bluuebunny/crossref_metadata_2025_split huggingface dataset:
COMPLEX SHOCK‐INDUCED Fe‐Ni‐S‐Cr‐C MELTS IN THE HAIG (IIIA) IRON METEORITE
Authors: Bevan A.W.R. , Kinder J. , Axon H.J. 
Published: June 2012

The Haig (IIIA) iron meteorite material (BM 1968,280) in the Collection of the British Museum (Natural History) displays pre‐terrestrial shear deformation which transects a small troilite‐daubréelite‐cohenite nodule. Five globular areas (< 1 mm) with dendritic structures indicating rapid solidification from melts occur within and around the larger part of the transected nodule. All shock deformation structures and shock‐heating effects exhibited by Haig. are of pre‐terrestrial origin and at least four successive alterations to the original structure are evident.Partial bulk analyses of the melt globules indicate complex mixtures of approximately 55 wt % troilite, 24 wt % metal, 14 wt % daubréelite and 7 wt % cohenite. It is suggested that a compressive environment maintained the melts as discrete pools of liquid.The diameters of the globules (< 0.5 mm) and spacing of the dendrite arms (< 1 μm) indicate solidification at > 106 °C sec−1 which is the fastest cooling rate yet recorded in meteorites.
THE NOMENCLATURE OF POLYMICT BASALTIC ACHONDRITES
Authors: Delaney Jeremy S. , Takeda H. , Prinz M. , Nehru C.E. , Harlow G.E. 
Published: June 2012

The subgroups within the basaltic achondrite suite are defined using the structural criterion of Wahl (1952). The ‘monomict’ meteorites are samples of a single lithology while the polymict meteorites are those containing two or more lithologies. The ‘monomict’ subgroups eucrites, cumulate eucrites and diogenites are subdivided into both brecciated and unbrecciated meteorites. The polymict achondrites sample a petrological‐compositional continuum that contains both mafic and ultramafic rock types and may be subdivided into several groups. Two groups of polymict basaltic achondrites, the polymict eucrites and howardites are separated using an arbitrarily defined criterion. The recommended criterion is based on the amount of magnesian ortho‐pyroxenite (diogenite) component in the meteorite. Howardites contain more than 10% and polymict eucrites contain less than 10%.The criteria proposed (perhaps with minor variations), appear to reconcile the ambiguities caused by the polymict eucrites. These meteorites, using earlier structural criteria, are howardites, but using mineralogical‐chemical criteria are eucrites. As a subgroup of the polymict achondrites, their relationship with the howardites is clear, and the preservation of the term ‘eucrite’ in their name highlights their modal affinity to the monomict eucrites.
E‐CHONDRITES: SIGNIFICANCE OF THE PARTITION OF ELEMENTS BETWEEN ‘SILICATE’ AND ‘SULPHIDE’
Authors: Easton A.J. 
Published: June 2012

Bulk chemical analyses of six E‐chondrites (Daniel's kuil, Khairpur, Kota Kota, Saint‐Sauveur, South Oman and St Mark's) are given, together with partial analyses of a further five (Blithfield, Hvittis, Indarch, Jajh deh Kot Lalu and Pillistfer). The distribution of some normally lithophile elements (Al, Ca, Cr, K, Mg, Na, P and Ti) between silicate and sulphide groups of minerals was determined using the selective attack by dry chlorine (350°C) on magnetically separated fractions. Subdivision of the E‐chondrites into types I and II (Yavnel;, 1963; Anders, 1964) is accepted and it is shown using chemical data that St Mark's and Saint‐Sauveur should be included in type I.Sulphides contribute an unexpectedly high proportion of several elements to the bulk: e.g. Ca (av. 88.5% type I, 66.3% type II); Ti(av. 77.1% type I, 84.8% type II) and P as phosphide (av. 44.4% type I, > 83.2% type II). The proportion of Ti contributed to the bulk composition by the sulphides in types I and II increases with increae in ‘thermal metamorphic effect’ (Easton, 1983b) within each type.There is marked variability in the relative abundances of metal, phosphide, silicate and sulphide among the members of each type in keeping with their aggregate nature.The chemical composition of the ‘silicate’ and ‘sulphide’ in type IE‐chondrites differs from that in type II (e.g. CaO in the silicates, Mg in the bulk sulphides) which therefore precludes the isochemical evolution of all E‐chondrites from a common parent material. Partition of Ti between silicate and sulphide groups of minerals indicates that types I and II E‐chondrites originated in separate, chemically distinct bodies.
THE VERKHNE DNIEPROVSK IRON METEORITE SPECIMENS IN THE VIENNA COLLECTION AND THE CONFUSION OF VERKHNE DNIEPROVSK WITH AUGUSTINOVKA
Authors: Buchwald V.F. , Clarke Roy S. 
Published: June 2012

It is now a hundred years since a small amount of meteoritic material labelled Verkhne Dnieprovsk was first described. Since then the material has been controversial, due to the corroded character and the very limited amount of material known. Authentic samples, totalling 8 g, have been identified in the Vienna collection, which confirm that Verkhne Dnieprovsk is a unique meteorite, both in its composition, belonging to group II E, and in its heavily shocked and distorted structure. The shock‐produced structures include micromelts with a phosphorus gradient, suggesting that the melts originated in situ from mm‐sized schreibersite crystals.Unfortunately, no additional information as to location and circumstances of find was discovered at this late date. Further work will probably require field work and interviews on the site and/or studies of Russian archives.
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.
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.
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.
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.
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.
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.
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.
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.