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1

Forsteritic Olivine Grains in Unequilibrated Ordinary Chondrites: Additional Evidence for a Link Between Ordinary and Carbonaceous Chondrites  

NASA Technical Reports Server (NTRS)

We report mineral-chemical and Secondary Ion Mass Spectrometry (SIMS) oxygen-isotopic studies of forsteritic olivine grains from various Unequilibrated Ordinary Chondrites (UOCs). Our studies provide additional evidence for a genetic link between ordinary and carbonaceous chondrites and between various lithologies in these meteorites.

Ruzicka, A.; Hiyagon, H.; Prinz, M.; Taylor, L. A.

2000-01-01

2

Inter-element relationships between trace elements in primitive carbonaceous and unequilibrated ordinary chondrites.  

NASA Technical Reports Server (NTRS)

The results of a search for significant interelement relationships among 13 trace elements in carbonaceous chondrites and 26 elements and the disequilibrium parameter for silicate phases in unequilibrated ordinary chondrites (UOC) indicate pronounced differences in the formation processes of these two sorts of primitive chondrites. Twenty-six pairs of elements are correlated in carbonaceous chondrites and these correlations lend support to a model involving mixing in different ratios of material differing in thermal history. Comparison of the 26 elements in UOC shows that 39 pairs of elements are significantly related and only very volatile elements are correlated with the disequilibrium parameter. Each of the interelement relationships can be specifically ascribed to a metal-silicate fractionation in the solar nebula or to a thermal fractionation.

Kurimoto, R. K.; Pelly, I. Z.; Laul, J. C.; Lipschutz, M. E.

1973-01-01

3

Metal and associated phases in Bishunpur, a highly unequilibrated ordinary chondrite  

NASA Astrophysics Data System (ADS)

Bishunpur is one of the most unequilibrated ordinary chondrites, and preserves a relatively unaltered record of solar nebular processes. A survey of three polished thin sections of Bishunpur revealed that metal occurs in three textural domains: (1) in the matrix, (2) within chondrules and (3) in coatings on chondrules. A table provides a textural classification of the various metal types found in Bishunpur and their composition. Electron-microprobe analyses are discussed, and similarities between Bishunpur metal and opaques and those in carbonaceous chondrites are considered. Attention is given to low-Ni kamacite grains in chondrule olivine, Si-bearing chondrule metal, spheroidal metal in chondrules, metal and sulfide-bearing rims, coarse matrix metal, and fine matrix metal formation.

Rambaldi, E. R.; Wasson, J. T.

1981-07-01

4

Widespread hydrothermal alteration minerals in the fine-grained matrices of the Tieschitz unequilibrated ordinary chondrite  

NASA Astrophysics Data System (ADS)

Mineralogic, textural, and compositional studies of black and white matrices in the unequilibrated ordinary chondrite Tieschitz (H/L, 3.6) show, for the first time in an ordinary chondrite, the presence of widespread, randomly distributed geode-like voids and veins. Scanning electron microscope (SEM) and transmission electron microscope (TEM) studies show that these voids and veins are partially or completely filled by sodic-calcic amphiboles (winchite and barroisite). The occurrence of amphiboles provides unequivocal evidence of the involvement of fluids in the metamorphic evolution of the parent body of Tieschitz. The presence of amphiboles as the main hydrous phases, rather than phyllosilicates, indicates that aqueous fluids were present at or close to the peak of thermal metamorphism, rather than during the waning stages of the cooling history of the parent body. In addition, ferrous olivine crystals, in association with the amphibole, also establish an important link between thermal metamorphism and hydrous phases formed at high temperatures. Mineralogic and textural evidence suggests that the white matrix and amphibole formed contemporaneously from the same hydrous fluid, prior to the formation of ferrous olivine crystals. Additionally, a dark inclusion identified in the host chondrite has mineralogic, petrologic, and bulk chemical characteristics that are similar to the black matrix of host Tieschitz, suggesting that this dark inclusion was emplaced before or during parent body metamorphism.

Dobric?, E.; Brearley, A. J.

2014-08-01

5

Fine, nickel-poor Fe-Ni grains in the olivine of unequilibrated ordinary chondrites  

NASA Astrophysics Data System (ADS)

Nickel-poor Fe-Ni grains smaller than 2.0 microns are common inclusions in ordinary, unequilibrated chondrites' porphyritic chondrule olivine, where the olivine grains seem to be relicts that survived chondrule formation without melting. This 'dusty' metal, whose most common occurrence is in the core of olivine grains having clear, Fe-poor rims, appears to be the product of the in situ reduction of FeO from the host olivine, with H2 or carbonaceous matter being the most likely reductants. H2 may have been implanted by solar wind or solar flare irradiation, but this requires the dissipation of nebular gas before the end of the chondrule formation process. Carbonaceous matter may have been implanted by shock. The large relict olivine grains may be nebular condensates or fragments broken from earlier chondrule generations.

Rambaldi, E. R.; Wasson, J. T.

1982-06-01

6

Trace elements in primitive meteorites—VII Antarctic unequilibrated ordinary chondrites  

NASA Astrophysics Data System (ADS)

We report RNAA results for Co, Au, Sb, Ga, Rb, Cs, Se, Ag, Te, Zn, In, Bi, Tl and Cd (in increasing order of metamorphic mobility) in 22 Antarctic unequilibrated ordinary chondrites (UOC). This brings to 38 the number of UOC for which data for highly volatile elements are known. For elements of lesser mobility (Co to Se, omitting Cs) overall variability in UOC are low, relative standard deviations (one sigma) being no more than a factor of two. For Ag, Te and Zn, relative standard deviations are 2-4×, while for Cs and the four most volatile elements, the variabilities are 8-110×. Elemental abundances do not vary with chemical type (H, L and LL) nor with UOC subtype (3.0-3.9). Contents of all elements reach levels up to, even exceeding, cosmic and all but Cd and the two alkalis, seem unaffected by post-accretionary processes. Contents of highly volatile elements are consistent with the idea that source regions producing contemporary falls and older Antarctic UOC differed in thermal histories. The presence or absence of carbide magnetite assemblages (CMA) generally accords with high or low Cd contents, respectively. This relationship accords with the prior suggestion that CMA formed by alteration of Fe-Ni metal by C-O-H-containing fluids at temperatures <700 K, generated by thermal metamorphism in parent body interiors. The absence of CMA in most UOC (and OC), may indicate that they were subsequently destroyed as metamorphic intensity increased. The high, often supercosmic, Rb and Cs levels in UOC may result from their high solubility in liquid water signalling their redistribution by C-O-H-containing fluid while in the liquid water field. Because of its uniquely high mobility, Cd could have been enriched by the C-O-H fluids and should have been lost from parent regions during later, higher temperature anhydrous metamorphism at temperatures in the 500-600 °C range.

Wang, Ming-Sheng; Lipschutz, Michael E.

2007-02-01

7

Na, K-Rich Rim Around a Chondrule in Unequilibrated Ordinary Chondrite Lew 86018 (L3.1)  

NASA Technical Reports Server (NTRS)

Ordinary chondrites represent the most abundant early Solar system extra-terrestrial (approximately 85% abundance) material available for laboratory studies and expectedly record the most extensive range of alterations effects from unmetamorphosed chondritic material to the highest temperatures of thermal metamorphism. The least metamorphosed chondrites belonging to petrologic type 3, the so called unequili-brated ordinary chondrites (UOCs), provide insights into alteration that happened during the primeval, ear-liest stage of Solar system formation. The higher grade petrologic types 4-6 ordinary chondrites on the other hand document up to near textural equilibrium (in type 6) extensive thermal metamorphism consisting of minerals and phases providing evidence of equilibration of heterogeneous mineral composition, solid-state recrystallization. Despite being the most abundant, the effect of alteration is less explicitly understood in ordinary chondrites (even less in UOCs) compared to other groups (e.g. CV, CO, CR). Additionally, the relationship between metasomatism (also referred as aqueous alteration or fluid-assisted metamorphism) and metamorphism (primarily thermal driven) has not been studied and alterations in the ordinary chondrites have been considered to have occurred in absence of fluids in general. Despite this conventional view, UOCs of lowest grades (3.0-3.2) show some evidence of low temperature (approximately 200 C), fluid assisted metamorphism in the form of the presence of phyllosilicates, ferroan olivine, and magnetites in their matrices and occasionally in chondrules. Here, we present petrographic and mineralogical studies of UOC, Lewis Hills (LEW) 86018 to further our understanding of the extent and relative importance of metasomatism and/or metamorphism in UOCs.

Mishra, R. K.; Simon, J. I.; Ross, D. K.; Needham, A. W.; Messenger, S.; Keller, L. P.; Han, J.; Marhas, K. K.

2015-01-01

8

Aqueous Alteration and Hydrogen Generation on Parent Bodies of Unequilibrated Ordinary Chondrites: Thermodynamic Modeling for the Semarkona Composition  

NASA Technical Reports Server (NTRS)

Ordinary chondrites are the most abundant class of meteorites that could represent rocky parts of solar system bodies. However, even the most primitive unequilibrated ordinary chondrites (UOC) reveal signs of mild alteration that affected the matrix and peripheral zones of chondrules. Major chemical changes include oxidation of kamacite, alteration of glass, removal of alkalis, Al, and Si from chondrules, and formation of phases enriched in halogens, alkalis, and hydrogen. Secondary mineralogical changes include formation of magnetite, ferrous olivine, fayalite, pentlandite, awaruite, smectites, phosphates, carbonates, and carbides. Aqueous alteration is consistent with the oxygen isotope data for magnetite. The presence of secondary magnetite, Ni-rich metal alloys, and ferrous silicates in UOC implies that H2O was the oxidizing agent. However, oxidation by H2O means that H2 is produced in each oxidative pathway. In turn, production of H2, and its redistribution and possible escape should have affected total pressure, as well as the oxidation state of gas, aqueous and mineral phases in the parent body. Here we use equilibrium thermodynamic modeling to explore water-rock reactions in UOC. The chemical composition of gas, aqueous, and mineral phases is considered.

Zolotov, M. Y.; Mironenko, M. V.; Shock, E. L.

2005-01-01

9

Fayalite-silica association in unequilibrated ordinary chondrites: Evidence for aqueous alteration on a parent body  

NASA Technical Reports Server (NTRS)

We report ten occurrences of high-fayalite (Fa56-99 mol%; four with Fa greater than 82 mol%) olivine in association with silica in type-3 ordinary chondrites. Pyroxene with high Fs contents is much less common; Fs contents do not exceed 66 mol%, and most maxima are less than 50 mol%. In those cases where the amount of fayalite is minor relative to that of silica, the fayalite forms a layer on the silica, and shows textural evidence of formation by reaction of silica with oxidized Fe; the latter seems to have resulted from reaction of metallic Fe-Ni with an oxidant, most likely H2O vapor. The fayalite is generally in contact with pyroxene (and, in one case, olivine) having a much lower Fe/(Fe + Mg) ratios, indicating that lattice diffusion has been minimal. Formation of fayalite from SiO2 explains the low Mg content of this olivine; the Mg was sequestered inside the lattices of mafic minerals and was thus inaccessible. In contrast, the moderately high Mn contents of the fayalite indicate that an appreciable fraction of the Mn in the precursor assemblage was accessible; it was probably sited in the matrix in the form of tiny, poorly crystallized oxide grains produced by nebular condensation at temperatures too low to permit diffusion into forsterite or enstatite. The reaction of SiO2 with FeO produced by oxidation (during metamorphism) of Fe-Ni can also account for fayalitic olivine associated with SiO2 microspherules in the fine-grained matrices of type-3 ordinary chondrites and, because matrix is SiO2 normative, for other occurrences of fayalite in matrix. The presence of Mn in the fayalitic rims on the olivine of carbonaceous chondrites does not require a nebular sign.

Wasson, John T.; Krot, Alexander N

1994-01-01

10

Anomalous REE patterns in unequilibrated enstatite chondrites: Evidence and implications  

NASA Technical Reports Server (NTRS)

We present here a study of Rare Earth Element (REE) microdistributions in unequilibrated enstatite chondrites (EOC's). Although the whole rock REE contents are similar in both unequilibrated and equilibrated chondrites, the host minerals of these refractory elements are different. In the least equilibrated ordinary chondrites (UOC's), the REE reside mainly in glass whereas, in their more equilibrated counterparts, the bulk of the REE is in calcium phosphate, a metamorphic mineral that formed by oxidation of phosphorous originally contained in metal. In the smaller group of enstatite (E) chondrites, calcium phosphate is absent and the phase that contains the highest REE concentrations is a minor mineral, CaS (oldhamite), which contains approximately 50 percent of the total Ca present. In E chondrites, elements typically considered to be lithophiles (such as Ca and Mn) occur in sulfides rather than silicates. This indicates formation under extremely reducing conditions, thus in a region of the solar nebula distinct from those that supplied the more abundant ordinary and carbonaceous chondrites. Previously, we observed a variety of REE patterns in the oldhamite of UEC's; they range from almost flat to some with pronounced positive Eu and Yb anomalies. Here, we searched for complementary REE patterns in other minerals from E chondrites and found them in the major mineral, enstatite. Whenever Eu and Yb anomalies are present in this mineral, they are always negative.

Crozaz, Ghislaine; Hsu, Weibiao

1993-01-01

11

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

12

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

13

Graphite-magnetite aggregates in ordinary chondritic meteorites  

NASA Technical Reports Server (NTRS)

The graphite-magnetite component has been found (1) as abundant isolated inclusions in eight ordinary-chondritic, regolith breccias; (2) as the sole matrix in a new kind of unequilibrated chondrite that forms clasts in these regolith breccias; and (3) together with a Huss matrix in six unequilibrated ordinary chondrites. It is suggested that the component was formed by low-temperature, gas-solid reactions before the accretion of the meteorite, and that the isolated inclusions of graphite-magnetite in regolith breccias were derived from bodies composed of the new kind of chondrite that has graphite-magnetite as its sole matrix.

Scott, E. R. D.; Taylor, G. J.; Rubin, A. E.; Keil, K.; Okada, A.

1981-01-01

14

Composition of the metal phases in ordinary chondrites - Implications regarding classification and metamorphism  

NASA Technical Reports Server (NTRS)

The paper examines the composition of metal phases and metamorphism in ordinary chondrites. It is shown that below 550 C increasing Co decreases the equilibrium kamacite Ni concentration of an alpha to gamma system, and that the equilibrated L chondrites have kamacite and taenite Co concentrations in the L-group range. Metal-phase studies of petrologic type-3 ordinary chondrites with highly unequilibrated silicates showed a wide range in the degree of matrix kamacite equilibration; in the three most unequilibrated chondrites most taenite is clear, and the high Ni content shows that metamorphic temperatures were lower than 400 C in these meteorites.

Afiattalab, F.; Wasson, J. T.

1980-01-01

15

Si-rich Fe-Ni grains in highly unequilibrated chondrites  

NASA Astrophysics Data System (ADS)

Consideration is given to the Si contents of Fe-Ni grains in highly unequilibrated chondrites, which have undergone little metamorphosis and thus best preserve the record of processes in the solar nebula. Electron microprobe determinations of silicon content in grains of the Bishunpur chondrite are presented for the six Si-bearing Fe-Ni grains for which data could be obtained, five of which were found to be embedded in olivine chondrules. In addition, all grains are found to be Cr-rich, with Cr increased in concentration towards the grain edge, and to be encased in FeS shells which evidently preserved the Si that entered the FeNi at higher temperatures. A mechanism for the production of Si-bearing metal during the condensation of the cooling solar nebula is proposed which considers the metal to have condensed heterogeneously while the mafic silicates condensed homogeneously with amounts of required undercooling in the low-pressure regions where ordinary and carbonaceous chondrites formed, resulting in Si mole fractions of 0.003 at nebular pressures less than 0.000001 atm.

Rambaldi, E. R.; Sears, D. W.; Wasson, J. T.

1980-10-01

16

Actinide abundances in ordinary chondrites  

NASA Technical Reports Server (NTRS)

Measurements of actinide and light REE (LREE) abundances and of phosphate abundances in equilibrated ordinary chondrites were obtained and were used to define the Pu abundance in the solar system and to determine the degree of variation of actinide and LREE abundances. The results were also used to compare directly the Pu/U ratio with the earlier obtained ratio determined indirectly, as (Pu/Nd)x(Nd/U), assuming that Pu behaves chemically as a LREE. The data, combined with high-accuracy isotope-dilution data from the literature, show that the degree of gram-scale variability of the Th, U, and LREE abundances for equilibrated ordinary chondrites is a factor of 2-3 for absolute abundances and up to 50 percent for relative abundances. The observed variations are interpreted as reflecting the differences in the compositions and/or proportions of solar nebula components accreted to ordinary chondrite parent bodies.

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

1990-01-01

17

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

18

Trapped xenon in ordinary chondrites  

NASA Astrophysics Data System (ADS)

A trapped component of heavy noble gates representing a distinct solar system (presumably asteroid belt) reservoir is known to be concentrated in carbonaceous carriers of chondritic meteorites. The isotopic signature of trapped Xe in separates of the H4 chondrite Forest Vale (FV) was determined by combusting its carrier phases at 600 C in oxygen, discriminating against in situ produced nucleogenic components which are released above 600 C. The isotopic abundances of FV combustion-Xe (FVC-Xe) are compared to signatures of bulk trapped Xe in chondritic meteorites. We conclude that FVC-Xe represents the predominant trapped component in ordinary chondrites (OC) for which we adopt the term OC-Xe. Its isotopic signature differs from Xe in ureilites, in 'average carbonaceous chondrites', in earth's atmosphere, and in the solar wind. Additional minor Xe components were identified in type 3 chondrites and in the metal phase of chondrites. We discuss relationships among solar system Xe reservoirs and show that OC-Xe signature is consistent with a mixture of HL-Xe with slightly mass fractionated solar-type Xe.

Lavielle, Bernard; Marti, Kurt

1992-12-01

19

Shock metamorphism of ordinary chondrites  

Microsoft Academic Search

This study proposes a revised petrographic classification of progressive stages of shock metamorphism of 26 ordinary chondrites. Six stages of shock (S1 to S6) are defined on the basis of shock effects in olivine and plagioclase as recognized by thin section microscopy, and the characteristic shock effects of each shock stage are described. It is concluded that shock effects and

Dieter Stoeffler; Klaus Keil; Edward R. D. Scott

1991-01-01

20

Porphyritic Olivine-Pyroxene Clast in Kaidun: First Discovery of an Ordinary Chondrite Clast?  

NASA Technical Reports Server (NTRS)

Kaidun is an enigmatic meteorite showing a micro-brecciated texture composed of variable kinds of lithic clasts and mineral fragments. The constituent components range from primitive chondritic materials to differentiated achondritic materials, and thus believed to have originated from a large parent body accumulating materials from many different bodies in the asteroid belt. One of the interesting observations is that no ordinary chondrite component has been found yet, although C and E chondrites components are abundant. In this abstract, we report mineralogy of the clast (Kaidun #15415- 01.3.13a) showing a porphyritic olivine-pyroxene chondrule-like texture similar to those found in unequilibrated ordinary chondrites.

Mikouchi, T.; Makishima, J.; Koizumi, E.; Zolensky, M. E.

2005-01-01

21

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

22

Al-rich objects in ordinary chondrites - Related origin of carbonaceous and ordinary chondrites and their constituents  

NASA Technical Reports Server (NTRS)

A description is given of 169 Al-rich objects (arbitrarily defined as having 10 wt pct or more of Al2O3) from 24 ordinary chondrites of types 3 and 4, five regolith breccias containing unequilibrated material, the unique meteorite Kakangari, and a few ordinary chondrites of types 5 and 6. On the basis of shape and texture, the Al-rich objects are divided into chondrules (round, with igneous textures), irregularly shaped inclusions (similar to type F and spinel-rich complex Ca-Al-rich inclusions), and fragments (probably fragments of Al-rich chondrules and inclusions). For descriptive purposes, the Al-rich chondrules are further subdivided into compositional subgroups, although they are entirely transitional.

Bischoff, A.; Keil, K.

1984-01-01

23

Shock metamorphism of ordinary chondrites  

NASA Technical Reports Server (NTRS)

This study proposes a revised petrographic classification of progressive stages of shock metamorphism of 26 ordinary chondrites. Six stages of shock (S1 to S6) are defined on the basis of shock effects in olivine and plagioclase as recognized by thin section microscopy, and the characteristic shock effects of each shock stage are described. It is concluded that shock effects and the sequence of progressively increasing degrees of shock metamorphosis are very similar in H, L, and LL groups. Differences in the frequency distribution of shock stages are relatively minor. It is suggested that the collisional histories of the H, L, and LL parent bodies were similar. Petrologic type-3 chondrites are deficient in stages S4 and S6 and, with increasing petrologic type, the frequency of stages S4 to S6 increases. It is suggested that the more porous and volatile-rich Type-3 chondrites are subject to melting at a lower shock pressure than the nonporous chondrites of higher petrologic type. Stage S3 is the most abundant in nearly all petrologic types.

Stoeffler, Dieter; Keil, Klaus; Scott, Edward R. D.

1991-01-01

24

Metallic copper in ordinary chondrites  

NASA Technical Reports Server (NTRS)

Metallic Cu of moderately high purity (approximately 985 mg/g Cu, approximately 15 mg/g Ni) occurs in at least 66% of ordinary chondrites (OC) as heterogeneously distributed, small (typically less than or equal to 20 micrometers) rounded to irregular grains. The mean modal abundance of metallic Cu in H, L and LL chondrites is low: 1.0 to 1.4 x 10(exp -4) vol%, corresponding to only 4 - 5 % of the total Cu in OC whole rocks. In more than 75% of the metallic-Cu-bearing OC, at least some metallic Cu occurs at metallic-Fe-Ni-troilite grain boundaries. In some cases it also occurs within troilite, within metallic Fe-Ni, or at the boundaries these phases form with silicates or chromite. Ordinary chondrites that contain a relatively large number of occurrences of metallic Cu/sq mm have a tendency to have experienced moderately high degrees of shock. Shock processes can cause local melting and transportation of metallic Fe-Ni and troilte; because metallic Cu is mainly associated with these phases, it also gets redistributed during shock events. In the most common petrographic assemblage containing metallic Cu, the Cu is adjacent to small irregular troilite grains surrounded by taenite plus tetrataenite; this assemblage resembles fizzed troilite and may have formed by localized shock melting or remelting of a metal-troilite assemblage.

Rubin, Alan E.

1994-01-01

25

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

26

Fossil records of high level of 60Fe in chondrules from unequilibrated chondrites  

NASA Astrophysics Data System (ADS)

The short-lived now-extinct nuclide (SLN) 60Fe, which decays to 60Ni with a half-life of 2.62 Ma, is uniquely of stellar origin. Hence, its Solar System initial abundance yields information about the source of SLNs and the astrophysical environment in which the Solar System was born. Only a few chondrules (?19) from unequilibrated ordinary chondrites have reported resolved 60Ni excesses using in situ secondary ion mass spectrometry implying Fe60/Fe56>?0.6×10-7 in the early Solar System, and among these very few (3) have higher excesses implying Fe60/Fe56?7×10-7 (Mishra et al., 2010; Mishra and Goswami, 2014; Telus et al., 2012). At variance, multi-collector inductively coupled plasma mass spectrometer studies of bulk samples and mineral separates from differentiated meteorites, angrites, achondrites, and chondrules suggest a low abundance of 60Fe/56Fe of ?1.4×10-8 which would rule out the need for an external seeding of the early Solar with stellar 60Fe (Quitté et al., 2011; Tang and Dauphas, 2012). Two Semarkona chondrules and one Efremovka chondrule analyzed in the present study have mass fractionation corrected excess of up to ?75 permil (‰) and give 60Fe isochrons with initial 60Fe/56Fe ratios of (7.8±3.7)×10-7, (3.8±1.6)×10-7, and (2.2±1.1)×10-7 (2?), for Efremovka Ch 1, Semarkona Ch 12, and Semarkona Ch J5 respectively. The higher values of 60Fe/56Fe ratios seen in the chondrules of these least altered meteorites samples concur with and lend greater credence to the suggestion of a massive star as the source of 60Fe, and possibly of other short-lived nuclides, to the early Solar System. However, no definitive explanation (e.g. sample bias, effects of metamorphism, 60Fe heterogeneity) to the apparent disagreement with studies of bulk chondrules and chondrule fragments has been found.

Mishra, Ritesh Kumar; Chaussidon, Marc

2014-07-01

27

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

28

Oxygen isotope studies of ordinary chondrites  

NASA Technical Reports Server (NTRS)

Several stages in the evolution of ordinary chondritic meteorites are recorded in the oxygen isotopic composition of the meteorites and their separable components (chondrules, fragments, clasts, and matrix). The whole-rock isotopic compositions reflect the iron-group of the meteorite (H, L, or LL). Isotopic uniformity of H3 to H6 and L3 to L6 are consistent with closed-system metamorphism within each parent body. LL3 chondrites differ slightly from LL4 to LL6, implying a small degree of open-system aqueous alteration and carbon reduction. On the scale of individual chondrules, the meteorites are isotopically heterogeneous, allowing recognition of the solar-nebular processes of chondrule formation. Chondrules for all classes of ordinary chondrites are derived from a common population, which was separate from the population of chondrules in carbonaceous or enstatite chondrites. Chondrules define an isotopic mixing line dominated by exchange between (O - 16)-rich and (O - 16)-poor reservoirs. The oxygen isotopic compositions of chondrites serve as 'fingerprints' for identification of genetic association with other meteorite types (achondrites and iron) and for recognition of source materials in meteoritic breccias.

Clayton, Robert N.; Mayeda, Toshiko K.; Olsen, Edward J.; Goswami, J. N.

1991-01-01

29

A comparison of FeO-rich, porphyritic olivine chondrules in unequilibrated chondrites and experimental analogues  

NASA Technical Reports Server (NTRS)

Experimentally produced analogues of porphyritic olivine (PO) chondrules in ordinary chondrites provide an important insight into chondrule formation processes. We have studied experimental samples with PO textures grown at three different cooling rates (2, 5 and 100 C/h), and samples that have been annealed at high temperatures (1000-1200 C) subsequent to cooling. These are compared with natural chondrules of similar composition and texture from the ordinary chondrites Semarkona (LL3.0) and ALH 81251 (LL3.3). Zoning properties of olivine grains indicate that the Semarkona chondrules cooled at comparable rates to the experiments. Zoning in olivine from chondrules in ALH 81251 is not consistent with cooling alone but indicates that the chondrules underwent an annealing process. Chromium loss from olivine is very rapid during annealing and calculated diffusion coefficients for Cr in olivine are very similar to those of Fe-Mg interdiffusion coefficients under the same conditions. Annealed experimental samples contain an aluminous, low-Ca pyroxene which forms by reaction of olivine and liquid. No similar reaction texture is observed in ALH 81251 chondrules, and this may be evidence that annealing of the natural samples took place at considerably lower temperatures than the experimental analogues. The study supports the model of chondrule formation in a cool nebula and metamorphism of partly equilibrated chondrites during reheating episodes on the chondrite parent bodies.

Jones, Rhian H.; Lofgren, Gary E.

1993-01-01

30

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

31

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

32

Chemical and physical studies of type 3 chondrites - VI: siderophile elements in ordinary chondrites  

SciTech Connect

The abundances of Fe, Ni, Co, Au, Ir, Ga, As and Mg have been determined by instrumental neutron activation analysis in 38 type 3 ordinary chondrites (10 of which may be paired) and 15 equilibrated chondrites. Classification of type 3 ordinary chondrites into the H, L and LL classes using oxygen isotopes and parameters which reflect oxidation state (Fa and Fs in the olivine and pyroxene, and Co in kamacite) is difficult or impossible. Bulk compositional parameters, based on the equilibrated chondrites, have therefore been used to classify the type 3 chondrites. The distribution of the type 3 ordinary chondrites over the classes is very different from that of the equilibrated chondrites, the LL chondrites being more heavily represented. The type 3 ordinary chondrites contain 5 to 15% lower abundances of siderophile elements, and a compilation of the present data and literature data indicates a small, systematic decrease in siderophile element concentration with decreasing petrologic type. The type 3 ordinary chondrites have, like the equilibrated ordinary chondrites, suffered a fractionation of their siderophile elements, but the loss of Ni in comparison with Au and Ir is greater for the type 3 chondrites. These siderophile element trends were established at the nebula phase of chondritic history and the co-variation with petrologic type implies onion-shell structures for the ordinary chondrite parent bodies. It is also clear that the relationship between the type 3 and the equilibrated ordinary chondrites involves more than simple, closed-system metamorphism.

Sears, D.W.G.; Weeks, K.S.

1986-12-01

33

Highly Porous and Compositionally Intermediate Ordinary Chondrite LAP 031047  

NASA Astrophysics Data System (ADS)

LAP 031047 is a highly porous ordinary chondrite with a very young Ar-Ar age, and oxygen isotopic, and bulk and silicate mineral composition intermediate between H- and L-chondrites: Shock-lithified debris of a distinct ordinary chondrite asteroid?

Wittmann, A.; Kring, D. A.; Friedrich, J. M.; Troiano, J.; Macke, R. J.; Britt, D. T.; Swindle, T. D.; Weirich, J. R.; Rumble, D.

2010-03-01

34

Ubiquitous brecciation after metamorphism in equilibrated ordinary chondrites  

NASA Technical Reports Server (NTRS)

Ten objects with aberrant Fe/(Fe + Mg) ratios have been found in apparently unbrecciated types 4-6 H and L chondrites. Since the Fe/(Fe + Mg) ratios of these objects are incompatible with the metamorphic history of the host chondrites, it is concluded that a high proportion of ordinary chondrites are breccias that were lithified after peak metamorphism. This is consistent with the results of Scott (1984), who concluded that most type three ordinary chondrites are breccias of materials with diverse thermal histories, even though they do not show prominent brecciation. It is found that the classification scheme of Van Schmus and Wood (1967) does not identify chondrites with similar thermal histories; the petrologic type of a chondrite is only a measure of the average thermal history of its ingredients. Chondrite and achondrite breccias are also compared in order to understand how brecciation of chondrites after metamorphism is so well camouflaged.

Scott, E. R. D.; Lusby, D.; Keil, K.

1985-01-01

35

Penecontemporaneous metamorphism, fragmentation, and reassembly of ordinary chondrite parent bodies  

NASA Technical Reports Server (NTRS)

The thermal histories of ordinary chondrites and the canonical internal heating or onion shell models, which predict an inverse relation between the petrologic type of chondrites and the metallographic cooling rate, are reviewed. The thermal and accretional requirements of the 'metamorphosed planetesimal' model proposed by Scott and Rajan (1981) are analyzed, and an alternative model consistent with the metallographic cooling rate constraints is suggested in which ordinary chondrite parent bodies are collisionally fragmented and then rapidly reassembled before metamorphic heat has been dissipated.

Grimm, R. E.

1985-01-01

36

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

37

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 ...

Vernazza, P.

38

Pore size distribution in an uncompacted equilibrated ordinary chondrite  

SciTech Connect

The extraordinarily uncompacted nature of the ordinary L chondrite fall Baszkowka gives a unique opportunity to investigate the potentially pre-compaction pore size distribution in an equilibrated ordinary chondrite. Using X-ray microtomography and helium pycnometry on two samples of Baszkowka, we have found that on average, two-thirds of the 19.0% porosity resides in inter- and intra-granular voids with volumes between {approx}3 x10{sup 05} and 3 mm{sup 3}. We show the cumulative number density of pore volumes observable by X-ray microtomography obeys a power law distribution function in this equilibrated ordinary chondrite. We foresee these data adding to our understanding of the impact processing of chondrites and their parent asteroids, where porosity and pore size play significant roles in the parameterization of impact events.

Friedrich, J.M.; Macke, R.J.; Wignarajah, D.P.; Rivers, M.L.; Britt, D.T.; Ebel, D.S. (Univ of Central FL); (Fordham Univ); (UofC); (Univ of Central FL); (AMNH); (Fordham Univ)

2008-05-30

39

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

40

Multiple parent bodies of ordinary chondrites  

NASA Astrophysics Data System (ADS)

Thermal histories of chondrite parent bodies are calculated from an initial state with material in a powder-like form, taking into account the effect of consolidation state on thermal conductivity. The very low thermal conductivity of the starting materials makes it possible for a small body with a radius of less than 100 km to be heated by several hundred degrees even if long-lived radioactive elements in chondritic abundances are the only source of heat. The maximum temperature is determined primarily by the temperature at which sintering of the constituent materials occurs. The thermal state of the interior of a chondrite parent body after sintering has begun is nearly isothermal. Near the surface, however, where the material is unconsolidated and the thermal conductivity is much lower, the thermal gradient is quite large. This result contradicts the conventional "onion-shell" model of chondrite parent bodies. But because the internal temperature is almost constant through the whole body, it supports a "multiple-parent bodies" model, according to which each petrologic type of chondrite comes from a different parent body.

Yomogida, K.; Matsui, T.

1984-04-01

41

Multiple parent bodies of ordinary chondrites  

NASA Technical Reports Server (NTRS)

Thermal histories of chondrite parent bodies are calculated from an initial state with material in a powder-like form, taking into account the effect of consolidation state on thermal conductivity. The very low thermal conductivity of the starting materials makes it possible for a small body with a radius of less than 100 km to be heated by several hundred degrees even if long-lived radioactive elements in chondritic abundances are the only source of heat. The maximum temperature is determined primarily by the temperature at which sintering of the constituent materials occurs. The thermal state of the interior of a chondrite parent body after sintering has begun is nearly isothermal. Near the surface, however, where the material is unconsolidated and the thermal conductivity is much lower, the thermal gradient is quite large. This result contradicts the conventional 'onion-shell' model of chondrite parent bodies. But because the internal temperature is almost constant through the whole body, it supports a 'multiple-parent bodies' model, according to which each petrologic type of chondrite comes from a different parent body.

Yomogida, K.; Matsui, T.

1984-01-01

42

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

43

Ca-Al-rich chondrules and inclusions in ordinary chondrites  

NASA Technical Reports Server (NTRS)

Ca-Al-rich objects, hitherto mostly found in carbonaceous chondrites, are shown to be widespread, albeit rare, constituents of type 3 ordinary chondrites. Widespread occurrence and textural similarities of Ca-Al-rich chondrules to common, Mg-Fe-rich chondrules suggest that they formed by related processes. It is suggested in this article that Ca-Al-rich chondrules were formed by total melting and crystallization of heterogeneous, submillimeter- to submillimeter-sized dustballs made up of mixtures of high-temperature, Ca-Al-rich and lower-temperature, Na-K-rich components.

Bischoff, A.; Keil, K.

1983-01-01

44

Chemical and physical studies of type 3 chondrites. XI - Metamorphism, pairing, and brecciation of ordinary chondrites  

NASA Technical Reports Server (NTRS)

The present study reports recent measurements of the induced thermoluminescence (TL) properties of 69 type-3 ordinary chondrites, bringing to 125 the number of type-3 ordinary chondrites for which TL data are available. The samples include several of the particularly low petrographic type and many breccias, some of them gas-rich. The significance of the data with respect to the physical conditions affecting metamorphism is discussed. The TL data, olivine heterogeneity, carbon content, and inert-gas content were used to assign the samples to petrologic types. Twelve meteorites were identified as being type 3.0-3.2, and 10 of the breccias were found to contain material that may also be of this type. The temperature and width of the induced TL peak are also related to thermal history, with type 3.2-3.4 chondrites tending to have narrower peaks at lower glow curve temperatures than the type 3.6-3.9 chondrites. Type 3 H chondrites were found to be a higher petrographic type than the type 3 L and LL chondrites.

Sears, D. W. G.; Hasan, F. A.; Batchelor, J. D.; Lu, J.

1991-01-01

45

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

46

Carbon in weathered ordinary chondrites from Roosevelt County  

NASA Technical Reports Server (NTRS)

A suite of Roosevelt County ordinary chondrites of known terrestrial age have been analyzed for carbon content and isotopic composition. Initial results indicate that significant carbon contamination is evident only in samples with a terrestrial age greater than 40 ka. These samples are of weathering grade D and E and contain three times more carbon than the less weathered samples. The soil in which they were preserved has a carbon content of ca. 1.5 percent. Over 200 meteorites have been recovered from a series of soil depleted areas of New Mexico and West Texas. Most have been recovered from blowouts near Clovis in Roosevelt County (RC) on the high plains of New Mexico. The mineralogical and petrologic Al effects of weathering upon these samples have been studied previously and show that the degree of weathering is largely depend ant upon the terrestrial residence time. The study was undertaken to determine the effects of prolonged exposure to the soil and climate of Roosevelt County upon ordinary chondrites in the hope that this will enable a better understanding of the problems associated with the collection of meteoritic falls. A suite of ten grade 4 to 6 H, L, and LL ordinary chondrites were analyzed for carbon content and isotopic composition.

Ash, R. D.; Pillinger, C. T.

1993-01-01

47

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

48

Metal Phases of Ordinary Chondrites: Melting Remnants or Nebular Condensates?  

NASA Astrophysics Data System (ADS)

Bulk metals of 10 H, 6 L and 7 LL chondrites were analyzed by INAA. A significant difference in the metallic compositions between EOCs and UOCs is noted for the abundances of three lithophile elements, Cr, Mn and V, and three weakly siderophile elements, W, Mo and Ga. The abundances of W, Mo and Ga are increased and those of Cr, Mn and V are decreased with increase of petrographic type. According to condensation sequence [1], Fe condensed into a metal phase at high temperature. With temperature falling, metallic Fe was partly oxidized into silicates and partly transferred into troilite during equilibrium with the solar nebula. If Fe could equilibrate with the solar nebula, it is not expected that V, Cr and Mn still remain partly in the metal phases since they would be oxidized at higher temperatures than that for oxidizing Fe. Rapid formation of silicates around metal grains might preserve these elements but should keep W and Mo quantitatively present in the metals. Our results show that relative to Ir and Os, W and Mo are both depleted in the UOC metals to some extents, implying that portions of W and Mo are present in the non-metal phases. It is difficult to envision that the "being reduced" V, Cr and Mn can coexist with the "being oxidized" W, Mo and Ga in the metallic fractions if the metallic fractions were nebula condensates. W, Mo and Ga are enriched in the metallic fractions of the EOCs in order of W>Mo>Ga, while in those of the UOCs the order changes to Mo>W>Ga. We believe that the truly equilibrated distributions of W and Mo among different phases are preserved in the equilibrated chondrites, because the redox states of the elements must have been readjusted to reach equilibrium or near to equilibrium during the thermal metamorphism. So, if the UOC metals were equilibrated condensates, the relative distributions of W and Mo in the UOC metals should be similar to those in the EOC metals. However, this is not the case. If the metals were interstellar grains and have not changed their characteristics before the accretion of chondrites, the compositions of the metals should be uniform for all ordinary chondrites of different chemical groups. In fact, they have changed. If the compositions of the metals were adjusted according to the redox condition in places where chondrites formed, the contradictory states of "being reduced" V, Mn and Cr and "being oxidized" W, Mo and Ga preserved in the UOC metals must be erased. Thus, it seems implausible that the metals of ordinary chondrites were the interstellar grains before their accreting into chondrites. Formation of chondritic metals seems to be attributable only to the remaining melting mechanism. Experimental results showed that the metal/silicate partition coefficients of W were always lower than those of Mo at temperature 1300 degrees C and oxygen fugacities between 10^-13 to 10^-11 bars [2]. Moreover, partition behaviors of Cr, V and Mn [3] are similar to those found in the UOCs. The consistence of experimental partition coefficients of W, Mo, Ga, V, Cr and Mn with their abundance ratios between metal and silicate phases of UOCs suggests that the UOC metals were formed by a melting mechanism. It is thus concluded that the metals of ordinary chondrites were the melting remnants before they were accreted into chondritic parent bodies. References: [1] Wasson J. T. (1985) in Meteorites: Their Record of Early Solar-System History, Freeman, New York. [2] Schmitt W. et al. (1989) GCA, 53, 173-185. [3] Drake M. J. et al. (1989) GCA, 53, 2101-2111.

Kong, P.; Ebihara, M.

1995-09-01

49

Defining the Petrology of Pseudotachylytes in Ordinary Chondrites: An Experimental and Deductive Approach  

NASA Technical Reports Server (NTRS)

Evidence for deformation in ordinary chondrites suggests that meteorite evolution involves high strain-rate processes. Unexpected experimental results and an analysis of physical properties of chondrite minerals supports and defines this contention.

vanderBogert, C. H.; Schultz, P. H.; Spray, J. G.

2000-01-01

50

The onset of metamorphism in ordinary and carbonaceous chondrites  

USGS Publications Warehouse

Ordinary and carbonaceous chondrites of the lowest petrologic types were surveyed by X-ray mapping techniques. A variety of metamorphic effects were noted and subjected to detailed analysis using electron microprobe, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and cathodoluminescence (CL) methods. The distribution of Cr in FeO-rich olivine systematically changes as metamorphism increases between type 3.0 and type 3.2. Igneous zoning patterns are replaced by complex ones and Cr-rich coatings develop on all grains. Cr distributions in olivine are controlled by the exsolution of a Cr-rich phase, probably chromite. Cr in olivine may have been partly present as tetrahedrally coordinated Cr3+. Separation of chromite is nearly complete by petrologic type 3.2. The abundance of chondrules showing an inhomogeneous distribution of alkalis in mesostasis also increases with petrologic type. TEM shows this to be the result of crystallization of albite. Residual glass compositions systematically change during metamorphism, becoming increasingly rich in K. Glass in type I chondrules also gains alkalis during metamorphism. Both types of chondrules were open to an exchange of alkalis with opaque matrix and other chondrules. The matrix in the least metamorphosed chondrites is rich in S and Na. The S is lost from the matrix at the earliest stages of metamorphism due to coalescence of minute grains. Progressive heating also results in the loss of sulfides from chondrule rims and increases sulfide abundances in coarse matrix assemblages as well as inside chondrules. Alkalis initially leave the matrix and enter chondrules during early metamorphism. Feldspar subsequently nucleates in the matrix and Na re-enters from chondrules. These metamorphic trends can be used to refine classification schemes for chondrites. Cr distributions in olivine are a highly effective tool for assigning petrologic types to the most primitive meteorites and can be used to subdivide types 3.0 and 3.1 into types 3.00 through 3.15. On this basis, the most primitive ordinary chondrite known is Semarkona, although even this meteorite has experienced a small amount of metamorphism. Allan Hills (ALH) A77307 is the least metamorphosed CO chondrite and shares many properties with the ungrouped carbonaceous chondrite Acfer 094. Analytical problems are significant for glasses in type II chondrules, as Na is easily lost during microprobe analysis. As a result, existing schemes for chondrule classification that are based on the alkali content of glasses need to be revised. ?? The Meteorological Society, 2005.

