bluuebunny/crossref_metadata_2025 huggingface dataset:
Asteroid Differentiation: Pyroclastic Volcanism to Magma Oceans
Authors: Taylor G. Jeffrey , Keil Klaus , McCoy Timothy , Haack Henning , Scott Edward R. D.
Published: June 2012

Abstract— Asteroid differentiation was driven by a complex array of magmatic processes. This paper summarizes theoretical and somewhat speculative research on the physics of these processes. Partial melts in asteroids migrate rapidly, taking < 106 years to reach surface regions. On relatively small (<100 km) asteroids with sufficient volatiles in partial melts (<3000 ppm), explosive volcanism accelerated melts to greater than escape velocity, explaining the apparent lack of basaltic components on the parent asteroids of some differentiated meteorites. Partial melting products include the melts (some eucrites, angrites), residues (lodranites, ureilites), and unfractionated residues (acapulcoites). The high liquidus temperatures of magmatic iron meteorites, the existence of pallasites with only olivine, and the fact that enstatite achondrites formed from ultramafic magmas argue for the existence of magma oceans on some asteroids. Asteroidal magma oceans would have been turbulently convective. This would have prevented crystals nucleated at the upper cooling surface (the only place for crystal nucleation in a low‐pressure body) from settling until the magma became choked with crystals. After turbulent convection slowed, crystals and magma would have segregated, leaving a body stratified from center to surface as follows: a metallic core, a small pallasite zone, a dunite region, a feldspathic pyroxenite, and basaltic intrusions and lava flows (if the basaltic components had not been lost by explosive volcanism). The pallasite and dunite zones probably formed from coarse (0.5–1 cm) residual olivine left after formation of the magma ocean at >50% partial melting of the silicate assemblage. Iron cores crystallized dendritically from the outside to the inside. The rapid melt migration rate of silicate melts suggests that 26Al could not be responsible for forming asteroidal magma oceans because it would leave the interior before a sufficient amount of melting occurred. Other heat sources are more likely candidates. Our analysis suggests that if Earth‐forming planetesimals had differentiated they were either small (<100 km) and poor in volatiles (<1000 ppm) or they were rich in volatiles and large enough (>300 km) to retain the products of pyroclastic eruptions; if these conditions were not met, Earth would not have a basaltic component.
The petrography, mineralogy and origins of calcium sulphate within the Cold Bokkeveld CM carbonaceous chondrite
Authors: Lee Martin R.
Published: June 2012

Abstract— A detailed scanning and transmission electron microscopy study of Cold Bokkeveld has shown that calcium sulphate is widespread, occluding ∼30 μm wide matrix‐cutting fractures in addition to μm‐sized veins and irregular dissolution pores within calcitized chondrules, matrix calcite grains and Ca‐ and Al‐rich inclusions (CAI). The majority of calcium sulphate crystals have fibrous habits, especially those which have grown within straight‐sided fractures and veins. Mineralogically, the calcium sulphate is composed of a fine‐scale mixture of hemihydrate and anhydrite which have probably formed by the dehydration of primary gypsum during sample preparation.

In all contexts, calcium sulphate precipitation was the last identifiable diagenetic event in the pre‐terrestrial history of Cold Bokkeveld and followed pervasive aqueous alteration of the meteorite matrix to phyllosilicates. The fibrous fracture‐ and vein‐filling calcium sulphates are morphologically similar to a terrestrial form of gypsum termed “satinspar” and so may have formed in a similar manner by precipitation from supersaturated aqueous solutions during fracture and vein dilation. The aqueous solutions were most probably generated by melting of water ice due to internal heating and/or post‐accretional impact heating of the parent body. Although impact‐produced fractures and veins may have provided conduits for fluid advection, the dissolution of calcite, alteration of metal sulphides and precipitation of gypsum probably took place when aqueous solutions were more‐or‐less static. Despite their similarity to late‐stage mineralized fractures in CI meteorites, the calcium sulphate‐filled fractures in Cold Bokkeveld probably do not have any significance regarding a shared CM‐CI parent body.
On the Bur Gheluai H5 chondrite and other meteorites with complex exposure histories
Authors: Vogt S. K. , Aylmer D. , Herzog G. F. , Wieler R. , Signer P. , Pellas P. , Fiéni C. , Tuniz C. , Jull A. J. T. , Fink D. , Klein J. , Middleton R.
Published: June 2012

Abstract— We present the 14C, 26Al, 10Be, 3He, 4He, 20Ne, 21Ne, 22Ne, 36Ar, 38Ar, and 40Ar concentrations and the track densities measured in up to 13 samples of the Bur Gheluai (H5) meteorite fall. Only a multi‐stage exposure history can explain the data in a self‐consistent way. Parameters for a model two‐stage history obtained by simultaneous, least‐squares fitting of the concentrations of 14C, 26Al, 10Be, and 21Ne were: first stage duration ∼10 Ma and radius >2 m; second stage duration ∼0.6 Ma and radius 40–100 cm.

Nominal one‐stage 21Ne production rates (P21) inferred from 26Al in Bur Gheluai samples exceed those inferred from 10Be as expected for a meteorite with a complex history. Nonetheless, data for other meteorites indicate that multi‐stage irradiations alone do not account for all the high reported values of P21 based on 26A***l: The equations describing the production of cosmogenic nuclides show that uncorrected shielding effects may also play a role.

