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1

Morphology and crystal structures of solar and presolar Al2O3 in unequilibrated ordinary chondrites  

NASA Astrophysics Data System (ADS)

Corundum, the thermodynamically stable phase of alumina (Al2O3), is one of the most refractory dust species to condense around evolved stars. Presolar alumina in primitive chondrites has survived various kinds of processing in circumstellar environments, the interstellar medium (ISM), the Sun's parent molecular cloud, and the protosolar disk. The morphology and crystal structure of presolar alumina grains may reflect their formation and evolution processes, but the relative importance of these two types of processes is poorly understood. In this study, we performed detailed morphological observations of 185 alumina grains extracted from unequilibrated ordinary chondrites (Semarkona, Bishunpur, and RC075). We also performed electron back-scattered diffraction analyses of 122 grains and oxygen isotopic analyses of 107 grains. Dissolution experiments on corundum and transition alumina phases were carried out to examine the possibility of the alteration of surface structures of alumina grains by the chemical separation procedures of chondrites.

Takigawa, Aki; Tachibana, Shogo; Huss, Gary R.; Nagashima, Kazuhide; Makide, Kentaro; Krot, Alexander N.; Nagahara, Hiroko

2014-01-01

2

Petrographic and oxygen-isotopic study of refractory forsterites from R-chondrite Dar al Gani 013 (R3.5-6), unequilibrated ordinary and carbonaceous chondrites  

NASA Astrophysics Data System (ADS)

We have conducted petrographic, chemical and in-situ oxygen isotopic studies of refractory forsterites from unequilibrated ordinary and carbonaceous chondrites as well as an unequilibrated R-chondrite. Refractory forsterites occur in all types of unequilibrated chondrites and all have very similar chemical composition with low FeO and high refractory lithophile element (RLE) contents. Refractory forsterites are typically enriched in 16O relative to 'normal' olivine independent of the bulk O-isotope ratios of the parent meteorites. Analyses of refractory forsterites spread along a ? 17O mixing line with ? 17O ranging from +2 to -10‰. Due to similarities in oxygen isotopes and chemical compositions, we conclude that refractory forsterites of various types of chondrites come from a single common reservoir. Implications of this hypothesis for the chemical and O-isotope evolution of silicates in the early solar nebular are discussed.

Pack, Andreas; Yurimoto, Hisayoshi; Palme, Herbert

2004-03-01

3

Oxygen Isotope Composition of Refractory Forsterite in R-Chondrite Dar Al Gani 013, Unequilibrated Ordinary, and Carbonaceous Chondrites  

NASA Astrophysics Data System (ADS)

We have measured O-isotope composition of refractory forsterite in different carbonaceous, ordinary and R-chondrites using SIMS. We will discuss a model for the formation of the population of refractory forsterite pre-dating the formation of the different chondrite types.

Pack, A.; Yurimoto, H.; Palme, H.

2002-03-01

4

A Petrologic and bulk Chemical Characterization of the Unequilibrated Ordinary Chondrite Northwest Africa 5717  

NASA Astrophysics Data System (ADS)

We examine the chemical group affinities of Northwest Africa 5717 (Type 3.05) in terms of its petrologic and bulk chemical characteristics and test its apparent dual lithology. Preliminary data suggest it to be related to L- and LL-chondrites.

Bigolski, J. N.; Friedrich, J. M.; Weisberg, M. K.; O'Keefe, M.-C.

2014-09-01

5

Rock magnetic properties of dusty olivine: a potential carrier of pre-accretionary remanence in unequilibrated ordinary chondrites  

NASA Astrophysics Data System (ADS)

The mechanism of chondrule formation is an important outstanding question in cosmochemistry. Magnetic signals recorded by Fe-Ni nanoparticles in chondrules could carry clues to their origin. Recently, research in this area has focused on 'dusty olivine' grains within ordinary chondrites as potential carriers of pre-accretionary remanence. Dusty olivine is characterised by the presence of sub-micron Fe-Ni inclusions within the olivine host. These metal particles form via subsolidus reduction of the olivine during chondrule formation and are thought to be protected from subsequent chemical and thermal alteration by the host olivine. Three sets of synthetic dusty olivines have been produced, using natural olivine (average Ni-content of 0.3 wt%), synthetic Ni-containing olivine (0.1wt% Ni) and synthetic Ni-free olivine as starting materials. The starting materials were ground to powders, packed into a 2-3 mm3 graphite crucible, heated up to 1350 °C under a pure CO gas flow and kept at this temperature for 10 minutes. After this the samples were held in a fixed orientation and quenched into water in a range of known magnetic fields, ranging from 0.2 mT to 1.5 mT. We present here for the first time an analysis of a new FORC-based method of paleointensity determination applied to metallic Fe-bearing samples [1, 2]. The method uses a first-order reversal curve (FORC) diagram to generate a Preisach distribution of coercivities and interaction fields within the sample and then physically models the acquisition of TRM as a function of magnetic field, temperature and time using thermal relaxation theory. The comparison of observed and calculated NRM demagnetisation spectra is adversely effected by a large population of particles in the single-vortex state. Comparison of observed and calculated REM' curves, however, yields much closer agreement in the high-coercivity SD-dominated range. Calculated values of the average REM' ratio show excellent agreement with the experimental values - including the observed non-linearity of the remanence acquisition curve - suggesting that this method has the potential to reduce the uncertainties in non-heating paleointensity methods for extraterrestrial samples. [1] AR Muxworthy and D Heslop(2011) A Preisach method for estimating absolute paleofield intensity under the constraint of using only isothermal measurements: 1. Theoretical framework. Journal of Geophysical Research, 116, B04102, doi:10.1029/2010JB007843. [2] AR Muxworthy, D Heslop, GA Paterson, and D Michalk. A Preisach method for estimating absolute paleofield intensity under the constraint of using only isothermal measurements: 2. Experimental testing. Journal of Geophysical Research, 116, B04103, doi:10.1029/2010JB007844.

Lappe, S. C. L. L.; Harrison, R. J.; Feinberg, J. M.

2012-04-01

6

Rock magnetic properties of dusty olivine: a potential carrier of pre-accretionary remanence in unequilibrated ordinary chondrites  

NASA Astrophysics Data System (ADS)

The mechanism of chondrule formation is an important outstanding question in cosmochemistry. Magnetic signals recorded by Fe-Ni nanoparticles in chondrules could carry clues to their origin. Recently, research in this area has focused on 'dusty olivine' grains within ordinary chondrites as potential carriers of pre-accretionary remanence. Dusty olivine is characterised by the presence of sub-micron Fe-Ni inclusions within the olivine host. These metal particles form via subsolidus reduction of the olivine during chondrule formation and are thought to be protected from subsequent chemical and thermal alteration by the host olivine. Three sets of synthetic dusty olivines have been produced, using natural Icelandic olivine (average Ni-content of 0.3 wt%), synthetic Ni-containing olivine (0.1wt% Ni) and synthetic Ni-free olivine as starting materials. The starting materials were ground to powders, packed into a 2-3 mm3 graphite crucible, heated up to 1350 °C under a pure CO gas flow and kept at this temperature for 10 minutes. After this the samples were held in a fixed orientation and quenched into water in a range of known magnetic fields, ranging from 0.2 mT to 1.5 mT. First-order reversal curve (FORC) diagrams contain a central ridge with a broad coercivity distribution extending to 600 mT, attributed to non-interacting single-domain (SD) particles. A braod vertically spread positive peak is centred on Hc = 56 ± 14 mT and Hu = -114 ± 41 mT, and is accompanied by a broad horizontaly spread negative peak at Hc = 183 ± 30 mT, just underneath the central ridge. The combination of positive and negative peaks can be attributed to the presence of single-vortex (SV) states. Average SV nucleation and annihilation fields of 58 ± 55 mT and 170 ± 55 mT, respectively, were extracted from the FORC diagrams, indicating that demagnetization to >>170 mT would be required to isolate the stable SD signal. Single-vortex states are likely to be important remanence carriers in dusty olivine. Accounting for their presence will be essential in interpreting the remanence of natural samples. All samples showed uni-directional, single-component demagnetization behaviour. Even after applying the highest possible AF-field of 150 mT it was not possible to fully demagnetize the samples. The REM ratio (NRM/SIRM) shows non-linear behaviour as a function of applied field, saturating at a value of ~0.3. Saturation of REM at a value < 1 is explained by the presence of particles that can adopt either stable SV or metastable SD states depending on the field. Such particles are likely to adopt low-remanence SV states during TRM acquisition and high-remanence SD states after appication of a saturating field, hence artificially lowering the REM value. A calibration factor f = 3000 ?T, relating paleofield to the REM value, was derived from the low-field region of the data, which matches well with literature values. A range of more sophisticated normalisation techniques are assessed for use in paleointensity determination from meteorties, including the newly proposed method based on Preisach analysis of FORC diagrams.

Lappe, S. L.; Harrison, R. J.; Feinberg, J. M.

2011-12-01

7

Roosevelt County 075: A petrologic chemical and isotopic study of the most unequilibrated known H chondrite  

NASA Astrophysics Data System (ADS)

Roosevelt County (RC) 075 was recovered in 1990 as a single 258-gram stone. Classification of this meteorite is complicated by its highly unequilibrated nature and its severe terrestrial weathering, but we favor H classification. This is supported by O isotopes and estimates of the original Fe, Ni metal content. The O isotopic composition is similar to that of a number of reduced ordinary chondrites (e.g., Cerro los Calvos, Willaroy), although RC 075 exhibits no evidence of reduced mineral compositions. Chondrule diameters are consistent with classification as an L chondrite, but large uncertainties in chondrule diameters of RC 075 and poorly constrained means of H, L and LL chondrites prevent use of this parameter for reliable classification. Other parameters are compromised by severe weathering (e.g., siderophile element abundances) or unsuitable for discrimination between unequilibrated H, L and LL chondrites (e.g., Co in kamacite delta C-13). Petrologic subtype 3.2 +/- 0.1 is suggested by the degree of olivine heterogeneity, the compositions of chondrule olivines, the thermoluminescence sensitivity, the abundances and types of chondrules mapped on cathodoluminescence mosaics, and the amount of presolar SiC. The meteorite is very weakly shocked (S2), with some chondrules essentially unshocked and, thus, is classified as an H3.2(S2) chondrite. Weathering is evident by a LREE enrichment due to clay contamination, reduced levels of many siderophile elements, the almost total loss of Fe, Ni metal and troilite, and the reduced concentrations of noble gases. Some components of the meteorite (e.g., type IA chondrules, SiC) appear to preserve their nebular states, with little modification from thermal metamorphism. We conclude that RC 075 is the most equilibrated H chondrite yet recovered and may provide additional insights into the origin of primitive materials in the solar nebula.

McCoy, T. J.; Keil, K.; Ash, R. D.; Morse, A. D.; Pillinger, C. T.; Wieler, R.; Mayeda, T. K.; Clayton, R. N.; Benoit, P. H.; Sears, D. W. G.; Casanova, I.; Muenow, D. W.; Moore, C. B.; Lewis, C. F.; Wilson, I. E.

1993-12-01

8

Roosevelt County 075: A petrologic chemical and isotopic study of the most unequilibrated known H chondrite  

NASA Technical Reports Server (NTRS)

Roosevelt County (RC) 075 was recovered in 1990 as a single 258-gram stone. Classification of this meteorite is complicated by its highly unequilibrated nature and its severe terrestrial weathering, but we favor H classification. This is supported by O isotopes and estimates of the original Fe, Ni metal content. The O isotopic composition is similar to that of a number of reduced ordinary chondrites (e.g., Cerro los Calvos, Willaroy), although RC 075 exhibits no evidence of reduced mineral compositions. Chondrule diameters are consistent with classification as an L chondrite, but large uncertainties in chondrule diameters of RC 075 and poorly constrained means of H, L and LL chondrites prevent use of this parameter for reliable classification. Other parameters are compromised by severe weathering (e.g., siderophile element abundances) or unsuitable for discrimination between unequilibrated H, L and LL chondrites (e.g., Co in kamacite delta C-13). Petrologic subtype 3.2 +/- 0.1 is suggested by the degree of olivine heterogeneity, the compositions of chondrule olivines, the thermoluminescence sensitivity, the abundances and types of chondrules mapped on cathodoluminescence mosaics, and the amount of presolar SiC. The meteorite is very weakly shocked (S2), with some chondrules essentially unshocked and, thus, is classified as an H3.2(S2) chondrite. Weathering is evident by a LREE enrichment due to clay contamination, reduced levels of many siderophile elements, the almost total loss of Fe, Ni metal and troilite, and the reduced concentrations of noble gases. Some components of the meteorite (e.g., type IA chondrules, SiC) appear to preserve their nebular states, with little modification from thermal metamorphism. We conclude that RC 075 is the most equilibrated H chondrite yet recovered and may provide additional insights into the origin of primitive materials in the solar nebula.

Mccoy, T. J.; Keil, K.; Ash, R. D.; Morse, A. D.; Pillinger, C. T.; Wieler, R.; Mayeda, T. K.; Clayton, R. N.; Benoit, P. H.; Sears, D. W. G.

1993-01-01

9

Multiple and Fast: The Accretion of Ordinary Chondrite Parent Bodies  

E-print Network

Although petrologic, chemical and isotopic studies of ordinary chondrites and meteorites in general have largely helped establish a chronology of the earliest events of planetesimal formation and their evolution, there are several questions that cannot be resolved via laboratory measurements and/or experiments only. Here we propose rationale for several new constraints on the formation and evolution of ordinary chondrite parent bodies (and by extension most planetesimals) from newly available spectral measurements and mineralogical analysis of main belt S-type asteroids (83 objects) and unequilibrated ordinary chondrite meteorites (53 samples). Based on the latter, we suggest spectral data may be used to distinguish whether an ordinary chondrite was formed near the surface or in the interior of its parent body. If these constraints are correct, the suggested implications include that: i) large groups of compositionally similar asteroids are a natural outcome of planetesimal formation and, consequently, meteor...

Vernazza, P; Binzel, R P; Hiroi, T; DeMeo, F E; Birlan, M; Hewins, R; Ricci, L; Barge, P; Lockhart, M

2014-01-01

10

Major element chemical compositions of chondrules in unequilibrated chondrites  

NASA Technical Reports Server (NTRS)

The chemical compositions (except for metals and sulfides in chondrules) of more than 500 chondrules from unequilibrated E, H, L, LL, and C chondrites were measured using a broad beam of an electron-probe microanalyzer. The compositions of chondrules can be represented by various mixtures of normative compositions of olivine, low-Ca pyroxene, plagioclase, and high-Ca pyroxene with minor amounts of spinel, feldspathoid, SiO2-minerals, etc., indicating that the chondrule precursor materials consisted of aggregates of these minerals. The Al, Na, and K contents of most chondrules reflect the compositions of the ternary feldspar (An-Ab-Kf) of the chondrule precursor materials, and chemical types of chondrules (KF, SP, IP, and CP) are defined on the basis of the atomic proportion of Al, Na, and K.

Ikeda, Y.

1984-01-01

11

Actinide abundances in ordinary chondrites  

USGS Publications Warehouse

Measurements of 244Pu fission Xe, U, Th, and light REE (LREE) abundances, along with modal petrographic determinations of phosphate abundances, were carried out on equilibrated ordinary chondrites in order to define better the solar system Pu abundance and to determine the degree of variation of actinide and LREE abundances. Our data permit comparison of the directly measured Pu/ U ratio with that determined indirectly as (Pu/Nd) ?? (Nd/U) assuming that Pu behaves chemically as a LREE. Except for Guaren??a, and perhaps H chondrites in general, Pu concentrations are similar to that determined previously for St. Se??verin, although less precise because of higher trapped Xe contents. Trapped 130Xe 136Xe ratios appear to vary from meteorite to meteorite, but, relative to AVCC, all are similar in the sense of having less of the interstellar heavy Xe found in carbonaceous chondrite acid residues. The Pu/U and Pu/Nd ratios are consistent with previous data for St. Se??verin, but both tend to be slightly higher than those inferred from previous data on Angra dos Reis. Although significant variations exist, the distribution of our Th/U ratios, along with other precise isotope dilution data for ordinary chondrites, is rather symmetric about the CI chondrite value; however, actinide/(LREE) ratios are systematically lower than the CI value. Variations in actinide or LREE absolute and relative abundances are interpreted as reflecting differences in the proportions and/or compositions of more primitive components (chondrules and CAI materials?) incorporated into different regions of the ordinary chondrite parent bodies. The observed variations of Th/U, Nd/U, or Ce/U suggest that measurements of Pu/U on any single equilibrated ordinary chondrite specimen, such as St. Se??verin, should statistically be within ??20-30% of the average solar system value, although it is also clear that anomalous samples exist. ?? 1990.

Hagee, B.; Bernatowicz, T. J.; Podosek, F. A.; Johnson, M. L.; Burnett, D. S.; Tatsumoto, M.

1990-01-01

12

Incompletely compacted equilibrated ordinary chondrites  

SciTech Connect

We document the size distributions and locations of voids present within five highly porous equilibrated ordinary chondrites using high-resolution synchrotron X-ray microtomography ({mu}CT) and helium pycnometry. We found total porosities ranging from {approx}10 to 20% within these chondrites, and with {mu}CT we show that up to 64% of the void space is located within intergranular voids within the rock. Given the low (S1-S2) shock stages of the samples and the large voids between mineral grains, we conclude that these samples experienced unusually low amounts of compaction and shock loading throughout their entire post accretionary history. With Fe metal and FeS metal abundances and grain size distributions, we show that these chondrites formed naturally with greater than average porosities prior to parent body metamorphism. These materials were not 'fluffed' on their parent body by impact-related regolith gardening or events caused by seismic vibrations. Samples of all three chemical types of ordinary chondrites (LL, L, H) are represented in this study and we conclude that incomplete compaction is common within the asteroid belt.

Sasso, M.R.; Macke, R.J.; Boesenberg, J.S.; Britt, D.T.; Rovers, M.L.; Ebel, D.S.; Friedrich, J.M.; (Fordham)

2010-01-22

13

KINETICS AND VOLATILIZATION OF SiC AND SiO2: IMPLICATIONS FOR METAMORPHISM OF UNEQUILIBRATED ORDINARY CHONDRITES; R.A. Mendybaev1,3, J.R. Beckett3, L. Grossman1,2, and E.  

E-print Network

of Chemically Vapor Deposited (CVD) -SiC, single crystal -SiC and fused silica glass with typical sizes of 6x3x0KINETICS AND VOLATILIZATION OF SiC AND SiO2: IMPLICATIONS FOR METAMORPHISM OF UNEQUILIBRATED the possibility of a more direct indicator based on the observation [1, 2] that abundances of diamond and SiC

Grossman, Lawrence

14

Oxygen Isotopes of CAIs from Unequilibrated Enstatite Chondrites: Characteristics and Implications  

NASA Technical Reports Server (NTRS)

Ion microprobe analyses of ten CAIs from enstatite chondrites show large O-16 excesses similar to CAIs in carbonaceous and ordinary chondrites, supporting the idea that most CAIs formed in a restricted nebular locale.

Guan, Y.; McKeegan, K. D.; MacPherson, G. J.

2000-01-01

15

Oxidation during metamorphism of the ordinary chondrites  

NASA Technical Reports Server (NTRS)

It is suggested that some current concepts about the conditions of metamorphism in ordinary chondrites may be flawed. These meteorites display small systematic variations in the oxidation state of Fe. Evidence is presented that oxidation of Fe is linked to metamorphic grade in types 4-6 ordinary chondrites. This conclusion is at variance with a commonly accepted model for chondrite metamorphism that assumes Fe reduction by graphite.

Mcsween, Harry Y., Jr.; Labotka, Theodore C.

1993-01-01

16

Multiple and Fast: The Accretion of Ordinary Chondrite Parent Bodies  

NASA Astrophysics Data System (ADS)

Although petrologic, chemical, and isotopic studies of ordinary chondrites and meteorites in general have largely helped establish a chronology of the earliest events of planetesimal formation and their evolution, there are several questions that cannot be resolved via laboratory measurements and/or experiments alone. Here, we propose the rationale for several new constraints on the formation and evolution of ordinary chondrite parent bodies (and, by extension, most planetesimals) from newly available spectral measurements and mineralogical analysis of main-belt S-type asteroids (83 objects) and unequilibrated ordinary chondrite meteorites (53 samples). Based on the latter, we suggest that spectral data may be used to distinguish whether an ordinary chondrite was formed near the surface or in the interior of its parent body. If these constraints are correct, the suggested implications include that: (1) large groups of compositionally similar asteroids are a natural outcome of planetesimal formation and, consequently, meteorites within a given class can originate from multiple parent bodies; (2) the surfaces of large (up to ~200 km) S-type main-belt asteroids mostly expose the interiors of the primordial bodies, a likely consequence of impacts by small asteroids (D < 10 km) in the early solar system; (3) the duration of accretion of the H chondrite parent bodies was likely short (instantaneous or in less than ~105 yr, but certainly not as long as 1 Myr); (4) LL-like bodies formed closer to the Sun than H-like bodies, a possible consequence of the radial mixing and size sorting of chondrules in the protoplanetary disk prior to accretion.

Vernazza, P.; Zanda, B.; Binzel, R. P.; Hiroi, T.; DeMeo, F. E.; Birlan, M.; Hewins, R.; Ricci, L.; Barge, P.; Lockhart, M.

2014-08-01

17

Survey of Large, Igneous-Textured Inclusions in Ordinary Chondrites  

NASA Astrophysics Data System (ADS)

Ordinary (O) chondrites are a class of primitive stony meteorites, and as a group comprise our most abundant samples of early solar system materials. Unique to O chondrites are igneous-textured inclusions up to 4 cm in diameter; about an order of magnitude larger than the much more abundant chondrules. These inclusions are almost always highly depleted in metal and sulfide relative to their host meteorite, but but otherwise have diverse characteristics. They exhibit a large range of textures, mineralogies, and bulk compositions, suggesting a variety of formation processes. They all crystallized from large melt volumes, the origins of which are poorly understood. Models proposed for their formation include (1) shock melting of ordinary chondrites with an associated loss of metal and sulfide; (2) melting of vapor-fractionated condensate mixture; (3) chondrule formation involving a larger melt production volume than typical for chondrules; and (4) igneous differentiation occurring within planetesimals sampled by ordinary chondrite parent bodies. Polished thin sections of inclusions from several O-chondrites have been examined with optical light microscopy (OLM) using a Leica DM 2500 petrographic microscope. Petrographic data such as texture, grain sizes and shapes were collected for the inclusions and their hosts in order to facilitate comparisons. Texturally, the inclusions were determined to fall into one of three distinct textural categories: porphyritic, fine granular, and skeletal. Mean grain sizes are on the order of 100 um for both microporphyritic and fine granular inclusions, with microporphyritic inclusions showing a much wider range of grain sizes. The largest grains in the microporphyritic inclusions are on average ~0.25 mm, with the grains of the mesostasis <100 microns. Skeletal olivine textures are defined as being dominated by crystals that are an order of magnitude longer across one direction than the other (e.g., 1 mm x 100 um). Five inclusions have been investigated with scanning electron microscopy (SEM) on a Zeiss Sigma FE-VP SEM at Portland State University. Backscatter electron micrographs were obtained in order to provide additional petrographic data, and olivine composition was determined using a silicon-drift energy dispersive X-ray (EDX) detector integrated with an Oxford Instruments AZtec X-ray analytical system. Olivine crystals of six inclusions were investigated with electron microprobe analysis (EMPA), performed with a Cameca SX-100 electron microprobe located at Oregon State University, and remotely operated from Portland State. The instrument will be operated at 15 kV accelerating voltage, with a 10-50 nA sample current and a beam diameter of approximately 1 um. Chemically, some inclusions were found to have equilibrated olivine, while others were uneqilibrated. This was also unrelated to host classification, as well as unrelated to host petrographic type. Of the two unequilibrated hosts studied, one had two unequilibrated inclusions, while the other had one equilibrated inclusion. Several eqilibrated hosts had equilibrated inclusion, while one equilibrated host had an unequilibrated inclusion. Neither texture nor chemistry was determined to be related to host type or related to whether the inclusion is a drop-formed mass or a clast.

Armstrong, K.; Ruzicka, A. M.

2013-12-01

18

The classification of ordinary chondrites according to chemical composition  

NASA Astrophysics Data System (ADS)

Recent data on the chemical classification of ordinary chondrites are examined. Graphs are presented which serve to separate these chondrites into types H, L, and LL according to bulk chemical composition and mineral composition (pyroxene, olivine, kamacite). Examples of ordinary chondrites of other types are indicated, along with anomalous meteorites that belong to this group of chondrites.

Iavnel, A. A.

19

{sup 60}Fe AND {sup 26}Al IN CHONDRULES FROM UNEQUILIBRATED CHONDRITES: IMPLICATIONS FOR EARLY SOLAR SYSTEM PROCESSES  

SciTech Connect

The presence of about a dozen short-lived nuclides in the early solar system, including {sup 60}Fe and {sup 26}Al, has been established from isotopic studies of meteorite samples. An accurate estimation of solar system initial abundance of {sup 60}Fe, a distinct product of stellar nucleosynthesis, is important to infer the stellar source of this nuclide. Previous studies in this regard suffered from the lack of exact knowledge of the time of formation of the analyzed meteorite samples. We present here results obtained from the first combined study of {sup 60}Fe and {sup 26}Al records in early solar system objects to remove this ambiguity. Chondrules from unequilibrated ordinary chondrites belonging to low petrologic grades were analyzed for their Fe-Ni and Al-Mg isotope systematics. The Al-Mg isotope data provide the time of formation of the analyzed chondrules relative to the first solar system solids, the Ca-Al-rich inclusions. The inferred initial {sup 60}Fe/{sup 56}Fe values of four chondrules, combined with their time of formation based on Al-Mg isotope data, yielded a weighted mean value of (6.3 {+-} 2) x 10{sup -7} for solar system initial {sup 60}Fe/{sup 56}Fe. This argues for a high-mass supernova as the source of {sup 60}Fe along with {sup 26}Al and several other short-lived nuclides present in the early solar system.

Mishra, R. K.; Goswami, J. N.; Rudraswami, N. G. [Physical Research Laboratory, Ahmedabad-380009 (India); Tachibana, S. [Department of Earth and Planetary Sciences, University of Tokyo, 7-3-1 Hongo, Tokyo 113-0033 (Japan); Huss, G. R., E-mail: goswami@prl.res.i [Hawaii Institute of Geophysics and Planetology, University of Hawaii at Manoa, Honolulu, HI 96822 (United States)

2010-05-10

20

Primitive ultrafine matrix in ordinary chondrites  

NASA Astrophysics Data System (ADS)

Ultrafine matrix material has been concentrated by sieving and filtering disaggregated samples of six ordinary chondrites of different classes. This component(s), 'Holy Smoke' (HS), is enriched in both volatile, e.g. Na, K, Zn, Sb, and Pb, as well as refractory elements, e.g. W and REE; however, the element ratios vary greatly among the different chondrites. SEM studies show that HS contains fragile crystals, differing in composition, and apparently in gross disequilibrium not only among themselves but also with the major mineral phases and consequently thermodynamic equilibration did not occur. Thus HS must have originated from impacting bodies and/or was inherent in the 'primitive' regolith. Subsequent impact brecciation and reheating appears to have altered, to varying degrees, the original composition of this ultrafine matrix material. Recent 'cosmic dust' studies may indicate that HS still exists in the solar system. Survival of such delicate material must be considered in all theories for the origin of chondrites.

Rambaldi, E. R.; Fredriksson, B. J.; Fredriksson, K.

1981-12-01

21

Primitive ultrafine matrix in ordinary chondrites  

NASA Technical Reports Server (NTRS)

Ultrafine matrix material has been concentrated by sieving and filtering disaggregated samples of six ordinary chondrites of different classes. This component(s), 'Holy Smoke' (HS), is enriched in both volatile, e.g. Na, K, Zn, Sb, and Pb, as well as refractory elements, e.g. W and REE; however, the element ratios vary greatly among the different chondrites. SEM studies show that HS contains fragile crystals, differing in composition, and apparently in gross disequilibrium not only among themselves but also with the major mineral phases and consequently thermodynamic equilibration did not occur. Thus HS must have originated from impacting bodies and/or was inherent in the 'primitive' regolith. Subsequent impact brecciation and reheating appears to have altered, to varying degrees, the original composition of this ultrafine matrix material. Recent 'cosmic dust' studies may indicate that HS still exists in the solar system. Survival of such delicate material must be considered in all theories for the origin of chondrites.

Rambaldi, E. R.; Fredriksson, B. J.; Fredriksson, K.

1981-01-01

22

Carbon in the matrices of ordinary chondrites  

NASA Astrophysics Data System (ADS)

Carbon in the petrologic matrices of a number of ordinary chondrites of groups H, L, and LL, and of types 3 through 6 was studied with a nuclear microprobe and a Raman microprobe. The majority of the matrices had carbon contents in the narrow range between 0.03 and 0.2 wt pct. The carbon content decreased only slightly with increasing petrologic type. Carbon-rich coats around troilite and/or metal phases occurred in five meteorites. Poorly ordered carbon was found in the matrices. The carbon in the meteorites of higher petrologic types was slightly better ordered than in the meteorites of lower types. The narrow range of carbon contents and the similarity of the structural form of carbon in the matrices of the measured ordinary chondrites, which represent all groups and types, imply that their matrices may contain a common component, which might be of interstellar origin.

Makjanic, J.; Vis, R. D.; Hovenier, J. W.; Heymann, D.

1993-03-01

23

The Abundance of Ordinary Chondrite Debris Among Antarctic Micrometeorites  

NASA Astrophysics Data System (ADS)

Interplanetary dust and meteorites are widely believed to originate predominantly from the asteroid belt [e.g., 1,2]. However, these two types of matter, which represent distinct mass classes (~10 micrograms and ~100 kg, respectively) seem to sample different reservoirs, as they are dominated by different types of extraterrestrial matter. The dust is mostly related to the CM-type chondrites [3], which are rare among meteorites that are otherwise dominated by ordinary chondrites (OCs) [2]. To quantify the contribution to the interplanetary dust by OC parent bodies we have studied 427 particles from the 100 - 400 micrometer size fraction of dust recovered from Antarctic ice [4], 303 of which were found to be of extraterrestrial origin. Of these, 41 (=13.5%) are cosmic spherules (CSs), 136 (= 44.9 %) scoriaceous micrometeorites (MMs), 65 (= 21.5%) consist of dehydrated phyllosilicates, 11 (=3.6 %) consist mainly of phyllosilicates, and 50 (= 16.5%) are coarse-grained crystalline MMs. Phase compositions of the crystalline MMs suggest a close relationship between these MMs and CM-type carbonaceous chondrites [e.g., 3]. Low-Ca pyroxenes and olivines are rich in Mg, Cr, and Mn, typical for carbonaceous chondrite phases [e.g., 5]. Only three crystalline MMs (~1% of the total extraterrestrial particle population) have phase compositions that are compatible with derivation from an OC precursor: Particle M6 (~200 micrometer diameter) has a porphyritic texture with olivine (Fa 18.7) and low-Ca pyroxene (Fs 16.6, Wo 0.6) in a fine-grained matrix. Micrometeorite AM1 (410 micrometers long) has also a porphyritic texture with olivines (Fa 16.2) set in a fine- grained, clinopyroxene-bearing matrix. Particle Mc7/10 (150 micrometers long) has a granular mosaic texture of intergrown olivine (Fa 17.6-19.8) and low-Ca pyroxene (Fs 14.1-16.3, Wo~1.2), and plagioclase (An 14), with very little intergranular matrix. Minor element contents of olivines in all three particles are low (CaO < 0.05 wt%, Al2O3 < 0.05 wt%, TiO2 < 0.05 wt%, Cr2O3 < 0.05 wt%, NiO < 0.02 wt%). The FeO/MnO ratios in olivine vary between 33 and 49, comparable to those of H-chondrite olivines [e.g., 6]. Two of the three particles were also analyzed by INAA [3]. Their trace element abundances match those of ordinary chondrites [e.g., 7]. We conclude that the three particles M6, AM1, and MC7/10 are related to H-chondrites and, thus, are likely to represent an asteroidal belt contribution to the interplanetary dust population. The abundance of OC-like dust is very low (1%), and up to now limited to H-chondritic particles - two equilibrated and one unequilibrated one. Acknowledgement: This work was supported by FWF (project P10688-GEO). References: [1] Brownlee D. E. (1981) in Comets and the Origin of Life (C. Ponnamperuma, ed.), 63-70. [2] Dodd R. T. (1981) Meteorites. [3] Kurat G. et al. (1994) GCA, 58, 3879-3904. [4] Maurette M. et al. (1991) Nature, 351, 44-47. [5] Steele I. M. (1986) GCA, 50, 1379-1395. [6] Brandstatter et al. (1985) Ann. Naturhist. Mus. Wien, 87A, 11-20. [7] Wasson J. T. and Kallemeyn G. W. (1988) Philos. Trans. R. Soc. Lond., A325, 535-544.

Walter, J.; Kurat, G.; Brandstatter, F.; Koeberl, C.; Maurette, M.

1995-09-01

24

The evolution of enstatite and chondrules in unequilibrated enstatite chondrites: Evidence from iron-rich pyroxene  

NASA Technical Reports Server (NTRS)

FeO-rich (Fs(sub 6)-34) pyroxene lacking cathodoluminescence (CL), hereafter black pyroxene, is a major constituent of some of the chondrules and fragments in unequilibrated (type 3) enstatite chondrites (UECs). It contains structurally oriented zones of Cr-, Mn-, V-rich, FeO-poor enstatite with red CL, associated with mm-sized blebs of low-Ni, Fe-metal and, in some cases, silica. These occurrences represent clear evidence of pyroxene reduction. The black pyroxene is nearly always rimmed by minor element (Cr, Mn, V)-poor enstatite having a blue CL. More commonly, red and blue enstatites, unassociated with black pyroxene, occur as larger grains in chondrules and fragments, and these constitute the major silicate phases in UECs. The rare earth element (REE) abundance patterns of the black pyroxene are LREE-depleted. The blue enstatite rims, however, have a near-flat to LREE-enriched pattern, approx. 0.5-4x chondritic. The petrologic and trace element data indicate that the black pyroxene is from an earlier generation of chondrules that formed in a nebular region that was more oxidizing than that of the enstatite chondrites. Following solidification, these chondrules experienced a more reducing nebular environment and underwent reduction. Some, perhaps most, of the red enstatite that is common throughout the UECs may be the product of solid-state reduction of black pyroxene. The blue enstatite rims grew onto the surfaces of the black pyroxene and red enstatite as a result of condensation from a nebular gas. The evolutionary history of some of the enstatite and chondrules in enstatite chondrites can be expressed in a four-stage model that includes: Stage 1. Formation of chondrules in an oxidizing nebular environment. Stage 2. Solid-state reduction of the more oxidized chondrules and fragments to red enstatite in a more reducing nebular environment. Stage 3. Formation of blue enstatite rims on the black pyroxene as well as on the red enstatite. Stage 4. Reprocessing, by various degrees of melting, of many of the earlier-formed materials.

Weisberg, Michael K.; Prinz, Martin; Fogel, Robert A.

1994-01-01

25

The evolution of enstatite and chondrules in unequilibrated enstatite chondrites: Evidence from iron-rich pyroxene  

NASA Astrophysics Data System (ADS)

FeO-rich (Fs6-34) pyroxene lacking cathodoluminescence (CL), hereafter black pyroxene, is a major constituent of some of the chondrules and fragments in unequilibrated (type 3) enstatite chondrites (UECs). It contains structurally oriented zones of Cr-, Mn-, V-rich, FeO-poor enstatite with red CL, associated with mm-sized blebs of low-Ni, Fe-metal and, in some cases, silica. These occurrences represent clear evidence of pyroxene reduction. The black pyroxene is nearly always rimmed by minor element (Cr, Mn, V)-poor enstatite having a blue CL. More commonly, red and blue enstatites, unassociated with black pyroxene, occur as larger grains in chondrules and fragments, and these constitute the major silicate phases in UECs. The rare earth element (REE) abundance patterns of the black pyroxene are LREE-depleted. The blue enstatite rims, however, have a near-flat to LREE-enriched pattern, approx. 0.5-4x chondritic. The petrologic and trace element data indicate that the black pyroxene is from an earlier generation of chondrules that formed in a nebular region that was more oxidizing than that of the enstatite chondrites. Following solidification, these chondrules experienced a more reducing nebular environment and underwent reduction. Some, perhaps most, of the red enstatite that is common throughout the UECs may be the product of solid-state reduction of black pyroxene. The blue enstatite rims grew onto the surfaces of the black pyroxene and red enstatite as a result of condensation from a nebular gas. The evolutionary history of some of the enstatite and chondrules in enstatite chondrites can be expressed in a four-stage model that includes: Stage 1. Formation of chondrules in an oxidizing nebular environment. Stage 2. Solid-state reduction of the more oxidized chondrules and fragments to red enstatite in a more reducing nebular environment. Stage 3. Formation of blue enstatite rims on the black pyroxene as well as on the red enstatite. Stage 4.

Weisberg, Michael K.; Prinz, Martin; Fogel, Robert A.

1994-05-01

26

Chromium on Eros: Further Evidence of Ordinary Chondrite Composition  

NASA Technical Reports Server (NTRS)

The surface major element composition of the near-earth asteroid 433-Eros has been determined by x-ray fluorescence spectroscopy (XRS) on the NEAR-Shoemaker spacecraft [1]. The abundances of Mg, Al, Si, Ca and Fe match those of ordinary chondrites [1]. However, the observation that Eros appears to have a sulfur abundance at least a factor of two lower than ordinary chondrites, suggests either sulfur loss from the surface of Eros by impact and/or radiation processes (space weathering) or that its surface is comprised of a somewhat more differentiated type of material than an ordinary chondrite [1]. A definitive match for an ordinary chondrite parent body has very rarely been made, despite the conundrum that ordinary chondrites are the most prevalent type of meteorite found on Earth. Furthermore, Eros is classified as an S(IV) type asteroid [2] and being an S, it is the second most prevalent type of asteroid in the asteroid belt [3].

Foley, C. N.; Nittler, L. R.; Brown, M. R. M.; McCoy, T. J.; Lim, L. F.

2005-01-01

27

A Weathering Scale for the Ordinary Chondrites  

NASA Astrophysics Data System (ADS)

Weathering categories A, B, and C are used by the Meteorite Working Group at the NASA Johnson Space Center in Houston for Antarctic meteorite finds, denoting minor, moderate, and severe rustiness of hand specimens. A different scale can be set up from the weathering effects seen in polished sections with the microscope. These weathering effects finally lead to the disintegration of the meteorite; they are important in connection with its terrestrial age and an estimate of the true fall rate of meteorites. In order to avoid confusion with the hand specimen classification A, B, C, the weathering grades determined on polished sections were named W1 to W6. Weathering affects first the metal grains, later troilite, and finally the silicates. The following progressive stages can be distinguished: W0: No visible oxidation of metal or sulfide. A limonitic staining may already be noticeable in transmitted light. Fresh falls are usually of this grade, although some are already W1. W1: Minor oxide rims around metal and troilite, minor oxide veins. W2: Moderate oxidation of metal, about 20-60% being affected. W3: Heavy oxidation of metal and troilite, 60-95% being replaced. W4: Complete (>95%) oxidation of metal and troilite, but no alteration of silicates. W5: Beginning alteration of mafic silicates, mainly along cracks. W6: Massive replacement of silicates by clay minerals and oxides. More or less massive veining with iron oxides can already be found in stage W2. These veins develop independently from the weathering grade, apparently in cracks that form through mechanical forces. Broad cracks are often filled with carbonates. Grades W5 and W6 are rare. The silicate alteration affects first the olivines; it starts inside the grains, not from the rim. In stage W6 intact chondrules were found, where olivines were completely replaced by a mixture of clay minerals and iron oxides, the feldspathic mesostasis being unaffected. A correlation between these weathering grades and the terrestrial ages was shown for meteorite finds from Roosevelt County, New Mexico [1]. In these climatic conditions the weathering grades W2 to W6 develop in the following times: W2, 5000 to 15,000 yr; W3, 15,000 to 30,000 yr; W4, 20,000 to 35,000 yr; W5 and W6, 30,000 to >45,000 yr. Similar terrestrial ages were found for chondrites of these weathering grades from the Lybian and Algerian Sahara [2,3]. Antarctic meteorite finds weather much more slowly. A check of 53 Antarctic ordinary chondrites (of hand specimen weathering categories A to C) showed only 9 of grade W2, the rest being W1. Among the W1s is ALHA77278 (category A) with a terrestrial age of 320,000 yr [4]. References: [1] Jull A. J. T. et al. (1991) LPSC XXII, 665. [2] Jull A. J. T. et al. (1990) GCA, 54, 2895. [3] Jull A. J. T. et al. (1993), this volume. [4] Nishiizumi K. et al. (1989) EPSL, 93, 299.

Wlotzka, F.

1993-07-01

28

Darkening in gas-rich ordinary chondrites: Spectral modelling and implications for the regoliths of ordinary chondrite parent bodies  

NASA Technical Reports Server (NTRS)

The dark fine grained matrix of gas-rich ordinary chondrites replicates many of the physical, morphological, and spectral characteristics of the highly shocked and optically altered black chondrites. Spectral mixture modeling shows that the darkening and spectral attenuation seen in the dark matrix can be simulated with realistic mass fractions of light host material and black chondritic material. All these factors point to the conclusion that the dark matrix of gas-rich ordinary chondrites is dark due to the same processes that darkens black chondrites, shock distributed small particle size FeNi metal and troilite. Because the darkening is not seen in any of the non-gas-rich light portions and is only seen in the gas rich grains of the meteorite, the shock darkening would have to occur as part of the matrix's exposure to regolith processes. Since all gas-rich grains are darkened, it follows that darkening is not only common, but pervasive in asteroidal regoliths. These results imply that the upper, optically active layer of an ordinary chondrite parent body should have the spectral characteristics of a black chondrite, which are a dark, relatively featureless spectrum with modest red slope in the infrared. These are the characteristics of special type C asteroids.

Britt, Daniel T.; Pieters, Carle M.

1991-01-01

29

A hydrogen isotope study of CO3 type carbonaceous chondrites; comparison with type 3 ordinary chondrites  

NASA Technical Reports Server (NTRS)

Meteorites of the Ornans type 3 carbonaceous chondrites exhibit a range in degree of equilibration, attributed to differing amounts of thermal metamorphism. These differences have been used to split the CO3 chondrites into petrologic sub-types from 3.0, least equilibrated, to 3.7, being most equilibrated. This is similar to the system of assigning the type 3 ordinary chondrites into petrologic sub-types 3.0 to 3.9 based upon thermoluminescence (TL) and other properties; however, the actual range of thermal metamorphism experienced by CO3 chondrites is much less than that of the type 3 ordinary chondrites. The least equilibrated ordinary chondrites show evidence of aqueous alteration and have high D/H ratios possibly due to a deuterium-rich organic carrier. The aim of this study was to determine whether the CO3 chondrites, which have experienced similar secondary conditions to the type 3 ordinary chondrites, also contain a similar deuterium-rich carrier. To date a total of 5 CO3 meteorites, out of a set of 11 for which carbon and nitrogen isotopic data are available, have been analyzed. Ornans has not been analyzed yet, because it does not appear to fit in with the metamorphic sequence exhibited by the other CO3 chondrites; it also has an extremely high delta-D value of +2150 percent, unusual for such a comparatively equilibrated meteorite (type 3.4). Initial results indicate that the more equilibrated CO3's tend to have lower delta-D values, analogous to the higher petrologic type ordinary chondrites. However this is complicated by the effects of terrestrial weathering and the small data-set.

Morse, A. D.; Newton, J.; Pillinger, C. T.

1993-01-01

30

Rapid Classification of Ordinary Chondrites Using Raman Spectroscopy  

NASA Technical Reports Server (NTRS)

Classification of ordinary chondrites is typically done through measurements of the composition of olivine and pyroxenes. Historically, this measurement has usually been performed via electron microprobe, oil immersion or other methods which can be costly through lost sample material during thin section preparation. Raman microscopy can perform the same measurements but considerably faster and with much less sample preparation allowing for faster classification. Raman spectroscopy can facilitate more rapid classification of large amounts of chondrites such as those retrieved from North Africa and potentially Antarctica, are present in large collections, or are submitted to a curation facility by the public. With development, this approach may provide a completely automated classification method of all chondrite types.

Fries, M.; Welzenbach, L.

2014-01-01

31

Did Ordinary Chondrite Impactors Deliver Olivine to Vesta?  

NASA Astrophysics Data System (ADS)

Ground-based and Hubble Space Telescope observations of asteroid Vesta suggested the presence of olivine. However, subsequent analysis of data from NASA’s Dawn mission proved that this “olivine-bearing unit”, identified as Oppia crater and its ejecta blanket, was composed of HED impact melt rather than olivine. The lack of widespread olivine in the 19 km deep Rheasilvia basin on the South Pole suggests that the crust-mantle boundary was not breached during the formation of the basin, and that Vesta’s crust is thicker than originally anticipated. Recently, local-scale olivine units have been reported in the walls and ejecta of two craters, Arruntia and Bellicia, located in the northern hemisphere of Vesta, 350-430 km from the Rheasilvia basin (Ammannito et al., 2013). These units were interpreted as exposed plutons by Clenet et al. (2014) rather than of mantle origin excavated during the formation of the Rheasilvia basin. We explored alternative sources for these olivine-rich units by reanalyzing the data published by Ammannito et al. (2013). Our mineralogical analysis gives olivine abundance between 70-80 vol.% consistent with those obtained previously (>60%). The pyroxene ferrosilite content and olivine abundance of the olivine-rich units are similar to ordinary chondrites. Meteoritic evidence suggests contamination of HEDs by several ordinary chondrite impactors including H, L and LL chondrites. This includes howardite JaH 556, which contains ~20 vol.% H chondrite material mixed with HED impact melt. Based on the non-diagnostic curve match and detailed mineralogical analysis using diagnostic spectral band parameters, we conclude that the olivine units in the northern hemisphere of Vesta could be explained by the delivery of exogenic H/L chondrite material rather than being a product of planetary differentiation.

Le Corre, Lucille; Reddy, Vishnu; Sanchez, Juan A.; Cloutis, Edward A.; Izawa, Matthew R.; Mann, Paul

2014-11-01

32

Matrix and fine-grained rims in the unequilibrated CO3 chondrite, ALHA77307 - Origins and evidence for diverse, primitive nebular dust components  

NASA Astrophysics Data System (ADS)

SEM, TEM, and electron microprobe analysis were used to investigate in detail the mineralogical and chemical characteristics of dark matrix and fine-grained rims in the unequilibrated CO3 chondrite ALHA77307. Data obtained revealed that there was a remarkable diversity of distinct mineralogical components, which can be identified using their chemical and textural characteristics. The matrix and rim components in ALHA77307 formed by disequilibrium condensation process as fine-grained amorphous dust that is represented by the abundant amorphous component in the matrix. Subsequent thermal processing of this condensate material, in a variety of environments in the nebula, caused partial or complete recrystallization of the fine-grained dust.

Brearley, A. J.

1993-04-01

33

Stable Isotope Fractionation of Cr in Carbonaceous and Ordinary Chondrites  

NASA Astrophysics Data System (ADS)

Difficulties with chemical separation and mass spectrometry combined with little expectation of isotopic fractionation at high temperature left the stable isotope geochemistry of Cr almost unknown [1]. The search for ^{53}Cr excess resulting from the decay of the radioactive nuclide ^{53}Mn (T1/2 = 3.5 My) was very successful but the small amount of data produced to date attests to the particularly difficult measurement by TIMS. This preliminary report describes evidence of mass-dependent fractionation of the stable Cr isotopes 50, 52, and 53 as measured by MC-ICPMS in meteorites relative to SRM 979 Cr standard. Cr was purified using cation-exchange chemistry. The yield is ~100 %. The samples were run on the Nu- Plasma HR of UC Davis in pseudo high-resolution mode. The absence of isotopic fractionation induced by the chemical purification has been double checked by 1) processing the standard through the column and 2) running the same sample several times through the columns. In both cases, we observe no difference in the measured isotopic ratio. The external reproducibility, estimated from 13 replicates of Bjurbole, is 50 ppm. The range of the fractionation per mass unit among 7 carbonaceous chondrites (CI, CM, CO, CV and CK) and 5 ordinary chondrites (H, L and LL) is 0.3 ‰. Individual chondrules from Chainpur and Bjurbole have a wider range (0.6 ‰). All the chondrites analyzed so far are isotopically lighter than the bulk silicate earth (? ^{50/52}Cr=0, [1]). As for Zn [2], Cr isotopes seem to be heavier in ordinary chondrites (-0.23 ‰) than in carbonaceous chondrites (-0.35 ‰). Also as for Zn and Cu [2-3], Cr stable isotopes in carbonaceous chondrites are correlated with ? 17O, suggesting a mixing between an isotopically heavy component and an isotopically light one. The correlation between mass-dependent fractionation of Cr and non-mass-dependent ? 17O requires attention and adequate interpretation. References: [1] Johnson and Bullen, 2004, Review in Mineralogy and Geochemistry. [2] Luck et al., 2005 GCA. [3] Luck et al., 2003 GCA.

Moynier, F.; Jacobsen, B.; Yin, Q.

2006-12-01

34

Fe-Ni metal in primitive chondrites: Indicators of classification and metamorphic conditions for ordinary and CO chondrites  

USGS Publications Warehouse

We report the results of our petrological and mineralogical study of Fe-Ni metal in type 3 ordinary and CO chondrites, and the ungrouped carbonaceous chondrite Acfer 094. Fe-Ni metal in ordinary and CO chondrites occurs in chondrule interiors, on chondrule surfaces, and as isolated grains in the matrix. Isolated Ni-rich metal in chondrites of petrologic type lower than type 3.10 is enriched in Co relative to the kamacite in chondrules. However, Ni-rich metal in type 3.15-3.9 chondrites always contains less Co than does kamacite. Fe-Ni metal grains in chondrules in Semarkona typically show plessitic intergrowths consisting of submicrometer kamacite and Ni-rich regions. Metal in other type 3 chondrites is composed of fine- to coarse-grained aggregates of kamacite and Ni-rich metal, resulting from metamorphism in the parent body. We found that the number density of Ni-rich grains in metal (number of Ni-rich grains per unit area of metal) in chondrules systematically decreases with increasing petrologic type. Thus, Fe-Ni metal is a highly sensitive recorder of metamorphism in ordinary and carbonaceous chondrites, and can be used to distinguish petrologic type and identify the least thermally metamorphosed chondrites. Among the known ordinary and CO chondrites, Semarkona is the most primitive. The range of metamorphic temperatures were similar for type 3 ordinary and CO chondrites, despite them having different parent bodies. Most Fe-Ni metal in Acfer 094 is martensite, and it preserves primary features. The degree of metamorphism is lower in Acfer 094, a true type 3.00 chondrite, than in Semarkona, which should be reclassified as type 3.01. ?? The Meteoritical Society, 2008.

Kimura, M.; Grossman, J.N.; Weisberg, M.K.

2008-01-01

35

Reflection spectra of shocked ordinary chondrites and their relationship to asteroids  

NASA Technical Reports Server (NTRS)

Spectral reflectance measurements are conducted of a number of mineralogically well-characterized, shock-blackened ordinary chondrites exhibiting four types of shock-generated black features: (1) opaque melt shock veins, (2) melt pockets and irregular interconnected melt veins, (3) melt dikes, and (4) black chondrites. While their spectra resemble those of C asteroids, these materials are found in impact crater basements and floors rather than surfaces and are of low abundances; they therefore cannot be responsible for large-scale spectral alterations of the parent asteroids of ordinary chondrites, and offer no support for the supposition that ordinary chondrite asteroids are hidden among C asteroids.

Keil, Klaus; Bell, Jeffrey F.; Britt, D. T.

1992-01-01

36

Minor Element Evidence that Asteroid 433 Eros is a Space-weathered Ordinary Chondrite Parent Body  

E-print Network

abundant in the inner asteroid belt, are the source of ordinary chondrites, the most abundant meteorites1 Minor Element Evidence that Asteroid 433 Eros is a Space-weathered Ordinary Chondrite Parent Body@dtm.ciw.edu #12;3 Abstract The NEAR mission to 433 Eros provided detailed data on the geology, mineralogy

Nittler, Larry R.

37

Organic compounds in the Forest Vale, H4 ordinary chondrite  

NASA Astrophysics Data System (ADS)

We have analyzed the H4 ordinary chondrite Forest Vale for polycyclic aromatic hydrocarbons (PAHs) using two-step laser mass spectrometry (L 2MS) and for amino acids using a standard Chromatographic method. Indigenous PAHs were identified in the matrices of freshly cleaved interior faces but could not be detected in pulverized silicates and chondrules. No depth dependence of the PAHs was found in a chipped interior piece. Amino acids, taken from the entire sample, consisted of protein amino acids that were nonracemic, indicating that they are terrestrial contaminants. The presence of indigenous PAHs and absence of indigenous amino acids provides support for the contention that different processes and environments contributed to the synthesis of the organic matter in the solar system.

Zenobi, Renato; Philippoz, Jean-Michel; Zare, Richard N.; Wing, Michael R.; Bada, Jeffrey L.; Marti, Kurt

1992-07-01

38

The formation of FeO-rich pyroxene and enstatite in unequilibrated enstatite chondrites: A petrologic-trace element (SIMS) study  

NASA Technical Reports Server (NTRS)

Enstatite (En) chondrites record the most reducing conditions known in the early solar system. Their oxidation state may be the result of condensation in a nebular region having an enhanced C/O ratio, reduction of more oxidized materials in a reducing nebula, reduction during metamorphic reheating in a parent body, or a combination of these events. The presence of more oxidized Fe-rich silicates, two types of En (distinguished by red and blue CL), and the juxtaposition of FeO-rich pyroxenes (Fe-pyx) surrounded by blue En (enstatite) in the UEC's (unequilibrated enstatite chondrites) is intriguing and led to the examination of the question of enstatite chondrite formation. Previously, data was presented on the petrologic-geochemical characteristics of the Fe-pyx and coexisting red and blue En. Here minor and trace element abundances (determined by ion probe-SIMS) on these three types of pyroxenes are reported on in the following meteorites: Kota Kota and LEW87223 (EH3), MAC88136 (EL3), St. Marks (EH4), and Hvittis (EL6). More data are currently being collected.

Weisberg, M. K.; Prinz, M.; Fogel, R. A.; Shimizu, N.

1993-01-01

39

Aluminum-, Calcium- And Titanium-Rich Oxide Stardust In Ordinary Chondrite Meteorites  

E-print Network

We report isotopic data for a total of 96 presolar oxide grains found in residues of several unequilibrated ordinary chondrite meteorites. Identified grain types include Al2O3, MgAl2O4, hibonite (CaAl12O19) and Ti oxide. This work greatly increases the presolar hibonite database, and is the first report of presolar Ti oxide. O-isotopic compositions of the grains span previously observed ranges and indicate an origin in red giant and asymptotic giant branch (AGB) stars of low mass (<2.5 MSun) for most grains. Cool bottom processing in the parent AGB stars is required to explain isotopic compositions of many grains. Potassium-41 enrichments in hibonite grains are attributable to in situ decay of now-extinct 41Ca. Inferred initial 41Ca/40Ca ratios are in good agreement with model predictions for low-mass AGB star envelopes, provided that ionization suppresses 41Ca decay. Stable Mg and Ca isotopic ratios of most of the hibonite grains reflect primarily the initial compositions of the parent stars and are generally consistent with expectations for Galactic chemical evolution, but require some local interstellar chemical inhomogeneity. Very high 17O/16O or 25Mg/24Mg ratios suggest an origin for some grains in binary star systems where mass transfer from an evolved companion has altered the parent star compositions. A supernova origin for the hitherto enigmatic 18O-rich Group 4 grains is strongly supported by multi-element isotopic data for two grains. The Group 4 data are consistent with an origin in a single supernova in which variable amounts of material from the deep 16O-rich interior mixed with a unique end-member mixture of the outer layers. The Ti oxide grains primarily formed in low-mass AGB stars. They are smaller and rarer than presolar Al2O3, reflecting the lower abundance of Ti than Al in AGB envelopes.

Larry R. Nittler; Conel M. O'D. Alexander; Roberto Gallino; Peter Hoppe; Ann N. Nguyen; Frank J. Stadermann; Ernst K. Zinner

2008-04-17

40

Ordinary Chondrite Spectral Signatures in the 243 Ida Asteroid System  

NASA Astrophysics Data System (ADS)

The NASA Galileo spacecraft observed asteroid 243 Ida and satellite Dactyl on August 28, 1993, with the Near Infrared Mapping Spectrometer (NIMS) at wavelengths ranging from 0.7 to 5.2 micrometers[Carlson et al., 1994]. Work is being conducted to produce radiance-calibrated spectral images of 243 Ida consisting of 17-channel, 299 meters per pixel files and a 102-channel, 3.2 kilometer per pixel NIMS observations of 243 Ida for the NASA Planetary Data System (PDS). These data are currently archived in PDS as uncalibrated data number counts. Radiometric calibrated 17-channel and 102-channel NIMS spectral data files of Dactyl and light curve 243 Ida observations are also being prepared. Analysis of this infrared asteroid data has confirmed that both 243 Ida and Dactyl are S-type asteroid objects and found that their olivine and pyroxene mineral abundances are consistent with that of ordinary chondrite meteorites. Tholen [1989] identified 243 Ida and Chapman et al. [1995] identified Dactyl as S-type asteroids on the basis of spectral data ranging from 0.4 to 1.0 micrometers. S-type are described [Tholen, 1989] as asteroids with a moderate albedos, a moderate to strong absorption feature shortward of 0.7 micrometers, and moderate to nonexistent absorption features longward of 0.7 micrometers. DeMeo et al. [2009] found 243 Ida to be a Sw asteroid based on Earth-based spectral observations 0.4 to 2.5 micrometers in range. Sw is a subclass of S-type asteroids that has a space weathering spectral component [DeMeo et al., 2009]. The NIMS data 243 Ida and Dactyl processed in this study exhibit signatures consistent with the Sw designation of DeMeo et al. [2009]. Measurements of olivine and pyroxene spectral bands were also conducted for the NIMS radiance data of 243 Ida and Dactyl. Band depth and band center measurements have been used to compare S-type asteroids with those of meteorites [Dunn et al., 2010; Gaffey et al., 1993]. The 243 Ida spectra were found to be consistent with those of Granahan [2002] and corresponded to measurements of LL chondrites. Dactyl was found to have spectral bands that correlate to L chondrite meteorite signatures as measured by Dunn et al. [2010]. The spectra band measurements of both objects correspond to those of the SIV class [Gaffey et al., 1993] of the S asteroids. Both L and LL chondrites are types of ordinary chondrite meteorites. Carlson, R. W., et al. (1994), Bulletin of the American Astronomical Society, 26, 1156. Chapman, C. R., et al. (1995), Nature, 374, 783-785. DeMeo, F. E., R. P. Binzel, S. M. Slivan, and S. J. Bus (2009), Icarus, 202, 160-180. Dunn, T. L., T. J. McCoy, J. M. Sunshine, and H. Y. McSween (2010), Icarus, 208, 789-797. Gaffey, M. J., J. F. Bell, R. H. Brown, T. H. Burbine, J. L. Piatek, K. L. Reed, and D. A. Chaky (1993), Icarus, 106, 573-602. Granahan, J. C. (2002), Journal of Geophysical Research Planets, 107(E10), 5090-5100. Tholen, D. J. (1989), in Asteroids II, edited by R. P. Binzel, T. Gehrels, and M.S. Matthews, pp. 1139-1150, University of Arizona Press, Tucson.

Granahan, J. C.

2012-12-01

41

The Chelyabinsk Fall Highly Siderophile Element Abundance and 187Os/188Os Composition and Comparison with Ordinary and Carbonaceous Chondrites  

NASA Astrophysics Data System (ADS)

New osmium isotope and highly siderophile element abundance data are presented for the Chelyabinsk ordinary chondrite fall (February 2013) and placed into context with new data for ordinary and carbonaceous chondrites.

Day, J. M. D.; Corder, C. A.; Dhaliwal, J. K.; Liu, Y.; Taylor, L. A.

2014-09-01

42

(7) Iris: a possible source of ordinary chondrites?  

NASA Astrophysics Data System (ADS)

Rotationally resolved visible spectroscopy (6000~9500Å) of (7) Iris is presented. Within a few percents, no variation in Iris' visible spectrum over a rotational period has been found. These data suggest that the mineralogic properties of Iris' surface are globally homogeneous, although we cannot exclude the presence of some texture and/or albedo variegation as suggested by previous photometric and polarimetric studies available in the literature. From a dynamical point of view, we estimate the ejection velocity required for collisional fragments from this asteroid to be injected into the surrounding chaotic regions. The resulting velocity values are fairly high, but not incompatible with the values suggested by the present knowledge of catastrophic break-up phenomena and by the observational constraints put by asteroid families. Taking into account the close similarity between Iris' spectrum and that of (6) Hebe, a typical S(IV)-type object according with the most modern spectral classifications, we believe that (7) Iris may be a not negligible source of ordinary chondrite meteorites.

Migliorini, F.; Manara, A.; Cellino, A.; di Martino, M.; Zappala, V.

1997-05-01

43

Chondrules in the Sharps H3 chondrite - Evidence for intergroup compositional differences among ordinary chondrite chondrules  

NASA Technical Reports Server (NTRS)

Bulk compositions of 19 chondrules and one matrix-rich sample from H3.4 Sharps were determined by instrumental neutron activation analysis. Samples were characterized petrographically, and mineral compositions were determined by electron microprobe analysis. There is constancy among ordinary chondrite (OC) groups in the compositional interrelationships of different chondrule types; e.g., in H3 as well as L3 and LL3 chondrites, porphyritic chondrules are more refractory than nonporphyritic chondrules. Precursor components of H3 chondrules are closely related to those of LL3 chondrules. The mean Ir/Ni, Ir/Co, and Ir/Au ratios of H3 chondrules differ from the corresponding ratios of LL3 chondrules at the 99, 90, and 79 percent confidence levels, respectively. The ratios in H3 chondrules exceed those in LL3 chondrules by amounts similar to those by which H whole-rocks exceed LL whole-rocks. These data suggest that there are primary systematic differences in bulk composition between H and LL chondrules. These differences support the inference that chondrule formation occurred after major nebular fractionation events had established the observed bulk compositional differences among OC groups.

Rubin, Alan E.; Pernicka, Ernst

1989-01-01

44

Metamorphism and aqueous alteration in low petrographic type ordinary chondrites  

NASA Technical Reports Server (NTRS)

In order to investigate the relative importance of dry metamorphism and aqueous alteration in the history of chondruies, chondruies were hand-picked from the Semarkona (petrographic type 3.0), Bishunpur (3. 1), Chainpur (3.4), Dhajala (3.8) and Allegan (5) chondrites, and matrix samples were extracted from the first three ordinary chondrites. The thermoluminescence (TL) properties of all the samples were measured, and appropriate subsets of the samples were analyzed by electron-microprobe and radiochemical neutron activation and the water and H-isotopic composition determined. The TL data for chondrules from Semarkona and Bishunpur scatter widely showing no unambiguous trends, although group B1 chondrules tend to have lower sensitivities and lower peak temperatures compared with group A5 chondrules. It is argued that these data reflect the variety of processes accompanying chondrule formation. The chondrules show remarkably uniform contents of the highly labile elements, indicating mineralogical control on abundance and volatile loss from silicates and loss and recondensation of mobile chalcophiles and siderophiles in some cases. Very high D/H values (up to approx. 8000% SMOW) are observed in certain Semarkona chondrules, a confirmation of earlier work. With increasing petrographic type, mean TL sensitivities of the chondrules increase, the spread of values within an individual meteorite decreases, and peak temperatures and peak widths show trends indicating that the TL is mainly produced by feldspar and that dry, thermal metamorphism is the dominant secondary process experienced by the chondrules. The TL sensitivities of matrix samples also increase with petrographic type. Chainpur matrix samples show the same spread of peak temperatures and peak widths as Chainpur chondruies, indicating metamorphism-related changes in the feldspar are responsible for the TL of the matrix. The TL data for the Semarkona and Bishunpur matrix samples provide, at best, only weak evidence for aqueous alteration, but the matrix contains H with approximately terrestrial D/H values, even though it contains much water. Secondary processes (probably aqueous alteration) presumably lowered the D/H of the matrix and certain chondrules. While chondrule properties appear to be governed primarily by formation processes and subsequent metamorphism, the matrix of Semarkona has a more complex history involving aqueous alteration as a meteorite-wide process.

