bluuebunny/crossref_metadata_2025 huggingface dataset:
A chemical sequence of macromolecular organic matter in the CM chondrites
Authors: NARAOKA Hiroshi , MITA Hajime , KOMIYA Masatoshi , YONEDA Shigekazu , KOJIMA Hideyasu , SHIMOYAMA Akira
Published: January 2010

Abstract— A new organic parameter is proposed to show a chemical sequence of organic matter in carbonaceous chondrites, using carbon, hydrogen, and nitrogen concentrations of solvent‐insoluble and high‐molecular weight organic matter (macromolecules) and the molecular abundance of solvent‐extractable organic compounds. The H/C atomic ratio of the macromolecule purified from nine CM chondrites including the Murchison, Sayama, and seven Antarctic meteorites varies widely from 0.11 to 0.72. During the H/C change of ˜0.7 to ˜0.3, the N/C atomic ratio remains at ˜0.04, followed by a sharp decline from ˜0.040 to ˜0.017 between H/C ratios from ˜0.3 to ˜0.1. The H/CN/C sequence shows different degrees of organic matter thermal alteration among these chondrites in which the smaller H/C‐N/C value implies higher alteration levels on the meteorite parent body. In addition, solvent‐extractable organic compounds such as amino acids, carboxylic acids, and polycyclic aromatic hydrocarbons are abundant only in chondrites with macromolecular H/C values >˜0.5. These organic compounds were extremely depleted in the chondrites with a macromolecular H/C value of <˜0.5. Possibly, most solvent‐extractable organic compounds could have been lost during the thermal alteration event that caused the H/C ratio of the macromolecule to fall below 0.4.
Radar observations of asteroid 25143 Itokawa (1998 SF36)
Authors: OSTRO Steven J. , BENNER Lance A. M. , NOLAN Michael C. , MAGRI Christopher , GIORGINI Jon D. , SCHEERES Daniel J. , BROSCHART Stephen B. , KAASALAINEN Mikko , VOKROUHLICKÝ David , CHESLEY Steven R. , MARGOT Jean‐Luc , JURGENS Raymond F. , ROSE Randy , YEOMANS Donald K. , SUZUKI Shigeru , de JONG Eric M.
Published: January 2010

Abstract— We observed 25143 Itokawa, the target of Japan's Hayabusa (MUSES‐C) sample‐return mission, during its 2001 close approach at Arecibo on twelve dates during March 18‐April 9 and at Goldstone on nine dates during March 20‐April 2. We obtained delay‐Doppler images with range resolutions of 100 ns (15 m) at Arecibo and 125 ns (19 m) at Goldstone. Itokawa's average circular polarization ratio at 13 cm, 0.26 ± 0.04, is comparable to that of Eros, so its cm‐to‐m surface roughness probably is comparable to that on Eros. Itokawa's radar reflectivity and polarization properties indicate a near‐surface bulk density within 20% of 2.5 g cm−3. We present a preliminary estimate of Itokawa's shape, reconstructed from images with rather limited rotation‐phase coverage, using the method of Hudson (1993) and assuming the lightcurve‐derived spin period (12.132 hr) and pole direction (ecliptic long., lat. = 355°, −84°) of Kaasalainen et al. (2003). The model can be described as a slightly asymmetrical, slightly flattened ellipsoid with extents along its principal axes of 548 times 312 times 276 m ± 10%. Itokawa's topography is very subdued compared to that of other asteroids for which spacecraft images or radar reconstructions are available. Similarly, gravitational slopes on our Itokawa model average only 9° and everywhere are less than 27°. The radar‐refined orbit allows accurate identification of Itokawa's close planetary approaches through 2170. If radar ranging planned for Itokawa's 2004 apparition succeeds, then tracking of Hayabusa during its 2005 rendezvous should reveal Yarkovsky perturbation of the asteroid's orbit.
Geology, petrography, shock petrography, and geochemistry of impactites and target rocks from the Kärdla crater, Estonia
Authors: PUURA V. , HUBER H. , KIRS J. , KÄRKI A. , SUUROJA K. , KIRSIMÄE K. , KIVISILLA J. , KLEESMENT A. , KONSA M. , PREEDEN U. , SUUROJA S. , KOEBERL C.
Published: January 2010

Abstract— The Kärdla crater is a 4 km‐wide impact structure of Late Ordovician age located on Hiiumaa Island, Estonia. The 455 Ma‐old buried crater was formed in shallow seawater in Precambrian crystalline target rocks that were covered with sedimentary rocks. Basement and breccia samples from 13 drill cores were studied mineralogically, petrographically, and geochemically. Geochemical analyses of major and trace elements were performed on 90 samples from allochthonous breccias, sub‐crater and surrounding basement rocks. The breccia units do not include any melt rocks or suevites. The remarkably poorly mixed sedimentary and crystalline rocks were deposited separately within the allochthonous breccia suites of the crater. The most intensely shockmetamorphosed allochthonous granitoid crystalline‐derived breccia layers contain planar deformation features (PDFs) in quartz, indicating shock pressures of 20–35 GPa. An apparent K‐enrichment and Ca‐Na‐depletion of feldspar‐ and hornblende‐bearing rocks in the allochthonous breccia units and sub‐crater basement is interpreted to be the result of early stage alteration in an impact‐induced hydrothermal system. The chemical composition of the breccias shows no definite sign of an extraterrestrial contamination. By modeling of the different breccia units with HMX‐mixing, the indigenous component was determined. From the abundances of the siderophile elements (Cr, Co, Ni, Ir, and Au) in the breccia samples, no unambiguous evidence for the incorporation of a meteoritic component above about 0.1 wt% chondrite‐equivalent was found.
Determining the possible building blocks of the Earth and Mars
Authors: Burbine Thomas H. , O'Brien Kevin M.
Published: January 2010

