norton County, which record early planetesimal and planet formation in the solar nebula, and the olivine achondrite (chassignite) Chassigny, a rock believed to originate from Mars, contain abundant glass inclusions in their main minerals enstatite and olivine, respectively. Glasses of glass‐bearing inclusions have a highly silicic and volatile‐rich chemical composition similar, but not identical, to that of glass inclusions in terrestrial upper mantle peridotite minerals. Furthermore, glass inclusions in olivines from the Moon (e.g., Roedder and Weiblen, 1977) are also silica‐rich.Because different physicochemical conditions prevail in the source regions of these rocks, the process of melting is, perhaps, not generally applicable for the generation of silica‐rich glasses. Alternatively, the glasses could have been formed via precipitation from silicate‐loaded fluids (Schneider and Eggler, 1986) or vapors. Another possible mechanism, not previously identified, could be dehydrogenation of nominally nonhydrous mafic minerals by heating or depressurization that should be accompanied by expulsion of excess silica and incompatible elements. This process will mimic low‐temperature, very low‐degree partial melting. It could account also for the highly variable glass/bubble ratios observed in glass inclusions in aubrite enstatites. We suggest that such a process could have been operating in the solar nebula, the Moon and Mars, and could be operating still on Earth.
Experimental studies of magnetite formation in the solar nebula
Authors: HONG Y. , FEGLEY B. 
Published: February 2010

Abstract— Oxidation of Fe metal and Gibeon meteorite metal to magnetite via the net reaction 3 Fe (metal) + 4 H2O (gas) = Fe3O4 (magnetite) + 4 H2 (gas) was experimentally studied at ambient atmospheric pressure at 91–442 °C in H2 and H2‐He gas mixtures with H2/H2O molar ratios of ∼4–41. The magnetite produced was identified by x‐ray diffraction. Electron microprobe analyses showed 3.3 wt% NiO and 0.24 wt% CoO (presumably as NiFe2O4 and CoFe2O4) in magnetite formed from Gibeon metal. The NiO and CoO concentrations are higher than expected from equilibrium between metal and oxide under the experimental conditions. Elevated NiO contents in magnetite were also observed by metallurgists during initial stages of oxidation of Fe‐Ni alloys. The rate constants for magnetite formation were calculated from the weight gain data using a constant surface area model and the Jander, Ginstling‐Brounshtein, and Valensi‐Carter models for powder reactions. Magnetite formation followed parabolic (i.e., diffusion‐controlled) kinetics. The rate constants and apparent activation energies for Fe metal and Gibeon metal are:These rate constants are significantly smaller than the parabolic rate constants for FeS growth on Fe metal in H2S‐H2 gas mixtures containing 1000 or 10 000 ppmv H2S (Lauretta et al., 1996a). The experimental data for Fe and Gibeon metal are used to model the reaction time of Fe alloy grains in the solar nebula as a function of grain size and temperature. The reaction times for 0.1–1 μm radius metal grains are generally within estimated lifetimes of the solar nebula (0.1–10 Ma). However, the calculated reaction times are probably lower limits, and further study of magnetite formation at larger H2/H2O ratios, at lower temperatures and pressures, and as a function of metal alloy composition is needed for further modeling of nebular magnetite formation.
Olivine in Martian meteorite Allan Hills 84001: Evidence for a high‐temperature origin and implications for signs of life
Authors: SHEARER C. K. , LESHIN L. A. , ADCOCK C. T. 
Published: February 2010

Abstract— Olivine from Martian meteorite Allan Hills (ALH) 84001 occurs as clusters within orthopyroxene adjacent to fractures containing disrupted carbonate globules and feldspathic shock glass. The inclusions are irregular in shape and range in size from ∼40 μm to submicrometer. Some of the inclusions are elongate and boudinage‐like. The olivine grains are in sharp contact with the enclosing orthopyroxene and often contain small inclusions of chromite. The olivine exhibits a very limited range of composition from Fo65 to Fo66 (n = 25). The δ18O values of the olivine and orthopyroxene analyzed by ion microprobe range from +4.3 to +5.3‰ and are indistinguishable from each other within analytical uncertainty.The mineral chemistries, O‐isotopic data, and textural relationships indicate that the olivine inclusions were produced at a temperature >800 °C. It is unlikely that the olivines formed during the same event that gave rise to the carbonates in ALH 84001, which have more elevated and variable δ18O values, and were probably formed from fluids that were not in isotopic equilibrium with the orthopyroxene or olivine. The reactions most likely instrumental in the formation of olivine could be either the dehydration of hydrous silicates that formed during carbonate precipitation or the reduction of orthopyroxene and spinel. If the olivine was formed by either reaction during a postcarbonate heating event, the implications are profound with regards to the interpretations of McKay et al. (1996). Due to the low diffusion rates in carbonates, this rapid, high‐temperature event would have resulted in the preservation of the fine‐scale carbonate zoning, while partially devolatilizing select carbonate compositions on a submicrometer scale (Brearley, 1998a). This may have resulted in the formation of the minute magnetite grains that McKay et al. (1996) attributed to biogenic activity.