bluuebunny/crossref_metadata_2025 huggingface dataset:
Tookoonooka, a large buried early Cretaceous impact structure in the Eromanga Basin of southwestern Queensland, Australia
Authors: GOSTIN V. A. , THERRIAULT A. M.
Published: February 2010

Abstract— The ∼66 km wide Tookoonooka impact structure (27°07′S, 142°50′E) was first recognised, from seismic profiles, as a circular structure consisting of a concentric arrangement of anticlines and synclines, which surround a complex central dome, ∼22 km wide. A gravity low and a central magnetic high characterize the structure. Now buried by up to 900 m of Cretaceous and Tertiary clastic sediments, the Tookoonooka structure was formed ∼128 Ma ago, during deposition of the paralic Cadna‐owie Formation. Thin sections from a centrally located exploration well reveal an impact melt breccia, composed of local Ordovician quartz‐mica schist bedrock. Detailed study of planar deformation features (PDFs) in quartz grains from this breccia show 64 lamellae sets in 25 grains. Most of the PDF measurements correspond to ζ {112∼2} andr/z {101∼1}/ {011∼1} crystallographic indices, with five other orientations also measured. This distribution of PDFs corresponds to that found in quartz from impact structures in porous sedimentary rock targets, thus confirming an impact origin for Tookoonooka.
Clues to the nature of the impacting bodies from platinum‐group elements (rhenium and gold) in borehole samples from the Clearwater East crater (Canada) and the Boltysh impact crater (Ukraine)
Authors: SCHMIDT GERHARD
Published: February 2010

Abstract— Seven large (10 g) impact melt rock samples from boreholes from the Boltysh impact crater (Ukraine) and six samples from the East Clearwater crater (Canada) were analyzed for Os, Ir, Ru, Rh, Pd, Re and Au by the nickel sulfide technique in combination with neutron activation. Earlier analyses of Clearwater East impact melt rocks have shown that they are strongly enriched in Ir, Os, Pd and Re. In this work, I confirm earlier findings and demonstrate similarly high enrichments of Rh and Ru. The average Os/Ir, Ru/Ir, Pd/Ir, Rh/Ir and Ru/Rh ratios of the melt rock samples from Clearwater East are CI‐chondritic and yield an average Ir content of 25.2 ± 6.5 ng/g relative to an average upper crust concentration of 0.03 ± 0.02 ng/g Ir. The amount of meteoritic component corresponds to 4 to 7% of a nominal CI component for Clearwater East.

The impact melt rock samples from a bore hole from Boltysh are low in Ir with an average of 0.2 ± 0.1 ng/g. The CI‐normalized abundances increase from the refractory to the more volatile siderophile elements (Os < Ir < Ru < Rh ∼ Pd ∼ Au ∼ Ni ∼ Co). Because of the low Ir anomaly and uncertainties in making corrections (correlations are weak) for indigenous siderophile elements, no clear projectile assignment can be made.
The fate of pyroclasts produced in explosive eruptions on the asteroid 4 Vesta
Authors: WILSON LIONEL , KEIL KLAUS
Published: February 2010

Abstract— We evaluate the consequences of explosive activity having taken place during volcanic eruptions on the differentiated asteroid 4 Vesta, which is the likely parent body of the howardite‐eucrite‐diogenite (HED) meteorites. For a wide range of magma volatile contents, we calculate the eruption speeds and subsequent trajectories of the pyroclastic magma droplets produced. By considering the size distribution and eruption speeds of the droplets, and the mass fluxes at which they are ejected, we show that, under all realistic circumstances, the droplets will have formed lava fountains that were extremely optically dense. As a result, virtually all of the droplets will have reached the surface having suffered a negligible amount of radiative cooling and will have coalesced into lava ponds feeding lava flows. Typically, <1% of the pyroclasts will have undergone enough cooling to allow them to accumulate into a recognizable fall deposit consisting of unwelded or partly welded volcanic glass beads. This result is consistent with the apparent absence of identifiable pyroclastic material in the HED (and other types of) differentiated meteorites.
Vesta as the howardite, eucrite and diogenite parent body: Implications for the size of a core and for large‐scale differentiation
Authors: RUZICKA ALEX , SNYDER GREGORY A. , TAYLOR LAWRENCE A.
Published: February 2010

Abstract—If Vesta is the parent body of the howardite, eucrite, and diogenite (HED) meteorites, then geo‐chemical and petrologic constraints for the meteorites may be used in conjunction with astronomical constraints for the size and mass of Vesta to (1) determine the size of a possible metal core in Vesta and (2) model the igneous differentiation and internal structure of Vesta.

The density of Vesta and petrologic models for HED meteorites together suggest that the amount of metal in the parent body is <25 mass%, with a best estimate of ∼5%, assuming no porosity. For a porosity of up to 5% in the silicate fraction of the asteroid, the permissible metal content is <30%. These results suggest that any metal core in the HED parent body and Vesta is not unusually large.

A variety of geochemical and other data for HED meteorites are consistent with the idea that they originated in a magma ocean. It appears that diogenites formed by crystal accumulation in a magma ocean cumulate pile and that most noncumulate eucrites (excepting such eucrites as Bouvante and Statinem) formed by subsequent crystallization of the residual melts. Modelling results suggest that the HED parent body is enriched in rare earth elements by a factor of ∼2.5–3.5 relative to CI‐chondrites and that it has approximately chondritic Mg/Si and Al/Sc ratios. Stokes settling calculations for a Vesta‐wide, nonturbulent magma ocean suggest that early‐crystallizing magnesian olivine, orthopyroxene, and pigeonite would have settled relatively quickly, permitting fractional crystallization to occur, but that later‐crystallizing phases would have settled (or floated) an order of magnitude more slowly, allowing, instead, a closer approach to equilibrium crystallization for the more evolved (eucritic) melts. This would have inhibited the formation of a plagioclase‐flotation crust on Vesta.