Abstract— To determine the possible building blocks of the Earth and Mars, 225,792,840 possible combinations of the bulk oxygen isotopic and chemical compositions of 13 chondritic groups at 5% mass increments were examined. Only a very small percentage of the combinations match the oxygen isotopic composition, the assumed bulk FeO concentration, and the assumed Fe/Al weight ratio for the Earth. Since chondrites are enriched in silicon relative to estimates of the bulk Earth, none of the combinations fall near the terrestrial magmatic fractionation trend line in Mg/Si‐Al/Si space. More combinations match the oxygen isotopic composition and the assumed bulk FeO concentration for Mars. These combinations fall near the trend for shergottite meteorites in Mg/Si‐Al/Si space. One explanation for the difficulty in forming Earth out of known chondrites is that the Earth may be composed predominately of material that did not survive to the present day as meteorites. Another explanation could be that significant amounts of silicon are sequestered in the core and/or lower mantle of the Earth.
The Peerless structure, Daniels County, northeastern Montana: A probable late Ordovician impact structure
Authors: Comstock J. M. , Dietz R. D. , Morrow J. R.
Published: January 2010

Abstract— The Peerless structure is an ˜6 km‐diameter sub‐surface anomaly located in Daniels County, northeastern Montana. The disruption of sedimentary rock in the structure lies between 2624 to 2818 m below the topographic surface. Seismic mapping shows a typical complex crater composed of a central uplift ˜2 km across, which shows structural uplift of up to 90 m, an annular ring ˜4 km across, and an outer rim ˜6 km in diameter. The youngest disrupted rock unit is the upper Ordovician Red River formation, which indicates that the structure was formed about 430–450 Ma ago.
Laboratory hydration of condensed magnesiosilica smokes with implications for hydrated silicates in IDPs and comets
Authors: Rietmeijer Frans J. M. , Nuth Joseph A. , Nelson Robert N.
Published: January 2010

Abstract— Samples of silica‐rich and MgO‐rich condensed, amorphous magnesiosilica smokes were hydrated to monitor systematic mineralogical and chemical changes as a function of time and temperature controlled by their unique metastable eutectic compositions, their porous texture, and the ultrafine, nanometer grain size of all entities. At water supersaturated conditions, proto‐phyllosilicates formed by spinodal‐type homogeneous nucleation. Their formation and subsequent growth was entirely determined by the availability of water via pore spaces inherited from the original smokes and the textural continuity of magnesiosilica material with a mostly smectite‐dehydroxylate composition. The results may have implications for the hydration of proto‐CI material, the presence of rare periclase and brucite in primitive solar system bodies, and the pervasiveness of hydrated amorphous magnesiosilica dust and saponite proto‐phyllosilicates in icy‐protoplanets, such as comet nuclei.
The preservation state of organic matter in meteorites from Antarctica
Authors: Sephton M. A. , Bland P. A. , Pillinger C. T. , Gilmour I.
Published: January 2010

Abstract— The recovery of large numbers of meteorites from Antarctica has dramatically increased the amount of extraterrestrial material available for laboratory studies of solar system origin and evolution. Yet, the great age of Antarctic meteorites raises the concern that significant amounts of terrestrial weathering has corrupted their pre‐terrestrial record. Organic matter found in carbonaceous chondrites is one of the components most susceptible to alteration by terrestrial processes. To assess the effects of Antarctic weathering on both non‐Antarctic and Antarctic chondritic organic matter, a number of CM chondrites have been analyzed. Mössbauer spectroscopy has been used to ascertain pre‐terrestrial and terrestrial oxidation levels, while pyrolysis‐gas chromatography‐mass spectrometry was used to determine the constitution of any organic matter present. Increased oxidation levels for iron bearing minerals within the non‐Antarctic chondrites are likely to be a response to increased amounts of parent body aqueous alteration. Parent body processing also appears to remove ether bonds from organic material and alkyl side chains from its constituent units. The iron in Antarctic chondrites is generally more oxidized than that in their non‐Antarctic counterparts, reflecting terrestrial weathering. Antarctic weathering of chondritic organic matter appears to proceed in a similar way to parent body aqueous alteration and simply enhances the organic responses observed in the non‐Antarctic data set. Degradation of the record of preterrestrial processes in Antarctic chondrites should be taken into account when interpreting data from these meteorites.
Noble gas studies in CAIs from CV3 chondrites: No evidence for primordial noble gases
Authors: Vogel Nadia , Baur Heinrich , Bischoff Addi , Leya Ingo , Wieler Rainer
Published: January 2010

Abstract— Calcium‐aluminum‐rich inclusions (CAIs) were among the first solids in the solar system and were, similar to chondrules, created at very high temperatures. While in chondrules, trapped noble gases have recently been detected, the presence of trapped gases in CAIs is unclear but could have important implications for CAI formation and for early solar system evolution in general. To reassess this question, He, Ne, and Ar isotopes were measured in small, carefully separated and, thus, uncontaminated samples of CAIs from the CV3 chondrites Allende, Axtell, and Efremovka.

The 20Ne/22Ne ratios of all CAIs studied here are <0.9, indicating the absence of trapped Ne as, e.g., Ne‐HL, Ne‐Q, or solar wind Ne. The 21Ne/22Ne ratios range from 0.86 to 0.72, with fine‐grained, more altered CAIs usually showing lower values than coarse‐grained, less altered CAIs. This is attributed to variable amounts of cosmogenic Ne produced from Na‐rich alteration phases rather than to the presence of Ne‐G or Ne‐R (essentially pure 22Ne) in the samples. Our interpretation is supported by model calculations of the isotopic composition of cosmogenic Ne in minerals common in CAIs. The 36Ar/38Ar ratios are between 0.7 and 4.8, with fine‐grained CAIs within one meteorite showing higher ratios than the coarse‐grained ones. This agrees with higher concentrations of cosmogenic 36Ar produced by neutron capture on 35Cl with subsequent β−‐decay in finer‐grained, more altered, and thus, more Cl‐rich CAIs than in coarser‐grained, less altered ones.