Xie, T.; Lipschutz, M. E.; Sears, D. W. G.; Guimon, R. K.; Jie, Lu; Benoit, P. H.; O'D. Alexander, C. M.; Wright, Ian; Pillinger, C.; Morse, A. D.; Hutchison, Robert

1995-01-01

45

Rhenium-osmium isotope systematics of ordinary chondrites and iron meteorites  

NASA Technical Reports Server (NTRS)

Using negative thermal ionization mass spectrometry, Re and Os abundances were determined by isotope dilution and Os-187/Os-186 measured in 11 ordinary chondrites, and also in 1 IIB and 3 IIIB irons. In addition, Os-186/Os-188 and Os-189/Os-188 ratios were precisely determined for 3 unspiked ordinary chondrites as a means of constraining the intensity of any neutron irradiation these meteorites may have experienced.

Walker, R. J.; Morgan, J. W.; Horan, M. F.; Grossman, J. N.

1993-01-01

46

Plutonium, uranium and rare earths in the phosphates of ordinary chondrites - The quest for a chronometer  

NASA Astrophysics Data System (ADS)

The distributions of Pu, U, and the REEs in single crystals of the calcium phosphates, merrillite, and apatite of ordinary chondrites were investigated, inferring limites on Pu concentrations from fossil track measurements. The study takes spallation-induced tracks into account. Despite the higher affinity of both Pu and the REEs for merrilite than apatite, no quantitative correlation is found between the abundances of these elements in merrillite grains from a given ordinary chondrite, indicating that Pu-244 cannot be used to determine the relative formation times of chondrites.

Crozaz, G.; Pellas, P.; Bourot-Denise, M.; de Chazal, S. M.; Fieni, C.; Lundberg, L. L.; Zinner, E.

1989-06-01

47

Ion microprobe magnesium isotope analysis of plagioclase and hibonite from ordinary chondrites  

NASA Technical Reports Server (NTRS)

Ion and electron microprobes were used to examine Mg-26 excesses from Al-26 decay in four Al-rich objects from the type 3 ordinary hibonite clast in the Dhajala chondrite. The initial Al-26/Al-27 ratio was actually significantly lower than Al-rich inclusions in carbonaceous chondrites. Also, no Mg-26 excesses were found in three plagioclase-bearing chondrules that were also examined. The Mg-26 excesses in the hibonite chondrites indicated a common origin for chondrites with the excesses. The implied Al-26 content in a proposed parent body could not, however, be confirmed as a widespread heat source in the early solar system.

Hinton, R. W.; Bischoff, A.

1984-01-01

48

Physical propoerties of incompletely compacted equilibrated ordinary chondrites: Implications for asteroidal structure and impact processing  

SciTech Connect

Aside from robotic exploration, meteorites are our primary source of information about the asteroids that they sample. Although there are some discrepancies, there are dynamical, spectral, and compositional evidence for an S-type asteroid connection to the ordinary chondrite meteorites. Reconciling the measured bulk density of chondrites with that of asteroids can yield important inferences about the internal structure of asteroids. For example, the bulk density of S-type asteroids is typically much less than the bulk density of chondrites, leading to the inference that asteroids contain a significant quantity of macroporosity. We have identified several unusual ordinary chondrites that have been incompletely compacted relative to petrologically similar but much less porous chondrites. Although these are equilibrated chondrites, they have extreme amounts of pore spaces between mineral grains. Here, we detail our efforts quantifying the nature of the pore spaces in these chondrites and we examine the implications for the structure and mechanical processing of the asteroids from which these chondrites originate. Our pore size distribution data may also provide constraints for the modeling of heat flow and shock waves within primordial chondritic parent bodies.

Sasso, M.R.; Macke, R.J.; Britt, D.T.; Rivers, M.L.; Ebel, D.S.; Friedrich, J.M. (Central Florida); (AMNH); (UC); (Fordham)

2009-03-19

49

Classification of five new ordinary chondrites (RC 073, 074, 076-078) from Roosevelt County, New Mexico  

NASA Astrophysics Data System (ADS)

Five new ordinary chondrites from Roosevelt County, New Mexico were examined by optical microscopy in transmitted and reflected light. The chondrites were moderately to heavily weathered and were assigned to a petrologic time, chemical group, and shock stage.

McCoy, T. J.; Keil, K.; Wilson, I. E.

1993-03-01

50

Classification of five new ordinary chondrites (RC 073, 074, 076-078) from Roosevelt County, New Mexico  

NASA Technical Reports Server (NTRS)

Five new ordinary chondrites from Roosevelt County, New Mexico were examined by optical microscopy in transmitted and reflected light. The chondrites were moderately to heavily weathered and were assigned to a petrologic time, chemical group, and shock stage.

Mccoy, Timothy J.; Keil, Klaus; Wilson, Ivan E.

1993-01-01

51

Discovery of a main-belt asteroid resembling ordinary chondrite meteorites.  

PubMed

Although ordinary chondrite material dominates meteorite falls, the identification of a main-belt asteroid source has remained elusive. From a new survey of more than 80 small main-belt asteroids comes the discovery of one having a visible and near-infrared reflectance spectrum similar to L6 and LL6 ordinary chondrite meteorites. Asteroid 3628 BoZnemcová has an estimated diameter of 7 kilometers and is located in the vicinity of the 3:1 Jovian resonance, a predicted meteorite source region. Although the discovery of a spectral match may indicate the existence of ordinary chondrite material within the main asteroid belt, the paucity of such detections remains an unresolved problem. PMID:17829382

Binzel, R P; Xu, S; Bus, S J; Skrutskie, M F; Meyer, M R; Knezek, P; Barker, E S

1993-12-01

52

Fragmental breccias and the collisional evolution of ordinary chondrite parent bodies  

NASA Technical Reports Server (NTRS)

The present investigation is concerned with the results of a survey of gas-poor, melt-rock, or exotic clast-bearing fragmental breccias among the ordinary chondrite groups. It is found that such breccias constitute 5 percent, 22 percent, and 23 percent of H, L, LL chondrites respectively. Four melt-rock-clast-bearing fragmental breccias were selected for more detailed study to determine petrologic relationships between blasts and hosts. Attention is given to the abundances of melt-rock or exotic clast-bearing fragmental breccias, the formation of fragmental breccias, and the implications of breccia abundances in different chondrite groups.

Rubin, A. E.; Peterson, E.; Keil, K.; Rehfeldt, A.; Jarosewich, E.

1983-01-01

53

Chromite and olivine in type II chondrules in carbonaceous and ordinary chondrites - Implications for thermal histories and group differences  

NASA Astrophysics Data System (ADS)

Unequilibrated chromite and olivine margin compositions in type II chondrules are noted to differ systematically among three of the chondrite groups, suggesting that type II liquids differed in composition among the groups. These differences may be interpreted as indicators of different chemical compositions of the precursor solids which underwent melting, or, perhaps, as differences in the extent to which immiscible metal sulfide droplets were lost during chondrule formation. Because zinc is detectable only in type II chromites which have undergone reequilibration, the high zinc contents reported for chondritic chromites in other studies probably reflect redistribution during thermal metamorphism.

Johnson, C. A.; Prinz, M.

1991-03-01

54

Bleached chondrules: Evidence for widespread aqueous processes on the parent asteroids of ordinary chondrites  

USGS Publications Warehouse

We present the first detailed study of a population of texturally distinct chondrules previously described by Kurat (1969), Christophe Michel-Levy (1976), and Skinner et al. (1989) that are sharply depleted in alkalis and Al in their outer portions. These 'bleached' chondrules, which are exclusively radial pyroxene and cryptocrystalline in texture, have porous outer zones where mesostasis has been lost. Bleached chondrules are present in all type 3 ordinary chondrites and are present in lower abundances in types 4-6. They are most abundant in the L and LL groups, apparently less common in H chondrites, and absent in enstatite chondrites. We used x-ray mapping and traditional electron microprobe techniques to characterize bleached chondrules in a cross section of ordinary chondrites. We studied bleached chondrules from Semarkona by ion microprobe for trace elements and H isotopes, and by transmission electron microscopy. Chondrule bleaching was the result of low-temperature alteration by aqueous fluids flowing through fine-grained chondrite matrix prior to thermal metamorphism. During aqueous alteration, interstitial glass dissolved and was partially replaced by phyllosilicates, troilite was altered to pentlandite, but pyroxene was completely unaffected. Calcium-rich zones formed at the inner margins of the bleached zones, either as the result of the early stages of metamorphism or because of fluid-chondrule reaction. The mineralogy of bleached chondrules is extremely sensitive to thermal metamorphism in type 3 ordinary chondrites, and bleached zones provide a favorable location for the growth of metamorphic minerals in higher petrologic types. The ubiquitous presence of bleached chondrules in ordinary chondrites implies that they all experienced aqueous alteration early in their asteroidal histories, but there is no relationship between the degree of alteration and metamorphic grade. A correlation between the oxidation state of chondrite groups and their degree of aqueous alteration is consistent with the source of water being either accreted ices or water released during oxidation of organic matter. Ordinary chondrites were probably open systems after accretion, and aqueous fluids may have carried volatile elements with them during dehydration. Individual radial pyroxene and cryptocrystalline chondrules were certainly open systems in all chondrites that experienced aqueous alteration leading to bleaching.

Grossman, J.N.; Alexander, C.M. O'D.; Wang, J.; Brearley, A.J.

2000-01-01

55

Restriction of parent body heating by metal-troilite melting: Thermal models for the ordinary chondrites  

NASA Astrophysics Data System (ADS)

Ordinary chondrite meteorites contain silicates, Fe,Ni-metal grains, and troilite (FeS). Conjoined metal-troilite grains would be the first phase to melt during radiogenic heating in the parent body, if temperatures reached over approximately 910-960 °C (the Fe,Ni-FeS eutectic). On the basis of two-pyroxene thermometry of 13 ordinary chondrites, we argue that peak temperatures in some type 6 chondrites exceeded the Fe,Ni-FeS eutectic and thus conjoined metal-troilite grains would have begun to melt. Melting reactions consume energy, so thermal models were constructed to investigate the effect of melting on the thermal history of the H, L, and LL parent asteroids. We constrained the models by finding the proportions of conjoined metal-troilite grains in ordinary chondrites using high-resolution X-ray computed tomography. The models show that metal-troilite melting causes thermal buffering and inhibits the onset of silicate melting. Compared with models that ignore the effect of melting, our models predict longer cooling histories for the asteroids and accretion times that are earlier by 61, 124, or 113 kyr for the H, L, and LL asteroids, respectively. Because the Ni/Fe ratio of the metal and the bulk troilite/metal ratio is higher in L and LL chondrites than H chondrites, thermal buffering has the greatest effect in models for the L and LL chondrite parent bodies, and least effect for the H chondrite parent. Metal-troilite melting is also relevant to models of primitive achondrite parent bodies, particularly those that underwent only low degrees of silicate partial melting. Thermal models can predict proportions of petrologic types formed within an asteroid, but are systematically different from the statistics of meteorite collections. A sampling bias is interpreted to explain these differences.

Mare, Eleanor R.; Tomkins, Andrew G.; Godel, Belinda M.

2014-04-01

56

Partial melting of ordinary chondrites: Lost City (H) and St. Severin (LL)  

NASA Astrophysics Data System (ADS)

Eucrites and diogenites are examples of asteroidal basalts and orthopyroxenites, respectively. As they are found intermingled in howardites, which are inferred to be regolith breccias, eucrites and diogenites are thought to be genetically related. But the details of this relationship and of their individual origins remain controversial. Work by Jurewicz et al. showed that 1170-1180 C partial melts of the (anhydrous) Murchison (CM) chondrite have major element compositions extremely similar to primitive eucrites, such as Sioux County. However, the MnO contents of these melts were about half that of Sioux County, a problem for the simple partial melting model. In addition, partial melting of Murchison could not produce diogenites, because residual pyroxenes in the Murchison experiments were too Fe- and Ca-rich and were minor phases at all but the lowest temperatures. A parent magma for diogenites needs an expanded low-calcium pyroxene field. In their partial melting study of an L6 chondrite, Kushiro and Mysen found that ordinary chondrites did have an expanded low-Ca pyroxene field over that of CV chondrites (i.e., Allende), probably because ordinary chondrites have lower Mg/Si ratios. This study expands that of both Kushiro and Mysen and Jurewicz et al. to the Lost City (H) and St. Severin (LL) chondrites at temperatures ranging from 1170 to 1325 C, at an fO2 of one log unit below the iron-wuestite buffer (IW-1).

Jurewicz, Amy J. G.; Jones, John H.; Weber, Egon T.; Mittlefehldt, David W.

1993-03-01

57

SType Asteroids, Ordinary Chondrites, and Space Weathering: The Evidence from Galileo's Flybys of Gaspra and Ida  

E-print Network

S­Type Asteroids, Ordinary Chondrites, and Space Weathering: The Evidence from Galileo's Fly 1996 Abstract. New observations of the S­type asteroids Gaspra and, especially, Ida by the GalileoŸneŸmcová. This article reviews the history of the S­type conundrum, which set the stage for Galileo's historic fly­bys. I

Chapman, Clark R.

58

Impact Experiments of Gypsum-Glass Beads Mixtures Simulating Parent Bodies of Ordinary Chondrites  

Microsoft Academic Search

We conducted impact experiments of porous gypsum-glass beads mixtures simulating the parent bodies of ordinary chondrites to examine the effect of glass beads on the impact strength. We found that the impact strength changed with the glass bead size and the impact velocity.

M. Yasui; M. Arakawa

2011-01-01

59

Impact Experiments of Gypsum-Glass Beads Mixtures Simulating Parent Bodies of Ordinary Chondrites  

NASA Astrophysics Data System (ADS)

We conducted impact experiments of porous gypsum-glass beads mixtures simulating the parent bodies of ordinary chondrites to examine the effect of glass beads on the impact strength. We found that the impact strength changed with the glass bead size and the impact velocity.

Yasui, M.; Arakawa, M.

2011-03-01

60

Effects of Metamorphism on the Valence and Coordination of Titanium in Ordinary Chondrites  

SciTech Connect

Despite years of study, the conditions under which ordinary chondrites were metamorphosed from grade 3 to grade 6 are not well defined. Wide ranges of peak temperature are inferred for each grade. The long-popular 'onion shell' model, in which higher metamorphic grade is attributed to greater depths of origin, implies a corresponding decrease in cooling rate with increasing grade, and there is disagreement as to whether or not this is observed. Redox conditions during chondrite metamorphism are also not well understood. Some workers have reported evidence for reduction, presumably by carbon, with increase in grade from 3-4, followed by oxidation during metamorphism to higher grades, but other work indicates little variation in fO{sub 2} as a function of metamorphic grade. During our investigation of the valence of Ti in planetary materials, we found high proportions of Ti{sup 3+} in olivine and pyroxene in chondrules in Semarkona (LL3.0) and low proportions in New Concord (L6) olivine, suggesting that Ti was oxidized during ordinary chondrite metamorphism. We have undertaken a study of L and LL chondrites of grades 3-6 to see how Ti valence and coordination vary with grade and to see if the variations can be used to constrain conditions of chondrite metamorphism.

Simon, S.B.; Sutton, S.R.; Grossman, L. (UC)

2012-04-02

61

Mn-Cr isotopic systematics of Chainpur chondrules and bulk ordinary chondrites  

NASA Technical Reports Server (NTRS)

We report on ongoing study of the Mn-Cr systematics of individual Chainpur (LL3.4) chondrules and compare the results to those for bulk ordinary chondrites. Twenty-eight chondrules were surveyed for abundances of Mn, Cr, Na, Fe, Sc, Hf, Ir, and Zn by INAA. Twelve were chosen for SEM/EDX and high-precision Cr-isotopic studies on the basis of LL-chondrite-normalized Mn(LL), Sc(LL), (Mn/Fe)(LL), and (Sc/Fe)(LL) as well as their Mn/Cr ratios. Classification into textural types follows from SEM/EDX examination of interior surfaces.

Nyquist, L.; Lindstrom, D.; Wiesmann, H.; Bansal, B.; Shih, C.-Y.; Mittlefehldt, D.; Martinez, R.; Wentworth, S.

1994-01-01

62

Variations of the isotopic composition of sulfur in enstatite and ordinary chondrites  

NASA Technical Reports Server (NTRS)

High-precision sulfur isotopic analyses (delta S-33, delta S-34, and delta S-36) of bulk ordinary and enstatite chondrites demonstrate that systematic variations exist. The average delta S-34 values are -0.26 +/- 0.07, -0.02 +/- 0.06, and 0.49 +/- 0.16 percent for enstatite and ordinary and carbonaceous chondrites, respectively. Isotopic variations of different sample specimens of primitive meteorites, e.g., Qingzhen and Abee, were observed which may be attributed to heterogeneity in the early solar nebula. Sulfur isotopic fractionations in both bulk samples and mineral separates are mass-dependent, and no nuclear isotopic anomalies were detected. The sulfur isotopic compositions of both mineral and density separates were measured. The sulfur isotopic compositions of separated chondrules from Chainpur and Bjurbole are reported. Significant isotopic difference for the chondrules from the bulk meteorite are noted for both meteorites.

Gao, Xia; Thiemens, Mark H.

1993-01-01

63

Experimental Space Weathering of Ordinary Chondrites by Nanopulse Laser: TEM Results  

NASA Technical Reports Server (NTRS)

A set of ordinary chondrite meteorites has been subjected to artificial space weathering by nanopulse laser to simulate the effects of micrometeorite bombardment. Three meteorites, an H (Ehole), L (Chateau Renard - CR), and LL (Appley Bridge - AB) were lasered following the method of Sasaki et al [1]. Near IR spectra were taken before and after exposure to examine the optical changes induced and the samples were examined by scanning and transmission electron microscopy (SEM and TEM) to understand the physical changes.

Noble, S. K.; Hiroi, T.; Keller, L. P.; Pieters, C. M.

2011-01-01

64

Chemical, isotopic and mineralogical evidence for the origin of matrix in ordinary chondrites  

NASA Astrophysics Data System (ADS)

Results are presented of a combined chemical, isotopic, and mineralogical study of fine-grained opaque matrix material from a type-3 ordinary chondrite Allan Hills A77299. It was found that the matrix of this chondrite (in contrast to chondrules) shows no siderophile element depletions and is remarkably unfractionated relative to CI chondrites. It was also found that the matrix lump has a unique oxygen isotopic composition which lies below the terrestrial fractionation line and differs markedly from the composition of fine-grained matrix lumps and chondrule rims from Semarkona chondrules (Grossman and Wasson, 1987; Grossman et al., 1987); the mineralogy and textures of the matrix lump (which consists of rare angular grains of pyroxene and olivine embedded within a ground-mass of rounded fine-grained olivines), as well as its major element composition, are typical of matrix material of other type-3 chondrites studied. It is concluded that the matrix lump in these chondrites consists largely of material that formed by annealing of amorphous presolar dust or nebular condensates.

Brearley, A. J.; Scott, E. R. D.; Keil, K.; Clayton, R. N.; Mayeda, T. K.; Boynton, W. V.; Hill, D. H.

1989-08-01

65

Iodine-xenon analysis of ordinary chondrite halide: implications for early solar system water  

NASA Astrophysics Data System (ADS)

We report the results of iodine-xenon analyses of irradiated halide grains extracted from the H-chondrite Monahans (1998) and compare them with those from Zag ( Whitby et al., 2000) to address the timing of aqueous processing on the H-chondrite parent body. Xe isotopic analyses were carried out using the RELAX mass spectrometer with laser stepped heating. The initial 129I/ 127I ratio in the Monahans halide was determined to be (9.37 ± 0.06) × 10 -5 with an iodine concentration of ˜400 ppb. Significant scatter, especially in the Zag data, indicates that a simple interpretation as a formation age is unreliable. Instead we propose a model whereby halide minerals in both meteorites formed ˜5 Ma after the enstatite achondrite Shallowater (at an absolute age of 4559 Ma). This age is in agreement with the timing of aqueous alteration on the carbonaceous chondrite parent bodies and ordinary chondrite metamorphism and is consistent with the decay of 26Al as a heat source for heating and mobilisation of brines on the H-chondrite parent body. Post accretion surface impact events may have also contributed to the heat source.

Busfield, A.; Gilmour, J. D.; Whitby, J. A.; Turner, G.

2004-01-01

66

A unique high Mn/Fe microgabbro in the Parnallee (LL3) ordinary chondrite - Nebular mixture or planetary differentiate from a previously unrecognized planetary body?  

NASA Technical Reports Server (NTRS)

We studied a unique microgabbro fragment from the Parnallee (LL3) unequilibrated ordinary chondrite. The fragment, which was originally identified by its ophitic to sub-ophitic texture, exhibits features characteristic of lunar and terrestrial tholeiitic basalts (i.e., extreme compositional zoning in clinopyroxene (Wo10En65Fs25 to Wo15En2FS83), a multiply saturated major element composition similar to mid-ocean ridge basalt with 3.1 wt pct Na2O and 0.15 wt pct K2O, and uniformly enriched rare earth elements (c. 10 x C1). A high bulk MnO/FeO ratio (0.064) distinguishes the microgabbro from other basaltic rocks and suggests the precursor material formed or reached equilibrium in a reducing environment. However, the absence of Fe metal and the extreme enrichment of FeO (up to 40 wt pct), in late crystallizing pyroxferroite, requires the last crystallization event to have occurred in a relatively oxidizing environment. We suggest the microgabbro formed by partial melting in a planetary body after removal of metallic Fe.

Kennedy, A. K.; Hutchison, R.; Hutcheon, I. D.; Agrell, S. O.

1992-01-01

67

Distribution of rare earth elements and uranium in various components of ordinary chondrites  

NASA Astrophysics Data System (ADS)

Rare earth elements (REE) and uranium were studied for their distributions in various component phases of four ordinary chondrites. Kesen (H4), Richardton (H5), Bruderheim (L6), and Saint Severin (LL6). A selective dissolution method was applied for the phase fractionation. The REE were analysed by neutron activation analysis, and U was determined by neutron-induced fission tracks. The present study revealed that both REE and U are highly enriched in the Ca-phosphate minerals with different enrichment factors, implying chemical fractionation between them. The phosphates seem to be responsible for more than 80 percent of the light REE in all chondrites. On the other hand, only 20-40 percent of the total U resides in the Ca-phosphates. This difference in enrichments might have been caused through the levels of metamorphic activity on the meteoritic parent bodies.

Ebihara, M.; Honda, M.

1984-06-01

68

Raman spectroscopic study of four Spanish shocked ordinary chondrites: Cañellas, Olmedilla de Alarcón, Reliegos and Olivenza.  

PubMed

Shock metamorphism in chondritic parent bodies produces typical textures, visible under the microscope, which are a consequence of structural deformation of the crystals. Such deformations can be studied with Raman spectroscopy. The vibrational characteristics of olivines and pyroxenes, structurally deformed by weak-to-moderate shock metamorphism, have been determined on four Spanish ordinary chondrites (Cañellas, Olmedilla de Alarcón, Reliegos and Olivenza). Such deformations would affect, in principle, the band positions and widths of the Raman spectra peaks. The measured band positions and relative intensities are consistent with chemical composition for olivines and pyroxenes, but show little influence on the degree of shock. However, the full spectral band width of the silicate internal modes shows some dependence on the impact grade, which could be attributed to inhomogeneous effects produced by the impacts. PMID:20529952

Rull, F; Muñoz-Espadas, M J; Lunar, R; Martínez-Frías, J

2010-07-13

69

The Cali Meteorite: Luminescence of a recently fallen H/L ordinary chondrite  

SciTech Connect

The Cali meteorite fall occurred on 6 July 2007 at 21h33m+-1m UTC. Some specimens were recovered just after their fall so they are extremely fresh materials. Mineral analysis and bulk chemistry revealed that the measured abundances for most elements closely match the values recorded for other ordinary chondrites classified as H/L. We present here thermoluminescence studies of this recently fallen meteorite in order to get additional information on the radiation environment, and the thermal history of this meteorite. Such information is revealed to be complementary with the range of orbital elements deduced from eyewitness reports of the fireball.

Trigo-Rodriguez, J. M. [Institute of Space Sciences (CSIC-IEEC). Campus UAB, Facultat de Ciencies, Torre C5-p2. 08193 Bellaterra (Spain); Llorca, J. [Institut de Tecniques Energetiques. Universitat Politecnica de Catalunya, Diagonal 647, ed. ETSEIB. 08028 Barcelona (Spain); Sears, D. W. G. [Arkansas Center for Space and Planetary Sciences, University of Arkansas, Fayetteville, Arkansas 72701 (United States)

2009-08-17

70

Spectral Properties of Near-Earth Asteroids: Evidence for Sources of Ordinary Chondrite Meteorites  

PubMed

Although ordinary chondrite (OC) meteorites dominate observed falls, the identification of near-Earth and main-belt asteroid sources has remained elusive. Telescopic measurements of 35 near-Earth asteroids ( approximately3 kilometers in diameter) revealed six that have visible wavelength spectra similar to laboratory spectra of OC meteorites. Near-Earth asteroids were found to have spectral properties that span the range between the previously separated domains of OC meteorites and the most common (S class) asteroids, suggesting a link. This range of spectral properties could arise through a diversity of mineralogies and regolith particle sizes, as well as through a time-dependent surface weathering process. PMID:8688076

Binzel; Bus; Burbine; Sunshine

1996-08-16

71

Volatile Element Chemistry during Metamorphism of Ordinary Chondritic Material and Some of its Implications for the Composition of Asteroids  

E-print Network

We used chemical equilibrium calculations to model thermal metamorphism of ordinary chondritic material as a function of temperature, pressure, and trace element abundance and use our results to discuss volatile mobilization during thermal metamorphism of ordinary chondrite parent bodies. The calculations include ~1,700 solids and gases of 40 elements. We compiled trace element abundances in H-, L-, and LL-chondrites for the elements Ag, As, Au, Bi, Cd, Cs, Cu, Ga, Ge, In, Pb, Rb, Sb, Se, Sn, Te, Tl, and Zn, and identified abundance trends as a function of petrographic type within each class. We found that abundance patterns within the H- and L- chondrites are consistent with mobilization of volatile elements in an onionshell-type parent body. LL-chondrites have more complex abundance patterns that may support a rubble-pile model for the LL-chondrite parent body. We calculated volatility sequences for the trace elements in the ordinary chondritic material, which differs significantly from the solar nebula volatility sequence.

Laura Schaefer; Bruce Fegley Jr

2008-01-07

72

Exposure history and terrestrial ages of ordinary chondrites from the Dar al Gani region, Libya  

NASA Astrophysics Data System (ADS)

We measured the concentrations of noble gases in 32 ordinary chondrites from the Dar al Gani (DaG) region, Libya, as well as concentrations of the cosmogenic radionuclides 14C, 10Be, 26Al, 36Cl, and 41Ca in 18 of these samples. Although the trapped noble gases in five DaG samples show ratios typical of solar or planetary gases, in all other DaG samples, they are dominated by atmospheric contamination, which increases with the degree of weathering. Cosmic ray exposure (CRE) ages of DaG chondrites range from ~1 Myr to 53 Myr. The CRE age distribution of 10 DaG L chondrites shows a cluster around 40 Myr due to four members of a large L6 chondrite shower. The CRE age distribution of 19 DaG H chondrites shows only three ages coinciding with the main H chondrite peak at ~7 Myr, while seven ages are <5 Myr. Two of these H chondrites with short CRE ages (DaG 904 and 908) show evidence of a complex exposure history. Five of the H chondrites show evidence of high shielding conditions, including low 22Ne/21Ne ratios and large contributions of neutron-capture 36Cl and 41Ca. These samples represent fragments of two or more large pre-atmospheric objects, which supports the hypothesis that the high H/L chondrite ratio at DaG is due to one or more large unrecognized showers. The 14C concentrations correspond to terrestrial ages <35 kyr, similar to terrestrial ages of chondrites from other regions in the Sahara but younger than two DaG achondrites. Despite the loss of cosmogenic 36Cl and 41Ca during oxidation of metal and troilite, concentrations of 36Cl and 41Ca in the silicates are also consistent with 14C ages <35 kyr. The only exception is DaG 343 (H4), which has a 41Ca terrestrial age of 150 ± 40 kyr. This old age shows that not only iron meteorites and achondrites but also chondrites can survive the hot desert environment for more than 50 kyr. A possible explanation is that older meteorites were covered by soils during wetter periods and were recently exhumed by removal of these soils due to deflation during more arid periods, such as the current one, which started ~3000 years ago. Finally, based on the 26Al/21Ne and 10Be/21Ne systematics in 16 DaG meteorites, we derived more reliable estimates of the 10Be/21Ne production rate ratio, which seems more sensitive to shielding than was predicted by the semi-empirical model of Graf et al. (1990) but less sensitive than was predicted by the purely physical model of Leya et al. (2000).

Welten, K. C.; Nishiizumi, K.; Finkel, R. C.; Hillegonds, D. J.; Jull, A. J. T.; Franke, L.; Schultz, L.

2004-03-01

73

Thermal History of Ordinary Chondrites: Comparison and Evaluation of Chronological Tools  

NASA Astrophysics Data System (ADS)

The structure and the thermal history of ordinary chondrites is disputed, because there is no agreement as to whether radiometric ages, metallographic cooling rates (MTCR) [1], fission-track cooling rates (FTCR) [2], and petrographic observations correlate [3,4]. The comparison of these published data is discussed in the case of the H chondrites with reference to the Pb/Pb systematics determined in their phosphates [5]. It is assumed that the age derived from each chronometer defines the time period after which the material reached its closure temperature, cooling down from higher temperatures. What is of interest for the Pb/Pb systematics is the time resolution of 10^6 yr and the knowledge of the closure temperature of the U/Pb system in the phosphates derived from experimental studies [6]: 710 K for a cooling rate of 5 K/m.y. 1. The Pb/Pb systematics define a time interval of 6 x 10^6 yr for the thermal processing of equilibrated H chondrites; this is coherent with the estimation previously derived from the Rb/Sr [7,8], Ar/Ar [9], and Pu chronologies [10]. 2. When the different metamorphic grades of equilibrated H chondrites are considered, no significant correlation exists between the Pb/Pb systematics and the Ar/Ar chronology; the chronology is based on the Sr initial method and the I-Xe systematics, whereas a positive correlation with the metallographic and fission-track cooling rates is seen. 3. The chronological tools (Pb/Pb, Ar/Ar, FTCR, MCR) are compared in the best- documented chondrites (H6 Guarena, H6 Kernouve, H5 Richardton) taking into account the estimated closure temperatures, which range from 900 to 380 K. This comparison does not point out either a monotonic cooling regime occurring in a parent body with a preserved layered structure or a two-step cooling regime (fast cooling at temperatures higher than 770 K and slower cooling at lower temperatures). Such an attempt to reconstruct the thermal history of ordinary chondrites is based on the interpretation of the radiochronometric data as translating the thermal closure of the different isotopic systems. This basic interpretation may be incorrect for some chondrites and must be evaluated before the chronometric informations are applied as precise time constraints in the 4.56- 4.4 aeon interval. References: [1] Taylor G. J. et al. (1987) Icarus, 69, 1-13. [2] Lipschutz M. E. et al. (1989) In Asteroids II (R. Binzel et al., eds.), 740-778, Univ. of Arizona. [3] Hutchison R. et al. (1980) Nature, 287, 787-790. [4] Christophe MichelLevy M. (1981) EPSL, 54, 67-80. [5] Gopel C. et al. (1990) Meteoritics, 25, 367-368. [6] Cherniak D. et al. (1991) GCA, 55, 1663-1673. [7] Minster J. F. et al. (1982) Nature, 300, 414-419. [8] Podosek F. A. and Brannon J. C. (1991) Meteoritics, 26, 145-152. [9] Turner G. et al. (1978) Proc. LPSC 9th, 989-1025. [10] Pellas P. and Storzer D. (1981) Proc. R. Soc. London, A374, 253-270.

Manhes, G.; Gopel, C.

1993-07-01

74

First occurrence of pyrophanite (MnTiO3) and baddeleyite (ZrO2) in an ordinary chondrite  

NASA Astrophysics Data System (ADS)

An examination is conducted of the distinct optical and compositional zoning exhibited by a Mg-Al-chromite fragment in the Raguli H3.8 ordinary chondrite. Two end-member pyrophanite grains occur in the fragment's outer portion; this is noted to be the first occurrence of pyrophanite in conjunction with baddeleyite in an ordinary chondrite. Two alternative models are presented for the formation of the fragment: a multistage nebular melting process, and the fragment's formation on a metamorphosed parent body. The latter alternative is favored.

Krot, A. N.; Rubin, A. E.; Kononkova, N. N.

1993-06-01

75

Evidence for a late thermal event of unequilibrated enstatite chondrites: a Rb-Sr study of Qingzhen and Yamato 6901 (EH3) and Khairpur (EL6)  

USGS Publications Warehouse

The Rb-Sr whole rock and internal systematics of two EH3 chondrites, Qingzhen and Yamato 6901, and of one EL6 chondrite, Khairpur, were determined. The internal Rb-Sr systematics of the EH3 chondrites are highly disturbed. Fractions corresponding to sulfide phases show excess 87Sr, while other fractions corresponding to silicate phases produce a linear trend on a Rb-Sr evolution diagram. If these linear relations are interpreted as isochrons, the ages of the silicate phases are 2.12?? 0.23 Ga and 2.05 ??0.33 Ga with the initial Sr isotopic ratios of 0.7112 ?? 0.0018 and 0.7089 ?? 0.0032, for Qingzhen and Yamato 6901, respectively. The Rb-Sr results are interpeted as indicative of a late thermal event about 2Ga ago on the parent bodies of these EH3 chondrites. These ages agree well with previously published K-Ar ages. An older isochron age of 4.481 ?? 0.036 Ga with a low initial Sr isotopic ratio of 0.69866 ?? 0.00038 was obtained for the data from silicate fractions of Khairpur, indicating early petrological equilibrium on the parent body of EL6 chondrites. -from Authors

Torigoye, N.; Shima, M.

1993-01-01

76

The Iodine-Xenon System in Outer and Inner Portions of Chondrules from the Unnamed Antarctic LL3 Chondrite  

NASA Technical Reports Server (NTRS)

Alteration processes may affect I-Xe system in unequilibrated ordinary chondrites. It was shown that at the edges, where a contribution is made by matrix material around the rim, *Xe-129/Xe-128 values are generally lower (later apparent ages) than in the main chondrule mass. In this work we attempted to investigate whether thermal metamorphism can affect the I-Xe system in LL3 chondrites which did not experienced aqueous alteration.

Meshik, A. P.; Pravdivtseva, O. V.; Hohenberg, C. M.; Amelin, Y.

2004-01-01

77

The Natural Thermoluminescence of Meteorites. Part 5; Ordinary Chondrites at the Allan Hills Ice Fields  

NASA Technical Reports Server (NTRS)

Natural thermoluminescence (TL) data have been obtained for 167 ordinary chondrites from the ice fields in the vicinity of the Allan Hills in Victoria Land, Antarctica, in order to investigate their thermal and radiation history, pairing, terrestrial age, and concentration mechanisms. Using fairly conservative criteria (including natural and induced TL, find location, and petrographic data), the 167 meteorite fragments are thought to represent a maximum of 129 separate meteorites. Natural TL values for meteorites from the Main ice field are fairly low (typically 5-30 krad, indicative of terrestrial ages of approx. 400 ka), while the Far western field shows a spread with many values 30-80 krad, suggestive of less then 150-ka terrestrial ages. There appear to be trends in TL levels within individual ice fields which are suggestive of directions of ice movement at these sites during the period of meteorite concentration. These directions seem to be confirmed by the orientations of elongation preserved in meteorite pairing groups. The proportion of meteorites with very low natural TL levels (less then 5 krad) at each field is comparable to that observed at the Lewis Cliff site and for modern non-Antarctic falls and is also similar to the fraction of small perihelia (less then 0.85 AU) orbits calculated from fireball and fall observations. Induced TL data for meteorites from the Allan Hills confirm trends observed for meteorites collected during the 1977/1978 and 1978/1979 field seasons which show that a select group of H chondrites from the Antarctic experienced a different extraterrestrial thermal history to that of non-Antarctic H chondrites.

Benoit, Paul H.; Sears, Hazel; Sears, Derek W. G.

1993-01-01

78

The cali meteorite fell: A new H/L ordinary chondrite  

USGS Publications Warehouse

The fall of the Cali meteorite took place on 6 July 2007 at 16 h 32 ?? 1 min local time (21 h 32 ?? 1 min UTC). A daylight fireball was witnessed by hundreds of people in the Cauca Valley in Colombia from which 10 meteorite samples with a total mass of 478 g were recovered near 3??24.3'N, 76??30.6'W. The fireball trajectory and radiant have been reconstructed with moderate accuracy. From the computed radiant and from considering various plausible velocities, we obtained a range of orbital solutions that suggest that the Cali progenitor meteoroid probably originated in the main asteroid belt. Based on petrography, mineral chemistry, magnetic susceptibility, fhermoluminescence, and bulk chemistry, the Cali meteorite is classified as an H/L4 ordinary chondrite breccia.

Rodriguez, J.M.T.; Llorca, J.; Rubin, A.E.; Grossman, J.N.; Sears, D.W.G.; Naranjo, M.; Bretzius, S.; Tapia, M.; Sepulveda, M.H.G.

2009-01-01

79

Cosmogenic Records in 18 Ordinary Chondrites from the Dar Al Gani Region, Libya. 2; Radionclides  

NASA Technical Reports Server (NTRS)

In the past decade more than 1000 meteorites have been recovered from the Dar al Gani (DaG) plateau in the Libyan part of the Sahara. The geological setting, meteorite pairings and density are described. So far, only a few terrestrial ages are known for DaG meteorites, e.g. 60+/- 20 kyr for the DaG 476 shergottite shower and 80+/- 20 kyr for the lunar meteorite DaG 262. However, from other desert areas, such as Oman, it is known that achondrites may survive much longer than chondritic meteorites, so the ages of these two achondrites may not be representative of the majority of the DaG meteorite collection, of which more than 90% are ordinary chondrites. In this work we report concentrations of the cosmogenic radionuclides, 14C (half-life = 5,730 yr), 41Ca (1.04x10 superscript 5 yr), Cl-36 (3.01x10 superscript 5 yr), Al-26 (7.05x10 superscript 5 yr) and 10Be (1.5x10 superscript 6 yr) to determine the terrestrial ages of DaG meteorites and constrain their pre-atmospheric size and exposure history.

Welten, K. C.; Nishiizumi, K.; Finkel, R. C.; Hillegonds, D. J.; Jull, A. J. T.; Schultz, L.

2003-01-01

80

Cracking the Space Weathering Code: Ordinary Chondrite Asteroids in the Near-Earth Population  

NASA Astrophysics Data System (ADS)

Hayabusa’s sample return confirmation [1] of the groundbased telescopic [2] and laboratory [3] predictions for the space-weathered [4] LL chondrite composition of asteroid Itokawa provides the key for unlocking the space weathering code for S-type asteroids. With the Hayabusa success as our foundation, we boldly de-weather [5] the visible to near-infrared spectra [6] of 200 near-Earth asteroids to find their compositional analogs among the H, L, and LL classes of ordinary chondrite meteorites. We employ principal component analysis for the asteroid-meteorite correlation, where we establish the probability locus for each class utilizing 100 meteorite spectra from the RELAB database (7). Our results for the near-Earth asteroid H, L, and LL compositional distributions, relative to meteorite fall statistics, have significant ramifications for our understanding of meteorite source regions and their dynamical delivery processes. This material is based upon work supported by the National Science Foundation under Grant No. 0907766. [1] Yurimoto et al. (2011), Science 333, 1116. [2] Binzel et al. (2001), MAPS 36, 1167. [3] Pieters et al. (2000), MAPS 35, 1001. [4] Noguchi et al. (2011), Science 333, 1121. [5] Brunetto et al. (2006), Icarus 184, 327. [6] Binzel et al. (2006), LPSC XXXVII, Abstract 37.1491. [7] http://www.planetary.brown.edu/relabdocs/relab.htm

Binzel, Richard P.; DeMeo, F. E.; Lockhart, M.; Burbine, T. H.; Kotson, M.; Polishook, D.; Vernazza, P.; Slivan, S. M.; Stepanova, C.

2012-10-01

81

Artificial weathering of the ordinary chondrite Allegan: Implications for the presence of Cl2 as a structural component in akaganeite  

Microsoft Academic Search

A sample of an ordinary chondrite fall, Allegan, was shown by 57 Fe Mossbauer spec- troscopy to be unweathered. Using aerated deionized water at 258 and 0 8C, and in one case with dissolved salts added, an attempt was made to simulate meteorite weathering processes in the hot and cold desert environments where these samples accumulate. The progress of artificial

P. A. BLAND; S. P. KELLEY; F. J. BERRY; J. M. CADOGAN; C. T. PILLINGER

82

Outgassing of ordinary chondritic material and some of its implications for the chemistry of asteroids, planets, and satellites  

NASA Astrophysics Data System (ADS)

We used chemical equilibrium calculations to model thermal outgassing of ordinary chondritic material as a function of temperature, pressure, and bulk composition and use our results to discuss outgassing on asteroids and the early Earth. The calculations include ˜1000 solids and gases of the elements Al, C, Ca, Cl, Co, Cr, F, Fe, H, K, Mg, Mn, N, Na, Ni, O, P, S, Si, and Ti. The major outgassed volatiles from ordinary chondritic material are CH 4, H 2, H 2O, N 2, and NH 3 (the latter at conditions where hydrous minerals form). Contrary to widely held assumptions, CO is never the major C-bearing gas during ordinary chondrite metamorphism. The calculated oxygen fugacity (partial pressure) of ordinary chondritic material is close to that of the quartz-fayalite-iron (QFI) buffer. Our results are insensitive to variable total pressure, variable volatile element abundances, and kinetic inhibition of C and N dissolution in Fe metal. Our results predict that Earth's early atmosphere contained CH 4, H 2, H 2O, N 2, and NH 3; similar to that used in Miller—Urey synthesis of organic compounds.

Schaefer, Laura; Fegley, Bruce

2007-02-01

83

Accretion, metamorphism, and brecciation of ordinary chondrites - Evidence from petrologic studies of meteorites from Roosevelt County, New Mexico  

NASA Astrophysics Data System (ADS)

The olivines and pyroxenes from twenty-nine ordinary chondrites from Roosevelt County, New Mexico are examined. The mineralogical properties of the chondrites studied are described. Correlations between mineral compositions and petrologic type and between petrologic type and bulk chemistry are analyzed. It is observed that mean CaO concentrations in olivine show significant variations among equilibrated chondrites, but these are not correlated with petrologic type; the degree of heterogeneity of FeO concentrations in olivines of types 4-6 is not correlated with the degree of metamorphism; and mean FeO concentrations of silicates show average increases of 3-5 percent from type 4 to type 6 in each group.

Scott, Edward R. D.; Taylor, G. Jeffrey; Keil, Klaus

1986-11-01

84

Accretion, metamorphism, and brecciation of ordinary chondrites - Evidence from petrologic studies of meteorites from Roosevelt County, New Mexico  

NASA Technical Reports Server (NTRS)

The olivines and pyroxenes from twenty-nine ordinary chondrites from Roosevelt County, New Mexico are examined. The mineralogical properties of the chondrites studied are described. Correlations between mineral compositions and petrologic type and between petrologic type and bulk chemistry are analyzed. It is observed that mean CaO concentrations in olivine show significant variations among equilibrated chondrites, but these are not correlated with petrologic type; the degree of heterogeneity of FeO concentrations in olivines of types 4-6 is not correlated with the degree of metamorphism; and mean FeO concentrations of silicates show average increases of 3-5 percent from type 4 to type 6 in each group.

Scott, Edward R. D.; Taylor, G. Jeffrey; Keil, Klaus

1986-01-01

85

The flux of meteorites to the Earth and weathering in hot desert ordinary chondrite finds  

NASA Astrophysics Data System (ADS)

The abundance of ferric iron, produced by weathering in ordinary chondrites collected from hot desert regions, is related to their terrestrial age, enabling a variety of processes involved in meteorite weathering to be deduced. Fe 0/Fe 2+/Fe 3+ content was measured quantitatively by 57Fe Mössbauer spectroscopy. It is observed that meteorites from different regions are oxidised at different rates. We also propose the tentative hypothesis that one source of scatter in total oxidation versus terrestrial age for a region is climatic change. A mechanism to explain the variable response to climatic conditions involves the high initial porosity of samples being reduced as ferric oxides and other alteration products are produced. Reliable recovery data from a meteorite accumulation site (Roosevelt County, New Mexico, USA) and a quantitative measure of weathering and terrestrial age permit an estimate of the flux of meteorites to the Earth's surface. Having established a decay constant for meteorites, and accounting for the area of searches and pairing, we estimate an accumulation rate of 159 falls of mass greater than 20 g per 10 6 km 2 per yr. This calculation is distinct from, but in broad agreement with, previous estimates from camera observations, suggesting that the accumulation rate of meteorite falls to the Earth's surface has remained essentially unchanged over the last 50,000 years at between 59 and 159 falls of mass exceeding 20 g per 10 6 km 2 per yr. The error for both methods is approximately a factor of 2.

Bland, P. A.; Berry, F. J.; Smith, T. B.; Skinner, S. J.; Pillinger, C. T.

1996-06-01

86

Study of iron nanophases in ordinary chondrites by means of near field microscopy  

NASA Astrophysics Data System (ADS)

The aim of this work is to study the role, the characteristics and the formation process of iron nanoparticles (npFe) in asteroids. These npFe are considered the main responsible for the reddening (i.e. red-IR reflectance increase at increasing wavelength) observed in the asteroids' spectra and it is believed that they are formed as consequence of the Space Weathering (i.e. the ensemble of processes acting on a body exposed to space environment). \\citet{mo05} discusses a scenario regarding npFe formation, according to which they originate from shock-induced phase transformations of Fe-Ni alloys caused by collisions. We looked for npFe in samples of Ordinary Chondrites (OCs), whose parent bodies are S-type asteroids, and are trying to link the amount of metal and the mechanical shock degree (which would confirm the scenario above mentioned). For this purpose, we have choosen to use SNOM (Scanning Near-field Optical Microscopy). This technique permits to collect at the same time high resolution topography images and optical images of the analyzed sample. For the first time, a multi-colour SNOM experiment (i.e. every sample has been analyzed at different wavelengths) has been performed on extraterrestrial samples: because npFe are more reflective at longer wavelengths, comparison of reflectance images obtained at different wavelength gives a strong aid in npFe detection and identification. Finally, laboratory analysis has been supported by simulation methods.

Longobardo, A.; Palomba, E.; Girasole, M.; Longo, G.; Pompeo, G.; Gori, P.; Cricenti, A.

87

Surface Properties of (6) Hebe: A Possible Parent Body of Ordinary Chondrites  

NASA Astrophysics Data System (ADS)

We report for the first time rotationally resolved spectroscopic observations, as well as new photometric and polarimetric measurements, of the large S-type asteroid (6) Hebe, always at near-equatorial aspects. We have found evidence for only minor variations in Hebe's visible reflectance spectrum over a rotational cycle, comparable to our measurement accuracy (a few percent) and consistent with an undifferentiated silicate assemblage on the surface. We have also confirmed previous results of the existence of small polarization changes, but they are not correlated with the (complex and asymmetric) photometric lightcurve of the asteroid. A plausible interpretation of these data is that Hebe's surface is composed of undifferentiated materials, but presents texture, albedo, and spectral changes possibly related to the occurrence of energetic cratering events. Given the comparatively large size of Hebe, its proximity to resonance-related chaotic zones of the orbital element space (Farinella et al. 1993, Celest. Mech.56,287-305, and Icarus101,174-187), and its assignment by Gaffey et al. (1993, Icarus106,573-602) to the S(IV) taxonomic subclass, our results support the idea that this asteroid may be the source of a significant fraction of the ordinary chondrite meteorites.

Migliorini, F.; Manara, A.; Scaltriti, F.; Farinella, P.; Cellino, A.; Di Martino, M.

1997-07-01

88

Partial melting of the St. Severin (LL) and Lost City (H) ordinary chondrites: One step backwards and two steps forward  

NASA Astrophysics Data System (ADS)

This study looks at partial melting in H and LL chondrites at nearly one atmosphere of total pressure as part of a continuing study of the origins of basaltic achondrites. Previously, melting experiments on anhydrous CM and CV chondrites showed that, near its solidus, the CM chondrite produced melts having major element chemistries similar to the Sioux County eucrite; but, the pyroxenes in the residuum were too iron-rich to form diogenites. Our preliminary results from melting experiments on ordinary (H, LL) chondrites suggested that, although the melts did not look like any known eucrites, pyroxenes from these charges bracketed the compositional range of pyroxenes found in diogenites. We had used the Fe/Mg exchange coefficients calculated for olivine, pyroxene, and melt in these charges to evaluate the approach to equilibrium, which appeared to be excellent. Unfortunately, mass balance calculations later indicated to us that, unlike our CM and CV charges, the LL and H experimental charges had lost significant amounts of iron to their (Pt or PtRh) supports. Apparently, pyroxene stability in chondritic systems is quite sensitive to the amount of FeO, and it was this unrecognized change in the bulk iron content which had stabilized the high temperature, highly magnesian pyroxenes. Accordingly, this work reinvestigates the phase equilibria of ordinary chondrites, eliminating iron and nickel loss, and reports significant differences. It also looks closely at how the iron and sodium in the bulk charge affect the stability of pyroxene, and it comments on how these new results apply to the problems of diogenite and eucrite petrogenesis.

Jurewicz, A. J. G.; Jones, J. H.; Mittlefehldt, D. W.

1994-03-01

89

Mineralogy and chemistry of Rumuruti: The first meteorite fall of the new R chondrite group  

NASA Astrophysics Data System (ADS)

The Rumuruti meteorite shower fell in Rumuruti, Kenya, on 1934 January 28 at 10:45 p.m. Rumuruti is an olivine-rich chondritic breccia with light-dark structure. Based on the coexistence of highly recrystallized fragments and unequilibrated components, Rumuruti is classified as a type 3-6 chondrite breccia. The most abundant phase of Rumuruti is olivine (mostly Fa(approximately 39) with about 70 vol%. Feldspar (approximately 14 vol%; mainly plagioclase), Ca-pyroxene (5 vol%), pyrrhotite (4.4 vol%), and pentlandite (3.6 vol%) are major constituents. All other phases have abundances below 1 vol%, including low-Ca pyroxene, chrome spinels, phosphates (chlorapatite and whitlockite), chalcopyrite, ilemenite, tridymite, Ni-rich and Ge-containing metals, kamacite, and various particles enriched in noble metals like Pt, Ir, and Au. The chemical composition of Rumuruti is chondritic. The depletion in refractory elements (Sc, REE, etc.) and the comparatively high Mn, Na, and K contents are characteristic of ordinary chondrites and distinguish Rumuruti from carbonaceous chondrites. However, S, Se, and Zn contents in Rumuruti are significantly above the level expected for ordinary chondrites. The oxygen isotope composition of Rumuruti is high in delta O-17 (5.52%) and delta O-18 (5.07%). With Rumuruti, nine meteorites samples exist that are chemically and mineralogically very similar. These meteorites are attributed to at least eight different fall events. It is proposed in this paper to call this group R chondrites (rumurutites) after the first and only fall among these meteorites. The meteorites have a close relationship to ordinary chondrites. However, they are more oxidized than any of the existing groups of ordinary chondrites. Small, but significant differences in chemical composition and in oxygen isotopes between R chondrites and ordinary chondrites exclude formation of R chondrites from ordinary chondrites by oxidation. This implies a separate, independent R chondrite parent body.

Schulze, H.; Bischoff, A.; Palme, H.; Spettel, B.; Dreibus, G.; Otto, J.

1994-03-01

90

Asteroid 6 Hebe: The probable parent body of the H-Type ordinary chondrites and the IIE iron meteorites  

NASA Astrophysics Data System (ADS)

The S(IV)-type asteroid 6 Hebe is identified as the probable parent body of the H-type ordinary chondrites and of the IIE iron meteorites. The ordinary chondrites are the most common type of meteorites falling to Earth, but prior to the present study no large mainbelt source bodies have been confirmed. Hebe is located adjacent to both the (6 and 3:1 resonances, and has been previously suggested as a major potential source of the terrestrial meteorite flux. Hebe exhibits subtle rotational spectral variations indicating the presence of some compositional variations across its surface. The silicate portion of the surface assemblage of Hebe is consistent, both in overall average and in its range of variation, with the silicate components in the suite of H-type chondrites. The high albedo of Hebe rules out a lunar-style space weathering process to produce the weakened absorption features and reddish spectral slope in the S-type spectrum of Hebe. Linear unmixing models show that a typical nickel-iron metal spectrum is consistent with the component which modifies an H-chondrite spectrum to produce the S-type spectrum of Hebe. Based on the association between the H chondrites and the IIE iron meteorites, our model suggests that large impacts onto the relatively metal-rich H chondrite target produced melt bodies (sheets or pods) which differentiated to form thin, laterally extensive near-surface layers of NiFe metal. Fragments of the upper silicate portions of these melt bodies are apparently represented by some of the igneous inclusions in H-chondrite breccias. Alternately, masses of metal could have been deposited on the surface of Hebe by the impact of a core or core fragment from a differentiated parent body of H chondrite composition. Subsequent impacts preferentially eroded and depleted the overlying silicate and regolith components exposing and maintaining large masses of metal at the optical surface of Hebe. In this interpretation, the nonmagmatic IIE iron meteorites are samples of the NiFe metal masses on the surface of Hebe while the H chondrites are samples from between and/or beneath the metal masses.

Gaffey, Michael J.; Gilbert, Sarah L.

1998-11-01

91

Silica-bearing objects in the Dengli H3.8 and Gorlovka H3-4 chondrites  

NASA Technical Reports Server (NTRS)

Silica-bearing objects are enigmatic components of the olivine-normative ordinary chondrites. Several papers have been devoted to the study of these objects in various chondrite types. While a relatively large body of information has been collected, the origin of these objects is still controversial. Here we report new data on silica-bearing objects in the unequilibrated H-chondrites Dengli and Gorlovka. The crystallization history of these objects could be explained on the basis of the phase diagram of the Q-Ol-Pl (Al2O3) system, but the origin of the silica-rich liquids remains unclear.

Ivanova, M. A.; Kononkova, N. N.; Petaev, M. I.

1993-01-01

92

The S-type asteroid ordinary chondrite controversy and discoveries by the Hayabusa mission to asteroid 25143 Itokawa. T. Hiroi1  

E-print Network

-standing controversy concerning the parent bodies of ordinary chondrites and the identity of the S-type asteroids that the S asteroids are ordinary chonrites has been altered greatly over history. Seven subclasses of S asteroids were September to December 2005, during which period it performed two-dimensional color imaging with the Asteroid

Hiroi, Takahiro

93

Magnetic properties of the LL5 ordinary chondrite Chelyabinsk (fall of February 15, 2013)  

NASA Astrophysics Data System (ADS)

Here we characterize the magnetic properties of the Chelyabinsk chondrite (LL5, S4, W0) and constrain the composition, concentration, grain size distribution, and mineral fabric of the meteorite's magnetic mineral assemblage. Data were collected from 10 to 1073 K and include measurements of low-field magnetic susceptibility (?0), the anisotropy of ?0, hysteresis loops, first-order reversal curves, Mössbauer spectroscopy, and X-ray microtomography. The REM and REM' paleointensity protocols suggest that the only magnetizations recorded by the chondrite are components of the Earth's magnetic field acquired during entry into our planet's atmosphere. The Chelyabinsk chondrite consists of light and dark lithologies. Fragments of the light lithology show log?0 = 4.57 ± 0.09 (s.d.) (n = 135), while the dark lithology shows 4.65 ± 0.09 (n = 39) (where ?0 is in 10-9 m3 kg-1). Thus, Chelyabinsk is three times more magnetic than the average LL5 fall, but is similar to a subgroup of metal-rich LL5 chondrites (Paragould, Aldsworth, Bawku, Richmond) and L/LL5 chondrites (Glanerbrug, Knyahinya). The meteorite's room-temperature magnetization is dominated by multidomain FeNi alloys taenite and kamacite (no tetrataenite is present). However, below approximately 75 K remanence is dominated by chromite. The metal contents of the light and dark lithologies are 3.7 and 4.1 wt%, respectively, and are based on values of saturation magnetization.

Bezaeva, Natalia S.; Badyukov, Dmitry D.; Nazarov, Mikhail A.; Rochette, Pierre; Feinberg, Joshua M.; Markov, Gennadiy P.; Borschneck, Daniel; Demory, FrançOis; Gattacceca, JéRôMe; Borisovskiy, Sergey E.; Skripnik, Anna Ya

2014-06-01

94

Relationships Among Intrinsic Properties of Ordinary Chondrites: Oxidation State, Bulk Chemistry, Oxygen-isotopic Composition, Petrologic Type, and Chondrule Size  

NASA Technical Reports Server (NTRS)

The properties of ordinary chondrites (OC) reflect both nebular and asteroidal processes. OC are modeled here as having acquired nebular water, probably contained within phyllosilicates, during agglomeration. This component had high Ai70 and acted like an oxidizing agent during thermal metamorphism. The nebular origin of this component is consistent with negative correlations in H, L, and LL chondrites between oxidation state (represented by olivine Fa) and bulk concentration ratios of elements involved in the metal-silicate fractionation (e.g., NdSi, Ir/Si, Ir/Mn, Ir/Cr, Ir/Mg, Ni/Mg, As/Mg, Ga/Mg). LL chondrites acquired the greatest abundance of phyllosilicates with high (delta)O-17 among OC (and thus became the most oxidized group and the one with the heaviest O isotopes); H chondrites acquired the lowest abundance, becoming the most reduced OC group with the lightest O isotopes. Chondrule precursors may have grown larger and more ferroan with time in each OC agglomeration zone. Nebular turbulence may have controlled the sizes of chondrule precursors. H-chondrite chondrules (which are the smallest among OC) formed from the smallest precursors. In each OC region, low-FeO chondrules formed before high-FeO chondrules during repeated episodes of chondrule formation. During thermal metamorphism, phyllosilicates were dehydrated; the liberated water oxidized metallic Fe-Ni. This caused correlated changes with petrologic type including decreases in the modal abundance of metal, increases in olivine Fa and low-Ca pyroxene Fs, increases in the olivine/pyroxene ratio, and increases in the kamacite Co and Ni contents. As water (with its heavy 0 isotopes) was lost during metamorphism, inverse correlations between bulk (delta)O-18 and bulk (delta)O-17 with petrologic type were produced. The H5 chondrites that were ejected from their parent body approx.7.5 Ma ago during a major impact event probably had been within a few kilometers of each other since they accreted approx.4.5 Ga ago. There are significant differences in the olivine compositional distributions among these rocks; these reflect stochastic nebular sampling of the oxidant (Le., phyllosilicates with high (delta)O-17) on a 0.1-1 km scale during agglomeration.

Rubin, Alan E.

2006-01-01

95

Raman Spectroscopy of Merrillite in Villalbeto de la Peña L6 Ordinary Chondrite  

NASA Astrophysics Data System (ADS)

Ca-phosphates were studied by means of Raman spectroscopy in the Villalbeto de la Peña L6 chondrite, which fell recently in Spain (2004). The presence of merrillite in the shock veins of the meteorite indicates that it was not severely shock-metamorphosed.

Llorca, J.; Trigo-Rodríguez, J. M.

2006-03-01

96

Thermoluminescence and the shock and reheating history of meteorites. IV. The induced TL properties of type 4-6 ordinary chondrites  

SciTech Connect

The induced thermoluminescene (TL) properties of 121 equilibrated ordinary chondrites have been measured. The samples were 74 H and 47 L chondrites, of which 33 H and 32 L were from Antarctica. The distribution of TL sensitivities for non-Antarctic L chondrites differs from that of non-Antarctic H chondrites, consistent with a greater proportion of the former class suffering post-metamorphic shock. Data on the effect of laboratory annealing on TL sensitivity, and step-wise Ar release measurements, enable the meteorites to be sorted into three shock-related temperature groups (<800{degree}C, 800-1000{degree}C, >1000{degree}C). The distribution of TL sensitivities of Antarctic meteorites suggests that only a few of the present samples have suffered intense shock. Antarctic H chondrites have TL sensitivities typically one third those of non-Antarctic H chondrites; this may reflect a greater proportion of meteorites which have suffered mild shock levels or greater degrees of weathering. On a diagram of TL leak temperature against peak width, L chondrites produce tight clusters with minimal overlap between Antarctic and non-Antarctic meteorites. Antarctic H chondrites also produce a tight cluster, but non-Antarctic chondrites plot in a band in which peak temperature increases with peak width, and there is little or no overlap between the Antarctic and non-Antarctic meteorites. Because TL peak temperature and width reflect the thermal history of the feldspar, and changes in these TL parameters can be produced by laboratory annealing experiments, this implies significant differences in the thermal (probably metamorphic) history of the Antarctic and non-Antarctic ordinary chondrites.

Haq, M.; Hasan, F.A.; Sears, D.W. (Univ. of Arkansas, Fayetteville (USA))

1988-06-01

97

Asteroid 6 Hebe: Spectral Evaluation of the Prime Large Mainbelt Ordinary Chondrite Parent Body Candidate with Implications from Space Weathering of Gaspra and the Ida-Dactyl System  

NASA Astrophysics Data System (ADS)

No large mainbelt asteroid has yet been confirmed as an ordinary chondrite parent body. A number of plausible candidates have been identified based on dynamical considerations and/or spectral evidence. The fifth largest S-asteroid, 6 Hebe, is the best current candidate for one of the long sought large mainbelt ordinary chondrite parent bodies. Its proximity to the chaotic zones associated with both the 3:1 proper motion and the nu(sub)6 (or g=g(sub)6) secular resonance "escape hatches" should make Hebe a major mainbelt contributor to the terrestrial meteorite flux. Hebe also exhibits a surface assemblage (subtype S(IV), the only subgroup among the S-asteroids that might include ordinary chondrite parent bodies) which allows (or more precisely, does not exclude) an ordinary chondrite affinity. An analysis of the rotational variations of spectra obtained in June 1979 and February 1989 provide a sophisticated test of whether or not Hebe is a viable ordinary chondrite parent body. If the rotational spectral variations of Hebe are consistent with an undifferentiated silicate assemblage, there still remains the mismatch in the overall spectral slope and band intensities. It has been suggested that the Gaspra and Ida-Dactyl encounters establish that space weathering causes this discrepancy. However, there are several inconsistencies in this simple picture which suggest that while the presence of a space weathering process on Ida and Gaspra appears well established, there still remains considerable uncertainty concerning its nature and ability to spectrally modify ordinary chondrites to match the slope and band depths of S-asteroids.

Gaffey, M. J.

