bluuebunny/crossref_metadata_2025 huggingface dataset:
Laser probe argon‐40/argon‐39 dating of pseudotachylyte from the Sudbury Structure: Evidence for postimpact thermal overprinting in the North Range
Authors: THOMPSON Lucy M. , SPRAY John G. , KELLEY Simon P.
Published: February 2010

Abstract— Ten pseudotachylyte samples from the North Range of the 1850 Ma Sudbury impact structure have been analyzed by the 40Ar/39Ar laser spot fusion method. Field and petrological evidence indicate that the pseudotachylytes were formed at 1850 Ma by comminution and frictional melting due to impact‐induced faulting. The cryptocrystalline to microcrystalline grain size (<30 μm) of the pseudotachylyte matrices and the predominance of orthoclase as the main K‐bearing phase, have rendered the rocks particularly susceptible to Ar loss. The age determinations range from ∼1850 to ∼1000 Ma, with some samples yielding multiple ages that cannot be correlated with known geological events in the area. However, if the finite‐difference algorithm of Wheeler (1996) is used to calculate combined Ar loss and the accumulation of radiogenic Ar for the K‐bearing phases, it is possible to reproduce the range of observed ages. The model infers that the long‐term volume diffusion of Ar has occurred and that, as a result, the Ar system cannot be treated with a conventional closure temperature approach. The algorithm requires burial of the impact structure to 5–6 km depth and 160–180 °C at 1850 Ma, followed by exhumation at ∼1000 Ma. These ages may be equated with two events: Penokean thin‐skinned overthrusting in the North Range, immediately following impact, and exhumation ∼850 Ma later, coincident with the Grenville orogeny to the southeast. The results suggest that, contrary to previously accepted paradigms, the North Range has been affected by a protracted period of postimpact, low‐grade thermal metamorphism. If these events also involved tectonic shortening within the North Range (as has been documented for the South Range), then the original size of the Sudbury impact structure has been underestimated.
Could G‐class asteroids be the parent bodies of the CM chondrites?
Authors: BURBINE THOMAS H.
Published: February 2010

Abstract— I review the dynamical and compositional evidence for possibly linking CM chondrites and asteroids having G‐class taxonomic designations. Three G asteroids have been identified through previous theoretical studies as being likely meteorite source bodies due to their locations near resonances. Two of these objects, 19 Fortuna and 13 Egeria, have spectral properties that are consistent with such a linkage with CM chondrites. Fortuna has a similar strength 0.7 μm absorption feature and near‐infrared spectral slope to CM chondrites but a weaker ultraviolet feature. Egeria also has the characteristic 0.7 μm feature of CM chondrite spectra but does not match as well in the near‐infrared. However, since the 0.7 μm feature is apparent in the spectra of approximately one‐half of measured C‐type asteroids, no definitive statement about any linkages can be made. Ceres is spectrally different from known meteorites in the 3 μm wavelength region and cannot be convincingly linked with any meteorite group.
A nitrogen and argon stable isotope study of Allan Hills 84001: Implications for the evolution of the Martian atmosphere
Authors: GRADY MONICA M. , WRIGHT IAN P. , PILLINGER COLIN T.
Published: February 2010

Abstract— The abundances and isotopic compositions of N and Ar have been measured by stepped combustion of the Allan Hills 84001 (ALH 84001) Martian orthopyroxenite. Material described as shocked is N‐poor ([N] ∼ 0.34 ppm; δ15N ∼ +23%); although during stepped combustion, 15N‐enriched N (δ15N ∼ +143%) is released in a narrow temperature interval between 700 °C and 800 °C (along with 13C‐enriched C (δ13C ∼ +19%) and 40Ar). Cosmogenic species are found to be negligible at this temperature; thus, the iso‐topically heavy component is identified, in part, as Martian atmospheric gas trapped relatively recently in the history of ALH 84001. The N and Ar data show that ALH 84001 contains species from the Martian lithosphere, a component interpreted as ancient trapped atmosphere (in addition to the modern atmospheric species), and excess 40Ar from K decay. Deconvolution of radiogenic 40Ar from other Ar components, on the basis of end‐member 36Ar/14N and 40Ar/36Ar ratios, has enabled calculation of a K‐Ar age for ALH 84001 as 3.5–4.6 Ga, depending on assumed K abundance. If the component believed to be Martian palaeoatmos‐phere was introduced to ALH 84001 at the time the K‐Ar age was set, then the composition of the atmosphere at this time is constrained to: δ15N ≥ +200%, 40Ar/36Ar ≤ 300 and 36Ar/14N ≥ 17 × 10−5. In terms of the petrogenetic history of the meteorite, ALH 84001 crystallised soon after differentiation of the planet, may have been shocked and thermally metamorphosed in an early period of bombardment, and then subjected to a second event. This later process did not reset the K‐Ar system but perhaps was responsible for introducing (recent) atmospheric gases into ALH 84001; and it might mark the time at which ALH 84001 suffered fluid alteration resulting in the formation of the plagioclase and carbonate mineral assemblages.
Survival strategies for microorganisms in hypersaline environments and their relevance to life on early Mars
Authors: LITCHFIELD CAROL D.
Published: February 2010