Plausible models for the interior of Vesta, which are consistent with the data for HED meteorites and Vesta, include a metal core (<130 km radius), an olivine‐rich mantle (∼65–220 km thick), a lower crustal unit (∼12–43 km thick) composed of pyroxenite, from which diogenites were derived, and an upper crustal unit (∼23–42 km thick), from which eucrites originated. The present shape of Vesta (with ∼60 km difference in the maximum and minimum radius) suggests that all of the crustal materials, and possibly some of the underlying olivine from the mantle, could have been locally excavated or exposed by impact cratering.
Mineralogical records of early planetary processes on the howardite, eucrite, diogenite parent body with reference to Vesta
Authors: TAKEDA HIROSHI
Published: February 2010

Abstract— Mineralogical information recovered from the howardite, eucrite, diogenite (HED) meteorites was employed to reconstruct the history of the parent body and relate it to 4 Vesta. These interpreted crustal evolution processes were then compared to the expected geological features on the surface of a likely proto‐planet, 4 Vesta. The original crustal materials of the HED parent body were preserved as mineral grains and lithic clasts, but in many eucrites, Fe/Mg ratios in pyroxenes were homogenized by diffusion after crystallization. The crystallization trend of the protocrust has been deciphered by (1) examining monomict and crystalline samples and using their mineralogical and chemical information to formulate a sequence of crystallization and cooling trends; and by (2) reconstructing the original crust prior to cratering events from lithic clasts and mineral fragments in polymict breccias such as howardites and polymict eucrites. Mineral components are identical, both in the individual HED and in polymict breccias, and no remnants of primitive materials were preserved in the polymict breccias. A layered crust model reconstructed from such breccias consists of an upper crust with extrusive lava‐like eucrites that have been brecciated and metamorphosed, diogenite mantle, and cumulate eucrites of varying thickness between them. This model can be used to explain the surface geological features of Vesta observed from the Hubble space telescope. A large crater with diogenitic orthopyroxene at the crater floor is consistent with the deepest diogenitic layer of the layered crust model; and an underlying olivine layer is expected from early crystallized olivine in the crystal fractionation model. The old terrain of eucritic surface materials of Vesta can be howardites, polymict eucrites, or regolith‐like eucrites produced from eucrites extruded and impacted on the surface. Partial melting models of eucrites seem to be favored by the rare‐earth element (REE) chemistry and experimental studies. Unfortunately, partial melting models have not demonstrated how the HED parent body is converted to a layered crust without producing any metamorphosed primitive material in the layered crust. The origin of cumulate eucrites with systematic variation of textures and chemistries of pyroxene can be explained by the layered crust model with excavation and mixing of trapped liquid. Discovery of basaltic materials with Na‐rich plagioclase and augite in iron meteorites, which are the products of partial melting, suggests that eucrites may be unique to a body that underwent large‐scale differentiation and metamorphism.
Vesta fragments from v6 and 3:1 resonances: Implications for V‐type near‐Earth asteroids and howardite, eucrite and diogenite meteorites
Authors: MIGLIORINI F. , MORBIDELLI A. , ZAPPALÀ V. , GLADMAN B. J. , BAILEY M. E. , CELLINO A.
Published: February 2010

Abstract— A large body of evidence, including the presence of a dynamical family associated with 4 Vesta, suggests that this asteroid might be the ultimate source of both the V‐type near‐Earth asteroids (NEAs) and howardite, eucrite and diogenite (HED) meteorites. Dynamical routes from Vesta to the inner regions of the solar system are provided by both the 3:1 mean‐motion resonance with Jupiter and the V6, secular resonance. For this reason, numerical integrations of the orbits of fictitious Vesta fragments injected in both of these resonances have been performed. At the same time, the orbital evolution of the known V‐type NEAs has been investigated. The results indicate that the dynamical half lifetimes of Vesta fragments injected in both the 3:1 and the V6, resonances are rather short ('2 Ma). The present location of the seven known V‐type NEAs is better explained by orbital evolutions starting from the v6 secular resonance. The most important result of the present investigation, however, is that we now face what we call the “Vesta paradox.” Roughly speaking, the paradox consists of the fact that the present V‐type NEAs appear to be too dynamically young to have originated in the event that produced the family, but they are too big to be plausible second‐generation fragments from the family members. The cosmic‐ray exposure (CRE) age distribution of HED meteorites also raises a puzzle, since we would expect an overabundance of meteorites with short CRE ages. We propose different scenarios to explain these paradoxes.
Galileiite: A new meteoritic phosphate minera
Authors: Olsen Edward J. , Steele Ian M.
Published: February 2010