Grossman, J.N.; Brearley, A.J.

2005-01-01

51

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

52

Metallographic cooling rates of L-group ordinary chondrites  

NASA Technical Reports Server (NTRS)

Shock metamorphism appears to be a ubiquitous feature in L-group ordinary chondrites. Brecciation and heterogeneous melting obscure much of the early history of this meteorite group and have caused confusion as to whether L chondrites have undergone thermal metamorphism within onion-shell or rubble-pile parent bodies. Employing the most recent shock criteria, we have examined 55 Antarctic and 24 non-Antarctic L chondrites in order to identify those which have been least affected by post-accretional shock. Six low-shock samples (those with shock grade less than S4) of petrographic types L3-L5 were selected from both populations and metallographic cooling rates were obtained following the technique of Willis and Goldstein. All non-Antarctic L6 chondrites inspected were too heavily shocked to be included in this group. However, 4 shocked L6 chondrites were analyzed in order to determine what effects shock may impose on metallographic cooling rates. Metallographic cooling rates were derived by analyzing the cores of taenite grains and then measuring the distance to the nearest grain edge. Taenites were identified using backscatter imaging on a Cameca SX-50 electron microprobe. Using backscatter we were able to locate homogeneous, rust-free, nearly spherical grains. M-shaped profiles taken from grain traverses were also used to help locate the central portions of selected grains. All points which contained phosphorus above detection limits were discarded. Plots of cooling-rate data are summarized and data from the high-shock samples are presented. The lack of coherency of cooling rates for individual samples is indicative of heterogeneous cooling following shock. The data confirms the statement expressed by numerous workers that extreme care must be taken when selecting samples of L chondrites for cooling-rate studies. Data for the 6 non-Antarctic low-shock samples are also presented. The samples display a general trend in cooling rates. The lowest metamorphic grade yielded the slowest cooling rates and an increase in grade follows an increase in cooling rate. This is the opposite relationship to that predicted by the onion-shell model.

Bennett, Marvin E.; Mcsween, Harry Y., Jr.

1993-01-01

53

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

54

Manganese-Chromium Isotope Systematics of Ordinary Chondrite Forest Vale (H4) and Enstatite Chondrite Indarch (EH4)  

NASA Astrophysics Data System (ADS)

Mn-Cr isochrons were determined on mineral fractions of the ordinary chondrite Forest Vale and the enstatite chondrite Indarch. The initial 53Mn/55Mn of Forest Vale is in good agreement with existing literature while Indarch displays an older age than reported previously.

Moseley, G. E.; Schönbächler, M.; Davies, C.; Horan, M. F.; Busefield, A.; Carlson, R. W.

2011-03-01

55

Formation of Metal in GRO 95551 and Comparison to Ordinary Chondrites  

E-print Network

components of the metal were not completely erased during equilibration at ~1020 K. The Ni-normalized bulkFormation of Metal in GRO 95551 and Comparison to Ordinary Chondrites ANDREW J. CAMPBELL* AND MUNIR­Siderophile element abundances in individual metal grains in the ungrouped chondrite GRO 95551 and in the ordinary

Campbell, Andrew

56

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 Galileo tend to convert spectra of ordinary chondrites to have the spectral traits of S­type asteroids

Chapman, Clark R.

57

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

58

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

59

A unique type 3 ordinary chondrite containing graphite-magnetite aggregates - Allan Hills A77011  

NASA Technical Reports Server (NTRS)

ALHA 77011, which is the object of study in the present investigation, is a chondrite of the 1977 meteorite collection from Allan Hills, Antarctica. It contains an opaque and recrystallized silicate matrix (Huss matrix) and numerous aggregates consisting of micron- and submicron-sized graphite and magnetite. It is pointed out that no abundant graphite-magnetite aggregates could be observed in other type 3 ordinary chondrites, except for Sharps. Attention is given to the results of a modal analysis, relations between ALHA 77011 and other type 3 ordinary chondrites, and the association of graphite-magnetite and metallic Fe, Ni. The discovery of graphite-magnetite aggregates in type 3 ordinary chondrites is found to suggest that this material may have been an important component in the formation of ordinary chondrites.

Mckinley, S. G.; Scott, E. R. D.; Taylor, G. J.; Keil, K.

1982-01-01

60

Igneous rock from Severnyi Kolchim (H3) chondrite: Nebular origin  

NASA Technical Reports Server (NTRS)

The discovery of lithic fragments with compositions and textures similar to igneous differentiates in unequilibrated ordinary chondrites (UOC's) and carbonaceous chondrites (CC's) has been interpreted as to suggest that planetary bodies existed before chondrites were formed. As a consequence, chondrites (except, perhaps CI chondrites) cannot be considered primitive assemblages of unprocessed nebular matter. We report about our study of an igneous clast from the Severnyi Kolchim (H3) chondrite. The results of the study are incompatible with an igneous origin of the clast but are in favor of a nebular origin similar to that of chondrules.

Nazarov, M. A.; Brandstaetter, F.; Kurat, G.

1993-01-01

61

The Origin of Silica-Rich Chondrules and Clasts in Ordinary and Carbonaceous Chondrites  

Microsoft Academic Search

Chondrules and clasts containing a silica mineral or a silica glass are a minor but important constituent in many ordinary (Planner, 1983; Brigham et al., 1986) and some carbonaceous (Olsen, 1983) chondrites, and have been considered somewhat enigmatic. The recent discovery of a large, silica-rich igneous clast in the Bovedy (L3) chondrite (Ruzicka and Boynton, 1992) sheds light on the

A. Ruzicka; W. V. Boynton

1992-01-01

62

SXRF determination of trace elements in chondrule rims in the unequilibrated CO3 chondrite, ALH A77307  

NASA Technical Reports Server (NTRS)

The concentrations of Ni, Cu, Zn, Ga, Ge, and Se in five chondrule rims in the CO3 chondrite ALH A77307 (3.0) using the synchrotron x-ray fluorescence (SXRF) microprobe at Brookhaven National Laboratory were determined. The data show that the trace element chemistry of rims on different chondrules is remarkably similar, consistent with data obtained for the major elements by electron microprobe. These results support the idea that rims are not genetically related to individual chondrules, but all sampled the same reservoir of homogeneously mixed dust. Of the trace elements analyzed Zn and Ga show depletions relative to CI chondrite values, but in comparison with bulk CO chondrites all the elements are enriched by approximately 1.5 to 3.5 x CO. The high concentrations of the highly volatile elements Se and Ga and moderately volatile Zn (1.5 to 2 x CO) in rims show that matrix is the major reservoir of volatile elements in ALH A77307.

Brearley, Adrian J.; Bajt, Sasa; Sutton, Steve R.; Papike, J. J.

1993-01-01

63

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

64

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

65

Metal phases in ordinary chondrites: Magnetic hysteresis properties and implications for thermal history  

NASA Astrophysics Data System (ADS)

Magnetic properties are sensitive proxies to characterize FeNi metal phases in meteorites. We present a data set of magnetic hysteresis properties of 91 ordinary chondrite falls. We show that hysteresis properties are distinctive of individual meteorites while homogeneous among meteorite subsamples. Except for the most primitive chondrites, these properties can be explained by a mixture of multidomain kamacite that dominates the induced magnetism and tetrataenite (both in the cloudy zone as single-domain grains, and as larger multidomain grains in plessite and in the rim of zoned taenite) dominates the remanent magnetism, in agreement with previous microscopic magnetic observations. The bulk metal contents derived from magnetic measurements are in agreement with those estimated previously from chemical analyses. We evidence a decreasing metal content with increasing petrologic type in ordinary chondrites, compatible with oxidation of metal during thermal metamorphism. Types 5 and 6 ordinary chondrites have higher tetrataenite content than type 4 chondrites. This is compatible with lower cooling rates in the 650-450 °C interval for higher petrographic types (consistent with an onion-shell model), but is more likely the result of the oxidation of ordinary chondrites with increasing metamorphism. In equilibrated chondrites, shock-related transient heating events above approximately 500 °C result in the disordering of tetrataenite and associated drastic change in magnetic properties. As a good indicator of the amount of tetrataenite, hysteresis properties are a very sensitive proxy of the thermal history of ordinary chondrites, revealing low cooling rates during thermal metamorphism and high cooling rates (e.g., following shock reheating or excavation after thermal metamorphism). Our data strengthen the view that the poor magnetic recording properties of multidomain kamacite and the secondary origin of tetrataenite make equilibrated ordinary chondrites challenging targets for paleomagnetic study.

Gattacceca, J.; Suavet, C.; Rochette, P.; Weiss, B. P.; Winklhofer, M.; Uehara, M.; Friedrich, Jon M.

2014-04-01

66

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

67

Aluminum-, Calcium- and Titanium-rich Oxide Stardust in Ordinary Chondrite Meteorites  

NASA Astrophysics Data System (ADS)

We report O-, Al-Mg-, K-, Ca-, and Ti-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 Msolar) 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 multielement 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.

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

2008-08-01

68

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

69

Ordinary chondrites - Multivariate statistical analysis of trace element contents  

NASA Technical Reports Server (NTRS)

The contents of mobile trace elements (Co, Au, Sb, Ga, Se, Rb, Cs, Te, Bi, Ag, In, Tl, Zn, and Cd) in Antarctic and non-Antarctic populations of H4-6 and L4-6 chondrites, were compared using standard multivariate discriminant functions borrowed from linear discriminant analysis and logistic regression. A nonstandard randomization-simulation method was developed, making it possible to carry out probability assignments on a distribution-free basis. Compositional differences were found both between the Antarctic and non-Antarctic H4-6 chondrite populations and between two L4-6 chondrite populations. It is shown that, for various types of meteorites (in particular, for the H4-6 chondrites), the Antarctic/non-Antarctic compositional difference is due to preterrestrial differences in the genesis of their parent materials.

Lipschutz, Michael E.; Samuels, Stephen M.

1991-01-01

70

Ordinary chondrites: Multivariate statistical analysis of trace element contents  

SciTech Connect

The authors used standard multivariate Discriminant Functions, borrowed from Linear Discriminant Analysis and Logistic Regression, to compare contents of mobile trace elements (Co, Au, Sb, Ga, Se, Rb, Cs, Te, Bi, Ag, In, Tl, Zn, Cd) in various populations of L4-6 or H4-6 chondrites. To aid in their analysis they developed a non-standard Randomization-Simulation method that permits probability assignments on a distribution-free basis. Because the sample database for Antarctic L4-6 chondrites is very limited, they could not establish that mildly and strongly shocked (<22 GPa and {ge}22 GPa, respectively) populations differ compositionally. For non-Antarctic L4-6 chondrites, where the sample data-base is larger and the degree of shock-loading in the strongly shocked population is greater on average, a highly significant compositional difference is evident. This difference probably reflects shock-induced loss of mobile trace elements from parent material of the strongly shocked population. The authors believe that the case for compositional difference between Antarctic and non-Antarctic H4-6 chondrite populations, as well as between these populations of L4-6 chondrites, in now conclusively established. Various lines of evidence demonstrate that for various sorts of meteorites, especially H4-6 chondrites, the Antarctic/non-Antarctic compositional difference is not due to trivial (terrestrial) causes but rather to preterrestrial differences in the genesis of their parent materials.

Lipschutz, M.E.; Samuels, S.M. (Purdue Univ., West Lafayette, IN (USA))

1991-01-01

71

Multiple impact events recorded in the NWA 7298 H chondrite breccia and the dynamical evolution of an ordinary chondrite asteroid  

NASA Astrophysics Data System (ADS)

The major geologic process that has shaped the asteroids and led to development of their regoliths is impact. Petrofabrics in ordinary chondrites are undoubtedly the result of impact events on their asteroidal parent bodies and the foliation present in a chondrite serves as an enduring record of the magnitude of the most intense compacting event experienced by the material. An overwhelming majority of chondrites have an internally consistent petrofabric contained within the spatial dimensions of the entire rock, including across clasts or different petrographic domains. This indicates that the magnitude of the most recent impact to have affected the assembled chondrite was significant enough to impart a foliation across all lithologies. Information of any previous impacts is largely lost because of the consistent, realigned foliations. We present X-ray microtomography derived 3D petrofabric intensity and orientation data for three lithologies in the NWA 7298 breccia. The internally inconsistent petrofabrics among differing lithologies indicate that the magnitude of the final impact event was smaller than previous ones. This latter case preserves fabric information recorded during previous impacts and allows a more complete interpretation of the impact history of a local region of the asteroidal parent. We used our data to infer the sequence and intensity of distinct impact events affecting the NWA 7298 parent asteroid. We suggest a near-surface impact debris zone on the H chondrite parent asteroid as an origin for NWA 7298. These observations yield new opportunities for investigating and interpreting the dynamic collisional evolution of asteroids.

Friedrich, Jon M.; Weisberg, Michael K.; Rivers, Mark L.

2014-05-01

72

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

73

The Cooling History and Structure of the Ordinary Chondrite Parent Bodies  

NASA Technical Reports Server (NTRS)

Most major meteorite classes exhibit significant ranges of metamorphism. The effects of metamorphism have been extensively characterized, but the heat source(s) and the metamorphic environment are unknown. Proposed beat sources include Al-26, Fe-60, electromagnetic induction, and impact. It is typically assumed that metamorphism occurred in parent bodies of some sort, but it uncertain whether these bodies were highly structured ("onion skins") or were chaotic mixes of material ("rubble piles"). The lack of simple trends of metallographic cooling rates with petrologic type has been considered supportive of both concepts. In this study, we use induced thermoluminescence (TL) as an indicator of thermal history. The TL of ordinary chondrites is produced by sodic feldspar, and the induced TL peak temperature is related to its crystallographic order/disorder. Ordered feldspar has TL peak temperatures of approx. 120 C, and disordered feldspar has TL peak temperatures of approx. 220 C. While ordered feldspar can be easily disordered in the laboratory by heating above 650 C and is easily quenched in the disordered form, producing ordered feldspar requires cooling at geologic cooling rates. We have measured the induced TL properties of 101 equilibrated ordinary chondrites, including 49 H, 29 L, and 23 LL chondrites. For the H chondrites there is an apparent trend of decreasing induced TL peak temperature with increasing petrologic type. H4 chondrites exhibit a tight range of TL peak temperatures, 190 C - 200 C, while H6 chondrites exhibit TL peak temperatures between 180 C and 190 C. H5 chondrites cover the range between H4 and H6, and also extend up to 210 C. Similar results are obtained for LL chondfiles and most L6 chondrites have lower induced TL peak temperatures than L5 chondrites.

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

1996-01-01

74

Elemental composition of individual chondrules from ordinary chondrites.  

NASA Technical Reports Server (NTRS)

Sequential nondestructive neutron activation analysis was used to determine the bulk abundance of Fe, Al, Na, Mn, Cr, Sc, Co, and Ir in approximately 300 individual chondrules from 16 chondrites representing the H(3-5), L4, and LL(3-6) compositional and petrologic classes. The histograms indicate that the most probable abundances for lithophilic elements, except Cr, are enriched in the chondrules, while the siderophilic elements are depleted in the chondrules compared to the whole chondrite. Some of the abundance populations, such as Al and Fe, appear to be multimodal. Systematic variations in the composition of the chondrules with increasing petrologic type were observed; most consistent are an increasing Na-Al and Cr-Al correlation, a decreasing Na-Mn correlation, increasing Na abundance, and decreasing Na and Mn dispersions among chondrules.

Osborn, T. W.; Schmitt, R. A.; Smith, R. H.

1973-01-01

75

Chelyabinsk — Not only Another Ordinary LL5 Chondrite, but a Spectacular Chondrite Breccia  

NASA Astrophysics Data System (ADS)

The Chelyabinsk chondrite is a breccia having different lithologies mixed together and lithified. Besides the LL5 and impact melt lithologies described earlier, it contains light-colored LL6 lithologies as well as shock-darkened fragments.

Bischoff, A.; Horstmann, M.; Vollmer, C.; Heitmann, U.; Decker, S.

2013-09-01

76

Elemental composition of individual chondrules from ordinary chondrites  

Microsoft Academic Search

Sequential non-destructive neutron activation analysis was used to determine the bulk abundance of Fe, Al, Na, Mn, Or, Sc, Co and Ir in approximately 300 individual chondrules from 16 chondrites representing the H (3-5), L4 and LL(3-6) compositional and petrologic classes. For some of the chondrules, Si, Ni, Ca and V were also determined. The histograms indicate that the most

T. W. Osborn; R. H. Smith; R. A. Schmitt

1973-01-01

77

Hysteresis properties of ordinary chondrites and implications for their thermal history  

NASA Astrophysics Data System (ADS)

We present a large dataset of magnetic hysteresis properties of ordinary chondrite falls. We show that hysteresis properties are distinctive of individual meteorites while homogeneous among meteorite subsamples. Except for the most primitive chondrites, these properties can be explained by a mixture of multidomain kamacite and tetrataenite (both in the cloudy zone and as larger grains in plessite and in the rim of zoned taenite). Kamacite dominates the induced magnetism whereas tetrataenite dominates the remanent magnetism, in agreement with previous microscopic magnetic observations. Type 5 and 6 chondrites have higher tetrataenite content than type 4 chondrites, suggesting they have lower cooling rates at least in the 650-450 °C interval, consistent with an onion-shell model. In equilibrated chondrites, shock-related transient heating events above ~500 °C result in the disordering of tetrataenite and associated drastic change in magnetic properties. As a good indicator of the amount of tetrataenite, hysteresis properties are a very sensitive proxy of the thermal history of ordinary chondrites, revealing low cooling rates during thermal metamorphism, and high cooling rates following shock reheating or excavation after thermal metamorphism.

Gattacceca, J.; Suavet, C. R.; Rochette, P.; Weiss, B. P.; Winklhofer, M.; Uehara, M.; Friedrich, J. M.

2013-12-01

78

The chemistry and origin of the ordinary chondrites Implications from refractory-lithophile and siderophile elements  

NASA Technical Reports Server (NTRS)

Thirty-eight ordinary chondrites (17 H, 20 L, and 1 LL) have been analyzed for major and selected trace elements. These data indicate that the lithophile elements Mg, Ca, Al, Cr, and V normalized to Si are in higher abundance in the H than in the L chondrites. The siderophile elements Ni, Co, and Fe show very good correlation within, as well as between, the two major ordinary chondrite groups. Twenty-four of the analyses are of Antarctic finds, while ten are samples of falls. Comparing the Antarctic data with the fall data reveals no evidence that any of the elements studied here have been mobilized by terrestrial weathering processes. Within the H and L chondrite groups there is little chemical variation, indicating that the source of these samples is remarkably homogeneous. Equilibrium condensate fractionation from a nebula of CI composition can result in the observed ordinary chondrite compositions. The fractionation of metal at about 1440 K (and 0.001 atm) into high and low iron groups, followed by a gas-solid fractionation at about 1380 K with the H group losing more solids than the L, will produce the observed H and L compositions and intragroup trends.

Fulton, C. R.; Rhodes, J. M.

1984-01-01

79

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

80

Reheated Ordinary Chondrites: The Record of Small Perihelia and Impacts Over the Last Million Years  

NASA Astrophysics Data System (ADS)

"Reheated" meteorites, i.e. meteorites that have experienced some significant degree of heating after metamorphism often within the last 100 million years or so, are fairly common among ordinary chondrites and basaltic meteorites. Heating is inferred to be by impact or by close passage to the Sun. Here I use the ratios of cosmogenic helium and neon and the natural thermoluminescence (TL) of individual meteorites to examine the timing and nature of reheating of ordinary chondrites. The noble gases can reflect reheating at any time over the entire cosmic ray exposure age (typically millions of years), while natural TL reflects reheating events within the last hundred thousand years. Natural TL can reflect thermal events of smaller magnitude than can the noble gases. About 40% of H and L modern falls have been reheated to some extent over their cosmic ray exposure history, but only about 25% of LL chondrites have apparently been reheated. The TL data indicate that, while about 20% of H chondrites have been reheated within the last 100,000 years, only about 12% of L and LL chondrites have experienced recent reheating. Data for Antarctic meteorites suggest that reheated meteorites were less common or even absent >200,000 years ago.

Benoit, P. H.

1996-03-01

81

Phosphate minerals in LL chondrites: A record of the action of fluids during metamorphism on ordinary chondrite parent bodies  

NASA Astrophysics Data System (ADS)

Ordinary chondrites contain two phosphate minerals, merrillite and chlorapatite, both of which are secondary minerals that developed in response to metamorphism on the chondrite parent bodies. We have studied the phosphate mineralogy of four LL chondrites, of petrologic types 3.9-6, in order to determine the petrogenesis of the two minerals and interpret the conditions under which they formed. Characterization of merrillite and apatite includes textural observations, mineral compositions determined by electron probe microanalysis, and ion microprobe analyses of trace element and volatile anion elemental abundances. Initial formation of phosphate minerals during mild metamorphism, to petrologic type 4 conditions, resulted in oxidation of P that was originally incorporated in metal, and growth of merrillite as inclusions within metal grains. Subsequent development of both phosphate minerals occurred in response to diffusional equilibration, possible precipitation from fluids as well as replacement reactions resulting from interactions with fluids. Porosity and vein-filling textures in both merrillite and chlorapatite, as well as textures indicating replacement of merrillite by chlorapatite, support a model in which fluid played a significant role and suggest an interface-coupled dissolution-reprecipitation mechanism during metasomatism. Some associations of phosphate minerals with chromite-plagioclase assemblages suggest that phosphate minerals could also be related to impact processes, either as precipitation from an impact melt or as a result of interactions with a fluid or vapor derived from an impact melt. Fluid compositions may have been water-bearing initially, at low temperatures of metamorphism, but later evolved to become halogen-rich and very dry. Late-stage halogen-rich fluids that dominated during cooling of LL chondrite material may have been derived from vaporization of partial melts in the interior of the parent body. Overall, the LL chondrite parent body underwent a complex chemical evolution, in which metasomatism played a significant role.

Jones, Rhian H.; McCubbin, Francis M.; Dreeland, Linda; Guan, Yunbin; Burger, Paul V.; Shearer, Charles K.

2014-05-01

82

Carbon-rich aggregates in type 3 ordinary chondrites - Characterization, origins, and thermal history  

NASA Technical Reports Server (NTRS)

Carbon-rich aggregates from three type 3.4-3.6 ordinary chondrites and two chondritic clasts have been characterized in detail, using TEM techniques. The aggregates in all the meteorites studied range in size from 5-1000 microns and consist of a fine scale intergrowth of poorly graphitized carbon, amorphous carbon, Fe,Ni metal, and minor chromite. Contrary to previous reports, well-crystallized graphite and magnetite are absent. The association of Fe,Ni metal and carbonaceous material suggests that the original carbonaceous material may have formed by Fischer-Tropsch (FT) type reactions at low temperatures (less than 400 K), possibly in the solar nebula. This carbonaceous material probably consisted of a complex mixture of hydrocarbons, kerogen-like material, and other complex organic molecules. The aggregates were subsequently accreted onto the ordinary chondrite parent bodies and underwent planetary thermal processing which resulted in the catalytic graphitization of hydrocarbons, in the presence of Fe,Ni metal, to produce poorly graphitized carbon. None of the meteorites studied experienced temperatures sufficiently high to produce crystalline, ordered graphite. Using the empirical geothermometer of Rietmeijer and Mackinnon (1985), the measured d(002) spacings of poorly graphitized carbon show that graphitization occurred at temperatures between 300 and 450 C. This range of temperatures is significantly lower than the generally quoted metamorphic temperatures for type 3.4-3.6 ordinary chondrites (about 450-500 C).

Brearley, Adrian J.

1990-01-01

83

The Oxygen Isotope Composition of Dark Inclusions in HEDs, Ordinary and Carbonaceous Chondrites  

NASA Technical Reports Server (NTRS)

Dark inclusions (DIs) are lithic fragments that form a volumetrically small, but important, component in carbonaceous chondrites. Carbonaceous clasts similar to DIs are also found in some ordinary chondrites and HEDs. DIs are of particular interest because they provide a record of nebular and planetary processes distinct from that of their host meteorite. DIs may be representative of the material that delivered water and other volatiles to early Earth as a late veneer. Here we focus on the oxygen isotopic composition of DIs in a variety of settings with the aim of understanding their formational history and relationship to the enclosing host meteorite.

Greenwood, R. C.; Zolensky, M. E.; Buchanan, P. C.; Franchi, I. A.

2015-01-01

84

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

85

Observations of 2002 NY 40: an ordinary chondrite?  

NASA Astrophysics Data System (ADS)

The near-Earth asteroid 2002 NY40 was discovered on July 14 2002 by the LINEAR survey. The object made a close pass by the Earth on August 18 when observations were obtained at a large range of wavelengths from visible to radar (12.6 cm). The combination of visible and near-infrared spectroscopy gives some indication of the composition. Thermal emission in the 3-micron region gives constraints on the visible albedo which are confirmed independently by the radar size and visible magnitude. The lightcurve was well measured by a large number of observers and the rotation period is well-determined at 19.99 hours. The spectrum and albedo are a very good match to an LL chondrite spectrum over the range measured. No appreciable reddening is seen in the asteroid spectrum which suggests that the surface has not been noticeably affected by the same processes seen in many other pyroxene and olivine-rich asteroids. The radar images show that this asteroid looks like two spheroidal units joined together. Analysis and implications of these observations will be discussed.

Howell, Ellen S.; Rivkin, Andrew S.; Nolan, Michael C.; Margot, Jean-Luc; Black, Gregory; Bus, Schelte J.; Hicks, Michael; Reach, Williamm T.; Jarrett, H. T.; Binzel, Richard P.

2005-01-01

86

Mineralogy and petrology of two ordinary chondrites and their correlation with other meteorites  

NASA Astrophysics Data System (ADS)

Two ordinary chondrites are compared and classified using transmitted and reflected light microscopy and electron microprobe analyses. Both meteorites were confiscated by the Polish Customs Service at the border with Belarus. The first meteorite (called in this paper Terespol-1) is a L/LL6 chondrite, its classification being supported by the equilibrated compositions of olivine and orthopyroxene and the presence of large recrystallized feldspars (< 150 ?m). The specimen examined experienced weak shock metamorphism (S3) and moderate weathering (although metal in the inner part of the meteorite seems to be unaffected by oxidization). The other meteorite (called in this paper Terespol-2) is a LL6 chondrite which experienced weak shock metamorphism (S3) and is unaffected by weathering. The Terespol-2 meteorite shares its classification with the Dhofar 1401 chondrite but the lack of data prevents further correlation. Both meteorites have been correlated with known findings from the Meteoritical Bulletin database and an attempt is made to identify their place of origin (fall event). Results indicate that Terespol-1 is most closely related to the Dhofar 1316 chondrite and we suggest that both meteorites at least came from the same parent body.

Owocki, Krzysztof; Pilski, Andrzej

2009-01-01

87

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

Microsoft Academic Search

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

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

1993-01-01

88

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

89

Minor element evidence that Asteroid 433 Eros is a space-weathered ordinary chondrite parent body  

NASA Astrophysics Data System (ADS)

The NEAR mission to 433 Eros provided detailed data on the geology, mineralogy, and chemistry of this S-class asteroid [McCoy, T.J., Robinson, M.S., Nittler, L.R., Burbine, T.H., 2002. Chem. Erde 62, 89-121; Cheng, A.F., 1997. Space Sci. Rev. 82, 3-29] with a key science goal of understanding the relationship between asteroids and meteorites [Cheng, A.F., 1997. Space Sci. Rev. 82, 3-29; Gaffey, M.J., Burbine, T.H., Piatek, J.L., Reed, K.L., Chaky, D.A., Bell, J.F., Brown, R.H., 1993a. Icarus 106, 573-602]. Previously reported major element data revealed a bulk surface similar to that of ordinary chondrites, with the notable exception of sulfur, which was highly depleted [Trombka, J.I., and 23 colleagues, 2000. Science 289, 2101-2105; Nittler, L.R., and 14 colleagues, 2001. Meteorit. Planet. Sci. 36, 1673-1695]. The origin of this sulfur deficiency, and hence the fundamental nature of the asteroid's surface, has remained controversial. We report a new analysis of NEAR X-ray spectrometer data, indicating that Eros has Cr/Fe, Mn/Fe, and Ni/Fe ratios similar to ordinary chondrite meteorites of type LL or L. Chondritic levels of Cr, Mn, and Ni argue strongly against a partial melting explanation for the sulfur depletion. Instead, our results provide definitive evidence that Eros is a primitive body with composition and mineralogy similar to ordinary chondrites, but with a surface heavily modified by interactions with the solar wind and micrometeorites, processes collectively termed space weathering.

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

2006-10-01

90

Volatile element chemistry during metamorphism of ordinary chondritic material and some of its implications for the composition of asteroids  

NASA Astrophysics Data System (ADS)

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. We compiled trace element abundances in H-, L-, and LL-chondrites for the elements Ag, As, Au, Bi, Br, Cd, Cs, Cu, Ga, Ge, I, In, Pb, Rb, Sb, Se, Sn, Te, Tl, and Zn, and identified abundance trends as a function of petrographic type within each class. We calculated volatility sequences for the trace elements in ordinary chondritic material, which differ significantly from the solar nebula volatility sequence. Our results are consistent with open-system thermal metamorphism. Abundance patterns of Ag and Zn remain difficult to explain.

Schaefer, Laura; Fegley, Bruce

2010-02-01

91

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

92

Trace element geochemistry of ordinary chondrite chondrules: the type I/type II chondrule dichotomy  

E-print Network

We report trace element concentrations of silicate phases in chondrules from LL3 ordinary chondrites Bishunpur and Semarkona. Results are similar to previously reported data for carbonaceous chondrites, with rare earth element (REE) concentrations increasing in the sequence olivine ~ 10 K/h) than type I chondrules. Appreciable Na concentrations (3-221 ppm) are measured in olivine from both chondrule types; type II chondrules seem to have behaved as closed systems, which may require chondrule formation in the vicinity of protoplanets or planetesimals. At any rate, higher solid concentrations in type II chondrule forming regions may explain the higher oxygen fugacities they record compared to type I chondrules. Type I and type II chondrules formed in different environments and the correlation between high solid concentrations and/or oxygen fugacities with rapid cooling rates is a key constraint that chondrule formation models must account for.

Jacquet, Emmanuel; Gounelle, Matthieu

2015-01-01

93

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

94

Bulk compositions of Al-rich chondrules in ordinary and carbonaceous chondrites: Variations and similarities  

NASA Technical Reports Server (NTRS)

An extended study of ordinary chondrites revealed that chondrules exist which are transitional in composition between Al-rich and Mg-Fe-rich types in contrast to the finding of Wlotzka, who inferred a gap in compositions between the Ca-Al-rich and Mg-Fe-rich chondrules. Transitional chondrule bulk compositions are plotted. They show that no compositional gap exists between the Mg-Fe-rich and Al-rich chondrules. Chondrules with Na2O-contents 3.0 wt.% are indicated. Variable CaO/Na2O-ratios for chondrule bulk compositions exist, similar to what was described for the subgroups of Al-rich chondrules. Al-rich and transitional chondrules similar to those described above were found also in carbonaceous chrondrites. Thirty-nine chondrules from the carbonaceous chondrites Leoville, Allende, Vigarano and Colony were investigated. Their bulk compositions in terms of Al2O3 vs. CaO were plotted.

Bischoff, A.

1984-01-01

95

The Ardón L6 ordinary chondrite: A long-hidden Spanish meteorite fall  

NASA Astrophysics Data System (ADS)

We report and describe an L6 ordinary chondrite fall that occurred in Ardón, León province, Spain (longitude 5.5605°W, latitude 42.4364°N) on July 9th, 1931. The 5.5 g single stone was kept hidden for 83 yr by Rosa González Pérez, at the time an 11 yr old who had observed the fall and had recovered the meteorite. According to various newspaper reports, the event was widely observed in Northern Spain. Ardón is a very well-preserved, fresh, strongly metamorphosed (petrologic type 6), and weakly shocked (S3) ordinary chondrite with well-equilibrated and recrystallized minerals. The mineral compositions (olivine Fa23.7±0.3, low-Ca pyroxene Fs20.4±0.2Wo1.5±0.2, plagioclase An10.3±0.5Ab84.3±1.2), magnetic susceptibility (log ? = 4.95 ± 0.05 × 10-9 m3 kg-1), bulk density (3.49 ± 0.05 g cm-3), grain density (3.58 ± 0.05 g cm-3), and porosity (2.5 vol%) are typical for L6 chondrites. Short-lived radionuclides confirm that the meteorite constitutes a recent fall. The 21Ne and 38Ar cosmic ray exposure ages are both about 20-30 Ma, similar to values for many other L chondrites. The cosmogenic 22Ne/21Ne ratio indicates that preatmospheric Ardón was a relatively large body. The fact that the meteorite was hidden in private hands for 83 yr makes one wonder if other meteorite falls may have experienced the same fate, thus possibly explaining the anomalously low number of falls reported in continental Spain in the 20th century.

Trigo-RodríGuez, Josep M.; Llorca, Jordi; Weyrauch, Mona; Bischoff, Addi; Moyano-Cambero, Carles E.; Keil, Klaus; Laubenstein, Matthias; Pack, Andreas; Madiedo, José MaríA.; Alonso-AzcáRate, Jacinto; Riebe, My; Wieler, Rainer; Ott, Uli; Tapia, Mar; Mestres, NarcíS.

2014-08-01

96

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

97

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

98

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 vol...

Schaefer, Laura

2008-01-01

99

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

100

Three-dimensional imaging of ordinary chondrite microporosity at 2.6 ?m resolution  

NASA Astrophysics Data System (ADS)

We show that high resolution (2.6 ?m/voxel) synchrotron X-ray microtomography (?CT) scans are able to observe the majority of microporosity in ordinary chondrites. This porosity is present in the form of microcracks and voids among and between mineral grains. We examined, in total, seven small (6-12 mm3) chips of the ordinary chondrites Baszkówka (L5, S1), ALH A77258 (H5, S2), Moorleah (L6, S3), and Kyushu (L6, S5). These four samples were chosen because of their variable impact histories. Using ?CT and various digital isolation and visualization techniques, we found that the structure of microporosity varies with the degree of compaction and shock loading experienced by the materials. The microporosity in the compacted and more strongly shock samples Moorleah and Kyushu is visible as sheet-like fractures within brittle silicates as well as in discontinuous, distributed voids sometimes associated with chondrule rims and grain boundaries. In samples that have experienced less shock and only mild compaction, we found few, if any, microcracks in the silicate grains of the materials. Microporosity in the Baszkówka and ALH A77258 samples is largely represented by intergranular voids, with occasional intragranular voids being present. Regardless of degree of shock loading, ductile Fe-Ni or FeS grains give no evidence of shock-related internal fractures contributing to porosity.

Friedrich, Jon M.; Rivers, Mark L.

2013-09-01

101

Nierite (Si3N4), a new mineral from ordinary and enstatite chondrites  

NASA Astrophysics Data System (ADS)

Nierite (Si3N4) is a new mineral that has been found in perchloric acid-resistant residues of three ordinary chondrites (Adrar 003 [LL3.2], Inman [L3.4] and Tieschitz [FI3.6]) and one enstatite chondrite (Indarch [EH4]). This mineral occurs as very small ˜2 × 0.4 ?m) lath-shaped grains, which have been characterised by transmission electron microscopy. The d-spacings of nierite are, within errors, comparable to those of synthetic ?-Si3N4, which has trigonal symmetry (P31c, a = 0.7758 nm, c = 0.5623 nm, V - 0.2931 nm3, Z = 4). Energy-dispersive x-ray analyses confirm that nierite is a Si- and N-rich mineral. A few nierite crystals in the Indarch, Inman and Tieschitz residues are intergrown with whiskers of another nitride. Only two crystals of this additional nitride were found that were of sufficient size to give electron diffraction patterns uncontaminated by nierite reflections. The d-spacings of this second nitride are comparable to those of ?Si3N4, the hexagonal polymorph of synthetic Si3N4. The majority of nierite crystals in Indarch are interpreted to have formed by exsolution of Si and N from kamacite, perryite and schreibersite during parent-body metamorphism. Some grains have evidence for two discrete episodes of nierite crystallization. The origin of nierite in Adrar 003, Inman and Tieschitz is not known, but formation during exsolution is again possible. The petrographic relationships between nierite and ?-Si3N4 in Indarch, Inman and Tieschitz suggests that the ?-Si3N4 whiskers predated nierite and acted as a seed on which nierite crystals later nucleated. The nierite/?-Si3N4 ratio in ordinary chondrites is controlled by their metamorphic grade and possibly also their oxidation state.

Lee, M. R.; Russell, S. S.; Arden, J. W.; Pillinger, C. T.

1995-07-01

102

An analytical electron microscopy (AEM) investigation of opaque inclusions in some type 6 ordinary chondrites  

NASA Astrophysics Data System (ADS)

A large number of ordinary chondrites contains micron-sized particles of metal and/or troilite dispersed in their silicate grains. Such metallic phases are responsible for the so-called darkening of the silicate grains and might be either precipitates, which formed during reduction of the silicates, or inclusions injected as a melt during a shock event. We have investigated these tiny foreign phases by analytical transmission electron microscopy in three unweathered, metamorphosed ordinary chondrites (Saint Séverin, LL6, Tsarev, L6 and Kernouvé, H6). We also looked for remnant shock indices. Our TEM observations suggest the following sequence of events in the three meteorites. First, a number of relatively strong shock events occurred on the parent body/bodies producing an Fe-FeS melt that was injected into silicate grains along a dense network of open fractures. Most of these shock defects were subsequently erased by high-temperature (700-900 °C) thermal metamorphism. Some remnants of the shock events are the observed trails of tiny metal and/or sulfide inclusions that formed as a result of fracture healing. Chemical homogenization of the silicates and limited oxidation of the metallic blebs also occurred during this high-temperature annealing event, resulting in Ni-rich inclusions. This effect was especially pronounced in the L and LL-chondrites studied. During subsequent cooling of the body/bodies, inclusions of chromite and phosphate precipitated, nucleating preferentially on lattice defects (dislocations, subgrain boundaries) and on the metal and sulfide inclusions. A later shock event of moderate intensity, probably corresponding to the separation of the meteorite from its parent body, produced new shock features in the silicate grains of the Saint Séverin meteorite, including mechanical twins in diopside and straight free screw dislocations in olivine.

Leroux, Hugues; Doukhan, Jean-Claude; Guyot, François

1996-11-01

103

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

NASA Technical Reports Server (NTRS)

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, Aleksandr N.; Rubin, Alan E.; Kononkova, Natal'ya N.

1993-01-01

104

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

105

The Lu–Hf and Sm–Nd isotopic composition of CHUR: Constraints from unequilibrated chondrites and implications for the bulk composition of terrestrial planets  

Microsoft Academic Search

The Lutetium–Hafnium radiogenic isotopic system is widely used as a chronometer and tracer of planetary evolution. In order for this isotopic system to fulfill its potential in planetary studies, the Lu–Hf system parameters need to be more tightly constrained, in particular the Lu–Hf isotopic composition of the chondritic uniform reservoir (CHUR) and, by extension, the bulk silicate Earth (BSE). We

Audrey Bouvier; Jeffrey D. Vervoort; P. Jonathan Patchett

2008-01-01

106

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

E-print Network

The S-type asteroid ­ ordinary chondrite controversy and discoveries by the Hayabusa mission to asteroid 25143 Itokawa. T. Hiroi1 , M. Abe2 , K. Kitazato2,3 , S. Abe4 , B. E. Clark5 , S. Sasaki6 , and M-standing controversy concerning the parent bodies of ordinary chondrites and the identity of the S-type asteroids

Hiroi, Takahiro

107

DERIVING THE DISTRIBUTION OF ORDINARY CHONDRITE (H, L, LL)-LIKE MATERIALS IN ASTEROIDS FROM THEIR VISIBLE AND NEAR-INFRARED REFLECTANCE SPECTROSCOPY. T.  

E-print Network

DERIVING THE DISTRIBUTION OF ORDINARY CHONDRITE (H, L, LL)-LIKE MATERIALS IN ASTEROIDS FROM reflects their abundance in the main asteroid belt. The abundant S-type asteroids and less abundant Q-type asteroids could contain significant amount of ordinary chondrite materials of different degrees of thermal

Hiroi, Takahiro

108

How much of the S-type asteroids are made of ordinary chondrite materials, and why are they so highly space-weathered? T. Hiroi1  

E-print Network

How much of the S-type asteroids are made of ordinary chondrite materials, and why are they so whether the high abundance of ordinary chondrites really reflects their abundance in the main asteroid belt. The abundant S-type asteroids and less abundant Q-type asteroids could contain significant amount

Hiroi, Takahiro

109

Chemical and physical studies of chondrites. X - Cathodoluminescence and phase composition studies of metamorphism and nebular processes in chondrules of type 3 ordinary chondrites  

NASA Technical Reports Server (NTRS)

The cathodoluminescence (CL) characteristics of eight type-3 ordinary chondrites and one L5 chondrite were investigated with particular emphasis on detailed compositions of the relevant phases in four of these chondrites: Semarkona (type-3.0); Krymka (3.1); Allan Hills A77214 (3.5); and Dhajala (3.8). By sorting the chondrules into eight groups according to the CL of mesostasis and to certain compositional criteria and by determining the number of chondrules in these groups as a function of petrological type, it was possible to deduce genetic/evolutionary sequences of the chondrules. It is shown that there are major compositional differences in chondrules, which account for their CL properties and the chondrule groups.

Dehart, John M.; Lofgren, Gary E.; Jie, LU; Benoit, Paul H.; Sears, Derek W. G.