A compilation of ordinary, solar‐gas‐poor chondrites for which two‐stage histories have been proposed includes many with short second stages but none with unambiguously long first stages (>0.2 Ga).
Depth‐profiles and surface enrichment of the halogens in four Antarctic H5 chondrites and in two non‐Antarctic chondrites
Authors: Langenauer Marcel , Krähenbühl Urs
Published: June 2012

Abstract— Depth‐profiles of F, Cl, Br and I concentrations were determined in four different Antarctic H5 chondrites from the Allan Hills and in the two chondrites Allende (C3) and Holbrook (L6). Pieces of the meteorites were studied by analysis of stepwise removed layers of 0.5–1.0 mm thickness up to a depth of 9 mm. Neutron activation analysis and ion‐selective potentiometry were used for the determination of Cl, Br, I and for F, respectively. The Antarctic meteorites show higher concentrations of the halogens at the surface compared to the interior. The highest enrichment factors are found for I and Cl and the lowest for Br. In contrast, F shows the steepest concentration gradient and is only enriched in the first 2.5 mm below the surface. The other halogens have penetrated deeper into the meteorites. The measured enrichments at the surfaces are not correlated to the visible degree of weathering. The analysed non‐Antarctic meteorites, which were recovered shortly after their observed fall, demonstrate similar halogen concentrations at the surface, including the fusion crust, as in the interior. Based on these results we present a model to estimate the degree of contamination and the relation to the duration of exposure at the surface of the Antarctic ice.
The stratigraphic age of australites revisited
Authors: Fudali R. F.
Published: June 2012

Abstract— The proposed stratigraphic age of 5000–15,000 years for australites found in the vicinity of Port Campbell, Victoria, is demonstrably incorrect. These tektites are not in situ and are also found in an older horizon than previously reported. A minimum stratigraphic age of 250,000 years is calculated from the cosmic‐ray‐produced 3He in alluvial diamonds from a horizon that also contains australites near Lake Argyle, Western Australia. There is no reason to believe that a true, rather than a minimum, stratigraphic age for Lake Argyle tektites would not match the many radiometric ages reported in the literature.
Meteorite finds by EUROMET near Frontier Mountain, North Victoria Land, Antarctica
Authors: Delisle George , Franchi Ian , Rossi Antonio , Wieler Rainer
Published: June 2012

Abstract— A team from EUROMET (a joint initiative of scientific institutions in Europe interested in meteorites) was sent for the first time to Antarctica in the 1990/91 season to undertake a systematic search for meteorites. The project was organised within the framework of the Italian Antarctic Program (Programma Nationale di Richerche in Antartide, PNRA). The search was carried out in the vicinity of Frontier Mountain (North Victoria Land) and 256 meteorite fragments were discovered, most of which were wind‐blown across the blue‐ice field to the NE of Frontier Mountain and finally caught in an ice depression about 5 km to the N. The larger meteorites which remained on the ice surface from which they were uncovered may have been transported down to the mountain edge where they have subsequently been destroyed or covered in debris. A search for meteorites at neighbouring Sequence Hills, where similar glaciological conditions as at Frontier Mountain exist, proved unsuccessful. At this location the surface of the blue ice in the valleys with suspected meteorite concentrations was covered by meltwater lakes.
Two chondrule groups each with distinctive rims in Murchison recognized by cathodoluminescence
Authors: Sears Derek W. G. , Benoit Paul H. , Jie Lu
Published: June 2012

Abstract— Two groups of chondrules in the Murchison CM chondrite, which have previously been identified on the basis of FeO in the chondrule grains, are readily identified from cathodoluminescence (CL) and belong to those of the ordinary chondrite group A and B chondrules of Sears et al. (1992a). All chondrules are surrounded by fine‐grained rims containing forsterite with bright red CL, but on group A chondrules an outer thin rim grades into a much thicker rim, with a lower density of forsterite grains, which in turn grades into the central chondrule. Group B chondrules have only the thin outer rim with a high density of small forsterite grains. This is the first time an unequivocal correlation has been observed between chondrule rim thickness and the composition of the object on which the rim is located. We suggest that while all objects in the meteorite (group B chondrules, refractory inclusions, mineral and chondrule fragments, clasts) acquired a very thin rim during processing in a wet regolith, the thick rims on group A chondrules were formed by aqueous alteration of precursor metal‐ and sulfide‐rich rims which are a characteristic of group A chondrules in ordinary chondrites.
The thermal history of interplanetary dust particles collected in the Earth's stratosphere
Authors: Nier A. O. , Schlutter D. J.
Published: June 2012

Abstract— Fragments of 24 individual interplanetary dust particles (IDPs) collected in the Earth's stratosphere were obtained from NASA's Johnson Space Center collection and subjected to pulse‐heating sequences to extract He and Ne and to learn about the thermal history of the particles. A motivation for the investigation was to see if the procedure would help distinguish between IDPs of asteroidal and cometary origin. The use of a sequence of short‐duration heat pulses to perform the extractions is an improvement over the employment of a step‐heating sequence, as was used in a previous investigation. The particles studied were fragments of larger parent IDPs, other fragments of which, in coordinated experiments, are undergoing studies of elemental and mineralogical composition in other laboratories. While the present investigation will provide useful temperature history data for the particles, the relatively large size of the parent IDPs (∼40 μm in diameter) resulted in high entry deceleration temperatures. This limited the usefulness of the study for distinguishing between particles of asteroidal and cometary origin.
The Meteoritical Bulletin, No. 75, 1993 December
Authors: Wlotzka Frank
Published: June 2012