Abstract— There are two groups of microorganisms that live and grow in hypersaline (>10–15% NaCl) environments: the halophilic Archaea and the halotolerant Bacteria and algae. In order to grow and reproduce in such high‐salt, low‐water activity environments, these organisms have made basic biochemical adaptations in their proteins, osmoregulation mechanisms, nucleic acids, and lipids. The environment of the halophiles and especially how the halophilic Archaea have adapted to that environment are reviewed in this paper. Along with this review is a brief description of how these adaptations could be important in the detection of life on early Mars assuming similar types of salts and a carbon‐based life.
Reevaluation of formation of metal nodules in ordinary chondrites
Authors: KONG PING , EBIHARA MITSURU , XIE XIANDE
Published: February 2010

Abstract— Compositions of four metal nodules from two ordinary chondrites, WIS91627 (H3.7) and Juin (H5), were determined by instrumental and radiochemical neutron activation analyses. Compared with bulk metal fractions, the metal nodules are characterized by strong and variable depletion of the refractory siderophile elements Re, Os, Ir, Ru, Pt and Rh but normal W and Mo, some fractionation of Co from Ni, and low Cu concentrations. These characteristics are difficult to explain by shock‐induced vaporization followed by fractional condensation, a mechanism suggested by Widom et al. (1986). We propose formation of metal nodules during metamorphism in the parent body. Refractory siderophile elements, such as Ir, Os, Rh, etc., are partly locked up in noble metal nuggets and cannot participate in kamacite formation. The occurrence of metal nodules in both equilibrated and unequilibrated ordinary chondrites suggests that diffusion along grain boundaries was important in the development of kamacite and taenite in ordinary chondrites.
The oxygen isotopic properties of olivines in the Semarkona ordinary chondrite
Authors: SEARS DEREK W. G. , LYON IAN , SAXTON JOHN , TURNER GRENVILLE
Published: February 2010

Abstract— In order to explore the origin of chondrules and the chondrites, the O isotopic compositions of nine olivine grains in seven chondrules from the primitive Semarkona LL3.0 chondrite have been determined by ion microprobe. The data plot in the same general region of the three‐isotope plot as whole‐chondrule samples from ordinary chondrites previously measured by other techniques. There are no significant differences between the O isotopic properties of olivine in the various chondrule groups in the present study, but there is a slight indication that the data plot at the 16O‐rich end of the ordinary chondrite field. This might suggest that the mesostasis contains isotopically heavy O. The olivines in the present study have O isotopic compositions unlike the 16O‐rich olivine grains from the Julesburg ordinary chondrite. Even though olivines in group A chondrules have several properties in common with them, the 16O‐rich Julesburg olivines previously reported are not simply olivines from group A chondrules.
Near‐infrared reflectance spectra from bulk samples of the two Martian meteorites Zagami and Nakhla
Authors: SCHADE Ulrich , WÄSCH Richard
Published: February 2010

Abstract— Zagami and Nakhla are achondrites and belong to the Shergotty‐Nakhla‐Chassigny (SNC) meteorite group. It is generally accepted that Mars is their parent body. Mineralogical and chemical analyses have revealed that the major mineral phases of these two meteorites are pyroxene, olivine, maskelynite, and plagioclase. In this work, near‐infrared biconical reflectance measurements were performed on sawed surfaces of chips from Zagami and Nakhla. Spectra obtained with an analytical spot diameter on the order of the mineral grain size reflect the heterogeneous distribution of different mineral phases. The characteristic absorption bands of the pyroxenes are numerically evaluated in terms of the modified Gaussian model. Spectra with overlapping absorption features are resolved into the basic absorption bands. From these results, it can be estimated what kind of clinopyroxenes belong to the investigated mineral assemblages. As a result, the major clinopyroxene phase in Nakhla is Ca‐rich augite, whereas in Zagami both Ca‐rich and Ca‐poor pyroxenes are present. By means of such a procedure, laboratory spectra of minerals become more informative and may help in discussing Martian remote sensing data in the near‐infrared region.
Carbonate‐silicate liquid immiscibility upon impact melting: Ries Crater, Germany
Authors: GRAUP Günther
Published: February 2010

Abstract— The 24 km diameter Ries impact crater in southern Germany is one of the most studied impact structures on Earth. The Ries impactor struck a Triassic to Upper Jurassic sedimentary sequence overlying Hercynian crystalline basement. At the time of impact (14.87 × 0.36 Ma; Storzer et al., 1995), the 350 m thick Malm limestone was present only to the south and east of the impact site. To the north and west, the Malm had been eroded away, exposing the underlying Dogger and Lias. The largest proportion of shocked target material is in the impact‐melt‐bearing breccia suevite. The suevite had been believed to be derived entirely from the crystalline basement. Calcite in the suevite has been interpreted as a postimpact hydrothermal deposit.

From optical inspection of 540 thin sections of suevite from 32 sites, I find that calcite in the suevite shows textural evidence of liquid immiscibility with the silicate impact melt. Textural evidence of liquid immiscibility between silicate and carbonate melt in the Ries suevite includes carbonate globules within silicate glass, silicate globules embedded in carbonate, deformable and coalescing carbonate spheres within silicate glass, sharp menisci or cusps and budding between silicate and carbonate melt, fluidal textures and gas vesicles in carbonate schlieren, a quench crystallization sequence of the carbonate, spinifex textured quenched carbonate, separate carbonate spherules in the suevite mineral‐fragment matrix, and inclusions of mineral fragments suspended in carbonate blebs. Given this evidence of liquid immiscibility, the carbonate in the suevite therefore has—like the silicate melt—a primary origin by impact‐shock melting.

