bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermoluminescence survey of 12 meteorites collected by the European 1988 Antarctic meteorite expedition to Allan Hills and the importance of acid washing for thermoluminescence sensitivity measurements
Authors: Benoit P. H. , Sears H. , Sears D. W. G.
Published: June 2012

Abstract— Natural and induced thermoluminescence (TL) data are reported for 12 meteorites recovered from the Allan Hills region of Antarctica by the European field party during the 1988/89 field season. The samples include one with extremely high natural TL, ALH88035, suggestive of exposure to unusually high radiation doses (i.e., low degrees of shielding), and one, ALH88034, whose low natural TL suggests reheating within the last 105 years. The remainder have natural TL values suggestive of terrestrial ages similar to those of other meteorites from Allan Hills. ALH88015 (L6) has induced TL data suggestive of intense shock. TL sensitivities of these meteorites are generally lower than observed falls of their petrologic types, as is also observed for Antarctic meteorites in general. Acid‐washing experiments indicate that this is solely the result of terrestrial weathering rather than a nonterrestrial Antarctic—non‐Antarctic difference. However, other TL parameters, such as natural TL and induced peak temperature‐width, are unchanged by acid washing and are sensitive indicators of a meteorite's metamorphic and recent radiation history.
The frequency of meteorite falls: Comments on two conflicting solutions to the problem
Authors: Halliday Ian , Blackwell Alan T. , Griffin Arthur A.
Published: June 2012

Abstract— Recent estimates of the current rate of meteorite falls have been derived from camera network observations and from the statistics of the recovery of small fragments in Roosevelt County, New Mexico. The results are discordant. The integrated sky coverage for the camera data is an order of magnitude greater than the long exposure over small areas in New Mexico, yet the number of inferred events is comparable. We examine potential problems and find no effects other than random ones to bias the camera data. New data on the total number of suitable fireballs indicate that the flux from the camera network is already close to the upper limit imposed by the count of over 700 fireballs.

By contrast, the calibration of the decay time for small fragments in New Mexico appears insecure and could account for a factor‐of‐three discrepancy. The large area of a typical strewn field relative to the small search areas is also a serious problem that remains uncalibrated. There are problems with the application of either the camera results or the New Mexico data to the statistics of recoveries in Antarctica since the Antarctic search areas are not free from the strewn‐field problem. Since there is no evidence for a substantial change in the infall rate in intervals less than the ages of the collecting surfaces, we believe the camera network flux data remain the best estimate for the arrival rate of small meteorites on Earth.
Classification of Streaky Bay, Mangalo, Ethiudna and Crockers Well: Stony meteorites from South Australia
Authors: Wallace Margaret , Pring Allan
Published: June 2012

Abstract— Four meteorites from South Australia are described and classified. Streaky Bay (L4b) and Mangalo (L6e) were received by the South Australian Museum in December, 1989. Ethiudna (L4a) and Crockers Well (LL7) were previously thought to be paired and were previously described only as chondrites.
On the origin of interplanetary dust within recorded history
Authors: Reach William T.
Published: June 2012

Abstract— The possibility of an abrupt origin of interplanetary dust as a result of a collision between asteroids or an extraordinary comet is considered. If all interplanetary dust were produced in one event within recorded history, it would have been visible from the Earth with the unaided eye. The rate, surface area, and brightness of asteroid collision remnants are derived. Ancient Chinese records are searched for extraordinary comets and bright pointlike objects with small angular motion and concentration to the ecliptic.
Dissemination and fractionation of projectile materials in the impact melts from Wabar Crater, Saudi Arabia
Authors: Mittlefehldt David W. , See Thomas H. , Hörz Friedrich
Published: June 2012

Abstract— We have analyzed small, ballistically dispersed melt samples in the form of aerodynamically shaped spheres, dumbbells, teardrops, etc., from Wabar Crater, Saudi Arabia, and have compared these to our previous study of the more massive, black and white melt specimens. The smaller melt samples differ from the more massive melts in that they are petrographically and chemically more homogeneous, possess fewer, more diffuse schlieren and contain much less clastic detritus. These observations suggest higher peak temperatures for the smaller melt samples than for the massive black and white melts which represent Wabar's major melt‐zone.

Analyses of the Wabar and Nejed (paired with Wabar) meteorites permit detailed comparison of the unaltered projectile with impactor residues in the melts. Siderophile element concentrations indicate that the small glass beads commonly contain > 10% meteoritic component, compared to < 5% for the massive black and white melts. One glass bead was found to contain ∼ 17% meteoritic component. Based on models for melt production during cratering, we deduce that more meteoritic material was mixed with the upper stratigraphic horizons of Wabar's melt zone than with the lower parts. Siderophile elements in all Wabar melt specimens are fractionated relative to the Wabar‐Nejed meteorite and have Fe/Ni ratios up to ∼ 1.8 times that of Wabar‐Nejed for the most siderophile element‐rich glasses. The abundance sequence of siderophiles in the melts relative to the projectile is Fe ≅ Co > Ni ≅ Ir ≅ As » Au. Although this sequence seems incompatible with simple vapor fractionation of either elements or oxides, we believe that a complex vapor fractionation process most likely produced the observed siderophile element abundances.