Abstract— A new mineral named galileiite, NaFe4(PO4)3, has been found within troilite nodules in iron meteorites of the IIIA and IIIB groups. the mineral is optically positive (ω = 1.72, ω = 1.75), colorless in transmitted light and pale amber in reflected light. Grains of galileiite are very small, generally 10 μm or less; rarely, grains are up to 30 μm. It is associated with Ca‐free graftonite (or Ca‐free sarcopside), chromite and, occasionally, schreibersite. Johnsomervilleite may occur within troilite nodules in the same meteorite as galileiite, but they have never been observed together in the same troilite nodule. Because of the small sample size, single crystal x‐ray work was not successful; however, Gandolfi diffraction measurements were made. The three strongest diffraction peaks are 2.71 Å, 3.01 Å and 4.13 Å. On the basis of its composition and similar diffraction pattern, it is considered to be related to johnsomervilleite, fillowite and chladniite, all of which are rhombohedral and isostructural. Galileiite may also be rhombohedral, but that is yet to be demonstrated.
Petrology, chemistry, and isotopic compositions of the lunar highland regolith breccia Dar al Gani 262
Authors: BISCHOFF A. , WEBER D. , CLAYTON R. N. , FAESTERMANN T. , FRANCHI I. A. , HERPERS U. , KNIE K. , KORSCHINEK G. , KUBIK P. W. , MAYEDA T. K. , MERCHEL S. , MICHEL R. , NEUMANN S. , PALME H. , PILLINGER C. T. , SCHULTZ L. , SEXTON A. S. , SPETTEL B. , VERCHOVSKY A. B. , WEBER H. W. , WECKWERTH G. , WOLF D.
Published: February 2010

Abstract— Lunar meteorite Dar al Gani 262 (DG 262)—found in the Libyan part of the Sahara—is a mature, anorthositic regolith breccia with highland affinities. The origin from the Moon is undoubtedly indicated by its bulk chemical composition; radionuclide concentrations; noble gas, N, and O isotopic compositions; and petrographic features. Dar al Gani 262 is a typical anorthositic highland breccia similar in mineralogy and chemical composition to Queen Alexandra Range (QUE) 93069.

About 52 vol% of the studied thin sections of Dar al Gani 262 consist of fine‐grained(100 μm) constituents, and 48 vol% is mineral and lithic clasts and impact‐melt veins. The most abundant clast types are feldspathic fine‐grained to microporphyritic crystalline melt breccias (50.2 vol%; includes recrystallized melt breccias), whereas mafic crystalline melt breccias are extremely rare (1.4 vol%). Granulitic lithologies are 12.8 vol%, intragranularly recrystallized anorthosites and cataclastic anorthosites are 8.8 and 8.2 vol%, respectively, and (devitrified) glasses are 2.7 vol%. Impact‐melt veins (5.5 vol% of the whole thin sections) cutting across the entire thin section were probably formed subsequent to the lithification process of the bulk rock at pressures below 20 GPa, because the bulk rock never experienced a higher peak shock pressure.

Mafic crystalline melt breccias are very rare in Dar al Gani 262 and are similar in abundance to those in QUE 93069. The extremely low abundance of mafic components and the bulk composition may constrain possible areas of the Moon from which the breccia was derived. The source area of Dar al Gani 262 must be a highland terrain lacking significant mafic impact melts or mare components.

On the basis of radionuclide activities, an irradiation position of DG 262 on the Moon at a depth of 55–85 g/cm3and a maximum transit time to Earth <0.15 Ma is suggested. Dar al Gani 262 contains high concentrations of solar‐wind‐implanted noble gases. The isotopic abundance ratio 40Ar/36Ar < 3 is characteristic of lunar soils.

The terrestrial weathering of DG 262 is reflected by the occurrence of fractures filled with calcite and by high concentrations of Ca, Ba, Cs, Br, and As. There is also a large amount of terrestrial C and some N in the sample, which was released at low temperatures during stepped heating. High concentrations of Ni, Co, and Ir indicate a significant meteoritic component in the lunar surface regolith from which DG 262 was derived.
Petrography and geochemistry of target rocks and impactites from the Ilyinets Crater, Ukraine
Authors: GUROV Eugene P. , KOEBERL Christian , REIMOLD Wolf Uwe
Published: February 2010

Abstract— The ∼400 Ma old Ilyinets impact structure was formed in the Precambrian basement of the Ukrainian Shield and is now mostly covered by Quaternary sediments. Various impact breccias and melts are exposed in its southern section. The crater is a complex structure with a central uplift that is surrounded by an annular deposit of breccias and melt rocks. In the annulus, brecciated basement rocks are overlain by up to 80 m of glass‐poor suevitic breccia, which is overlain (and partly intercalated) by glass‐rich suevite with a thickness of up to 130 m. Impact‐melt rocks occur within and on top of the suevites—in some cases in the form of devitrified bomb‐shaped impact‐glass fragments. We have studied the petrographic and geochemical characteristics of 31, mostly shocked, target rock samples (granites, gneisses, and one amphibolite) obtained from drill cores within the structure, and impact breccias and melt rock samples from drill cores and surface exposures. Multiple sets of planar deformation features (PDFs) are common in quartz, potassium feldspar, and plagioclase of the shocked target rocks. The breccias comprise more or less devitrified impact melt with shocked clasts. The impact‐melt rocks (“bombs”) show abundant vesicles and, in some cases, glass is still present as brownish patches and schlieren. All impact breccias (including the melt rocks) are strongly altered and have significantly elevated K contents and lower Na contents than the target rocks. The alteration could have occurred in an impact‐induced hydrothermal system. The bomb‐shaped melt rocks have lower Mg and Ca contents than other rock types at the crater. Compared to target rocks, only minor enrichments of siderophile element contents (e.g., Ni, Co, Ir) in impact‐melt rocks were found.
Survey and evaluation of eucrite bulk compositions
Authors: KITTS K. , LODDERS K.
Published: February 2010