Evidence of carbonate‐silicate liquid immiscibility is abundant in the suevites from the southwest to east of the Ries crater. The rarer suevites to the west to northeast of the crater are nearly devoid of carbonate melts. This correspondence between the occurrence of outcropping limestones at the target surface and the formation of carbonate melt indicates that the Malm limestones are the source rocks of the carbonate impact melt. This correspondence shows that the suevites preserve a compositional memory of their source rocks. From the regional distribution of suevites with or without immiscible carbonate melts, it is inferred that the Ries impactor hit the steep Albtrauf escarpment at its toe, in an oblique impact from the north.
Laboratory simulation of the physical processes occurring on and near the surfaces of comet nuclei
Authors: SEARS Derek W. G. , KOCHAN Hermann W. , HUEBNER Walter F.
Published: February 2010

Abstract— Laboratory comet simulation experiments are discussed in the context of theoretical models and recent ground‐based and spacecraft observations, especially the Giotto observations of P/Halley. The set‐up of various comet simulation experiments is reviewed. A number of small‐scale experiments have been performed in many laboratories since the early 1960s. However, the largest and most ambitious series of experiments were the comet simulation experiments known as KOSI (German = Kometen Simulation). These experiments were prompted by the appearance of Comet P/Halley in 1986 and in planning for the European Space Agency's Rossetta mission that was originally scheduled to return samples. They were performed between 1987 and 1993 using the German Space Agency's (DLR) space hardware testing facilities in Cologne. As with attempts to reproduce any natural phenomenon in the laboratory, there are deficiencies in such experiments while there are major new insights to be gained. Simulation experiments have enabled the development of methods for making comet analogues and for exploring the properties of such materials in detail. These experiments have provided new insights into the morphology and physical behavior of aggregates formed from silicate grains likely to exist in comets. Formation of a dust mantle on the surfaces and a system of ice layers below the mantle caused by chemical differentiation have been identified after the insolation of the artificial comet. The mechanisms for heat transfer between the comet's surface and its interior, the associated gas diffusion from the interior of the surface, and compositional, structural, and isotopic changes that occur near the surface have been described by modeling the experimental results. The mechanisms of the ejection of dust and ice grains from the surface and the importance of gas‐drag in propelling grains have also been explored.
An interdisciplinary study of weathering effects in ordinary chondrites from the Acfer region, Algeria
Authors: STELZNER TH. , HEIDE K. , BISCHOFF A. , WEBER D. , SCHERER P. , SCHULTZ L. , HAPPEL M. , SCHRÖN W. , NEUPERT U. , MICHEL R. , CLAYTON R. N. , MAYEDA T. K. , BONANI G. , HAIDAS I. , IVY‐OCHS S. , SUTER M.
Published: February 2010

Abstract— Weathering effects on meteorite finds from the Acfer region were studied by various analytical techniques and in dependence on the depth of sampling. In thin sections of weathered meteorites, weathering effects usually decrease from the outside to the interior of the meteorite. The results of evolved gas analysis indicate that variation in weathering between surface and core is not significant in respect to the formation of Fe‐oxyhydroxides. The secondary alteration effects in the noble gases are distributed unevenly throughout the specimens, as seen in the nonsystematic differences observed for the heavy noble gases. Chemical analyses show significant enrichment of Ba and Sr in the outer parts of the weathered samples due to element contamination through aqueous solution. Iron, Ni, and Co are partly flushed from the system as the metal oxidation proceeds. Oxygen isotopes show increases in δ18O and δ17O with increasing terrestrial age. For a set of H3 chondrites, the degree of weathering determined from the water content was correlated with terrestrial ages and is discussed with respect to possible weathering mechanisms.
Petrology of unique achondrite Queen Alexandra Range 93148: A piece of the pallasite (howardite‐eucrite‐diogenite?) parent body?
Authors: GOODRICH Cyrena Anne , RIGHTER Kevin
Published: February 2010

Abstract— Queen Alexandra Range (QUE) 93148 is a small (1.1 g) olivine‐rich achondrite (mg 86) that contains variable amounts of orthopyroxene (mg 87) and kamacite (6.7 wt% Ni), with minor augite. Olivine in QUE 93148 contains an unusual suite of inclusions: (1) 5 × 100 μm sized lamellae with a CaO‐ and Cr2O3‐rich (∼10 and 22 wt%, respectively) composition that may represent a submicrometer‐scale intergrowth of chromite and pyroxene(s); (2) 75 × 500 μm sized lamellar symplectites composed of chromite and two pyroxenes, with minor metal; (3) 15–20 μm sized, irregularly‐shaped symplectites composed of chromite and pyroxene(s); (4) 100–150 μm sized, elliptical inclusions composed of chromite, two pyroxenes, metal, troilite, and rare whitlockite. Type 1, 2, and 3 inclusions probably formed by exsolution from the host olivine during slow cooling, whereas type 4 more likely resulted from early entrapment of silicate and metallic melts followed by closed‐system oxidation.