Our sample suite should be representative of all materials found in and around the Wabar structure, and we conclude that substantial quantities of the projectile were lost to the atmosphere, most likely as vapor. No fractionation of lithophile elements is observed in the glasses relative to the target rocks. Although fractionation of the impactor must have occurred prior to intimate mixing of projectile and target, details of the actual fractionation mechanism(s) remain poorly understood. The results of this study indicate that caution is necessary when attempting to define impactor types and masses from compositional data for impact melts from other craters.
Search for 248Cm in the early Solar System
Authors: Lavielle B. , Marti K. , Pellas P. , Perron C.
Published: June 2012

Abstract— Possible evidence for the presence of 248Cm in the early Solar System was reported from fission gas studies (Rao and Gopalan, 1973) and recently from studies of very high nuclear track densities (≥ 5 × 10g cm−2) in the merrillite of the H4 chondrite Forest Vale (F. V.) (Pellas et al., 1987). We report here an analysis of the isotopic abundances of xenon in F. V. phosphates and results of track studies in phosphate/pyroxene contacts. The fission xenon isotopic signature clearly identifies 244Pu as the extinct progenitor. We calculate an upper limit 248Cm/244Pu < 1.5 × 10−3 at the beginning of Xe retention in F. V. phosphates. This corresponds to an upper limit of the ratio 248Cm/235U ≤ 5 × 10−5, further constraining the evidence for any late addition of freshly synthesized actinide elements just prior to Solar System formation. The fission track density observed after annealing the phosphates at 290 °C (1 hr, which essentially erases spallation recoil tracks) is also in agreement with the 244Pu abundance inferred from fission Xe. The spallation recoil tracks produced during the 76 Ma cosmic‐ray exposure account for the very high track density in merrillites.
Mass distribution of Antarctic ordinary chondrites and the estimation of the fall‐to‐specimen ratios
Authors: Ikeda Yukio , Kimura Makoto
Published: June 2012

Abstract— The cumulative mass distributions (mass range > 100 g) of each type of Japanese and U.S. Antarctic ordinary chondrites are compared with those of non‐Antarctic falls and those obtained from the present‐day flux of meteorites. The steeper slope of the mass distribution of Antarctic chondrites is indicative of the presence of several chondrite showers. The fall‐to‐specimen ratio of Antarctic ordinary chondrites larger than 100 g is about 1:2, indicating that half of them are shower components. The fall‐to‐specimen ratios of each group range from 1:1 to 1:6; those of the Japanese and U.S. Antarctic meteorite collections are 1:1 to 1:2 and 1:4 for H chondrites, 1:1 to 1:2 and 1:2 for L chondrites, and 1:2 and 1:6 for LL chondrites, indicating that the Japanese collection includes less abundant shower components than the U.S. collection. The fall‐to‐specimen ratios of each H4‐6 and L4‐6 type range from 1:1 to 1:4, and U.S. H6 and Japanese H4 have the low ratios of 1:4.
Araguainha impact crater, Brazil. I. The interior part of the uplift
Authors: Engelhardt Wolf V. , Matthäi Stephan K. , Walzebuck Johannes
Published: June 2012

Abstract— The central uplift of the 40‐km wide Araguainha impact structure, Brazil, consists of a ring, about 8 km in diameter, of up to 150‐m high blocks of Devonian Furnas sandstone, which surround a central depression of elliptical shape (4.5 × 3.0 km). The depression is occupied by a pre‐Devonian alkali‐feldspar granite, shocked by pressures of 20–25 GPa and permeated by cataclastic shear zones and dikes of shocked granitic material. The granite is flanked and partly covered by several impact breccias: (1) Impact breccia with melt matrix overlies the granite in places and forms hills, bordering the granitic center in the S and SW. It is chemically identical with the granite and consists of thermally altered granitic clasts in a matrix of sanidine, quartz, biotite, muscovite, chlorite and riebeckite. (2) Polymict breccias form hills which border the central depression in the N and NW. Components are unshocked and shocked sediments, shock‐melted sandstone, shocked granite and shock melt rocks in irregular masses and individual bodies, embedded in a fine‐grained matrix. 40Ar/39Ar analyses show that the melt rocks solidified 246 Ma ago, indicating that the impact occurred at near the Permian‐Triassic boundary, possibly when the area was covered by a shallow sea. The present chemistry and petrography of the melt rocks suggest that by reacting with seawater granitic impact melt was depleted of K and Rb and enriched in Na, and that later diagenetic processes produced replacement of feldspar by quartz and deposition of hematite. (3) Monomict breccias, consisting of unshocked, shocked and shock‐fused quartz sandstones, form hills which surround the central depression in the SE and S.

The Araguainha structure is an eroded complex crater, produced by an impact, 246 Ma ago. The depth of excavation was about 2.4 km, comprising Permian, Permo‐Carboniferous and Devonian sediments and the granitic basement. The diameter of the transient crater was about 24 km. Erosion and weathering have removed most of the original crater fill and ejecta deposits, with the exception of remnants, preserved in the central uplift.
An overlooked fragment of the Santa Catharina ataxite
Authors: Tassel R. Van , Dillen H. , Vochten R. , DeGrave E. , Hertogen J.
Published: June 2012

Abstract— An undocumented mass of 28 kg, recovered from a museum collection, is examined by several methods: optical microscopy, scanning electron microscopy, X‐ray diffraction, Mössbauer spectroscopy and chemical analyses by atomic absorption, energy‐ and wavelength‐dispersive X‐ray spectrometry and, with respect to the trace elements Ir, As, Au, by neutron activation. The structure and the mineralogical chemical composition of the mass identify it as a fragment of the Santa Catharina iron meteorite from Brazil.
Vaca Muerta mesosiderite strewnfield
Authors: Pedersen Holger , de Bon Claudio Canut , Lindgren Harri
Published: June 2012

