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1

Chromites in unequilibrated ordinary chondrites  

NASA Astrophysics Data System (ADS)

Minor but significant amounts of chromian spinels and spinels are ubiquitous components of ordinary chondrites (OCs). Earlier studies of equilibrated OCs have shown that chromite compositions and textural settings are related to the petrologic type of ordinary chondrite (H, L, LL) and their metamorphic history. These have been shown to be compositionally uniform in each meteorite type and within each meteorite. Consistency within individual OCs has been shown to be inaccurate in studies of chromites from some type 4-6 OCs. More importantly, the extent of the variations in chromite compositions and textural settings from well characterized unequilibrated ordinary chondrites (UOCs) have been sparse in the literature. In particular, there have been no systematic studies that relate the chromites in UOCs to the progressive metamorphism scale as determined by thermoluminescence (TL) sensitivity. Is there a progression of changes in chromites from H3.4-3.8, from L3.3-3.8, or from LL3.0-3.8? Are chromites in UOCs sensitive to TL parameters? Are there differences between the chromite populations in low type 3 H, L and LL chromites? What is the significance of these results?

Nehru, C. E.; Weisberg, M. K.; Prinz, M.

1997-03-01

2

Abundance patterns of thirteen trace elements in primitive carbonaceous and unequilibrated ordinary chondrites  

Microsoft Academic Search

A neutron activation analysis technique was used to determine Au, Re, Co, Mo, As, Sb, Ga, Se, Te, Hg, Zn, Bi and Tl in 11 carbonaceous chondrites, 12 unequilibrated ordinary chondrites (UOC), and 4 equilibrated ordinary chondrites. The first 6 elements are `undepleted', the next 3 `normally-depleted' and the last 4 `strongly-depleted'. Except for Hg, `depleted-element' abundances in carbonaceous chondrites

D. R. Case; J. C. Laul; I. Z. Pelly; M. A. Wechter; M. E. Lipschutz; F. Schmidt-Bleek

1973-01-01

3

Ultrarapid chondrite formation by hot chondrule accretion? Evidence from unequilibrated ordinary chondrites  

NASA Astrophysics Data System (ADS)

Unequilibrated ordinary chondrites (UOCs) of all groups (H, L, LL) contain unique chondrite clasts, which are characterized by a close-fit texture of deformed and indented chondrules. These clasts, termed "cluster chondrites," occur in 41% of the investigated samples with modal abundances between 5 and 90 vol% and size variations between <1 mm and 10 cm. They show the highest chondrule abundances compared with all chondrite classes (82-92 vol%) and only low amounts of fine-grained interchondrule matrix and rims (3-9 vol%). The mean degree of chondrule deformation varies between 11% and 17%, compared to 5% in the clastic portions of their host breccias and to values of 3-5% found in UOC literature, respectively. The maximum deformation of individual chondrules is about 50%, a value which seemingly cannot be exceeded due to geometric limitations. Both viscous and brittle chondrule deformation is observed. A model for cluster chondrite formation is proposed where hot and deformable chondrules together with only small amounts of co-accreting matrix formed a planetesimal or reached the surface of an already existing body within hours to a few days after chondrule formation. They deformed in a hot stage, possibly due to collisional compression by accreting material. Later, the resulting rocks were brecciated by impact processes. Thus, cluster chondrite clasts are interpreted as relicts of primary accretionary rocks of unknown original dimensions. If correct, this places a severe constraint on chondrule-forming conditions. Cluster chondrites would document local chondrule formation, where chondrule-forming heating events and the accretion of chondritic bodies were closely linked in time and space.

Metzler, Knut

2012-12-01

4

Compositional trends in chondrules from unequilibrated enstatite chondrite, Parsa  

NASA Astrophysics Data System (ADS)

Multielemental analysis of chondrules from the unequilibrated E3 chondrite Parsa shows that the lithophile elements, both refractory and volatile, are enriched and siderophiles are depleted relative to C1 abundances. This behaviour is generally similar to chondrules from unequilibrated ordinary chondrites (UOC). A detailed comparison of compositional trends in chondrules from E3 chondrites (Parsa and Quingzhen) with UOC's indicates that some of the precursor components of chondrules of E3's are different from those of UOC's.

Shukla, P. N.; Bhandari, N.

5

Anomalous REE patterns in unequilibrated enstatite chondrites: Evidence and implications  

NASA Astrophysics Data System (ADS)

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

1993-03-01

6

I-Xe dating of chondrules from the Qingzhen unequilibrated enstatite chondrite  

NASA Astrophysics Data System (ADS)

It is shown that in Qingzhen, the I-Xe chronometer is decoupled from, and more stable than, both Ar-Ar and Rb-Sr chronometers, which were reset by unknown processes in the 1.4-2.8 Ga period. Because the range of I-Xe ages obtained are comparable to those observed in most unequilibrated ordinary chondrite chondrules, the enstatite chondrite region of the nebula was subject to the same processes at the same time as more oxidized regions of the nebula.

Ash, R. D.; Gilmour, J. D.; Whitby, J.; Prinz, M.; Turner, G.

1997-03-01

7

Physical properties of ordinary chondrites  

Microsoft Academic Search

Results are presented from an investigation of 11 non-Antarctic ordinary chondrites. The porosity of the chondrites is less than 20 percent, indicating that some mechanism acts to lower the porosity of chondrite parent bodies, if such objects originated as aggregates of dust. The elastic and thermal properties of ordinary chondrites vary markedly with porosity. It is thought that cracks originating

Kiyoshi Yomogida; Takafumi Matsui

1983-01-01

8

Actinide abundances in ordinary chondrites  

SciTech Connect

The authors objective in this study was to obtain additional data on actinide and light REE (LREE) abundances in equilibrated ordinary chondrites, testing the internal consistency of the direct approach and comparing the direct and indirect approaches on the same sample. Representative aliquots were analyzed for Xe by noble gas mass spectrometry or for U, Th, Ce, Nd, and Sm concentrations by isotope dilution. The nature and abundances of the phosphate phases, known to be major carriers for these elements, were determined petrographically. The high-accuracy isotopic dilution data provide a test of the assumptions of the uniformity of absolute and relative abundances of refractory lithophile elements in ordinary chondrites. Their results also provide the first determinations of the key Nd/U ratio on the same chondrite specimens.

Hagee, B.; Bernatowicz, T.J.; Podosek, F.A. (Washington Univ., St. Louis, MO (USA)); Johnson, M.L.; Burnett, D.S. (California Institute of Technology, Pasadena (USA)); Tatsumoto, M. (Geological survey, Denver, CO (USA))

1990-10-01

9

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

10

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

11

Noble Gases in Desert Meteorites: Howardities, Unequilibrated Chondrites, Regolith Breccias and an LL7  

NASA Astrophysics Data System (ADS)

We present He, Ne, and Ar data of 39 samples from 17 meteorites of various types. For three CV3 and two unequilibrated ordinary chondrites Kr and Xe data are also reported. The analyses served various purposes, e. g. to check for presence of solar noble gases, to determine concentrations of primordial noble gases, to study cosmic ray exposure ages including possible parent body exposures, and to recognize paired meteorites. The data are shown in Tables 1 and 2. Ne-21 exposure ages are calculated with the cosmogenic nuclide production model by Leya et al., assuming average chemical composition of the respective meteorite class and taking the (Ne-22/Ne-21)cos ratio as shielding parameter. In some cases we had to assume additionally a meteoroid radius <32 cm. We report an age range (T(sup 21) min - T(sup 21) max) rather than a single age to indicate that even when (Ne-22/Ne-21)cos is available, meteoroid size and sample depth are not unambiguously known, hence the Ne-21 production rate is only constrained to within certain limits. The mean production rates used here compare well with those given by Eugster and Eugster and Michel for (Ne-22/Ne-21)cos values between 1.08 - 1.12 (chondrites) and 1.10 - 1.15 (howardites), respectively. On the other hand, our values are up to 30% lower for high (Ne-22/Ne-21)cos values, i.e. small meteorites and low shielding.

Wieler, R.; Baur, H.; Busemann, H.; Heber, V. S.; Leya, I.

2000-01-01

12

Incompletely compacted equilibrated ordinary chondrites  

SciTech Connect

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

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

2010-01-22

13

Aqueous Alteration on Ordinary Chondrite Parent Bodies The Oxygen Isotopic Composition of Water.O  

Microsoft Academic Search

It has become increasingly apparent that aqueous alteration has been a major process on meteorite parent bodies. Understanding the details of such processes can be greatly improved by a knowledge of the isotopic composition of water taking part in aqueous alteration. Studies of the unequilibrated ordinary chondrites (1, 2) have identified the presence of phyllosilicates which necessarily require reaction with

L. Baker; I. A. Franchi; I. P. Wright; C. T. Pillinger

2003-01-01

14

Hydrogen isotope abundances in the solar system. Part I. Unequilibrated chondrites  

SciTech Connect

Concentrations and isotopic compositions of H extracted by pyrolysis under a He flow were determined in three unequilibrated type 3 ordinary chondrites: Chainpur, Bishunpur and Ngawi. In Chainpur, a D-depleted component is removed at low temperature (200 to 400/sup 0/C), whereas at temperatures ranging between 450/sup 0/C and 900/sup 0/C, a D-rich component is evolved with a bimodal release pattern. The isotopic composition patterns reported as a function of temperature are qualitatively similar in the three meteorites. Consequently, the bulk isotopic composition of each meteorite is interpreted as resulting from the mixing of two components, the low deltaD fraction constituting 80 to 90% of the total H. The assumption that a carbonaceous chondrite-like polymer is the carrier of the D-rich H is supported by two observations: (i) the D-rich H is released with bimodal patterns, and (ii) oxidation of whole-rock samples with H/sub 2/O/sub 2/ removes this D-rich hydrogen. For each meteorite the peak in H concentration associated with the marked increase in the deltaD patterns permits one to calculate an isotopic composition for the D-rich H. The calculated deltaD values never exceed ca. + 5500 per thousand and no experimental indication of the presence of any D-richer H was found. Uncertainties on these determinations do not permit one to establish the presence of a unique D-rich component, common to these three meteorites.

Robert, F.; Javoy, M.; Halbout, J.; Dimon, B.; Merlivat, L.

1987-07-01

15

Semarkona meteorite: first recorded occurrence of smectite in an ordinary chondrite, and its implications  

SciTech Connect

Semarkona is an unshocked unequilibrated ordinary chondrite. Much of the interchondrule matrix and the mesostases of some chondrules and clasts have been hydrothermally altered. Analyses of altered materials and opaque matrix are presented. Ca and Fe have been redistributed from primary, anhydrous phases into calcite and Na, Fe smectite, respectively. In Semarkona the process possibly requires open system behavior inconsistent with the conventional view of metamorphism of the ordinary chondrites. The low petrologic type previously assigned to Semarkona is the result of retrograde metamorphism, under aqueous conditions, of a higher temperature mineral assemblage. Semarkona, and possibly Bishunpur, should be assigned to petrologic type 2.

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

1987-07-01

16

Partial Melting of Ordinary Chondrite Under Reducing Conditions  

NASA Astrophysics Data System (ADS)

A critical parameter in determining the nature and processes of differentiation of planetary materials in the early solar system is oxygen fugacity. Chondrites record a range of oxygen fugacities from approximately 5 log units below the iron-wustite (Fe-FeO) buffer (enstatite chondrites) to close to QFM (some carbonaceous chondrites). Among the equilibrated chondrites, an "oxidation gap" appears to exist between ordinary chondrites and enstatite chondrites, although several groups of unequilibrated carbonaceous chondrites appear to occupy this "gap". Some primitive achondrites fill this gap (e.g. pallasites, acapulcoites, lodranites, winonaites, and silicate-bearing IAB and IIE irons), although the precursors to these groups are poorly known. In this experimental study, we have determined the modification in mineral compositions during partial melting under reducing conditions and explore the idea that the primitive achondrites may be formed through differentiation under reducing conditions of a more oxidized precursor. Partial melting experiments were conducted on an H6 chondrite (Kernouve) under reducing conditions at 1 atm and at 1.3 GPa pressure in a solid media deformation apparatus. In the 1 atm experiments, fO2 was buffered by gas mixing and sealed silica tube techniques to values determined from thermodynamic calculations of primitive achondrites; in the deformation experiments, aluminum jackets were used. The experiments suggest that partial melting of an oxidized precursor under reducing conditions can produce some of the reduced features observed in primitive achondrites such as magnesian olivine, pyroxene and chromite compositions typical of primitive achondrites at temperatures of 1200-1300 ° C, as well as chalcophilic behavior of previously lithophillic ions (e.g., Cr in sulfide) at temperatures at 1000° C. Some features of primitive achondrites (e.g. oxygen isotopic compositions and Cr/(Cr+Al) ratios of chromites) appear to be intrinsic to the precursor chondrite. Further, mafic silicate and chromite reduction (increased Mg/(Mg+Fe)) required higher temperatures than those inferred for primitive achondrite formation. We suggest that the precurser chondrite for many primitive achondrites could have been somewhat more oxidized and subsequent melting under reducing conditions (e.g. in the presence of graphite) produced the reduction of mafic silicates and chromites in addition to chalcophilic behavior in some elements. Melt migration, solid-melt reactions and removal of key elements (e.g., S, Al) during melting might be enhanced by deformation and/or open system conditions, producing more dramatic changes in the residual solid. Other features however, must have been inherited from the precursor chondrite and therefore do not reflect changes produced during melting under reducing conditions.

Ford, R.; Rushmer, T.; Benedix, G.; McCoy, T.

2004-12-01

17

Source of potassium in shocked ordinary chondrites  

NASA Astrophysics Data System (ADS)

Argon–argon dating (a variation of potassium–argon dating) of ordinary chondrites is being used to reconstruct the collisional impact history of their parent bodies. However, due to the fine-grained, multi-mineral, highly shocked nature of chondrites, the sources of potassium (K) in these meteorites have not been fully identified. By locating and isolating the different sources prior to analysis, better ages can be obtained. To distinguish between possible sources, we have analyzed Chico and Northwest Africa 091 (both L6 chondrites) via K mass balance, Raman spectroscopy, and argon (Ar) diffusion studies.In accordance with previous studies on other ordinary chondrites, the Ar in these two chondrites is nearly equally split between two releases, and the lower temperature release is identified as sodium-rich feldspar. Various scenarios for the higher temperature release are investigated, but no scenario meets all the required criteria. The Ar activation energy of the higher temperature release is the same as pyroxene, but the pyroxene has no detectable K. The K mass balance shows feldspar can account for all the K in the chondrite; hence feldspar must be the ultimate source of the higher temperature release. Raman spectroscopy rules out a high-pressure phase of feldspar. Neither melt veins, nor feldspar inclusions in pyroxene, are abundant enough to account for the higher temperature release in these meteorites.

Weirich, J. R.; Swindle, T. D.; Isachsen, C. E.; Sharp, T. G.; Li, C.; Downs, R. T.

2012-12-01

18

Classification of four ordinary chondrites from Spain  

NASA Astrophysics Data System (ADS)

Based on optical microsocpy and electron microprobe analysis of mafic minerals, four previously poorly described ordinary chondrites from Spain are classified. The classifications of Guarena (H6), Olmedilla de Alarcon (H5) and Reliegos (L5) are confirmed. Molina is reclassified as H5, based on new data.

McCoy, T. J.; Casanova, I.; Keil, K.; Wieler, R.

1990-06-01

19

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

SciTech Connect

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

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

2010-05-10

20

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

21

Chemical and physical studies of type 3 chondrites. VI - Siderophile elements in ordinary chondrites  

NASA Astrophysics Data System (ADS)

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 oxgen 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 percent 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, Derek W. G.; Weeks, Karen S.

1986-12-01

22

The duration of ordinary chondrite metamorphism inferred from tungsten microdistribution in metal  

NASA Astrophysics Data System (ADS)

Precise ratios of W and Re relative to Ir determined by laser ablation ICP-MS reveal that matrix metal in equilibrated ordinary chondrites (EOC) exhibits a correlated variation of these ratios. In unequilibrated ordinary chondrites (UOC), the W/Ir ratio varies by over two orders of magnitude (W/Ir=0.003-0.6), and shows no correlation with any other siderophile element. Most matrix metal in UOC is depleted in W relative to metal in EOC. Thus, W must enter metal during metamorphism. The correlation between W/Ir and Re/Ir is evident in type 4 chondrites. This implies that the abundance (and isotopic composition) of W is set in ordinary chondrite metal by petrologic type 4, and that the reductant must be exhausted to limit further isotopic exchange, as indicated by the 182Hf-182W ages of ordinary chondrite metal [Lee and Halliday, Science 274 (1996) 1876-1879]. This offers a means of dating the onset of metamorphic heating of OC parent bodies. A discrepancy in ages between 182Hf-182W [Lee and Halliday, Science 274 (1996) 1876-1879] and 207Pb-206Pb [Göpel et al., Earth Planet. Sci. Lett. 121 (1994) 153-171] (or 129I-129Xe [Brazzle et al., Geochim. Cosmochim. Acta 63 (1999) 739-760]) dating is real, and measures the interval of metamorphism: the time difference between reduction of W during the onset of heating and isotopic closure of Pb (or Xe) by cooling, e.g., ?Tm=2-12 Myr for H chondrites. The 187Re-187Os and 182Hf-182W ages are set by the same process, metamorphic equilibration, establishing an important link between an absolute chronometer (t1/2[187Re]=41.6 billion years) and a short-lived radioisotope system (t1/2[182Hf]=9 Myr).

Humayun, Munir; Campbell, Andrew J.

2002-04-01

23

Magnetic classification of stony meteorites: 2. Non-ordinary chondrites  

Microsoft Academic Search

A database of magnetic susceptibility (chi) measurements on different non-ordinary chondrites (C, E, R, and ungrouped) populations is presented and compared to our previous similar work on ordinary chondrites. It provides an exhaustive study of the amount of iron-nickel magnetic phases (essentially metal and magnetite) in these meteorites. In contrast with all the other classes, CM and CV show a

Pierre Rochette; Jérôme Gattacceca; Lydie Bonal; Michèle Bourot-Denise; Vincent Chevrier; Jean-Pierre Clerc; Guy Consolmagno; Luigi Folco; Matthieu Gounelle; Tomas Kohout; Lauri Pesonen; Eric Quirico; Leonardo Sagnotti; Anna Skripnik

2008-01-01

24

Re-assessing the ordinary chondrites paradox  

NASA Astrophysics Data System (ADS)

Context. The so-called ordinary chondrite paradox has been a recurring topic in planetary science in the past twenty years. This paradox originated from the first comparisons between spectrophotometric measurements of meteorites and asteroids. Basically it is based on the lack of spectral analogs of the ordinay chondrites (OC) among the Main Belt asteroids, although present among the NEAs. Several hypothesis to account for the paradox have been published, all considering the effect of space weathering and different degrees of resurfacing on the asteroids surfaces. Aims: The aim of the present paper is to further investigate this intriguing problem considering that the small-sized population of Main Belt asteroids has not yet been analyzed. Methods: Spectroscopic observations of Main Belt asteroids with a size smaller than 5 km - similar to that of NEAs - were performed with the 8-m Gemini telescope. Furthermore, spectra obtained in large spectroscopic surveys were used to perform a statistical analysis of the fraction of spectral analogous to the OCs in the Main Belt and NEA populations. Results: The main result of this work is that the vast majority of the Main Belt Sk- and Sq-class asteroids can be matched to OC meteorites in the visible part of the spectrum. Conclusions: Our results suggest that a considerable fraction of the OC material in the Main Belt is presently unweathered enough to be comparable to meteorite laboratory spectra.

Mothé-Diniz, T.; Jasmin, F. L.; Carvano, J. M.; Lazzaro, D.; Nesvorný, D.; Ramirez, A. C.

2010-05-01

25

The Parent Asteroids of Ordinary Chondrite Meteorites  

NASA Astrophysics Data System (ADS)

Ordinary chondrites account for 80% of meteorite falls, but twenty years of searching have found only a very few direct spectral matches between OC's and asteroids. Those asteroids that do match are small, rare, and all but one are in the planet crossing asteroid population. The one OC match in the main belt, 3628 Boznemcova, is very small (7 km) and the only OC found out of a thousand asteroids examined by the Binzel et al. search. Why can't we find a large reservoir of ordinary chondrite parent bodies? The three commonly cited theories on OC parent bodies each have their flaws. Bell's approach, that OC's have been smashed by collisional evolution into fragments smaller than 10 km diameter has not been supported by the results of the extensive Binzel search. Chapman has suggested that the S-asteroids may be OC's that have "space weathered". S-asteroids are abundant and have "approximately" OC-like albedo and spectral features. But the work of Gaffey et al. has shown that the S class is really a grab-bag of radically different mineralogies and only the S(IV) subclass has OC-like mineralogies. In addition, extensive spectral and petrologic work with regolith OC's and space weathering experiments with OC material have shown that OC's do not "space weather" to match the spectral features of S-asteroids. But S(IV)/OC link also has several problems: (1) S asteroids have weaker absorption bands than OC's; (2) S asteroids have a much stronger spectral "red" slope from 0.6 to 1.6 microns; (3) S asteroids have a characteristic "leveling off" of the spectral slope longwards of 1.6 microns.

Britt, D. T.

1996-03-01

26

Thermoluminescence of Primitive Ordinary Chondrites, Semarkona and Bishunpur  

Microsoft Academic Search

A thermoluminescence (TL) spatial distribution readout system attached to a microscope has been developed (1). This system has become a time-resolving spectroscopy system, substituting a spectroscope for the microscope (2). The induced TL sensitivity of ordinary chondrites increases by a factor of 10^5 with metamorphism and the primitive ordinary chondrites such as Semarkona (LL3.0) and Bishunpur (LL3.1) have the lowest

K. Ninagawa; I. Yamamoto; M. Kohata; T. Wada; Y. Yamashita; J. Lu; D. W. G. Sears; S. Matsunami; H. Nishimura

1992-01-01

27

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

28

Kamacite and olivine in ordinary chondrites: Intergroup and intragroup relationships  

Microsoft Academic Search

The three principal groups of ordinary chondrites (OCs), H (high total Fe), L (low total Fe), and LL (low total Fe, low metallic Fe), constitute â¼80% of all meteorites observed to fall. In going from H to L to LL chondrites, the abundances of siderophile elements decrease and the degree of oxidation increases. The proportion of oxidized Fe (i.e., FeO

A RUBIN

1990-01-01

29

The mineralogy of ordinary chondrites and implications for asteroid spectrophotometry  

NASA Astrophysics Data System (ADS)

Published data from bulk chemical analyses of 94 ordinary chondrites are compiled in a table of normative mineralogy and discussed in detail. Significant variations in olivine, pyroxene, and metal abundance ratios are found within each chondrite class and attributed to redox processes superimposed on initial differences in metal/silicate ratios. The use of the diagrams constructed here to predict the mineralogic characteristics of asteroids on the basis of spectrophotometric observations is suggested.

McSween, H. Y.; Bennett, M. E.; Jarosewich, E.

1991-03-01

30

Ordinary Chondrites Viewed as Reassembled 'Splash Ejecta'  

NASA Astrophysics Data System (ADS)

A case has already been made favouring chondrites as re-assembled "splash ejecta" following low velocity collisions between molten planetesimals[1]. Here I briefly review this hypothesis, then develop further arguments in its support. The scenario envisaged may be summarized as follows. Planetesimals grew to radii greater than 30 km in less than 1 Ma after the formation of CAIs, and they were heated rapidly by the decay of 26Al. By 2 Ma each planetesimal had a molten interior insulated by a cool, dusty carapace. Low velocity collisions at this stage released enormous, turbulent, expanding clouds of incandescent spray mixed with dust and solid grains from the carapace. The cloud constituted a rather special, transient nebular environment; as it cooled the melt droplets became chondrules. Much of the cloud's contents re-assembled under gravity onto the surface of the hot, residual planetesimal and the accumulated debris became re-heated and metamorphosed. Collisions recurred over the few million years that relative velocities remained low and planetesimals remained molten. Thus, the cumulative debris contained many recycled and broken chondrules. This scenario is apparently reconcilable with chondrule cooling rates, the preservation of clasts of "planetary" rock in chondrites, the retention of volatiles in chondrules, the preservation of solar chemistry and more than a dozen other features. Is it reasonable to claim that 30 km radius bodies existed by 1 Ma, and were substantially molten by 2 Ma? Cameron[2] argued that CAIs were saved from drifting into the sun by their incorporation, soon after formation, into planetesimals whose mass was sufficient to hold them in orbits, decoupled from the drag of nebular gas. Wetherill's models [3] show that many bodies >100 km radius may have formed on a timescale of 10^5 years. In these terms, the proposed 30 km by 1 Ma is quite conservative. Regarding 26Al heating, the remarkably constant initial ratio of 26Al/27Al (5 x 10^-5) in CAIs from different classes of meteorite [4] suggests that 26Al was uniformly distributed in the dust which eventually formed the chondrite parent bodies. This amount of 26Al translates to some 7000 J g^-1. A simple finite element calculation was made to assess the likely thermal evolution of planetesimals of different sizes, starting from 300K at different times. The proposed body of 30 km radius at 1 Ma was found to be a limit for substantial internal melting. Its interior would have remained molten for several million years. Earlier accretion, or larger planetesimals, would have generated even more melt. It seems, therefore, that molten planetesimals were abundant in the early solar system. Moreover, they evidently suffered collision and accretion. If their collision products were not chondrules, then what were they? Two further arguments favouring the proposed scenario concern the age difference of CAIs and chondrules, and the existence of macrochondrules. Cameron's Leonard Award address [2] was stimulated by the inferred time interval of several million years between the formation of CAIs and chondrules. Chondrules were interpreted as dust melted by solar flare activity, the dust having been produced by late collisions between planetesimals. If, as is argued here, the planetesimals were already internally molten, chondrules would have been produced directly, without need to invoke a solar flare heat source. A separate issue is the existence of porphyritic olivine macrochondrules up to 4 cm across [5]. Macrochondrules are not easily reconcilable with chondrule formation by radiative heating in a nebular setting. Such a mechanism predicts an inverse relationship between chondrule diameter and temperature rise, which is not observed. However, in the present scenario macrochondrules are interpreted simply as examples of large blobs of frozen melt. References: [1] Sanders I. S. (1994) Meteoritics, 29, 527. [2] Cameron A. G. W. (1995) Meteoritics, 30, 133-161. [3] Wetherill G. W. (1989) in Asteroids II (R. P. Binzel et al., eds.), 661-

Sanders, I. S.