1996-03-01

98

Differences of Terrestrial Alteration Effects in Ordinary Chondrites from Hot and Cold Deserts: Petrography and Noble Gases  

NASA Astrophysics Data System (ADS)

Several differences between Antarctic and non-Antarctic meteorite populations have been recognized that are attributed to two main causes, namely a general difference in their parent meteoroid populations and/or secondary effects like weathering or pairing (see e.g.[1]). In the last few years several hundred new meteorites have become available from hot desert areas (Nullabor Plain, Roosevelt County, Sahara Desert). Compared to Antarctic meteorites these stones are stored on Earth in very different climatic environments. Thus, both groups should show different patterns of weathering. In this paper we report petrographic observations and noble gas measurements concerning terrestrial alterations of a suite of ordinary chondrites from the Sahara desert and Antarctica. Forty thin sections of desert meteorites (Acfer, El Djouf, Illafegh, Daraj, and Roosevelt County) and 60 thin sections of Antarctic ordinary chondrites (Allan Hills and Frontier Mountain) were investigated microscopically. In addition, in some of these meteorites the concentration and isotopic composition of all noble gases were determined. In this report we will discuss the trapped Kr and Xe only. As already noted by Jull et al. [2] many desert meteorites are heavily weathered. Compared to Antarctic meteorites their proportion of metal and troilite is smaller, while iron oxides and iron hydroxides are more abundant. In Antarctic meteorites most silicates are not severely altered. H- and L-group chondri- tes from the Acfer region and Roosevelt County, however, show a remarkable weathering feature of some silicates: In many of these samples nest-like structures are found that consist of silicate fragments embedded in iron oxide or hydroxide. Different stages of their development can be observed. It starts with the filling by these iron compounds of fine cracks of the original grains. With the process of weathering proceeding these cracks grow and finally destroy larger crystals completely to smaller fragments. Together with the oxides and hydroxides these mineral fragments then form distinct clusters sometimes without direct contact to FeNi or FeS. In Antarctic chondrites, oxides and hydroxides are mostly observed around metal. The concentrations of trapped noble gases in ordinary chondrites are correlated with the chemical-petrological classification [3]. Generally, for types 5 and 6 of modern falls or Antarctic finds, concentrations of ^84Kr and ^132Xe are less than 1 10^-10 and 2 10^-10 cm^3STP/g, respectively. In chondrites from hot deserts, however, especially the concentration of Kr is higher. This can be explained by adsorption and incorporation of atmospheric Kr and Xe ((^84Kr/^132Xe)(sub)atm = 27.8) into weathering products, resulting in higher Kr/Xe-ratios. The presence of atmospheric Xe also shows up in its isotopic composition. Several authors have reported on adsorbed noble gases with isotope ratios similar to those in the terrestrial atmosphere that are tightly bound to the minerals of stony meteorites or lunar rocks, i.e., these gases are not removed by a preheating of the sample at several hundred degrees C [4,5]. This has been attributed to an "irreversible adsorption process" [5]. However, as demonstrated here, weathering on Earth can also influence the concentration of Kr and Xe. Stepwise heating experiments and mineral separations are in progress to determine the siting and retentivity of this terrestrial contamination. References: [1] Koeberl C. and Cassidy W.A. (eds.) (1990) LPI Tech. Rep. 90-01, 102 pp. [2] Jull A.J.T., Wlotzka F., Palme H. and Donahue D.J. (1990) Geochim. Cosmochim. Acta 54, 2895. [3] Weber H.W., Schultz L. and Begemann F. (1990) Meteoritics 25, 405. [4] Schelhaas N., Ott U. and Begemann F. (1990) Geochim Cosmochim. Acta 54, 2869. [5] Niedermann S. and Eugster 0. (1992) Geochim. Cosmochim. Acta 56, 493.

Scherer, P.; Loeken, T.; Schultz, L.

1992-07-01

99

Weathering of ordinary chondrites from the Atacama Desert, Chile, by Mössbauer spectroscopy and synchrotron radiation X-ray diffraction  

NASA Astrophysics Data System (ADS)

Some terrestrial areas have climatic and geomorphologic features that favor the preservation, and therefore, accumulation of meteorites. The Atacama Desert in Chile is among the most important of such areas, known as DCA. This desert is the driest on Earth, one of the most arid, uninhabitable localities with semiarid, arid, and hyper-arid conditions. The meteorites studied here were collected from within the DCA of San Juan and Pampa de Mejillones, located, respectively, in the Central Depression and the Coastal Range of the Atacama Desert. 57Fe Mössbauer spectroscopy was used for quantitative analysis of the degree of weathering of the meteorites, through the determination of the proportions of the various Fe-bearing phases and in particular the amount of oxidized iron in terrestrial alteration products. The abundance of ferric ions in weathered chondrites can be related to specific precursor compositions and to the level of terrestrial weathering. The aim of the study was the identification, quantification, and differentiation of the weathering products in the ordinary chondrites found in the San Juan and the Pampa de Mejillones areas of the Atacama Desert. The 57Fe Mössbauer spectroscopy study was complemented by synchrotron radiation X-ray diffraction and magnetic susceptibility measurements. The results allow a clear differentiation of the rate of weathering in meteorite samples collected from the San Juan versus the Pampa de Mejillones areas of the Atacama Desert.

Munayco, Pablo; Munayco, Jimmy; Avillez, Roberto R.; Valenzuela, Millarca; Rochette, Pierre; Gattacceca, JéRôMe; Scorzelli, Rosa B.

2013-03-01

100

Mossbauer Spectra of Weathered H5 Ordinary Chondrites from Reg EL Acfer, Algeria  

NASA Astrophysics Data System (ADS)

Approximately 380 meteorite specimens have been retrieved from the Acfer region of the Sahara desert, Algeria. To date, 26 of these have been classified H5 (Bischoff et al., 1990, 1991, 1992). Being the most common meteorite type and having a tightly constrained mineralogy (Mason, 1965), H5 chondrites are ideal candidates for investigating terrestrial weathering products in meteorites. Arid climate, uniform topography, and lack of a concentration/movement mechanism makes it likely that meteorites throughout Reg el Acfer were weathered by a common mechanism. Jull et al. (1991) showed a correlation in meteorites from Roosevelt County between terrestrial ^14C ages and a qualitative weathering scale. An aim of the present study is to provide a quantitative measure of weathering for the Acfer region that might allow an estimate of terrestrial age, as well as information on pairing. Meteorite Specimens: Approximately 1 g of sample was used, prepared by grinding under acetone to prevent oxidation during crushing, until a homogenized powder was produced. Mossbauer spectra were recorded at 298 degrees K with a microprocessor controlled Mossbauer spectrometer using a ^57Co/Rh source. Drive velocity was calibrated with the same source and a metallic iron foil. Results: The H5 chondrite Acfer 146 (Bischoff, forthcoming Meteoritical Bulletin) was found on 19/11/90 at coordinates 27 degrees 38'N, 4 degrees 05'E. This meteorite gave a spectrum dominated by quadrupole split absorption characteristics of Fe^2+ in a forsteritic olivine structure. A sample of the outer crust showed the additional presence of Fe^3+. XRD was insensitive to the unequivocal identification of the phases present in the two samples and given that the Mossbauer parameters of the hydrolyzed Fe^3+ species and ferric oxyhydroxides are very similar it is not possible at this stage to identify the oxidized phase. Clearly, however, the results demonstrate the sensitivity of Mossbauer spectroscopy to the products of terrestrial weathering processes in meteorites. The investigation was extended to the H5 chondrite Acfer 098 (Bischoff, 1991) recovered on 19/4/90 from a location coordinates 27 degrees 28'N, 3 degrees 53'E. This meteorite was chosen because in hand specimen it "looked"' severely weathered. The sawn surface shows reddish brown staining, is friable, and cut by veins of alteration products. This sample showed the presence of a much greater proportion of Fe^3+ than with the Acfer 146 interior or crust, confirming the findings of Fisher and Burns (1992) in work on H5 chondrites from Antarctica. Given that samples recovered from the Reg el Acfer had resided in geologically and physiographically similar areas, the differences observed by Mossbauer spectroscopy may be estimating changes in the degree of weathering and hence possibly the relative time that the meteorite had spent on the Earth's surface. Considerably more work is needed, however, to ascertain whether a quantitatively useful weathering scale can be derived with sufficient resolution to be of value. Any correlation may be complicated by the climatic changes that occurred at the Pleistocene/Holocene boundary in North Africa (Butzer et al., 1972), as the results of Jull et al. (1990) in relation to the distribution of terrestrial ages of meteorites from western Libya have shown. References: Bischoff A. et al. (Analyst) (1990) Meteoritical Bulletin No. 69, Meteoritics 25, 237. (1991) Meteoritical Bulletin No. 71, Meteoritics 26. (1992) Meteoritical Bulletin No. 72, Meteoritics 27, 109-110. Butzer K. W., Isaac G. L., Richardson J. L., and Washbourn-Kamau C. (1972) Science 175, 1069-1076. Fisher S. D. and Burns R. G. (1992) Lunar Planet. Sci. XXIII, 367-368. Jull A. J. T., Wlotzka F., Palme H., and Donahue D. J. (1990) Geochim. Cosmochim. Acta. 54, 2895-2898. Jull A. J. T., Wlotzka F., and Donahue D. J. (1991) Lunar Planet. Sci. XXII, 667-668. Mason B. (1965) Am. Mus. Novitates 2223, 1-38.

Berry, F.; Oates, G.; Bland, P.; Pillinger, C. T.

1992-07-01

101

Trace-Element Constraints on Origin of SiO2-bearing Clasts in Ordinary Chondrites  

NASA Astrophysics Data System (ADS)

Silica-rich igneous-textured clasts are found in OC [1-6]. The SiO2-bearing clasts found in the Parnallee (LL3.6) and Farmington (L5) chondrites are isotopically unique [4-6]. They plot on a mixing line defined between UOC chondrules and an 16(sub)O-depleted end member in the oxygen three isotope diagram. We analyzed trace elements including REE by MSID technique for SiO2-bearing clasts (CB1, CB4, CB7, and CB8) from Parnallee. Some major and minor elements of CB8 were determined by AA or ICP-AES. The CI-chondrite normalized REE patterns of the clasts are shown in Fig. 1. CB8 has a high Si/Mg ratio (2.5), although its bulk Mg/(Mg + Fe) and Fe/Mn ratios (0.79 and 51, respectively) are within the range of chondritic values. Refractory elements Ca and Al are highly fractionated in CB8; the clast is enriched in Ca (3 x CI) but depleted in Al (0.7 x CI). CB1, CB4, and CB7 also show Ca enrichment (3-7 x CI). CB8 is depleted in moderately volatile lithophiles Mn, Na, K, and Rb (0.18-0.71 x CI), siderophile elements Fe, Co, and Ni (0.0041-0.39 x CI), and chalcophile element Zn (0.076 x CI). The SiO2-bearing clasts analyzed exhibit a gradual depletion from LREE to HREE (CI-normalized La/Lu ratios vary from 1.6 to 18) and a large positive Eu anomaly (Eu/Eu*=2.4-14) along with a depletion of La. This LREE/HREE fractionation is inversely correlated with SiO2 contents of the clasts. Abundance of Sr is parallel to that of Eu in CB8. However, Sr is depleted compared with Eu in the other clasts. These abundance patterns are quite different from those of typical ferromagnesian chondrules in UOCs, SiO2-bearing pyroxene-rich clast in Hedjaz (L3.7) [3], and silica-rich orthopyroxenite Bo-1 in Bovedy (L3) [7]. Absence of metal and sulfide, low abundances of siderophile and chalcophile elements in the clasts imply that metal and sulfide were removed from precursor material before or during clast formation. General REE patterns of SiO2-bearing clasts from Parnallee suggest that they were produced by igneous fractionation controlled by the plagioclase component. Extensive olivine extraction followed plagioclase crystallization from the residua may be able to explain the REE pattern of CB8 [5, 6]. However, simple fractional crystallization or extraction of partial melting liquid from a chondritic source could explain neither large fractionation of La/Lu nor enrichment of Eu relative to Sr observed in CB1, CB4, and CB7. Detailed fractionation processes occurred on a parent body still remain unsolved. References: [1] Olsen E. J. et al. (1981) EPSL, 56, 82-88. [2] Brigham C. A. et al. (1986) GCA, 50, 1655-1666. [3] Nakamura N. et al. (1990) EPSL, 99, 290-302. [4] Bridges J. C. et al. (1993) Meteoritics, 28, 329-330. [5] Bridges J. C. et al. (1994) Meteoritics, 29, 448-449. [6] Bridges J. C. et al. (1995) Meteoritics, submitted. [7] Ruzicka A. et al. (1995) Meteoritics, 30, 57-70.

Misawa, K.; Kanazawa, M.; Bridges, J. C.; Nakamura, N.; Hutchison, R.

1995-09-01

102

An Ordinary Chondrite Impactor Composition for the Bosumtwi Impact Structure, Ghana, West Africa: Discussion of Siderophile Element Contents and Os and Cr Isotope Data  

NASA Technical Reports Server (NTRS)

Osmium isotope data had shown that Ivory Coast tektites contain an extraterrestrial component, but do not allow distinction between chondritic and iron meteorite contamination. PGE abundances of Ivory Coast tektites and impactites and target rocks from the Bosumtwi crater, the source crater of the Ivory Coast tektites, were all relatively high and did not allow to resolve the presence, or identify the nature, of the meteoritic component. However, Cr isotope analyses of an Ivory Coast tektite yielded a distinct 53Cr excess of 0.30+/-0.06, which indicates that the Bosumtwi impactor was an ordinary chondrite.

Koeberl, Christian; Shukolyukov, Alex; Lugmair, Guenter

2004-01-01

103

The influence of weathering on the measured oxygen isotopic composition of ordinary chondrites  

NASA Astrophysics Data System (ADS)

The effects of weathering on the O isotopic composition were studied in a suite of meteorites from Roosevelt County with known terrestrial ages. To determine the extent of terrestrial weathering the samples were first analyzed by Fe-57 Mossbauer spectroscopy. The contribution to the Mossbauer spectra recorded from the ferromagnesian silicates, olivine and pyroxene, for the suite of Roosevelt County meteorites indicate a clear trend showing a decreasing contribution from these phases with increasing terrestrial age. The parallel increase in Fe(3+) and the nature of the new phases show that it is dissolution and oxidation of the meteorites that is destroying iron metal and Fe(2+) phases. The rate of dissolution and oxidation of the ferromagnesian silicates is approximately 6% per 5000 yr. With the Mossbauer method for clearly defining the extent of weathering in each meteorite in a well-constrained environment we have extended the effort to evaluate the possibility of observing concurrent changes in the measured oxygen isotopic composition during erosion. Preliminary results from eight meteorites are presented. Replicate analyses are generally in good agreement. Results appear to indicate evidence for a correlation between O isotopic compositions and terrestrial age, and by inference, degree of weathering. The trend is essentially the reverse of what is expected from a simple system as it is the youngest, least-weathered meteorites, which display the largest shifts in (delta)O-18 from a typical chondrite fall. The exact nature of the relationship between the degree of weathering and the oxygen isotopic composition of the meteorites is unclear, highlighting, the complex effects of weathering and the caution required when interpreting results from finds.

Franchi, I. A.; Bland, P.; Berry, F. J.; Speck, A.; Pillinger, C. T.

1994-07-01

104

Impact experiments of porous gypsum–glass bead mixtures simulating parent bodies of ordinary chondrites: Implications for re-accumulation processes related to rubble-pile formation  

Microsoft Academic Search

Laboratory impact experiments were conducted for gypsum–glass bead targets simulating the parent bodies of ordinary chondrites. The effects of the chondrules included in the parent bodies on impact disruption were experimentally investigated in order to determine the impact conditions for the formation of rubble-pile bodies after catastrophic disruption. The targets included glass beads with a diameter ranging from 100?m to

Minami Yasui; Masahiko Arakawa

2011-01-01

105

"Sweating meteorites"—Water-soluble salts and temperature variation in ordinary chondrites and soil from the hot desert of Oman  

NASA Astrophysics Data System (ADS)

The common appearance of hygroscopic brine ("sweating") on ordinary chondrites (OCs) from Oman during storage under room conditions initiated a study on the role of water-soluble salts on the weathering of OCs. Analyses of leachates from OCs and soils, combined with petrography of alteration features and a 11-month record of in situ meteorite and soil temperatures, are used to evaluate the role of salts in OC weathering. Main soluble ions in soils are Ca2+, SO42-, HCO3-, Na+, and Cl-, while OC leachates are dominated by Mg2+ (from meteoritic olivine), Ca2+ (from soil), Cl- (from soil), SO42- (from meteoritic troilite and soil), and iron (meteoritic). "Sweating meteorites" mainly contain Mg2+ and Cl-. The median Na/Cl mass ratio of leachates changes from 0.65 in soils to 0.07 in meteorites, indicating the precipitation of a Na-rich phase or loss of an efflorescent Na-salt. The total concentrations of water-soluble ions in bulk OCs ranges from 600 to 9000 ?g g-1 (median 2500 ?g g-1) as compared to 187-14140 ?g g-1 in soils (median 1148 ?g g-1). Soil salts dissolved by rain water are soaked up by meteorites by capillary forces. Daily heating (up to 66.3 °C) and cooling of the meteorites cause a pumping effect, resulting in a strong concentration of soluble ions in meteorites over time. The concentrations of water-soluble ions in meteorites, which are complex mixtures of ions from the soil and from oxidation and hydrolysis of meteoritic material, depend on the degree of weathering and are highest at W3. Input of soil contaminants generally dominates over the ions mobilized from meteorites. Silicate hydrolysis preferentially affects olivine and is enhanced by sulfide oxidation, producing local acidic conditions as evidenced by jarosite. Plagioclase weathering is negligible. After completion of troilite oxidation, the rate of chemical weathering slows down with continuing Ca-sulfate contamination.

Zurfluh, Florian J.; Hofmann, Beda A.; Gnos, Edwin; Eggenberger, Urs

2013-10-01

106

Chromite-Plagioclase Assemblages as a New Shock Indicator; Implications for the Shock and Thermal Histories of Ordinary Chondrites  

NASA Technical Reports Server (NTRS)

Chromite in ordinary chondrites (OC) can be used as a shock indicator. A survey of 76 equilibrated H, L and LL chondrites shows that unshocked chromite grains occur in equant, subhedral and rounded morphologies surrounded by silicate or intergrown with metallic Fe-Ni and/or troilite. Some unmelted chromite grains are fractured or crushed during whole-rock brecciation. Others are transected by opaque veins; the veins form when impacts cause localized heating of metal-troilite intergrowths above the Fe-FeS eutectic (988 C), mobilization of metal-troilite melts, and penetration of the melt into fractures in chromite grains. Chromite-plagioclase assemblages occur in nearly every shock-stage S3-S6 OC; the assemblages range in size from 20-300 microns and consist of 0.2-20-micron-size euhedral, subhedral, anhedral and rounded chromite grains surrounded by plagioclase or glass of plagioclase composition. Plagioclase has a low impedance to shock compression. Heat from shock-melted plagioclase caused adjacent chromite grains to melt; chromite grains crystallized from this melt. Those chromite grains in the assemblages that are completely surrounded by plagioclase are generally richer in Al2O3, than unmelted, matrix chromite grains in the same meteorite. Chromite veinlets (typically 0.5-2 microns thick and 10-300 microns long) occur typically in the vicinity of chromite-plagioclase assemblages. The veinlets formed from chromite-plagioclase melts that were injected into fractures in neighboring silicate grains; chromite crystallized in the fractures and the residual plagioclase-rich melt continued to flow, eventually pooling to form plagioclase-rich melt pockets. Chromite-rich chondrules (consisting mainly of olivine, plagioclase-normative mesostasis, and 5-15 vol.% chromite) occur in many shocked OC and OC regolith breccias but they are absent from primitive type-3 OC. They may have formed by impact melting chromite, plagioclase and adjacent mafic silicates during higher-energy shock events. The melt was jetted from the impact site and formed droplets due to surface tension. Crystallization of these droplets may have commenced in flight, prior to landing on the parent-body surface. Chromite-plagioclase assemblages and chromite veinlets occur in 25 out of 25 shock-stage S1 OC of petrologic type 5 and 6 that I examined. Although these rocks contain unstrained olivine with sharp optical extinction, most possess other shock indicators such as extensive silicate darkening, numerous occurrences of metallic Cu, polycrystalline troilite, and opaque veins. It seems likely that these rocks were shocked to levels at least as high as shock-stage S3 and then annealed by heat generated during the shock event. During annealing, the olivine crystal lattices healed but other shock indicators survived. Published Ar-Ar age data for some SI OC indicate that many shock and annealing events occurred very early in the history of the parent asteroids. The common occurrence of shocked and annealed OC is consistent with collisions being a major mechanism responsible for metamorphosing OC.

Rubin, Alan E.

2006-01-01

107

Climate and rock weathering: a study of terrestrial age dated ordinary chondritic meteorites from hot desert regions  

NASA Astrophysics Data System (ADS)

Ordinary chondrites (OC) recovered from the desert areas of Roosevelt County, New Mexico, the Nullarbor Region of Western Australia, and the Algerian and Libyan Sahara, for which 14C terrestrial ages have been determined, were examined by 57Fe Mössbauer spectroscopy. OC were chosen as a standard sample to investigate weathering processes as their well constrained trace and bulk element chemistry, normative mineralogy and isotopic composition define a known, pre-weathering, starting composition. Given that terrestrial ages are known, it is possible to compare (initially very similar) samples that have been subsequently weathered in a range of climatic regimes from the present day to > 44 ka BP. In addition, recently fallen equilibrated OC contain iron only as Fe 0 and Fe 2+, thus the abundance of ferric iron is directly related to the level of terrestrial weathering. Mössbauer spectroscopy identifies two broad types of ferric alteration: paramagnetic phases (akaganéite, lepidocrocite, and goethite), and magnetically ordered (principally magnetite and maghemite). OC finds show a range in the percentage of total Fe existing as Fe 3+ from zero to over 80%. However, oxidation is comparable between fragments of the same OC separated since their time of fall (i.e., paired meteorites). Our results indicate several features of meteorite weathering that may result from climatic or geomorphologic conditions at the accumulation site: (1) Saharan samples are, overall, less weathered than non-Saharan samples, which may be related to the relatively recent age (ca. 20 ka) of the Saharan accumulation surface; (2) broad differences between sites in the rate of weathering, arising from regional differences in climate; (3) consistent differences in the weathering products between samples that fell during humid periods and those that fell during more arid periods (those falling during humid periods contain a higher proportion of magnetically ordered ferric oxides); (4) one region (the Nullarbor) that shows a variation in the total amount of ferric species that closely matches the climatic record for this area of Australia for the last 30 ka. Points (3) and (4) may be related to the identification of a rapid initial weathering phase: the majority of weathering occurs in the first few hundred years after fall, followed by passivation of weathering by porosity reduction. Porosity reduction, and the associated restriction in the ability of water to penetrate the sample, appears to be the mechanism whereby a weathering assemblage formed during the brief initial period of oxidation is preserved through subsequent climatic cycles over the terrestrial lifetime of the sample.

Bland, P. A.; Sexton, A. S.; Jull, A. J. T.; Bevan, A. W. R.; Berry, F. J.; Thornley, D. M.; Astin, T. R.; Britt, D. T.; Pillinger, C. T.

1998-09-01

108

Al-26 and Fe-60 nuclides as heat source of ordinary chondrite parent bodies: Evaluation by U-Pb systematics  

NASA Astrophysics Data System (ADS)

In order to evaluate if the Al-26 and Fe-60 nuclides have been a general heat source of the meteorite parent bodies, it is important to establish the in-situ decay of these nuclides in the various materials; evaluate how widely these nuclides were distributed in the solar nebula; and elucidate if the various thermal intensities recorded by the meteorites result from an inhomogeneous distribution of these nuclides in the solar nebula and/or from differences in the accretion times of their parent bodies. We illustrate the coupling between the systematics of these two short-lived nuclides and the U-Pb chronology in the case of chondrites. We quantify how the heating of equilibrated H chondrites by Al-26 and Fe-60 is compatible with the record of these nuclides in the Allende inclusions and with the U-Pb systematics in both materials. In order to define the amount of energy necessary to heat the H chondritic material, the heat capacity is calculated from its specific chemical composition and from the thermodynamical data of the minerals present in equilibrated chondrites. Assuming that the refractory inclusions in Allende record the Al and Fe isotopic compositions in the solar nebula at the time of their formation, the contribution of the Al-26 and Fe-60 decay to the heating of the H chondrite material is calculated as a function of its accretion time. The most radiogenic isotopic compositions of Pb extracted from Allende inclusions define an age of 4556-1/+2 m.y. Phosphates in H4 chondrites correspond to an age as old as 4562.7 +/- 0.6 m.y. If the 3-m.y. difference is interpreted as the time delay between the formation of the refractory material and the accretion of the H chondrite material, the energy released by simultaneous in-situ decay of Al-26 and Fe-56 accounts for metamorphism in H6 chondrites.

Manhes, G.; Gopel, C.

1994-07-01

109

Fe-Ni metal and sulfide minerals in CM chondrites: An indicator for thermal history  

USGS Publications Warehouse

CM chondrites were subjected to aqueous alteration and, in some cases, to secondary metamorphic heating. The effects of these processes vary widely, and have mainly been documented in silicate phases. Herein, we report the characteristic features of Fe-Ni metal and sulfide phases in 13 CM and 2 CM-related chondrites to explore the thermal history of these chondrites. The texture and compositional distribution of the metal in CM are different from those in unequilibrated ordinary and CO chondrites, but most have similarities to those in highly primitive chondrites, such as CH, CR, and Acfer 094. We classified the CM samples into three categories based on metal composition and sulfide texture. Fe-Ni metal in category A is kamacite to martensite. Category B is characterized by pyrrhotite grains always containing blebs or lamellae of pentlandite. Opaque mineral assemblages of category C are typically kamacite, Ni-Co-rich metal, and pyrrhotite. These categories are closely related to the degree of secondary heating and are not related to degree of the aqueous alteration. The characteristic features of the opaque minerals can be explained by secondary heating processes after aqueous alteration. Category A CM chondrites are unheated, whereas those in category B experienced small degrees of secondary heating. CMs in category C were subjected to the most severe secondary heating process. Thus, opaque minerals can provide constraints on the thermal history for CM chondrites. ?? The Meteoritical Society, 2011.

Kimura, M.; Grossman, J.N.; Weisberg, M.K.

2011-01-01

110

Chondrules in the bishunpur L13 chondrite  

NASA Technical Reports Server (NTRS)

Twenty-six chondrules, chondrule fragments or clasts were analyzed. An automated wavelength dispersive instrument with a 90 micrometer beam integrated a series of analyses in traverses across each object. Depending on the size of the cross-sectional area, from 1 to 21 analyses were performed for each bulk analysis. Si, Ti, Al, Cr, Fe, Ni, Mn, Mg, Ca, Na, K and S were determined, and an analyzed augite was used as a secondary standard before and after each set of analyses. The work is part of a study of chondrule rims, interchondrule matrix, chondrules and clasts in unequilibrated ordinary chondrites. Only two of the twenty-six objects analyzed have Ca/Al atomic ratios greater than the ordinary chondritic average of 0.74. The bulk meteorite has a normal Ca/Al ratio, so presumably a Ca-rich, Al-poor component must be present to compensate for chondrules and chlasts. This component is unlikely to be rim or matrix, but may be phosphate associated with metal or sulphide. Na/Al ratios range from 1 to almost zero, but there is no hiatus as in a suite of Manych chondrules and glasses.

Hutchison, R.; Alexander, C.; Barber, D. J.

1984-01-01

111

The Search for Meterorites with Complex Exposure Histories Amoung Ordinary Chondrites with Low 3HE/21NE Ratios  

SciTech Connect

In calculating cosmic-ray exposure ages of meteorites it is generally assumed that the meteoroids were expelled from a shielded position within their parent body and then experienced a single stage exposure before colliding with Earth. The combination of noble gas and radionuclide measurements in several large meteorites, such as Jilin and Bur Ghelaui, have revealed complex exposure histories: i.e. an initial exposure on the surface of an asteroid (or within meter-sized meteoroid), followed by a second exposure as a smaller object. In fact, orbital dynamics calculations predicted that at least 30% of the meteorites arriving on Earth experienced two- or multiple-stage exposure histories [1]. More recently, after the recognition that the Yarkovsky effect plays an important role in delivering meteorites from the asteroid belt to Earth-crossing orbits, it was confirmed that complex exposure histories should be common [2]. Nevertheless, despite the ability to measure a wide range of radionuclides with accelerator mass spectrometry (AMS), only a few meteorites with complex exposure histories have been identified [e.g. 3,4]. The question is whether the relatively paucity of complex exposure histories is real or have we simply overlooked complex-exposure histories. In this work we focus on meteorites with low {sup 3}He/{sup 21}Ne ratios, since it is known that most meteorites with complex exposure histories have relatively low {sup 3}He/{sup 21}Ne ratios, i.e. the {sup 3}He/{sup 21}Ne ratio is below the ''Bern-line''. Several hypotheses have been suggested for these low {sup 3}He/{sup 21}Ne ratios, including solar heating in low-perihelion orbits, shock-related diffusion of He during the collision that ejected the meteoroid, or an artifact of high shielding conditions [4]. The first two hypotheses seem to be supported by low radiogenic {sup 4}He concentrations in samples with low {sup 3}He, whereas Monte Carlo calculations have shown that some of the low {sup 3}He/{sup 21}Ne ratios may be due to high shielding conditions in objects with radii > 1m [5]. To elucidate these issues, we selected 15 samples with known noble gas concentrations [6] for radionuclide studies and obtained aliquots of the samples adjacent to those measured for noble gases. The specific goal is the identification of complex exposure histories among samples having low {sup 3}He/{sup 21}Ne ratios. All samples have {sup 3}He deficiencies of >20% relative to the ''Bern-line'' (Table 1). Most of the selected samples also have low {sup 22}Ne/{sup 21}Ne ratios ({le}1.1), indicative of high shielding during most of their cosmic-ray exposure (Table 1), whereas one sample (Suizhou) was selected because of its relatively low {sup 81}Kr concentration [7]. In addition, we selected QUE 93021, for which initial radionuclide results suggested a short exposure age. Here we present cosmogenic {sup 10}Be, {sup 26}Al and {sup 36}Cl in stone and metal fractions for the 16 ordinary chondrites listed in Table 1.

Welton, K C; Nishiizumi, K; Caffee, M W

2001-04-30

112

Alkali-granitoids as fragments within the ordinary chondrite Adzhi-Bogdo: Evidence for highly fractionated, alkali-granitic liquids on asteroids  

NASA Technical Reports Server (NTRS)

Adzhi-Bogdo is an ordinary chondrite regolith breccia (LL3-6) that fell October 30, 1949 in Gobi Altay, Mongolia. The rock consists of submm- to cm-sized fragments embedded in a fine-grained elastic matrix. The breccia contains various types of clasts, some of which must be of foreign heritage. Based on chemical compositions of olivine some components have to be classified as L-type. Components of the breccia include chondrules, impact melts (some are K-rich, similar to those found in other LL-chondrites, highly recrystalized rock fragments ('granulites'), pyroxene-rich fragments with achondritic textures, and alkali-granitoidal fragments that mainly consist of K-feldspar and quartz or tridymite. Probably, this is the first report on granitoids from asteroids. It can be ruled out that these fragments represent huge rock assemblages of the parent body like granites do on Earth. Therefore, to avoid misunderstandings, these rocks will be designated as granitoids. In one thin section four granitoids were observed. The main phases within these clasts are K-feldspar and SiO2-phases. Minor phases include albite, Cl-apatite, whitlockite, ilmenite, zircon, Ca-poor pyroxene, and an unidentified Na,Ti-bearing silicate. Based on chemical composition and on optical properties quartz appears to be the SiO2-phase in two fragments, whereas tridymite seems to occur in the other two. The calculated formula of the unknown Na,Ti-rich silicate is very close to (Na,Ca)2.7(Fe,Mg)6(Ti)1.3(Si)7(O)24. Quartz and K-feldspar can reach sizes of up to 700 microns. Thus, the fragments can be described as coarse-grained (by chondritic standards). This is especially the case considering that quartz and K-feldspar are very rare minerals in ordinary chondrites. Representative analyses of minerals from some granitoidal clasts are given. Based on the mineral compositions and the modal abundances the bulk compositions were calculated. Besides these granitoidal rocks, pyroxene-rich fragments occur that show exsolution textures that are similar to those found in eucrites.

Bischoff, A.

1993-01-01

113

Impact experiments of porous gypsum-glass bead mixtures simulating parent bodies of ordinary chondrites: Implications for re-accumulation processes related to rubble-pile formation  

NASA Astrophysics Data System (ADS)

Laboratory impact experiments were conducted for gypsum-glass bead targets simulating the parent bodies of ordinary chondrites. The effects of the chondrules included in the parent bodies on impact disruption were experimentally investigated in order to determine the impact conditions for the formation of rubble-pile bodies after catastrophic disruption. The targets included glass beads with a diameter ranging from 100 ?m to 3 mm and the volume fraction was 0.6, similar to that of ordinary chondrites, which is about 0.65-0.75. Nylon projectiles with diameters of 10 mm and 2 mm were impacted at 60-180 m s -1 by a single-stage gas gun and at 4 km s -1 by a two-stage light gas gun, respectively. The impact strength of the gypsum-glass bead target was found to range from 56 to 116 J kg -1 depending on the glass bead size, and was several times smaller than that of the porous gypsum target, 446 J kg -1 in low-velocity collisions. The impact strengths of the 100 ?m bead target and the porous gypsum target strongly depended on the impact velocity: those obtained in high-velocity collisions were several times greater than those obtained in low-velocity collisions. The velocities of fragments ejected from two corners on the impact surface of the target, measured in the center of the mass system, were slightly dependent on the target materials, irrespective of impact velocity. These results suggest that chondrule-including planetesimals (CiPs) can reconstruct rubble-pile bodies in catastrophic disruptions at the size of the planetesimal smaller than that of planetesimals without chondrules.

Yasui, Minami; Arakawa, Masahiko

2011-08-01

114

The S(IV)-type Asteroids as Ordinary Chondrite Parent Body Candidates: Implications for the Completeness of the Meteorite Sample of Asteroids  

NASA Astrophysics Data System (ADS)

The discrepancy between the abundance of ordinary chondrites (OCs) among the meteorites and the rarity of unambiguously similar assemblages in the asteroid belt has been a major point of discussion within and between the asteroid and meteorite communities. Various resolutions to this apparent paradox have been proposed [e.g., 1-5], including: 1) interpretations of S-type asteroid spectra are incorrect due to space weathering effects; 2) ordinary chondrites derive from a few rare but favorably situated parent bodies; 3) OCs come from a residual population of small unheated mainbelt asteroids; 4) shock effects darken OC parent body surfaces disguising them as C-type asteroids, and 5) OCs come from inner solar system planetesimals ejected to the Oort cloud which have been recently perturbed into Earth-crossing orbits. Although none of these possibilities has yet been rigorously excluded, recent investigations suggest that the resolution of the apparent paradox lies in some combination of the first three options. For option 3, the discovery of a small mainbelt asteroid with an OC-like spectrum indicates OC-assemblages among the smaller mainbelt asteroids [6], although their abundance is still low in the current sample [7]. For option 2, the mineralogical survey indicated that while most S-asteroids could be rigorously excluded on mineralogical criteria, the S(IV) subtype of this class has silicate compositions within the OC range [8]. The S(IV)-objects are concentrated near the 3:1 secular resonance at 2.5 AU providing an efficient escape into Earth-crossing orbits. Unfortunately for a simple resolution of the OC parent body question, S(IV) spectra still exhibit weaker silicate features and redder spectral slopes than OC assemblages. Although significant uncertainties remain, optical alteration of asteroid surfaces interpreted from the Galileo images of Ida and Gaspra may reconcile the mismatch between OC and S(IV) spectra [option 1]. Although only a subset of the S(IV) objects are viable OC-parent bodies [3 Juno, 6 Hebe, and 7 Iris are the leading candidates], their proximity to the 3:1 chaotic zone would allow them to contribute a significant portion of the ordinary chondrites. In particular, dynamical models suggest that Hebe should be a major contributor to the terrestrial meteorite flux [9]. Each leading contender is currently undergoing detailed spectral evaluation as a potential OC source. From both asteroid observational constraints and from chemical and isotopic studies of meteorites, the ordinary chondrites appear to represent an extensive and relatively complete (by meteoritic standards) sample of a few asteroid source bodies. In a similar fashion, the Howardite-Eucrite-Diogenite suite sample a single primary parent body (Vesta) and are over-represented in meteorite collections due to a fortuitous (and temporary on a solar system timescale) emplacement of Vesta ejecta fragments close to the 3:1 resonance. This suggests that the particular value of the ordinary chondrites lies in the good sample provided for each source body rather than as representatives of an abundant asteroid type. Acknowledgments: Various portions of this research were supported by NASA Planetary Geology and Geophysics grant NAGW-642 and NSF Planetary Astronomy grant AST-9012180. References: [1] Wetherill G. W. and Chapman C. R. (1988) in Meteorites and the Early Solar System, pp. 35-67, Univ. of Arizona. [2] Bell J. F. et al. (1989) in Asteroids II, pp. 921-945, Univ. of Arizona. [3] Gaffey M. J. et al. (1989) in Asteroids II, pp. 98-127, Univ. of Arizona. [4] Britt D. T. and Pieters C. M. (1991) LPS XXII, 141-142. [5] Gaffey M. J. (1984) Icarus, 60, 83-114. [6] Binzel R. P. et al. (1993) Science, 262, 1541-1543. [7] Shui X. et al. (1995) Icarus, 115, 1-35. [8] Gaffey M. J. et al. (1993) Icarus, 106, 573-602. [9] Farinella P. et al. (1993) Icarus, 101, 174-187.

Gaffey, M. J.

1995-09-01

115

Calibration of cosmogenic noble gas production in ordinary chondrites based on 36Cl-36Ar ages. Part 1: Refined produced rates for cosmogenic 21Ne and 38Ar  

NASA Astrophysics Data System (ADS)

We measured the concentrations and isotopic compositions of He, Ne, and Ar in bulk samples and metal separates of 14 ordinary chondrite falls with long exposure ages and high metamorphic grades. In addition, we measured concentrations of the cosmogenic radionuclides 10Be, 26Al, and 36Cl in metal separates and in the nonmagnetic fractions of the selected meteorites. Using cosmogenic 36Cl and 36Ar measured in the metal separates, we determined 36Cl-36Ar cosmic-ray exposure (CRE) ages, which are shielding-independent and therefore particularly reliable. Using the cosmogenic noble gases and radionuclides, we are able to decipher the CRE history for the studied objects. Based on the correlation 3He/21Ne versus 22Ne/21Ne, we demonstrate that, among the meteorites studied, only one suffered significant diffusive losses (about 35%). The data confirm that the linear correlation 3He/21Ne versus 22Ne/21Ne breaks down at high shielding. Using 36Cl-36Ar exposure ages and measured noble gas concentrations, we determine 21Ne and 38Ar production rates as a function of 22Ne/21Ne. The new data agree with recent model calculations for the relationship between 21Ne and 38Ar production rates and the 22Ne/21Ne ratio, which does not always provide unique shielding information. Based on the model calculations, we determine a new correlation line for 21Ne and 38Ar production rates as a function of the shielding indicator 22Ne/21Ne for H, L, and LL chondrites with preatmospheric radii less than about 65 cm. We also calculated the 10Be/21Ne and 26Al/21Ne production rate ratios for the investigated samples, which show good agreement with recent model calculations.

Dalcher, N.; Caffee, M. W.; Nishiizumi, K.; Welten, K. C.; Vogel, N.; Wieler, R.; Leya, I.

2013-10-01

116

Organic Analysis of Catalytic Fischer-Tropsch Synthesis Products and Ordinary Chondrite Meteorites by Stepwise Pyrolysis-GCMS: Organics in the Early Solar Nebula  

NASA Technical Reports Server (NTRS)

Abiotic generation of complex organic compounds, in the early solar nebula that formed our solar system, is hypothesized by some to occur via Fischer-Tropsch (FT) synthesis. In its simplest form, FT synthesis involves the low temperature (<300degC) catalytic reaction of hydrogen and carbon monoxide gases to form more complex hydrocarbon compounds, primarily n-alkanes, via reactive nano-particulate iron, nickel, or cobalt, for example. Industrially, this type of synthesis has been utilized in the gas-to-liquid process to convert syngas, produced from coal, natural gas, or biomass, into paraffin waxes that can be cracked to produce liquid diesel fuels. In general, the effect of increasing reaction temperature (>300degC) produces FT products that include lesser amounts of n-alkanes and greater alkene, alcohol, and polycyclic aromatic hydrocarbon (PAH) compounds. We have begun to experimentally investigate FT synthesis in the context of abiotic generation of organic compounds in the early solar nebula. It is generally thought that the early solar nebula included abundant hydrogen and carbon monoxide gases and nano-particulate matter such as iron and metal silicates that could have catalyzed the FT reaction. The effect of FT reaction temperature, catalyst type, and experiment duration on the resulting products is being investigated. These solid organic products are analyzed by thermal-stepwise pyrolysis-GCMS and yield the types and distribution of hydrocarbon compounds released as a function of temperature. We show how the FT products vary by reaction temperature, catalyst type, and experimental duration and compare these products to organic compounds found to be indigenous to ordinary chondrite meteorites. We hypothesize that the origin of organics in some chondritic meteorites, that represent an aggregation of materials from the early solar system, may at least in part be from FT synthesis that occurred in the early solar nebula.

Locke, Darren R.; Yazzie, Cyriah A.; Burton, Aaron S.; Niles, Paul B.; Johnson, Natasha M.

2014-01-01

117

Primordial noble gases in "Phase Q" in carbonaceous and ordinary chondrites studied by closed system stepped etching  

NASA Astrophysics Data System (ADS)

HF/HCl-resistant residues of the chondrites CM2 Cold Bokkeveld, CV3 (ox.) Grosnaja, CO3.4 Lancé, CO3.7 Isna, LL3.4 Chainpur and H3.7 Dimmitt have been measured by closed system stepped etching (CSSE) in order to better characterise the noble gases in "phase Q", a major carrier of primordial noble gases. All isotopic ratios in phase Q of the different meteorites are quite uniform, except for (20Ne/22Ne)Q. As already suggested by precise earlier measurements (Schelhaas et al., 1990; Wieler et al., 1991; 1992), (20Ne/22Ne)Q is the least uniform isotopic ratio of the Q noble gases. The data cluster around 10.1 for Cold Bokkeveld and Lancé and 10.7 for Chainpur, Grosnaja and Dimmitt, respectively. No correlation of (20Ne/22Ne)Q with the classification or the alteration history of the meteorites has been found. The Ar, Kr and Xe isotopic ratios for all six samples are identical within their uncertainties and similar to earlier Q determinations as well as to Ar-Xe in ureilites. Thus, an unknown process probably accounts for the alteration of the originally incorporated Ne-Q. The noble gas elemental compositions provide evidence that Q consists of at least two carbonaceous carrier phases "Q1" and "Q2" with slightly distinct chemical properties. (Ar/Xe)Q and (Kr/Xe)Q reflect both thermal metamorphism and aqueous alteration. These parent body processes have led to larger depletions of Ar and Kr relative to Xe. In contrast, meteorites that suffered severe aqueous alteration, such as the CM chondrites, do not show depletions of He and Ne relative to Ar but rather the highest (He/Ar)Q and (Ne/Ar)Q ratios. This suggests that Q1 is less susceptible to aqueous alteration than Q2. Both sub-phases may well have incorporated noble gases from the same reservoir, as indicated by the nearly constant, though very large depletion of the lighter noble gases relative to solar abundances. However, the elemental ratios show that Q1 and Q2 must have acquired (or lost) noble gases in slightly different element proportions. Cold Bokkeveld suggests that Q1 may be related to presolar graphite. Q1 and Q2 might be related to the sub-phases that have been suggested by Gros and Anders (1977). The distribution of the 20Ne/22Ne ratios can not be attributed to the carriers Q1 and Q2. The residues of Chainpur and Cold Bokkeveld contain significant amounts of Ne-E(L), and the data confirm the suggestion of Huss (1997) that the 22Ne-E(L) content, and thus the presolar graphite abundances, are correlated with the metamorphic history of the meteorites.

Busemann, Henner; Baur, Heinrich; Wieler, Rainer

2000-09-01

118

Nebula Formation of the H, L, and LL Parent Bodies from a Single Batch of Chondritic Materials  

NASA Astrophysics Data System (ADS)

Introduction: Studies of ordinary chondrites have established that a) components in H chondrites are chemically and isotopically indistinguishable from those in L and LL chondrites; b) the chondrules show similar but larger variations than the chondrite groups; and c) mean chondrule sizes increase from H through L to LL. Correlations between chondrule size and oxygen isotopes [1], FeO [2], and metal spherule size in CR chondrites [3] suggest that size sorting of chondritic ingredients from a single reservoir could be responsible for all of the differences between H, L, and LL. Oxygen isotopes: Clayton et al. [1] found that the smallest chondrules in Dhajala (H3.8) and Weston (H4) plot closer to the terrestrial fractionation line than the large chondrules. Since H-chondrites have smaller chondrules and oxygen isotope ratios closer to the terrestrial fractionation line, size sorting of a single population of chondrules could produce the observed variation through the equilibrated ordinary chondrites. Differences in FeO: Two populations of chondrules with distinctly different metal and FeO contents have been identified among the chondrules in unequilibrated ordinary chondrites: type I and type II [2,4] with type I being more reduced than type II chondrules. Type I and type II chondrules found in H chondrites are vitually identical in mineral composition to type I and II chondrules in LL chondrites [5,6]. The differences in FeO between equilibrated H, L, and LL chondrites can be explained solely in terms of different proportions of type I and II if the type I/type II ratio is higher in H than in LL chondrites. We have studied Semarkona (LL3.0) and Roosevelt County 075, which has been classified as H3.2 [5]. We find that: a) type I chondrules are smaller than type II chondrules b) type I chondrules are relatively more abundant in RC075. Size sorting of chondrules is therefore consistent with our observations and tends to make H chondrites more reduced than L and LL chondrites. Metal: Metal is more abundant in H than L and LL. This is partly due to a higher proportion of metal-rich type I chondrules but is also due to a higher abundance of individual metal particles and spherules in H-chondrites. Because the aerodynamic processes must have operated on the metal spherules as well this would imply that the mean size of metal spherules in the source region was much smaller than the mean size of the silicate chondrules. Since metal spherules are probably ejected from chondrules, this is consistent with expectations. Conclusions: We find that size sorting of chondrules from a common source region can explain the major differences between ordinary chondrites. This would require the chondritic components found in the ordinary chondrites to have formed in the same region of the nebula, during a limited period of time. Aerodynamic sorting of the chondrules seems to be the most viable mechanism to produce size-sorting of chondrules. Since small chondrules take longer to spiral inwards through the nebula we would predict that the H parent body was farthest from the Sun, contrary to [6]. References: [1] Clayton R. N. et al. (1991) GCA, 55, 2317-2337. [2] Scott E. R. D and Taylor G. J. (1983) JGR, 88, B275-B286. [3] Skinner W. R. and Leenhouts J. M. (1993) LPS XXIV, 1315-1316. [4] McSween H. Y (1985) Meteoritics, 20, 523-540. [5] McCoy T. J. et al (1993) Meteoritics (submitted). [6] Jones R. H. (1990) GCA, 54, 1785-1802. [7] Wasson J. T. (1985) Meteorites, 267, Freeman.

Haack, H.; Scott, E. R. D.

1993-07-01

119

CONDENSATION AND EVAPORATION FOR THERMALLY UNEQUILIBRATED PHASES  

E-print Network

CONDENSATION AND EVAPORATION FOR THERMALLY UNEQUILIBRATED PHASES R. A. Marcus1 , A. V. Fedkin2-K) equation for the rate of condensation of a gas or evaporation of a solid or liquid is used for systems, and apply it to shock wave- induced evaporation and condensation of a chondrule precursor. Theory

Grossman, Lawrence

120

Impact experiments of porous gypsum-glass bead mixtures simulating parent bodies of ordinary chondrites: Implications for re-accumulation processes related to rubble-pile formation  

NASA Astrophysics Data System (ADS)

Most of asteroids are expected to be impact fragments produced by collisions among planetesimals or rubble-pile bodies produced by re-accumulation of fragments. In order to study the formation processes of asteroids, it is necessary to examine the collisional disruption and re-accumulation conditions of planetesimals. Most of meteorites recovered on the Earth are ordinary chondrites (OCs). The OCs have the components of millimeter-sized round grains (chondrules) and submicron-sized dusts (matrix). So, the planetesimals forming the parent bodies of OCs could be mainly composed of chondrules and matrix. Therefore, we conducted impact experiments with porous gypsum mixed with glass beads having the spherical shape with various diameters simulating chondrules, and examined the effect of chondrules on the ejecta velocity and the impact strength. The targets included glass beads with a diameter ranging from 100 ?m to 3 mm and the volume fraction was 0.6, similar to that of ordinary chondrites, which is about 0.65-0.75. We also prepared the porous gypsum sample without glass bead to examine the effect of volume fraction. Nylon projectiles with the diameters of 10 mm and 2 mm were impacted at 60-180 m/s by a single-stage gas gun and at about 4 km/s by a two-stage light gas gun, respectively. After the shot, we measured the mass of the recovered fragments to calculate the impact strength Q defined by Q=mpVi^2/2(mp+Mt), where Vi is the impact velocity, and mp and Mt are the mass of projectile and target, respectively. The collisional disruption of the target was observed by a high-speed video camera to measure the ejecta velocity. The antipodal velocity Va increased with the increase of Q, irrespective of glass bead size and volume fraction. However, the Va for low-velocity collisions at 60-180 m/s was an order magnitude larger than that for high-velocity collisions at 4 km/s. The velocities of fragments ejected from two corners on the impact surface of the target Vc-g measured in the center of the mass system, were independent on the target materials. The impact strength of the mixture target was found to range from 56 to 116 J/kg depending on the glass bead size, and was several times smaller than that of the gypsum target, 446 J/kg in low-velocity collisions. The impact strengths of the 100 ?m bead target and the gypsum target strongly depended on the impact velocity: those obtained in high-velocity collisions were several times greater than those obtained in low-velocity collisions. The obtained results of Vc-g were compared to the escape velocity of chondrule-including planetesimals (CiPs) to study the conditions for the formation of rubble-pile bodies after the catastrophic disruption. The fragments of CiPs for catastrophic disruption could be re-accumulated at the radius of a body larger than 3 km, irrespective of chondrule size included in the CiPs, which is rather smaller than that for basalt bodies. Thus, we suggested that there were more parent bodies of OCs having a rubble-pile structure.

Yasui, M.; Arakawa, M.

2011-12-01

121

ACFER 217 - A new member of the Rumuruti chondrite group (R)  

NASA Astrophysics Data System (ADS)

Previously, three meteorites from Australia and Antarctica were described as a new chondritic 'grouplet' (Carlisle Lakes, Allan Hills (ALH)85151, Yamato (Y)-75302; Rubin and Kallemeyn, 1989). This grouplet was classified as the 'Carlisle-Lakes-type' chondrites (Weisberg et al., 1991). Recently, one Saharan sample and four more Antarctic meteorites were identified to belong to this group (Acfer 217, Y-793575, Y-82002, PCA91002, PCA91241). The latter two are probably paired. With the meteorite Rumuruti, the first fall of this type of chondrite is known (Schulze et al., 1994). We report here on the Saharan meteorite Acfer 217 which has chemical and mineralogical properties very similar to Rumuruti and Carlisle Lakes. All eight members of this group, Rumuruti, Carlisle Lakes, ALH85151, Y-75302, Y-793575, Y-82002, Acfer 217, and the paired samples PCA91002 and PCA91241 justify the introduction of a new group of chondritic meteorites, the Rumuruti meteorites (R). Acfer 217 is a regolith breccia consisting of up to cm-sized clasts (approximately 33 vol%) embedded in a fine-grained, well-lithified clastic matrix. The most abundant mineral is olivine (approximately 72 vol%), which has a high Fa-content of 37-39 mol%. The major minerals (olivine, low-Ca pyroxene, Ca-pyroxene, and plagioclase) show some compositional variability indicating a slightly unequilibrated nature of the meteorite. Considering the mean olivine composition of Fa(37.8 +/- 5.7), a classification of Acfer 217 as a R3.8 chondrite would result; however, Acfer 217 is a regolith breccia consisting of clasts of various petrologic types. Therefore, we suggest to classify Acfer 217 as a R3-5 chondrite regolith breccia. The bulk meteorite is very weakly shocked (S2). The bulk comparison of Acfer 217 and other R-meteorites show that the R-meteorites are basically chondritic in composition. The pattern of moderately volatile elements is unique in R chondrites; Na and Mn are essentially undepleted, similar to ordinary chondrites, while Zn and Se contents are similar to concentrations in CM chondrites. The oxygen isotopic composition in Acfer 217 is similar to that of Rumuruti, Carlisle Lakes, ALH 85151, and Y-75302. In a delta O-17 vs. delta O-18-diagram, the R-meteorites from a group well resolved form other chondrite groups. Acfer 217 was a meteoroid of common size with a radius between 15-65 cm and with a single stage exposure history.

Bischoff, A.; Geiger, T.; Palme, H.; Spettel, B.; Schultz, L.; Scherer, P.; Loeken, T.; Bland, P.; Clayton, R. N.; Mayeda, T. K.; Herpers, U.; Meltzow, B.; Michel, R.; Dittrich-Hannen, B.

1994-03-01

122

Intrinsic oxygen fugacity measurements on seven chondrites, a pallasite, and a tektite and the redox state of meteorite parent bodies  

USGS Publications Warehouse

Intrinsic oxygen-fugacity (fO2) measurements were made on five ordinary chondrites, a carbonaceous chondrite, an enstatite chondrite, a pallasite, and a tektite. Results are of the form of linear log fO2 - 1 T plots. Except for the enstatite chondrite, measured results agree well with calculated estimates by others. The tektite produced fO2 values well below the range measured for terrestrial and lunar rocks. The lowpressure atmospheric regime that is reported to follow large terrestrial explosions, coupled with a very high temperature, could produce glass with fO2 in the range measured. The meteorite Salta (pallasite) has low fO2 and lies close to Hvittis (E6). Unlike the other samples, results for Salta do not parallel the iron-wu??stite buffer, but are close to the fayalite-quartz-iron buffer in slope. Minor reduction by graphite appears to have taken place during metamorphism of ordinary chondrites. fO2 values of unequilibrated chondrites show large scatter during early heating suggesting that the constituent phases were exposed to a range of fO2 conditions. The samples equilibrated with respect to fO2 in relatively short time on heating. Equilibration with respect to fO2 in ordinary chondrites takes place between grades 3 and 4 of metamorphism. Application of P - T - fO2 relations in the system C-CO-CO2 indicates that the ordinary chondrites were metamorphosed at pressures of 3-20 bars, as it appears that they lay on the graphite surface. A steep positive thermal gradient in a meteorite parent body lying at the graphite surface will produce thin reduced exterior, an oxidized near-surface layer, and an interior that is increasingly reduced with depth; a shallow thermal gradient will produce the reverse. A body heated by accretion on the outside will have a reduced exterior and oxidized interior. Meteorites from the same parent body clearly are not required to have similar redox states. ?? 1984.

Brett, R.; Sato, M.

1984-01-01

123

The Natural Thermoluminescence Survey of Antarctic Meteorites: Ordinary Chondrites at the Grosvenor Mountains, MacAlpine Hills, Pecora Escarpment and Queen Alexandra Range, and New Data New Data for the Elephant Moraine, Ice Fields  

NASA Technical Reports Server (NTRS)

The natural TL survey of Antarctic meteorites was started in 1987 at the request of the Antarctic Meteorite Working Group in order to provide an initial description of radiation and thermal histories. It was intended to be a complement to the mineralogical and petrographic surveys performed at the Johnson Space Center and the Smithsonian Institution. All ANSMET samples recovered since then, besides those that were heated throughout by atmospheric passage, have been measured. To date this amounts to about 1200 samples. As the data for each ice field reaches a significant level, we have been conducting a thorough examination of the data for that field with a view to (1) identifying pairing, (2) providing an estimate of terrestrial age and residence time on the ice surface, (3) looking for differences in natural TL between ice fields, (4) looking for variations in natural TL level with location on the ice, (5) looking for meteorites with natural TL levels outside the normal range. Pairing is a necessary first step in ensuring the @ost productive use of the collection, while geographical variations could perhaps provide clues to concentration mechanisms. Samples with natural TL values outside the normal range are usually inferred to have had either small perihelia or recent changes in orbital elements. In addition, induced TL data have enabled us to (5) look for evidence for secular variation in the nature of the flux of meteorites to Earth, and (6) look for petrologically unusual meteorites, such as particularly primitive ordinary chondrites, heavily shocked meteorites, or otherwise anomalous meteorites. To date we have published studies of the TL properties of 167 ordinary chondrites from Allan Hills, 107 from Elephant Moraine and 302 from Lewis Cliff and we have discussed the TL properties of fifteen H chondrites collected at the Allan Hills by Euromet after a storm during the 1988 season. We now have additional databases for a reasonable number of ordinary chondrites from Grosvenor Mountains (39 meteorites), MacAlpine Hills (70 meteorites), Pecora Escarpment (60 meteorites), and Queen Alexandra Range (173 meteorites) and we have data for a further 101 samples from Elephant Moraine. The results are summarized in Table 1. We also have fairly minimal databases (10-15 meteorites) for Dominion Range, Graves Nunataks, Reckling Peak and Wisconsin Range that will not be discussed here.

Benoit, Paul H.; Sears, Derek W. G.

2000-01-01

124

The Natural Thermoluminescence Survey of Antarctic Meteorites: Ordinary Chondrites at the Grosvenor Mountains, Macalpine Hills, Pecora Escarpment and Queen Alexandra Range, and New Data for the Elephant Moraine, Ice Fields  

NASA Technical Reports Server (NTRS)

The natural TL (Thermoluminescence) survey of Antarctic meteorites was started in 1987 at the request of the Antarctic Meteorite Working Group in order to provide an initial description of radiation and thermal histories. It was intended to be a complement to the mineralogical and petrographic surveys performed at the Johnson Space Center and the Smithsonian Institution. All ANSMET (Antarctic Search for Meteorites) samples recovered since then, besides those that were heated throughout by atmospheric passage, have been measured. To date this amounts to about 1200 samples. As the data for each ice field reaches a significant level, we have been conducting a thorough examination of the data for that field with a view to identifying pairing, providing an estimate of terrestrial age and residence time on the ice surface, looking for differences in natural TL between ice fields, looking for variations in natural TL level with location on the ice, looking for meteorites with natural TL levels outside the normal range. Pairing is a necessary first step in ensuring the most productive use of the collection, while geographical variations could perhaps provide clues to concentration mechanisms. Samples with natural TL values outside the normal range are usually inferred to have had either small perihelia or recent changes in orbital elements. In addition, induced TL data have enabled us to look for evidence for secular variation in the nature of the flux of meteorites to Earth, and look for petrologically unusual meteorites, such as particularly primitive ordinary chondrites, heavily shocked meteorites, or otherwise anomalous meteorites. To date we have published studies of the TL properties of 167 ordinary chondrites from Allan Hills, 107 from Elephant Moraine and 302 from Lewis Cliff and we have discussed the TL properties of fifteen H chondrites collected at the Allan Hills by Euromet after a storm during the 1988 season. We now have additional databases for a reasonable number of ordinary chondrites from Grosvenor Mountains (39 meteorites), MacAlpine Hills (70 meteorites), Pecora Escarpment (60 meteorites), and Queen Alexandra Range (173 meteorites) and we have data for a further 101 samples from Elephant Moraine. The results are summarized. We also have fairly minimal databases (10-15 meteorites) for Dominion Range, Graves Nunataks, Reckling Peak and Wisconsin Range that will not be discussed here.

Benoit, Paul H.; Sears, Derek W. G.

1999-01-01

125

The Seoni chondrite.  

NASA Technical Reports Server (NTRS)

Description of the Seoni (India, 1966) chondrite in terms of its mineralogy, bulk chemistry, and sample shape and mass. It is an H6 group ordinary chondrite that contains olivine, orthopyroxene, clinopyroxene, plagioclase, together with chromite, troilite, kamacite, taenite, chlorapatite, and whitlockite. Recrystallization has been quite extensive, as indicated by the presence of a few remnant chondrules, low abundance of clinopyroxene, and relatively high abundance of well formed plagioclase.

Bunch, T. E.; Mall, A. P.; Lewis, C. F.

1972-01-01

126

Chondrites and their Components  

NASA Astrophysics Data System (ADS)

What are Chondrites?Chondrites are meteorites that provide the best% clues to the origin of the solar system. They are the oldest known rocks - their components formed during the birth of the solar system ca. 4,567 Ma - and their abundances of nonvolatile elements are close to those in the solar photosphere. Chondrites are broadly ultramafic in composition, consisting largely of iron, magnesium, silicon, and oxygen. The most abundant constituents of chondrites are chondrules, which are igneous particles that crystallized rapidly in minutes to hours. They are composed largely of olivine and pyroxene, commonly contain metallic Fe,Ni and are 0.01-10 mm in size. Some chondrules are rounded as they were once entirely molten but many are irregular in shape because they were only partly melted or because they accreted other particles as they solidified. Chondrites themselves were never molten. The definition of a chondrite has expanded recently with the discovery in Antarctica and the Sahara Desert of extraordinary meteorites with chondrules 10-100 ?m in size, and chondrites so rich in metallic Fe,Ni that they were initially classified as iron meteorites with silicate inclusions. Thus, in meteoritics, as in other fields of planetary science, new discoveries sometimes require definitions to be modified.Chondrites are so diverse in their mineralogical and textural characteristics that it is not possible to describe a typical chondrite. We show one with diversely textured chondrules including prominent, aesthetically pleasing, rounded chondrules (Figure 1(a)), and another with more uniformly textured chondrules (Figure 1(b)). Owing to the high abundance of rounded or droplet chondrules in the abundant, so-called "ordinary" chondrites ( Figure 1(a)), studies of the origin of chondrules have commonly been based on these chondrites. (7K)Figure 1. Maps showing magnesium concentrations in two chondrites: (a) PCA91082, a CR2 carbonaceous chondrite, and (b) Tieschitz, an H/L3.6 ordinary chondrite. In CR chondrites, as in most carbonaceous chondrites, nearly all chondrules have porphyritic textures and are composed largely of forsterite (white grains), enstatite (gray), and metallic Fe,Ni (black). The subscripts show type I chondrules, which are common, and type II, which are FeO-rich and rare in this chondrite. Tieschitz, like other ordinary chondrites, is composed of all kinds of chondrules with diverse FeO concentrations. Key to chondrule types: BO, barred olivine; C, cryptocrystalline, PO, porphyritic olivine; POP, porphyritic olivine-pyroxene; PP, porphyritic pyroxene; RP, radial pyroxene. These maps were made with an electron microprobe from Mg K? X-rays. Chondrites contain diverse proportions of three other components: refractory inclusions (0.01-10 vol.%), metallic Fe,Ni (<0.1-70%), and matrix material (1-80%). Refractory inclusions are tens of micrometers to centimeters in dimensions, lack volatile elements, and are the products of high-temperature processes including condensation, evaporation, and melting. Two types are recognized: calcium- and aluminum-rich inclusions or CAIs, and amoeboid olivine aggregates. CAIs are composed of minerals such as spinel, melilite, hibonite, perovskite and Al-Ti-diopside, which are absent in other chondritic components (see Chapter 1.08). Amoeboid olivine aggregates consist of fine-grained olivine, Fe,Ni metal, and a refractory component largely composed of aluminum-diopside, anorthite, spinel and rare melilite. Grains of metallic Fe,Ni occur inside and outside the chondrules as grains up to a millimeter in size and, like the chondrules and refractory inclusions, formed at high temperatures. Matrix material is volatile-rich, and fine-grained (5-10 ?m) and forms rims on other components and fills the interstices between them. Chondrite matrices have diverse mineralogies: most are disequilibrium mixtures of hydrated and anhydrous silicates, oxides, metallic Fe,Ni, sulfides, and organic material and contain rare presolar grains.

Scott, E. R. D.; Krot, A. N.

2003-12-01

127

Relationships between chondritic meteorites and planets  

NASA Technical Reports Server (NTRS)

Chondrites formed in the solar nebula prior to the formation of planets; they probably constituted the bulk of preplanetary solids in the inner solar system. In the highly reduced enstatite chondrites 10% of Si is metallic; in the highly oxidized CM and CI chondrites 20-30% of Fe is in the +3 state. The high density of Mercury implies that nebular Fe was reduced, whereas the low density of Mars indicates that a large fraction was oxidized. Most rare gases in the terrestrial planets seem to have accreted trapped in grains; Venusian interelement ratios resemble those in enstatite chondrites; Earth and Mars ratios are more like those in ordinary or carbonaceous chondrites. These observations imply that enstatite chondrites formed near the Sun (near Venus?), the carbonaceous chondrites formed far from the Sun, the ordinary chondrites at an intermediate location. Compositional data on Mercury, comets, an asteroidal fragment, and the moons of Mars are badly needed.

Wasson, J. T.