Abstract A field investigation is presented of the strewnfield of the mesosiderite Vaca Muerta, originally found in 1861. The area, 11.5 km long, 2.1 km wide, is located about 60 km southeast of Taltal, Chile, in the Atacama Desert. It has yielded 80 meteorites with a total mass exceeding 3782 kg. Most fragments were found in an undisturbed state, but some had been broken by prospectors. The present studies, in connection with historical records, indicate that the original mass of Vaca Muerta exceeded 6 metric tons. One impact feature, somewhat modified by man, consists of a 10.5‐m diameter, 1.7‐m deep hole, without an uplifted rim. Small masses were scattered up to 85 m from the hole.
A unique, (almost) unaltered spinel‐rich fine‐grained inclusion in Kainsaz
Authors: Holmberg B. B. , Hashimoto A.
Published: June 2012

Abstract We report a unique, spinel‐rich, extremely porous fine‐grained inclusion in the Kainsaz (CO3) meteorite. This inclusion is the least altered fine‐grained inclusion yet discovered, having escaped almost entirely the secondary alterations experienced by Allende fine‐grained inclusions. The inclusion is comprised of loosely packed 5–30 μm spinel grains mantled by thin layers of melilite, anorthite, and diopsidic pyroxene. The inclusion, which has over 30 vol% void space, is one of the most spinel‐rich, most porous fine‐grained inclusions seen to date. The mineralogy of the inclusion matches that which has been predicted for a precursor of the altered mineral assemblages of Allende fine‐grained inclusions, though a lack of interstitial material in the Kainsaz inclusion reduces the likelihood of a direct genetic relationship between the two (Allende fine‐grained inclusions contain abundant interstitial material). Its mineralogical composition confirms that the precursors of other, more altered, fine‐grained inclusions were assemblages of refractory minerals exclusively.
Dahmani, a highly oxidised LL6 chondrite bearing Ni‐rich taenite
Authors: Michel‐Levy M. Christophe , Denise M. Bourot
Published: June 2012

Abstract Dahmani is a shocked LL6 fragmental breccia. According to the composition of the silicates (olivine Fa30,32.6, orthopyroxene Fs24.5–26.3) and of the metal (a 60% Ni taenite) it is one of the most oxidised known.
Uranium accumulation during weathering of Cañon Diablo meteoritic iron
Authors: Hofmann Beda A.
Published: June 2012

Abstract— Cañon Diablo meteoritic iron oxide consists mainly of goethite and maghemite and contains 209 to 630 ppb uranium compared to <0.02 ppb in the unweathered octahedrite. Significant radioactive disequilibria between 238U, 234U and 230Th indicate that uranium was sorbed from soil porewater during terrestrial weathering after meteorite impact 50 ka ago. Depending on the model assumed for U uptake, corrected 230Th‐234U ages of 24 to 48 ka were obtained. While the data presented may not allow an unambiguous interpretation, the potential of this approach in obtaining minimum terrestrial ages for weathered meteorites is demonstrated.
Chemical and isotopic constraints on the formation and crystallization of SA‐1, a basaltic Allende plagioclase‐olivine inclusion
Authors: Kennedy Allen K. , Hutcheon Ian D.
Published: June 2012

Abstract— SA‐1, an unusual basaltic plagioclase‐olivine inclusion (POI) in Allende, has concentric textural and mineralogic zones, a fine‐grained, 100μm outer border and a coarse‐grained interior with subophitic texture. Fassaite, diopside and olivine from the exterior border and interior of SA‐1 have uniform intrinsic mass fractionation with isotopically heavy Mg (FMg = 3.6 ± 1.8‰/amu). In contrast, spinels from the spinel‐rich regions adjacent to the fine‐grained border have normal Mg isotopic composition (FMg = 0.1 ± 1.5‰/amu). The cores of large calcic (An90,99) plagioclase have no excess 26Mg, corresponding to 26Mg*/ 27Al < 3.7 × 10−6. The Mg isotopic heterogeneity in SA‐1 requires initial cooling rates of spinel‐rich regions adjacent to the fine‐grained border to be greater than ∼75 °C/hr. In contrast, the subophitic texture of the interior suggests cooling rates of 5–20 °C/ hr. The minerals in SA‐1 exhibit a wide range of REE abundances. Lanthanum concentrations vary from 1 × chondritic (ch) in early crystallizing diopside to 100 × ch in late crystallizing fassaite. Nepheline has 18–20 × ch LREE and 11–25 × ch HREE and iron‐rich mesostasis is highly enriched in the REE with 270–400 × ch LREE and 230–280 × ch HREE. The complementary REE patterns of clinopyroxene and plagioclase and the enrichment of incompatible trace elements in the mesostasis and late crystallizing phases is consistent with closed system crystallization. The REE data for nepheline and the iron‐rich mesostasis indicate these phases are in equilibrium and that nepheline crystallized from a melt. Influx of alkalies, minor Fe and halogens must have occurred during the last stages of crystallization or the inclusion must have been partially molten during Na influx as both anorthite (An99) and nepheline are present in this inclusion. The preservation of isotopic heterogeneity in an inclusion that crystallized from a melt implies that melting was incomplete, allowing for survival of the relict spinels. The major and trace element abundances in SA‐1 are inconsistent with formation as a mixture of nebular materials and suggest that SA‐1 contains a chemically fractionated component produced by igneous differentiation.
Halogens in tektites and impact glasses
Authors: Meisel Thomas , Langenauer Marcel , Krähenbühl Urs
Published: June 2012

Abstract— Impact glasses, tektites and some related basement rocks were analyzed for F, Cl, Br and I. The tektite and impact glasses show similar abundance patterns within the groups. Muong Nong‐type tektites indicate that the halogens have been depleted in the order I > Br > Cl > F in their melt under oxidizing conditions. For Darwin Glass selective volatilization of F from the melt is a major depleting process. Cl, Br and I are lost to a lesser extent.
Authentication controversies and impactite petrography of the New Quebec Crater
Authors: Marvin Ursula B. , Kring David A.
Published: June 2012