1992-01-01

110

Trace element geochemistry of ordinary chondrite chondrules: The type I/type II chondrule dichotomy  

NASA Astrophysics Data System (ADS)

We report trace element concentrations of silicate phases in chondrules from LL3 ordinary chondrites Bishunpur and Semarkona. Results are similar to previously reported data for carbonaceous chondrites, with rare earth element (REE) concentrations increasing in the sequence olivine < pyroxene < mesostasis, and heavy REE (HREE) being enriched by 1-2 orders of magnitude (CI-normalized) relative to light REE (LREE) in ferromagnesian silicates, although no single olivine with very large LREE/HREE fractionation has been found. On average, olivine in type II chondrules is poorer in refractory lithophile incompatible elements (such as REE) than its type I counterpart by a factor of ?2. This suggests that olivine in type I and II chondrules formed by batch and fractional crystallization, respectively, implying that type II chondrules formed under faster cooling rates (>?10 K/h) than type I chondrules. Appreciable Na concentrations (3-221 ppm) are measured in olivine from both chondrule types; type II chondrules seem to have behaved as closed systems, which may require chondrule formation in the vicinity of protoplanets or planetesimals. At any rate, higher solid concentrations in type II chondrule forming regions may explain the higher oxygen fugacities they record compared to type I chondrules. Type I and type II chondrules formed in different environments and the correlation between high solid concentrations and/or oxygen fugacities with rapid cooling rates is a key constraint that chondrule formation models must account for.

Jacquet, Emmanuel; Alard, Olivier; Gounelle, Matthieu

2015-04-01

111

The Danebury Iron Age meteorite—An H5 ordinary chondrite "find" from Hampshire, England  

NASA Astrophysics Data System (ADS)

What remains of a 30 g sample, first recognized as a meteorite in 1989 during characterization of metalworking debris from Danebury, an Iron Age hillfort, in Hampshire, England, has been classified as an H5 ordinary chondrite. Its arrival on Earth has been dated as 2350 ± 120 yr BP, making it contemporary with the period of maximum human activity at the recovery site. Despite its considerable terrestrial residence age, the interior of the specimen is remarkably fresh with a weathering index of W1/2. There is, however, no evidence of human intervention in its preservation. Its near-pristine state is explained in terms of its serendipitous burial during the back-fill of a pit dug into chalk by prehistoric people for the storage of grain. This chance discovery has interesting ramifications for the survival of meteorites in areas having a high pH because of a natural lime content arising as a result of the local geology.

Pillinger, C. T.; Pillinger, J. M.; Johnson, D.; Greenwood, R. C.; Tindle, A. G.; Jull, A. J. T.; Allen, D. H.; Cunliffe, B.

2014-06-01

112

doi:10.1016/j.gca.2004.11.024 An ordinary chondrite impactor for the Popigai crater, Siberia  

E-print Network

doi:10.1016/j.gca.2004.11.024 An ordinary chondrite impactor for the Popigai crater, Siberia ROALD in Northern Siberia is the largest crater known in the Cenozoic. The concentrations in platinum group elements of the crater to identify the composition of the projectile. The method selected was preconcentration by Ni

Claeys, Philippe

113

Chemical and physical studies of chondrites: 10. Cathodoluminescence and phase composition studies of metamorphism and nebular processes in chondrules of type 3 ordinary chondrites  

SciTech Connect

The cathodoluminescence (CL) properties of eight type 3 ordinary chondrites and one L5 chondrite have been determined, and phenocryst and mesostasis compositions have been analyzed in the chondrules of four of them (Semarkona, type 3.0; Krymka, 3.1; Allan Hills A77214, 3.5; and Dhajala, 3.8) in order to investigate their origins and metamorphic history. In the present study, the authors discuss the CL properties of nine ordinary chondrites of a variety of petrologic types with particular emphasis on detailed studies of the compositions of the relevant phases in four of these: Semarkona (3.0), Krymka (3.1), Allan Hills A77214 (3.5), and Dhajala (3.8). They describe a means of classifying chondrules that is based on the composition of their two major components, the mesostasis and phenocrysts. The system is applicable to > 90-95% off the chondrules in a given meteorite and it describes the range of material produced by nebular material and of the effect of metamorphism on the chondrules. They also discuss the relevance of the results for the origin of the nine chondrite classes.

DeHart, J.M.; Lu Jie; Benoit, P.H.; Sears, D.W.G. (Univ. of Arkansas, Fayetteville (United States)); Lofgren, G.E. (NASA Johnson Space Center, Houston, TX (United States))

1992-10-01

114

Chromite-rich mafic silicate chondrules in ordinary chondrites: Formation by impact melting  

NASA Technical Reports Server (NTRS)

Chromium-rich chondrules constitute less than 0.1 percent of all ordinary chondrite (OC) chondrules and comprise three groups: chromian-spinel chondrules, chromian-spinel inclusions, and chromite-rich mafic silicate (CRMS) chondrules. Chromian-spinel chondrules (typically 100-300 microns in apparent diameter) exhibit granular, porphyritic and unusual textures and occur mainly in H chondrites. Their morphologies are distinct from the irregularly shaped chromian-spinel inclusions of similar mineralogy. Chromian-spinel chondrules and inclusions consist of grains of chromian-spinel embedded in plagioclase (Pl) or mesostasis of Pl composition. Many also contain accessory ilmenite (Ilm), high-Ca pyroxene (Px), merrillite (Mer), and rare olivine (Ol); some exhibit concentric mineral and chemical zoning. CRMS chondrules (300-1100 microns in apparent diameter) are generally larger than chromian-spinel chondrules and occur in all metamorphosed OC groups. Most CRMS chondrules are nearly spherical although a few are ellipsoidal with a/b aspect ratios ranging up to 1.7. Textures include cryptocrystalline, granular, radial, barred, and porphyritic varieties; some contain apparently relict grains. The chondrules consist of chromite (Chr), Ol and Pl, along with accessory Mer, troilite (Tr), metallic Fe-Ni (Met), Px and Ilm. The mesostasis in CRMS chondrules is nearly opaque in transmitted light; thus, they can be easily recognized in the optical microscope. Based on the similarity of mineralogy and chemistry between CRMS chondrules of different textures (opaque chromite-rich mesostasis, skeletal morphology of Ol grains, similar bulk compositions) we suggest that these chondrules form a genetically related population.

Krot, Alexander N.; Rubin, Alan E.

1993-01-01

115

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

116

The Origin of Silica-Rich Chondrules and Clasts in Ordinary and Carbonaceous Chondrites  

NASA Astrophysics Data System (ADS)

Chondrules and clasts containing a silica mineral or a silica glass are a minor but important constituent in many ordinary (Planner, 1983; Brigham et al., 1986) and some carbonaceous (Olsen, 1983) chondrites, and have been considered somewhat enigmatic. The recent discovery of a large, silica-rich igneous clast in the Bovedy (L3) chondrite (Ruzicka and Boynton, 1992) sheds light on the possible origin of other silica-rich objects. As discussed in Ruzicka and Boynton (1992), the Bovedy clast probably crystallized from an Lchondrite silicate magma in a relatively large magma body that had previously undergone olivine fractionation. The existence of similar fractionating magmas can also account for the origin of other silica-rich objects, as shown below. Pyroxene-silica objects. Chondrules (drop-formed objects) and clasts (irregularly shaped objects) consisting essentially of a mixture of orthopyroxene (opx) and a silica mineral (SiO2) have been found in various ordinary chondrites (Brigham et al., 1986). Brigham and coworkers (1986) proposed that these objects could be condensates. However, fractional crystallization of a liquid similar in composition to the Bovedy clast (Ruzicka and Boynton, 1992) will produce (Morse, 1980) the following solids: (a) orthopyroxenite, (b) an opx + SiO2 rock, and (c) a feldspar, SiO2 and pyroxene rock. Brecciation or remelting of rock (b), which lies on the opx-SiO2 join in the cristobalite primary crystallization field, could have produced the pyroxene-silica objects of Brigham et al. (1986) and Planner (1983). Fayalite-silica clasts. These clasts consist of SiO2, olivine (ol, Fa(sub)63-96), and highly variable amounts of opx and clinopyroxene (Brigham et al., 1986). Brigham et al. (1986) discussed various origins for these objects and concluded that none were entirely satisfactory, but that an accidental mixture of the various phases in them was probably the best hypothesis. However, a rock mainly containing SiO2 and fayalitic ol (Fa(sub)>59) can form as a late-stage differentiate of a melt of any ol + opx or opx + SiO2 mixture (Bowen and Schairer, 1935). The presence of some opx in these objects suggests disequilibrium and incomplete removal of opx from the fractionating liquids. The absence of appreciable feldspar in the fayalite-silica objects may indicate that the parent melt formed from an opx or opx + SiO2 cumulate. Murchison chondrules. Olsen (1983) described two chondrules in Murchison that contain opx (En(sub)99-97Wo(sub)O.5-0.7) set in a groundmass of feldspar or feldspathic glasses, Mgclinopyroxene, and pods of silica glass. Cr-bearing metal also occurs in the chondrules. Olsen (1983) proposed that the two chondrules experienced a nearly equilibrium cooling history from a melt composition projecting in the opx primary crystallization field. These melt compositions are best explained as the result of ol and opx fractionation from a magma of CM-like composition. CM-chondrites have a high bulk CaAl2Si2O7:SiO2 ratio compared to L-chondrites, and this can account for the more feldspathic compositions of the Murchison chondrules compared to that of the Bovedy clast (Ruzicka and Boynton, 1992). Remelting of the differentiate produced by ol and opx fractionation could have formed the two objects. Their Mg-rich pyroxene compositions imply either that the initial magmatic or that the chondrule-forming event was accompanied by reduction. References Bowen N.L. and Schairer J.F. (1935) The system MgO-FeO-SiO2. Am. J. Sci., 5th ser., 29, 151-217. Brigham C.A., H. Yabuki, Z. Ouyang, M.T. Murrell, A. El Goresy and D.S. Burnett (1986) Silica-bearing chondrules and clasts in ordinary chondrites. Geochim. Cosmochim. Acta. 50, 1655-1666. Morse S.A. (1980) Basalts and Phase Diagrams. An Introduction to the Quantitative Use of Phase Diagrams in Igneous Petrology. Springer-Verlag. 493 pp. Olsen E.J. (1983) SiO2-bearing chondrules in the Murchison meteorite. In Chondrules and Their Origins (ed. E.A. King), pp. 223-234. Lunar and Planetary Institute, Houston. Planner H.N. (1983) Phase separation in

Ruzicka, A.; Boynton, W. V.

1992-07-01

117

Space Weathering of Ordinary Chondrite Parent Bodies, Its Impact on the Method of Distinguishing H, L, and LL Types and Implications for Itokawa Samples Returned by the Hayabusa Mission  

NASA Technical Reports Server (NTRS)

As the most abundance meteorites in our collections, ordinary chondrites potentially have very important implications on the origin and formation of our Solar System. In order to map the distribution of ordinary chondrite-like asteroids through remote sensing, the space weathering effects of ordinary chondrite parent bodies must be addressed through experiments and modeling. Of particular importance is the impact on distinguishing different types (H/L/LL) of ordinary chondrites. In addition, samples of asteroid Itokawa returned by the Hayabusa spacecraft may re veal the mechanism of space weathering on an LLchondrite parent body. Results of space weathering simulations on ordinary chondrites and implications for Itokawa samples are presented here.

Hiroi, T.; Sasaki, S.; Noble, S. K.; Pieters, C. M.

2011-01-01

118

Thursday, March 16, 2006 POSTER SESSION II: ORDINARY AND ENSTATITE CHONDRITES  

E-print Network

­6 Fragmental Breccia with Huge L Chondritic Clasts [#1625] Glanerbrug is a very complex fragmental breccia and has been previously classified as an LL breccia or L/LL5 chondrite. We classify Glanerbrug as an LL4­6 fragmental breccia with huge L-chondritic clasts. Dunaway J. K. Moersch J. Taylor L. A. Petrogenesis

Rathbun, Julie A.

119

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

120

A shock-metamorphic model for silicate darkening and compositionally variable plagioclase in CK and ordinary chondrites  

SciTech Connect

Silicate darkening in ordinary chondrites (OC) is caused by tiny grains of metallic Fe-Ni and troilite occurring mainly within curvilinear trails that traverse silicate interiors and decorate or, in some cases, cut across silicate grain boundaries. Highly shocked OC tend to have greater degrees of silicate darkening than lightly shocked OC; this indicates that silicate darkening is probably a result of shock metamorphism. The low Fe-FeS eutectic temperature (988C) renders metal and troilite susceptible to melting and mobilization during shock heating. Unshocked OC tend to have plagioclase with uniform compositions; shocked OC tend to have plagioclase with more variable (albeit still stoichiometric) compositions. The low impedance of plagioclase to shock compression makes it particularly susceptible to melting and mobilization; this is consistent with the molten appearance of plagioclase in highly shocked OC (e.g., Rose City and Paragould). CK chondrites also have compositionally variable plagioclase. The common association of silicate darkening with compositionally variable plagioclase is consistent with the hypothesis that both are products of shock metamorphism. Some CK and OC chondrites exhibit light shock effects in olivine that are consistent with equilibrium peak shock pressures that are too low to account for the silicate darkening or opaque shock veins in these meteorites. Therefore, the olivine in these chondrites may have been annealed after intense shock produced these effects. A few CK chondrites that contain olivine with undulose or mosaic extinction (e.g., LEW87009 and EET83311) may have been shocked again, after annealing.

Rubin, A.E. (Univ. of California, Los Angeles (United States))

1992-04-01

121

Presolar SiC in chondrites - How variable and how many sources?  

NASA Astrophysics Data System (ADS)

The carbon and silicon isotropic compositions of 246 isotopically anomalous SiC grains measured in low concentration residues are reported. The residues were prepared from nine chondrites, namely, 6 unequilibrated ordinary chondrites (UOCs), Qingzhen (EH3), Leoville (CV3), and Murchison (CM2). Murchison is used as a standard to which all the other meteorites studied are compared. The range of isotopic compositions exhibited by UOC SiC is found to be similar to Murchison, except in Inman. Inman SiC has a distinctly different distribution of its silicon isotopic composition compared to the other meteorites. Residues from Qingzhen and Leoville produce only one anomalous SiC grain each.

Alexander, C. M. O'd.

1993-06-01

122

Chondrules in the Murray CM2 meteorite and compositional differences between CM-CO and ordinary chondrite chondrules  

NASA Astrophysics Data System (ADS)

Thirteen of the least aqueously altered chondrules in Murray (CM2) were analyzed for bulk compositions, by means of a broad beam electron microprobe, to explore the compositional differences between the CM-CO, and the ordinary chondrite OC chondrules. The CO chondrules are richer in refractory lithophiles and poorer in Cr, Mn, and volatile lithophiles than the OC chondrules; much lower refractory lithophile abundances in CM chondrules resulted from aqueous alteration. Evidence is found for two important lithophile precursor components of CM-CO chondrite chondrules: (1) pyroxene- and refractory-rich, FeO-poor, and (2) olivine-rich, refractoryand FeO-poor. It is suggested that the pyroxene- and refractory-rich, FeO-poor lithophile precursor component has formed by an incomplete evaporation of presolar silicates that brought these materials into the enstatite stability field.

Rubin, A. E.; Wasson, J. T.

1986-02-01

123

Thursday, March 26, 2009 POSTER SESSION II: CHONDRITES, THEIR CLASTS, AND ALTERATION  

E-print Network

. The Highly Unequilibrated EH Chondrite, Sahara 97072, May Be a Primitive Breccia [#2154] We have investigated a breccia lump in the unequilibrated enstatite chondrite Sahara 97072, which we interpret to be a primitive breccia. Macke R. J. Britt D. T. Consolmagno G. J. Enstatite Chondrite Physical Properties: Density

Rathbun, Julie A.

124

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

125

Optical Effects of Regolith Processes on S-Asteroids as Simulated by Laser Shots on Ordinary Chondrite and Other Mafic Materials  

Microsoft Academic Search

Laboratory results from a simulation of possible optical effects of impact melting and repeated crystallization on asteroidal surfaces are presented. Quick melting and crystallization of surface materials were simulated by impulse laser treatment of powdered materials in vacuum. The mafic materials used in this study were: ordinary chondrite (OC) ElenovkaL5, carbonaceous chondrite Allende CV3, terrestrial olivine, clinopyroxene, and olivine–clinopyroxene mixture

L. V. Moroz; A. V. Fisenko; L. F. Semjonova; C. M. Pieters; N. N. Korotaeva

1996-01-01

126

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

127

The thermoluminescence sensitivity-metamorphism relationship in ordinary chondrites - Experimental data on the mechanism and implications for terrestrial systems  

NASA Technical Reports Server (NTRS)

Hydrothermal annealing experiments have been performed on samples of the Sharps meteorite in order to investigate the mechanism responsible for the metamorphism-related, 10-to-the-5th-fold range in the thermoluminescence (TL) sensitivity in ordinary chondrites. Duplicate 50 mg samples of meteorite were annealed under the following conditions: (1) 168 h at 785 C and 1 kbar; (2) the same time, temperature and pressure, but with 2 wt pct water; (3) 174 h at 855 C and 0.77 kbar with 2 wt pct water and 2 molal sodium disilicate (NadiSi); (4) the same time, temperature and pressure as the preceding samples, but with 10 wt pct H2O and 2 molal NadiSi. Samples annealed under the first three sets of conditions showed little or no change in their TL sensitivities, however the samples annealed with 10 wt pct water and 2 molal NadiSi showed a three-fold to 10-fold increase in TL sensitivity, and the temperature of the TL peak was suggestive of feldspar in the high-temperature form. It is suggested that these data are consistent with the TL sensitivity-metamorphism relationship in ordinary chondrites being due to the formation of the TL phosphor, feldspar, by the crystallization of chondrule glass.

Guimon, R. K.; Sears, D. W. G.; Lofgren, G. E.

1986-01-01

128

Complex zoning behavior in pyroxene in FeO-rich chondrules in the Semarkona ordinary chondrite  

NASA Technical Reports Server (NTRS)

A detailed understanding of the properties of silicate minerals in chondrules is essential to the interpretation of chondrule formation conditions. This study is further work in a series of petrologic studies of chondrules in the least equilibrated LL chondrite, Semarkona (LL3.0). The objectives of this work are as follows: (1) to understand chondrule formation conditions and nebular processes; and (2) to use the data as a basis for understanding the effects of metamorphism in more equilibrated chondrites. FeO-rich pyroxene in the chondrules described shows complex zoning behavior. Low-Ca clinopyroxene, orthopyroxene, pigeonite, and augite are all observed, in various associations with one another. Coexisting olivine phenocrysts are also FeO-rich and strongly zoned. Compositional and zoning properties are similar to those observed in boninites and are interpreted as resulting from rapid cooling of individual chondrules.

Jones, Rhian H.; Papike, J. J.

1993-01-01

129

Metallic minerals, thermal histories and parent bodies of some xenolithic, ordinary chondrite meteorites  

NASA Technical Reports Server (NTRS)

The metal grains were investigated in the hosts and lithic fragments of various petrologic types in four xenolithic chondrites using reflected-light microscopy and electron-probe analysis. The kamacite, taenite, tetrataenite, and troilite in Weston and Fayetteville have many textures; on a Wood plot of the central Ni content vs dimensions, the taenite content shows scatter if metal grains had cooled at rates of 10-1000 and 1-100 K/Myr through 700 K. In contrast, metallic minerals in Bhola and Mezo-Madaras have uniform textures and plot coherently, indicating cooling rates of 0.1 and 1 K/Myr, respectively, in the 700-600 K range. It is concluded that the host and xenoliths in these chondrites were cooled slowly after compaction; their clasts underwent peak metamorphic temperatures and slow cooling through 700 K in different environments.

Scott, E. R. D.; Rajan, R. S.

1981-01-01

130

Sodic plagioclase thermometry of type 6 ordinary chondrites: Implications for the thermal histories of parent bodies  

NASA Astrophysics Data System (ADS)

The structural states of sodic plagioclase crystals of about 50 microns in size from three H6, two L6 and one LL6 chondritic meteorites have been determined by measuring the delta 131 parameter with a Gandolfi camera after analyzing chemical compositions. The temperature for each sodic plagioclase crystal has been determined by plotting the delta 131 parameter, corrected for the influence of K, on the relation diagram between the delta 131 parameter and temperature of synthesis of sodic plagioclase by Smith (1972). The temperature obtained is assigned to the crystallization temperature of sodic plagioclase and the maximum plagioclase temperature for each meteorite can be assumed to correspond to the maximum temperature attained by each meteorite during metamorphism. The maximum metamorphic temperatures estimated are 725-742 degC for H6, 808-820 degC for L6 and 800 degC for LL6 chondrites. These temperatures are lower than those based on Ca contents of clinopyroxenes (Dodd, 1981; McSween et al., 1988), but are consistent with those based on Ca contents of orthopyroxenes (McSween and Patchen, 1989; Langenhorst et al., 1995; Jones, 1997). The K content of sodic plagioclase correlates with the temperature obtained from the structural state. This positive correlation suggests that sodic plagioclase has formed in the course of equilibration processes of alkali elements in prograde metamorphism, i.e. during heating processes. The results of this study, i.e. the maximum metamorphic temperature of the H6 chondrite is lower than that of the L6 chondrite by about 80 degC and the meteorites of the same chemical group show very similar maximum metamorphic temperatures, are in accordance with the predictions of calculations based on the 26Al heat source and the onion-shell structure model of the parent bodies.

Nakamuta, Y.; Motomura, Y.

1999-09-01

131

Radial Heterogeneity of 53-Mn in the Early Solar System and the Place of Origin of Ordinary Chondrites  

NASA Astrophysics Data System (ADS)

The earlier results of our studies of 53Mn-53Cr isotope systematics (T(sub)1/2 of 53Mn = 3.7 My) in angrites (LEW 86010, Angra dos Reis) and in some eucrites (Chervony Kut [CK], Juvinas [JI3V1) have suggested that the resolution of small age differences between these differentiated objects is possible if the assumption is true that 53Mn was homogeneously distributed at least in that region of the solar nebula where the meteorite parent bodies formed. The fact that the present day and the initial 53Cr/52Cr ratios in both meteorite classes are significantly higher than the terrestrial and lunar values led us to test the 53Mn-53Cr systematics in several ordinary chondrites, the putative building blocks of planetesimals. We found that these chondrites possess uniform and higher than terrestrial bulk 53Cr/52Cr ratios (0.5 epsilon; 1 epsilon = l x 10^-4) but more than a factor of two lower than the bulk eucrites. Thus, it became clear that the original assumption of 53Mn homogeneity on a large scale may not be valid and that the low abundance on earth of the 53Mn decay product may be the consequence of a solar system wide phenomenon rather than, say, simply depletion at 1 AU due to volatility. The idea of a radially heterogeneous 53Mn distribution in the nebula was suggested and tests of this hypothesis were undertaken.

Lugmair, G. W.; Shukolyukov, A.; MacIsaac, Ch.

1996-03-01

132

Optical effects of regolith processes on S asteroids as simulated by laser impulse alteration of ordinary chondrite  

NASA Technical Reports Server (NTRS)

The spectral properties of some powdered chondrites and minerals altered by Isser impulse are studied in order to estimate possible optical effects of regolith processes (micrometeoritic bombardment). Gradual reduction of overall reflectance and spectral contrast, the increase of continuum slope, the increase of spectrally derived olivine/pyroxene ratio and Fs content of orthopyroxene with increasing alteration degree show that regolith processes could affect optical properties of surface material more heavily than has been previously appreciated. Ordinary chondrites (OC's) are known to account for 80 percent of observed meteorite falls, but so far no main belt parent bodies have been identified for these meteorites. S-asteroids resemble OC's spectrally, but are characterized by a steeper red continuum unlike that of OC's and their spectrally derived mineralogies are far outside OC range. Attempts were made to explain the spectral mismatch between OC's and S asteroids by some process, which alters optical properties of uppermost regolith. However, the spectral studies of shocked (black) OC's, gas-rich OC's, melted OC's and synthetic metal-rich regoliths derived from OC's demonstrate that such altered OC materials darken, but do not redden.

Moroz, L. V.; Fisenko, A. V.; Semjonova, L. F.; Pieters, C. M.

1993-01-01

133

Partitioning of Nd, Tb, Lu, and Hf Between Garnet and Ordinary Chondrite Melt at 5 to 9 GPa: Applications to Martian Differentiation  

NASA Technical Reports Server (NTRS)

One explanation for Al and REE depletions in SNC meteorites is early majorite fractionation in a deep martian magma ocean. We report initial results from an experimental investigation of partitioning between majoritic garnet and ordinary chondrite liquid. Additional information is contained in the original extended abstract.

Draper, D. S.; Chabot, N. L.; Xirouchakis, D.; Wasserman, A. A.; Agee, C. B.

2001-01-01

134

Towards a Novel Classification of Chondrules: Examples From the L4 Ordinary Chondrite Saratov  

NASA Astrophysics Data System (ADS)

In order to classify and thoroughly investigate the origin of chondrites, the most primitive class of meteorites, exhaustive and systematic textural and mineralogical observations of chondrules are required. Long-standing mineralogical-textural classifications for chondrules obscure relevant data. Accepted classification schemes place chondrules in relatively few categories (e.g. radiating, cryptocrystalline, granular, porphyritic, barred) but ignore abundant micron-scale features within chondrules (relict crystals, overgrowths, zonations, quench textures) that provide invaluable evidence of chondrule history. Chondrule mineralogy and textures in polished thin sections and slabs of Saratov (L4) have been recorded using a scanning electron microscope (SEM). The most detailed work so far, on a single section, has mapped the size, sorting, packing, mineralogy and textures of 370 chondrules greater than 100 microns in diameter. Using back-scatter electron (BSE) images, a photomosaic of the entire thin section was created, and overlain with a grid system to locate and map specific chondrules. Textures and mineral phases were documented with BSE images, energy-dispersive spectrometry (EDS) and cathodoluminescence (CL). Chondrule textures are akin to those of igneous and metamorphic Earth rocks, and the processes forming them can be likewise interpreted. Many different heating, cooling and annealing histories, for chondrules now found associated in the same chondrite, are implied. Groups of chondrules with similar provenance, different from other groups, may be recognized by their analogous textural histories. Each chondrule has had at least a two-stage origin. Many show the effects of multi-stage processing. We anticipate that our conclusions will contribute to a new comprehensive classification scheme for chondrules and chondrites, and encourage others to examine the petrology of these complex and fascinating rocks.

Herd, R. K.; Dixon, L.; Samson, C.; Hunt, P. A.

2009-05-01

135

Metamorphic Temperature Estimation for Equilibrated Ordinary Chondrites by a Plagioclase Thermometer  

NASA Astrophysics Data System (ADS)

Individual plagioclase grains of about 50 micrometers in size from H6, L6 and LL6 chondrites were X-rayed by a Gandolfi camera after the analysis of chemical compositions by an electron probe microanalyzer. The X-ray powder pattern recorded on a film was scanned by a microdensitometer and taken into a personal computer for precise examinations. The distance between 1-31 and 131 reflections in the x-ray powder pattern which is very sensitive to the structural state and correlates to the equilibration temperature of plagioclase was determined precisely by applying a profile-fitting technique. The distance between 1-31 and 131 reflections was corrected for the influence of Or content by using the correction diagram. The maximum temperatures for H6, L6 and LL6 chondrites obtained by using the relation diagram between [2 theta(131)-2 theta(1-31)] and equilibration temperature are 755, 840, and 830 degrees C, respectively.

Nakamuta, Y.; Motomura, Y.

1996-03-01

136

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

137

Occurrence of noble metals in aluminum- and chromium-rich objects in ordinary chondrites and of baddeleyite ZrO2 in a chromite inclusion  

NASA Astrophysics Data System (ADS)

Platinum group elements (PGE) enrichments are found in Fe-Ni blebs (less than 1 micron) in Al- and Cr-rich objects in the ordinary chondrites Ste. Marguerite, Forest Vale, Montferre. In Ste. Marguerite, high ZrO2 concentrations (Baddeleyite) are also present in a chromite inclusion. Iridium enrichment in this material compared to its metal content is confirmed by Instrumental Neutron Activation Analysis (INAA). The widespread occurrence of PGE in Al- and Cr-rich objects, mostly present in H-group chondrites of nearly equilibrated types, must be taken into account to understand their conditions of formation.

Michel-Levy, M. Christophe; Robin, E.; Blanc, Ph.

1995-01-01

138

Investigation of the H7 ordinary chondrite, Watson 012: Implications for recognition and classification of Type 7 meteorites  

NASA Astrophysics Data System (ADS)

Despite the fact that the number of officially classified meteorites is now over 45,000, we lack a clearly defined sequence of samples from a single parent body that records the entire range in metamorphic temperatures from pristine primitive meteorites up to the temperatures required for extensive silicate partial melting. Here, we conduct a detailed analysis of Watson 012, an H7 ordinary chondrite, to generate some clarity on the textural and chemical changes associated with equilibrium-based silicate partial melting in chondritic meteorites. To do this we compare the textures in the meteorite with those preserved in metamorphic contact aureoles on Earth. The most distinctive texture generated by the partial melting that affected Watson 012 is an extensively interconnected plagioclase network, which is clearly observable with a petrographic microscope. Enlarged metal-troilite grains are encapsulated at widenings in this plagioclase network, and this is clearly visible in reflected light. Together with these features, we define a series of other characteristics that can be used to more clearly classify chondritic meteorites as being of petrologic Type 7. To provide comprehensive evidence of silicate partial melting and strengthen the case for using simple petrographic observations to classify similar meteorites, we use high-resolution X-ray computed tomography to demonstrate that the plagioclase network has a high degree of interconnectedness and crystallised as large (cm-scale) skeletal crystals within an olivine-orthopyroxene-clinopyroxene framework, essentially pseudomorphing a melt network. Back-scattered electron imaging and element mapping are used to show that some of the clino- and orthopyroxene in Watson 012 also crystallised from silicate melt, and the order of crystallisation was orthopyroxene ? clinopyroxene ? plagioclase. X-ray diffraction data, supported by bulk geochemistry, are used to show that plagioclase and ortho- and clinopyroxene were added to the Watson 012 sample by through-flowing basaltic melt. Along with the absence of glass and granophyre, this interconnected network of coarse-grained skeletal plagioclase indicates that the sample cooled slowly at depth within the parent body. The evidence of melt flux indicates that Watson 012 formed in the presence of a gravitational gradient, and thus at significant distance from the centre of the H chondrite parent body (the gravitational gradient at the centre would be zero). Our interpretation is that incipient silicate partial melting in Watson 012 occurred when a region of radiogenically heated H6 material located at considerable depth (possibly at ?15-20 km from surface) was heated by an additional ca. 200-300 °C in association with a large shock event. Due to insulation at depth within an already hot parent body, the post-shock temperature equilibrated and remained above the solidus long enough for widespread equilibrium-based silicate partial melting, and for melt to migrate. Although the observed melting may have been facilitated by additional heating from an impact event, this is not an example of instantaneous shock melting, which produces thermal disequilibrium at short length scales and distinctly different textures. A small number of H, L and LL chondrites have been previously classified as being of petrologic Type 7; with our new criteria to support that classification, these represent our best opportunity to explore the transition from high temperature sub-solidus metamorphism through the onset of silicate partial melting in three different parent bodies.

Tait, Alastair W.; Tomkins, Andrew G.; Godel, Bélinda M.; Wilson, Siobhan A.; Hasalova, Pavlina

2014-06-01

139

Agglomeratic olivine (AO) objects and Type II chondrules in ordinary chondrites: Accretion and melting of dust to form ferroan chondrules  

NASA Astrophysics Data System (ADS)

Agglomeratic olivine objects (AO objects) and possibly related chondrules in three ordinary chondrites (NWA 4910 [LL3.1], NWA 3127 [LL3.1], Sahara 98175 [LL3.5]) were studied using petrographic and microanalytical techniques to evaluate the origins of these materials. AO objects are mixtures of fine-grained (?5-10 ?m-diameter) ferroan (Fa 12-35) olivine, troilite that is often concentrated towards the periphery of objects, pyroxene, feldspathic material, relict magnesian olivine and pyroxene grains, and relict chondrules. One micro-CAI with a grossite core was also found. AO objects commonly rim chondrules. AO objects show transitional variations in texture and chemistry with Type II chondrules, ranging from AO objects that are finer grained and show no evidence of melting (AO-U objects), to weakly melted and more melted AO objects (AO-WM and AO-M objects, respectively), to fine-grained Type II chondrules (olivine grain size ˜5-60 ?m), to coarse-grained Type II chondrules (olivine grain size ˜10-250 ?m across); S contents and Na/Al values are typically higher in AO objects than in Type II chondrules. The properties of AO objects and Type II chondrules are interpreted to reflect progressive heating of dust of quasi-chondritic composition, accompanied by grain coarsening during melting, partial loss of the most volatile elements (chiefly S, also Na) during evaporative melting, and back-reaction with gas, to form troilite-rimmed AO objects. Data-model comparisons suggest that progressive heating of chondritic dust to form AO objects and Type II chondrules could have occurred in a dusty environment to yield a transient, oxidizing gas of high pressure (˜10 -3 bar), with gas derived from vaporized dust being much (>500-1000× or even up to 10 4-10 5×) more abundant than ambient solar composition gas. AO objects are protochondrules, but are themselves composed of chondrule debris of different types, suggesting that they represent one step of a chondrule recycling process that also included chondrule disaggregation and additional chemical processing. Our data appear to be compatible with the nebular shock wave model for chondrule formation.

Ruzicka, Alex; Floss, Christine; Hutson, Melinda

2012-01-01

140

Preliminary results of sulfide melt/silicate wetting experiments in a partially melted ordinary chondrite  

NASA Technical Reports Server (NTRS)

Recently, mechanisms for core formation in planetary bodies have received considerable attention. Most current theories emphasize the need for large degrees of silicate partial melting to facilitate the coalescence and sinking of sulfide-metal liquid blebs through a low strength semi-crystalline silicate mush. This scenario is based upon observations that sulfide-metal liquid tends to form circular blebs in partially molten meteorites during laboratory experiments. However, recent experimental work by Herpfer and Larimer indicates that some sulfide-Fe liquids have wetting angles at and slightly below 60 deg in an olivine aggregate, implying an interconnected melt structure at any melt fraction. Such melt interconnectivity provides a means for gravitational compaction and extraction of the majority of a sulfide liquid phase in small planetary bodies without invoking large degrees of silicate partial melting. Because of the important ramifications of these results, we conducted a series of experiments using H-chondrite starting material in order to evaluate sulfide-liquid/silicate wetting behavior in a more complex natural system.

Jurewicz, Stephen R.; Jones, John H.

1994-01-01

141

The natural thermoluminescence of meteorites. 7: Ordinary chondrites from the Elephant Moraine region, Antarctica  

NASA Technical Reports Server (NTRS)

We report natural and induced thermoluminescence (TL) measurements for meteorites from the Elephant Moraine region (76 deg 17 min S, 157 deg 20 min E) of Antarctica. We use our data to identify fragmented meteorites (i.e., 'pairings'); our dataset of 107 samples represents at most 73 separate meteorite falls. Pairing groups are generally confined to single icefields, or to adjacent icefields, but a small proportion cross widely separated icefields in the region, suggesting that the fields can be considered as a single unit. Meteorites from this region have high natural TL levels, which indicates that they have small terrestrial surface exposure ages (less than 12,500 years). There do not appear to be significant differences in natural TL levels (and hence surface exposure ages) between individual blue icefields in the region. The proportion of reheated meteorites from the Elephant Moraine region is similar to that of other Antarctic sites and modern falls, consistent with the uniformity of the meteoritic flux in this regard. An unusual subset of H-chondrites, with high induced TL peak temperatures, is absent among the data for meteorites collected in the Elephant Moraine region, which stresses their similarity to modern falls. We suggest that the Elephant Moraine region, which stresses their similarity to modern falls. We suggest that the Elephant Moraine icefields formed through shallow ablation of the ice. Unlike the Allan Hills sites to the south, lateral transport is probably less important relative to the infall of meteorites in concentrating meteorites on these icefields.

Benoit, P. H.; Roth, J.; Sears, H.; Sears, D. W. G.

1994-01-01

142

Effect of hot desert weathering on the bulk-rock iron isotope composition of L6 and H5 ordinary chondrites  

NASA Astrophysics Data System (ADS)

Although iron isotopes are increasingly used for meteorites studies, no attempt has been made to evaluate the effect of terrestrial weathering on this isotopic tracer. We have thus conducted a petrographic, chemical, and iron isotopic study of equilibrated ordinary chondrites (OC) recovered from hot Moroccan and Algerian Saharan deserts environment. As previously noticed, we observe that terrestrial desertic weathering is characterized by the oxidation of Fe-Ni metal (Fe0), sulfide and Fe2+ occurring in olivine and pyroxene. It produces Fe-oxides and oxyhydroxides that partially replace metal, sulfide grains and also fill fractures. The bulk chemical compositions of the ordinary chondrites studied show a strong Sr and Ba enrichment and a S depletion during weathering. Bulk meteoritic iron isotope compositions are well correlated with the degree of weathering and S, Sr, and Ba contents. Most weathered chondrites display the heaviest isotopic composition, by up to 0.1‰, which is of similar magnitude to the isotopic variations resulting from meteorite parent bodies' formation and evolution. This is probably due to the release of isotopically light Fe2+ to waters on the Earth's surface. Hence, when subtle Fe isotopic effects have to be studied in chondrites, meteorites with weathering grade above W2 should be avoided.

Saunier, Gaëlle; Poitrasson, Franck; Moine, Bertrand; Gregoire, Michel; Seddiki, Abdelmadjid

2010-02-01

143

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

144

"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

145

Carbon-rich Chondritic Clast PV1 from the Plainview H-chondrite Regolith Formation from H3 Chondrite Material by Possible Cometary Impact  

NASA Technical Reports Server (NTRS)

Chondritic clast PV1 from the Plainview H-chondrite regolith breccia is a subrounded, 5-mm diameter unequilibrated chondritic fragment that contains 13 wt% C occurring mainly within irregularly shaped 30-400-micron-size opaque patches. The clast formed from H3 chondrite material as indicated by the mean apparent chondrule diameter (310 micron vs. approximately 300 micron in H3 chondrites), the mean Mg-normalized refractory lithophile abundance ratio (1.00 +/- 0.09 XH), the previously determined 0-isotopic composition (Delta O-17 = 0.66% vs. 0.68 +/- 0.04%0 in H3 chondrites and 0.73 +/- 0.09% in H4-6 chondrites), the heterogeneous olivine compositions in grain cores (with a minimum range of Fal-19), and the presence of glass in some chondrules. Although the clast lacks the fine-grained, ferroan silicate matrix material present in type 3 ordinary chondrites, PV1 contains objects that appear to be recrystallized clumps of matrix material. Similarly, the apparent dearth of radial pyroxene and cryptocrystalline chondrules in PV1 is accounted for by the presence of some recrystallized fragments of these chondrule textural types. All of the chondrules in PV1 are interfused indicating that temperatures must have briefly reached approximately 1100C (the approximate solidus temperature of H-chondrite silicate). The most likely source of this heating was by an impact. Some metal was lost during impact heating as indicated by the moderately low abundance of metallic Fe-Ni in PV1 (approximately 14 wt%) compared to that in mean H chondrites (approximately 18 wt%). The carbon enrichment of the clast may have resulted from a second impact event, one involving a cometary projectile, possibly a Jupiter-family comet. As the clast cooled, it experienced hydrothermal alteration at low water/rock ratios as evidenced by the thick rims of ferroan olivine around low-FeO olivine cores. The C-rich chondritic clast was later incorporated into the H-chondrite parent-body regolith and extensively fractured and faulted.

Rubin, Alan E.; Trigo-Rodriguez, Josep M.; Kunihiro, Takuya; Kallemeyn, Gregory W.; Wasson, John T.

2006-01-01

146

Using the Fe/Mn Ratio of FeO-Rich Olivine In WILD 2, Chondrite Matrix, and Type IIA Chondrules to Disentangle Their Histories  

NASA Technical Reports Server (NTRS)

The Stardust Mission returned a large abundance of impactors from Comet 81P/Wild2 in the 5-30 m range. The preliminary examination of just a limited number of these particles showed that the collection captured abundant crystalline grains with a diverse mineralogy [1,2]. Many of these grains resemble those found in chondrite matrix and even contain fragments of chondrules and CAIs [1-3]. In particular, the olivine found in Wild 2 exhibits a wide compositional range (Fa0-97) with minor element abundances similar to the matrix olivine found in many carbonaceous chondrites (CCs) and unequilibrated ordinary chondrites (UOCs). Despite the wide distribution of Fa content, the olivine found in the matrices of CCs, UOCs, and Wild 2 can be roughly lumped into two types based solely on fayalite content. In fact, in some cases, a distinct bi-modal distribution is observed.

Frank, David R.; Le, L.; Zolensky, M. E.

2012-01-01

147

Comparison of Nickel XANES Spectra and Elemental Maps from a Ureilite, a LL3.8 Ordinary Chondrite, Two Carbonaceous Chondrites and Two Large Cluster IDPs  

NASA Technical Reports Server (NTRS)

Nickel in the extraterrestrial world is commonly found in both Fe-Ni sulfide and Fe-Ni met-al forms [1] and in the pure metal state in the interior of iron meteorites where it is not easily oxidized. Ni is also found in olivine, pyroxene and glasses and in some melts the partitioning of Ni between the olivines and glass is controlled by the amount of S in the melt [2]. Its most common valence state is Ni(2+) but Ni also occurs as Ni(0), Ni(+), and Ni(3+) and rarely as Ni(2-), Ni(1-) and Ni(4+) [3]. It's valence state in olivines is Ni(2+) in octa-hedral coordination on the M1 site and rarely on the M2 site.[4]. The chemical sensitivity of X-ray absorp-tion near-edge structure (XANES) spectroscopy is well established and can be used to determine not only va-lence states but also coordination sites [5]. We report here Ni XANES spectroscopy and elemental maps collected from 2 carbonaceous chondrites, 2 large clus-ter IDPs, 1 ureilite and 1 LL3 orginary chondrite.Using XANES it may be possible to find a common trait in the large cluster IDPs that will also be found in mete-orite samples.