1985-01-01

128

Lunar and Planetary Science XXXV: Carbonaceous Chondrites  

NASA Technical Reports Server (NTRS)

The titles in this section include: 1) A Quantitative NMR Analysis of Phosphorus in Carbonaceous and Ordinary Chondrites; 2) An Infrared Study of the Matrices of CI1 and CM2 Chondrites; 3) A Study of the Morphology, Composition and Mineral Associations of Fe-Ni Sulphides in CM Carbonaceous Chondrites; 4) Aqueous Alteration Mineralogy in CM Carbonaceous Chondrites; 5) In Situ Location and Characterization of Carbon-bearing Phases in Carbonaceous; 6) Chondrites: Insights from Yamato 791198, a Weakly-altered CM2 Chondrite; 7) Unique Texture in EET 83389: Clues to Formation of Fine Grained Rims in CM Chondrites; 8) Amoeboid Olivine Aggregates in the NWA 760 CV3 Chondrite; 9) Petrologic Type of CV3 Chondrites as Revealed by Raman Spectroscopy of Organic Matter; 10) A First Look at Acfer 324: Evidence for Another CR 3 Chondrite? 11) Hydrogen Isotopic Composition of the Bencubbin Meteorite; 12) The Fountain Hills Meteorite: A New CBa Chondrite from Arizona; 13) Shock Effects in the Metal-rich Chondrites QUE 94411, Hammadah al Hamra 237 and Bencubbin; 14) Mineralogy and Petrology of Al-rich Objects in the CH Carbonaceous Chondrite North West Africa 739.

2004-01-01

129

Osmium isotope evidence for an s-process carrier in primitive chondrites.  

PubMed

Osmium extracted from unequilibrated bulk chondrites has isotope anomalies consistent with an insoluble s-process carrier, termed Os(i) here. Osmium from metamorphosed bulk chondrites does not have isotope anomalies, implying that the Os(i) carrier was destroyed by metamorphism. The isotopic homogeneity of metamorphosed bulk chondrites is consistent with extremely effective mixing of presolar grains from varied sources in the nebula. Osmium in the Os(i) carrier is likely from nucleosynthetic sites with a neutron density about two to four times as high as that of the average solar s-process Os. PMID:16109878

Brandon, A D; Humayun, M; Puchtel, I S; Leya, I; Zolensky, M

2005-08-19

130

Ardón: A Long Hidden L6 Chondrite Fall  

NASA Astrophysics Data System (ADS)

A L6 ordinary chondrite fall that occurred in Ardón, León province, Spain on July 9, 1931 is described. The 5.5 g stone was kept hidden for 83 years by Rosa González Pérez, who recovered the meteorite. Ardón is still a fresh ordinary chondrite.

Trigo-Rodriguez, J. M.; Llorca, J.; Weyrauch, M.; Bischoff, A.; Moyano-Cambero, C. E.; Keil, K.; Laubenstein, M.; Pack, A.; Madiedo, J. M.; Alonso-Azcárate, J.; Riebe, M.; Wieler, R.; Ott, U.; Tapia, M.; Mestres, N.

2014-09-01

131

Osmium Isotopic Compositions of Chondrites and Earth's Primitive Upper Mantle: Constraints on the Late Veneer  

NASA Technical Reports Server (NTRS)

The 187 Os/188 Os of carbonaceous chondrites averages approximately 2% lower than for enstatite and ordinary chondrites. The primitive upper mantle ratio for the Earth best matches that of ordinary and enstatite chondrites. Additional information is contained in the original extended abstract.

Walker, R. J.; Horan, M. F.; Morgan, J. W.; Meisel, T.

2001-01-01

132

Formation of niningerite by silicate sulfidation in EH3 enstatite chondrites  

NASA Astrophysics Data System (ADS)

Unequilibrated EH chondrites contain silica-bearing chondrules with abundant niningerite [(Mg,Fe,Mn)S] and troilite (FeS), distinguishing them from the silica-bearing chondrules in ordinary and carbonaceous chondrites. The conventional explanation for the origin of niningerite and oldhamite (CaS) is that they are condensates from C-rich nebular gas. However, models of condensation from a solar gas with an elevated C/O ratio predict mineralogy that is inconsistent with petrographic observations. We report petrographic and chemical evidence from 45 silica-bearing chondrules from the EH3 chondrites Sahara 97072 and Alan Hills 84170 for formation of niningerite and oldhamite by sulfidation of ferromagnesian silicates. The results indicate extensive thermal processing of the chondrules including melting before, during, and after sulfidation. Bulk compositions of chondrules exhibiting varied degrees of sulfidation suggest that depletion of Mg and enrichment of Fe, Mn, and Na accompany the reactions. Sulfidation of FeO-bearing silicates, which formed at oxidizing conditions (at least IW-3), can occur with exposure to a H-poor, C- and S-rich gaseous reservoir 6-8 fO2 log units below the IW buffer at temperatures high enough for partial melting of silicates. Physicochemical analysis of mineral reactions inferred from sulfidized chondrules suggests a melted metal-sulfide assemblage (in a H-poor environment) is capable of generating sufficient S vapor to drive sulfidation. The reaction of silicates with the S gas will result in progressive extraction of Fe, Ca, and Mg into sulfides, with the stoichiometric amounts of silica either reacting with olivine to form enstatite or, when olivine is exhausted, precipitating as free silica. The sulfidation environment drastically increases Mg volatility, resulting in evaporative loss until saturation in the ambient gas is reached. The newly formed Mg-rich niningerite will tend to reach equilibrium composition by losing Mg and gaining Fe plus Mn from the ambient gas, consistent with the observed chemical fractionation in the sulfidized chondrules. Therefore, sulfidation of ferromagnesian silicates can also explain the low bulk Mg/Si ratios of the enstatite chondrites if the sulfidizing gas was lost before accretion of the enstatite chondrite parent body.

Lehner, S. W.; Petaev, M. I.; Zolotov, M. Yu.; Buseck, P. R.

2013-01-01

133

Lea County 001, an H5 chondrite, and Lea County 002, an ungrouped type 3 chondrite  

NASA Technical Reports Server (NTRS)

A search of active deflation basins near Jal, Lea County, New Mexico resulted in the discovery of two meteorites, Lea County 001 and 002. Lea County 001 has mean olivine and low-Ca pyroxene compositions of Fa(19) and Fs(17), respectively. These and all other mineralogical and petrological data collected indicate a classification of H5 for this stone. Lea County 002 has mean olivine and low-Ca pyroxene compositions of Fa(2) and Fs(4), and is unequilibrated. Although it is mineralogically most similar to Kakangari and chondritic clasts within Cumberland Falls, the high modal amount of forsterite makes Lea County a unique type 3 chondrite. Oxygen isotope data for Lea County 002 fall on an 0-16-mixing line through those of the enstatite meteorites and IAB irons, a feature shared by Kakangari.

Zolensky, Michael E.; Score, Roberta; Clayton, Robert N.; Mayeda, Toshiko K.; Schutt, John W.

1989-01-01

134

Constraints on the Thermal History of H Chondrites Deduced From the U-Pb Systematics of Phosphates  

NASA Astrophysics Data System (ADS)

Pb/Pb ages of phosphates separated from equilibrated H chondrites vary from 4.563 to 4.502 aeons and show a negative correlation with the metamorphic grade of the host meteorite. This is the first clear relationship in ordinary chondrites ever observed between a long-lived chronometer and the intensity of metamorphism [1]. The range of the Pb/Pb ages, 6 x 10^7 y indicates the period for the thermal processing of equilibrated chondrites. The U/Pb systematics do however not allow to distinguish if this thermal activity has an episodic character (metamorphic event) or if it was a continuous process (internal heating followed by slow cooling). In the case of the second hypothesis the precision of the Pb/Pb chronometer with an age resolution of about 1 myr and the estimate of the temperature for the thermal U/Pb closure deduced from experimental studies of Pb diffusion in apatites [2] allow us to derive sharp and absolute chronological constraints for the thermal evolution of the H-chondrite parent body. The calculated temperature for the U/Pb closure in phosphates in chondrites of grade 5-6 is 710 +- 20 K for a cooling rate of 5 +- 2 K/10^6 y. We consider a classical modelization for the thermal evolution of the H parent body assuming that the accretion of the primitive material occured at low temperatures and in a short time interval relative to the mean life of ^26Al. The inferred value of 1150 K for the peak temperature of type 6 chondrites defines a value for the ^27Al/^26A = 5 +- 1 x 10^-6 at the time of accretion. The Pb/Pb systematics indicate that the accretion of the H chondrite parent body occurred at 4.564 aeons. The time interval between the Pb/Pb age of the Allende refractory inclusions and the accretion of the H chondrite parent body (Delta T = 3.0 +- 2.6 x 10^6 y) is compatible with this ^26Al time constraint. The radius of the H chondrite parent body is about 80 km, similar to that previously defined by [3]. The Pb/Pb chronology of phosphates from equilibrated chondrites supports the model of a ~10^2 km large parent body, which preserved its layered structure and, which was heated by heat furnished from ^26Al in situ decay if the Pb/Pb ages are interpreted as indicating the accurate time of the thermal U/Pb closure. This interpretation is, however, not coherent with the few internal Pb/Pb ages determined in unequilibrated chondrites, which show ages lying around 4.48 aeons [4]. Moreover, this model postulates that the most equilibrated material spent about 3 x 10^6 y at temperatures higher than 1100 K. Such a long period and slow cooling at high temperatures however is incompatible with petrographic observations made in this material, they require a very short time interval and a fast cooling period at temperatures above 1000 K. References: [1] Gopel C. et al. (1990) Meteoritics, 25, 367-368. [2] Cherniak D. et al. (1991) GCA, 55, 1663-1673. [3] Miyamato M. et al. (1981) LPS XII, 1145-1152. [4] Hanan B. B. and Tilton G. R. (1985) EPSL, 74, 209219.

Gopel, C.; Manhes, G.; Allegre, C. J.

1993-07-01

135

I-Xe systematics in LL chondrites  

NASA Technical Reports Server (NTRS)

A stepwise heating analysis of Ar and Xe data from five neutron-irradiated whole rock LL chondrites (Soko Banja, Alta Ameen, Tuxtuac, Guidder, and Olivenza) is presented, emphasizing the complicated thermal history of ordinary chondrites. None of the present meteorites show a well-defined (Ar-40)-(Ar-39) apparent age plateau comprised of more than two release fractions. Most of the samples are found to yield well-defined high-temperature correlations between Xe-129/Xe-130 and Xe-128/Xe-130, and thus determinations of I-129/I-127 and Xe-129/Xe-130 at the time of isotopic closure for Xe. As in the case of other ordinary chondrites, the I-Xe systematics for LL chondrites correlate neither with a metamorphic grade nor with chronologies based opon other methods.

Bernatowicz, T. J.; Podosek, F. A.; Swindle, T. D.; Honda, M.

1988-01-01

136

Discovery of Hg-Cu-bearing metal-sulfide assemblages in a primitive H-3 chondrite: Towards a new insight in early solar system processes  

NASA Astrophysics Data System (ADS)

We report here the discovery of a novel meteoritic paragenesis consisting of sub-micrometric HgS, Cu sulfides, and Hg metal, associated with polycrystalline fine-grained native Cu in opaque mineral aggregates heterogeneously distributed in the matrix of the H-3 Tieschitz unequilibrated ordinary chondrite (UOC). The systematic association of Hg with Cu in Tieschitz chondrite provides a unique opportunity to place robust constraints on the origin of these assemblages either by condensation and sulfidation in a local nebular reservoir of non-solar composition, followed by gentle and fast accretion, or by sublimation of Hg from the hot interior of the asteroid and recondensation in its cold outer regions. The sulfide phase relations support low temperature conditions (<300 °C), implying that subsequent to accretion indigenous hydrothermal processing, oxidation/sulfidation, transportation, or shock-induced thermal processing of the assemblage on the parent body earlier proposed are very unlikely and unrealistic. Origin of HgS by sublimation of Hg from the hotter asteroid interior and precipitation as cinnabar in the colder surface regions is discrepant with our findings and can be ruled out because cinnabar occurs only in Tieschitz matrix in alternating rhythmic intergrowth with Cu-sulfide. The sublimation scenario calls for co-evaporation of both the highly volatile Hg as HgS and Hg metal and the moderately volatile Cu both as Cu metal, or their sulfides and deposition as sulfides in alternating episodes. Our findings provide further ample evidence refuting the repeated claim of formation of native copper in chondritic metal by shock-induced impact melting. Cold accretion is the only reasonable possibility to preserve the delicate accretionary intergrowth textures, the polycrystallinity of FeNi-metal, native Cu, Hg-Cu-sulfides and native Hg globules and the high Hg concentration retained in this meteorite. Our findings strongly suggest that Tieschitz resided near the cold surface of the parent asteroid.

Caillet Komorowski, Catherine; El Goresy, Ahmed; Miyahara, Masaaki; Boudouma, Omar; Ma, Chi

2012-10-01

137

The Bencubbin chondrite breccia and its relationship to CR chondrites and the ALH85085 chondrite  

NASA Astrophysics Data System (ADS)

Bencubbin is an unclassified meteorite breccia which consists mainly of host silicate (˜40 vol.%) and host metal (˜60%) components. Rare (<1%) ordinary chondrite clasts and a dark xenolith (formerly called a carbonaceous chondrite clast) are also found. A petrologic study of the host silicates shows that they have textures, modes, mineralogy and bulk compositions that are essentially the same as that of barred olivine (BO) chondrules, and they are considered to be BO chondritic material. Bulk compositions of individual host silicate clasts are identical and differ only in their textures which are a continuum from coarsely barred, to finely barred, to feathery microcrystalline; these result from differing cooling rates. The host silicates differ from average BO chondrules only in being angular clasts rather than fluid droplet-shaped objects, and in being larger in size (up to 1 cm) than most chondrules; but large angular to droplet-shaped chondrules occur in many chondrites. Bencubbin host metallic FeNi clasts have a positive Ni-Co trend, which coincides with that of a calculated equilibrium nebular condensation path. This appears to indicate a chondritic, rather than impact, origin for this component as well. The rare ordinary chondrite clast and dark xenolith also contain FeNi metal with compositions similar to that of the host metal. Two scenarios are offered for the origin of the Bencubbin breccia. One is that the Bencubbin components are chondritic and were produced in the solar nebula. Later brecciation, reaggregation and minor melting of the chondritic material resulted in it becoming a monomict chondritic breccia. The alternative scenario is that the Bencubbin components formed as a result of major impact melting on a chondritic parent body; the silicate fragments were formed from an impact-induced lava flow and are analogous to the spinifex-textured rocks characteristic of terrestrial . Both scenarios have difficulties, but the petrologic, chemical and isotopic data are more consistent with Bencubbin being a brecciated chondrite. Bencubbin has a number of important chemical and isotopic characteristics in common with the major components in the CR (Renazzo-type) chondrites and the unique ALH85085 chondrite, which suggests that their major components may be related. These include: (1) Mafic silicates that are similarly Mg-rich and formed in similar reducing environments. (2) Similarly low volatiles; TiO2, Al2O3 and Cr2O3 contents are also similar. (3) Similar metallic FeNi compositions that sharply differ from those in other chondrites. (4) Remarkable enrichments in 15N. (5) Similar oxygen isotopic compositions that lie on the same mixing line. Thus, the major components of the Bencubbin breccia are highly similar to those of the ALH85085 and CR chondrites and they may have all formed in the same isotopic reservoir, under similar conditions, in the CR region of the solar nebula.

Weisberg, Michael K.; Nehru, Cherukupalli E.; Prinz, Martin

1990-12-01

138

Roedderite in the Qingzhen (EH3) chondrite  

NASA Technical Reports Server (NTRS)

The rare mineral roedderite, (Na1.09 K0.89 Ca0.02)2.00 (Mg4.71 Fe0.27)4.98 (Si11.80 Al0.09)11.89 O30 has been found in accessory amounts in the highly unequilibrated enstatite chondrite, Qingzhen. It occurs in association with minor amounts of albite and SiO2 as inclusions within the metal or sulfide phases of metal-sulfide assemblages. The roedderite crystals are connected through oxide and silicate veins to the surrounding matrix. The presence of glass coated vesicles on the surface of the assemblages strongly suggests that roedderite originated in the presence of a fluid phase, presumably during post-accretional planetary processes.

Rambaldi, E. R.; Rajan, R. S.; Housley, R. M.

1986-01-01

139

Shock-Melted Regions in the Krymka (LL3) Chondrite  

Microsoft Academic Search

Shock effects of various intensities are common in all kinds of meteorites, but, in ordinary chondrites, the most severe ones are observed mostly in metamorphosed chondrites (petrologic types 5 and 6), and they are rare in type 3 [1]. However, we report here observations of strong shock effects in a specimen of the Krymka (LL3.1\\/S3) chondrite, one of the three

V. P. Semenenko; C. Perron

1995-01-01

140

The Effect of Aqueous Alteration and Metamorphism in the Survival of Presolar Silicate Grains in Chondrites  

NASA Astrophysics Data System (ADS)

Relatively small amounts (typically between 2 and 200 ppm) of presolar grains have been preserved in the matrices of chondritic meteorites. The measured abundances of the different types of grains are highly variable from one chondrite to another, but are higher in unequilibrated chondrites that have experienced little or no aqueous alteration and/or metamorphic heating than in processed meteorites. A general overview of the abundances measured in presolar grains (particularly the recently identified presolar silicates) contained in primitive chondrites is presented. Here we will focus on the most primitive chondrite groups, as typically the highest measured abundances of presolar grains occur in primitive chondrites that have experienced little thermal metamorphism. Looking at the most aqueously altered chondrite groups, we find a clear pattern of decreasing abundance of presolar silicate grains with increasing levels of aqueous alteration. We conclude that measured abundances of presolar grains in altered chondrites are strongly biased by their peculiar histories. Scales quantifying the intensity of aqueous alteration and shock metamorphism in chondrites could correlate with the content of presolar silicates. To do this it would be required to infer the degree of destruction or homogenization of presolar grains in the matrices of primitive meteorites. To get an unbiased picture of the relative abundance of presolar grains in the different regions of the protoplanetary disk where first meteorites consolidated, future dedicated studies of primitive meteorites, IDPs, and collected materials from sample-return missions (like e.g. the planned Marco Polo) are urgently required.

Trigo-Rodriguez, Josep M.; Blum, Jürgen

2009-09-01

141

Metasomatic Processes in the Early Solar System: The Record from Chondritic Meteorites  

NASA Astrophysics Data System (ADS)

Chondritic meteorites are among the oldest solar system materials available for study in the laboratory. These unique samples contain a complex record of processes that occurred during the earliest stages of solar system evolution, including evidence of metasomatism. The effects of metasomatism are variably among the different chondrite groups, being most well developed in the CV group, with more limited effects in the CO3 and unequilibrated ordinary chondrite groups. Unlike most metasomatized terrestrial rocks, the chondrite metasomatism has not caused detectable changes in the bulk chondrite composition. Instead, it occurs at a highly localized scale and has involved elemental exchange between the different chondrite components - chondrules, matrix and Ca,Al-rich inclusions (CAIs) with vastly differing mineralogies. These components respond in different ways to metasomatism and the resultant alteration assemblages are largely dependent on the local bulk composition/mineralogy of the objects that are being metasomatized. As a consequence, there is remarkable diversity in the alteration mineralogy on the scale of 10-100?m. In CV chondrites, the secondary alteration is characterized by the introduction of alkalis, Cl and Fe into metasomatized chondrules and CAIs and the loss of Ca from these objects into the matrix. Chondrule glass has been replaced by nepheline, sodalite and other minor phases, forsteritic olivine phenocrysts have developed overgrowths of ferroan olivine, clinoenstatite is replaced by ferroan olivine and metal/sulfide nodules have been replaced by magnetite, Ni-rich metal and Fe,Ni-carbides. In CAIs, the main refractory phases, melilite, Al-Ti-rich pyroxene, anorthite, spinel and perovskite show variable degrees of alteration with the formation of a large number of secondary phases including grossular, andradite, nepheline, sodalite, wadalite Di-Hd pyroxenes, kushiroite, wollastonite, monticellite, ilmenite and, in some cases, minor amounts of phyllosilicates such as margarite, clintonite and kaolinite. The fine-grained matrix mineralogy has been extensively modified to form platy ferroan olivine associated with lesser amounts of Di-Hd pyroxenes, andradite, wollastonite, nepheline, sodalite etc. The environment in which metasomatism occurred has been the subject of extensive debate. Several studies have argued for high-temperature (>1000°C) gas-solid interactions in the solar nebula prior to asteroidal accretion, but more recent work has provided a body of evidence favoring fluid-mineral interactions below 300°C in an asteroidal environment. These include (a) in situ oxygen-isotope measurements of secondary minerals showing large mass-dependent fractionation effects of minerals precipitating from aqueous solutions, indicative of low-temperature formation, (2) dating of secondary minerals using 26Al-Mg and 53Mn-53Cr short-lived isotope chronologies suggesting late-stage alteration, several Myr after CAIs, and (3) evidence of mass transfer between CAIs and matrix and lithic clasts (dark inclusion) and Allende host, indicative of in situ alteration.

Brearley, A. J.; Krot, A.

2012-12-01

142

Thermal Histories of CO3 Chondrites: Constraints on Parent Body Size and Time of Accretion  

NASA Astrophysics Data System (ADS)

Metallographic cooling rates were determined for three CO3 chondrites using the Wood technique. Rates of 2°–5°C/Myr are consistent with other data for type 3 ordinary chondrites and imply a parent body radius for the CO3 chondrites of 50 km or more.

Krot, T. V.; Scott, E. R. D.; Goldstein, J. I.

2014-09-01

143

Paired Renazzo-type (CR) carbonaceous chondrites from the Sahara  

NASA Astrophysics Data System (ADS)

Data on the chemical composition, mineralogy, abundance, and isotopic composition of recently found Sahara meteorites are presented. The nine Acfer samples and the El Djouf 001 meteorite are considered to belong to the same parent meteoroid and are classified as a CR chondrite. The Acfer-El Djouf meteorite has a CI-chondritic composition of nonvolatile elements, in particular CI ratios of refractory elements to Mg. The presence of metal with chondritic Fe/Ni ratios, olivine with relatively low FeO contents and with high Cr is attributed to the primitive, unequilibrated nature of Acfer-El Djouf and other CR chondrites. The carbon and nitrogen stable isotropic composition of the Acfer-El Djouf chondrite lies within the range of other members of the CR group. Rare gases of the Acfer-El Djouf meteorite contain a comparatively large solar wind component, in excess of that in Renazzo. The cosmic-ray exposure age of the Acfer-El Djouf meteorite is about 6 million years.

Bischoff, A.; Palme, H.; Ash, R. D.; Clayton, R. N.; Schultz, L.; Herpers, U.; Stoffler, D.; Grady, M. M.; Pillinger, C. T.; Spettel, B.; Weber, H.; Grund, T.; Endress, M.; Weber, D.

1993-04-01

144

Chondrites: The Compaction of Fine Matrix and Matrix-like Chondrule Rims  

NASA Astrophysics Data System (ADS)

Primitive chondritic meteorites mainly consist of chondrules, sulfide+/-metal, and fine-grained matrix. The most unequilibrated chondrites preserve in their phase compositions and, to a lesser degree, their textures, many details about processes that occurred in the solar nebula. On the other hand, much of the textural evidence records processes that occurred in or on the parent body. I suggest that the low-porosity of chondrule matrix and matrix-like rims reflects compaction processes that occurred in asteroid-size bodies, and that neither matrix lumps nor compact matrix-like rims on chondrules could have achieved their observed low porosities in the solar nebula. Recent theoretical studies by Donn and Meakin (1) and Chokshi et al. (2) have concluded that grain-grain sticking in the solar nebula mainly produces fluffy structures having very high porosities (probably >>50%). If these structures grow large enough, they can provide an aerogel-like matrix that can trap chondrules as well as metal and sulfide grains, and thus form suitable precursors of chondritic meteorites. However, the strength of any such structure formed in the solar nebula must be a trivial fraction of that required to survive passage through the Earth's atmosphere in order to fall as a meteorite. The best evidence of accretionary structures appears to be that reported by Metzler et al. (3). They made SEM images of entire thin sections of CM chondrites, and showed that, in the best preserved chondrites, rims are present on all entitities--on chondrules, chondrule fragments, refractory inclusions, etc. A study by Krot and Wasson (4) shows a more complex situation in ordinary chondrites. Although matrix is common, a sizable fraction of chondrules are not surrounded by matrix-like rims. As summarized by Rubin and Krot (1995), there are reports of small textural and compositional differences between matrix lumps and mean matrix-like chondrule rims, but there is so much overlap in properties between these two classes that I will assume that they can be treated as parts of a single statistical population. Published SEM images of matrix lumps and matrix-like rims show them to be relatively compact. Although some porosity is surely present as indicated by broad-beam electron-probe analysis totals <100%, it never reaches values comparable to those expected from low-velocity collisions in the solar nebula. Most chondrite researchers seem to hold that the low porosities reflect efficient packing of each grain as it accreted to the assemblage (i.e., as micrometer-size grains gradually covered the surface of a chondrule to form the matrix-like rim). I find this process very difficult to envision. If the velocities are low, the fluffy structures of Dodd and Meakin (1) should result; if the velocities are high, then rim erosion would seem to be more probable than growth. A possible scenario that avoids this dilemma is to form cm to m-size fluffy structures in low-turbulence regions of the nebular midplane. During accretion of these larger objects these experienced enough compaction to form tough, low-porosity (but unequilibrated) chondrites. If no chondrules were in a region, matrix lumps formed; if chondrules were widely separated, a matrix-like rim resulted. And, if chondrules were close to other chondrules or chondrule fragments, only small amounts of intervening fine-grained materials now separate them from their neighbors. During the compaction event, gas and dust migration occurred, and matrix filled all interstices, as now observed in the most primitive chondrites. According to this picture there could have been more diversity in the fine-grained nebular component before compaction occurred. These differences would be best preserved in matrix-like rims and matrix lumps. Much of the interchondrule matrix should consist of homogenized dust that was mixed during compaction-induced transport. References: [1] Donn B. and Meakin P. (1989) Proc. LPSC 19th, 577-580. [2] Chokshi A. et al. (1993) Astrophys. J., 407, 806-819. [3] Metzler K. et al. (1992) GCA,

Wasson, J. T.

1995-09-01

145

On Type III plessite in chondrites  

NASA Astrophysics Data System (ADS)

Questions are raised concerning the possible sources of heat necessary for converting martensite to coarse Type III plessite in ordinary chondrites. It is suggested that the unusual Type III plesite in the Kingfisher, Oklahoma black chondrite was formed by partial homogenization of preexisting Type III plessite as a result of shock reheating of the metal into the gamma field of the Fe-Ni phase diagram, rather than by decomposition of shock reheated prior martensite in the alpha + gamma field, as originally proposed by Taylor and Heymann. Because martensite is sporadically distributed within Kingfisher plessite it is suggested that microstructures of this kind be called Type II-III plessite.

Knox, R., Jr.

1980-03-01

146

Primitive material surviving in chondrites - Matrix  

NASA Technical Reports Server (NTRS)

A logical place to search for surviving pristine nebular material is in the fine-grained matrices of ordinary and carbonaceous chondrites of petrographic type 3. Unfortunately, many of these chondrites have experienced brecciation, thermal metamorphism, and aqueous alteration, so that interpreting individual features in terms of specific nebular conditions and/or processes is difficult. It follows that the origin and evolutionary history of such matrix phases are controversial, and a consensus is difficult to define. In this chapter, therefore, after summarizing the salient mineralogical, petrographic, chemical, and isotopic features of matrix in apparently primitive chondrites, an attempt is made to provide an overview both of areas of agreement and of topics that are currently in dispute.

Scott, E. R. D.; Barber, D. J.; Alexander, C. M.; Hutchinson, R.; Peck, J. A.

1988-01-01

147

The Thermal History of Enstatite Chondrites  

NASA Astrophysics Data System (ADS)

In an attempt to decipher the complicated thermal history of the enstatite chondrites, the CaS enstatite (Larimer and Buseck, 1974; Fogel et al., 1989), cubic sulfide (Skinner and Luce, 1971) and sphalerite (Kissin, 1989; El Goresy and Ehlers, 1989) systems have been applied, but the results have not been straightforward. The CaS-En thermometer gives metamorphic temperatures which appear reasonable, but which do not correlate well with petrologic type. The cubic sulfides yield reasonable temperatures for the EH chondrites, but the values for EL chondrites are very low. To some extent, the problem has been the lack of low petrologic type EL chondrites. Here we discuss data for the recently discovered EL3 chondrites (Chang et al., 1992) and we examine the applicability of the Fe-Ni-P system for thermometry. The CaS-En thermometer uses three reactions including equilibria between metal, CaS, SiO2, enstatite and FeS. The method is crucially dependent on the activity coefficients for Si and CaSiO3 which are in solid solutions with metal and enstatite, respectively. The cubic sulfide thermometer uses the solubility of FeS in MgS and MnS, while the ZnS thermometer (which is pressure-dependent) uses the solubility of FeS in ZnS. Current equilibration temperature estimates for enstatite chondrites including the EL3 chondrites are listed in Table 1. Table 1. Estimates of equilibration temperatures (degrees C) for enstatite chondrites.* Petrologic type EH EL System 3 4 5 6 3 4 5 6 En-CaS 1030 950 830 - 830 - - 1025 Cubic sulf 400 680 600 - <<400 - - <400 ZnS 410 (1859)+ - - 500 - - 550 Fe-Ni-P <450 500 550 - <<450 - - <450 *Literature data (see text), present data (bold type). +Heavily shocked. In an attempt to use the Fe-Ni-P system as a thermometer for enstatite chondrites, we used the phase diagram of Doan and Goldstein (1970). Like the other systems, this required extrapolation to lower temperatures (Fig. 1). The temperatures calculated from this system mirror those of the sulfides, suggesting major differences in the thermal history of the EL and EH chondrites. Two points may be made from the data in Table 1. The EH3 and EL3 chondrites have similar En-CaS equilibration temperatures to those of the higher petrologic types which we suspect reflect pre-metamorphic equilibria. Second, both the cubic sulfides and the phosphides yield metamorphic temperatures for the EH chondrites which are similar to those for ordinary chondrites, while EL chondrites yield very low temperatures. The EL chondrite parent body must have cooled at especially slow rates, perhaps because it was much larger than the EH parent body, or maybe the cooling rate on EL body was governed by the attenuation of the heat source rather than burial depth. Chang Y., Benoit P.H. and Sears D.W.G. (1992) Lunar and Planet. Sci. 23, 217-218. Doan A.S. and Goldstein J.I. (1970) Met. Trans. 1, 1759-1767. El Goresy A. and Ehlers K (1989) Geochim. Cosmochim. Acta 53, 1657-1668. Fogel R.A., Hess P.C. and Rutherford M.C. (1989) Geochim. Cosmochim. Acta 53, 2735-2746. Kissin S.A.(1989) Geochim. Cosmochim. Acta 53, 1649-1655. Larimer J.W. and Buseck P.R. (1974) Geochim. Cosmochim. Acta 38, 471-477. Skinner B.J. and Luce F.D. (1971) Amer. Min. 56, 1269-1296. Figure 1, which in the hard copy appears here, shows isotherm from the Fe-Ni-P phase diagram with data for enstatite chondrites superimposed.

Zhang, Y.; Benoit, P. H.; Sears, D. W. G.

1992-07-01

148

Relationships Among Chondrite Groups as Inferred from Presolar-Grain Abundances  

NASA Technical Reports Server (NTRS)

Presolar-grain abundances show that C chondrites consist of two quite distinct groups, those containing primitive material, and those consisting of processed material. Ordinary chondrites are intermediate in many properties between these groups. Additional information is contained in the original extended abstract.

Huss, G. R.; Meshik, A. P.; Hohenberg, C. M.; Smith, J. B.

2002-01-01

149

The stable carbon isotopes in enstatite chondrites and Cumberland Falls  

NASA Astrophysics Data System (ADS)

The carbon-isotopic composition (CIC) of the total carbon in the enstatite chondrites Indarch, Abee, St. Marks, Pillistfer, Hvittis and Daniel's Kuil and the enstatite achondrite Cumberland Falls has been measured. The empirical relationship between CIC and total carbon content is distinct from that of carbonaceous and ordinary chondrites. Within the enstatite chondrite group the average C-13 content increases with petrographic type: E4 less than E5 less than E6. Daniel's Kuil shows the largest C-13 enrichment in the bulk carbon of any meteorite. The CIC is most clearly correlated with the abundance of the elements Zn, Cd, and In. Insofar as these elements may hold the key to the understanding of enstatite chondrites, more detailed combined CIC and trace-element studies of these meteorites will play an important role in the deciphering of their history.

Deines, P.; Wickman, F. E.

1985-01-01

150

Cosmogenic Nuclides in Katol (L6-7) Ordinary Chondrite  

NASA Astrophysics Data System (ADS)

Neutron effects show that Katol meteorite is a large preatmospheric object of radius 85–120 cm. An exposure age of 50 Ma is derived based on cosmogenic 38Ar. Epithermal neutron fluence of 3.9xE(+13)n/cm2 is obtained based on (80Kr)n.

Murty, S. V. S.; Mahajan, R. R.; Shukla, A. D.; Ranjith Kumar, P. M.

2014-09-01

151

The Wold Cottage meteorite: Not just any ordinary chondrite  

NASA Astrophysics Data System (ADS)

The Wold Cottage meteorite (fell, 1795), as is well known, played an important part in meteorites being accepted as stones from the sky. In most cases, the very select group of people who have been privileged to witness any meteorite fall, let alone one as important as Wold Cottage, enjoy a moment's fame but then disappear into obscurity. In this respect, Wold Cottage is very different; Edward Topham, the man who reported the fall and who became the meteorite's publicist, was already very well known for many other reasons. This fact contributed substantially to the evidence provided by his workmen being accepted, following two public exhibitions of the meteorite, the second after sworn testimonies were obtained. Here we explore Topham's background in order to reveal his character, particularly the value he placed on truth. When he passed the meteorite over to a public museum, he did so in the belief that he was acting for the benefit of posterity. At a time when the idea of meteorites being extraterrestrial was still controversial, the Wold Cottage stone vitally prompted the observation that specimens from different parts of the globe closely resembled each other, thus stimulating the crucial chemical analyses which verified that they were indeed related. During its first twenty years on Earth, the Wold Cottage meteorite was a prized specimen, a public attraction and sought after for scientific teaching purposes. In researching Wold Cottage, we have been able to discover information about many of the personalities who were involved in providing and studying the first few meteorites to become available for scientific research. The Wold Cottage story gives an interesting perspective on the cultural scene at the end of the eighteenth and beginning of the nineteenth centuries when there was no clear distinction between the arts and sciences, and meteoritics was the prerogative of often rather flamboyant gentlemen.

Pillinger, C. T.; Pillinger, J. M.

1996-09-01

152

Siderophile element fractionation in enstatite chondrites  

NASA Technical Reports Server (NTRS)

Analysis of the concentration of 10 to 15 siderophile elements was made in the magnetic regions of Abee (E4) and Hvittis (E6). All elements, except Cu, W, and Fe were concentrated in the metal phase; unlike ordinary chondrites, the metal phase Abee and Hvittis consists of homogeneous, uniform grain size kamacite. The Ir/Ni ratio was 25% lower in Abee than in Hvittis, showing that more Ir was lost from Abee during the refractory element fractionation; Abee and other E4-5 members were not depleted in moderately volatile elements. It was concluded that E4-5 and E6 chondrites evolved from two different reservoirs, and that exchange of material among them has not occurred.

Rambaldi, E. R.; Cendales, M.

1980-01-01

153

Experimental Impacts into Chondritic Targets. Part 1; Disruption of an L6 Chondrite by Multiple Impacts  

NASA Technical Reports Server (NTRS)

A fragment of an L6 chondrite (ALH 85017,13) with an initial mass (M(sub 0)) of 464.1 g was the target in a series of experimental impacts in which the largest remaining fragment (M(sub R)) after each shot was impacted by a 3.18-mm ceramic sphere at a nominal speed of 2 km/s. This continued until the mass of the largest remaining piece was less than half the mass of the target presented to that shot (M(sub S)). Two chunks of Bushveldt gabbro with similar initial masses were also impacted under the same conditions until M(sub R) was less than half M(sub 0). The two gabbro targets required a total of 1.51x10(exp 7) and 1.75x10(exp 7) erg/g to attain 0.27 and 0.33 M(sub R)/M(sub 0), respectively; the chondrite, however, was considerably tougher, reaching 0.40 and 0.21 M(sub R)/M(sub 0) only after receiving 2.37x10(exp 7) and 3.10x10(exp 7) erg g-1, respectively. The combined ejecta and spallation products from the gabbro impacts were coarser than those from the chondrite and in sufficient quantities that the new surface areas exceeded those from the meteorite until the fifth shot in the chondrite series, which was the number of impacts required to disrupt each gabbro target (i.e., MR/M0 = 0.5). Unlike the behavior shown in previous regolith-evolution series, neither gabbro target produced an enhancement in the size fraction reflecting the mean size of the crystals composing the rock (about 3 mm), an effect possibly related to the width of the shock pulse. The original chondrite was so fine-grained and fractured, and the variance in its grain-size distribution so large, that effects related to grain-size were relegated to the <63- m fraction. Impacts into ALH 85017 produced abundant, fine-grained debris, but otherwise the slopes of its size distributions were comparable to those from other experiments involving natural and fabricated terrestrial targets. The characteristic slopes of the chondrite's size distributions, however, were notably more constant over the entire nine-impact series than those from any of the terrestrial targets, a testament to the control over comminution apparently exerted by pre-existing fractures and other, microscopic damage in the meteorite. The enhancement in the finer fraction of debris from ALH 85017 indicates that ordinary chondrites in solar orbit would be very efficient contributors to the cosmic-dust complex. At the same time, the greater resistance to disruption displayed by ordinary chondrites relative to that exhibited by igneous rocks indicates that a selection effect could be operative between the annealed, ordinary-chondritic breccias and relatively weaker, differentiated meteorites. Preferential survival from their time in the regoliths of their parent bodies through their transit to Earth and passage through the atmosphere suggests that meteorite collections could be biased in favor of the ordinary chondrites.

Cintala, Mark J.; Horz, Friedrich

2007-01-01

154

Further Observations of Fe-60-Ni-60 and Mn-53-Cr-53 Isotopic Systems in Sulfides from Enstatite Chondrites  

NASA Technical Reports Server (NTRS)

Recent studies have shown that short-lived Fe-60 (t(sub 1/2) = 1.5 Ma) was present in some components of ordinary and enstatite chondrites when they formed. Here we report additional data on Fe-60 from sulfides in enstatite chondrites and on the potential relationship between the Fe-60-Ni-60 and Mn-53-Cr-53 systems.

Guan, Y.; Huss, G. R.; Leshin, L. A.

2004-01-01

155

Comparative 187Re-187Os systematics of chondrites: Implications regarding early solar system processes  

USGS Publications Warehouse

A suite of 47 carbonaceous, enstatite, and ordinary chondrites are examined for Re-Os isotopic systematics. There are significant differences in the 187Re/188Os and 187Os/188Os ratios of carbonaceous chondrites compared with ordinary and enstatite chondrites. The average 187Re/188Os for carbonaceous chondrites is 0.392 ?? 0.015 (excluding the CK chondrite, Karoonda), compared with 0.422 ?? 0.025 and 0.421 ?? 0.013 for ordinary and enstatite chondrites (1?? standard deviations). These ratios, recast into elemental Re/Os ratios, are as follows: 0.0814 ?? 0.0031, 0.0876 ?? 0.0052 and 0.0874 ?? 0.0027 respectively. Correspondingly, the 187Os/188Os ratios of carbonaceous chondrites average 0.1262 ?? 0.0006 (excluding Karoonda), and ordinary and enstatite chondrites average 0.1283 ?? 0.0017 and 0.1281 ?? 0.0004, respectively (1?? standard deviations). The new results indicate that the Re/Os ratios of meteorites within each group are, in general, quite uniform. The minimal overlap between the isotopic compositions of ordinary and enstatite chondrites vs. carbonaceous chondrites indicates long-term differences in Re/Os for these materials, most likely reflecting chemical fractionation early in solar system history. A majority of the chondrites do not plot within analytical uncertainties of a 4.56-Ga reference isochron. Most of the deviations from the isochron are consistent with minor, relatively recent redistribution of Re and/or Os on a scale of millimeters to centimeters. Some instances of the redistribution may be attributed to terrestrial weathering; others are most likely the result of aqueous alteration or shock events on the parent body within the past 2 Ga. The 187Os/188Os ratio of Earth's primitive upper mantle has been estimated to be 0.1296 ?? 8. If this composition was set via addition of a late veneer of planetesimals after core formation, the composition suggests the veneer was dominated by materials that had Re/Os ratios most similar to ordinary and enstatite chondrites. ?? 2002 Elsevier Science Ltd.

Walker, R. J.; Horan, M. F.; Morgan, J. W.; Becker, H.; Grossman, J. N.; Rubin, A. E.

2002-01-01

156

Isotopic Composition of Silicon Carbide in the CO3 Chondrite Colony  

NASA Technical Reports Server (NTRS)

Presolar grains have been identified in primitive members of all chondrite classes. The isotopic compositions of presolar grains provide probes of galactic evolution and nucleosynthesis in stars, while the abundances and characteristics of presolar grains contain a record of thermal processing in the solar system. Most of the detailed isotopic work has been done on SiC from Murchison and Orgueil, supplemented by a few studies of ordinary and enstatite chondrites. This work investigates SiC in the Colony CO3.O meteorite. SiC is present in Colony at a matrix-normalized abundance of approximately 3.7 ppm, much less than in CI chondrites and the matrixes of CM and primitive ordinary and enstatite chondrites. The abundances of SiC and other presolar grains in Colony seem to correlate with the chemical processing that produced CO3 chondrites. This implies that the known presolar grains experienced the same processing as the bulk CO3 material and assumes that the parent material was the same as that for other chondrites, including CI. That parent material is most plausibly the average material in the sun s parent molecular cloud. One test of this idea is to look for primary differences between SiC in Colony (and other meteorites) and that in CI and CM chondrites. True differences not related to thermal processing would falsify the assumption that all chondrite classes originated from the same reservoir of presolar dust.

Smith, J. B.; Huss, G. R.

2003-01-01

157

Rhenium-osmium isotope systematics of carbonaceous chondrites  

USGS Publications Warehouse

Rhenium and osmium concentrations and Os isotopic compositions of eight carbonaceous chondrites, one LL3 ordinary chondrite, and two iron meteorites were determined by resonance ionization mass spectrometry. Iron meteorite 187Re/186Os and 187OS/186Os ratios plot on the previously determined iron meteorite isochron, but most chondrite data plot 1 to 2 percent above this meteorite isochron. This suggests either that irons have significantly younger Re-Os closure ages than chondrites or that chondrites were formed from precursor materials with different chemical histories from the precursors of irons. Some samples of Semarkona (LL3) and Murray (C2M) meteorites plot 4 to 6 percent above the iron meteorite isochron, well above the field delineated by other chondrites. Murray may have lost Re by aqueous leaching during its preterrestrial history. Semarkona could have experienced a similar loss of Re, but only slight aqueous alteration is evident in the meteorite. Therefore, the isotopic composition of Semarkona could reflect assembly of isotopically heterogeneous components subsequent to 4.55 billion years ago or Os isotopic heterogeneities in the primordial solar nebula.

Walker, R.J.; Morgan, J.W.

1989-01-01

158

Paleomagnetism of enstatite chondrites  

NASA Astrophysics Data System (ADS)

Chondritic meteorites are widely thought to have originated on unmelted parent bodies. However, recent studies of CV carbonaceous chondrites have observed stable remanent magnetization acquired after accretion that may have been imparted by a core dynamo on the parent body. This suggests that CV chondrites may have originated from an internally melted, partially differentiated parent body with a relic chondritic crust. Although diverging from the predominant view that chondrites are samples of unmelted bodies, this idea has deep roots in the history of meteoritics. In particular, a common parent body has often been invoked for enstatite chondrites and enstatite achondrites (aubrites), which share many compositional, mineralogical, and isotopic similarities. Therefore, enstatite chondrites are a natural target for further testing the partial differentiation hypothesis. However, there are very few previous paleomagnetic studies of these meteorites. To address this, we studied the magnetic properties and paleomagnetism of three enstatite chondrites (Pillistfer EL6, Eagle EL6, and Sahara 97158 EH3) to examine the feasibility of dynamo generation on the enstatite chondrite parent body. In Pillistfer, our alternating field (AF) demagnetization of mutually oriented interior and fusion-crusted subsamples revealed three low coercivity components blocked from ~1.5-2.5 mT (component A1), ~2.5-7 mT (component A2), and ~7-9 mT (component A3). The A2 and A3 components are poorly defined, likely due to spurious anhysteretic remanent magnetization (ARM) acquired during AF demagnetization. Thermal demagnetization revealed low temperature (T1) and medium temperature (T2) components, ranging from 50-600°C and 600-700°C, respectively. The A1 and T1 components coincided, while the A2 and T2 components were more scattered (although nonrandomly distributed). Components A1 and A2 of fusion-crusted samples were similarly oriented to those of interior samples. The ratio of natural remanent magnetization (NRM) to isothermal remanent magnetization (IRM) over the A1 coercivity range is 10%. Combined with the failed fusion crust test, this high value of NRM/IRM suggests the sample has been partially, but not completely, remagnetized since arriving on Earth (perhaps by a hand magnet). Furthermore, we found that using AF paleointensity methods, we are only capable of recovering paleointensities from thermoremanence in Pillistfer down to 200 ?T, indicating it has poor magnetic recording properties and preventing us from obtaining paleointensities for the A2 and A3 components. Electron microscopy analyses of Pillistfer show the prevalence of FeNi metal with varying amounts of nickel (ranging in composition from kamacite into the taenite equilibrium fields and schriebersite as the most abundant ferromagnetic phases). Preliminary results on Eagle and Sahara 97158 enstatite chondrites indicate that, like in Pillistfer, the remanence is dominated by soft multidomain kamacite, making them poor paleomagnetic recorders. It is currently unclear whether enstatite chondrites may be suitable for retaining paleomagnetic fields imparted from a parent body-generated dynamo.

Feng, H.; Weiss, B. P.; Tikoo, S. M.; Gattacceca, J.; Suavet, C. R.; Andrade Lima, E.

2013-12-01

159

Re-Os Systematics and HSE Distribution in Metal from Ochansk (H4) Chondrite  

NASA Technical Reports Server (NTRS)

Previous studies of the Re-Os systematics of chondrites have documented considerable variation in the Re/Os ratios of whole rock samples. For some whole rock chondrites, Re-Os systematics display large deviations from the primitive isochron that are considerably larger than deviations in other isotope systems. Possible interpretation of these facts is that the Re-Os system in chondrites is particularly sensitive to post-formation alteration processes, thus providing a useful tool to examine such processes. Significant variations that have been detected in highly siderophile element (HSE) patterns for ordinary chondrites support this conclusion. We report Re-Os isotope data for metal separates from the Ochansk H4 chondrite coupled with abundance data for Ru, Pd, Ir, and Pt, determined in the same samples by isotope dilution. We chose this meteorite mainly because it is an observed fall with minimal signs of weathering, and its low metamorphic grade (H4) and shock stage (S3).

Smoliar, M. I.; Horan, M. F.; Alexander, C. M. OD.; Walker, R. J.

2003-01-01

160

LEW 87223: A Unique E Chondrite with Possible Links to H Chondrites  

NASA Astrophysics Data System (ADS)

LEW87223 (paired with LEW87057, 87220, and 87234) is an enstatite chondrite with unique textural and compositional properties. The Si content of metal (~0.5%), the presence of alabandite instead of niningerite, and the bulk WNi ratio in this chondrite are all consistent with an EL classification, but the high metal (23 wt%) and siderophile element abundances are closer to those in the EH group [1,2]. The moderately volatile elements, Mn, Na, K, As, Ga, and Se are all depleted relative to EH and EL chondrites [2]. The presence of olivine is consistent with an E3 classification. Oxygen isotopes in LEW87220 and 87234 are in the EH and EL chondrite field [R. Clayton, priv. comm., 1993]. Zhang et al. [2] suggested that this meteorite formed from an EL3 chondrite that experienced fractionation during impact and brecciation. Shock and thermal processing undoubtedly occurred, but our work suggests that LEW87223 was not derived from normal EL starting material. A precursor with properties intermediate between H and E chondrites seems to be indicated. LEW87223 has an opaque-mineral assemblage unlike that of other E chondrites. It has EH-like amounts of metal and troilite, schreibersite is common, but penyite, sphalerite, and djerfisherite (all found in EH3 and EL3 chondrites; [3]) were not observed. Oldhamite does occur as rare, transparent, pink crystals up to 100 micrometers in size, completely enclosed in kamacite. Metal grains are comparable in size to chondrules, and equant. Although it is a type 3, LEW87223 chondrules commonly appear to be welded together, and share long boundaries with other chondrules and metal grains. The olivines show features consistent with shock stage 2 of Stoffler et al. [4]. Alabandite is Fe-rich [2] and occurs as recrystallized aggregates along FeS grain boundaries [A. El Goresy, priv. comm., 1993]. Many chondrules appear dark or opaque in transmitted light due to abundant sub-micrometer, pure Fe metal intergrown with enstatite and silica, all of which partially replace ferroan pyroxene ^FS(sub)15-18). All of these features are consistent with a history involving strong reduction, shock, and heating. We analyzed four large, unweathered oldhamite grains in LEW87220 and 87234 by ion probe, and found trace element characteristics similar to those seen in MAC88136, the only known EL3 chondrite [3]: Mg, Sr, and Zr are lower, and Mn is higher than in EH oldhamite. One grain has a REE pattem that is flat at 60 x CI for LREE, and decreases from 46 x CI at Eu to 15 x CI at Lu, with a positive Yb anomaly (Yb/Yb*=3). The other grains have flat REE patterns near 75 x CI, with negative Eu anomalies (Eu/Eu*=0.4). The first pattern is most likely nebular in origin. The second, more common pattern, with the negative Eu anomaly is unlikely to be nebular, and may be metamorphic in origin, in which case the meteorite contains a mixture of nebular and metamorphic oldhamite. Zhang et al. [2] explained the low abundances of alkalis, Mn, Ga, and Se, and high abundance of siderophiles in LEW87223 as being due to the addition of EL metal, and removal of sulfides during shock and thermal processing of a normal EL3. This seems highly implausible to us because of the physical difficulty of completely separating minor sulfides from FeS and metal, and because perryite, which is intimately associated with metal in E chondrites, is missing. It is more likely that the chondrite represents an entirely new group of E chondrites. The high abundance (10s of %) of blackened (reduced) chondrules also indicates a population of chondrules that was initially quite oxidized; in fact, the measured compositions of surviving ferroan pyroxene are in the H-chondrite range. Also evident in the published trace element data [2] is a siderophile element abundance pattern identical to that in H chondrites but different from those in EH and EL chondrites. LEW87223 may be a link between the ordinary and enstatite chondrite groups. References: [1] Mason (1989,1992) Ant. Meteor. Newslett., 12(1) and 15(1,2). [2] Zhang et al. (1993) LPS XXIV, 1571. [3] Li

Grossman, J. N.; MacPherson, G. J.; Crozaz, G.

1993-07-01

161

Modal abundances of CAIs: Implications for bulk chondrite element abundances and fractionations  

NASA Astrophysics Data System (ADS)

Modal abundances of Ca,Al-rich inclusions (CAIs) are poorly known and reported data scatter across large ranges. CAIs are Poisson distributed, and if only small areas (<1000 mm2) are studied, the data are probably not representative of the true CAI modal abundances, explaining their reported large scatter in a single chondrite group. We combine reported CAI modal abundances and our own set, and present a complete list of CAI modal abundances in carbonaceous chondrites. This includes (in area%): CV: 2.98, CM: 1.21, Acfer 094: 1.12, CO: 0.99, CK/CV (Ningqiang and Dar al Gani [DaG] 055): 0.77, CK: 0.2, CR: 0.12 and CB: 0.1. CAIs are Poisson distributed and if only small areas are studied, the data are probably not representative of the true CAI modal abundances, Carbonaceous chondrites have excess bulk Al concentrations when compared to the CI-chondritic value. We find a correlation between this excess and CAI modal abundances and conclude that the excess Al was delivered by CAIs. The excess Al is only a minor fraction (usually ˜10 rel%, but 25 rel% in case of CVs) of the bulk chondrite Al and cannot have contributed much 26Al to heat the chondrite parent body. Ordinary, enstatite, R and K chondrites have an Al deficit relative to CI chondrites and only very low CAI modal abundances, if any are present at all. Carbonaceous chondrites also had an initial Al deficit if the contribution of Al delivered by CAIs is subtracted. Therefore all chondrites probably lost a refractory rich high-T component. Only minor amounts of CAIs are present in the matrix or have been present in the chondrule precursor aggregates. Most CAI size distributions contain more than one size population, indicating that CAIs from within a single meteorite group had different origins.

Hezel, Dominik C.; Russell, Sara S.; Ross, Aidan J.; Kearsley, Anton T.

2008-11-01

162

Composition and classification of clasts in the St. Mesmin LL chondrite breccia  

NASA Astrophysics Data System (ADS)

Seven samples of the St. Mesmin meteorite, which is unique in being the only ordinary chondrite known to contain an unmelted xenolith of another ordinary chondrite, have been analyzed by both instrumental and radiochemical neutron activation for Na, Ca, Sc, Cr, Mn, Fe, Co, Ni, Zn, Ga, Ge, Se, In, Sm, Yb, Ir, and Au. It is found that, as in other regolithic chondrites, the dark host has higher contents of highly volatile elements than do the light clasts; it is suggested that this is the result of a combination of differences in intensity of preexisting metamorphism, as well as a redistribution of volatiles during regolith gardening. It is also determined that while the H-group xenolith in St. Mesmin is a relatively recent addition to the parent body, this fact does not require regolith activity at that time.

Chou, C.-L.; Sears, D. W.; Wasson, J. T.

1981-08-01

163

Photographic observations of Neuschwanstein, a second meteorite from the orbit of the Príbram chondrite  

Microsoft Academic Search

Photographic observations of meteoroids passing through the atmosphere provide information about the population of interplanetary bodies in the Earth's vicinity in the size range from 0.1m to several metres. It is extremely rare that any of these meteoroids survives atmospheric entry to be recovered as a meteorite on the ground. Príbram was the first meteorite (an ordinary chondrite) with a

Pavel Spurný; Jürgen Oberst; Dieter Heinlein

2003-01-01

164

Ar-40/Ar-39 dating of collisional events in chondrite parent bodies  

NASA Technical Reports Server (NTRS)

Ar-40/Ar-39 age dating of a number of shocked ordinary chondrites is interpreted in terms of collisional degassing events of meteorite parent bodies, probably in the asteroid belt. Examples of L, H, and at least one LL chondrite show episodic degassing. Degassing ages suggest several distinct events ranging from about 0.03 aeon to 0.7 aeon and probably higher. All specimens of either the H or L chondrites are not consistent with a single age event. A direct correlation exists between the degree of shock heating and the fraction of argon lost during degassing. However, no chondrite yet analyzed shows complete degassing of its high-temperature phase. Consequently, whole rock K-Ar ages are not accurate monitors of the time of the shock event.

Bogard, D. D.; Wright, R. J.; Husain, L.

1976-01-01

165

On the Relationship between Cosmic Ray Exposure Ages and Petrography of CM Chondrites  

NASA Technical Reports Server (NTRS)

Carbonaceous (C) chondrites are potentially the most primitive among chondrites because they mostly escaped thermal metamorphism that affected the other chondrite groups. C chondrites are chemically distinguished from other chondrites by their high Mg/Si ratios and refractory elements, and have experienced various degrees of aqueous alteration. They are subdivided into eight subgroups (CI, CM, CO, CV, CK, CR, CB and CH) based on major element and oxygen isotopic ratios. Their elemental ratios vary over a wide range, in contrast to those of ordinary and enstatite chondrites which are relatively uniform. It is critical to know how many separate bodies are represented by the C chondrites. In this study we defined 4 distinct cosmic-ray exposure (CRE) age groups of CMs and systematically characterized the petrography in each of the 4 CRE age groups to determine whether the groups have significant petrographic differences with such differences probably reflecting different parent body (asteroid) geological processing, or multiple original bodies. We have reported the results of a preliminary grouping at the NIPR Symp. in 2013 [3], however, we revised the grouping and here report our new results.

Takenouchi, A.; Zolensky, M. E.; Nishiizumi, K.; Caffee, M.; Velbel, M. A.; Ross, K.; Zolensky, A.; Lee, L.; Imae, N.; Yamaguchi, A.; Mikouchi, T.

2014-01-01

166

Thermal evolution model for the H chondrite asteroid-instantaneous formation versus protracted accretion  

NASA Astrophysics Data System (ADS)

We present a model of the thermal evolution of asteroids. Assuming an onion shell model for the H chondrite parent body we obtain constraints for the H chondrite asteroid parameters by fitting empirical H chondrite cooling ages of Estacado, Guareña, Kernouvé, Mt. Browne, Richardton, Allegan, Nadiabondi, Ste. Marguerite, and Forest Vale by using a genetic algorithm for parameter optimisation. The model improves previous calculations on the thermal history calculated in the instantaneous accretion approximation considering sintering and porosity dependent heat conduction. The model is extended to include a finite growth time of the parent body to study whether the meteoritic record constrains the duration of the growth phase of the parent body where it assembles most of its mass. It is found that only short accretion times of up to 0.1 Ma are compatible with the empirical data on H chondrite cooling histories. Best fit models yield excellent agreement with the cooling age data. Particularly, they indicate that (i) 26Al was the major heat source driving metamorphism, while 60Fe contributed rather marginally, (ii) maximum temperatures remained below partial melting temperatures throughout the body, indicating that no partial differentiation occurred on the H chondrite parent asteroid, (iii) the H chondrite asteroid formed 2 Ma after CAIs, briefly after most ordinary chondrite chondrules formed (if 26Al abundance defines a chronological sequence).

Henke, S.; Gail, H.-P.; Trieloff, M.; Schwarz, W. H.

2013-09-01

167

Magnesium isotopic composition of the Earth and chondrites  

NASA Astrophysics Data System (ADS)

To constrain further the Mg isotopic composition of the Earth and chondrites, and investigate the behavior of Mg isotopes during planetary formation and magmatic processes, we report high-precision (±0.06‰ on ? 25Mg and ±0.07‰ on ? 26Mg, 2SD) analyses of Mg isotopes for (1) 47 mid-ocean ridge basalts covering global major ridge segments and spanning a broad range in latitudes, geochemical and radiogenic isotopic compositions; (2) 63 ocean island basalts from Hawaii (Kilauea, Koolau and Loihi) and French Polynesia (Society Island and Cook-Austral chain); (3) 29 peridotite xenoliths from Australia, China, France, Tanzania and USA; and (4) 38 carbonaceous, ordinary and enstatite chondrites including 9 chondrite groups (CI, CM, CO, CV, L, LL, H, EH and EL). Oceanic basalts and peridotite xenoliths have similar Mg isotopic compositions, with average values of ? 25Mg = -0.13 ± 0.05 (2SD) and ? 26Mg = -0.26 ± 0.07 (2SD) for global oceanic basalts ( n = 110) and ? 25Mg = -0.13 ± 0.03 (2SD) and ? 26Mg = -0.25 ± 0.04 (2SD) for global peridotite xenoliths ( n = 29). The identical Mg isotopic compositions in oceanic basalts and peridotites suggest that equilibrium Mg isotope fractionation during partial melting of peridotite mantle and magmatic differentiation of basaltic magma is negligible. Thirty-eight chondrites have indistinguishable Mg isotopic compositions, with ? 25Mg = -0.15 ± 0.04 (2SD) and ? 26Mg = -0.28 ± 0.06 (2SD). The constancy of Mg isotopic compositions in all major types of chondrites suggest that primary and secondary processes that affected the chemical and oxygen isotopic compositions of chondrites did not significantly fractionate Mg isotopes. Collectively, the Mg isotopic composition of the Earth's mantle, based on oceanic basalts and peridotites, is estimated to be -0.13 ± 0.04 for ? 25Mg and -0.25 ± 0.07 for ? 26Mg (2SD, n = 139). The Mg isotopic composition of the Earth, as represented by the mantle, is similar to chondrites. The chondritic composition of the Earth implies that Mg isotopes were well mixed during accretion of the inner solar system.

Teng, Fang-Zhen; Li, Wang-Ye; Ke, Shan; Marty, Bernard; Dauphas, Nicolas; Huang, Shichun; Wu, Fu-Yuan; Pourmand, Ali

2010-07-01

168

Opaque Mineral Assemblages at Chondrule Boundaries in the Vigarano CV Chondrite: Evidence for Gas-Solid Reactions Following Chondrule Formation  

NASA Technical Reports Server (NTRS)

Recent studies of opaque minerals in primitive ordinary chondrites suggest that metal grains exposed at chondrule boundaries were corroded when volatile elements recondensed after the transient heating event responsible for chondrule formation. Metal grains at chondrule boundaries in the Bishunpur (LL3.1) chondrite are rimmed by troilite and fayalite. If these layers formed by gas solid reaction, then the composition of the corrosion products can provide information on the chondrule formation environment. Given the broad similarities among chondrules from different chondrite groups, similar scale layers should occur on chondrules in other primitive meteorite groups. Here I report on metal grains at chondrule boundaries in Vigarano (CV3).

Lauretta, Dante S.

2004-01-01

169

Ordinary electromagnetic mode instability  

NASA Technical Reports Server (NTRS)

The instability of the ordinary electromagnetic mode propagating perpendicular to an external magnetic field is studied for a single-species plasma with ring velocity distribution. The marginal instability boundaries for both the purely growing mode and the propagating growing modes are calculated from the instability criteria. The dispersion characteristics for various sets of plasma parameters are also given. The typical growth rates are of the order of the cyclotron frequency.

Cheng, C. Z.

1974-01-01

170

Formation and Processing of Amorphous Silicates in Primitive Carbonaceous Chondrites and Cometary Dust  

NASA Technical Reports Server (NTRS)

Chondritic-porous interplanetary dust particles (CP IDPs) exhibit strongly heterogeneous and unequilibrated mineralogy at sub-micron scales, are enriched in carbon, nitrogen and volatile trace elements, and contain abundant presolar materials [1-4]. These observations suggest that CP IDPs have largely escaped the thermal processing and water-rock interactions that have severely modified or destroyed the original mineralogy of primitive meteorites. CP IDPs are believed to represent direct samples of the building blocks of the Solar System - a complex mixture of nebular and presolar materials largely unperturbed by secondary processing. The chemical and isotopic properties of CP IDPs and their atmospheric entry velocities are also consistent with cometary origins. GEMS (glass with embedded metal and sulfides) grains are a major silicate component of CP IDPs. GEMS grains are < 0.5 microns in diameter objects that consist of numerous 10 to 50 nm-sized Fe-Ni metal and Fe-Ni sulfide grains dispersed in a Mg-Si-Al-Fe amorphous silicate matrix [2, 5]. Based on their chemistry and isotopic compositions, most GEMS appear to be non-equilibrium condensates from the early solar nebula [2]. If GEMS grains are a common nebular product, then they should also be abundant in the matrices of the most physically primitive chondritic meteorites. Although amorphous silicates are common in the most primitive meteorites [6-9], their relationship to GEMS grains and the extent to which their compositions and microstructure have been affected by parent body processing (oxidation and aqueous alteration) is poorly constrained. Here we compare and contrast the chemical, microstructural and isotopic properties of amorphous silicates in primitive carbonaceous chondrites to GEMS grains in IDPs.

Keller, Lindsay P.; Messenger, S.

2012-01-01

171

To Be an Ordinary Department  

ERIC Educational Resources Information Center

In this article, the author shares his experience being the "chair" of the Department of Latin American and Puerto Rican Studies at Lehman College of the City University of New York. He also shares how this department proved to be an "ordinary" department at an "ordinary" liberal arts college. However, to conclude that they are an ordinary

Colburn, Forrest D.

2003-01-01

172

Nonlinear ordinary difference equations  

NASA Technical Reports Server (NTRS)

Future space vehicles will be relatively large and flexible, and active control will be necessary to maintain geometrical configuration. While the stresses and strains in these space vehicles are not expected to be excessively large, their cumulative effects will cause significant geometrical nonlinearities to appear in the equations of motion, in addition to the nonlinearities caused by material properties. Since the only effective tool for the analysis of such large complex structures is the digital computer, it will be necessary to gain a better understanding of the nonlinear ordinary difference equations which result from the time discretization of the semidiscrete equations of motion for such structures.

Caughey, T. K.