Abstract— A meteoritic origin was proposed for the New Quebec Crater in 1949 on the basis of an aerial photograph showing its unique circularity and raised rim amid Precambrian gneisses of the Canadian Shield. At that time, only those few craters associated with meteorites were generally accepted as of impact origin. When the earliest field expeditions failed to find meteorites or impact products, two leading meteoriticists, Frederick C. Leonard and Lincoln LaPaz, cited the “Chubb” Crater as a flagrant example for which claims of meteoritic origin were advanced without valid proof. They also listed the Lake Bosumtwi Crater in Ashanti (now Ghana) among crater‐like features, clearly of non‐meteoritic origin, misidentified as meteorite craters. Controversy over the origin these two craters continued for decades.

In Part I of this paper, we trace the investigations that led to the current acceptance of New Quebec as an authentic impact crater. We note that, for reasons that are not entirely clear, a meteoritic origin for the New Quebec Crater achieved wider acceptance at an earlier date than for the Lake Bosumtwi Crater, where petrographic and chemical evidence is more abundant and compelling.

In Part II, we describe the petrography of two impact melt samples from the New Quebec Crater and present new evidence on the degrees of shock metamorphism affecting the accessory minerals: apatite, sphene, magnetite and zircon. Zircon, in particular, shows a range from euhedral grains with no signs of alteration to those decomposed to baddeleyite plus silica.
Search for microaustralites in deep‐sea sediments less than 20,000 years old
Authors: Glass B. P. , Wu Jiquan
Published: June 2012

Abstract— Several authors have proposed that australites fell less than 20,000 years ago. We searched for microtektites in the tops of 46 deep‐sea cores and were unable to find evidence for a microtektite layer less than 20,000 years old. Either the australite fall was not accompanied by microtektites, or the strewnfield did not extend into the area searched, or the australites fell about 0.77 Ma ago as indicated by their radiometric ages.
Carbon in the matrices of ordinary chondrites
Authors: Makjanic J. , Vis R. D. , Hovenier J. W. , Heymann D.
Published: June 2012

Abstract— Carbon in the petrologic matrices of a number of ordinary chondrites of groups H, L, and LL, and of types 3 through 6 was studied with a nuclear microprobe and a Raman microprobe. The majority of the matrices had carbon contents in the narrow range between 0.03 and 0.2 wt%. The carbon content decreased only slightly with increasing petrologic type. Carbon‐rich coats around troilite and/or metal phases occured in five meteorites. Poorly ordered carbon was found in the matrices. The carbon in the meteorites of higher petrologic types was slightly better ordered than in the meteorites of lower types. The narrow range of carbon contents and the similarity of the structural form of carbon in the matrices of the measured ordinary chondrites, which represent all groups and types, imply that their matrices may contain a common component, which might be of interstellar origin.
Preterrestrial aqueous alteration of the Lafayette (SNC) meteorite
Authors: Treiman Allan H. , Barrett Ruth A. , Gooding James L.
Published: June 2012

Abstract— The Lafayette meteorite, a nakhlite of the SNC (Martian?) group, contains hydrous alteration materials as intergranular films and as veinlets and patches replacing olivine, pyroxenes, and high‐Si glass. The alteration materials (“iddingsite”) consist of ferroan smectite clays, magnetite (or maghemite), and ferrihydrite, as shown by SEM and TEM. Three varieties of veinlets are present and formed in the order: coarse phyllosilicate; fine‐grained (phyllosilicate‐oxide), and porous oxide. Veinlets of fine‐grained material cross‐cut coarse phyllosilicate veinlets. The alteration materials are preterrestrial, as they are older than Lafayette's fusion crust, which is glassy and not affected by any alterations. Approaching the crust, the veinlets are progressively modified to the point of melting, and progressively depleted in adsorbed volatile constituents (S, Cl, and P). Bulk compositions of the alteration veinlets (SEM and TEM EDX) are consistent with the observed mineralogy, and suggest: that the smectite contains significant adsorbed S and Cl; that the ferrihydrite contains significant adsorbed S, but not Cl; that rare grains of sulfate (Ca?) and chloride (Na or K?) are present; and that the compositions of the alteration materials are approximated by Lafayette's olivine + high‐Si glass + water. We estimate that Lafayette's alteration materials formed at less than 100 °C. The oxidation potential of the water was near or slightly below that of the magnetite‐hematite buffer. The presence of sulfate and chloride in discrete phases and as adsorbates on ferrihydrite and smectite suggests that the altering solutions were saline. However, relatively little mass was transferred into or out of Lafayette because the bulk composition of the alteration materials is nearly isochemical with a mixture of magmatic silicate phases and water. Chemical transport within Lafayette was also limited, as alteration materials preserve some chemical signature of their host minerals. Presence of alteration materials along only some grain boundaries and some cracks suggests that Lafayette was not soaked in fluid. These last two inferences suggest that the alteration of Lafayette took place during episodic infiltrations of small volumes of saline water.
Magnetite‐sulfide chondrules and nodules in CK carbonaceous chondrites: Implications for the timing of CK oxidation
Authors: Rubin Alan E.
Published: June 2012

