bluuebunny/crossref_metadata_2025 huggingface dataset:
PETROLOGY OF NINE ORDINARY CHONDRITE FALLS FROM CHINA
Authors: Wang Daode , Rubin Alan E.
Published: June 2012

Nine twentieth‐century ordinary chondrite falls from China are described and classified. They include: Nantong (H6), Zaoyang (H5), Zhaodong (L4), Qidong (L‐LL5), Raoyang (L6), Sheyang (L6), Guangnan (L6), Suizhou (L6) and Nan Yang Pao (L6). Kamacite in Qidong is rare and contains much more Co (15 mg/g) than is characteristic of L‐group chondrites; Qidong may be a member of a chondrite group intermediate in its properties between L and LL. Zhaodong, Qidong, Raoyang, Sheyang and Suizhou have several olivine and/or low‐Ca pyroxene grains with aberrant Fel(Fe + Mg) ratios; it is probable that these five chondrites are fragmental breccias. The lack of correlation between shock facies and occurrence of aberrant silicate grains suggests that breccia lithification caused only minimal shock effects in many meteorites. Alternatively, postshock annealing may have resulted in the recrystallization of shock‐indicating phases, leading to assignment of a shock facies that is lower than that present immediately after the shock event.
THE L5 BAYARD METEORITE: A 1982 FIND
Authors: Struempler Arthur W. , Kaelin Roy
Published: June 2012

The Bayard chondrite, found in western Nebraska in 1982, is a single mass of 75 kg. Composition of olivine (Fa 24.5) and orthopyroxene (Fs 22.0), along with bulk composition, support an L‐classification. The presence of equilibrated and partially recrystallized minerals indicate petrologic type 5 classification.
The Ningqiang Meteorite: Classification and Petrology of an Anomalous CV Chondrite
Authors: Rubin Alan E. , Wang Daode , Kallemeyn Gregory W. , Wasson John T.
Published: June 2012

Abstract— Ningqiang is an anomalous CV chondrite (oxidized subgroup) containing a high abundance of aggregational inclusions (13.7 vol.%) and low abundances of refractory inclusions (1.0+1.0–0.5 vol.%) and bulk refractory lithophiles (∼0.82 × CV). Ningqiang may have agglomerated after most refractory inclusions at the nebular midplane had already been incorporated into other objects. Coarse‐grained rims surround only ∼5% of Ningqiang chondrules, compared to ∼50% in normal CV chondrites. Aggregational inclusions appear to have formed by incipient melting of fine‐grained aggregates at relatively low temperatures in the solar nebula, possibly by the mechanism responsible for chondrule formation. Granoblastic porphyritic chondrules, which contain olivines forming 120° triple junctures and no mesostasis, probably formed in the solar nebula by incomplete melting of precursor materials that were olivine normative and had relatively low concentrations of Si, Ca, Al, Fe and Na.
Guangnan (L6) and Ningqiang (CV3): Exposure Ages and Radiogenic Ages of Two Unusual Chondrites
Authors: Eugster O. , Michel Th. , Niedermann S.
Published: June 2012

Abstract— The isotopic abundances of the noble gases in bulk samples of the Guangnan L6 chondrite and of the anomalous CV3 chondrite Ningqiang were measured. Guangnan yields a cosmic‐ray exposure age of 2.9 ± 0.4 Ma and belongs to the group of L chondrites with low exposure ages. Ningqiang, however, shows a cosmic‐ray exposure age of 42.2 ± 4.0 Ma, the highest for a CV3 chondrite. The concentrations of radiogenic 4He and 40Ar in Guangnan are the lowest observed in any ordinary chondrite. A U/Th‐4He age of 27 ± 16 Ma and a 40K–40Ar age of 142 ± 14 Ma are calculated assuming L chondritic U, Th, and K concentrations. This assumption is justified considering the fact that a mineralogical composition typical for L chondrites was reported for this meteorite. The observed severe gas losses must have occurred at or before the onset of the exposure of the meteoroid to the cosmic radiation. For the Ningqiang carbonaceous chondrite concordant gas retention ages are obtained: The U/Th‐4He age is 4170 ± 160 Ma whereas the 40K–40Ar age is 4260 ± 70 Ma, assuming average U, Th, and K concentrations for C3 chondrites.
Camel Donga: A Eucrite with High Metal Content
Authors: Palme H. , Wlotzka F. , Spettel B. , Dreibus G. , Weber H.
Published: June 2012

Abstract— The Camel Donga eucrite is unique since it contains about 2% metallic iron. Chemical composition, mineralogy, and noble gas contents of Camel Donga are, however, indistinguishable from other eucrites. The bulk iron content and the composition of the metal show that the Camel Donga metal was formed by reduction of FeO and FeS, probably through loss of S2 and SO2. Since coarse‐ and fine‐grained lithologies are affected it is likely that the reduction occurred after brecciation. The inhomogeneous distribution of metal suggests that reduction is limited to areas where sulfides were present. The fact that major parts of the meteorite still contain sulfides, in many cases associated with metal, indicates that the reduction process did not go to completion. A comparatively short heating period is suggested, perhaps in an ejecta blanket.
Partitioning of Rare Earth Elements Between Hibonite and Melt and Implications for Nebular Condensation of the Rare Earth Elements
Authors: Drake Michael J. , Boynton William V.
Published: June 2012