1979-01-01

173

Partial asteroid differentiation revealed by paleomagnetism of R-chondrite meteorites  

NASA Astrophysics Data System (ADS)

The study of the paleomagnetism of extraterrestrial material allows constraining magnetic fields in the early solar system. This can help us to understand primordial aspects of the history of the early solar system. Indeed, nebular or solar magnetic fields could have played a major role in the accretion process that generated the primary components of our solar system. Internal fields (i.e. generated by a dynamo within a solid body) are also of substantial interest since they provide information on parent body evolution, especially on parent body differentiation. In this study we focused on Rumuruti chondrites (R chondrites) [1]. This meteorite group is of particular interest because R chondrites parent body is believed to have formed at a heliocentric distance greater than ordinary chondrites and less than carbonaceous chondrites [2]. As such, more than a simple new chondrite group, R chondrites offer the possibility to estimate the magnetic fields strength present in a yet unstudied part of the early solar system. Only preliminary paleomagnetic data are available for these meteorites [3]. We performed a detailed magnetic and paleomagnetic study of two R chondrites, PCA91002 and LAP03639. Our aim was to establish the nature and the origin of the magnetic field recorded in these meteorites. Our results show that these two meteorites contain sulfide (pyrrhotite). Magnetite was also found in PCA91002. Paleomagnetic analyses using thermal and alternating field demagnetization evidenced a stable and homogenous magnetization in both R chondrites. Because magnetic carriers in these meteorites are secondary phases formed during a metamorphic event several Myr after the parent body formation (I-Xe dating on magnetite, [4]), the magnetization was acquired after the possible existence of solar and nebular magnetic fields. Therefore the magnetizing field was most probably of internal origin. Using alternating field normalizing methods we estimate that the magnetization was acquired in a magnetic field of about 5 µT. In view of the intensity and the likely internal (dynamo) origin of the magnetizing field, partial differentiation of the R chondrite parent body seems necessary. This idea, with a chondritic crust overlying a differentiated inner body has recently been proposed for CV chondrites parent body [5,6]. [1] Schulze et al., 1994. Meteoritics 29, 275-286. [2] Khan et al., 2013. 44th Lunar and Planet. Sci. Conf., abstract 2059. [3] Gattacceca and Rochette 2004. Earth Planet . Sci. Lett., 277, 377-393. [4] Claydon et al., 2013. 44th Lunar and Planet. Sci. Conf., abstract 2211. [5] Carporzen et al., 2011. Proc. National Acad. Sci., 108, 6386-6389. [6] Elkins-Tanton et al., 2011. Earth Planet . Sci. Lett., 305, 1-10.

Cournède, Cécile; Gattacceca, Jérôme; Rochette, Pierre

2014-05-01

174

ALH85085: a unique volatile-poor carbonaceous chondrite with possible implications for nebular fractionation processes  

USGS Publications Warehouse

Allan Hills 85085 is a unique chondrite with affinities to the Al Rais-Renazzo clan of carbonaceous chondrites. Its constituents are less than 50 ??m in mean size. Chondrules and microchondrules of all textures are present; nonporphyritic chondrules are unusually abundant. The mean compositions of porphyritic, nonporphyritic and barred olivine chondrules resemble those in ordinary chondrites except that they are depleted in volatile elements. Ca-, Al-rich inclusions are abundant and largely free of nebular alteration; they comprise types similar to those in CM and CO chondrites, as well as unique types. Calcium dialuminate occurs in several inclusions. Metal, silicate and sulfide compositions are close to those in CM-CO chondrites and Al Rais and Renazzo. C1-chondrite clasts and metal-rich "reduced" clasts are present, but opaque matrix is absent. Siderophile abundances in ALH85085 are extremely high (e.g., Fe Si = 1.7 ?? solar), and volatiles are depleted (e.g., Na Si = 0.25 ?? solar, S Si = 0.03 ?? solar). Nonvolatile lithophile abundances are similar to those in Al Rais, Renazzo, and CM and CO chondrites. ALH85085 agglomerated when temperatures in the nebula were near 1000 K, in the same region where Renazzo, Al Rais and the CI chondrites formed. Agglomeration of high-temperature material may thus be a mechanism by which the fractionation of refractory lithophiles occurred in the nebula. Chondrule formation must have occurred at high temperatures when clumps of precursors were small. After agglomeration, ALH85085 was annealed and lightly shocked. C1 and other clasts were subsequently incorporated during late-stage brecciation. ?? 1988.

Grossman, J.N.; Rubin, A.E.; MacPherson, G.J.

1988-01-01

175

Reflectance spectra of primitive chondrites  

NASA Astrophysics Data System (ADS)

We are studying a wide sample of pristine carbonaceous chondrites from the NASA Antarctic collection in order to get clues on the physico-chemical processes occurred in the parent bodies of these meteorites. We are obtaining laboratory reflectance spectra of different groups of carbonaceous chondrites, but here we focus in CM and CI chondrites. We discuss the main spectral features that can be used to identify primitive carbonaceous asteroids by remote sensing techniques. Two different spectrometers were used covering the entire 0.3 to 30 ?m electromagnetic window. Only a handful of Near Earth Objects (NEOs) exhibit bands or features clearly associated with aqueous alteration. Among them are the target asteroids of Osiris Rex and Marco Polo-R missions.

Trigo-Rodríguez, J. M.; Moyano-Cambero, C. E.; Llorca, J.

2013-05-01

176

Magnetite-sulfide chondrules and nodules in CK carbonaceous chondrites - Implications for the timing of CK oxidation  

NASA Astrophysics Data System (ADS)

CK carbonaceous chondrites contain rare (about 0.1 vol pct) magnetite-sulfide chondrules that range from about 240 to 500 microns in apparent diameter and have ellipsoidal to spheroidal morphologies, granular textures, and concentric layering. They resemble the magnetite-sulfide nodules occurring inside mafic silicate chondrules in CK chondrites. It seems likely that the magnetite-sulfide chondrules constitute the subset of magnetite-sulfide nodules that escaped as immiscible droplets from their molten silicate chondrule hosts during chondrule formation. The intactness of the magnetite-sulfide chondrules and nodules implies that oxidation of CK metal occurred before agglomeration. Hence, the pervasive silicate darkening of CK chondrites was caused by the shock mobilization of magnetite and sulfide, not metallic Fe-Ni and sulfide as in shock-darkened ordinary chondrites.

Rubin, A. E.

1993-03-01

177

Origin and chronology of chondritic components: A review  

NASA Astrophysics Data System (ADS)

Mineralogical observations, chemical and oxygen-isotope compositions, absolute 207Pb- 206Pb ages and short-lived isotope systematics ( 7Be- 7Li, 10Be- 10B, 26Al- 26Mg, 36Cl- 36S, 41Ca- 41K, 53Mn- 53Cr, 60Fe- 60Ni, 182Hf- 182W) of refractory inclusions [Ca,Al-rich inclusions (CAIs) and amoeboid olivine aggregates (AOAs)], chondrules and matrices from primitive (unmetamorphosed) chondrites are reviewed in an attempt to test (i) the x-wind model vs. the shock-wave model of the origin of chondritic components and (ii) irradiation vs. stellar origin of short-lived radionuclides. The data reviewed are consistent with an external, stellar origin for most short-lived radionuclides ( 7Be, 10Be, and 36Cl are important exceptions) and a shock-wave model for chondrule formation, and provide a sound basis for early Solar System chronology. They are inconsistent with the x-wind model for the origin of chondritic components and a local, irradiation origin of 26Al, 41Ca, and 53Mn. 10Be is heterogeneously distributed among CAIs, indicating its formation by local irradiation and precluding its use for the early solar system chronology. 41Ca- 41K, and 60Fe- 60Ni systematics are important for understanding the astrophysical setting of Solar System formation and origin of short-lived radionuclides, but so far have limited implications for the chronology of chondritic components. The chronological significance of oxygen-isotope compositions of chondritic components is limited. The following general picture of formation of chondritic components is inferred. CAIs and AOAs were the first solids formed in the solar nebula ˜4567-4568 Myr ago, possibly within a period of <0.1 Myr, when the Sun was an infalling (class 0) and evolved (class I) protostar. They formed during multiple transient heating events in nebular region(s) with high ambient temperature (at or above condensation temperature of forsterite), either throughout the inner protoplanetary disk (1-4 AU) or in a localized region near the proto-Sun (<0.1 AU), and were subsequently dispersed throughout the disk. Most CAIs and AOAs formed in the presence of an 16O-rich (? 17O ˜ -24 ± 2‰) nebular gas. The 26Al-poor [( 26Al/ 27Al) 0 < 1 × 10 -5], 16O-rich (? 17O ˜ -24 ± 2‰) CAIs - FUN (fractionation and unidentified nuclear effects) CAIs in CV chondrites, platy hibonite crystals (PLACs) in CM chondrites, pyroxene-hibonite spherules in CM and CO chondrites, and the majority of grossite- and hibonite-rich CAIs in CH chondrites—may have formed prior to injection and/or homogenization of 26Al in the early Solar System. A small number of igneous CAIs in ordinary, enstatite and carbonaceous chondrites, and virtually all CAIs in CB chondrites are 16O-depleted (? 17O > -10‰) and have ( 26Al/ 27Al) 0 similar to those in chondrules (<1 × 10 -5). These CAIs probably experienced melting during chondrule formation. Chondrules and most of the fine-grained matrix materials in primitive chondrites formed 1-4 Myr after CAIs, when the Sun was a classical (class II) and weak-lined T Tauri star (class III). These chondritic components formed during multiple transient heating events in regions with low ambient temperature (<1000 K) throughout the inner protoplanetary disk in the presence of 16O-poor (? 17O > -5‰) nebular gas. The majority of chondrules within a chondrite group may have formed over a much shorter period of time (<0.5-1 Myr). Mineralogical and isotopic observations indicate that CAIs were present in the regions where chondrules formed and accreted (1-4 AU), indicating that CAIs were present in the disk as free-floating objects for at least 4 Myr. Many CAIs, however, were largely unaffected by chondrule melting, suggesting that chondrule-forming events experienced by a nebular region could have been small in scale and limited in number. Chondrules and metal grains in CB chondrites formed during a single-stage, highly-energetic event ˜4563 Myr ago, possibly from a gas-melt plume produced by collision between planetary embryos.

Krot, A. N.; Amelin, Y.; Bland, P.; Ciesla, F. J.; Connelly, J.; Davis, A. M.; Huss, G. R.; Hutcheon, I. D.; Makide, K.; Nagashima, K.; Nyquist, L. E.; Russell, S. S.; Scott, E. R. D.; Thrane, K.; Yurimoto, H.; Yin, Q.-Z.

2009-09-01

178

Magnetite-Pentlandite Chondrules in CK Chondrites  

NASA Astrophysics Data System (ADS)

Opaque-mineral-rich chondrules are among the least common chondrule types and have received scant attention since their discovery by Gustav Rose in 1864. This category includes chondrules comprised principally of metallic Fe-Ni (Tschermak, 1885; Gooding and Keil, 1981) or chrome-spinel (Ramdohr, 1967; Krot et al., 1992). Here I report the occurrence of seven magnetite-pentlandite chondrules in Karoonda (CK4), PCA82500 (CK4/5) and EET90007 (CK5). The chondrules range in size from 225x255 micrometers to 440x570 micrometers and have ellipsoidal or spheroidal morphologies. All are concentrically layered: five of the chondrules have 20-60-micrometer-thick magnetite rims surrounding pentlandite-rich cores or mantles; two of the chondrules have thin pentlandite rims surrounding magnetite-rich cores and mantles. One chondrule from Karoonda has four distinct alternating layers of magnetite and pentlandite. Accessory phases, which occur in one or more of the chondrules, include pyrrhotite, chlorapatite, ilmenite, and chalcopyrite. The chondrules have finely to coarsely granular textures; in the center of one chondrule from PCA82500 there is a 25x100 micrometers subhedral crystal of pentlandite. All of the chondrules appear to be recrystallized, presumably due to metamorphism of their host rocks. The magnetite-pentlandite chondrules are very similar to the magnetite-pentlandite-rich nodules within mafic silicate chondrules in CK chondrites. I examined four nodules that range in size from 58x64 micrometers to 400x670 micrometers and have ellipsoidal or spheroidal morphologies. All but one are concentrically layered; one nodule from a Karoonda chondrule has four concentric layers of magnetite+-pentlandite. The nodules probably formed from immiscible sulfide-oxide droplets within their molten silicate chondrule hosts during chondrule formation. Upon cooling, magnetite and monosulfide solid solution (Mss) precipitated during cotectic crystallization; the Mss transformed into pentlandite after cooling below 610 degrees C. Dense immiscible liquid droplets tend to get expelled from the equators of their spinning molten spheroidal hosts if they do not happen to be located in the molten spheroids' centers where the centrifugal forces are minimal. This phenomenon also affected the four magnetite-pentlandite nodules: one nodule is near the margin and three are at the centers of their host silicate chondrules. The similarities in size, shape, mineralogy, and texture between the magnetite-pentlandite chondrules and nodules indicate that these chondrules constitute the set of immiscible nodule droplets that were lost to their mafic silicate chondrule hosts after melting. The occurrence of magnetite-pentlandite chondrules and nodules has important implications for the timing of CK chondrite oxidation. If oxidation had occurred after agglomeration and transformed metallic Fe-Ni into magnetite, the large (factor of 2) increase in molar volume would have disrupted the nodules and chondrules and destroyed the evidence for rhythmic layering. The intactness of the chondrules and nodules implies that the oxidation of fine-grained metallic Fe-Ni into magnetite probably occurred before agglomeration, either during chondrule formation in a region of high fo(sub)2 or within porous chondrule-precursor dust clumps after nebular temperatures cooled below ~130 degrees C. Hence, the pervasive silicate darkening of CK chondrites (Kallemeyn et al., 1991; Rubin, 1992) was caused by the shock mobilization of magnetite and pentlandite, not metallic Fe-Ni and troilite as in shock-darkened ordinary chondrites. References: Gooding J.L. and Keil K. (1981) Meteoritics 16, 17- 43; Kallemeyn G.W., Rubin A.E. and Wasson J.T. (1991) Geochim. Cosmochim. Acta 55, 881-892; Krot A., Ivanova M.A. and Wasson J.T. (1992) Earth Planet. Sci. Lett., submitted; Ramdohr P. (1967) Geochim. Cosmochim. Acta 31, 1961-1967; Rubin A.E. (1992) Geochim. Cosmochim. Acta 56, 1705-1714; Tschermak G. (1885) Die Mikroskopische Beschaffenheit der Meteoriten. Schweizerbart'sche Verlagshandlung, Stuttga

Rubin, A. E.

1992-07-01

179

Disruption of the L chondrite parent body: New oxygen isotope evidence from Ordovician relict chromite grains  

NASA Astrophysics Data System (ADS)

Mid-Ordovician fossil meteorites found in the Thorsberg quarry, southern Sweden, are believed to have been deposited during a period of enhanced meteorite flux following the fragmentation of the L chondrite parent body. During diagenesis, the fossil meteorites were largely replaced by a secondary mineral assemblage. However, primary chromite grains have been preserved. High-precision oxygen isotope analysis by laser-assisted fluorination has been undertaken in order to confirm the chemical group (H, L or LL) to which the fossil meteorites belong. To test our methodology, chromites extracted from recent ordinary chondrite falls (Holbrook L6, Appley Bridge LL6 and Kernouve H6) have been analyzed and these show that ordinary chondrites can be classified into their respective groups (H, L, or LL) using the oxygen isotopic composition of chromite alone. Results from the Golvsten 001 meteorite demonstrate that this sample is an equilibrated L chondrite. The uniform major and minor element composition of chromites throughout the southern Swedish fossil meteorite section means that it is highly probable that all are L chondrites. High-precision oxygen isotope analysis of relict chromites thus further strengthens the link between the fossil meteorites and the disruption of the L chondrite parent body. The evidence presented here demonstrates that relict chromite grains survive diagenesis and can be used to classify ancient meteoritic material. Analysis of such fossil grains may prove to be a powerful tool, not only in the case of the mid-Ordovician event, but also in examining changes in the relative distribution of meteorite groups throughout geological time.

Greenwood, R. C.; Schmitz, B.; Bridges, J. C.; Hutchison, R.; Franchi, I. A.

2007-10-01

180

Magnetic study of CM chondrites  

NASA Astrophysics Data System (ADS)

The study of the paleomagnetism of carbonaceous chondrites can lead to an estimate of the magnetic fields present in the early solar system. CM chondrites contain abundant magnetite formed during aqueous alteration on their parent body, and have not been heated after that, making them interesting targets for paleomagnetism. We performed a detailed and comparative magnetic study (paleomagnetism and rock magnetism) of three CM chondrites: Paris, Cold Bokkeveled and Murchison. These three meteorites cover a wide range of aqueous alteration, with increasing alteration from Paris [1] to Murchison to Cold Bokkeveld [2]. Paris is a unique CM chondrite significantly less aqueously altered than other CM chondrites. Our magnetic data show that in contrast with other CM, Paris meteorite contains abundant FeNi metal (of nebular origin) together with magnetite and pyrrhotite (of asteroidal origin). Paleomagnetic results of Paris show that unfortunately the meteorite has been exposed to a strong artificial magnetic field (magnet), precluding the study of the natural magnetization (of possible nebular origin) carried by FeNi. However, a high-coercivity magnetization carried by pyrrhotite is still preserved in the meteorite. It is homogeneous in direction and intensity at the scale of the meteorite. We interpret this high-coercivity magnetization as a pre-terrestrial chemical remanent magnetization acquired on the parent body in a field of a few µT. Our preliminary results on Murchison also evidenced an stable and homogeneous magnetization in the meteorite. Therefore a long-lasting stable magnetizing field seems necessary to account for the paleomagnetism of both meteorites. Because crystallization of pyrrhotite and magnetite occurred several Myr after the formation of the parent body [3] (i.e. after possible existence of strong solar and nebular magnetic field), the magnetizing field was most probably created on the parent body. In view of its intensity, the most plausible origin for the magnetizing field is an internally generated dynamo field. This would imply that the parent body of CM chondrites was partially differentiated with a convecting metallic core. Such process has recently been proposed for the parent body of CV chondrites [4, 5]. [1] Zanda et al., 2010. Meteoritics Planetary Sci., 45, 222-222. [2] Rubin et al., 2007. Geo. et Cosmo. Acta, 71, 2361-2382 [3] Krot et al., 2005. UCRL-BOOK-217207 [4] Carporzen et al., 2011. Proc. National Acad. Sci., 108, 6386-6389. [5] Elkins-Tanton et al., 2011. Earth Planet . Sci. Lett., 305, 1-10.

Cournède, C.; Gattacceca, J.; Zanda, B.; Rochette, P.

2012-04-01

181

Petrography, stable isotope compositions, microRaman spectroscopy, and presolar components of Roberts Massif 04133: A reduced CV3 carbonaceous chondrite  

NASA Astrophysics Data System (ADS)

Here, we report the mineralogy, petrography, C-N-O-stable isotope compositions, degree of disorder of organic matter, and abundances of presolar components of the chondrite Roberts Massif (RBT) 04133 using a coordinated, multitechnique approach. The results of this study are inconsistent with its initial classification as a Renazzo-like carbonaceous chondrite, and strongly support RBT 04133 being a brecciated, reduced petrologic type >3.3 Vigarano-like carbonaceous (CV) chondrite. RBT 04133 shows no evidence for aqueous alteration. However, it is mildly thermally altered (up to approximately 440 °C); which is apparent in its whole-rock C and N isotopic compositions, the degree of disorder of C in insoluble organic matter, low presolar grain abundances, minor element compositions of Fe,Ni metal, chromite compositions and morphologies, and the presence of unequilibrated silicates. Sulfides within type I chondrules from RBT 04133 appear to be pre-accretionary (i.e., did not form via aqueous alteration), providing further evidence that some sulfide minerals formed prior to accretion of the CV chondrite parent body. The thin section studied contains two reduced CV3 lithologies, one of which appears to be more thermally metamorphosed, indicating that RBT 04133, like several other CV chondrites, is a breccia and thus experienced impact processing. Linear foliation of chondrules was not observed implying that RBT 04133 did not experience high velocity impacts that could lead to extensive thermal metamorphism. Presolar silicates are still present in RBT 04133, although presolar SiC grain abundances are very low, indicating that the progressive destruction or modification of presolar SiC grains begins before presolar silicate grains are completely unidentifiable.

Davidson, Jemma; Schrader, Devin L.; Alexander, Conel M. O'd.; Lauretta, Dante S.; Busemann, Henner; Franchi, Ian A.; Greenwood, Richard C.; Connolly, Harold C.; Domanik, Kenneth J.; Verchovsky, Alexander

2014-11-01

182

Assessment of nebular versus parent body processes on presolar components present in chondrites: Evidence from osmium isotopes  

NASA Astrophysics Data System (ADS)

We report Os isotope compositions of acid residues separated from six carbonaceous chondrites that were subjected to varying degrees of aqueous alteration on their parent bodies. The residues from three enstatite chondrites were also investigated in order to evaluate the effects of nebular and parent body processing on the survival of presolar grains in meteorites formed under redox conditions that were markedly reduced, compared to those under which carbonaceous and ordinary chondrites formed. All acid residues from CM and CR chondrites show enrichments in s-process Os isotopes relative to the Solar System average recorded in bulk chondrites. The extent of the anomaly present positively correlates with the degree of aqueous alteration of the host chondrites. This correlation was probably caused by selective destruction/modification of presolar grains carrying r-process-enriched Os during progressive aqueous alteration on the parent bodies. The r-process-enriched component was likely either presolar silicates formed in Type II supernova ejecta, or other unidentified reduced presolar phases such as metal alloys, carbides and silicides. Acid residues from enstatite chondrites have Os isotope anomalies that are much more enriched in the s-process components, relative to the residues from carbonaceous and ordinary chondrites that experienced the same grade of thermal metamorphism. This most likely reflects the selective destruction of s-process-enriched presolar phases that occurred under the more oxidized conditions experienced by carbonaceous and ordinary chondrites, either while components formed in the nebula, or on their parent bodies. To account for the uniform, terrestrial Os isotopic composition in all types of bulk chondrites, it is required that r-process or s-process-enriched Os, released from presolar phases during nebular or parent body processing, was re-incorporated into a new phase(s) which was not lost from the location where the bulk meteorites were derived. However, because parent body processing might have acted differently on other elements (e.g., open system behavior of fluid mobile elements during aqueous alteration), recent findings of isotopic heterogeneities in bulk meteorites should be evaluated not just by invoking nebular heterogeneities, but by also considering the effects of parent body processing.

Yokoyama, Tetsuya; Alexander, Conel M. O'D.; Walker, Richard J.

2011-05-01

183

2D Size Distribution of Chondrules and Chondritic Fragments of an Ordinary Chondrite from Lut Desert (Iran)  

NASA Astrophysics Data System (ADS)

2D size measurement of chondrules and chondiritic fragments of a meteorite from Lut desert of Iran is conducted. Chondrules exhibit a size range of 55–1800 µm (average 437 µm). Chondiritic fragments show a size range of 46–1220 µm (average 261 µm).

Pourkhorsandi, H.; Mirnejad, H.

2014-09-01

184

Rare-earth abundances in chondritic meteorites  

NASA Technical Reports Server (NTRS)

Fifteen chondrites, including eight carbonaceous chondrites, were analyzed for rare earth element abundances by isotope dilution. Examination of REE for a large number of individual chondrites shows that only a small proportion of the analyses have flat unfractionated REE patterns within experimental error. While some of the remaining analyses are consistent with magmatic fractionation, many patterns, in particular those with positive Ce anomalies, can not be explained by known magmatic processes. Elemental abundance anomalies are found in all major chondrite classes. The persistence of anomalies in chondritic materials relatively removed from direct condensational processes implies that anomalous components are resistant to equilibrium or were introduced at a late stage of chondrite formation. Large-scale segregation of gas and condensate is implied, and bulk variations in REE abundances between planetary bodies is possible.

Evensen, N. M.; Hamilton, P. J.; Onions, R. K.

1978-01-01

185

Birth in an Ordinary Instant  

PubMed Central

Our daily lives are a series of ordinary moments and unnoticed thresholds—times that define us in ways we often do not give much attention. While we consider childbirth to be one of life's extra-ordinary events, the hours of labor and birth need not be dramatic (or traumatic) ones. I describe a quiet, well-supported birth in the Netherlands that is cause for celebration of the beauty of an ordinary instant that can define and enrich the human experience. PMID:21629383

De Vries, Charlotte

2010-01-01

186

Calcium-48 isotopic anomalies in bulk chondrites and achondrites: Evidence for a uniform isotopic reservoir in the inner protoplanetary disk  

NASA Astrophysics Data System (ADS)

Thermal ionization mass spectrometry (TIMS) was used to measure the calcium isotopic compositions of carbonaceous, ordinary, enstatite chondrites as well as eucrites and aubrites. We find that after correction for mass-fractionation by internal normalization to a fixed 42Ca/44Ca ratio, the 43Ca/44Ca and 46Ca/44Ca ratios are indistinguishable from terrestrial ratios. In contrast, the 48Ca/44Ca ratios show significant departure from the terrestrial composition (from -2 ? in eucrites to +4 ? in CO and CV chondrites). Isotopic anomalies in ?48Ca correlate with ?50Ti: ? 48Ca=(1.09±0.11)×? 50Ti+(0.03±0.14). Further work is needed to identify the carrier phase of 48Ca-50Ti anomalies but we suggest that it could be perovskite and that the stellar site where these anomalies were created was also responsible for the nucleosynthesis of the bulk of the solar system inventory of these nuclides. The Earth has identical 48Ca isotopic composition to enstatite chondrites (EH and EL) and aubrites. This adds to a long list of elements that display nucleosynthetic anomalies at a bulk planetary scale but show identical or very similar isotopic compositions between enstatite chondrites, aubrites, and Earth. This suggests that the inner protoplanetary disk was characterized by a uniform isotopic composition (IDUR for Inner Disk Uniform Reservoir), sampled by enstatite chondrites and aubrites, from which the Earth drew most of its constituents. The terrestrial isotopic composition for 17O, 48Ca, 50Ti, 62Ni, and 92Mo is well reproduced by a mixture of 91% enstatite, 7% ordinary, and 2% carbonaceous chondrites. The Earth was not simply made of enstatite chondrites but it formed from the same original material that was later modified by nebular and disk processes. The Moon-forming impactor probably came from the same region as the other embryos that made the Earth, explaining the strong isotopic similarity between lunar and terrestrial rocks.

Dauphas, Nicolas; Chen, James H.; Zhang, Junjun; Papanastassiou, Dimitri A.; Davis, Andrew M.; Travaglio, Claudia

2014-12-01

187

A refractory inclusion in the Kaba CV3 chondrite - Some implications for the origin of spinel-rich objects in chondrites  

NASA Technical Reports Server (NTRS)

The first detailed petrographic and mineralogical study of a Ca, Al-rich inclusion (CAI) from the Kaba CV3 chondrite is reported. This 'fine-grained' CAI contains abundant small, rounded, rimmed, spinel-rich objects which have important features in common with the spinel-rich objects in other carbonaceous and ordinary chondrites. These nodules are interpreted as fractionated distillation residues of primitive dust. However, the available data do not unambiguously rule out a condensation origin for at least some of these objects. Finally, the preservation of distinct diopside-hedenbergite rims on the spinel-rich bodies and the small grain size of many minerals in the CAI matrix material both suggest that the CAI accreted cool and had a relatively cool thermal history in the Kaba parent body.

Fegley, B., Jr.; Post, J. E.

1985-01-01

188

The extent of aqueous alteration in C-class asteroids, and the survival of presolar isotopic signatures in chondrites  

NASA Astrophysics Data System (ADS)

Several sample return missions are being planned by different space agencies for in situ sampling of undifferentiated bodies. Such missions wish to bring back to Earth pristine samples from C-class asteroids and comets to obtain clues on solar system formation conditions. A careful selection of targeted areas is required as many C-class asteroids and periodic comets have been subjected to collisional and space weathering processing since their formation. Their surfaces have been reworked by impacts as pointed out by the brecciated nature of many chondrites arrived to Earth, exhibiting different levels of thermal and aqueous alteration. It is not surprising that pristine chondrites can be considered quite rare in meteorite collections because they were naturally sampled in collisions, but several groups of carbonaceous chondrites contain a few members with promising unaltered properties. The CI and CM groups suffered extensive aqueous alteration [1], but for the most part escaped thermal metamorphism (only a few CMs evidence heating temperature over several hundred K). Both chondrite groups are water-rich, containing secondary minerals as consequence of the pervasive alteration of their primary mineral phases [2]. CO, CV, and CR chondrite groups suffered much less severe aqueous alteration, but some CRs are moderately aqueously altered. All five groups are good candidates to find unequilibrated materials between samples unaffected by aqueous alteration or metamorphism. The water was incorporated during accretion, and was released as consequence of shock after impact compaction, and/or by mild radiogenic heating. Primary minerals were transformed by water into secondary ones. Water soaking the bodies participated in chemical homogenization of the different components [1]. Hydrothermal alteration and collisional metamorphism changed the abundances of isotopically distinguishable presolar silicates [3]. Additional instruments in the landers to identify aqueous alteration signatures could help to get samples unbiased by parent body processes. Future work in this regard could be essential to successfully getting back to Earth samples to unveil the conditions in which the solar system formed. REF: [1] Trigo-Rodriguez J.M. & Blum J. 2009. Plan. Space Sci.57,243; [2] Rubin et al. (2007) GCA 71,2361; [3] Trigo-Rodriguez J.M. & Blum J. (2009). Pub.Ast.Soc.Aust.26,289

Trigo-Rodriguez, J. M.

2011-05-01

189

Oxygen Isotope Systematics of Chondrules from the Least Equilibrated H Chondrite  

NASA Technical Reports Server (NTRS)

Oxygen isotope compositions of bulk chondrules and their mineral separates in type 3 ordinary chondrites (UOC) show several % variability in the oxygen three isotope diagram with slope of approx.0.7 [1]. In contrast, ion microprobe analyses of olivine and pyroxene phenocrysts in ferromagnesian chondrules from LL 3.0-3.1 chondrites show mass dependent isotopic fractionation as large as 5% among type I (FeO-poor) chondrules, while type II (FeO-rich) chondrules show a narrow range (less than or equal to 1%) of compositions [2]. The .Delta(exp 17)O (=delta(exp 17)O-0.52xdelta(exp 18)O) values of olivine and pyroxene in these chondrules show a peak at approx.0.7% that are systematically lower than those of bulk chondrule analyses as well as the bulk LL chondrites [2]. Further analyses of glass in Semarkona chondrules show .17O values as high as +5% with highly fractionated d18O (max +18%), implying O-16-poor glass in chondrules were altered as a result of hydration in the parent body at low temperature [3]. Thus, chondrules in LL3.0-3.1 chondrites do not provide any direct evidence of oxygen isotope exchange between solid precursor and O-16-depleted gas during chondrule melting events. To compare the difference and/or similarity between chondrules from LL and H chondrites, we initiated systematic investigations of oxygen isotopes in chondrules from Yamato 793408 (H3.2), one of the least equilibrated H chondrite [4]. In our preliminary study of 4 chondrules, we reported distinct oxygen isotope ratios from dusty olivine and refractory forsterite (RF) grains compared to their host chondrules and confirmed their relict origins [5].

Kita, N. T.; Kimura, M.; Ushikubo, T.; Valley, J. W.; Nyquist, L. E.

2008-01-01

190

Chondritic meteorites and the formation of planets  

NASA Astrophysics Data System (ADS)

Estimating the chemical composition of solar system planets is presently undertaken through an exploration of the clues offered by chondritic meteorites, which have been hypothesized to be relic samples of the types of matter that accreted to form the planets. While carbonaceous chondrites have the highest inventory of volatile elements and may accordingly have formed at the greatest distance from the sun, most other chondrite and achondrite classes contain small chunks of carbonaceous chondrites, and represent meteoroids that struck asteroids closer to the sun and were incorporated into their surface material. Attention is given to bulk compositions of the four inner planets estimated on the basis of chondrite-component mixing and condensation. The compositions are presented in terms of a refractory component, siderophile components, and a magnesium silicate component.

McSween, H. Y.

1989-04-01

191

Ordinary People, Ordinary Places: The Civil Rights Movement. [Lesson Plan].  

ERIC Educational Resources Information Center

Martin Luther King, Jr. framed the goals and strategies of the Civil Rights Movement for a national audience, and with his message of nonviolent protest, he inspired ordinary African Americans to demand equal rights as American citizens. This lesson focuses on the individual men and women who embraced King's message and advanced the Civil Rights…

2002

192

Thermally Mobile Trace Elements in Carbonaceous Chondrites from Cold and Hot Deserts  

NASA Technical Reports Server (NTRS)

Some decades ago, Anders and co-workers used RNAA to classify a number of trace elements as being volatile during nebular condensation and accretion into primitive objects based upon their strong depletion in (equilibrated) ordinary chondrites relative to C1 chondrites. Such elements, e.g. Ag, Bi, Cd, Cs, In, Se, Te, Tl, Zn and others, exhibit nearly constant, C1-normalized atomic abundances in C2 (CM2) and in C3 chondrites. They interpreted the near-constancy of these abundances according to a 2-component model in which volatiles were introduced into carbonaceous (and other) chondrites as Cl material which was diluted with differing proportions of high-temperature (i.e. volatile-free) components. In this view, mean volatile element abundances of 0.48 in C2 and 0.24-0.29 x C1 in C3 chondrites indicated that C2 and C3 chondrites are, respectively, about 1:1 and 1:2-3 mixtures of Cl-like and high temperature materials. More recently, C1 normalized abundances of such volatile elements are nearly constant in most C2-6 chondrites (i.e. 25 non-Antarctic meteorites, nearly all falls, and 36 Antarctic finds) consistent with a 2- component mixing model. However, rather than being quantized, mean volatile element contents in each chondrite define a continuum from 0.92-0.14 x Cl for these 61 chondrites. A few carbonaceous chondrites - the first having been the NIPR consortium samples B-7904, Y-82162 and Y-86720 - show an altered pattern: many of the volatile elements in each exhibit the usual constancy of C1-normalized atomic abundances, but modified by further depletion of Cd and other elements like Tl and Bi. These are the most mobile trace elements, i.e. those most readily vaporized and lost from primitive meteorites during week-long heating at greater than or equal to 400 C under low ambient pressures (initially 10 (exp -5) atm H2), simulating metamorphic conditions in a primitive parent body. Similarities between mobile element data for B-7904, Y-82162 and Y-86720 with those for Murchison heated at 500-700 C suggest that these Antarctic C1 and C2-like chondrites were metamorphosed at temperatures like these in the interiors of their parent bodies. Metamorphic temperatures inferred from RNAA data and textural/mineralogic alterations are internally consistent, agreeing with those evident in heated Murchison samples. These 3 chondrites were also heated late in their histories since all have lost cosmogenic 3-He, presumably during close solar approach, and B-7904 and Y-86720 seem also to have lost substantial proportions of radiogenic He-4 and Ar-40, cf. data. Similarities in spectral reflectance data for C-, G-, B- and F- asteroids, for these meteorites and for heated Murchison samples suggest that thermally metamorphosed interior materials in these asteroids were excavated by impacts and re-deposited on them, forming their present surfaces. Establishment of the thermal metamorphic histories of carbonaceouis chondrites, then, is essential to establishing the evolution and present-day nature of C-type and related asteroids.

Lipschutz, M. E.

1999-01-01

193

Thermally Mobile Trace Elements in Carbonaceous Chondrites From Cold and Hot Deserts  

NASA Technical Reports Server (NTRS)

Some decades ago, Anders and co-workers used RNAA to classify a number of trace elements as being volatile during nebular condensation and accretion into primitive objects based upon their strong depletion in (equilibrated) ordinary chondrites relative to C1 chondrites. Such elements, e.g. Ag, Bi, Cd, Cs, In, Se, Te, Tl, Zn and others, exhibit nearly constant, C1-normalized atomic abundances in C2 (CM2) and in C3 chondrites. They interpreted the near-constancy of these abundances according to a 2-component model in which volatiles were introduced into carbonaceous (and other) chondrites as C1 material which was diluted with differing proportions of high-temperature (i.e. volatile-free) components. In this view, mean volatile element abundances of 0.48 in C2 and 0.24-0.29 x C1 in C3 chondrites indicated that C2 and C3 chondrites are, respectively, about 1:1 and 1:2-3 mixtures of C1-like and high temperature materials. More recently, Xiao and Lipschutz found that C-normalized abundances of such volatile elements are nearly constant in most C2-6 chondrites (i.e. 25 non-Antarctic meteorites, nearly all falls, and 36 Antarctic finds) consistent with a 2-component mixing model. However, rather than being quantized, mean volatile element contents in each chondrite define a continuum from 0.92-0.14 x C1 for these 61 chondrites. A few carbonaceous chondrites, the first having been the NIPR consortium samples B-7904, Y-82162 and Y-86720, show an altered pattern: many of the volatile elements in each exhibit the usual constancy of C1-normalized atomic abundances, but modified by further depletion of Cd and other elements like Tl and Bi. These are the most mobile trace elements, i.e. those most readily vaporized and lost from primitive meteorites during week-long heating at greater than or equal to 400 C under low ambient pressures (initially 10(exp -5) atm H2), simulating metamorphic conditions in a primitive parent body. Similarities between mobile element data for B-7904, Y-82162 and Y-86720 with those for Murchison heated at 500-700 C, suggest that these Antarctic C1 - and C2-like chondrites were metamorphosed at temperatures like these in the interiors of their parent bodies. Metamorphic temperatures inferred from RNAA data and textural/mineralogic alterations are internally consistent, agreeing., with those evident in heated Murchison samples. These 3 chondrites were also heated late in their histories since all have lost cosmogenic He-3, presumably during close solar approach, and B-7904 and Y-86720 seem also to have lost substantial proportions of radiogenic He-4 and Ar-40 cf. data in. Similarities in spectral reflectance data for C-, G-, B- and F- asteroids, for these meteorites and for heated Murchison samples suggest that thermally metamorphosed interior materials in these asteroids were excavated by impacts and re-deposited on them, forming their present surfaces. Establishment of the thermal metamorphic histories of carbonaceous chondrites, then, is essential to establishing the evolution and present-day nature of C-type and related asteroids.

Lipschutz, M. E.

2000-01-01

194

What Are Space Exposure Histories Telling Us about CM Carbonaceous Chondrites?  

NASA Technical Reports Server (NTRS)

Chondrites are chemically primitive and carbonaceous (C) chondrites are potentially the most primitive among them because they mostly escaped thermal metamor-phism that affected the other chondrite groups and ratios of their major, non-volatile and most of the volatile elements are similar to those of the Sun. Therefore, C chondrites are ex-pected to retain a good record of the origin and early history of the solar system. Carbonaceous chondrites are chemically differentiated from other chondrites by their high Mg/Si ratios and refractory elements, and have experienced various degrees of aqueous alteration. They are subdivided into eight subgroups (CI, CM, CO, CV, CK, CR, CB and CH) based on major element and oxygen isotopic ratios. Their elemental ratios spread over a wide range though those of ordinary and enstatite chondrites are relatively uniform. It is critical to know how many sepa-rate bodies are represented by the C chondrites. In this study, CM chondrites, the most abundant carbona-ceous chondrites, are examined. They are water-rich, chon-drule- and CAI-bearing meteorites and most of them are brec-cias. High-temperature components such as chondrules, iso-lated olivine and CAIs in CMs are frequently altered and some of them are replaced by clay minerals and surrounded by sul-fides whose Fe was derived from mafic silicates. On the basis of degrees of aqueous alteration, CMs have been classified into subtypes from 1 to 2, although Rubin et al. [1] assigned subtype 1 to subtype 2 and subtype 2 to subtype 2.6 using various petrologic properties. The classification is based on petrographic and mineralogic properties. For example, though tochilinite (2[(Fe, Mg, Cu, Ni[])S] 1.57-1.85 [(Mg, Fe, Ni, Al, Ca)(HH)2]) clumps are produced during aqueous alteration, they disappear and sulfide appears with increasing degrees of aqueous alteration. Cosmic-ray exposure (CRE) age measurements of CM chondrites reveal an unusual feature. Though CRE ages of other chondrite groups range from several Myr to tens of Myr, CMs exposure ages are not longer than 7 Myr with one-third of the CM having less than 1 Myr CRE age. For those CM chondrites that have CRE ages <1 Myr, there are two discern-able CRE peaks. Because a CRE age reflects how long a me-teorite is present as a separate body in space, the peaks pre-sumably represent collisional events on the parent body (ies) [2]. In this study we defined 4 distinct CRE age groups of CMs and systematically characterized the petrography in each of the 4 CRE age groups to determine whether the groups have significant petrographic differences, with such differences probably reflecting different parent body (asteroid) geological processing, or multiple original bodies.

Takenouchi, A.; Zolensky, Michael E.; Nishiizumi, K.; Caffee, M.; Velbel, M. A.; Ross, K.; Zolensky, P.; Le, L.; Imae, N.; Yamaguchi, A.; Mikouchi, T.

2013-01-01

195

Simulation of possible regolith optical alteration effects on carbonaceous chondrite meteorites  

NASA Technical Reports Server (NTRS)

As the spectral reflectance search continues for links between meteorites and their parent body asteroids, the effects of optical surface alteration processes need to be considered. We present the results of an experimental simulation of the melting and recrystallization that occurs to a carbonaceous chondrite meteorite regolith powder upon heating. As done for the ordinary chondrite meteorites, we show the effects of possible parent-body regolith alteration processes on reflectance spectra of carbonaceous chondrites (CC's). For this study, six CC's of different mineralogical classes were obtained from the Antarctic Meteorite Collection: two CM meteorites, two CO meteorites, one CK, and one CV. Each sample was ground with a ceramic mortar and pestle to powders with maximum grain sizes of 180 and 90 microns. The reflectance spectra of these powders were measured at RELAB (Brown University) from 0.3 to 2.5 microns. Following comminution, the 90 micron grain size was melted in a nitrogen controlled-atmosphere fusion furnace at an approximate temperature of 1700 C. The fused sample was immediately held above a flow of nitrogen at 0 C for quenching. Following melting and recrystallization, the samples were reground to powders, and the reflectance spectra were remeasured. The effects on spectral reflectance for a sample of the CM carbonaceous chondrite called Murchison are shown.

Clark, Beth E.; Fanale, Fraser P.; Robinson, Mark S.

1993-01-01

196

H/L chondrite LaPaz Icefield 031047 ? A feather of Icarus?  

SciTech Connect

Antarctic meteorite LAP 031047 is an ordinary chondrite composed of loosely consolidated chondritic fragments. Its petrography, oxygen isotopic composition and geochemical inventory are ambiguous and indicate an intermediate character between H and L chondrites. Petrographic indicators suggest LAP 031047 suffered a shock metamorphic overprint below {approx}10 GPa, which did not destroy its unusually high porosity of {approx}27 vol%. Metallographic textures in LAP 031047 indicate heating above {approx}700 C and subsequent cooling, which caused massive transformation of taenite to kamacite. The depletion of thermally labile trace elements, the crystallization of chondritic glass to microcrystalline plagioclase of unusual composition, and the occurrence of coarsely crystallized chondrule fragments is further evidence for post-metamorphic heating to {approx}700-750 C. However, this heating event had a transient character because olivine and low-Ca pyroxene did not equilibrate. Nearly complete degassing up to very high temperatures is indicated by the thorough resetting of LAP 031047's Ar-Ar reservoir {approx}100 {+-} 55 Ma ago. A noble gas cosmic-ray exposure age indicates it was reduced to a meter-size fragment at < 0.5 Ma. In light of the fact that shock heating cannot account for the thermal history of LAP 031047 in its entirety, we test the hypothesis that this meteorite belonged to the near-surface of an Aten or Apollo asteroid that underwent heating during orbital passages close to the Sun.

Wittmann, Axel; Friedrich, Jon M.; Troiano, Julianne; Macke, Robert J.; Britt, Daniel T.; Swidle, Timothy D.; Weirich, John R.; Rumble III, Douglas; Lasue, Jeremie; King, David A. (Central Florida); (Lunar and Planetary Institute); (CIW); (Ariz); (Fordham); (LANL)

2011-10-28

197

Evidence for a source of H chondrites in the outer main asteroid belt  

NASA Astrophysics Data System (ADS)

Aims: In this paper we report near-infrared spectroscopic observations of one of the largest potentially hazardous asteroids, (214869) 2007 PA8. Mineralogical analysis of this object was followed by the investigation of the dynamical delivery mechanism from its probable source region, based on long-term numerical integrations. Methods: The spectrum of (214869) 2007 PA8 was analysed using the positions of 1 ?m and 2 ?m bands and by curve-matching with RELAB meteorites spectra. Its dynamical evolution was investigated by means of a 200 000-year numerical integration in the past of 1275 clones followed to the source region. Results: (214869) 2007 PA8 has a very young surface with a composition more akin to H chondrites than to any other type of ordinary chondrite. It arrived from the outer Main Belt in the near-Earth space via the 5:2 mean motion resonance with Jupiter by eccentricity pumping. Identification of its source region far from (6) Hebe raises the possibility of the existence of a second parent body of the H chondrites that has a radically different post-accretion history. Future spectroscopic surveys in the 5:2 resonance region will most likely discover other asteroids with an H chondrite composition. Figure 2 is available in electronic form at http://www.aanda.org

Nedelcu, D. A.; Birlan, M.; Popescu, M.; B?descu, O.; Pricopi, D.

2014-07-01

198

Organic constituents of carbonaceous chondrites.  

PubMed

From a brief discussion of forms of meteorite carbon it is concluded that almost all the carbon in the carbonaceous chondrites is present as organic matter. Attempts to extract and identify this organic matter are then reviewed. It is shown that only 25 per cent has been extracted and only about 5 per cent chemically characterized. Of this 5 per cent, most is a complex mixture of hydroxylated aromatic acids together with various hydrocarbons of the paraffin, naphthene and aromatic series. Small amounts of amino acids, sugars and fatty acids also are present. The possible chemical nature of the major fraction is discussed. It is suggested to be a mixture of high-molecular weight aromatic and hydrocarbon polymers. Possible sources of contamination of the meteorites are described and evidence indicating a general lack of organic contaminants is presented. It is concluded, that most of the organic constituents are indigenous to the meteorites and are extra terrestrial in origin. Synthetic processes for the compounds are mentioned and it is concluded that the organic material is probably of abiogenic origin. A brief review on studies of "organized elements" contained within the meteorites is presented. Difficulties of identification are discussed and photographs of some microstructures of several carbonaceous chondrites are presented. No final conclusion about the nature of these objects is possible, but some appear to be various indigenous organic and mineral structures, while others are terrestrial contaminants. PMID:11881656

Briggs, M H; Mamikunian, G

1964-01-01

199

Carbonates in CM chondrites: Complex formational histories and comparison to carbonates in CI chondrites  

NASA Astrophysics Data System (ADS)

CM chondrites are primitive solar-system materials that have undergone high degrees of aqueous alteration, resulting in the formation of secondary minerals including carbonates. Two different carbonate minerals (calcite/aragonite and dolomite) together constitute 1.4-2.8 vol% of CM chondrites. In contrast, CI chondrites contain four different carbonate minerals: calcite/aragonite, dolomite, breunnerite, and siderite. CI chondrites have abundant dolomite, a mineral that seems to be absent in the most aqueously altered CM chondrites. In this study, carbonates in seven CM chondrites (Y-791198, LaPaz Icefield 04796, Cold Bokkeveld, Nogoya, Queen Alexandra Range 93005, Allan Hills 83100, and Meteorite Hills 01070) were studied petrographically and by electron microprobe. The results indicate that carbonate formation in CM chondrites differs from that in CI chondrites and is more complex than previously recognized. Our studies of CM chondrites indicate that (1) carbonates formed on the parent asteroid in an aqueous environment that gradually changed in composition, (2) at some stage, Ca and Mg activities in the environment were high enough to form metastable dolomite, and (3) dolomites disappeared in the most aqueously altered CM chondrites.

de Leuw, Simone; Rubin, Alan E.; Wasson, John T.

2010-04-01

200

Porosity and Permeability of Chondritic Materials  

NASA Technical Reports Server (NTRS)

We have investigated the porosity of a large number of chondritic interplanetary dust particles and meteorites by three techniques: standard liquid/gas flow techniques, a new, non-invasive ultrasonic technique, and image processing of backscattered images . The latter technique is obviously best suited to sub-kg sized samples. We have also measured the gas and liquid permeabilities of some chondrites by two techniques: standard liquid/gas flow techniques, and a new, non-destructive pressure release technique. We find that chondritic IDP's have a somewhat bimodal porosity distribution. Peaks are present at 0 and 4% porosity; a tail then extends to 53%. These values suggest IDP bulk densities of 1.1 to 3.3 g/cc. Type 1-3 chondrite matrix porosities range up to 30%, with a peak at 2%. The bulk porosities for type 1-3 chondrites have the same approximate range as exhibited by matrix, indicating that other components of the bulk meteorites (including chondrules and aggregates) have the same average porosity as matrix. These results reveal that the porosity of primitive materials at scales ranging from nanogram to kilogram are similar, implying similar accretion dynamics operated through 12 orders of size magnitude. Permeabilities of the investigated chondrites vary by several orders of magnitude, and there appears to be no simple dependence of permeability with degree of aqueous alteration, or chondrite type.

Zolensky, Michael E.; Corrigan, Catherine M.; Dahl, Jason; Long, Michael

1996-01-01

201

The Dresden (Ontario) H6 Chondrite, Part II: Classification Estimated Fireball Trajectory, and Possible Origin  

NASA Astrophysics Data System (ADS)

The Dresden (Ontario) meteorite fell in southwestern Ontario on the early evening of July 11, 1939. We re-examine this historic Canadian fall, consider the mineralogy, physical properties, and bulk chemistry of the meteorite, and estimate its trajectory and pre-atmospheric orbit based on visual accounts of the event. Mineralogical examination of several fragments of the meteorite reveals poor definition of chondrule margins, lack of glass, and the presence of minor feldspar, confirming Dresden (Ontario) to be an H6 ordinary chondrite. The bulk of the stone has undergone a low level of shock (S2) as indicated by generally clean extinction of silicate grains. A 12-g bulk sample of the Dresden (Ontario) main mass has elemental abundances that agree well with the H-chondrite average. The bulk density for Dresden (3.48+/-0.07 g/cm3) and porosity (4.9%) are also typical of H chondrites. Several accounts of the fall event constrain the Dresden fireball to have had a ground projection azimuth of ~050, passing from north of London, Ontario southwestwards toward Dresden. The tightly grouped strewnfield of fusion-encrusted fragments recovered ~10 km southwest of Dresden, Ontario suggests that the fireball trajectory was steep. Dark-flight simulations using the 050 azimuth best reproduce the recovered strewnfield distribution with an entry angle of >70°. The range of potential orbits derived from this inferred steep trajectory is consistent with previous orbits measured for meteorite-producing fireballs, and suggest that the Dresden meteoroid had an Apollo asteroid-type orbit, with a perihelion just inside that of the Earth's and a low-to-moderate inclination. The Dresden (Ontario) H6 chondrite is thus petrologically and dynamically similar to other H chondrites with known orbits. A comparison of the known H-chondrite orbits with a modelled debiased distribution of near-Earth objects indicates that the H chondrites were most likely delivered to the Earth via the v6 and the 3:1 resonances, thus strengthening the dynamical case for the linkage of H-chondrite meteorites with the S-type asteroid 6 Hebe as suggested by Gaffey et al. (1993).

McCausland, Phil J. A.; Brown, Peter G.; Wilson, Graham C.

2006-06-01

202

Origin of spinel-rich chondrules and inclusions in carbonaceous and ordinary chondrites  

NASA Technical Reports Server (NTRS)

The evaluation of three models of the origin of spinel-rich chondrules and inclusions presented here includes new calculations of the major-element refractory mineral condensation sequence from a gas of solar composition over a wide pressure interval. Condensation calculations show that spinel-rich chondrules did not crystallize from metastable liquid condensates, and that spinel-rich inclusions are not aggregates of refractory nebular condensates. It is proposed that spinel-rich objects are fractionated distillation residues of small aggregates of primitive dust that lost Ca, Si-rich partial melts by evaporation, ablation, or splashing during collisions. This model also explains why spinel-rich chondrules and inclusions (1) are usually smaller than melilite-rich chondrules and inclusions; (2) often have highly fractionated trace-element compositions; and (3) usually do not contain Pt-metal nuggets even when they are more enriched in the Pt-group metals than nugget-bearing melilite-rich objects.

Kornacki, A. S.; Fegley, B., Jr.

1984-01-01

203

Formation of Metal in GRO 95551 and Comparison to Ordinary Chondrites  

E-print Network

of the condensable material in the inner solar nebula, and hosts the siderophile elements. However, most of the metal to solar gas, but which does not appear to reflect equilibrium with the solar nebula (Campbell et al., 2002 to be consistent with condensation in a rapidly cooling gas of approximately solar composition (Weisberg et al

Campbell, Andrew

204

Cosmogenic Records in 18 Ordinary Chondrites from the Dar Al Gani Region, Libya. 1; Noble Gases  

NASA Technical Reports Server (NTRS)

In the last decade thousands of meteorites have been recovered from hot deserts in the Sahara and Oman. One of the main meteorite concentration surfaces in the Sahara is the Dar al Gani plateau in Libya, which covers a total area of 8000 km2. More than 1000 meteorites have been reported from this area. The geological setting, meteorite pairings and the meteorite density of the Dar al Gani (DaG) field are described in more detail in [1]. In this work we report concentrations of the noble gas isotopes of He, Ne, Ar as well as 84Kr and 132Xe in 18 DaG meteorites. In a separate paper we will report the cosmogenic radionuclides [2]. We discuss the thermal history and cosmic-ray exposure (CRE) history of these meteorites, and evaluate the effects of the hot desert environment on the noble gas record.

Schultz, L.; Franke, L.; Welten, K. C.; Nishiizumi, K.; Jull, A. J. T.

2003-01-01

205

Cosmogenic Records in 18 Ordinary Chondrites from the Dar Al Gani Region, Libya: I Noble Gases  

NASA Astrophysics Data System (ADS)

Noble gas results in 18 DaG meteorites show that contamination with atmospheric noble gases increases with the degree of weathering, whereas loss of cosmogenic 3He and radiogenic gases is not due to weathering but to solar or impact-related heating.

Schultz, L.; Franke, L.; Welten, K. C.; Nishiizumi, K.; Jull, A. J. T.

2003-03-01

206

Cosmogenic Records in 18 Ordinary Chondrites from the Dar Al Gani Region, Libya: II Radionuclides  

NASA Astrophysics Data System (ADS)

Radionuclide measurements of 18 DaG meteorites show that most have terrestrial ages <30 kyr, whereas DaG 343 has an age of 160 kyr. Five meteorites show evidence of a large pre-atmospheric size, while DaG 908 experienced a complex exposure history.

Welten, K. C.; Nishiizumi, K.; Finkel, R. C.; Hillegonds, D. J.; Jull, A. J. T.; Schultz, L.

2003-03-01

207

Evidence for primitive nebular components in chondrules from the Chainpur chondrite  

NASA Astrophysics Data System (ADS)

In view of the fact that the least equilibrated ordinary chondrites contain chondrules that have changed little since the time of their formation in the early solar system, and are therefore excellent indicators of the physical and chemical nature of the solar nebula, 36 chondrules were separated from the Chainpur chondrite and analyzed for 20 elements and petrographic properties. The dominant nebular components found are: (1) a mixture of metal and sulfide whose composition is similar to whole rock metal and sulfide, (2) Ir-rich metal, (3) olivine-rich silicates, (4) pyroxene-rich silicates, and possibly (5) a component containing the more volatile lithophiles. Although etching experiments confirm that chondrule rims are enriched in metal, troilite and moderately volatile elements relative to the bulk chondrules, a large fraction of the volatiles remains in the unetched interior.

Grossman, J. N.; Wasson, J. T.

1982-06-01

208

Tin in a chondritic interplanetary dust particle  

NASA Technical Reports Server (NTRS)

Submicron platey Sn-rich grains are present in chondritic porous interplanetary dust particle (IDP) W7029 A and it is the second occurrence of a tin mineral in a stratospheric micrometeorite. Selected Area Electron Diffraction data for the Sn-rich grains match with Sn2O3 and Sn3O4. The oxide(s) may have formed in the solar nebula when tin metal catalytically supported reduction of CO or during flash heating on atmospheric entry of the IDP. The presence of tin is consistent with enrichments for other volatile trace elements in chondritic IDPs and may signal an emerging trend toward nonchondritic volatile element abundances in chondritic IDPs. The observation confirms small-scale mineralogical heterogeneity in fine-grained chondritic porous interplanetary dust.

Rietmeijer, Frans J. M.

1989-01-01

209

Formation of opaque minerals in CK chondrites  

Microsoft Academic Search

The opaque minerals of 19 CK chondrites from Antarctica and the Nullarbor Region, Australia were studied mineralogically by optical and analytical methods. The most striking feature of the CK chondrites—indicating the oxidized nature of these meteorites—is the presence of magnetite as the most abundant opaque phase. It occurs in modal abundances between 1.2 and 8.1 vol.%, averaging about 4 vol.%.

T. Geiger; A. Bischoff

1995-01-01

210

Differentiated meteorites and the components of chondrites  

NASA Technical Reports Server (NTRS)

Findings are summarized from research conducted to develop a detailed classification of all kinds of meteorites in an effort to determine the conditions in the solar nebula, the processes that produced chemical fractionations in chondrites and formed chondrules, as well as ascertain the processes that occurred in the parent bodies of differentiated meteorites (which preserve a partial record of the chondritic materials from which they formed). Fractionation patterns within iron meteorite groups are analyzed.

Wasson, J. T.

1984-01-01

211

Chondritic models of 4 Vesta: Implications for geochemical and geophysical properties  

NASA Astrophysics Data System (ADS)

Simple mass-balance and thermodynamic constraints are used to illustrate the potential geochemical and geophysical diversity of a fully differentiated Vesta-sized parent body with a eucrite crust (e.g., core size and density, crustal thickness). The results of this analysis are then combined with data from the howardite-eucrite-diogenite (HED) meteorites and the Dawn mission to constrain Vesta's bulk composition. Twelve chondritic compositions are considered, comprising seven carbonaceous, three ordinary, and two enstatite chondrite groups. Our analysis excludes CI and LL compositions as plausible Vesta analogs, as these are predicted to have a negative metal fraction. Second, the MELTS thermodynamic calculator is used to show that the enstatite chondrites, the CV, CK and L-groups cannot produce Juvinas-like liquids, and that even for the other groups, depletion in sodium is necessary to produce liquids of appropriate silica content. This conclusion is consistent with the documented volatile-poor nature of eucrites. Furthermore, carbonaceous chondrites are predicted to have a mantle too rich in olivine to produce typical howardites and to have Fe/Mn ratios generally well in excess of those of the HEDs. On the other hand, an Na-depleted H-chondrite bulk composition is capable of producing Juvinas-like liquids, has a mantle rich enough in pyroxene to produce abundant howardite/diogenite, and has a Fe/Mn ratio compatible with eucrites. In addition, its predicted bulk-silicate density is within 100 kg m-3 of solutions constrained by data of the Dawn mission. However, oxidation state and oxygen isotopes are not perfectly reproduced and it is deduced that bulk Vesta may contain approximately 25% of a CM-like component. Values for the bulk-silicate composition of Vesta and a preliminary phase diagram are proposed.

Toplis, M. J.; Mizzon, H.; Monnereau, M.; Forni, O.; McSween, H. Y.; Mittlefehldt, D. W.; McCoy, T. J.; Prettyman, T. H.; De Sanctis, M. C.; Raymond, C. A.; Russell, C. T.

2013-11-01

212

New L Chondrites from Antofagasta, Chile  

NASA Astrophysics Data System (ADS)

Desert regions can be productive meteorite recovery locations because of low humidity, minimal ground cover and, in favorable situations, high prevailing winds to deflate surfaces. For these reasons we have made reconnaissance searches of a particularly arid Atacama Desert tract between Antofagasta and Mejillones, Chile (approx. 23 degrees 15'S, 70 degrees 30'W). One of us (EMR) had previously collected new ordinary chondrites from this same area, which has been named Pampa (a), (b), (c), and (e). The Pampa de Agua Blanca (PAB) chondrite is also apparently from this same area. In our brief 1991 reconnaissance we found additional specimens of (a) and (c). All of these meteorites have been found as multiple stones, necessitating pairing studies. Consequently, we examined our finds (a, b, c, and e), borrowed specimens from the Field Museum (a, b, PAB) and Robert Haag (c), and have performed the first detailed studies of the Pampa meteorites. Here we summarize results of these studies. Shock levels refer to the classification developed by Stoffler et al. (1991). PAMPA (a): This weathered meteorite is represented by several partially fusion-crusted fragments with a combined mass of approximately 380 g. No distinct chondrules are evident in thin section, although some chondrule fragments are present; considerable recrystallization is evident and plagioclase (Ab(sub)80Or5-Ab(sub)83Or(sub)5) is present as clear grains. Diopside and hydroxylapatite are also present. Olivine (Fo(sub)75.0 mean, 0.4% mean deviation-PMD) exhibits no shock effects. We classify Pampa (a) as L6, shock level 1. PAMPA (b): This is a weathered meteorite represented by numerous individual stones with a combined weight of approximately 10 kg. We examined thin sections from four individual stones of (b). A few distinct barred chondrules are evident in thin section, along with numerous chondrule and aggregate fragments. Olivine (Fo(sub)74.8 mean, 0.9 PMD) exhibits undulatory extinction, planar fractures, minor mosaicism and very rare (<25%) planar deformation features. We classify Pampa (b) as L4/5, shock level 4. PAMPA (c): This is a highly weathered, desert-varnished meteorite represented by numerous stones with a combined weight of approximately 25 kg. We examined sections from three stones of (c); the most notable feature of the meteorite is considerable darkening. Metal is almost entirely weathered. A few distinct barred and excentroradial chondrules are evident, along with numerous chondrule and aggregate fragments. Olivine (Fo(sub)75.3 mean, 0.8 PMD) exhibits undulatory extinction, planar fractures, mosaicism, planar deformation features, and melt veins and pockets. Some turbid glass is present. We classify Pampa (c) as L4, shock level 6. The classification of Pampa (c) given in the Meteoritical Bulletin (Graham, 1989) (L6) is incorrect. PAMPA (e): This is a weathered meteorite represented by numerous individual stones with an unknown total mass. No distinct chondrules are present in the single thin section available to us. Considerable recrystallization is evident, and clear plagioclase grains are present. Olivine (Fo(sub)75.0 mean, 0.07 PMD) exhibits no shock effects. We classify Pampa (e) as L6, shock level 1. PAMPA de AGUA BLANCA: This is a weathered meteorite represented by specimens totaling 10 g. No distinct chondrules are evident in thin section. Olivine (Fo(sub)75.2 mean, 0.2 PMD) exhibits undulatory extinction, planar fractures, minor mosaicism and very rare (<25%) planar deformation features. Clear plagioclase (Ab(sub)76Or(sub)8-Ab(sub)84Or(sub)5) grains are present. We classify Pampa de Agua Blanca as L6, shock level 4. We conclude by noting that the Atacama Desert in general, and the Antofagasta area in particular, appears to be a fruitful region for future meteorite searches. We note with curiosity that all chondrites found to date in the Antofogasta-Mejillones area have been of the L persuasion. METEORITE OLIVINE (Fo) PYROXENE (En) GLASS? SHOCK CLASS. MEAN PMD CaO MEAN PMD Pampa (a) L6 75.0 0.4 <=0.05 77.2 0.7 NO 1 Pampa (b) L

Martinez, R.; Zolensky, M.; Martinez de Los Rios, E.