Queen Alexandra Range 93148 can be distinguished from most other olivine‐rich achondrites (ureilites, winonaites, lodranites, acapulcoites, brachinites, Eagle‐Station‐type pallasites, and pyroxene pallasites), as well as from mesosiderites, by some or all of the following properties: O‐isotopic composition, Fe‐Mn‐Mg relations of olivine, CaO and Cr2O3 contents of olivine, orthopyroxene compositions, molar Cr/(Cr + Al) ratios of chromite, metal composition, texture, and the presence of the inclusions. In terms of many of these properties, it shows an affinity to main‐group pallasites. Nevertheless, it cannot be identified as belonging to this group. Meteorite QUE 93148 appears to be a unique achondrite. Possibly it should be considered to be a pyroxene pallasite that is genetically related to main‐group pallasites. Alternatively, it may be derived from the mantle of the pallasite (howardite‐eucrite‐diogenite?) parent body.
Shock experiments with the H6 chondrite Kernouvé: Pressure calibration of microscopic shock effects
Authors: SCHMITT R. T.
Published: February 2010

Abstract—Shock‐recovery experiments were carried out on samples of the H6 chondrite Kernouvé at shock pressures of 10, 15, 20, 25, 30, 35, 45, and 60 GPa and preheating temperatures of 293 K (low‐temperature experiments) and 920 K (high‐temperature experiments). Using a calculated equation of state of Kernouvé, pressure‐pulse durations of 0.3 to 1.2 μs were estimated. The shocked samples were investigated by optical microscopy to calibrate the various shock effects in olivine, orthopyroxene, oligoclase, and troilite.

The following pressure calibration is proposed for silicates: (1) undulatory extinction of olivine <GPa; (2) weak mosaicism of olivine from 10–15 GPa to 20–25 GPa; (3) onset of strong mosaicism of olivine at 20–25 GPa; (4) transformation of oligoclase to diaplectic glass completed at 25–30 GPa (low‐temperature experiments) and at 20–25 GPa (high‐temperature experiments); (5) onset of weak mosaicism in orthopyroxene at 30–35 GPa (low‐temperature experiments) and at 25–30 GPa (high‐temperature experiments); and (6) recrystallization or melting of olivine starting at 45–60 GPa (low‐temperature experiments) and at 35–45 GPa (high‐temperature experiments), and completed above 45–60 GPa in the high‐temperature experiments.

Troilite displays distinct differences between the samples shocked at low and high temperatures. In the low‐temperature experiments, the following effects can be observed in troilite: (1) undulatory extinction up to 25 GPa, (2) twinning up to 45 GPa, (3) partial recrystallization from 30 to 60 GPa, and (4) complete recrystallization >35 GPa; whereas in the high‐temperature experiments, troilite shows (1) complete recrystallization from 10 up to 45 GPa and (2) melting and crystallization above 45 GPa.

Localized shock‐induced melting is observed in samples shocked to pressures >15 GPa in the high‐temperature experiments and >30 GPa for the low‐temperature experiments in the form of FeNi metal and troilite melt injections and intergrowths and as pockets and veins of whole‐rock melt. Obviously, the onset and abundance of shock‐induced localized melting strongly depends on the initial temperature of the sample.
A nitrogen isotope study of bencubbinites
Authors: SUGIURA N. , ZASHU S. , WEISBERG M. , PRINZ M.
Published: February 2010

Abstract— ‐Nitrogen‐isotopic compositions of the bencubbinites—Bencubbin, Hammadah al Hamra (HH) 237, and Queen Alexandra Range (QUE) 94411—and in a petrographically similar chondrite Grosvenor Mountains (GRO) 95551 were measured by stepped‐combustion static mass spectrometry. Hammadah al Hamra 237 and QUE 94411 contain isotopically heavy N, but not as heavy as that in Bencubbin or Weatherford. Grosvenor Mountains 95551 contains isotopically near‐normal N and light N and, hence, it is not related to the bencubbinites, which is also indicated by its O‐isotopic composition. The N carriers in these meteorites were investigated using secondary ion mass spectrometry. In the bencubbinites, N is mostly located around sulfide in metal clasts and in impact‐melt areas. The N carriers in the former are taenite, carbide, or both; whereas those in the latter are molten metal, tiny graphitic carbon in metal, oxi‐nitride glass, or both. In the various N carriers, N is isotopically equilibrated, and therefore the carriers are not pristine presolar grains. Isotopically near‐normal N in GRO 95551 is located in graphite. The carrier of isotopically light N in GRO 95551 has not been found.
Correlation between crystallographic structure and infrared spectra of silicon oxide films containing iron or magnesium atoms
Authors: SUZUKI N. , KIMURA S. , NAKADA T. , KAITO C. , SAITO Y. , KOIKE C.
Published: February 2010

Abstract— Films condensed from vapors containing SiO, Fe, or Mg showed an amorphous structure. Infrared (IR) spectra and electron microscopic characterization have been carried out on these films. After the heat treatment of these films in air, IR peaks at approximately 18–23 μm appeared, in addition to peaks attributable to SiO2. These peaks can be attributed to metallic oxides such as FeO, Fe2O3, and MgO. It can be concluded that Fe‐ or Mg‐bearing silicate minerals cannot be produced by the rapid cooling of SiO, Fe, or Mg vapors. Although IR spectra of FeO have been discussed in order to match some spectra obtained with the Infrared Space Observatory, the identification of FeO as the impurity would be very important because the IR spectra of FeO grains are very dependent on the shape and size of the grains. These impurities can also influence the IR spectral feature of SiO2.
Investigations into an unknown organism on the martian meteorite Allan Hills 84001
Authors: Steele Andrew , Goddard David t. , Stapleton Dave , Toporski Jan k. w. , Peters Vanessa , Bassinger Virginia , Sharples George , Wynn‐Williams David d. , Mckay David s.
Published: February 2010