Abstract—The purpose of this survey is to establish reference bulk elemental abundances for the eucrites and thereby provide the basis to test core formation models as well as partial melting, fractional crystallization and magma ocean theories for the eucrite parent body. In order to evaluate bulk elemental abundances for the eucrites, 296 peer‐reviewed articles, monographs, theses or books and 143 abstracts dating from 1938 to 1997 were surveyed. Of the 101 eucrites having at least one set of elemental abundance analyses reported in the literature, 20 were selected for in‐depth examination. The selection criteria of our sample were based on the total number of analyses available for a given eucrite and the total number of elements for which data exist. The mean bulk elemental abundance, 1σ standard deviation, and the percent deviation were calculated for each element in a given eucrite. In order to evaluate the quality of the mean abundances, the elements were then grouped according to availability of data and percent deviations. Possible reasons for the different deviations in the different groups are briefly discussed. From the major element abundances, the normative (CIPW) composition, the molar compositions of pyroxene, olivine and plagioclase, and the bulk densities were calculated and compared to petrographic observations. The calculated norms for the noncumulates agree well with the observations while the norms for the cumulates do not. Possible reasons for this are discussed. Unfortunately, analyses of many elements are poorly represented in the literature and many bulk analyses suffer from unacceptable levels of uncertainty. Therefore, future work requires bulk elemental analyses for some of the more poorly characterized elements in eucrites, especially those of key elements used for planetary modeling.
Unusual forms of magnetite in the Orgueil carbonaceous chondrite
Authors: HUA Xin , BUSECK Peter R.
Published: February 2010

Abstract— The Orgueil CI carbonaceous chondrite contains magnetite (Fe3O4) that displays a rich and seemingly unique variety of morphologies. While many have already been described, recent images provide far greater definition and, thus, provide more unambiguous identification of trapezohedral crystals and possibly also trisoctahedral forms. Although it is an extremely abundant terrestrial mineral and commonly occurs in well‐developed crystals, neither of these forms have been recognized previously from magnetite. The barrel‐shaped arrays of magnetite discs (“plaquettes”) are also unique. It appears as if the circumstances for the formation of these unusual crystals were somehow exceptional. Their morphologies and association with sulfates and carbonates suggest an aqueous origin.
The Meteoritical Bulletin, No. 82, 1998 July
Authors: GROSSMAN Jeffrey N.
Published: February 2010

Abstract— Meteoritical Bulletin No. 82 lists information for 974 new meteorites, including 521 finds from Antarctica, 401 finds from the Sahara, 21 finds from the Nullarbor region of Australia, and 7 falls (Ban Rong Du, Burnwell, Fermo, Jalanash, Juancheng, Monahans (1998), and Silao). Many rare types of meteorites are reported: counting pairing groups as one, these include one CR chondrite, two CK chondrites, two CO chondrites, four CV chondrites, one CH chondrite or Bencubbin‐like, six C2 (unclassified) chondrites, two EH chondrites, two EL chondrites, three R chondrites, thirty unequilibrated ordinary chondrites, one un‐grouped chondrite, three eucrites, six howardites, one diogenite, eleven ureilites, nine iron meteorites, one mesosiderite, two brachinites, one lodranite, one winonaite, and two lunar meteorites (Dar al Gani 400 and EET 96008). All italicized abbreviations refer to addresses tabulated at the end of this document.
Agate as an indicator of impact structures: An example from Sääksjärvi, Finland
Authors: KINNUNEN KARI A. , LINDQVIST KRISTIAN
Published: February 2010

Abstract— Mineralogical, petrographical and chemical determinations were made for 743 agate (banded variety of chalcedonic quartz) nodules (diameters from 5 mm to 5 cm) formed during postimpact, low‐temperature hydrothermal activity as vesicle fillings in the melt rocks of the Sääksjärvi meteorite impact structure (diameter 5 km) in southwest Finland. Other hydrothermal vesicle fillings in the impact melt rocks include chlorite, mordenite, smectite and kaolinite. The agates were classified into two types, whose mineralogical properties and chemical compositions fall within the range of volcanic agates (basaltic and rhyolitic host rocks). The relatively high age (∼510 Ma) of the Sääksjärvi impact melt rocks, however, is reflected by the presence of recrystallization textures, which are rare in younger volcanic agates. The Sääksjärvi structure was initially located after following the fortuitous discovery of agate “path‐finders” in the glacial overburden. It is recommended that wherever volcanic type agates are found as float in Precambrian shield areas devoid of younger volcanic rocks, the possible presence of impact (or volcanic) craters in the vicinity should be considered.
The “European Fireball Network”: Current status and future prospects
Authors: OBERST J. , MOLAU S. , HEINLEIN D. , GRITZNER C. , SCHINDLER M. , SPURNY P. , CEPLECHA Z. , RENDTEL J. , BETLEM H.
Published: February 2010