1992-07-01

213

The LaPaz Icefield 04840 meteorite: Mineralogy, metamorphism, and origin of an amphibole- and biotite-bearing R chondrite  

NASA Astrophysics Data System (ADS)

The R chondrite meteorite LaPaz Icefield (LAP) 04840 is unique among metamorphosed, non-carbonaceous chondrites in containing abundant OH-bearing silicate minerals: ˜13% ferri-magnesiohornblende and ˜0.4% phlogopite by volume. Other minerals include olivine (Fo 62), orthopyroxene (En 69Fs 30Wo 1), albite (An 8Ab 90Or 2), magnetite, pyrrhotite, pentlandite, and apatite. Ferromagnesian minerals are rich in Fe 3+, as determined by Mössbauer spectrometry and electron microprobe chemical analyses. Fe 3+/Fe tot values are olivine ?5%, amphibole 80%, phlogopite 65%, and magnetite 42%. Mineral compositions are nearly constant across grains and the section, except for a small variability in amphibole compositions reflecting the edenite exchange couple ( ANa + IVAl ? A? + Si). These mineral compositions, the absence of Fe-Ni metal, and the oxygen isotope data support its classification as an R (Rumuruti) chondrite. LAP 04840 is classified as petrologic grade 5, based on the chemical homogeneity of its minerals, and the presence of distinctly marked chondrules and chondrule fragments in a fine-grained crystalline matrix. The mineral assemblage of LAP 04840 allows calculation of physical and chemical conditions at the peak of its metamorphism: T = 670 ± 60 °C from a amphibole-plagioclase thermometer; PO between 250 and 500 bars as constrained by the assemblage phlogopite + orthopyroxene + olivine + feldspar and the absence of diopside; P unconstrained; f at QFM + 0.5 log units; log(f/fO)?-5.8;log(f/fO)?-3.3;andlog(f/f)?-2.6. The hydrogen in LAP 04840 is very heavy, an average ?D value of +3660 ± 75‰ in the magnesiohornblende. Only a few known sources of hydrogen have such high ?D and are suitable sources for LAP 04840: ordinary chondrite phyllosilicates (as in the Semarkona chondrite), and insoluble organic matter (IOM) in ordinary chondrites and CR chondrites. Hydrogen from the IOM could have been released by oxidation, and then reacted with an anhydrous R chondrite (at high temperature), but it is not clear whether this scenario is correct.

McCanta, M. C.; Treiman, A. H.; Dyar, M. D.; Alexander, C. M. O.'D.; Rumble, D., III; Essene, E. J.

2008-12-01

214

Calcium-Aluminum-rich Inclusions in Chondritic Meteorites  

NASA Astrophysics Data System (ADS)

Calcium-aluminum-rich inclusions (CAIs) are submillimeter- to centimeter-sized clasts in chondritic meteorites, whose ceramic-like chemistry and mineralogy set them apart from other chondrite components. Since their first descriptions more than 30 years ago (e.g., Christophe Michel-Lévy, 1968), they have been the objects of a vast amount of study. At first, interest centered on the close similarity of their mineralogy to the first phases predicted by thermodynamic calculations to condense out of a gas of solar composition during cooling from very high temperatures (e.g., Lord, 1965; Grossman, 1972). Immediately thereafter, CAIs were found to be extremely old (4.56 Ga) and to possess unusual isotopic compositions (in particular, in magnesium and oxygen) suggestive of a presolar dust component. In short, they appear to be the oldest and most primitive objects formed in the infant solar system.In the late 1980s (e.g., MacPherson et al., 1988), the attention of most workers in the field was focused on understanding the petrogenesis and isotopic compositions of CAIs within a relatively restricted number of chondrite varieties. Much has changed since then. We now have extended our data sets beyond CV and CM chondrites to CAIs from ordinary, enstatite, and a wider range of carbonaceous chondrites. Out of this has emerged an ironic fact: the large centimeter-sized CAI "marbles" (the so-called type Bs; see below) that are so prominent in CV chondrites, and upon which so many of the original concepts were based owing to the abundance and availability of material from the Allende meteorite, turn out to be the exceptions rather than the norm. Indeed, we now know that the Allende parent body itself experienced so much postaccretion reprocessing that its CAIs reveal only a murky picture of the early solar nebula. Another profound change since 1988 has been the development of ion microprobe technology permitting microanalysis of oxygen isotopes within standard petrographic thin sections. One of the debates raging in 1988 centered on the difficulty of making CAIs at the distance of the asteroid belt where the host chondrites presumably accreted. Since then, a combination of isotopic (especially beryllium-boron and oxygen) evidence and theoretical modeling have suggested the interesting possibility that CAIs all formed very close to the infant sun and were later dispersed out to the respective chondrite accretion regions. Yet another difference from 1988 is that the science of meteoritics has matured past the point where workers study CAIs without consideration of other chondritic components, most notably chondrules. Bulk composition differences aside, CAIs and chondrules are both products of very high temperature events in the earliest solar system. Like chondrules, many CAIs apparently solidified from partially to completely molten droplets. Moreover, chondrules and CAIs both have far more complex histories than was generally recognized in the late 1980s: both may have experienced multiple melting episodes, followed by prolonged nebular and/or asteroidal modification due to gaseous or liquid interactions and reheating as a result of shock processes. In short, although CAIs are still recognized as being the oldest objects formed in our solar system and possessing isotopic traces of the presolar dust from which they ultimately formed, they are a long way from being the primitive condensates they were once thought to be. Rather than stressing the unusual isotopic characteristics of CAIs and the presolar implications, this chapter will instead treat CAIs as probes of the earliest solar system that reveal the nature of the high-temperature events, their chronology, and the likely locales where such events occurred.This chapter is not, and does not pretend to be, an exhaustive review of the sum of knowledge about CAIs. Indeed, so much new data have been generated since 1988, especially isotopic data from an ever-growing number of sophisticated ion microprobe labs, that it would far beyond the space limitations of this chapter to a

MacPherson, G. J.

2003-12-01

215

In Situ Investigation of Preirradiated Olivines in CM Chondrites  

NASA Astrophysics Data System (ADS)

Most CM chondrites are breccias that contain fragments of primary rock representing densely packed agglomerates of chondrules, CAIs, etc., all of which are mantled by thick layers of fine-grained mineral dust [1]. These dust mantles seem to be the result of dust sampling by the various components during their isolated existence in the solar nebula prior to the formation of the CM parent body [1]. Metzler et al. [1] concluded that these rock fragments are well-preserved remnants of the freshly accreted CM parent body(ies). There is an opposing hypothesis that favors an origin of the dust mantles in an active regolith on the CM parent body [e.g., 2]. A list of arguments against the latter view is given by Metzler et al. [1], including a hint at the absence of solar-wind-implanted gases in dust mantles and in fragments of primary rock. In analogy to brecciated ordinary chondrites and lunar breccias, the most probable residence of the solar gases in CM chondrites is their clastic matrix. The same holds for track-rich olivines that were observed in CM chondrites. The occurrence of these grains in the clastic matrix and their absence in the primary rock would give an additional argument for the idea of a dust mantle origin in the solar nebula rather than in a planetary regolith. To answer this important question, mosaics of backscattered electron images of several large polished thin sections of Murchison and Cold Bokkeveld were prepared. The thin sections (1.5-5 cm^2 each) were etched in a WN solution [3] for about 4 hr to reveal the heavy ion tracks in olivines. Results: The background GCR track density produced during meteoroid transit is on the order of 10^4 tracks/cm^2, as was previously observed by [4]. Following the definition given by Goswami and Lal [4], olivines with track densities >10^5 tracks/cm^2 were classified as preirradiated grains and were found in both meteorites in a very small quantity. In both meteorites, 39 preirradiated isolated olivine grains were found in the clastic matrix, whereas the investigated fragments of primary rock do not contain preirradiated olivines. In Murchison about 1.8% (15 out of 850 investigated grains) of the isolated olivines in the clastic matrix show high track densities in the range between 1.9 x 10^6 and >5 x 10^7, comparable to the results of Goswami and co-workers [4,5]. Both Fe-poor and Fe-rich olivines with grain sizes between 40 and 710 micrometers were found to be preirradiated. Track gradients were found in 33% of these olivines, which is very similar to the values obtained by Goswami and Lal [4] and identical to those obtained by MacDougall and Phinney [6]. About 0.4% (2 out of 530) of the investigated olivine-bearing chondrules and chondrule fragments are preirradiated. In the case of Cold Bokkeveld, 3.7% (24 out of 650) of the isolated olivines show high track densities. Thirteen of these 24 grains were found to be concentrated in a distinct inclusion (1 x 4 mm) that is characterized by its elongated appearence and clastic fabric. The track densities of its preirradiated olivines show a very narrow range, indicating a common irradiation history of these grains. The petrography of this inclusion is currently under investigation. Conclusions: Track-rich (preirradiated) olivines in CM chondrites occur exclusively in the clastic matrix of these meteorites, comparable to observations in brecciated ordinary chondrites. Fragments of primary rock in CM chondrites do not contain solar-wind-implanted gases [1] or preirradiated grains. This confirms the view that the dust mantles around various components of these rocks are the products of dust accretion in the solar nebula rather than of regolith processes on the parent body surface. References: [1] Metzler K. et al. (1992) GCA, 56, 2873. [2] Kerridge J. (1992) personal communication. [3] Krishnaswami S. et al. (1971) Science, 174, 287. [4] Goswami J. N. and Lal D.(1979) Icarus, 40, 510. [5] Goswami J. N. and MacDougall J. D. (1983) Proc. LPSC 13th, in JGR, 88, A755. [6] MacDougall J. D. and Phinney D. (1977) Proc. LS

Metzler, K.

1993-07-01

216

The Compositional Classification of Chondrules and the Petrologic Type of an Especially Primitive H Chondrite  

NASA Astrophysics Data System (ADS)

While LL chondrites of petrologic type <3.4 are relatively common, it has been only recently that a few H chondrites of type <3.4 have been reported. One of them is the heavily weathered Roosevelt County 075 [1]. Weathering and the lack of equilibration make classification uncertain, but it is probably an H chondrite. Weathering also makes it very difficult to assign a petrologic type. For example, removal of the weathering products by acid washing increased the TL sensitivity of RC075 by a factor of ~7, equivalent to a change in petrologic type estimate from 3.0 to 3.3, a major difference. The compositional classification scheme for chondrules [2,3] summarizes considerably more information than previous schemes [4-6], not least being that it tracks metamorphic effects as well as more thoroughly monitoring primary chondrule differences. It is also very easy to apply and almost 100% of the chondrules can be classified. As an example of its utility, we here show that application of the scheme to the chondrules in RC075 provides the best means of determining the petrologic type of this highly weathered, but very important, unequilibrated chondrite. The compositional classification scheme for chondrules divides them into eight classes (A1, A2, A3, A4, A5, B1, B2, B3) on the basis of the composition of the two major phases (phenocrysts and mesostasis) [2,3]. Among the changes that occur during metamorphism, olivines lose CaO and acquire uniform FeO, while the mesostases acquire oligoclase compositions having originally included compositions that were SiO2 rich (the B series), CaO rich (the A series), and Na2O rich (A5). These changes give rise to CL properties that can be used as an alternative to microprobe analysis and which, like microprobe data, are insensitive to weathering. Thus we were able to assign all of the almost 100 chondrules present in a 7 x 5-mm section of RC075 to compositional classes. The results are shown in Fig. 1, along with similar data from [3]. The relative abundance and classes of chondrules present provides an excellent method of assigning petrographic type. The relative abundance of group B chondrules in RC075 is less than Semarkona (3.0), and comparable with the higher types, while the abundance of A5 chondrules is comparable to that in Krymka (3.1) and intermediate between that in Semarkona and Chainpur (3.4). Most significantly, the fraction of A1 chondrules is very large and comparable (within error) to that of Semarkona, while the large number of group A3 chondrules is comparable only to Krymka. Apparently, RC075 is intermediate to Semarkona and Chainpur and comparable to Krymka in its petrologic type. McCoy et al. [1] report means ranging from 0.07 to 7.2 mol% Fa and 0.11 to 0.36 wt% CaO for olivine in six type-IA chondrules and 12.3-20.2 mol% Fa for five type-II chondrules in RC075 [1]. Four of the type IA chondrules resembled those of Semarkona in olivine composition (<2 mol% Fa). Unlike the compositional classification scheme, which leads fairly simply to unambiguous petrologic type assignment, it seems difficult to assign RC075 to a petrologic type on the basis of olivine compositions and texture alone. Other advantages of the new scheme are (1) that it applies to individual chondrules and makes no assumptions about average response of chondrules to metamorphism; (2) it is insensitive to brecciation, which is common in UOC [7]; and (3) it is quantitative, and does not require subjective evaluations of texture, although textural descriptions may be used with the compositional class (just as they are for chondrites). The compositional classification scheme is certainly subject to improvement(e.g. class A5, both in type 3 and higher types). However, as it currently stands the scheme clearly provides the best way of not only describing individual chondrules, but of assessing primary chondrule properties and the extent of changes experienced during metamorphism. Thus it provides the best method for assigning the weathered and highly unequilibrated RC075 meteorite to a petrologic ty

Sears, D. W. G.; Huang, S.; Benoit, P. H.

1993-07-01

217

Determining the Relative Extent of Alteration in CM Chondrites.  

National Technical Information Service (NTIS)

The aqueous alteration of CM chondrites provides a record of the processes attending the earliest stages of parent body evolution. However, resolving the alteration pathways of chondritic evolution requires a means for distinguishing the relative extent o...

L. B. Browning, H. Y. Mcsween, M. Zolensky

1993-01-01

218

A strongly hydrated microclast in the Rumuruti chondrite NWA 6828: Implications for the distribution of hydrous material in the solar system  

NASA Astrophysics Data System (ADS)

Hydrous carbonaceous microclasts are by far the most abundant foreign fragments in stony meteorites and mostly resemble CI1-, CM2-, or CR2-like material. Their occurrence is of great importance for understanding the distribution and migration of water-bearing volatile-rich matter in the solar system. This paper reports the first finding of a strongly hydrated microclast in a Rumuruti chondrite. The R3-6 chondrite Northwest Africa 6828 contains a 420 × 325 ?m sized angular foreign fragment exhibiting sharp boundaries to the surrounding R-type matrix. The clast is dominantly composed of magnetite, pyrrhotite, rare Ca-carbonate, and very rare Mg-rich olivine set in an abundant fine-grained phyllosilicate-rich matrix. Phyllosilicates are serpentine and saponite. One region of the clast is dominated by forsteritic olivine (Fa<2) supported by a network of interstitial Ca-carbonate. The clast is crosscut by Ca-carbonate-filled veins and lacks any chondrules, calcium-aluminum-rich inclusions, or their respective pseudomorphs. The hydrous clast contains also a single grain of the very rare phosphide andreyivanovite. Comparison with CI1, CM2, and CR2 chondrites as well as with the ungrouped C2 chondrite Tagish Lake shows no positive match with any of these types of meteorites. The clast may, thus, either represent a fragment of an unsampled lithology of the hydrous carbonaceous chondrite parent asteroids or constitute a sample from an as yet unknown parent body, maybe even a comet. Rumuruti chondrites are a unique group of highly oxidized meteorites that probably accreted at a heliocentric distance >1 AU between the formation regions of ordinary and carbonaceous chondrites. The occurrence of a hydrous microclast in an R chondrite attests to the presence of such material also in this region at least at some point in time and documents the wide distribution of water-bearing (possibly zodiacal cloud) material in the solar system.

Greshake, Ansgar

2014-05-01

219

Summary of several recent chondrite finds from the Texas Panhandle  

NASA Technical Reports Server (NTRS)

Eleven recent chondrite finds from the Texas Panhandle have been examined and classified according to mineralogical and petrological criteria: five H's, five L's, and one LL chondrite. Five are distinct from nearby finds, while three remain ambiguous and three are related to previously reported chondrites. In addition, data are provided to classify the Muleshoe, Silverton, and Vigo Park chondrites, all of which were previously undescribed in the literature.

Sipiera, P. S.; Olsen, E. J.; Eatough, D. L.; Dod, B. D.

1983-01-01

220

146Sm-142Nd systematics measured in enstatite chondrites reveals a heterogeneous distribution of 142Nd in the solar nebula  

PubMed Central

The short-lived 146Sm–142Nd chronometer (T1/2 = 103 Ma) is used to constrain the early silicate evolution of planetary bodies. The composition of bulk terrestrial planets is then considered to be similar to that of primitive chondrites that represent the building blocks of rocky planets. However for many elements chondrites preserve small isotope differences. In this case it is not always clear to what extent these variations reflect the isotope heterogeneity of the protosolar nebula rather than being produced by the decay of parent isotopes. Here we present Sm–Nd isotopes data measured in a comprehensive suite of enstatite chondrites (EC). The EC preserve 142Nd/144Nd ratios that range from those of ordinary chondrites to values similar to terrestrial samples. The EC having terrestrial 142Nd/144Nd ratios are also characterized by small 144Sm excesses, which is a pure p-process nuclide. The correlation between 144Sm and 142Nd for chondrites may indicate a heterogeneous distribution in the solar nebula of p-process matter synthesized in supernovae. However to explain the difference in 142Nd/144Nd ratios, 20% of the p-process contribution to 142Nd is required, at odds with the value of 4% currently proposed in stellar models. This study highlights the necessity of obtaining high-precision 144Sm measurements to interpret properly measured 142Nd signatures. Another explanation could be that the chondrites sample material formed in different pulses of the lifetime of asymptotic giant branch stars. Then the isotope signature measured in SiC presolar would not represent the unique s-process signature of the material present in the solar nebula during accretion. PMID:21515828

Gannoun, Abdelmouhcine; Boyet, Maud; Rizo, Hanika; El Goresy, Ahmed

2011-01-01

221

The Campos Sales Brazil meteorite: A lightly shocked L5 chondrite fall  

NASA Astrophysics Data System (ADS)

The Campos Sales meteorite fell close to the town of Campos Sales, in the northeastern Brazilian state of Ceara (72' deg S; 4010' deg W), on 31 January 1991, at 10:00 PM (local time). Several fragments were recovered from an area estimated to be 3 km ? 1 km. The stone is an ordinary chondrite, L5 ( Fa25.0 and Fs21.6 ), lightly shocked, S1. Metal phases present are kamacite, tetrataenite and antitaenite. Noble gases He, Ne, Ar, Kr and Xe have been analyzed in 2 bulk samples of Campos Sales. All exposure ages based on determination of cosmogenic 3He, 21Ne, 38Ar, 83Kr, 126Xe abundances and on cosmogenic 81Kr/83Kr ratio agree well, suggesting no gas loss during cosmic-ray exposure. The cosmic-ray exposure age is 23.3 +- 1.0 Ma, which falls in the range observed for L5 chondrites (20-30 Ma). The gas-retention ages indicate He loss that must have occurred prior to or during ejection from the L-chondrite parent body.

Scorzelli, R. B.; Michel-Levy, M. Christophe; Gilabert, E.; Lavielle, B.; Souza Azevedo, I.; Vieira, V. W.; Costa, T. V. V.; Araujo, M. A. B.

1998-11-01

222

Workshop on Parent-Body and Nebular Modification of Chondritic Materials  

NASA Technical Reports Server (NTRS)

The purpose of the workshop was to advance our understanding of solar nebula and asteroidal processes from studies of modification features in chondrites and interplanetary dust particles. As reflected in the program contained in this volume, the workshop included five regular sessions, a summary session, and a poster session. Twenty-three posters and 42 invited and contributed talks were presented. Part 1 of this report contains the abstracts of these presentations. The focus of the workshop included: (1) mineralogical, petrologic, chemical, and isotopic observations of the alteration mineralogy in interplanetary dust particles, ordinary and carbonaceous chondrites, and their components (Ca-Al-rich inclusions, chondrules, and matrix) to constrain the conditions and place of alteration; (2) sources of water in chondrites; (3) the relationship between aqueous alteration and thermal metamorphism; (4) short-lived radionuclides, AI-26, Mn-53, and I-129, as isotopic constraints on timing of alteration; (5) experimental and theoretical modeling of alteration reactions; and (6) the oxidation state of the solar nebula. There were approximately 140 participants at the workshop, probably due in part to the timeliness of the workshop goals and the workshop location. In the end few new agreements were achieved between warring factions, but new research efforts were forged and areas of fruitful future exploration were highlighted. Judged by these results, the workshop was successful.

Krot, A. N. (Editor); Zolensky, M. E. (Editor); Scott, E. R. D. (Editor)

1997-01-01

223

Degree of Weathering of H-Chondrites From Frontier Mountain, Antarctica  

NASA Technical Reports Server (NTRS)

One of the factors that determines the survival time of meteorites on the Earth's surface is the rate of weathering. For meteorites from hot deserts, a clear correlation is found between the degree of weathering, and the terrestrial age, but for Antarctic meteorites this correlation is weak or even lacking. The lack of a clear correlation can partly be attributed to the two-stage history of many Antarctic meteorites, which spend part of their terrestrial residence time in the ice before they are exposed on the ice. Recently, it was found that for Lewis Cliff (LEW) meteorites local conditions on the ice play an important role in the weathering process. This work focuses on weathering effects in ordinary chondrites from Frontier Mountain (FRO), North Victoria Land. Although most FRO meteorites were classified as weathering category A or B, many are contaminated with terrestrial uranium, deposited from meltwater. This suggests that weathering plays a more significant role than the qualitative A-B-C weathering index indicates. We therefore determined the degree of weathering more quantitatively, by deriving the amount of oxidized metal from the concentrations of Fe and Ni in the nonmagnetic fraction of 23 H-chondrites and 1 L-chondrite The results will be compared with those of LEW meteorites and will be discussed in terms of terrestrial age and location of find on the ice.

Welten, K. C.; Nishiizumi, K.

2000-01-01

224

Degree of Weathering of H-Chondrites from Frontier Mountain, Antarctica  

NASA Technical Reports Server (NTRS)

One of the factors that determines the survival time of meteorites on the Earth's surface is the rate of weathering. For meteorites from hot deserts, a clear correlation is found between the degree of weathering and the terrestrial age, but for Antarctic meteorites this correlation is weak or even lacking. The lack of a clear correlation can partly be attributed to the two-stage history of many Antarctic meteorites, which spend part of their terrestrial residence time in the ice before they are exposed on the ice. Recently, it was found that for Lewis Cliff (LEW) meteorites local conditions on the ice play an important role in the weathering process. This work focuses on weathering effects in ordinary chondrites from Frontier Mountain (FRO), North Victoria Land. Although most FRO meteorites were classified as weathering category A or B, many are contaminated with terrestrial uranium, deposited from meltwater. This suggests that weathering plays a more significant role than the qualitative A-B-C weathering index indicates. We therefore determined the degree of weathering more quantitatively, by deriving the amount of oxidized metal from the concentrations of Fe and Ni in the nonmagnetic fraction of 23 H-chondrites and 1 L-chondrite. The results will be compared with those of LEW meteorites and will be discussed in terms of terrestrial age and location of find on the ice.

Welten, K. C.; Nishiizumi, Kunihiko

1999-01-01

225

Early Solar System hydrothermal activity in chondritic asteroids on 1-10-year timescales.  

PubMed

Chondritic meteorites are considered the most primitive remnants of planetesimals from the early Solar System. As undifferentiated objects, they also display widespread evidence of water-rock interaction on the parent body. Understanding this history has implications for the formation of planetary bodies, the delivery of water to the inner Solar System, and the formation of prebiotic molecules. The timescales of water-rock reactions in these early objects, however, are largely unknown. Here, we report evidence for short-lived water-rock reactions in the highly metamorphosed ordinary chondrite breccia Villalbeto de la Peña (L6). An exotic clast (d = 2cm) has coexisting variations in feldspar composition and oxygen isotope ratios that can only result from hydrothermal conditions. The profiles were modeled at T = 800 °C and P(H(2)O) = 1 bar using modified grain-boundary diffusion parameters for oxygen self-diffusion and reaction rates of NaSiCa(-1)Al(-1) exchange in a fumarole. The geochemical data are consistent with hydrothermal activity on the parent body lasting only 1-10 y. This result has wide-ranging implications for the geological history of chondritic asteroids. PMID:23093668

Dyl, Kathryn A; Bischoff, Addi; Ziegler, Karen; Young, Edward D; Wimmer, Karl; Bland, Phil A

2012-11-01

226

Olivine in terminal particles of Stardust aerogel tracks and analogous grains in chondrite matrix  

NASA Astrophysics Data System (ADS)

The dearth of both major and minor element analyses of anhydrous silicate phases in chondrite matrix has thus far hindered their comparison to the Wild 2 samples. We present 68 analyses of olivine (Fa0-97) in the coarse-grained terminal particles of Stardust aerogel tracks and a comprehensive dataset (>103 analyses) of analogous olivine grains (5-30 ?m) isolated in CI, CM, CR, CH, CO, CV3-oxidized, CV3-reduced, C3-ungrouped (Acfer 094 and Ningqiang), L/LL 3.0-4, EH3, and Kakangari chondrite matrix. These compositions reveal that Wild 2 likely accreted a diverse assortment of material that was radially transported from various carbonaceous and ordinary chondrite-forming regions. The Wild 2 olivine includes amoeboid olivine aggregates (AOAs), refractory forsterite, type I and type II chondrule fragments and/or microchondrules, and rare relict grain compositions. In addition, we have identified one terminal particle that has no known compositional analog in the meteorite record and may be a signature of low-temperature, aqueous processing in the Kuiper Belt. The generally low Cr content of FeO-rich olivine in the Stardust samples indicates that they underwent mild thermal metamorphism, akin to a petrologic grade of 3.05-3.15.

Frank, David R.; Zolensky, Michael E.; Le, Loan

2014-10-01

227

Extraterrestrial Nucleobases in Carbonaceous Chondrites  

NASA Astrophysics Data System (ADS)

Nucleobases in Carbonaceous Chondrites Z. Martins (1), O. Botta (2), M. L. Fogel (3), M. A. Sephton (4), D. P. Glavin (2), J. S. Watson (5), J. P. Dworkin (2), A. W. Schwartz (6) and P. Ehrenfreund (1,6). (1) Astrobiology Laboratory, Leiden Institute of Chemistry, Leiden, The Netherlands, (2) NASA Goddard Space Flight Center, Goddard Center for Astrobiology, Greenbelt, MD, USA, (3) GL, Carnegie Institution of Washington, Washington DC, USA, (4) Impacts and Astromaterials Research Centre, Department of Earth Science and Engineering, South Kensington Campus, Imperial College, London, UK, (5) Planetary and Space Sciences Research Institute, The Open University, Walton Hall, Milton Keynes, UK, (6) Radboud University Nijmegen, Nijmegen, The Netherlands. E-mail: z.martins@chem.leidenuniv.nl/Phone:+31715274440 Nucleobases are crucial compounds in terrestrial biochemistry, because they are key components of DNA and RNA. Carbonaceous meteorites have been analyzed for nucleobases by different research groups [1-5]. However, significant quantitative and qualitative differences were observed, leading to the controversial about the origin of these nucleobases. In order to establish the origin of these compounds in carbonaceous chondrites and to assess the plausibility of their exogenous delivery to the early Earth, we have performed formic acid extraction of samples of the Murchison meteorite [6], followed by an extensive purification procedure, analysis and quantification by high-performance liquid chromatography with UV absorption detection and gas chromatography-mass spectrometry. Our results were qualitatively consistent with previous results [3, 4], but showed significant quantitative differences. Compound specific carbon isotope values were obtained, using gas chromatography-combustion- isotope ratio mass spectrometry. A soil sample collected in the proximity of the Murchison meteorite fall site was subjected to the same extraction, purification and analysis procedure. Our stable carbon isotope measurements clearly demonstrate that the nucleobases in the Murchison meteorite are indigenous to the meteorite, and clearly differ from the values determined for the terrestrial nucleobases measured in the soil collected at the impact site. These results support the hypothesis that nucleobases were exogenously delivered to the early Earth, and may have been important for the prebiotic chemistry on our young planet. With regard to the detection of traces of life on other planets such as Mars it is essential to characterize organic materials that have been exogenously delivered to the early planets. The analysis of the composition and isotopic fractionation of extraterrestrial material using complementary techniques can provide crucial insights into the formation of our Solar System, extraterrestrial delivery processes and subsequent addition and incorporation into the carbonaceous material available on the young planets. Ultimately, these parameters form an essential reference point for interpreting biosignatures that may be left in the ancient rock record on a planetary body. References: [1] Hayatsu R. et al. 1975. Geochimica et Cosmochimica Acta 39: 471- 488. [2] Folsome C. E. et al. 1971. Nature 232: 108-109. [3] Stoks P. G. & Schwartz A. W. 1979. Nature 282: 709-710. [4] Stoks P.G. & Schwartz A. W. 1981. Geochimica et Cosmochimica Acta 45: 563-569. [5] Shimoyama A. et al. 1990. Geochemical Journal 24: 343-348. [6] Martins Z. et al. 2004. Meteoritics & Planetary Science 39: A5145. 2

Martins, Z.; Botta, O.; Fogel, M.; Sephton, M.; Glavin, D.; Watson, J.; Dworkin, J.; Schwartz, A.; Ehrenfreund, P.

228

Experimental vaporization of the Holbrook chondrite  

NASA Technical Reports Server (NTRS)

The vapor phase composition obtained by heating samples of the Holbrook L6 chondrite to 1300 C was determined quantitatively by Knudsen cell-quadrupole mass spectrometry. Maximum observed vapor pressures, produced at 1200 C, are reported for Na, K, Fe, and Ni, and the implications of the Na/K ratio are considered. The Fe and Ni data are discussed with attention to their migration in individual equilibrated chondrites. S2 (with minor SO2), H2O, and CO2 were also present in the high-temperature gas phase. Vesicles formed by the release of intrinsically derived volatiles are compared with vesicles in the Ibitira eucrite. Chondrite evolution is briefly discussed.

Gooding, J. L.; Muenow, D. W.

1977-01-01

229

Pb Pb dating constraints on the accretion and cooling history of chondrites  

NASA Astrophysics Data System (ADS)

We have analyzed the Pb isotopic compositions of whole-rocks and various components (CAIs, chondrules, and/or mineral separates) of two carbonaceous chondrites, Allende (CV3) and Murchison (CM2), and nine ordinary chondrites, Sainte Marguerite (H4), Nadiabondi and Forest City (H5), Kernouvé (H6), Bjurböle (L/LL4), Elenovka and Ausson (L5), Tuxtuac (LL5), and Saint-Séverin (LL6) by MC-ICP-MS. Three CAI fractions from Allende define an isochron with an age of 4568.1 ± 9.4 Ma (MSWD = 0.08) and plot on the same isochron as fragments of the Efremovka inclusion E60 analyzed by Amelin et al. [Amelin, Y., Krot, A. N., Hutcheon, I. D., and Ulyanov, A. A. (2002a). Lead isotopic ages of chondrules and calcium-aluminum-rich inclusions. Science297, 1679-1683]. When these two groups of samples are combined, the isochron yields an age of 4568.5 ± 0.5 (MSWD = 0.90), which is our best estimate of the age of the Solar System. Chondrules and pyroxene-olivine fractions from the ordinary chondrites yield ages that reflect the blocking of Pb isotope equilibration with the nebular gas. The combination of these ages with the corresponding metamorphic phosphate ages provides constraints on the thermal history of the different chondrite parent bodies. Among the H chondrites, Sainte Marguerite cooled to below ˜1100 K within a few My at 4565 Ma and to ˜800 K at 4563 Ma. Nadiabondi appears to have experienced a slightly more protracted cooling history with the corresponding interval lasting from 4559 to 4556 Ma. The data from Forest City and Kernouvé show evidence of late-stage perturbation with resulting U/Pb fractionation. Likewise, Pb isotopes in Tuxtuac (LL5) record a cooling history lasting from ˜4555 to 4544 Ma, which may indicate that the cooling history for the LL parent body was more prolonged than for the H parent body. We suggest a thermal evolution model for the growth of the planetary bodies based on the release of radiogenic heat from 26Al and 60Fe. This model incorporates the accretion rate, which determines the time at which the radiogenic heat becomes efficiently trapped, and the terminal size of the parent body, which controls its overall thermal inertia. The parent bodies of carbonaceous chondrites, which show little indication of metamorphic transformation, collect cooler nebular material at a relatively late stage. Small asteroids of ˜10-50 km radius accreting within 1-3 My could be the parent bodies of H and LL chondrites. The parent body of the L chondrites is likely to be a larger asteroid ( r > 100 km) or possibly the product of collisions of smaller planetary bodies.

Bouvier, Audrey; Blichert-Toft, Janne; Moynier, Frédéric; Vervoort, Jeffrey D.; Albarède, Francis

2007-03-01

230

Mineralogy and matrix composition of CR chondrites Renazzo and EET 87770, and ungrouped chondrites Essebi and MAC 87300  

NASA Technical Reports Server (NTRS)

The fine-grained mineralogy of the matrix of two CR chondrites, Renazzo and EET 87770, and the ungrouped (but possible related) Essebi and MAC 87300 chondrites was characterized using standard microprobe (focussed beam) and transmission electron microscopy (TEM) techniques (using ultramicrotomed sections). These results are compared to previously obtained results for 31 other carbonaceous chondrites.

Zolensky, Michael E.

1991-01-01

231

Non-nebular origin of dark mantles around chondrules and inclusions in CM chondrites  

NASA Astrophysics Data System (ADS)

Our examination of nine CM chondrites that span the aqueous alteration sequence leads us to conclude that compact dark fine mantles surrounding chondrules and inclusions in CM chondrites are not discrete fine-grained rims acquired in the solar nebula as modeled by Metzler et al. [Accretionary dust mantles in CM chondrites: evidence for solar nebula processes. Geochim. Cosmochim. Acta56, 1992, 2873-2897]. Nebular processes that lead to agglomeration produce materials with porosities far higher than those in the dark mantles. We infer that the mantles were produced from porous nebular materials on the CM parent asteroid by impact-compaction (a process that produces the lowest porosity adjacent to chondrules and inclusions). Compaction was followed by aqueous alteration that formed tochilinite, serpentine, Ni-bearing sulfide, and other secondary products in voids in the interchondrule regions. Metzler et al. reported a correlation between mantle thickness and the radius of the enclosed object. In Yamato 791198 we find no correlation when all sizes of central objects and dark lumps are included but a significant correlation ( r2 = 0.44) if we limit consideration to central objects with radii >35 ?m; a moderate correlation is also found in QUE 97990. We suggest that impact-induced shear of a plum-pudding-like precursor produced the observed "mantles"; these were shielded from comminution during impact events by the adjacent stronger chondrules and inclusions. Some mantles in CM chondrites with low degrees of alteration show distinct layers that may largely reflect differences in porosity. Typically, a gray, uniform inner layer is surrounded by an outer layer consisting of darker silicates with BSE-bright speckles. The CM-chondrite objects characterized as "primary accretionary rocks" by Metzler et al. did not form in the nebula, but rather on the parent body. The absence of solar-flare particle tracks and solar-wind-implanted rare gases in these clasts reflect their lithified nature and low surface/volume ratios during the period when they resided in the regolith and were subject to irradiation by solar particles. The clasts are analogous to the light-colored metamorphosed clasts in ordinary-chondrite regolith breccias (which also lack solar-flare particle tracks and solar-wind gas).

Trigo-Rodriguez, Josep M.; Rubin, Alan E.; Wasson, John T.

2006-03-01

232

Zaoyang chondrite cooling history from pyroxene Fe(2+)-Mg intracrystalline ordering and exolutions  

NASA Technical Reports Server (NTRS)

The Zaoyang ordinary chondrite fell as a single 14.15-kg mass in Hubey province (China) in October 1984 and was classified as a non-brecciated H5 chondrite, shock facies b. Cooling rate in pyroxenes can be calculated down to about 1000 C by using fine textures and at still lower temperatures (700 to 200 C) by intracrystalline ordering processes. The crystal chemistry of clinopyroxene and orthopyroxene from the matrix of the H5 Zaoyang chondrite has been investigated by X-ray structure refinement and detailed microprobe analysis. By comparison with terrestrial pyroxenes cell and polyhedral volumes in clino- and orthopyroxenes show a low crystallization pressure. Fe(2+) and Mg are rather disordered in M1 and M2 sites of clino- and orthopyroxenes; the closure temperatures of the exchange reaction are 600 and 512 C respectively, which is consistent with a quite fast cooling rate, estimated of the order of one degree per day. The closure temperature for the intercrystalline Ca-Mg exchange reaction for clino- and orthopyroxene showing clinopyroxene lamellae about 10 microns thick. Kinetic evaluations based on the thickness of exolved lamellae give a cooling rate of not more than a few degrees per 10(exp 4) years. The different cooling rates obtained from Fe(2+)-Mg intracrystalline partitioning and exolution lamellae suggest an initial episode of slow cooling at 900 C, followed by faster cooling at temperatures of 600-500 C at low pressure conditions. The most probable scenario of the meteorite history seems that the exolved orthopyroxene entered the parental chondrite body after exolution had taken place at high temperature. Subsequent fast cooling occurred at low temperature after the formation of the body.

Molin, G. M.; Tribaudino, M.; Brizi, E.

1993-01-01

233

Intensive parameters of enstatite chondrite metamorphism  

NASA Technical Reports Server (NTRS)

A geothermometer based on the assemblage kamacite-quartz-enstatite-oldhamite-troilite found in enstatite chondrites is described. Data obtained with the geothermometer reveal that the EL6 meteorites experienced temperatures exceeding 1000 C. These temperatures imply a metal-sulfide melting event that may have fractionated the melt from the source region.

Fogel, Robert A.; Hess, Paul C.; Rutherford, Malcolm J.

1989-01-01

234

Chondritic Meteorite Fragments Associated with the Permian-  

E-print Network

Chondritic Meteorite Fragments Associated with the Permian- Triassic Boundary in Antarctica Asish R meteorite fragments have been found in two sedimentary rock samples from an end-Permian bed at Graphite Peak and pyroxene; and the chemistry of Fe-, Ni-, P-, and S-bearing oxide in the meteorite fragments are typical

Basu, Asish R.

235

Noble Gases in Five Rumuruti Chondrites  

NASA Astrophysics Data System (ADS)

Concentration and isotopic composition have been measured in five new R-chondrites: Dar al Gani 417, Northwest Africa 053, Ouzina, Sahara 98248, and Sahara 99531. Two of these meteorites contain solar trapped gases, NWA 053 has an unusual short exposure age of 0.2 Ma.

Weber, H. W.; Schultz, L.

2001-03-01

236

Do Enstatite Chondrites Record Multiple Oxidation States?  

NASA Astrophysics Data System (ADS)

Cr XANES of forsterite and sulfides in an the MAC 88316 EL3 chondrite indicate Cr^2^+ is the dominant species, suggesting a common oxidation state for these phases and requiring S-S bonding in the structure of highly-reduced sulfides.

McCoy, T. J.; McKeown, D. A.; Buechele, A. C.; Tappero, R.; Gardner-Vandy, K. G.

2013-09-01

237

Progressive aqueous alteration of CM carbonaceous chondrites  

NASA Astrophysics Data System (ADS)

CM chondrites are aqueously altered rocks that contain ˜9 wt% H 2O + (i.e., indigenous water) bound in phyllosilicates; also present are clumps of serpentine-tochilinite intergrowths (previously called "poorly characterized phases" or PCP), pentlandite and Ni-bearing pyrrhotite. We studied 11 CM chondrites that span the known range from least altered to most altered. We used various petrologic properties (many previously identified) that provide information regarding the degree of aqueous alteration. There are no known unaltered or slightly altered CM chondrites (e.g., rocks containing numerous chondrules with primary igneous glass). Some CM properties result from processes associated with early and intermediate stages of the alteration sequence (i.e., hydration of matrix, alteration of chondrule glass, and production of large PCP clumps). Other petrologic properties reflect processes active throughout the alteration sequence; these include oxidation of metallic Fe-Ni, alteration of chondrule phenocrysts, changes in PCP composition (reflecting an increase in the phyllosilicate/sulfide ratio), and changes in carbonate mineralogy (reflecting the development of dolomite and complex carbonates at the expense of Ca carbonate). On the basis of these parameters, we propose a numerical alteration sequence for CM chondrites. Because there are no known CM samples that display only incipient alteration, the least altered sample was arbitrarily assigned to subtype 2.6. The most altered CM chondrites, currently classified CM1, are assigned to subtype 2.0. These highly altered rocks have essentially no mafic silicates; they contain chondrule pseudomorphs composed mainly of phyllosilicate. However, their bulk compositions are CM-like, and they are closer in texture to other C2 chondrites than to CI1 chondrites (which lack chondrule pseudomorphs). Using several diagnostic criteria, we assigned petrologic subtypes (±0.1) to every CM chondrite in our study: QUE 97990, CM2.6; Murchison, CM2.5; Kivesvaara, CM2.5; Murray, CM2.4/2.5; Y 791198, CM2.4; QUE 99355, CM2.3; Nogoya, CM2.2; Cold Bokkeveld, CM2.2; QUE 93005, CM2.1; LAP 02277, CM2.0; MET 01070, CM2.0. The proposed CM numerical alteration sequence improves upon the existing scheme of Browning et al. (1996) in that it does not require a complicated algorithm applied to electron-microprobe data to determine the average matrix phyllosilicate composition. The new sequence is more comprehensive and employs petrologic subtypes that are easier to use and remember than mineralogic alteration index values. New neutron-activation analyses of QUE 97990, QUE 93005, MET 01070, Murchison and Crescent, together with literature data, confirm the compositional uniformity of the CM group; different degrees of alteration among CM chondrites do not lead to resolvable bulk compositional differences. This suggests that the textural differences among individual CM chondrites reflect progressive alteration of similar hypothetical CM3.0 starting materials in different regions of the same parent body, with minimal aqueous transport of materials over appreciable (e.g., meters) distances.

Rubin, Alan E.; Trigo-Rodríguez, Josep M.; Huber, Heinz; Wasson, John T.

2007-05-01

238

Correlated alteration effects in CM carbonaceous chondrites  

NASA Astrophysics Data System (ADS)

Three parameters are proposed to determine the relative extent of alteration in CM chondrites. The mineralogic alteration index monitors the relative progress of coupled substitutions in the progressive alteration of cronstedtite to Mg-serpentine and increases with increasing alteration. To calculate values of this index, an algorithm has been developed to estimate the average matrix phyllosilicate composition in individual CM chondrites. The second parameter is the volume percent of isolated matrix silicates, which decreases with progressive alteration due to mineral hydration. Finally, the volume percent of chondrule alteration monitors the extent of chondrule phyllosilicate production and increases as alteration proceeds. These parameters define the first CM alteration scale that relies on multiple indicators of progressive alteration. The following relative order of increasing alteration is established by this model: Murchison ? Bells < Pollen ? Murray < Mighei < Nogoya < Cold Bokkeveld. The relative degree of aqueous processing Cochabamba and Boriskino experienced is less precisely constrained, although both fall near the middle of this sequence. A comparison between the mineralogic alteration index and literature values for the whole-rock chemistry of CM chondrites reveals several correlations. A positive, nearly linear correlation between bulk H content and progressive CM alteration suggests an approximately constant production rate of new phyllosilicates relative to the mineralogical transition from cronstedtite to Mg-serpentine. The abundance of trapped planetary 36Ar decreases systematically in progressively altered CM chondrites, suggesting the wholesale destruction of primary noble gas carrier phase (s) by aqueous reactions. Because low temperature fluid-rock reactions are generally associated with large isotopic mass fractionation factors, we also compared our model predictions with ?18O values for bulk CM samples. Although some of these data are poorly resolved, the order of increasing ?18O values approximates the order of increasing alteration predicted by our model parameters. Multiple correlations between diverse alteration parameters strongly suggest that (a) different CM chondrites experienced similar kinds of processes and conditions, and (b) CM materials experienced in situ alteration on the CM parent body or bodies.

Browning, Lauren B.; McSween, Harry Y., Jr.; Zolensky, Michael E.

1996-07-01

239

Correlated Alteration Effects in CM Carbonaceous Chondrites  

NASA Astrophysics Data System (ADS)

Three parameters are proposed to determine the relative extent of alteration in CM chondrites. The mineralogic alteration index monitors the relative progress of coupled substitutions in the progressive alteration of cronstedtite to Mg-serpentine, and increases with increasing alteration. To calculate values of this index, an algorithm has been developed to estimate the average matrix phyllosilicate composition in individual CM chondrites. The second parameter is the volume percent of isolated matrix silicates, which decreases with progressive alteration due to mineral hydration. Finally, the volume percent of chondrule alteration monitors the extent of chondrule phyllosilicate production, and increases as alteration proceeds. These parameters define the first CM alteration scale that-relies on multiple indicators of progressive alteration. The following relative order of increasing alteration is established by this model: Murchison less than or equal to Bells less than Pollen less than or equal to Murray less than Mighei less than Nogoya less than Cold Bokkeveld. Bulk delta18O values generally increase with progressive alteration, providing additional support for this sequence. The relative degree of aqueous processing Cochabamba and Boriskino experienced is less precisely constrained, although both fall near the middle of this sequence. A comparison between the mineralogic alteration index and literature values of the whole-rock chemistry of CM chondrites reveals several correlations. For example, a positive, nearly linear correlation between bulk H content and progressive CM alteration suggests an approximately constant production rate of new phyllosilicates relative to the mineralogical transition from cronstedtite to Mg-serpentine. Furthermore, the abundance of trapped planetary Ar-36 decreases systematically in progressively altered CM chondrites, suggesting the wholesale destruction of primary noble gas carrier phase(s) by aqueous reactions. Multiple correlations between diverse alteration parameters indicate that different CM chondrites probably experienced the same kinds of processes and conditions during in situ parent body alteration.

Zolensky, Michael E.; Browning, Lauren B.; McSween, Harry Y., Jr.

1996-01-01

240

Kaupapa maori: explaining the ordinary.  

PubMed

This paper gives an overview of the kaupapa and processes of a Maori health research unit and it's researchers within the university environment. It begins with an understanding that research is often viewed with suspicion by Maori, is implicated in the process of colonisation and that Maori research has, in part, grown out of dissatisfaction with prevailing methodologies. Unfortunately this has also involved confronting the argument that there is no such thing as kaupapa maori research. Defining kaupapa maori research is therefore not a comfortable exercise. The need to define, discuss or explain its existence in itself serves as a reminder of the power of colonisation. Kaupapa maori begins as a challenge to accepted norms and assumptions about knowledge and the way it is constructed and continues as a search for understanding within a Maori worldview. If kaupapa maori is about taking for granted a Maori worldview, then this discourse in itself subverts our right to be maori-ordinary. We are now the other in our own country. While kaupapa maori research may be seen as taking a distinctive approach and having underlying principles or aspects which are based on this Maori worldview, methods are likely to be subordinate to the issues and utility of the research and may be drawn from a range of methodologies. By taking a position that challenges norms and assumptions, kaupapa maori research involves a concept of the possibility and desirability of change. The research should aim to make a positive difference (Smith, 1999) and therefore the use, usefulness and ownership of the research are of paramount importance. PMID:11709875

Barnes, H M

2000-03-01

241

A Unique Type 4 Chondrite from the Sahara-Acfer 217  

NASA Astrophysics Data System (ADS)

In 1991 a single stone weighing 174 g was recovered from the Sahara desert, Algeria (27 degrees 36'N, 3 degrees 53'E). From this a 36.83-g fragment was obtained that has 2 sawn surfaces and adjacent surface of partially weathered fusion crust. The sawn surface shows "brownish" weathering products that have generally produced alteration of the matrix in which a few relict chondrules and inclusions are set. One 4 by 5 mm triangular area bordering the fusion crust is dark grey in colour with small inclusions set in it. This may be an area of local shock melt glass. Mineralogy and petrography: In a polished thin section, area 20 mm^2, we found few chondrules, mainly olivine clasts in a weathered olivine-rich matrix, with minor pyroxene. The largest relict chondrule was type "I" (McSween, 1977) with a diameter of 350 micrometers; a 200-micrometer-diameter type "II" (McSween, 1977) barred olivine chondrule showed devitrified glass in the interstices of the olivine. The sample is highly brecciated with fractures cutting the section and offsetting chondrule fragments, but in PTS is only very weakly shocked: olivine shows occasional undulatory extinction, i.e., stage "S2" in the classification of Stoffler et al. (1991). Mineral Chemistry: 95% of olivine is close to Fa(sub)39 but a few grains lie in the range Fa(sub)17 to Fa(sub)43 and one is zoned from a Fa(sub)17 core to a Fa(sub)43 rim. The majority of pyroxene is Ca-rich at a mean composition of Fs(sub)21 Wo(sub)45. Low-Ca pyroxene is also unequilibrated with a mean close to Fs(sub)31 and one has a composition of Fs(sub)10 Wo(sub)2. Plagioclase is a common interstitial phase in the matrix and is variable in composition, but high-Na oligoclase or albite. Minor opaque phases are dominated by Cr-rich (32-38 wt% Cr2O3) spinel, which also contains significant Ti (5.3 wt% TiO2). For charge balance substantial Fe^3+ is required indicating that Fe is partitioned between approximately 13-21 wt% Fe2O3 and 35 wt% FeO. The spinel therefore is a mixture between chromite, magnetite, and ulvospinel. Variation in the composition of this phase is principally in total Fe and Cr, which vary inversely. No Fe-Ni metal was found and troilite is extremely rare; the only analysis has trace Ni. Ni is undetectable in olivine and is depleted in the sample as a whole and this, together with higher mean Fa-values, would tend to rule out a relationship with CK-chondrites (Kallemeyn et al., 1990). Similarly, whilst the fayalite content in olivine might suggest a high-grade CO chondrite the lack of troilite, kamacite, and taenite and the abundance of Cr-rich spinel would tend to preclude this (McSween, 1976). Acfer 217 is a chondrite that is exceptionally poor in metal and sulfide and rich in oxidised Fe. It appears to be unique. Further work will include an oxygen isotope study to determine any relationship with known groups of meteorites. References: Kallemeyn G. W., Rubin A. E. and Wasson J. T. (1990) Geochim. Cosmochim. Acta 55, 881-892. McSween H. Y. (1976) Geochim. Cosmochim. Acta 41, 477-491. McSween H. Y. (1977) Geochim. Cosmochim. Acta 41, 1843-60. Stoffler D., Keil K. and Scott E.R.D. (1991) Geochim. Cosmochim. Acta 55, 3845-3867.

Bland, P.; Hutchison, R.; Pillinger, C. T.; Bischoff, A.

1992-07-01

242

Mn-Cr ages of dolomites in CI chondrites and the Tagish Lake ungrouped carbonaceous chondrite  

NASA Astrophysics Data System (ADS)

53Mn-53Cr ages have been measured for dolomites in three CI chondrites and an ungrouped C2 chondrite Tagish Lake. For an accurate age determination, we utilized, in contrast to previous works, a matrix-matched carbonate standard to appropriately correct the observed Mn/Cr ratios. The Mn-Cr data of the dolomites most likely represent isochrons with chronological significances and the obtained ages are concentrated in 4563.8-4562.5 million years ago (4.4-5.7 million years after the birth of the solar system). The ages of the CI and Tagish Lake dolomites are very similar to those of carbonates in CM chondrites, although CI and CM chondrites are likely to have different alteration histories. The similar carbonate ages in various carbonaceous chondrites suggest that the aqueous activities in hydrous asteroids initiated almost concurrently. If this is the case, the most plausible heat source for the aqueous alteration is the decay energy of short-lived radionuclides, especially 26Al. We carried out a model calculation for the thermal history of the CI chondrite parent body assuming that 26Al is the dominant heat source. By two different approaches to estimate the accretion time of the CI chondrite parent body, we conclude that it accreted 3.0-3.9 million years after the birth of the solar system. This is also likely to be the case for the CM chondrite and Tagish Lake parent bodies, because the result of the calculation is not sensitive to the ice abundance. Therefore, we stress that near the condensation front of water ice, meteorite parent bodies with abundant ice accreted almost simultaneously at 3-4 million years after CAI formation. Combining our Mn-Cr ages of the dolomites with those of breunnerites reported previously (the youngest one is 4554.6 million years ago), we found that the aqueous alteration in the CI chondrite parent body lasted for at least 9 million years. Therefore, the parent body should be large enough (>50 km in radius) so that the internal heat had been kept for 9 million years.

Fujiya, Wataru; Sugiura, Naoji; Sano, Yuji; Hiyagon, Hajime

2013-01-01

243

The Jolomba, Angola LL6 chondrite  

NASA Astrophysics Data System (ADS)

Accompanied by loud thunder at about 1.30 pm (local time) on February 3, 1974, a single stone weighing about 480 g was seen to fall and was recovered near the Jolomba village, Huambo District, Angola. The stone is strongly brecciated, has dark-greyish angular fragments within a lighter matrix and does not exhibit any chondritic textures. Jolomba consists of olivine (Fa 31), orthopyroxene (Fs 25), sodic plagioclase (An 11), sulphides (troilite), very scarce nickel-iron (Ni up to 56 percent), oxides (chromite and ilmenite) and apatite. Pervasive fracturing of silicates suggests that Jolomba suffered strong brecciation and partial recrystallization. Mineralogy and bulk chemical analysis indicate that Jolomba belongs to the LL group of chondrites (amphoterites). Uniform olivine and pyroxene composition, well-crystallized plagioclase, and textural features in general indicate that Jolomba belongs to the petrologic type 6.

Sighinolfi, G. P.; Garuti, G.; Morais, E.

1991-03-01

244

Sm-Nd isotopic evolution of chondrites  

NASA Astrophysics Data System (ADS)

The Nd-143/Nd-144 and Sm-147/Nd-144 ratios measured in 5 chondrites and the Juvinas achondrite correlated with the variation of 4.2% in Sm-147/Nd-144. Most of the spread in the range of these ratios results from small heterogeneities in the chondrites and does not reflect the large-scale volumetric averages. A new set of self-consistent reference values were selected for the 'chrondritic uniform reservoir' (CHUR); the new Sm-147/Nd-144 value is 1.6% higher than the previous value assigned to CHUR using the Juvinas data of Lugmair (1975). The new CHUR curve indicates significant changes in model ages for lunar rocks and in the interpretation of early lunar chronology.

Jacobsen, S. B.; Wasserburg, G. J.

1980-10-01

245

Polyhedral serpentine grains in CM chondrites  

NASA Astrophysics Data System (ADS)

We used high-resolution transmission electron microscopy (HRTEM), electron tomography, electron energy-loss spectroscopy (EELS), and energy-dispersive spectroscopy (EDS) to investigate the structure and composition of polyhedral serpentine grains that occur in the matrices and fine-grained rims of the Murchison, Mighei, and Cold Bokkeveld CM chondrites. The structure of these grains is similar to terrestrial polygonal serpentine, but the data show that some have spherical or subspherical, rather than cylindrical morphologies. We therefore propose that the term polyhedral rather than polygonal be used to describe this material. EDS shows that the polyhedral grains are rich in Mg with up to 8 atom% Fe. EELS indicates that 70% of the Fe occurs as Fe3+. Alteration of cronstedtite on the meteorite parent body under relatively oxidizing conditions is one probable pathway by which the polyhedral material formed. The polyhedral grains are the end-member serpentine in a mineralogic alteration sequence for the CM chondrites.

Zega, Thomas J.; Garvie, Laurence A. J.; Dódony, István; Friedrich, Heiner; Stroud, Rhonda M.; Buseck, Peter R.

2006-05-01

246

Chemical characteristics and origin of H chondrite regolith breccias  

NASA Technical Reports Server (NTRS)

Petrologic data and contents of Ag, Bi, Cd, Co, Cs, Ga, In, Rb, Se, Te, Tl and Zn-trace elements spanning the volatility/mobility range-in light and dark portions of H chondrite regolith breccias and L chondrite fragmental breccias are reported. The chemical/petrologic characteristics of H chondrite regolith breccias differ from those of nonbrecciated chondrites or fragmental breccias. Petrologic characteristics and at least some trace element contents of H chondrite regolith breccias reflect primary processes; contents of the most volatile/mobile elements may reflect either primary or secondary processing, possibly within layered H chondrite parent object(s). Chemical/petrologic differences existed in different regions of the parent(s). Regoligh formation and gardening and meteoroid compaction were not so severe as to alter compositions markedly.

Lipschutz, M. E.; Biswas, S.; Mcsween, H. Y., Jr.

1983-01-01

247

Toward an Astrophysical Theory of Chondrites  

Microsoft Academic Search

The chondrules, calcium-aluminum-rich inclusions (CAIs), and rims in chondritic meteorites could be formed when solid bodies are lifted by the aerodynamic drag of a magnetocentrifugally driven wind out of the relative cool of a shaded disk close to the star into the heat of direct sunlight. For reasonable self-consistent parameters of the bipolar outflow, the base and peak temperatures reached

Frank H. Shu; Hsien Shang; Typhoon Lee

1996-01-01

248

Polyhedral Serpentine Grains in CM Chondrites  

NASA Technical Reports Server (NTRS)

CM chondrites are primitive rocks that experienced aqueous alteration in the early solar system. Their matrices and fine-grained rims (FGRs) sustained the effects of alteration, and the minerals within them hold clues to the aqueous reactions. Sheet silicates are an important product of alteration, and those of the serpentine group are abundant in the CM2 chondrites. Here we expand on our previous efforts to characterize the structure and chemistry of serpentines in CM chondrites and report results on a polyhedral form that is structurally similar to polygonal serpentine. Polygonal serpentine consists of tetrahedral (T) sheets joined to M(2+)-centered octahedral (O) sheets (where (M2+) is primarily Mg(2+) and Fe(2+)), which give rise to a 1:1 (TO) layered structure with a 0.7-nm layer periodicity. The structure is similar to chrysotile in that it consists of concentric lizardite layers wrapped around the fiber axis. However, unlike the rolled-up chrysotile, the tetrahedral sheets of the lizardite layers are periodically inverted and kinked, producing sectors. The relative angles between sectors result in 15- and 30-sided polygons in terrestrial samples.

Zega, Thomas J.; Garvie, Laurence A. J.; Dodony, Istvan; Stroud, Rhonda M.; Buseck, Peter R.

2005-01-01

249

The meteorite Moss - a rare carbonaceous chondrite  

NASA Astrophysics Data System (ADS)

On July 14, 2006, at about 10:20 a.m. local daylight time (UTC+2), a bright fireball travelling SSE-NNV was witnessed from the Baltic Sea to SE Norway. On the east side of the Oslo fiord, around Moss, an explosion and a rumbling sound was heard, and pieces were observed falling. Rapid recovery of meteorite stones gave an opportunity for detailed petrological and geochemical investigations, including analyses of indigenous organic species, and short lived isotopes. The meteorite is a chondritic stone meteorite, with some carbon (0.21-0.25 wt% C). The cosmic-ray exposure (CRE) age is 14 Ma, i.e. when Moss was ejected from its parent body. Gas retention ages are approximately 3.95x10^9 yr (U/Th/He) and 4.43x10^9 yr (K/Ar), respectively. The meteorite has the official name Moss, and is classified as carbonaceous chondrite type CO3.6. It was the first witnessed fall of a CO3 chondrite since Kainsaz in Russia in 1937.

Bilet, M.; Roaldset, E.

2014-07-01

250

Ordinary Stoichiometry of Extraordinary Microbes  

NASA Astrophysics Data System (ADS)

Life on Earth seems to be composed of the same chemical elements in relatively conserved stoichiometric proportions. However, this observation is largely based on observations of biota from habitats spanning a moderate range of temperature and chemical composition (e.g., temperate lakes, forests, grasslands, oceanic phytoplankton). Whether this stoichiometry is conserved in settings that differ radically from such "normal" planetary settings may provide insight into the habitability of environments with radically different stoichiometries, and into possible stoichiometries for putative life beyond Earth. Here we report the first measurements of elemental stoichiometries of microbial extremophiles from hot springs of Yellowstone National Park (YNP). These phototrophic and chemotrophic microbes were collected in locations spanning large ranges of temperature (ambient to boiling) and pH (1 to 9). Microbial biomass was carefully extracted from hot spring sediment substrata following a procedure adapted from [1], which conserves cellular elemental abundances [2]. Their C and N contents were determined by Elemental Analysis Isotope Ratio Mass Spectrometry, and their P and trace element (Mg, Ca, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, and non-biogenic Al and Ti) contents were measured by Inductively Coupled Plasma Mass Spectrometry. Residual mineral contamination was an issue in some samples with low measured C and N; we eliminated these from our results. Even in the remaining samples, contamination sometimes prevented accurate determinations of cellular Mg, Ca, Mn, and Fe abundances; however, the cellular Ni, Cu, Zn, and Mo contents were several-fold above contamination level. Although hot spring water and sediment elemental abundances varied by orders of magnitude, the data showed that the extremophiles have a major and trace element stoichiometry similar to those previously measured in "normal" microbial biomass [3-6]. For example, biomass C:N:P ratios resembled those commonly observed in temperate lakes (e.g., C:P ratios of 260 to 1600 and N:P ratios of 35 to 200) while cellular C:Fe ratios were of a similar magnitude to those of marine phytoplankton. Exceptions were Al and Ti, much higher than previously measured, likely because of contamination from residual sediment. Moreover, the low phosphorus contents (high C:P and N:P ratios) are suggestive of limited P supply. Chemotrophs and phototrophs had similar elemental compositions to one another, although Mg, Mn, Ni, and Zn abundances were higher and nearly constant in phototrophs, due to their importance in phototrophic metabolism. Despite the tremendous physical and chemical diversity of YNP environments, the stoichiometry of life in these settings is surprisingly ordinary. Thus, our study supports the view that the biological stoichiometry of life is heavily constrained by the elemental composition of core biomolecules, and that even life in extreme environments must operate within these constraints. In the frame of life detection in exotic locales, these results suggest a general elemental biosignature for life as we know it. References: [1] Amalfitano and Fazi. 2008. J. Microbiol. Meth. 75:237 [2] Neveu et al. L&O: Meth., in review [3] Ho et al. 2003. J. Phycol. 39:1145 [4] Nuester et al. 2012. Front. Microbiol. 3:150 [5] Sterner and Elser. 2002. Ecological Stoichiometry. Princeton U. Press [6] Twining et al. 2011. Deep-Sea Res. II 58:325

Neveu, M.; Poret-Peterson, A. T.; Anbar, A. D.; Elser, J. J.

2013-12-01

251

Aubrites - Their origin and relationship to enstatite chondrites  

NASA Technical Reports Server (NTRS)

A study of aubrites and their origin and relationship to enstatite chondrites is presented. Aubrites contain enstatite, plagioclase, diopside, and olivine; based on similarities in bulk chemistry of the silicate portions and inferred oxygen fugacity it is shown that E6 chondrites are the most likely parent material for chondrites. It is concluded that the addition of 10% plagioclase of An15 composition to the bulk composition of the silicate portion of the aubrites results in good agreement with that of E6 chondrites.

Watters, T. R.; Prinz, M.

1979-01-01

252

On the aerodynamic redistribution of chondrite components in protoplanetary disks  

NASA Astrophysics Data System (ADS)

Despite being all roughly of solar composition, primitive meteorites (chondrites) present a diversity in their chemical, isotopic and petrographic properties, and in particular a first-order dichotomy between carbonaceous and non-carbonaceous chondrites. We investigate here analytically the dynamics of their components (chondrules, refractory inclusions, metal/sulfide and matrix grains) in protoplanetary disks prior to their incorporation in chondrite parent bodies. We find the dynamics of the solids, subject to gas drag, to be essentially controlled by the “gas-solid decoupling parameter”S ? St/?, the ratio of the dimensionless stopping time to the turbulence parameter. The decoupling of the solid particles relative to the gas is significant when S exceeds unity. S is expected to increase with time and heliocentric distance. On the basis of (i) abundance of refractory inclusions, (ii) proportion of matrix, (iii) lithophile element abundances, and (iv) oxygen isotopic composition of chondrules, we propose that non-matrix chondritic components had S < 1 when carbonaceous chondrites accreted and S > 1 when the other chondrites accreted. This suggests that accretion of carbonaceous chondrites predated on average that of the other chondrites and that refractory inclusions are genetically related to their host carbonaceous chondrites.

Jacquet, Emmanuel; Gounelle, Matthieu; Fromang, Sébastien

2012-07-01

253

Fire Classifications Fires involving the ordinary  

E-print Network

Fire Classifications Fires involving the ordinary combustible materials such as wood, cloth, paper, plastics, etc. Fires involving combustible or flammable liquids such as gasoline, kerosene, oils, grease, paints and chemicals. Fires involving energized electrical equipment such as appliances, including

Jia, Songtao

254

Solutions of systems of ordinary differential equations  

E-print Network

Page V 14 18 18 18 19 22 25 TABLE I LIST OF TABLES RESULTS FOR THE CONSISTENT AND INCONSISTENT PROBLEMS WITH THE ANALYTICAL SOLUTION TO THE CONSISTENT ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ Page 17 TABLE 2 THEORETICAL AND COMPUTED VALUES... of ordinary and partial differential equations by linear programming is a relatively recent development (1). Saye (2) found that in certain problems involving numerical solutions to ordinary differential equations, the method treated herein may be used...