Although our data do not strictly contradict the presence of small amounts of Ne‐G, Ne‐R, or trapped Ar in the CAIs, our noble gas signatures are most simply explained by cosmogenic production, mainly from Na‐, Ca‐, and Cl‐rich minerals.
Fine‐grained, spinel‐rich inclusions from the reduced CV chondrites Efremovka and Leoville: I. Mineralogy, petrology, and bulk chemistry
Authors: KROT Alexander N. , MacPHERSON Glenn J. , ULYANOV Alexander A. , PETAEV Michail I.
Published: January 2010

Abstract— Fine‐grained, spinel‐rich inclusions in the reduced CV chondrites Efremovka and Leoville consist of spinel, melilite, anorthite, Al‐diopside, and minor hibonite and perovskite; forsterite is very rare. Several CAIs are surrounded by forsterite‐rich accretionary rims. In contrast to heavily altered fine‐grained CAIs in the oxidized CV chondrite Allende, those in the reduced CVs experienced very little alteration (secondary nepheline and sodalite are rare). The Efremovka and Leoville fine‐grained CAIs are 16O‐enriched and, like their Allende counterparts, generally have volatility fractionated group II rare earth element patterns. Three out of 13 fine‐grained CAIs we studied are structurally uniform and consist of small concentrically zoned nodules having spinel ± hibonite ± perovskite cores surrounded by layers of melilite and Al‐diopside. Other fine‐grained CAIs show an overall structural zonation defined by modal mineralogy differences between the inclusion cores and mantles. The cores are melilite‐free and consist of tiny spinel ± hibonite ± perovskite grains surrounded by layers of anorthite and Al‐diopside. The mantles are calcium‐enriched, magnesium‐depleted and coarsergrained relative to the cores; they generally contain abundant melilite but have less spinel and anorthite than the cores. The bulk compositions of fine‐grained CAIs generally show significant fractionation of Al from Ca and Ti, with Ca and Ti being depleted relative to Al; they are similar to those of coarsegrained, type C igneous CAIs, and thus are reasonable candidate precursors for the latter. The finegrained CAIs originally formed as aggregates of spinel‐perovskite‐melilite ± hibonite gas‐solid condensates from a reservoir that was 16O‐enriched but depleted in the most refractory REEs. These aggregates later experienced low‐temperature gas‐solid nebular reactions with gaseous SiO and Mg to form Al‐diopside and ±anorthite. The zoned structures of many of the fine‐grained inclusions may be the result of subsequent reheating that resulted in the evaporative loss of SiO and Mg and the formation of melilite. The inferred multi‐stage formation history of fine‐grained inclusions in Efremovka and Leoville is consistent with a complex formation history of coarse‐grained CAIs in CV chondrites.
Dynamic tensile strength of terrestrial rocks and application to impact cratering
Authors: Ai Huirong‐Anita , Ahrens Thomas J.
Published: January 2010

Abstract— Dynamic tensile strengths and fracture strengths of 3 terrestrial rocks, San Marcos gabbro, Coconino sandstone, and Sesia eclogite were determined by carrying out flat‐plate (PMMA and aluminum) impact experiments on disc‐shaped samples in the 5 to 60 m/sec range. Tensile stresses of 125 to 300 MPa and 245 to 580 MPa were induced for gabbro and eclogite, respectively (with duration time of ˜1 μs). For sandstone (porosity 25%), tensile stresses normal to bedding of ˜13 to 55 MPa were induced (with duration times of 2.4 and ˜1.4 μs). Tensile crack failure was detected by the onset of shock‐induced (damage) P and S wave velocity reduction.

The dynamic tensile strength of gabbro determined from P and S wave velocity deficits agrees closely with the value of previously determined values by post‐impact microscopic examination (˜150 MPa). Tensile strength of Coconino sandstone is 20 MPa for a 14 μs duration time and 17 MPa for a 2.4 μs duration time. For Sesia eclogite, the dynamic tensile strength is ˜240 MPa. The fracture strength for gabbro is ˜250 MPa, ˜500 MPa for eclogite, and ˜40 MPa for sandstone. Relative crack‐induced reduction of S wave velocities is less than that of post‐impact P wave velocity reductions for both gabbro and eclogite, indicating that the cracks were predominantly spall cracks.

Impacts upon planetary surfaces induce tensile failure within shock‐processed rocks beneath the resulting craters. The depth of cracking beneath impact craters can be determined both by seismic refraction methods for rocks of varying water saturation and, for dry conditions (e.g., the Moon), from gravity anomalies. In principle, depth of cracking is related to the equations‐of‐state of projectile and target, projectile dimension, and impact velocity. We constructed a crack‐depth model applicable to Meteor Crater. For the observed 850 m depth of cracking, our preferred strength scaling model yields an impact velocity of 33 km/s and impactor radius of 9 m for an iron projectile.
Experimental ejection angles for oblique impacts: Implications for the subsurface flow‐field
Authors: Anderson Jennifer L. B. , Schultz Peter H. , Heineck James T.
Published: January 2010

