bluuebunny/crossref_metadata_2025 huggingface dataset:
Tsunami generation and propagation from the Mjølnir asteroid impact
Authors: Glimsdal S. , Pedersen G. K. , Langtangen H. P. , Shuvalov V. , Dypvik H.
Published: January 2010

Abstract— In the late Jurassic period, about 142 million years ago, an asteroid hit the shallow paleo‐Barents Sea, north of present‐day Norway. The geological structure resulting from the impact is today known as the Mjølnir crater. The present work attempts to model the generation and the propagation of the tsunami from the Mjølnir impact. A multi‐material hydrocode SOVA is used to model the impact and the early stages of tsunami generation, while models based on shallow‐water theories are used to study the subsequent wave propagation in the paleo‐Barents Sea. We apply several wave models of varying computational complexity. This includes both three‐dimensional and radially symmetric weakly dispersive and nonlinear Boussinesq equations, as well as equations based on nonlinear ray theory. These tsunami models require a reconstruction of the bathymetry of the paleo‐Barents Sea.

The Mjølnir tsunami is characteristic of large bolides impacting in shallow sea; in this case the asteroid was about 1.6 km in diameter and the water depth was around 400 m. Contrary to earthquake‐ and slide‐generated tsunamis, this tsunami featured crucial dispersive and nonlinear effects: a few minutes after the impact, the ocean surface was formed into an undular bore, which developed further into a train of solitary waves. Our simulations indicate wave amplitudes above 200 m, and during shoaling the waves break far from the coastlines in rather deep water. The tsunami induced strong bottom currents, in the range of 30–90 km/h, which presumably caused a strong reworking of bottom sediments with dramatic consequences for the marine environment.
Crater geometry and ejecta thickness of the Martian impact crater Tooting
Authors: Mouginis‐Mark Peter J. , Garbeil Harold
Published: January 2010

Abstract— We use Mars Orbiter Laser Altimeter (MOLA) topographic data and Thermal Emission Imaging System (THEMIS) visible (VIS) images to study the cavity and the ejecta blanket of a very fresh Martian impact crater ˜29 km in diameter, with the provisional International Astronomical Union (IAU) name Tooting crater. This crater is very young, as demonstrated by the large depth/diameter ratio (0.065), impact melt preserved on the walls and floor, an extensive secondary crater field, and only 13 superposed impact craters (all 54 to 234 meters in diameter) on the ˜8120 km2 ejecta blanket. Because the pre‐impact terrain was essentially flat, we can measure the volume of the crater cavity and ejecta deposits. Tooting crater has a rim height that has >500 m variation around the rim crest and a very large central peak (1052 m high and >9 km wide). Crater cavity volume (i.e., volume below the pre‐impact terrain) is ˜380 km3 the volume of materials above the pre‐impact terrain is ˜425 km3. The ejecta thickness is often very thin (<20 m) throughout much of the ejecta blanket. There is a pronounced asymmetry in the ejecta blanket, suggestive of an oblique impact, which has resulted in up to ˜100 m of additional ejecta thickness being deposited down‐range compared to the up‐range value at the same radial distance from the rim crest. Distal ramparts are 60 to 125 m high, comparable to the heights of ramparts measured at other multi‐layered ejecta craters. Tooting crater serves as a fresh end‐member for the large impact craters on Mars formed in volcanic materials, and as such may be useful for comparison to fresh craters in other target materials.
The Villalbeto de la Peña meteorite fall: III. Bulk chemistry, porosity, magnetic properties, 57Fe Mössbauer spectroscopy, and Raman spectroscopy
Authors: Llorca Jordi , Gich Martí , Molins Elies
Published: January 2010

Abstract— Detailed mineralogical and chemical studies and measurements of the magnetic properties and porosity of the Villalbeto de la Peña (L6) chondrite are reported. The measured abundances of 36 chemical elements are within the range observed for L6 chondrites for most elements, except for Pd and Os, which are particularly abundant in Villalbeto de la Peña. The specific magnetic susceptibility of the meteorite is 4.85 ± 0.05 (in 10−9m3kg−1) and the porosity is 4.7%. The JRS/JS (1.2 ± 0.2 × 10−3) and HC (3.3 × 10−4 T) values recorded are among the lowest ever reported for a chondrite. 57Fe Mössbauer spectroscopy of the whole rock indicates that the meteorite faced oxidizing conditions prior to fall. The Mössbauer spectrum of the metal fraction shows the presence of the only ferromagnetic phases kamacite and taenite. No tetrataenite is present, which is in total accordance to magnetic studies. Raman spectra yield compositional values for olivine (χMg ∼0.76), orthopyroxene (χMg ∼0.79), and clinopyroxene (χMg ∼0.49). Raman spectra of phosphate in shock veins indicates that Villalbeto de la Peña was not severely shock‐metamorphosed.
Ernst Florens Friedrich Chladni (1756–1827) and the origins of modern meteorite research
Authors: Marvin Ursula B.
Published: January 2010

