• Ulasitai: A new iron meteorite likely paired with Armanty (IIIE)

      Xu, Lin; Miao, Bingkui; Lin, Yangting; Ouyang, Ziyuan (The Meteoritical Society, 2008-01-01)
      The Ulasitai iron was recently found about 130 km southeast to the find site of the Armanty (Xinjiang, IIIE) meteorite. It is a coarse octahedrite with a kamacite bandwidth of 1.2 +/- 0.2 (0.9-1.8) mm. Plessite is abundant, as is taenite, kamacite, cohenite, and schreibersite with various microstructures. Schreibersite is Ni-rich (30.5-55.5 wt%) in plessite or coexisting with troilite and daubreelite, in comparison with the coarse laths (20.621.2 wt%) between the Widmanstätten pattern plates. The correlation between the center Ni content and the half bandwidth of taenite suggest a cooling rate of ~20 degrees C/Myr based on simulations. The petrography and mineral chemistry of Ulasitai are similar to Armanty. The bulk samples of Ulasitai were measured, together with Armanty, Nandan (IIICD), and Mundrabilla (IIICD), by inductively coupled plasma atomic emission spectrometry (ICP-AES) and mass spectrometry (ICP-MS). The results agree with literature data of the same meteorites, and our analyses of four samples of Armanty (L1, L12, L16, L17) confirm a homogeneous composition (Wasson et al. 1988). The bulk composition of Ulasitai is identical to that of Armanty, both plotting within the IIIE field. We classify Ulasitai as a new IIIE iron and suggest that it pairs with Armanty.
    • Ultraviolet photolysis of anthracene in H2O interstellar ice analogs: Potential connection to meteoritic organics

      Ashbourn, S. F. M.; Elsila, J. E.; Dworkin, J. P.; Bernstein, M. P.; Sandford, S. A.; Allamandola, L. J. (The Meteoritical Society, 2007-01-01)
      The polycyclic aromatic hydrocarbon (PAH) anthracene was oxidized by exposure to ultraviolet (UV) radiation in H2O ice under simulated astrophysical conditions, forming several anthracene ketones (9-anthrone, 1,4-anthraquinone, and 9,10-anthraquinone) and alcohols (1-anthrol and 2-anthrol). Two of the ketones produced have been detected in the Murchison meteorite but, to our knowledge, there has been no search for the alcohols or other oxidized anthracenes in meteorites. These results seem consistent with the possibility that interstellar ice photochemistry could have influenced the inventory of aromatics in meteorites. Since quinones are also fundamental to biochemistry, their formation in space and delivery to planets is relevant to studies relating to the habitability of planets and the evolution of life.
    • Understanding the textures and origin of shock melt pockets in Martian meteorites from petrographic studies, comparisons with terrestrial mantle xenoliths, and experimental studies

      Walton, E. L.; Shaw, C. S. J. (The Meteoritical Society, 2009-01-01)
      We present a textural comparison of localized shock melt pockets in Martian meteorites and glass pockets in terrestrial, mantle-derived peridotites. Specific textures such as the development of sieve texture on spinel and pyroxene, and melt migration and reaction with the host rock are identical between these two apparently disparate sample sets. Based on petrographic and compositional observations it is concluded that void collapse/variable shock impedance is able to account for the occurrence of pre-terrestrial sulfate-bearing secondary minerals in the melts, high gas emplacement efficiencies, and S, Al, Ca, and Na enrichments and Fe and Mg depletion of shock melt compositions compared to the host rock; previously used as arguments against such a formation mechanism. Recent experimental studies of xenoliths are also reviewed to show how these data further our understanding of texture development and can be used to shed light on the petrogenesis of shock melts in Martian meteorites.
    • Unusual large chromite crystals in the Saint Aubin iron meteorite

      Fehr, K. T.; Carion, A. (The Meteoritical Society, 2004-01-01)
      In the Saint Aubin octahedrite, chromite crystals of up to 3 cm occur enclosed in the metal phase. They are twinned along [111] according to the spinel law and display pseudohexagonal shapes in cross-sections. The crystals are homogeneous and exhibit compositions close to pure chromite endmember. Vanadium is the only additional element observed in appreciable amounts of up to 0.73 wt%. Chromite in the Saint Aubin meteorite crystallized from liquids with very low amounts of Cr and O close to the Fe-FeS join as indicated by its composition and phase relations. The growth of large chromite crystals implies stable supersaturated conditions for a long period in the meteorite parent body of Saint Aubin.
    • Upper limit concentrations of trapped xenon in individual interplanetary dust particles from the stratosphere