Abstract— A simple analytical solution for subsurface particle motions during impact cratering is useful for tracking the evolution of the transient crater shape at late times. A specific example of such an analytical solution is Maxwell's Z‐Model, which is based on a point‐source assumption. Here, the parameters for this model are constrained using measured ejection angles from both vertical and oblique experimental impacts at the NASA Ames Vertical Gun Range. Data from experiments reveal that impacts at angles as high as 45° to the target's surface generate subsurface flow‐fields that are significantly different from those created by vertical impacts. The initial momentum of the projectile induces a subsurface momentum‐driven flow‐field that evolves in three dimensions of space and in time to an excavation flow‐field during both vertical and oblique impacts. A single, stationary point‐source model (specifically Maxwell's Z‐Model), however, is found inadequate to explain this detailed evolution of the subsurface flow‐field during oblique impacts. Because 45° is the most likely impact angle on planetary surfaces, a new analytical model based on a migrating point‐source could prove quite useful. Such a model must address the effects of the subsurface flow‐field evolution on crater excavation, ejecta deposition, and transient crater morphometry.
The Bagnone iron meteorite (Tuscany, Italy): History, mineralogy, and chemical classification
Authors: D'Orazio M. , Folco L. , Perchiazzi N.
Published: January 2010

Abstract— Bagnone, the largest Italian iron meteorite (48 kg), was found as a single mass at the beginning of the 20th century while ploughing a field close to the Bagnone Castle (Massa Carrara, northern Tuscany). The morphology of the external surface suggests that Bagnone represents a complete individual. It is classified as a medium octahedrite (average bandwidth = 0.96 mm) of the IIIAB chemical group, based on inductively coupled plasma mass spectrometry analyses.
Artifacts in Polish collections made of meteoritic iron
Authors: Kotowiecki Andrzej
Published: January 2010

Abstract— Only several artifacts made of meteoritic iron have been found throughout the world. The number of these artifacts is still overstated and has never been verified because museums do not allow specialists to test these objects. Until now, a few objects made of meteoritic iron were discovered in Poland. An axe from Wietrzno‐Bobrka and bracelets from Częstochowa‐Raków are listed as Polish meteorites—the latter ones as Częstochowa‐Raków I and Częstochowa‐Raków II. In my opinion, a special meteoritic category should be created for artifacts made of meteorites: meteoritic antiques or manmade artifacts of meteorites and tektite glass. Within such a category, further categorization could be made, based on the material a given meteorite is made of.
Petrography and mineral chemistry of the Reliegos chondrite
Authors: Lozano Rafael P. , Martin‐Crespo Tomás
Published: January 2010

Abstract— The Reliegos meteorite is an L5 ordinary chondrite. The chondrules are embedded in a fine‐grained matrix that predominantly consists of olivine and orthopyroxene, with accessory clinopyroxene, troilite, apatite, and a mesostasis of feldspar composition. The metal phase is predominantly kamacite with subordinate taenite and traces of native Cu. The bulk composition of Reliegos compares well with other L5 chondrites, except for a distinctly lower Cr content. A Cr‐rich object has been identified, which shows a concentric mineral and chemical zoning and is composed mainly of chromite and plagioclase, with minor amounts of merrillite and Mg, V‐rich ilmenite.
Beni M'hira: A new chondritic (L6) meteorite fall from Tunisia
Authors: Ouazaa N. Laridhi , Perchiazzi N. , D'Orazio M. , Rochette P. , Clocchiatti R. , Folco L.
Published: January 2010

Abstract— The Beni M'hira meteorite fell on January 8, 2001 in southeastern Tunisia. This is only the fifth observed fall from Tunisia. On the basis of mineralogical, petrographic, and geochemical data, the stone can be classified as an L6 chondrite of shock stage S5.
Accessory silicate mineral assemblages in the Bilanga diogenite: A petrographic study
Authors: Domanik Kenneth , Kolar Serena , Musselwhite Donald , Drake Michael J.
Published: January 2010

Abstract— The petrographic relationships in diogenites between orthopyroxene and minor phases such as chromite, troilite, diopside, plagioclase, and silica are often obscured by the intense brecciation that characterizes these meteorites. Although brecciated, Bilanga preserves numerous clasts displaying primary textural relations between orthopyroxene and these minor phases that are large enough to analyze by electron microprobe. In this study, we focus on the distribution, composition, and origin of the minor phases in Bilanga to provide new insights into the crystallization and metamorphic history of these rocks.

The samples examined consist mainly of orthopyroxene grains plus five types of assemblages containing diopside + a Fe‐rich phase (chromite, troilite, and/or Fe‐Ni metal) ± plagioclase ± silica. We interpret type 1 assemblages as being remnants of intercumulus melt trapped in the interstices between orthopyroxene grains after crystal settling in a magma chamber. Type 2 assemblages appear to have formed by heterogeneous exsolution during thermal metamorphism. Type 3 assemblages are believed to be remnants of other assemblages that have been shocked, melted, and rapidly recrystallized by impact events. Type 4 assemblages consist of veins that also appear to have formed from trapped intercumulus melt. Regions of silica‐rich mesostasis (type 5) appear to be larger patches of more evolved intercumulus melt that have been significantly affected by late‐stage impact melting. Finally, large clasts containing plagioclase ± diopside are interpreted to be exotic fragments of a different but possibly related rock type incorporated in the Bilanga breccia.
REE abundances in the matrix of the Allende (CV) meteorite: Implications for matrix origin
Authors: Inoue Mutsuo , Kimura Makoto , Nakamura Noboru
Published: January 2010