Abstract— In 1794, Ernst F. F. Chladni published a 63‐page book, Über den Ursprung der von Pallas gefundenen und anderer ihr änlicher Eisenmassen und üsber einige damit in Verbindung stehende Naturerscheinungen, in which he proposed that meteor‐stones and iron masses enter the atmosphere from cosmic space and form fireballs as they plunge to Earth. These ideas violated two strongly held contemporary beliefs: 1) fragments of rock and metal do not fall from the sky, and 2) no small bodies exist in space beyond the Moon. From the beginning, Chladni was severely criticized for basing his hypotheses on historical eyewitness reports of falls, which others regarded as folk tales, and for taking gross liberties with the laws of physics. Ten years later, the study of fallen stones and irons was established as a valid field of investigation. Today, some scholars credit Chladni with founding meteoritics as a science; others regard his contributions as scarcely worthy of mention. Writings by his contemporaries suggest that Chladni's book alone would not have led to changes of prevailing theories; thus, he narrowly escaped the fate of those scientists who propose valid hypotheses prematurely. However, between 1794 and 1798, four falls of stones were witnessed and widely publicized. There followed a series of epoch‐making analyses of fallen stones and “native irons” by the chemist Edward C. Howard and the mineralogist Jacques‐Louis de Bournon. They showed that all the stones were much alike in texture and composition but significantly different from the Earth's known crustal rocks. Of primary importance was Howard's discovery of nickel in the irons and the metal grains of the stones. This linked the two as belonging to the same natural phenomenon. These chemical results, published in February 1802, persuaded some of the leading scientists in England, France, and Germany that bodies do fall from the sky. Within a few months, chemists in France reported similar results and a new field of study was inaugurated internationally, although opposition lingered on until April 1803, when nearly 3,000 stones fell at L'Aigle in Normandy and transformed the last skeptics into believers. Chladni immediately received full credit for his hypothesis of falls, but decades passed before his linking of falling bodies with fireballs received general acceptance. His hypothesis of their origin in cosmic space met with strong resistance from those who argued that stones formed within the Earth's atmosphere or were ejected by lunar volcanoes. After 1860, when both of these hypotheses were abandoned, there followed a century of debate between proponents of an interstellar versus a planetary origin. Not until the 1950s did conclusive evidence of their elliptical orbits establish meteorite parent bodies as members of the solar system. Thus, nearly 200 years passed before the questions of origin that Chladni raised finally were resolved.
Physical properties of Martian meteorites: Porosity and density measurements
Authors: COULSON Ian M. , BEECH Martin , NIE Wenshuang
Published: January 2010

Abstract— Martian meteorites are fragments of the Martian crust. These samples represent igneous rocks, much like basalt. As such, many laboratory techniques designed for the study of Earth materials have been applied to these meteorites. Despite numerous studies of Martian meteorites, little data exists on their basic structural characteristics, such as porosity or density, information that is important in interpreting their origin, shock modification, and cosmic ray exposure history. Analysis of these meteorites provides both insight into the various lithologies present as well as the impact history of the planet's surface. We present new data relating to the physical characteristics of twelve Martian meteorites. Porosity was determined via a combination of scanning electron microscope (SEM) imagery/image analysis and helium pycnometry, coupled with a modified Archimedean method for bulk density measurements. Our results show a range in porosity and density values and that porosity tends to increase toward the edge of the sample. Preliminary interpretation of the data demonstrates good agreement between porosity measured at 100× and 300× magnification for the shergottite group, while others exhibit more variability. In comparison with the limited existing data for Martian meteorites we find fairly good agreement, although our porosity values typically lie at the low end of published values. Surprisingly, despite the increased data set, there is little by way of correlation between either porosity or density with parameters such as shock effect or terrestrial residency. Further data collection on additional meteorite samples is required before more definitive statements can be made concerning the validity of these observations.
Reclassification and thermal history of Trenzano chondrite
Authors: FIORETTI A. M. , DOMENEGHETTI M. C. , MOLIN G. , CÁMARA F. , ALVARO M. , AGOSTINI L.
Published: January 2010

Abstract— We present a new single‐crystal X‐ray diffraction (XRD) study performed on a suite of six orthopyroxene grains from the low‐shocked H6 Trenzano meteorite. The quenched intracrystalline Fe2+‐Mg ordering state in orthopyroxene preserves the memory of the cooling rate near closure temperature Tc, thus yielding useful constraints on the last thermal event undergone by the host rock. The orthopyroxene Tc of 522 ± 13 °C, calculated using a new calibration equation obtained by Stimpfl (2005b), is higher than in previously published H chondrite data. The orthopyroxene cooling rate at this Tc is about 100 °C/kyr. This fast rate is inconsistent with the much slower cooling rate expected for H6 in the onion shell structural and thermal model of chondrite parent bodies. A petrographic study carried out at the same time indicated that the Trenzano meteorite is an H5 chondrite and not an H6 chondrite, as it is officially classified. Furthermore, the two‐pyroxene equilibrium temperature of Trenzano (824 ± 24 °C), calculated with QUILF95, is similar to the two‐pyroxene temperature of 750–840 °C obtained for the Carcote (H5) chondrite (Kleinschrot and Okrusch 1999).
Mass‐dependent fractionation of nickel isotopes in meteoritic metal
Authors: COOK David L. , WADHWA Meenakshi , CLAYTON Robert N. , DAUPHAS Nicolas , JANNEY Philip E. , DAVIS Andrew M.
Published: January 2010