      Kehm, K.; Crowther, S.; Gilmour, J. D.; Mohapatra, R. K.; Hohenberg, C. M. (The Meteoritical Society, 2009-01-01)
      The Xe contents in 25 individual stratospheric interplanetary dust particles were measured in two different laboratories using focused laser micro-gas extraction and (1) a conventional low-blank magnetic sector mass spectrometer (Washington University), and (2) a resonance ionization time of flight mass spectrometer (RELAX-University of Manchester). Data from both laboratories yielded a remarkably similar upper-limit 132Xe concentration in the IDPs (<2.7, 6.8 and 2.2 x 10^(-8) ccSTP/g for Washington University Run 1, Washington University Run 2 and University of Manchester analyses, respectively), which is up to a factor of five smaller than previous estimates. The upper-limit 132Xe/36Ar ratio in the IDPs (132Xe/36Ar <~8 x 10^(-4) for Run 1 and 132Xe/36Ar <~19 x 10^(-4) for Run 2), computed using 36Ar concentration data reported elsewhere is consistent with a mixture between implanted solar wind, primordial, and atmospheric noble gases. Most significantly, there is no evidence that IDPs are particularly enriched in primordial noble gases compared to chondritic meteorites, as implied by previous work.
    • Uppermost impact fallback layer in the Bosumtwi crater (Ghana): Mineralogy, geochemistry, and comparison with Ivory Coast tektites

      Koeberl, C.; Brandstätter, F.; Glass, B. P.; Hecht, L.; Mader, D.; Reimold, W. U. (The Meteoritical Society, 2007-01-01)
      In 2004, an International Continental Scientific Drilling Program (ICDP) drilling project at the Bosumtwi impact crater, Ghana (10.5 km in diameter, 1.07 Myr old), was performed to study the sediments that fill the lake as well as the underlying impactites. In one (LB-05) of 16 cores drilled into the lake sediments, the zone between the impact breccias and the post-impact sediments was penetrated, preserving the final, fine-grained impact fallback layer. This ~30 cm thick layer contains in the top 10 cm "accretionary" lapilli, microtektite-like glass spherules, and shocked quartz grains. Glass particlesmostly of splash form less than 1 mm size--make up the bulk of the grains (~70-78% by number) in the coarser size fraction (>125 micrometers) of the top of the fallback layer. About one-third of all quartz grains in the uppermost part of the layer are shocked, with planar deformation features (PDFs); almost half of these grains are highly shocked, with 3 or more sets of PDFs. K-feldspar grains also occur and some show shock deformation. The abundance of shocked quartz grains and the average shock level as indicated by the number of sets of PDFs, for both quartz and K-feldspar, decrease with depth into the layer. The well-preserved glass spherules and fragments are chemically rather homogeneous within each particle, and also show relatively small variations between the various particles. On average, the composition of the fallback spherules from core LB-5B is very similar to the composition of Ivory Coast tektites and microtektites, with the exception of CaO contents, which are about 1.5 to 2 times higher in the fallback spherules. This is a rare case in which the uppermost fallback layer and the transition to the post-impact sediments has been preserved in an impact structure; its presence indicates that the impactite sequence at Bosumtwi is complete and that Bosumtwi is a very well-preserved impact crater.
    • Ureilite petrogenesis: A limited role for smelting during anatexis and catastrophic disruption