Abstract— CK carbonaceous chondrites contain rare (∼0.1 vol%) magnetite‐sulfide chondrules. These objects range from ∼240 to 500 μm in apparent diameter and have ellipsoidal to spheroidal morphologies, granular textures and concentric layering. They are very similar in size, shape, texture, mineralogy and mineral composition to the magnetite‐sulfide nodules which occur inside mafic silicate chondrules in CK chondrites. It seems likely that the magnetite‐sulfide chondrules constitute the subset of magnetite‐sulfide nodules that escaped as immiscible droplets from their molten silicate chondrule hosts during chondrule formation. The intactness of the magnetite‐sulfide chondrules and nodules implies that oxidation of CK metal occurred before agglomeration; otherwise, the factor of two increase in molar volume associated with the conversion of metallic Fe‐Ni into magnetite would have disrupted the objects and destroyed their concentrically layered textures. Hence, the pervasive silicate darkening of CK chondrites documented previously was caused by the shock mobilization of magnetite and sulfide, not metallic Fe‐Ni and sulfide as in shock‐darkened ordinary chondrites.
The effect of Na vapor on the Na content of chondrules
Authors: Lewis R. Dean , Lofgren Gary E. , Franzen Hugo F. , Windom Kenneth E.
Published: June 2012

Abstract— Chondrules contain higher concentrations of volatiles (Na) than expected for melt droplets in the solar nebula. Recent studies have proposed that chondrules may have formed under non‐canonical nebular conditions such as in particle/gas‐rich clumps. Such chondrule formation areas may have contained significant Na vapor. To test the hypothesis of whether a Na‐rich vapor would minimize Na volatilization reaction rates in a chondrule analog and maintain the Na value of the melt, experiments were designed where a Na‐rich vapor could be maintained around the sample. A starting material with a melting point lower that typical chondrules was required to keep the logistics of working with Na volatilization from NaCl within the realm of feasiblity. The Knippa basalt, a MgO‐rich alkali olivine basalt with a melting temperature of 1325°± 5 °C and a Na2O content of 3.05 wt%, was used as the chondrule analog. Experiments were conducted in a 1 atm, gas‐mixing furnace with the fO2 controlled by a CO/CO2 gas mixture and fixed at the I‐W buffer curve. To determine the extent of Na loss from the sample, initial experiments were conducted at high temperatures (1300 °C–1350 °C) for duration of up to 72 h without a Na‐rich vapor present. Almost all (up to 98%) Na was volatilized in runs of 72 h. Subsequent trials were conducted at 1330 °C for 16 h in the presence of a Na‐rich vapor, supplied by a NaCl‐filled crucible placed in the bottom of the furnace. Succeeding Knudsen cell weight‐loss mass‐spectrometry analysis of NaCl determined the PNa for these experimental conditions to be in the 10−6 atm range. This value is considered high for nebula conditions but is still plausible for non‐canonical environments. In these trials the Na2O content of the glass was maintained or in some cases increased; Na2O values ranged from 2.62% wt to 4.37% wt.

The Na content of chondrules may be controlled by the Na vapor pressure in the chondrule formation region. Most heating events capable of producing chondrules are sufficient to volatilize Na. Sodium volatilization reaction rates will be reduced to varying degrees from melt droplets, depending on the magnitude of the PNa generated. A combination of Na vapor during, and Na diffusion back into chondrules after, formation could maintain and/or enrich Na concentrations in chondrules.
Carbonaceous chondrite clasts in the howardites Bholghati and EET87513
Authors: Buchanan P. C. , Zolensky M. E. , Reid A. M.
Published: June 2012

Abstract— Twenty‐two carbonaceous chondrite clasts from the two howardites Bholghati and EET87513 were analyzed. Clast N from EET87513 is a fragment classified as CM2 material on the basis of texture, bulk composition, mineralogy, and bulk O isotopic composition. Carbonaceous chondrite clasts from Bholghati, for which less data are available because of their small size, can be divided into two petrologic types: C1 and C2. C1 clasts are composed of opaque matrix with rare coarse‐grained silicates as individual mineral fragments; textures resemble CI meteorites and some dark inclusions from CR meteorites. Opaque matrix is predominantly composed of flaky saponite; unlike typical CI and CR meteorites, serpentine is absent in the samples we analyzed. C2 clasts contain chondrules, aggregates, and individual fragments of coarse‐grained silicates in an opaque matrix principally composed of saponite and anhydrous ferromagnesian silicates with flaky textures similar to phyllosilicates. These anhydrous ferromagnesian silicates are interpreted as the product of heating of pre‐existing serpentine. The carbonaceous chondrite clasts we have studied from these two howardites are, with one notable exception (clast N from EET87513), mineralogically distinct from typical carbonaceous chondrites. However, these clasts have very close affinities to carbonaceous chondrites and have also experienced thermal metamorphism and aqueous alteration, but to different degrees.
Roosevelt County 075: A petrologic, chemical and isotopic study of the most unequilibrated known H chondrite
Authors: McCoy T. J. , Keil K. , Ash R. D. , Morse A. D. , Pillinger C. T. , Wieler R. , Mayeda T. K. , Clayton R. N. , Benoit P. H. , Sears D. W. G. , Casanova I. , Muenow D. W. , Moore C. B. , Lewis C. F. , Wilson I. E.
Published: June 2012