Abstract— We measured nickel isotopes via multicollector inductively coupled plasma mass spectrometry (MC‐ICPMS) in the bulk metal from 36 meteorites, including chondrites, pallasites, and irons (magmatic and non‐magmatic). The Ni isotopes in these meteorites are mass fractionated; the fractionation spans an overall range of ∼0.4‰ amu−1. The ranges of Ni isotopic compositions (relative to the SRM 986 Ni isotopic standard) in metal from iron meteorites (∼0.0 to ∼0.3‰ amu−1) and chondrites (∼0.0 to ∼0.2‰ amu−1) are similar, whereas the range in pallasite metal (∼–0.1 to 0.0‰ amu−1) appears distinct. The fractionation of Ni isotopes within a suite of fourteen IIIAB irons (∼0.0 to ∼0.3‰ amu−1) spans the entire range measured in all magmatic irons. However, the degree of Ni isotopic fractionation in these samples does not correlate with their Ni content, suggesting that core crystallization did not fractionate Ni isotopes in a systematic way. We also measured the Ni and Fe isotopes in adjacent kamacite and taenite from the Toluca IAB iron meteorite. Nickel isotopes show clearly resolvable fractionation between these two phases; kamacite is heavier relative to taenite by ∼0.4‰ amu−1. In contrast, the Fe isotopes do not show a resolvable fractionation between kamacite and taenite. The observed isotopic compositions of kamacite and taenite can be understood in terms of kinetic fractionation due to diffusion of Ni during cooling of the Fe‐Ni alloy and the development of the Widmanstätten pattern.
Extraterrestrial chromite in latest Maastrichtian and Paleocene pelagic limestone at Gubbio, Italy: The flux of unmelted ordinary chondrites
Authors: CRONHOLM Anders , SCHMITZ Birger
Published: January 2010

Abstract— –The distribution of sediment‐dispersed extraterrestrial (ordinary chondritic) chromite (EC) grains (>63 μm) has been studied across the latest Maastrichtian and Paleocene in the Bottaccione Gorge section at Gubbio, Italy. This section is ideal for determining the accumulation rate of EC because of its condensed nature and well‐constrained sedimentation rates. In a total of 210 kg of limestone representing eight samples of 14–28 kg distributed across 24 m of the Bottaccione section, only 6 EC grains were found (an average of 0.03 EC grains kg−1). In addition, one probable pallasitic chromite grain was found. No EC grains could be found in two samples at the Cretaceous‐Tertiary (K‐T) boundary, which is consistent with the K‐T boundary impactor being a carbonaceous chondrite or comet low in chromite. The average influx of EC to Earth is calculated to ∼∼0.26 grain m−2 kyr−1. This corresponds to a total flux of ∼∼200 tons of extraterrestrial matter per year, compared to ∼∼30,000 tons per year, as estimated from Os isotopes in deep‐sea sediments. The difference is explained by the EC grains representing only unmelted ordinary chondritic matter, predominantly in the size range from ∼∼0.1 mm to a few centimeters in diameter. Sedimentary EC grains can thus give important information on the extent to which micrometeorites and small meteorites survive the passage through the atmosphere. The average of 0.03 EC grain kg−1 in the Gubbio limestone contrasts with the up to ∼∼3 EC grains kg−1 in mid‐Ordovician limestone that formed after the disruption of the L chondrite parent body in the asteroid belt at ∼∼470 Ma. The two types of limestone were deposited at about the same rate, and the difference in EC abundance gives support for an increase by two orders of magnitude in the flux of chondritic matter directly after the asteroid breakup.
The regolith portion of the lunar meteorite Sayh al Uhaymir 169
Authors: AL‐KATHIRI A. , GNOS E. , HOFMANN B. A.
Published: January 2010

Abstract— –Sayh al Uhaymir (SaU) 169 is a composite lunar meteorite from Oman that consists of polymict regolith breccia (8.44 ppm Th), adhering to impact‐melt breccia (IMB; 32.7 ppm Th). In this contribution we consider the regolith breccia portion of SaU 169, and demonstrate that it is composed of two generations representing two formation stages, labeled II and III. The regolith breccia also contains the following clasts: Ti‐poor to Ti‐rich basalts, gabbros to granulites, and incorporated regolith breccias. The average SaU 169 regolith breccia bulk composition lies within the range of Apollo 12 and 14 soil and regolith breccias, with the closest correspondence being with that of Apollo 14, but Sc contents indicate a higher portion of mare basalts. This is supported by relations between Sm‐Al2O3, FeO‐Cr2O3‐TiO2, Sm/Eu and Th‐K2O. The composition can best be modeled as a mixture of high‐K KREEP, mare basalt and norite/troctolite, consistent with the rareness of anorthositic rocks. The largest KREEP breccia clast in the regolith is identical in its chemical composition and total REE content to the incompatible trace‐element (ITE)‐ rich high‐K KREEP rocks of the Apollo 14 landing site, pointing to a similar source. In contrast to Apollo 14 soil, SaU 169 IMB and SaU 169 KREEP breccia clast, the SaU 169 regolith is not depleted in K/Th, indicating a low contribution of high‐Th IMB such as the SaU 169 main lithology in the regolith. The data presented here indicate the SaU 169 regolith breccia is from the lunar front side, and has a strong Procellarum KREEP Terrane signature.
An integrated geophysical and geological study of the Monturaqui impact crater, Chile
Authors: UGALDE Hernan , VALENZUELA Millarca , MILKEREIT Bernd
Published: January 2010

Abstract— –The Monturaqui impact crater (350–370 m in diameter and 0.1 Ma old), located in a remote area in northern Chile, was surveyed in December 2003 with detailed geophysics (gravity and magnetics), topography, petrophysics, and geology. The geology of the Monturaqui area is characterized by a basement of Paleozoic granites overlain by Pliocene ignimbrite units. No impact breccia was found in the area. The granites are the main lithology affected by the impact. Although the granite samples analyzed did not show evidence of shock metamorphism, quartz, and to a lesser extent feldspar and biotite grains from impactite samples exhibit different degrees of shock, ranging from planar microdeformation and cleavage to the development of intense planar deformation features (PDFs) and diaplectic glasses in some grains. The differential GPS survey allowed the creation of a detailed digital elevation model of the crater. Its dimensions are 370 m along the east‐west direction, 350 m along the north‐south direction, and ∼∼34 m deep. The crater exhibits a circular morphology with a preferred northwest‐southeast elongation that coincides with the steepest slopes (∼∼35°) on the southeast edge. The newly acquired gravity data shows a negative anomaly of ∼∼1 mGal at the center and allowed the creation of a 3‐D model with a RMS error of <0.1 mGal, which supports the predictions of a fracturing‐induced low‐density granitic layer on top of the unfractured basement.
Petrography, geochemistry, and alteration of country rocks from the Bosumtwi impact structure, Ghana
Authors: KARIKARI Forson , FERRIÈRE Ludovic , KOEBERL Christian , REIMOLD Wolf Uwe , MADER Dieter
Published: January 2010