Abstract— The partitioning of the rare earth elements (REE) between hibonite and silicate melt has been investigated at 1470 °C in the system calcium tschermak's molecule‐diopside. Oxygen fugacity was varied between air and the iron‐wustite buffer using conventional gas mixing, and to “infinitely reducing” using Sr2+ as a surrogate for Eu2+. The partition coefficient (D) pattern is light REE enriched with D(La) = 7.15 and D(Yb) = 0.1. D(Eu) varied from about 2 in air to about 0.55 in an “infinitely reducing” atmosphere. Experiments were reversed for Eu and, by implication, a close approach to equilibrium was achieved for other elements. Absolute activity coefficients for REE in hibonite were estimated, yielding γLa = 330, γEu3+ = 1200, and γYb = 24 000. These results suggest that unless the principal phase(s) into which a trace element is dissolving and the activity—composition relationships for that trace element in that phase(s) are known, condensation temperatures based on assumed ideal solution behavior will generally be in error.
The Salem, Oregon L6 Chondrite
Authors: Clarke Roy S. , Pugh Richard N.
Published: June 2012

Abstract— The Salem, Oregon meteorite fall of 1:05 a.m. (07:05 GMT) May 13, 1981 (lat. 44°58′45″N., long. 123°58′10″W) was heard by two observers. A 22.2 g fragment was recovered immediately from a total recovery of 61.4 g from a single individual. No other fall related phenomena were observed. It is a heavily fusion‐crusted, shock‐veined, L6 chondrite.
The Tuxtuac, Mexico, Meteorite, an LL5 Chondrite Fall
Authors: Graham A. L. , Michel‐Levy M. Christophe , Danon J. , Easton A. J.
Published: June 2012

Abstract— The Tuxtuac meteorite fell in Zacatecas state, Mexico, on 16 October 1975, at 1820 hours. Two partly crusted masses, weighing 1924 g and 2340 g, were recovered. The stone is an ordinary chondrite, LL5, with olivine Fa30 and 19.22 weight % total iron. The silicates contain numerous voids and a froth‐like mesostasis is present within some chondrules. Metal phases present are kamacite (5.7–6.4% Ni, 6–7% Co) and high nickel metal (taenite 37–41% Ni, 1.7 ± 0.3% Co; tetrataenite 47–52% Ni, 0.8–1.4% Co). The stone is unusual for an LL‐group chondrite in that it exhibits neither large‐scale brecciation features nor dark veins.
Carbon Stable Isotope Analyses of Individual Deep‐Sea Spherules
Authors: Wright I. P. , Carr R. H. , Pillinger C. T.
Published: June 2012

Abstract— A preliminary investigation into the carbon isotopic composition of deep‐sea spherules has been undertaken. A variety of particles have been analysed including both melted and unmelted samples of type S (stony) and type I (iron) spherules, emphasis being placed on surveying the carbon in different sorts of particles rather than analysing large numbers of samples. Some general observations can be made: there appear to be four different sorts of carbonaceous materials in the spherules. Melted and unmelted spherules of either type I or S, apparently contain two forms of low temperature combustible carbon distinguished, not by combustion temperature, but by isotopic composition. The low temperature of combustion is commensurate with these forms of carbon being organic in nature. The most likely explanation for this carbon is terrestrial biogenic contamination although there exists the possibility that there are some indigenous organic materials. Unmelted type S spherules contain a high temperature carbon component, characterised by a very minor 13C‐enrichment, which is considered to be indigenous to the sample. All melted samples contain only small amounts of high temperature carbon with an isotopic composition suggestive of handling blank.
Mount Morris (Wisconsin): A Fragment of the IAB Iron Pine River?
Authors: Bevan A. W. R. , Grady M. M.
Published: June 2012

Abstract— The Pine River IAB iron‐with‐silicate‐inclusions and the anomalous stony meteorite Mount Morris (Wisconsin) were recovered from closely neighbouring localities. Literature data on the petrography, mineralogy, and oxygen isotopic compositions of Mt. Morris (Wis.) and silicates in Pine River are virtually identical. Additionally, total carbon contents and carbon isotopic compositions (δ13C rel. to PDB) of both meteorites (this work) are within experimental error. These data combined with historical and geographical evidence suggest that Mt. Morris (Wis.) and Pine River are pieces of the same meteorite.
The Greenwell Springs LL4 Chondrite: A New Fall from Louisiana, USA
Authors: Byerly G. R. , Jarosewich E. , Mason B. , Clarke R. S.
Published: June 2012

Abstract— A 664 gm stone fell into suburban Baton Rouge in November 1987. The stone has a nearly complete fusion crust and was undamaged upon impact. The ordinary chondrite contains equilibrated olivine, Fa28, and largely equilibrated bronzite, Fs23. Some bronzite is still compositionally zoned and polysynthetically twinned, thus requiring petrologic classification of the meteorite as a type 4. A major element analysis of the meteorite falls exclusively into the field for the LL compositional group.
40Ar‐39Ar Ages of Types 3 and 4, L and H Chondrites from Antarctica
Authors: Stephan Thomas , Jessberger Elmar K.
Published: June 2012

Abstract— This is a report on 40Ar‐39Ar studies of 7 low petrographic type L and H chondrites from Antarctica.

From petrographic similarities it has been argued that the L3 chondrites ALHA77015, −77167, −77249, and −77260 are pieces from a common fall (McKinley et al., 1981). Our results now confirm this supposition: The four meteorites have identical characteristic Ar‐degassing patterns, very similar K, Ca, Cl, and 36Artrapped contents, and similar 40Ar‐39Ar ages of <4 Ga which are rather unusual for ordinary chondrites and might be due to shock. The undulating age patterns could be due to weathering or to 39Ar recoil.