Wirick, S.; Flynn, G. J.; Sutton, S.; Zolensky, M. E.

2014-01-01

148

Chemical and physical studies of type 3 chondrites. IX. Thermoluminescence and hydrothermal annealing experiments and their relationship to metamorphism and aqueous alteration in type < 3. 3 ordinary chondrites  

SciTech Connect

Samples of four type 3 chondrites have been annealed at 400-850/sup 0/C and 0.77-1 kbar for 10-500 h in the presence of various amounts of water (0-10 wt.%) and sodium disilicate (0-2 molal) and their thermoluminescence properties measured. After annealing for > 20 h at temperatures > 600/sup 0/C, the TL sensitivity of the samples increased by factors of up to 40. After annealing at < 600/sup 0/C for 10-500 h, or relatively short periods at high temperatures (e.g., less than or equal to 20 h at 850/sup 0/C), the TL sensitivity of the samples decreased by up to 2 orders of magnitude (depending on the original value). The TL peak temperatures observed in the present experiments are consistent with a low form of feldspar (the TL phosphor) being produced at < 800/sup 0/C and a high form being produced at > 800/sup 0/C. When both high and low forms were present originally, the low-form was destroyed preferentially. The authors suggest that these data are consistent with the TL-metamorphism trends observed in type > 3.2 chondrites, being due to the formation of feldspar by the devitrification of chondrule glass during metamorphism. For types < 3.2, the TL data are equally consistent with these types experiencing lower levels of metamorphism than the higher types, or with type 3.0 being produced from higher types by aqueous alteration. The presence of water with non-terrestrial D/H ratios, and petrographic evidence for aqueous alteration in Semarkona, lead to favoring the aqueous alteration hypothesis.

Guimon, R.K.; Lofgren, G.E.; Sears, D.W.G.

1988-01-01

149

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

150

Volatile element chemistry during metamorphism of ordinary chondritic material and some of its implications for the composition of asteroids  

E-print Network

-chondrites for the elements Ag, As, Au, Bi, Br, Cd, Cs, Cu, Ga, Ge, I, In, Pb, Rb, Sb, Se, Sn, Te, Tl, and Zn, and identified volatile trace elements (Ag, As, Au, Bi, Br, Cd, Cs, Cu, Ga, Ge, I, In, Pb, Rb, Sb, Se, Sn, Te, Tl, and Zn of Ag and Zn remain difficult to explain. Ã? 2009 Elsevier Inc. All rights reserved. 1. Introduction

Fegley Jr., Bruce

151

Cooling rate of chondrules in ordinary chondrites revisited by a new geospeedometer based on the compensation rule  

NASA Astrophysics Data System (ADS)

For several decades efforts to constrain chondrite cooling rates from diffusion zoning in olivine gave rise to a range of values from 5 to 8400 K/h (Desch, S.J., Connolly Jr., H.C., 2002. A model for the thermal processing of particles in solar nebula shocks: application to cooling rates of chondrules. Meteorit. Planet. Sci. 37, 183-208; Greeney, S., Ruzicka, A., 2004. Relict forsterite in chondrules: implications for cooling rates. Lunar Planet. Sci. XXXV, abstract # 1246.). Such large uncertainties directly reflect the variability of diffusion data. Alternatively, from this variability results a compensation rule, log D0 = a + bE (diffusion coefficients are written D = D0 exp(- E/ RT)). We test a new geospeemetry approach, based on this rule, on cooling of chondrules in chondrites, Sahara-97210 LL 3.2 and Wells LL 3.3. Greeney and Ruzicka (2004) matched Fe-Mg diffusion profiles in olivine from these chondrites with cooling rates between 200 and 6000 K/h. In our geospeedometry model, the use of the compensation rule greatly reduces the uncertainties by avoiding the choice of one diffusion coefficient among many. The cooling rates we found are between 700 and 3600 K/h for Sahara and 700-1600 K/h for Wells. Finally, we discuss the influence of our analytical model parameters on our cooling rate estimates.

Béjina, Frédéric; Sautter, Violaine; Jaoul, Olivier

2009-01-01

152

Cooling rates of porphyritic olivine chondrules in the Semarkona (LL3.00) ordinary chondrite: A model for diffusional equilibration of olivine during fractional crystallization  

NASA Astrophysics Data System (ADS)

Cooling rates of chondrules provide important constraints on the formation process of chondrite components at high temperatures. Although many dynamic crystallization experiments have been performed to obtain the cooling rate of chondrules, these only provide a possible range of cooling rates, rather than providing actual measured values from natural chondrules. We have developed a new model to calculate chondrule cooling rates by using the Fe-Mg chemical zoning profile of olivine, considering diffusional modification of zoning profiles as crystals grow by fractional crystallization from a chondrule melt. The model was successfully verified by reproducing the Fe-Mg zoning profiles obtained in dynamic crystallization experiments on analogs for type II chondrules in Semarkona. We applied the model to calculating cooling rates for olivine grains of type II porphyritic olivine chondrules in the Semarkona (LL3.00) ordinary chondrite. Calculated cooling rates show a wide range from 0.7 °C/h to 2400 °C/h and are broadly consistent with those obtained by dynamic crystallization experiments (10-1000 °C/h). Variations in cooling rates in individual chondrules can be attributed to the fact that we modeled grains with different core Fa compositions that are more Fe-rich either because of sectioning effects or because of delayed nucleation. Variations in cooling rates among chondrules suggest that each chondrule formed in different conditions, for example in regions with varying gas density, and assembled in the Semarkona parent body after chondrule formation.

Miyamoto, M.; Mikouchi, T.; Jones, R. H.

2009-05-01

153

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

154

Thermal history of type-3 chondrites in the NASA antarctic collection  

NASA Astrophysics Data System (ADS)

Chondrites are the most primitive meteorites. However, they were all modified in some ways by post-accretion geological processes operating on their asteroidal parent bodies. Hence, to decipher the formation(s) and origin(s) of their components, we must first understand how chondritic materials were modified in their asteroidal parent bodies. The modifications induced by secondary processes should not be underestimated and have to be precisely estimated before any interpretation of chondrite properties in terms of cosmochemistry. In particular, all chondrites contain some organic components that were potentially chemically and physically modified through post-accretion processes. A thin understanding of the induced evolution is required to allow for pertinent comparisons with other primitive extraterrestrial materials, such as cometary grains, to finally address questions such as the origin of organics in the Solar System. Type 3 chondrites experienced thermal metamorphism on their asteroidal parent body due to the radioactive decay of elements such as ^{26}Al. Temperatures higher than 300 °C were experienced on timescales of several thousands of years. Still, type 3 chondrites remain as unequilibrated rocks and common mineralogical thermometers cannot be applied. The polyaromatic carbonaceous matter is sensitive to thermal episodes (of long and short duration) experienced by the host meteorite. In particular, its structural order directly reflects the thermal history experienced on their parent bodies. The structural modification of the aromatic carbonaceous matter towards a higher order is irreversible, and independent of the mineralogy and degree of aqueous alteration. It is mainly controlled by the peak metamorphic temperature. Moreover, under the assumption of fairly similar organic precursors among chondrites of distinct groups, the structural order of polyaromatic organic matter allows for a direct comparison of their metamorphic grades. It is then possible to evaluate the metamorphic grade of the objects and to assign a petrologic type along a unique petrologic scale [1-4]. This technique has been successfully applied to type 3 Unequilibrated Ordinary Chondrites [1], carbonaceous CV chondrites [2], and CO chondrites [3]. The interpretation of the structural order of the polyaromatic carbonaceous matter in terms of thermal history is thus reliable. Raman spectroscopy enables the determination of the degree of structural order of the polyaromatic organic matter present in the matrix of chondrites. Both falls and finds, from Antarctica [4] and elsewhere, have been analyzed. It does not require a large amount of samples and is relatively easy to implement. Raman spectroscopy is particularly sensitive to the lowest petrologic types (3.0-3.2). The present NASA collection of Antarctic meteorites represents an incredible source of precious samples for our community. The present work finely characterizes the thermal history of most of the type 3 chondrites (UOCs, CVs, and COs) from that collection. At the present time, the objectives are threefold: (i) determination of reliable petrologic types indispensable for our community; (ii) identification of the most primitive type 3 chondrites (petrologic type ? 3.1); and (iii) identification of potential ''anomalous'' samples having experienced a slightly different thermal history. The JSC Meteorite Working Group generously allocated us with more than 150 chondrites (UOCs, CVs, and COs). The following points summarize the main results. (i) At the present time, the thermal histories of more than 100 samples have been characterized. (ii) The terrestrial weathering experienced by several chondrites (˜25 chondrites) has been too pervasive for the method to be applied. For these meteorites, as signatures of oxide minerals dominate Raman spectra of the matrix, the organic matter might have been significantly altered through oxidation. (iii) Real discrepancies with the preliminary JSC petrologic type attributions were found for several chondrites with mostly underestimations of the

Bonal, L.; Quirico, E.; Montagnac, G.

2014-07-01

155

Textural properties of iron-rich phases in H ordinary chondrites and quantitative links to the degree of thermal metamorphism  

NASA Astrophysics Data System (ADS)

The textural characteristics of opaque iron-rich phases (kamacite-taenite and troilite) have been quantified in the eight H-chondrites (two H4, three H5 and three H6) that have been the subject of previous thermo-chronological studies. These samples are of interest as they have temperature-time paths during cooling that have been shown to be consistent with radiogenic heating by 26Al on a single parent-body, thus offering the possibility to quantitatively link textural characteristics to thermal history. In addition to these eight samples, two other H5 samples (Forest City & Misshof) and two primitive achondrites (Acapulco & Lodran) were studied for comparison. The textural characteristics measured include: (i) phase proportions, (ii) the length of metal-sulphide contacts, (iii) dihedral angle at contacts with silicate grains, (iv) grain shape and circularity, (v) grain size and size distributions. The absolute and relative proportions of metals and sulphides are found to be approximately constant in all studied H chondrites, consistent with evolution in a chemically closed system. With increasing degree of thermal metamorphism, H-chondrites are found to show evidence for separation of metal and sulphide phases, increasing grain circularity, increasing grain size, and modification of size distributions characterized by the elimination of small grains. Variations of these parameters are found to be almost identical for sulphides and metals suggesting similar growth mechanisms for these two phases. Furthermore, trends between samples place them consistently in the same order: Sainte Marguerite (H4), Forest Vale (H4), Nadiabondi (H5), Richardton (H5), Forest City (H5), Misshof (H5), Allegan (H5), Kernouvé (H6), Guareña (H6) and Estacado (H6). In all cases Acapulco and Lodran extend the trends observed among the H-chondrites. In general, it is found that characteristics requiring material transport over shorter length scales (i.e. within grains) show greater variation for low petrographic type (H4/H5) and reach textural equilibrium earlier in the sequence than characteristics which require transport over larger distances (i.e. between grains). In the latter case (e.g. slopes of crystal size distribution), variations are most marked for H6 samples, trends that are significantly extended by Acapulco and Lodran, highlighting the role of silicate melt on variations in textural properties. Crystal size distributions imply normal grain growth (NGG) for both metals and sulphides, possibly controlled by grain boundary migration of olivine and/or pyroxene. Comparison of these results with geochemically constrained thermal models of the H-chondrite parent body shows an excellent correlation between average crystal sizes, and inferred depths in the original parent body, consistent with expectations based on thermal modelling. This study highlights the potential of grain-size as a quantitative marker of the degree of thermal metamorphism, although further work on a wider set of samples will be required to explore the limits of this approach.

Guignard, J.; Toplis, M. J.

2015-01-01

156

Micron-scale D/H heterogeneity in chondrite matrices: a signature of the pristine solar system water?  

E-print Network

Organic matter and hydrous silicates are intimately mixed in the matrix of chondrites and in-situ determination of their individual D/H ratios is therefore challenging. Nevertheless, the D/H ratio of each pure component in this mixture should yield a comprehensible signature of the origin and evolution of water and organic matter in our solar system. We measured hydrogen isotope ratios of organic and hydrous silicates in the matrices of two carbonaceous chondrites (Orgueil CI1 and Renazzo CR2) and one unequilibrated ordinary chondrite (Semarkona, LL3.0). A novel protocol was adopted, involving NanoSIMS imaging of H isotopes of monoatomatic ($H^-$) and molecular ($OH^-$) secondary ions collected at the same location. This allowed the most enriched component with respect to D to be identified in the mixture. Using this protocol, we found that in carbonaceous chondrites the isotopically homogeneous hydrous silicates are mixed with D-rich organic matter. The opposite was observed in Semarkona. Hydrous silicates i...

Piani, Laurette; Remusat, Laurent

2015-01-01

157

Coupled 63Cu and 16O excesses in chondrites  

NASA Astrophysics Data System (ADS)

Recent developments in multiple-collector magnetic-sector ICP-MS (inductively coupled plasma-mass spectrometry) have permitted the relative abundances of the two isotopes 63 and 65 of copper to be measured with unprecedented precision (40 ppm). Here, we report Cu isotopic variations among eight carbonaceous chondrites (CCs) from the CI, CM, CO, and CV groups and the presently ungrouped Tagish Lake, and 10 ordinary chondrites (OCs) from the H, L, and LL groups. The widest isotopic range of ˜0.8‰ per a.m.u. is observed for the carbonaceous chondrites. Copper in carbonaceous chondrites becomes isotopically lighter with petrologic type in the order 1 to 3 but seems extremely homogeneous for each type. The Cu isotopic composition of Tagish Lake confirms its other characteristics that are intermediate between CI and CM. In three of the groups (CI-CM-CO), as well as for Tagish Lake, 63Cu excess over terrestrial mantle abundances correlates well with 16O excess. For all four groups, 63Cu excess also correlates remarkably well with elemental refractory/volatile ratios (e.g., Ca/Mn). For ordinary chondrites, small differences exist between the H, L, and LL groups, with Cu becoming isotopically heavier in that order. Equilibrated and unequilibrated samples, however, exhibit the same Cu isotopic signature within each group. Although the range of Cu isotopic compositions in ordinary chondrites is smaller than in carbonaceous chondrites, 63Cu excesses still correlate with 16O excesses. The observed trends of isotopic variation seem incompatible with a single-stage fractionation process by either volatilization or low-temperature metamorphism. The correlations between 63Cu excesses and 16O excesses suggest the presence of at least two and perhaps three isotopically distinct Cu reservoirs in the early Solar System: (1) an Earth-like reservoir common to the CI and LL probably representing the main Cu stock of the inner Solar System, (2) a reservoir present in all carbonaceous chondrites, but most abundant in CV, with large 63Cu and 16O excesses (this reservoir is probably hosted in refractory material), and (3) possibly a third reservoir present in ordinary chondrites. The OC trend may also be explained as a mixture of the first two Cu reservoirs if its oxygen was first equilibrated with nebular gas. The coexistence of 63Cu and 16O excesses in the same component raises the issue of how volatile Cu was preserved in refractory material. A strong correlation between 63Cu/ 65Cu and Ni/Cu ratios suggests that 63Cu excess may have originated as more refractory 63Ni (T 1/2 = 100 yr) upon irradiation of refractory grains by electromagnetic flares and particle bursts during the T-Tauri phase of the Sun.

Luck, J. M.; Othman, D. Ben; Barrat, J. A.; Albarède, F.

2003-01-01

158

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

159

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

160

Micron-scale D/H heterogeneity in chondrite matrices: A signature of the pristine solar system water?  

NASA Astrophysics Data System (ADS)

Organic matter and hydrous silicates are intimately mixed in the matrix of chondrites and in-situ determination of their individual D/H ratios is therefore challenging. Nevertheless, the D/H ratio of each pure component in this mixture should yield a comprehensible signature of the origin and evolution of water and organic matter in our solar system. We measured hydrogen isotope ratios of organic and hydrous silicates in the matrices of two carbonaceous chondrites (Orgueil CI1 and Renazzo CR2) and one unequilibrated ordinary chondrite (Semarkona, LL3.0). A novel protocol was adopted, involving NanoSIMS imaging of H isotopes of monoatomatic (H-) and molecular (OH-) secondary ions collected at the same location. This allowed the most enriched component with respect to D to be identified in the mixture. Using this protocol, we found that in carbonaceous chondrites the isotopically homogeneous hydrous silicates are mixed with D-rich organic matter. The opposite was observed in Semarkona. Hydrous silicates in Semarkona display highly heterogeneous D/H ratios, ranging from 150 to 1800 ×10-6 (?DSMOW = - 40 to 10 600‰). Organic matter in Semarkona does not show such large isotopic variations. This suggests limited isotopic exchange between the two phases during aqueous alteration. Our study greatly expands the range of water isotopic values measured so far in solar system objects. This D-rich water reservoir was sampled by the LL ordinary chondrite parent body and an estimate (?9%) of its relative contribution to the D/H ratio of water in Oort cloud family comets is proposed.

Piani, Laurette; Robert, François; Remusat, Laurent

2015-04-01

161

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

162

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

163

The solar nebula redox state as recorded by the most reduced chondrules of five primitive chondrites  

NASA Technical Reports Server (NTRS)

Mafic minerals in the most reduced chondrules of five primitive meteorites were analyzed with an electron microprobe to determine the lower limit on their FeO contents. The accuracy obtained was + or - 0.01 weight percent FeO. The thermodynamic relationship between mole fraction FeSiO3 and pO2 of the ambient nebular gas at the time of mineral equilibration was established, and was used to infer the local O/H ratio of the nebular gas during chondrule formation. The lowest ferrosilite compositions reflected equilibration at 1500 K with a gas 2-18 times more oxidizing than a gas of solar composition. Olivines in low-FeO unequilibrated ordinary chondrites (UOC) chondrules are uniformly more FeO-rich than coexisting pyroxenes. This discrepancy suggests that a significant change in the O/H ratio of the nebular gas occurred between the time of olivine and pyroxene crystallization in the region of the nebula where UOCs formed. Mineral compositions in the chondrules of two C2 chondrites studied suggest they formed in a more homogeneous region of the nebula than the UOCs.

Johnson, M. C.

1986-01-01

164

Shock metamorphism of carbonaceous chondrites  

NASA Technical Reports Server (NTRS)

Shock effects were studied in 69 carbonaceous chondrites, including CM2, CO3, CV3, ungrouped C2-C4, and CK4-6 chondrites, using optical microscopy of thin sections. It is shown that the classification scheme of Stoeffler et al. (1991) for the progressive stages of shock metamorphism in ordinary chondrites is also applicable to carbonaceous chondrites. On the basis of shock effects in olivine, the 69 carbonaceous chondrites could be assigned to four shock stage, S1 to S4. The CM2 and CO3 groups were found to be the least shocked chondrite groups, whereas the CK4-6 and CV3 were the most strongly shocked groups.

Scott, Edward R. D.; Keil, Klaus; Stoeffler, Dieter

1992-01-01

165

Chemical and physical studies of type 3 chondrites. IX - Thermoluminescence and hydrothermal annealing experiments and their relationship to metamorphism and aqueous alteration in type below 3.3 ordinary chondrites  

NASA Technical Reports Server (NTRS)

Thermoluminescence (TL) properties were measured in samples of four type-3.0 chondrites annealed at 400-850 C and 0.77-1 kbar in the presence of various amounts of water and sodium disilicate. Several changes recorded in TL characteristics, such as the lowering of TL sensitivity in certain samples, its increase in other samples, and changes in the peak position and peak width of TL suggested the occurrence of metamorphic processes in these samples. It is suggested that, for the chondrite types above 3.2, the observed changes in TL are consistent with the TL-metamorphism trends, being due to the formation of feldspar by the devitrification of chondrule glass during metamorphism. For types below 3.2, the TL data are consistent with the hypothesis that these chondrules experienced lower levels of metamorphism than the higher types or, alternatively, with the hypothesis that the type 3.0 chondrules are being produced from higher types by aqueous alteration.

Guimon, R. Kyle; Sears, Derek W. G.; Lofgren, Gary E.

1988-01-01

166

Parent-Body Modification of Chondritic Meteorites  

NASA Technical Reports Server (NTRS)

This proposal focused on the parent-body modification of chondritic materials and substantial progress was made in the last year. A summary of the work accomplished during this period is discussed. The topics include: 1) Chromite-Plagioclase Assemblages in Ordinary Chondrites; 2) The Gujba Bencubbin-like meteorite fall; 3) NWA428: A rock that Experienced Impact-induced Annealing; 4) Spade: An Annealed H-chondrite Impact-melt Breccia; and 5) Post-shock Annealing in Ordinary Chondrites. A list of the papers submitted or published during the period is also presented.

Rubin, Alan

2003-01-01

167

The effect of aqueous alteration and metamorphism in the survival of presolar silicate grains in chondrites  

E-print Network

Relatively small amounts (typically between 2-200 parts per million) 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 level of aqueous alteration. We conclude that the measured abundances of presolar grains...

Trigo-Rodriguez, Josep M

2009-01-01

168

A partial melting study of an ordinary (H) chondrite composition with application to the unique achondrite Graves Nunataks 06128 and 06129  

NASA Astrophysics Data System (ADS)

Melting experiments of a synthesized, alkali-bearing, H-chondrite composition were conducted at ambient pressure with three distinct oxygen fugacity conditions (IW-1, IW, and IW+2). Oxygen fugacity conditions significantly influence the compositions of partial melts. Partial melts at IW-1 are distinctly enriched in SiO2 relative to those of IW and IW+2 melts. The silica-enriched, reduced (IW-1) melts are characterized by high alkali contents and have silica-oversaturated compositions. In contrast, the silica-depleted, oxidized (?IW) melts, which are also enriched in alkali contents, have distinctly silica-undersaturated compositions. These experimental results suggest that alkali-rich, felsic, asteroidal crusts as represented by paired achondrites Graves Nunataks 06128 and 06129 should originate from a low-degree, relatively reduced partial melt from a parent body having near-chondritic compositions. Based on recent chronological constraints and numerical considerations as well as our experimental results, we propose that such felsic magmatism should have occurred in a parent body that is smaller in size and commenced accreting later than those highly differentiated asteroids having basaltic crusts and metallic cores.

Usui, Tomohiro; Jones, John H.; Mittlefehldt, David W.

2015-04-01

169

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

170

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

171

Petrology of Unique Impact Melt Rock, Ramsdorf (L Chondrite)  

NASA Astrophysics Data System (ADS)

We have studied a unique impact melt rock, the Ramsdorf L chondrite. We have discovered that Ramsdorf contains not only clast-poor impact melt but also a chondritic portion (>60 g) with prominent chondritic texture. Detailed mineralogical studies suggest that most (~90 vol%) of the chondritic portion was melted by shock. Ramsdorf was produced by melting of a type 3-4 chondrite and crystallization in situ. The associated shock pressure could have been ~75-90 GPa, with a post shock temperature of ~1400 degrees-1600 degrees C. The shock stage of this rock may be the highest among ordinary chondrites and other rocks, namely shock stage S6+.

Yamaguchi, A.; Scott, E. R. D.; Keil, K.

1996-03-01

172

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

173

Thermoluminescence of shocked chondrites and regolith breccias  

SciTech Connect

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 from TL annealing experiments and {sup 40}Ar step-wise release measurements enables the meteorites to be sorted into three post-shock temperature groups (<800 C, 800-1000C,> 1000C). The TL sensitivities of Antarctic H chondrites are typically 1/3 those of non-Antarctic H chondrites. On TL peak temperature-peak width diagram, L chondrites produce tight clusters with only partial overlap between those of Antarctic and non-Antarctic L chondrites. H chondrites from Antarctic also from tight clusters but non-Antarctic H chondrites plot in a band of increasing peak temperature and width, with no overlap between the data for Antarctic and non-Antarctic meteorites. On TL peak temperature-peak width plots for meteorites with greater regolith maturity the clast and matrix form two separate clusters, while meteorites with lower regolith maturity showed no difference in their matrix and clast data. The data are consistent with the dark matrix being comminuted clast material contaminated with another component. The Cumberland Falls inclusions produced glow curves with similar shapes to those of type 3 ordinary chondrites and very different to those of the host samples. TL sensitivities for the inclusions were in the range of type 3.4-3.6 ordinary chondrites. The TL data are consistent with the inclusions are metamorphic series of primitive ordinary chondrites. The inclusions have not been heated in excess of 800C for 100 hours since the formation of feldspar.

Haq, M.U.

1987-01-01

174

Opaque Assemblages in CK and CV Carbonaceous Chondrites  

NASA Technical Reports Server (NTRS)

CK carbonaceous chondrites are the only group of carbonaceous chondrites that exhibit thermal metamorphism. As a result, CKs display features of metamorphism such as silicate darkening, recrystallization and shock veins. Calcium Aluminum Inclusions and Fe-Ni metal are rare. CV carbonaceous chondrites are unequilibrated and have two subgroups; oxidized and reduced. The CV and CK carbonaceous chondrite groups have been compared to each other often because of petrographic similarities, such as overlapping oxygen isotopic ratios. Scientists have suggested the two groups of carbonaceous chondrites formed from the same parent body and CKs are equilibrated CV chondrites [1, 2]. The oxidized CV group has been most closely related to CKs. This study examines the petrology and mineralogy of CKs and CVs focusing on opaque minerals found in the meteorites. Using the oxide, metal and sulfide assemblages, constraints can be placed on the temperature and oxygen fugacity at which the meteorites equilibrated. The temperature and oxygen fugacity of the CK and CV chondrites can be compared in order to help define their formation history.

Neff, K. E.; Righter, K.

2006-01-01

175

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

SciTech Connect

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. 28 refs.

Zolensky, M.E.; Score, R.; Clayton, R.N.; Mayeda, T.K.; Schutt, J.W. (NASA, Johnson Space Center, Houston, TX (USA) Lockheed Engineering and Sciences Co., Houston, TX (USA) Chicago Univ., IL (USA))

1989-12-01

176

The record of cosmogenic, radiogenic, fissiogenic, and trapped noble gases in recently recovered Chinese and other chondrites  

NASA Astrophysics Data System (ADS)

Noble-gas isotopic abundances were determined in 36 recently recovered chondrites including 27 chondrites recovered in China. The comparison of the release patterns of trapped noble gases from ordinary and from carbonaceous chondrites showed that the planetary trapped noble gases in ordinary chondrites were released mainly above 1200 C, whereas more than 85 percent of noble gases trapped in carbonaceous chondrites were released at or below 1200 C, indicating that the carrier phases of the trapped noble gases in ordinary and in carbonaceous chondrites may not be the same. It is suggested that the ordinary chondrites started to retain fission Xe about 48 +/- 30 Ma earlier than Angra dos Reis. No systematic differences were observed between H, L, and LL or type 5 and 6 chondrites with respect to the time of fission Xe retention. Eight chondrites displayed neutron capture effects due to secondary cosmic-ray-produced neutrons.

Eugster, O.; Michel, Th.; Niedermann, S.; Wang, D.; Yi, W.

1993-03-01

177

26Al in plagioclase-rich chondrules in carbonaceous chondrites: Evidence for an extended duration of chondrule formation  

NASA Astrophysics Data System (ADS)

The 26Al- 26Mg isotope systematics in 33 petrographically and mineralogically characterized plagioclase-rich chondrules (PRCs) from 13 carbonaceous chondrites (CCs) - one ungrouped (Acfer 094), six CR, five CV, and one CO - reveal large variations in the initial 26Al/ 27Al ratio, ( 26Al/ 27Al) 0. Well-resolved 26Mg excesses (? 26Mg) from the in situ decay of the short-lived nuclide 26Al ( t1/2 ˜ 0.72 Ma) were found in nine chondrules, two from Acfer 094, five from the CV chondrites, Allende and Efremovka, and one each from the paired CR chondrites, EET 92147 and EET 92042, with ( 26Al/ 27Al) 0 values ranging from ˜3 × 10 -6 to ˜1.5 × 10 -5. Data for seven additional chondrules from three CV and two CR chondrites show evidence suggestive of the presence of 26Al but do not yield well defined values for ( 26Al/ 27Al) 0, while the remaining chondrules do not contain excess radiogenic 26Mg and yield corresponding upper limits of (11-2) × 10 -6 for ( 26Al/ 27Al) 0. The observed range of ( 26Al/ 27Al) 0 in PRCs from CCs is similar to the range seen in chondrules from unequilibrated ordinary chondrites (UOCs) of low metamorphic grade (3.0-3.4). However, unlike the UOC chondrules, there is no clear trend between the ( 26Al/ 27Al) 0 values in PRCs from CCs and the degree of thermal metamorphism experienced by the host meteorites. High and low values of ( 26Al/ 27Al) 0 are found equally in PRCs from both CCs lacking evidence for thermal metamorphism (e.g., CRs) and CCs where such evidence is abundant (e.g., CVs). The lower ( 26Al/ 27Al) 0 values in PRCs from CCs, relative to most CAIs, are consistent with a model in which 26Al was distributed uniformly in the nebula when chondrule formation began, approximately a million years after the formation of the majority of CAIs. The observed range of ( 26Al/ 27Al) 0 values in PRCs from CCs is most plausibly explained in terms of an extended duration of ˜2-3 Ma for the formation of CC chondrules. This interval is in sharp contrast to most CAIs from CCs, whose formation appears to be restricted to a narrow time interval of less than 10 5 years. The active solar nebula appears to have persisted for a period approaching 4 Ma, encompassing the formation of both CAIs and chondrules present in CCs, and raising important issues related to the storage, assimilation and mixing of chondrules and CAIs in the early solar system.

Hutcheon, I. D.; Marhas, K. K.; Krot, A. N.; Goswami, J. N.; Jones, R. H.

2009-09-01

178

The formation of Ca-, Fe-rich silicates in reduced and oxidized CV chondrites: The roles of impact-modified porosity and permeability, and heterogeneous distribution of water ices  

NASA Astrophysics Data System (ADS)

CV (Vigarano type) carbonaceous chondrites, comprising Allende-like (CVoxA) and Bali-like (CVoxB) oxidized and reduced (CVred) subgroups, experienced differing degrees of fluid-assisted thermal and shock metamorphism. The abundance and speciation of secondary minerals produced during asteroidal alteration differ among the subgroups: (1) ferroan olivine and diopside-hedenbergite solid solution pyroxenes are common in all CVs; (2) nepheline and sodalite are abundant in CVoxA, rare in CVred, and absent in CVoxB; (3) phyllosilicates and nearly pure fayalite are common in CVoxB, rare in CVred, and virtually absent in CVoxA; (4) andradite, magnetite, and Fe-Ni-sulfides are common in oxidized CVs, but rare in reduced CVs; the latter contain kirschsteinite instead. Thus, a previously unrecognized correlation exists between meteorite bulk permeabilities and porosities with the speciation of the Ca-, Fe-rich silicates (pyroxenes, andradite, kirschsteinite) among the CVox and CVred meteorites. The extent of secondary mineralization was controlled by the distribution of water ices, permeability, and porosity, which in turn were controlled by impacts on the asteroidal parent body. More intense shock metamorphism in the region where the reduced CVs originated decreased their porosity and permeability while simultaneously expelling intergranular ices and fluids. The mineralogy, petrography, and bulk chemical compositions of both the reduced and oxidized CV chondrites indicate that mobile elements were redistributed between Ca,Al-rich inclusions, dark inclusions, chondrules, and matrices only locally; there is no evidence for large-scale (>several cm) fluid transport. Published 53Mn-53Cr ages of secondary fayalite in CV, CO, and unequilibrated ordinary chondrites, and carbonates in CI, CM, and CR chondrites are consistent with aqueous alteration initiated by heating of water ice-bearing asteroids by decay of 26Al, not shock metamorphism.

MacPherson, Glenn J.; Krot, Alexander N.

2014-07-01

179

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

180

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

181

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

182

Shock-Melted Regions in the Krymka (LL3) Chondrite  

NASA Astrophysics Data System (ADS)

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 most primitive ordinary chondrites. Examination of various samples of Krymka in the Ukrainian meteorite collection has already revealed evidences of shock effects, indicative of pressures of 25-45 GPa (assuming non-porous material) and temperatures <= 500 degrees C, with local excursions to >=988 degrees C (melting of Fe-FeS eutectic) [2]. Sample N1290/29 (134 g), from the same collection, contains light-colored, friable, completely melted zones. Observations were made on 6 polished sections from that specimen, with a total area of 14 cm2. In 4 of these, 4 melted regions occupy a total of ~3 cm2. They are chondrule-free and consist of porphyritic and skeletal silicates (mainly olivine) in a cryptocrystalline mesostasis, along with metal-troilite mixtures with dendritic and cellular structures. Olivine composition is variable (Fa(sub)10-26) but to a lesser extent than in Krymka chondrules (Fa(sub)0-35). The mesostasis is also inhomogeneous. Apart from a few notable exceptions, olivine crystals are normally zoned, with FeO increasing from core to rim. Fe-Ni cells are zoned as well, consisting of a core with 11.2-22.6 wt%Ni and 0.83-0.96 wt%Co (probably martensite), and a Ni-rich rim (up to 51.3 wt%Ni, probably tetrataenite). The metal contains P (0.12-0.43 wt%), which seems to be, at least in part, in tiny schreibersite inclusions, and the troilite contains Ni (0.05- 4.2 wt%Ni). Metal-troilite mixtures contain abundant globules (up to 15 microns in diameter) of a Fe-Na phosphate (maybe maricite). These globules are usually rimmed with numerous euhedral micrometer-sized chromites. Larger euhedral chromites also occur isolated in metal-troilite. The melted regions are surrounded by a transition zone with chondritic texture, containing completely melted troilite and partially melted metal. The highly variable Co concentration (0.2-13.0 wt%) of the metal grains in this zone reflects the high degree of unequilibration of the Krymka chondrite. Shock pressure in the range 75-90 GPa is normally required to induce local complete melting of chondritic matter, but, in the present case, pressure as low as 30 GPa may be responsible for the observed effects, because of the porous nature of type 3 material [1]. In any case, the temperature must have been larger than 1450 degrees C. Experimental data on zoning trends in olivine [3] and Ni content in troilite [4] suggest a cooling rate of at least 100 degrees C/h. The association of P and Cr with metal-troilite reflects their association with metal in the host: Ca- phosphates are common at the boundaries of Krymka metal grains and many of these contain myriads of tiny chromites [5]. P and Cr were probably reduced at high temperature and they dissolved in metal-troilite liquid. Upon cooling, they reoxidized and crystallised. The unusual phosphate may result from higher volatility and mobility of Na relative to Ca. Mechanical deformations (shear) of some of these phosphate globules and of melted troilite attest that, after complete solidification of the melted regions, Krymka was subjected to other, less intense shock(s). References: [1] St"ffler D. et al. (1991) GCA, 55, 3845. [2] Semenenko V. P. et al. (1987) The Meteorites of Ukraine, 218 pp., Naukova Dumka (in Russian). [3] Radomsky P. M. and Hewins R. H. (1990) GCA, 54, 3475. [4] Smith B. A. and Goldstein J. I. (1977) GCA, 41, 1061. [5] Perron C. and Bourot-Denise M. (1992) LPS XXIII, 1055.

Semenenko, V. P.; Perron, C.

1995-09-01

183

Aqueous Alteration of Enstatite Chondrites  

NASA Technical Reports Server (NTRS)

The Kaidun meteorite is different from all other meteorites [1], consisting largely of a mixture of “incompatible” types of meteoritic material – carbonaceous and enstatite chondrites, i.e. corre-sponding to the most oxidized and the most reduced samples of meteorite materials, including CI1, CM1-2, CV3, EH3-5, and EL3. In addition to these, minor amounts of ordinary and R chondrites are present. In addition, approximately half of the Kaidun lithologies are new materials not known as separate meteorites. Among these are aqueously altered enstatite chondrites [1], which are of considerable interest because they testify that not all reduced asteroids escaped late-stage oxidation, and hydrolysis, and also because hydrated poorly crystalline Si-Fe phase, which in turn is re-placed by serpentine (Figs 3-5). In the end the only indication of the original presence of metal is the re-sidual carbides. In other enstatite chondrite lithogies (of uncertain type) original silicates and metal have been thoroughly replaced by an assemblage of authi-genic plagioclase laths, calcite boxwork, and occasion-al residual grains of silica, Cr-rich troilite, ilmenite, and rare sulfides including heideite (Fig. 6). Fe and S have been largely leached from the rock (Fig. 4). Again the accessory phases are the first clue to the original character of the rock, which can be verified by O isotopes. It is fortunate that Kaidun displays every step of the alteration process.

Zolensky, M. E.; Ziegler, K.; Weisberg, M. K.; Gounelle, M.; Berger, E. L.; Le, L.; Ivanov, A.

2014-01-01

184

Rhenium-osmium isotope systematics of carbonaceous chondrites  

NASA Astrophysics Data System (ADS)

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 Re-187/Os-186 and Os-187/Os-186 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. 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 nebular.

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

1989-01-01

185

Thermal histories of CO3 chondrites - Application of olivine diffusion modelling to parent body metamorphism  

NASA Technical Reports Server (NTRS)

The petrologic sequence observed in the CO3 chondrite group has been suggested to be the result of thermal metamorphism on a parent body. A model developed to examine the possibility that chondrule and matrix olivines equilibrated in situ, during parent body metamorphism is presented. The model considers Fe-Mg interdiffusion between chondrule and matrix olivines. Zoning profiles comparable to those observed in chondrule olivines from partially equilibrated members of the series are reproduced successfully. Metamorphism of CO3 chondrites on a parent body is therefore a viable model for the observed equilibration. Results indicate that peak metamorphic temperatures experienced by the CO3 chondrites were around 500 C, and that the range of peak temperatures between unequilibrated and equilibrated subtypes was relatively narrow, around 100 C.

Jones, Rhian H.; Rubie, David C.

1991-01-01

186

New kind of type 3 chondrite with a graphite-magnetite matrix  

NASA Technical Reports Server (NTRS)

Four clasts in three ordinary-chondrite regolith breccias are discovered which are a new kind of type 3 chondrite. As with ordinary and carbonaceous type 3 chondrites, they have distinct chondrules, some of which contain glass, highly heterogeneous olivines and pyroxenes, and predominantly monoclinic low-Ca pyroxenes. Instead of the usual, fine-grained, Fe-rich silicate matrix, however, the clasts have a matrix composed largely of aggregates of micron- and submicron-sized graphite and magnetite. The bulk compositions of the clasts, as well as the types of chondrules (largely porphyritic), are characteristic of type 3 ordinary chondrites, although chondrules in the clasts are somewhat smaller (0.1-0.5 mm). A close relationship with ordinary chondrites is also suggested by the presence of similar graphite-magnetite aggregates in seven type 3 ordinary chondrites. It is thought that this new kind of chondrite is probably the source of the abundant graphite-magnetite inclusions in ordinary-chondrite regolith breccias and that it may be more common than indicated by the absence of whole meteorites made of chondrules and graphite-magnetite.

Scott, E. R. D.; Rubin, A. E.; Taylor, G. J.; Keil, K.

1981-01-01

187

Petrology and Cosmochemistry of a Suite of R Chondrites  

NASA Technical Reports Server (NTRS)

Chondrites are among the most primitive surviving materials from the early solar system. They are divided into groups based on chemical types defined by mineralogy, bulk composition, and oxygen isotope compositions. Chondrites range in petrographic grade from type 1 to type 7. Type 3 chondrites are the most primitive and are little changed from the nebular solids accreted to form asteroids. They are composed of chondrules, fine-grained matrix, metal and sulfide, plus or minus Ca-Al-rich inclusions. With increasing aqueous alteration at low temperatures, members of some chondrite classes transformed from type 3 towards type 1. With increasing thermal metamorphism and low fluid content, members of other classes changed from type 3 towards type 7. Rumuruti (R) chondrites are a rare group (0.1% of falls) similar to ordinary chondrites in some properties but different in others. They are characterized by low chondrule/matrix modal abundance ratios, high oxidation state, small mean chondrule size, abundant sulfides and low metal contents. R chondrites vary in petrologic type from 3 to 6. They are important objects to study because some of them have undergone metamorphism at high temperatures in the presence of aqueous fluids. In contrast, CM and CI chondrites were heated to low temperatures in the presence of aqueous fluids leading to alteration; they contain low-T hydrous phases (phyllosilicates) and little or no remaining metal. Ordinary chondrites were heated to high temperatures in a low-fluid environment resulting in anhydrous metamorphic rocks. R6 chondrites are highly metamorphosed and some contain the high-T hydrous phases mica and amphibole. R chondrites are thus unique and give us an opportunity to examine whether there are compositional effects caused by high-T, highfluid metamorphism of nebular materials.

Torrano, Z. A.; Mittlefehldt, D. W.; Peng, Z. X.

2015-01-01

188

Coarse-grained chondrule rims in type 3 chondrites  

NASA Astrophysics Data System (ADS)

Coarse-grained rims composed of olivine, with or without low-Ca pyroxene, occur around all types of chondrules and compound chondrules in type 3 carbonaceous chondrites and around ordinary chondrites. The dark zoned chondrules and coarse grained rims were formed by the heating of clumps of opaque matrix material to subsolidus-subliquidus temperatures in the solar nebula. The most likely source of the heat that formed the coarse grained rims is the mechanism responsible for chondrule formation. CV chondrites may have formed in a region where the chondrule formation mechanism was less efficient, probably at greater solar distances than the ordinary chondrites. Alternatively, CV chondrules may have suffered fewer particle collisions prior to agglomeration.

Rubin, A. E.