Abstract— Samples of the country rocks that likely constituted the target rocks at the 1.07 Myr old Bosumtwi impact structure in Ghana, West Africa, collected outside of the crater rim in the northern and southern parts of the structure, were studied for their petrographic characteristics and analyzed for their major‐ and trace‐element compositions. The country rocks, mainly meta‐graywacke, shale, and phyllite of the Early Proterozoic Birimian Supergroup and some granites of similar age, are characterized by two generations of alteration. A pre‐impact hydrothermal alteration, often along shear zones, is characterized by new growth of secondary minerals, such as chlorite, sericite, sulfides, and quartz, or replacement of some primary minerals, such as plagioclase and biotite, by secondary sericite and chlorite. A late, argillic alteration, mostly associated with the suevites, is characterized by alteration of the melt/glass clasts in the groundmass of suevites to phyllosilicates. Suevite, which occurs in restricted locations to the north and to the south‐southwest of the crater rim, contains melt fragments, diaplectic quartz glass, ballen quartz, and clasts derived from the full variety of target rocks. No planar deformation features (PDFs) in quartz were found in the country rock samples, and only a few quartz grains in the suevite samples show PDFs, and in rare cases two sets of PDFs. Based on a total alkali element‐silica (TAS) plot, the Bosumtwi granites have tonalitic to quartz‐dioritic compositions. The Nb versus Y and Ta versus Yb discrimination plots show that these granites are of volcanic‐arc tectonic provenance. Provenance studies of the metasedimentary rocks at the Bosumtwi crater have also indicated that the metasediments are volcanic‐arc related. Compared to the average siderophile element contents of the upper continental crust, both country rocks and impact breccias of the Bosumtwi structure show elevated siderophile element contents. This, however, does not indicate the presence of an extraterrestrial component in Bosumtwi suevite, because the Birimian country rocks also have elevated siderophile element contents, which is thought to result from regional hydrothermal alteration that is also related to widespread sulfide and gold mineralization.
The ICDP Lake Bosumtwi impact crater scientific drilling project (Ghana): Core LB‐08A litho‐log, related ejecta, and shock recovery experiments
Authors: DEUTSCH Alexander , LUETKE Sabine , HEINRICH Volker
Published: January 2010

Abstract— The 1.07 Myr old Lake Bosumtwi impact crater in Ghana was drilled within the framework of the International Continental Scientific Drilling Project (ICDP). Hole LB‐08A, drilled into the outer flank of the central uplift and with a total depth of 451 m, yielded 215.71 m of impact‐related rocks. This paper summarizes observations of the lithological logging on core LB‐08A. Between a depth of 235.6 and ∼260 m, the section consists of a melt‐bearing allochthonous, polymict, and mostly clast‐supported impact breccia. Down to ∼418 m, the section comprises a rather uniform unit of meta‐graywacke alternating with phyllite to slate (lower greenschist facies); few (par‐) autochthonous impact breccia bodies and rare impact dike breccias are present. The lowermost part of the section contains several centimeter‐ to decimeter‐thick melt‐bearing breccia dikes in country rocks identical to those occurring above. Omnipresent fracturing was mapped in a qualitative manner. Most prominent shock effects in the uplifted target rocks comprise planar fractures and deformation elements in quartz and polysynthetic twinning in carbonate minerals; the maximum shock pressure as evidenced by quartz is below 26 GPa. The allochthonous breccias occasionally contain a few vol% of melt particles. Suevites occur outside the crater rim, carrying diaplectic crystals, coesite, and ballen quartz as well as true melt glasses and a variety of lithic clasts, among those spectacular staurolite‐rich mica‐schists. The recorded shock level in the uplifted target rocks is lower than expected and modeled. Shock recovery experiments with analogue carbonaceous graywackes at 34 and 39.5 GPa yielded nearly complete transformation of quartz into diaplectic glass. We therefore exclude a specific shock behavior of the soft, fluid‐rich target material (carbonaceous graywackes, shales, slates) in core LB‐08A as the prime or only reason for the melt deficit and the generally low shock levels recorded inside the Lake Bosumtwi impact crater.
Geochemistry of impactites and basement lithologies from ICDP borehole LB‐07A, Bosumtwi impact structure, Ghana
Authors: CONEY Louise , REIMOLD Wolf Uwe , GIBSON Roger L. , KOEBERL Christian
Published: January 2010