Abstract— Meteoritical Bulletin, Number 75 lists 138 new meteorites, including seven falls. Sixty are from North Africa (Acfer, Aguemour, Tanezrouft), and 53 are from Frontier Mountain, Antarctica. There are three achondrites (Caldera, a eucrite, and the brachinites Nova 003 and Reid 013), four carbonaceous chondrites (Acfer 289, CR2, Mundrabilla 012, CV2?, Nova 002, CV3, and Watson 002, the second known CK3), one enstatite chondrite (Acfer 287). Also noteworthy is Rumuruti, the first Carlisle‐Lakes‐like chondrite observed fall, which fell in 1934.
Asteroid spectroscopy: Progress and perspectives
Authors: Gaffey Michael J. , Burbine Thomas H. , Binzel Richard P.
Published: June 2012

AbstractThe following discussion is divided into seven major sections. The first section outlines the scientific background and justification for asteroid studies in the context of understanding the formation and early evolution of the solar system. The second section briefly reviews the nature and distribution of the asteroid population. The third section discusses several major unresolved issues in asteroid and meteorite science which can potentially be addressed by asteroid remote sensing investigations. The fourth section outlines the nature and definition of the asteroid taxonomic classes. The fifth section summarizes the existing asteroidal spectral (and other remote sensing) data sets which are used to determine compositions and the techniques employed in the interpretation of such data. The sixth section explores the compositional meaning and diversity of these taxonomic classes and suggests meteoritic analogues for the taxonomic types. The seventh section describes the conclusions—or preliminary results—of several recent asteroid investigations which have focused on particular unsolved issues of the asteroid‐meteorite relationship and of the early solar system properties. The final section discusses the overall conclusions and future directions.
Carbon‐14 terrestrial ages and weathering of 27 meteorites from the southern high plains and adjacent areas (USA)
Authors: Jull A. J. T. , Donahue D. J. , Cielaszyk E. , Wlotzka F.
Published: June 2012

Abstract We report on a series of 27 14C terrestrial ages of meteorites from four states in the central and southwestern USA. These results were compared to the earlier work of Boeckl (1972). Our results showed that the weathering rate for destruction of meteorites is lower than suggested by Boeckl (1972). We estimated a “half‐life” for removal of meteorites of about 10 to 15 ka, similar to that derived for Roosevelt County meteorites. We also studied the weathering of these meteorites compared to terrestrial age. Only a weak correlation was observed, and for these meteorites the degree of weathering can only be taken as a weak indicator of terrestrial residence time. We also measured the δ 13C and 14C and amount of weathering‐product carbonates which show some interesting variations with the length of time the meteorites have been exposed to weathering.
Basait generation at the Apollo 12 site, Part 2: Source heterogeneity, multiple melts, and crustal contamination
Authors: Neal Clive R. , Hacker Matthew D. , Snyder Gregory A. , Taylor Lawrence A. , Liu Yun‐Gang , Schmitt Roman A.
Published: June 2012

Abstract— The petrogenesis of Apollo 12 mare basalts has been examined with emphasis on trace‐element ratios and abundances. Vitrophyric basalts were used as parental compositions for the modelling, and proportions of fractionating phases were determined using the MAGFOX program of Longhi (1991). Crystal fractionation processes within crustal and sub‐crustal magma chambers are evaluated as a function of pressure. Knowledge of the fractionating phases allows trace‐element variations to be considered as either source related or as a product of post‐magma‐generation processes. For the ilmenite and olivine basalts, trace‐element variations are inherited from the source, but the pigeonite basalt data have been interpreted with open‐system evolution processes through crustal assimilation. Three groups of basalts have been examined: (1) Pigeonite basalts — produced by the assimilation of lunar crustal material by a parental melt (up to 3% assimilation and 10% crystal fractionation, with an “r” value of 0.3). (2) Ilmenite basalts — produced by variable degrees of partial melting (4–8%) of a source of olivine, pigeonite, augite, and plagioclase, brought together by overturn of the Lunar Magma Ocean (LMO) cumulate pile. After generation, which did not exhaust any of the minerals in the source, these melts experienced closed‐system crystal fractionation/accumulation. (3) Olivine basalts — produced by variable degrees of partial melting (5–10%) of a source of olivine, pigeonite, and augite. After generation, again without exhausting any of the minerals in the source, these melts evolved through crystal accumulation. The evolved liquid counterparts of these cumulates have not been sampled. The source compositions for the ilmenite and olivine basalts were calculated by assuming that the vitrophyric compositions were primary and the magmas were produced by non‐modal batch melting. Although the magnitude is unclear, evaluation of these source regions indicates that both be composed of early‐ and late‐stage Lunar Magma Ocean (LMO) cumulates, requiring an overturn of the cumulate pile.
The age of the Saltpan impact crater, South Africa
Authors: Koeberl Christian , Storzer Dieter , Reimold Wolf Uwe
Published: June 2012