Abstract— The trace element distributions in the matrix of primitive chondrites were examined using four least‐contaminated matrix specimens from the polished sections of the Allende (CV) meteorite. Analysis of rare earth element (REE), Ba, Sr, Rb, and K abundances by isotope dilution mass spectrometry revealed that the elemental abundances of lithophile elements except for alkali metals (K, Rb) in the specimens of the Allende matrix studied here are nearly CI (carbonaceous Orgueil) chondritic (∼1 × CI). Compared to refractory elements, all the matrix samples exhibited systematic depletion of the moderately volatile elements K and Rb (0.1–0.5 × CI). We suggest that the matrix precursor material did not carry significant amounts of alkali metals or that the alkalis were removed from the matrix precursor material during the parent body process and/or before matrix formation and accretion. The matrix specimens displayed slightly fractionated REE abundance patterns with positive Ce anomalies (CI‐normalized La/Yb ratio = 1.32–1.65; Ce/Ce* = 1.16–1.28; Eu/Eu* = 0.98–1.10). The REE features of the Allende matrix do not indicate a direct relationship with chondrules or calcium‐aluminum‐rich inclusions (CAIs), which in turn suggests that the matrix was not formed from materials produced by the breakage and disaggregation of the chondrules or CAIs. Therefore, we infer that the Allende matrix retains the REE features acquired during the condensation process in the nebula gas.
“Comet‐tail” ejecta streaks: A predicted cratering landform unique to Titan
Authors: Lorenz Ralph D.
Published: January 2010

Abstract— A model for an impact ejecta landform peculiar to Saturn's moon Titan is presented. Expansion of the ejecta plume from moderate‐sized craters is constrained by Titan's thick atmosphere. Much of the plume is collimated along the incoming bolide's trajectory, as was observed for plumes from impacts on Jupiter of P/Shoemaker‐Levy‐9, but is retained as a linear, diagonal ejecta cloud, unlike on Venus where the plume “blows out.” On Titan, the blowout is suppressed because the vertically‐extended atmosphere requires a long wake to reach the vacuum of space, and the modest impact velocities mean plume expansion along the wake is slow enough to allow the wake to close off. Beyond the immediate ejecta blanket around the crater, distal ejecta is released into the atmosphere from an oblique line source: this material is winnowed by the zonal wind field to form streaks, with coarse radar‐bright particles transported less far than fine radar‐dark material. Thus, the ejecta form two distinct streaks faintly reminiscent of dual comet tails, a sharply W‐E radar‐dark one, and a less swept and sometimes comma‐shaped radar‐bright one.
The fall, recovery, and classification of the Park Forest meteorite
Authors: Simon S. B. , Grossman L. , Clayton R. N. , Mayeda T. K. , Schwade J. R. , Sipiera P. P. , Wacker J. F. , Wadhwa M.
Published: January 2010

Abstract— On the night of March 26, 2003, a large meteorite broke up and fell upon the south suburbs of Chicago. The name Park Forest, for the village that is at the center of the strewnfield, has been approved by the nomenclature committee of the Meteoritical Society. Satellite data indicate that the bolide traveled from the southwest toward the northeast. The strewnfield has a southeast‐northwest trend; however, this is probably due to the effects of strong westerly winds at high altitudes. Its very low 56Co and very high 60Co activities indicate that Park Forest had a preatmospheric mass that was at least ∼900 kg and could have been as large as ∼7 times 103 kg, of which only ∼30 kg have been recovered. The average compositions of olivine and low‐Ca pyroxene, Fa24.7 ± 1.1 and Fs20.8 ± 0.7, respectively, and its bulk oxygen isotopic composition, δ18O = +4.68%o, δ17O = +3.44%o, show that Park Forest is an L chondrite. The ferromagnesian minerals are well equilibrated, chondrules are easily recognized, and maskelynite is mostly ≤50 μm across. Based on these observations, we classify Park Forest as type 5. The meteorite has been strongly shocked, and based on the presence of maskelynite, mosaicism and planar deformation features in olivine, undulatory extinction in pyroxene, and glassy veins, the shock stage is S5. The meteorite is a monomict breccia, consisting of light‐colored, angular to rounded clasts in a very dark host. The light and dark lithologies have essentially identical mineral and oxygen isotopic compositions. Their striking difference in appearance is due to the presence of a fine, pervasive network of sulfide veins in the dark lithology, resulting in very short optical path lengths. The dark lithology probably formed from the light lithology in an impact that formed a sulfide‐rich melt and injected it into cracks.
Magnetic mineralogy of the Yaxcopoil‐1 core, Chicxulub
Authors: Pilkington Mark , Ames Doreen E. , Hildebrand Alan R.
Published: January 2010

Abstract— Core from the Yaxcopoil‐1 (Yax‐1) hole, drilled as a result of the Chicxulub Scientific Drilling Project (CSDP), has been analyzed to investigate the relationship between opaque mineralogy and rock magnetic properties. Twenty one samples of suevite recovered from the depth range 818–894 m are generally paramagnetic, with an average susceptibility of 2000 times 10−6 SI and have weak remanent magnetization intensities (average 0.1 A/m). The predominant magnetic phase is secondary magnetite formed as a result of low temperature (<150 °C) alteration. It occurs in a variety of forms, including vesicle infillings associated with quartz and clay minerals and fine aggregates between plagioclase/diopside laths in the melt. Exceptional magnetic properties are found in a basement clast (metamorphosed quartz gabbro), which has a susceptibility of >45000 times 10−6 SI and a remanent magnetization of 77.5 A/m. Magnetic mafic basement clasts are a common component in the Yax‐1 impactite sequence. The high susceptibility and remanence in the mafic basement clasts are caused by the replacement of amphiboles and pyroxenes by an assemblage with fine <1 μm magnetite, ilmenite, K‐feldspar, and stilpnomelane. Replacement of the mafic minerals by the magnetic alteration assemblage occurred before impact. Similar alteration mechanisms, if operative within the melt sheet, could explain the presence of the high amplitude magnetic anomalies observed at Chicxulub.
Major and trace element characteristics of impactites from the Yaxcopoil‐1 borehole, Chicxulub structure, Mexico
Authors: Tuchscherer Martin G. , Reimold W. Uwe , Koeberl Christian , Gibson Roger L.
Published: January 2010

Abstract— Approximately 100 m of impactites were retrieved from the ICDP borehole Yaxcopoil‐1 (Yax‐1), located ∼60 km south‐southwest from the center of the Chicxulub impact crater on the Yucatán Peninsula of Mexico. Here, we characterize and discuss this impact breccia interval according to its geochemical characteristics.