1995-09-01

31

UPb systematics of phosphates from equilibrated ordinary chondrites  

Microsoft Academic Search

U-Pb systematics were determined from fifteen phosphate separates from equilibrated ordinary chondrites and from small bulk fragments of the same meteorites. The high U-238\\/Pb-204 ratios of thirteen of these phosphate separates lead to extremely radiogenic Pb whose Pb-206\\/Pb-204 ratios range from 250 up to 3500. The Pb\\/Pb model ages for these phosphates range from 4.563 to 4.502 Ga, with an

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

1994-01-01

32

An ordinary chondrite impactor for the Popigai crater, Siberia  

NASA Astrophysics Data System (ADS)

With a diameter of ˜100 km, Popigai in Northern Siberia is the largest crater known in the Cenozoic. The concentrations in platinum group elements (PGE) were analyzed in twenty samples of homogeneous impact melt collected in the northwestern flank of the crater to identify the composition of the projectile. The method selected was preconcentration by NiS fire assay followed by inductively coupled plasma-mass spectrometry (ICP-MS). This technique measures all the PGE (except Os) and by using aliquots >10g, the results are highly reproducible. The major and trace element composition of the impact melt resembles that of gneissic lithologies of the Anabar shield, which are representative of the target rock. The PGE are enriched in the melt by factors of 3 to 14 compared to the main target lithology, but the meteoritic contamination is only around 0.2 wt.%. Using plots of elemental ratios such as Ru/Rh vs. Pt/Pd or Ru/Rh vs. Pd/Ir, the Popigai impactor is clearly identified as an ordinary chondrite and most likely L-chondrite. This study indicates that PGE elemental ratios allow discrimination of the type of impactor, even in the case of low meteoritic contamination. This study confirms that a significant fraction of the crater-forming projectiles presently documented could have an ordinary chondrite composition. Their probable source, the S-type asteroids, appears to form the majority of the bodies in the main asteroid belt and among Near Earth Objects (NEOs). The ordinary chondrite origin of the Popigai projectile supports an asteroidal origin for the late Eocene impacts as a plausible alternative to the comet shower scenario proposed by Farley et al. (1998).

Tagle, Roald; Claeys, Philippe

2005-06-01

33

U-Pb systematics of phosphates from equilibrated ordinary chondrites  

NASA Astrophysics Data System (ADS)

U-Pb systematics were determined from fifteen phosphate separates from equilibrated ordinary chondrites and from small bulk fragments of the same meteorites. The high U-238/Pb-204 ratios of thirteen of these phosphate separates lead to extremely radiogenic Pb whose Pb-206/Pb-204 ratios range from 250 up to 3500. The Pb/Pb model ages for these phosphates range from 4.563 to 4.502 Ga, with an analytical precision of 106y and the U-Pb system is apparently concordant. The time interval observed 60 x 106y, reflects the thermal processing of the equilibrated chondrites and is consistent with that previously derived from the Rb/Sr, K/Ar and Pu chronologies. The Pb/Pb ages of the phosphates from the seven H chondrites show a negative correlation versus their metamorphic grade. This is the first clear relationship ever observed between a long-lived chronometer and the intensity of metamorphism as reflected by metamorphic grade. Assuming that the Pb/Pb age indicates the accurate U-Pb closure time in phosphates, the Pb/Pb chronology is compatible with the model of a layered H chondrite parent body. However, this interpretation of the U/Pb systematics is not unique; it postulates a slow cooling of the equilibrated materials at high temperature, in apparent conflict with petrological observations. Except for the H chondrites, which agree rather well with Pu systematics, comparison of the Pb/Pb chronology with published radiochronometric data does not reveal simple correlations. In the present debate concerning the thermal history of chondrites, the chronometric information derived from each isotope system is interpreted as the time of its thermal closure. However, this basic assumption may not be correct for all the radio-chronologies and must be evaluated before the radiochronometric data can be applied as compelling time constraints for the period of 4.56 - 4.4 Ga of proto-planetary history.

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

1994-01-01

34

Petrology of nine ordinary chondrite falls from China  

NASA Astrophysics Data System (ADS)

Nine twentieth-century ordinary chondrite falls from China are described and classified. They include: Nantong (H6), Zaoyang (H5), Zhaodong (L4), Qidong (L-LL5), Raoyang (L6), Sheyang (L6), Guangnan (L6), Suizhou (L6) and Nan Yang Pao (L6). Kamacite in Qidong is rare and contains much more Co (15 mg/g) than is characteristic of L-group chondrites; Qidong may be a member of a chondrite group intermediate in its properties between L and LL. Zhaodong, Qidong, Raoyang, Sheyang and Suizhou have several olivine and/or low-Ca pyroxene grains with aberrant Fe/(Fe + Mg) ratios; it is probable that these five chondrites are fragmental breccias. The lack of correlation between shock facies and occurrence of aberrant silicate grains suggests that breccia lithification caused only minimal shock effects in many meteorites. Alternatively, postshock annealing may have resulted in the recrystallization of shock-indicating phases, leading to assignment of a shockfacies that is lower than that present immediately after the shock event.

Wang, D.; Rubin, A. E.

1987-03-01

35

Unusual olivine and pyroxene composition in interplanetary dust and unequilibrated ordinary chondrites  

NASA Astrophysics Data System (ADS)

The presence, in both a number of interplanetary dust particles (IDPs) and in meteorite matrices, of olivine and orthopyroxene grains, low in FeO but containing up to 5 wt pct MnO, is reported. The majority of olivines and pyroxenes in meteorites contain less than 0.5 wt pct MnO. The presence of these low-iron, manganese-enriched (LIME) olivines and pyroxenes in IDPs and meteorites may indicate a link between the origin and history of IDPs and the matrix material of primitive meteorites. The origin of the LIME silicates could be explained by condensation from a gas of solar composition. Forsterite is the first major silicate phase to condense from a solar nebula gas, and Mn, which is not stable as a metal under solar nebula conditions, would condense at about 1100 K as Mn2SiO4 in solid solution with forsterite.

Klock, W.; Thomas, K. L.; McKay, D. S.; Palme, H.

1989-05-01

36

Ordinary chondrite-like colors in small Koronis family members  

NASA Astrophysics Data System (ADS)

A survey of small (<5-10 km diameter) members of the Koronis family shows some objects with visible-wavelength broadband colors consistent with membership in the Q-class (Tholen, D.J. [1984]. Asteroid taxonomy from cluster analysis of photometry. Ph.D. Dissertation, University of Arizona, Tucson, AZ; Bus, S.J., Binzel, R.P. [2002]. Icarus 158, 146-177). This agrees with an ordinary chondritic composition for this family and suggests the timescale for changing Q-class to S-class spectra in the main belt is roughly comparable to the regolith refresh time in the 2-5 km size range.

Rivkin, Andrew S.; Thomas, Cristina A.; Trilling, David E.; Enga, Marie-therese; Grier, Jennifer A.

2011-02-01

37

Asteroidal source of ordinary chondrites (Meteoritical Society Presidential Address 1984)  

NASA Astrophysics Data System (ADS)

The orbital evolution of asteroidal fragments injected into the 3-1 Kirkwood gap resonance at 2.5 AU is investigated on the basis of a Monte Carlo simulation. The diameters of the fragments in the simulation were between 10 cm and 20 km, and it was assumed that the fragments cross the orbital path of the earth every one million years. The effects of close encounter planetary perturbations, the nu dot 6 secular resonance, and the ablative effects of the earth atmosphere were also taken into account. It is found that: (1) the predicted meteorite orbits closely matched the known orbits of ordinary chondrites; and (2) the total flux was in approximate agreement with the observed fall rate of ordinary chondrites. About 90 percent of the predicted impacting bodies were created by fragmentation of larger earth crossing asteroidal fragments, the largest of which were observed in the vicinity of the Apollo-Amor objects. The numerical results are presented in a series of graphs.

Wetherill, G. W.

1985-03-01

38

Carbide-magnetite assemblages in type-3 ordinary chondrites  

NASA Astrophysics Data System (ADS)

Abundant carbide-magnetite assemblages occur in matrix, chondrules, and chondrule rims in several H3, L3, and LL3 chondrites. Carbides, cohenite ((Fe,Ni)3C), and haxonite ((Fe,Ni)23C6) show compositional variations between different meteorites and appreciable ranges within meteorites. Carbides in H chondrites have lower Co contents (0 0.6 wt%) than those in L and LL chondrites (0.3 1.2 wt%). Metal associated with carbides and magnetite consists of high-Ni (50 70 wt%) taenite and, in L and LL chondrites, Co-rich (up to 35 wt%) kamacite; minor element contents of troilite and magnetite are very low. Textural observations indicate that carbide-magnetite assemblages formed by replacement of metal-sulfide nodules. The high Co contents of residual kamacite in association with carbides indicates that Co is not incorporated into carbides (i.e., Fe/Co is much higher in the carbides than in kamacite). Because Ni in carbides and magnetite is low, the Ni contents of residual taenite tend to be high. Ni-rich sulfides were found only in LL3 chondrites, possibly indicating their more extensive oxidation and/or aqueous alteration. We suggest that carbide-magnetite assemblages in type-3 ordinary chondrites formed as the result of hydrothermal alteration of metallic Fe in metal-troilite nodules by a COH-bearing fluid on their parent bodies. This alteration resulted in carbidization of FeNi metal, probably by CO gas (e.g., 15 Fe(s) + 4 CO(g) = Fe3C(s) + Fe3O4(s) or 3 Fe(s) + 2 CO(g) = Fe3C(s) + CO2(g)), and oxidation, probably by H2O gas (e.g., 3Fe(s) + 4H2O(g) = Fe3O4(S) + 4H2(g)). The COH-bearing fluids, which were possibly released during metamorphism and transported through zones of high permeability, may have been derived from ices, adsorbed gases, or hydrated minerals. The CO may be the result of the reaction of carbon compounds (e.g., hydrocarbons) with water vapor or magnetite.

Krot, Alexander N.; Zolensky, Michael E.; Wasson, John T.; Scott, Edward R. D.; Keil, Klaus; Ohsumi, Kazumasa

1997-01-01

39

Kamacite and olivine in ordinary chondrites: Intergroup and intragroup relationships  

SciTech Connect

The three principal groups of ordinary chondrites (OCs), H (high total Fe), L (low total Fe), and LL (low total Fe, low metallic Fe), constitute {approximately}80% of all meteorites observed to fall. In going from H to L to LL chondrites, the abundances of siderophile elements decrease and the degree of oxidation increases. The proportion of oxidized Fe (i.e., FeO in silicates) increases at the expense of metallic Fe. Because Fe is more readily oxidized than Ni or Co, bulk metal becomes increasingly rich in Ni and Co (e.g., Prior, 1916). Equilibrated LL chondrites are thus characterized by high FeO/(FeO + MgO) ratios in olivine and low-Ca pyroxene, high taenite/kamacite ratios, and the occurrence of Co-rich kamacite. The present study reports high-precision electron microprobe analyses of olivine and kamacite in a large suite of OCs. The purpose of the study was sixfold: (1) rigorously define the compositional ranges of these phases for each OC group, (2) identify anomalous OCs whose olivine and/or kamacite compositions lie outside the established ranges, and hence may not belong to the three main OC groups, (3) characterize the phases in the chondritic clasts of the Netschaevo iron meteorite and determine how closely related Netschaevo is to OCs, (4) determine if there are intragroup variations of olivine and kamacite compositions with petrologic type, (5) identify those OCs as fragmental breccias that contain some olivine and/or kamacite grains with aberrant compositions, and (6) search for new metallic Fe-Ni phases with extreme compositions. An expected by-product of this investigation was that a few meteorites that previously had not been well-characterized would be reclassified.

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

1990-05-01

40

Thermoluminescence of Primitive Ordinary Chondrites, Semarkona and Bishunpur  

NASA Astrophysics Data System (ADS)

A thermoluminescence (TL) spatial distribution readout system attached to a microscope has been developed (1). This system has become a time-resolving spectroscopy system, substituting a spectroscope for the microscope (2). The induced TL sensitivity of ordinary chondrites increases by a factor of 10^5 with metamorphism and the primitive ordinary chondrites such as Semarkona (LL3.0) and Bishunpur (LL3.1) have the lowest TL sensitivities (3). However, we investigated induced TL images and glow curves of them by the TL spatial distribution readout system over a wide range of wavelengths with Corning 4-96 filter. A chondrule with anorthite-normative mesostasis in Semarkona, which is a porphyritic olivine chondrule [Fo(sub)99.5-99.7] of type IA according to Scott and Taylor (4), shows especially high induced TL intensity with a 300 degree C glow peak and a zonal structure. We measured high TL intensity although it would have the lowest TL sensitivity. The TL spectra from Semarkona were also measured by the time-resolving spectroscopy system. While the TL spectra of equilibrated ordinary chondrites are known to have a 450-nm peak in a low-temperature region and a 400-nm peak in a high-temperature region, they have a peak at ~570 nm and agree with those of some plagioclase feldspars in which Mn^2+ ions act as luminescence centers (5). The Corning 4-69 and 7-59 filter assemblies used in usual TL measuring systems limit the detection wavelength from 320 nm to 480 nm while the 4-96 filter transmits 570-nm emission. The "low TL sensitivity" of the primitive ordinary chondrites is in part due to limiting the detection wavelengths to ultraviolet-blue region. The cathodoluminescence of this chondrule was measured. This chondrule shows the yellow cathodoluminescence in anorthite- normative mesostasis and the zonal structure, and it is classified to group A1 of Sears et al. (6). The yellow cathodoluminescence is consistent with the ~570-nm TL emission. A barred olivine chondrule in Bishunpur shows also an unusual glow curve with a ~110 degrees C peak and a peak above 440 degrees C, different from the above glow curve. The TL spectra from Bishunpur have the same ~570-nm peaks. This barred olivine chondrule shows also the yellow cathodoluminescence in anorthite- normative mesostasis, and it is classified to group A1. On the other hand, a porphyritic olivine chondrule of type II in Bishunpur shows a usual glow curve with a ~170 degree C peak and blue cathodoluminescence in albite-normative mesostasis, and it is classifed to group A5. The results are that 1) some chondrules in Semarkona and Bishunpur show high TL intensities although such primitive ordinary chondrites would have low TL sensitivity, 2) these high TL intensities are due to ~570-nm emission, which is consistent with the yellow cathodoluminescences in anorthite-normative mesostases, beside the usual blue TL emissions from albite- normative mesostasis, 3) they show a variety of glow curve shapes inspite of the same yellow cathodoluminescence. References (1) Ninagawa et al. (1990) Proc. NIPR Symp. Ant. Met. 3, 244-253. (2) Ninagawa et al. (1986) Bull. Okayama Univ. Sci. 21A, 49-54. (3) Sears (1988) Nucl. Tracks Radiat. Meas. 14, 5-17. (4) Scott and Taylor (1983) Proc. LPSC 14, B275-B286. (5) Huntley et al. (1988) J. Lumin. 39, 123-136. (6) Sears et al. (1992) Nature, in press.

Ninagawa, K.; Yamamoto, I.; Kohata, M.; Wada, T.; Yamashita, Y.; Lu, J.; Sears, D. W. G.; Matsunami, S.; Nishimura, H.

1992-07-01

41

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

NASA Astrophysics Data System (ADS)

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.

1993-03-01

42

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

43

Silica-Fayalite-bearing Chondrules in Ordinary Chondrites: Evidence of Oxidation in the Solar Nebula  

NASA Astrophysics Data System (ADS)

Most ordinary chondrite (OC) chondrules have compositions similar to those of bulk OC in terms of lithophile-element abundances. There are only a few rare chondrule classes that deviate significantly from OC-like compositions; these include Al-rich chondrules, chromitic and chromite-bearing silicate chondrules, and silica-rich chondrules. We studied 41 thin sections of unequilibrated OC and found 82 silica-bearing chondrules that can be divided into two major categories: silica-pyroxene chondrules and silica-fayalite- pyroxene chondrules. These chondrules are more common in H (>3/cm^2) than in L and LL chondrites (<1/cm^2). Silica-pyroxene chondrules consist mainly of low-Ca pyroxene and silica and have radial and porphyritic textures. Silica-bearing radial pyroxene (RP) chondrules contain 5-10 vol% silica grains; the low-Ca pyroxene is uniform in individual chondrules but varies from one chondrule to another (Fs(sub)10.2- Fs(sub)31.5). Silica-bearing porphyritic pyroxene (PP) chondrules contain 15- 40 vol% silica; the low-Ca pyroxene varies in composition within individual PP chondrules and tends to be more magnesian than in the silica-bearing RP chondrules (Fs(sub)5.0-Fs(sub)21.1). Petrographic observations suggest that some PP chondrules were not completely molten; they appear to have cooled more slowly than the silica-bearing RP chondrules. Silica-fayalite-pyroxene chondrules consist of silica, fayalite, and low-Ca pyroxene; accessory high-Ca pyroxene, plagioclase mesostasis, troilite, and metallic Fe-Ni are also present. Based on texture and the modal abundances of pyroxene and silica these chondrules can be divided into two types: (1) radial or porphyritic silica-fayalite-pyroxene chondrules containing 5-40 vol% silica and (2) granular silica-fayalite-pyroxene chondrules consisting almost entirely (90-95 vol%) of silica. Silica-fayalite-bearing pyroxene chondrules are texturally and compositionally similar to the silica-bearing pyroxene chondrules described above; the principal difference between them is the presence of fayalite-forming veins within or rims around the silica grains. The continuum between these chondrule categories implies that they are genetically related: We infer that the fayalite veins and rims formed by nebular alteration of the silica grains. Fayalite forms veins along the silica grain boundaries in granular silica-fayalite-bearing chondrules. Fragments of granular silica chondrules occur as relict clasts within two pyroxene chondrules in Sharps. These fragments were altered after chondrule solidification. Conclusions: (1) Silica-bearing chondrules have similar textures to common mafic silicate chondrules and were formed by melting silica-rich precursor material that possibly formed by nonequilibrium condensation. (2) The higher abundance of silica-bearing chondrules in H than in L and LL chondrites may indicate a greater degree of silica condensation in the H-formation region. (3) Silica-fayalite-bearing chondrules formed by alteration of silica-bearing chondrules. The common occurrence of both categories within the same chondrite suggests that oxidation and fayalite formation by nebular gas was an inefficient process.

Krot, A. N.; Wasson, J. T.

1993-07-01

44

Ordinary chondrite metallography: Part 2 Formation of zoned and unzoned metal particles in relatively unshocked H, L, and LL chondrites  

Microsoft Academic Search

We studied the metallography of Fe-Ni metal particles in 17 relatively unshocked ordinary chondrites and interpreted their microstructures using the results of P-free, Fe-Ni alloy cooling experiments (described in Reisener and Goldstein 2003). Two types of Fe-Ni metal particles were observed in the chondrites: zoned taenite + kamacite particles and zoneless plessite particles, which lack systematic Ni zoning and consist

R. J. Reisener; J. I. Goldstein

2003-01-01

45

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

SciTech Connect

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

Rubin, A.E. (Univ. of California, Los Angeles (USA)); Pernicka, E. (Max-Planck-Institute fuer Kernphysik, Heidelberg (West Germany))

1989-01-01

46

New Primitive Ordinary Chondrite: Northwest Africa 7731 (L3.00)  

NASA Astrophysics Data System (ADS)

We report data on a new primitive ordinary chondrite NWA 7731 (L3.00). Ferroan olivne has Cr-compositions strikingly similar to Semarkona (LL3.00). NWA 7731 also possesses sulfur-rich opaque matrix indicative of the most primitive type 3 chondrites.

Agee, C. B.; Burkemper, L. K.; Muttik, N.; Spilde, M. N.

2013-09-01

47

Comparative stable isotope geochemistry of Ni, Cu, Zn, and Fe in chondrites and iron meteorites  

Microsoft Academic Search

High-precision Ni isotopic variations are reported for the metal phase of equilibrated and unequilibrated ordinary chondrites, carbonaceous chondrites, iron meteorites, mesosiderites, and pallasites. We also report new Zn and Cu isotopic data for some of these samples and combine them with literature Fe, Cu, and Zn isotope data to constrain the fractionation history of metals during nebular (vapor\\/solid) and planetary

Frédéric Moynier; Janne Blichert-Toft; Philippe Telouk; Jean-Marc Luck; Francis Albarède

2007-01-01

48

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

NASA Astrophysics Data System (ADS)

In a search for 26Mg excesses generated by 26Al decay the authors analysed four Al-rich objects from the type 3 ordinary chondrites using an ion microprobe. They report here the presence of 26Mg excesses of up to 100% in an unusually pure hibonite clast from the Dhajala chondrite; this 26Mg excess is the first to be found in an ordinary chondrite. No 26Mg excesses were observed in the three plagioclase-bearing chondrules analysed. It is concluded that 26Al may not have been sufficiently plentiful to act as a major heat source in condensed Solar System bodies.

Hinton, R. W.; Bischoff, A.

1984-03-01

49

Concentration of rare earth elements in five ordinary chondrites  

Microsoft Academic Search

The concentration of rare-earth elements in the chondrites Saratov, ; Elenovka, Pervomaiskii Poselok (L group), Zaisan, and Zhovtnevyi Khutor (H group) ; was determined by neutron activation. It was established that (1) in meteorites ; of the L group in comparison with the chondrites of the H group the light rare-; earth elements (from La to Eu) slightly predominate; (2)

Kolesov

1974-01-01

50

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

51

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

NASA Astrophysics Data System (ADS)

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

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

1993-03-01

52

Ordinary chondrites - Multivariate statistical analysis of trace element contents  

NASA Astrophysics Data System (ADS)

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, M. E.; Samuels, S. M.

1991-01-01

53

Hydrogen Isotope Study of CO3 Type Carbonaceous Chondrites; Comparison with Type 3 Ordinary Chondrites.  

National Technical Information Service (NTIS)

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, l...

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

1993-01-01

54

Iron Isotopic Signature for Fe-Ni Metal of Ordinary Chondrite Using Newly Developed Technique; LAL-MC-ICPMS  

NASA Astrophysics Data System (ADS)

Fe-isotopic compositions of Fe-Ni metals in ordinary chondrites were measured using laser ablation in liquid (LAL)-MC-ICPMS technique. We found that Fe-Ni metals in H chondrites have slightly lighter Fe-isotopic signature than L and LL chondrites.

Okabayashi, S.; Yokoyama, T.; Hirata, T.

2012-03-01

55

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

56

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

NASA Astrophysics Data System (ADS)

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.

1984-02-01

57

Weathering of Ordinary Chondrites from Algeria and Australia as a Climatic Indicator  

Microsoft Academic Search

Introduction: Recently it has been recognized that ordinary chondrite meteorites resident in desert regions may preserve information about the climate at the time of their arrival on Earth in the degree to which they are weathered [1], providing that a stable surface has existed at the accumulation site. We present here a comparison of ^57Fe Mossbauer spectroscopy data for additional

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

1995-01-01

58

The histories of ordinary chondrite parent bodies - U, Th-He age distributions  

SciTech Connect

Age patterns observed in meteorite groups reflect the different thermal or impact histories experienced by their parent bodies. To assess the number of ordinary chondrite (OC) parent bodies, rare-gas data in the Schultz and Kruse (1989) data base were used to calculate U, Th-He gas-retention ages. Most H- and LL-chondrite ages are high; about 81 percent are greater than 2.2 Ga. In contrast, most L-chondrite ages are low; about 69 percent are not greater than 2.2 Ga, and about 35 percent are not greater than 0.9 Ga. The latter fraction is substantially lower than the value of 44 percent given by Heymann (1967). The difference is attributed to the preferential inclusion of shocked L chondrites in early studies. Broad age peaks in the H and LL groups near 3.4 Ga probably reflect thermal loss during metamorphism, but in the H distribution there is a hint of minor outgassing 'events' near 1 Ga. The L/LL chondrites have chemical properties intermediate between and unresolvable from L and LL chondrites. The high ages of most L/LL chondrites are evidence against these originating on the L parent body; the L/LL age distribution is consistent with an origin on the LL parent body or on an independent body. 22 refs.

Wasson, J.T.; Wang, Sichao (California, University, Los Angeles (USA) Purple Mountain Observatory, Nanjing (People's Republic of China))

1991-06-01

59

Redox effects in ordinary chondrites and implications for asteroid spectrophotometry  

NASA Astrophysics Data System (ADS)

The sensitivity of reflectance spectra to mean ferrous iron content and olivine and pyroxene proportion enhancements in the course of metamorphic oxidation is presently used to examine whether metamorphically-induced ranges in mineralogy, and corresponding spectral parameters, may explain the observed variations in S-asteroid rotational spectra. The predicted spectral variations within any one chondrite class are, however, insufficient to account for S-asteroid rotational spectra, and predicted spectral-range slopes have a sign opposite to the rotational measurements. Metamorphic oxidation is found unable to account for S-asteroid rotational spectra.

McSween, Harry Y., Jr.

1992-02-01

60

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

SciTech Connect

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

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

2012-04-02

61

Ordinary chondrite-related giant (>800 ?m) cosmic spherules from the Transantarctic Mountains, Antarctica  

NASA Astrophysics Data System (ADS)

In order to identify the parent bodies of cosmic spherules (melted micrometeorites) with porphyritic olivine (PO) and cryptocrystalline (CC) textures, we measured the oxygen isotopic composition of 15 giant (>800 ?m) cosmic spherules recovered in the Transantarctic Mountains, Antarctica, with IR-laser fluorination/mass spectrometry, and we conducted a characterization of their petrographic and magnetic properties. Samples include 6, 8 and 1 spherules of PO, CC and barred olivine (BO) textural types, respectively. Eleven spherules (˜70% of the total: 4/6 PO and 6/8 CC, and the BO spherule) are related to ordinary chondrites based on oxygen isotopic compositions. Olivines in ordinary chondrite-related spherules have compositions Fa 8.5-11.8, they are Ni-poor to Ni-rich (0.04-1.12 wt.%), and tend to be richer in CaO than other spherules (0.10-0.17 wt.%). Ordinary-chondrite related spherules also have high magnetite contents (˜2-12 wt.%). One PO and one CC spherules are related to previously identified 17O-enriched cosmic spherules for which the parent body is unknown. One CC spherule has an oxygen isotopic signature relating it to CM/CR carbonaceous chondrites. The majority of PO/CC cosmic spherules derive from ordinary chondrites; this result exemplifies how the texture of cosmic spherules is not only controlled by atmospheric entry heating conditions but also depends on the parent body, whether be it through orbital parameters (entry angle and velocity), or chemistry, mineralogy, or grain size of the precursor.

Suavet, Clément; Cordier, Carole; Rochette, Pierre; Folco, Luigi; Gattacceca, Jérôme; Sonzogni, Corinne; Damphoffer, Dorian

2011-10-01

62

Analysis of ordinary chondrites using powder X-ray diffraction: 1. Modal mineral abundances  

NASA Astrophysics Data System (ADS)

Powder X-ray diffraction (XRD) is used to quantify the modal abundances (in wt%) of 18 H, 17 L, and 13 LL unbrecciated ordinary chondrite falls, which represents the complete petrologic range of equilibrated ordinary chondrites (types 4-6). The XRD technique presents an effective alternative to traditional methods for determining modal abundances, such as optical point counting and electron microprobe phase (EMP) mapping. The majority of chondrite powders in this study were previously prepared for chemical characterization from 8 to 20g of material, which is consistent with the suggested mass (10g) necessary to provide representative sampling of ordinary chondrites. Olivine and low-Ca pyroxene are the most abundant phases present, comprising one-half to three-fourths of total abundances, while plagioclase, high-Ca pyroxene, troilite, and metal comprise the remaining XRD-measured mineralogy. Pigeonite may also be present in some samples, but it is fitted using a high-Ca pyroxene standard, so exact abundances cannot be measured directly using XRD. Comparison of XRD-measured abundances with calculated Cross, Iddings, Pirsson, Washington (CIPW) normative abundances indicates that systematic discrepancies exist between these two data sets, particularly in olivine and high-Ca pyroxene. This discrepancy is attributed to the absence of pigeonite as a possible phase in the CIPW normative mineralogy. Oxides associated with pigeonite are improperly allocated, resulting in overestimated normative olivine abundances and underestimated normative high-Ca pyroxene abundances. This suggests that the CIPW norm is poorly suited for determining mineralogical modal abundances of ordinary chondrites.