Kitchens, Claude Evans

2012-06-07

255

Sulfur and Selenium in Chondritic Meteorites  

NASA Astrophysics Data System (ADS)

Selenium is the only truly chalcophile element in chondritic meteorites. It has no other host phases except sulfides. Since Se-volatility is similar to S-volatility one may expect constant S/Se ratios. To test this hypothesis chondritic meteorites were analyzed for Se and S. To avoid problems from inhomogeneous distribution of sulfides the same samples that had been analyzed for Se by INAA were analyzed for S (see Table 1) using a Leybold Heraeus Carbon and Sulfur Analyser (CSA 2002). Solar System Abundances of S and Se: The average S-content of CI- meteorites is with 5.41% in agreement with an earlier average of 5.25% for Orgueil [1], but not with higher S-contents for Ivuna, Alais, and Tonk. Inclusion of these data led to an average CI- content of 6.25% in the Anders and Grevesse compilation [2]. The essentially constant average S/Se ratio in all groups of carbonaceous chondrites of 2563 +- 190 suggests that our Orgueil S-content provides a reliable estimate for the average solar system. The new solar S/Se ratio and the CI-value of Se of 21.3 ppm [3] yield an atomic S/Se ratio of 6200 +- 170, 24% below that calculated from [2]. Weathering Effects: Some of the carbonaceous chondrite finds have similar S/Se ratios as falls (see Table 1). However the badly- weathered Arch (CVR) and Colony (CO) and the two C4-chondrites Mulga West and Maralinga have much lower S and somewhat lower Se contents compared to unweathered meteorites. Their S/Se ratios of 1000-230 indicate higher losses of S--probably by oxidation--as of Se. The low Na-contents in Arch and Colony rel. to CV3 and CO3 may also reflect weathering. Low S/Se ratios in the Sahara meteorites are also indicative of weathering processes. The depletion factors for the CV3- chondrite Acfer086 are, relative to average CV, 10 (S), 5 (Se), 6 (Na), and 4 (Ni). Lower absolute depletions, but the same depletion sequence are found for the CO-meteorite Acfer 202. In the CO/CM Acfer 094 only S and Na are depleted. The influence of weathering in the two CR-types Acfer 097 and Acfer 270 is less obvious. Although Se does not appear to be depleted in these meteorites [4] the lower S/Se ratios of 1660 res. 1970 rel. to CI and the low Na-contents indicate weathering related losses of S and Na. Losses of Ni by weathering are more pronounced in meteorites containing Ni-rich sulfides, whereas metallic Ni is apparently less affected (CR-meteorites). A high depletion of S and Ni but none for Se and Na is found in the Carlisle Lake-type, Acfer 217. In summary, weathering effects in the carbonaceous chondrites result in losses of S, Se, Na, and Ni. Sulfur is in all cases significantly more affected by weathering than Se resulting in low S/Se ratio rel. to CI. References: [1] Mason B. (1962) Space Sci. Rev., 1, 621-646. [2] Anders E. and Grevesse N. (1989) GCA, 53, 197-214. [3] Spettel B. et al. (1993) this volume. [4] Bischoff A. et al. (1993) GCA, 57, in press.

Dreibus, G.; Palme, H.; Spettel, B.; Wanke, H.

1993-07-01

256

5 CFR 845.305 - Ordinary and necessary living expenses.  

Code of Federal Regulations, 2010 CFR

...2010-01-01 false Ordinary and necessary living expenses. 845.305 Section 845... § 845.305 Ordinary and necessary living expenses. An individual's ordinary and necessary living expenses include rent, mortgage...

2010-01-01

257

22 CFR 17.6 - Ordinary and necessary living expenses.  

Code of Federal Regulations, 2010 CFR

...2010-04-01 false Ordinary and necessary living expenses. 17.6 Section 17.6 ...FSPS) § 17.6 Ordinary and necessary living expenses. An individual's ordinary and necessary living expenses include rent, mortgage...

2010-04-01

258

31 CFR 29.525 - Ordinary and necessary living expenses.  

Code of Federal Regulations, 2010 CFR

...2010-07-01 false Ordinary and necessary living expenses. 29.525 Section 29.525...Overpayments § 29.525 Ordinary and necessary living expenses. An individual's ordinary and necessary living expenses include rent, mortgage...

2010-07-01

259

5 CFR 831.1405 - Ordinary and necessary living expenses.  

Code of Federal Regulations, 2010 CFR

...2010-01-01 false Ordinary and necessary living expenses. 831.1405 Section 831... § 831.1405 Ordinary and necessary living expenses. An individual's ordinary and necessary living expenses include rent, mortgage...

2010-01-01

260

Relict silicate inclusions in extraterrestrial chromite and their use in the classification of fossil chondritic material  

NASA Astrophysics Data System (ADS)

Chromite is the only common meteoritic mineral surviving long-term exposure on Earth, however, the present study of relict chromite from numerous Ordovician (470 Ma) fossil meteorites and micrometeorites from Sweden, reveals that when encapsulated in chromite, other minerals can survive for hundreds of millions of years maintaining their primary composition. The most common minerals identified, in the form of small (<1-10 ?m) anhedral inclusions, are olivine and pyroxene. In addition, sporadic merrillite and plagioclase were found. Analyses of recent meteorites, holding both inclusions in chromite and corresponding matrix minerals, show that for olivine and pyroxene inclusions, sub-solidus re-equilibration between inclusion and host chromite during entrapment has led to an increase in chromium in the former. In the case of olivine, the re-equilibration has also affected the fayalite (Fa) content, lowering it with an average of 14% in inclusions. For Ca-poor pyroxene the ferrosilite (Fs) content is more or less identical in inclusions and matrix. By these studies an analogue to the commonly applied classification system for ordinary chondritic matrix, based on Fa in olivine and Fs in Ca-poor pyroxene, can be established also for inclusions in chromite. All olivine and Ca-poor pyroxene inclusions (>1.5 ?m) in chromite from the Ordovician fossil chondritic material plot within the L-chondrite field, which is in accordance with previous classifications. The concordance in classification together with the fact that inclusions are relatively common makes them an accurate and useful tool in the classification of extraterrestrial material that lacks matrix silicates, such as fossil meteorites and sediment-dispersed chromite grains originating primarily from decomposed micrometeorites but also from larger impacts.

Alwmark, Carl; Schmitz, Birger

2009-03-01

261

Large spinel grains in a CM chondrite (Acfer 331): Implications for reconstructions of ancient meteorite fluxes  

NASA Astrophysics Data System (ADS)

By dissolving 30-400 kg of marine limestone in HCl and HF acid, our group has previously recovered common relict chromite grains (approximately 63-250 ?m) from ordinary chondritic micrometeorites that fell on ancient sea floors, up to 500 Myr old. Here, we evaluate if CM group carbonaceous chondritic material, which makes up an important fraction of the micrometeorite flux today, contains analogous grains that can be searched for in acid residues. We dissolved 8 g of CM2 meteorite Acfer 331 in HF, which yielded a characteristic assemblage of both transparent Mg-Al- and opaque Cr-spinels >28 ?m. We find on average 4.6 and 130 Mg-Al-spinel grains per gram in the 63-250 and 28-63 ?m size fractions, respectively. These grains are mostly pink or colorless, and often characterized by heterogeneous Cr-content. Black, opaque Cr-spinel grains are absent from the >63 ?m fraction, but in the 28-63 ?m fraction we find approximately 65 such grains per gram meteorite. The individual grains have a characteristic composition, with heterogeneous major element compositions (e.g., 44.4-61.7 wt% Cr2O3), but narrow ranges for maximum TiO2 (0.6-1.6 wt%) and V2O3 (0.5-1.0 wt%) concentrations. The content of spinel grains in the 28-63 ?m fraction of CM meteorites appears comparable at the order of magnitude level with the content of >63 ?m sized chromite grains in fossil L-chondrites from Ordovician limestone. Our approach of recovering meteoritic spinel from sediment may thus be extended to include CM meteorites, but the smaller size fraction of the acid residues should be searched.

BjäRnborg, Karolina; Schmitz, Birger

2013-02-01

262

Unraveling the evolution of chondrite parent asteroids by precise U-Pb dating and thermal modeling  

NASA Astrophysics Data System (ADS)

U-Th-Pb isotopic data are reported for mineral fractions, individual chondrules and fractions of chondrule fragments from the equilibrated ordinary chondrite Richardton (H5). Chondrules and milligram-sized fractions of pyroxene-rich chondrule fragments contain highly radiogenic Pb and concordant or nearly concordant U-Th-Pb isotopic systems, and are suitable for precise Pb-Pb age determinations. Olivine and sulfide have low U concentrations and contain less radiogenic Pb. The ages of individual chondrules, pyroxene-rich and phosphate fractions are determined using U-Pb and Pb-Pb isochron and model date calculations. The Pb-Pb isochron date of 4562.7 ± 1.7 Ma of the Richardton chondrules and chondrule fragments is resolved from the Pb-Pb isochron date of 4550.7 ± 2.6 Ma obtained from multiple phosphate fractions. Possible biases of the isochron dates due to single-stage approximation of multi-stage evolution, contamination with modern common Pb, and disturbance to the system by reheating, are examined and are found to be insignificant. The chondrule and phosphate dates are interpreted as the timing of cessation of Pb diffusion during cooling following metamorphism in chondrite parent bodies. The difference in estimated closure temperatures, ˜950-1150 K for pyroxenes, and 700-800 K for phosphates (temperature estimates are based on published diffusion rates for Pb in pyroxenes and apatite), allows evaluation of the average cooling rate at 26 ± 13 K/million years for the Richardton parent body over the period of 4563-4551 my. Thermal modeling of the H-chondrite parent body (which is assumed to be asteroid 6 Hebe, heated by decay of 26Al) suggests a scenario in which accretion initiated at 1.7 m.y. after formation of calcium-aluminum-rich inclusions and continued for 3.5 m.y.

Amelin, Yuri; Ghosh, Amitabha; Rotenberg, Ethan

2005-01-01

263

Mineral and chemical composition of the Jezersko meteorite—A new chondrite from Slovenia  

NASA Astrophysics Data System (ADS)

The Jezersko meteorite is a newly confirmed stony meteorite found in 1992 in the Karavanke mountains, Slovenia. The meteorite is moderately weathered (W2), indicating short terrestrial residence time. Chondrules in partially recrystallized matrix are clearly discernible but often fragmented and have mean diameter of 0.73 mm. The meteorite consists of homogeneous olivine (Fa19.4) and low-Ca pyroxenes (Fs16.7Wo1.2), of which 34% are monoclinic, and minor plagioclase (Ab83An11Or6) and Ca-pyroxene (Fs6Wo45.8). Troilite, kamacite, zoned taenite, tetrataenite, chromite, and metallic copper comprise about 16.5 vol% of the meteorite. Phosphates are represented by merrillite and minor chlorapatite. Undulatory extinction in some olivine grains and other shock indicators suggests weak shock metamorphism between stages S2 and S3. The bulk chemical composition generally corresponds to the mean H chondrite composition. Low siderophile element contents indicate the oxidized character of the Jezersko parent body. The temperatures recorded by two-pyroxene, olivine-chromite, and olivine-orthopyroxene geothermometers are 854 °C, 737-787 °C, and 750 °C, respectively. Mg concentration profiles across orthopyroxenes and clinopyroxenes indicate relatively fast cooling at temperatures above 700 °C. A low cooling rate of 10 °C Myr-1 was obtained from metallographic data. Considering physical, chemical, and mineralogical properties, meteorite Jezersko was classified as an H4 S2(3) ordinary chondrite.

Miler, Miloš; Ambroži?, Bojan; Mirti?, Breda; Gosar, Mateja; Å turm, Sašo.; Dolenec, Matej; Jeršek, Miha

2014-10-01

264

Oxygen Isotope Compositions of the Kaidun Meteorite - Indications for Aqeuous Alteration of E-Chondrites  

NASA Technical Reports Server (NTRS)

The Kaidun microbreccia is a unique meteorite due to the diversity of its constituent clasts. Fragments of various types of carbonaceous (CI, CM, CV, CR), enstatite (EH, EL), and ordinary chondrites, basaltic achondrites, and impact melt products have been described, and also several unknown clasts [1, and references therein]. The small mm-sized clasts represent material from different places and times in the early solar system, involving a large variety of parent bodies [2]; meteorites are of key importance to the study of the origin and evolution of the solar system, and Kaidun is a collection of a range of bodies evidently representing samples from across the asteroid belt. The parent-body on which Kaidun was assembled is believed to be a C-type asteroid, and 1-Ceres and the martian moon Phobos have been proposed [1-4]. Both carbonaceous (most oxidized) and enstatite (most reduced) chondrite clasts in Kaidun show signs of aqueous alterations that vary in type and degree and are most likely of pre-Kaidun origin [1, 4].

Ziegler, K.; Zolensky, M.; Young, E. D.; Ivanov, A.

2012-01-01

265

Oxygen isotopic composition of chondritic interplanetary dust particles: A genetic link between carbonaceous chondrites and  

E-print Network

techniques. All IDPs have isotopic compositions tightly clustered around that of solar system planetary a high temperature inner solar system origin. The small variations in the 16 O content of GEMS-rich IDPs, and comet Wild 2 belong to a single family of objects of car- bonaceous chondrite chemical affinity

266

Preliminary Compositional Comparisons of H-Chondrite Falls to Antarctic H-Chondrite Populations  

NASA Astrophysics Data System (ADS)

In a series of papers [e.g., 1,2], Lipschutz and co-workers compared trace- element RNAA data from Antarctic and non-Antarctic H4-6 chondrites and concluded that the two populations have significantly different concentrations of several trace elements including Co, Se, and Sb. They interpreted their data as indicating that these Antarctic H chondrites form different populations than observed H falls and may have originated in separate parent bodies. Recent work by Sears and co-workers [e.g., 3] has shown that there seem to be distinct populations of Antarctic H chondrites, distinguishable on the bases of induced thermoluminescence (TL) peak temperature, metallographic cooling rate, and cosmic ray exposure age. They showed that a group of Antarctic H chondrites having abnormally high induced TL peak temperatures (>=190 degrees C) also has cosmic ray exposure ages <20 Ma (mostly ~8 Ma) and fast metallographic cooling rates (~100 K/Ma). Another group having induced TL peak temperatures <190 degrees C has exposure ages >20 Ma and slower cooling rates (~10-20 K/Ma). We studied 24 H4-6 chondrites from Victoria Land (including 12 previously analyzed by the Lipschutz group) by optical microscopy and electron microprobe. Many of the Antarctic H chondrites studied by Lipschutz and co- workers are unsuitable for proper compositional comparisons with H chondrite falls: Four are very weathered, five are extensively shocked, and two are extensively brecciated. Furthermore, at least five of the samples contain solar-wind gas (and hence are regolith breccias) [4]. These samples were rejected because of possible compositional modification by secondary processes. For our INAA study we chose a suite of relatively unweathered and unbrecciated Antarctic H chondrites (including nine from the Lipschutz set): ALHA 77294 (H5, S3); ALHA 79026 (H5, S3); ALHA 79039 (H5, S3); ALHA 80131 (H5, S3); ALHA 80132 (H5, S4); ALHA 81037 (H6, S3); EETA 79007 (H5, S4); LEW 85320 (H6, S4); LEW 85329 (H6, S3); RKPA 78002 (H5, S2); and RKPA 78004 (H4, S4). Single samples were each analyzed for 27 elements. Only four of our samples have been analyzed by TL. Concentrations of siderophile elements (Fe, Co, Ni, Ga, As, Au) in the Antarctic H chondrites tend to scatter more than those of 24 H falls studied in replicate at UCLA. This is probably due in part to the fact that replicate samples of the Antarctic chondrites have not yet been analyzed. The median concentrations of siderophile elements also tend to be slightly lower in Antarctic H chondrites, although 95% confidence intervals on the medians overlap with those of H falls for every element. Concentration ranges and median values of two chalcophile elements, Se and Zn, are nearly identical between the Antarctic H chondrites and H falls. Kolmogorov-Smirnov two-tailed tests on these elements show no significant differences between the two populations. Three of the elements analyzed in this study (Co, Se, Sb) are among those reported to vary significantly between Antarctic H chondrites and H falls by Dennison and Lipschutz [1], who found that median concentrations of these elements were slightly higher in Antarctic H chondrites. As noted earlier, we determined slightly lower median concentrations for Co and Sb in Antarctic H chondrites than in H falls; median Se concentrations were identical. The slightly lower median concentration values that we found for siderophile elements in general are probably indicative of a slight weathering loss of metal. Based on our compositional data, the Victoria Land H chondrites and non-Antarctic H falls do not require derivation from separate parent populations. References: [1] Dennison J. E. and Lipschutz M. E. (1987) GCA, 51, 741-754. [2] Lipschutz M. E. and Samuels S. M. (1991) GCA, 55, 19-34. [3] Benoit P. H. and Sears D. W. G. (1993) Icarus, 101, 188-200. [4] Schultz L. et al. (1991) GCA, 55, 59-66.

Kallemeyn, G. W.; Krot, A. N.; Rubin, A. E.

1993-07-01

267

REE and actinide microdistribution in Sahara 97072 and ALHA77295 EH3 chondrites: A combined cosmochemical and petrologic investigation  

NASA Astrophysics Data System (ADS)

We report the results of rare earth elements (REEs) and U-Th inventory of individual minerals (oldhamite, enstatite and niningerite) in two of the most unequilibrated and primitive EH3 known so far, ALHA77295 and Sahara 97072. Under the highly reducing condition that prevailed during the formation of enstatite chondrites, REEs are mainly chalcophile and concentrated in oldhamite. The study is guided by detailed petrographic investigations of the individual minerals in chondrules, complex sulfide-metal clasts and enstatite-dominated matrices. We developed two textural parameters in order to resolve the evolution of oldhamite condensates and their residence in the solar gas prior to their accretion in the individual objects or in matrices and relate these textural features to the measured REE patterns of the individual oldhamite crystals. These textural parameters are the crystal habit of oldhamite grains (idiomorphic or anhedral) and their host assemblages. REE concentrations were measured by SIMS and LA-ICPMS. Oldhamite grains display REE enrichments (10-100 × CI). Four types of REE patterns are encountered in oldhamite in ALHA77295. In general the REE distributions cannot be assigned to a specific oldhamite-bearing assemblage. The most represented REE pattern is characterized by both slight to large positive Eu and Yb anomalies and is enriched in light REEs relative to heavy REEs. This pattern is present in 97% of oldhamite in Sahara 97072, suggesting a different source region in the reduced part of the nebula or different parental EH asteroids for the two EH3 chondrites. Different parental asteroids are also supported by MgS-FeS zoning profiles in niningerite grains adjacent to troilite revealing both normal and reverse zoning trends and different MnS contents. The observed homogeneity of REE distribution in oldhamite grains in Sahara 97072 is not related to the mild metamorphic event identified in this meteorite that caused breakdown of the major K- and Rb-bearing sulfide (djerfisherite). REE concentrations in enstatite range between 0.2 and 8 × CI. Hence, enstatite is an important REE host next to oldhamite. Most patterns are characterized by negative Eu and Yb anomalies. Niningerites are negligible contributors to bulk EH3 REE inventory. Average positive Eu and Yb anomalies observed in most oldhamite are complimentary to the negative ones in enstatite thus explaining the flat patterns of the bulk meteorites. The condensation calculations based on cosmic abundances predict that the first oldhamite condensates should have flat REE patterns with Eu and Yb depletions since Eu and Yb condense at lower temperature than other REE. However, this pattern is seen in enstatite. Our findings are at odds with the predicted negative Eu and Yb anomalies in oldhamite earliest condensates from a closed system in a reduced solar source. Our petrographic, mineral chemistry and REE abundances of oldhamite, enstatite and niningerite discards an origin of oldhamite by impact melting ( Rubin et al., 2009). Our results do not support in first order the scenario of the incorporation of REE in the Earth's core to explain 142Nd excess in terrestrial samples relative to chondrites because oldhamite is the major REE carrier phase and has super-chondritic Sm/Nd ratios.

Gannoun, A.; Boyet, M.; El Goresy, A.; Devouard, B.

2011-06-01

268

REE Abundances in Matrix of Allende (CV) Chondrite  

NASA Astrophysics Data System (ADS)

In order to examine trace element distributions in matrix material of primitive chondrites, four interchondrule matrix specimens (sample weight ~100 micrograms) were carefully excavated using a microdrill from the petrographically characterized areas of the published sections of Allende (CV) chondrite and were precisely analyzed for REE, Ba, Sr, Rb, K, Ca and Mg by direct loading isotope dilution method (DL-IDMS).

Inoue, M.; Nakamura, N.; Kimura, M.

1996-03-01

269

Evolutionary history of CI and CM chondrites  

NASA Technical Reports Server (NTRS)

It is now clear that several different processes have acted upon various components of carbonaceous chondrites, and that at least some of those processes occurred very early in solar system history. Because these meteorites are breccias, petrographic relationships are seldom informative about the order in which those processes took place. Nonetheless, information about such an evolutionary sequence would be of potential value in defining the nature of the source region for these meteorites. Implantation of solar wind derived noble gases into CI magnetite apparently postdated the period of aqueous activity believed to be responsible for magnetite production. Carbonate crystallization roughly coincided with one or more episodes of impact driven brecciation.

Kerridge, J. F.; Macdougall, J. D.

1984-01-01

270

Annuities: Ordinary? Due? What do I do?  

NSDL National Science Digital Library

Created and maintained by John M. Wachowicz, Jr., Professor of Finance at the University of Tennessee, Annuities: Ordinary? Due? What do I do? is a wonderful tutorial that will help students of finance "better identify, understand, and calculate future and present values of both ordinary annuities and annuities due." The tutorial begins by citing resources found on the Internet, including online lectures and tutorials to start building users's basic knowledge of annuities. The second page covers the definitions of "annuity," "ordinary annuity," and "annuity due," and leads users through calculations to figure out what kind of annuities they are dealing with. The final page offers a multiple choice quiz, complete with a detailed answer key.

Wachowicz, John M., Jr.

271

ACFER 182 and paired samples, an iron-rich carbonaceous chondrite - Similarities with ALH85085 and relationship to CR chondrites  

NASA Astrophysics Data System (ADS)

Data are presented on the minerology, chemical composition, and rare gas composition of three paired meteorite samples of a new Fe-rich chondrite found in the Sahara in 1990 and 1991 (Acfer 182, Acfer 207, and Acfer 214), designated as meteorite Acfer 182. The major components of Acfer 182 are (in decreasing order of abundance): (1) highly altered matrix, (2) mineral and polymineralic silicate fragments and aggregates, (3) chondrule fragments, (4) chondrules, (5) metal, and (6) fine-grained dark inclusions. The chemical composition of Acfer 182 was found to be almost indistinguishable from that of ALH85085. Considering their affinity to carbonaceous chondrites and their high bulk iron content, Acfer 182 and ALH85085 are designated as CH chondrites. Their relation to other groups of chondritic meteorites, such as CR chondrites, is discussed.

Bischoff, A.; Palme, H.; Schultz, L.; Weber, D.; Weber, H. W.; Spettel, B.

1993-06-01

272

Evidence for differences in the thermal histories of Antarctic and non-Antarctic H chondrites with cosmic-ray exposure ages less than 20 Ma  

NASA Technical Reports Server (NTRS)

Antarctic H chondrites show a different range of induced thermoluminescence properties compared with those of H chondrites that have fallen elsewhere in the world. Recent noble gas data of Schultz et al. (1991) show that this difference is displayed most dramatically by meteorites with cosmic-ray exposure ages less than 20 Ma, and they confirm that the differences cannot be attributed to weathering or to the presence of a great many fragments of an unusual Antarctic meteorite. Annealing experiments on an H5 chondrite, and other measurements on a variety of ordinary chondrites, have shown that induced TL properties are sensitive to the thermal histories of the meteorities. It is concluded that the events(s) that released the less than 20 Ma samples, which are predominantly those with exposure ages of 8 + or - 2 Ma, produced two groups with different thermal histories, one that came to earth several 100,000 years ago and that are currently only found in Antarctica, and one that is currently falling on the earth.

Sears, Derek W. G.; Benoit, Paul; Batchelor, J. David

1991-01-01

273

Mineralogy, Reflectance Spectra, and Physical Properties of the Chelyabinsk LL5 Chondrite - Insight Into Shock Induced Changes in Asteroid Regoliths  

NASA Astrophysics Data System (ADS)

On February 15, 2013, at 9:22 am, an exceptionally bright and long duration fireball was observed by many eyewitnesses in the Chelyabinsk region, Russia. Two days later the first fragments of the Chelyabinsk meteorite were reported to be found in the area, located approximately 40 km south of Chelyabinsk. We have examined a large number of the recovered Chelyabinsk meteorite fragments. Three lithologies, the light-colored, dark-colored, and impact melt, were found within the recovered meteorites. The light colored lithology is a LL5 ordinary chondrite (Fa 28, Fs 23) shocked to S4 level. The dark colored lithology is of identical LL5 composition (Fa 28, Fs 23). However, it is shocked to higher level (shock-darkened) with fine grained metal and sulfide-rich melt forming a dense network of fine veins impregnating the inter- and intra-granular pore space within crushed silicate grains. The impact melt lithology is a whole-rock melt derived from the same LL5 source material and is present within the light-colored and dark-colored lithology as inter-granular veins. The measured bulk and grain densities and the porosity closely resemble other LL chondrites. Based on the magnetic susceptibility, the Chelyabinsk meteorites are richer in metallic iron as compared to database of other LL chondrites. All three Chelyabinsk lithologies are of identical LL5 composition and origin. Both impact melting and shock darkening cause a decrease in reflectance and a suppression of the silicate absorption bands in the reflectance spectra. Such spectral changes are similar to the space weathering effects observed on asteroids. However, space weathering of chondritic materials is often accompanied with a significant spectral slope change (reddening). In our case, only negligible to minor change in the spectral slope is observed. Thus, it is possible that some dark asteroids with invisible silicate absorption bands may be composed of relatively fresh shock-darkened chondritic material. The main spectral difference of chondritic asteroid surfaces dominated by impact melt, shock darkening, or space weathering, is a significant spectral slope change in the latter case. Thus, shock does not have significant effect on meteorite properties, but causes spectral darkening and suppression of silicate absorption bands.

Gritsevich, Maria; Muinonen, Karri; Kohout, Tomas; Grokhovsky, Victor; Yakovlev, Grigoriy; Haloda, Jakub; Halodova, Patricie; Michallik, Radoslaw; Penttilä, Antti

274

A Second H Chondrite Stream of Falls  

NASA Astrophysics Data System (ADS)

Earlier, Dodd et al. [1] described a statistically significant concentration of 17 H4-6 chondrite falls in May between 1855 and 1895, that clustered on a year-day plot, indicating a coorbital meteoroid stream or two closely-related ones. Contents of 10 thermally labile trace elements (Rb, Ag, Se, Cs, Te,Zn, Cd, Bi, Tl, In) determined by RNAA demonstrated that 13 of these H Cluster 1 (hereafter HC1) falls are compositionally distinguishable from another 45 non-H Cluster 1 (non-HC1) falls [1] (as are Antarctic samples with nominal terrestrial ages >50 ky [2,3]). This compositional distinguishability is demonstrable using two standard, model-dependent multivariate statistical tests (linear discriminant analysis LDA or logistic regression LR) or the model-independent, randomization-simulation (R-S) methods of Lipschutz and Samuels [4]. Despite petrographic and cosmic ray exposure age variabilities, like Antarctic suites [2] HC1 meteorites seemingly derive from coorbital meteoroids (from their circumstances of fall) and apparently have a common thermal history (reflected in contents of thermally labile trace elements) distinguishable from those of other H4-6 chondrite falls [1]. Other explanations seem inviable [5]. During days 220-300 when streams of large fireballs [6] and near-Earth asteroids [7] occur several H chondrite concentrations are evident (Fig. 1), particularly if petrographic type becomes a criterion [1]. Here, we focus on H Clusters 2 through 4 (HC2-4) containing, respectively, 10 H4-6, 5 H5 and 12 H6 chondrite members, for which full data sets exist because of the generosity of many colleagues/institutions. H chondrite clusters in the same time-span might include samples derived from related parent regions. Hence, we changed our comparison-base to approximate a random background of falls by including only the 34 non-Cluster H chondrites, HC0; this also simplified our calculations. To establish whether this choice impacts our observations, we compared 13 HC1 with 34 HC0 meteorites (Table 1). As is evident, the LDA, LR and R-S results are nearly identical to those obtained by comparing 13 HC1 with 45 non- HC1 falls [1]. As Table 1 shows, 10 HC2 chondrites are not compositionally distinguishable from 34 HC0 falls by any criterion. However, 12 HC4 falls may be compositionally distinguishable from the HC0 suite using model-dependent LDA and LR techniques. The small HC3 suite seems to lie on an extension of HC4 (Fig. 1) and we compared the 17-member combined suite, HC34, with HC0. Model-dependent or -independent results (Table 1) provide strong evidence for a compositional difference: apparently HC34, like HC1 [1], derive from coorbital meteoroid streams. The oldest and youngest HC34 members are particularly interesting: Borodino fell 5 Sept. 1812 just before the battle there: its fall is unrecorded in military histories of the era [8]. The final orbit of the Peekskill fall in 1992 is particularly well-established [9] linking HC34 to a specific orbit. Acknowledgments: Support from NASA grant NAGW-3396 and DOE grant DE-FG07-80ER1-072SJ. References: [1] Dodd R. T. et al. (1993) JGR, 98, 15105-15118. [2] Michlovich S. et al. (1995) JGR, 100, 3317-3333. [3] Wolf S. F. and Lipschutz M. E. (1995) JGR, 100, 3335-3349. [4] Lipschutz M. E. and Samuels S. M. (1991) GCA, 55, 19-47. [5] Wolf S. F. and Lipschutz M. E. (1995) JGR, 100, 3297-3316. [6] Halliday I. et al. (1990) Meteoritics, 24, 93-99. [7] Drummond J. D. (1991) Icarus, 89, 14-25. [8] Rothenberg G. E., personal communication. [9] Brown P. et al. (1994) Nature, 367, 624-626. Table 1 shows multivariate statistical comparisons of RNAA data for 10 thermally-labile trace elements in various putative suites of H4-6 chondrite falls.

Wolf, S. F.; Wang, M.-S.; Dodd, R. T.; Lipschutz, M. E.

1995-09-01

275

Nucleosynthetic Nd isotope anomalies in primitive enstatite chondrites  

NASA Astrophysics Data System (ADS)

We carried out stepwise dissolutions of four primitive enstatite chondrites (EC) belonging to the EH subgroup. Large Nd isotope anomalies are found in the most refractory phases, dissolved using strong acids. Residues are characterized by excesses in 142Nd and deficits in 145Nd, 148Nd and 150Nd isotopes. The Nd anomalies measured in the ALHA77295 residue are even greater than those measured in the Murchison carbonaceous chondrite (CC) using a similar analytical technique (Qin et al., 2011). Once corrected for a common Sm/Nd evolution, the 142Nd excess in the ALHA77295 residue is equal to 700 ppm relative to the terrestrial standard value. The Nd isotope patterns measured in EC and CC residues can be adjusted to coincide by adding a small amount of an s-process-rich carrier phase such as SiC and 0.075% is required to fit the ALHA7795 residue. Small isotope differences still persist between these residues even if they can be considered similar within error. In enstatite chondrites, residues have a deficit in 150Nd similar to or smaller than that measured in 148Nd, whereas in SiC extracted from carbonaceous chondrites or in whole rock, the deficit in 150Nd is always greater than that in 148Nd. Moreover in a binary 142Nd-148Nd diagram, the best-fit lines obtained for leachates and residues from carbonaceous chondrites and enstatite chondrites have slightly different slopes. For the same 148Nd/144Nd ratio, the anomalous component in an enstatite chondrite has a higher 142Nd/144Nd ratio compared to carbonaceous chondrites, a feature already observed at the whole rock scale. Our results suggest that different chondrite groups sample different reservoirs of presolar grains formed in different environments. Assuming that the carrier of this anomalous component measured in residues of enstatite chondrites are SiC, our results may suggest that different meteorite parent bodies sample reservoirs of presolar SiC formed in different stellar environments. This could explain why ALHA77295, the sample which is the most enriched in presolar grains, has a bulk 142Nd isotope composition similar to the terrestrial value. Further investigation of enstatite chondrites is needed to test whether the isotope composition of the most refractory phases is similar to that measured in carbonaceous chondrites and in particular the 144Sm that is a p-process isotope only. Finally this study highlights the difficulty of interpreting the 142Nd excess in terrestrial samples relative to chondrites since incomplete mixing of nucleosynthetic material in the solar nebula creates significant 142Nd variation, as shown by ALHA77295.

Boyet, M.; Gannoun, A.

2013-11-01

276

The UThPb age of equilibrated L chondrites and a solution to the excess radiogenic Pb problem in chondrites  

USGS Publications Warehouse

U, Th, and Pb analyses of whole-rock and troilite separates from seven L chondrites suggest that the excess radiogenic Pb relative to U and the large variations in PbPb model ages commonly observed in chondritic meteorites are largely due to terrestrial Pb contamination induced prior to analyses. Using the Pb isotopic composition of troilite separates to calculate the isotopic composition of the Pb contaminants, the whole-rock data have been corrected for pre-analysis terrestrial Pb contamination. Two approaches have been used: (1) the chondrite-troilite apparent initial Pb isotopic compositions were used to approximate the mixture of indigenous intial Pb and terrestrial Pb in the whole-rock sample, and (2) a single-stage (concordant) model was applied using the assumption that the excess radiogenic Pb in these samples was terrestrial. Data for L5 and L6 chondrites yield a 4551 ?? 7 My age using the former correction and a 4550 ?? 5 My age using the latter one. Corrected data for one L4 chondrite, Tennasilm, yield a 4552 ?? 13 My age which is indistinguishable from that of the L5-L6 chondrites. However, the other L4 chondrite, Bjurbo??le, yields a 4590 ?? 6 My. ThUPb data suggest that this older age may be an artifact of the correction procedure, and that some of the discordancy of the Bjurbo??le data is the result of either a recent geologic disturbance to the UThPb system or to terrestrial U loss. Some aliquots of the L5L6 chondrites also show small amounts of discordancy (??? 10%) which are not easily attributable to terrestrial Pb contamination. The data from the L5-L6 chondrites and Tennasilm suggest that there are no more than ??? 15 MY differences in the ages of L24-L6 chondrites. ?? 1982.

Unruh, D.M.

1982-01-01

277

Internal Structure and Mineralogy of Differentiated Asteroids Assuming Chondritic Bulk Composition: The Case of Vesta  

NASA Technical Reports Server (NTRS)

Bulk composition (including oxygen content) is a primary control on the internal structure and mineralogy of differentiated asteroids. For example, oxidation state will affect core size, as well as Mg# and pyroxene content of the silicate mantle. The Howardite-Eucrite-Diogenite class of meteorites (HED) provide an interesting test-case of this idea, in particular in light of results of the Dawn mission which provide information on the size, density and differentiation state of Vesta, the parent body of the HED's. In this work we explore plausible bulk compositions of Vesta and use mass-balance and geochemical modelling to predict possible internal structures and crust/mantle compositions and mineralogies. Models are constrained to be consistent with known HED samples, but the approach has the potential to extend predictions to thermodynamically plausible rock types that are not necessarily present in the HED collection. Nine chondritic bulk compositions are considered (CI, CV, CO, CM, H, L, LL, EH, EL). For each, relative proportions and densities of the core, mantle, and crust are quantified. Considering that the basaltic crust has the composition of the primitive eucrite Juvinas and assuming that this crust is in thermodynamic equilibrium with the residual mantle, it is possible to calculate how much iron is in metallic form (in the core) and how much in oxidized form (in the mantle and crust) for a given bulk composition. Of the nine bulk compositions tested, solutions corresponding to CI and LL groups predicted a negative metal fraction and were not considered further. Solutions for enstatite chondrites imply significant oxidation relative to the starting materials and these solutions too are considered unlikely. For the remaining bulk compositions, the relative proportion of crust to bulk silicate is typically in the range 15 to 20% corresponding to crustal thicknesses of 15 to 20 km for a porosity-free Vesta-sized body. The mantle is predicted to be largely dominated by olivine (>85%) for carbonaceous chondrites, but to be a roughly equal mixture of olivine and pyroxene for ordinary chondrite precursors. All bulk compositions have a significant core, but the relative proportions of metal and sulphide can be widely different. Using these data, total core size (metal+ sulphide) and average core densities can be calculated, providing a useful reference frame within which to consider geophysical/gravity data of the Dawn mission.

Toplis, M. J.; Mizzon, H.; Forni, O.; Monnereau, M.; Prettyman, T. H.; McSween, H. Y.; McCoy, T. J.; Mittlefehldt, D. W.; DeSanctis, M. C.; Raymond, C. A.; Russell, C. T.

2012-01-01

278

Can Halogen Enrichment in Reduced Enstatite Chondrites Provide Clues to Volatile Accretion in the Early Earth?  

NASA Astrophysics Data System (ADS)

Understanding how the Earth obtained and ultimately retained its volatiles is important for our overall understanding of large scale planetary evolution. Numerous models exist for the heterogeneous accretion of volatiles to early Earth, but accounting for all elements through accretion of typical planetary building blocks (e.g., CI chondrites) is difficult. Proto-planetary collisions resulting in the accretion of volatile-poor material under reducing conditions followed by accretion of volatile-rich material under oxidizing conditions has been suggested in such models [e.g., 1]. The heavy halogens (Cl, Br and I), a group of moderately volatile elements, are excellent tracers of planetary processing due to their low abundance and incompatible nature. Therefore characterizing halogen abundance and distribution in materials that accreted to form the planets, e.g., primitive meteorites, is crucial. One group of primitive meteorites, the enstatite chondrites (EC's), are amongst the most reduced materials in the solar system as evidenced by their unique mineral assemblage. Yet despite forming under ultra-reducing conditions, they are enriched in the moderately volatile elements, such as the halogens. The ECs are of particular interest owing to their oxygen isotopic composition which plots along the terrestrial fractionation line, linking them isotopically to the Earth-Moon system. These samples can thus potentially provide clues on the accretion of moderately volatile element rich material under reducing conditions, such as it may have existed during the early stages of Earth's accretion. Chlorine, Br and I concentrations in ECs were determined through step-heating small neutron-irradiated samples (0.3 to 3.3 mg) and measured by mass spectrometry using the noble gas proxy isotopes 38ArCl/Cl, 80KrBr/Br and 128XeI/I. The EH chondrites are consistently enriched in the heavy halogens (up to 330 ppm Cl, 2290 ppb Br and 180 ppb I), compared to other ordinary and carbonaceous chondrites measured and have high molar I/Cl (~10-3) and Br/Cl (~10-3) ratios. For comparison, the ordinary chondrites have highly variable halogen concentrations and very low molar I/Cl (~10-6) and Br/Cl (~10-4) ratios. Halogen concentrations in the ECs are up to ~ 8 times higher for Cl, up to ~ 40 times higher for Br and up to ~ 50 times higher for I, when compared to estimates of halogen concentrations in the primitive mantle [2]. Potential halogen carrier phases in the ECs include Cl-rich feldspathic glass in chondrules, enstatite and/or the halogen-bearing sulfide djerfisherite. Accretion of halogen-rich, reduced material such as that observed here with the ECs could support models for heterogeneous accretion. Ongoing analyses of the primitive enstatite achondrites will shed additional light on these issues. [1] Wänke, H. Dreibus, G., Jagoutz E., Archaean Geochemistry, A. Kröner, G. N. Hanson, A. M. Goodwin, Eds. (Springer, Berlin, 1984), pp. 1-24. [2] Newsom, H.E., 1995. Global Earth Physics, A Handbook of Physical Constants, AGU Reference Shelf, vol. 1. American Geophysical Union, Washington.

Clay, P. L.; Burgess, R.; Busemann, H.; Ruzié, L.; Joachim, B.; Ballentine, C.

2013-12-01

279

Homeless Young People and Technology: Ordinary  

E-print Network

consequences for the U.S. By one estimate, 3 million young people experience homelessness annu- ally; that is, about 1 percent of the U.S. population is both young and homeless at some point each year [1- munity of homeless young people in Seattle, Washington, allowing us to explore ordinary uses of digital

Anderson, Richard

280

Compositions, geochemistry, and shock histories of recrystallized LL chondrites  

NASA Astrophysics Data System (ADS)

To examine compositional changes associated with high degrees of apparent thermal metamorphism among the LL chondrites, we have examined seven LL chondrites originally classified as being petrographic type 7. For comparison, we also analyzed the L6/7 chondrite Y-790124. We found that A-880933 is actually an LL4-6 genomict breccia and Y-790124 is best described as an L6 (S3) chondrite. The remaining six chondrites (EET 92013, Uden, Y-74160, Y-790144, Y-791067, Y-82067) are clearly of LL provenance, and each experienced temperatures high enough for them to have been recrystallized. In four of these samples (EET 92013, Uden, Y-74160, Y-790144) we find elemental patterns suggesting Fe(Ni)-FeS mobilization. Others (Y-791067, Y-82067) have compositions identical to average equilibrated LL chondrites. From our compositional data, we infer that EET 92013, Uden, Y-74160, Y-790144 experienced very low degrees of partial melting prior to recrystallization, but Y-791067 and Y-82067 experienced isochemical solid state recrystallization. The heat source responsible for the high degrees of thermal alteration of these meteorites is limited to either the decay of now extinct radionuclides (26Al) or impact-related heating. To evaluate the nature of the heat source, we use 40Ar-39Ar literature data and petrographic examinations to infer the cooling history and shock history of these chondrites. We find that heating due to impact is the most likely heat source for the heating of the recrystallized chondrites. The potential impacts occurred well after the initial stages of LL chondrite thermal metamorphism, but still early in the LL parent body’s history, probably ?4.2-4.3 Ga ago. These rocks experienced mild shock histories following their recrystallization.

Friedrich, Jon M.; Perrotta, Grace C.; Kimura, Makoto

2014-08-01

281

Iodine-Xenon Systematics of Mineral Separates from the Ordinary Chondrite Allegan and the Acapulcoite Dhofar 125  

NASA Astrophysics Data System (ADS)

We present I-Xe data for mineral separates from Allegan (H5) and Dhofar 125 (acapulcoite). Metals show younger ages (4500–4550 Ma) than silicates (Allegan:4563–4566 Ma and Dhofar 125: 4557.1 ± 0.5 Ma) for both meteorites.

Schönbächler, M.; Theis, K. J.; Crowther, S. A.; Gilmour, J. D.

2014-09-01

282

Thermal history modelling of the H chondrite parent body  

NASA Astrophysics Data System (ADS)

Context. The cooling histories of individual meteorites can be empirically reconstructed by using ages obtained from different radioisotopic chronometers having distinct closure temperatures. For a given group of meteorites derived from a single parent body such data permit the detailed reconstruction of the cooling history of that body. Particularly suited for this purpose are H chondrites because (i) all of them are thought to derive from a single parent body (possibly asteroid (6) Hebe) and (ii) for several specimens precise radiometric ages over a wide range of closure temperatures are available. Aims: A thermal evolution model for the H chondrite parent body is constructed by using the cooling histories of all H chondrites for which at least three different precise radiometric ages are available. The thermal model thus obtained is then used to constrain some important basic properties of the H chondrite parent body. Methods: Thermal evolution models are calculated using our previously developed code, which incorporates the effects of sintering and uses new thermal conductivity data for porous materials. Several key parameters determining the thermal evolution of the H chondrite parent body are varied together with the unknown original location of the H chondrites within their parent body until an optimal fit between the radiometric age data and the properties of the model is obtained. The fit is performed in an automated way based on an "evolution algorithm" to allow for a simultaneous fit of a large number of data, which depend in a complex way on several parameters. Empirical data for the cooling history of H chondrites are taken from the literature and the thermal model is optimised for eight samples for which radiometric ages are available for at least three different closure temperatures. Results: A set of parameters for the H chondrite parent body is found that yields excellent agreement (within error bounds) between the thermal evolution model and empirical data for the cooling histories of six of the examined eight H chondrites. For two of the samples significant discrepancies exist between model and empirical data, most likely reflecting inconsistencies in the empirical cooling data. The new thermal model constrains the radius and formation time of the H chondrite parent body, and the initial burial depths of the individual H chondrites. In addition, the model provides an estimate for the average surface temperature of the body, the average initial porosity of the material the body accreted from, and the initial 60Fe content of the H chondrite parent body.

Henke, S.; Gail, H.-P.; Trieloff, M.; Schwarz, W. H.; Kleine, T.

2012-09-01

283

Organic analysis of the Antarctic carbonaceous chondrites  

NASA Technical Reports Server (NTRS)

Thus far, organic analysis of carbonaceous chondrites has proven the only fruitful means of examining complex organic matter of extraterrestrial origin. The present paper presents the results of organic analysis of two Antarctic meteorites, Allan Hills (77306) and Yamato (74662), which may be considered free from terrestrial contamination. Ion-exchange chromatography, gas chromatography and mass spectrometery of meteorite samples reveal the presence in Yamato of 15 and in Allan Hills of 20 protein and nonprotein amino acids, the most abundant of which are glycine and alanine. Abundances of the D and L enantiomers of each amino acid are also found to be nearly equal. Data thus indicate an abiotic extraterrestrial origin for the matter, and confirm a lack of terrestrial contamination.

Kotra, R. K.; Shimoyama, A.; Ponnamperuma, C.; Hare, P. E.; Yanai, K.

1981-01-01

284

Analysis of the Allende chondritic meteorite's remanence  

NASA Astrophysics Data System (ADS)

We report a paleomagnetic study of the magnetic remanence recorded by a piece of the Allende carbonaceous chondritic meteorites. We have cut the sample up into sub-millimetre pieces to access the uniformity of the natural remanent magnetisation recorded through the meteorite. We have measured the anisotropy of anhysteretic remanent magnetization in the samples, to assess the degree to which magnetic fabrics may affect the recorded magnetic remanence. The main magnetic carrier was found to pyrrhotite. In addition, we have determined the ancient magnetic field intensities (paleointensities) recorded by the Allende meteorites. We have employed two non-heating methods of determining the ancient field intensity: (1) the calibrated REM method and (2) the newly developed Preisach-based approach that determines absolute paleointensities.

Muxworthy, A. R.; Moore, J.; Bland, P.

2010-12-01

285

Semarkona: Lessons for chondrule and chondrite formation  

E-print Network

We consider the evidence presented by the LL3.0 chondrite Semarkona, including its chondrule fraction, chondrule size distribution and matrix thermal history. We show that no more than a modest fraction of the ambient matrix material in the Solar Nebula could have been melted into chondrules; and that much of the unprocessed matrix material must have been filtered out at some stage of Semarkona's parent body formation process. We conclude that agglomerations of many chondrules must have formed in the Solar Nebula, which implies that chondrules and matrix grains had quite different collisional sticking parameters. Further, we note that the absence of large melted objects in Semarkona means that chondrules must have exited the melting zone rapidly, before the chondrule agglomerations could form. The simplest explanation for this rapid exit is that chondrule melting occurred in surface layers of the disk. The newly formed, compact, chondrules then settled out of those layers on short time scales.

Hubbard, Alexander

2014-01-01

286

Origin of organic compounds in carbonaceous chondrites  

NASA Astrophysics Data System (ADS)

Carbonaceous chondrites, a class of primitive meteorite, have long been known to contain their complement of carbon largely in the form of organic, i.e., hydrocarbon-related, matter. Both discrete organic compounds and an insoluble, macromolecular material are present. Several characteristics of these materials provide evidence for their abiotic origin. The principal formation hypothesis have invoked chemistry occurring either in the solar nebula or on the parent body. However, recent stable isotope analyses of the meteorite carboxylic acids and amino acids indicate that they may be related to interstellar cloud compounds. These results suggest a formation scheme in which interstellar compounds were incorporated into the parent body and subsequently converted to the present suite of meteorite organics by the hydrothermal process believed to have formed the clay minerals of the meteorite matrix.

Cronin, J. R.

287

Origin of plagioclase-olivine inclusions in carbonaceous chondrites  

NASA Astrophysics Data System (ADS)

The origin of plagioclase-olivine inclusions (POIs) from three CV chondrites and one ungrouped chondrite was investigated by examining the chemical, mineralogical, and isotopic characteristics of a group of POIs from these chondrites. Results of these analyses demonstrate that the mixing and the partial melting processes in these inclusions were superimposed on more ancient isotopically heterogeneous material. A comparison of the essential characteristics of POIs and CAIs suggests that the major processes leading to the formation of POIs (such as condensation, dust/gas fractionation, aggregation of chemically and isotopically disparate materials, and partial melting) are common to most CAIs and chondrules. A scenario for the origin of POIs is proposed, showing that the homogeneity of the final assemblage (whether a POI, a CAI, or a chondrite) is primarily a reflection of the thermal history rather than the nature of precursor materials.

Sheng, Y. J.; Hutcheon, I. D.; Wasserburg, G. J.

1991-02-01

288

Sm-Nd isotopic evolution of chondrites and achondrites. II  

NASA Astrophysics Data System (ADS)

The chondrite data obtained as a result of an investigation of Sm-147-Nd-143 and Sm-146-Nd142 isotope systematics in five chondrites and the Moama and Andra dos Reis (ADOR) achondrites are consistent with previously reported reference values for the chondritic uniform reservoir (CHUR) of 0.511847 and 0.1967. The Nd-143/Nd-144 and Sm-147/Nd-144 values of the bulk chondrites analyzed suggest that the CHUR evolution is known to within 0.5 epsilon-units and 0.15 percent of the CHUR values for the entire history of the solar system. The Sm-146-Nd-142 systematics of ADOR and Moama support the hypothesis that Sm-146 was present in the early solar system, suggesting a high Sm-146/Sm-144 ratio that cannot be explained as a late injection forma supernova, and must instead be due to galactic nucleosynthesis.

Jacobsen, S. B.; Wasserburg, G. J.

1984-02-01

289

Thermomagnetic analysis of meteorites, 2. C2 chondrites  

USGS Publications Warehouse

Samples of all eighteen of the known C2 chondrites have been analyzed thermomagnetically. For eleven of these, initial Fe3O4 content is low (generally <1%) and theJs-T curves are irreversible. The heating curves show variable greater (up to 10 times) than it is initially. This behavior is attributed to the production of magnetite from a thermally unstable phase - apparently FeS. Four of the remaining seven C2 chondrites contain Fe3O4 as the only significant magnetic phase: initial magnetite contents range from 4 to 13%. The remaining three C2 chondrites contain iron or nickel-iron in addition to Fe3O4. These seven C2 chondrites show little evidence of the breakdown of a thermally unstable phase. ?? 1975.

Watson, D.E.; Larson, E.E.; Herndon, J.M.; Rowe, M.W.

1975-01-01

290

The Dark Side of the CI Chondrite Orgueil  

NASA Astrophysics Data System (ADS)

Reflectance spectra of coals and their mixture with mineral phases are presented. The spectra of Orgueil is presented together with that of carbonaceous chondrites with contrasted parent body history. The nature of the darkening agent is discussed.

Beck, P.; Journaux, B.; Quirico, E.; Pommerol, A.; Bonal, L.; Schmitt, B.; Garenne, A.; Moynier, F.

2014-09-01

291

Cr Isotopic Anomalies and Fractionation in Carbonaceous Chondrites  

NASA Astrophysics Data System (ADS)

Cr isotopic compositions have been measured in fraction extracted by stepwise dissolution of Crabonaceous chondrites to look if the other isotopes than 54Cr are in anomalous (non mass dependent) proportions. Only 54Cr is anomalous.

Birck, J. L.; Göpel, C.

2012-09-01

292

Luminescence Characterization of Different Lithologies in Chelyabinsk LL5 Chondrite  

NASA Astrophysics Data System (ADS)

The present study is focused on the comparative analysis of spectral characteristics for light- and dark-colored lithologies in Chelyabinsk chondrite by means of photo-, thermo- and cathodoluminescence techniques.

Weinstein, I. A.; Vokhmintsev, A. S.; Ishchenko, A. V.; Grokhovsky, V. I.

2014-09-01

293

Parameter estimation in ordinary differential equations  

E-print Network

: Bart Childs (Chair of Committee) Daren B.H. Cline (Member) Vivek Sarin (Member) Valerie E. Taylor (Head of Department) May 2003 Major Subject: Computer Science iii ABSTRACT Parameter Estimation in Ordinary Differential Equations. (May 2003) Chee Loong... in Temasek Polytechnic v ACKNOWLEDGMENTS My greatest gratification and appreciation goes to Professor Childs, Professor Cline and Professor Sarin for their guidance and assistance. They have made my learning experiences at Texas A&M a fruitful and memorable...

Ng, Chee Loong

2004-09-30

294

Gamma Ray Bursts from Ordinary Cosmic Strings  

E-print Network

We give an upper estimate for the number of gamma ray bursts from ordinary (non-superconducting) cosmic strings expected to be observed at terrestrial detectors. Assuming that cusp annihilation is the mechanism responsible for the bursts we consider strings arising at a GUT phase transition and compare our estimate with the recent BATSE results. Further we give a lower limit for the effective area of future detectors designed to detect the cosmic string induced flux of gamma ray bursts.

R. H. Brandenberger; A. T. Sornborger; M. Trodden

1993-02-12

295

Maps between Deformed and Ordinary Gauge Fields  

E-print Network

In this paper, we introduce a map between the q-deformed gauge fields defined on the GL$_{q}(N) $-covariant quantum hyperplane and the ordinary gauge fields. Perturbative analysis of the q-deformed QED at the classical level is presented and gauge fixing $\\grave{a} $ la BRST is discussed. An other star product defined on the hybrid $(q,h) $% -plane is explicitly constructed .

L. Mesref

2005-04-13

296

Sulfide-rich metallic impact melts from chondritic parent bodies  

NASA Astrophysics Data System (ADS)

Sacramento Wash 005 (SaW) 005, Meteorite Hills 00428 (MET) 00428, and Mount Howe 88403 (HOW) 88403 are S-rich Fe,Ni-rich metal meteorites with fine metal structures and homogeneous troilite. We compare them with the H-metal meteorite, Lewis Cliff 88432. Phase diagram analyses suggest that SaW 005, MET 00428, and HOW 88403 were liquids at temperatures above 1350°C. Tridymite in HOW 88403 constrains formation to a high-temperature and low-pressure environment. The morphology of their metal-troilite structures may suggest that MET 00428 cooled the slowest, SaW 005 cooled faster, and HOW 88403 cooled the quickest. SaW 005 and MET 00428 contain H-chondrite like silicates, and SaW 005 contains a chondrule-bearing inclusion that is texturally and compositionally similar to H4 chondrites. The compositional and morphological similarities of SaW 005 and MET 00428 suggest that they are likely the result of impact processing on the H-chondrite parent body. SaW 005 and MET 00428 are the first recognized iron- and sulfide-rich meteorites, which formed by impact on the H-chondrite parent body, which are distinct from the IIE-iron meteorite group. The morphological and chemical differences of HOW 88403 suggest that it is not from the H-chondrite body, although it likely formed during an impact on a chondritic parent body.

Schrader, Devin L.; Lauretta, Dante S.; Connolly, Harold C. _jr., Jr.; Goreva, Yulia S.; Hill, Dolores H.; Domanik, Ken J.; Berger, Eve L.; Yang, Hexiong; Downs, Robert T.

2010-05-01

297

Petrologic study of the Belgica 7904 carbonaceous chondrite - Hydrous alteration, oxygen isotopes, and relationship to CM and CI chondrites  

NASA Technical Reports Server (NTRS)

The genetic relationships between the petrology, hydration reactions, and isotopic oxygen composition in the Belgica 7904 (B7904) carbonaceous chondrite, and the relationship between B7904 and the CM and CI chondrites were investigated by characterizing seven components separated from B7904. The seven specimens included two partially altered chondrules, two phylosilicate clasts, two olivine fragments, and one matrix sample. The results of the analyses and thermodynamic calculations suggest that CI chondrites may have been produced in a two-stage alteration process from materials similar to that of the B7904 matrix, by reactions with liquid water in their parent body. The common CM chondrites may have undergone aqueous alteration in the parent body, in addition to hydration in the nebula, resulting in two-stage alterations; the parent body may have been different from that of B7904.

Ikeda, Y.; Prinz, M.

1993-01-01

298

Amoeboid olivine aggregates from CH carbonaceous chondrites  

NASA Astrophysics Data System (ADS)

Amoeboid olivine aggregates (AOAs) in CH carbonaceous chondrites are texturally and mineralogically similar to those in other carbonaceous chondrite groups. They show no evidence for alteration and thermal metamorphism in an asteroidal setting and consist of nearly pure forsterite (Fa<3; in wt%, CaO = 0.1-0.8, Cr2O3 = 0.04-0.48; MnO < 0.5), anorthite, Al-diopside (in wt%, Al2O3 = 0.7-8.1; TiO2 < 1), Fe,Ni-metal, spinel, and, occasionally, low-Ca pyroxene (Fs1Wo2-3), and calcium-aluminum-rich inclusions (CAIs). The CAIs inside AOAs are composed of hibonite, grossite, melilite (Åk13-44), spinel, perovskite, Al,Ti-diopside (in wt%, Al2O3 up to 19.6; TiO2 up to 13.9), and anorthite. The CH AOAs, including CAIs within AOAs, have isotopically uniform 16O-rich compositions (average ?17O = -23.4 ± 2.3‰, 2SD) and on a three-isotope oxygen diagram plot along ?slope-1 line. The only exception is a low-Ca pyroxene-bearing AOA 1-103 that shows a range of ?17O values, from -24‰ to -13‰. Melilite, grossite, and hibonite in four CAIs within AOAs show no evidence for radiogenic 26Mg excess (?26Mg). In contrast, anorthite in five out of six AOAs measured has ?26Mg corresponding to the inferred initial 26Al/27Al ratio of (4.3 ± 0.7) × 10-5, (4.2 ± 0.6) × 10-5, (4.0 ± 0.3) × 10-5, (1.7 ± 0.2) × 10-5, and (3.0 ± 2.6) × 10-6. Anorthite in another AOA shows no resolvable ?26Mg excess; an upper limit on the initial 26Al/27Al ratio is 5 × 10-6. We infer that CH AOAs formed by gas-solid condensation and aggregation of the solar nebula condensates (forsterite and Fe,Ni-metal) mixed with the previously formed CAIs. Subsequently they experienced thermal annealing and possibly melting to a small degree in a 16O-rich gaseous reservoir during a brief epoch of CAI formation. The low-Ca pyroxene-bearing AOA 1-103 may have experienced incomplete melting and isotope exchange in an 16O-poor gaseous reservoir. The lack of resolvable ?26Mg excess in melilite, grossite, and hibonite in CAIs within AOAs reflects heterogeneous distribution of 26Al in the solar nebula during this epoch. The observed variations of the inferred initial 26Al/27Al ratios in anorthite of the mineralogically pristine and uniformly 16O-rich CH AOAs could have recorded (i) admixing of 26Al in the protoplanetary disk during the earliest stages of its evolution and/or (ii) closed-system Mg-isotope exchange between anorthite and Mg-rich minerals (spinel, forsterite, and Al-diopside) during subsequent prolonged (days-to-weeks) thermal annealing at high temperature (?1100 °C) and slow cooling rates (?0.01 K h-1) that has not affected their O-isotope systematics. The proposed thermal annealing may have occurred in an impact-generated plume invoked for the origin of non-porphyritic magnesian chondrules and Fe,Ni-metal grains in CH and CB carbonaceous chondrites about 5 Myr after formation of CV CAIs.

Krot, Alexander N.; Park, Changkun; Nagashima, Kazuhide

2014-08-01

299

Insights on Asteroid Partial Differentiation and Early Solar System Magnetic Fields Revealed by Paleomagnetism of Carbonaceous Chondrites  

NASA Astrophysics Data System (ADS)

Through a paleomagnetic study we test the new hypothesis that chondrites may originate from partially differentiated bodies (previously proposed for Allende (CV)). It appears that Kaba, another CV chondrite, and R chondrites confirm this possibility.

Cournède, C.; Gattacceca, J.; Rochette, P.; Weiss, B. P.

2014-09-01

300

Distinct Purine Distribution in Carbonaceous Chondrites  

NASA Technical Reports Server (NTRS)

Carbonaceous chondrite meteorites are known to contain a diverse suite of organic compounds, many of which are essential components of biochemistry. Amino acids, which are the monomers of proteins, have been extensively studied in such meteorites (e.g. Botta and Bada 2002; Pizzarello et aI., 2006). The origin of amino acids in meteorites has been firmly established as extraterrestrial based on their detection typically as racemic mixtures of amino acids, the presence of many non-protein amino acids, and non-terrestrial values for compound-specific deuterium, carbon, and nitrogen isotopic measurements. In contrast to amino acids, nucleobases in meteorites have been far less studied. Nucleobases are substituted one-ring (pyrimidine) or two-ring (purine) nitrogen heterocyclic compounds and serve as the information carriers of nucleic acids and in numerous coenzymes. All of the purines (adenine, guanine, hypoxanthine, and xanthine) and pyrimidines (uracil) previously reported in meteorites are biologically common and could be interpreted as the result of terrestrial contamination (e.g. van del' Velden and Schwartz, 1974.) Unlike other meteoritic organics, there have been no observations of stochastic molecular diversity of purines and pyrimidines in meteorites, which has been a criterion for establishing extraterrestrial origin. Maltins et al. (2008) performed compound-specific stable carbon isotope measurements for uracil and xanthine in the Murchison meteorite. They assigned a non-terrestrial origin for these nucleobases; however, the possibility that interfering indigenous molecules (e.g. carboxylic acids) contributed to the 13C-enriched isotope values for these nucleobases cannot be completely ruled out. Thus, the origin of these meteoritic nucleobases has never been established unequivocally. Here we report on our investigation of extracts of II different carbonaceous chondrites covering various petrographic types (Cl, CM, and CR) and degrees of aqueous alteration (l, 2, and 3) and one ureilite. Analysis via liquid chromatography coupled with electrospray triple-stage mass spectrometry or orbitrap mass spectrometry employed a targeted approach for analysis focused on the five canonical RNA/DNA nucleobases as well as 14 non-canonical pyrimidines and purines, which have bcen observed under plausible prebiotic reactions.

Callahan, Michael P.; Smith, Karen E.; Cleaves, Henderson J.; Ruzicka, Josef; Stern, Jennifer C.; Glavin, Daniel P.; House, Christopher H.; Dworkin, Jason P.

2011-01-01

301

The Glanerbrug Breccia: Evidence for a Separate L/LL-Chondritic Parent Body?  

NASA Astrophysics Data System (ADS)

INTRODUCTION. On April 7, 1990, a brecciated ordinary chondrite fell through the roof of a house near Glanerbrug in the Netherlands and was shattered to pieces. The total weight of the recovered fragments was about 800 g, the largest piece weighing 135 g. This main fragment clearly shows the inhomogeneous structure of the Glanerbrug: a dark-grey breccia occasionally containing blackish inclusions, separated from a light-grey breccia by a sharp boundary. Chondrules seem to be more common in the light grey parts. On the basis of earlier electron microprobe analyses of olivines and pyroxenes the light-grey portion was classified at the high Fa-Fs end of the L-field and the dark-grey part at the high Fa-Fs end of the LL-field [1]. Since it is not likely that the L and LL chondritic fragments originated on a single parent body, two alternative explanations were suggested: (i) The light-dark structure of the Glanerbrug is a characteristic feature of regolithic breccias, which once resided on or close to the surface of its parent body [2]. This lends some support to the idea that the light portion is an exotic clast in a dark host rock or vice versa; (ii) the two lithologies represent materials of a body having compositions between L and LL tentatively designated as L/LL [3,4]. Therefore additional electron microprobe analyses (EPMA) of silicates and kamacites in combination with neutron-activation analyses (INAA) of a light and a dark fragment and a noble gas analysis of a mixed light-dark fragment were undertaken. RESULTS and DISCUSSION. The light lithology in two thin sections shows olivine compositions in the L range (24.5+-0.3% Fa) and kamacite compositions (13.0+-1.3 mg/g Co) close to the LL range, plotting in the L/LL rather than in the L field on a kamacite-Co vs. olivine-Fa diagram [3,4]. Whereas only one aberrant olivine grain (out of 50) was found in the light portion, the dark portion is less homogeneous: one thin section shows olivine and kamacite compositions low in the LL field (27.0+-1.5% Fa and 15.0+-1.0 mg/g Co) whereas the olivines and kamacites in another thin section plot higher in the LL field (30.0+-1.0% Fa and 24+-4 mg/g Co). It also contains a small H chondritic inclusion (100 x 140 micrometers) and a blackish OC-fragment with widely varying silicate compositions and small (~10 micrometers) martensite grains a metal phase containing 97+-8 mg/g Ni typical for shock-reheated OCs [4]. Although this indicates that the dark portion once resided close to the surface of a parent body, no solar-wind implanted noble gases were found in a fragment consisting of both light and dark material [5] indicating that the Glanerbrug is a fragmental rather than a regolithic breccia [2]. The INAA study is still in progress but our first results on the light-grey sample show that the siderophiles are more like LL than L chondrites. These results leave two possible conclusions: (i) the Glanerbrug breccia originated on a single LL parent body, with the light and dark portions representing materials that formed from widely separated regions of the LL chondrite agglomeration zone; (ii) a light xenolithic L/LL fragment is incorporated into a dark LL chondritic host, while the latter was close to the surface of its parent body. The former would imply that at least some of the L/LL chondrites plotting in the upper part of the L/LL field on a kam-Co vs. ol-Fa diagram are a subgroup of the LL chondrites. However, since an olivine-Fa content of 24.5% is far below the LL range, such a conclusion can not be drawn solely on the basis of the Glanerbrug and therefore we prefer the second conclusion. From noble gas measurements [5] an average U,Th-He age of about 3.4 Ga was calculated, falling in the generally observed range of L/LL and LL chondrites [6], neither confirming nor rejecting our conclusions. Acknowledgements. We thank Dr. H.W. Weber and coworkers for the noble gas measurements. One of the authors (K.W.) is greatly indebted to Prof. Wasson and coworkers for their hospitality at UCLA. This work was financially supported by the &q

Welten, K. C.; Lindner, L.; Poorter, R. P. E.; Kallemeyn, G. W.; Rubin, A. E.; Wasson, J. T.