Abstract— The 1.13‐km‐diameter Pretoria Saltpan impact crater is located about 40 km NNW of Pretoria, South Africa. The crater is situated in 2.05 Ga old Nebo granite of the Bushveld Complex that is locally intruded by about 1.3 Ga old volcanic rocks. In 1988, a borehole was drilled in the center of the crater. At depths >90 m, breccias were found that contained minerals with characteristic shock‐metamorphic features, thus confirming the impact origin of the crater. Fragments of impact glass were recovered from the melt breccias and several hundred sub‐millimeter‐sized glass fragments were subjected to fission track analysis. The measurements were complicated by the inhomogeneous composition of the impact glasses, but analysis of a large number of tracks yielded an age of 220 ± 52 ka for the Saltpan crater.
Grain size of the surface regolith of asteroid 4 Vesta estimated from its reflectance spectrum in comparison with HED meteorites
Authors: Hiroi Takahiro , Pieters Carlé M. , Takeda Hiroshi
Published: June 2012

Abstract— The grain‐size distribution of the regolith of asteroid 4 Vesta has been estimated by comparing its reflectance spectra (0.3–2.6 μm) with those of HED meteorites. The finest grain‐size separate (<25 μm) of a particular howardite has a reflectance spectrum most similar to Vesta's. In order to better simulate Vesta's surface mineralogy, reflectance spectra of those finest HED meteorite powders were linearly combined, and Vesta's spectrum was scaled for the best fit between them. Both the albedo and the shape of reflectance spectrum of Vesta were well reproduced by regional mixtures of the finest (<25 μm) powders of HED meteorites. The result suggests the heterogeneity of Vesta's surface and provides an estimate of the visible reflectance of Vesta that is close to its IRAS albedo. Thus, this suggests that fine grains can be generated and retained by relatively small bodies (Vesta is approximately 500 km in diameter).
Petrology and mineralogy of the Yamato‐86751 CV3 chondrite
Authors: Murakami Toshio , Ikeda Yukio
Published: June 2012

Abstract— The Y‐86751 chondrite (CV3) consists of fine‐grained Ca‐ and Al‐rich inclusions (CAIs), amoeboid olivine inclusions (AOIs), spinel‐rich inclusions, chondrules with and without dark rims, dark inclusions, isolated minerals, metal‐sulfide aggregates, and matrix. Olivines in chondrules without dark rims and AOIs coexist with magnetite and show strong zoning from a magnesian core to a ferroan rim. Spinels in spinel‐rich inclusions show similar zoning. This zoning seems to be caused by exchange reaction of olivine and spinel with an oxidized nebular gas prior to the accretion onto the parent body, and the Mg/Fe diffusion in olivines and spinels took place at a temperature of about 830–860 K. At the same time, enstatite in chondrules without dark rims was replaced by ferroan olivine at the grain boundaries. This feature suggests that chondrules without dark rims, fine‐grained CAIs, spinel‐rich inclusions, and AOIs have experienced oxidation in an oxidizing nebular gas. The oxygen fugacity of the oxidized nebular gas was >10−27.3 bars at about 830 K, being more than 104x larger than that of the canonical nebular gas. Magnetite occurs in the Y‐86751 matrix in close association with Ni‐rich taenite and Co‐rich metal, and it was produced under a condition with the oxygen fugacity of ∼10−38 bars at a temperature of about 620–650 K. On the other hand, olivines in chondrules with dark rims and dark inclusions are magnesian and rich in MnO. They do not show such strong zoning. Probably they were in equilibrium with a nebular gas under a redox condition different from the oxidized nebular gas that produced the zoned olivines in chondrules without dark rims.
In search of the Australasian tektite source crater: The Tonle Sap hypothesis
Authors: Hartung Jack , Koeberl Christian
Published: June 2012

Abstract— The source crater for Australasian tektites remains to be positively identified We suggest that Tonle Sap, a roughly oval lake in south‐central Cambodia, may represent the remnant of that crater. The size of the lake (about 100 km × 35 km), location (Indochina), inferred geologic age (recent), and orientation of the lake, as well as the geographical distribution of tektites, are consistent with this suggestion. The elongated shape of the lake with its long axis pointing toward Australia may be the result of an oblique impact of a NW to SE‐moving object a few km in diameter. The absence of a raised rim and a central peak may be related to a low impact angle, soft target rocks, or high post‐impact erosion and sedimentation rates. The scarcity of Muong Nong‐type (layered) tektites near Tonle Sap may be due to extensive post‐impact alluvial deposition, which buried the tektites. The chemical composition of Upper Indosinias formation sandstones from Phnom Batheay was determined. There are significant differences between the composition of indochinite tektites and these rocks, which are thus unlikely to represent tektite source rocks.
Shock metamorphism of quartz in nature and experiment: I. Basic observation and theory*
Authors: Stöffler Dieter , Langenhorst Falko
Published: June 2012

Abstract— Quartz, as a ubiquitous mineral constituent of the Earth's crust, displays the greatest variety of well‐defined residual shock effects among all rock‐forming minerals. It represents an important and most reliable shock barometer and thermometer for terrestrial impact formations. In this paper, the current status of knowledge about the nature, origin, and experimental pressure‐temperature calibration of shock‐induced deformations and phase transformations is reviewed for natural and experimental shock conditions.
Comparison of the LEW88516 and ALHA77005 martian meteorites: Similar but distinct
Authors: Treiman A. H. , McKay G. A. , Bogard D. D. , Mittlefehldt D. W. , Wang M.‐S. , Keller L. , Lipschutz M. E. , Lindstrom M. M. , Garrison D.
Published: June 2012