      Warren, Paul H.; Huber, Heinz (The Meteoritical Society, 2006-01-01)
      A popular model for ureilites assumes that during anatexis in an asteroidal mantle, pressure-buffered equilibrium smelting (partial reduction coincident with partial melting) engendered their conspicuous mafic-silicate-core mg diversity (75-96 mol%). Several mass-balance problems arise from this hypothesis. Smelting inevitably consumes a large proportion of any plausible initial carbon while generating significant proportions of Fe metal and copious proportions of CO gas. The most serious problem concerns the yield of CO gas. If equilibrium smelting produced the ureilites' entire 21 mol% range in olivine-core mg, the proportion of gas within the asteroidal mantle (assuming plausibly low pressure <∼80 bar) should have reached greater than or equal to 85 vol%. Based on the remarkably stepwise cooling history inferred from ureilite texture and mineralogy, a runaway, CO-leaky process that can loosely be termed smelting appears to have occurred, probably triggered by a major impact. The runaway scenario appears likely because, by Le Châtelier’s principle, CO leakage would tend to accelerate the smelting process. Also, the copious volumes of gas produced by smelting would have led to explosive, mass-leaky eruptions into the vacuum surrounding the asteroid. Loss of mass would mean diminution of interior pressure, which would induce further smelting, leading to further loss of mass (basalt), and so on. Such a disruptive runaway process may have engendered the ureilites’ distinctive reduced olivine rims. But the only smelting, according to this scenario, was a short-lived disequilibrium process that reduced only the olivine rims, not the cores; and the ureilites were cooling, not melting, during the abortive “smelting” episode.
    • UV photolysis of quinoline in interstellar ice analogs

      Elsila, Jamie E.; Hammond, Matthew R.; Bernstein, Max P.; Sandford, Scott A.; Zare, Richard N. (The Meteoritical Society, 2006-01-01)
      The polycyclic aromatic nitrogen heterocycle (PANH) quinoline (C9H7N) was frozen at 20 K in interstellar ice analogs containing either pure water or water mixed with methanol or methane and exposed to ultraviolet (UV) radiation. Upon warming, the photolysis products were analyzed by high-performance liquid chromatography and nanoscale liquid chromatography-electrospray ionization mass spectrometry. A suite of hydroxyquinolines, which were formed by the addition of oxygen atoms to quinoline, was observed as the primary product in all the ices. Quinoline N oxide was not formed, but five hydroxyquinoline isomers were produced with no clear dominance of one isomer. Reduction products, formed by hydrogen atom addition, were also created. Ices created at 20 K with H2O: quinoline ratios of 10:1 to 100:1 showed similar product distributions to those at 122 K, with no apparent temperature or concentration dependence. Increasing the UV dose led to a decrease in overall yield, indicating that quinoline and its products may be photo-destroyed. Methylquinolines were formed upon photolysis of the methanol- and methane-containing ices. In addition, possible methoxyquinolines or quinoline methylene alcohols were formed in the methanolcontaining ice, while methylhydroxyquinolines were created in the methane-containing ice. This work indicates that oxidation of PANHs could occur in icy extraterrestrial environments and suggests that a search for such compounds in carbonaceous meteorites could illuminate the possible link between interstellar ice chemistry and meteoritic organics. Given the importance of oxidized and alkylated PANHs to biochemistry, the formation and delivery of such molecules to the early Earth may have played a role in the origin and evolution of life.
    • Valence state partitioning of V between pyroxene-melt: Effects of pyroxene and melt composition, and direct determination of V valence states by XANES. Application to Martian basalt QUE 94201 composition

      Karner, J. M.; Papike, J. J.; Sutton, S. R.; Shearer, C. K.; Burger, P.; McKay, G.; Le, L. (The Meteoritical Society, 2008-01-01)
      Experiments on a Martian basalt composition show that DV augite/melt is greater than DV pigeonite/melt in samples equilibrated under the same fO2 conditions. This increase is due to the increased availability of elements for coupled substitution with the V3+ or V4+ ions, namely Al and Na. For this bulk composition, both Al and Na are higher in concentration in augite compared with pigeonite; therefore more V can enter augite than pigeonite. Direct valence state determination by XANES shows that the V3+ and V4+ are the main V species in the melt at fO2 conditions of IW-1 to IW+3.5, whereas pyroxene grains at IW-1, IW, and IW+1 contain mostly V3+. This confirms the idea that V3+ is more compatible in pyroxene than V4+. The XANES data also indicates that a small percentage of V2+ may exist in melt and pyroxene at IW-1. The similar valence of V in glass and pyroxene at IW-1 suggests that V2+ and V3+ may have similar compatibilities in pyroxene.
    • Validation of numerical codes for impact and explosion cratering: Impacts on strengthless and metal targets