1992-07-01

302

Internal structure and mineralogy of differentiated asteroids assuming chondritic bulk composition: The case of Vesta  

NASA Astrophysics Data System (ADS)

Bulk composition (including oxygen content) is a primary control on the internal structure and mineralogy of differentiated asteroids. For example, oxidation state will affect core size, as well as Mg# and pyroxene content of the silicate mantle. The Howardite-Eucrite-Diogenite class of meteorites (HED) provide an interesting test-case of this idea, in particular in light of results of the Dawn mission which provide information on the size, density and differentiation state of Vesta, the parent body of the HED's. In this work we explore plausible bulk compositions of Vesta and use mass-balance and geochemical modelling to predict possible internal structures and crust/mantle compositions and mineralogies. Models are constrained to be consistent with known HED samples, but the approach has the potential to extend predictions to thermodynamically plausible rock types that are not necessarily present in the HED collection. Nine chondritic bulk compositions are considered (CI, CV, CO, CM, H, L, LL, EH, EL). For each, relative proportions and densities of the core, mantle, and crust are quantified. Considering that the basaltic crust has the composition of the primitive eucrite Juvinas and assuming that this crust is in thermodynamic equilibrium with the residual mantle, it is possible to calculate how much iron is in metallic form (in the core) and how much in oxidized form (in the mantle and crust) for a given bulk composition. Of the nine bulk compositions tested, solutions corresponding to CI and LL groups predicted a negative metal fraction and were not considered further. Solutions for enstatite chondrites imply significant oxidation relative to the starting materials and these solutions too are considered unlikely. For the remaining bulk compositions, the relative proportion of crust to bulk silicate is typically in the range 15 to 20% corresponding to crustal thicknesses of 15 to 20 km for a porosity-free Vesta-sized body. The mantle is predicted to be largely dominated by olivine (>85%) for carbonaceous chondrites, but to be a roughly equal mixture of olivine and pyroxene for ordinary chondrite precursors. All bulk compositions have a significant core, but the relative proportions of metal and sulphide can be widely different. Using these data, total core size (metal+ sulphide) and average core densities can be calculated, providing a useful reference frame within which to consider geophysical/gravity data of the Dawn mission. Further to these mass-balance calculations, the MELTS thermodynamic calculator has been used to assess to what extent chondritic bulk compositions can produce Juvinas-like liquids at relevant degrees of partial melting/crystallization. This work implies that alkali contents play a key role on the major element chemistry of basaltic liquids, and that basaltic eucrites were produced from melting and/or crystallization of an alkali-poor source. Overall, these results provide a useful and self-consistent reference frame for interpretation of the data from the VIR and GRaND instruments onboard the Dawn spacecraft.

Toplis, M. J.; Mizzon, H.; Forni, O.; Monnereau, M.; Prettyman, T. H.; McSween, H. Y.; McCoy, T. J.; Mittlefehldt, D. W.; De Sanctis, M. C.; Raymond, C. A.; Russell, C. T.

2012-12-01

303

7 CFR 28.407 - Good Ordinary Color.  

Code of Federal Regulations, 2010 CFR

... 2010-01-01 false Good Ordinary Color. 28.407 Section 28.407 Agriculture...Cotton Standards of the United States for the Color Grade of American Upland Cotton § 28.407 Good Ordinary Color. Good Ordinary Color is color...

2010-01-01

304

Is the Chondritic Earth model still viable? (Invited)  

NASA Astrophysics Data System (ADS)

Following the discovery by Boyet and Carlson in 2005 that the terrestrial 142Nd\\144Nd ratio is about 20 ? units higher than chondrites, papers with four different ideas explaining the observed difference have appeared in the literature. The first idea is that there is an early differentiated hidden reservoir on earth (Boyet & Carlson, 2005, 2006; Andreasen & Sharma, 2006, 2007; Andreasen et al., 2008; Carlson & Boyet, 2008). The second idea is that the solar nebula was isotopically heterogeneous (Ranen and Jacobsen, 2006). The third idea explains the isotope ratio difference as resulting from fractionation between Sm and Nd during condensation of solid materials from a nebula with higher Sm/Nd ratio (Allegre et al., 2008). The fourth idea suggests large-scale rare earth element fractionation following nebular condensation and possibly during the planetary accretionary phase (O’Neill & Palme, 2008; Warren, 2008). This last idea has gained currency as it has been argued that Mars is non-chondritic Sm/Nd ratio (Bourdon et al., 2008; Caro et al, 2008) and therefore the Earth-Moon system is also non-chondritic. All above scenarios, except for the first one imply a non-chondritic earth and therefore change the fundamental benchmark parameters against which we have been assessing the sense and magnitude of terrestrial evolution over thirty years. Is this really needed? How can we test some of the non-chondritic scenarios? If not, should we be seriously considering them even if they appear to be aesthetically appealing? In this paper I will review each of these scenarios and demonstrate why a chondritic earth model still remains attractive and provides testable explanations of the observed excess of 142Nd in terrestrial upper mantle over chondrites.

Sharma, M.

2009-12-01

305

Aqueous alteration of kamacite in CM chondrites  

NASA Astrophysics Data System (ADS)

The study of aqueous alteration of kamacite in CM chondrites provides insight on the conditions, products, and relative timing of aqueous alteration. We studied unaltered, partially altered, and fully altered kamacite grains from Murray, Murchison, Cold Bokkeveld, and Nogoya using optical microscopy, electron microprobe analysis, scanning electron microscopy, and Raman spectroscopy. From textual evidence and chemical analysis, we established three separate microchemical environments. 1) In a microchemical environment with a high S activity, kamacite alters to form tochilinite, P-bearing sulfides, eskolaite, and schreibersite. Mass balance calculations show that 81% of the Fe in kamacite is removed from the alteration region, making it available for the formation of other minerals or Fe-rich aureoles. The release of Fe can alter the mesostasis of type-I chondrules forming cronstedtite. 2) In a microchemical environment with a high Si activity and a low S activity, kamacite alters to form cronstedtite with small accessory sulfide inclusions. 3) A microchemical environment with limited S and Si activity results in kamacite alteration forming magnetite. The resulting magnetite retains associated Ni that can distinguish it from precipitated magnetite. In addition, the accessory phases of pentlandite and apatite can be formed if S or Ca are present. Finally, we note that small tochilinite grains in the matrix lack typical Ni, P, and Co levels, suggesting that they did not form from kamacite but possibly by sulfidization of magnetite.

Palmer, Eric E.; Lauretta, Dante S.

2011-10-01

306

Early Chronology of the H Chondrite Asteroid  

NASA Astrophysics Data System (ADS)

We are actually witnessing an exciting transition between our past ignorance on asteroid prehistories and a better understanding of their early thermal evolution. This is the result of data from absolute (U/Pb, Ar-Ar) and relative (^244Pu, ^26Al) chronologies obtained on one object having the simplest post-accretional thermal history: the H-asteroid. The motor of this deciphering has been the recent confirmation of the previously suggested "onion-shell" model (Pellas and Storzer, 1981), with U/Pb absolute ages anticorrelated with petrological types (Gopel et al., 1991). The very fast cooling of three (unshocked) H4 chondrites (Ste Marguerite: SM, Forest Vale and Beaver Creek: BC) from their peak metamorphic temperature (700 K) was confirmed both by metallography and Pu fission track thermometry (Lipschutz et al., 1989). This observation, first made on BC, led to predict the possible presence of live ^26Al in feldspars of this chondrite (Pellas and Storzer, 1981). This prediction is confirmed today by the discovery of live ^26Al in SM feldspars (Zinner and Gopel, this conf.), with an abundance sufficient to explain the mild metamorphism of petrological type 4, together with the fact that the more metamorphosed H6 chondrites did not melt. From this observation an upper limit of 3 Ma can be inferred between the condensation-accretion, the heating spike due to ^26Al decay, and the cooling which has frozen the feldspar phase of SM. Such an upper limit corresponds to the formation time of the H-asteroid. The fast cooling of some H4 materials does also preclude the existence of an insulating regolith of petrologic type 3, which would have drastically slowed down the cooling process, as already suggested (Pellas and Storzer, 1981). Consequently, accretion of type 3 materials must have occurred later. This result appears to discard the hypothesis of electromagnetic induction in the protosolar wind as the effective heat source (Herbert et al., 1991). The ^26Al heating also has important implications for our understanding of the compositional gradient in the asteroid belt (Gradie and Tedesco, 1982), which must be an inherent property of the condensing nebula (as is the case for the planets). This confirms the conclusions of Wood and Pellas (1991). From the above observations, and provided that a phase with high Fe/Ni ratios is found, it seems safe to predict that live ^60Fe could also be detected in those H4 chondrites that cooled fast, and which therefore must present a much higher ^60Fe/^56Fe ratio than that measured in Chervony Kut eucrite (Shukolyukov and Lugmair, 1992). Thus it seems that we are close to finally understanding the motor(s) of metamorphism and differentiation to which planetesimals were subjected around 4.565 Ga ago, in full agreement with Urey's earlier suggestions (1955). REFERENCES: Gopel C., Manhes G., and Allegre C. (1991) Meteoritics 26, 338. Gradie J.C. and Tedesco E. (1982) Science 216, 1405-1407. Herbert F., Sonett C.P., and Gaffey M.J. (1991) in The Sun in Time (eds. C.P. Sonett, M.S. Giampapa, and M.S. Matthews) pp. 710-739. Univ. Arizona Press, Tucson, Arizona. Lipschutz M.E., Gaffey M.J., and Pellas P. (1989) in Asteroids II (eds. R.P. Binzel, T. Gehrels and M.S. Matthews) pp. 740-777. Pellas P. and Storzer D. (1981) Proc. R. Soc. Lond. A374, 253-270. Shukolyukov A. and Lugmair G.W. (1992) Lunar Planet. Sci. (abstract) 23, 1295. Wood J.A. and Pellas P. (1991) in The Sun in Time (eds. C.P. Sonett, M.S. Giampapa, and M.S. Matthews) pp. 740-760. Urey H.C. (1955) Proc. Acad. Sci. U.S. 41, 127-144. Zinner E. and Gopel C. (1992) Abstract 55th Annual Meeting Meteoritical Soc. (this volume).

Pellas, P.

1992-07-01

307

Shock Heating: Effects on Chondritic Material  

NASA Technical Reports Server (NTRS)

At the 1994 Conference on Chondrules and the Protoplanetary Disk, shock waves were discussed as mechanisms that may have been responsible for forming chondrules, millimeter-sized igneous spheres which are significant components of chondritic meteorites, and references therein]. At the time, shock waves were appealing because they were thought to be brief, repetitive events that were quantitatively shown to be able to rapidly heat silicates to the appropriate temperatures for chondrule formation. Since that meeting, more detailed models for the thermal processing of material in shock waves have been developed. These models have tracked the thermal evolution of the silicates for longer periods of time and found that their cooling rates are also consistent with what has been inferred for chondrules. In addition to the thermal histories of these particles, shock waves may be able to explain a number of other features observed in primitive meteorites. Here, we review the recent work that has been done in studying the interaction of solids with shock waves in the solar nebula.

Desch, S. J.; Ciesla, F. J.; Hood, L. L.; Nakamoto, T.

2004-01-01

308

published in Nordic Journal of Computing, 6:462-468, 1999 Finding an ordinary conic and an ordinary  

E-print Network

published in Nordic Journal of Computing, 6:462-468, 1999 Finding an ordinary conic and an ordinary an ordinary conic, that is, a conic passing through exactly five points, assuming that all the points do not lie on the same conic. Both our proofs of existence and the consequent algorithms are simpler than

Paris-Sud XI, Université de

309

Chemical fractionations in meteorites. XI - C2 chondrites  

NASA Technical Reports Server (NTRS)

Measurements of the compositions of 20 trace elements in the representative C2 chondrites Boriskino, Cold Bokkeveld, Erakot, Essebi, Haripura, Santa Cruz and Al Rais are reported. The contents of Ag, Au, Bi, Cd, Cs, Ge, In, Ir, Ni, Os, Pd, Rb, Re, Sb, Se, Sn, Te, Tl, U, and Zn were determined by radiochemical neutron activation analysis. The siderophile abundances of the C2 chondrites are found to be less uniform than those of other carbonaceous chondrites, while the C2R chondrite Al Rais is systematically lower in 12 volatiles than the C2M chondrites. Enrichment of Bi and Tl found in Erakot and Haripura indicate the possible presence of the late condensate mysterite. Volatile abundances are shown to agree with matrix contents for meteorites that have suffered little aqueous alteration, however to be 20-30% lower for the more altered meteorites. Finally, the decline of element abundance with volatility is shown to be consistent with the sigmoid curve explained by the two-component model.

Wolf, R.; Richter, G. R.; Woodrow, A. B.; Anders, E.

1980-01-01

310

Chemical fractionations in meteorites. XI - C2 chondrites  

NASA Astrophysics Data System (ADS)

Measurements of the compositions of 20 trace elements in the representative C2 chondrites Boriskino, Cold Bokkeveld, Erakot, Essebi, Haripura, Santa Cruz and Al Rais are reported. The contents of Ag, Au, Bi, Cd, Cs, Ge, In, Ir, Ni, Os, Pd, Rb, Re, Sb, Se, Sn, Te, Tl, U, and Zn were determined by radiochemical neutron activation analysis. The siderophile abundances of the C2 chondrites are found to be less uniform than those of other carbonaceous chondrites, while the C2R chondrite Al Rais is systematically lower in 12 volatiles than the C2M chondrites. Enrichment of Bi and Tl found in Erakot and Haripura indicate the possible presence of the late condensate mysterite. Volatile abundances are shown to agree with matrix contents for meteorites that have suffered little aqueous alteration, however to be 20-30% lower for the more altered meteorites. Finally, the decline of element abundance with volatility is shown to be consistent with the sigmoid curve explained by the two-component model.

Wolf, R.; Richter, G.; Woodrow, A.; Anders, E.

1980-05-01

311

Primitive Fine-Grained Matrix in the Unequilbrated Enstatite Chondrites  

NASA Technical Reports Server (NTRS)

Enstatite chondrites (EC) have important implications for constraining conditions in the early solar system and for understanding the evolution of the Earth and other inner planets. They are among the most reduced solar system materials as reflected in their mineral compositions and assemblage. They are the only chondrites with oxygen as well as Cr, Ti, Ni and Zn stable isotope compositions similar to the earth and moon and most are completely dry, lacking any evidence of hydrous alteration; the only exception are EC clasts in the Kaidun breccia which have hydrous minerals. Thus, ECs likely formed within the snow line and are good candidates to be building blocks of the inner planets. Our goals are to provide a more detailed characterization the fine-grained matrix in E3 chondrites, understand its origin and relationship to chondrules, decipher the relationship between EH and EL chondrites and compare E3 matrix to matrices in C and O chondrites as well as other fine-grained solar system materials. Is E3 matrix the dust remaining from chondrule formation or a product of parent body processing or both?

Weisberg, M. K.; Zolensky, M. E.; Kimura, M.; Ebel, D. S.

2014-01-01

312

Magnetic evidence for a partially differentiated carbonaceous chondrite parent body  

PubMed Central

The textures of chondritic meteorites demonstrate that they are not the products of planetary melting processes. This has long been interpreted as evidence that chondrite parent bodies never experienced large-scale melting. As a result, the paleomagnetism of the CV carbonaceous chondrite Allende, most of which was acquired after accretion of the parent body, has been a long-standing mystery. The possibility of a core dynamo like that known for achondrite parent bodies has been discounted because chondrite parent bodies are assumed to be undifferentiated. Resolution of this conundrum requires a determination of the age and timescale over which Allende acquired its magnetization. Here, we report that Allende’s magnetization was acquired over several million years (Ma) during metasomatism on the parent planetesimal in a >  ? 20 ?T field up to approximately 9—10 Ma after solar system formation. This field was present too recently and directionally stable for too long to have been generated by the protoplanetary disk or young Sun. The field intensity is in the range expected for planetesimal core dynamos, suggesting that CV chondrites are derived from the outer, unmelted layer of a partially differentiated body with a convecting metallic core.

Carporzen, Laurent; Weiss, Benjamin P.; Elkins-Tanton, Linda T.; Shuster, David L.; Ebel, Denton; Gattacceca, Jerome

2011-01-01

313

The Lockne Impact is not Related to the Ordivician L-Chondrite Shower  

NASA Astrophysics Data System (ADS)

Geochemistry of projectile traces from the Lockne impact structure, Sweden suggests the presence of a non-chondritic projectile, negating previous claims of a connection of this crater to the Ordovician L-chondrite shower.

Tagle, R.; Schmitt, R. T.; Erzinger, J.

2008-03-01

314

GRO 95577 and MIL 090292: The Most Aqueously Altered CR Chondrites  

NASA Astrophysics Data System (ADS)

The CR Chondrite group exhibits the full range of aqueous alteration. MIL 090292 is an aqueously altered chondrite with abundant phyllosilicate and oxides similar to GRO 95577. It appears to be the second fully altered CR2.0.

Harju, E. R.; Rubin, A. E.

2013-09-01

315

Do We Already have Samples of Ceres? H Chondrite Halites and the Ceres-Hebe Link  

NASA Astrophysics Data System (ADS)

We investigate the hypothesis that halites in the H chondrites Zag and Monahans originate from Ceres. Evidence includes mineralogy of the halites and orbital simularities between 1 Ceres and the purported H chondrite parent body 6 Hebe.

Fries, M.; Messenger, S.; Steele, A.; Zolensky, M.

2013-09-01

316

The High-Temperature History and Primary Structure of the L Chondrite Parent Body  

NASA Astrophysics Data System (ADS)

We present internal Hf-W isochrons for 8 equilibrated L chondrites of all petrologic types. Decreasing Hf-W ages with increasing petrologic type show that the L chondrite parent body had a concentrically layered primary structure.

Sprung, P.; Göpel, C.; Kleine, T.; van Orman, J. A.; Maden, C.

2011-03-01

317

Some evidence for the possible presence of peptides in two chondrites by use of a sequencing procedure  

NASA Astrophysics Data System (ADS)

In hot water extracts of samples from interior of two ordinary chondrites (Goumoshnik and Pavel) after acid hydrolysis using diphenylindonyl-isothiocyanate (DIITC) and fluorescent detection (FD) of the obtained diphenylindonyl thiohydantoins (ITH) 10 to 13 protein and nonprotein amino acids were found. In the same manner the presence of compounds containing amino groups but not of free amino acids was established in nonhyhdrolysed extracts. 'Sequencing' was performed on the amino compounds using DIITC and FD of the cleaved ITH up to 9 steps with extracts of Goumoshnik and up to 14 with those of Pavel. At each step 1 to 6 different protein and nonprotein amino acids were liberated. The presence of nonprotein amino acids supports the view that the peptides in meteorites are indigenous.

Ivanov, Ch. P.; Stoyanova, R. Zh.; Mancheva, I. N.

1984-12-01

318

Gas flow and fluidization in a thick dynamic regolith: A new mechanism for the formation of chondritic meteorites  

NASA Technical Reports Server (NTRS)

We have previously shown that size and density sorting in a regolith which has been 'fluidized' by the passage or gases from the interior or the body can quantitatively explain metal-silicate fractionation, an important property of ordinary chondrites. Here we discuss whether the flow rates and flux or volatiles expected from a primitive parent body are likely to be sufficient for this mechanism. Many meteorite parent bodies may have contained volatiles. From a consideration of heat diffusion and fluid mechanics, we calculate the gas flow rate of volatiles (e.g., water) in the regolith of an asteroid-sized object heated by Al-26. Our calculations show that the flow velocities and flux of water vapor are sufficient to produce conditions suitable for fluidization. Other heat sources have yet to be considered, but literature work suggests that they may be equally effective.

Huang, Shaoxiong; Sears, Derek W. G.

1995-01-01

319

57 Fe Mössbauer spectroscopy studies of chondritic meteorites from the Atacama Desert, Chile: Implications for weathering processes  

NASA Astrophysics Data System (ADS)

Some terrestrial areas have climatic and geomorphologic features that favor the preservation, and therefore, accumulation of meteorites. The Atacama Desert in Chile is among the most important of such areas, known as dense collection areas. This desert is the driest on Earth, one of the most arid, uninhabitable locals with semi-arid, arid and hyper-arid conditions. The meteorites studied here were collected from within the dense collection area of San Juan at the Central Depression and Coastal Range of Atacama Desert. 57Fe Mössbauer spectroscopy was used for quantitative analysis of the degree of weathering of the meteorites, through the determination of the proportions of the various Fe-bearing phases and in particular the amount of oxidized iron in the terrestrial alteration products. The abundance of ferric ions in weathered chondrites can be related to specific precursor compositions and to the level of terrestrial weathering. The aim of the study was the identification, quantification and differentiation of the weathering products in the ordinary chondrites found in the San Juan area of Atacama Desert.

Munayco, P.; Munayco, J.; Valenzuela, M.; Rochette, P.; Gattacceca, J.; Scorzelli, R. B.

2014-01-01

320

Organic Analysis of Catalytic Fischer-Tropsch Type Synthesis Products: Are they Similar to Organics in Chondritic Meteorites?  

NASA Technical Reports Server (NTRS)

Fischer-Tropsch Type (FTT) synthesis of organic compounds has been hypothesized to occur in the early solar nebula that formed our Solar System. FTT is a collection of abiotic chemical reactions that convert a mixture of carbon monoxide and hydrogen over nano-catalysts into hydrocarbons and other more complex aromatic compounds. We hypothesized that FTT can generate similar organic compounds as those seen in chondritic meteorites; fragments of asteroids that are characteristic of the early solar system. Specific goals for this project included: 1) determining the effects of different FTT catalyst, reaction temperature, and cycles on organic compounds produced, 2) imaging of organic coatings found on the catalyst, and 3) comparison of organic compounds produced experimentally by FTT synthesis and those found in the ordinary chondrite LL5 Chelyabinsk meteorite. We used Pyrolysis Gas Chromatography Mass Spectrometry (PY-GCMS) to release organic compounds present in experimental FTT and meteorite samples, and Scanning Electron Microscopy (SEM) to take images of organic films on catalyst grains.

Yazzie, Cyriah A.; Locke, Darren R.; Johnson, Natasha M.

2014-01-01

321

Chondritic Meteorites: Nebular and Parent-Body Formation Process  

NASA Technical Reports Server (NTRS)

Chondritic meteorites are the products of condensation, agglomeration and accretion of material in the solar nebula; these objects are the best sources of information regarding processes occurring during the early history of the solar system. We obtain large amounts of high-quality chemical and petrographic data and use them to infer chemical fractionation processes that occurred in the solar nebula and on meteorite parent bodies during thermal metamorphism, shock metamorphism and aqueous alteration. We compare diverse groups of chondrites and model their different properties in terms of processes that differed at different nebular locations or on different parent-bodies. In order to expand our set of geochemically important elements (particularly Si, C, P and S) and to distinguish the different oxidation states of Fe, Greg Kallemeyn spent three months (1 Sept. - 30 Nov. 1995) at the Smithsonian Institution to learn Eugene Jarosewich's wet chemical techniques. Key specimens from the recently established CK, CR and R chondrite groups were analyzed.

Rubin, Alan E.

1997-01-01

322

A Weathering Index for CK and R Chondrites  

NASA Technical Reports Server (NTRS)

We present a new weathering index (wi) for the metallic-Fe-Ni-poor chondrite groups (CK and R) based mainly on transmitted light observations of the modal abundance of crystalline material that is stained brown in thin sections: wi-0, <5 vol%; wi-1, 5-25 vol%; wi-2,25-50 vol%; wi-3,50- 75 vol%; wi-4, 75-95 vol%; wi-5, >95 vol%, wi-6, significant replacement of mafic silicates by phyllosilicates. Brown staining reflects mobilization of oxidized iron derived mainly from terrestrial weathering of Ni-bearing sulfide. With increasing degrees of terrestrial weathering of CK and R chondrites, the sulfide modal abundance decreases, and S, Se, and Ni become increasingly depleted. In addition, bulk Cl increases in Antarctic CK chondrites, probably due to contamination from airborne sea mist.

Rubin, Alan E.; Huber, Heinz

2006-01-01

323

Fine structures of mutually normalized rare-earth patterns of chondrites  

Microsoft Academic Search

REE abundances in ten chondrites (nine falls and one find) were determined very accurately by mass-spectrometric stable isotope dilution techniques. All of the chondrites have different relative and absolute REE patterns. Except for Eu and, rarely, for Ce, the REE abundances in chondrites are smoothly fractionated from sample to sample. Notwithstanding differences in the abundances of common REE, four of

Akimasa Masuda; Noboru Nakamura; Tsuyoshi Tanaka

1973-01-01

324

Diverse and Unusual O-Chondrites from the Lut Desert, Iran  

NASA Astrophysics Data System (ADS)

We discuss unusual textural features of three new type 3 chondrites (H3, L3, LL3) from the Lut desert. Together with a new H4 chondrite and Shahdad (H5), there appears to be a great variety of O-chondrites in the Lut desert of Iran.

Hutson, M. L.; Ruzicka, A. M.; Nazari, M.

2014-09-01

325

Chemical fractionations in meteorites--III. Major element fractionations in chondrites  

Microsoft Academic Search

Some 20 elements, including the major constituents of chondritic matter, are fractionated among the several chondrite classes. We have tried to explain these fractionations on the assumption that they occurred in the solar nebula, starting from material of carbonaceous chondrite composition. 1. (1) Lithophile elements (Al, Ca, Cr, Hf, Mg, Sc, Si, Th, Ti, U, Y, Zr, and lanthanides) may

J. W. Larimer; Edward Anders

1970-01-01

326

Non-nebular origin of dark mantles around chondrules and inclusions in CM chondrites  

Microsoft Academic Search

Our examination of nine CM chondrites that span the aqueous alteration sequence leads us to conclude that compact dark fine mantles surrounding chondrules and inclusions in CM chondrites are not discrete fine-grained rims acquired in the solar nebula as modeled by Metzler et al. [Accretionary dust mantles in CM chondrites: evidence for solar nebula processes. Geochim. Cosmochim. Acta56, 1992, 2873

Josep M. Trigo-Rodriguez; Alan E. Rubin; John T. Wasson

2006-01-01

327

Speciation of sulfur in the insoluble organic matter from carbonaceous chondrites by XANES spectroscopy  

E-print Network

Speciation of sulfur in the insoluble organic matter from carbonaceous chondrites by XANES-edge XANES aqueous alteration carbonaceous chondrites oxidation sulfur speciation Sulfur speciation chondrites has been studied by K-edge XANES micro-spectroscopy. Five main sulfur groups were identified: (1

328

Mn-53-Cr-53 Systematics of R-Chondrite NWA 753  

NASA Technical Reports Server (NTRS)

Chondrules and chondrites are interpreted as objects formed in the early solar system, and it is important to study them in order to elucidate its evolution. Here, we report the study of the Mn-Cr systematics of the R-Chondrite NWA753 and compare the results to other chondrite data. The goal was to determine Cr isotopic and age variations among chondrite groups with different O-isotope signatures. The Mn-53-Cr-53 method as applied to individual chondrules [1] or bulk chondrites [2] is based on the assumption that 53Mn was initially homogeneously distributed in that portion the solar nebula where the chondrules and/or chondrites formed. However, different groups of chondrites formed from regions of different O-isotope compositions. So, different types of chondrites also may have had different initial Mn-53 abundances and/or Cr isotopic compositions. Thus, it is important to determine the Cr isotopic systematics among chondrites from various chondrite groups. We are studying CO-chondrite ALH83108 and Tagish Lake in addition to R-Chondrite NWA753. These meteorites have very distinct O-isotope compositions (Figure 1).

Jogo, K.; Shih, C-Y.; Reese, Y. D.; Nyquist, L. E.

2006-01-01

329

Universal formats for nonlinear ordinary differential systems  

SciTech Connect

It is shown that very general nonlinear ordinary differential systems (embracing all that arise in practice) may, first, be brought down to polynomial systems (where the nonlinearities occur only as polynomials in the dependent variables) by introducing suitable new variables into the original system; second, that polynomial systems are reducible to ''Riccati systems,'' where the nonlinearities are quadratic at most; third, that Riccati systems may be brought to elemental universal formats containing purely quadratic terms with simple arrays of coefficients that are all zero or unity. The elemental systems have representations as novel types of matrix Riccati equations. Different starting systems and their associated Riccati systems differ from one another, at the final elemental level, in order and in initial data, but not in format.

Kerner, E.H.

1981-07-01

330

Ordinary planetary systems - Architecture and formation  

NASA Technical Reports Server (NTRS)

Today we believe ordinary planetary systems to be an unremarkable consequence of star formation. The solar system, so far the only confidently known example in the universe of a planetary system, displays a set of striking structural regularities. These structural regularities provide fossil clues about the conditions and mechanisms that gave rise to the planets. The formation of our planetary system, as well as its general characteristics, resulted from the physical environment in the disk-shaped nebula that accompanied the birth of the sun. Observations of contemporary star formation indicate that the very conditions and mechanisms thought to have produced our own planetary system are widely associated with the birth of stars elsewhere. Consequently, it is reasonable to believe that planetary systems occur commonly, at least in association with single, sunlike stars. Moreover, it is reasonable to believe that many planetary systems have gross characteristics resembling those of our own solar system.

Levy, E. H.

1993-01-01

331

A few remarks on ordinary differential equations  

SciTech Connect

We present in this note existence and uniqueness results for solutions of ordinary differential equations and linear transport equations with discontinuous coefficients in a bounded open subset {Omega} of R{sup N} or in the whole space R{sup N} (N {ge} 1). R.J. Di Perna and P.L. Lions studied the case of vector fields b with coefficients in Sobolev spaces and bounded divergence. We want to show that similar results hold for more general b: we assume in the bounded autonomous case that b belongs to W{sup 1,1}({Omega}), b.n = 0 on {partial_derivative}{Omega}, and that there exists T{sub o} > O such that exp(T{sub o}{vert_bar}div b{vert_bar}) {element_of} L{sup 1}({Omega}). Furthermore, we establish results on transport equations with initial values in L{sup p} spaces (p > 1). 9 refs.

Desjardins, B. [Universite Paris Dauphine (France)

1996-12-31

332

Carbonaceous Chondrite Fragments in the Polymict Eucrite Yamato 791834  

NASA Technical Reports Server (NTRS)

Buchanan et al. and Zolensky et al. described carbonaceous chondrite fragments in a variety of howardites and concluded that the majority are CM2 and CR2 materials. Gounelle et al. also described similar, but very small, fragments in these meteorites. These clasts are important because they represent materials that were in orbital proximity to the HED parent body (4 Vesta) and they may be similar to the primitive materials that originally accreted to form this body. The present study describes two carbonaceous chondrite clasts in the Yamato 791834 (Y791834) polymict eucrite.

Buchanan, P. C.; Zolensky, M. E.

2003-01-01

333

Refractory inclusions in the Ornans C30 chondrite  

NASA Technical Reports Server (NTRS)

Several types of metedorites contain unusual objects 10 micrometers to 2 centimeters across that are enriched in refractory elements such as calcium, aluminum and titanium. These objects, commonly known as refractory inclusions, are most abundant in the meteorites known as carbonaceous chondrites. The refractory inclusions that have been found in the Ornans metedorite, a member of a little-studied group of carbonaceous chondrites are described. Some refractory inclusions in Ornans resemble those found in other meteorites, while others are unlike any seen before. The unusual inclusions in Ornans contain minerals with extraordinary enrichments in highly refractory elements.

Davis, A. M.

1985-01-01

334

The Kramer Creek, Colorado meteorite - A new L4 chondrite  

NASA Technical Reports Server (NTRS)

Results of bulk chemical analyses and mineralogical and petrographic studies of a chondrite found at Kramer Creek, Colorado, are reported. The meteorite has been classified as an L-group chondrite on the basis of its bulk chemistry, the fayalite content of its olivine (21.7%) and the ferrosilicate content of its pyroxene (18.3%). The presence of interstitial glass and the iron oxide percent mean deviations for olivine and low-Ca pyroxene (2.4 and 4.6%) place the specimen in petrologic group 4 of the Van Schmus and Wood classification (1967)

Gibson, E. K., Jr.; Lange, D. E.; Keil, K.; Schmidt, T. E.; Rhodes, J. M.

1977-01-01

335

Micrometeorite precursors: Clues from the mineralogy and petrology of their relict minerals  

NASA Astrophysics Data System (ADS)

We analyzed 91 relict grain-bearing micrometeorites (MMs) from two Antarctic collections: Tottuki icefield and the South Pole Water Well. To determine if the MMs are related to specific meteorite groups, we analyzed their relict olivines and low-Ca pyroxenes and compared them with olivines and pyroxenes we analyzed in various meteorites: an enstatite chondrite (EH3), a suite of carbonaceous chondrites (CM2, CR2, CV3.2, CO3.0, and CO3.2), an ungrouped carbonaceous chondrite (Tagish Lake), various unequilibrated ordinary chondrites (H3.2, L3.7, LL3.0, LL3.2, LL3.3), and a Rumuruti chondrite (R3.5/5 breccia). Mg-rich olivines are the most common relict mineral in the MMs studied (42%), followed by Fe-rich olivines (16%), Mg-rich low-Ca pyroxenes (15%), and MMs containing both Mg-rich olivine and low-Ca pyroxene (13%). If one corrects for the effects of atmospheric heating on the proportion of olivines and pyroxenes, then 59% of MMs are related to carbonaceous chondrites, 22% to ordinary chondrites (mostly unequilibrated, UOCs), and 19% to a high-Mn group. Results of textural observations suggest that four MMs resemble chondrules from CO3 carbonaceous chondrites, and one is a shock-melted H chondrite. MMs from the high-Mn group appear to have crystallized from a melt and might be fragments of chondrule-like objects similar to those found in comet 81P/Wild 2.

Imae, Naoya; Taylor, Susan; Iwata, Naoyoshi

2013-01-01

336

Pyroxene structures, cathodoluminescence and the thermal history of the enstatite chondrites  

NASA Technical Reports Server (NTRS)

In order to explore the thermal history of enstatite chondrites, we examined the cathodoluminescence (CL) and thermoluminescence (TL) properties of 15 EH chondrites and 21 EL chondrites, including all available petrographic types, both textural types 3-6 and mineralogical types alpha-delta. The CL properties of EL3(alpha) and EH3(alpha) chondrites are similar. Enstatite grains high in Mn and other transition metals display red CL, while enstatite with low concentrations of these elements show blue CL. A few enstatite grains with greater than 5 wt% FeO display no CL. In contrast, the luminescent properties of the metamorphosed EH chondrites are very different from those of metamorphosed EL chondrites. While the enstatites in metamorphosed EH chondrites display predominantly blue CL, the enstatites in metamorphosed EL chondrites display a distinctive magenta CL with blue and red peaks of approximately equal intensity in their spectra. The TL sensitivities of the enstatite chondrites correlate with the intensity of the blue CL and, unlike other meteorite classes, are not simply related to metamorphism. The different luminescent properties of metamorphosed EH and EL chondrites cannot readily be attributed to compositional differences. But x-ray diffraction data suggests that the enstatite in EH5(gamma),(delta) chondrites is predominantly disordered orthopyroxene, while enstatite in EL6(beta) chondrites is predominantly ordered orthopyroxene. The difference in thermal history of metamorphosed EL and EH chondrites is so marked that the use of single 'petrographic' types is misleading, and separate textural and mineralogical types are preferable. Our data confirm earlier suggestions that metamorphosed EH chondrites underwent relatively rapid cooling, and the metamorphosed EL chondrites cooled more slowly and experienced prolonged heating in the orthopyroxene field.

Zhang, Yanhong; Huang, Shaoxiong; Schneider, Diann; Benoit, Paul H.; Sears, Derek W. G.; DeHart, John M.; Lofgren, Gary E.

1996-01-01

337

Large silica-rich igneous-textured inclusions in the Buzzard Coulee chondrite: Condensates, differentiates, or impact melts?  

NASA Astrophysics Data System (ADS)

We studied three large (2-4 mm diameter) igneous-textured inclusions in the Buzzard Coulee (H4) chondrite using microanalytical techniques (OLM, SEM, EMPA, SIMS) to better elucidate the origins of igneous inclusions in ordinary chondrites. The inclusions are clasts that come in two varieties (1) white inclusions Bz-1 and Bz-2 represent a nearly holocrystalline assemblage of low-Ca and high-Ca pyroxene (63-66 area%) and cristobalite (33-36%) and (2) tan inclusion Bz-3 is glass-rich (approximately 60%) with low-Ca and high-Ca pyroxene phenocrysts. The bulk compositions of the inclusions determined by modal reconstruction are all SiO2-rich (approximately 67 wt% for Bz-1 and Bz-2, approximately 62% for Bz-3), but Bz-3 is enriched in incompatible elements (e.g., REE approximately 4-5 × CI abundances), whereas Bz-2 and Bz-1 are depleted in those elements that are most incompatible in pyroxene (e.g., La-Ho approximately 0.15-0.4 × CI abundances). These bulk compositions do not resemble what one would expect for partial or complete shock melting of a chondritic precursor, and show no evidence for overall volatility control. We infer that the inclusions originated through igneous differentiation and FeO reduction, with Bz-3 forming as an "andesitic" partial melt (approximately 30-40% partial melting of an H chondrite precursor), and Bz-1 and Bz-2 forming as pyroxene-cristobalite cumulates from an Si-rich melt. We suggest that both types of melts experienced a period of transit through a cold, low-pressure space environment in which cooling, FeO reduction, and interaction with a vapor occurred. Melts may have been lofted into space by excavation or splashing during collisions, or by pyroclastic volcanism. Our results indicate intriguing similarities between the inclusions in Buzzard Coulee and the silicates in some iron (IIE-type) and stony iron (IVA-type) meteorites, suggesting a genetic relationship.

Ruzicka, Alex; Hutson, Melinda; Floss, Christine; Hildebrand, Alan

2012-11-01

338

I-Xe Dating: The Time Line of Chondrule Formation and Metamorphism in LL Chondrites  

NASA Technical Reports Server (NTRS)

Refractory inclusions, considered to be the oldest solids formed in the solar nebula. (4567.2 0.6 Ma) [1], are common in many carbonaceous and in some ordinary and enstatite chondrites. High-precision Pb- Pb ages for CAI s and chondrules (from different meteorites) suggested that chondrule formation appeared to have started about 2 Ma later than that of CAIs [1]. However, recent 26Al/26Mg data suggest simultaneous formation of CAI s and chondrules in Allende [2]. The I-Xe ages of CAI s in Allende are about 2 Ma younger than the I-Xe ages of Allende chondrules [3] but, like all chronometers, the I-Xe system records closure time of its particular host phase. In the case of Allende CAI s, the major iodine-bearing phase is sodalite, a secondary phase presumably formed by aqueous alteration, so I-Xe reflects the post-formational processes in these objects. In chondrules the iodine host phases vary and can reflect formation and/or alteration but, to put chondrule ages on a quantative basis, some problems should first be addressed.

Pravdivtseva, O. V.; Hohenberg, C. M.; Meshik, A. P.

2005-01-01

339

A Collisional Origin to Earth's Non-chondritic Composition?  

E-print Network

Several lines of evidence indicate a non-chondritic composition for Bulk Earth. If Earth formed from the accretion of chondritic material, its non-chondritic composition, in particular the super-chondritic 142Nd/144Nd and low Mg/Fe ratios, might be explained by the collisional erosion of differentiated planetesimals during its formation. In this work we use an N-body code, that includes a state-of-the-art collision model, to follow the formation of protoplanets, similar to proto-Earth, from differentiated planetesimals (> 100 km) up to isolation mass (> 0.16 M_Earth). Collisions between differentiated bodies have the potential to change the core-mantle ratio of the accreted protoplanets. We show that sufficient mantle material can be stripped from the colliding bodies during runaway and oligarchic growth, such that the final protoplanets could have Mg/Fe and Si/Fe ratios similar to that of bulk Earth, but only if Earth is an extreme case and the core is assumed to contain 10% silicon by mass. This may indicat...

Bonsor, Amy; Carter, Philip J; Elliott, Tim; Walter, Michael J; Stewart, Sarah T

2014-01-01

340

Cosmic Ray Exposure Ages of Six Chondritic Almahata Sitta Fragments  

NASA Astrophysics Data System (ADS)

Cosmic ray exposure (CRE) ages of six chondrite fragments from the Almahata Sitta strewn field do not show any evidence for pre-exposure. All samples but one has 21Ne/26Al-based CRE ages of ~20 Ma. MS-179 (EL-breccia) has a lower CRE age of ~10 Ma.

Riebe, M.; Welten, K. C.; Meier, M. M. M.; Caffee, M. W.; Nishiizumi, K.; Bischoff, A.; Wieler, R.

2014-09-01

341

Regolith breccia consisting of H and LL chondrite mixture  

NASA Technical Reports Server (NTRS)

Antarctic meteorite Yamato-8424 (Y-8424) is a regolith breccia that is homogenized mixture of H and LL chondrite components. The breccia consists mainly of a fine-grained material with mineral fragments of olivine, pyroxene, and Fe-Ni metal with traces of plagioclase.

Yanai, Keizo; Kojima, Hideyasu

1993-01-01

342

Highly Siderophile Elements in Shocked and Unshocked Chondrites  

NASA Technical Reports Server (NTRS)

High precision abundances of Re, Os, Pt, Ir, Ru, and Pd are combined with Re-Os isotopic data to demonstrate that HSE provide a distinctive fingerprint for each of the chondrite groups. Additional information is contained in the original extended abstract.

Horan, M. F.; Walker, R. J.; Rubin, A. E.

2001-01-01

343

Spectra Luminescence of Extraterrestrial Calcium Phosphates in Mexican Chondrites  

Microsoft Academic Search

Merrillite and apatite crystals from four historical Mexican chondrites were studied by Environmental Scanning Electron Microscopy (ESEM), Energy Dispersive Spectrometry (EDS), Back-scattering (BS), Spectra cathodoluminescence (CL), and Micro-Raman Spectroscopy (MRS). CL is a powerful technique for exciting light emission from intrinsic relaxations, impurities, and imperfections in the outer few microns of the surface of minerals. The spectra CL patterns of

Leticia Alba Aldave; Javier García Guinea; Laura Tormo

2011-01-01

344

Paleomagnetism of a new magnetite-rich carbonaceous chondrite  

NASA Astrophysics Data System (ADS)

Recent studies of CV carbonaceous chondrites have led to the conclusion that their parent body was partially differentiated and possessed a convecting core [1]. This possibility has been validated by modeling of asteroid accretion [2]. Were partially differentiated chondritic asteroid the rule or the exception? We will present petrographic and paleomagnetic data obtained on an unusual carbonaceous chondrite that we discovered in 2011 in the Atacama desert. This meteorite is a fully crusted stone with a total weight of 2.4 g. Although classification is still ongoing, its petrography, and oxygen isotopes (d18O=-1.74‰, d17O=-5.15‰, D17O=-4.25‰) point to a C2 ungrouped chondrite. Preliminary Raman spectroscopy data confirm that it has not suffered thermal metamorphism. Magnetic properties show that the meteorite contains ~13 wt.% of pseudo-single domain magnetite, making it a rock with remarkable paleomagnetic recorder. Indeed, this is the most magnetic magnetite-bearing chondrite ever described. Paleomagnetic measurements show that the meteorite possesses a uniform and unidirectional stable component of magnetization unblocked up to 120 mT during alternating field demagnetization. Paleointensity is estimated to a few ?T using normalization techniques [3]. The nature of the magnetizaiton, and the origin of the magnetizing field will be discussed. [1] Carporzen et al., 2011. Proc. National Acad. Sci., 108, 6386-6389. [2] Elkins-Tanton et al., 2011. Earth Planet . Sci. Lett., 305, 1-10. [3] Gattacceca and Rochette P. 2004 Earth Planet . Sci. Lett., 227, 377-393.

Gattacceca, J.; Rochette, P.; Gounelle, M.; Bonal, L.; Weiss, B. P.; Sonzogni, C.

2012-12-01

345

Recent Mobilization of PB and Volatile Elements in Chondrites  

NASA Astrophysics Data System (ADS)

Unshocked chondrites show large apparent Pb/Pb age differences up to 80 x 10^6 y. All of them appear to contain more radiogenic lead than could have been derived from U- and Th decay since 4.56 aeons, assuming the Pb isotopic composition of Canon Diablo as primordial (Tatsumoto et al., 1973). Three general interpretations have been proposed to explain this apparent excess of radiogenic Pb and apparent age differences: 1) complex U-Pb evolutionary histories, 2) variable primordial Pb isotopic compositions and 3) terrestrial Pb contamination in excess of that accounted for by analytical blanks. The terrestrial Pb contamination hypothesis has been first rejected by Gale et al. (1972). Until now no extraterrestrial mechanism has been proposed to explain this pervasive recent U-Pb mobility in chondrites. We consider this apparent excess of radiogenic Pb as real; we interpret it as an addition of mobile Pb produced during the recent impact that has extracted the meteorite from its parent body. The isotopic composition of this "exotic Pb" is deduced from published and new U-Pb data from chondrites: it defines a Pb/Pb model age of ~4.45 aeons. This isotopic signature identifies the nature of the projectile: volatile-rich chondritic material. A consequence of this interpretation concerns the distribution of the highly volatile elements in equilibrated chondrites: it does not reflect a primitive fractionation but results from mobilization caused by the recent impact that has excavated the meteorite. References: Gale N.H., Arden J., and Hutchison R. (1972) Nat. Phys. Sci. 240, 56-57. Tatsumoto M., Knight R.J., and Allegre C.J. (1973) Science 180, 1278-1283

Manhes, G.; Gopel, Ch.; Allegre, C. J.

1992-07-01

346

The Paris CM chondrite: Secondary minerals and asteroidal processing  

NASA Astrophysics Data System (ADS)

We report a petrographic and mineralogical survey of Paris, a new CM chondrite considered to be the least-altered CM identified so far (Hewins et al.). Compared to other CMs, Paris exhibits (1) a higher concentration of Fe-Ni metal beads, with nickel contents in the range 4.1-8.1 wt%; (2) the systematic presence of thin lamellae and tiny blebs of pentlandite in pyrrhotite grains; and (3) ubiquitous tochilinite/cronstedtite associations with higher FeO/SiO2 and S/SiO2 ratios. In addition, Paris shows the highest concentration of trapped 36Ar reported so far for a CM chondrite (Hewins et al.). In combination with the findings of previous studies, our data confirm the reliability of (1) the alteration sequence based on the chemical composition of tochilinite/cronstedtite associations to quantify the fluid alteration processes and (2) the use of Cr content variability in type II ferroan chondrule olivine as a proxy of thermal metamorphism. In contrast, the scales based on (1) the Fe3+ content of serpentine in the matrix to estimate the degree of aqueous alteration and (2) the chemical composition of Fe-Ni metal beads for quantifying the intensity of the thermal metamorphism are not supported by the characteristics of Paris. It also appears that the amount of trapped 36Ar is a sensitive indicator of the secondary alteration modifications experienced by chondrites, for both aqueous alteration and thermal metamorphism. Considering Paris, our data suggest that this chondrite should be classified as type 2.7 as it suffered limited but significant fluid alteration and only mild thermal metamorphism. These results point out that two separated scales should be used to quantify the degree of the respective role of aqueous alteration and thermal metamorphism in establishing the characteristics of CM chondrites.

Marrocchi, Yves; Gounelle, Matthieu; Blanchard, Ingrid; Caste, Florent; Kearsley, Anton T.

2014-07-01

347

Non-chondritic sulphur isotope composition of the terrestrial mantle.  

PubMed

Core-mantle differentiation is the largest event experienced by a growing planet during its early history. Terrestrial core segregation imprinted the residual mantle composition by scavenging siderophile (iron-loving) elements such as tungsten, cobalt and sulphur. Cosmochemical constraints suggest that about 97% of Earth's sulphur should at present reside in the core, which implies that the residual silicate mantle should exhibit fractionated (34)S/(32)S ratios according to the relevant metal-silicate partition coefficients, together with fractionated siderophile element abundances. However, Earth's mantle has long been thought to be both homogeneous and chondritic for (34)S/(32)S, similar to Canyon Diablo troilite, as it is for most siderophile elements. This belief was consistent with a mantle sulphur budget dominated by late-accreted chondritic components. Here we show that the mantle, as sampled by mid-ocean ridge basalts from the south Atlantic ridge, displays heterogeneous (34)S/(32)S ratios, directly correlated to the strontium and neodymium isotope ratios (87)Sr/(86)Sr and (143)Nd/(144)Nd. These isotope trends are compatible with binary mixing between a low-(34)S/(32)S ambient mantle and a high-(34)S/(32)S recycled component that we infer to be subducted sediments. The depleted end-member is characterized by a significantly negative ?(34)S of -1.28?±?0.33‰ that cannot reach a chondritic value even when surface sulphur (from continents, altered oceanic crust, sediments and oceans) is added. Such a non-chondritic (34)S/(32)S ratio for the silicate Earth could be accounted for by a core-mantle differentiation record in which the core has a (34)S/(32)S ratio slightly higher than that of chondrites (?(34)S = +0.07‰). Despite evidence for late-veneer addition of siderophile elements (and therefore sulphur) after core formation, our results imply that the mantle sulphur budget retains fingerprints of core-mantle differentiation. PMID:24005324

Labidi, J; Cartigny, P; Moreira, M

2013-09-12

348

Entropy: From Black Holes to Ordinary Systems  

E-print Network

Several results of black holes thermodynamics can be considered as firmly founded and formulated in a very general manner. From this starting point we analyse in which way these results may give us the opportunity to gain a better understanding in the thermodynamics of ordinary systems for which a pre-relativistic description is sufficient. First, we investigated the possibility to introduce an alternative definition of the entropy basically related to a local definition of the order in a spacetime model rather than a counting of microstates. We show that such an alternative approach exists and leads to the traditional results provided an equilibrium condition is assumed. This condition introduces a relation between a time interval and the reverse of the temperature. We show that such a relation extensively used in the black hole theory, mainly as a mathematical trick, has a very general and physical meaning here; in particular its derivation is not related to the existence of a canonical density matrix. Our dynamical approach of thermodynamic equilibrium allows us to establish a relation between action and entropy and we show that an identical relation exists in the case of black holes. The derivation of such a relation seems impossible in the Gibbs ensemble approach of statistical thermodynamics. From these results we suggest that the definition of entropy in terms of order in spacetime should be more general that the Boltzmann one based on a counting of microstates. Finally we point out that these results are obtained by reversing the traditional route going from the Schr\\"{o}dinger equation to statistical thermodynamics.

J. P. Badiali

2005-05-11

349

7 CFR 28.406 - Strict Good Ordinary Color.  

Code of Federal Regulations, 2010 CFR

Strict Good Ordinary Color is color which is within the range represented by a set of samples in the custody of the United States Department of Agriculture in a container marked “Original Official Cotton Standards of the United States, American Upland, Strict Good Ordinary, effective July 1,...

2010-01-01

350

Diperna-Lions and Ambrosio's approach to ordinary differential equations  

E-print Network

Diperna-Lions and Ambrosio's approach to ordinary differential equations Shizan FANGa , a I.M.B. B and self-contained exposition on Diperna-Lions and Ambrosio's approach to ordinary differential equations and P.L. Lions [7] treated vector fields in W1,1 loc (Rd). For the procedure of approximation, instead

Fang, Shizan

351

A 160 cm Synchro and Variable Energy Ordinary Cyclotron  

Microsoft Academic Search

A 160-cm cyclotron which can be used as a variable energy ordinary ; cyclotron as well as a synchro-cyclotron by changing the dee-system and the ; oscillator system is described. As an ordinary cyclotron it can produce protons ; of any desired energy between 7.5 and 15 Mev, deuterons between 15 and 21 Mev, ; and alpha particles between 30

Seishi Kikuchi; Itaru Nonaka; Hiroshi Ikeda; Hiroo Kumagai; Yoshio Saji; Junpei Sanada; Shigeki Suwa; Akira Isoya; Izuo Hayashi; Kazuhisa Matsuda; Hisashi Yamaguchi; Takashi Mikumo; K. Nishimura; Takashi Karasawa; Shinsaku Kobayashi; Ken Kikuchi; Satoru Ito; Arata Suzuki; Seiichiro Takeuchi; Hirotsugu Ogawa

1960-01-01

352

Noble Gases in the LEW 88663 L7 Chondrite  

NASA Astrophysics Data System (ADS)

LEW88663 and some meteorites (e.g. Shaw) are the most highly metamorphosed meteorites among L group chondrites. Although the abundances of lithophile elements and oxygen isotopic compositions of the L7 chondrite LEW88663 (total recovered mass: 14.5g) are close to those of the range for L chondrites [1,2], metallic iron is absent and concentrations of siderophile elements are about half of typical values for L chondrites [3,4]. Petrographical and geochemical observation suggested that this meteorite has experienced partial melting [5]. As a part of our study on differentiated meteorites, we also investigated noble gases in this meteorite. We present here noble gas compositions of LEW88663 and discuss history of this meteorite. In addition, we will consider whether there is any evidence for bridging between chondrites and achondrites. Noble gases were extracted from a whole rock sample weighing 66.31 mg by total fusion, and all stable noble gas isotopes as well as cosmogenic radioactive 81Kr were analyzed using a mass spectrometer at ISEI, Okayama University. The results are summarized in the table. The concentrations of cosmogenic ^3He, ^21Ne, and ^38Ar are 7.3, 1.6 and 3.1x10^-8 cm^3STP/g, respectively. The cosmic-ray exposure ages based on them are calculated to be 4.7, 6.9 and 8.8 m.y., respectively, using the production rates proposed by [6, 7] and mean chemical compositions of L chondrites. The shorter cosmic-ray exposure ages T(sub)3 and T(sub)21 than T(sub)38 would be due to diffusive loss of lighter noble gases from the meteorite. The concentrations of trapped Kr and Xe in LEW88663 are lower than those for L6 chondrites [8], supporting thermal metamorphism for the meteorite higher than that for L6 chondrites. The Kr and Xe are isotopically close to those of the terrestrial atmospheric Kr and Xe, and elemental abundance ratios for Ar, Kr and Xe suggest adsorbed noble gas patterns of the terrestrial atmosphere. The terrestrial atmospheric Ar, Kr and Xe (most likely terrestrial contamination in origin) rather than chondritic ones seem to be dominant in LEW88663. A K-Ar age of 4.3 +/- 0.2 b.y. is obtained assuming K content of 660 ppm by [9], implying radiogenic ^40Ar is almost retained. Because of low abundance of trapped Xe in the meteorite compared with the abundances in other chondrites, ^244Pu-derived fission Xe could be evaluated more precisely. According to the measured Xe data (for this, three isotope plots such as ^134Xe/^130Xe versus ^136Xe/^130Xe are useful), we conclude that Xe in LEW88663 is the mixture of ^244Pu-derived fission Xe and the terrestrial atmospheric Xe with possibility that a small amount of chondritic Xe is contained. Using the same procedure described in [10], we obtained excess ^136Xe concentration, 1.4 x 10^-12 cm^3STP/g with about 20% uncertainty, of which about 3% is from contribution of ^238U-derived ^136Xe if average U content for L chondrite (14 ppb) is assumed. The calculated Pu abundance of 0.21 ppb is slightly higher than those reported for L chondrites Barwell (0.11 +/- 0.05 ppb [11]) and Marion (0.10+/-0.40 ppb [11]). Acknowledgments: We thank Meteorite Working Group for providing the sample. We are also grateful to Dr. D. Mittlefehldt for showing us his chemical composition data. This work is supported by Research Fellowships of the Japan Society for the Promotion of Science for Young Scientists. References: [1] Mason B. et al. (1992) Antarc. Meteorite Newsletter, 15(2), 30. [2] Mason B. and Marlow R. (1992) Antarc. Meteorite Newsletter, 15(1), 16. [3] Davis A. M. et al. (1993) LPS XXIV, 375-376. [4] Mittlefehldt D. W. (1993) Meteoritics, 28, 401-402. [5] Hervey R. P. (1993) Meteoritics, 28, 360. [6] Eugster O. (1988) GCA, 52, 1649-1662. [7] Marti K. and Graf T.(1992) Annu. Rev. Earth Planet Sci., 20, 221-243. [8] E.g. Marti K. (1967) EPSL, 2, 193-196. [9] Mittlefehldt D. W., personal communication. [10] Miura Y. et al. (1993) GCA, 57, 1857-1866. [11] Hagee B. et al. (1990) GCA, 54, 2847-2858. Table 1 shows noble gases in L7 chondrite LEW88663 (66.31 mg).

Miura, Y. N.; Sugiura, N.; Nagao, K.

1995-09-01

353

Thermomagnetic analysis of meteorites, 3. C3 and C4 chondrites  

USGS Publications Warehouse

Thermomagnetic analysis was made on samples of all known C3 and C4 chondrites in a controlled oxygen atmosphere. Considerable variation was noted in the occurrence of magnetic minerals, comparable to the variation observed earlier in the C2 chondrites. Magnetite was found as the only major magnetic phase in samples of only three C3 chondrites (2-4 wt.%) and the Karoonda C4 chondrite (7.7 wt.%). The magnetite content of these three C3 chondrites is only about one-third that observed in the C1 and C2 chondrites which were found to contain magnetite as the only magnetic phase. Five C3 chondrites were observed to undergo chemical change during heating, producing magnetite: this behavior is characteristic of troilite oxidation. Upper limits on initial magnetite content of about 1-9% were established for these meteorites. Samples of the remaining five C3 chondrites and the Coolidge C4 chondrite were found to contain both magnetite and metallic iron. In two samples, iron containing ???2% Ni was observed, while in the other four, the iron contained 6-8 wt.% Ni. In addition to containing both magnetite and iron metal, three of these samples reacted during heating to form additional magnetite. Variations in the magnetic mineralogy and, hence by inference bulk mineralogy, of C3 and C4 chondrites indicate a more complex genesis than is evident from whole-rock elemental abundance patterns. ?? 1976.

Herndon, J.M.; Rowe, M.W.; Larson, E.E.; Watson, D.E.

1976-01-01

354

Lead Isotope Investigation of the Tagish Lake Carbonaceous Chondrite  

NASA Astrophysics Data System (ADS)

Chondritic meteorites (chondrites) are the most ancient rocks formed in our Solar system providing unique opportunities to constrain physical and chemical processes that were active both in the accretionary disk (Solar nebula) of our early sun, and on the parent bodies of the chondrites themselves. In particular, intense focus has been devoted to the Tagish Lake (CI UNGR) chondrite since its fall and recovery [1,2]. This interest in Tagish is due to the (A) similarity and distinctiveness of Tagish mineralogy to both CI and CM chondrites including at least two lithologies: a dominant carbonate-poor lithology and a less-abundant carbonate-rich lithology [3,4]; (B) unique interstellar and organic features detected in the meteorite [1-5], and (C) correlation of Tagish with D-type outer Solar system asteroids, which have never been previously sampled [6]. Here we present results from a high-precision Pb-isotope study of four different samples of the Tagish Lake chondrite by isotope-dilution thermal ionization mass spectrometry (ID-TIMS). The four Tagish samples (obtained from the University of Calgary c/o Dr. A. Hildebrand) span the carbonate-rich and poor lithologies and are: MM47/66, MG-62, MM-87 and HG-11(1). Results will be discussed in the context of the 'primordial' lead present in the early Solar system. Preliminary results of analyzes on the first whole-rock sample (HG-11) yield slightly radiogenic lead that is consistent with an initial lead isotopic composition similar to that in Canyon Diablo troilite [7]. SEM-BSE and electron microprobe results from thin-microtomed sections of Tagish chondrules obtained from these samples will also be presented. Preliminary SEM-BSE on the chondrules suggest that significant aqueous alteration on the parent body may have disturbed their lead isotope systematics. Therefore Tagish chondrules may themselves be unsuitable for 207Pb/206Pb dating. [1] Brown et al., (2000) Science 290, 320-325. [2] Hildebrand et al., (2006) Met.Plan.Sci. 41, 407-431. [3] Zolensky et al., (2002) Met.Plan.Sci. 37, 737-761. [4] Simon & Grossman (2003) Met.Plan.Sci. 38, 813-825. [5] Nakamura-Messenger et al., (2006) Science 314, 1439-1442. [6] Hiroi et al., (2001) Science 293, 2234-2236. [7] Tatsumoto et al. (1973) Science 180, 1279-1283.

Charles, C. R.; Davis, D. W.

2009-05-01

355

Records of the Moon-forming impact and the 470 Ma disruption of the L chondrite parent body in the asteroid belt from U-Pb apatite ages of Novato (L6)  

NASA Astrophysics Data System (ADS)

Novato, a newly observed fall in the San Francisco Bay area, is a shocked and brecciated L6 ordinary chondrite containing dark and light lithologies. We have investigated the U-Pb isotope systematics of coarse Cl-apatite grains of metamorphic origin in Novato with a large geometry ion microprobe. The U-Pb systematics of Novato apatite reveals an upper intercept age of 4472 ± 31 Ma and lower intercept age of 473 ± 38 Ma. The upper intercept age is within error identical to the U-Pb apatite age of 4452 ± 21 Ma measured in the Chelyabinsk LL5 chondrite. This age is interpreted to reflect a massive collisional resetting event due to a large impact associated with the peak arrival time at the primordial asteroid belt of ejecta debris from the Moon-forming giant impact on Earth. The lower intercept age is consistent with the most precisely dated Ar-Ar ages of 470 ± 6 Ma of shocked L chondrites, and the fossil meteorites and extraterrestrial chromite relicts found in Ordovician limestones with an age of 467.3 ± 1.6 Ma in Sweden and China. The lower intercept age reflects a major disturbance related to the catastrophic disruption of the L chondrite parent body most likely associated with the Gefion asteroid family, which produced an initially intense meteorite bombardment of the Earth in Ordovician period and reset and degassed at least approximately 35% of the L chondrite falls today. We predict that the 470 Ma impact event is likely to be found on the Moon and Mars, if not Mercury.

Yin, Qing-Zhu; Zhou, Qin; Li, Qiu-Li; Li, Xian-Hua; Liu, Yu; Tang, Guo-Qiang; Krot, Alexander N.; Jenniskens, Peter

2014-08-01

356

Chemical characterization of a unique chondrite - Allan Hills 85085  

NASA Astrophysics Data System (ADS)

Allan Hills 85085 is a new and very important addition to the growing list of unique carbonaceous chondrites because of its unique chemical and mineralogical properties. This chemical study provides more precise data on the major, minor, and trace element characteristics of ALH85085. ALH85085 has compositional, petrological, and isotopic affinities to AL Rais and Renazzo, and to Bencubbin-Weatherford. The similarities to Al Rais and Renazzo suggest similar formation locations and thermal processing, pos