1984-09-01

189

The Pasamonte unequilibrated eucrite: Pyroxene REE systematic and major-, minor-, and trace-element zoning. [Abstract only  

NASA Technical Reports Server (NTRS)

We are evaluating the trace-element concentrations in the pyroxenes of Pasamonte. Pasamonte is a characteristic member of the main group eucrites, and has recently been redescribed as a polymict eucrite. Our Pasamonte sample contained eucritic clasts with textures ranging from subophitic to moderately coarse-grained. This study concentrates on pyroxenes from an unequilibrated, coarse-grained eucrite clast. Major-, minor-, and trace-element analyses were measured for zoned pyroxenes in the eucritic clast of Pasamonte. The major- and minor-element zoning traverses were measured using the JEOL 733 electron probe with an Oxford-Link imaging/analysis system. Complemenatry trace elements were then measured for the core and rim of each of the grains by SIMS. The trace elements analyzed consisted of eight REE, Sr, Y, and Zr. These analyses were performed on a Cameca 4f ion probe. The results of the CI chondrite normalized (average CI trace-element analyses for several grains and the major- and minor-element zoning patterns from a single pyroxene grain are given. The Eu abundance in the cores of the pyroxenes represents the detection limit and therefore the (-Eu) anomaly is a minimum. Major- and minor-element patterns are typical for igneous zoning. Pyroxene cores are Mg enriched, whereas the rims are enriched in Fe and Ca. Also, Ti and Mn are found to increase, while Cr and Al generally decrease in core-to-rim traverses. The cores of the pyroxenes are more depleted in the Rare Earth Elements (REE) than the rims. Using the minor- and trace-element concentrations of bulk Pasamonte and the minor- and trace-element concentrations from the cores of the pyroxenes in Pasamonte measured in this study, we calculated partition coefficients between pyroxene and melt. This calculation assumes that bulk Pasamonte is representative of a melt composition.

Pun, A.; Papike, J. J.

1994-01-01

190

Chondrites and the Protoplanetary Disk, Part 2  

NASA Technical Reports Server (NTRS)

Contents include the following: On the Dynamical Evolution of a Nebula and Its Effect on Dust Coagulation and the Formation of Centimeter-sized Particles. The Mineralogy and Grain Properties of the Disk Surfaces in Three Herbig Ae/Be Stars. Astrophysical Observations of Disk Evolution Around Solar Mass Stars. The Systematic Petrology of Chondrites: A Consistent Approach to Assist Classification and Interpretation. Understanding Our Origins: Formation of Sun-like Stars in H II Region Environments. Chondrule Crystallization Experiments. Formation of SiO2-rich Chondrules by Fractional Condensation. Refractory Forsterites from Murchison (CM2) and Yamato 81020 (CO3.0) Chondrites: Cathodoluminescence, Chemical Compositions and Oxygen Isotopes. Apparent I-Xe Cooling Rates of Chondrules Compared with Silicates from the Colomera Iron Meteorite. Chondrule Formation in Planetesimal Bow Shocks: Physical Processes in the Near Vicinity of the Planetesimal. Genetic Relationships Between Chondrules, Rims and Matrix. Chondrite Fractionation was Cosmochemical; Chondrule Fractionation was Geochemical. Chondrule Formation and Accretion of Chondrite Parent Bodies: Environmental Constraints. Amoeboid Olivine Aggregates from the Semarkona LL3.0 Chondrite. The Evolution of Solids in Proto-Planetary Disks. New Nickel Vapor Pressure Measurements: Possible Implications for Nebular Condensates. Chemical, Mineralogical and Isotopic Properties of Chondrules: Clues to Their Origin. Maximal Size of Chondrules in Shock-Wave Heating Model: Stripping of Liquid Surface in Hypersonic Rarefied Gas Flow. The Nature and Origin of Interplanetary Dust: High Temperature Components. Refractory Relic Components in Chondrules from Ordinary Chondrites. Constraints on the Origin of Chondrules and CAIs from Short-lived and Long-lived Radionuclides. The Genetic Relationship Between Refractory Inclusions and Chondrules. Contemporaneous Chondrule Formation Between Ordinary and Carbonaceous Chondrites. Chondrules and Isolated Grains in the Fountain Hills Bencubbinite. Implications of Chondrule Formation in a Gas of Solar Composition. Implications of Meteoritic Cl-36 Abundance for the Origin of Short-lived Radionuclides in the Early Solar System. Size Sorting and the Chondrule Size Spectrum. Comparative Study of Refractory Inclusions from Different Groups of Chondrites. In Situ Investigation of Mg Isotope Distributions in an Allende CAI by Combined LA-ICPMS and SIMS Analyses Photochemical Speciation of Oxygen Isotopes in the Solar Nebula.

2004-01-01

191

Thermal metamorphism of CI and CM carbonaceous chondrites - An internal heating model  

SciTech Connect

Infrared diffuse reflectance spectra were measured for several thermally metamorphosed carbonaceous chondrites with CI-CM affinities which were recently found from Antarctica. Compared with other CI or CM carbonaceous chondrites, these Antarctic carbonaceous chondrites show weaker absorption bands near 3 microns due to hydrous minerals, and weaker absorption bands near 6.9 microns due to carbonates, interpreted as thermal metamorphic features. These absorption bands also disappear in the spectra of samples of the Murchison (CM) carbonaceous chondrite heated above 500 C, implying that the metamorphic temperatures of the Antarctic carbonaceous chondrites considered here were higher than about 500 C. Model calculations were performed to study thermal metamorphism of carbonaceous chondrites in a parent body internally heated by the decay of the extinct nuclide Al-26. The maximum temperature of the interior of a body more than 20 km in radius is 500-700 C for the bulk Al contents of CI and CM cabonaceous chondrites, assuming a ratio of Al-26/Al-27 = 5 {times} 10 to the -6th which has been previously proposed for an ordinary-chondrite parent body. The metamorphic temperatures experienced by the Antarctic carbonaceous chondrites considered here may be attainable by an internally heated body with an Al-26/Al-27 ratio similar to that inferred for an ordinary-chondrite parent body. 30 refs.

Miyamoto, M. (Tokyo, University (Japan))

1991-06-01

192

Chemical and physical studies of type 3 chondrites - VIII: Thermoluminescence and metamorphism in the CO chondrites  

SciTech Connect

The thermoluminescence properties of nine CO chondrites have been measured. With the exception of Colony and Allan Hills A77307 (ALHA 77307), whose maximum induced TL emission is at approximately 350{degree}C, CO chondrites exhibit two TL peaks, one at 124 {plus minus} 7{degree}C (130{degree}C peak) and one at 252 {plus minus} 7{degree}C (250{degree}C peak). The 130{degree}C peak shows a 100-fold range in TL sensitivity and correlates with various metamorphism-related phenomena, such as silicate heterogeneity, metal composition and McSween's metamorphic subtypes. The peak at 250{degree}C does not show these correlations and, Colony excepted, varies little throughout the class. Mineral separation experiments, and a series of annealing experiments on Isna, suggest that the TL properties for CO chondrites reflect the presence of feldspar in two forms, (1) a form produced during metamorphism, and analogous to the dominant form of feldspar in type 3 ordinary chondrites, and (2) a primary, metamorphism-independent form, perhaps associated with the amoeboid inclusions. If this interpretation is correct, then the CO chondrites have not experienced temperatures above the order/disorder temperature for feldspar (500-600{degree}C) and they cooled more slowly than comparable type 3 ordinary chondrites. Colony and ALHA 77307 have atypical TL properties, including very low TL sensitivity, suggesting that phosphors other than feldspar are important. They have apparently experienced less metamorphism than the others, and may have also been aqueously altered.

Keck, B.D.; Sears, D.W.G. (Univ. of Arkansas, Fayetteville (USA))

1987-11-01

193

Chondrite chronology by initial Sr-87/Sr-86 in phosphates?  

NASA Technical Reports Server (NTRS)

New data are presented on Rb-Sr isotope analyses of phosphates from nine ordinary chondrites, including accurate identification of initial Sr-87/Sr-86. The initial Sr-87/Sr-86 ratios found in this study were generally significantly higher than the more primitive initial Sr-87/Sr-86 ratios inferred for carbonaceous chondrite refractory inclusions, basaltic achondrites, or bulk ordinary chondrites. Such elevation of initial Sr-87/Sr-86 is generally considered to reflect isotopic redistribution during metamorphism. However, in this study, no evident correlation was found between the phosphate initial Sr-87/Sr-86 compositions and the metamorphic grade. Two possible alternative hypotheses for high initial Sr-87/Sr-86 ratios are considered.

Podosek, Frank A.; Brannon, Joyce C.

1991-01-01

194

The Olton, Texas, H chondrite regolith breccia - Paired with Dimmitt  

NASA Technical Reports Server (NTRS)

The Olton ordinary chondrites (two stones found in 1948) are H group, solar wind-bearing regolith breccias. The proximity of the recovery site to the Dimmitt strewnfield, and the similarity in texture, composition, noble gas contents and isotopic ratios to Dimmitt indicate that Olton is paired with Dimmitt.

Keil, Klaus; Ehlmann, A. J.; Wieler, Rainer

1990-01-01

195

Chemical Fractionation in Chondrites by Aerodynamic Sorting of Chondritic Materials  

NASA Astrophysics Data System (ADS)

Aerodynamic sorting in the nebula has been invoked directly or indirectly to account for the size variations of chondrules in different groups [1], associated size variations of chondrules and metal spherules in a CR chondrite [2], and variations in the oxygen isotopic compositions of H-L-LL chondrules and whole rocks [3]. We suggest that aerodynamic sorting processes affected the relative abundances of all chondritic ingredients and were therefore a major source of chemical differences between asteroids and perhaps planets [4]. For chondrites that were derived from the same batch of chondritic ingredients, e.g., ordinary chondrites, aerodynamic sorting may account for all chemical differences [5]. Matrix Material: Matrix material accretes into planetesimals largely in the form of rims on all particles rather than as individual dust grains [6,7]. Aerodynamic sorting of particles does not cause significant chemical variation in bulk matrix abundance or composition because rim composition is not correlated with particle composition [6,7], and rim thickness apparently correlates with particle radius [7]. Metal-Troilite Spherules: There are at least two metal-troilite components: poorly characterized spherules that are probably ejected during chondrule formation and fine-grained material associated with matrix rims. Skinner and Leenhouts [2] suggest that aerodynamic sorting of the spherules was a potent metal-silicate fractionation process. Our preliminary data for metal-troilite spherules in Lance (CO3) support their model. Spherules and chondrules are closer in size than in the CR chondrite they studied, but this may result from the very much higher troilite abundance in CO chondrites, which produced a smaller density difference between chondrules and spherules. But we cannot exclude the possibility that the size distribution of metallic spherules was controlled by that of the chondrules from which they were ejected and not by aerodynamic sorting of spherules. Matrix rims on spherules preclude the possibility that the spherules were released from chondrules during parent body impacts. Refractory Inclusions: The similarity in the order of chondrule and CAI sizes suggests a common size sorting process. Chondrules decrease in mean size in the order CV (1.0 mm) > CM (0.3 mm) > CO (0.15 mm) > ALH85085 (0.02 mm) [8]. Refractory inclusions decrease in size in the order CV (commonly >1 cm) > CO > CM (<1 mm) > ALH85085 (0.03 mm) [8,9]. Although many chondrules and CAIs in ALH85085 are broken, mean sizes were not much bigger originally as the grain sizes of fragments are comparable to those of complete objects [6]. Size sorting must postdate CAI formation as these size relationships hold for all kinds of CAI that formed in very different ways. Density differences cannot account for the apparently larger mean size of CAIs relative to chondrules in CV3 chondrites. Model: We suggest that a common aerodynamic sorting process may have affected all ingredients during their fall toward the proto-Sun through nebula gas. This sorting probably occurred after chondrule formation and rim acquisition in a turbulent environment [7] and ended when planetesimal accretion halted inward motion. Intermittent turbulence may have cleared the midplane of chondritic materials to allow episodic accretion of distinctly different batches of material. This model and runaway accretion of planetesimals accounts for the correlation of chondrule size with metamorphic type in CO3 chondrites [8] and provides a mechanism for understanding chemical and isotopic variations within asteroids such as the ureilite parent body. References: [1] Rubin A. E. and Keil K. (1984) Meteoritics, 19, 135-143. [2] Skinner W. R. and Leenhouts J. M. (1993) LPSC XXIV, 1315-1316. [3] Clayton R. N. et al. (1991) GCA, 55, 2317-2337. [4] Scott E. R. D. and Newsom H. E. (1989) Z. Naturforsch., 44a, 924-934. [5] Haack H. and Scott E. R. D. (1993), this volume. [6] Scott E. R. D. et al. (1984) GCA, 48, 1741-1757. [7] Metzler K. et al. (1992) GCA, 56, 2873-2987.

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

1993-07-01

196

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

197

Young Pb-Isotopic Ages of Chondrules in CB Carbonaceous Chondrites  

NASA Technical Reports Server (NTRS)

CB (Bencubbin-type) carbonaceous chondrites differ in many ways from more familiar CV and CO carbonaceous chondrites and from ordinary chondrites. CB chondrites are very rich in Fe-Ni metal (50-70 vol%) and contain magnesian silicates mainly as angular to sub-rounded clasts (or chondrules) with barred olivine (BO) or cryptocrystalline (CC) textures. Both metal and silicates appear to have formed by condensation. The sizes of silicate clasts vary greatly between the two subgroups of CB chondrites: large (up to one cm) in CB(sub a) chondrites, and typically to much much less than 1 mm in CB(sub b) chondrites. The compositional and mineralogical differences between these subgroups and between the CB(sub s) and other types of chondrites suggest different environment and possibly different timing of chondrule formation. In order to constrain the timing of chondrule forming processes in CB(sub s) and understand genetic relationship between their subgroups, we have determined Pb-isotopic ages of silicate material from the CB(sub a) chondrite Gujba and CB(sub b) chondrite Hammadah al Hamra 237 (HH237 hereafter).

Amelin, Yuri; Krot, Alexander N.

2005-01-01

198

The Parsa enstatite chondrite  

NASA Astrophysics Data System (ADS)

The two meteoritic stones weighing about 600 and 200 g which fell at Parsa and Paru, India, respectively on April 14, 1942 and which have been classified as enstatite chondrites are discussed. Parsa represents the eighth member of the EH (high-Fe) group of enstatite chondrites, and the sixth observed fall. In most compositional aspects it is a typical EH chondrite, although its mineralogical composition and possibly its elemental abundance pattern have been altered by terrestrial weathering. In addition, the presence of a large (4 cm) enstatite inclusion was observed, and a cosmic ray exposure age of 17 million years, which is twice as high as that of any other EH enstatite chondrite, has been reported.

Bhandari, N.; Shah, V. B.; Wasson, J. T.

1980-09-01

199

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

200

Chemical and physical studies of type 3 chondrites 12: The metamorphic history of CV chondrites and their components  

NASA Technical Reports Server (NTRS)

The induced thermoluminescence (TL) properties of 16 CV and CV-related chondrites, four CK chondrites and Renazzo (CR2) have been measured in order to investigate their metamorphic history. The petrographic, mineralogical and bulk compositional differences among the CV chondrites indicate that the TL sensitivity of the approximately 130 C TL peak is reflecting the abundance of ordered feldspar, especially in chondrule mesostasis, which in turn reflects parent-body metamorphism. The TL properties of 18 samples of homogenized Allende powder heated at a variety of times and temperatures, and cathodoluminescence mosaics of Axtell and Coolidge, showed results consistent with this conclusion. Five refractory inclusions from Allende, and separates from those inclusions, were also examined and yielded trends reflecting variations in mineralogy indicative of high peak temperatures (either metamorphic or igneous) and fairly rapid cooling. The CK chondrites are unique among metamorphosed chondrites in showing no detectable induced TL, which is consistent with literature data that suggests very unusual feldspar in these meteorites. Using TL sensitivity and several mineral systems and allowing for the differences in the oxidized and reduced subgroups, the CV and CV-related meteorites can be divided into petrologic types analogous to those of the ordinary and CO type 3 chondrites. Axtell, Kaba, Leoville, Bali, Arch and ALHA81003 are type 3.0-3.1, while ALH84018, Efremovka, Grosnaja, Allende and Vigarano are type 3.2-3.3 and Coolidge and Loongana 001 are type 3.8. Mokoia is probably a breccia with regions ranging in petrologic type from 3.0 to 3.2. Renazzo often plots at the end of the reduced and oxidized CV chondrite trends, even when those trends diverge, suggesting that in many respects it resembles the unmetamorphosed precursors of the CV chondrites. The low-petrographic types and low-TL peak temperatures of all samples, including the CV3.8 chondrites, indicates metamorphism in the stability field of low feldspar (i.e., less than 800 C) and a metamorphic history similar to that of the CO chondrites but unlike that of the ordinary chondrites.

Guimon, R. Kyle; Symes, Steven J. K.; Sears, Derek W. G.

1995-01-01

201

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

202

Chondrites as samples of differentiated planetesimals  

NASA Astrophysics Data System (ADS)

Chondritic meteorites are unmelted, variably metamorphosed samples of the earliest solids of the solar system. A recent paleomagnetic study of CV chondrites suggests that their parent body was internally differentiated and produced a core magnetic dynamo (Carporzen et al., submitted, and this session). Here we show that a parent body that accreted to >250 km in radius by ~1.7 Ma after the formation of CAIs could retain a solid undifferentiated crust overlying a differentiated interior, and would be consistent with formational and evolutionary constraints on the CV parent body. Further, this body could have produced a magnetic field lasting more than 10 Ma. CV chondritic meteorites contain the oldest known solids: calcium-aluminum-rich inclusions (CAIs). The variety of metamorphic textures in ordinary chondrites motivated the "onion shell" model in which chondrites originated at varying depths within a parent body heated primarily by the short-lived radioisotope 26Al, with the highest metamorphic grade originating nearest the center. The large abundances and sizes of CAIs in CV chondrites have long suggested an early parent body accretion age. New Pb-Pb and Al-Mg ages of chondrules in CVs are consistent with the CV parent body having largely completed accretion by the youngest chondrule age of ~1.7-3 Ma. The CV chondrite parent body likely reached peak metamorphic temperatures around 7 to 10 Ma after CAIs, based on I-Xe chronometry for Allende and Mn-Cr chronometry for Mokoia. Bodies that accreted to more than >~20 km radius before ~1.3 to 3 Ma after the formation of CAIs likely contained sufficient 26Al to melt internally from the insulated cumulative effects of radiogenic heating. These early-accreting bodies will melt from the interior out, sometimes forming an interior magma ocean under a solid, conductive, undifferentiated shell. This shell would consist of the same chondritic material that made up the bulk accreting body before melting began. The presence of talc and the absence of serpentine indicate peak temperatures of ~300-350°C. Subsequent to the analysis of natural remanent magnetization in angrites, Carporzen et al. (2009, submitted, and this conference) have described how unidirectional magnetization in Allende is consistent with a long-lived internally generated field. The metamorphic, magnetic, and exposure age data collectively indicate a new model for the CV chondrite parent body in which interior melting is incomplete and the magma ocean remains capped by an undifferentiated chondritic shell. This conductive lid insulates the internal magma ocean, slowing its cooling and solidification by orders of magnitude while still allowing sufficient heat flux out of the core to produce a dynamo with intensities consistent with magnetization in Allende. Materials in the undifferentiated lid experienced varying metamorphic conditions. Bodies that are internally differentiated in the manner described here may well exist undetected in the asteroid belt. The shapes and masses of the two largest asteroids, 1 Ceres and 2 Pallas, can be consistent with differentiated interiors, conceivably with small iron cores with hydrated silicate or ice-silicate mantles. Other asteroids may have lost their hydrostatic shapes through later impacts, and their surfaces may never have been covered with erupted basalt; surfaces of these bodies may have remained chondritic throughout this process. Such surfaces will therefore be irregular, space-weathered primitive material, perhaps with highly altered or even differentiated material at the bottoms of the largest craters and in crater ejecta. This scenario can explain the mismatch between the enormous diversity (> 130) of parent bodies represented by achondrites and the paucity (< 10) of basaltic asteroids.

Elkins-Tanton, Linda; Weiss, Benjamin P.; Zuber, Maria T.

2010-05-01

203

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

204

Rhenium-osmium isotope systematics of carbonaceous chondrites.  

PubMed

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 (187)Re/(186)Os and (l87)Os/(l86)Os 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. PMID:17799187

Walker, R J; Morgan, J W

1989-01-27

205

Crustal structure and igneous processes in a chondritic Io  

NASA Technical Reports Server (NTRS)

Liquid sulfur can form when metal-free C1 or C2 chondrites are heated. It may be obtained either by direct melting of native sulfur in disequilibrated C1 or C2 chondrites or by incongruent melting of pyrite and other sulfides in thermodynamically equilibrated rocks of the same composition. Hence, Lewis considered C2 chondrites to be the best meteoritic analog for Io's bulk composition. Metal-bearing C3 and ordinary chondrites are too chemically reduced to yield liquid sulfur and are not thought to represent plausible analogs of Io's bulk composition. An important aspect of Lewis' work is that CaSO4 and MgSO4 are predicted to be important in Io. Real C1 and C2 chondrites contain averages of, respectively, 11 percent and 3 percent by mass of salts (plus water of hydration). The most abundant chondritic salts are magnesium and calcium sulfates, but other important components include sulfates of sodium, potassium, and nickel and carbonates of magnesium, calcium, and iron. It is widely accepted that chondritic salts are formed by low-temperature aqueous alteration. Even if Io originally did not contain salts, it is likely that aqueous alteration would have yielded several percent sulfates and carbonates. In any event, Io probably contains sulfates and carbonates. This report presents the results of a model of differentiation of a simplified C2 chondrite-like composition that includes 1.92 percent MgSO4, 0.56 percent CaSO4, 0.53 percent CaCO3, and 0.094 percent elemental sulfur. The temperature of the model is gradually increased; ensuing fractional melting results in these components extruding or intruding at gravitationally stable levels in Io's crust. Relevant phase equilibria were reviewed. A deficiency of high-pressure phase equilibria renders the present model qualitative.

Kargel, J. S.

1993-01-01

206

In-Situ Oxygen Isotopic Composition of Tagish Lake: An Ungrouped Type 2 Carbonaceous Chondrite  

NASA Technical Reports Server (NTRS)

We have measured the oxygen isotopic composition of several components of Tagish Lake by ion microprobe. This meteorite constitutes the best preserved sample of C2 matter presently available for study. It presents two different lithologies (carbonate-poor and -rich) which have fairly comparable oxygen isotopic composition, with regard to both the primary or secondary minerals. For the olivine and pyroxene grains, their delta O-18 values range from - 10.5% to + 7.4% in the carbonate-poor lithology, with a mean Delta O-17 value of - 3.7 2.4%. In the carbonate-rich lithology, delta O-18 varies from - 7.9% to + 3.3%, and the mean Delta O-17 value is - 4.7 +/- 1.4%. Olivine inclusions (Fo(sub >99)) with extreme O-16-enrichment were found in both lithologies: delta O-18 = - 46.1 %, delta O-187= - 48.3% and delta O-18 = - 40.6%, delta O-17 = - 41.2% in the carbonate-rich lithology; delta O-18 = - 41.5%, delta O-17 = -43.4%0 in the carbonate-poor lithology. Anhydrous minerals in the carbonate-poor lithology are slightly more O-16-rich than in the carbonate-rich one. Four low-iron manganese-rich (LIME) olivine grains do not have an oxygen isotopic composition distinct from the other "normal" olivines. The phyllosilicate matrix presents the same range of oxygen isotopic compositions in both lithologies: delta O-18 from approximately 11 % to approximately 6%, with an average Delta. O-17 approximately 0%. Because the bulk Tagish Lake oxygen isotopic composition given by Brown et al. is on the high end of our matrix analyses, we assume that this "bulk Tagish Lake" composition probably only represents that of the carbonate-rich lithology. Calcium carbonates have delta O-18 values up to 35%, with Delta O-17 approximately 0.5%0. Magnetite grains present very high Delta O-17 values approximately + 3.4%0 +/- 1.2%. Given our analytical uncertainties and our limited carbonate data, the matrix and the carbonate seem to have formed in isotopic equilibrium. In that case, their large isotopic fractionation would argue for a low temperature (CM-like, T approximately 0 deg) formation. Magnetite probably formed during a separate event. Tagish Lake magnetite data is surprisingly compatible with that of R-chondrites and unequilibrated ordinary (LL3) chondrites. Our oxygen isotope data strongly supports the hypothesis of a single precursor for both lithologies. Drastic mineralogical changes between the two lithologies not being accompanied with isotopic fractionation seem compatible with the alteration model presented by Young et aI. Tagish Lake probably represents the first well preserved large sample of the C2 matter that dominates interplanetary matter since the formation of the solar system.

Zolensky, Michael E.; Engrand, Cecile; Gounelle, Matthieu; Zolensky, Mike E.

2001-01-01

207

Stable Isotope Fractionation of Cr in Carbonaceous and Ordinary Chondrites  

Microsoft Academic Search

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

F. Moynier; B. Jacobsen; Q. Yin

2006-01-01

208

Artificial Weathering of the H5 Ordinary Chondrite Fall, Allegan  

NASA Astrophysics Data System (ADS)

Introduction: We conducted experiments to induce weathering in the Allegan H5 fall by immersion in aerated water, using: (i) de-ionized ice water - experiment A (ii) de-ionized water at room temperature - experiment B (iii) water at room temperature with a 0.2 molar solution of NaCl - experiment C. Water was changed at regular intervals. In each case, oxidation as a function of time was monitored by removing the sample and measuring the production of ferric iron components using 57Fe Mossbauer spectroscopy. In an earlier study [1], weathering was induced in the Noblesville H4/H6 fall by aerated ice water, with the unexpected result that Fe-Ni metal was relatively resistant to weathering. It was to test this finding, and hypotheses resulting from our own earlier studies [2], that these experiments were initiated. Results: In experiment A, after an initial period of rapid oxidation lasting 15-20 days, production of ferric species proceeded in a linear fashion. The bulk of the weathering products were observed as paramagnetic Fe^3+, which at 77K was resolved as principally akaganeite. Magnetically ordered iron oxides/oxyhydroxides (maghemite, magnetite and goethite) were observed after 93 days. The primary Fe2+/-containing phases (olivine, pyroxene and troilite) weathered at similar rates, whilst Fe-Ni was initially preferentially weathered. For both the B and C experiments, magnetically ordered iron oxides were observed within the first 12 days of weathering, however, a higher proportion of paramagnetic Fe^3+ was seen in C than B. Discussion: The observation of increased akaganeite in C vs. B is consistent with a situation in which increased supply of Cl-ions enhances the thermodynamic range over which akaganeite is stable. The lower proportion of paramagnetic Fe^3+ observed in the room temperature experiments, compared to that seen at 0 degrees C (experiment A), suggests that higher temperatures enhance the degradation of akaganeite to maghemite and goethite. This agrees with observations of [3] and [4]. The fact that Fe-Ni was not preferentially weathered in these experiments may be because the water was changed at regular intervals: Fisher and Bums (1992) proposed that acifification of porewaters by dissolution of FeS led to accelerated chemical weathering of olivine and pyroxene. The presence of akaganeite in samples weathered in de-ionized water is surprising as the accepted wisdom is that Cl- in tunnel sites is essential for the stability of this phase [5], [6], [7]. Akaganeite may contain 3.2-6.9 wt% chlorine [6], indicating around 1 wt% chlorine in our sample. Allegan has a chlorine content of only 9-14 ppm [8] and the water in which the sample was weathered was chlorine-free. Therefore, either chlorine was introduced by contamination; or akaganeite may be stable without Cl- in tunnel sites, possibly substituting OH- In this second hypothesis, it is suggested that Cl- has an affinity to akaganeite, but is not mandatory for stability. It indicates that akaganeite may be a true iron oxyhydroxide and that a review of its chemical formula may be required. References: [1] Fisher D. S. and Burns R. G. (1992) LPS XXIII 369-370. [2] Bland P. A. et al. (1995) LPI Tech. Rpt., in press. [3] Buchwald V. F. (1989) LPI Tech. Rpt. 90-01, 24-26. [4] Buchwald V. F. and Clarke R. S. Jr. (1989) Am. Mineral., 74, 656-667. [5] Chambaere D. G. and DeGrave E. (1984) Phys. Stat. Sol., 83, 93-102. [6] Johnston J. H. and Logan N. E. (1979) J. Chem. Soc., 13-16. [7] Post J. E. and Buchwald V. F. (1991) Am. Mineral., 76, 272-277. [8] Tarter J. G. et al. (1980) Meteoritics, 15, 373-374.

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

1995-09-01

209

Xenon in chondritic metal.  

NASA Astrophysics Data System (ADS)

The authors report xenon isotopic abundances observed in the stepwise release of noble gases in a high-purity metal separate of the Forest Vale (H4) chondrite. They identify a 244Pu-derived fission component, due to recoils into the metal, a cosmic-ray-produced spallation component and a new trapped component which is isotopically distinct from known solar system reservoirs. The authors discuss several processes which might account for observed isotopic shifts and conclude that the signature of FVM xenon may provide clues regarding the origin of chondritic metal.

Marti, K.; Kim, J. S.; Lavielle, B.; Pellas, P.; Perron, C.

1989-10-01

210

Heterogeneities in the solar nebula. [oxygen isotopic composition in carbonaceous chondrites  

NASA Technical Reports Server (NTRS)

Oxygen isotopic compositions of the high-temperatue phases in carbonaceous chondrites define a mixing line with an O-16 rich component and show little superimposed chemical isotope fractionation. Within a single inclusion in Allende, variations of delta O-18 and delta O-17 of 39% are found. The ordinary chondrites are slightly displaced from the terrestrial fractionation trend, implying that at least 0.2% of the oxygen in terrestrial rocks was derived from the O-16 rich component.

Clayton, R.; Grossman, L.; Mayeda, T. K.; Onuma, N.

1974-01-01

211

Chondrites - Initial strontium-87/strontium-86 ratios and the early history of the solar system.  

NASA Technical Reports Server (NTRS)

A sodium-poor, calcium-rich inclusion in the carbonaceous chondrite Allende had a Sr-87/Sr-86 ratio at the time of its formation of 0.69880, as low a value as that found in any other meteorite. The higher Sr-87/Sr-86 ratios found in ordinary chondrites indicate that their formation or isotopic equilibration occurred tens of millions of years later.

Wetherill, G. W.; Mark, R.; Lee-Hu, C.

1973-01-01

212

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

213

The chlorine isotope composition of chondrites and Earth  

NASA Astrophysics Data System (ADS)

The chlorine isotope composition of chondrites provides information about isotopic reservoirs that were present in the solar nebula and the effects of secondary processes on their isotopic composition. We analyzed chlorine isotope ratios of 19 chondrites that included both unaltered (type 3) and altered (types 1,2 and 4-6) chondrites from the carbonaceous, ordinary, and enstatite classes as well as an enstatite chondrite impact melt breccia and a partial melt residue. Chlorine isotope compositions (?37Cl, ‰ vs. SMOC) and 1? uncertainty () are as follows (excluding melt residue and anomalous Parnallee): Material Carbonaceous chondrites Ordinary chondrites Enstatite chondrites Structurally-bound Cl -0.3(0.6) -0.4(0.6) 0.4(0.4) Water-soluble Cl -0.9(0.9) 0.3(2.1) 0.4(0.6) Bulk (total) Cl -0.2(0.6) 0.4(0.7) 0.4(0.3) Petrologic type 3 chondrites are the least equilibrated and are those most likely to retain primary nebular signatures. Type 3 carbonaceous chondrites have bulk ?37Cl values that average -0.3 ± 0.5‰ and structurally-bound Cl values of -0.3 ± 0.3‰. These values are indistinguishable from the ?37Cl values of the bulk Earth (-0.2‰) and close to the lowest measured value of the Moon (-0.7‰). From this similarity, we conclude that the inner regions of the early solar nebula had a homogeneous chlorine isotope reservoir. For samples that have undergone secondary processing, ?37Clbulk values range from -1.2‰ to 0.8‰ for metamorphosed samples (average 0.0‰) and -0.3‰ to 0.3‰ (average 0.1‰) for aqueously-altered samples (Orgueil, Ivuna, Murray, and Murchison). Most of the data can be explained in terms of fractionation processes similar to those that occur on the Earth, such as interaction with pore waters. No apparent correlations exist with Cl concentration data. Ordinary chondrites have the lowest and most restricted range of Cl concentration, but the largest range in ?37Cl values. Carbonaceous and enstatite chondrites have wide ranges of Cl concentration and more restricted ranges of ?37Cl values. We have analyzed additional terrestrial mantle-derived materials of the Earth in order to better constrain the ?37Cl value of this reservoir and compare with the chondrite data. The mantle data cluster at -0.3‰ to -0.1‰, and support the idea that the most pristine type C chondrites and the bulk Earth have the same ?37Cl value, indicating that no fractionation by evaporative processes occurred during the formation of the Earth. The discrepancy between our data and previously published results is discussed.

Sharp, Z. D.; Mercer, J. A.; Jones, R. H.; Brearley, A. J.; Selverstone, J.; Bekker, A.; Stachel, T.

2013-04-01

214

Structure, composition, and location of organic matter in the enstatite chondrite Sahara 97096 (EH3)  

NASA Astrophysics Data System (ADS)

The insoluble organic matter (IOM) of an unequilibrated enstatite chondrite Sahara (SAH) 97096 has been investigated using a battery of analytical techniques. As the enstatite chondrites are thought to have formed in a reduced environment at higher temperatures than carbonaceous chondrites, they constitute an interesting comparative material to test the heterogeneities of the IOM in the solar system and to constrain the processes that could affect IOM during solar system evolution. The SAH 97096 IOM is found in situ: as submicrometer grains in the network of fine-grained matrix occurring mostly around chondrules and as inclusions in metallic nodules, where the carbonaceous matter appears to be more graphitized. IOM in these two settings has very similar ?15N and ?13C; this supports the idea that graphitized inclusions in metal could be formed by metal catalytic graphitization of matrix IOM. A detailed comparison between the IOM extracted from a fresh part and a terrestrially weathered part of SAH 97096 shows the similarity between both IOM samples in spite of the high degree of mineral alteration in the latter. The isolated IOM exhibits a heterogeneous polyaromatic macromolecular structure, sometimes highly graphitized, without any detectable free radicals and deuterium-heterogeneity and having mean H- and N-isotopic compositions in the range of values observed for carbonaceous chondrites. It contains some submicrometer-sized areas highly enriched in 15N (?15N up to 1600‰). These observations reinforce the idea that the IOM found in carbonaceous chondrites is a common component widespread in the solar system. Most of the features of SAH 97096 IOM could be explained by the thermal modification of this main component.

Piani, Laurette; Robert, François; Beyssac, Olivier; Binet, Laurent; Bourot-Denise, Michèle; Derenne, Sylvie; Le Guillou, Corentin; Marrocchi, Yves; Mostefaoui, Smail; Rouzaud, Jean-Noël.; Thomen, Aurélien

2012-01-01

215

Chemical Variations Among L-Chondrites--IV. Analyses, with Petrographic Notes, of 13 L-group and 3 LL-group Chondrites  

NASA Astrophysics Data System (ADS)

We review our procedures for selecting, preparing and analyzing meteorite samples, present new analyses of 16 ordinary chondrites, and discuss variations of Fe, S and Si in the L-group. A tendency for Fe/Mg, S/Mg and Si/Mg to be low in L chondrites of facies d to f testifies that post-metamorphic shock melting played a significant role in the chemical diversification of the L-group. However, these ratios also vary widely and sympathetically in melt-free chondrites, indicating that much of the L-group's chemical variation arose prior to thermal metamorphism and is in that sense primary. If all L chondrites come from one parent body, type-correlated chemical trends suggest: 1) that the body had a traditional "onion skin" structure, with metamorphic intensity increasing with depth; and 2) that it formed from material that became more homogeneous, slightly poorer in iron, and significantly richer in sulfur as accretion proceeded.

Jarosewich, E.; Dodd, R. T.

1985-03-01

216

Watson 002--The First CK/Type 3 Chondrite  

NASA Astrophysics Data System (ADS)

The CK chondrites studied so far are all of petrologic types 4-6. In 1991 Watson 002, a petrologic type 3 carbonaceous chondrite, was found in the Nullarbor Region, South Australia and was classified as "CK3 anomalous" [1]. The supplement "anomalous" was added because it shows some features that do not fit into the mineralogical [2] or into the bulk chemical characteristics [3] of the CK chondrite group. Here we report on the petrography and mineralogy as well as on the bulk chemistry and on the oxygen isotopic composition of Watson 002. Petrograpy and mineralogy: The piece we studied has a 3-5 mm wide margin that shows a less compacted texture, which seems to be caused by terrestrial weathering. Watson 002 has a chondritic texture characterized by abundant chondrules, inclusions, and fragments embedded in a matrix. Matrix is the most comprehensive textural unit making up 70 vol% of the meteorite. Chondrules, inclusions, and fragments (grain size >100 micrometers) are present in modal portions of about 10 vol% each determined by point counting methods. The mean apparent diameter of 43 detected chondrules is 870 +- 380 micrometers ranging from 160 to 2100 micrometers. The mineral chemistry of olivines, pyroxenes, and plagioclases is comparable to other CK chondrites. Olivines and pyroxenes in some chondrules and fragments are not equilibrated. Almost pure forsterites (FaO.3) and enstatites (Fs1.6) occur in the core. Olivines at the edge contain ~20 mol% Fa. Like in other CK chondrites chondrules are frequently rimmed by magnetite. Matrix olivines have a mean Fa content of 34.4 mol% (range 31-38 mol%), and contain an average of 0.35 wt% NiO. Pyroxenes are less equilibrated than olivines; the composition of the clinopyroxenes vary from 6.7 to 19.9 mol% Fs. Two low-Ca pyroxenes with Fs 23.1 and 24.4 were found. Plagioclases occur with An contents from 26.8 to 50.1 mol%. Unlike the other known CK chondrites, Watson 002 contains abundant CAIs that consist of An-rich plagioclase, olivine, and green pleonast-spinel as the main phases. Similar spinel phases were reported from Maralinga 001 [4], and Karoonda [5]. The pleonasts are containing small amounts of Cr and Ti (0.25 wt% Cr203 and TiO2, respectively). Like in other CK chondrites the most abundant opaque phase is magnetite containing about 3.1 wt% Cr203 and 1 wt% TiO2, but we did not find the exsolution of ilmenite and spinel [6]. Sulfides are rare--only a few micron-sized pentlandite grains were found. Bulk chemistry and oxygen/isotopes: Watson 002 shows an unusual enrichment of Na, K, Ba, and light REE. Different INA-analyses of the core and the weathered margin show enrichment of these elements in the margin up to 50 x CI, whereas the core shows a "normal" CK pattern. Therefore we conclude that the high abundance of these elements in the weathered margin is due to terrestrial weathering. Besides that, there is also a strong enrichment of Ca (4.7 x CI) and Ti (~9 x CI) in the core, which can be explained in the case of Ca by the high abundance of CAls compared to other CK chondrites. Ti is predominantly located in magnetite and spinels. The oxygen isotopic composition differs from that of other CK chondrites. Previously analyzed CK chondrites plot within the range of the CO chondrites [7] but Watson plots at the uppermost end of the CV chondrite range and the lowermost end of the CM range. The oxygen isotopic ratios are delta^18O = +5.12 and delta^17O = -0.55. The composition of a single chondrite was found to be delta^18O = +0.56,delta^17O = -3.31, which lies within the range of CV chondrules, and is unequilibrated with the bulk meteorite. References: [1] Wlotzka F. (1993) Met. Bull., 74, Meteoritics 28, 1. [2] Geiger T. and Bischoff A. (1991) Meteoritics, 26, 4, 337. [3] Kallemeyn et al. (1991) GCA, 55, 881-892. [4] Keller L. P. et al. (1991) Meteoritics, 27, 1, 87-91. [5] MacPherson G. J. and Delaney J. S. (1985) LPSC XVI, 515-516. [6] Geiger T. and Bischoff A. (1990) LPSC XXI, 409-410. [7] Clayton R. N. and Mayeda T. K. (1989) LPSC XX,

Geiger, T.; Spettel, B.; Clayton, R. N.; Mayeda, T. K.; Bischoff, A.

1993-07-01

217

Evidence against a chondritic Earth.  

PubMed

The (142)Nd/(144)Nd ratio of the Earth is greater than the solar ratio as inferred from chondritic meteorites, which challenges a fundamental assumption of modern geochemistry--that the composition of the silicate Earth is 'chondritic', meaning that it has refractory element ratios identical to those found in chondrites. The popular explanation for this and other paradoxes of mantle geochemistry, a hidden layer deep in the mantle enriched in incompatible elements, is inconsistent with the heat flux carried by mantle plumes. Either the matter from which the Earth formed was not chondritic, or the Earth has lost matter by collisional erosion in the later stages of planet formation. PMID:22460899

Campbell, Ian H; O'Neill, Hugh St C

2012-03-29

218

A search for spectral alteration effects in chondritic gas-rich breccias  

NASA Technical Reports Server (NTRS)

Several samples of gas-rich breccias were selected, including slabs of the Kapoeta howardite, the ordinary chondrites Dubrovnik, Cangas de Onis, and Dimmit. Numerous 0.8 to 2.5 micron reflection spectra of selected areas on sawed or broken surfaces were measured with the Planetary Geosciences Division spectrogoniometer. While these spectra are not directly comparable to those of powered samples, comparisons within the data set should reveal any spectral differences due to weathering. These results indicate that unknown regolith processes do not confer the ordinary-chondrite parent bodies with an altered layer exhibiting S-class spectral properties. This is consistent with recent interpretations of the new Q-class of asteroids as the ordinary-chondrite parent bodies. However, significant spectral effects do occur in asteroid regoliths: darkening and suppression of absorption bands in highly shocked material, as seen previously in the so-called black chondrites; and segregation of metal in large impact melt pools on chondritic asteroids, which may have achondritic spectra. Neither of these effects is likely to be significant in interpreting current integral-disk spectra, but should be searched for in spectral maps returned by future spacecraft.

Bell, J. F.; Keil, Klaus

1987-01-01

219

Temperature and Oxygen Fugacity Constraints on CK and R Chondrites and Implications for Water and Oxidation in the Early Solar System  

NASA Technical Reports Server (NTRS)

Recent chondritic meteorite finds in Antarctica have included CB, CH, CK and R chondrites, the latter two of which are among the most oxidized materials found in meteorite collections. In this study we present petrographic and mineralogic data for a suite of CK and R chondrites, and compare to previous studies of CK and R, as well as some CV chondrites. In particular we focus on the opaque minerals magnetite, chromite, sulfides, and metal as well as unusual silicates hornblende, biotite, and plagioclase. Several mineral thermometers and oxy-barometers are utilized to calculate temperatures and oxygen fugacities for these unusual meteorites compared to other more common chondrite groups. R and CK chondrites show lower equilibrium temperatures than ordinary chondrites, even though they are at similar petrologic grades (e.g., thermal type 6). Oxygen fugacity calculated for CV and R chondrites ranges from values near the iron-wustite (IW) oxygen buffer to near the fayalite-magnetite-quartz (FMQ) buffer. In comparison, the fO2 recorded by ilmenite-magnetite pairs from CK chondrites are much higher, from FMQ+3.1 to FMQ+5.2. The latter values are the highest recorded for materials in meteorites, and place some constraints on the formation conditions of these magnetite-bearing chondrites. Differences between mineralogic and O isotopic compositions of CK and R chondrites suggest two different oxidation mechanisms, which may be due to high and low water: rock ratios during metamorphism, or to different fluid compositions, or both.