      Pierazzo, E.; Artemieva, N.; Asphaug, E.; Baldwin, E. C.; Cazamias, J.; Coker, R.; Collins, G. S.; Crawford, D. A.; Davison, T.; Elbeshausen, D.; et al. (The Meteoritical Society, 2008-01-01)
      Over the last few decades, rapid improvement of computer capabilities has allowed impact cratering to be modeled with increasing complexity and realism, and has paved the way for a new era of numerical modeling of the impact process, including full, three-dimensional (3D) simulations. When properly benchmarked and validated against observation, computer models offer a powerful tool for understanding the mechanics of impact crater formation. This work presents results from the first phase of a project to benchmark and validate shock codes. A variety of 2D and 3D codes were used in this study, from commercial products like AUTODYN, to codes developed within the scientific community like SOVA, SPH, ZEUS-MP, iSALE, and codes developed at U.S. National Laboratories like CTH, SAGE/RAGE, and ALE3D. Benchmark calculations of shock wave propagation in aluminum-on-aluminum impacts were performed to examine the agreement between codes for simple idealized problems. The benchmark simulations show that variability in code results is to be expected due to differences in the underlying solution algorithm of each code, artificial stability parameters, spatial and temporal resolution, and material models. Overall, the inter-code variability in peak shock pressure as a function of distance is around 10 to 20%. In general, if the impactor is resolved by at least 20 cells across its radius, the underestimation of peak shock pressure due to spatial resolution is less than 10%. In addition to the benchmark tests, three validation tests were performed to examine the ability of the codes to reproduce the time evolution of crater radius and depth observed in vertical laboratory impacts in water and two well-characterized aluminum alloys. Results from these calculations are in good agreement with experiments. There appears to be a general tendency of shock physics codes to underestimate the radius of the forming crater. Overall, the discrepancy between the model and experiment results is between 10 and 20%, similar to the inter-code variability.
    • Variation of chemical composition in Australasian tektites from different localities in Vietnam

      Amare, Kassa; Koeberl, Christian (The Meteoritical Society, 2006-01-01)
      One hundred and thirteen Australasian tektites from Vietnam (Hanoi, Vinh, Dalat, and Saigon areas) were analyzed for their major and trace element contents. The tektites are either of splash form or Muong Nong-type. The splash-form tektites have SiO2 contents ranging from 69.7 to 76.8 wt%, whereas Muong Nong-type tektites, which are considerably larger than splash-form tektites and have a blocky and chunky appearance, have slightly higher silica contents in thev range of 74-81 wt%. Major-element relationships, such as FeO versus major oxides, Na2O versus K2O, and oxide ratio plots, were used to distinguish the different groups of the tektites. In addition, correlation coefficients have been calculated for each tektite group of this study. Many chemical similarities are noted between Hanoi and Vinh tektites from the north of Vietnam, except that the Hanoi tektites contain higher contents of CaO than Vinh; the higher content of CaO might be due to some carbonate parent material. Both Dalat and Saigon tektites have nearly similar composition, whereas the bulk chemistries of the tektites from Hanoi and Vinh appear different from those of Saigon and Dalat. There are differences, especially in the lower CaO and Na2O and higher MgO, FeO, for the tektites of Dalat and Saigon in comparison to that of Hanoi tektites. Furthermore, the Dalat and Saigon tektites show enrichments by factors of 3 and 2 for the Ni and Cr contents, respectively, compared to those of Hanoi and Vinh. The difference in chemistry between the North Vietnam tektites (Hanoi, Vinh) to that of South Vietnam tektites (Saigon, Dalat) of this study indicate that the parent material was heterogeneous and possibly mixing between different source rocks took place.Muong Nong-type tektites are enriched in the volatile elements such as Br, Zn, As, and Sb compared to the average splash-form tektites of this study. The chemical compositions of the average splash-form and Muong Nong-type tektites of this study closely resemble published data for average splash-form and Muong Nong-type indochinites, indicating that they have the same source. The trace element ratios Ba/Rb (2.7), Th/U (5.2), Th/Sc (1.3), Th/Sm (2.2), and the rare earth element (REE) abundances of this study show close similarities to those of aerageupper continental crust.
    • Vesta and the HED meteorites: Mid-infrared modeling of minerals and their abundances