Abstract— Examination of fracture surfaces near the fusion crust of the martian meteorite Allan Hills (ALH) 84001 have been conducted using scanning electron microscopy (SEM) and atomic force microscopy (AFM) and has revealed structures strongly resembling mycelium. These structures were compared with similar structures found in Antarctic cryptoendolithic communities. On morphology alone, we conclude that these features are not only terrestrial in origin but probably belong to a member of the Actinomycetales, which we consider was introduced during the Antarctic residency of this meteorite. If true, this is the first documented account of terrestrial microbial activity within a meteorite from the Antarctic blue ice fields. These structures, however, do not bear any resemblance to those postulated to be martian biota, although they are a probable source of the organic contaminants previously reported in this meteorite.
Micro Raman spectroscopy of amphiboles and pyroxenes in the martian meteorites Zagami and Lewis Cliff 88516
Authors: MIKOUCHI Takashi , MIYAMOTO Masamichi
Published: February 2010

Abstract— We studied micro Raman spectroscopy of amphiboles and pyroxenes in the martian meteorites Zagami and Lewis Cliff (LEW) 88516. The obtained Raman spectra of the amphiboles are similar to those of kaersutite, reconfirming the previous studies that they are kaersutitic amphiboles enriched in Ca, Al, and Ti. Even though actinolite belongs to the same amphibole group (calcic amphibole) as kaersutite, the Raman spectra of terrestrial actinolite are distinct from those of kaersutite, probably reflecting complex amphibole crystal structures. The Al‐Ti‐rich pyroxene observed in the magmatic inclusions within LEW 88516 olivine is compositionally similar to kaersutite but shows Raman spectra nearly identical to the regular pyroxene rather than amphibole. In contrast to amphibole, this will be due to relatively simple crystal structures of pyroxene. Thus, the Raman spectra of Al‐Ti‐rich phases in the martian meteorites are distinct between kaersutite and Al‐Ti‐rich pyroxene, and this study demonstrates that micro Raman spectroscopy is one of the best tools to perform mineralogical characterization of mineral phases in martian meteorites.
Mössbauer spectroscopic studies of the Piplia Kalan (eucrite) and Lohawat (howardite) meteorites
Authors: TRIPATHI R. P. , SHARMA S. K. , SHRIVASTAVA K. L. , VERMA H. C.
Published: February 2010

Abstract—Two meteorites belonging to the howardite‐eucrite‐diogenite (HED) group fell recently in Rajasthan, India. One of these, Piplia Kalan, was classified as a eucrite and the other, Lohawat, as a howardite. In this study, we present the results of Mössbauer spectroscopic investigations of these two meteorites. We also compare the results with the Mössbauer experiments reported for the Kapoeta howardite and look for systematics in the Mössbauer spectra of HED meteorites.
Description of new shock‐induced phases in the Shergotty, Zagami, Nakhla and Chassigny meteorites
Authors: Malavergne Valérie , Guyot François , Benzerara Karim , Martinez Isabelle
Published: February 2010

Abstract— The Shergottite, Nakhlite and Chassignite (SNC) meteorites, Shergotty, Zagami, Nakhla and Chassigny, have been studied by analytical transmission electron microscopy. New phases, characteristic of strong shock conditions, have been discovered: calcium‐rich majorites in Shergottty, wadsleyite with anomalously elevated iron content in Chassigny, and impact melts in Shergotty, Zagami and Nakhla. Cristobalites (α and β polymorphs) observed in Shergotty and Zagami may also be related to shock and are interpreted as back transformation products of post‐stishovite silica polymorphs. Shocks corresponding to pressure and temperature conditions characteristic of the Earth's transition zone and lower mantle have occurred in those meteorites. Moreover, impact melts indicate high‐temperature conditions in localized areas. On the other hand, no massive impact melting is observed in those meteorites, consistent with previous descriptions. These observations provide evidence of highly heterogeneous shock conditions at the scale of few micrometers in these meteorites. Strongly heterogeneous conditions such as those suggested by the present study may help to explain the preservation in martian meteorites of phases practically unaffected by shock being very close to strongly shock‐metamorphized minerals.
Ecological catastrophe in connection with the impact of the Kaali meteorite about 800–400 B.C. on the island of Saaremaa, Estonia
Authors: Veski Siim , Heinsalu Atko , Kirsimäe Kalle , Poska Anneli , Saarse Leili
Published: February 2010

Abstract—A sequence of peat enriched with impact ejecta (allochthonous minerals and iridium) from Piila bog, 6 km away from the Kaali impact crater (island of Saaremaa, Estonia), was examined using pollen, radiocarbon, loss‐on‐ignition, and x‐ray diffraction analyses to date and assess the environmental effect of the impact. The vegetation in the surroundings of the Piila bog before the Kaali impact was a fen surrounded by forest in natural conditions. Significant changes occur in pollen accumulation and composition of pollen in the depth interval 170–178 cm, which contains above background values of iridium (up to 0.53 ppb). Two samples from the basal silt layer inside the main crater at Kaali contain 0.8 ppb of iridium, showing that iridium was present in the impact ejecta. The impact explosion swept the surroundings clean of forest shown by the threefold decrease in the total pollen influx (especially tree pollen influx), increase in influx and diversity of herb taxa, and the relative dominance of pine. Increased input of mineral matter measured by loss‐on‐ignition and the composition mineral matter (increased input of allochthonous minerals) together with an extensive layer of charcoal and wood stumps in Piila bog at the same depth interval points to an ecological catastrophe, with local impact‐induced wildfires reaching at least 6 km northwest of the epicenter. The disappearance of cereals in the pollen record suggests that farming, cultivation and possibly human habitation in the region ceased for a period of ∼100 years. The meteorite explosion at Kaali ranged between the effects of Hiroshima and Tunguska. The age of the Kaali impact event is placed between 800–100 B.C. based on radiocarbon dating of the peat enriched with impact ejecta in the Piila bog.
The Lohawat howardite: Mineralogy, chemistry and cosmogenic effects
Authors: Sisodia M. S. , Shukla A. D. , Suthar K. M. , Mahajan R. R. , Murty S. V. S. , Shukla P. N. , Bhandari N. , Natarajan R.
Published: February 2010