Righter, K.; Neff, K. E.

2007-01-01

220

Chondrite thermal histories from Low-CA pyroxene microstructures: Autometamorphism versus prograde metamorphism revisited  

NASA Technical Reports Server (NTRS)

In order to constrain the thermal histories of chondritic meteorites, a detailed study of the microstructures of low-Ca pyroxenes produced experimentally and in types 4 and 5 ordinary chondrites was carried out. Cooling experiments on synthetic MgSiO3 at cooling rates between 2 and 10000 C/hr from the protopyroxene stability field into that of orthopyroxene (OPX) were performed and the products of these experiments were annealed for a variety of annealing times. There are clear microstructural differences between samples which were cooled and those which were subsequently annealed. A comparison of the microstructures observed in the experimental samples with those in H4-5 ordinary chondrites shows that they cannot have experienced a single stage cooling history, as proposed for the autometamorphism model.

Brearley, Adrian J.; Jones, Rhian H.; Papike, J. J.

1993-01-01

221

The fate of magmas in planetesimals and the retention of primitive chondritic crusts  

NASA Astrophysics Data System (ADS)

High abundances of short-lived radiogenic isotopes in the early solar system led to interior melting and differentiation on many of the first planetesimals. Petrologic, isotopic, and paleomagnetic evidence suggests that some differentiated planetesimals retained primitive chondritic material. The preservation of a cold chondritic lid depends on whether deep melts are able to ascend and breach the chondritic crust. We evaluate the likelihood of melt ascent on a range of chondritic parent bodies. We find that, due to the efficient ascent of free volatiles in the gas and supercritical fluid phases at temperatures still below the solidus for silicates and metals, mobile silicate melts on planetesimals were likely volatile-depleted. By calculating the densities of such melts, we show that silicate melts likely breached crusts of enstatite chondrite compositions but did not ascend in the CV and CM parent bodies. Ordinary chondrite melts represent an intermediate case. These predictions are consistent with paleomagnetic results from CV and CM chondrites as well as spectral observations of large E-type asteroids.

Fu, Roger R.; Elkins-Tanton, Linda T.

2014-03-01

222

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

223

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

224

Non-chondritic magnesium and the origins of the inner terrestrial planets  

Microsoft Academic Search

High-precision magnesium (Mg) isotope data obtained using a large geometry high resolution MC-ICPMS are reported for 9 carbonaceous and ordinary chondrites, 9 eucrites and diogenites generally considered to originate from Asteroid 4 Vesta, together with 4 martian meteorites, and a variety of terrestrial and lunar materials. The variation in Mg isotopic composition found for mafic and ultramafic rocks, mafic minerals

Uwe Wiechert; Alex N. Halliday

2007-01-01

225

The origin of chondrites: Metal-silicate separation experiments under microgravity conditions - II  

Microsoft Academic Search

In order to understand mechanical processes likely to be occurring on the surfaces of asteroids, we have performed experiments with mineral mixtures on NASA's KC-135 microgravity facility. The behavior of sand and iron filing mixtures, the sand and metal being in the proportions and with grain sizes of ordinary chondrite meteorites, was observed with digital cameras as gas was flowed

S. R. Moore; M. Franzen; P. H. Benoit; D. W. G. Sears; A. Holley; M. Meyer; R. Godsey; J. Czlapinski

2003-01-01

226

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

227

Effect of metamorphism on isolated olivine grains in CO3 chondrites  

NASA Technical Reports Server (NTRS)

The presence of a metamorphic sequence in the CO3 chondrite group has been shown previously to result in changes in properties of chondrule silicates. However, the role of isolated olivine grains during metamorphism of these chondrites has not been addressed. Isolated olivine grains in two metamorphosed CO3 chondrites, Lance and Isna, have been investigated in this study in order to assess the compositional properties of isolated olivine grains that may be attributable to metamorphism. Compositional changes in isolated olivines with increasing petrologic subtype are very similar to changes in chondrule olivines in the same chondrites. Olivine compositions from all occurrences (chondrules, isolated grains, and matrix) converge with increasing petrologic subtype. The degree of equilibration of minor elements is qualitatively related to the diffusion rate of each element in olivine, suggesting that diffusion-controlled processes are the most important processes responsible for compositional changes within the metamorphic sequence. The data are consistent with metamorphism taking place in a closed system on the CO3 chondrite parent body. Fe-poor olivine grains in metamorphosed chondrites are characterized by an Fe-rich rim, which is the result of diffusion of Fe into the grains from Fe-rich matrix. In some instances, 'complex', Fe-rich rims have been identified, which appear to have originated as igneous overgrowths and subsequently to have been overprinted by diffusion processes during metamorphism. Processes experienced by CO3 chondrites are more similar to those experienced by the ordinary chondrites than to those encountered by other carbonaceous chondrites, such as the CV3 group.

Jones, Rhian H.

1993-01-01

228

Studies of kamacite, perryite and schreibersite in E-chondrites and aubrites  

NASA Astrophysics Data System (ADS)

The bulk composition of metal (kamacite plus perryite) was determined in eleven E-chondrites and eight aubrites. The data are compatible with the subdivision of the E-chondrites into two groups (Yavnel, 1963; Anders, 1964), St Mark's and St Sauveur belonging to type I (Easton, 1985). The Ni content of kamacite plus perryite in Kota Kota (5.49 percent) is within the range covered by the remaining E-chondrites. Normative perryite constitutes 2.1 percent of Kota Kota and 2.7 percent of South Oman. The Ni content in the bulk metal of Aubres, Bishopville, Norton County and Pena Blanca Spring is about half the average Ni content in the metal of E-chondrites or the remaining aubrites (Bustee, Khor Temiki, Mayo Belwa and Shallowater). High Ga/Ni ratios distinguish the metal in E-chondrites and aubrites from that in ordinary chondrites. The composition of both bulk metal and individual grains in aubrites makes it unlikely that they represent residual metal trapped during magmatic differentation and/or fractional crystallization of E6 material. Compositional differences between metal grains strongly indicate that the aubrites are polymict breccias.

Easton, A. J.

1986-03-01

229

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

230

RAS Ordinary Meeting  

NASA Astrophysics Data System (ADS)

Here are summarized talks from the February and March RAS Ordinary Meetings. The February meeting also enjoyed the Eddington Lecture from Prof. Lisa Kewley (Australian National University) on galaxy evolution in 3D.

2014-08-01

231

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

232

Chondritic meteorites and the solar nebula  

NASA Astrophysics Data System (ADS)

Present understanding of the formation of chondritic meteorites in the solar nebula is reviewed, focusing on the nebular history of chondritic material. The stages in the history of chondritic material are summarized. The processing of chondrules and refractory inclusions is considered, and the relatedness of chondrules and refractory inclusions is discussed.

Wood, J. A.

233

Serpentine Nanotubes in CM Chondrites  

NASA Technical Reports Server (NTRS)

The CM chondrites are primitive meteorites that formed during the early solar system. Although they retain much of their original physical character, their matrices and fine-grained rims (FGRs) sustained aqueous alteration early in their histories [1- 3]. Serpentine-group minerals are abundant products of such alteration, and information regarding their structures, compositions, and spatial relationships is important for determining the reactions that produced them and the conditions under which they formed. Our recent work on FGRs and matrices of the CM chondrites has revealed new information on the structures and compositions of serpentine-group minerals [4,5] and has provided insights into the evolution of these primitive meteorites. Here we report on serpentine nanotubes from the Mighei and Murchison CM chondrites [6].

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

2004-01-01

234

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

NASA Technical Reports Server (NTRS)

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, Alan E.

1993-01-01

235

Porosity of Chondrites: Some Regularities  

NASA Astrophysics Data System (ADS)

Porosity depends on processes of formation and evolutionary history of composite materials of chondrites. The same processes may stipulate, in particular, the content of radiogenic 4He and 40Ar in the meteorites. We have analysed the distribution of porosity of H and L chondrites depending on ratio of T(sub)4/T(sub)40, (where T(sub)4 and T(sub)40 are U, Th-He and K-Ar gas-retention ages, respectively) for determination of possible interrelation between these features of meteorites.

Alexeev, V. A.; Kuyunko, N. S.

1996-03-01

236

Spectral alteration effects in chondritic gas-rich breccias - Implications for S-Class and Q-Class asteroids  

NASA Technical Reports Server (NTRS)

Reflection spectra were obtained from sawed or freshly broken surfaces of gas-rich matrix regions in a number of ordinary chondrites (Dubrovnik, Cangas de Onis, Olivenza, and Dimmitt) which are believed to represent lithified portions of asteroid regoliths that were once directly exposed to space, with the purpose of relating these chondrites to Class S asteroids. However, the observations did not detect curved red continuum characteristic for Class S asteroid spectra, suggesting that it is unlikely for any well-observed Class S asteroid to be a source of ordinary chondrites. It is suggested that the newly discovered spectral class 'Q', of which asteroid 1982 Apollo is the prototype, provides a viable alternative of a parent body.

Bell, Jeffrey F.; Keil, Klaus

1988-01-01

237

Refractory precursor components of Semarkona chondrules and the fractionation of refractory elements among chondrites  

NASA Astrophysics Data System (ADS)

Instrumental neutron activation analysis has been used to measure about 20 of the lithophile elements in 30 chondrules from the Semarkona chondrite. The amounts of oxidized iron were calculated from other compositional parameters, and Si concentrations are estimated from mass-balance considerations. It is suggested that the refractory component probably forms from fine grained materials that were able to equilibrate down to lower nebular temperatures. The chondrite matrix may have had an origin similar to that of the nonrefractory material. The low abundance of refractories and Mg in ordinary and enstatite chondrites was produced by the loss of materials having a higher refractory element/Mg ratio than that of the refractory element of the chondrules.

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

1983-04-01

238

Aqueous activity and sources of water on the chondrite parent asteroids  

NASA Astrophysics Data System (ADS)

Ages of aqueous alteration of asteroids: Most chondrite parent asteroids experienced aqueous alteration resulting in the formation of secondary minerals, including phyllosilicates, magnetite, Fe,Ni-sulfides, carbonates [(Ca,Mg,Fe,Mn)CO_3)], and fayalite [(Fe,Mn)_2SiO_4] [1]. Mineralogical observations and thermodynamic analysis suggest that the alteration of the various chondrite groups occurred under different physico-chemical conditions (temperature, redox conditions, pH, water/rock ratio). The chronology of aqueous activity on the chondrite parent asteroids can be inferred from ^{53}Mn-^{53}Cr dating (^{53}Mn decays to ^{53}Cr with half-life of 3.7 Myr) of aqueously-formed carbonates and fayalite measured with secondary ion mass-spectrometry. Recently reported ^{53}Mn-^{53}Cr ages of carbonates in CM [2,3], CI [4], CR [5] chondrites, and fayalite in CV [6], CO [6], and LL [7] chondrites indicate that aqueous alteration on the ordinary and carbonaceous chondrite (CC) parent asteroids occurred nearly contemporaneously, ˜3-5 Myr after formation of Ca,Al-rich inclusions (CAIs), the earliest Solar System solids dated [8]. Accretion ages of chondrite parent asteroids: Assuming uniform distribution of a short-lived radionuclide ^{26}Al (decays to ^{26}Mg with half-life of ˜0.7 Myr) in the disk at the canonical level (^{26}Al/^{27}Al ˜5×10^{-5}), the timing of aqueous alteration combined with estimates of peak metamorphic temperatures and thermal modelling of the ordinary and CC parent asteroids suggest that these bodies accreted ˜2-3 Myr after CAI formation [2,3,7]. The inferred accretion ages of ordinary and CC parent asteroids are generally consistent with average ^{26}Al-^{26}Mg ages (^{26}Al decays to ^{26}Mg with half-life of ˜0.7 Myr) of their chondrules [9,10], suggesting that chondrule formation was rapidly followed by accretion and that ^{26}Al was the major heating source of aqueous alteration and thermal metamorphism on these bodies. The observed variations in the degree of aqueous alteration within a chondrite group may indicate that water ices accreted heterogeneously or that there was a fluid flow in their parent bodies. Sources of water on the chondrite parent asteroids: According to the Grand Tack and Nice models, the extensively hydrated (C-, D-, and P-type) asteroids formed between and beyond the giant planets and were scattered into the main asteroid belt during a period of giant planet migration [11,12]. Bulk D/H ratio of chondrite water ices can potentially be used for testing this model, but cannot be measured directly. Alexander et al. [13] used the bulk hydrogen and carbon isotopic compositions of chondrites to estimate the water D/H ratio for a number of chondrite groups. The estimated D/H ratio of water in the extensively hydrated CI, CM, CR and ungrouped carbonaceous chondrite Tagish Lake (spectrally similar to D-type asteroids) are significantly lower than in the measured comets from Oort Cloud comets; the D/H ratio of water in CRs, however, is similar to that in the Jupiter Family Comet Hartley 2 [14]. Alexander et al. [13] concluded that CC parent asteroids accreted ˜3-7 au from the Sun. These data provide important constraints on the Grand Tack and Nice models.

Krot, A.; Alexander, C.; Nagashima, K.; Ciesla, F.; Fujiya, W.

2014-07-01

239

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

2014-12-01

240

Extraterrestrial Nucleobases in Carbonaceous Chondrites  

Microsoft Academic Search

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,

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

2006-01-01

241

Igneous Graphite in Enstatite Chondrites  

NASA Technical Reports Server (NTRS)

Igneous graphite. a rare constituent in terrestrial mafic and ultramafic rocks. occurs in three EH and one EL enstatite chondrite impact-melt breccias as 2-150 Ilm long euhedrallaths. some with pyramidal terminations. In contrast. graphite in most enstatite chondrites exsolved from metallic Fe-Ni as polygonal. rounded or irregular aggregates. Literature data for five EH chondrites on C combusting at high temperatures show that Abee contains the most homogeneous C isotopes (i.e. delta(sup 13)C = -8.1+/-2.1%); in addition. Abee's mean delta(sup l3)C value is the same as the average high-temperature C value for the set of five EH chondrites. This suggests that Abee scavenged C from a plurality of sources on its parent body and homogenized the C during a large-scale melting event. Whereas igneous graphite in terrestrial rocks typically forms at relatively high pressure and only moderately low oxygen fugacity (e.g., approx. 5 kbar. logfO2, approx. -10 at 1200 C ). igneous graphite in asteroidal meteorites formed at much lower pressures and oxygen fugacities.

Rubin, Alan E.

1997-01-01

242

Celebrating the Ordinary  

ERIC Educational Resources Information Center

Memento. Memoir. Memorable. Memory. Memorial. Commemorate. In Memoriam. These words may remind a person of stone monuments, or larger-than-life heroes and loved ones far distanced by space and time. The act of remembering, though, also belongs in the world of the everyday and the ordinary, and has a valuable place in an art classroom. In this…

Horst, Carol

2010-01-01

243

Ordinary Differential Equations  

Microsoft Academic Search

\\u000a The main objective of this chapter is to ensure that the reader understands the “existence theorem” (Sect. 15.2.3) and the\\u000a “unique theorem” (Sect. 15.2.4) for a first-order ordinary differential equation. These theorems prove the existence and uniqueness\\u000a of a solution of the differential equation and delineate the conditions that should be satisfied by the functions that are\\u000a to be differentiated.

Grigorios A. Pavliotis; Tsuneyoshi Nakayama; Paola Gervasio

244

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

245

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

246

New component of the Mezo-Madaras breccia - a microchondrule- and carbon-bearing L-related chondrite  

SciTech Connect

Microchondrules with apparent diameters 2-150 microns are found in a black carbon-bearing inclusion in Mazo-Madaras. Some are homogeneous (glassy or microcrystalline); others show two phases (mainly silica and pyroxene-rich glass). The bulk chemical composition of the inclusion is related to the host chondrite, in which silica-pyroxene chondrules are ubiquitous. Small black lumps of the same kind are dispersed in bulk Mezo-madaras. This L-related carbon-bearing material may represent a new specimen of C-rich ordinary chondrite. 13 references.

Michel-Levy, M.C.

1988-03-01

247

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

248

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

249

The compositional classification of chondrites. V - The Karoonda (CK) group of carbonaceous chondrites  

NASA Astrophysics Data System (ADS)

In the Karoonda, or 'CK' group of carbonaceous chondrites, all normal members are metamorphosed and, while some contain shock veins, all exhibit various degrees of blackening due to fine sulfide and magnetite particle dispersions in silicates. The elemental abundance patterns in CK chondrites are similar to those in CO chondrites, and rather more similar to those in CV chondrites; CK refractory siderophile abundances are intermediate between CV and CO levels. The exceptional abundance of CK chondrites in Antarctica is accounted for in light of the fragmentation of the CK parent objects, which produced a greater proportion of small micrometeoroids.

Kallemeyn, G. W.; Rubin, A. E.; Wasson, J. T.

1991-03-01

250

Chemical and physical studies of type 3 chondrites. I - Metamorphism related studies of Antarctic and other type 3 ordinary chondrites  

NASA Technical Reports Server (NTRS)

New thermoluminescence (TL) sensitivity measurements on 17 finds and one fall are presented, and petrologic assignments are made on the basis of TL sensitivity and silicate heterogeneity. The correlation that exists between TL sensitivity and glow curve shape is discussed, with the difference in the glow curve shapes of meteorite types 3.4 and less and type 3.5 and greater being tentatively attributed to an order-disorder transition in plagioclase, the TL phosphor. A correlation between TL sensitivity and heteogeneity of the silicate composition is found, but it tends to break down in the most heterogeneous meteorites. For Antarctic meteorites, the TL data show a much more restricted range in TL sensitivity than in silicate heterogeneity. The Quinyambie meteorite is the only one not consistent with the observed trend. Several explanations are offered, none of them totally satisfactory.

Sears, D. W.; Grossman, J. N.; Melcher, C. L.

1982-01-01

251

The Metal-Phosphate Connection in Chondrites  

NASA Astrophysics Data System (ADS)

Phosphates in ordinary chondrites are frequently associated with metal and troilite (e.g., Murrell and Burnett, 1983). They also constitute a large fraction of the inclusions present inside these two phases (Perron et al., 1990), in which they seem to have evolved from tiny precipitates formed from P solid solution in Fe-Ni (Zanda et al., 1990). Here, we further characterize these inclusions, and the external phosphates as well ("external" and "internal" will refer to phosphates located outside and inside metal grains, respectively). Polished sections of Dhajala, H3.8, and Forest Vale, H4 (hereafter DH and FV) were etched to reveal tracks in phosphates. Track densities were obtained with an SEM in internal phosphates in DH and FV, and in external phosphates in DH . The area of all phosphates larger than about 4 micrometers (224 grains in DH, 106 in FV) was measured, and their location noted. REE were measured with an ion probe in internal phosphates. Xe was analysed by stepwise heating in separated metal grains from both chondrites. A ^244Pu fission Xe component (Xe(sub)f) was released at low temperature, attributed to recoils from external phosphates, and another one at high temperature, attributed to internal phosphates. The strong link between phosphates and metal is confirmed: 74% by area (and thus, approximately, by mass) of the phosphates in DH are associated with metal, whether internal, or external in contact with metal (62% in FV). This translates into a ratio of metal-associated P to metal of 0.3% by mass, comparable to the P concentration in the metal of CM2 chondrites (Grossman and Olsen, 1974), of Semarkona (Paris, 1992), and of Leoville (under the form of tiny inclusions, Zanda et al., 1990). It is thus likely that a large proportion of chondritic phosphates formed from P originally contained in Fe-Ni as solid solution, through exsolution followed by growth of the original precipitates during parent-body metamorphism. Mean track densities of internal merrillites agree with those measured here in external grains for DH, and by Lavielle et al. (1992) for FV. So, in the moderately metamorphosed chondrites studied here, merrillite inclusions in metal had already their full share of Pu, as compared to external merrillites. On the other hand, REE abundances in internal merrillites are about a factor of two lower than in typical OC merrillites (Crozaz et al., 1989), with a less pronounced Eu anomaly. The elemental pattern varies somewhat from grain to grain (especially in FV) displaying sometimes a steady decrease of the CI-normalized abundances from light to heavy REE. This, together with the presence, inside the metal, of "exotic" phases like farringtonite (Perron et al., 1990), shows that internal phosphates are not completely equilibrated with the external ones. Track densities are considerably lower in DH (-50 x 10^6 cm^-2) than in FV (-350 x 10^6 cm^-2), which points to a lower Pu concentration or a slower cooling rate for the former. On the other hand, the fission Xe released at high temperature by the metal is larger for DH than for FV (~5 and ~3 x 10^-14 cm^3 ^136Xe/g, respectively). This is also true for low temperature Xe(sub)f (a factor -2 difference between DH and FV). Resolution of this conflict must await the measurement of Xe(sub)f in DH external phosphates. References: Crozaz G., Pellas P., Bourot-Denise M., de Chazal S.M., Fieni C., Lundberg L.L. and Zinner E. (1989) Earth Planet. Sci. Lett. 93, 157-169. Grossman L. and Olsen E. (1974) Geochim. Cosmochim. Acta 38, 173-187. Lavielle B., Marti K., Pellas P. and Perron C. (1992) Meteoritics, submitted. Murrell M.T. and Burnett D.S. (1983) Geochim. Cosmochim. Acta 47, 1999-2014. Perron C., Bourot-Denise M., Pellas P. and Marti K. (1990) Meteoritics (abstract) 25, 398-399. Zanda B., Bourot-Denise M. and Perron C. (1990) Meteoritics (abstract) 25, 422-423.

Perron, C.; Bourot-Denise, M.; Marti, K.; Kim, J. S.; Crozaz, G.

1992-07-01

252

Linearisable Third Order Ordinary Differential Equations  

E-print Network

words and phrases: Nonlinear ordinary differential equations, Linearisation, Invertible Transformations Linearisable Third Order Ordinary Differential Equations and M. Euler, Linearisable Third Order Ordinary Differential Equations and Generalised Sundman

Wolf, Thomas

253

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

254

Micro-Scale Distributions of Major and Trace Elements in Chondrites  

NASA Technical Reports Server (NTRS)

The Hayabusa spacecraft has successfully returned to Earth after two touchdowns on the surface of Asteroid 25143 Itokawa. This asteroid is classified as an S-type and inferred to consist of materials similar to ordinary chondrites or primitive achondrites [1]. More than 1500 particles have been identified consisting of olivine, pyroxene, plagioclase, Fe sulfide and Fe metal, with compositions consistent with being of LL origin. While the chondritic components are familiar to us, the level of detail to which the Itokawa samples will be exposed to will be unprecedented given that the samples are reasonably large and accessible to a wide variety of techniques. In many ways, we expect that our knowledge base of the comparator chondrites will be found to be wanting. Chondrites are the building blocks of the solar system. However, these rocks are essentially breccias and they are quite variable in bulk element compositions as well as compositions of the individual components. We have initiated a program of analysis for chondrites focusing on major and trace element distributions between the mineral components and the matrix. The issues to be addressed include the homogeneity of matrix and chondrule components and the representivity of any given sample to the bulk meteorite. This may be particularly important given the limited numbers of Itokawa grains that may be available for a specific analysis. As an initial study, we have taken thin sections of carbonaceous chondrites to study the representivity of the matrix compositions. Spot locations were constrained to limited regions of the sections so as to assess the variability of a local scale. Further work will be required to assess variability over a centimeter scale.

Ireland, T. R.; Zolensky, M.

2011-01-01

255

Pore Water Convection in Carbonaceous Chondrite Planetesimals  

Microsoft Academic Search

Chondritic meteorites are so named because they nearly all contain chondrules - small spherules of olivine and pyroxene that condensed and crystallized in the solar nebula and then combined with other material to form a matrix. Their parent bodies did not differentiate, i.e., form a crust and a core. Carbonaceous chondrites (CCs) derived from undifferentiated icy planetesimals. Asteroids of the

B. J. Travis; G. Schubert

2004-01-01

256

Vacuum ultraviolet spectra of carbonaceous chondrites  

Microsoft Academic Search

In the present paper, the vacuum ultraviolet reflection spectra of carbonaceous chondrite polished thin-section and powder are compared in terms of the energy-gap (Eg) value within the region from 5 to 14 eV. The comparison is carried out for the Essebi, Isna, Vigarano, Karoonda, Orgueil, and Allende chondrites and for meteoritic fassites, fayelites, and forsteritic peridot crystals.

A. J. Cohen; J. K. Wagner; B. W. Hapke; W. D. Partlow

1978-01-01

257

Amino acids in an Antarctic carbonaceous chondrite  

NASA Technical Reports Server (NTRS)

Amino acids have been found in aqueous extracts of a C2 carbonaceous chondrite recovered from Antarctica. The composition of the amino acids strongly suggests that they have a meteoritic origin. Comparison of these results with those obtained with other C2 chondrites supports the view that Antarctic meteorites have not been significantly altered by terrestrial processes since their fall.

Cronin, J. R.; Pizzarello, S.; Moore, C. B.

1979-01-01

258

Carbonaceous chondrites as bioengineered comets  

NASA Astrophysics Data System (ADS)

The discovery of microfossils on carbonaceous meteorites has electrified the public with the first concrete evidence of extraterrestrial biology. But how these organisms colonized and grew on the parent body-the comet-remains a mystery. We report on several features of cyanobacteria that permit them to bioengineer comets, as well as a tantalizing look at interplanetary uses for magnetite framboids that are found in abundance on carbonaceous chondrites. We argue that these structures provide important directionality and energy harvesting features similar to magnetotactic bacteria found on Earth.

Sheldon, Robert B.; Hoover, Richard

2012-10-01

259

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

260

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

261

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

262

Phase relations of a carbonaceous chondrite at lower mantle conditions  

Microsoft Academic Search

The refractory element ratios of Earth's mantle are close to carbonaceous chondrite values. One of the ideas on Earth's bulk composition is that the Earth is made of carbonaceous chondrite-like materials, but the redox state of Earth is closer to that of Enstatite chondrite than carbonaceous chondrite. We do not know exactly when and how the reduction event was occurred

Y. Asahara; E. Ohtani; T. Kondo; T. Kubo

2002-01-01

263

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

264

Origin and history of chondrite regolith, fragmental and impact-melt breccias from Spain  

NASA Technical Reports Server (NTRS)

Six ordinary chondrite breccias from the Museo Nacional de Ciencias Naturales, Madrid (Spain), are described and classified as follows: the solar gas-rich regolith breccia Oviedo (H5); the premetamorphic fragmental breccias Cabezo de Mayo (type 6, L-LL), and Sevilla (LL4); the fragmental breccias Canellas (H4) and Gerona (H5); and the impact melt breccia, Madrid (L6). It is confirmed that chondrites with typical light-dark structures and petrographic properties typical of regolith breccias may (Oviedo) or may not (Canellas) be solar gas-rich. Cabezo de Mayo and Sevilla show convincing evidence that they were assembled prior to peak metamorphism and were equilibrated during subsequent reheating. Compositions of olivine and low-Ca pyroxene in host chondrite and breccia clasts in Cabezo de Mayo are transitional between groups L and LL. It is suggested, based on mineralogic and oxygen isotopic compositions of host and clasts, that the rock formed on the L parent body by mixing, prior to peak metamorphism. This was followed by partial equilibrium of two different materials: the indigenous L chondrite host and exotic LL melt rock clasts.

Casanova, I.; Keil, K.; Wieler, R.; San Miguel, A.; King, E. A.

1990-01-01

265

Origin and history of chondrite regolith, fragmental and impact-melt breccias from Spain  

NASA Astrophysics Data System (ADS)

Six ordinary chondrite breccias from the Museo Nacional de Ciencias Naturales, Madrid (Spain), are described and classified as follows: the solar gas-rich regolith breccia Oviedo (H5); the premetamorphic fragmental breccias Cabezo de Mayo (type 6, L-LL), and Sevilla (LL4); the fragmental breccias Canellas (H4) and Gerona (H5); and the impact melt breccia, Madrid (L6). It is confirmed that chondrites with typical light-dark structures and petrographic properties typical of regolith breccias may (Oviedo) or may not (Canellas) be solar gas-rich. Cabezo de Mayo and Sevilla show convincing evidence that they were assembled prior to peak metamorphism and were equilibrated during subsequent reheating. Compositions of olivine and low-Ca pyroxene in host chondrite and breccia clasts in Cabezo de Mayo are transitional between groups L and LL. It is suggested, based on mineralogic and oxygen isotopic compositions of host and clasts, that the rock formed on the L parent body by mixing, prior to peak metamorphism. This was followed by partial equilibrium of two different materials: the indigenous L chondrite host and exotic LL melt rock clasts.

Casanova, I.; Keil, K.; Wieler, R.; San Miguel, A.; King, E. A.

1990-06-01

266

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

267

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

NASA Astrophysics Data System (ADS)

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 ˜10 GPa, which did not destroy its unusually high porosity of ˜27 vol%. Metallographic textures in LAP 031047 indicate heating above ˜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 ˜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 ˜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.; Swindle, Timothy D.; Weirich, John R.; Rumble, Douglas; Lasue, Jeremie; Kring, David A.

2011-10-01

268

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

269

Various Nitrogen Isotopic Compositions in H-Chondrite Metal  

NASA Astrophysics Data System (ADS)

Previous works of the authors (1,2) have revealed that nitrogen isotopes in bulk ordinary chondrites are various in a range of - 15< delta^15N < +45 o/oo (after reduction of the contribution of cosmogenic nitrogen). Recently, the isotopically anomalous nitrogen components in equilibrated H-chondrites, both the heavy nitrogen and the light nitrogen, have proved to be concentrated in the metal portion. The metal portion was prepared by etching the magnetic portion by a concentrated NaOH at 100-160 degrees C which dissolves phosphate and troilite, and attacks the silicates together with a slight amount of metal. Nitrogen is extracted from the purified metal by a stepwise combustion method and its isotope is measured by a mass-spectrometer with a high sensitivity. The results of nitrogen analyses are described in the table. The remarkable point is that nitrogen contents in the metal are almost constant, though the isotopic ratio differs by approximately 160 o/oo. Since behaviors of nitrogen in the metal are very sensitive to temperature, nitrogen study in the metal phase of ordinary chondrites is possible to give us interesting information concerning the behavior of volatile elements during the metamorphic and/or cooling sequences. The large differences of nitrogen isotopic ratios among H-chondrites suggest that isotopic heterogeneity already existed during the accretionary stage, since there seems to be little chance to explain the observations by any other processes expected after the formation of their parent bodies. Acknowledgement: We are indebted to Drs. C. Perron and P. Pellas of Museum National d'Histoire Naturelle, Paris, for introducing to us the etching technique to purify the metal. References: (1) Hashizume K. and Sugiura N. (1990) Meteoritics 25, 370. (2) Hashizume K. and Sugiura N. ( 1992) submitted to Geochim. Cosmochim. Acta. Table 1. Nitrogen isotopic composition in H-chondrite metal. -----------------------Metal---------------------------Whole Rock Sample------Class-N----delta^15N(mean)-delta^15N(peak)-N---- delta^15N(mean) Forest Vale-H4-------------------------48+-12----------3.07-10+-8 Ochansk-----H4----1.73-14.1+-2.3-------15+-7----------------- Allegan-----H5----1.71-13.8+-2.0-------16+-4-----------0.70--8+-4 Jilin-------H5----1.56-99.4+-7.0-------119+-7----------0.89-4.5+- 3 Plainview---H5----1.92-61.1+-3.7-------99+-4-----------1.72-33+-1 Guarena-----H6----(<2)------------------44+-4----------1.14--15+- 2 Nitrogen content (N) and delta^15N are in units of ppm and o/oo, respectively. Errors are 1 sigma. Whole rock data are from references (1,2). Nitrogen amounts and mean delta^15N are taken from 800 degrees C and above fractions. (They were not available for Forest Vale and Guarena due to large amounts of contaminating nitrogen.)

Hashizume, K.; Sugiura, N.

1992-07-01

270

Thermal metamorphism. [of chondrite parent bodies  

NASA Technical Reports Server (NTRS)

Most chondrites have experienced thermal metamorphism, resulting in changes in texture, mineralogy and possibly chemical composition. The physical conditions for metamorphism range from approximately 400 to 1000 C at low lithostatic pressure. Metamorphism may have resulted from decay of short-lived radionuclides, electromagnetic induction or accretion of hot materials. Several thermal models for chondrite parent bodies have been proposed. The least metamorphosed type-3 chondrites probably carry the most information about the early solar system, but even these have been affected to some degree by thermal processing.

Mcsween, Harry Y., Jr.; Sears, Derek W. G.; Dodd, Robert T.

1988-01-01

271

In Search of Ordinary Heroes.  

ERIC Educational Resources Information Center

Inspired by Miep Gies's selfless hiding of Anne Frank, a class of urban middle schoolers came up with definitions and characteristics of "ordinary," nonglitzy heroes. One student suggested that the school create its own ordinary hero hall of fame; students then researched possible nominees and held an induction ceremony for those nominated. (MLH)

Reissman, Rose

1995-01-01

272

Hotter, Faster: A Thermal Model for the H-Chondrite Parent Body Consistent with Chronology and Cooling Rates  

NASA Astrophysics Data System (ADS)

HOTTER, FASTER: A THERMAL MODEL FOR THE H-CHONDRITE PARENT BODY CONSISTENT WITH CHRONOLOGY AND COOLING RATES. H. Y. McSween, Jr. and M. E. Bennett, III, Department of Geological Sciences, University of Tennessee, Knoxville, TN 37996, USA. Because of the abundant sampling and relatively low shock levels of H chondrites, their thermal histories are more tightly constrained than for other ordinary chondrites; consequently, rigorous models for the thermal evolution of their parent asteroid can be formulated that are not possible for other chondrite groups. A revised thermal model for the H-chondrite parent asteroid [Bennett and McSween], based on heating by decay of 26Al, follows the formulation of [Miyamoto and Fujii] except: the unfounded constraint that the relative volumes of different petrologic types must mimic meteorite fall statistics is removed, a shortened thermal history of 60 Ma [Gopel et al] rather than 100 Ma is adopted, and improved geothermometry constraints and measurements of thermal properties [Yomogida and Matsui] are used. Our new model predicts a parent body of approximately 88 kilometers radius, containing a much larger volumetric proportion (71%) of H6 material than in the previous model, with a high thermal gradient and correspondingly small proportions of H5 and H4 material (together comprising 10%) near the surface. Constraints on chronology and cooling rates from H chondrites are used as independent tests of the model. 26Al heating requires that the body accreted 1.5-3.1 Ma after formation of CAIs to reach the measured peak temperature for H6 chondrites, consistent with the 3.0 + 2.6 Ma estimate from Pb/Pb chronology [Gopel et al]. Times of Pb isotopic closure, relative to CAIs, in H-chondrite phosphates (3-5 Ma for H4, 10-16 Ma for H5, 42-62 Ma for H6, from [Gopel et al]) precisely overlap the thermal model estimates. In particular, the markedly shorter duration of heating for H4-5 chondrites agrees with model predictions. The model also predicts post-metamorphic cooling rates through the temperature interval 800-500K of 26 K/Ma for H4, 22 K/Ma for H5, and 16 K/Ma for H6. These values approximately coincide, in both trend and magnitude, with metallographic and fission track cooling rate data for unshocked H chondrites [Lipschutz et al]. _

McSween, H. Y., Jr.; Bennett, M. E., III

1995-09-01

273

Alkali differentiation in LL-chondrites  

NASA Astrophysics Data System (ADS)

The Kraehenberg and Bhola LL-group chondrites are heterogeneous agglomerates which contain a variety of lithic fragments and chondrules as well as crystal fragments. Both meteorites contain large, cm-sized fragments with high K enrichments. The K-rich inclusions are fragments of larger rock bodies which crystallized from melts of chondritic parent material that had previously been enriched in K and in heavier alkalies,while also being depleted in Na and metal. It is suggested that the K enrichment occurred as an exchange for Na in feldspars via a vapor phase, whose presence on the chondrite parent body (or bodies) is supported by the recent finding of fluid inclusions in chondritic silicates. Cooling rate considerations indicate that the K-rich rock units could not have been very large, implying that the K-rich materials were locally molten by, for example, impact.

Wlotzka, F.; Palme, H.; Spettel, B.; Wanke, H.; Fredriksson, K.; Noonan, A. F.

1983-04-01

274

Cathodoluminescence of Enstatite in E-Chondrite  

NASA Astrophysics Data System (ADS)

We have clarified luminescence centers of extraterrestrial enstatite and comparatively discuss the CL of terrestrial and extraterrestrial enstatite in meteorites (E-chondrite; Dar al Gani 734, Sahara 97096 and Yamato 86004).

Ohgo, S. O.; Mishima, M. M.; Nishido, H. N.; Ninagawa, K. N.

2014-09-01

275

Lithic clasts in the Supuhee chondrite  

NASA Technical Reports Server (NTRS)

Bulk chemical analyses of three foreign lithic clasts from Supuhee, a shocked and brecciated H6 chondrite, were carried out in an attempt to locate 'mysterite', a volatile-rich material postulated to be present. Clast 1 bears some similarities to C1 and C2 chondrites, but its relatively low (less than 9.4%) volatile content suggests a different set of physicochemical conditions during low-temperature condensation. Clast 2 was apparently derived from H-group chondrite material by loss of metal and sulfide. Clast 3 is an unusual meteorite type whose chemical composition is reminiscent of the unique chondrite Kakangari (Graham, et al., 1977). These chemically distinct bodies were apparently not present during the metamorphic event which affected Supuhee. Although the presence of mysterite was not confirmed or refuted, the present results indicate that conditions were favorable for the formation, incorporation and preservation of volatile-rich materials.

Leitch, C. A.; Grossman, L.

1977-01-01

276

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

277

Short duration thermal metamorphism in CR chondrites  

NASA Astrophysics Data System (ADS)

CR chondrites are considered as one of the most primitive classes of meteorites. Most of them experienced a mild aqueous alteration and show no evidence of significant effect of thermal metamorphism. We present here a search for low degree metamorphic effects in CR chondrites. We studied 15 CR chondrites using different metamorphic indicators: (1) structure and Ni content of metal grains; (2) hydration state of matrix; (3) structure and composition of organic matter. The different metamorphic indicators show that two of the analyzed CR chondrites, GRA 06100 and GRO 03116, experienced thermal metamorphism. Indeed, all of the metal grains in GRA 06100 and half of the metal grains in GRO 03116 show Ni-rich phases; the matrix of GRA 06100 is almost completely dehydrated, and the matrix of GRO 03116 is partially dehydrated; Raman spectra of organic matter in these two meteorites are clearly different from those obtained for organic matter in the other CR chondrites, which resemble Raman spectra of organic matter in unmetamorphosed, CM2 meteorites; IR spectra of insoluble organic matter extracted from GRA 06100 and GRO 03116 show lower carbonyl abundance and higher CH2/CH3 ratio with respect to organic matter of unmetamorphosed chondrites. The other CR chondrites analyzed here lack these characteristics and only show a few metal grains with Ni-rich inclusions. Our results also show that the metamorphic effects observed in GRA 06100 and GRO 03116 are different from those observed in type 3 chondrites, which experienced long-duration metamorphism of radiogenic origin. We infer that thermal processing in these two CRs extended over a short duration and was triggered by impacts.

Briani, G.; Quirico, E.; Gounelle, M.; Paulhiac-Pison, M.; Montagnac, G.; Beck, P.; Orthous-Daunay, F.-R.; Bonal, L.; Jacquet, E.; Kearsley, A.; Russell, S. S.

2013-12-01

278

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

279

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

280

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

281

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

282

Chemical and physical studies of type 3 chondrites. VIII - Thermoluminescence and metamorphism in the CO chondrites  

NASA Technical Reports Server (NTRS)

A possible relationship between the thermoluminescence (TL) properties of CO chondrites and their metamorphic history was investigated by measuring the TL properties of seven normal CO chondrites and of the Colony and the Allan Hills A77307 (ALHA 77307) CO-related chondrites. With the exception of Colony and ALHA 77307, whose maximum induced TL emission is at approximately 350 C, the CO chondrites were found to exhibit two TL peaks: a 130 C and a 250 C peaks. Among the CO chondrites, the 130 C peak showed a 100-fold range in TL sensitivity and was found to correlate with various metamorphism-related phenomena, such as silicate heterogeneity, metal composition, and McSween's metamorphic subtypes. The peak at 250 did not show these correlations and, with exception of Colony, showed little variation.

Keck, Bradly D.; Sears, Derek W. G.

1987-01-01

283

Effects of Microsecond Pulse Laser Irradiation on Vis-NIR Reflectance Spectrum of Carbonaceous Chondrite Simulant: Implications for Martian Moons and Primitive Asteroids  

NASA Technical Reports Server (NTRS)

Goal of this study is to make a progress in understanding the optical effects of space weathering on small bodies believed to be similar in composition to carbonaceous chondrites: C, G, B, F, T, D, and P asteroids and possibly Martian satellites Phobos and Deimos. The companion work focuses on petrological and mineralogical aspects of this process. One of the main factors of space weathering is meteorite and micrometeorite bombardment leading, in particular, to impact melting of components of the regolith. Studies of lunar regolith and laboratory experiments simulating impact melting show that the melting products differ from the unmelted material in mineralogy and distribution of chemical components among different phases that results in spectral changes. We simulate impact melting of CM chondrite by pulse laser irradiation of an artificial analog of such a meteorite. The analog is a mixture of 46 wt.% non-magnetic fraction of L5 ordinary chondrite Tsarev, 47 wt.% serpentine, 5 wt.% kerite, and 2 wt.% calcite. It simulates rather well bulk chemistry, including volatiles such as H2O and CO2, and only approximately the CM chondrite mineralogy. Thus, we do not expect the mixture to be spectrally similar to CM chondrites, but expect the laser melting products to be similar to those formed by impact melting of natural CM chondrites.