Dunn, Tasha L.; Cressey, Gordon; McSween, Harry Y. _jr., Jr.; McCoy, Timothy J.

2010-01-01

63

Systematics of Mössbauer absorption areas in ordinary chondrites and applications to a newly fallen meteorite in Jodhpur, India  

NASA Astrophysics Data System (ADS)

Mössbauer absorption areas corresponding to 57Fe in olivine, pyroxene, troilite, and the metallic phase in ordinary chondrites are shown to exhibit certain systematic behaviors. H chondrites occupy 2 distinct regions on the plot of metallic phase absorption area versus silicate absorption area, while L/LL chondrites fall in a separate region. Similar separation is also observed when pyroxene absorption area is plotted against olivine absorption area. The one-dimensional plot for the ratio of olivine area to pyroxene area separates L and LL chondrites. Based on these systematics, a newly fallen meteorite at Jodhpur, India is suggested to be an LL chondrite.

Verma, H. C.; Jee, K.; Tripathi, R. P.

2003-06-01

64

Uranium-Thorium-Helium and Potassium-Argon Ages of Ordinary Chondrites  

NASA Astrophysics Data System (ADS)

Calculated U, ThHe and KAr ages are reported for upwards of 800 Antarctic and non-Antarctic H-, L-, and LL-chondrites. It is shown that L-chondrites are generally characterized by lower age values than are H- and LL-chondrites; this is due to the loss of radiogenic 4He and 40Ar in a catastrophic collision of the parent body of the L-chondrites 350 30 Myr ago. The age of the non-Antarctic finds is, on average, less than the age of fall because of the loss of inert gases in the process of the weathering of the meteorites on the Earth; the losses of inert gases in weathering are substantially lower in the Antarctic finds than in the non-Antarctic finds. The distributions of the KAr fall ages of ordinary chondrites exhibit a peak at 4.3 Gyr. The ages of about 85% of the H- and LL-chondrites and 45% of the L-chondrites are clustered in the vicinity of this peak. Most probably, the material of these chondrites lost 40Ar chiefly in the period of the metamorphism of the parent bodies early in the evolution of the material of the Solar System. The difference in the distributions of the gas- retention ages of the falls and Antarctic finds (for meteorites with a ratio of radiogenic ages t3 / t21 < 1) may be due to the distinct thermal histories of the chondrites that fall to the Earth today and those that fell several hundred thousand years ago, and to the loss of some of the cosmogenic 3He from the fine-grained mineral component of the chondrites in Antarctic conditions. Both H- and L-chondrites with low radiogenic ages exhibit a tendency toward low gas-retention ages. This effect may be associated with the spalling off of such meteorites from the par- ent body by a severe shock, which caused both a partial loss of radiogenic gases (owing to the heating of the mete- oritic material) and a deflection of the meteorites to an orbit with a short lifetime before capturing by the Earth.

Alekseev, V. A.

65

Ordinary chondrite metallography: Part 1 Fe-Ni taenite cooling experiments  

Microsoft Academic Search

Cooling rate experiments were performed on P-free Fe-Ni alloys that are compositionally similar to ordinary chondrite metal to study the taenite taenite + kamacite reaction. The role of taenite grain boundaries and the effect of adding Co and S to Fe-Ni alloys were investigated. In P-free alloys, kamacite nucleates at taenite\\/taenite grain boundaries, taenite triple junctions, and taenite grain corners.

R. J. Reisener; J. I. Goldstein

2003-01-01

66

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

Microsoft Academic Search

We measured the concentrations of noble gases in 32 ordinary chondrites from the Dar al Gani (DaG) region, Libya, as well as concentrations of the cosmogenic radionuclides 14C, 10Be, 26Al, 36Cl, and 41Ca in 18 of these samples. Although the trapped noble gases in five DaG samples show ratios typical of solar or planetary gases, in all other DaG samples,

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

2004-01-01

67

Coincidental Compositional and Orbital Correspondences Among Some Ordinary Chondrites: No Strong Evidence for Meteoroid Streams  

Microsoft Academic Search

Previous attempts to assign ordinary chondrites (OC) to meteoroid streams have been unsuccessful because the orbits of the proposed members had different radiants and, in some cases, the meteorites had significantly different cosmic-ray exposure (CRE) ages. Using more conservative criteria, we have identified four pairs of equilibrated OC (L6 Nejo, Salem; L6 Perpeti, Vouillé; L6 Drake Creek, Forsyth; H5 Okabe,

Alan E. Rubin; Robert D. Matson

2008-01-01

68

Coincidental Compositional and Orbital Correspondences Among Some Ordinary Chondrites: No Strong Evidence for Meteoroid Streams  

Microsoft Academic Search

Previous attempts to assign ordinary chondrites (OC) to meteoroid streams have been unsuccessful because the orbits of the\\u000a proposed members had different radiants and, in some cases, the meteorites had significantly different cosmic-ray exposure\\u000a (CRE) ages. Using more conservative criteria, we have identified four pairs of equilibrated OC (L6 Nejo, Salem; L6 Perpeti,\\u000a Vouillé; L6 Drake Creek, Forsyth; H5 Okabe,

Alan E. Rubin; Robert D. Matson

2008-01-01

69

Pressure demagnetization of ordinary chondrites up to 1.8 GPa: new experimental data  

NASA Astrophysics Data System (ADS)

We conducted hydrostatic pressure demagnetization experiments up to 1.8 GPa on H, L, and LL ordinary chondrite samples (FeNi-bearing). We used a new non-magnetic pressure clamp cell made of "Russian" alloy (NiCrAl) together with a liquid pressure transmitting medium (polyethylsiloxane) to ensure purely hydrostatic pressure. This technique allowed to measure magnetic remanence of investigated samples directly under pressure as well as after pressure release. Pressure was always applied in low magnetic field (<5?T). The experiments revealed that under hydrostatic pressure up to 1.8 GPa, ordinary chondrite samples lost up to 51% of their initial saturation isothermal remanent magnetization. Pressure demagnetization degree is directly proportional to ln(Bcr), where Bcr is the coercivity of remanence, similar to what is observed for other ferrimagnetic minerals (Bezaeva et al., submitted). For samples with Bcr>80 mT, no pressure demagnetization effect is observed under 1.8 GPa. Using this new experimental data, we propose a simple model to predict the amount of pressure demagnetization of ordinary chondrites as a function of pressure (up to 1.8 GPa). The physical mechanism of the pressure demagnetization effect and the implications of this new experimental data for extraterrestrial paleomagnetism will be discussed. Acknowledgements This work was partially supported by the CNRS-RFFI PICS program (grant 07-05-92165). The conference attendance by N.S. Bezaeva is funded by Rosnauka (president grant MK-3252.2009.5).

Bezaeva, N. S.; Gattacceca, J.; Rochette, P.; Sadykov, R. A.

2009-12-01

70

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

71

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

72

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

National Technical Information Service (NTIS)

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, (sup 129)*Xe/(sup 128)Xe values are generally lower (later apparent ages) th...

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

2005-01-01

73

An 57Fe Mössbauer Study of the Olivine Solid Solution Series: Implications for Meteorite Classification and Deconvolution of Unequilibrated Chondrite Spectra  

Microsoft Academic Search

The olivine solid solution series was investigated by 57Fe Mössbauer spectroscopy. The study aims to improve interpretation of meteorite spectra and provide a rapid method of characterizing silicate chemistry and degree of equilibration in chondrites.

O. N. Menzies; P. A. Bland; F. J. Berry

2001-01-01

74

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

NASA Astrophysics Data System (ADS)

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

Trigo-Rodríguez, J. M.; Llorca, J.; Sears, D. W. G.

2009-08-01

75

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

SciTech Connect

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

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

2009-08-17

76

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

NASA Astrophysics Data System (ADS)

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

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

2004-03-01

77

Cosmochemistry of thorium, samarium, and cesium in the substance of ordinary chondrites and problem of disposal of actinide and fission product concentrates in the Earth crust  

Microsoft Academic Search

The hydrothermal treatment of the substance of unequilibrated Krymka chondrite is studied. This substance is a sample of the\\u000a oldest basalts of the Earth group planets and is considered as a natural analog of matrices for immobilization of Th, Sm,\\u000a and Cs. It is shown that Th and Sm are mainly fixed in phosphates, whereas Cs becomes a scattered element.

R. A. Kuznetsov

2011-01-01

78

Origin of SiO 2-rich components in ordinary chondrites  

NASA Astrophysics Data System (ADS)

Silica-rich objects are common minor components in ordinary chondrites (OC), occurring as fragments and as chondrules. Their typical paragenesis is orthopyroxene + SiO 2 (with bulk SiO 2 >65 wt%) and occasionally with additional olivine and/or spinel. Individual silica-rich components (SRC) have previously been studied in various types of OCs, although there is only one comprehensive study of these objects by Brigham et al. [Brigham, C.A., Murrell, M.T., Yabuki, H., Ouyang, Z., El Goresy, A., 1986. Silica-bearing chondrules and clasts in ordinary chondrites. Geochim. Cosmochim. Acta 50, 1655-1666]. Several different explanations of how SRCs formed have been published. The main question is how silica-enrichment was achieved, because CI-chondritic atomic Mg/Si-ratio is 1.07 and as a consequence only olivine and pyroxene, but no free silica should be stable. There are two basic possibilities for the SiO 2-enrichment: (1) a RedOx-mechanism or magmatic fractionation on the parent body and (2) fractional condensation or recycling of chondrule mesostasis in the solar nebula. To better constrain the origin of these objects, we measured major and rare earth elements in SRCs of various types of ordinary chondrites, and in addition, we studied silica polymorphism in these objects using an in situ micro-Raman technique. Bulk chondrule compositions define mixing lines between the compositions of olivine and pyroxene. The SRCs extend these lines to an SiO 2 end member. In contrast, magmatic trends grossly deviate from these mixing lines. Concentrations of CaO, Al 2O 3, and REE in the pyroxenes of the SRCs are low (0.01 to 1× CI) and the CI-normalized REE-patterns are virtually flat, typical of bulk chondrules, but untypical of magmatic trends. We therefore conclude that SiO 2-rich objects are not of magmatic origin. They are the result of fractional condensation in the solar nebula. The silica in SRCs occurs mainly as tridymite and sometimes as cristobalite or—in very rare cases—as quartz. Some SiO 2-phases yielded a yet unknown micro-Raman spectrum, which we were unable to identify. The often chondrule-like shape of SRCs as well as the presence of high-temperature SiO 2-polymorphs lead to the following model for the origin of SRCs: formation of SiO 2-rich precursors in the solar nebula by fractional condensation, reheating to temperatures between 1140 and >1968 K, thereby forming the SRCs,—probably during the chondrule-forming process—followed by rapid cooling.

Hezel, Dominik C.; Palme, Herbert; Nasdala, Lutz; Brenker, Frank E.

2006-03-01

79

Hf–W internal isochrons for ordinary chondrites and the initial 182 Hf\\/ 180 Hf of the solar system  

Microsoft Academic Search

Three ordinary chondrites, Forest Vale (H4), Ste. Marguerite (H4) and Richardton (H5) have been studied with 182Hf–182W system (t1\\/2=9 million years [m.y.]) in order to provide constraints on the initial 182Hf\\/180Hf for the chondritic parent body and the solar system. All three samples display positive correlations between 182W\\/184W and 180Hf\\/184W, providing confirmation that live 182Hf was present in these samples.

Der-Chuen Lee; Alex N Halliday

2000-01-01

80

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

81

The chronology of ordinary chondrites by laser Ar-Ar and I-Xe  

NASA Astrophysics Data System (ADS)

We have separated a suite of chondrules, exotic clasts, and matrices from ordinary chondrites for the extraction of gases by laser ablation and stepped heating for Ar-Ar and I-Xe dating. A portion of each separated phase was also used for petrographic and mineralogical analysis. The age determined for a large equilibrated H chondrite clast from Barwell was found to be indistinguishable from the age of whole-rock samples of Barwell. The laser extraction method produces ages in good agreement with conventional extraction methods. Four samples from Parnallee have been analyzed and show a range of ages indicative of a highly complex chronology. The whole-rock stepped heating analysis for Parnallee shows that it is a highly disturbed system, but the variable Ar-Ar ages obtained for the inclusions indicate that this is not only due to the partial resetting of the Ar by a shock event about 1.9 Ga, but is also due to the different ages and age structures of the constituent components. The ages obtained by laser extraction for inclusions from other meteorites ranged from 0.9 b.y. to 3.6 b.y., with one exception. An age of 4.63 (+/- 0.04) b.y. was obtained for a large clast, from Quenggouk, containing mosaicized olivine and blebs of Fe-Ni metal that may have been subject high shock. This can lead to anomalously high ages as shown previously. It is hoped that I-Xe dating of this inclusion will help to show the causes of this anomalously high age and the degassing history of this inclusion. It is hoped that the complexities of the ordinary chondrite thermal histories will be clarified by the application of these high-sensitivity techniques to individual component parts of these meteorites.

Ash, R. D.; Gilmour, J. D.; Turner, G.; Bridges, J. C.; Hutchison, R.

1994-07-01

82

Zn and Cu isotopic variations in chondrites and iron meteorites: Early solar nebula reservoirs and parent-body processes  

Microsoft Academic Search

High-precision Zn isotopic variations are reported for carbonaceous chondrites (CC), equilibrated (EOC) and unequilibrated (UOC) ordinary chondrites, iron meteorites from the IAB-IIICD (nonmagmatic) and IIIA (magmatic) groups, and metal from the Brenham pallasite. For irons, ?65Cu values are also reported. Data have also been obtained on a coarse-grained type-B calcium-, aluminum-rich refractory inclusion (CAI) from Allende and on acid leaches

Jean-Marc Luck; Dalila Ben Othman; Francis Albarède

2005-01-01

83

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

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

84

The Cali meteorite fall: A new H/L ordinary chondrite  

NASA Astrophysics Data System (ADS)

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

Trigo-Rodríguez, J. M.; Llorca, J.; Rubin, A. E.; Grossman, J. N.; Sears, D. W. G.; Naranjo, M.; Bretzius, S.; Tapia, M.; Guarín Sepúlveda, M. H.

2009-03-01

85

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

USGS Publications Warehouse

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

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

2009-01-01

86

The structure and composition of metal particles in two type 6 ordinary chondrites  

SciTech Connect

The microstructure and composition of taenite particles were examined in two type-6 ordinary chondrites, Kernouve (H6) and Saint Severin (LL6), using reflected light microscopy and a combination of electron optical instruments. It was found that, in both meteorites, the taenite particles consisted of a narrow rim of high-Ni taenite and a central region of cloudy zone similar to those present in iron meteorites. The microstructure of the cloudy zone in Saint Severin was coarser than that in Kernouve , due to the higher Ni content and slower cooling rate of the former. Three microstructural zones were observed in the outer taenite rim of both meteorites, the origin of which is considered likely to be due to the presence of ordered domain boundaries or to the presence of two phases FeNi and FeNi3 in the high-Ni region of the outer taenite rim. 21 refs.

Holland-duffield, C.E.; Williams, D.B.; Goldstein, J.I. (Intel Corp., Albuquerque, NM (USA) Lehigh University, Bethlehem, PA (USA))

1991-06-01

87

Mössbauer study of the Ordinary-Chondrite meteorite Thylacine Hole-001  

NASA Astrophysics Data System (ADS)

The Thylacine Hole-001 meteorite was recovered from the Nullarbor Desert (Australia) in 1977 and is an Ordinary Chondrite, Group H4/5br, which has undergone moderate to severe (B/C) weathering. We have characterised the Fe-bearing phases in Thylacine Hole-001 by 57Fe Mössbauer Spectroscopy at 300 K, 100 K, 50 K and 4 K. The spectrum at 300 K is dominated by the paramagnetic doublets of Olivine, Pyroxene and a Ferric component which is most likely nanoparticulate Goethite. Magnetically split sextets due to Maghemite or Magnetite are also present, consistent with the relatively advanced terrrestrial age of 28,500 yrs The nanoparticulate Goethite component shows a blocked, magnetically split sextet at low temperatures. We also observe the effects of magnetic ordering of the Olivine and Pyroxene below 50 K.

Cadogan, J. M.; Devlin, E. J.

2012-03-01

88

Precise Reflectance Spectra of Ordinary Chondrites in the Visible and UV: Exploring the Variability of S-Class Asteroidal Spectra  

NASA Astrophysics Data System (ADS)

We used a UV-Vis-NIR spectrometer to get reflectance spectra of several ordinary chondrites. The results are compared with the averaged reflectance of S-class asteroids. We explore the importance of roughness in the diversity observed for the S-class.

Trigo-Rodríguez, J. M.; Llorca, J.; Madiedo, J. M.; Rivkin, A. S.; de León, J.; Pinilla-Alonso, N.

2011-03-01

89

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

NASA Astrophysics Data System (ADS)

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

Schaefer, Laura; Fegley, Bruce

2007-02-01

90

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

Microsoft Academic Search

We used chemical equilibrium calculations to model thermal outgassing of ordinary chondritic material as a function of temperature, pressure, and bulk composition and use our results to discuss outgassing on asteroids and the early Earth. The calculations include ?1000 solids and gases of the elements Al, C, Ca, Cl, Co, Cr, F, Fe, H, K, Mg, Mn, N, Na, Ni,

Laura Schaefer; Bruce Fegley; Jr

2007-01-01

91

New Evidence for 26Al in CAI and Chondrules from Type 3 Ordinary Chondrites  

NASA Astrophysics Data System (ADS)

We have known since 1976 that 26A1 (tl/2 = 7.2 x 105 yrs) was alive in the early solar system, at a level of (26Al/27Al)o z 5 x 10-5 in calcium-aluminum inclusions (CAI). However, several outstanding questions remain. Little evidence for 26A1 has been found in other chondritic material, and none has been found in differentiated meteorites. These results might imply that 26A1 was heterogeneously distributed in the nebula or by mineralogic site in nebular dust, or they might reflect differences in time of formation. There are strict limitations on finding evidence of 26A1 in normal chondrules with bulk Al/Mg ~ 0.1, since even quenched, perfectly preserved, late-stage glasses would have low Al/Mg. Primary plagioclase crystals provide the only possibility, but these only crystallize rarely in melts within the compositional range of normal chondrules. Also, metamorphism can erase the evidence in high-AI/Mg phases. To address these issues, we have conducted a search for chondrules and CAI with high-Al/Mg phases suitable for ion-probe measurement in type 3 ordinary chondrites. Previous work has revealed evidence for 26Al in a plagioclase bearing, olivine-pyroxene class from Semarkona (LL3.0; (26Al/27Al)o = 7.7+/-2.1 x 10-6)), a plagioclase-rich object from Bovedy (L3.7?; 2.5+/-1.2 x 10-7), in separated plagioclase from St. Marguerite (H4; 2.0+/-0.6 x 10-7), an isolated hibonite grain from Dhajala (H3.8; 8.4+0.5 x 10-6), and in Al2O3 and hibonite grains ((26Al/27Al)o = 2-5 x 10-5; [GRH, unpublished]) from acid residues of Semarkona, Bishunpur (LL3.1), and Krymka (LL3.1). We have identified and measured Al-Mg isotope systematics in two CAI and seven chondrules from ordinary chondrites of low metamorphic grade and have found clear evidence for 26A1 in both CAI and in two chondrules.

Srinivasan, G.; Russell, S. S.; MacPherson, G. J.; Huss, G. R.; Wasserburg, G. J.

1996-03-01

92

Coincidental Compositional and Orbital Correspondences Among Some Ordinary Chondrites: No Strong Evidence for Meteoroid Streams  

NASA Astrophysics Data System (ADS)

Previous attempts to assign ordinary chondrites (OC) to meteoroid streams have been unsuccessful because the orbits of the proposed members had different radiants and, in some cases, the meteorites had significantly different cosmic-ray exposure (CRE) ages. Using more conservative criteria, we have identified four pairs of equilibrated OC (L6 Nejo, Salem; L6 Perpeti, Vouillé; L6 Drake Creek, Forsyth; H5 Okabe, Kerilis) wherein each member of the pair could conceivably have been derived from the same immediate precursor body (IPB). The members of each pair are of the same chondrite group and petrologic type; they have similar CRE ages and fell within 1 calendar day of each other (in different years). Because there is a moderate range in oxidation state (represented by mean olivine Fa) among equilibrated OC in each group, similarities in this intrinsic geochemical property between the members of two of the proposed pairs offer some support for the hypothesis that these rocks were derived from the same IPB. If the pairs are genuine, their precursor bodies were probably meter-size near-Earth asteroids (NEAs) with aphelia within or beyond the Main Asteroid Belt. Fragmentation of such NEAs is most likely to have occurred near aphelia; in principle, the ejecta could have spread somewhat along the NEAs’ orbits and collided with Earth on approximately the same calendar date but in different years. However, literature data show that, although ˜670 meteorites with masses ?10 kg reach the Earth’s surface each year, only five or six falls (typically in this mass range) are observed and recovered. This suggests that the chances of recovering more than one meteorite from a disrupted meter-size body in Earth-crossing orbit are small. It thus seems likely that the similar properties of the proposed OC pairs are due to coincidence.

Rubin, Alan E.; Matson, Robert D.

2008-12-01

93

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

94

Partial Melting of Ordinary Chondrite: Implications for Siderophile Behavior During Early Differentiation  

NASA Astrophysics Data System (ADS)

Core formation scenarios in growing planetesimals include a variety of possible physical mechanisms such as segregation in a solid or partially molten silicate body or whether or not the body was actively deforming. The resulting geochemical composition of the metal and silicate phases will also be a function of bulk composition, percent of metal melted and oxygen fugacity. To explore the relationship between physical core formation scenarios and geochemistry, deformation experiments have been conducted on a H6 ordinary chondrite at different stages of melting. Deformation experiments provide a dynamic component that allows liquid metal to segregate from solid silicate, or from matrices containing various amounts of silicate melt. Geochemical analyses of metal quench in several experimental charges and on metal grains in the Kernouve H6 starting material have been performed by LA-ICP-MS (Hummayun &\\ Campbell, EPSL, 2002; Rushmer et.al., Geochem. Cosmochem. Acta, Goldschmidt Conf. Abs,, 2002). Below the silicate solidus (KM-10, 1.0 GPa, 925°C, 1x10-5 s-1), analyses of compatible (Re, Os) and incompatible (Pd, Au) siderophiles in residual, strained Fe-Ni metal and unmodified metal show little variation. These data suggest even though metamorphosed, siderophile abundances are not strongly modified by shearing. At higher temperatures, (KM-17, 1.2 GPa, 940°C, 10-6 s-1) data from metal quench representing early formed liquid (S-rich and possibly O-rich) and of residual Fe-Ni metal have been plotted on a Fe, H-chondrite normalized plot with starting Kernouve metal and bulk H4-6 metal compositions. The quench metal resembles liquid, being depleted in compatible siderophiles, e.g., Re, Os, Ir, and enriched in Ni, Pd. Residual metal mirrors the quench metal and is enriched in compatible elements and depleted in the incompatibles when compared with bulk H metal. Ga and Ge show slight fractionation. Ga, Ge, Co and Ir vs. Ni plots show quench metal compositions are similar to natural IIE iron meteorites, providing some support for the hypothesis that these irons come from an H-chondrite like precursor. Partitioning data collected from these charges also suggest deformation may play an important role in enhancing kinetics during partial melting.

Rushmer, T.

2002-12-01

95

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

NASA Astrophysics Data System (ADS)

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

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

1994-03-01

96

Uranium-Thorium-Helium and Potassium-Argon Ages of Ordinary Chondrites  

Microsoft Academic Search

Calculated U, ThHe and KAr ages are reported for upwards of 800 Antarctic and non-Antarctic H-, L-, and LL-chondrites. It is shown that L-chondrites are generally characterized by lower age values than are H- and LL-chondrites; this is due to the loss of radiogenic 4He and 40Ar in a catastrophic collision of the parent body of the L-chondrites 350 30

V. A. Alekseev

1996-01-01

97

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

NASA Astrophysics Data System (ADS)

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

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

98

Micro-Raman of mineral phases in the strongly shocked Taiban ordinary chondrite: ringwoodite coloration  

NASA Astrophysics Data System (ADS)

High pressure polymorphs of major minerals are commonly found in shocked meteorites. During the formation evolution of the Solar System asteroids have collided with each other and with larger bodies triggering shock waves. The produced Meteorites show different shock effects depending on the peak pressures and temperatures, and duration of the collision events [5]. Taiban is a very strongly shocked, shock stage S6 ordinary L6 chondrite. It shows multiple veins of opaque shock melt forming a network of complex branches surrounding pockets of highly shock altered, mosaicized, relict or recrystalized silicates, and their high pressure polymorphs [4,5]. Micro-Raman spectroscopy has been used to provide univocal identification of minerals and glassy phases in meteorites as well as a tool to obtain additional information on structural and compositional variations inside mineral grains [7]. We studied the polished thin section UNM297 of Taiban meteorite with micro-Raman spectroscopy and Raman mapping to identify and characterize major and minor phases. Ringwoodite g-(Fe,Mg)2Si04 is the high-pressure polymorph of olivine with the spinel structure.

Acosta, T. E.; Scott, E. R. D.; Sharma, S. K. S.; Misra, A. K.

2012-09-01

99

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

100

Good Vibrations: Recent Near-Earth Encounters as the Missing Piece of the S-Asteroid and Ordinary Chondrite Meteorite Puzzle  

NASA Astrophysics Data System (ADS)

Close Earth encounters that induce seismic shaking of near-Earth asteroids are found to produce surfaces free of space weathering. These "Q-type asteroids" are direct spectral matches to the most commonly falling meteorites, the ordinary chondrites.

Binzel, R. P.; Morbidelli, A.; Merouane, S.; DeMeo, F. E.; Birlan, M.; Vernazza, P.; Thomas, C. A.; Rivkin, A. S.; Bus, S. J.; Tokunaga, A. T.

2010-03-01

101

The Fayalite Content of Chondritic Olivine: Obstacle to Understanding the Condensation of Rocky Material  

Microsoft Academic Search

Solar gas is too reducing for the equilibrium XFa in condensate olivine to reach the minimum XFa of the precursors of chondrules in unequilibrated ordinary chondrites (UOCs), 0.145, at temperatures above those where Fe-Mg interdiffusion in olivine stops. Vaporization of a region enriched in dust relative to gas compared to solar composition yields higher fO2, and condensate grains with higher

A. V. Fedkin; L. Grossman

2006-01-01

102

An 57Fe Mössbauer study of three Australian L5 ordinary-chondrite meteorites: dating Kinclaven-001  

NASA Astrophysics Data System (ADS)

Three L5-type ordinary chondrite meteorites recovered from the Nullarbor Region of Western Australia were studied by 57Fe Mössbauer spectroscopy: Kinclaven-001, Camel Donga-007 and Gunnadorah-002. The relative amounts of the various Fe-bearing phases including the primary minerals (Olivine, Pyroxene, Troilite and Fe-Ni metal) and the ferric alteration products (Goethite, Maghemite/Magnetite) were obtained to determine the percentage of iron converted to Fe3 + by weathering processes. These data allow us to estimate the terrestrial age of Kinclaven-001 at 1,700 ± 1,300 yrs.