Abstract—The Lohawat meteorite is a texturally heterogeneous breccia having a variety of mineral and lithic fragments. Among mineral fragments, pyroxenes show a wide range of composition (Wo0.011–0.17En0.37–0.78Fs0.21–0.60) whereas plagioclase is anorthitic (An0.92Ab0.07Or0.007). Abundant rounded “chondrule‐like” objects ranging in size up to ∼7 mm, some with concentric layering, have been observed. Petrographic features, trace element composition and rare earth element patterns show the presence of eucritic and diogenitic components confirming that it is a typical howardite. Cosmogenic tracks, rare gases (He, Ne, and Ar) and radionuclides (22Na and26Al) were measured. Track density in olivine and plagioclase varies between 0.7 to 6 times 106/cm2.38Ar exposure age is estimated to be ∼110 Ma, being the highest among howardites. The track production rates correspond to ablation of 9 to 15 cm, implying a radius for its preatmospheric size of ∼27 cm.22Na/26Al ∼ 1, as expected from the production models and solar modulation of galactic cosmic‐ray fluxes before its fall, suggesting that the meteoroid did not undergo any fragmentation during the past ∼2 Ma in interplanetary space. The radiogenic age based on K‐Ar method is 4.3 Ga while the U‐Th‐4He age is 3.3 Ga indicating partial loss of He.
The composition of 433 Eros: A mineralogical—chemical synthesis
Authors: McCoy T. J. , Burbine T. H. , Mcfadden L. A. , Starr R. D. , Gaffey M. J. , Nittler L. R. , Evans L. G. , Izenberg N. , Lucey P. G. , Trombka J. I. , Bell J. F. , Clark B. E. , Clark P. E. , Squyres S. W. , Chapman C. R. , Boynton W. V. , Veverka J.
Published: February 2010

Abstract— The near‐Earth asteroid rendezvous (NEAR) mission carried x‐ray/gamma‐ray spectrometers and multi‐spectral imager/near‐infrared spectrometer instrument packages which gave complementary information on the chemistry and mineralogy, respectively, of the target asteroid 433 Eros. Synthesis of these two data sets provides information not available from either alone, including the abundance of non‐mafic silicates, metal and sulfide minerals. We have utilized four techniques to synthesize these data sets. Venn diagrams, which examine overlapping features in two data sets, suggest that the best match for 433 Eros is an ordinary chondrite, altered at the surface of the asteroid, or perhaps a primitive achondrite derived from material mineralogically similar to these chondrites. Normalized element distributions preclude FeO‐rich pyroxenes and suggest that the x‐ray and gamma‐ray data can be reconciled with a common silicate mineralogy by inclusion of varying amounts of metal. Normative mineralogy cannot be applied to these data sets owing to uncertainties in oxygen abundance and lack of any constraints on the abundance of sodium. Matrix inversion for simultaneous solution of mineral abundances yields reasonable results for the x‐ray‐derived bulk composition, but seems to confirm the inconsistency between mineral compositions and orthopyroxene/clinopyroxene ratios. A unique solution does not seem possible in synthesizing these multiple data sets. Future missions including a lander to fully characterize regolith distribution and sample return would resolve the types of problems faced in synthesizing the NEAR data.
Radar constraints on asteroid regolith properties using 433 Eros as ground truth
Authors: Magri Christopher , Consolmagno Guy J. , Ostrch Steven J. , Benner Lance A. M. , Beeney Brett R.
Published: February 2010

Abstract— Radar data enable us to estimate an asteroid's near‐surface bulk density, thus providing a joint constraint on near‐surface porosity and solid density. We investigate two different approaches to simplifying this joint constraint: estimating solid densities by assuming uniform porosities for all asteroids; and estimating porosities by assuming uniform mineralogy within each taxonomic class. Methods used to estimate asteroids' near‐surface solid densities from radar data have not previously been calibrated via independent estimates. Recent spacecraft results on the chondritic nature of 433 Eros now permit such a check, and also support porosity estimation for S‐class objects.