Abstract— Among the three large camera networks carrying out fireball observations through the seventies and eighties, the “European Fireball Network” is the last one still in operation. The network today consists of more than 34 all‐sky and fish‐eye cameras deployed with ∼100 km spacing and covering an area of ∼106 km2, in the Czech and Slovak Republics, Germany, as well as parts of Belgium, Switzerland, and Austria. Network operation results in ∼10 000 image exposures per year, which represent on average 1200 h of clear sky observations—as imaging periods are restricted due to daylight, moonlight, and clouds. The cameras detect currently large meteors at a rate of ∼50 per year; this is in good agreement with the encounter rates determined in previous fireball studies. From sightings of “meteorite candidates” (fireballs that may have deposited meteorites) and meteorite recoveries in the network area, we estimate that 15% of the influx of meteoritic matter is currently observed by the cameras, whereas <1% is recovered on the ground. Issues to be addressed by future fireball observations include the study of very large meteoroids (>1000 kg) for which statistics are currently very poor and an examination of their relationship to NEOs (near‐Earth objects) identified by current NEO search programs.
Investigation of a bright flying object over northwest Spain, 1994 January 18
Authors: DOCOBO J. A. , SPALDING R. E. , CEPLECHA Z. , DIAZ‐FIERROS F. , TAMAZIAN V. , ONDA Y.
Published: February 2010

Abstract— On the early morning of 1994 January 18, a very bright luminous object crossed the sky of Santiago de Compostela, Spain. From visual sightings, it is concluded that the object wasn't a meteoric fireball (bolide). A surface “crater” in Cando (close to Santiago) with dimensions 29 × 13 m and 1.5 m deep was later discovered within 1 km of the projected “impact” point of the luminous object. At this site, in addition to the topsoil, full‐grown pine trees >20 m high were thrown downhill over a nearby road, leaving the down‐slope edge of the “crater” untouched and with a steep interior wall (this would not be the case if a regular landslide were responsible for the transport). Standing trees below the “crater” showed embedded soil and plant residues up to heights >3 m. No strange materials (meteorites or artifacts) were recovered in or close to the “crater”; all materials belonged to the site and were not shocked; thus, an impact is very improbable.

A possible explanation capable of reconciling all of the observations is presented. It hypothesizes an eruption of earth gases to create the crater, with the rising gas plume then interacting with atmospheric electricity to produce the propagating fireball that was observed.
Thermal processing of chondrule precursors in planetesimal bow shocks
Authors: HOOD LON L.
Published: February 2010

Abstract— We test the hypothesis that chondrules (and Type B and C calcium‐aluminum‐rich inclusions, CAIs) originated during passage of precursors through bow shocks upstream of planetesimals moving supersonically relative to nebula gas. A two‐dimensional piecewise parabolic method (PPM) hydrocode, supplemented by a one‐dimensional adiabatic shock model, is employed to simulate the postshock gas density, temperature, and velocity fields for given planetesimal sizes, velocities, and ambient nebular densities and temperatures. Thermal histories of incident silicate particles are calculated in the free molecular flow approximation by integration of the one‐dimensional equations of gas‐grain energy and momentum transfer. For gas number densities >1014 cm−3, Mach numbers in the range of 4 to 5 are sufficient to melt isolated spherical particles with radii in the range 0.05 to 0.5 mm during passage of shocked gas thicknesses of 25–35 km. Minimum gas‐planetesimal relative velocities are in the range 5.5–7 km/s, implying orbital eccentricities >0.2 and/or inclinations >15°. Melting of centimeter‐sized CAI precursors requires either higher Mach numbers (6–7) or ambient gas densities >1015 cm−3. For a constant radial distribution of planetesimal orbital eccentricities and inclinations, the model predicts more efficient melting of precursor particles at decreasing radial distances from the Sun where planetesimal velocities are largest. In order to process a significant fraction of solids in the nebula, planetesimals near ∼2.5 AU during the chondrule formation epoch must have had a range of eccentricities and inclinations comparable to those presently observed in the residual asteroid belt. The most likely energy source for maintaining the necessary gas‐planetesimal relative velocities is external gravitational perturbations associated with the forming outer planets, primarily Jupiter.
Rapid weathering in Holbrook: An iron‐57 Mössbauer spectroscopy study
Authors: BLAND P. A. , BERRY F. J. , PILLINGER C. T.
Published: February 2010

Abstract— Samples of Holbrook (an L6 chondrite that fell in Arizona in 1912) were analysed by 57Fe Mössbauer spectroscopy to determine the proportion of the total Fe that had been converted to Fe3+ by weathering processes. Although samples recovered in 1912 showed negligible (<1%) alteration, a spectrum recorded from a specimen recovered in 1968 showed that 9.7% of the total Fe was present as Fe3+. Given the existence of samples in similar semiarid environments with terrestrial ages >40 ka, a linear rate of weathering is unrealistic, rapidly producing very high levels of oxidation in samples with low terrestrial ages. However if weathering follows an approximate power law, then we can model a rapid initial phase and the levels of oxidation that are more typical in samples with much longer terrestrial residence times recovered from Roosevelt County. Our analysis, together with work on terrestrial age dated samples, indicates that hot desert weathering of ordinary chondrites is at least a two‐stage process, with an initial rapid phase lasting <500 years before oxidation is passivated.
Parent bodies of L and H chondrites: Times of catastrophic events
Authors: ALEXEEV V. A.
Published: February 2010

Abstract— An analysis of the distribution of 3He and 4He in L and H chondrites has shown that the parent body of L chondrites underwent a catastrophic collision in space 340 ± 50 Ma ago. This age differs considerably from the collision age of 520 ± 60 Ma given previously (Heymann, 1967). The parent body of H chondrites may also have undergone local heating and degassing ∼200 Ma ago. Data for L chondrites argue in favour of Antarctic and non‐Antarctic meteorites having originated from a common parent body.
The silicate inclusions of the Ocotillo IAB iron meteorite
Authors: OLSEN EDWARD J. , SCHWADE JAMES
Published: February 2010