Cadogan, J. M.; Rebbouh, L.; Mills, J. V. J.; Bland, P. A.

2012-09-01

103

Chemical and physical studies of type 3 chondrites. II Thermoluminescence of sixteen type 3 ordinary chondrites and relationships with oxygen isotopes  

NASA Astrophysics Data System (ADS)

Thermoluminescence (TL) sensitivity values for sixteen type 3 ordinary chondrites, fourteen of them from Antarctica, have been measured. The values obtained (normalized to the TL sensitivity of the Dhajala meteorite) range from 1.6 (Allan Hills A77216) to 0.010 (Allan Hills A77176), and include two (Reckling Peak A80207 and Allan Hills A77176) that are particularly low. They fill a hiatus in the TL distribution that previously existed between St. Mary's County and Bishunpur, the latter being a meteorite with one of the lowest TL sensitivities known. The histogram of TL sensitivity values now shows a single distribution with higher values preferred; it resembles the histogram for L chondrites occupying the petrologic types 3, 4, 5, and 6. There is a tendency for the TL sensitivity of meteorites to decrease as delta O-18 increases. Theoretically, it is possible that the range of delta O-18 values observed may reflect progressive loss of O in the form of CO at very low temperatures, but very restrictive physical conditions and a complex history seem to be required.

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

1983-11-01

104

The fine-grained matrix of the Semarkona LL3.0 ordinary chondrite: An induced thermoluminescence study  

NASA Astrophysics Data System (ADS)

To investigate the nature, origin, and history of the fine-grained matrix in Semarkona and develop techniques suitable for small samples, we have measured the induced thermoluminescence properties of six matrix samples 10 µm to 400 µm in size. The samples had TL sensitivities comparable with 4 mg of bulk samples of type 3.2-3.4 ordinary chondrites, which is very high relative to bulk Semarkona. The other induced TL properties of these samples, TL peak temperatures, and TL peak widths distinguish them from other ordinary chondrite samples where the TL is caused by feldspar. Cathodoluminescence images and other data suggest that the cause of the luminescence in the Semarkona fine-grained matrix is forsterite. In some respects the matrix TL data resemble that of Semarkona chondrules, in which the phosphor is forsterite and terrestrial forsterites from a variety of igneous and metamorphic environments. However, differences in the TL peak temperature versus TL peak width relationship between the matrix samples and the other forsterites suggest a fundamentally different formation mechanism. We also note that forsterite appears to be a major component in many primitive materials, such as nebulae, cometary dust, and Stardust particles.

Craig, J. P.; Sears, D. W. G.

2009-07-01

105

Esperance: A New Type 3 L\\/LL Ordinary Chondrite from Western Australia  

Microsoft Academic Search

The following article is a preliminary commentary on the petrographic characteristics found in our investigation of the recently discovered Esperance chondrite. The material on which this study is based consists of a thin section made from the near-surface portion of the meteorite, combined with a small sample displaying its exterior features. A thin, dull, dark brown fusion crust is present

D. E. Davis; A. K. Petersen

1992-01-01

106

A noble gas and cosmogenic radionuclide analysis of two ordinary chondrites from Almahata Sitta  

NASA Astrophysics Data System (ADS)

We present the results of a noble gas (He, Ne, Ar) and cosmogenic radionuclide (10Be, 26Al, 36Cl) analysis of two chondritic fragments (#A100, L4 and #25, H5) found in the Almahata Sitta strewn field in Sudan. We confirm their earlier attribution to the same fall as the ureilites dominating the strewn field, based on the following findings: (1) both chondrite samples indicate a preatmospheric radius of approximately 300 g cm-2, consistent with the preatmospheric size of asteroid 2008 TC3 that produced the Almahata Sitta strewn field; (2) both have, within error, a 21Ne/26Al-based cosmic ray exposure age of approximately 20 Ma, identical to the reported ages of Almahata Sitta ureilites; (3) both exhibit hints of ureilitic Ar in the trapped component. We discuss a possible earlier irradiation phase for the two fragments of approximately 10-20 Ma, visible only in cosmogenic 38Ar. We also discuss the approximately 3.8 Ga (4He) and approximately 4.6 Ga (40Ar) gas retention ages, measured in both chondritic fragments. These imply that the two chondrite fragments were incorporated into the ureilite host early in solar system evolution, and that the parent asteroid from which 2008 TC3 is derived has not experienced a large break-up event in the last 3.8 Ga.

Meier, Matthias M. M.; Welten, Kees C.; Caffee, Marc W.; Friedrich, Jon M.; Jenniskens, Peter; Nishiizumi, Kunihiko; Shaddad, Muawia H.; Wieler, Rainer

2012-06-01

107

Lavras do Sul: A New Equilibrated Ordinary L5 Chondrite from Rio Grande do Sul, Brazil  

NASA Astrophysics Data System (ADS)

The new Brazilian chondrite, Lavras do Sul, was found in 1985 at Lavras do Sul, Rio Grande do Sul State-Brazil (33°30'48?S; 53°54'65?W). It consists of a single mass weighing about 1 kg, covered by a black fusion crust with grayish interior. Four polished thin sections were prepared from a slice weighing 67 g on deposit at the Museu Nacional/UFRJ. It consists mostly of chondrules and chondrule fragments dispersed in a recrystallized matrix. Most chondrules are poorly defined and range in size from 300 to 2,000 ?m, although some of them show distinct outlines, particularly when viewed under cross-polarized transmitted and reflected light. The texture of chondrules varies from non-porphyritic (e.g., barred-olivine, radial-pyroxene) to porphyritic ones (e.g., granular olivine as well as olivine-pyroxene). The meteorite contains mainly olivine (Fa24.9), low-Ca pyroxene (Fs22.6) and metal phases, with minor amounts of plagioclase, chromite and magnetite. Mössbauer Spectroscopy studies indicate that the metal phase is kamacite, tetrataenite and antitaenite. Veins of secondary iddingsite crosscut the thin section and some ferromagnesian silicates. The chemical composition indicates that Lavras do Sul is a member of the low iron L chondrite group. The poorly delineated chondritic texture with few well-defined chondrules, the occurrence of rare clinopyroxene and plagioclase (and maskelynite) with apparent diameters ranging from 5 to 123 ?m led us to classify Lavras do Sul as an equilibrated petrologic type 5. The shock features of some minerals suggest a shock stage S3, and the presence of a small amount of secondary minerals such as iddingsite and goethite, a degree of weathering W1. The meteorite name was approved by the Nomenclature Committee (Nom Com) of the Meteoritical Society (Meteoritic Bulletin Nº99).

Zucolotto, M. E.; Antonello, L. L.; Varela, M. E.; Scorzelli, R. B.; Ludka, Isabel P.; Munayco, P.; dos Santos, E.

2012-03-01

108

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

109

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

NASA Astrophysics Data System (ADS)

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

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

1995-09-01

110

Terrestrial weathering of Antarctic stone meteorites - Formation of Mg-carbonates on ordinary chondrites  

NASA Astrophysics Data System (ADS)

Results are presented on the mineralogy, chemistry, and origin of white efflorescences on the surface of Lewis Cliff (Antarctica) 85320 (H5) chondrite (LEW 85320). Particular attention is given to determining the sources of the cations and anions of the evaporite, in order to establish the relative importance of the meteoritic element distribution and terrestrial contamination in the evaporite formation during the weathering process. The data on Na, K, Ca, and Rb abundances in efflorescence from LEW 85320 suggest that cations in evaporite minerals on Antarctic meteorites are not the products of contamination by terrestrial (marine) salts. It is suggested that the Mg in efflorescence on LEW 85320 originated from weathering of meteoritic olivine.

Velbel, M. A.; Long, D. T.; Gooding, J. L.

1991-01-01

111

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

NASA Astrophysics Data System (ADS)

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

112

Esperance: A New Type 3 L/LL Ordinary Chondrite from Western Australia  

NASA Astrophysics Data System (ADS)

The following article is a preliminary commentary on the petrographic characteristics found in our investigation of the recently discovered Esperance chondrite. The material on which this study is based consists of a thin section made from the near-surface portion of the meteorite, combined with a small sample displaying its exterior features. A thin, dull, dark brown fusion crust is present on one side of the small specimen, while the remainder of the sample shows a highly weathered and irregular interior surface with some cracking and numerous exposed chondrules and cavities. In thin section, however, the weathering effects are limited and mainly restricted to a superficially light brown staining on silicates and around metal, close to the penetrating fractures that traverse the sample. These fractures are filled with oxidation products and are a continuation of those seen in the hand sample. The thin section shows a close-packed aggregate of sharply defined chondrules and chondrule fragments set in a dark opaque matrix. A great variety of chondrule types are present with sizes up to approx. 3 mm in diameter, ranging in form from perfectly spherical to rather irregular shapes. Several examples of chondrules within chondrules as well as rimmed, armored, and dark-zoned varieties are well-displayed features seen in thin section. Other prominent characteristics are transparent pale brown glass within many chondrules and abundant polysynthetically twinned pyroxenes and zoned olivines. Metal alloy and iron sulphide, the dominant opaque mineral phases, occur within chondrules, as chondrule rims or in the matrix. Although they occupy the same mode of occurrence they are rarely seen in intimate intergrowth. A large fraction of the metal consists of several up to mm sized interstitial grains. The remaining metal and the iron sulphide both occur finely dispersed throughout the section associated with small but abundant chromite and phosphate grains and rare ilmenite. Chromite is also found within chondrules associated with both olivine and pyroxene. Within the matrix, following a rather straight narrow zone, numerous small globules of iron sulphide and metal result in thin, more or less interconnecting veins. These opaque veins are exclusively confined to matrix regions, although small globules are often seen in connection with aggregates that make up opaque chondrule rims. Quite often small vein-like strings are seen to occur in the immediate vicinity of large interstitial opaque grains. These rapidly thin out in abundance and size, a short distance away from the larger grains. Locally melt pockets are evident, either as completely isolated enclaves or as junctions between melt veins. Both melt pockets and the thin veins can be distinguished from the dark matrix by their slightly lighter colour. These features, combined with many of the larger olivine crystals showing sets of parallel planar fractures and undulatory to mosaic extinction, indicate a degree of shock deformation. According to the petrographic classification of progressive stages of shock metamorphism by Stoffler, Keil, and Scott (1991), the Esperance can at present be placed in the catergories of weakly to moderately shocked chondrites (S3-S4). A microprobe investigation of the silicate fraction of the meteorite has revealed a pronounced chemical zoning of both olivines and pyroxenes in many chondrules. Measured Fa variations in single olivine crystals have, in the most extreme cases, been found to range from Fa=5,9% in the core, to Fa=25,8% at the rim. The highest Fa content encountered at present is 27,6% in a homogeneous matrix crystal. A frequency plot of rim and matrix olivine Fa contents, groups around a peak of 25%. The chemical composition of Fs contents in pyroxenes are seen to range continuously from 0,6% to 29,2%. Several low-Ca pyroxenes show a notable Fe-Mg zoning that, however, does not exceed approx. 10% difference from core to rim. Frequently chemical compositions consistent with augite, endiopside and pigeonite are seen as overgrowths on the low-Ca

Davis, D. E.; Petersen, A. K.

1992-07-01

113

"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

114

Chromite and olivine in type 2 chondrules in carbonaceous and ordinary chondrites: Implications for thermal histories and group differences  

SciTech Connect

Analyses of chromite and olivine in type 2 chondrules in CM, CO, CV, CR, H, L, LL, and two ungrouped chondrites indicate that chromites are extremely sensitive indicators of thermal metamorphism. Chromite-olivine pairs in chondrites of petrographic types {le}3.0 have iron-magnesium partitioning characteristic of phsases which crystallized from silicate melts at temperatures > 1,400C; paris in chondrites of types > 3.0 have partitioning characteristic of reequilibration at lower temperatures. With the possible exception of the CR group, chondrite chemical groups underwent either substantial aqueous alteration (CM) or sufficient heating to reset type 2 chromites, but not both. The CR parent body may have been heated following aqueous alteration, although our data are insufficient to support a firm conclusion. Chromite and olivine compositions differ systematically among three of the chondrite groups, which suggest that type 2 melts differed in composition. Whether differences existed among the other groups is uncertain.

Johnson, C.A.; Prinz, M. (American Museum of Natural History, New York, NY (United States))

1991-03-01

115

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

NASA Astrophysics Data System (ADS)

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.

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

2011-03-01

116

An Experimental Study of Partially Molten Ordinary Chondrite Under Dynamic Conditions: Siderophile Abundances in Quench Fe-S-Ni Liquids  

NASA Astrophysics Data System (ADS)

Early differentiation in planetesimals involved a variety of different physical mechanisms. Fe-rich metallic liquid segregation can occur in a solid, partially molten or purely molten silicate body, with or without the presence of deformation. Deformation may assist the segregation of low degree metallic melts. Segregation of Fe-S-Ni liquids formed by variable degrees of partial melting of chondrites also imparts distinct geochemical signatures on the composition of the resulting metal. These chemical signatures vary according to initial parent body composition, segregation mechanisms and the degree to which early S-rich, and possibly O-bearing, core-forming liquids were extracted. In addition, the presence of deformation may both enhance kinetics and efficiency of the physical segregation process. To explore the relationship between core formation scenarios and geochemistry, deformation experiments on the Kernouve H6 ordinary chondrite were performed under partially molten conditions. The siderophile element compositions of quench Fe-S-Ni liquids dynamically segregated at different degrees of partial melting and associated Fe-Ni metal were then determined by laser ablation ICP-MS. Partition coefficients have been calculated for residual metal and the associated quench composition in the different experiments; KM-12 (P=1.2 GPa, T=900oC, strain rate= 10-6/s, no silicate melt present,10% strain) which contains the highest sulfur quench compositions and represents the lowest degree Fe-S-Ni partial melt, KM-10 (P=1.0 GPa, T=925oC, strain rate=10-5/s, 40%\\ strain), KM-17 (P=1.2 GPa, T=940oC, strain rate = 10-6/s, 12% silicate melt present, 10% strain) and KM-11 (P=1.0 GPa, T=990oC, strain rate=10-5/s, 15-18% silicate melt present, 15% strain) which shows the lowest sulfur quench composition of the highest degree Fe-S-Ni partial melt. Clear trends exist in the data from high to low wt% S content. Cu partitions into the S-bearing liquid under all conditions and Ds range from 0.19 at high S contents to 0.56 at low S contents. As goes from compatible to incompatible at approximately 15 wt%\\ S in the liquid. Ir, Ge and Ga show large changes in D as a function of S, ranging from >100 to approximately 1.0 from high to low S content but remain compatible. W and Os remain compatible and range from 1 - 5 and 5 - 7 at 13-15 wt%\\ S and 6-8 wt%\\ S, respectively. We find that the lower temperatures produce Fe-S-Ni liquid compositions observed at higher T in other studies. Part of the difference is likely due to the temperature gradient in the charge, but in addition, deformation may play an important role in enhancing reaction kinetics. The results also show that high sulfur, low degree partial melts have too low Ga, Ge and Ir to form IIE irons. Intermediate degrees of partial melting, represented by melt pools and veins in KM10 and KM17, are closest in composition. The compositional range of experimental melt compositions exceeds the IIE irons observed range. The IIE irons represent a limited portion of the experimental Ni-Co trend, implying generation from a limited range of redox conditions.

Rushmer, T.; Humayun, M.; Campbell, A. J.

2004-05-01

117

Comparison of cosmic-ray exposure ages and trapped noble gases in chondrule and matrix samples of ordinary, enstatite, and carbonaceous chondrites  

NASA Astrophysics Data System (ADS)

We performed a comprehensive study of the He, Ne, and Ar isotopic abundances and of the chemical composition of bulk material and components of the H chondrites Dhajala, Bath, Cullison, Grove Mountains 98004, Nadiabondi, Ogi, and Zag, of the L chondrites Grassland, Northwest Africa 055, Pavlograd, and Ladder Creek, of the E chondrite Indarch, and of the C chondrites Hammadah al Hamra 288, Acfer 059, and Allende. We discuss a procedure and necessary assumptions for the partitioning of measured data into cosmogenic, radiogenic, implanted, and indigenous noble gas components. For stone meteorites, we derive a cosmogenic ratio 20Ne/22Ne of 0.80 ± 0.03 and a trapped solar 4He/3He ratio of 3310 ± 130 using our own and literature data. Chondrules and matrix from nine meteorites were analyzed. Data from Dhajala chondrules suggest that some of these may have experienced precompaction irradiation by cosmic rays. The other chondrules and matrix samples yield consistent cosmic-ray exposure (CRE) ages within experimental errors. Some CRE ages of some of the investigated meteorites fall into clusters typically observed for the respective meteorite groups. Only Bath's CRE age falls on the 7 Ma double-peak of H chondrites, while Ogi's fits the 22 Ma peak. The studied chondrules contain trapped 20Ne and 36Ar concentrations in the range of 10-6-10-9 cm3 STP/g. In most chondrules, trapped Ar is of type Q (ordinary chondritic Ar), which suggests that this component is indigenous to the chondrule precursor material. The history of the Cullison chondrite is special in several respects: large fractions of both CR-produced 3He and of radiogenic 4He were lost during or after parent body breakup, in the latter case possibly by solar heating at small perihelion distances. Furthermore, one of the matrix samples contains constituents with a regolith history on the parent body before compaction. It also contains trapped Ne with a 20Ne/22Ne ratio of 15.5 ± 0.5, apparently fractionated solar Ne.

Eugster, Otto; Lorenzetti, Silvio; KräHenbühl, Urs; Marti, Kurt

2007-08-01

118

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

SciTech Connect

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

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

2001-04-30

119

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

120

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

121

The formation of weathering products on the LEW 85320 ordinary chondrite - Evidence from carbon and oxygen stable isotope compositions and implications for carbonates in SNC meteorites  

SciTech Connect

Isotopic analysis of nesquehonite recovered from the surface of the LEW 85320 H5 ordinary chondrite shows that the delta C-13 and delta O-18 values of the two generations of bicarbonate (Antarctic and Texas) are different: delta C-13 = + 7.9 per mil and + 4.2 per mil; delta O-18 = + 17.9 per mil and + 12.1 per mil, respectively. Carbon isotopic compositions are consistent with equilibrium formation from atmospheric carbon dioxide at - 2 + or - 4 C (Antarctic) and + 16 + or - 4 C (Texas). Oxygen isotopic data imply that the water required for nesquehonite precipitation was derived from atmospheric water vapor or glacial meltwater which had locally exchanged with silicates, either in the meteorite or in underlying bedrock. Although carbonates with similar delta C-13 values have been identified in the SNC meteorites EETA 79001 and Nakhla, petrographic and temperature constraints argue against their simply being terrestrial weathering products. 35 refs.

Grady, M.M.; Wright, I.P.; Pillinger, C.T.; Gibson, E.K. Jr. (Open Univ., Milton Keynes (England); NASA, Johnson Space Center, Houston, TX (USA))

1989-03-01

122

Compositional studies of type 3 chondritic meteorites  

SciTech Connect

Instrumental Neutron Activation Analysis (INAA) has been performed on 3 type 3 enstatite chondrites, 2 equilibrated enstatite chondrites, 1 type 3 carbonaceous chondrite, 38 type 3 ordinary chondrites, and 15 equilibrated ordinary chondrites. Additionally, a thermoluminescence study was performed on 15 of the type 3 ordinary chondrites. Type 3 chondrites are aggregates of the most primitive material in the solar system and it has been postulated that such material is the precursor to the other planetary objects, in particular, the equilibrated chondrites. This study was made in order to provide some insight into the formation and origin of chondritic meteorites, and the relationship between the type 3 chondrites and the more abundant equilibrated chondrites. The type 3 enstatite chondrites plot with the equilibrated EH chondrites, or at the low end of the EH range. Therefore it is concluded that the type 3 enstatite chondrites are EH chondrites that equilibrated at lower temperatures than the type 4-6 enstatite chondrites. Of the two equilibrated enstatite chondrites analyzed, RKPA 80259 was determined to be EL5 chondrite which provides evidence for a dual genetic sequence (EH3-5 and EL5-6) analogous to the three sequences formed by the ordinary chondrite classes, H, L, and LL. The Colony meteorite is one of the least metamorphosed CO3 carbonaceous chondrites which exhibits compositional variations not previously recognized in normal CO3 chondrites.

Weeks, K.S.

1985-01-01

123

Alteration of Chondrites on the Sea Floor: Mezö-Madaras (L3.7)  

NASA Astrophysics Data System (ADS)

We quantify abundances and elemental compositions of acid-resistant minerals in unequilibrated L chondrite Mezö-Madaras. The results from this study will serve as a proxy to classify extraterrestrial minerals found in sediments and fossil meteorites.

Holstein, J. L.; Schmitz, B.; Heck, P. R.

2013-09-01

124

Origin of iron-rich olivine in the matrices of type 3 ordinary chondrites - an experimental study  

NASA Astrophysics Data System (ADS)

The reaction of metallic iron and enstatite, with and without forsterite and SiO2, is experimentally studied at temperatures between 1150 and 800 C in order to investigate the origin of iron-rich olivine in the matrices of type 3 chondrites. The composition of olivine is shown to become more iron-rich with increasing silica/enstatite ratio. Possible scenarios for the origin of this olivine include: (1) free silica having been present if the iron-rich olivine was formed by solid-state reactions under oxidizing conditions in the solar nebula; and (2) the reaction of silicon-rich gas with metallic iron having taken place under oxidizing conditions in the solar nebula.

Nagahara, H.; Kushiro, I.

1987-10-01

125

Kosmochloric Ca-rich pyroxenes and FeO-rich olivines (Kool grains) and associated phases in Stardust tracks and chondritic porous interplanetary dust particles: Possible precursors to FeO-rich type II chondrules in ordinary chondrites.  

NASA Astrophysics Data System (ADS)

Terminal particles and mineral fragments from comet 81P/Wild 2 were studied in 16 aerogel tracks by transmission and secondary electron microscopy. In eight tracks clinopyroxenes with correlated Na2O and Cr2O3 contents as high as 6.0 wt% and 13.0 wt%, respectively, were found. Kosmochloric (Ko) clinopyroxenes were also observed in 4 chondritic interplanetary dust particles (IDPs). The Ko clinopyroxenes were often associated with FeO-rich olivine ± Cr-rich spinel ± aluminosilicate glass or albitic feldspar, assemblages referred to as Kool grains (Ko = kosmochloric Ca-rich pyroxene, ol = olivine). Fine-grained (submicron) Kool fragments have textures suggestive of crystallization from melts while coarse-grained (>1 µm) Kool fragments are often glass-free and may have formed by thermal metamorphism in the nebula. Average major and minor element distributions between clinopyroxenes and coexisting FeO-rich olivines are consistent with these phases forming at or near equilibrium. In glass-bearing fine-grained Kool fragments, high concentrations of Na in the clinopyroxenes are inconsistent with existing experimentally determined partition coefficients at equilibrium. We speculate that the availability of Cr in the melt increased the clinopyroxene Na partition coefficient via a coupled substitution thereby enhancing this phase with the kosmochlor component. The high temperature minerals, fine-grain sizes, bulk compositions and common occurrence in the SD tracks and IDPs support the idea that Kool grains could have been precursors to type II chondrules in ordinary chondrites. These grains, however, have not been observed in these meteorites suggesting that they were destroyed during chondrule formation and recycling or were not present in the nebula at the time and location where meteoritic chondrules formed.

Joswiak, D. J.; Brownlee, D. E.; Matrajt, G.; Westphal, A. J.; Snead, C. J.

2009-11-01

126

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

127

Thermal history of the H-group of chondritic meteorites  

NASA Astrophysics Data System (ADS)

The Tieschitz unequilibrated H-group chondrite accreted at 800 + or - 100 C during rapid cooling. From their mineral chemistry, nine other H-group chondrites, exhibiting greater degrees of equilibration, also formed hot. Degree of equilibration is equated with slowness of cooling, especially below about 700 C. If metamorphism is defined as change brought about by an increase in temperature, in the H-group chondrites it is recognized only in the localized effects of transient reheating, probably induced by shock.

Hutchison, R.; Bevan, A. W. R.; Agrell, S. O.; Ashworth, J. R.

1980-10-01

128

Comparative stable isotope geochemistry of Ni, Cu, Zn, and Fe in chondrites and iron meteorites  

NASA Astrophysics Data System (ADS)

High-precision Ni isotopic variations are reported for the metal phase of equilibrated and unequilibrated ordinary chondrites, carbonaceous chondrites, iron meteorites, mesosiderites, and pallasites. We also report new Zn and Cu isotopic data for some of these samples and combine them with literature Fe, Cu, and Zn isotope data to constrain the fractionation history of metals during nebular (vapor/solid) and planetary (metal/sulfide/silicate) phase changes. The observed variations of the 62Ni/58Ni, 61Ni/58Ni, and 60Ni/58Ni ratios vary linearly with mass difference and define isotope fractionation lines in common with terrestrial samples. This implies that Ni was derived from a single homogeneous reservoir. While no 60Ni anomaly is detected within the analytical uncertainties, Ni isotopic fractionation up to 0.45‰ per mass-difference unit is observed. The isotope compositions of Ni and Zn in chondrites are positively correlated. We suggest that, in ordinary chondrites, exchange between solid phases, in particular metal and silicates, and vapor followed by mineral sorting during accretion are the main processes controlling these isotopic variations. The positive correlation between Ni and Zn isotope compositions contrasts with a negative correlation between Ni (and Zn) and Cu isotope compositions, which, when taken together, do not favor a simple kinetic interpretation. The observed transition element similarities between different groups of chondrites and iron meteorites are consistent with the genetic relationships inferred from oxygen isotopes (IIIA/pallasites and IVA/L chondrites). Copper is an exception, which we suggest may be related to separate processing of sulfides either in the vapor or during core formation.

Moynier, Frédéric; Blichert-Toft, Janne; Telouk, Philippe; Luck, Jean-Marc; Albarède, Francis

2007-09-01

129

A simple chondritic model of Mars  

Microsoft Academic Search

SNC meteorites (Shergottites, Nakhlites and Chassigny) define a fractionation line in a ?17O\\/?18O diagram as expected for rocks differentiated from a formerly homogenized parent body, which is intermediate between H ordinary chondrites and EH enstatite chondrites. The planet Mars is located between the Earth and the asteroid belts, the potential source of ordinary chondrites. Since oxygen is a major component

C. Sanloup; A. Jambon; P. Gillet

1999-01-01

130

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

131

A comparison of sulfur isotope ratio measurement using two ion microprobe techniques and application to analysis of troilite in ordinary chondrites  

SciTech Connect

Continual improvements in the precision of isotope ratio measurements made by ion microprobe and the attempt to resolve smaller isotopic differences using this technique means that it is increasingly important to demonstrate the accuracy of calibration of this method, particularly when it is impossible to mount a standard with the unknown being analyzed. An assessment of the accuracy and precision using ion microprobe methods for the measurement of isotope ratios is made analyzing a pyrite standard mounted in several thin sections and troilite in ordinary chondrite meteorites. We compare two methods, the traditional high mass resolution approach and the more recent extreme energy filtering technique. The results indicate that both techniques offer precise measurements for analyses made within a single thin-section. However, the accuracy of the high mass resolution results are significantly worse than those obtained using extreme energy filtering when a standard cannot be mounted with the unknown. For analysis of a standard pyrite mounted in different thin sections, the measured instrumental mass bias varied by up to 7{per_thousand}. Analysis of the same samples using extreme energy filtering showed no variation in instrumental mass bias within 0.5{per_thousand}. Similar results were observed in analysis of troilite. Whereas the extreme energy filtering results are within error of the expected 0{per_thousand}, values obtained using high mass resolution differ by up to {+-}3{per_thousand}. Our results indicate that it is possible to analyze {delta}{sup 34}S values in sulfides using an ion microprobe with precision and accuracy of {+-}0.25{per_thousand} (1{sigma}) in 12 min, with a spatial resolution under 20 {mu}m. 28 refs., 3 figs., 3 tabs.