Abstract— Roosevelt County (RC) 075 was recovered in 1990 as a single 258‐gram stone. Classification of this meteorite is complicated by its highly unequilibrated nature and its severe terrestrial weathering, but we favor H classification. This is supported by O isotopes and estimates of the original Fe, Ni metal content. The O isotopic composition is similar to that of a number of reduced ordinary chondrites (e.g., Cerro los Calvos, Willaroy), although RC 075 exhibits no evidence of reduced mineral compositions. Chondrule diameters are consistent with classification as an L chondrite, but large uncertainties in chondrule diameters of RC 075 and poorly constrained means of H, L and LL chondrites prevent use of this parameter for reliable classification. Other parameters are compromised by severe weathering (e.g., siderophile element abundances) or unsuitable for discrimination between unequilibrated H, L and LL chondrites (e.g., Co in kamacite, δ13C). Petrologic subtype 3.2± 0.1 is suggested by the degree of olivine heterogeneity, the compositions of chondrule olivines, the thermoluminescence sensitivity, the abundances and types of chondrules mapped on cathodoluminescence mosaics, and the amount of presolar SiC. The meteorite is very weakly shocked (S2), with some chondrules essentially unshocked and, thus, is classified as an H3.2(S2) chondrite. Weathering is evident by a LREE enrichment due to clay contamination, reduced levels of many siderophile elements, the almost total loss of Fe, Ni metal and troilite, and the reduced concentrations of noble gases. Some components of the meteorite (e.g., type IA chondrules, SiC) appear to preserve their nebular states, with little modification from thermal metamorphism. We conclude that RC 075 is the most unequilibrated H chondrite yet recovered and may provide additional insights into the origin of primitive materials in the solar nebula.
A comparison of FeO‐rich, porphyritic olivine chondrules in unequilibrated chondrites and experimental analogues
Authors: Jones Rhian H. , Lofgren Gary E.
Published: June 2012

Abstract Experimentally produced analogues of porphyritic olivine (PO) chondrules in ordinary chondrites provide an important insight into chondrule formation processes. We have studied experimental samples with PO textures grown at three different cooling rates (2, 5 and 100 *C/h), and samples that have been annealed at high temperatures (1000–1200 °C) subsequent to cooling. These are compared with natural chondrules of similar composition and texture from the ordinary chondrites Semarkona (LL3.0) and ALH 81251 (LL3.3). Zoning properties of olivine grains indicate that the Semarkona chondrules cooled at comparable rates to the experiments. Zoning in olivine from chondrules in ALH 81251 is not consistent with cooling alone but indicates that the chondrules underwent an annealing process. Chromium loss from olivine is very rapid during annealing and calculated diffusion coefficients for Cr in olivine are very similar to those of Fe‐Mg interdiffusion coefficients under the same conditions. Annealed experimental samples contain an aluminous, low‐Ca pyroxene which forms by reaction of olivine and liquid. No similar reaction texture is observed in ALH 81251 chondrules, and this may be evidence that annealing of the natural samples took place at considerably lower temperatures than the experimental analogues. The study supports the model of chondrule formation in a cool nebula and metamorphism of partly equilibrated chondrites during reheating episodes on the chondrite parent bodies.
Are crystalline C‐(H‐O‐N) carbons the elusive meteoritic carbynes?
Authors: Rietmeijer Frans J. M.
Published: June 2012

Abstract I present an internally consistent reinterpretation of carbyne diffraction data making a few plausible assumptions. The results support that carbynes could be crystalline, randomly interstratified (or mixed‐layered) carbons with variable C/(C+H+O+N) ratios rather than thermodynamically stable carbon allotropes. The metastable carbynes are likely the result of incomplete, kinetically‐inhibited, low‐temperature pyrolysis of precursor material. A renewed interest in meteoritic carbynes should seek to combine light‐element chemistry and crystallography of these elusive carbons.
H4 and H5 chondrites from the Rub'al Khali Desert
Authors: Krot Alexander N.
Published: June 2012

Abstract Al‐Jimshan is a highly weathered 11.45 kg chondrite that was found in 1955 in the Rub' al Khali Desert, Saudi Arabia (20*42′N, 52*50E) about 240 km south‐east of the town of al‐Hadidah. The main mass is now at UCLA. Based on texture and mineral composition (olivine Fa17.7 ± 0.4; pyroxene Fs15.7 ± 1.0 Wo13 ± 0.4), al‐Jimshan is classified as an H4 chondrite of shock stage S2. The Bir‐Hadi and ad‐Dahbubah H chondrites, which also were found in the Rub'al Khali (Holm, 1962), are probably not paired with al‐Jimshan. They are classified as H5, shock stage S3 (Fa18.1 ± 0.5, n = 10; Fs16.0 ± 0.6, Wo1.1 ± 0.4, n = 9) and H5, shock stage S2 (Fa17.9 ± 0.3, n = 10; FS15.5 ± 0.2 Wo1.0 ± 0.4, n = 10), respectively.
An improbable concentration of basaltic meteorite falls (HED and mesosiderite) in the mid‐20th century
Authors: Treiman Allan H.
Published: June 2012

Abstract The fall rate of HED basaltic meteorites (howardites, eucrites, diogenites) has not been constant in the 20th century, while the fall rate of chondrites has been constant within error. Thirteen of the 26 dated HED falls (day of fall known, 1900 through 1989) fell in 1924 through 1939. A fall cluster (not a meteorite stream) like this will occur in less than one in 100 random distributions of fall days. The proportions of HED types in the whole cluster are statistically identical to those of the whole historical record of HED falls, as is the distribution of cosmic ray exposure ages. In a subset of the cluster, 1924 through 1933, eight of those nine HED falls from have exposure ages of 10–20 Ma; this grouping is statistically distinct from that of the historical record. The mesosiderite meteorites share many chemical and isotopic properties with the HEDs but are not from the same parent body. However, the dates of the three mesosiderite falls of the 20th century (all in 1924 through 1939) are a likely sampling of the distribution of HED fall dates; less than one in 200 random distributions of three fall dates would have them all in a given IS year interval of the 20th century. If the concentration of HED and mesosiderite falls in 1924 through 1939 is not a result of chance (odds of less than 1 in 200), it must have had a cause or causes. The cause(s) are not dear but appear(s) to have operated: on parent bodies only of basaltic meteorites; on a number of such parent bodies (mesosiderite and at least one HED); distant from Earth; and so as to produce a duster of only 15 years duration. This duration is much shorter than the expected time scales or orbital evolution of asteroidal fragments.
Basalt generation at the Apollo 12 site, Part 1: New data, classification, and re‐evaluation
Authors: Neal Clive R. , Hacker Matthew D. , Snyder Gregory A. , Taylor Lawrence A. , Liu Yun‐Gang , Schmitt Roman A.
Published: June 2012