The L4 chondrite ALHA77230 shows no age plateau and only a lower limit for the time of a severe degassing, 4.0 Ga, can be given. ALHA77226 and RKPA78002, two H4 chondrites, exhibit reasonably well defined age plateaus at about 4.3 and 4.4 Ga. Two individual chondrules from RKPA78002 have the same age as the whole rock sample.
Composition of the Crystalline Basement and Shock Metamorphism of Crystalline and Sedimentary Target Rocks at the Haughton Impact Crater, Devon Island, Canada
Authors: Metzler A. , Ostertag R. , Redeker H.‐J. , Stöffler D.
Published: June 2012

Abstract— About 100 cobble‐sized samples collected from the surface of the central polymict breccia formation of Haughton impact crater, Canada, have been studied microscopically and chemically. Breccia clasts derived from the 1700 m deep Precambian basement consist of 13 rock types which can be grouped into sillimanite‐ and garnet‐bearing gneiss; alkali feldspar‐rich aplitic or biotite‐hornblende‐bearing gneiss; biotite and hornblende gneiss; apatite‐rich biotite and biotite‐hornblende gneiss; calcitediopside gneiss; amphibolite; tonalitic orthogneiss; and basalts. The range of chemical compositions of these rocks is wide: e.g., SiO2 ranges from 40–85 wt.%; Al2O3 from 7–20 wt.%; CaO from 0.01–25 wt.%; or P2Os from <0.01–5 wt.%. Nearly all samples of crystalline rocks are shock metamorphosed up to about 60 GPa. Most conspicuous is the absence of whole‐rock melts and the very rare occurrence of unshocked rocks. The 45 samples examined can be classified into the following shock stages: stage 0 (<5 GPa): 4.5%, stage Ia (10–20 GPa): 9.0%, stage Ib (20–35 GPa): 33%, stage II (35–45 GPa): 29%, stage III (45–55 GPa): 18%, stage III–IV (55–60 GPa): 6.5%. Among Paleozoic sedimentary rock clasts higher degrees of shock than within crystalline rocks were observed such as highly vesiculated, whole‐rock melts of sandstones and shales. Within the northern and eastern sectors of the allochthonous breccia no distinct radial variation of the cobble‐sized lithic clasts regarding abundance, rock type, and degree of shock was observed, with the exception that clasts of shock‐melted sedimentary rocks and of highly shocked basement rocks (stage III–IV) are strongly concentrated near the center of the crater. Based on our field and laboratory investigations we conclude that vaporization and melting due to the Haughton impact affected the lower section of the sedimentary strata from about 900 to 1700 m depth (Eleanor River limestones and dolomites, Lower Ordovician and Cambrian limestones, dolomites, shales, and sandstones). The 60‐GPa shock pressure isobar reached only the uppermost basement rocks so that whole rock melting of the crystalline rocks was not possible.
The Surface Structure of the Haughton Impact Crater, Devon Island, Canada
Authors: Bischoff L. , Oskierski W.
Published: June 2012

Abstract— Recent geological and structural investigations support the existing descriptions of the Haughton structure being a dome‐like structure. The central area represents the central uplift and is formed by blocks of rocks belonging to the oldest part of the Devon Island Paleozoic sediment cover. The orientation of the blocks partly reflects this dome‐like structure. The morphologically defined “inner ring” is a structurally distinct zone, predominated by gypsum beds of the Bay Fiord Formation. These beds dip 30 to 40° outward and are asymmetrically folded. The outer radius of this ring is 5 to 5.5 km. A 1 to 1.5 km broad zone follows outward of more chaotically orientated blocks of rocks, which may be considered a megablock‐zone. The next ring‐like zone is strongly faulted (“faulted annulus”) and obviously represents the downfaulted, once uplifted crater rim. Within this structural annulus, a marked asymmetry of the crater structure is expressed by the attitude of the faulted blocks. The structure of the northern and eastern segments of the faulted annulus differ substantially from those of the southern and western segments. This asymmetry may reflect heterogeneities in the pre‐crater geology or a low angle impact. No evidence was found in support of the theory that the Haughton structure represents a multiring structure.
The Stratigraphy, Sedimentology, and Fossils of the Haughton Formation: A Post‐Impact Crater‐Fill, Devon Island, N.W.T., Canada
Authors: Hickey Leo J. , Johnson Kirk R. , Dawson Mary R.
Published: June 2012

Abstract—After the impact that formed Haughton crater, 22.4 ± 1.4 Ma ago (early Miocene), the cavity filled with water and began to accumulate lacustrine sediments. These preserve detailed evidence of pre‐impact stratigraphy and post‐impact morphology and development of the crater, as well as of the climatic and biotic regime in which it lay. In this report we formally designate these sediments as the Haughton Formation, of which only a 48 m thick remnant covering approximately 7 km2still exists. Dolomite‐rich, poorly‐sorted silt, fine sand, and mud are the principal lithologies. The formation unconformably overlies a blanket of allochthonous impact breccia forming the floor of the original crater. Presence of a debris‐flow deposit in the base of the sequence indicates that lacustine deposition began very shortly after crater formation.