Paterson, B.A. [Oak Ridge National Lab., TN (United States)]|[Univ. of Tennessee, Knoxville, TN (United States); Riciputl, L.R. [Oak Ridge National Lab., TN (United States); McSween, H.Y. Jr. [Univ. of Tennessee, Knoxville, TN (United States)

1997-02-01

132

Shock metamorphism of carbonaceous chondrites  

Microsoft Academic Search

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

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

1992-01-01

133

A reappraisal of the metamorphic history of EH3 and EL3 enstatite chondrites  

NASA Astrophysics Data System (ADS)

The thermal history of a series of EH3 and EL3 chondrites has been investigated by studying the degree of structural order of the organic matter (OM) located and characterized in matrix areas by Raman micro-spectroscopy. By comparison with unequilibrated ordinary chondrites (UOCs) and CO and CV carbonaceous chondrites, the following petrologic types have been assigned to various E chondrites: Sahara 97096 and Allan Hills 84206: 3.1-3.4; Allan Hills 85170 and Parsa: 3.5; Allan Hills 85119: 3.7; Qingzhen, MacAlpine Hills 88136 and MacAlpine Hills 88184: 3.6-3.7. The petrologic type of Qingzhen is consistent with the abundance of the P3 noble gas component, a sensitive tracer of the grade of thermal metamorphism. The petrologic types are qualitatively consistent with the abundance of fine-grained matrix for the whole series. No significant effects of shock processes on the structure of OM were observed. However such processes certainly compete with thermal metamorphism and the possibility of an effect cannot be fully discarded, in particular in the less metamorphosed objects. The OM precursors accreted by the EH3 and EL3 parent bodies appear to be fairly similar to those of UOCs and CO and CV carbonaceous chondrites. Raman data however show some slight structural differences that could be partly accounted for by shock processes. The metamorphic history of EH3 and EL3 chondrites has often been described as complex, in particular regarding the combined action of shock and thermal metamorphism. Because OM maturity is mostly controlled by the temperature of peak metamorphism, it is possible to distinguish between the contributions of long duration thermal processes and that of shock processes. Comparison of the petrologic types with the closure temperatures previously derived from opaque mineral assemblages has revealed that the thermal history of EH3 and EL3 chondrites is consistent with a simple asteroidal onion shell model. Thermal metamorphism in enstatite chondrites appears to be fairly similar to that which takes place in other chondrite classes. The complex features recorded by mineralogy and petrology and widely reported in the literature appear to be mostly controlled by shock processes.

Quirico, Eric; Bourot-denise, Michèle; Robin, Christophe; Montagnac, Gilles; Beck, Pierre

2011-06-01

134

Highly siderophile elements in chondrites  

USGS Publications Warehouse

The abundances of the highly siderophile elements (HSE), Re, Os, Ir, Ru, Pt and Pd, were determined by isotope dilution mass spectrometry for bulk samples of 13 carbonaceous chondrites, 13 ordinary chondrites and 9 enstatite chondrites. These data are coupled with corresponding 187Re-187Os isotopic data reported by Walker et al. [Geochim. Cosmochim. Acta, 2002] in order to constrain the nature and timing of chemical fractionation relating to these elements in the early solar system. The suite of chondrites examined displays considerable variations in absolute abundances of the HSE, and in the ratios of certain HSE. Absolute abundances of the HSE vary by nearly a factor of 80 among the chondrite groups, although most vary within a factor of only 2. Variations in concentration largely reflect heterogeneities in the sample aliquants. Different aliquants of the same chondrite may contain variable proportions of metal and/or refractory inclusions that are HSE-rich, and sulfides that are HSE-poor. The relatively low concentrations of the HSE in CI1 chondrites likely reflect dilution by the presence of volatile components. Carbonaceous chondrites have Re/Os ratios that are, on average, approximately 8% lower than ratios for ordinary and enstatite chondrites. This is also reflected in 187Os/188Os ratios that are approximately 3% lower for carbonaceous chondrites than for ordinary and enstatite chondrites. Given the similarly refractory natures of Re and Os, this fractionation may have occurred within a narrow range of high temperatures, during condensation of these elements from the solar nebula. Superimposed on this major fractionation are more modest movements of Re or Os that occurred within the last 0-2 Ga, as indicated by minor open-system behavior of the Re-Os isotope systematics of some chondrites. The relative abundances of other HSE can also be used to discriminate among the major classes of chondrites. For example, in comparison to the enstatite chondrites, carbonaceous and ordinary chondrites have distinctly lower ratios of Pd to the more refractory HSE (Re, Os, Ir, Ru and Pt). Differences are particularly well resolved for the EH chondrites that have Pd/Ir ratios that average more than 40% higher than for carbonaceous and ordinary chondrite classes. This fractionation probably occurred at lower temperatures, and may be associated with fractionation processes that also affected the major refractory lithophile elements. Combined, 187Os/188Os ratios and HSE ratios reflect unique early solar system processing of HSE for each major chondrite class. ?? 2002 Elsevier Science B.V. All rights reserved.

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

2003-01-01

135

Chondrites and their Components  

NASA Astrophysics Data System (ADS)

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

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

2003-12-01

136

Collisional history of H chondrites  

Microsoft Academic Search

The cosmic ray exposure histories of ordinary chondrites were recently rreviewed (Marti and Graf, 1992). Here, we discuss in detail currently available cosmic ray exposure records and the adopted exposure ages of individual H chondrites. We further present analyses of the distinct histograms of petrographic subgroups and the implications for orbital evolution and collisional records. In addition to the stochastic

Thomas Graf; Kurt Marti

1995-01-01

137

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

Microsoft Academic Search

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

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

1993-01-01

138

Gas permeability of shocked chondrites  

NASA Astrophysics Data System (ADS)

The gas permeability of 11 ordinary chondrites was measured at various gas pressures (0.5-2.5 bars) under confining pressures up to 120 bars. The gas permeability ranges from less than a nanodarcy to a few millidarcies. There is a positive correlation between the permeability and the porosity. The permeabilithy decreased by as much as 50 percent when the confining pressure was increased from 10 to 100 bars, suggesting that the permeability of some chondrites is partly due to cracks. A linear relation between gas flow pressure dependence and confining pressure dependence of the gas permeability is observed, suggesting that on average, crack apertures are larger than pore spaces. The permeabilithy of heavily-shocked chondrites is less than of mildly shocked chondrites. Using the measured permeability data the size of a possible shocked-chondrite precursor body is estimated.

Matsui, T.; Sugiura, N.; Brar, N. S.

1986-03-01

139

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

140

Formation of niningerite by silicate sulfidation in EH3 enstatite chondrites  

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

141

Equilibrium condensation from chondritic porous IDP enriched vapor: Implications for Mercury and enstatite chondrite origins  

NASA Astrophysics Data System (ADS)

The origin of Mercury's anomalous core and low FeO surface mineralogy are outstanding questions in planetary science. Mercury's composition may result from cosmochemical controls on the precursor solids that accreted to form Mercury. High temperatures and enrichment in solid condensates are likely conditions near the midplane of the inner solar protoplanetary disk. Silicate liquids similar to the liquids quenched in ferromagnesian chondrules are thermodynamically stable in oxygen-rich systems that are highly enriched in dust of CI-chondrite composition. In contrast, the solids surviving into the orbit of Mercury's accretion zone were probably similar to highly unequilibrated, anhydrous, interstellar organic- and presolar grain-bearing chondritic, porous interplanetary dust particles (C-IDPs). Chemical systems enriched in an assumed C-IDP composition dust produce condensates (solid+liquid assemblages in equilibrium with vapor) with super-chondritic atomic Fe/Si ratios at high temperatures, approaching 50% of that estimated for bulk Mercury. Sulfur behaves as a refractory element, but at lower temperatures, in these chemical systems. Stable minerals are FeO-poor, and include CaS and MgS, species found in enstatite chondrites. Disk gradients in volatile compositions of planetary and asteroidal precursors can explain Mercury's anomalous composition, as well as enstatite chondrite and aubrite parent body compositions. This model predicts high sulfur content, and very low FeO content of Mercury's surface rocks.

Ebel, D. S.; Alexander, C. M. O'D.

2011-12-01

142

Petrology of types 4-6 carbonaceous chondrites  

NASA Astrophysics Data System (ADS)

A comparative mineralogic study has been made of Coolidge, Karoonda, and new C4 chondrites in order to clarify the origin of C4-6 chondrites. It is shown that the properties of all C4-6 chondrites are consistent with an origin by metamorphism of C3-like precursors by processes analogous to those operating in ordinary chondrite parent bodies or planetesimals. However, type 4-6 material was not well mixed with type 3 material in the CV3 parent body. It is concluded that C4-6 chondrites may come from one or more separate parent bodies.

Scott, E. R. D.; Taylor, G. J.

1985-02-01

143

The relationship between CK and CV chondrites  

NASA Astrophysics Data System (ADS)

CK chondrites are highly oxidized meteorites containing abundant magnetite and trace amounts of Fe,Ni metal. Although the group is predominately composed of equilibrated meteorites (types 4-6), in recent years a significant number of new samples have been classified as being either CK3 or CK3-anomalous. These unequilibrated CKs often display a close affinity with members of the CV oxidized subgroup. CKs and CVs (oxidized subgroup) may therefore form a continuum and by implication could be derived from a single common parent body. To investigate the relationship between these two groups a detailed study of the oxygen isotope composition, opaque mineralogy and major and trace element geochemistry of a suite of CV and CK chondrites has been undertaken. The results of oxygen isotope analysis confirm the close affinity between CV and CK chondrites, while excluding the possibility of a linkage between the CO and CK groups. Magnetites in both CV and CK chondrites show significant compositional similarities, but high Ti contents are a diagnostic feature of the latter group. The results of major and trace element analysis demonstrate that both CV and CK chondrites show overlapping variation. Supporting evidence for a single common source for both groups comes from their similar cosmic-ray exposure age distributions. Recent reflectance spectral analysis is consistent with both the CVs and CKs being derived from Eos family asteroids, which are believed to have formed by the catastrophic disruption of a single large asteroid. Thus, a range of evidence appears to be consistent with CV and CK chondrites representing samples from a single thermally stratified parent body. In view of the close similarity between CV and CK chondrites some modification of the present classification scheme may be warranted, possibly involving integration of the two groups. One means of achieving this would be to reassigned CK chondrites to a subgroup of the oxidized CVs. It is recognized that a full evaluation of this proposal may require further study of the still poorly understood CK3 chondrites.

Greenwood, R. C.; Franchi, I. A.; Kearsley, A. T.; Alard, O.

2010-03-01

144

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

NASA Astrophysics Data System (ADS)

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

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

1990-12-01

145

The Effects of Saharan Weathering on Light Element Contents of Various Primitive Chondrites  

NASA Astrophysics Data System (ADS)

In recent years the Sahara Desert, particularly the Acfer region, has proven itself a rich source of meteoritic material, with over 400 samples from North Africa now residing in research laboratories. Among the samples retrieved has been a number of primitive chondrites, including CVs, CRs, COs, an odd CM/CO specimen, and several fragments similar to the "unique" chondrite ALH 85085 and a type 3.0-3.2 ordinary chondrite. Samples of each of these have been analyzed for carbon content and delta^13C and some for nitrogen and hydrogen content, delta^5N and deltaD. Each of these elements shows a lower concentration in the Saharan samples than those determined for non-Saharan, including Antarctic samples of the same group. Carbon. The carbon content of the Saharan carbonaceous chondrites analyzed were between 25 and 50% of the mean of the non-Saharan members of the group (the one exception is Allende, which is known to have a lower carbon content that any other members of the CV group). Stepped combustion showed that a low organic carbon content of these samples was the cause of the overall carbon depletion. Nitrogen. The nitrogen contents of the Acfer region CR chondrites was substantially lower than that of their non-Saharan equivalents. The nitrogen of the CR chondrites is isotopically distinct from terrestrial samples and from other carbonaceous chondrites in that it is highly enriched in ^15N. The isotopic composition of the Saharan samples shows no gross difference in the delta^15N, but there is some internal variation, due to differential weathering and the rusting of metal leading to the presence of trapped atmospheric nitrogen and consequently the delta^15N becoming variably lighter. Hydrogen. The hydrogen contents of the Saharan CR chondrites and the 3.0-3.2 ordinary chondrite Adrar 003 were found to be lower than the non-Saharan counterparts: The deltaD of the samples were isotopically normal quite unlike their non-Saharan counterparts, which are known to be the most enriched in deltaD known. The stepped combustion of the whole-rock Saharan chondrites shows that organic contamination is minimal, but evaporitic carbonate occurs in some samples with ca. 1200 ppm in the most affected. This is a localized feature as some possibly paired meteorites from the same fall sometimes show no evidence for the presence of terrestrial carbonates. Given the range of meteorites over which the observations are made it it necessary to question whether the difference in abundance and isotopic composition are primary effects. Perhaps the data are more easily explained by the destruction of macromolecular carbon as a result of extreme weathering conditions, a temperature cycle of over 150 degrees C and desiccation followed by rehydration. Such circumstances may lead to the volatilization of side chains, the degradation and removal of the organic material. The most important implication of the effects may be in terms of identifying the site of the heavy hydrogen in the CR (Kolodny et al., 1980) and unequilibrated ordinary chondrites (Robert et al., 1979; McNaughton et al., 1981, 1982) as it appears to be in a form that can be easily exchanged with terrestrial water or destroyed by mild but prolonged heating. It would seem to preclude a phyllosilicate carrier as exchange of waters of hydration occurs only above 200 degrees C, thus supporting the labile side chains of the macromolecular species or soluble organic material as the major carrier of the deuterium anomaly. References: Kolodny, Y., Kerridge, J.F., and Kaplan I.R. (1980) EPSL, 46, 149-158. McNaughton, N.J., Fallick, A.E., and Pillinger, C.T. (1982) J. Geophys. Res. 87, A297-302. McNaughton, N.J., Borthwick, J., Fallick A.E., and Pillinger, C.T. (1981) Nature 294, 639-641. Robert, F., Melivat, L., and Javoy, M. (1979) Nature 282, 785-789.

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

1992-07-01

146

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

147

The Metal-Phosphate Connection in Chondrites  

Microsoft Academic Search

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

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

1992-01-01

148

Elemental variations in bulk chondrites - A brief review  

NASA Astrophysics Data System (ADS)

The three classes of chondrites - carbonaceous, ordinary and enstatite - are clearly delineated into nine separate groups by their elemental abundances. Several analytical techniques are available for determining these elemental abundances. They include wet-chemical methods, X-ray fluorescence analysis, fused-bead analysis, instrumental and radiochemical neutron-activation analysis, and isotope-dilution mass spectroscopy. The four carbonaceous-chondrite groups are also readily distinguished by their volatile-element abundances.

Kallemeyn, Gregory W.

149

Moessbauer study of the Putinga chondrite  

NASA Astrophysics Data System (ADS)

The Putinga meteorite, classified as an L-6 ordinary chondrite, was studied by 57Fe Mössbauer spectroscopy at 300K and 80K. The iron mineral phases present in the Putinga meteorite were determined to be olivine, orthopyroxene, troilite, paramagnetic taenite, kamacite and an Fe3+-compound. It is suggested that the Fe3+-compound has originated from oxidation of the sample in the earth atmosphere.

de Oliveira, J. C. P.; da Costa, M. I., Jr.; Vasquez, A.; Roisenberg, A.; Vieira, N., Jr.

1988-01-01

150

Composition of Chondrules and the Assessment of Chondritic Abundances: A Planetary Perspective  

NASA Astrophysics Data System (ADS)

We have measured refractory trace-element ratios in chondrules from enstatite, ordinary and carbonaceous chondrites and find a high intrameteorite variability that has consequences for the modeling of planetary compositions.

McDonough, W. F.; Ash, R. D.; Puchtel, V.

2011-03-01

151

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

NASA Astrophysics Data System (ADS)

Oxygen isotopes were measured in four chondritic hydrated interplanetary dust particles (IDPs) and five chondritic anhydrous IDPs including two GEMS-rich particles (Glass embedded with metal and sulfides) by a combination of high precision and high lateral resolution ion microprobe techniques. All IDPs have isotopic compositions tightly clustered around that of solar system planetary materials. Hydrated IDPs have mass-fractionated oxygen isotopic compositions similar to those of CI and CM carbonaceous chondrites, consistent with hydration of initially anhydrous protosolar dust. Anhydrous IDPs have small 16O excesses and depletions similar to those of carbonaceous chondrites, the largest 16O variations being hosted by the two GEMS-rich IDPs. Coarse-grained forsteritic olivine and enstatite in anhydrous IDPs are isotopically similar to their counterparts in comet Wild 2 and in chondrules suggesting a high temperature inner solar system origin. The small variations in the 16O content of GEMS-rich IDPs suggest that most GEMS either do not preserve a record of interstellar processes or the initial interstellar dust is not 16O-rich as expected by self-shielding models, although a larger dataset is required to verify these conclusions. Together with other chemical and mineralogical indicators, O isotopes show that the parent-bodies of carbonaceous chondrites, of chondritic IDPs, of most Antarctic micrometeorites, and comet Wild 2 belong to a single family of objects of carbonaceous chondrite chemical affinity as distinct from ordinary, enstatite, K- and R-chondrites. Comparison with astronomical observations thus suggests a chemical continuum of objects including main belt and outer solar system asteroids such as C-type, P-type and D-type asteroids, Trojans and Centaurs as well as short-period comets and other Kuiper Belt Objects.

Aléon, J.; Engrand, C.; Leshin, L. A.; McKeegan, K. D.

2009-08-01

152

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

153

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

SciTech Connect

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. 34 refs.

Podosek, F.A.; Brannon, J.C. (Washington University, Saint Louis, MO (USA))

1991-06-01

154

Compositions of chondrites  

Microsoft Academic Search

A compilation of data on 78 elements in the nine groups of chondrites shows each to be isochemical with the exception of a few volatiles. With the exception of the most volatile elements, the groups have solar abundances to within a factor of two. The solar abundances and the chemical and physical properties of phases in the least-altered chondrites indicate

J. T. Wasson; G. W. Kallemeyn

1988-01-01

155

Sulfur and selenium in chondritic meteorites  

NASA Astrophysics Data System (ADS)

We report here new analyses of S and Se in carbonaceous chondrites (2 CIs, 11 CMs, 6 CO3s, 7 CV3s, 2 C4s, 4 CRs, and 1 CH), 2 rumurutiites, ordinary chondrites (2 Hs, 2 Ls, and 1 LL), 3 anomalous chondrites, 3 acapulcoites, 3 lodranites, and in silicate inclusions of the Landes lAB iron meteorite. To avoid problems from inhomogeneous distribution of sulfides, the same samples that had been analysed for Se by INAA were analysed for S using a Leybold Heraeus Carbon and Sulfur Analyser (CSA 2002). With the measured CI contents of 5.41% S and 21.4 ppm Se a CI S/Se ratio of 2540 is obtained. A nearly identical S/Se ratio of 2560±150 is found for carbonaceous chondrites (average of falls). The average ratio of all meteorite falls analysed in this study was 2500 + 270. These data suggest that the new S content of Orgneil with 5.41% provides a reliable estimate for the average Solar System. The new solar system abundance of S of 4.62 × 105 (atoms/1O6 Si) is in good agreement with the solar photospheric abundance of 7.21 (log (a(H)) = E12) (Anders and Grevesse, 1989). Among the 50 analysed meteorites, 24 were finds from hot (Australia, Africa) and cold (Antarctica) deserts. Weathering effects in the carbonaceous chondrites and in one lodranite from the hot deserts resulted in losses of S, Se, Na and occasionally Ni. Sulfur is apparently more affected by weathering than Se. No losses were observed in ordinary chondrite finds and in meteorites collected in the Antarctica, except for the obvious loss of Na in the CM-chondrite Y 74662. The low S-content of 0.096% in Gibson, a lodranite, is probably not representative of this group of meteorites. Gibson is a find from the Australian desert and has lost S and also Se by weathering. Two other lodranites, finds from Antarctica, have about 2% 5.

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

1995-07-01

156

The Origin of Chondrules and Refractory Inclusions in Chondritic Meteorites  

Microsoft Academic Search

Examples of calcium-aluminum-rich inclusions (CAIs) surrounded by thick chondrule mantles have been found in chondritic meteorites and cast doubt on the conventional belief that CAIs and chondrules possessed different spacetime origins in the primitive solar nebula. We study specific processes by which such objects, and the more common ordinary CAIs and chondrules, might have formed by flare heating of primitive

Hsien Shang; Matthieu Gounelle; Alfred E. Glassgold; Typhoon Lee

2001-01-01

157

Experimental impacts into chondritic targets, part I: Disruption of an L6 chondrite by multiple impacts  

NASA Astrophysics Data System (ADS)

A fragment of an L6 chondrite (Allan Hills [ALH] 85017,13) with an initial mass (M0) of 464.1 g was the target in a series of experimental impacts in which the largest remaining fragment (MR) after each shot was impacted by a 3.18 mm ceramic sphere at a nominal speed of 2 km s-1. This continued until the mass of the largest remaining piece was less than half the mass of the target presented to that shot (MS). Two chunks of Bushveldt gabbro with similar initial masses were also impacted under the same conditions until MR was less than half M0. The two gabbro targets required a total of 1.51 × 107 and 1.75 × 107 erg g-1 to attain 0.27 and 0.33 MR/M0, respectively; the chondrite, however, was considerably tougher, reaching 0.40 and 0.21 MR/M0 only after receiving 2.37 × 107 and 3.10 × 107 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.; Hörz, Friedrich

2008-04-01

158

Accumulation mechanisms and the weathering of Antarctic equilibrated ordinary chondrites  

Microsoft Academic Search

Induced thermoluminescence (TL) is used to quantitatively evaluate the degree of weathering of meteorites found in Antarctica. We find a weak correlation between TL sensitivity and descriptions of weathering in hand specimens, the highly weathered meteorites having lower TL sensitivity than unweathered meteorites. Analysis of samples taken throughout large meteorites shows that the heterogeneity in TL sensitivity within meteorite finds

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

1999-01-01

159

Magnetic Properties of LL6 Ordinary Chondrite St. Severin  

NASA Astrophysics Data System (ADS)

The LL6 St. Severin possesses an ancient stable natural remanent magnetization (NRM), whose higher unblocking fractions (520-560°C) are randomly oriented yet lower unblocking fractions (<520°C) form a potential magnetic foliation. The St. Severin contains paramagnetic troilite, Cr-Fe-Ti-oxide and potentially ferromagnetic Fe-Ni system. A sharp unblocking around 560°C during thermal demagnetization strongly indicates that tetrataenite is the sole remanence carrier in the St. Severin. However, the absence of ferromagnetic signal in kamacite and the presence of a randomly oriented higher unblocking fraction (520-560°C) of NRM for tetrataenite indicate a multi-stage shock-induced metamorphism of the St. Severin rather than a thermal origin of NRM. More than an order difference in NRM/ARM (anhysteretic remanent magnetization) and NRM/SIRM (saturation isothermal remanent magnetization) with respect to a terrestrial signal can be a manifestation of taenite conversion to tetrataenite.

Doh, S.; Yu, Y.; Kim, W.; Min, K. K.

2010-12-01

160

Cosmogenic Nuclides and Noble Gas Evidence that Almahata Sitta Chondrites Represent Fragments of Asteroid 2008 TC3  

NASA Astrophysics Data System (ADS)

We present evidence that two ordinary chondrites from the Almahata Sitta strewnfield were part of asteroid 2008 TC3 and may have been incorporated into the ureilitic host during a catastrophic collision ~3.8 Ga ago.

Welten, K. C.; Meier, M. M. M.; Caffee, M. W.; Nishiizumi, K.; Wieler, R.; Jenniskens, P.; Shaddad, M. H.

2011-03-01

161

Petrology and oxygen isotopes of NWA 5492, a new metal-rich chondrite  

NASA Astrophysics Data System (ADS)

Northwest Africa 5492 is a new metal-rich chondrite breccia that may represent a new oxygen reservoir and new chondrite parent body. It has some textural similarities to CB and CH chondrites, but silicates are more reduced, sulfides are more common and not associated with metal, and metal compositions differ from CB and CH chondrites. Oxygen isotope ratios indicate that Northwest Africa (NWA) 5492 components (chondrules and lithic fragments) formed in at least two different oxygen reservoirs. The more common, and presumably host, component plots in a region above the terrestrial fractionation line, below ordinary chondrite compositions, and just above enstatite chondrites in 3-oxygen space. The only other chondritic materials that plot in this region are chondrules from the Grosvenor Mountains (GRO) 95551 ungrouped metal-rich chondrite. The other rare component plots near the CR, CB, and CH chondrites. Based on petrologic characteristics and oxygen isotopic compositions, NWA 5492 appears to be related to the ungrouped metal-rich GRO 95551 chondrite.

Weisberg, Michael K.; Bunch, Ted E.; Wittke, James H.; Rumble, Douglas; Ebel, Denton S.

2012-03-01

162

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

163

Boron in chondritic meteorites  

Microsoft Academic Search

The B and Li content and distribution in 14 chondrites are investigated experimentally by means of prompt gamma neutron activation on bulk samples, EMPA, and alpha-track imaging of thin polished sections attached to neutron-irradiated cellulose nitrate films. Alpha-track and transmitted-light images are shown, and numerical results are presented in extensive tables. Chondrites of lower equilibration grades are found to contain

D. M. Shaw; M. D. Higgins; R. W. Hinton; M. G. Truscott; T. A. Middleton

1988-01-01

164

"Ordinary People": Extraordinary Lives  

ERIC Educational Resources Information Center

Describes Judith Guest's "Ordinary People," a novel about abandoning the protection of being ordinary that can provide insight for both adolescents and adults. Suggestions for using the novel in the classroom are provided by Jona J. Mann. (KS)

Hadley, Lee

1977-01-01

165

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

166

Chondrites and the Protoplanetary Disk  

Microsoft Academic Search

Major advances in deciphering the record of nebula processes in chondrites can be attributed to analytical improvements that allow coordinated isotopic and mineralogical studies of components in chondrites and to a wealth of new meteorites from hot and cold deserts. These studies have identified a few rare pristine chondrites that largely escaped heating and alteration in asteroids, which have matrices

Edward R. D. Scott

2007-01-01

167

Cathodoluminescence properties of components in enstatite chondrites  

NASA Astrophysics Data System (ADS)

As a group, the enstatite chondrites are notable by the extremely low FeO content of most of their silicates. This property predisposes many of these materials to emit Cathodoluminescence (CL). Since examination of the CL properties of meteoritic components in ordinary and carbonaceous chondrites have proven to be a useful technique, we have initiated a survey of the enstatite chondrites in order to better characterize the chemical and physical properties of their luminescing phases. Because of the diversity encountered in this study, it is first necessary to describe the number and types of materials observed to emit CL in these meteorites. Two CL techniques were used. First, the initial survey work was conducted at low magnification using a Nuclide (now MAAS) Luminoscope mounted to a Wild MP binocular microscope equipped for photo-microscopy. The beam conditions used were 14 +/- KeV and 7 +/- 1 milliamps, with the beam focussed to the diameter of the field of view of the microscope at 20x (appox. 1.25 cm). Photomosaics were produced for each section using Ecktar 1000 film and an exposure time of 15 to 30 seconds. Second, high magnification (400x) photos were obtained of individual components of interest by mounting a 35mm camera to the optical system of the Cameca Camebax microprobe located at the Johnson Space Center. Beam conditions used were 15 KeV and 600 nA. Ecktar 1000 film was also used, but exposure times of 6 minutes were necessary to produce a useful image. The components in E chondrites that produce CL can be divided into four broad categories. These are clasts and aggregates, chondrules, matrix components, and refractory objects. Components in each category are discussed.