Chemical analysis of samples from all five recognized breccia units reveals that the impactites are of heterogeneous composition with regard to both major and trace elements at the single sample (8–16 cm3) scale. This is primarily due to a strong mixing relationship between carbonate and silicate fractions. However, averaged compositions for suevitic units 1 to 3 are similar, and the silicate fraction (after removal of the carbonate component) indicates thorough mixing and homogenization. Analysis of the green melt breccia horizon, unit 4, indicates that it contains a distinct mafic component. Large brown melt particles (in units 2, 3, and 4) represent a mixture of feldspathic and mafic components, with high CaO abundances. Unit 5 shows the greatest compositional diversity, with highly variable abundances of SiO2, CaO, and MgO.

Inter‐sample heterogeneity is the result of small sample size combined with inherent heterogeneous lithological compositions, highly variable particle size of melt and lithic components, and post‐depositional alteration. In contrast to samples from the Y6 borehole from closer to the center of the structure, Yax‐1 impactites have a strong carbonate component. Elevated loss on ignition, Rb, and Cs contents in the upper two impactite units indicate strong interaction with seawater. The contents of the siderophile elements, including Ni, Co, Ir, and Cr, do not indicate the presence of a significant extraterrestrial component in the Yax‐1 impactites.
Discovery of Earth's quasi‐satellite
Authors: Connors Martin , Veillet Christian , Brasser Ramon , Wiegert Paul , Chodas Paul , Mikkola Seppo , Innanen Kimmo
Published: January 2010

Abstract— The newly discovered asteroid 2003 YN107 is currently a quasi‐satellite of the Earth, making a satellite‐like orbit of high inclination with apparent period of one year. The term quasi‐satellite is used since these large orbits are not completely closed, but rather perturbed portions of the asteroid's orbit around the Sun. Due to its extremely Earth‐like orbit, this asteroid is influenced by Earth's gravity to remain within 0.1 AU of the Earth for approximately 10 years (1997 to 2006). Prior to this, it had been on a horseshoe orbit closely following Earth's orbit for several hundred years. It will re‐enter such an orbit, and make one final libration of 123 years, after which it will have a close interaction with the Earth and transition to a circulating orbit. Chaotic effects limit our ability to determine the origin or fate of this object.
Origin and emplacement of the impact formations at Chicxulub, Mexico, as revealed by the ICDP deep drilling at Yaxcopoil‐1 and by numerical modeling
Authors: Stöffler Dieter , Artemieva Natalya A. , Ivanov Boris A. , Hecht Lutz , Kenkmann Thomas , Schmitt Ralf Thomas , Tagle Roald Alberto , Wittmann Axel
Published: January 2010

We present and interpret results of petrographic, mineralogical, and chemical analyses of the 1511 m deep ICDP Yaxcopoil‐1 (Yax‐1) drill core, with special emphasis on the impactite units. Using numerical model calculations of the formation, excavation, and dynamic modification of the Chicxulub crater, constrained by laboratory data, a model of the origin and emplacement of the impact formations of Yax‐1 and of the impact structure as a whole is derived. The lower part of Yax‐1 is formed by displaced Cretaceous target rocks (610 m thick), while the upper part comprises six suevite‐type allochthonous breccia units (100 m thick). From the texture and composition of these lithological units and from numerical model calculations, we were able to link the seven distinct impact‐induced units of Yax‐1 to the corresponding successive phases of the crater formation and modification, which are as follows: 1) transient cavity formation including displacement and deposition of Cretaceous “megablocks;” 2) ground surging and mixing of impact melt and lithic clasts at the base of the ejecta curtain and deposition of the lower suevite right after the formation of the transient cavity; 3) deposition of a thin veneer of melt on top of the lower suevite and lateral transport and brecciation of this melt toward the end of the collapse of the transient cavity (brecciated impact melt rock); 4) collapse of the ejecta plume and deposition of fall‐back material from the lower part of the ejecta plume to form the middle suevite near the end of the dynamic crater modification; 5) continued collapse of the ejecta plume and deposition of the upper suevite; 6) late phase of the collapse and deposition of the lower sorted suevite after interaction with the inward flowing atmosphere; 7) final phase of fall‐back from the highest part of the ejecta plume and settling of melt and solid particles through the reestablished atmosphere to form the upper sorted suevite; and 8) return of the ocean into the crater after some time and minor reworking of the uppermost suevite under aquatic conditions. Our results are compatible with: a) 180 km and 100 km for the diameters of the final crater and the transient cavity of Chicxulub, respectively, as previously proposed by several authors, and b) the interpretation of Chicxulub as a peak‐ring impact basin that is at the transition to a multi‐ring basin.
Secondary alteration of the impactite and mineralization in the basal Tertiary sequence, Yaxcopoil‐1, Chicxulub impact crater, Mexico
Authors: AMES Doreen E. , KJARSGAARD Ingrid M. , POPE Kevin O. , DRESSLER Burkhard , PILKINGTON Mark
Published: January 2010

Abstract The 65 Ma Chicxulub impact crater formed in the shallow coastal marine shelf of the Yucatán Platform in Mexico. Impacts into water‐rich environments provide heat and geological structures that generate and focus sub‐seafloor convective hydrothermal systems. Core from the Yaxcopoil‐1 (Yax‐1) hole, drilled by the Chicxulub Scientific Drilling Project (CSDP), allowed testing for the presence of an impact‐induced hydrothermal system by: a) characterizing the secondary alteration of the 100 m‐thick impactite sequence; and b) testing for a chemical input into the lower Tertiary sediments that would reflect aquagene hydrothermal plume deposition. Interaction of the Yax‐1 impactites with seawater is evident through redeposition of the suevites (unit 1), secondary alteration mineral assemblages, and the subaqueous depositional environment for the lower Tertiary carbonates immediately overlying the impactites.