Abstract By mineral and bulk compositions, the Lewis Cliff (LEW) 88516 meteorite is quite similar to the ALHA77005 martian meteorite. These two meteorites are not paired because their mineral compositions are distinct, they were found 500 km apart in ice fields with different sources for meteorites, and their terrestrial residence ages are different. Minerals in LEW88516 include: olivine, pyroxenes (low‐ and high‐Ca), and maskelynite (after plagioclase); and the minor minerals chromite, whitlockite, ilmenite, and pyrrhotite. Mineral grains in LEW88516 range up to a few mm. Texturally, the meteorite is complex, with regions of olivine and chromite poikilitically enclosed in pyroxene, regions of interstitial basaltic texture, and glass‐rich (shock) veinlets. Olivine compositions range from Fo64 to Fo70, (avg. Fo67), more ferroan and with more variation than in ALHA77005 (Fo69 to Fo73). Pyroxene compositions fall between En77Wo4 and En65Wo15 and in clusters near En63Wo9 and En53Wo33, on average more magnesian and with more variation than in ALHA77005. Shock features in LEW88516 range from weak deformation through complete melting. Bulk chemical analyses by modal recombination of electron microprobe analyses, instrumental neutron activation, and radiochemical neutron activation confirm that LEW88516 is more closely related to ALHA77005 than to other known martian meteorites. Key element abundance ratios are typical of martian meteorites, as is its non‐chondritic rare earth pattern. Differences between the chemical compositions of LEW88516 and ALHA77005 are consistent with slight differences in the proportions of their constituent minerals and not from fundamental petrogenetic differences. Noble gas abundances in LEW88516, like those in ALHA77005, show modest excesses of 40Ar and 129Xe from trapped (shock‐implanted) gas. As with other ALHA77005 and the shergottite martian meteorites (except EETA79001), noble gas isotope abundances in LEW88516 are consistent with exposure to cosmic rays for 2.5–3 Ma. The absence of substantial effects of shielding from cosmic rays suggest LEW88516 spent this time as an object no larger than a few cm in diameter.
Boron cosmochemistry. Part I: Boron in meteorites
Authors: Zhai Mingzhe , Shaw Denis M.
Published: June 2012

Abstract Thirty‐six fragments of meteorite falls, never touched by water or other possible sources of B contamination, were analyzed for B by prompt gamma‐ray neutron activation analysis at McMaster University and at the U.S. National Institute of Standards and Technology. Boron concentrations are close to the sensitivity limit in both laboratories. Results between the two laboratories agree well but with slight systematic differences attributable to blank and background correction factors.

The mean B concentrations in different meteorites are similar, from 0.5 to 1.1 ppm. The ranges in different CC, OC and ACH classes overlap, mostly from 0.4 to 1.4 ppm, which is similar to previous measurements on falls. The H, L and LL meteorites overlap in B content with Antarctic chondrites.

The solar system abundance, taken as the mean B content of the matrix in all CC, was calculated from seven samples and is 0.69 ± 0.09 ppm. When normalized, this abundance is 16.9 ± 2.2 (atoms/106Si).

Normalized B and S concentrations show a linear relationship in the CC; the average OC lies on the same line, but individual OCs are dispersed.
Helium and neon in lunar ilmenites of different antiquities
Authors: Nier A. O. , Schlutter D. J.
Published: June 2012

Abstract Helium and neon were extracted from individual lunar ilmenite grains, approximately 100 μm in diameter, using a pulsed step‐heating technique. Grains from lunar samples 71501 and 79035, believed to have been exposed to solar corpuscular radiation at greatly different times, were studied. The results found were consistent with the hypothesis that in addition to solar‐wind‐implanted gas, a second more deeply implanted component was present in both species of grains.

Average isotopic ratios were determined giving equal weight to each of the particles. As found in depth studies employing chemical etching, both the 3He/4He and 20He/22Ne ratios were lower in the more deeply implanted gas than in the solar wind component. The 3He/4He ratio in the solar wind component of the more ancient grains was lower than that in the more recently exposed ones, whereas no difference was found for the more deeply embedded He. In the deeply embedded component of the ancient grains, the 4He/20Ne ratio was ∼2×that found in the more recently exposed grains. In the shallowly implanted component, the ratio varied greatly from grain to grain, preventing comparison with the solar wind elemental composition.
Nitrogen components in lunar soil 12023: Complex grains are not the carrier of isotopically light nitrogen
Authors: Brilliant D. R. , Franchi I.A. , Pillinger C.T.
Published: June 2012

Abstract High‐resolution stepped combustion is used to release isotopically distinct N components of different thermal stability in lunar soil 12023. The isotopically light gas in this soil appears to be the same as that found in the lunar breccia 79035, but the latter material has little of an isotopically heavy component of only slightly lower thermal stability. Complex grains in 12023, which probably only release their N on melting, contain a mixture of the heavy and light N in approximately the same proportions as the unaggregated soil. Ideas that require complex grains to be enriched in a light‐N component, synonymous with the ancient solar wind, therefore, cannot be correct. The implications for models invoking solar‐wind secular variation are discussed.
Solar wind noble gases and nitrogen in metal from lunar soil 68501
Authors: Becker Richard H. , Pepin Robert O.
Published: June 2012