Abstract— New data are reported from five previously unanalyzed Apollo 12 mare basalts that are incorporated into an evaluation of previous petrogenetic models and classification schemes for these basalts. This paper proposes a classification for Apollo 12 mare basalts on the basis of whole‐rock Mg# [molar 100*(Mg/(Mg+Fe))] and Rb/Sr ratio (analyzed by isotope dilution), whereby the ilmenite, olivine, and pigeonite basalt groups are readily distinguished from each other. Scrutiny of the Apollo 12 feldspathic “suite” demonstrates that two of the three basalts previously assigned to this group (12031, 12038, 12072) can be reclassified: 12031 is a plagioclase‐rich pigeonite basalt (Nyquist et al, 1979); and 12072 is an olivine basalt Only basalt 12038 stands out as a unique sample (Nyquist et al., 1981) to the Apollo 12 she, but whether this represents a single sample from another flow at the Apollo 12 site or is exotic to this site is equivocal.

The question of whether the olivine and pigeonite basalt suites are co‐magmatic is addressed by incompatible trace‐element chemistry: the trends defined by these two suites when Co/Sm and Sm/Eu ratios are plotted against Rb/Sr ratio demonstrate that these two basaltic types cannot be co‐magmatic. Crystal fractionation/accumulation paths have been calculated and show that neither the pigeonite, olivine, or ilmenite basalts are related by this process. Each suite requires a distinct and separate source region. This study also examines sample heterogeneity and the degree to which whole‐rock analyses are representative, which is critical when petrogenetic interpretation is undertaken. Sample heterogeneity has been investigated petrographically (inhomogeneous mineral distribution) with consideration of duplicate analyses, and whether a specific sample (using average data) plots consistently upon a fractionation trend when a number of different compositional parameters are considered. Using these criteria, four basalts have been identified where reported analyses are not representative of the whole‐rock composition: 12005, an ilmenite basalt; 12006 and 12036, olivine basalts; and 12031 previously classified as a feldspathic basalt, but reclassified as part of the pigeonite suite (Nyquist et al., 1979).
The evolution of enstatite and chondrules in unequilibrated enstatite chondrites: Evidence from iron‐rich pyroxene
Authors: Weisberg Michael K. , Prinz Martin , Fogel Robert A.
Published: June 2012

Abstract— FeO‐rich (Fs6–34) pyroxene lacking cathodoluminescence (CL), hereafter black pyroxene, is a major constituent of some of the chondrules and fragments in unequilibrated (type 3) enstatite chondrites (UECs). It contains structurally oriented zones of Cr‐, Mn‐, V‐rich, FeO‐poor enstatite with red CL, associated with mm‐sized blebs of low‐Ni, Fe‐metal and, in some cases, silica. These occurrences represent clear evidence of pyroxene reduction. The black pyroxene is nearly always rimmed by minor element (Cr, Mn, V)‐poor enstatite having a blue CL. More commonly, red and blue enstatites, unassociated with black pyroxene, occur as larger grains in chondrules and fragments, and these constitute the major silicate phases in UECs. The REE abundance patterns of the black pyroxene are LREE‐depleted. The blue enstatite rims, however, have a near‐flat to LREE‐enriched pattern, ∼0.5–4x chondritic. The petrologic and trace element data indicate that the black pyroxene is from an earlier generation of chondrules that formed in a nebular region that was more oxidizing than that of the enstatite chondrites. Following solidification, these chondrules experienced a more reducing nebular environment and underwent reduction. Some, perhaps most, of the red enstatite that is common throughout the UECs may be the product of solid‐state reduction of black pyroxene. The blue enstatite rims grew onto the surfaces of the black pyroxene and red enstatite as a result of condensation from a nebular gas.

The evolutionary history of some of the enstatite and chondrules in enstatite chondrites can be expressed in a four‐stage model that includes: Stage 1. Formation of chondrules in an oxidizing nebular environment Stage 2. Solid‐state reduction of the more oxidized chondrules and fragments to red enstatite in a more reducing nebular environment Stage 3. Formation of blue enstatite rims on the black pyroxene as well as on the red enstatite. Stage 4. Reprocessing, by various degrees of melting, of many of the earlier‐formed materials.
Denman 002: A new CV3 chondrite from South Australia
Authors: Dominik B. , Bussy F.
Published: June 2012

Abstract— Denman 002 is a new Australian carbonaceous chondrite. A single stone of 30 g was recovered in 1991 May near Fisher Station on the Trans Australian Railway, Nullarbor Plain, South Australia (30°36′S, 130°04′E). Texture, mineral and chemical composition indicate that it is a CV3 chondrite of oxidised subgroup with several similarities to Allende. It is composed of sharply defined chondrules, Ca‐Al rich inclusions up to 3.5 mm across, olivine aggregates and fine‐grained, nearly opaque matrix (40 vol%). Silicates are compositionally highly heterogeneous (olivine Fa: 0.2–45.6 mol%, PMD: 109.7). Denman 002 shows shock effects of stage SI and weathering of category A.
Textural variations and impact history of the Millbillillie eucrite
Authors: Yamaguchi Akira , Takeda Hiroshi , Bogard Donald D. , Garrison Daniel
Published: June 2012