We use radar albedos and polarization ratios estimated for 36 main‐belt asteroids and nine near‐Earth asteroids to estimate near‐surface solid densities using two methods, one of which is similar to the uncalibrated algorithms used in previous studies, the other of which treats Eros as a calibrator. We also derive porosities for the same sample by assigning solid densities for each taxonomic class in advance. Density‐estimation results obtained for Eros itself are consistent with the uncalibrated method being valid in the mean; those derived for the full sample imply that uncalibrated solid densities are, at most, a few tens of percent too large on average. However, some derived densities are extremely low, whereas most porosity estimates are physically plausible. We discuss the relative merits of these two approaches.
Iron isotopes in chondrules: Implications for the role of evaporation during chondrule formation
Authors: ALEXANDER C. M. O'D. , WANG J.
Published: February 2010

Abstract— We have measured the δ57Fe of olivines in nine Chainpur chondrules. All are within error of normal (typically 2σ ≤ 1–2%0). Most of the chondules could not have lost more than ∼20% of their FeO by Rayleigh evaporation and none can have lost more than ∼61%. Yet, the range of Fo contents in these chondrules is Fo78–99.9. The isotopic compositions of the chondrules clearly demonstrate that, for instance, type I chondrules cannot form from type II chondrules by evaporation of FeO under Rayleigh conditions. The isotopic compositions also place constraints on the minimum cooling rates these chondrules could have experienced. These cooling rates must also be equal to or slower than those required to produce the chondrule textures. Assuming flash heating and evaporation rates like those measured in vacuum, the minimum cooling rates necessary to prevent detectable Fe isotopic fractionation via Rayleigh evaporation approach those needed to produce barred and porphyritic textures. The presence of hydrogen in the nebula, non‐linear cooling and other effects will all tend to increase the cooling rates required to prevent δ57Fe > 1–2%0, perhaps by as much as 1–2 orders of magnitude. The two most likely ways that the cooling rates required to prevent δ57Fe >1–2%0 can be kept below those needed to produce barred and porphyritic textures are (1) the pH2 in the nebula was low enough to keep evaporation rates close to those in vacuum, or (2) back reaction of chondrules with Fe in the gas suppressed isotopic fractionation.
Exposure history of separated phases from the Kapoeta meteorite
Authors: CAFFEE Marc W. , NISHIIZUMI Kunihiko
Published: February 2010

Abstract— The cosmogenic radionuclides, 10Be, 26Al, 36Cl, and 53Mn were measured in selected clasts and matrix samples from the howardite Kapoeta. Previous measurements of cosmogenic 21Ne indicate higher cosmic‐ray exposure ages for bulk samples than for some separated clasts or mineral separates. A possible interpretation for this difference in apparent exposure ages is a complex recent exposure history for Kapoeta. In this scenario some constituents are exposed to cosmic rays in a 2π geometry as part of a larger body immediately preceding its 4π exposure in a smaller body. To test this scenario we measured cosmogenic radionuclides in several clasts from Kapoeta. These measurements are consistent with a simple single‐stage 4π exposure history during which the entire inventory of cosmogenic radionuclides was produced. Taken together, these data are most consistent with a single‐stage 4π exposure lasting ∼3 Ma. This scenario is nevertheless consistent with models in which the exposure of some constituents of Kapoeta to energetic particles occurred at an earlier time, as is indicated by 21Ne measurements. However, from our data we conclude that insubstantial quantities of cosmogenic radionuclides were inherited from this earlier irradiation; this earlier exposure to energetic particles must have predated the recent exposure by at least ∼10 Ma to allow for the decay of the long half‐life cosmogenic radionuclides.
Mineralogy and petrography of amoeboid olivine aggregates from the reduced CV3 chondrites Efremovka, Leoville and Vigarano: Products of nebular condensation, accretion and annealing
Authors: KOMATSU Mutsumi , KROT Alexander N. , PETAEV Mikhail I. , ULYANOV Alexander A. , KEIL Klaus , MIYAMOTO Masamichi
Published: February 2010

Abstract— Amoeboid olivine aggregates (AOAs) from the reduced CV chondrites Efremovka, Leoville and Vigarano are irregularly‐shaped objects, up to 5 mm in size, composed of forsteritic olivine (Fa<10) and a refractory, Ca, Al‐rich component. The AOAs are depleted in moderately volatile elements (Mn, Cr, Na, K), Fe, Ni‐metal and sulfides and contain no low‐Ca pyroxene. The refractory component consists of fine‐grained calcium‐aluminum‐rich inclusions (CAIs) composed of Al‐diopside, anorthite (An100), and magnesium‐rich spinel (∼1 wt% FeO) or fine‐grained intergrowths of these minerals; secondary nepheline and sodalite are very minor. This indicates that AOAs from the reduced CV chondrites are more pristine than those from the oxidized CV chondrites Allende and Mokoia. Although AOAs from the reduced CV chondrites show evidence for high‐temperature nebular annealing (e.g., forsterite grain boundaries form 120° triple junctions) and possibly a minor degree of melting of Al‐diopside‐anorthite materials, none of the AOAs studied appear to have experienced extensive (>50%) melting. We infer that AOAs are aggregates of high‐temperature nebular condensates, which formed in CAI‐forming regions, and that they were absent from chondrule‐forming regions at the time of chondrule formation. The absence of low‐Ca pyroxene and depletion in moderately volatile elements (Mn, Cr, Na, K) suggest that AOAs were either removed from CAI‐forming regions prior to condensation of these elements and low‐Ca pyroxene or gas‐solid condensation of low‐Ca‐pyroxene was kinetically inhibited.
Comment on “Origin of a late Eocene to pre‐Miocene buried crater and breccia lens at Fohn‐1, North Bonaparte Basin, Timor Sea: A probable extraterrestrial connection” by J. D. Gorter and A. Y. Glikson
Authors: Reimold Wolf U. , Koeberl Christian , Wright Cedric , McDonald Iain
Published: February 2010