Abstract Noble gases and N were analyzed in handpicked metal separates from lunar soil 68501 by a combination of step‐wise combustions and pyrolyses. Helium and Ne were found to be unfractionated with respect to one another when normalized to solar abundances, for both the bulk sample and for all but the highest temperature steps. However, they are depleted relative to Ar, Kr and Xe by at least a factor of 5. The heavier gases exhibit mass‐dependent fractionation relative to solar system abundance ratios but appear unfractionated, both in the bulk metal and in early temperature steps, when compared to relative abundances derived from lunar ilmenite 71501 by chemical etching, recently put forward as representing the abundance ratios in solar wind. Estimates of the contribution of solar energetic particles (SEP) to the originally implanted solar gases, derived from a basic interpretation of He and Ne isotopes, yield values of about 10%. Analysis of the Ar isotopes requires a minimum of 20% SEP, and Kr isotopes, using our preferred composition for solar wind Kr, yield a result that overlaps both of these values. It is possible to reconcile the data from these gases if significant loss of solar wind Ar, Kr and presumably Xe has occurred relative to the SEP component, most likely by erosive processes that are mass independent, although mass‐dependent losses (Ar > Kr > Xe) cannot be excluded. If such losses did occur, the SEP contribution to the solar implanted gases must have been no more than a few percent.

Nitrogen is a mixture of indigenous meteoritic N, whose isotopic composition is inferred to be relatively light, and implanted solar N, which has probably undergone diffusive redistribution and fractionation. If the heavy noble gases have not undergone diffusive loss, then N/Ar in the solar wind can be inferred to be at least several times the accepted solar ratio. The solar wind N appears, even after correction for fractionation effects, to have a minimum δ15N value ≥+150‰ and a more probable value ≥+200‰.
Noble gases in presolar diamonds II: Component abundances reflect thermal processing
Authors: Huss Gary R. , Lewis Roy S.
Published: June 2012

Abstract— Using the isotopic compositions derived in Huss and Lewis, 1994a (Paper I), abundances of the P3, HL, and P6 noble‐gas components were determined for 15 diamond separates from primitive chondrites of 8 chondrite classes. Within a meteorite class, the relative abundances of these components correlate with the petrologic subtype of the host meteorite, indicating that metamorphism is primarily responsible for the variations. Relative abundances of P3, HL, and P6 among diamond samples can be understood in terms of thermal processing of a single mixture of diamonds like those now found in CI and CM2 chondrites. With relatively gentle heating, primitive diamonds first lose their low‐temperature P3 gases and a “labile” fraction of the HL component. Mass loss associated with release of these components produces an increase in the HL and P6 content of the remaining diamond relative to unprocessed diamond. Higher temperatures initiate destruction of the main HL carrier, while the HL content of the surviving diamonds remains essentially constant. At the same time, the P6 carrier begins to preferentially lose light noble gases. Meteorites that have experienced metamorphic temperatures ≳650 °C have lost essentially all of their presolar diamond through chemical reactions with surrounding minerals.

The P3 abundance seems to be a function only of the maximum temperature experienced by the diamonds and thus is independent of the nature of the surrounding environment. If all classes inherited the same mixture of primitive diamonds, then P3 abundances would tie together the metamorphic scales in different meteorite classes. However, if the P3 abundance indicates a higher temperature than do other thermometers applicable to the host meteorite, then the P3 abundance may contain information about heating prior to accretion. Diamonds in the least metamorphosed EH, CV, and CO chondrites seem to carry a record of pre‐accretionary thermal processing.
Fractionated martian atmosphere in the nakhlites?
Authors: Drake Michael J. , Swindle Timothy D. , Owen Tobias , Musselwhite Donald S.
Published: June 2012

Abstract— Considerable evidence points to a martian origin of the SNC meteorites. Noble gas isotopic compositions have been measured in most SNC meteorites. The 129Xe/132Xe vs. 84Kr/132Xe ratios in Chassigny, most shergottites, and lithology C of EETA 79001 define a linear array. This array is thought to be a mixing line between martian mantle and martian atmosphere. One of the SNC meteorites, Nakhla, contains a leachable component that has an elevated 129Xe/132Xe ratio relative to its 84Kr/132Xe ratio when compared to this approximately linear array. The leachable component probably consists in part of iddingsite, an alteration product produced by interaction of olivine with aqueous fluid at temperatures lower than 150 °C. The elevated Xe isotopic ratio may represent a distinct reservoir in the martian crust or mantle. More plausibly, it is elementally fractionated martian atmosphere. Formation of sediments fractionates the noble gases in the correct direction. The range of sediment/atmosphere fractionation factors is consistent with the elevated 129Xe/132Xe component in Nakhla being contained in iddingsite, a low temperature weathering product. The crystallization age of Nakhla is 1.3 Ga. Its low‐shock state suggests that it was ejected from near the surface of Mars. As liquid water is required for the formation of iddingsite, these observations provide further evidence for the near surface existence of aqueous fluids on Mars more recently than 1.3 Ga.
Carbonates and sulfates in the Chassigny meteorite: Further evidence for aqueous chemistry on the SNC parent planet
Authors: Wentworth Susan J. , Gooding James L.
Published: June 2012