The least‐altered silicate melt composition intersected in Yax‐1 is that of a calc‐alkaline basaltic andesite with 53.4–56 wt% SiO2(volatile‐free). The primary mineralogy consists of fine microlites of diopside, plagioclase (mainly Ab 47), ternary feldspar (Ab 37 to 77), and trace apatite, titanite, and zircon. The overprinting alteration mineral assemblage is characterized by Mg‐saponite, K‐montmorillonite, celadonite, K‐feldspar, albite, Fe‐oxides, and late Ca and Mg carbonates. Mg and K metasomatism resulted from seawater interaction with the suevitic rocks producing smectite‐K‐feldspar assemblages in the absence of any mixed layer clay minerals, illite, or chlorite. Rare pyrite, sphalerite, galena, and chalcopyrite occur near the base of the impactites. These secondary alteration minerals formed by low temperature (0–150°C) oxidation and fixation of alkalis due to the interaction of glass‐rich suevite with down‐welling seawater in the outer annular trough intersected at Yax‐1. The alteration represents a cold, Mg‐K‐rich seawater recharge zone, possibly recharging higher temperature hydrothermal activity proposed in the central impact basin. Hydrothermal metal input into the Tertiary ocean is shown by elevated Ni, Ag, Au, Bi, and Te concentrations in marcasite and Cd and Ga in sphalerite in the basal 25 m of the Tertiary carbonates in Yax‐1. The lower Tertiary trace element signature reflects hydrothermal metal remobilization from a mafic source rock and is indicative of hydrothermal venting of evolved seawater into the Tertiary ocean from an impact‐generated hydrothermal convective system.
Composition of impact melt particles and the effects of post‐impact alteration in suevitic rocks at the Yaxcopoil‐1 drill core, Chicxulub crater, Mexico
Authors: HECHT Lutz , WITTMANN Axel , SCHMITT Ralf‐Thomas , STöFFLER Dieter
Published: January 2010

Abstract Petrographical and chemical analysis of melt particles and alteration minerals of the about 100 m‐thick suevitic sequence at the Chicxulub Yax‐1 drill core was performed. The aim of this study is to determine the composition of the impact melt, the variation between different types of melt particles, and the effects of post‐impact hydrothermal alteration. We demonstrate that the compositional variation between melt particles of the suevitic rocks is the result of both incomplete homogenization of the target lithologies during impact and subsequent post‐impact hydrothermal alteration. Most melt particles are andesitic in composition. Clinopyroxene‐rich melt particles possess lower SiO2 and higher CaO contents. These are interpreted by mixing of melts from the silicate basement with overlying carbonate rocks. Multi‐stage post‐impact hydrothermal alteration involved significant mass transfer of most major elements and caused further compositional heterogeneity between melt particles. Following backwash of seawater into the crater, palagonitization of glassy melt particles likely caused depletion of SiO2, Al2O3, CaO, Na2O, and enrichment of K2O and FeOtot during an early alteration stage. Since glass is very susceptible to fluid‐rock interaction, the state of primary crystallization of the melt particles had a significant influence on the intensity of the post‐impact hydrothermal mass transfer and was more pronounced in glassy melt particles than in well‐crystallized particles. In contrast to other occurrences of Chicxulub impactites, the Yax‐1 suevitic rocks show strong potassium metasomatism with hydrothermal K‐feldspar formation and whole rock K20 enrichment, especially in the lower unit of the suevitic sequence. A late stage of hydrothermal alteration is characterized by precipitation of silica, analcime, and Na‐bearing Mg‐rich smectite, among other minerals. This indicates a general evolution from a silica‐undersaturated fluid at relatively high potassium activities at an early stage toward a silica‐oversaturated fluid at relatively high sodium activities at later stages in the course of fluid rock interaction.
Evidence for ocean water invasion into the Chicxulub crater at the Cretaceous/Tertiary boundary
Authors: GOTO Kazuhisa , TADA Ryuji , TAJIKA Eiichi , BRALOWER Timothy J. , HASEGAWA Takashi , MATSUI Takafumi
Published: January 2010

Abstract The possibility of ocean water invasion into the Chicxulub crater following the impact at the Cretaceous/Tertiary boundary was investigated based on examination of an impactite between approximately 794.63 and 894.94 m in the Yaxcopoil‐1 (Yax‐1) core. The presence of cross lamination in the uppermost part of the impactite suggests the influence of an ocean current at least during the sedimentation of this interval. Abundant occurrence of nannofossils of late Campanian to early Maastrichtian age in the matrices of samples from the upper part of the impactite suggests that the carbonate sediments deposited on the inner rim margin and outside the crater were eroded and transported into the crater most likely by ocean water that invaded the crater after its formation. The maximum grain size of limestone lithics and vesicular melt fragments, and grain and bulk chemical compositions show a cyclic variation in the upper part of the impactite. The upward fining grain size and the absence of erosional contact at the base of each cycle suggest that the sediments were derived from resuspension of units elsewhere in the crater, most likely by high energy currents association with ocean water invasion.
Infrared spectroscopic taxonomy for carbonaceous chondrites from speciation of hydrous components
Authors: OSAWA Takahito , KAGI Hiroyuki , NAKAMURA Tomoki , NOGUCHI Takaaki
Published: January 2010