Abstract— In 2004, a drilling project by the International Continental Scientific Drilling Program (ICDP) at the Bosumtwi impact crater, Ghana (1.07 Myr old and 10.5 km in diameter), obtained drill core LB‐07A, which sampled impactites and underlying metasediments in the crater moat surrounding the small central uplift of the structure. The LB‐07A core consists of three sequences: 82.29 m of an upper impactite sequence of alternating polymict lithic and suevitic impact breccias overlying 54.88 m of so‐called lower impactite of monomict impact breccia with several suevite intercalations, and 74.53 m of meta‐graywacke and altered shale of the basement, also containing a number of suevite intercalations. Major‐ and trace‐element characteristics of all three sequences have been determined to investigate breccia formation and the role of the respective basement lithologies therein. Compositions of polymict impact breccias of the crater fill revealed by core LB‐07A are compared with the compositions of the Ivory Coast tektites and the fallout suevites. The impactites of the LB‐07A borehole appear well homogenized with respect to the silicate component, and little change in the ranges of many major‐ and trace‐element differences is seen along the length of the borehole (except for Fe2O3, MgO, and CaO contents). Much scatter is observed for a number of elements, and in many cases this increases with depth. It is proposed that any variability in composition is likely the function of clast population differences (i.e., also of relatively small sample sizes). No systematic compositional difference between polymict lithic and suevitic impact breccias is evident. An indication of carbonate enrichment due to hydrothermal alteration is observed in samples from all lithologies. The impactites of the borehole generally show intermediate compositions to previously defined target rocks. The fallout suevites have comparable major element abundances, except for relatively lower MgO contents. The Ivory Coast tektites are generally similar in composition to the LB‐07A suevites, but broader ranges in MgO and CaO contents are observed for the LB‐07A suevites.
Platinum group elements provide no indication of a meteoritic component in ICDP cores from the Bosumtwi crater, Ghana
Authors: GODERIS S. , TAGLE R. , SCHMITT R. T. , ERZINGER J. , CLAEYS Ph.
Published: January 2010

Abstract— In an attempt to identify the type of projectile, 14 samples from the Bosumtwi crater in Ghana were analyzed for platinum group element (PGE) concentrations by nickel sulfide fire assay inductively coupled plasma—mass spectrometry (ICP‐MS). The majority of the samples come from the impactite material recovered by cores LB‐07A and LB‐08A, which were drilled by the International Continental Scientific Drilling program (ICDP). One sample originates from the fallback material found at the contact between the impactite and the overlying lake sediment in core LB‐05B. No clear signature of a meteoritic contamination was identified in the 13 impactite samples. The target rock apparently dominates the PGE contribution in the impactites. These results agree with the PGE concentrations reported for the suevites collected at the crater rim and in other parts of the Bosumtwi ICDP cores. However, based on Cr and Os isotopic signatures, a meteoritic component could be present in the sample of fallback material, supporting the reports of the existence of meteoritic material in the Ivory Coast tektites. Further analyses of the fallback material from the Bosumtwi drill cores should confirm (or not) this first result.
Lithological and structural characteristics of the Lake Bosumtwi impact crater, Ghana: Interpretation of acoustic televiewer images
Authors: HUNZE Sabine , WONIK Thomas
Published: January 2010

Abstract— Bosumtwi is a very well‐preserved 1.07 Myr old, complex terrestrial impact crater located in south‐central Ghana, West Africa. The impact structure has a diameter of about 10.5 km and was formed in 2.1–2.2 Gyr Precambrian metasedimentary and metavolcanic rocks. Drilling and logging was carried out during the Lake Bosumtwi Drilling Project (BCDP) which was supported by the International Continental Scientific Drilling Program (ICDP). One of the aims of this project is to achieve detailed information on the subsurface structure and crater fill of one of the best preserved large young impact structures.

We interpreted the wireline logs and televiewer images. The physical properties including shallow resistivity, p‐wave velocity, magnetic susceptibility, and borehole diameter of the breccia differ significantly from those of the meta‐graywackes and slate/phyllites. Fractures observed in the televiewer images are interpreted to determine their characteristic structural features. The fracture dip angles are steep (50–70°) and the two main dip directions are southeast and southwest. Most fractures observed in the borehole are open. The indicated main stress direction is north‐south.
Petrography and shock‐related remagnetization of pyrrhotite in drill cores from the Bosumtwi Impact Crater Drilling Project, Ghana
Authors: KONTNY Agnes , ELBRA Tiiu , JUST Jana , PESONEN Lauri J. , SCHLEICHER Anja M. , ZOLK Jochen
Published: January 2010

Abstract— Rock magnetic and magnetic mineralogy data are presented from the International Continental Scientific Drilling Program (ICDP) drill cores LB‐07A and LB‐08A of the Bosumtwi impact structure in order to understand the magnetic behavior of impact and target lithologies and their impact‐related remagnetization mechanism. Basic data for the interpretation of the magnetic anomaly patterns and the magnetic borehole measurements as well as for new magnetic modeling are provided. Magnetic susceptibility (150–500 × 10−6 SI) and natural remanent magnetization (10−3−10−1 A/m) are generally weak, but locally higher values up to 10.6 × 10−3 SI and 43 A/m occur. Sixty‐three percent of the investigated rock specimens show Q values above 1 indicating that remanence clearly dominates over induced magnetization, which is a typical feature of impact structures. Ferrimagnetic pyrrhotite is the main magnetite phase, which occurs besides minor magnetite and a magnetic phase with a Curie temperature between 330 and 350 °C, interpreted as anomalous pyrrhotite. Coercive forces are between 20 and 40 mT. Brecciation and fracturing of pyrrhotite is a common feature confirming its pre‐impact origin. Grain sizes of pyrrhotite show a large variation but the numerous stress‐induced nanostructures observable by transmission electron microscopy (TEM) are assumed to behave as single‐domain grains. We suggest that the drilled rocks lost their pre‐shock remanence memory during the shock event and acquired a new, stable remanence during shock‐induced grain size reduction. The observed brittle microstructures indicate temperatures not higher than 250 °C, which is below the Curie temperature of ferrimagnetic pyrrhotite (310 °C).
The Lake Bosumtwi meteorite impact structure, Ghana—Where is the magnetic source?
Authors: UGALDE Hernan , MORRIS William A. , PESONEN Lauri J. , DANUOR Sylvester K.
Published: January 2010