      Donaldson Hanna, K.; Sprague, A. L. (The Meteoritical Society, 2009-01-01)
      We demonstrate that the use of an established spectral deconvolution algorithm with midinfrared spectral libraries of mineral separates of varying grain sizes is capable of identifying the known mineral compositions and abundances of a selection of howardite, eucrite, and diogenite (HED) meteorite samples. In addition, we apply the same technique to mid-infrared spectral emissivity measurements of Vesta that have been obtained from Cornells Mid-Infrared Asteroid Spectroscopy (MIDAS) Survey and the Infrared Space Observatory (ISO). Each Vesta measurement was made over a different range of longitudes. Our spectral deconvolution results to the Vesta spectra corroborate that Vestas surface is howardite or eucrite-like in composition and heterogeneous across its surface. The spectral fits produced by the linear deconvolution algorithm yields good results for the HED samples of known composition, thus giving us a high degree of confidence that our results for Vesta are valid.
    • Volume 37 2002: The Year at a Glance

      The Meteoritical Society, 2002-01-01
    • Weathering features in shocked quartz from the Ries impact crater, Germany

      Leroux, H. (The Meteoritical Society, 2005-01-01)
      Shocked quartz from the ejecta of the Ries impact structure has been investigated by analytical transmission electron microscopy (ATEM). Quartz grains display numerous planar fractures (PFs) and planar deformation features (PDFs). Both are partly or fully replaced by a mineral of the kaolinite group (likely halloysite). Its formation involves fluid circulation into the dense fracture networks, dissolution and removal of the amorphous phase initially present in PDFs, and finally, precipitation and crystallization of the kaolinite group mineral from solutions resulting from the chemical alteration of adjacent minerals (feldspars and biotite). Kaolinite group minerals are typical of hydrothermal alteration at low temperature, in humid climate, and under moderately acid conditions and, thus, this alteration may not be directly related to the impact event itself. However, the weathering features were strongly enhanced by the shock-generated microstructure, in particular by fractures that provided pathways for fluid circulation.
    • Weathering of meteorites from Oman: Correlation of chemical and mineralogical weathering proxies with 14C terrestrial ages and the influence of soil chemistry

      Al-Kathiri, A.; Hofmann, B. A.; Jull, A. J. T.; Gnos, E. (The Meteoritical Society, 2005-01-01)
      Fifty-four fragments of ordinary chondrites from 50 finds representing all searched areas in central Oman and all weathering stages were selected to compare the physical, chemical, and mineralogical effect of terrestrial weathering with 14C terrestrial ages. 14C ages range from 2.0 to >49 kyr with a median value of 17.9 kyr. The peak of the age range, which is between 10-20 kyr, falls in an arid climate period. A comparison of the chemical composition of Omani chondrites with literature data for unweathered H and L chondrites demonstrates a strong enrichment in Sr and Ba, and depletion in S during weathering. Water contents in H chondrites increase with terrestrial age, whereas L chondrites show a rapid initial increase followed by nearly constant water content. Correlating Sr, Ba, and H2O with age indicates two absorption trends: i) an initial alteration within the first 20 kyr dominated by H2O uptake, mainly reflecting Fe-Ni metal alteration, and ii) a second Baand Sr-dominated stage correlated with slower and less systematic weathering of troilite that starts after H2O reaches ~2 wt%. Sulfur released from troilite partly combines with Ba and Sr to form sulfate minerals. Other parameters correlated with 14C age are degree of weathering, color of powdered meteorites, and the Ni/Fe ratio. Chemical analyses of 145 soils show a high degree of homogeneity over the entire interior Oman Desert, indicating large-scale mixing by wind. Soil samples collected from beneath meteorite finds typically are enriched in Ni and Co, confirming mobilization from the meteorites. High Cr and Ni concentrations in reference soil samples, which decrease from NE to SW, are due to detrital material from ultramafic rocks of the Oman Mountains.
    • Weston: Revised position for a historically significant meteorite fall