Dehart, John M.; Lofgren, Gary E.

1993-03-01

168

Rare earth elements in Ca-phosphates of Allende carbonaceous chondrite  

SciTech Connect

The Ca-phosphate phases in the Allende CV3 meteorite were selectively dissolved in ammoniacal EDTA solution and measured for abundances of the rare earth elements (REE) by radiochemical neutron activation and mass-spectrometric isotope dilution analyses. The REE abundances in CA-phosphates of Allende are remarkably different from those of ordinary chondrites. All the REE except Eu were observed to be enriched by factors of 50-100 relative to the Cl values. This is 3-4 times lower than concentrations of REE in the ordinary-chondrite phosphates. Allende phosphates have a small positive Eu anomaly, in contrast to the large negative Eu anomaly in phosphates from ordinary chondrites. Though the positive Eu anomaly in Allende Ca-phosphates is puzzling, the lack of a negative Eu anomaly in Allende Ca-phosphates suggests that they never have been in equilibrium with Allende coarse-grained Ca, Al-rich inclusions or their precursor materials. 42 references.

Ebihara, M.; Honda, M.

1987-09-01

169

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

170

The carbonaceous chondrites  

Microsoft Academic Search

The carbonaceous chondrites are a group of stony meteorites characterized by the presence of an appreciable amount of carbonaceous material other than free carbon (diamond and graphite). They have been divided into three subgroups known respectively as Type I, Type II, and Type III. Analyses of Type I meteorites show about 3–5% of carbon and 20% of combined water; they

Brian Mason

1963-01-01

171

The Th and U abundances in chondritic meteorites  

NASA Astrophysics Data System (ADS)

We present new analyses of Th-232/U-238 in CI and CM meteorites. The relative abundance of these nuclides is important in estimates of the age of r-process elements. The cosmochronology based upon the Th-232/U-238 ratio (kappa) depends on the precise determinations of these two different elements in meteorites and on the production ratios. Both parameters are subject to substantial errors. Recent recalculations of this chronology have used selected values from compilations but do not adequately address the errors in terms of a reliable data base. Morgan and Lovering provided extensive neutron activation analyses for ordinary chondrites which yield an average kappa of 3.6 +/- 0.4. Their work on carbonaceous chondrites showed a wide range in kappa from 2 to 6. More recent investigations by isotopic dilution have established the following: (1) highly variable kappa from 2.7 to 11 in Allende Ca-Al-rich inclusions and a value of 3.6 in the Orgueil CI1 chondrite; (2) a range from 2.71 to 6.63 for 7 L-type chondrites and a range from 2.7 to 4.4 for 6 L, H, and LL chondrites. A further investigation of this subject matter is presented.

Chen, J. H.; Wasserburg, G. J.; Papanastassiou, D. A.

1993-03-01

172

Ordinary Cokriging Revisited  

Microsoft Academic Search

This paper sets up the relations between simple cokriging and ordinary cokriging with one or several unbiasedness constraints. Differences between cokriging variants are related to differences between models adopted for the means of primary and secondary variables. Because it is not necessary for the secondary data weights to sum to zero, ordinary cokriging with a single unbiasedness constraint gives a

P. Goovaerts

1998-01-01

173

Magnetic anisotropy and porosity of chondrites  

NASA Astrophysics Data System (ADS)

The measured magnetic anisotropy and porosity of various chondrites are found to be inversely correlated when they are considered by class of chondrites (E, H and L + LL). For chondrites with similar porosities, the anisotropies for H and E chondrites are smaller than for L and LL chondrites, which have lower metal contents. The anisotropy and porosity are not dependent on the metamorphic grade of chondrites. K-Ar ages of strongly anisotropic and/or less porous chondrites are younger than those of less anisotropic and/or more porous chondrites. These observations suggest that impacts which reset the K-Ar ages produced the anisotropy and reduced the porosity of chondrites.

Sugiura, N.; Strangway, D. W.

1983-01-01

174

Portales Valley Meteorite: The Brecciated and Metal-veined Floor of a >20 KM Diameter Crater on an H-Chondrite Asteroid  

Microsoft Academic Search

We describe a new meteorite, Portales Valley, which is the first known ordinary chondrite with Widmanstatten structure. The structure occurs in large metal-rich veins that appear to have been produced by an impact event on an asteroid.

D. A. Kring; D. H. Hill; J. D. Gleason

1999-01-01

175

Portales Valley Meteorite: The Brecciated and Metal-veined Floor of a >20 KM Diameter Crater on an H-Chondrite Asteroid  

NASA Astrophysics Data System (ADS)

We describe a new meteorite, Portales Valley, which is the first known ordinary chondrite with Widmanstatten structure. The structure occurs in large metal-rich veins that appear to have been produced by an impact event on an asteroid.

Kring, D. A.; Hill, D. H.; Gleason, J. D.

1999-03-01

176

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

2012-03-28

177

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

NASA Astrophysics Data System (ADS)

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

1987-05-01

178

Oxidized H, L, and LL chondrites  

NASA Astrophysics Data System (ADS)

The association consisting predominantly of massive magnetite, carbides, kamacite, troilite and accessory taenite, and pentlandite was previously described in LL3.0 Semarkona, LL3.7 ALHA 77278, LL3.2/3.7 Ngawi, and in the Study Butte H regolith breccia. Taylor et al. suggested that this mineral assemblage formed in the solar nebula by condensation of Cr, Si, and P-rich metal; reaction of metal with S at 700 K resulting in the formation of troilite; carbonization of metal-troilite assemblages at less than 450 K; accretion of fine-grained silicate matrix material; oxidation of metal-troilite-carbide assemblages at about 400 K and formation of magnetite; and additional accretion of magnetite. Hutchison et al. concluded that the carbide-magnetite-metal assemblage in Semarkona formed in the solar nebula and then underwent accretion followed/accompanied by mild brecciation, a second period of magnetite crystallization, crystallization of carbide veins, and hydrous alteration and resorption of some magnetite. We studied 122 type 3 ordinary chondrites (OC) using optical microscopy, scanning electron microscopy, and electron-probe microanalysis and found that 19 of them contain abundant Fe, Ni carbides associated with metallic Fe-Ni, troilite, and, in many cases, massive magnetite. The presence of massive magnetite, Ni-rich metal, and Co-rich kamacite in 14% of H, 16% of L, and 17% of LL type 3 chondrites suggests that these meteorites experienced significant oxidation. The carbides have variable compositions within individual chondrites and were possibly formed by carburization of metallic Fe-Ni by Co-rich vapor. Carburization and oxidation of metallic Fe, Ni could take place at low temperatures in the solar nebula or on a parent body during its degassing.

Krot, A. N.

1994-07-01

179

Rhodium, gold and other highly siderophile element abundances in chondritic meteorites  

Microsoft Academic Search

The abundances of the highly siderophile elements (HSE) Re, Os, Ir, Ru, Pt, Rh, Pd and Au, and 187Os\\/188Os isotope ratios have been determined for a set of carbonaceous, ordinary, enstatite and Rumuruti chondrites, using an analytical technique that permits the precise and accurate measurement of all HSE from the same digestion aliquot. Concentrations of Re, Os, Ir, Ru, Pt

M. Fischer-Gödde; H. Becker; F. Wombacher

2010-01-01

180

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

Microsoft Academic Search

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

Pavel Spurný; Jürgen Oberst; Dieter Heinlein

2003-01-01

181

Chondrites, S Asteroids, and Space Weathering: Thumping Noises from the Coffin.  

National Technical Information Service (NTIS)

Most of the spectral characteristics of ordinary chondrites and S-asteroids in the visible and infrared can be reduced to three numerical values. These values represent the depth of the absorption band resulting from octahedrally coordinated Fe(sup 2+), t...

F. P. Fanale B. E. Clark

1993-01-01

182

The Early History of Chondritic Metal  

Microsoft Academic Search

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

J. S. Kim

1992-01-01

183

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

184

Sculptures of Ordinary People.  

ERIC Educational Resources Information Center

Discusses the presence of ordinary people in art. Features four sculptors and examples of their work: (1) "Janitor" by Duane Hanson; (2) "The Red Light" by George Segal; (3) "The Sodbuster" by Luis A. Jimenez; and (4) "The Driller" by Mahonri Young. (CMK)

Hubbard, Guy

2000-01-01

185

Sculptures of Ordinary People.  

ERIC Educational Resources Information Center

|Discusses the presence of ordinary people in art. Features four sculptors and examples of their work: (1) "Janitor" by Duane Hanson; (2) "The Red Light" by George Segal; (3) "The Sodbuster" by Luis A. Jimenez; and (4) "The Driller" by Mahonri Young. (CMK)|

Hubbard, Guy

2000-01-01

186

Chondrite thermal histories - Clues from electron microscopy of orthopyroxene  

NASA Astrophysics Data System (ADS)

Optically 'striated' orthopyroxenes in two ordinary chondrites, Allegan (H5) and Quenggouk (H4), are compared with shock-affected orthopyroxenes in Saint-Severin (LL6) and Ambapur Nagla (H5) by high-voltage transmission electron microscopy. The striated orthopyroxenes have very many, thin, evenly distributed lamellae of clinopyroxene. They are undeformed and also lack evidence of partial inversion from clinopyroxene to orthopyroxene. Striated orthopyroxene does not seem to be a reliable indicator of prograde metamorphism. Instead, it is interpreted as inverted protopyroxene, produced during the cooling of chondrules at slower rates than the rapid quenching of Type 3 chondrules. The conclusions are consistent with retrograde models for the evolution of H-group chondrites, in which the higher petrologic types are attributed to retarded cooling due to accretionary processes leading to the growth of the parent body.

Ashworth, J. R.

1980-01-01

187

Boron in chondritic meteorites  

Microsoft Academic Search

Alpha-track images (ATI), prepared by etching neutron-irradiated cellulose nitrate films attached to polished thin sections of meteorites, provide useful qualitative maps of boron and lithium distribution. However, extreme care must be taken to avoid contamination during preparation, particularly by boron in diamond polishing paste. Boron and lithium are virtually absent from chondrules, metal and sulfide grains in carbonaceous and ordinary

D. M. Shaw; M. D. Higgins; R. W. Hinton; M. G. Truscott; T. A. Middleton

1988-01-01

188

Magnetite in carbonaceous chondrites  

NASA Astrophysics Data System (ADS)

Magnetite (Fe3O4) occurs in many carbonaceous chondrites (CCs) and has long attracted the attention of meteorite researchers. However, its origin is unresolved; suggestions range from condensates from the solar nebular to products from aqueous alteration on the meteorite parent body. The report of possible evidence of former life in ancient Martian meteorite ALH84001 suggested an additional and highly intriguing origin for certain meteoritic magnetite, namely as magnetosomes from bacteria. However, a recent publication reports TEM evidence of spiral defects running through some of the the magnetite in ALHA84001, interpreted as evidence for a high temperature origin. These studies provide special interest to the occurrence of magnetite in meteorites. Using SEM, we studied magnetite from the Orgueil, Murchison, and Kaba and Mokoia meteorites, and obtained images at a nm-scale. We also did EMPA measurements to determine the compositions of the magnetite and surrounding minerals.

Hua, Xin; Buseck, Peter R.

1997-03-01

189

Chondrules and other components in C, O, and E chondrites Similarities in their properties and origins  

NASA Astrophysics Data System (ADS)

Three types of chondrules are described that are common to H3, LL3, CM2, CO3, and CV3 chondrites. Low- and high-FeO, porphyritic olivine chondrules contain olivine with Fa0.3-8 and Fa5-50 respectively, and can easily be distinguished petrographically. Poikilitic pyroxene chondrules have 1-20 vol pct olivine (Fa0.2-8) enclosed by low-Ca pyroxene (Fs0.5-7), and also occur in E chondrites. These three types formed in separate nebular regions which had dimensions and spacings such that a few percent of the chondrules that collided to form compound chondrules were of different types. Sorting of chondrule precursor material and mixing of chondrule types probably account for most variations in bulk and mineral chemistry among chondrite groups. Metallic Fe,Ni grains containing 0.1-1 percent Cr, Si, and P are present in low-FeO olivine chondrules from all type 2 and least metamorphosed type 3 chondrites. Metal compositions reflect reduction during chondrule formation in the nebula, not nebular condensation. Opaque matrices in type 3 ordinary and carbonaceous chondrites are somewhat similar in composition and mineralogy, and probably have related origins. It is concluded that chondrules in all known chondrite groups share similar nebular origins.

Scott, E. R. D.; Taylor, G. J.

1983-11-01

190

Deuterium-depleted hydrogen in acid-insoluble residues of the Efremovka chondrite  

NASA Astrophysics Data System (ADS)

The paper presents results of an analysis of the isotope composition of hydrogen in three acid-insoluble residues of the Efremovka carbonaceous chondrite. The magnitude of deuterium depletion in two of these residue samples is similar to that observed in ordinary and enstatitic chondrites, suggesting that a single reservoir of hydrogen with D/H = 0.0001 existed in the early solar system. This reservoir might have been formed as the result of mixing of interstellar hydrogen with hydrogen released during the vaporization of deuterium-enriched interstellar dust.

Fisenko, A. V.; Devirts, A. L.; Lagutina, E. P.; Semenova, L. F.; Lavrukhina, A. K.

191

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

192

REE and Hf distribution among mineral phases in the CV-CK clan: A way to explain present-day Hf isotopic variations in chondrites  

NASA Astrophysics Data System (ADS)

Chondrites are among the most primitive objects in the Solar System and constitute the main building blocks of telluric planets. Among the radiochronometers currently used for dating geological events, Sm-Nd and Lu-Hf are both composed of refractory, lithophile element. They are thought to behave similarly as the parent elements (Sm and Lu) are generally less incompatible than the daughter elements (Nd and Hf) during geological processes. As such, their respective average isotopic compositions for the solar system should be well defined by the average of chondrites, called Chondritic Uniform Reservoir (CHUR). However, while the Sm-Nd isotopic system shows an actual spread of less than 4% in the average chondritic record, the Lu-Hf system shows a larger variation range of 28% [Bouvier A., Vervoort J. D. and Patchett P. J. (2008) The Lu-Hf and Sm-Nd isotopic composition of CHUR: Constraints from unequilibrated chondrites and implications for the bulk composition of terrestrial planets. Earth Planet. Sci. Lett.273, 48-57]. To better understand the contrast between Sm-Nd and Lu-Hf systems, the REE and Hf distribution among mineral phases during metamorphism of Karoonda (CK) and Vigarano-type (CV) carbonaceous chondrites has been examined. Mineral modes were determined from elemental mapping on a set of five CK chondrites (from types 3-6) and one CV3 chondrite. Trace-element patterns are obtained for the first time in all the chondrite-forming minerals of a given class (CK chondrites) as well as one CV3 sample. This study reveals that REE are distributed among both phosphates and silicates. Only 30-50% of Sm and Nd are stored in phosphates (at least in chondrites types 3-5); as such, they are not mobilized during early stages of metamorphism. The remaining fraction of Sm and Nd is distributed among the same mineral phases; these elements are therefore not decoupled during metamorphism. Of the whole-rock total of Lu, the fraction held in phosphate decreases significantly as the degree of metamorphism increases (30% for types 3 and 4, less than 5% in type 6). In contrast to Lu, Hf is mainly hosted by silicates with little contribution from phosphates throughout the CK metamorphic sequence. A significant part of Sm and Nd are stored in phosphates in types 3-5, and these elements behave similarly during CK chondrite metamorphism. That explains the robustness of the Sm/Nd ratios in chondrites through metamorphism, and the slight discrepancies observed in the present-day isotopic Nd values in chondrites. On the contrary, Lu and Hf are borne by several different minerals and consequently they are redistributed during metamorphism-induced recrystallization. The Lu/Hf ratios are therefore significantly disturbed during chondrites metamorphism, leading to the high discrepancies observed in present-day Hf isotopic values in chondrites.

Martin, Céline; Debaille, Vinciane; Lanari, Pierre; Goderis, Steven; Vandendael, Isabelle; Vanhaecke, Frank; Vidal, Olivier; Claeys, Philippe

2013-11-01

193

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

NASA Astrophysics Data System (ADS)

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, J. E.; Keil, K.

194

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

NASA Astrophysics Data System (ADS)

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

Rubin, A. E.

1993-03-01

195

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

196

Chemical Fractionation in Chondrites by Aerodynamic Sorting of Chondritic Materials  

Microsoft Academic Search

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

E. R. D. Scott; H. Haack

1993-01-01

197

Accretion, dispersal, and reaccumulation of the Bishunpur (LL3.1) brecciated chondrite - Evidence from troilite-silicate-metal inclusions and chondrule rims  

NASA Astrophysics Data System (ADS)

A set of troilite-silicate-metal (TSM) inclusions and chondrule rims in the Bishunpur (LL3.1) chondrite provide information regarding impact brecciation of small bodies in the early solar system. The TSM inclusions and chondrule rims consist of numerous angular to subrounded silicate grains that are individually enclosed by fine networks of troilite. FeNi metal also occurs in the troilite matrix. The silicates include olivine (Fo 55-98), low-Ca pyroxene (En 78-98), and high-Ca pyroxene (En 48-68Wo 11-32). Al- and Si-rich glass coexists with the silicates. Relatively coarse silicate grains are apparently fragments of chondrules typical of petrologic type-3 chondrites. Troilite fills all available cracks and pores in the silicate grains. Some of the TSM inclusions and rims are themselves surrounded by fine-grained silicate-rich rims (FGR). The TSM inclusions and rims texturally resemble the troilite-rich regions in the Smyer H-chondrite breccia. They probably formed by shock-induced mobilization of troilite during an impact event on a primitive asteroidal body. Because silicates in the TSM inclusions and rims have highly unequilibrated compositions, their precursor was presumably type-3 chondritic material like Bishunpur itself. The TSM inclusions and the chondrules with the TSM rims were fragmented and dispersed after the impact-induced compaction, then reaccreted onto the Bishunpur parent body. FGR probably formed around the TSM inclusions and rims, as well as around some chondrules, during the reaccumulation process. Components of most type-2 and 3 chondrites probably experienced similar processing, i.e., dispersal of unconsolidated materials and subsequent reaccumulation.

Kojima, Tomoko; Lauretta, Dante S.; Buseck, Peter R.

2003-08-01

198

Magnetite-Pentlandite Chondrules in CK Chondrites  

NASA Astrophysics Data System (ADS)

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

Rubin, A. E.

1992-07-01

199

Ordinary Explanations and Career Theories.  

ERIC Educational Resources Information Center

Highlights the relatively unexplored relationship between ordinary language explanations of career behavior and formal theories of career development. Classifies ordinary explanations of career behavior along two dimensions--extent to which explanations are founded in person or situation and extent to which they account for predictability.…

Young, Richard A.

1988-01-01

200

Birth in an ordinary instant.  

PubMed

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

201

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

202

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

203

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

204

(TEM) observations of shock damage in the Tenham chondrite  

NASA Astrophysics Data System (ADS)

Among the ordinary chondrites, the Tenham meteorite (L6) is an instructive example of strong shock metamorphism. It is randomly pervaded by pseudotachylite-like shock veins that contain ringwoodite and majorite, the high-pressure phases of olivine and pyroxene, respectively. According to the revised shock nomenclature of ordinary chondrites, this shock signature is characteristic for shock stage S6 with pressures in excess of 50-55 GPa. In contrast to previous transmission electron microscope (TEM) studies, concentrating on the formation of the high-pressure phases in shock veins, our goal was to characterize the shock defects in olivine, pyroxene, and plagioclase occurring in the bulk of Tenham, i.e., outside shock veins. In olivine, shock has caused the formation of irregular and planar fractures as well as the activation of numerous dislocations. Planar fractures can be either filled with alteration products of Fe-Ni alloy. By far, diopside displays the greatest diversity of shock-induced defects; these are mechanical twins, numerous dislocations, and planar deformation features (PDFs). Diffuse scattering rings in electron diffraction patterns reveal that they consist of amorphous material. In analogy to quartz, it is reasonable to call them PDFs, too. The predominant shock effect in plagioclase is the formation of PDFs. Up to three crossing sets of such parallel, amorphous lamellae have been observed. It is concluded that almost all lattice defects observed in the silicate phases of Tenham are compatible with an impact origin. Some of the defects have been calibrated by shock experiments and, hence, give clues to the shock pressure.

Langenhorst, F.; Joreau, P.; Doukhan, J. C.

1994-07-01

205

The Origin of Chondrules and Chondrites  

NASA Astrophysics Data System (ADS)

1. Historical introduction; 2. Potential meteorite parent bodies; 3. Chondrites and their main properties; 4. Chondrules and their main properties; 5. Theories for the origin of chondrules; 6. Discussion of theories for the origin of chondrules; 7. Making the chondrites: chondrule sorting and metal-silicate fractionation; 8. So how far have we come and where do we go next?

Sears, Derek W. G.

2011-11-01

206

Simulation of possible regolith optical alteration effects on carbonaceous chondrite meteorites  

NASA Astrophysics Data System (ADS)

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

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

1993-03-01

207

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

208

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

NASA Astrophysics Data System (ADS)

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

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

2006-06-01

209

Organic constituents of carbonaceous chondrites.  

PubMed

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

Briggs, M H; Mamikunian, G

1964-01-01

210

Shock Effects in Experimentally Shocked Samples of the H6 Chondrite Kernouve  

NASA Astrophysics Data System (ADS)

Introduction: A new classification of shock metamorphism in chondrites has recently been published [1]. This classification scheme, which is based on a microscopic investigation of shock effects in olivine and plagioclase, was calibrated using shock recovery experiments with single crystals and natural rocks. In the past, only a few shock experiments have been made with ordinary chondrite material [2-4]. Here, we report the first results of shock experiments using the H6 chondrite Kernouve. Kernouve is one of the best examples for an unshocked ordinary chondrite and results of previous shock experiments are also available for this meteorite [4]. Experimental methods: Sample disks (diameter: 13 mm, thickness: 0.5 mm) of Kernouve (provided by B. Zanda, Paris) were used for shock-loading experiments at room temperature and pressures of 10, 15, 20, 35 and 60 GPa. The experimental set-up with a high-explosive-driven flyer plate was described earlier by [5]. Microscopic Shock Effects: Olivine of the unshocked chondrite shows sharp extinction and some irregular fractures. Olivine in the experimentally shocked samples displays the following pressure dependent features: Irregular fractures (10-60 GPa); undulatory extinction (10-20 GPa); planar fractures (10-60 GPa); weak mosaickism with a domain size of 25 micrometers diameter (10-20 GPa); strong mosaickism with a domain size of 5 micrometers (20-60 GPa); planar deformation features (20-60 GPa); and staining (60 GPa). The abundance of planar fractures in olivine decreases with increasing shock pressure from 94% in the 10-GPa sample to 14% in the 60-GPa sample. Well- developed planar deformation features (PDFs) were found in the 35-GPa sample. PDFs and planar fractures both display a similar orientation. In contrast to natural PDFs [1], PDFs in olivine grains from experimentally shocked Kernouve samples are shorter (up to 20 micrometers) and weakly bent. Plagioclase of the unshocked sample is characterized by sharp extinction. In the pressure range from 10 to 20 GPa, plagioclase displays undulatory extinction. In the 35-GPa sample most of the plagioclase is transformed to maskelynite (diaplectic glass). This transformation is complete in the 60-GPa sample. The first effects of localized shock-induced melting are observed in the 35- GPa sample, where a few melt pockets occur. The 60-GPa sample shows abundant melt pockets, shock veins, and troilite injections into fractures of the silicates. Troilite of the unshocked sample is monocrystalline. In the pressure range from 10 to 20 GPa, troilite shows undulatory extinction and twinning. The 35- and 60-GPa samples contain only recrystallized troilite. This troilite is polycrystalline and consists of equant grains with 120-degree angles between grain boundaries. Shock Classification and Conclusions: Using the classification scheme of [1], the experimentally shocked Kernouve samples can be classified into the following stages: Unshocked--S1; 10 GPa--S3; 15 and 20 GPa--S4; 35 GPa--S5; and 60 GPa--S6. The transition between shock stage 3 and 4 appears to be somewhat lower than proposed by [1] and occurs in the pressure range of 10 to 15 GPa, probably near to 15 GPa.The investigation of the experimentally shocked chondrite Kernouve shows the same pressure-dependent features as observed in naturally shocked ordinary chondrites [1]. For this reason shock recovery experiments provide an important basis for a better understanding of natural shock features in ordinary chondrites. References: [1] St"ffler D. et al. (1991) GCA, 55, 3845-3867. [2] Bogard D. D. et al. (1987) GCA, 51, 2035-2044. [3] Dai C.-D. et al. (1991) Chin. Sci. Bull., 36, 1984-1988. [4] Sears D. W. et al. (1984) GCA, 48, 343-360. [5] M ller W. F. and Hornemann U. (1969) EPSL, 7, 251-264.

Schmitt, R. T.; Deutsch, A.; Stoffler, D.

1993-07-01

211

Origin of rapidly solidified metal-troilite grains in chondrites and iron meteorites  

NASA Astrophysics Data System (ADS)

Quantitative evidence is adduced by cooling rate calculations for the impact melting, on the surface of a parent body, of troilite and metallic Fe, Ni inclusions found on 12 ordinary chondrites rather than their formation at depth from an internally derived melt. In the case of the Shaw and Rose City breccias of unmelted and melted material, their melted metal need not have cooled through 1000 C within a few meters of the surface. Shock-melted, fine-grained, irregular intergrowths of metal and troilite form in situ in many irons and some chondrites by rapid solidification at cooling rates greater than 100,000 C/sec, so that their kamacite and taenite compositions may result from annealing of metallic glass or very fine quench products at about 250 C.

Scott, E. R. D.