Abstract— The Bosumtwi impact structure (Ghana) is a young and well‐preserved structure where a vast amount of information is available to constrain any geophysical model. Previous analysis of the airborne magnetic data and results of numerical simulation of impact predicted a strongly magnetic impact‐melt body underneath the lake. Recent drilling through the structure did not penetrate such an expected impact‐melt rock magnetic source. A new 3‐D magnetic model for the structure was constructed based on a newly acquired higher‐resolution marine magnetic data set, with consideration of the observed gravity data on the lake, previous seismic models, and the magnetic properties and lithology identified in the two International Continental Scientific Drilling Program (ICDP) deep boreholes. The new model contains highly magnetic bodies located in the northeast sector of the structure, not centered onto the drilling sites. As in previous models, higher magnetization than that measured in outcropping impactites had to be assigned to the unexposed source bodies. Integration of the new model with the borehole petrophysics and published geology indicates that these bodies likely correspond to an extension to the south of the Kumasi batholith, which outcrops to the northeast of the structure. The possibility that these source bodies are related to the seismically identified central uplift or to an unmapped impact‐melt sheet predicted by previous models of the structure is not supported. Detailed magnetic scanning of the Kumasi batholith to the north, and the Bansu intrusion to the south, would provide a test for this interpretation.
Zoning patterns of Fe and V in spinel from a type B Ca‐Al‐rich inclusion: Constraints on subsolidus thermal history
Authors: PAQUE J. M. , BURNETT D. S. , BECKETT J. R.
Published: January 2010

Abstract We obtained two‐dimensional concentration maps for the minor elements Fe and V in 21 spinel crystals in the Allende type B1 inclusion TS‐34 with a 4–5 μm resolution. Locally high concentrations of Fe occur along at least one edge of the spinels and decrease toward the center of the grains. Enrichment in V can also occur along edges or at corners. In general, there is no overall correlation of the Fe and V distributions, but in local regions of two grains, the V and Fe distributions are correlated, strongly suggesting a local source for both elements. In these two grains, opaque assemblages are present that appear to locally control the V distributions. This, coupled with previous work, suggests that prior to alteration, TS‐34 contained V‐rich metal. Oxidation of this metal during alteration can account for the edge/corner V enrichments, but provide only minor FeO contributions, explaining the overall lack of correlation between Fe and V. Most of the FeO appears to have been externally introduced along spinel boundaries during alteration. These alteration phases served as sources for diffusion of FeO into spinel. FeO distributions in spinel lead to a mean attenuation length of ˜8 μm and, using literature diffusion coefficients in isothermal and exponential cooling approximations for peak temperatures in the range 600–700°C, this leads to a time scale for calcium‐aluminum‐rich inclusion (CAI) alteration in the range of decades to centuries.
An integrated approach to understanding Apollo 16 impact glasses: Chemistry, isotopes, and shape
Authors: DELANO J. W. , ZELLNER N. E. B. , BARRA F. , OLSON E. , SWINDLE T. D. , TIBBETTS N. J. , WHITTET D. C. B.
Published: January 2010

Abstract The major‐ and minor‐element abundances were determined by electron microprobe in 1039 glasses from regoliths and regolith breccias to define the compositional topology of lunar glasses at the Apollo 16 landing site in the central highlands of the Moon. While impact glasses with chemical compositions similar to local materials (i.e., Apollo 16 rocks and regoliths) are abundant, glasses with exotic compositions (i.e., transported from other areas of the Moon) account for up to ˜30% of the population. A higher proportion of compositionally exotic, angular glass fragments exists when compared to compositionally exotic glass spherules. Ratios of non‐volatile lithophile elements (i.e., Al, Ti, Mg) have been used to constrain the original source materials of the impact glasses. This approach is immune to the effects of open‐system losses of volatile elements (e.g., Si, Na, K). Four impact glasses from one compositionally exotic group (low‐Mg high‐K Fra Mauro; lmHKFM) were selected for 40Ar/39 Ar dating. The individual fragments of lmHKFM glass all yielded ages of ˜3750 ± 50 Ma for the time of the impact event. Based on the petrography of these individual glasses, we conclude that the likely age of the impact event that formed these 4 glasses, as well as the possible time of their ballistic arrival at the Apollo 16 site from a large and distant cratering event (perhaps in the Procellarum KREEP terrain) (Zeigler et al. 2004), is 3730 ± 40 Ma, close to the accepted age for Imbrium.
Curation, spacecraft recovery, and preliminary examination for the Stardust mission: A perspective from the curatorial facility
Authors: Zolensky Michael , Nakamura‐Messenger Keiko , Fletcher Lisa , See Thomas
Published: January 2010

Abstract— We describe briefly some of the challenges to the Stardust mission, curation, and sample preliminary analysis from the perspective of the Curation Office at the Johnson Space Center. Our goal is to inform persons planning future sample returns so that they may learn from both our successes and challenges (and avoid some of our mistakes). The Curation Office played a role in the mission from its inception, most critically assisting in the design and implementation of the spacecraft contamination control plan, and in planning and documenting the recovery of the spacecraft re‐entry capsule in Utah. A unique class 100 cleanroom was built to maintain the returned comet and interstellar samples in clean comfort, and to permit dissection and allocation of samples for analysis.
A TEM study of thermally modified comet 81P/Wild 2 dust particles by interactions with the aerogel matrix during the Stardust capture process
Authors: Leroux Hugues , Rietmeijer Frans J. M. , Velbel Michael A. , Brearley Adrian J. , Jacob Damien , Langenhorst Falko , Bridges John C. , Zega Thomas J. , Stroud Rhonda M. , Cordier Patrick , Harvey Ralph P. , Lee Martin , Gounelle Matthieu , Zolensky Mike E.
Published: January 2010