The Haughton Formation contains a moderately diverse and highly endemic vertebrate fauna as well as palynomorphs and plant macrofossils that indicate a cool‐temperate climatic regime. A small percentage of reworked Late Cretaceous and early Tertiary palynomorphs point to the former existence of the Eureka Sound Formation in the drainage area of the crater. In addition, the distribution of the lake beds indicates the absence of an inner ring on the west side of the crater, and the 3° to 3.5° inward dip of Haughton strata implies that the central mass has subsided approximately 300 to 350 m since deposition began.
A statistical comparison of Antarctic finds and modern falls: Mass frequency distributions and relative abundance by type
Authors: Harvey R. P. , Cassidy W. A.
Published: June 2012

Abstract— The relative abundance of different compositional types and mass frequency distributions are presented for four meteorite samples (the modern falls, Antarctic finds, Yamato finds and Allan Hills Main Icefield finds). The modern falls sample represents continuous collection of a known number of falls over a short timespan, while the Antarctic samples represent a longer timespan and an unknown number of falls. The Allan Hills Main Icefield sample has many desirable collection characteristics indicating it best represents Antarctic meteorites. By retabulating the modern falls to create a sample with characteristics similar to those of the Allan Hills Main Icefield finds, we can directly compare the two.

The mass frequency distributions of Antarctic samples exhibit a tail toward the larger sizes and thus differ from that of the modern falls (which approximates a normal curve). In general, normal and power law models prove to be inadequate to explain the observed mass frequency distributions, possibly because they fail to correctly account for atmospheric and collection effects. Non‐parametric statistics show that it is unlikely that the two are good samples of a single steady‐state meteoritic complex. In addition, there is an excess in numbers of small H chondrites in Allan Hills Main Icefield finds relative to modern falls which is not easy to explain given modern showerfall rates of occurrence. This supports the view that the delivery of meteoritic material to Earth might be variable over the short timescale represented by these samples.
Cratering of the terrestrial planets by Apollo objects
Authors: Wetherill G. W.
Published: June 2012

Abstract— Absolute and relative cratering rates on the terrestrial planets have been calculated using the same asteroidal collision model and Monte Carlo program used for previous studies of the terrestrial meteorite flux, the steady‐state number of Apollo‐Amor objects, and the orbital distribution of both meteorites and Apollo‐Amor objects. The most straightforward result is that projectiles from the asteroid belt appear to provide about one‐third the observed present‐day production of terrestrial craters larger than 10 km in diameter. When uncertainties in the calculations and observations are included, it cannot be excluded that the entire terrestrial cratering flux is asteroidal. On the other hand, assumption of an additional Apollo‐Amor source of extinct comets, in the same quantity permitted by Apollo‐Amor observations, provides better agreement with the observed cratering rate. In addition, a significant (e.g., ∼30%) terrestrial contribution from active long and short period comets is acceptable within the uncertainties of the assumptions required.

The ratios of the cratering rates on the different terrestrial planets are somewhat sensitive to the assumed source. A purely asteroidal source predicts a martian cratering rate per unit area about four times that on Earth, whereas the difference is reduced to about a factor of two for the mixed asteroid‐extinct comet source. The opposite effect is found for Mercury. As discussed by previous authors, the predicted lunar cratering rate is significantly higher than that observed. It is not clear whether this is a result of scaling to impacts on a body considerably smaller than Earth, or if it indicates an increase in the cratering flux during the Phanerozoic.
Possible relationship between the Farmington meteorite and a seismically detected swarm of meteoroids impacting the Moon
Authors: Oberst Jürgen
Published: June 2012

Abstract— The Farmington ordinary L5 chondrite with its uniquely short cosmic‐ray exposure age of less than 25 000 years may have been a member of a large meteoroid swarm which was detected by the Apollo seismic network when it encountered the Moon in June 1975. The association implies that the parent body of the Farmington meteorite was in an Earth‐crossing orbit at the time the swarm was formed. This supports the idea that at least some meteorites are derived from the observable population of Earth‐crossing asteroids.
The Wilder H5 chondrite: A 1982 find from Idaho
Authors: White Craig M.
Published: June 2012

Abstract— The Wilder chondrite, a single stone of 1970 g, was found in southwestern Idaho in 1982. A classification of H5 is indicated by the mean compositions of olivines (Fa18.4) and orthopyroxenes (Fs16.3), and the narrow range in mineral compositions, recrystallized nature of the matrix, and mean Wo content of the orthopyroxenes (Wo1.34).
Meteorites from the Nullarbor Region, Western Australia: II. Recovery and classification of 34 new meteorite finds from the Mundrabilla, Forrest, Reid and Deakin areas
Authors: Bevan A. W. R. , Binns R. A.
Published: June 2012

Abstract— The discovery of 34 new stony meteorites is reported from those areas of the Nullarbor Region, Western Australia named after Mundrabilla, Forrest, Reid and Deakin sidings on the Trans Australian Railway line. The recoveries include 15 H‐, and 15 L‐group equilibrated (types 4–6) ordinary chondrites, two distinct H3 chondrites (Mundrabilla 003 and Forrest 003), a genomict H‐group chondrite breccia (Reid 011) comprising types 3–6, and one structurally anomalous chondrite (Deakin 001). Seventy‐eight distinct meteorites are now known from the region.
A preliminary investigation into the nature of carbonaceous material in ordinary chondrites
Authors: Grady Monica M. , I. P. Wright  , Pillinger C. T.
Published: June 2012

Abstract— The nature and isotopic composition of carbonaceous components in a variety of ordinary chondrites have been studied using stepped combustion. The samples were chosen to include falls, finds and Antarctic meteorites; specimens from all three chemical groups (H, L and LL) have been analysed. Effort was concentrated mostly on the low petrologic type meteorites (i.e., type 3); however, types 4–6 were also included in the study. Apart from terrestrial contaminants and weathering products, some of the unequilibrated ordinary chondrites appear to contain an indigenous organic component. In addition, most of the samples studied show evidence for an amorphous/graphitic component. This exists as C‐rich aggregates or as carbon associated with “Huss” matrix. There does not appear to be any difference in δ13C for this carbon between Antarctic and non‐Antarctic meteorites. In contrast, low temperature carbon in Antarctic samples is characterized by a 13C‐enrichment. This is thought to be due to the influence of terrestrial weathering products introduced in the Antarctic. Curiously, the low temperature carbon in non‐Antarctic finds appears to be intermediate in δ13C between Antarctic finds and non‐Antarctic falls. This suggests that the weathering processes which are so obviously apparent from Antarctic samples may also extend, albeit in a more limited way, to non‐Antarctic meteorites.
Size‐frequency distributions of chondrules in CO3 chondrites
Authors: Rubin Alan E.
Published: June 2012