Abstract— The Ocotillo IAB iron meteorite contains small silicate inclusions consisting of olivine, low‐Ca pyroxene, chromian diopside, plagioclase, magnesiochromite, apatite, troilite and metal. The ferromagnesian silicates have a small range of Fe/(Fe + Mg) ratios that are not due to zoning. These phases appear to be not well equilibrated. The FeO content of magnesiochromite is lower than values normally seen in silicate assemblages in IAB iron meteorites. The minerals in Ocotillo are generally like silicate assemblages in other IAB meteorites, covering similar composition ranges and exhibiting a metamorphic (granoblastic) texture. An estimate was made of the bulk composition of Ocotillo silicate inclusions. The bulk composition is close to that of ordinary chondrites with the exception of a deficiency in CaO that might be due to a sampling problem associated with the method used to estimate the bulk composition.
Corundum‐bearing residues produced through the evaporation of natural and synthetic hibonite
Authors: FLOSS CHRISTINE , GORESY AHMED EL , ZINNER ERNST , PALME HERBERT , WECKWERTH GERD , RAMMENSEE WERNER
Published: February 2010

Abstract— We have produced corundum‐bearing residues through the evaporation of natural and synthetic hibonite samples. The sequence of major element losses as well as volatility related trace element fractionations in these residues are similar to those previously observed in residues from the evaporation of chondritic starting material, which suggests that the processes by which these fractionations occur may be largely independent of the starting material used. However, the mineralogy of the residues does depend on the composition of the starting material and, to some extent, on the conditions under which evaporation took place. Similarly, the degree of isotopic mass fractionation observed in the residues is composition‐dependent. This observation means that it may be possible to use isotopic data for several elements to constrain the compositions of precursor materials of Ca‐Al‐rich inclusions, which have an evaporation origin. Although corundum‐bearing inclusions are known, their origins are complex and variable, and the scarcity of such inclusions indicates that melting of hibonite, with or without concomitant evaporation, must have been a rare process in the solar nebula. By evaporating mixtures of synthetic oxides of the rare earth elements, we have reproduced the patterns of Group III inclusions and some of the characteristics of ultrarefractory patterns. However, the extreme conditions required to do so indicate that refractory inclusions with these patterns probably have a condensation rather than evaporation origin.
Geochemical and petrographic studies of oldhamite, diopside, and roedderite in enstatite meteorites
Authors: HSU WEIBIAO
Published: February 2010

Abstract— In Qingzhen (EH3), oldhamite contains numerous types of inclusions and intergrows with other phases; but in equilibrated enstatite chondrites and aubrites, it usually occurs as individual grains. I suggest that oldhamite in unequilibrated enstatite chondrites (UECs) crystallized from a melt, probably during chondrule formation. Subsequent thermal metamorphism on the parent bodies further modified the oldhamite occurrences in enstatite chondrites. This suggestion is consistent with the results of melting experiments on UECs and aubrites and with the volatile element enrichments in this mineral.

I analyzed minor and trace element abundances in diopside from two aubrites. These data and petrographic observations suggest that diopside formed by igneous crystallization.

I report the first known occurrence of roedderite in an aubrite and its major, minor, and trace element concentrations. This mineral is rich in alkalis but is depleted in siderophile and refractory lithophile elements.

A negative Sm anomaly was noted in albite from equilibrated enstatite chondrites and aubrites.
Chemical studies of H chondrites 9: Volatile trace element composition and petrographic classification of equilibrated H chondrites
Authors: WOLF STEPHEN F. , LIPSCHUTZ MICHAEL E.
Published: February 2010

Abstract— To examine the thermal history of the parent body/bodies of equilibrated H chondrites, we treated data for 11 volatile trace elements (Co, Rb, Ag, Se, Cs, Te, Zn, Cd, Bi, Tl, and In in order of putative volatility) in 90 falls: 15 H4; 46 H5, and 29 H6. Using univariate statistical tests, contents of few of these elements differ significantly between any two of these suites. One element, Cs, differs systematically between all three pairs of suites; Co and Tl differ between two pairs of suites. For Co and Cs, contents varied as H4 > H5 > H6; while for Tl, contents varied as H4 < H5 < H6. Using multivariate statistical tests, all three suites can be distinguished compositionally, with trace element contents in the H5 suite being intermediate to those of H4 and H6. Surprisingly, the multivariate distinguishability reflects contents of less volatile Co, Rb, Ag, Se and Cs, and not of highly volatile Te, Zn, Cd, Bi, Tl and In. The compositional trends apparently reflect heterogeneous accretion >600 K, with the suites deriving from a stratified parent body/bodies.
Cosmic‐ray produced, radiogenic, and solar noble gases in lunar meteorites Queen Alexandra Range 94269 and 94281
Authors: POLNAU ERNST , EUGSTER OTTO
Published: February 2010