Abstract— Mid‐infrared absorption spectra for all types of carbonaceous chondrites were obtained in this study to establish a versatile method for spectroscopic classification of carbonaceous chondrites. Infrared spectra were measured using a conventional KBr pellet method and diamond press method. Spectra of hydrous carbonaceous chondrites exhibit intense O‐H stretching vibrations. CI chondrites are identifiable by a characteristic sharp absorption band appearing at 3685 cm−1, which is mainly attributable to serpentine. X‐ray diffraction analysis showed the presence of serpentine. However, Yamato (Y‐) 82162 (C1) does not have the band at 3685 cm−1 because of its thermal metamorphism. CM and CR chondrites have an intense absorption band at approximately 3600 cm−1. This absorption tends to appear in CM chondrites more strongly than CR chondrites because the intensity ratios of an OH stretching mode at 3520 cm−1 compared to 3400 cm−1 for CM chondrites are in the range of 0.95–1.04, which is systematically higher than those of CR chondrites (0.86–0.88). Therefore, the two types of chondrites are distinguishable by their respective infrared spectra. The spectrum feature of the Tagish Lake meteorite is attributable to neither CI nor CM chondrites. CO chondrites are characterized by weak and broad absorption at 3400 cm−1. CV chondrites have weak or negligible absorption of water. CK chondrites also have no water‐induced absorption. CH and CB chondrites have a sharp absorption at 3692 cm−1 indicating the presence of chrysotile, which is also supported by observations of X‐ray diffraction and TEM. The combination of spectroscopic classification and the diamond press method allows classification of carbonaceous chondrites of very valuable samples with small quantities. As one example, carbonaceous chondrite clasts in brecciated meteorites were classified using our technique. Infrared spectra for a fragment of carbonaceous clasts (<1 μg) separated from Willard (b) and Tsukuba were measured. The 3685 cm−1 band found in CI chondrites was clearly detected in the clasts, indicating that they are CI‐like clasts.
Chondrule and metal grain size sorting from jet flows
Authors: LIFFMAN Kurt
Published: January 2010

Abstract—We examine the size sorting of chondrules and metal grains within the context of the jet flow model for chondrule/CAI formation. In this model, chondrules, CAIs, AOAs, metal grains, and related components of meteorites are assumed to have formed in the outflow region of the innermost regions of the solar nebula and then were ejected, via the agency of a bipolar jet flow, to outer regions of the nebula. We wish to see if size sorting of chondrules and metal grains is a natural consequence of this model. To assist in this task, we used a multiprocessor system to undertake Monte Carlo simulations of the early solar nebula. The paths of a statistically significant number of chondrules and metal grains were analyzed as they were ejected from the outflow and travelled over or into the solar nebula. For statistical reasons, only distances ≤3 AU from the Sun were examined.

Our results suggest that size sorting can occur provided that the solar nebula jet flow had a relatively constant flow rate as function of time. A constant flow rate outflow produces size sorting, but it also produces a sharp size distribution of particles across the nebula and a metal‐rich Fe/Si ratio. When the other extreme of a fully random flow rate was examined, it was found that size sorting was removed, and the initial material injected into the flow was simply spread over most of the the solar nebula. These results indicate that the outflow can act as a size and density classifier. By simply varying the flow rate, the outflow can produce different types of proto‐meteorites from the same chondrule and metal grain feed stock.

As a consequence of these investigations, we observed that the number of particles that impact into the nebula drops off moderately rapidly as a function of distancerfrom the Sun. We also derive a corrected form of the Epstein stopping time.
Mineralogy and petrology of the angrite Northwest Africa 1296
Authors: Jambon A. , Barrat J. A. , Boudouma O. , Fonteilles M. , Badia D. , Göpel C. , Bohn M.
Published: January 2010

Abstract— We report on a new angrite, Northwest Africa (NWA) 1296, a fine‐grained rock with a magmatic texture of rapid cooling. Dendritic olivine (≅Fo50) crystallized first in association with anorthite microcrysts (An98–100) forming composite chains separated from one another by intergrown Al‐Fe diopside‐hedenbergite pyroxenes. In addition, some olivines with lower Mg# and increased CaO (up to 12%) are found between the chains as equant microphenocrysts. Pyroxenes and olivines are both normally zoned from Mg# = 0.52 to less than 0.01 in the rims. Ca‐rich olivines are surrounded by, intergrown with, or replaced by subcalcic kirschsteinite. They appear after plagioclase crystallization stopped, at the end of the crystallization sequence. Minor phases are pyrrhotite, F‐apatite, and titanomagnetite. Pyroxene is the last silicate phase to grow, interstitial to idiomorphic olivine‐kirschsteinite. Numerous small vesicles and some channels are filled with microcristalline carbonate. The mode (vol%) is about 28% olivine, 3% kirschsteinite, 32% anorthite, 34% pyroxene, and 3% of the minor phases—close to that reported previously for D'Orbigny and Sahara (SAH) 99555. The bulk chemical composition of NWA 1296 is similar to D'Orbigny and SAH 99555; NWA 1296 differs by its texture and mineralogy, which are interpreted as resulting from rapid crystallization—an evidence of impact melting. Angrites cannot be produced by partial melting of a CV source because segregation of a “planetary” core is necessary to explain the low FeO/MgO ratio of magnesian olivines. Neither the odd Ca/Al ratio nor the very low SiO2 content can be explained by conventional partial melting scenarios. We suggest that carbonate is the key to angrite genesis. This is supported by the striking similarities with terrestrial melilitites (low SiO2, superchondritic Ca/Al ratio, presence of carbonate). The lack of alkalies could be the result of either loss after impact melting or absence of alkalies in the source.