Hiroi, T.; Moroz, L. V.; Shingareva, T. V.; Basilevsky, A. T.; Pieters, M.

2003-01-01

284

Progressive aqueous alteration of CR carbonaceous chondrites  

NASA Astrophysics Data System (ADS)

The wide range in the degree of aqueous alteration of CR chondrites prompted us to formulate a numerical sequence for these rocks that ranges from petrologic type 2.0 to 2.8. (Hypothetical CR3.0 chondrites should be completely free of aqueous alteration effects.) About 70% of CR chondrites are slightly altered, type-2.8 rocks that exhibit heterogeneous alteration; these meteorites contain moderately abundant metallic Fe-Ni, no magnetite, and generally, a few chondrules with clear glassy mesostases. None of the chondrules in these rocks shows evidence of alteration of mafic silicate phenocrysts, but several chondrules are surrounded by phyllosilicate-rich rims that appear “smooth” when viewed by back-scattered-electron imaging. Matrix regions in slightly altered CR chondrites contain high S (?3 wt.%), but some matrix patches in the same thin sections record alteration effects and contain appreciably less S (<1.5 wt.%). In CR chondrites that have been more-significantly altered (e.g., Renazzo and Al Rais), metallic Fe-Ni has been partially replaced by magnetite ± sulfide; mafic silicates have been partly altered to phyllosilicates, particularly along edges, fractures and twin boundaries. One of the most-altered CR chondrites (type-2.0 GRO 95577) contains abundant magnetite, additional oxide phases, iron carbonate, only very rare metallic Fe-Ni and essentially no mafic silicate grains. The whole-rock O-isotopic compositions of CR chondrites correlate with the degree of aqueous alteration: ?17O ranges from ?-2.6‰ in type-2.8 samples to ?-0.4‰ in type 2.0.

Harju, Ellen R.; Rubin, Alan E.; Ahn, Insu; Choi, Byeon-Gak; Ziegler, Karen; Wasson, John T.

2014-08-01

285

Petrologic evidence for collisional heating of chondritic asteroids  

NASA Technical Reports Server (NTRS)

The identification of the mechanism(s) responsible for heating asteroids is among the major problems in planetary science. Because of difficulties with models of electromagnetic induction and the decay of short-lived radionuclides, it is worthwhile to evaluate the evidence for collisional heating. New evidence for localized impact heating comes from the high proportion of relict type-6 material among impact-melt-bearing ordinary chondrites (OC). This relict material was probably metamorphosed by residual heat within large craters. Olivine aggregates composed of faceted crystals with 120 deg triple junctions occur within the melted regions of the Chico and Rose City OC melt rocks; the olivine aggregates formed from shocked, mosaicized olivine grains that underwent contact metamorphism. Large-scale collisional heating is supoorted by the correlation in OC between petrologic type and shock stage; no other heating mechanism can readily account for this correlation. The occurrence of impact-melt-rock clasts in OC that have been metamorphosed along with their whole rocks indicates that some impact events preceded or accompanied thermal metamorphism. Such impacts events, occurring during or shortly after accretion, are probably responsible for substantially melting approximately 0.5% of OC. These events must have heated a larger percentage of OC to subsolidus temperatures sufficient to have caused significant metamorphism. If collisional heating is viable, then OC parent asteroids must have been large; large OC asteroids in the main belt may include those of the S(IV) spectral subtype. Collisional heating is inconsistent with layered ('onion-shell') structures in OC asteroids (wherein the degree of metamorphism increases with depth), but the evidence for such structures is weak. It seems likely that collisional heating played an important role in metamorphosing chondritic asteroids.

Rubin, Alan E.

1995-01-01

286

Depth Profiles of Cosmogenic Noble Gases in the Chondrite Knyahinya  

NASA Astrophysics Data System (ADS)

Concentrations and isotopic ratios of Ne, Ar, Kr, and Xe have been analyzed in 5-g size samples from different positions within the L5 chondrite Knyahinya. A previous work [1] has shown that Knyahinya experienced a single-stage exposure history (duration 40.5 Ma) as a meteoroid of approximately spherical shape (radius 45 cm). For these reasons, this meteorite represents a very interesting object to study depth profiles of cosmogenic nuclide concentrations and to test and improve model calculations of production rates. The procedure of extraction of noble gases adopted for this work, includes two pyrolyses respectively at about 450 degrees C and 650 degrees C, followed by a combustion step in pure O2 (15-25 torr pressure) at 650 degrees C before the complete melting of the sample [2]. This procedure allows a low-temperature extraction of a significant fraction of the Kr and Xe trapped noble gas component, leading to an enrichment of the cosmogenic component during the last temperature step. Concentration of trapped Ar, Kr, and Xe is 2-3 times lower than expected for a type 5 chondrite. The isotopic composition of the trapped Xe component analyzed in the combustion step is identical with the OC- Xe composition measured in Forest Vale [3]. Preliminary results show that concentration of cosmogenic 83Kr increases by 16% from the surface to the center when the ratio of cosmogenic 78Kr to 83Kr decreases from 0.157 to 0.136. The concentration of 81Kr has been measured in each sample. It increases from 0.0220 10^-12 cm^3 STP/g near the surface to 0.0255 10^-12 cm^3 STP/g at the center, in excellent agreement with the variations measured by Eugster [4] in other ordinary chondrites. Acknowledgments: This work was supported by C.N.R.S., by IN2P3 and by INSU (Programme National de Planetologie). References: [1] Graf Th. et al. (1990) GCA, 54, 2511-2520. [2] Gilabert E. and Lavielle B. (1991) Meteoritics, 26, 337. [3] Lavielle B. and Marti K. (1992) JGR, 97, 20875-20881. [4] Eugster O. (1988) GCA, 52, 1649-1662.

Toe, S.; Lavielle, B.; Gilabert, E.; Simonoff, G. N.

1993-07-01

287

Silicate sulfidation and chemical differences between enstatite chondrites and Earth  

NASA Astrophysics Data System (ADS)

Isotopic similarity between the Earth-Moon system and enstatite chondrites (ECs) led to the idea that ECs were Earth's building blocks [1-3]. However, compared to Earth's mantle, ECs have low Fe0/Fe ratios, are enriched in volatile elements, and depleted in refractory lithophile elements and Mg [4]. Therefore, deriving Earth composition from ECs requires a loss of volatiles during or prior to accretion and sequestering a large fraction of Si in the deep Earth. Alternatively, the isotopic similarity between the Earth and ECs is explained by their formation from a common precursor that experienced different evolutionary paths resulting in the chemical difference [4]. The vestiges of such a precursor are still present in the unequilibrated ECs as FeO-rich silicates with O isotopic compositions identical to bulk ECs and Earth [5]. Conversion of such a precursor into the characteristic EC mineral assemblage requires high-temperature processing in an H-poor environment with high fS2 and fO2 close to that of the classic solar nebula [6], consistent with redox conditions inferred from Ti4+/Ti3+ ratios in EC pyroxene [7]. Under such conditions reaction of FeO-rich silicates with S-rich gas results in their replacement by the assemblage of FeO-poor silicates; Fe, Mg, Ca sulfides; free silica; and Si-bearing Fe,Ni metal alloy. The progressive sulfidation of ferromagnesian silicates in chondrules results in loss of Mg and addition of Fe, Mn, S, Na, K and, perhaps, other volatiles [6]. At the advanced stages of silicate sulfidation recorded in the metal-sulfide nodules [8], a portion of Si is reduced and dissolved in the Fe,Ni metal. This process is known to fractionate Si isotopes [9,10] and would explain the differences between the ECs and Earth's mantle [11]. The sulfidation of silicates also produces porous S-rich silica, a peculiar phase observed so far only in the ECs. It consists of a sinewy SiO2-rich framework enclosing numerous vesicles filled with beam-sensitive material and contains minor elements such as Na, Ca, Mg, or Fe, which also occur in the adjacent minerals. Its high S content and vesicular nature point to formation by quenching of a high-temperature melt saturated with a gaseous phase. The porous silica occurs in ~50% of chondrules [12], metal-sulfide nodules, and as inter-chondrule clasts, suggesting it is a good tracer of silicate sulfidation. Refs: [1] Javoy M. (1995) GRL 22: 2219-2222. [2] Javoy M. et al. (2010) EPSL 293: 259-268. [3] Kaminski E. & Javoy M. (2013) EPSL 365: 97-107. [4] Jacobsen S.B. et al. (2013) LPSC 44: #2344. [5] Weisberg M.K. et al. (2011) GCA 75: 6556-6569. [6] Lehner S.W. et al. (2013) GCA 101: 34-56. [7] Simon S.B. et al. (2013) LPSC 44: #2270. [8] Lehner S.W. et al. (2012) LPSC 43: #2252. [9] Shahar A. et al. (2011) GCA 75: 7688-7697. [10] Kempl J. et al. (2013) EPSL 368: 61-68. [11] Fitoussi C. & Bourdon B. (2012) Science 335: 1477-1480. [12] Piani L. et al. (2013) MetSoc 76: # 5178.

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

2013-12-01

288

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

289

Magnetic Evidence for a Partially Differentiated Carbonaceous Chondrite Parent Body  

E-print Network

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. ...

Shuster, David L.

290

Significance of Fe/Mg Ratios in Chondritic Meteorites  

NASA Astrophysics Data System (ADS)

The Fe/Mg ratios of most chondritic meteorites are close to solar, although Fe and Mg are very differently distributed among chondrites phases. Chondrules, matrix and metal must have formed from a single approximately solar reservoir.

Palme, H.; Friend, P.; Hezel, D.; Bischoff, A.

2014-09-01

291

A three-dimensional study of metal grains in equilibrated, ordinary chondrites  

NASA Astrophysics Data System (ADS)

Metal particles in Guarena (H6), Colby (L6) and St. Severin (LL6) were studied by optical microscopy and by electron microprobe analysis. Observations from successive polished sections through the metal particles show that kamacite and taenite grains, which often appear to be isolated particles, are connected directly or by intervening sulfides. Also tetrataenite rims are widest when adjacent to sulfide or kamacite. These observations indicate that transfer of Ni during cooling when kamacite-taenite phase growth takes place does not occur through the silicate phases but proceeds through metal and sulfide phases or along grain boundaries. By utilizing the central Ni content of taenite grains from successive sections, metallographic cooling rates were determined more precisely than by using one arbitrary section. Cooling rates determined in this manner for Guarena, Colby, and St. Severin are 4.3 K, 4.0 K, and 1.0 K per million years, respectively.

Willis, J.; Goldstein, J. I.

1983-11-01

292

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

293

Fusion Crust and the Measurement of Surface Ages of Antarctic Ordinary Chondrites  

NASA Technical Reports Server (NTRS)

Natural thermoluminescence (TL) reflects radiation exposure and storage temperature. Meteorites generally exhibit thermoluminescence acquired during their long exposure to galactic cosmic rays in space. During atmospheric passage, temperatures are high enough to completely drain the TL, in the first mm of material under the fusion crust. We therefore refer to this surface layer as "fusion crust" although it does include some unmelted material just below the crust. When the meteorite lands on earth this drained layer will begin to build up natural TL once again due to radiation from cosmic rays and internal radionuclides. Cosmic ray annual dose is estimated to be between 0.04 and 0.06 rad/yr on the earth's surface in Antarctica while the internal radionuclides contribute only about 0.01 rad/yr. Therefore the total annual dose received by the meteorite while it is on the surface is between 0.05 and 0.07 rad/yr. If the meteorite is buried deeply in the ice it is effectively shielded from most cosmic rays and thus only internal radioactivity contributes to the annual dose.

Akridge, Jannette M. C.; Benoit, Paul H.; Sears, Derek W. G.

1997-01-01

294

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

295

Mobile trace element contents in Jilin chondrite  

NASA Technical Reports Server (NTRS)

A determination is conducted of ppm-ppt levels of Co, Se, Ga, Rb, Cs, Te, Bi, Ag, In, Tl, Zn and Cd (arranged empirically in order of increasing mobility at 1000 C) by radiochemical neutron activation analysis in eight Jilin samples of known Ar-40 content and a large vein from one of these. The trace element contents of the vein do not differ markedly from those of Jilin whole-rock samples. Only Rb correlates with Ar-40, possibly due to chance. All elements but Cd are present at levels similar to thdse in H4-6 chondrites with long K/Ar age (i.e., presumably mildly shocked). These levels are low relative to those in analogous L4-6 chondrites suggesting that H chondrites formed and/or evolved under higher pre-shock temperatures than did mildly shocked L chondrites. Time-temperature conditions during shock-loading of Jilin parent material were mild relative to those in strongly shocked L chondrites, being sufficient at most only to mobilize Cd.

Sakuragi, Y.; Lipschutz, M. E.

1985-01-01

296

Exposure ages of carbonaceous chondrites, 1  

NASA Technical Reports Server (NTRS)

The recent exposure histories of carbonaceous chondrites have been investigated using cosmogenic radionuclides. Our results may indicate a clustering of exposure ages of C1 and C2 chondrites into two peaks, 0.2 My and 0.6 My, perhaps implying two collisional events of Earth-crossing parent bodies. Among carbonaceous chondrites are some having short exposure ages which Mazor et al. hypothesized cluster into a small number of families. This hypothesis is based on spallogenic Ne-21 exposure ages, which in some instances are difficult to determine owing to the large amounts of trapped noble gases in carbonaceous chondrites. Also, since Ne-21 is stable, it integrates a sample's entire exposure history, so meteorites with complex exposure histories are difficult to understand using exclusively Ne-21. Cosmogenic radionuclides provide an alternative means of determining the recent cosmic ray exposure duration. To test the hypothesis of Mazor et al. we have begun a systematic investigation of exposure histories of Antarctic and non-Antarctic carbonaceous chondrites especially C2s.

Nishiizumi, K.; Arnold, J. R.; Caffee, M. W.; Finkel, R. C.; Southon, J. R.; Nagai, H.; Honda, M.; Sharma, P.; Imamura, M.; Kobayashi, K.

1993-01-01

297

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

PubMed

The short-lived (146)Sm-(142)Nd chronometer (T(1/2) = 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 (142)Nd/(144)Nd ratios that range from those of ordinary chondrites to values similar to terrestrial samples. The EC having terrestrial (142)Nd/(144)Nd ratios are also characterized by small (144)Sm excesses, which is a pure p-process nuclide. The correlation between (144)Sm and (142)Nd for chondrites may indicate a heterogeneous distribution in the solar nebula of p-process matter synthesized in supernovae. However to explain the difference in (142)Nd/(144)Nd ratios, 20% of the p-process contribution to (142)Nd is required, at odds with the value of 4% currently proposed in stellar models. This study highlights the necessity of obtaining high-precision (144)Sm measurements to interpret properly measured (142)Nd 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

2011-05-10

298

Heterogeneous distribution of solar and cosmogenic noble gases in CM chondrites and implications for the formation of CM parent bodies  

NASA Astrophysics Data System (ADS)

Distribution of solar, cosmogenic, and primordial noble gases in thin slices of Murchison, Murray, and Nogoya CM carbonaceous chondrites was determined by the laser microprobe analysis so as to put some constraints on the parent-body processes in the CM chondrite formation. The main lithological units of the three meteorite slices were located by electron microscope observations and classified into clastic matrix and clasts of primary accretionary rocks (PARs) based on the classification scheme of texture of CM chondrites. All sample slices contain both clastic matrix and PARs. Clastic matrix shows a comminuted texture formed by fragmentation and mechanical mixing of rocks due to impacts, whereas PARs preserve the original textures prior to the mechanical disruption. Solar-type noble gases are detected in all sample slices. They are located preferentially in clastic matrix. The distribution of solar gases is similar to that in ordinary chondrites where these gases reside in clastic dark portions of these meteorites. The heterogeneous distribution of solar gases in CM chondrites suggests that these gases were acquired not in a nebular accretion process but in parent body processes. Solar energetic particles (SEP) are predominant in CM chondrites. The low abundance of low energy solar wind (SW) component relative to SEP suggests preferential loss of SW from minerals comprising the clastic matrix, due to aqueous alteration in the parent bodies. Cosmogenic noble gases are also enriched in some portions in clastic matrix, indicating that some parts of clastic matrix were exposed to solar and galactic cosmic rays prior to the final consolidation of the CM parent bodies. Primordial noble gases are rich in fine-grained rims around chondrules in all three meteorites. However, average concentrations of heavy primordial gases in the rims differ among meteorites and correlate inversely to the degree of aqueous alteration that the meteorites have experienced. This appears to have been caused by aqueous alteration reactions between fluids and carbonaceous carrier phases of noble gases.

Nakamura, Tomoki; Nagao, Keisuke; Metzler, Knut; Takaoka, Nobuo

1999-01-01

299

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

300

Friday, March 16, 2007 METAL-RICH CHONDRITES  

E-print Network

by metal grains and silicate components in CH chondrites provide constraints on different processes. WeFriday, March 16, 2007 METAL-RICH CHONDRITES 1:30 p.m. Crystal Ballroom B Chairs: D. S. Lauretta J Histories of CH Chondrites: Reconciling the Silicate and Metal Phases [#1984] Thermal histories recorded

Rathbun, Julie A.

301

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

302

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

303

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

PubMed Central

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(H2O) = 1 bar using modified grain-boundary diffusion parameters for oxygen self-diffusion and reaction rates of NaSiCa-1Al-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.

2012-01-01

304

Zr isotope anomalies in chondrites and the presence of 92Nb in the early solar system  

NASA Astrophysics Data System (ADS)

The presence of Zr isotope anomalies in the early solar system is demonstrated with the identification of 92Zr excesses and 96Zr deficits in several chondrites and the CAI Allende inclusions. The isotopic composition of Zr in carbonaceous, enstatite, and ordinary chondrites, along with four SNC meteorites, was analyzed by plasma source mass spectrometry. Most chondrite samples show negative96Zr anomalies, which indicate the presence of a pre-solar nucleosynthetic component. Six of them also display a distinct negative92Zr anomaly, reaching down to -2.7±0.8 ? units for Forest Vale (H4). The CAI inclusions from Allende, which are among the oldest known igneous objects of the solar system and have the highest Zr/Nb ratios, also show negative ?92Zr of -2.4±0.5. Although a substantial fraction of the Zr isotope variability may be due to pre-solar nucleosynthetic processes, part of the 92Zr excess must result from the decay of the now extinct 92Nb.

Sanloup, Chrystèle; Blichert-Toft, Janne; Télouk, Philippe; Gillet, Philippe; Albarède, Francis

2000-12-01

305

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

306

Thermomagnetic analysis of meteorites. I - Cl chondrites  

NASA Technical Reports Server (NTRS)

Samples of all five of the known Cl chondrites have been analyzed thermomagnetically. The only magnetic phase found in four of the chondrites (Alais, Ivuna, Orgueil, Tonk) was magnetite containing less than 6% nickel. The Revelstoke Cl chondrite contains essentially Ni-free Fe3O4 as the predominant phase; however, a small amount of a thermally unstable iron compound (presumably FeS) is additionally present. Estimates of the weight percentage of magnetite, based on saturation moments, are: Alais, 5.3 plus or minus 0.4%; Ivuna, 12.2 plus or minus 0.9%; Orgueil, 11.9 plus or minus 0.8%; Revelstoke, 7.2 plus or minus 0.5%; and Tonk, 9.4 plus or minus 0.6%.

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

1974-01-01

307

Early planetary metamorphism in chondritic meteorites  

NASA Astrophysics Data System (ADS)

The record of early events in the solar system is presently sought, together with information on the isotopic composition of primordial lead, in the lead isotope relations of whole rock and separated phases of Mezo-Madaras (L3) and Sharps (H3) chondrites; the respective ages of 4.48 and 4.47 billion years are not significantly changed when Canyon Diablo troilite lead is included in the data sets, suggesting that the initial Pb isotopic composition in both meteorites was the same as that in the troilite. The 4.48 billion year age, which is younger than the well established 4.54-4.56 billion years of the Allende chondrite and Angra dos Reis achondrite, appears to date an early metamorphic event rather than the formation of the chondrites.

Hanan, B. B.; Tilton, G. R.

1985-07-01

308

First known EL5 chondrite - Evidence for dual genetic sequence for enstatite chondrites  

NASA Technical Reports Server (NTRS)

The compositionally distinct EH and EL groups together with four (3-6) petrologic types which constitute the enstatite chondrites represent increasing degrees of metamorphic alteration. Although bulk composition variations preclude a simple conversion of EH4 into EL6 material, complex models which involve simultaneous bulk composition and petrologic type variations may be implied by other classification schemes in common use. Attention is presently given to the discovery of the first EL5 chondrite, which breaks the EH3,4-EH5-EL6 sequence and indicates that the enstatite chondrites constitute the two discrete, isochemical metamorphic sequences EH3-5 and EL5-6.

Sears, D. W. G.; Weeks, K. S.; Rubin, A. E.

1984-01-01

309

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

310

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

311

Potentially hazardous Asteroid 2007 LE: Compositional link to the black chondrite Rose City and Asteroid (6) Hebe  

NASA Astrophysics Data System (ADS)

The research is an integrated effort beginning with telescopic observations and extending through detailed mineralogical characterizations to provide constraints on the albedo, diameter, composition, and meteorite affinity of near-Earth object-potentially hazardous asteroid (NEO-PHA 2007 LE). Results of the analysis indicate a diameter of 0.56 kilometers (km) and an albedo of 0.08. 2007 LE exhibits a 1-?m absorption feature without a discernible Band II feature. Compositional analysis of 2007 LE reveal Fs17 and Fa19 values, which are consistent with the Fa and Fs values for the H-type ordinary chondrites (Fs14.5-18 and Fa16-20) and of Asteroid (6) Hebe (Fs17 and Fa15). Spectroscopically, 2007 LE does not appear like the average H-chondrite spectra, exhibiting a reddened spectrum and subdued absorption feature. Further investigation of the meteorite classes yielded a black chondrite, Rose City, which is both similar in mineralogy and spectrally to PHA 2007 LE. Dynamical analysis could not directly link the fall of the Rose City meteorite to 2007 LE. As it stands, 2007 LE and Rose City have a compositional link, and both could come from the same parent body/possible family, one known source of the H chondrites is (6) Hebe.

Fieber-Beyer, Sherry K.; Gaffey, Michael J.; Bottke, William F.; Hardersen, Paul S.

2015-04-01

312

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

313

Non-nebular Origin of Dark Mantles Around Chondrules and Inclusions in CM Chondrites  

NASA Technical Reports Server (NTRS)

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. Acta 56, 1992, 2873-28971. 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 791 198 we find no correlation when all sizes of central objects and dark lumps are included but a significant correlation (r(sup 2) = 0.44) if we limit consideration to central objects with radii >35 microns; 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-Rodriquez, Josep M.; Rubin, Alan E.; Wasson, John T.

2006-01-01

314

Hydrogen and major element concentrations on 433 Eros: Evidence for an L- or LL-chondrite-like surface composition  

NASA Astrophysics Data System (ADS)

A reanalysis of NEAR X-ray/gamma-ray spectrometer (XGRS) data provides robust evidence that the elemental composition of the near-Earth asteroid 433 Eros is consistent with the L and LL ordinary chondrites. These results facilitated the use of the gamma-ray measurements to produce the first in situ measurement of hydrogen concentrations on an asteroid. The measured value, 1100-700+1600 ppm, is consistent with hydrogen concentrations measured in L and LL chondrite meteorite falls. Gamma-ray derived abundances of hydrogen and potassium show no evidence for depletion of volatiles relative to ordinary chondrites, suggesting that the sulfur depletion observed in X-ray data is a surficial effect, consistent with a space-weathering origin. The newfound agreement between the X-ray, gamma-ray, and spectral data suggests that the NEAR landing site, a ponded regolith deposit, has an elemental composition that is indistinguishable from the mean surface. This observation argues against a pond formation process that segregates metals from silicates, and instead suggests that the differences observed in reflectance spectra between the ponds and bulk Eros are due to grain size differences resulting from granular sorting of ponded material.

Peplowski, Patrick N.; Bazell, David; Evans, Larry G.; Goldsten, John O.; Lawrence, David J.; Nittler, Larry R.

2015-03-01

315

Petrographic, chemical and spectroscopic evidence for thermal metamorphism in carbonaceous chondrites I: CI and CM chondrites  

NASA Astrophysics Data System (ADS)

We present a comprehensive description of petrologic, chemical and spectroscopic features of thermally metamorphosed CI-like and CM (and CM-like) chondrites. Only two such CI chondrites have so far been discovered i.e. Y-86029 and Y-82162. Thermal metamorphism in these chondrites is apparent in their low contents of H2O, C and the most thermally labile trace elements, partial dehydration of matrix phyllosilicates and abundance of thermally decomposed Ca-Mg-Fe-Mn carbonates, which apparently resulted from heating of Mg-Fe carbonate precursors. The CM chondrites exhibit a wide range of aqueous and thermal alteration characteristics. This alteration was almost complete in Y-86720 and Y-86789, which also escaped alternating episodes of oxidation and sulfidization experienced by the others. Thermal metamorphism in the CM chondrites is apparent in loss of thermally labile trace elements and also in partial to almost complete dehydration of matrix phyllosilicates: heating was less uniform in them than in CI chondrites. This dehydration is also evident in strength and shapes of integrated intensities of the 3 ?m bands except in PCA 91008, which experienced extensive terrestrial weathering. Tochilinite is absent in all but Y-793321 probably due to heating. Textural evidence for thermal metamorphism is conspicuous in blurring or integration/fusion of chondrules with matrix in the more extensively heated (?600 °C) CM chondrites like PCA 91008 and B-7904. TEM and XRD analyses reveal that phyllosilicate transformation to anhydrous phases proceeds via poorly crystalline, highly desiccated and disordered 'intermediate' phases in the least and moderately heated (400-600 °C) carbonaceous chondrites like WIS 91600, PCA 91008 and Y-86029. These findings are significant in that they confirm that these phases occur in meteorites as well as terrestrial samples. Thermal alteration in these meteorites can be used to identify other carbonaceous chondrites that were thermally metamorphosed in their parent bodies. Combining RNAA trace element data for experimentally heated Murchison CM2 samples with petrographic and spectroscopic data, these thermally metamorphosed carbonaceous chondrites can be ordered by severity of open system heating as 400 °C ? Y-793321 < WIS91600 = EET90043 = A881655 < PCA91008 < B-7904 = Y-86029 < Y-82162 < Y-86720 = Y-86789 ? 700 °C. Nearly all heated carbonaceous chondrites discovered so far have been found in Antarctica, which is known to have sampled the flux of near-Earth material for much longer than exemplified by current falls.

Tonui, Eric; Zolensky, Mike; Hiroi, Takahiro; Nakamura, Tomoki; Lipschutz, Michael E.; Wang, Ming-Sheng; Okudaira, Kyoko

2014-02-01

316

Alkaline Element Fractionations in LL-chondritic Breccias  

NASA Astrophysics Data System (ADS)

Introduction: Fractionation of moderately volatile lithophile elements including alkaline elements was an important process in the early solar system. Alkali-rich igneous fragments (K-rich fragments) were found in brecciated LL-chondrites. These fragments in Kraehenberg (LL5), Bhola (LL3-6), and Yamato (Y)-74442 (LL4) show fractionated alkaline element patterns; for example, abundances of alkaline elements in the Kraehenberg fragment are ~0.5 x CI for Na, ~12 x CI for K,~45 x CI for Rb, and ~70 x CI for Cs [1]. In order to understand moderately volatile element fractionations, we have undertaken mineralogical and petrological studies on K-rich fragments in Kraehenberg [1], Bhola [2], and Y-74442 [3, 4]. Results and Discussion: Kraehenberg, Bhola, and Y-74442 consist of mineral fragments, K-rich fragments, impact-melt clasts, chondrules, and matrix. K-rich fragments in these meteorites are composed of 10-100 µm-sized euhedral olivine (~60 vol.%) and groundmass of brown glasses (~40 vol.%, including microcrystalline pyroxene) which are highly enriched in alkaline elements. Dendritic pyroxene and chromite (~1 µm in size) along with troilite (~10 µm in size) are commonly observed in the groundmass. The textures are different from those of impact melt clasts in ordinary chondrites. Chemical compositions of olivine in the K-rich fragments fall within the compositional range of equilibrated LL-chondrites (Fa26-32 [5]). Groundmass glasses in the Kraehenberg, Bhola, and Y-74442 fragments are almost identical in composition when plotted on a Na+K+Al-oxides-Ca+Mg+Fe-oxides-SiO2 ternary diagram [1]. The fractionation trend is also observed in an angular igneous fragment in Siena (LL5) [6]. The lack of K isotopic fractionation effects in the K-rich clast in Kraehenberg [7] implies that the enrichment of (heavier) alkaline elements occurred near-equilibrium conditions. The K-rich fragments in Kraehenberg and Y-74442 could be early solar system materials (~4.56 Ga [8, 9]). Similarities in textures, compositions, and fractionation patterns of the K-rich fragments suggest that they might be formed from related precursor materials with related processes. Complementarity of K-rich fragments and differentiated body alkali abundance patterns suggests that the fractionation could have occurred in the early solar nebula. Refs: [1] Wlotzka F. et al. (1983) Geochim. Cosmochim. Acta 47, 743. [2] Noonan A.F. et al. (1978) Geol. Survey Open File Report 78-701, 311. [3] Yanai K. et al. (1978) Mem. Natl. Inst. Polar Res. Spec. Issue 8, 110. [4] Ikeda Y. and Takeda H. (1979) Mem. Natl. Inst. Polar Res. Spec. Issue 15, 123. [5] Dodd R.T. (1981) Meteorites pp. 368, Cambridge Univ. Press. [6] Fodor R.V. and Keil K. (1978) Catalog of lithic fragments in LL-chondrites, Inst. Meteoritics Spec. Publ. No. 19, pp. 38, Univ. New Mexico, Albuquerque. [7] Humayun M. and Clayton R.N. (1995) Geochim. Cosmochim. Acta 59, 2131. [8] Kempe W. and Mueller O. (1969) Meteorite Res., pp. 418. [9] Nishiya N. et al. (1995) Okayama Univ. Earth Sci. Rep. 2, 91.

Misawa, K.; Yokoyama, T.; Okano, O.

2010-12-01

317

Collision condition indicted by High Pressure Phases in a Chondrite  

NASA Astrophysics Data System (ADS)

It has been generally recognized that there were many collisions during planetary accretion. Chondrites include the materials at the time of formation of the solar system. It is essential to unravel the shock history in meteorites and the parent planet in order to understand such collisional processes. In this study, we investigate a thin section of ordinary chondrite Y-790729 classified as L6 in which high-pressure minerals are found in the about 620-?m-wide shock vein. The mineralogical and chemical features give us detailed information to constrain the shock conditions. We have tried to constrain the P-T condition from the viewpoints of the mineral assemblage and cathodoluminescense (CL) spectroscopy. Y-790729 consists mostly of olivine and pyroxene and has shock veins. To identify high pressure phases, we used an optical microscope, a scanning electron microscope (SEM), micro Raman spectroscopy, and electron probe micro analyzer (EPMA). In addition, scanning electron microscopy-cathodoluminescence (SEM-CL) analysis, detectable shock-induced defect centers, was used to characterize the shock metamorphism in feldspar minerals. The presence of shock vein, maskelynite, and high pressure phases confirms shock record. 7 high pressure phases of ringwoodite, high-pressure clinoenstatite (HPC), majorite, merrillite, lingunite, high-pressure chromite and akimotoite were found in this section. All of them exist only in a shock vein, but maskelynite occurs everywhere in the section. From these observations, it is obvious that the shock vein experienced the high pressure and high temperature generated by shock wave. If some of the high pressure minerals are equilibrated, the P-T condition can be estimated. Based on the equilibrium phase diagram of MgSiO3 polymorphs (Presnall. 1995), the P-T conditions for crystallization of majorite, HPC and akimotoite is about 17 GPa and 1600 oC, because the compositions of the three phases are close to MgSiO3. It is consistent with the stability fields for ringwoodite, merrillite and diopside. Employing the shock properties of an ordinary chondrite (F. Zhang and T. Sekine, 2007) and the impedance match method, an impact velocity of 1.74 km/s is obtained for a symmetrical head-on impact. CL spectroscopy of experimentally shocked sanidine gives us a linear correlation between integral intensity of emission components at 2.948 eV and the applied peak shock pressure. Then, a pressure over 15 GPa can be estimated based on these relationships and the intensities at 2.948 eV derived from maskelynite in Y-790729, covering the value estimated from the high pressure phase assemblage. We plan to investigate the detailed microstructures and the particle sizes of the high pressure minerals in the shock vein by transmission electron microscope (TEM). By examining minerals in the shock vein in detail, it is expected that the formation mechanism of the high pressure phases will be understood and that the collisional process will be unraveled from the material evolution. In addition, the shock duration, the parent body size, and the time required for the crystal growth need to be estimated as further development.

Kato, Y.; Sekine, T.; Kayama, M.; Miyahara, M.; Yamaguchi, A.

2012-12-01

318

Evidence of Microfossils in Carbonaceous Chondrites  

NASA Technical Reports Server (NTRS)

Investigations have been carried out on freshly broken, internal surfaces of the Murchison, Efremovka and Orgueil carbonaceous chondrites using Scanning Electron Microscopes (SEM) in Russia and the Environmental Scanning Electron Microscope (ESEM) in the United States. These independent studies on different samples of the meteorites have resulted in the detection of numerous spherical and ellipsoidal bodies (some with spikes) similar to the forms of uncertain biogenicity that were designated "organized elements" by prior researchers. We have also encountered numerous complex biomorphic microstructures in these carbonaceous chondrites. Many of these complex bodies exhibit diverse characteristics reminiscent of microfossils of cyanobacteria such as we have investigated in ancient phosphorites and high carbon rocks (e.g. oil shales). Energy Dispersive Spectroscopy (EDS) analysis and 2D elemental maps shows enhanced carbon content in the bodies superimposed upon the elemental distributions characteristic of the chondritic matrix. The size, distribution, composition, and indications of cell walls, reproductive and life cycle developmental stages of these bodies are strongly suggestive of biology' These bodies appear to be mineralized and embedded within the meteorite matrix, and can not be attributed to recent surface contamination effects. Consequently, we have interpreted these in-situ microstructures to represent the lithified remains of prokaryotes and filamentous cyanobacteria. We also detected in Orgueil microstructures morphologically similar to fibrous kerite crystals. We present images of many biomorphic microstructures and possible microfossils found in the Murchison, Efremovka, and Orgueil chondrites and compare these forms with known microfossils from the Cambrian phosphate-rich rocks (phosphorites) of Khubsugul, Northern Mongolia.

Hoover, Richard B.; Rozanov, Alexei Y.; Zhmur, S. I.; Gorlenko, V. M.

1998-01-01

319

Intensive parameters of enstatite chondrite metamorphism  

NASA Astrophysics Data System (ADS)

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, R. A.; Hess, P. C.; Rutherford, M. J.

1989-10-01

320

Uranium Isotopic Composition of Carbonaceous Chondrites  

NASA Astrophysics Data System (ADS)

We present uranium isotope and concentration data of 12 carbonaceous chondrites, analyzed by MC-ICPMS.Minor variations in the ^2^3^8U/^2^3^5U ratios are detected, showing that it is necessary for a reliable Pb-Pb chronology to analyze U and Pb isotopes.

Kaltenbach, A.; Stirling, C. H.; Amelin, Y.

2012-03-01

321

Csátalja, the largest H4-5 chondrite from Hungary  

NASA Astrophysics Data System (ADS)

We report here for the first time the composition and mineralogical studies on a new meteorite, which was found in August 2012 near the village of Csátalja, Hungary (46°0'21''N; 18°59'27'E). The Csátalja meteorite is classified as a H4-5 ordinary chondrite with shock stage S2 and a degree of weathering W1 and the total mass is 15 kg. The Csátalja meteorite is characterized by well-defined chondrules composed either of olivine or pyroxene. X-ray diffractogram shows the primary phases olivine, pyroxene, kamacite, and albite. Metal particles were extracted from the bulk powdered samples exhibit only kamacite and small amounts of the intergrowth taenite/kamacite. Raman spectra of forsterite indicate that Csátalja meteorite suffered from relatively low shock pressure regime. The texture of chondrules varies from nonporphyritic (e.g., barred olivine, radial pyroxene) to porphyritic ones (e.g., granular olivine as well as olivine pyroxene). The meteorite name has not yet approved by the Nomenclature Committee of the Meteoritical Society.

Kovács, János; Sajó, István; Márton, Zsuzsanna; Jáger, Viktor; Hegedüs, Tibor; Berecz, Tibor; Tóth, Tamás; Gyenizse, Péter; Podobni, András

2015-01-01

322

Chondrites and the Protoplanetary Disk, Part 3  

NASA Technical Reports Server (NTRS)

Contents include the following: Ca-, Al-Rich Inclusions and Ameoboid Olivine Aggregates: What We Know and Don t Know About Their Origin. Aluminium-26 and Oxygen Isotopic Distributions of Ca-Al-rich Inclusions from Acfer 214 CH Chondrite. The Trapping Efficiency of Helium in Fullerene and Its Implicatiion to the Planetary Science. Constraints on the Origin of Chondritic Components from Oxygen Isotopic Compositions. Role of Planetary Impacts in Thermal Processing of Chondrite Materials. Formation of the Melilite Mantle of the Type B1 CAIs: Flash Heating or Transport? The Iodine-Xenon System in Outer and Inner Portions of Chondrules from the Unnamed Antarctic LL3 Chondrite. Nucleosynthesis of Short-lived Radioactivities in Massive Stars. The Two-Fluid Analysis of the Kelvin-Helmholtz Instability in the Dust Layer of a Protoplanetary Disk: A Possible Path to the Planetesimal Formation Through the Gravitational Instability. Shock-Wave Heating Model for Chonodrule Formation: Heating Rate and Cooling Rate Constraints. Glycine Amide Hydrolysis with Water and OH Radical: A Comparative DFT Study. Micron-sized Sample Preparation for AFM and SEM. AFM, FE-SEM and Optical Imaging of a Shocked L/LL Chondrite: Implications for Martensite Formation and Wave Propagation. Infrared Spectroscopy of Chondrites and Their Components: A Link Between Meteoritics and Astronomy? Mid-Infrared Spectroscopy of CAI and Their Mineral Components. The Origin of Iron Isotope Fractionation in Chondrules, CAIs and Matrix from Allende (CV3) and Chainpur (LL3) Chondrites. Protoplanetary Disk Evolution: Early Results from Spitzer. Kinetics of Evaporation-Condensation in a Melt-Solid System and Its Role on the Chemical Composition and Evolution of Chondrules. Oxygen Isotope Exchange Recorded Within Anorthite Single Crystal in Vigarano CAI: Evidence for Remelting by High Temperature Process in the Solar Nebula. Chondrule Forming Shock Waves in Solar Nebula by X-Ray Flares. Organic Globules with Anormalous Nitrogen Isotopic Compositions in the Tagish Lake Meteorite: Products of Primitive Organic Reactions. Yet Another Chondrule Formation Scenario. CAIs are Not Supernova Condensates. Microcrystals and Amorphous Material in Comets and Primitive Meteorites: Keys to Understanding Processes in the Early Solar System. A Nearby Supernova Injected Short-lived Radionuclides into Our Protoplanetary Disk. REE+Y Systematics in CC and UOC Chondrules. Meteoritic Constraints on Temperatures, Pressures, Cooling Rates, Chemical Compositions, and Modes of Condensation in the Solar Nebula. The I-Xe Record of Long Equilibration in Chondrules from the Unnamed Antarctic Meteorite L3/LL3. Early Stellar Evolution.

2004-01-01

323

Reclassification of Villalbeto de la Peña—Occurrence of a winonaite-related fragment in a hydrothermally metamorphosed polymict L-chondritic breccia  

NASA Astrophysics Data System (ADS)

The Villalbeto de la Peña meteorite that fell in 2004 in Spain was originally classified as a moderately shocked L6 ordinary chondrite. The recognition of fragments within the Villalbeto de la Peña meteorite clearly bears consequences for the previous classification of the rock. The oxygen isotope data clearly show that an exotic eye-catching, black, and plagioclase-(maskelynite)-rich clast is not of L chondrite heritage. Villalbeto de la Peña is, consequently, reclassified as a polymict chondritic breccia. The oxygen isotope data of the clast are more closely related to data for the winonaite Tierra Blanca and the anomalous silicate-bearing iron meteorite LEW 86211 than to the ordinary chondrite groups. The REE-pattern of the bulk inclusion indicates genetic similarities to those of differentiated rocks and their minerals (e.g., lunar anorthosites, eucritic, and winonaitic plagioclases) and points to an igneous origin. The An-content of the plagioclase within the inclusion is increasing from the fragment/host meteorite boundary (approximately An10) toward the interior of the clast (approximately An52). This is accompanied by a successive compositionally controlled transformation of plagioclase into maskelynite by shock. As found for plagioclase, compositions of individual spinels enclosed in plagioclase (maskelynite) also vary from the border toward the interior of the inclusion. In addition, huge variations in oxygen isotope composition were found correlating with distance into the object. The chemical and isotopical profiles observed in the fragment indicate postaccretionary metamorphism under the presence of a volatile phase.

Bischoff, Addi; Dyl, Kathryn A.; Horstmann, Marian; Ziegler, Karen; Wimmer, Karl; Young, Edward D.