Abstract— We have investigated 10 new specimens of the Millbillillie eucrite to study its textures and mineral compositions by electron probe microanalyser and scanning electron microscope. Although originally described as having fine‐grained texture, the new specimens show diversity of texture. The compositions (Mg/Fe ratios) of the host pigeonites and augite lamellae are homogeneous, respectively, in spite of the textural variation. In addition to their chemical homogeneity, pyroxenes in coarse and fine‐grained clasts are partly inverted to orthopyroxene. Chemical zoning of plagioclase during crystal growth is preserved. This eucrite includes areas of granulitic breccias and impact melts. Large scale textures show a subparallel layering suggesting incomplete mixing and deposition of impact melt and lithic fragments. An 39Ar‐40Ar age determination for a coarse‐grained clast indicates a strong degassing event at 3.55 ± 0.02 Ga. We conclude that Millbillillie is among the most equilibrated eucrites produced by thermal annealing after impact brecciation. According to the classification of impact breccias, Millbillillie can be classified as a mixture of granulitic breccias and impact melts. The last significant thermal event is characterized by network‐like glassy veins that run through clasts and matrices. Consideration of textural observations and requirements for Ar‐degassing suggests that the 39Ar‐40Ar age could in principle date either the earilier brecciation and annealing event or the event which produced the veins.
Acfer 217‐A new member of the Rumuruti chondrite group (R)
Authors: Bischoff A. , Geiger T. , Palme H. , Spettel B. , Schultz L. , Scherer P. , Loeken T. , Bland P. , Clayton R. N. , Mayeda T. K. , Herpers U. , Meltzow B. , Michel R. , Dittrich‐Hannen B.
Published: June 2012

Abstract— Previously, three meteorites from Australia and Antarctica were described as a new chondritic “grouplet” (Carlisle Lakes, Allan Hills (ALH) 85151, Yamato (Y) −75302; Rubin and Kallemeyn, 1989). This grouplet was classified as the “Carlisle Lakes‐type” chondrites (Weisberg et al., 1991). Recently, one Saharan sample and four more Antarctic meteorites were identified to belong to this group (Acfer 217, Y‐793575, Y‐82002, PCA91002, PCA91241). The latter two are probably paired. With the meteorite Rumuruti, the first fall of this type of chondrite is known (Schulze et al., 1994). We report here on the Saharan meteorite Acfer 217 which has chemical and mineralogical properties very similar to Rumuruti and Carlisle Lakes. All eight members of this group, Rumuruti, Carlisle Lakes, ALH85151, Y‐75302, Y‐793575, Y‐82002, Acfer 217, and the paired samples PCA91002 and PCA91241 justify the introduction of a new group of chondritic meteorites, the Rumuruti meteorites (R).

Acfer 217 is a regolith breccia consisting of up to cm‐sized clasts (∼33 vol%) embedded in a fine‐grained, well‐lithified clastic matrix. The most abundant mineral is olivine (∼72 vol%), which has a high Fa‐content of 37–39 mol%. The major minerals (olivine, low‐Ca pyroxene, Ca‐pyroxene, and plagioclase) show some compositional variability indicating a slightly unequilibrated nature of the meteorite. Considering the mean olivine composition of Fa37.8 ± 5.7, a classification of Acfer 217 as a R3.8 chondrite would result; however, Acfer 217 is a regolith breccia consisting of clasts of various petrologic types. Therefore, we suggest to classify Acfer 217 as a R3–5 chondrite regolith breccia. The bulk meteorite is very weakly shocked (S2).

The bulk composition of Acfer 217 and other R‐meteorites show that the R‐meteorites are basically chondritic in composition. The pattern of moderately volatile elements is unique in R chondrites; Na and Mn are essentially undepleted, similar to ordinary chondrites, while Zn and Se contents are similar to concentrations in CM chondrites. The oxygen isotopic composition in Acfer 217 is similar to that of Rumuruti, Carlisle Lakes, ALH 85151, and Y‐75302. In a δ17O vs. δ18O‐diagram, the R‐meteorites form a group well resolved from other chondrite groups.

Acfer 217 was a meteoroid of common size with a radius between 15–65 cm and with a single stage exposure history. Based on 21Ne, an exposure age of about 35 Ma was calculated.
Krypton and xenon from the solar wind and solar energetic particles in two lunar ilmenites of different antiquity
Authors: Wieler Rainer , Baur Heinrich
Published: June 2012

Abstract We present Kr and Xe isotope data obtained by closed system stepped etching of ilmenite separates from two lunar samples exposed to the solar corpuscular radiation at different epochs. Helium, neon, and argon in the same samples were reported to consist of two components: isotopically unfractionated solar wind (SW) released in the first steps, and an isotopically heavier component (SEP) released later and, thus, sited at larger depth. The same release characteristic is now observed for the heavy noble gases. We also conclude that solar Kr and Xe consist of two isotopically different components, implanted with different energies. The SW‐Kr in a recently irradiated soil has a composition very close to atmospheric Kr, which agrees with other newly reported data from stepped etch‐ and combustion runs. No clear evidence for temporally variable SW‐Kr or SW‐Xe spectra was found. “Surface correlated” Kr and Xe components “SUCOR” and “BEOC 12001” are a mixture of SW and SEP. The isotopic fractionation factors relating SW and SEP are close to the square of the mass ratios for all five noble gases. We infer that the measured Kr/Xe ratio in ilmenite is essentially identical to this ratio in the solar corpuscular radiation.