      Robson, M.; Pagliaro, F. (The Meteoritical Society, 2009-01-01)
      Weston is the first well-documented meteorite fall in the New World. The fall occurred on December 14, 1807. The Weston event began the study of meteoritics in the United States in the decade that science accepted that stones do, in fact, fall from the sky. It is unfortunate that much of the literature regarding this historically significant fall is erroneous. This paper will deal with the geographic position of the fall site. One of us (Robson 2007) proposed a new set of coordinates for Weston that was accepted by the Meteoritical Society. At the societys 70th annual meeting, new Weston coordinates were suggested; with the caveat that research was ongoing. However, it was also stated in the presentation that it was unlikely that either coordinate would change by as much as a minute. Further research indicates a final revision is required. Our revised mean fall position of the seven documented fragments of Weston is: 41 degrees 16' N, 73 degrees 16' W (WGS 84 coordinates, to the nearest minute). A quirk of history is a main factor in the derivation of faulty positions for Weston. The historically changing positions given for the fall are explored. Our methodology is discussed and the newly discovered Weston manuscripts, maps, and communications of Yales foremost meteoric astronomer, Professor H. A. Newton, support our findings.
    • What metal-troilite textures can tell us about post-impact metamorphism in chondrite meteorites

      Tomkins, A. G. (The Meteoritical Society, 2009-01-01)
      Metal-troilite textures are examined in metamorphosed and impact-affected ordinary chondrites to examine the response of these phases to rapid changes in temperature. Complexly intergrown metal-troilite textures are shown to form in response to three different impact-related processes. (1) During impacts, immiscible melt emulsions form in response to spatially focused heating. (2) Immediately after impact events, re-equilibration of heterogeneously distributed heat promotes metamorphism adjacent to zones of maximum impact heating. Where temperatures exceed ~850 degrees degrees C, this post-impact metamorphism results in melting of conjoined metal-troilite grains in chondrites that were previously equilibrated through radiogenic metamorphism. When the resulting Fe-Ni-S melt domains crystallize, a finely intergrown mixture of troilite and metal forms, which can be zoned with kamacite-rich margins and taenite-rich cores. (3) At lower temperatures, post-impact metamorphism can also cause liberation of sulfur from troilite, which migrates into adjacent Fe-Ni metal, allowing formation of troilite and occasionally copper within the metal during cooling. Because impact events cause heating within a small volume, post-impact metamorphism is a short duration event (days to years) compared with radiogenic metamorphism (>10^6 years). The fast kinetics of metal-sulfide reactions allows widespread textural changes in conjoined metal-troilite grains during post-impact metamorphism, whereas the slow rate of silicate reactions causes these to be either unaffected or only partially annealed, except in the largest impact events. Utilizing this knowledge, information can be gleaned as to whether a given meteorite has suffered a post-impact thermal overprint, and some constraints can be placed on the temperatures reached and duration of heating.
    • William Lee Quaide, 1927-2004

      French, B. (The Meteoritical Society, 2005-01-01)
    • Woodleigh impact structure, Australia: Shock petrography and geochemical studies

      Reimold, W. U.; Koeberl, C.; Hough, R. M.; McDonald, I.; Bevan, A.; Amare, K.; French, B. M. (The Meteoritical Society, 2003-01-01)
      The large, complex Woodleigh structure in the Carnarvon basin of Western Australia has recently been added to the terrestrial impact crater record. Many aspects of this structure are, however, still uncertain. This work provides a detailed petrographic assessment of a suite of representative drill core samples from the borehole Woodleigh 1 that penetrated uplifted basement rocks of the central part of this structure. Fundamental rock and mineral deformation data and high-precision chemical data, including results of PGE and oxygen isotopic analysis, are presented. The sampled interval displays likely impact-produced macrodeformation in the form of fracturing and breccia veining at the microscopic scale. Contrary to earlier reports that these breccias represent pseudotachylite (friction melt) or even shock/shear-produced pseudotachylitic melt breccia cannot be confirmed due to pervasive post-impact alteration. Abundant planar deformation features (PDFs) in quartz, in addition to diaplectic glass and partial isotropization, are the main shock deformation effects observed, confirming that Woodleigh is of impact origin. Over the investigated depth interval, the statistics of quartz grains with a variable number of sets of PDFs does not change significantly, and the patterns of crystallographic orientations of PDFs in randomly selected quartz grains does not indicate a change in absolute shock pressure with depth either. The value of oxygen isotopes for the recognition of meteoritic contamination, as proposed by earlier Woodleigh workers, is critically assessed. Neither INA nor PGE analyses of our samples support the presence of a meteoritic component within this basement section, as had been claimed in earlier work.
    • Workshop on Chondrites and the Protoplanetary Disk Kaua'i, Hawai'i, 2004

      Liffman, Kurt (The Meteoritical Society, 2006-01-01)