2013-04-01

324

Nucleosynthetic strontium isotope anomalies in carbonaceous chondrites  

NASA Astrophysics Data System (ADS)

Precise Sr isotopic compositions in samples from sequential acid leaching experiments have been determined for three carbonaceous chondrites, Allende, Murchison, and Tagish Lake, together with those in the bulk aliquots of these meteorites. The chondritic acid leachates and residues were characterized by Sr isotope anomalies with variable ?84Sr values (106 relative deviation from a standard material) ranging from +120 to - 4700 ppm, documenting multiple nucleosynthetic sources within a single meteorite. In addition, the ?84Sr patterns across leaching samples for individual chondrites differed from one another. The highest ?84Sr values were observed for leaching Step 3 (HCl+H2O, 75 °C) for Allende and Murchison likely because of the incorporation of calcium and aluminum-rich inclusions (CAIs). In contrast, extremely low ?84Sr values were observed in the later fractions (Steps 6 and 7) for Murchison and Tagish Lake, suggesting the existence of s-process-enriched presolar SiC grains derived from AGB stars. A ?84Sr-?54Cr diagram was prepared with the CAIs and bulk aliquots of carbonaceous chondrites and other meteorites (noncarbonaceous) that were plotted separately; however, they still formed a global positive correlation. CAIs presented the highest ?84Sr and ?54Cr values, whereas carbonaceous chondrites and noncarbonaceous meteorites had intermediate and the lowest ?84Sr and ?54Cr values, respectively. The positive trend was interpreted as resulting from global thermal processing in which sublimation of high ?84Sr and ?54Cr carriers generated the excess ?84Sr and ?54Cr signatures in CAIs, while noncarbonaceous planetesimals accreted from materials that underwent significant thermal processing and thus had relatively low ?84Sr and ?54Cr values. Apart from the global trend, the carbonaceous chondrites and noncarbonaceous meteorites both exhibited intrinsic variations that highlight an isotopic dichotomy similar to that observed in other isotope combinations (e.g., ?54Cr-?50Ti, ?54Cr-?17O). A plausible scenario for creation of the intrinsic variations involves local thermal processing (e.g., flash heating for chondrule formation) caused by additional selective destruction of presolar grains differently than that caused by global thermal processing. The existence of such a global positive trend and local variations for two meteorite groups suggests a complicated dynamic history for the dust grains with respect to thermal processing, material transportation, and mixing in the protoplanetary disk prior to planetesimal formation.

Yokoyama, Tetsuya; Fukami, Yusuke; Okui, Wataru; Ito, Nobuaki; Yamazaki, Hiroshi

2015-04-01

325

On the chemical composition of L-chondrites  

NASA Technical Reports Server (NTRS)

Radiochemical neutron activation analysis of Ag, As, Au, Bi, Co, Cs, Ga, In, Rb, Sb, Te, Tl, and Zn and major element data in 14 L4-6 and 3 LL5 chondrites indicates that the L group is unusually variable and may represent at least 2 subgroups differing in formation history. Chemical trends in the S/Fe rich subgroup support textural evidence indicating late loss of a shock formed Fe-Ni-S melt; the S/Fe poor subgroup seemingly reflects nebular fractionation only. Highly mobile In and Zn apparently reflect shock induced loss from L chondrites. However, contrasting chemical trends in several L chondrite sample sets indicate that these meteorites constitute a more irregular sampling of, or more heterogeneous parent material than do carbonaceous or enstatite chondrites. Data for 15 chondrites suggest higher formation temperatures and/or degrees of shock than for LL5 chondrites.

Neal, C. W.; Dodd, R. T.; Jarosewich, E.; Lipschutz, M. E.

1980-01-01

326

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

327

Deducing Wild 2 Components with a Statistical Dataset of Olivine in Chondrite Matrix  

NASA Technical Reports Server (NTRS)

Introduction: A preliminary exam of the Wild 2 olivine yielded a major element distribution that is strikingly similar to those for aqueously altered carbonaceous chondrites (CI, CM, and CR) [1], in which FeO-rich olivine is preferentially altered. With evidence lacking for large-scale alteration in Wild 2, the mechanism for this apparent selectivity is poorly understood. We use a statistical approach to explain this distribution in terms of relative contributions from different chondrite forming regions. Samples and Analyses: We have made a particular effort to obtain the best possible analyses of both major and minor elements in Wild 2 olivine and the 5-30 micrometer population in chondrite matrix. Previous studies of chondrite matrix either include larger isolated grains (not found in the Wild 2 collection) or lack minor element abundances. To overcome this gap in the existing data, we have now compiled greater than 10(exp 3) EPMA analyses of matrix olivine in CI, CM, CR, CH, Kakangari, C2-ungrouped, and the least equilibrated CO, CV, LL, and EH chondrites. Also, we are acquiring TEM/EDXS analyses of the Wild 2 olivine with 500s count times, to reduce relative errors of minor elements with respect to those otherwise available. Results: Using our Wild 2 analyses and those from [2], the revised major element distribution is more similar to anhydrous IDPs than previous results, which were based on more limited statistics (see figure below). However, a large frequency peak at Fa(sub 0-1) still persists. All but one of these grains has no detectable Cr, which is dissimilar to the Fa(sub 0-1) found in the CI and CM matrices. In fact, Fa(sub 0-1) with strongly depleted Cr content is a composition that appears to be unique to Kakangari and enstatite (highly reduced) chondrites. We also note the paucity of Fa(sub greater than 58), which would typically indicate crystallization in a more oxidizing environment [3]. We conclude that, relative to the bulk of anhydrous IDPs, Wild 2 may have received a larger contribution from the Kakangari and/or enstatite chondrite forming regions. Alternatively, Wild 2 may have undergone accretion in an anomalously reducing region, marked by nebular condensation of this atypical forsterite. In [4], a similar conclusion was reached with an Fe-XANES study. We will also use similar lines of reasoning, and our previous conclusions in [5], to constrain the relative contributions of silicates that appear to have been radially transported from different ordinary and carbonaceous chondrite forming regions to the Kuiper Belt. In addition, the widespread depletion of Cr in these FeO-rich (Fa(sub greater than 20)) fragments is consistent with mild thermal metamorphism in Wild 2.

Frank, D. R.; Zolensky, M. E.; Le, L.

2012-01-01

328

MATH 411 SPRING 2001 Ordinary Differential Equations  

E-print Network

MATH 411 SPRING 2001 Ordinary Differential Equations Schedule # 749025 TR 01:00-02:15 316 Boucke will be an introduction to ordinary differential equations. During the classes basic concepts of theory theory and implementations of ordinary differential equations. Text. Ray Redhefer Differential equations

Alekseenko, Alexander

329

The formation conditions of chondrules and chondrites.  

PubMed

Chondrules, which are roughly millimeter-sized silicate-rich spherules, dominate the most primitive meteorites, the chondrites. They formed as molten droplets and, judging from their abundances in chondrites, are the products of one of the most energetic processes that operated in the early inner solar system. The conditions and mechanism of chondrule formation remain poorly understood. Here we show that the abundance of the volatile element sodium remained relatively constant during chondrule formation. Prevention of the evaporation of sodium requires that chondrules formed in regions with much higher solid densities than predicted by known nebular concentration mechanisms. These regions would probably have been self-gravitating. Our model explains many other chemical characteristics of chondrules and also implies that chondrule and planetesimal formation were linked. PMID:18566282

Alexander, C M O'D; Grossman, J N; Ebel, D S; Ciesla, F J

2008-06-20

330

Trace element geochemistry of CR chondrite metal  

E-print Network

We report trace element analyses by laser ablation inductively coupled plasma mass spectrometry of metal grains from 9 different CR chondrites, distinguishing grains from chondrule interior ("interior grains"), chondrule surficial shells ("margin grains") and the matrix ("isolated grains"). Save for a few anomalous grains, Ni-normalized trace element patterns are similar for all three petrographical settings, with largely unfractionated refractory siderophile elements and depleted volatile Au, Cu, Ag, S. All types of grains are interpreted to derive from a common precursor approximated by the least melted, fine-grained objects in CR chondrites. This also excludes recondensation of metal vapor as the origin of the bulk of margin grains. The metal precursors presumably formed by incomplete condensation, with evidence for high-temperature isolation of refractory platinum-group-element (PGE)-rich condensates before mixing with lower temperature PGE-depleted condensates. The rounded shape of the Ni-rich, interior ...

Jacquet, Emmanuel; Alard, Olivier; Kearsley, Anton T; Gounelle, Matthieu

2015-01-01

331

Chondrule-matrix relationships in chondritic meteorites  

NASA Technical Reports Server (NTRS)

The relationship between chondrules and matrix (fine grained material with a grain size less than 5 micrometers) in chondritic meteorites has been the subject of considerable controversy and no consensus currently exists. The coexistence of these two components in meteorites with bulk compositions that deviate only slightly from CI abundances suggests that cosmochemically their origins are closely linked. Any consideration of the relationship between chondrules and matrix hinges to a large degree on the origin of matrix. The entire spectrum of models exists from matrix as a nebular product to derivation entirely from chondrules. Early models of solar nebular evolution viewed chondrites as a two-component mixture of high- and low-temperature condensates. However, this model has been challenged by the recognition that the nebula was probably not uniformly vaporized.

Brearley, A. J.

1994-01-01

332

Rhodium and other platinum-group elements in carbonaceous chondrites  

Microsoft Academic Search

Five carbonaceous chondrites (including the CI chondrites Orgueil and Ivuna) were analyzed by spark source mass spectrometry (SSMS) for the platinum-group elements Ru, Rh, Os, Ir, Pt, as well as W, Re, An, Th, and U. Conventional photoplate detection and a recently developed multi-ion counting system were used for ion detection.Results obtained for CI chondrites agree with compiled values within

K. P. Jochum

1996-01-01

333

Evidence for association between Ir and Al in L chondrites.  

NASA Technical Reports Server (NTRS)

The nature of the Al-Ir association was investigated by plotting the whole chondrite abundance of Ir as determined by Mueller et al. (1971), and the Al abundance for the same chondrites. Ten of the 11 L chondrites plotted show a definite positive trend. The results are most consistent with the condensation mechanism of Larimer (1967) and the prediction of Larimer and Anders (1970).

Osborn, T. W.

1972-01-01

334

Amino acids of the Nogoya and Mokoia carbonaceous chondrites  

NASA Technical Reports Server (NTRS)

Amino acids were found in acid hydrolyzed, hot water extracts of the Nogoya (C2) and Mokoia (C3V) chondrites. About 40 n moles/g of amino acids were found in the Nogoya extract while Mokoia contained less than 1 n mole/g. The amino acid composition of Nogoya differs from that of other C2 chondrites studied earlier. The results from Mokoia are similar to previous data obtained from the C3V chondrite Allende.

Cronin, J. R.; Moore, C. B.

1976-01-01

335

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

336

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

337

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

338

Carbonate abundances and isotopic compositions in chondrites  

NASA Astrophysics Data System (ADS)

We report the bulk C abundances, and C and O isotopic compositions of carbonates in 64 CM chondrites, 14 CR chondrites, 2 CI chondrites, LEW 85332 (C2), Kaba (CV3), and Semarkona (LL3.0). For the unheated CMs, the total ranges of carbonate isotopic compositions are ?13C ? 25-75‰ and ?18O ? 15-35‰, and bulk carbonate C contents range from 0.03 to 0.60 wt%. There is no simple correlation between carbonate abundance and isotopic composition, or between either of these parameters and the extent of alteration. Unless accretion was very heterogeneous, the uncorrelated variations in extent of alteration and carbonate abundance suggests that there was a period of open system behavior in the CM parent body, probably prior to or at the start of aqueous alteration. Most of the ranges in CM carbonate isotopic compositions can be explained by their formation at different temperatures (0-130 °C) from a single fluid in which the carbonate O isotopes were controlled by equilibrium with water (?18O ? 5‰) and the C isotopes were controlled by equilibrium with CO and/or CH4 (?13C ? -33‰ or -20‰ for CO- or CH4-dominated systems, respectively). However, carbonate formation would have to have been inefficient, otherwise carbonate compositions would have resembled those of the starting fluid. A quite similar fluid composition (?18O ? -5.5‰, and ?13C ? -31‰ or -17‰ for CO- or CH4-dominated systems, respectively) can explain the carbonate compositions of the CIs, although the formation temperatures would have been lower (~10-40 °C) and the relative abundances of calcite and dolomite may play a more important role in determining bulk carbonate compositions than in the CMs. The CR carbonates exhibit a similar range of O isotopes, but an almost bimodal distribution of C isotopes between more (?13C ? 65-80‰) and less altered samples (?13C ? 30-40‰). This bimodality can still be explained by precipitation from fluids with the same isotopic composition (?18O ? -9.25‰, and ?13C ? -21‰ or -8‰ for CO- or CH4-dominated systems, respectively) if the less altered CRs had higher mole fractions of CO2 in their fluids. Semarkona and Kaba carbonates have some of the lightest C isotopic compositions of the meteorites studied here, probably because they formed at higher temperatures and/or from more CO2-rich fluids. The fluids responsible for the alteration of chondrites and from which the carbonates formed were almost certainly accreted as ices. By analogy with cometary ices, CO2 and/or CO would have dominated the trapped volatile species in the ices. The chondrites studied are too oxidized for CO-dominated fluids to have formed in their parent bodies. If CH4 was the dominant C species in the fluids during carbonate formation, it would have to have been generated in the parent bodies from CO and/or CO2 when oxidation of metal by water created high partial pressures of H2. The fact that the chondrite carbonate C/H2O mole ratios are of the order predicted for CO/CO2-H2O ices that experienced temperatures of >50-100 K suggests that the chondrites formed at radial distances of <4-15 AU.

Alexander, C. M. O'd.; Bowden, R.; Fogel, M. L.; Howard, K. T.

2015-04-01

339

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

340

Carbonate abundances and isotopic compositions in chondrites  

NASA Astrophysics Data System (ADS)

We report the bulk C abundances, and C and O isotopic compositions of carbonates in 64 CM chondrites, 14 CR chondrites, 2 CI chondrites, LEW 85332 (C2), Kaba (CV3), and Semarkona (LL3.0). For the unheated CMs, the total ranges of carbonate isotopic compositions are ?13C ? 25-75‰ and ?18O ? 15-35‰, and bulk carbonate C contents range from 0.03 to 0.60 wt%. There is no simple correlation between carbonate abundance and isotopic composition, or between either of these parameters and the extent of alteration. Unless accretion was very heterogeneous, the uncorrelated variations in extent of alteration and carbonate abundance suggests that there was a period of open system behavior in the CM parent body, probably prior to or at the start of aqueous alteration. Most of the ranges in CM carbonate isotopic compositions can be explained by their formation at different temperatures (0-130 °C) from a single fluid in which the carbonate O isotopes were controlled by equilibrium with water (?18O ? 5‰) and the C isotopes were controlled by equilibrium with CO and/or CH4 (?13C ? -33‰ or -20‰ for CO- or CH4-dominated systems, respectively). However, carbonate formation would have to have been inefficient, otherwise carbonate compositions would have resembled those of the starting fluid. A quite similar fluid composition (?18O ? -5.5‰, and ?13C ? -31‰ or -17‰ for CO- or CH4-dominated systems, respectively) can explain the carbonate compositions of the CIs, although the formation temperatures would have been lower (~10-40 °C) and the relative abundances of calcite and dolomite may play a more important role in determining bulk carbonate compositions than in the CMs. The CR carbonates exhibit a similar range of O isotopes, but an almost bimodal distribution of C isotopes between more (?13C ? 65-80‰) and less altered samples (?13C ? 30-40‰). This bimodality can still be explained by precipitation from fluids with the same isotopic composition (?18O ? -9.25‰, and ?13C ? -21‰ or -8‰ for CO- or CH4-dominated systems, respectively) if the less altered CRs had higher mole fractions of CO2 in their fluids. Semarkona and Kaba carbonates have some of the lightest C isotopic compositions of the meteorites studied here, probably because they formed at higher temperatures and/or from more CO2-rich fluids. The fluids responsible for the alteration of chondrites and from which the carbonates formed were almost certainly accreted as ices. By analogy with cometary ices, CO2 and/or CO would have dominated the trapped volatile species in the ices. The chondrites studied are too oxidized for CO-dominated fluids to have formed in their parent bodies. If CH4 was the dominant C species in the fluids during carbonate formation, it would have to have been generated in the parent bodies from CO and/or CO2 when oxidation of metal by water created high partial pressures of H2. The fact that the chondrite carbonate C/H2O mole ratios are of the order predicted for CO/CO2-H2O ices that experienced temperatures of >50-100 K suggests that the chondrites formed at radial distances of <4-15 AU.

Alexander, C. M. O'd.; Bowden, R.; Fogel, M. L.; Howard, K. T.

2015-01-01

341

Primary Oxygen Isotope Signatures of Chondrules in R Chondrites  

NASA Astrophysics Data System (ADS)

Chondrules in R3 clast from NWA 753 (R3-5) breccia show oxygen isotope ratios similar to those in LL3 chondrites. ?^17O values of most chondrules distribute between 0‰ and +1.5‰, significantly lower than that of bulk R chondrites (~2.7‰).

Kita, N. T.; Tenner, T. J.; Nakashima, D.; Ushikubo, T.; Bischoff, A.

2013-09-01

342

Chondrites: A Trace Fossil Indicator of Anoxia in Sediments  

Microsoft Academic Search

The trace fossil Chondrites, a highly branched burrow system of unknown endobenthic deposit feeders, occurs in all types of sediment, including those deposited under anaerobic conditions. In some cases, such as the Jurassic Posidonienschiefer Formation of Germany, Chondrites occurs in black, laminated, carbonaceous sediment that was deposited in chemically reducing conditions. In other cases, such as numerous oxic clastic and

Richard G. Bromley; A. A. Ekdale

1984-01-01

343

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

344

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

345

The Berduc L6 chondrite fall: Meteorite characterization, trajectory, and orbital elements  

NASA Astrophysics Data System (ADS)

The fall of the Berduc meteorite took place on April 7, 2008, at 01h 02min 28s+/-1s UTC. A daylight fireball was witnessed by hundreds of people from Argentina and Uruguay, and also recorded by an infrasound array in Paraguay. From the available data, the fireball trajectory and radiant have been reconstructed with moderate accuracy. The modeled trajectory was tested to fit the infrasound and strewn field data. From the computed apparent radiant ?=87+/-2° and ?=-11+/-2° and taking into account a range of plausible initial velocities, we obtained a range of orbital solutions. All of them suggest that the progenitor meteoroid originated from the main asteroid belt and followed an orbit of low inclination. Based on petrography, mineral chemistry, magnetic susceptibility, and bulk chemistry, the Berduc meteorite is classified as an L6 ordinary chondrite.

Trigo-Rodríguez, Josep M.; Llorca, Jordi; Madiedo, José M.; Tancredi, Gonzalo; Edwards, Wayne N.; Rubin, Alan E.; Weber, Patrick

2010-03-01

346

Olivine and Pyroxene Compositions in Fine-Grained Chondritic Materials  

NASA Technical Reports Server (NTRS)

Our analyses of the Wild-2 samples returned by the Stardust Mission have illuminated critical gaps in our understanding of related astromaterials. There is a very large database of olivine and low-calcium pyroxene compositions for coarse-grained components of chondrites, but a sparse database for anhydrous silicate matrix phases. In an accompanying figure, we present comparisons of Wild-2 olivine with the available chondrite matrix olivine major element data. We thus have begun a long-term project measuring minor as well as major element compositions for chondrite matrix and chondritic IDPs, and Wild 2 grains. Finally, we wish to re-investigate the changes to fine-grained olivine and low-Ca pyroxene composition with progressive thermal metamorphism. We have examined the LL3-4 chondrites which because of the Hayabusa Mission have become very interesting.

Zolensky, Michael E.; Frank, D.

2011-01-01

347

Chondritic meteorites and the lunar surface.  

PubMed

The landing dynamics of and soil penetration by Surveyor I indicated that the lunar soil has a porosity in the range 0.35 to 0.45. Experiments with Surveyor III's surface sampler for soil mechanics show that the lunar soil is approximately incompressible (as the word is used in soil mechanics) and that it has an angle of internal friction of 35 to 37 degrees; these results likewise point to a porosity of 0.35 to 0.45 for the lunar soil. Combination of these porosity measurements with the already-determined radar reflectivity fixes limits to the dielectric constant of the grains of the lunar soil. The highest possible value is about 5.9, relative to vacuum; a more plausible value is near 4.3. Either figure is inconsistent with the idea that the lunar surface is covered by chondritic meteorites or other ultrabasic rocks. The data point to acid rocks, or possibly vesicular basalts; carbonaceous chondrites are not excluded. PMID:17734304

O'keefe, J A; Scott, R F

1967-12-01

348

Structural deformation of the Leoville chondrite  

NASA Astrophysics Data System (ADS)

A petrofabric study of the Leoville chondrite was performed in order to gain an understanding of its deformation process. Strain values were determined from the chondrules' axial ratios or by the all-object-separation method, and the compaction required to deform Leoville chondrules was calculated from the decrease of radius in the circle-to-ellipse transformation. Structural and strain studies indicate the following order of events experienced by Leoville: (1) formation as an accretionary breccia, (2) compaction and development of foliation, (3) fracturing, possibly due to impact on earth, and (4) terrestrial weathering. Similarities between the axial ratios of chondrules (1.9-2.0) and of the whole meteorite (2.0) indicate either that Leoville deformed homogeneously or that it deformed as a framework of touching chondrules. This amount of strain corresponds to approximately 33 percent uniaxial shortening, assuming constant volume, and is likely to have been caused by compaction due to overburden from progressive accretion on the chondrite body. Diffusional flow is believed to be the mechanism by which olivines in these chondrules deformed.

Cain, P. M.; McSween, H. Y.; Woodward, N. B.

1986-03-01

349

Structural deformation of the Leoville chondrite  

NASA Technical Reports Server (NTRS)

A petrofabric study of the Leoville chondrite was performed in order to gain an understanding of its deformation process. Strain values were determined from the chondrules' axial ratios or by the all-object-separation method, and the compaction required to deform Leoville chondrules was calculated from the decrease of radius in the circle-to-ellipse transformation. Structural and strain studies indicate the following order of events experienced by Leoville: (1) formation as an accretionary breccia, (2) compaction and development of foliation, (3) fracturing, possibly due to impact on earth, and (4) terrestrial weathering. Similarities between the axial ratios of chondrules (1.9-2.0) and of the whole meteorite (2.0) indicate either that Leoville deformed homogeneously or that it deformed as a framework of touching chondrules. This amount of strain corresponds to approximately 33 percent uniaxial shortening, assuming constant volume, and is likely to have been caused by compaction due to overburden from progressive accretion on the chondrite body. Diffusional flow is believed to be the mechanism by which olivines in these chondrules deformed.

Cain, P. M.; Mcsween, H. Y., Jr.; Woodward, N. B.

1986-01-01

350

The Early History of Chondritic Metal  

NASA Astrophysics Data System (ADS)

Recently several related studies of chondritic metal were performed in order to obtain information on its origin and history. Most chondritic metal grains contain inclusions such as silica, chromite, and phosphate. Some inclusions in metal of low petrographic type chondrites contain chain-like structures which suggest that metal agglomerated from relic grains (Perron et al., 1989). Rb-Sr studies on chondritic metal show evolved initial ^87Sr (Podosek et al., 1991). Chronometric information can be obtained from studies of fission Xe from extinct ^244Pu, radiogenic ^129Xe from extinct ^129I, and radiogenic ^40Ar from long-lived ^40K. Therefore, the study of noble gas in chondritic metal can provide independent information on origin and thermal history. Some constraints on the origin and thermal history of metal which are based on detailed noble gas studies are discussed. High-purity (>99.5% by microscopic inspection) metal separates from H3.8 Dhajala (Dh), H4 Ste Marguerite (SM), H4 Forest Vale (FV), and H6 Estacado (Es), were obtained and studied for Ar and Xe isotopic abundances. They contain several noble gas components: fission Xe due to ^244Pu recoils and ^244Pu in inclusions, FVM-Xe (Marti et al., 1989), radiogenic ^129Xe, and radiogenic ^40Ar, together with in situ spallogenic products. 1). The ^244Pu fission Xe record: ^244Pu fission Xe which recoiled from adjacent phosphates is observed in decreasing amounts as Dh > FV=SM >> Es. The release of substantial amounts of ^244Pu-derived fission Xe at low temperatures (600 degrees C) in H4 metal implies that these metal grains were never heated to 600 degrees C after the decay of ^244Pu. 2). FVM-Xe: The metal of low petrographic type chondrites (H3 and 4) contains the novel component FVM-Xe (Marti et al., 1989). The most plausible source of FVM-Xe is a mixture of a ^235U neutron- induced fission Xe component with solar Xe (Kim and Marti, 1992). The phosphate separate from Forest Vale that contains most uranium does not show a neutron irradiation effect (Lavielle et al., 1992). Therefore the neutron irradiation occurred before the Xe closure time of phosphates. Possible sources of neutrons include: secondary neutrons produced by proto-solar activity and neutrons produced by fission of transuranic elements. 3). Radiogenic ^129Xe: All chondritic metals show ^129Xe(sub)r excesses, but the amounts of retained radiogenic ^129Xe(sub)r decrease with increasing petrographic type. The ratios ^129Xe/^132Xe in metal phases are not higher than those of bulk samples, indicating that metamorphic events may have taken place after decay of much of the ^129I. However, Estacado metal was not totally melted during metamorphism because its ^129Xe(sub)r is associated with inclusions. 4). Radiogenic ^40Ar: The amounts of radiogenic ^40Ar are very similar in the different petrographic types as expected for a parent with long half life. Also, the metamorphic event did not strongly fractionate potassium in the metal. In conclusion, acceptable models for the origin of chondritic metal need to consider the following constraints: Before or during accretion in the solar system, nebular materials including metal were exposed to a neutron fluence (>10^16 n/cm^2). After accretion of these early metal grains, secondary processing and metamorphism occurred, and the high petrographic types (H6) lost most of their fission Xe together with FVM-Xe and trapped gases. However, H4 metal was not heated to 600 degrees C after the decay of ^244Pu. References Kim J. S. and Marti K. (1992) Lunar Planet. Sci. (abstract) 23, 689. Lavielle B., Marti K., Pellas P., and Perron C. (1992) Search for 248Cm in the early solar system. Meteoritics (in Press). Marti K., Kim J. S., Lavielle B., Pellas P., and Perron C. (1989) Z. Naturforsch. 44a, 963-967. Perron C., Bourot-Denise M., Pellas P., Marti K., Kim J. S., and Lavielle B. (1989) Lunar Planet. Sci. (abstract) 20, 838. Podosek F. A., Brannon J. C., Perron C., and Pellas P. (1991) Lunar Planet. Sci. (abstract) 22, 1081.

Kim, J. S.

1992-07-01

351

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

352

Manganese chromium isotope systematics of carbonaceous chondrites  

NASA Astrophysics Data System (ADS)

In this article we present the results of Cr isotope investigations of different types of carbonaceous chondrites and of the pallasite Eagle Station. The 53Cr/ 52Cr ratios in the bulk samples of carbonaceous chondrites are correlated with 55Mn/ 52Cr ratios. The slope of the correlation line yields a 53Mn/ 55Mn ratio of (8.5 ± 1.5) × 10 - 6 at the time of Mn/Cr fractionation. Mapping this ratio onto an absolute time scale yields a time for this event of 4568.1 + 0.8/- 1.1 Ma ago. This time is very similar to the formation age of Efremovka CAIs of 4567.2 ± 0.6 Ma [Y. Amelin, A. N. Krot, I. D. Hutcheon, A. A. Ulyanov, Lead isotopic ages of chondrules and calcium-aluminum-rich inclusions, Science 297 (2002) 1678-1683], to a time of the chondrule formation of 4568 ± 1 Ma ago [L.E. Nyquist, D. Lindstrom, D. Mittlefehldt, C.-Y. Shih, H. Wiesmann, S. Wentworth, R. Martinez, Manganese-chromium formation intervals for chondrules from the Bishunpur and Chainpur meteorites, Meteorit. Planet. Sci. 36 (2001) 911-938], which, most likely, constrains early global high-temperature Mn/Cr fractionation in a nebular setting. The bulk samples of carbonaceous chondrites exhibit clear 54Cr excesses ( 54Cr *) that are correlated with the 53Cr excesses ( 53Cr *) and also with Mn/Cr ratios. One possible explanation of this correlation is that 54Cr * is also radiogenic, like 53Cr *, and was formed by the decay of the short-lived parent radionuclide 54Mn. The very short half-life of 54Mn of 312 days would require that both short-lived radionuclides 53Mn and 54Mn were generated locally in spallation reactions during the early period of an active sun. The alternative and possibly more plausible explanation is the heterogeneous addition of presolar material. The presolar component, enriched in 54Cr, is mostly contained in the matrix of carbonaceous chondrites. The relative amount of matrix decreases in the sequence CI > CM > CO,CV. A large proportion of Mn is associated with the matrix while Cr preferentially resides in the chondrules. Thus, the Mn/Cr ratio also follows the sequence CI > CM > CO > CV and is correlated with 54Cr. The acid-resistant residues of carbonaceous chondrites are characterized by relatively large excesses of 54Cr and moderate deficits of 53Cr. The magnitude of these excesses and deficits decreases in the sequence CI, CM, CV and may imply that Cr in the CM, and CV residues is increasingly more equilibrated with Cr from the rest of the meteorites. The 53Cr/ 52Cr and 54Cr/ 52Cr ratios in the residues are anti-correlated indicating that there are at least two Cr components of possibly presolar origin. All residues have large excesses of the most neutron-rich Ti isotope, 50Ti *. The pattern of 50Ti * does not exactly follow that observed for 54Cr * but it is generally similar. The Cr isotope systematic of the pallasite Eagle Station indicates that the precursor of this meteorite was a CV-type material. The 53Mn- 53Cr system indicates that the Cr isotopes equilibrated in this meteorite 4557.5 ± 0.6 Ma ago.

Shukolyukov, A.; Lugmair, G. W.

2006-10-01

353

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

354

Meromorphic solutions of nonlinear ordinary differential equations  

Microsoft Academic Search

Exact solutions of some popular nonlinear ordinary differential equations are analyzed taking their Laurent series into account. Using the Laurent series for solutions of nonlinear ordinary differential equations we discuss the nature of many methods for finding exact solutions. We show that most of these methods are conceptually identical to one another and they allow us to have only the

Nikolai A. Kudryashov

2010-01-01

355

The ordinary school – what is it?  

Microsoft Academic Search

In this paper we describe some of the complexities involved in the construction of a sample of ‘ordinary’ schools. We outline the policy context in England that produces pressures to resist ‘ordinariness’. The paper then explores two theoretical tools, fabrication and rhetoric, that are deployed in an analysis of some key artefacts of fabrication from schools in England. Through an

Meg Maguire; Jane Perryman; Stephen Ball; Annette Braun

2011-01-01

356

The Ordinary School--What Is It?  

ERIC Educational Resources Information Center

In this paper we describe some of the complexities involved in the construction of a sample of "ordinary" schools. We outline the policy context in England that produces pressures to resist "ordinariness". The paper then explores two theoretical tools, fabrication and rhetoric, that are deployed in an analysis of some key artefacts of fabrication…

Maguire, Meg; Perryman, Jane; Ball, Stephen; Braun, Annette

2011-01-01

357

Multistep Filtering Operators for Ordinary Differential Equations  

E-print Network

Multistep Filtering Operators for Ordinary Differential Equations Micha Janssen, Yves Deville­la­Neuve, Belgium fmja,yde,pvhg@info.ucl.ac.be Abstract Interval methods for ordinary differential equations (ODEs Differential equations (DE) are important in many scientific applications in areas such as physics, chemistry

Deville, Yves

358

Ordinary Differential Equations 1 An Oscillating Pendulum  

E-print Network

Ordinary Differential Equations 1 An Oscillating Pendulum applying the forward Euler method using 1 / 39 #12;Ordinary Differential Equations 1 An Oscillating Pendulum applying the forward Euler Equations 4 October 2013 2 / 39 #12;a simple pendulum Imagine a sphere attached to a massless rod oscilating

Verschelde, Jan

359

FE2713 Ordinary Least Squares (OLS) 1 FE2713 Ordinary Least Squares (OLS)  

E-print Network

FE2713 Ordinary Least Squares (OLS) 1 FE2713 Ordinary Least Squares (OLS) Ordinary least squares (OLS), also known as the method of least squares, is a technique used to determine how one quantity Y relationship that holds between X and Y . OLS provides such a linear relationship that is optimal in a sense

Magdon-Ismail, Malik

360

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

361

The compositional classification of chondrites. IV - Ungrouped chondritic meteorites and clasts  

NASA Astrophysics Data System (ADS)

INAA and RNAA are used to determine the abundances of 30 elements in the unusual chondrites Acapulco (A), Allan Hills A77081 (AH), Cumberland Falls (CF), Enon, Tierra Blanca (TB), and Udei Station (US). The results are presented in tables and graphs and characterized in detail. A, AH, and Enon are grouped together on the basis of their subpristine composition; US is classified as IAB; TB is found to have an altered composition with evidence of phosphate-phase loss like US but is left ungrouped due to its high delta-(O-18); and CF is found to resemble the LL chondrites, with evidence of in situ reduction by exchange with the aubritic host.

Kallemeyn, G. W.; Wasson, J. T.

1985-01-01

362

Origins and Distribution of Chondritic Olivine Inferred from Wild 2 and Chondrite Matrix  

NASA Technical Reports Server (NTRS)

To date, only 180 particle impact tracks from Wild 2 have been extracted from the Stardust aerogel collector and even fewer have been thoroughly characterized. In order to provide a cohesive compositional dataset that can be compared to the meteorite record, we have made both major and minor element analyses (TEM/EDXS) of olivine and low-Ca pyroxene for 39 particles harvested from 26 tracks. However, the dearth of equivalent analyses for these phases in chondrite matrix hinders their comparison to the Wild 2 samples. To properly permit comparison of chondritic olivine and pyroxene to the Wild 2 samples, we have also provided a large, comprehensive EPMA dataset (greater than10(exp 3) analyses) of analogous grains (5-30 micrometers) isolated in L/LL3.0-4, CI, CM, CR, CH, CO, CV, Acfer 094, EH3, EL6, and Kakangari matrix

Frank, D. R.; Zolensky, M. E.

2014-01-01

363

Labile trace elements in carbonaceous chondrites - A survey  

NASA Technical Reports Server (NTRS)

Data are presented on 14 trace elements, including Co, Au, Ga, Rb, Sb, Ag, Se, Cs, Te, Zn, Cd, Bi, Tl, and In (nearly all of which are moderately or highly labile in meteorites), obtained by radiochemical neutron activation analyses of 42 C2-C6 chondrites, all but three from Antarctica. The data indicate that carbonaceous chondrites of petrographic types 2-6 define compositional continua. It is suggested that carbonaceous C2-C6 chondrites may reflect a mixture of material that formed at low temperatures and that contained cosmic levels of highly labile elements, with material that was devoid of them.

Xiao, Xiaoyue; Lipschutz, Michael E.

1992-01-01

364

Chondritic Meteorites: Nebular and Parent-Body Formation Processes  

NASA Technical Reports Server (NTRS)

It is important to identify features in chondrites that formed as a result of parent-body modification in order to disentangle nebular and asteroidal processes. However, this task is difficult because unmetamorphosed chondritic meteorites are mixtures of diverse components including various types of chondrules, chondrule fragments, refractory and mafic inclusions, metal-sulfide grains and fine-grained matrix material. Shocked chondrites can contain melt pockets, silicate-darkened material, metal veins, silicate melt veins, and impact-melt-rock clasts. This grant paid for several studies that went far in helping to distinguish primitive nebular features from those produced during asteroidal modification processes.

Rubin, Alan E.; Lindstrom, David (Technical Monitor)

2002-01-01

365

Yes, Kakangari is a unique chondrite. [meteoritic composition  

NASA Technical Reports Server (NTRS)

The position of the Kakangari chondrite as the representative of a new class of chondrites is considered, taking into account the results of the analysis of a 17.1-mg piece of Kakangari for 20 elements. Elemental concentration data are compared for Kakangari and other meteorite groups. Data for the most similar groups, C2, C3(V), L, and E4 chondrites are represented in a graph along with Kakangari data. It is found that pronounced differences exist between Kakangari and the other meteorite classes.

Davis, A. M.; Grossman, L.; Ganapathy, R.

1977-01-01

366

Thulium anomalies and rare earth element patterns in meteorites and Earth: Nebular fractionation and the nugget effect  

E-print Network

This study reports the bulk rare earth element (REEs, La-Lu) compositions of 41 chondrites, including 32 falls and 9 finds from carbonaceous (CI, CM, CO and CV), enstatite (EH and EL) and ordinary (H, L and LL) groups, as well as 2 enstatite achondrites (aubrite). The CI-chondrite-normalized REE patterns and Eu anomalies in ordinary and enstatite chondrites show more scatter in more metamorphosed than in unequilibrated chondrites. This is due to parent-body redistribution of the REEs in various carrier phases during metamorphism. The dispersion in REE patterns of equilibrated ordinary chondrites is explained by the nugget effect associated with concentration of REEs in minor phosphate grains. Terrestrial rocks and samples from ordinary and enstatite chondrites display negative Tm anomalies of ~-4.5 % relative to ca chondrites. In contrast, CM, CO and CV (except Allende) show no significant Tm anomalies. Allende CV chondrite shows large excess Tm (~+10 %). These anomalies are similar to those found in group II...

Dauphas, N

2015-01-01

367

Semarkona: Lessons for chondrule and chondrite formation  

NASA Astrophysics Data System (ADS)

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; Ebel, Denton S.

2015-01-01

368

Carbonaceous chondrites and the origin of life  

NASA Technical Reports Server (NTRS)

Organic matter in carbonaceous chondrites can be separated into three fractions. The first component, the fraction that is insoluble in chloroform and methanol, has a part which is of interstellar origin. The other two fractions (chloroform-soluble hydrocarbons and methanol-soluble polar organics) are hypothesized to have been synthesized on a planetoid body. We propose that the polar organics, i.e., amino acids, were synthesized close to its surface by the radiolysis of hydrocarbons and ammonium carbonate in a liquid water environment. Some hydrocarbons may have been synthesized by a Fischer-Tropsch mechanism in the interior of the body. Ferrous ion acted as a protection against back reactions. The simultaneous synthesis of iron-rich clays with the polar organics may be indicative of events related to the origin of life on Earth.

Hartman, Hyman; Sweeney, Michael A.; Kropp, Michael A.; Lewis, John S.

1993-01-01

369

Relationships with CM-type Chondrites  

NASA Astrophysics Data System (ADS)

Colleagues still have trouble understanding how the dominant relationship between CM-type chondrites and AMMs was established. They also wonder about the meaning of this relationship in terms of solar system history, and they generally expect that it has been markedly altered upon atmospheric entry, except for the smallest particles collected in the stratosphere. They are also confused when hearing that in spite of strong similarities there are also marked differences between these two varieties of solar system materials. Consequently, some of them believe that this relationship has not been convincingly established. This section mostly relies on arguments already presented by Kurat and Maurette (1997) in a book published in French, which have only been improved recently through the analysis of the Concordia Antarctic micrometeorites (Duprat et al., 2003 and 2004).

Maurette, Michel

370

Behavior of Chromium in Chondritic Materials  

NASA Astrophysics Data System (ADS)

To survey the existence forms and existence patterns of Cr and Ru in high-temperature condensate, we have continued to carry out elemental analyses of primitive meteorites particularly acid insoluble fractions and metal phases from them. In addition, condensation calculation, which assume ideal solid solution in the multicomponent alloy, by using thermodynamic data have been performed. Noting that acid residues would contain the high-temperature condensate component, we considerd chemical compositions of acid residues by relating to the condensation process from the solar nebula. In this paper, we present the representative elemental compositions of some chondritic meteorites and discuss the implications of these data to consider the behavior of Cr in meteoritical samples.

Kano, N.; Matsuzaki, H.; Nogami, K.; Imamura, M.

1996-03-01

371

Trace element geochemistry of CR chondrite metal  

NASA Astrophysics Data System (ADS)

We report trace element analyses by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) of metal grains from nine different CR chondrites, distinguishing grains from chondrule interior ("interior grains"), chondrule surficial shells ("margin grains"), and the matrix ("isolated grains"). Save for a few anomalous grains, Ni-normalized trace element patterns are similar for all three petrographic settings, with largely unfractionated refractory siderophile elements and depleted volatile Au, Cu, Ag, S. All three types of grains are interpreted to derive from a common precursor approximated by the least-melted, fine-grained objects in CR chondrites. This also excludes recondensation of metal vapor as the origin of the bulk of margin grains. The metal precursors were presumably formed by incomplete condensation, with evidence for high-temperature isolation of refractory platinum-group-element (PGE)-rich condensates before mixing with lower temperature PGE-depleted condensates. The rounded shape of the Ni-rich, interior grains shows that they were molten and that they equilibrated with silicates upon slow cooling (1-100 K h-1), largely by oxidation/evaporation of Fe, hence their high Pd content, for example. We propose that Ni-poorer, amoeboid margin grains, often included in the pyroxene-rich periphery common to type I chondrules, result from less intense processing of a rim accreted onto the chondrule subsequent to the melting event recorded by the interior grains. This means either that there were two separate heating events, which formed olivine/interior grains and pyroxene/margin grains, respectively, between which dust was accreted around the chondrule, or that there was a single high-temperature event, of which the chondrule margin records a late "quenching phase," in which case dust accreted onto chondrules while they were molten. In the latter case, high dust concentrations in the chondrule-forming region (at least three orders of magnitude above minimum mass solar nebula models) are indicated.

Jacquet, Emmanuel; Paulhiac-Pison, Marine; Alard, Olivier; Kearsley, Anton T.; Gounelle, Matthieu

2013-10-01

372

Thermomagnetic analysis of meteorites, 2: C2 chondrites  

NASA Technical Reports Server (NTRS)

Samples of all eighteen of the known C2 chondrites were analyzed thermomagnetically. For eleven of these, initial Fe3O4 content is low(generally 1%) and the J sub s-T curves are irreversible. The heating curves show variable and erratic behavior, whereas the cooling curves appear to be that of Fe3O4. The saturation moment after cooling is greater (up to 10 times larger) than it is initially. This behavior is interpreted to be the result of the production of magnetite from a thermally unstable phase--apparently FeS. Four of the remaining 7 C2 chondrites contain Fe3O4 as the only significant magnetic phase: initial magnetite contents range from 4 to 13 percent. 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.

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

1974-01-01

373

Thermomagnetic analysis of meteorites, 2.C2 chondrites  

NASA Technical Reports Server (NTRS)

Samples of all eighteen known C2 chondrites have been analyzed thermomagnetically. For eleven of these, initial Fe3O4 content is low (generally less than 1%) and the saturation magnetization-vs.-temperature curves are irreversible. Th