Abstract— Scanning electron microscopy and energy‐dispersive X‐ray spectrometry of untreated interior chips from three different specimens of the Chassigny meteorite confirm the presence of discrete grains of Ca‐carbonate, Mg‐carbonate, and Ca‐sulfate. Morphologies of these salt grains suggest that the Ca‐carbonate is calcite (CaCO3) and that the Ca‐sulfate is gypsum (CaSO4·2H2O) or bassanite (CaSO4·1/2H2O). The morphologic identification of the Mg‐carbonate is equivocal, but rhombohedral and acicular crystal habits suggest magnesite and hydromagnesite, respectively. The salts in Chassigny occur as discontinuous veins in primary igneous minerals and are similar to those previously documented in the nakhlites, Nakhla and Lafayette, and in shergottite EETA79001. Unlike those in nakhlites, however, the Chassigny salts occur alone, without associated ferric oxides or aluminosilicate clays. Traces of Cl and P in Chassigny salts are consistent with precipitation of the salts from short‐lived, saline, aqueous solutions that postdated igneous crystallization. In contrast with the clear case for nakhlites, stratigraphic evidence for a preterrestrial origin of the salts in Chassigny is ambiguous; however, a preterrestrial origin of the Chassigny salts best explains all available evidence. The water‐precipitated salts provide clear physical evidence for the hypothesis, proposed by other workers, that the igneous amphiboles in Chassigny might have experienced isotope‐exchange reactions with near‐surface water, thereby compromising the original stable‐isotope signature of any magmatic water in melt inclusions.
The Meteoritical Bulletin, No. 77, 1994 November*
Authors: Wlotzka Frank
Published: June 2012

Abstract— This Meteoritical Bulletin is again dominated by meteorite finds from hot and cold deserts: 99 from the Nullarbor, 12 from the Sahara, and 35 from Antarctica. Besides 161 ordinary chondrites, it lists 5 irons (Cotton, Hidden Valley, Miles, Tagounite, Tres Castillos), 2 ureilites (FRO90168, Hughes 009), 1 howardite (ALH 88135), 1 CV3 (Axtell), 1 CK4 (Sleeper Camp 006), and 2 enstatite chondrites (ALH 88070, Forrest 033). Three of the meteorites are falls.
Origin and diagenesis of K/T impact spherules—From Haiti to Wyoming and beyond
Authors: Bohor Bruce F. , Glass Billy P.
Published: June 2012

Abstract— Impact spherules in Cretaceous/Tertiary (K/T) boundary clays and claystones consist of two types; each type is confined to its own separate layer of the boundary couplet in the Western Hemisphere. The form and composition of each of the spherule types result from its own unique mode of origin during the K/T event. Type 1 splash‐form spherules occur only in the melt‐ejecta (basal) layer of the K/T couplet. This layer was deposited from a ballistic ejecta curtain composed of melt‐glass droplets transported mostly within the atmosphere. In contrast, Type 2 spherules are accreted, partially crystalline, spheroidal bodies that formed by condensation of vaporized bolide and target‐rock materials in an expanding fireball cloud, from which they settled out of buoyant suspension to form the fireball layer. Dendritic and skeletal Ni‐rich spinel crystals are unique to these Type 2 spherules in the fireball layer.

Compositions of relict glasses found in Type 1 K/T spherules from Haiti indicate that they were derived from intermediate silicic target rocks. These melt‐glass droplets were deposited into an aqueous environment at both continental and marine sites. We propose that the surfaces of the hot melt droplets hydrated rapidly in water and that these hydrated glass rims then altered to palagonite. Subsequent alteration of the palagonite rims to smectite, glauconite, chlorite, kaolinite, or goyazite occurred later during various modes of progressive diagenesis, accompanied by dissolution of some of the glass cores in spherules from continental sections and from marine sections that were subsequently raised above sea level. In many of the nonmarine sections in the Western Interior, the glass cores altered to kaolinite instead of dissolving.

Directly comparable spherule morphologies (splash forms), textural features of the altered shells, and scalloping and grooving of relict glass cores or secondary casts demonstrate that the Haitian and Wyoming spherules are equivalent altered Type 1 melt‐droplet bodies. The spherules at both locations were deposited in a melt‐ejecta layer as part of the K/T impact event.

Previously, two types of relict impact glasses had been identified in the Haitian spherule beds: black glass of andesitic composition and high‐Ca yellow glass with an unusually high S content. Most workers agree that the latter probably formed by impact melting and mixing of surficial carbonate (and minor anhydrite) rocks with the more deeply‐buried crystalline parent rocks of the black glasses. However, some workers have suggested that an intermediate compositional gap exists between the two groups of glasses, implying a different origin than simple mixing of end members during impact. We report glass compositional analyses with values extending throughout this intermediate range, lending support to the impact‐mixing model. Inclusions of CaSO4 found by us in relict yellow glasses further support this model.
Lunar behaviour of boron contrasted with the terrestrial boron cycle
Authors: Shaw Denis M.
Published: June 2012

Abstract— Fifty‐eight lunar rocks have been analysed by prompt gamma neutron activation for B, Gd and Sm. The data were interpreted together with published analyses for Li and other elements.

The behaviour of B in lunar rocks is virtually identical to that of Sm, Gd, Li and the other incompatible LIL (Large Ion Lithophile) and HFS (High Field Strength) elements, collectively known as the KREEP component. To a first approximation, the distribution of B concentrations in all lunar rocks can be described as a two‐component mixture of KREEP, with ∼32 ppm, and B‐free mare basalts and anorthositic rocks.

The lunar B abundance, estimated from correlations with other KREEP elements, is ∼0.14 ppm.