Abstract— The size‐frequency distributions of chondrules in 11 CO3 chondrites were determined by petrographic analysis of thin sections. CO chondrites have the smallest chondrules of any major chondrite group. In order of decreasing chondrule size, chondrite groups can be arranged as CV ≥ LL > L > H ≥ CM ≥ EH > CO. Chondrule size varies significantly among different CO chondrites; there is a tendency for chondrules to increase in average size with increasing metamorphic grade of the whole‐rock. Different chondrule types in CO chondrites have distinct size‐frequency distributions: in order of decreasing chondrule size, BO > PO > PP > POP > RP = C. The large size of BO chondrules is problematic; however, PO chondrules are among the largest because ∼20% of them contain very coarse relict olivine grains that constitute 40–90 vol.% of the individual chondrules. PP chondrules may be larger than POP chondrules because some of them contain coarse relict pyroxene grains; a compound object consisting of a POP chondrule attached to a large relict pyroxene grain occurs in Lancé.

The mean proportions of chondrule types in CO chondrites are estimated to be 69% POP, 18% PP, 8% PO, 2% BO, 2% RP, 1% C and <0.1% GOP. CO chondrites thus contain a smaller proportion of nonporphyritic chondrules than ordinary or EH chondrites, but a larger proportion than CV chondrites. Relative proportions of chondrule types vary with size interval: PO chondrules decrease fairly regularly in abundance with decreasing chondrule size, and RP chondrules appear to be most abundant in the smallest size intervals.
The Olton, Texas, H chondrite regolith breccia: Paired with Dimmitt
Authors: Keil Klaus , Ehlmann A. J. , Wieler Rainer
Published: June 2012

Abstract— The Olton ordinary chondrites (two stones found in 1948) are H group, solar wind‐bearing regolith breccias. The proximity of the recovery site to the Dimmitt strewnfield, and the similarity in texture, composition, noble gas contents and isotopic ratios to Dimmitt indicate that Olton is paired with Dimmitt.
Helium and neon isotopes in stratospheric particles
Authors: Nier A. O. , Schlutter D. J.
Published: June 2012

Abstract— Helium and neon isotope ratios were determined for 16 interplanetary dust particles (IDPs) collected in the stratosphere. The concentration of helium observed varied greatly from particle to particle, with the highest values approaching those found for lunar surface fines and some gas‐rich meteorites. With the exception of one particle, for which the 3He/4He was (1.45 ± 0.05) × 10−3, the remainder of the particles had ratios falling between 1.4 and 3.1 × 10−4, with an average of (2.4 ± 0.3) × 10−4, substantially less than is associated with the solar wind or observed in average lunar fines or in lunar fines having sizes comparable to those of the IDPs studied. The average 20Ne/22Ne found was 12.0 ± 0.5. Only three reasonably reliable 21Ne/22Ne ratios could be determined, and for these the average was 0.035 ± 0.006. The isotopic ratios appear to preclude the presence of any appreciable amount of cosmic ray‐produced spallogenic products. The high 4He concentrations observed for some of the particles, approaching those observed for lunar surface grains, suggest they were not heated to high temperatures and degassed as they descended in the earth's atmosphere. From Flynn's study of the dynamics of IDPs entering the earth's atmosphere this could mean they entered the atmosphere at relatively low velocities, and hence may be primarily of asteroidal rather than cometary origin.
The Loxton meteorite: A new olivine‐bronzite chondrite from South Australia
Authors: Wallace Margaret , Pring Allan
Published: June 2012

Abstract— The Loxton meteorite is a single stone of 22 g found in South Australia in 1968. It has been classified as an L5 chondrite, shock facies ‘a,’ and contains olivine (Fa24), orthopyroxene (Fs21–22), clinopyroxene (Wo44.7En45.9Fs9.4), nickel‐iron, troilite, chromite and chlorapatite.
40Ar‐39Ar ages of Dellen, Jänisjärvi, and Sääksjärvi impact craters
Authors: Müller Norbert , Hartung Jack B. , Jessberger Elmar K. , Reimold Wolf U.
Published: June 2012

Abstract— 40Ar‐39Ar age measurements were made for three whole rock melt samples produced during impact events which formed the Dellen, Jänisjärvi, and Sääksjärvi craters on the Baltic Shield. An age of 109.6 ± 1.0 Ma was obtained for the Dellen sample based on an age spectrum plateau. The age spectrum shows a small (7%) loss of radiogenic 40Ar from low temperature fractions. Ages of 698 ± 22 Ma and 560 ± 12 Ma were obtained from isochrons for the Jänisjärvi and Sääksjärvi samples, respectively. Data obtained by laser degassing support the Sääksjärvi result. The presence of excess 40Ar is indicated in lower temperature fractions for both samples and is correlated with K concentrations in the Sääksjärvi sample. Models explaining these results may require a change in the local “atmospheric” Ar isotopic composition as cooling of melt rocks proceeded. However, it cannot be excluded that devitrification and/or alteration changed the Ar budget. A crater production rate on the Baltic Shield based on measured ages of 6 craters is (0.3 ± 0.2) · 10−14 20‐km‐and‐larger craters per km2 per year, in satisfactory agreement with previous estimates.
New mineralogical and chemical data on the Machinga (L6) chondrite, Malawi
Authors: Koeberl Christian , Reimold Wolf Uwe , Horsch Hanna E. , Merkle Roland K. W.
Published: June 2012