Abstract— We measured the noble gas isotopic abundances in lunar meteorite QUE 94269 and in bulk‐, glass‐, and crystal‐phases of lunar meteorite QUE 94281. Our results confirm that QUE 94269 originated from the same meteorite fall as QUE 93069: both specimens yield the same signature of solar‐particle irradiation and also the cosmogenic noble gases are in agreement within their uncertainities. Queen Alexandra Range 93069/94269 was exposed to cosmic rays in the lunar regolith for ∼1000 Ma, and it trapped 3.5 × 10−4 cm3STP/g solar 36Ar, the other solar noble gases being present in proportions typical for the solar‐particle irradiation. The bulk material of QUE 94281 contains about three times less cosmogenic and trapped noble gases than QUE 93069/94269 and the lunar regolith residence time corresponds to 400 ± 60 Ma. We show that in lunar meteorites the trapped solar 20Ne/22Ne ratio is correlated with the trapped ratio 40Ar/36Ar, that is, trapped 20Ne/22Ne may also serve as an antiquity indicator. The upper limits of the breccia compaction ages, as derived from the trapped ratio 40Ar/36Ar for QUE 93069/94269 and QUE 94281 are ∼400 Ma and 800 Ma, respectively. We found very different regolith histories for the glass phase and the crystals separated from QUE 94281. The glass phase contains much less cosmogenic and solar noble gases than the crystals, in contrast to the glasses of lunar meteorite EET 87521, that were enriched in noble gases relative to the crystalline material. The QUE 94281 phases yield a 40K‐40Ar gas retention age of 3770 Ma, which is in the range of that for lunar mare rocks.
Martian basalt (shergottite) Queen Alexandra Range 94201 and lunar basalt 15555: A tale of two pyroxenes
Authors: WADHWA M. , CROZAZ G. , TAYLOR L. A. , MCSWEEN H. Y.
Published: February 2010

Abstract— We present here ion microprobe analyses of rare earth and other selected trace and minor elements in pyroxenes of shergottite Queen Alexandra Range 94201 and lunar basalt 15555. Pyroxene zonation patterns record the crystallization histories of these two basaltic samples from Mars and the Moon, respectively, and allow a comparison of mafic melt evolution on these two planetary bodies. Elemental abundances and trends in pyroxenes of these two rocks indicate that their minerals formed by continuous, closed system fractional crystallization of their respective parent melts. This further supports the idea that QUE 94201 closely represents the composition of a true Martian basaltic melt (McSween et al., 1996). The main differences in pyroxene elemental zonation patterns in these two objects are attributed to earlier crystallization of whitlockite in QUE 94201 (i.e., before the Fe‐rich pyroxenes) than in 15555 (after the Fe‐rich pyroxenes). The size of Eu anomalies in pyroxenes of QUE 94201 is intermediate between that in pyroxenes of 15555 and the other shergottites and may imply that fO2 conditions during crystallization of this Martian basalt were significantly more reducing than for other shergottites, although not quite as reducing as for lunar basalts. Cerium anomalies appear to be less prevalent in pyroxenes of QUE 94201 than other Antarctic shergottites and could be indicative of lesser degree of weathering in the Antarctic.
Origin and emplacement of Offset Dykes in the Sudbury impact structure: Constraints from Hess
Authors: WOOD CHRISTINA R. , SPRAY JOHN G.
Published: February 2010

Abstract— The Hess Offset is a steeply dipping dyke located 12–15 km north of the 1.85 Ga Sudbury igneous complex (SIC) within the 200–250 km diameter Sudbury impact structure. It is up to 60 m wide and strikes subconcentrically to the SIC for at least 23 km. The main phase of the dyke is granodioritic, but it conforms with what is locally referred to as Quartz Diorite: a term used for all the Offset Dykes of the Sudbury impact structure. Rare earth element data shows that the Hess Offset is genetically related to the SIC. Hess is most closely affiliated with an evolved Felsic Norite component of SIC and not bulk impact melt. This indicates that Hess was emplaced during fractionation of the impact melt sheet, rather than immediately following impact. The main Quartz Diorite phase of the dyke comprises a quartz + plagioclase + hornblende + biotite ± clinopyroxene ± orthopyroxene assemblage. Critically, the Hess Offset occupies a concentric fault system that marks the northern limit of a pseudotachylyte‐rich, shatter cone‐bearing annulus about the SIC. This fault system was active during the modification stage of the impact process.
Popigai crater: Origin and distribution of diamond‐bearing impactites
Authors: MASAITIS V. L.
Published: February 2010

Abstract— About three decades ago, a formerly unknown genetic type of natural diamonds was discovered in impact craters. Impact diamonds are currently known from a number of impact structures in Europe, Asia and North America, and it's likely that the number of finds will increase with time. The Popigai crater, Northern Siberia, where impact diamonds were first found, was specifically investigated in terms of geology, geophysics, petrography and mineralogy. Large resources of industrial impact diamonds were discovered, and these minerals were studied in detail.

Authigenic impact diamonds occur in situ in shocked graphite‐bearing gneisses that are found as inclusions in impact melt rocks: tagamites and suevites. According to the observed transformation of coexisting minerals, the lower estimated pressure of the coherent martensite transition of graphite to diamonds is 35 GPa. Impact diamonds inherit the original shape of graphite crystals and are composed of a polycrystalline structured aggregate of cubic and probably hexagonal carbon microcrystals 1–5 μm across. Numerous properties of diamonds depend on the high density of defects in the crystal lattice. Allothigenic impact diamonds occur in rocks produced by the homogenization and solidification of impact melt, which originated from the complete fusion of graphite‐bearing precursor gneisses. These diamonds usually reflect the influence of the hot melt and are strongly corroded.