Alpha‐track images of the analysed lunar rocks were made from thin sections specially prepared to avoid contamination from terrestrial B. They provided surprising evidence that the distributions of B and Li within individual rocks fall into four categories: (1) substitution in mineral structures; (2) in irregular minute particles, disseminated through the rock with no apparent connection with mineralogy; (3) as aggregate properties of rock fragments, acquired prior to assembly in a breccia; and, (4) as aggregate properties of a breccia matrix, distinct from unaffected clasts.

Only category (1) is encountered in terrestrial rocks. Categories (2), (3) and (4) become progressively more important as the abundance of KREEP components increases, and it is concluded that the alpha‐track images probably show the localisation of not only B and Li but all the KREEP elements. In terrestrial rocks, such textures could be understood in terms of successive episodes of permeation by solutions followed by brecciation, then cementation. It is difficult to adapt such a mechanism to a dry Moon, with brecciation imposed by impact melting.

The linear correlation of lunar B and Gd contrasts strongly with the relationship seen in terrestrial rocks, where the presence of water creates a terrestrial B cycle quite different from that of Gd and other lunar incompatible elements.
40Ar/39Ar dating of the Araguainha impact structure, Mato Grosso, Brazil
Authors: Hammerschmidt Konrad , VON Engelhardt WOLF
Published: June 2012

Abstract— Pursuing the exploration of the Araguainha impact structure (Engelhardt et al., 1992), we present 40Ar/39Ar ages (1) of biotite samples from the granite, which forms the central uplift of the structure, and (2) of a melt rock, formed by the impact.

Total degassing ages of biotites from granite samples range from 326 to 481 Ma. The variation is explained by Ar losses due to the oxidation of divalent Fe and by removal of K. The K loss depends on the time that the granite was exposed to weathering at particular outcrops. The oldest age of the least oxidized biotite from a granite sample, collected at a site most recently exposed, signifies that the ascending granite passed the 300° isotherm earlier than 481 Ma ago. Early Devonian Furnas sandstones, the oldest sediments exposed by the impact, were deposited on this granite basement 410–396 Ma ago.

The 40Ar/39Ar analyses of two size fractions of an impact melt rock, resulting in plateau ages of 245.5 ± 3.5 Ma and 243.3 ± 3.0 Ma, respectively, indicate that the Araguainha impact occurred close to the Permian‐Triassic boundary.
Recognizing mercurian meteorites
Authors: Love Stanley G. , Keil Klaus
Published: June 2012

Abstract— With the recent realization that some meteorites may come from Mars and the Moon, it is worthwhile to consider whether meteorites from Mercury could exist in our collections and, if so, whether they could be recognized. The current state of ignorance about Mercury both increases the potential scientific value of mercurian meteorites and aggravates the problem of identifying them. Here, we review evidence supporting the possibility of impact launch and subsequent orbital evolution that could deliver rocks from Mercury to Earth and suggest criteria that could help identify a mercurian meteorite. Mercurian rocks are probably differentiated igneous rocks or breccias or melt rocks derived therefrom. Solar nebula models suggest that they are probably low in volatiles and moderately enriched in Al, Ti, and Ca oxides. Mercurian surface rocks contain no more than 5% FeO and may contain plagioclase. A significant fraction may be volcanic. They may possess an unusual isotopic composition. Most pristine mercurian rocks should have solidification ages of ∼3.7 to ∼4.4 Ga, but younger impact‐remelted materials are possible. Because we know more about the space environment of Mercury than we do about the planet itself, surface‐exposed rocks would be easiest to identify as mercurian. The unique solar‐to‐galactic cosmic‐ray damage track ratio expected in materials exposed near the Sun may be useful in identifying a rock from Mercury. Mercury's magnetic field stands off the solar wind, so that solar‐wind implants in mercurian regolith breccias may be scarce or fractionated compared to lunar ones. Mercurian regolith breccias should contain more agglutinates (or their recrystallized derivatives) and impact vapor deposits than any other and should show a higher fraction of exogenic chondritic materials than analogous lunar breccias. No known meteorite group matches these criteria. A misclassified mercurian meteorite would most likely be found among the aubrites or the anorthositic lunar meteorites.
Stable nickel isotopes and cosmogenic beryllium‐10 and aluminum‐26 in metallic spheroids from Meteor Crater, Arizona
Authors: Xue S. , Herzog G. F. , Hall G. S. , Klein J. , Middleton R. , Juenemann D.
Published: June 2012

Abstract— The isotopic abundances of Ni in 17 metallic spheroids from Meteor Crater, Arizona, were determined by inductively coupled plasma mass spectrometry (ICP‐MS). Sixteen spheroids have normal isotopic abundances. A 17th shows a marginally detectable mass fractionation of 0.40 ± 0.14 %/AMU in favor of the heavier isotopes. The general absence of mass fractionation indicates that open system evaporation caused little loss of Ni.

Variable activities of the cosmogenic radionuclides 10Be and 26Al were measured by accelerator mass spectrometry in separate suites of spheroids. Activities of 26Al in most samples and of 10Be in metal cores separated from spheroids indicate that they either (1) come from greater depths in the parent meteoroid than do hand specimens, or (2) lost Al and Be during the process of spheroid formation. One individual spheroid has 10Be and 26Al activities comparable to those of bulk specimens. This result suggests that spheroid formation may occasionally include material from the outermost meter or so of the impactor. Relatively high activities of 10Be, ∼3 dpm/kg, in the siliceous shells of Canyon Diablo spheroids very likely have a meteoric origin.