Abstract— The Machinga, southern Malawi, Africa, L6 chondrite (observed fall, 22 January 1981) contains accessory phases of metal, troilite, chromite, and native Cu (which is associated with limonite and found in zones of aqueous alteration). Rare accessory phases are apatite and pentlandite, which are uncommon in L6 chondrites. Major mineral constituents (olivine, orthopyroxene, and plagioclase) indicate shock effects at a level of about 15–20 GPa shock pressure. The meteorite is thus classified to be of L6d type. Melt pockets of widely variable composition are abundant.
Meteorite infall as a function of mass: Implications for the accumulation of meteorites on Antarctic ice
Authors: Huss Gary R.
Published: June 2012

Abstract— Antarctic meteorites are considerably smaller, on average, than those recovered elsewhere in the world, and seem to represent a different portion of the mass distribution of infalling meteorites. When an infall rate appropriate to the size of Antarctic meteorites is used (1000 meteorites 10 grams or larger/km2/106 years), it is found that direct infall can produce the meteorite accumulations found on eight ice fields in the Allan Hills region in times ranging from a few thousand to nearly 200 000 years, with all but the Allan Hills Main and Near Western ice fields requiring less than 30 000 years. Meteorites incorporated into the ice over time are concentrated on the surface when the ice flows into a local area of rapid ablation. The calculated accumulation times, which can be considered the average age of the exposed ice, agree well with terrestrial ages for the meteorites and measured ages of exposed ice. Since vertical concentration of meteorites through removal of ice by ablation is sufficient to explain the observed meteorite accumulations, there is no need to invoke mechanisms to bring meteorites from large areas to the relatively small blue‐ice patches where they are found. Once a meteorite is on a bare ice surface, freeze‐thaw cycling and wind break down the meteorite and remove it from the ice. The weathering lifetime of a 100‐gram meteorite on Antarctic ice is on the order of 10 000 ± 5000 years.
Chemical characterization of a unique chondrite: Allan Hills 85085
Authors: Gosselin David C. , Laul J. C.
Published: June 2012

Abstract— Allan Hills 85085 is a new and very important addition to the growing list of unique carbonaceous chondrites because of its unique chemical and mineralogical properties. Previously published data on ALH85085 have established its bulk composition, gross levels of volatile depletion, siderophile enrichment, and the unique character of this unique meteorite. This chemical study provides more precise data on the major, minor, and trace element characteristics of ALH85085. ALH85085 has compositional, petrological, and isotopic affinities to Al Rais and Renazzo, and to Bencubbin‐Weatherford. The similarities to Al Rais and Renazzo, in particular, suggest similar formation locations and thermal processing, possibly in the vicinity of CI chondrites. Petrologic, compositional and isotopic studies indicate that the components that control the abundance of the various refractory and volatile elements were not allowed to equilibrate with the nebula as conditions changed. This lack of equilibration could explain some of the compositional and petrologic variations within and between these meteorites and the inconsistencies in the classification of these meteorites using known taxonomic parameters. It is also apparent that the compositional trends implied by the application of taxonomic parameters probably did not vary simply with heliocentric distance. In addition, variations in the agglomeration of diverse nebular phases along with local and regional temperature events may strongly influence the bulk composition of meteorites.
Origin and history of chondrite regolith, fragmental and impact‐melt breccias from Spain
Authors: Casanova I. , Keil K. , Wieler R. , Miguel A. San , King E. A.
Published: June 2012

Abstract— Six ordinary chondrite breccias from the Museo Nacional de Ciencias Naturales, Madrid (Spain), are described and classified as follows: the solar gas‐rich regolith breccia Oviedo (H5); the pre‐metamorphic fragmental breccias Cabezo de Mayo (type 6, L‐LL), and Sevilla (LL4); the fragmental breccias Cañellas (H4) and Gerona (H5); and the impact melt breccia, Madrid (L6). We confirm that chondrites with typical light‐dark structures and petrographic properties typical of regolith breccias may (Oviedo) or may not (Cañellas) be solar gas‐rich. Cabezo de Mayo and Sevilla show convincing evidence that they were assembled prior to peak metamorphism and were equilibrated during subsequent reheating. These meteorites contain small melt rock clasts that were incorporated into the host chondrite while still molten and/or plastic and cooled rapidly and, yet, are totally equilibrated with their hosts. Compositions of olivine and low‐Ca pyroxene in host chondrite and breccia clasts in Cabezo de Mayo are transitional between groups L and LL. It is suggested, based on mineralogic and oxygen isotopic compositions of host and clasts, that the rock formed on the L parent body by mixing, prior to peak metamorphism. This was followed by partial equilibration of two different materials: the indigenous L chondrite host and exotic LL melt rock clasts.
Spherules and shard‐like clasts from the late Proterozoic Acraman impact ejecta horizon, South Australia
Authors: Wallace Malcolm W. , Gostin Victor A. , Keays Reid R.
Published: June 2012