Abstract— We report the results of high‐resolution, analytical and scanning transmission electron microscopy (STEM), including intensive element mapping, of severely thermally modified dust from comet 81P/Wild 2 caught in the silica aerogel capture cells of the Stardust mission. Thermal interactions during capture caused widespread melting of cometary silicates, Fe‐Ni‐S phases, and the aerogel. The characteristic assemblage of thermally modified material consists of a vesicular, silica‐rich glass matrix with abundant Fe‐Ni‐S droplets, the latter of which exhibit a distinct core‐mantle structure with a metallic Fe,Ni core and a iron‐sulfide rim. Within the glassy matrix, the elemental distribution is highly heterogeneous. Localized amorphous “dust‐rich” patches contain Mg, Al, and Ca in higher abundances and suggest incomplete mixing of silicate progenitors with molten aerogel. In some cases, the element distribution within these patches seems to depict the outlines of ghost mineral assemblages, allowing the reconstruction of the original mineralogy. A few crystalline silicates survived with alteration limited to the grain rims. The Fe‐ and CI‐normalized bulk composition derived from several sections show CI‐chondrite relative abundances for Mg, Al, S, Ca, Cr, Mn, Fe, and Ni. The data indicate a 5 to 15% admixture of fine‐grained chondritic comet dust with the silica glass matrix. These strongly thermally modified samples could have originated from a finegrained primitive material, loosely bound Wild 2 dust aggregates, which were heated and melted more efficiently than the relatively coarse‐grained material of the crystalline particles found elsewhere in many of the same Stardust aerogel tracks (Zolensky et al. 2006).
Origin and formation of iron silicide phases in the aerogel of the Stardust mission
Authors: Rietmeijer Frans J. M. , Nakamura Tomoki , Tsuchiyama Akira , Uesugi Kentaro , Nakano Tsukasa , Leroux Hugues
Published: January 2010

Abstract—Suessite along with hapkeite and more Fe‐rich iron‐silicides up to Fe7Si2formed near the entrance of aerogel track #44. These phases are ˜100 nm, quenched‐melt spheres, but the post‐impact cooling regime was such that melt vitrification produced a poly cry stalline mixture of Fe silicides and kamacite. The compositional similarities of the impact‐produced Fe‐Si phases and the Fe‐Ni‐S phases scattered throughout the aerogel capture medium strongly supports the idea that Fe silicides resulted from a reaction between molten Fe‐Ni‐S phases and aerogel at very high heating and cooling rates. Temperatures of around 1500 °C are inferred from the observed compositions had the silicide spheres formed at thermodynamic equilibrium, which seems unlikely. When the conditions were kinetically controlled, they could have been similar to those leading to the formation of solids with predictable deep metastable eutectic compositions in laboratory condensation experiments.
Transmission electron microscopy of cometary residues from micron‐sized craters in the Stardust Al foils
Authors: Leroux Hugues , STroud Rhonda M. , Dai Zu Rong , Graham Giles A. , Troadec David , Bradley John P. , Teslich Nick , Borg Janet , Kearsley Anton T. , Hörz Friedrich
Published: January 2010

Abstract— We report transmission electron microscopy (TEM) investigations of micro‐craters that originated from hypervelocity impacts of comet 81P/Wild 2 dust particles on the aluminium foil of the Stardust collector. The craters were selected by scanning electron microscopy (SEM) and then prepared by focused ion beam (FIB) milling techniques in order to provide electron transparent cross‐sections for TEM studies. The crater residues contain both amorphous and crystalline materials in varying proportions and compositions. The amorphous component is interpreted as resulting from shock melting during the impact and the crystalline phases as relict minerals. The latter show evidence for shock metamorphism. Based on the residue morphology and the compositional variation, the impacting particles are inferred to have been dominated by mixtures of submicron olivine, pyroxene and Fe sulfide grains, in agreement with prior results of relatively coarse‐grained mineral assemblages in the aerogel collector.
Chemical composition and heterogeneity of Wild 2 cometary particles determined by synchrotron X‐ray fluorescence
Authors: Lanzirotti A. , Sutton S. R. , Flynn G. J. , Newville M. , Rao W.
Published: January 2010

Abstract— Seven cometary dust particle tracks in Stardust aerogel were studied using synchrotron X‐ray fluorescence methods at the National Synchrotron Light Source (NY) and Advanced Photon Source (IL). Elemental maps were produced for each of the tracks and elemental abundances for 156 individual fragments within these tracks were determined. Whole‐track elemental abundances were inferred by summing the elemental masses for the fragments in each track and scaling by the ratio of total Fe in the map and total Fe in the fragments. In general, whole‐track and terminal‐particle abundances are dissimilar. The total Fe masses ranged from 4 to 2200 pg, corresponding to impactors in the size range of 2.7 to 22 μm if Fe abundances are equal to the chondritic value. Systematic variations in element abundance with fragment distance from the aerogel entry point were generally subtle but were pronounced in one track (C2115,19). In this track, Zn/Fe was about three orders of magnitude higher at the top, Cr/Fe was two orders of magnitude higher at the bottom, and S was relatively uniform. Compositional convergence data showed that typically analysis of ˜10 fragments was needed to reach convergent whole‐track abundance. Zinc was an exception, showing non‐convergent profiles and steps due to the presence of rare, high‐Zn fragments. The resulting whole‐track elemental abundances show diverse patterns that are generally chondritic (i.e., within a factor of three of CI abundances) with some exceptions, notably depletions in S and enrichments in the moderately volatile elements Cu, Zn, and Ga. Enrichments in large ion lithophile elements relative to Fe were observed in one track. Correlation matrices showed several strong elemental correlations, notably selenium associated with sulfur (sulfides), a ubiquitous correlation of the first‐row transition metals Cr, Mn, and Fe attributed to the presence of pyroxene, and enrichments of gallium associated with calcium, likely affiliated with Mg‐Al glass.
TOF‐SIMS analysis of cometary matter in Stardust aerogel tracks
Authors: Stephan Thomas , Rost Detlef , Vicenzi Edward P. , Bullock Emma S. , MacPherson Glenn J. , Westphal Andrew J. , Snead Christopher J. , Flynn George J. , Sandford Scott A. , Zolensky Michael E.
Published: January 2010