1982-05-01

212

Spectral reflectance properties of carbonaceous chondrites: 2. CM chondrites  

NASA Astrophysics Data System (ADS)

We have examined the spectral reflectance properties and available modal mineralogies of 39 CM carbonaceous chondrites to determine their range of spectral variability and to diagnose their spectral features. We have also reviewed the published literature on CM mineralogy and subclassification, surveyed the published spectral literature and added new measurements of CM chondrites and relevant end members and mineral mixtures, and measured 11 parameters and searched pair-wise for correlations between all quantities. CM spectra are characterized by overall slopes that can range from modestly blue-sloped to red-sloped, with brighter spectra being generally more red-sloped. Spectral slopes, as measured by the 2.4:0.56 ?m and 2.4 ?m:visible region peak reflectance ratios, range from 0.90 to 2.32, and 0.81 to 2.24, respectively, with values <1 indicating blue-sloped spectra. Matrix-enriched CM spectra can be even more blue-sloped than bulk samples, with ratios as low as 0.85. There is no apparent correlation between spectral slope and grain size for CM chondrite spectra - both fine-grained powders and chips can exhibit blue-sloped spectra. Maximum reflectance across the 0.3-2.5 ?m interval ranges from 2.9% to 20.0%, and from 2.8% to 14.0% at 0.56 ?m. Matrix-enriched CM spectra can be darker than bulk samples, with maximum reflectance as low as 2.1%. CM spectra exhibit nearly ubiquitous absorption bands near 0.7, 0.9, and 1.1 ?m, with depths up to 12%, and, less commonly, absorption bands in other wavelength regions (e.g., 0.4-0.5, 0.65, 2.2 ?m). The depths of the 0.7, 0.9, and 1.1 ?m absorption features vary largely in tandem, suggesting a single cause, specifically serpentine-group phyllosilicates. The generally high Fe content, high phyllosilicate abundance relative to mafic silicates, and dual Fe valence state in CM phyllosilicates, all suggest that the phyllosilicates will exhibit strong absorption bands in the 0.7 ?m region (due to Fe3+-Fe2+ charge transfers), and the 0.9-1.2 ?m region (due to Fe2+ crystal field transitions), and generally dominate over mafic silicates. CM petrologic subtypes exhibit a positive correlation between degree of aqueous alteration and depth of the 0.7 ?m absorption band. This is consistent with the decrease in fine-grained opaques that accompanies aqueous alteration. There is no consistent relationship between degree of aqueous alteration and evidence for a 0.65 ?m region saponite-group phyllosilicate absorption band. Spectra of different subsamples of a single CM can show large variations in absolute reflectance and overall slope. This is probably due to petrologic variations that likely exist within a single CM chondrite, as duplicate spectra for a single subsample show much less spectral variability. When the full suite of available CM spectra is considered, few clear spectral-compositional trends emerge. This indicates that multiple compositional and physical factors affect absolute reflectance, absorption band depths, and absorption band wavelength positions. Asteroids with reflectance spectra that exhibit absorption features consistent with CM spectra (i.e., absorption bands near 0.7 and 0.9 ?m) include members from multiple taxonomic groups. This suggests that on CM parent bodies, aqueous alteration resulted in the consistent production of serpentine-group phyllosilicates, however resulting absolute reflectances and spectral shapes seen in CM reflectance spectra are highly variable, accounting for the presence of phyllosilicate features in reflectance spectra of asteroids across diverse taxonomic groups.

Cloutis, E. A.; Hudon, P.; Hiroi, T.; Gaffey, M. J.; Mann, P.

2011-11-01

213

Micro-Raman Mapping of Mineral Phases in the Strongly Shocked Taiban Ordinary Chondrite  

NASA Astrophysics Data System (ADS)

Micro-Raman mapping of a thin-section of the highly shocked Taiban meteorite revealed new minor phases around the ringwoodite grains. These phases include wadsleyite and olivine surrounded by pyroxene and majorite.

Acosta, T. E.; Scott, E. R. D.; Sharma, S. K.

2012-03-01

214

An interdisciplinary study of weathering effects in ordinary chondrites from the ACFER region, Algeria  

Microsoft Academic Search

Weathering effects on meteorite finds from the Acfer region were studied by various analytical techniques and in dependence on the depth of sampling. In thin sections of weathered meteorites, weathering effects usually decrease from the outside to the interior of the meteorite. The results of evolved gas analysis indicate that variation in weathering between surface and core is not significant

Th. Stelzner; K. Heide; A. Bischoff; D. Weber; P. Scherer; L. Schultz; M. Happel; W. Schrön; U. Neupert; R. Michel; R. N. Clayton; T. K. Mayeda; G. Bonani; I. Haidas; S. Ivy-Ochs; M. Suter

1999-01-01

215

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

Microsoft Academic Search

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,

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

2006-01-01

216

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

Microsoft Academic Search

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.

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

2006-01-01

217

Carbon, nitrogen and hydrogen in Saharan chondrites: The importance of weathering  

NASA Astrophysics Data System (ADS)

The Sahara Desert is a region of high diurnal temperature variation and sporadic rainfall that has recently yielded over 450 meteorites. Eighteen of these Saharan samples are carbonaceous chondrites, of which we have analyzed 17 for C content and isotopic composition. Ten of the 18 are paired CR chondrites, of which four have also had N and H contents and compositions determined. A primitive ordinary chondrite (L/LL3.2) found in the region has also been analyzed for C, N and H contents and isotopic composition. Saharan samples contain between 21% and 45% of the light elements of their non-Saharan counterparts. Paired Saharan samples show a greater heterogeneity in both C content and isotopic composition than multiple analyses of non-Saharan samples. The cause of the observed isotopic and abundance effects is due to the hot desert weathering processes experienced by these samples. Peak temperatures of meteorites on the desert floor may be in excess of 100 C, leading to low-temperature hydrous pyrolysis and oxidation reactions, liberating volatile organics and CO2. This may also cause the remaining material to become partially solubilised and ultimately lost during rainfall. The low delta D of the CR and ordinary chondrites can be attributed to the destruction and loss of organic material through dehydrogenation and exchange reactions on the desert surface. The increased C-13 abundance suggests that the less tightly bound C from the macromolecular organic material is isotopically lighter than the remaining C. Carbon contents and isotopic compositions are also affected by the addition of terrestrial calcitic evaporite deposites, up to 10,000 ppm carbonate has been measured, with a delta (13)C of between 0 and -10 per mil.

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

1995-01-01

218

Mineralogy and possible origin of an unusual Cr-rich inclusion in the LOS Martinez (L6) chondrite  

NASA Astrophysics Data System (ADS)

During a petrological study of the previously unclassified ordinary chondrite Los Martinez a highly unusual Cr-rich inclusion is found which is unique in both extraterrestrial and terrestrial mineralogy. Detailed SEM and TEM studies show that the inclusion consists of a highly zoned single crystal of plagioclase intergrown with chromium-rich spinel which indicates that it is the product of exsolution. The Cr-rich precursors of the inclusion probably have close affinities to the chronite-plagioclase chrondrules observed by Ramdohr (1967) in several ordinary chondrites. Based on the zoning in the inclusion it is suggested that it is the product of fractional crystallization from a melt, which may have formed as a liquid condensate, or by melting of solid condensates, in the solar nebula. Subsequent cooling of this melt condensate resulted in crystallization of the unidentified phase. After crystallization, the inclusion was probably incorporated into a parent body where it underwent metamorphism and was probably shocked to some degree. During this period of parent body metamorphism, exsolution and decomposition of the unknown precursor occurred to produce the observed intergrowth of plagioclase and chromite. Los Martinez is classified as an L6 ordinary chondrite breccia.

Brearley, Adrian J.; Casanova, Ignacio; Miller, Mark L.; Keil, Klaus

1991-12-01

219

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

220

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

221

Variations of Li and Mg isotope ratios in bulk chondrites and mantle xenoliths  

NASA Astrophysics Data System (ADS)

We present whole rock Li and Mg isotope analyses of 33 ultramafic xenoliths from the terrestrial mantle, which we compare with analyses of 30 (mostly chondritic) meteorites. The accuracy of our new Mg isotope ratio measurement protocol is substantiated by a combination of standard addition experiments, the absence of mass independent effects in terrestrial samples and our obtaining identical values for rock standards using two different separation chemistries and three different mass-spectrometric introduction systems. Carbonaceous, ordinary and enstatite chondrites have irresolvable mean stable Mg isotopic compositions (? 25Mg = -0.14 ± 0.06; ? 26Mg = -0.27 ± 0.12‰, 2SD), but our enstatite chondrite samples have lighter ? 7Li (by up to ˜3‰) than our mean carbonaceous and ordinary chondrites (3.0 ± 1.5‰, 2SD), possibly as a result of spallation in the early solar system. Measurements of equilibrated, fertile peridotites give mean values of ? 7Li = 3.5 ± 0.5‰, ? 25Mg = -0.10 ± 0.03‰ and ? 26Mg = -0.21 ± 0.07‰. We believe these values provide a useful estimate of the primitive mantle and they are within error of our average of bulk carbonaceous and ordinary chondrites. A fuller range of fresh, terrestrial, ultramafic samples, covering a variety of geological histories, show a broad positive correlation between bulk ? 7Li and ? 26Mg, which vary from -3.7‰ to +14.5‰, and -0.36‰ to + 0.06‰, respectively. Values of ? 7Li and ? 26Mg lower than our estimate of primitive mantle are strongly linked to kinetic isotope fractionation, occurring during transport of the mantle xenoliths. We suggest Mg and Li diffusion into the xenoliths is coupled to H loss from nominally anhydrous minerals following degassing. Diffusion models suggest that the co-variation of Mg and Li isotopes requires comparable diffusivities of Li and Mg in olivine. The isotopically lightest samples require ˜5-10 years of diffusive ingress, which we interpret as a time since volatile loss in the host magma. Xenoliths erupted in pyroclastic flows appear to have retained their mantle isotope ratios, likely as a result of little prior degassing in these explosive events. High ? 7Li, coupled with high [Li], in rapidly cooled arc peridotites may indicate that these samples represent fragments of mantle wedge that has been metasomatised by heavy, slab-derived fluids. If such material is typically stirred back into the convecting mantle, it may account for the heavy ? 7Li seen in some oceanic basalts.

Pogge von Strandmann, Philip A. E.; Elliott, Tim; Marschall, Horst R.; Coath, Chris; Lai, Yi-Jen; Jeffcoate, Alistair B.; Ionov, Dmitri A.

2011-09-01

222

The Bawku LL5 Chondrite  

NASA Astrophysics Data System (ADS)

Introduction: A 59-g piece of stony meteorite with black fusion crust and medium grey interior was recovered in 1992 from Northern Ghana by Dr. S. Abudulai of the Centre for African Studies, University of Cambridge. This meteorite was reported to be part of a fall that occurred in the vicinity of Bawku (11 degrees 05'N, 0 degrees 11'W) at 1630 hours (local time) on December 29, 1989; the meteorite was found between the villages of Naarango-Anisi and Kpukparigu, east of Bawku. A further mass of 1.5 kg was recovered by Dr. Abudulai during a visit in January 1993. The name "Bawku" is proposed for this meteorite. Description: The Bawku chondrite is a monomict breccia. Some well-preserved chondrules with a variety of textures are present. Olivine exhibits undulose extinction and extensive irregular cracking. Other shock features include cracks infilled with metal/troilite. Electron microprobe analyses of olivines gave a mean Fe/Fe + Mg ratio of 26.8%, with a standard deviation of 1.0% (relative) and an average CaO content of 0.03% (by weight). The mean Fe/Fe + Mg content of orthopyroxene was found to be 22.6% (standard deviation 1.2% relative). Small (10-micrometer) grains of plagioclase (75-85% Ab) were found. Automated point counting (700 points) gave volume fractions of 4.6% troilite and 1.3% metal. Compositions of 200 randomly selected points on metal grains fell into three groups, corresponding to kamacite (4-7% Ni, 1.4% Co), taenite (34-38% Ni, 0.35% Co), and tetrataenite (48-56% Ni, 0.2% Co). The inferred volume fractions of these phases were 52%, 45%, and 3% respectively. The average Ni content of the metal was 21%, with 0.9% Co. On etching, Neumann lamellae became visible in kamacite, while the taenite took on a cloudy appearance. Tetrataenite was observed as narrow rims adjacent to cloudy taenite, but also occurred sometimes in larger areas. Minor phases noted included chromite, ilmenite, apatite, and whitlockite. Classification: The Fe/Fe + Mg ratios of olivine and pyroxene place this chondrite at the lower limit of the range for the LL group, adjacent to the hiatus between LL and L [1]. The low metal content is consistent with this classification. The relatively high proportion of kamacite compared to other LL chondrites is in accordance with Prior's law, which applies within this group, unlike others [2]. The homogeneity of olivine and orthopyroxene, the existence of moderately abundant preserved chondrules, and the presence of feldspar grains comparable in size to those observed in LL5 chondrites [3] point to Bawku being a member of this class. The undulose extinction and irregular fracturing of olivine are indicative of shock class S2 [4]. References: [1] Fredriksson K. et al. (1978) In Origin and Distribution of the Elements (L. Ahrens, ed.), 457-466, Pergamon, Oxford. [2] Sears D. W. and Axon H. J. (1976) Meteoritics, 11, 97-100. [3] Heyse J. V. (1978) EPSL, 40, 365-381. [4] Stoffler D. et al. (1991) GCA, 55, 3845-3867.

Reed, S. J. B.; Chinner, G. A.

1993-07-01

223

Trace Element Microdistribution in Carbonaceous Chondrite Chondrules  

NASA Astrophysics Data System (ADS)

We present LA-ICP-MS analyses of silicate phases in chondrules of CR and CV chondrites. Olivine/mesostasis REE partitioning approach equilibrium for the coarser-grained chondrules. Pyroxene data offer further evidence of gas-melt interaction.

Jacquet, E.; Gounelle, M.; Alard, O.

2012-03-01

224

Carbonaceous chondritic asteroids - The ideal extraterrestrial resource  

NASA Astrophysics Data System (ADS)

It is proposed that carbonaceous chondritic asteroids be used as extraterrestrial resources because they contain biogenic resources, water, hydrocarbons and water soluble metal salts. The chemical composition determined for carbonaceous chondritic asteroids is presented in tables and the processes for extracting iron ore and silicon, aluminum, magnesium, calcium, sulfur, and phosphorus compounds from them are examined. It is suggested that these asteroids could provide valuable resources for lunar and LEO colonies.

Kuck, David L.

225

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

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

226

Oxygen Isotopic Relationships Between the LEW85332 Carbonaceous Chondrite and CR Chondrites.  

National Technical Information Service (NTIS)

LEW85332, originally described as a unique C3 chondrite, was shown to be a C2 chondrite with important linkages to the CR clan. An important petrologic aspect of LEW85332 is that it contains anhydrous chondrules and hydrated matrix, and new oxygen isotopi...

M. Prinz M. K. Weisberg R. N. Clayton T. K. Mayeda

1993-01-01

227

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

NASA Astrophysics Data System (ADS)

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, B. D.; Sears, D. W. G.

1987-11-01

228

Shock Metamorphism in L Chondrites Above Shock Stage S6  

NASA Astrophysics Data System (ADS)

We investigated several L6 chondrites shocked to between stage S6 and whole rock melting. The study presents the effects of high post-shock temperature and the annealing of high-pressure evidence in highly shocked chondrites.

Hu, J.; Sharp, T. G.; De Carli, P. S.

2013-09-01

229

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

230

Noble gases, Kr-81-Kr ages, and Be-10 of chondrites from China  

NASA Astrophysics Data System (ADS)

A comprehensive study of the cosmic-ray exposure history of ordinary chondrites from China was carried out using measurements of the noble gas isotopic abundances and Be-10 concentrations. The following average cosmic-ray exposure ages, based on cosmogenic Ne-21 and on Kr-81-Kr dating were obtained: Zhaodong (L4) - 15.7 + or - 3.0 Myr, Nan Yang Pao (L6) - 48 + or - 10.0 Myr, Guangrao (L6) - 16.8 + or - 3.5 Myr, and Lunan (H6) - 26.7 + or - 5.0 Myr. The H5 chondrite Zaoyang was exposed for only 0.90 + or - 0.12 Myr to Galactic cosmic rays, as calculated from the Be-10 activity and from the low amounts of cosmic-ray-produced noble gases. The Zaodong chondrite contains large amounts of Kr-80 and Kr-82 produced by neutron capture of bromine. From the high slowing down density for neutrons, a preatmospheric mass of more than 1800 kg is derived for this meteorite.

Eugster, O.; Shen, Ch.; Beer, J.; Suter, M.; Wolfli, W.; Yi, W.; Wang, D.

1987-06-01

231

Summary of several recent chondrite finds from the Texas Panhandle  

NASA Astrophysics Data System (ADS)

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

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

1983-03-01

232

EL3 Chondrite (not Aubrite) Northwest Africa 2828: An Unusual Paleo-meteorite Occurring as Cobbles in a Terrestrial Conglomerate  

NASA Astrophysics Data System (ADS)

Although we recently classified NWA 2828 as an aubrite [1], our examination of new material (now comprising over 120 stones totaling >27 kg) requires revision of that classification. New information on the find site in Algeria indicates that these stones were excavated from a subsurface deposit, and we have found terrestrial rhyolite pebbles and sandy matrix attached to several NWA 2828 stones (see images at http://www.ess.washington.edu/meteoritics). Thus this is a rare example of a paleo-meteorite or 'fossil' meteorite. Some stones contain sparse (<5 vol.%) but very distinct round, radial pyroxene chondrules (up to 3 mm across), as well as rounded, fine-grained aggregates (up to 6 mm across) rich in either enstatite or sodic plagioclase. Remnant Na-Al-Si-rich glass is present within cavities in chondrules, both between enstatite blades and in annular zones. The matrix contains pervasive 0.2-0.5 mm cavities with coatings of calcite and minor halite and gypsum. Iron sulfate (after troilite), jarosite, an inhomogeneous (possibly amorphous) phase rich in Fe, Cr, Si, Ca, Ti, P, S and Cl, minor native sulfur and silica also are present, and brown Fe-rich rinds on one stone contain up to 6.5 wt.% Ni. These secondary minerals signify terrestrial alteration of primary metal, sulfides, phosphides, nitrides and glass in an ancient fluvial and/or acidic lacustrine environment. The dominant primary phase in NWA 2828 is enstatite (En98.4Wo1.4), which forms stubby prismatic grains (lacking polysynthetic twinning indicative of inverted clinoenstatite [cf., 1]). Our original classification was based on a very small specimen of an apparently igneous-textured rock, but the discovery of chondrules and the absence of twinned enstatite now suggests that it is instead an unequilibrated enstatite chondrite. Additional primary phases noted previously [1] are sodic plagioclase (An14- 15Or3-4), troilite, graphite, daubreelite, alabandite, oldhamite, schreibersite, glass and very rare kamacite. The well-formed, round chondrules containing glass coupled with the unrecrystallized matrix lead us to re-classify NWA 2828 as an EL3 chondrite. We also must revise our opinion [1] about the relationship between NWA 2828 and material classified as EL chondrites NWA 2965 and NWA 2736, which evidently come from the more extensively weathered top of the same ancient conglomerate layer as NWA 2828. [1] Irving A.J. et al. (2006) 69th Met. Soc. Mtg., #5264 (MAPS 41 Suppl., A84)

Kuehner, S. M.; Irving, A. J.; Bunch, T. E.; Wittke, J. H.

2006-12-01

233

Morphological Study of Insoluble Organic Matter Residues from Primitive Chondrites  

NASA Astrophysics Data System (ADS)

By studying the morphologies of IOM residues from a range of CM and CR chondrites, we have identified a coarsening in the texture of IOM from the more altered chondrites. Thus, parent body alteration altered/formed IOM in the CM and CR chondrites.

Changela, H.; Stroud, R. M.; Peeters, Z.; Nittler, L. R.; Alexander, C. M. O'd.; de Gregorio, B. T.; Cody, G. D.

2012-03-01

234

Fluid Flow and Chemical Alteration in Carbonaceous Chondrite Parent Bodies  

Microsoft Academic Search

Carbonaceous chondrites are a suite of primitive meteorites with bulk chemical compositions that closely resemble solar values for non-volatile elements. On this basis, carbonaceous chondrites are considered among the most primitive materials available for study and, therefore, a critical source of information on the formation and evolution of our planetary system. However, despite carbonaceous chondrites' primitive characteristics, mineralogical and isotopic

J. Palguta; G. Schubert; B. J. Travis

2009-01-01

235

Hydrothermal circulation and geochemical processing on carbonaceous chondrite parent bodies  

Microsoft Academic Search

Carbonaceous chondrites are a suite of primitive meteorites with bulk chemical compositions that closely resemble solar values for non-volatile elements. On this basis, carbonaceous chondrites are considered among the most primitive materials available for study and, therefore, a critical source of information on the formation and evolution of our planetary system. However, despite carbonaceous chondrites' primitive traits, mineralogical and isotopic

Jennifer Lynn Palguta

2009-01-01

236

Spatial prediction and ordinary kriging  

SciTech Connect

Suppose data /Z(s/sub i/):i = 1,...,n/ are observed at spatial locations /s/sub i/:i = 1,...,n/. From these data, an unknown Z(s/sub 0/) is to be predicted at a known location s/sub 0/, or, if Z(s/sub 0/) has a component of measurement error, then a smooth version S(s/sub 0/) should be predicted. This article considers the assumptions needed to carry out the spatial prediction using ordinary kriging, and looks at how nugget effect, range, and sill of the variogram affect the predictor. It is concluded that certain commonly held interpretations of these variogram parameters should be modified.

Cressie, N.

1988-05-01

237

Ordinary Percolation with Discontinuous Transitions  

NASA Astrophysics Data System (ADS)

We study percolation on hierarchical networks using generating functions and renormalization group techniques. Our exact results show the presence of novel features in these networks including the existence of non-trivial critical points, three distinct regimes in the phase diagram and, most importantly, a discontinuity in the formation of the extensive cluster at a critical point pc<1 . At pc , the order parameter P? describing the probability of any node to be a part of the largest cluster, jumps instantly to a finite value. We present simple examples of small-world networks with various hierarchies of long range bonds, indicating that the presence of discontinuous transitions is generic.[4pt] [1] S. Boettcher, V. Singh, and R.M. Ziff. Ordinary Percolation with Discontinuous Transitions. Arxiv preprint arXiv:1110.4288, (2):25, 2011.

Singh, Vijay; Boettcher, Stefan

2012-02-01

238

Portales Valley: A meteoritic sample of the brecciated and metal-veined floor of an impact crater on an H-chondrite asteroid  

NASA Astrophysics Data System (ADS)

A shower of meteorite fragments fell at about 0730 hours local time on 13 June 1998 near the town of Portales, New Mexico. Thus far, 51 pieces of the Portales Valley (H6) meteorite have been recovered. This meteorite has an unusually large number of metallic veins. Some of these veins are also unusually thick, having widths on the order of centimeters. These wide veins have fine Widmanstätten structure, which is the first time it has been seen in an ordinary chondrite. This structure indicates the metallic veins and the host chondrite cooled slowly. These veins appear to have been produced by shock-metamorphic processes, which we infer produced a >20 km diameter impact crater on an H-chondrite planetesimal.

Kring, David A.; Hill, Dolores H.; Gleason, James D.; Britt, Daniel T.; Consolmagno, Guy J.; Farmer, Mike; Wilson, Skip; Haag, Robert

1999-07-01

239

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

240

An H chondrite stream: Identification and confirmation  

SciTech Connect

Fall data indicate that a significant, elongate cluster of co-orbital H chondrite falls in May between 1855 and 1895 (H Cluster 1) records encounters with two or three closely spaced and probably related meteoroid stream components, each of which was met near its perihelion. Although meteorites included in the Cluster vary widely in petrographic type (3-6), shock facies (a-d), and {sup 21}Ne exposure age (<5 to 50 Ma), they have a distinct labile trace element signature that confirms a common thermal history and, thus, a common source region within an H chondrite parent body. Hence, meteorites selected by one criterion (fall parameters) as distinguishable from all other H chondrites, are distinguished from them by another completely different criterion (contents of labile trace elements). 36 refs., 12 figs., 7 tabs.

Dodd, R.T. [State Univ. of New York, Stony Brook, NY (United States); Wolf, S.F.; Lipschutz, M.E. [Purdue Univ., West Lafayette, IN (United States)

1993-08-25

241

K-rich Lithic Clasts in the ACFER 111 H-Chondrite  

NASA Astrophysics Data System (ADS)

Acfer 111 is a regolith breccia with exceptionally unfractionated solar noble gases (Pedroni and Weber, 1991). It consists of an unequilibrated host containing lithic clasts of higher petrologic type. Two mm-sized clasts were found that consist of euhedral to skeletal olivine crystals (Fa 18.5) in a K-rich mesostasis, similar to the clasts found before only in LL-chondrites (Wlotzka et al., 1983). The bulk composition of these clasts is close to the mean bulk H-chondrite silicate composition, but with higher K (and Rb, Cs) and lower Na (Table 1). The REE, which are usually enriched together with K in igneous differentiations, are also close to normal, see Fig. 1 (except for a negative Eu anomaly that was also found in the K-rich clasts in LL chondrites). This shows that these clasts were not formed by igneous differentiation. The Na-K relations in the host and equilibrated clasts also show deviations from the average chondritic Na/K ratio of 8.0. In the feldspar and feldspar glasses of the host this ratio varies between 1.0 and 80, mean 13.5. An H5 clast has a low bulk K content of 350 ppm, Na/K is 18; in the feldspars Na/K is 21 +-9. It seems significant that the average Na/K is higher than the chondritic ratio, indicating K loss. Acfer 111 also contains several fragments (about 100 micrometers) of K-rich crystalline feldspar (18 to 33% Or) in the host. The chondritic bulk silicate composition of the K-rich clasts suggests an origin as impact melt that lost metal and sulfide. It remains to explain the differentiation of the alkalies. One possible way is vapour/solid fractionation, where K is preferentially incorporated into cold solid feldspar or feldspar glass, while Na stays in the vapour (Wlotzka et al., 1983). This relation between K and Na in vapour and solid has been established experimentally (Orville, 1963). A location for this process can be found on the cold surface or cold pocklets in a primordial regolith of a parent body, alkali-containing vapours coming from hot spots in the interior. Material like the H5 clast with low K may have lost its K in this process. The K/Ar-ages of the two K-rich clasts deduced from ^40Ar concentrations of (6.4 - 6.8)x10^-4 cc stp/g are 4.5+-0.1 GA and show that the source rocks were formed very early in the history of the parent body. Cosmogenic ^21Ne in the K-rich clasts are comparable (when corrected for the target element abundances) to the average observed for the normal clasts (see Pedroni, this volume). References: Jarosewich E. (1990) Meteoritics 25, 323-337. Kallemeyn G.W., Rubin A.E., Wang D., Wasson J.T. (1989) Geochim. Comochim. Acta 53, 2747-2767. Orville, P.M. (1963) Amer. J. Sci. 261, 201-237. Pedroni, A. and Weber H. (1991) Meteoritics 26, 383. Wlotzka, F., Palme H., Spettel B., Wanke H., Fredriksson K., Noonan A.F. (1983) Geochim. Cosmochim. Acta 47, 743-757. Table 1 SiO2 TiO2 Al2O3 Cr2O3 FeO MnO MgO CaO Na2O K2O Acfer 111 K-rich clast S 49.7 0.16 2.56 0.68 13.40 0.38 29.3 2.02 0.77 1.04 Av. H-chondrite silicate 48.2 0.16 2.82 0.68 13.56 0.41 30.6 2.29 1.13 0.12 Figure 1, which in the hard copy appears here, shows element abundance for K-rich clast S versus mean H-chondrite silicate composition (Jarosewich, 1990; Kallemeyn et al., 1989).