Abstract— Gorter and Glikson (2000) proposed that the Fohn‐1 structure in the Timor Sea north of Australia probably is an impact structure. Examination of their evidence reveals that it is almost impossible to confirm any of their conclusions, as the authors do not provide sufficient detail of their experimental methods. Problems with the presentation of both seismic and geochemical data cast further doubt on their conclusions. Absence of evidence for shock metamorphism and non‐chondritic siderophile element patterns in the few samples analysed make it likely that Fohn‐1 is neither a probable, nor even a possible, impact structure.
Phase equilibria of the Shergotty meteorite: Constraints on pre‐eruptive water contents of martian magmas and fractional crystallization under hydrous conditions
Authors: Dann J. C. , Holzheid A. H. , Grove T. L. , Mcsween H. Y.
Published: February 2010

Abstract—An experimental investigation of the Shergotty meteorite was performed at 0.1 MPa under anhydrous conditions at the quartz‐fayalite‐magnetite buffer and at 100 and 200 MPa under H2O‐saturated conditions at the nickel‐nickel oxide buffer. The results of these experiments are used to infer magmatic conditions recorded by co‐crystallization of augite and pigeonite phenocrysts found in Shergotty and to investigate the effect of H2O on fractional crystallization paths followed by shergottite magmas. The phase relations and compositions of the homogeneous magnesian pyroxene cores in Shergotty are most closely approximated by crystallization under H2O‐saturated conditions at 1120 °C (± 10 °C) and 56 MPa (± 18 MPa), corresponding to dissolved H2O contents of 1.8 wt% (± 0.6 wt%) and a depth of 5 km (± 1.5 km) in the martian crust (uncertainties are 2s̀ values). The Shergotty magma then lost this water during ascent and eruption. Fractional crystallization of the Shergotty magma under anhydrous conditions produces liquids that follow a strong Fe‐enrichment trend at nearly constant SiO2. Crystallization under H2O‐saturated conditions generates derivative liquids, depleted in FeO and Al2O3and enriched in SiO2, that are compositionally similar to the Mars Pathfinder andesite rock composition. The presence of ∼1.8 wt% water in Shergotty parental magmas could result from assimilation of hydrated crustal materials or from dehydration of hydrous phases in the mantle source region.
Siderophile elements in Earth's upper mantle and lunar breccias: Data synthesis suggests manifestations of the same late influx
Authors: MORGAN J. W. , WALKER R. J. , BRANDON A. D. , HORAN M. F.
Published: February 2010

Abstract— The platinum group elements (PGE; Ru, Rh, Pd, Os, Ir, Pt), Re and Au comprise the highly siderophile elements (HSE). We reexamine selected isotopic and abundance data sets for HSE in upper mantle peridotites to resolve a longstanding dichotomy. Re‐Os and Pt‐Os isotope systematics, and approximately chondritic proportions of PGE in these rocks, suggest the presence in undepleted mantle of a chondrite‐like component, which is parsimoniously explained by late influx of large planetisimals after formation of the Earth's core and the Moon. But some suites of xenolithic and orogenic spinel lherzolites, and abyssal peridotites, have a CI‐normalized PGE pattern with enhanced Pd that is sometimes termed “non‐chondritic”. We find that this observation is consistent with other evidence of a late influx of material more closely resembling enstatite, rather than ordinary or carbonaceous, chondrites. Regional variations in HSE patterns may be a consequence of a late influx of very large objects of variable composition.

Studies of many ancient (>3.8 Ga) lunar breccias show regional variations in Au/Ir and suggest that “graininess” existed during the early bombardment of the Earth and Moon. Reliable Pd values are available only for Apollo 17 breccias 73215 and 73255, however. Differences in HSE patterns between the aphanitic and anorthositic lithologies in these breccias show fractionation between a refractory group (Re, Os and Ir) and a normal (Pd, Ni, and Au) group and may reflect the compositions of the impacting bodies. Similar fractionation is apparent between the EH and EL chondrites, whose PGE patterns resemble those of the aphanitic and anorthositic lithologies, respectively.

The striking resemblance of HSE and chalcogen (S, Se) patterns in the Apollo aphanites and high‐Pd terrestrial peridotites suggest that the “non‐chondritic” abundance ratios in the latter may be reflected in the composition of planetisimals striking the Moon in the first 700 Ma of Earth–Moon history. Most notably, high Pd may be part of a general enhancement of HSE more volatile than Fe suggesting that the Au abundance in at least parts of the upper mantle may be 1.5 to 2x higher than previously estimated.

The early lunar influx may be estimated from observed basin‐sized craters. Comparison of relative influx to Earth and Moon suggests that the enrichment of HSE is limited to the upper mantle above 670 km. To infer enrichment of the whole mantle would require several large lunar impacts not yet identified.
An Aspect of the Infinite: New Zealand Talks
Authors: Carr David
Published: January 2010

Fresh encounters with Māori treasures first seen by the author at the Metropolitan Museum in 1984 revealed the concentrated power of these objects and the importance of their presence among the beliefs and continuities of their makers’ culture. A masterwork viewed in a museum may evoke a strong and sometimes inarticulate response. We might say the inability to articulate reflects a larger dimension—an aspect of the infinite—residing in the object. Museum objects return us to the human culture and knowledge we carry with us; they stimulate reflective impulses essential to the shared threads of democracy. They allow us to locate ourselves and each other, and our shared horizons.