Abstract—Cometary matter in aerogel samples from the Stardust mission was investigated with TOF‐SIMS for its elemental and organic composition. While single grains >1 μm are highly variable in their chemical composition, nanometer‐scale material found in the wall of one track has within a factor of 1.22 bulk CI chondritic element ratios relative to Fe for Na, Mg, A1, Ti, Cr, Mn, and Co. Compared to CI, a depletion in Ca by a factor of four and an enrichment in Ni by a factor of two was observed. These results seem to confirm recent reports of a CI‐like bulk composition of Wild 2. The analysis of organic compounds in aerogel samples is complicated by the presence of contaminants in the capture medium. However, polycyclic aromatic hydrocarbons that could possibly be attributed to the comet were observed.
Comparing Wild 2 particles to chondrites and IDPs
Authors: Zolensky Michael , Nakamura‐Messenger Keiko , Rietmeijer Frans , Leroux Hugues , Mikouchi Takashi , Ohsumi Kazumasa , Simon Steven , Grossman Lawrence , Stephan Thomas , Weisberg Michael , Velbel Michael , Zega Thomas , Stroud Rhonda , Tomeoka Kazushige , Ohnishi Ichiro , Tomioka Naotaka , Nakamura Tomoki , Matrajt Graciela , Joswiak David , Brownlee Donald , Langenhorst Falko , Krot Alexander , Kearsley Anton , Ishii Hope , Graham Giles , Dai Zu Rong , Chi Miaofang , Bradley John , Hagiya Kenji , Gounelle Matthieu , Keller Lindsay , Bridges John
Published: January 2010

Abstract— We compare the observed composition ranges of olivine, pyroxene, and Fe‐Ni sulfides in Wild 2 grains with those from chondritic interplanetary dust particles (IDPs) and chondrite classes to explore whether these data suggest affinities to known hydrous materials in particular. Wild 2 olivine has an extremely wide composition range, from Fa0–96, with a pronounced frequency peak at Fa1. The composition range displayed by the low‐calcium pyroxene is also very extensive, from Fs48 to Fs0, with a significant frequency peak centered at Fs5. These ranges are as broad or broader than those reported for any other extraterrestrial material. Wild 2 Fe‐Ni sulfides mainly have compositions close to that of FeS, with less than 2 atom% Ni; to date, only two pentlandite grains have been found among the Wild grains, suggesting that this mineral is not abundant. The complete lack of compositions between FeS and pentlandite (with intermediate solid solution compositions) suggests (but does not require) that FeS and pentlandite condensed as crystalline species, i.e., did not form as amorphous phases, which later became annealed. While we have not yet observed any direct evidence of water‐bearing minerals, the presence of Ni‐bearing sulfides, and magnesium‐dominated olivine and low‐Ca pyroxene does not rule out their presence at low abundance. We do conclude that new investigations of major‐ and minor‐ element compositions of chondrite matrix and IDPs are required.
Silicate minerals and Si‐O glass in comet Wild 2 samples: Transmission electron microscopy
Authors: Tomeoka Kazushige , Tomioka Naotaka , Ohnishi Ichiro
Published: January 2010

Abstract— A transmission electron microscope (TEM) study of seven comet Wild 2 samples shows that three samples consist mainly of olivine and pyroxene and four samples consist of Mg‐Fe‐bearing Si‐O glass with minor amounts of Fe‐Ni sulfide and metal. The olivine in the silicate‐rich samples differs in fayalite content between the samples and shows a wide range of fayalite content within individual samples, indicating that the degree of thermal metamorphism on the comet, if any, was extremely low. One olivine grain has a high density of dislocations with Burgers vector b = [001], suggesting that the Wild 2 particles experienced hypervelocity impacts before capture. The structural type and composition of pyroxene differ between the samples and within individual samples. Both low‐Ca and high‐Ca pyroxenes are present. Enstatite occurs as ortho‐ and clinoenstatite, suggesting that the Wild 2 particles contain materials that went through distinct high‐temperature and cooling histories.

One silicate‐rich sample exhibits a zone texture consisting of a core of low‐Ca pyroxene surrounded by an inner rim of Mg‐Fe‐bearing Si‐O‐rich glass and an outer rim of melted aerogel. The texture suggests that the inner rim was formed by the mixing of melted cometary low‐Ca pyroxene and melted aerogel during capture heating.

The four Mg‐Fe‐bearing, Si‐O glass‐rich samples show close similarities in mineralogy and texture to the inner rim of the zoned silicate‐rich sample. The four samples are probably secondary products formed by interaction between melted cometary silicates and melted aerogel during the capture process.