Diamond‐bearing tagamites and suevites in the Popigai crater interior occur as extended lens and sheets bodies and also as irregular small bodies. Diamond distribution depends on the original abundance of precursor graphite in the target rocks, on the superimposed shock‐metamorphic zonation, and on the character of the ejection of shocked and melted material along different trajectories and azimuths. This has resulted in radial and concentric inhomogeneities in diamond distribution in the crater interior. On a second order, the distribution depends on the scale of melt contamination by clasts and fragments and by the duration of cooling of certain melt bodies and their constituents. Enrichment in diamonds at the margins of thick tagamite sheets is the result of rapid cooling, which prevents combustion of diamonds. A positive correlation between diamond content and the amount of phosphorus pentoxide in impactites indicates links to C and P probably in organic matter of the primary sedimentary rocks, which were subjected to granulitic metamorphism 2.4 Ga ago and melted at the time of impact 35.7 Ma ago.
Ion probe measurements of carbon and nitrogen in iron meteorites
Authors: SUGIURA NAOJI
Published: February 2010

Abstract— Carbon and nitrogen distributions in iron meteorites, their concentrations in various phases, and their isotopic compositions in certain phases were measured by secondary ion mass spectrometry (SIMS). Taenite (and its decomposition products) is the main carrier of C, except for IAB iron meteorites, where graphite and/or carbide (cohenite) may be the main carrier. Taenite is also the main carrier of N in most iron meteorites unless nitrides (carlsbergite CrN or roaldite (Fe, Ni)4N) are present. Carbon and N distributions in taenite are well correlated unless carbides and/or nitrides are exsolved.

There seem to be three types of C and N distributions within taenite. (1) These elements are enriched at the center of taenite (convex type). (2) They are enriched at the edge of taenite (concave type). (3) They are enriched near but some distance away from the edge of taenite (complex type). The first case (1) is explained as equilibrium distribution of C and N in Fe‐Ni alloy with M‐shape Ni concentration profile. The second case (2) seems to be best explained as diffusion controlled C and N distributions. In the third case (3), the interior of taenite has been transformed to the α phase (kamacite or martensite). Carbon and N were expelled from the α phase and enriched near the inner border of the remaining γ phase. Such differences in the C and N distributions in taenite may reflect different cooling rates of iron meteorites.

Nitrogen concentrations in taenite are quite high approaching 1 wt% in some iron meteorites. Nitride (carlsbergite and roaldite) is present in meteorites with high N concentrations in taenite, which suggests that the nitride was formed due to supersaturation of the metallic phases with N. The same tendency is generally observed for C (i.e., high C concentrations in taenite correlate with the presence of carbide and/or graphite). Concentrations of C and N in kamacite are generally below detection limits.

Isotopic compositions of C and N in taenite can be measured with a precision of several permil. Isotopic analysis in kamacite in most iron meteorites is not possible because of the low concentrations. The C isotopic compositions seem to be somewhat fractionated among various phases, reflecting closure of C transport at low temperatures. A remarkable isotopic anomaly was observed for the Mundrabilla (IIICD anomalous) meteorite. Nitrogen isotopic compositions of taenite measured by SIMS agree very well with those of the bulk samples measured by conventional mass spectrometry.
Origin of hibonite‐pyroxene spherules found in carbonaceous chondrites
Authors: SIMON STEVEN B. , DAVIS ANDREW M. , GROSSMAN LAWRENCE , ZINNER ERNST K.
Published: February 2010

Abstract— We have studied both of the known glass‐free, hibonite‐pyroxene spherules: MYSM3, from Murray (CM2), and Y17–6, from Yamato 791717 (CO3). They consist of hibonite plates (∼2 wt% TiOtot2) enclosed in Al‐rich pyroxene that has such high amounts of CaTs (CaAl2SiO6) component, up to ∼80 mol%, that it must have crystallized metastably. Within the pyroxene, abundances of MgO and SiO2 are strongly correlated with each other and are anticorrelated with those of Al2O3, reflecting an anticorrelation between the diopside and CaTs components of the pyroxene. In contrast with previous results for Type B fassaite, however, we do not observe an anticorrelation between MgO and TiOtot2, possibly reflecting different relative distribution coefficients for Ti3+ and Ti4+ in the aluminous pyroxene of the spherules from those found for fassaite in Type B inclusions. Previously described hibonite‐silicate spherules have 26Mg deficits but the present samples do not. Furthermore, the pyroxene in Y17‐6 has excess 26Mg, while the hibonite it encloses does not, indicating that the two phases either had different initial 26Al/27Al ratios or different initial 26Mg/24Mg ratios. The Ti isotopic compositions of the present samples are highly unusual: δ50Ti = 103.4 ± 5.2%o in MYSM3 and ‐61.4 ± 4.1%0 in Y17‐6, which are among the largest 50Ti anomalies reported for any refractory inclusion. The textures suggest that hibonite crystallized first; but based on the calculated bulk compositions of both spherules, it is not the liquidus phase in either sample, which suggests that the hibonite in both samples is relict. The presence of ragged hibonite grains in MYSM3 and rounded hibonite grains in Y17‐6 and a lack of isotopic equilibrium between pyroxene and hibonite support this conclusion. The spherules crystallized from liquid droplets that probably formed as a result of the melting of solid precursor grains that included hibonite. The heating events were too short and/or not hot enough to melt all the hibonite. The droplets cooled quickly enough that CaTs‐rich pyroxene crystallized instead of anorthite. Based on the observed differences in isotopic composition, it is unlikely that the precursors of the present samples formed in the same reservoir as each other or as the previously described hibonite‐silicate spherules, providing further evidence of the isotopic heterogeneity of the early solar nebula.