Abstract— Spherules and irregular shard‐like particles consisting of authigenic mineral phases have been identified in the Acraman impact ejecta horizon preserved within the late Proterozoic shales of the Adelaide Geosyncline, South Australia. The spherules (150 μm to 1 mm diameter) range in shape from near‐spherical through ellipsoidal to extended ellipsoidal‐dumbbell. The distinctive morphology of the spherules and shard‐like particles and their restriction to the ejecta horizon, suggest that they were deposited initially as glassy bodies which subsequently have been pseudomorphed by more stable authigenic phases like calcite, quartz, albite, and barite.
Lewis Cliff 85332: A unique carbonaceous chondrite
Authors: Rubin Alan E. , Kallemeyn Gregory W.
Published: June 2012

Abstract— Lewis Cliff 85332 (LEW85332) is a highly unequilibrated (type 3.0–3.1) unique carbonaceous chondrite. It resembles CI and “CR” chondrites in its abundance ratios of refractory lithophiles and refractory siderophiles, but differs significantly from these groups in important ways: relative to CI chondrites, LEW85332 has low abundances of Mn, Se, Zn and most volatile siderophiles; relative to “CR” chondrites, LEW85332 has high abundance ratios of Mn and most volatile siderophiles. Although several petrologic characteristics of LEW85332 resemble those of CO chondrites, LEW85332 differs from this group in having lower abundance ratios of refractory lithophiles and higher abundance ratios of common and volatile siderophiles. Chondrules (mean diameter of 170 μm) are smaller than those in CV and CM chondrites and bigger than those in most CO chondrites. Two melilite‐rich (Åk 22) fluffy type‐A refractory inclusions were observed. Weathering of LEW85332 has resulted in the formation of 6.2 vol.% limonite; 3.9 vol.% metallic Fe‐Ni remains. The inferred original metallic Fe‐Ni abundance (13–15 wt.%) is very high for a carbonaceous chondrite and is most similar to those of Kainsaz and Colony (both CO3).

LEW85332 is a breccia: the one thin section we examined contains (a) ≥ 10 primitive carbonaceous chondrite clasts (with both C1 and C2 affinities) that contain magnetite framboids and platelets, (b) two clasts containing numerous 10‐μm‐size clusters of troilite grains, and (c) one clast containing small needles of schreibersite embedded in fine‐grained silicate matrix. The unique nature of LEW85332 underscores the wide diversity of materials produced in the solar nebula.
A possible new impact structure near Lac de la Presqu‘île, Québec, Canada
Authors: Higgins Michael , Tait Larry
Published: June 2012

Abstract— Lac de la Presqu'île is a sub‐circular lake, about 7 km in diameter with a prominent central peninsula. The shape of this lake and the occurrence of shatter cones to the east suggest that an impact created a crater with an original diameter of at least 12 km (Tait, 1990). Deep erosion of the structure suggests that it was formed in the distant past, at least several hundred million years ago.
Black ordinary chondrites: An analysis of abundance and fall frequency
Authors: Britt Daniel T. , Pieters Carle M.
Published: June 2012

Abstract— Black ordinary chondrite meteorites sample the spectral effects of shock on ordinary chondrite material in the space environment. Since shock is an important regolith process, these meteorites may provide insight into the spectral properties of the regoliths on ordinary chondrite parent bodies. To determine how common black chondrites are in the meteorite collection and, by analogy, the frequency of shock‐alteration in ordinary chondrites, several of the world's major meteorite collections were examined to identify black chondrites. Over 80% of all catalogued ordinary chondrites were examined and, using an optical definition, 61 black chondrites were identified. Black chondrites account for approximately 13.7% of ordinary chondrite falls. If the optically altered gas‐rich ordinary chondrites are included, the proportion of falls that exhibit some form of altered spectral properties increases to 16.7%. This suggests that optical alteration of asteroidal material in the space environment is a relatively common process.
The Sfax L6 chondrite: A new fall from Tunisia
Authors: Amouri M. , Ouazaa N. Laridhi , Michel‐Lévy M. Christophe , Rekhiss F.
Published: June 2012

Abstract— The Sfax meteorite fell on 16 October 1989. Four pieces totaling less than 10 kg were recovered from a much larger meteoroid, according to the cosmogenic gas measurements. It is an L6 chondrite, strongly degassed and shocked, with olivine of composition Fa24.
Impact melt rocks from New Quebec Crater, Quebec, Canada
Authors: Grieve Richard A. F. , Bottomley Richard B. , Bouchard Michel A. , Robertson P. Blyth , Orth Charles J. , Attrep Moses
Published: June 2012

Abstract— Approximately 1500 g of float samples of impact melt rocks have been recovered from gravel deposits ∼4 km north and northeast of the rim of the 3.4 km diameter New Quebec Crater (61°17′N; 73°40′W) in northern Quebec, Canada. Previously, only two small samples of impact melt rocks were known. The newly recovered samples have cryptocrystalline to microcrystalline matrices with microlites of andesine and pigeonite. Mineral clasts of quartz and feldspar occur and, in some cases, show shock metamorphic features. The melt rocks have a normative mineralogy corresponding to ∼70% quartz, orthoclase and albite and are compositionally similar. Their major element composition can be modeled as a mix of granitic gneisses that make up the target rocks. The melt rocks show enrichments, however, in Cr (21 ppm), Co (9 ppm), Ni (12 ppm) and Ir (1.5 ppb) over the target rocks. Interelement ratios suggest a chondritic impacting body, although they do not define a specific type. Assuming a C‐1 chondrite, the impact melt rocks average ∼2% meteoritic contamination. Stepwise 40Ar‐39Ar dating using a laser on three chips from three samples give integrated ages of 0.6–2.5 Ma. From the best plateau ages, the age of the New Quebec impact is taken to be 1.4 ± 0.1 Ma, which places it before the first major northern hemisphere continental glaciation of the Pleistocene. A number of considerations suggest that the impact melt rocks were originally deposited in fractures in the crater wall and later transported to their discovery site by glacial ice and melt water.
Thermal metamorphism of CI and CM carbonaceous chondrites: An internal heating model
Authors: Miyamoto M.
Published: June 2012

Abstract— Infrared diffuse reflectance spectra were measured for several thermally metamorphosed carbonaceous chondrites with CI‐CM affinities which were recently found from Antarctica. Compared with other CI or CM carbonaceous chondrites, these Antarctic carbonaceous chondrites show weaker absorption bands near 3 μm due to hydrous minerals, and weaker absorption bands near 6.9 μm due to carbonates, interpreted as thermal metamorphic features. These absorption bands also disappear in the spectra of samples of the Murchison (CM) carbonaceous chondrite heated above 500 °C, implying that the metamorphic temperatures of the Antarctic carbonaceous chondrites considered here were higher than about 500 °C. Model calculations were performed to study thermal metamorphism of carbonaceous chondrites in a parent body internally heated by the decay of the extinct nuclide 26Al. The maximum temperature of the interior of a body more than 20 km in radius is 500–700 °C for the bulk Al contents of CI and CM carbonaceous chondrites, assuming a ratio of 26Al/27Al = 5 × 10−6 which has been previously proposed for an ordinary‐chondrite parent body. The metamorphic temperatures experienced by the Antarctic carbonaceous chondrites considered here may be attainable by an internally heated body with an 26Al/27Al ratio similar to that inferred for an ordinary‐chondrite parent body.
Organic compounds in the Murchison and Allende carbonaceous chondrites studied by photoionization mass spectrometry
Authors: Tingle Tracy N. , Becker Christopher H. , Malhotra Ripudaman
Published: June 2012

Abstract— Organic compounds in the Murchison (C2M) and Allende (CV3) carbonaceous chondrites were analyzed by photoionization time‐of‐flight mass spectrometry; thermal (25–850 °C) and stimulated (7 keV Ar+) desorption were combined with either nonresonant single‐photon ionization using 118 nm light or resonantly enhanced multiphoton ionization (selective for aromatic compounds) using 266 nm light. Samples weighing only 1–10 mg were sufficient for sensitive quantitative analysis of aromatic compounds using thermal desorption. The detection limits for phenanthrene and pyrene using 118 nm light were determined to be 0.8 and 1.4 picomoles, respectively, and the concentrations of these compounds (including their isomers anthracene and fluoranthene) in the Murchison meteorite were determined to be 9 and 12 μg/g, respectively, in good agreement with previously published values. Thermal‐desorption (–75–500 °C) field‐ionization mass spectra (activated foil‐type ionizing source and magnetic sector mass analyzer) of 20–40 mg of the same meteorite material were obtained to verify that the 118 nm photoionization mass spectra were not affected by photofragmentation or photodecomposition and were representative of the organic material extracted by thermal desorption. Photoionization mass spectrometry is a useful technique for studying small quantities (< 1 nanomole) of organic matter in terrestrial and extraterrestrial samples. The present study aims to provide the background and analytical methods necessary for application to new and unsolved cosmochemical problems. Some potential applications are discussed.
Chondrite chronology by initial 87Sr/86Sr in phosphates?
Authors: Podosek Frank A. , Brannon Joyce C.
Published: June 2012

Abstract— We report Rb‐Sr analyses of phosphates from nine ordinary chondrites, more than doubling the number of meteorites for which such data are available. Ordinary chondrite phosphates characteristically have Rb/Sr ratios sufficiently low to permit accurate identification of initial 87Sr/86Sr, which is generally (but not in all cases) found to be significantly higher than the more primitive initial 87Sr/86Sr ratios inferred for carbonaceous chondrite refractory inclusions (ALL), basaltic achondrites (BABI), or bulk ordinary chondrites (in the ALL‐BABI range). Such elevation of initial 87Sr/86Sr is generally considered to reflect isotopic redistribution during metamorphism, and with a model for Rb/Sr in this environment can lead to an inferred metamorphic timescale. For whole rock Rb/Sr the inferred formation intervals are typically tens of Ma (range nil to > 100 Ma).

There is no evident relation between initial Sr elevation and metamorphic grade. There is not a clear difference in initial Sr effects between H and L chondrites; LL chondrites show much less (if any) elevation of initial Sr, but data are available for only two meteorites. For the first time it is possible to make a detailed comparison of initial Sr and I‐Xe chronologies for several meteorites: these two potential metamorphic chronometers conspicuously fail to agree, in terms of both age and sequence of ages. A comparably definitive assessment of the comparison between initial Sr and Pb‐Pb chronologies is not yet possible, but presently available data suggest that these two approaches to chondrite chronology also fail to agree. Without a correlation with metamorphic grade, or detailed agreement with an independent chronometer, it remains unclear whether initial 87Sr/86Sr in phosphates can be translated into a reliable chronometer for ordinary chondrite metamorphism, at least within simple interpretational frameworks.
Australites from Northern Australia
Authors: Fudali R. F. , Miller Andrew , Bevan A. W. R.
Published: June 2012

Abstract— Abundant tektites have been found in buried alluvial gravels at the south end of Lake Argyle in far northern Australia. The recovered tektites are unusual in that an astounding number are very large and 75% of those analyzed to date are HMg tektites, heretofore a very rare type in Australia. It is now clear that the paucity of tektites in northern Australia is due to the former high energy erosional environment rather than to crossing the strewnfield boundary, as has been previously suggested. The N‐S extent of the australite strewnfield encompasses the entire continent.