Wlotzka, F.; Spettel, B.; Pedroni, A.

1992-07-01

242

Mineralogy of chondritic interplanetary dust particles  

NASA Astrophysics Data System (ADS)

This paper presents a synopsis of current investigations on the mineralogy of chondritic micrometeorites obtained from the lower stratosphere using flat-plate collection surfaces attached to high-flying aircraft. A compilation of detailed mineralogical analyses for 30 documented chondritic interplanetary dust particles indicates a wide variety of minerals present in assemblages which, as yet, are poorly defined. Two possible assemblages are: (1) carbonaceous phases and layer silicates and (2) carbonaceous and chain silicates or nesosilicates. Particles with both types of silicate assemblages are also observed.

MacKinnon, I. D. R.; Rietmeijer, F. J. M.

1987-08-01

243

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

244

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

Microsoft Academic Search

Oxygen isotopes were measured in four chondritic hydrated interplanetary dust particles (IDPs) and five chondritic anhydrous IDPs including two GEMS-rich particles (Glass embedded with metal and sulfides) by a combination of high precision and high lateral resolution ion microprobe techniques.All IDPs have isotopic compositions tightly clustered around that of solar system planetary materials. Hydrated IDPs have mass-fractionated oxygen isotopic compositions

J. Aléon; C. Engrand; L. A. Leshin; K. D. McKeegan

2009-01-01

245

Oxygen isotope studies of carbonaceous chondrites  

Microsoft Academic Search

The carbonaceous chondrites display the widest range of oxygen isotopic composition of any meteorite group, as a consequence of the interaction of primordial isotopic reservoirs in the solar nebula. These isotopic variations can be used to identify the reservoirs and to determine conditions and loci of their interactions. We present a comprehensive set of whole-rock analyses of CV, CO, CK,

Robert N. Clayton; Toshiko K. Mayeda

1999-01-01

246

Hydrothermal convection in carbonaceous chondrite parent bodies  

Microsoft Academic Search

Numerical simulations of the thermal evolution of carbonaceous chondrite parent bodies indicate a period of several million years during which convective motion of water could occur. The present study considers variations of permeability, radiogenic heating, and body radius. The model accounts for the radial variation of gravity within the body, melting of ice, freezing of liquid water, and variable water

Bryan J. Travis; Gerald Schubert

2005-01-01

247

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

248

High-pressure melting of carbonaceous chondrite  

NASA Astrophysics Data System (ADS)

Phase equilibria experiments investigating the melting and differentiation of the primordial Earth require a realistic 'initial' chemical composition. Carbonaceous chondrites are good analogues for the initial bulk chemical composition of an accreting early Earth because they contain approximately solar abundances of the non-volatile elements and are the most primitive objects yet sampled in the solar system.

Agee, Carl B.

249

Progressive aqueous alteration of CM carbonaceous chondrites  

NASA Astrophysics Data System (ADS)

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

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

2007-05-01

250

Chondritic Mg isotope composition of the Earth  

NASA Astrophysics Data System (ADS)

The processes of planetary accretion and differentiation have potentially been recorded as variations in the stable isotope ratios of the major elements between planetary objects. However, the magnitude of observed isotopic variations for several elements (Mg, Fe, Si) is at the limit of what current analytical precision and accuracy are able to resolve. Here, we present a comprehensive data set of Mg isotope ratios measured in ocean island and mid-ocean ridge basalts, peridotites and chondrites. The precision and accuracy were verified by isotopic standard addition for two samples, one carbonaceous chondrite (Murchison) and one continental flood basalt (BCR-1). In contrast with some previous studies, our data from terrestrial and chondritic materials have invariant Mg isotope ratios within the uncertainty of the method (0.1‰ for the 26Mg/ 24Mg ratio, 2SD). Although isotopic variations of less than about 0.1‰ could still be present, the data demonstrate that, at this level of uncertainty, the bulk silicate Earth and chondritic Mg reservoir have a homogeneous ? 26Mg = -0.23‰ ( 26Mg/ 24Mg ratio of the sample relative to the DSM3 standard set to zero by definition). This implies that neither planetary accretion processes nor partial mantle melting and subsequent shallow-level differentiation have fractionated Mg isotope ratios. These observations imply in particular that the formation of the Earth cannot stem from preferential sorting of chondrite constituents that would have been fractionated in their Mg isotope composition. It also implies that unlike oxygen isotopes, there was no zonation in Mg isotopes in the inner solar system.

Bourdon, Bernard; Tipper, Edward T.; Fitoussi, Caroline; Stracke, Andreas

2010-09-01

251

Evidence for a Carbonaceous Chondrite Parent Body With Near-TFL Oxygen Isotopes From Unique Metachondrite Northwest Africa 2788  

NASA Astrophysics Data System (ADS)

Metachondrites: Metachondrites are newly recognized groups of stony meteorites that lack chondrules, but which have elemental and oxygen isotopic compositions and textures suggesting that they have been transformed by metamorphism or partial melting from precursor ordinary and carbonaceous chondrites on relatively large parent bodies [1]. The best known examples have affinities to CR (e.g., LEW 88763), CV (e.g., NWA 3133), H, L and LL chondrites; conversely there is evidence that winonaites and acapulcoites also are metachondrites derived from chondritic precursors (represented by rare chondrites such as NWA 1463 and Monument Draw). With increased sampling of new meteorites from both hot and cold desert regions, there is an emerging realization that the early solar system was populated with many relatively large differentiated planetary bodies complete with metallic cores, silicate mantles and chondritic regoliths of various types. The affinity of a particular metachondrite to a specific chondrite class relies mainly on oxygen isotopic analysis combined with distinctive elemental ratios in bulk rocks and constituent minerals (notably Fe/Mn and Ca/Na ratios, which are quite different for ordinary vs. various carbonaceous chondrite classes). Northwest Africa 2788: This specimen exhibits a metamorphic texture with triple grain junctions (grain size is mostly <0.5 mm, a few grains reach nearly 1 mm), and is composed of orthopyroxene (63 vol.%, Fs18.0Wo1.3, FeO/MnO = 30), olivine (27 vol.%, Fa21.4, FeO/MnO = 57-61), clinopyroxene (5 vol.%, Fs7.4Wo49.8, TiO2 = 0.74 wt.%, Cr2O3 = 0.63 wt.%, FeO/MnO = 19), plagioclase (5 vol.%, An53.9Or3), and accessory merrillite, troilite and metal. Replicate oxygen isotopic analyses of acid-washed bulk samples by laser fluorination gave ?18O = 6.004, 6.082; ?17O = 3.082, 3.102; ?17O = -0.076, -0.097 per mil (for TFL slope of 0.526); these values plot close to but below the TFL. The elevated Fe/Mn ratios in the mafic silicates coupled with the relatively calcic plagioclase are hallmarks of carbonaceous chondrite bulk compositions [2], but the oxygen isotopic compositions are quite unlike those of any known chondrite class. Bulk rock abundances by INAA relative to Allende analyzed simultaneously are 0.89 times for Fe and ~1.2 times for Cr, REE and Hf. We conclude that NWA 2788 is a unique metachondrite sampled from a new, perhaps now-disaggregated parent body accreted from a distinctive oxygen isotopic reservoir. It is possible that this body also may harbor or have harbored chondrule-bearing carbonaceous regolith materials ('CT chondrites') that are yet to be found or recognized. [1] Irving A. J. et al. (2005) 68th Met. Soc. Mtg., #5218; Bunch T. E. et al. (2005) LPS XXXVI, #2308 [2] Wasson J. T. and Kallemyn G. W. (1988) Phil. Trans. Roy. Soc. Lond. A325, 535-544.

Bunch, T. E.; Irving, A. J.; Rumble, D.; Korotev, R. L.

2006-12-01

252

Making Differences Ordinary in Inclusive Classrooms  

Microsoft Academic Search

This article addresses the need to make differences ordinary as inclusive school programs are developed and implemented. Qualities that are hallmarks of inclusive classrooms and that ensure that differences become an ordinary part of classroom practices are then addressed. These qualities ensure that supports provided in the inclusive classroom are as natural and unobtrusive as possible, arranging student schedules so

James Mcleskey; Nancy L. Waldron

2007-01-01

253

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

254

Dhofar 225 and Dhofar 735: Relationship to CM2 chondrites and metamorphosed carbonaceous chondrites, Belgica-7904 and Yamato-86720  

NASA Astrophysics Data System (ADS)

Dhofar (Dho) 225 and Dho 735 are carbonaceous chondrites found in a hot desert and having affinities to Belgica-like Antarctic chondrites (Belgica [B-] 7904 and Yamato [Y-] 86720). Texturally they resemble CM2 chondrites, but differ in mineralogy, bulk chemistry and oxygen isotopic compositions. The texture and main mineralogy of Dho 225 and Dho 735 are similar to the CM2 chondrites, but unlike CM2 chondrites they do not contain any (P, Cr)-sulfides, nor tochilinite 6Fe0.9S*5(Fe,Mg)(OH)2. H2O-contents of Dho 225 and Dho 735 (1.76 and 1.06 wt%) are lower than those of CM2 chondrites (2-18 wt%), but similar to those in the metamorphosed carbonaceous chondrites of the Belgica-like group. Bulk compositions of Dho 225 and Dho 735, as well as their matrices, have low Fe and S and low Fe/Si ratios relative to CM2 chondrites. X-ray powder diffraction patterns of the Dho 225 and Dho 735 matrices showed similarities to laboratory-heated Murchison CM2 chondrite and the transformation of serpentine to olivine. Dho 225 and 735's oxygen isotopic compositions are in the high 18O range on the oxygen diagram, close to the Belgica-like meteorites. This differs from the oxygen isotopic compositions of typical CM2 chondrites. Experimental results showed that the oxygen isotopic compositions of Dho 225 and Dhofar 725, could not be derived from those of typical CM2 chondrites via dehydration caused by thermal metamorphism. Dho 225 and Dho 735 may represent a group of chondrites whose primary material was different from typical CM2 chondrites and the Belgica-like meteorites, but they formed in an oxygen reservoir similar to that of the Belgica-like meteorites.

Ivanova, Marina A.; Lorenz, Cyrill A.; Nazarov, Mikhail A.; Brandstaetter, Franz; Franchi, Ian A.; Moroz, Lyuba V.; Clayton, Robert N.; Bychkov, Andrew Yu.

2010-07-01

255

Mineralogy of Frontier Mountains L7 Chondrites with Reference to the Chondrite-Achondrite Transition  

NASA Astrophysics Data System (ADS)

Achondrites have been generally assumed to be derived from magma formed from some chondritic melts or mixtures and the genetic model often proposes specific crystallization sequences to account for particular achondrite properties. However, some achondrites such as primitive achondrites (Acapulco-type chondrites and/or Lodranites) and ureilites still preserve primitive signatures of chondritic source materials (Palme et al., 1981). To account for formation of such meteorites, a model involving formation of ultramafic meteorites without invoking large-scale melting such as magmatic process has been proposed (Takeda, 1989). The process to form extensively recrystallized chondrites (H7,L7,LL7) should be investigated as a first step to make such meteorites. We investigated the textures and chemical compositions of two L7 chondrites from Frontier Mountains by electron probe microanalysis (EPMA) and scanning electron microscope (JEOL 840A SEM) with chemical mapping analysis (CMA) utility, and compared them with other type 7 chondrites, primitive achondrites, and ureilites. Two polished thin sections, FRO90058,001 and FRO90066,001 have been supplied from the EUROMET. The textures of FRO90058 and FRO90066 are very similar. Textural characteristics of some parts of the samples are rather similar to primitive achondrites than chondrites. However, a few chondrules still remain in FRO90058. Two samples are composed of subangular recrystallized clasts and much comminuted grains of clasts and minerals filling interstices between the clasts. The facts indicate that they are partly brecciated. The recrystallized parts show coarse-grained textures of orthopyroxene(opx), olivine(oliv) and opaque minerals. In fine- grained portions, silicate minerals exhibit granoblastic texture. Plagioclase is present as elongated, irregular grains in the fine-grained portion, while in coarser regions, plagioclase fills interstices or channels and is intruded by opx. Olivine grains are compositionally uniform with mean Fa=25. Opx of FRO90058 and FRO90066 are similar and their chemical compositions are nearly uniform from grain to grain and within the range of Mg# (=Mg x 100/(Mg+Fe) mol%) from 79 to 80. In the present L7 chondrites, the Ca content of opx is lower and the Ca-content of augite is higher than that of Y74160(LL7) and that of augite is higher, indicating that temperature of equilibration is lower than that of Y74160(LL7) (Takeda et al., 1984). The plagioclase compositions in the LL7(Y74160) chondrite show chemical zoning and their ranges differ from one place to another. The plagioclase compositions of FRO L7 chondrites also show minor chemical variation (Ab80-87), though it is not as large as Y74160. We interpret these zonings as resulted from plagioclase growth in localized areas where compositions of Ca-Na-Al-rich materials in their regions are slightly variable. For an internal heat source, such as radioactive decay, temperature increase and decrease would require longer time and plagioclase compositions would be homogenized. Impact process seems more likely heat source although shock features seem to have been erased by subsequent recrystallization. From mineralogical and chemical observations, these chondrites appear to show L6 chondrite-like features, although their textures are rather similar to those of some primitive achondrites. This type of chondrite may be on the road to becoming achondrites, but loss of low-temperature melts are not clearly shown in these samples. We thank EUROMET for the meteorite samples. References: Takeda H. (1989) Earth Planet. Sci. Lett. 93, 181- 194; Takeda H., Huston T.J., and Lipschutz M.E. (1984) Earth Planet. Sci. Lett. 71, 329-339; Palme H., Schultz L., Spettel B., Weber H.W., Wanke H., Michel-Levy M.C., and Lorin J.C. (1981) Geochim. Cosmochim. Acta 45, 727-752.

Baba, T.; Takeda, H.

1992-07-01

256

Formation conditions of plagioclase-bearing type I chondrules in CO chondrites: A study of natural samples and experimental analogs  

NASA Astrophysics Data System (ADS)

About ten percent of type I, FeO-poor chondrules in unequilibrated CO chondrites contain plagioclase that appears to be igneous in origin, crystallizing at a late stage of solidification of host chondrule melts. We have studied plagioclase-bearing chondrules in detail, and compared them with plagioclase-free chondrules, in order to determine the formation conditions of plagioclase and the constraints that the presence of plagioclase places on the conditions of chondrule formation. Plagioclase-bearing chondrules have similar textures, mineral compositions and bulk compositions to plagioclase-free chondrules. The only possible chemical difference that might control the presence or absence of plagioclase in a given chondrule is that most plagioclase-bearing chondrules have a slightly higher bulk Al/Ca ratio than plagioclase-free chondrules. We carried out dynamic cooling experiments on a type IAB chondrule analog in order to investigate chondrule formation conditions. Our experiments at slow cooling rates, <25 °C/hr, reproduce natural type I chondrule textures as well as mineral and glass compositions very closely. We attempted to facilitate nucleation and growth of plagioclase by optimizing several parameters, including using a bulk composition for our experiments comparable to natural plagioclase-bearing chondrules, using slow cooling rates, quenching from low temperatures, seeding the experiments with anorthite crystals, and maintaining a Na-rich atmosphere around the experimental charges. Of all these parameters, we only succeeded in growing plagioclase in the slowest cooled experiment, which included multiple linear cooling steps with a final cooling stage of 1 °C/hr between 1000 and 800 °C. Our experiments indicate that type I chondrules can plausibly be formed at slow cooling rates, and slow cooling rates may actually be a requirement for production of plagioclase. The cooling histories we examined are very similar to those predicted in recent shock wave models for chondrule formation.

Wick, Molly J.; Jones, Rhian H.

2012-12-01

257

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

NASA Astrophysics Data System (ADS)

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 and chondrites is smaller than reported previously. The range of ?26Mg and ?25Mg of 0.6‰ and 0.3‰ defines a single mass-dependent fractionation line consistent with a homogeneous mix of nucleosynthetic components. Data for the Earth, Mars and Vesta display no systematic Mg isotopic differences despite large variations in the level of depletion in moderately volatile elements. Lunar mare basalts exhibit a significant range in ?26Mg (- 0.53‰ to + 0.05‰) and ?25Mg (- 0.27‰ to + 0.02‰) attributable to magmatic differentiation in the lunar magma ocean (LMO). Lunar basalts derived from early segregated cumulates and thought to be the most primitive are on average slightly ˜ 0.17‰ ( ?26Mg) heavy relative to basalts from the Earth, Mars and Vesta. However, the difference is not well-resolved. More strikingly, all differentiated planets and planetesimals, as sampled, have Mg that is on average isotopically heavy compared with most chondrites analyzed thus far. Chondrules and CAIs also are generally heavy in terms of Mg, so this might reflect sorting of material in the proto-planetary disk. Such an explanation would be similar to one previously proposed (Hewins R. H. and Herzberg C. T. (1996) Earth Planet. Sci. Lett. 144, 1-7.) to explain the non-chondritic Si/Mg of the Earth. In this model chondrule-like objects separate from volatile rich planetary dust by accumulation in stagnant regions between eddies in the solar nebula. Small (˜ 1 km) planetesimals formed by accumulation of such molten material then develop into planetary embryos and thence to larger terrestrial planets by combinations of runaway growth and collisions. As such accumulation of molten chondrule-like droplets provides an explanation that obviates some of the dynamic difficulties associated with the onset of planetary accretion. The non-chondritic Mg isotopic composition of the Earth is consistent with data for Li and has important implications for Earth's bulk composition and putative hidden reservoirs.

Wiechert, Uwe; Halliday, Alex N.

2007-04-01

258

Pyroxene Structures, Cathodoluminescence and the Thermal History of the Enstatite Chondrites.  

National Technical Information Service (NTIS)

In order to explore the thermal history of enstatite chondrites, we examined the cathodoluminescence (CL) and thermoluminescence (TL) properties of 15 EH chondrites and 21 EL chondrites, including all available petrographic types, both textural types 3-6 ...

Y. Zhang S. Huang D. Schneider P. H. Benoit D. W. G. Sears

1996-01-01

259

The Structure and Composition of Large Metal Nodule from the Ghubara L5 Chondrite  

NASA Astrophysics Data System (ADS)

The large metal nodule was found in the Ghubara L5 chondrite. The metal demonstrates widmannstätten texture that is unique in chondritic metal. The nodule could be formed by the partial or complete impact melting of chondritic precursor.

Lorenz, C. A.; Teplyakova, S. N.; Korochantsev, A. V.; Kononkova, N. N.; Roshina, I. A.; Sadilenko, D. A.

2009-03-01

260

Silicon isotope evidence against an enstatite chondrite Earth.  

PubMed

The compositions of Earth materials are strikingly similar to those of enstatite chondrite meteorites in many isotope systems. Although this suggests that Earth largely accreted from enstatite chondrites, definitive proof of this model has been lacking. By comparing the silicon (Si) isotope signatures of several extraterrestrial materials with terrestrial samples, we show that they cannot be explained by core-formation scenarios involving a bulk Earth of enstatite chondrite composition. Si isotope similarities between the bulk silicate Earth and the Moon preclude the existence of a hidden reservoir in the lower mantle, a necessary condition of the enstatite chondrite model, and require an equilibrium process after the Moon-forming impact. A three-end-member chondritic mixing model for Earth reconciles the Si isotope similarities between enstatite chondrites and Earth. PMID:22383806

Fitoussi, Caroline; Bourdon, Bernard

2012-03-01

261

The formation conditions of chondrules and chondrites  

USGS Publications Warehouse

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.

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

2008-01-01

262

The chondrite Mihonoseki: New observed fall  

NASA Astrophysics Data System (ADS)

On 10 Dec. 1992, 21:00 hours Japanese standard time, a stone weighing 6.385kg, struck a two-story house in Mihonoseki-machi, Yatsuka-gun, Shimane-ken, Japan, 35 deg 34.1 min N, 133 deg 13.2 min E. Through petrographical and mineralogical examination and rare gas analysis, the meteorite was classified as an L6 chondrite. The preatmospheric chondrite is rather small in size (Ne-22/Ne-21 = 1.180 and extremely low Co-60 activity), and shocked features are not distinct. Cosmic-ray exposure ages obtained from He-3, Ne-21, and Ar-38 are 61 m.y., and K-40/Ar-40 age is 4.41 b.y. Measurements of cosmogenic radioactive nuclides and chemical analyses are now proceeding.

Shima, Masako; Okada, A.; Nagao, K.

1993-03-01

263

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

264

A Second H Chondrite Stream of Falls  

Microsoft Academic Search

Earlier, Dodd et al. [1] described a statistically significant concentration of 17 H4-6 chondrite falls in May between 1855 and 1895, that clustered on a year-day plot, indicating a coorbital meteoroid stream or two closely-related ones. Contents of 10 thermally labile trace elements (Rb, Ag, Se, Cs, Te,Zn, Cd, Bi, Tl, In) determined by RNAA demonstrated that 13 of these

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

1995-01-01

265

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

266

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

NASA Astrophysics Data System (ADS)

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

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

2011-06-01

267

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

268

Oxygen isotopic compositions of chondrules: Implications for evolution of oxygen isotopic reservoirs in the inner solar nebula  

Microsoft Academic Search

We review the oxygen isotopic compositions of minerals in chondrules and compound objects composed of a chondrule and a refractory inclusion, and bulk oxygen isotopic compositions of chondrules in unequilibrated ordinary, carbonaceous, enstatite, and Kakangari-like chondrites, focusing on data acquired using secondary ion mass-spectrometry and laser fluorination coupled with mass-spectrometry over the last decade. Most ferromagnesian chondrules from primitive (unmetamorphosed)

Alexander N. Krot; Hisayoshi Yurimoto; Kevin D. McKeegan; Laurie Leshin; Marc Chaussidon; Guy Libourel; Miwa Yoshitake; Gary R. Huss; Yunbin Guan; Brigitte Zanda

2006-01-01

269

The relative formation ages of ferromagnesian chondrules inferred from their initial aluminum-26\\/aluminum-27 ratios  

Microsoft Academic Search

We performed a systematic high precision SIMS 26Al-26Mg isotopic study for 11 ferromagnesian chondrules from the highly unequilibrated ordinary chondrite Bishunpur (LL3.1). The chondrules are porphyritic and contain various amounts of olivine and pyroxene and interstitial plagioclase and\\/or glass. The chemical compositions of the chondrules vary from FeO-poor to FeO-rich. Eight chondrules show resolvable 26Mg-excesses with a maximum ?26Mg of

Smail Mostefaoui; Noriko T. Kita; Shigeko Togashi; Shogo Tachibana; Hiroko Nagahara; Yuichi Morishita

2002-01-01

270

The compositional classification of chondrites: 5. The Karoonda (CK) group of carbonaceous chondrites  

Microsoft Academic Search

Petrographic and bulk compositional data reveal the existence of a new group of carbonaceous chondrites consisting of the observed fall, Karoonda, one large find from Maralinga, Australia, and 6-11 small finds from five sites in Antarctica. Ningqiang, also a fall, is genetically related to the group. Compositional, textural, and O-isotope data show that the new group is closely related to

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

1991-01-01

271

The integral enstatite chondrite model of the earth  

Microsoft Academic Search

The only primitive meteorites that match satisfactorily both the stable isotope and redox characteristics of the Earth are the Enstatite chondrites. I present an integral Enstatite chondrite model in which the Earth is built from essentially pure EH material, which is justified by the above similarities and by the fact that most elements in these meteorites exist in very refractory

M. Javoy

1995-01-01

272

Rb-Sr Ages of Chondrules and Carbonaceous Chondrites  

Microsoft Academic Search

Determinations of Rb, Sr, and K contents and isotopic compositions of Sr are reported for the carbonaceous chondrites Orgueil, Murray, Mokoia, and Lance, the hypersthene chondrite Peace River, and four chondrules from the Peace River meteorite. In accordance with previous work, the abundances of Rb and K in type I is greater than in type III; 8r is relatively constant.

V. Rama Murthy; W. Compston

1965-01-01

273

Are C1 chondrites chemically fractionated - A trace element study  

Microsoft Academic Search

Six C1 chondrite samples and a C2 xenolith from the Plainview H5 chondrite were analyzed by radiochemical neutron activation for a large variety of elements, including rare earths. The sample processing is described, including the irradiation, chemical procedure, rare earths separation, counting techniques, radiochemical purity check, and chemical yields. The results of consistency checks on a number of elements are

Mitsuru Ebihara; Rainer Wolf; Edward Anders

1982-01-01

274

Hydrothermal Convection and Aqueous Alteration in Carbonaceous Chondrite Parent Bodies  

Microsoft Academic Search

Carbonaceous chondrites (CCs) are derived from undifferentiated icy planetesimals and are the most primitive meteorites. The information that we can derive from CCs depends largely on our understanding the effects of water in carbonaceous chondrite parent bodies (CCPBs). The way water influenced the parent bodies' evolution depends partly on the flow rates and patterns of the water circulation. The first

Jennifer Palguta; B. J. Travis; G. Schubert

2006-01-01

275

Fluid flow and chemical alteration in carbonaceous chondrite parent bodies  

Microsoft Academic Search

Carbonaceous chondrites are a class of primitive meteorites that likely represent early solar system materials, thus providing critical insights about planetary evolution. However, evidence shows that they have undergone considerable processing. Elucidating the complex formation history of aqueously altered chondrite groups has been a principal objective of cosmochemistry. Fulfilling this objective requires understanding the nature of the water–rock interactions involved.

Jennifer Palguta; Gerald Schubert; Bryan J. Travis

2010-01-01

276

Water-Rock Interactions in Carbonaceous Chondrite Parent Bodies  

Microsoft Academic Search

Carbonaceous chondrites (CCs) form the most primitive class of meteorites and are vestiges of the planetesimals that formed the building blocks of the planets. Consequently, they possess a wealth of information pertaining to the early solar system. Carbonaceous chondrite parent bodies (CCPBs) are the bodies in which the CCs acquired their current chemical and mineralogical characteristics. There is abundant evidence

J. Palguta; B. J. Travis; G. Schubert

2006-01-01

277

Rare Earth Elements in CI1-Chondrites and Planetary Samples  

NASA Astrophysics Data System (ADS)

We present high-precision LA-ICPMS data about rare earth elements, which show that planetary samples have a Tm-anomaly compared to CI1-chondrites. We conclude that a Tm-rich refractory phase was added to the CI1-chondrites.

Bendel, V.; Pack, A.; O'Neill, H.

2012-03-01

278

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

279

Terrestrial microbes in martian and chondritic meteorites  

NASA Astrophysics Data System (ADS)

Good extraterrestrial analogs for microbiology are SNC meteorites as Mars analogs, and chondrites as early planet analogs. Chondrites and SNCs are used to trace processes in the early solar system and on Mars. Yet, questions about terrestrial contamination and its effects on the isotopic, chemical and mineral characteristics often arise. A wide biodiversity was found in 21 chondrites of groups CR, CV, CK, CO from ANSMET, CI and CM Falls, and 8 SNCs. Studies documented the alteration of meteorites by weathering and biology [1]-[6], and during aqueous extraction for oxygen isotopic analysis [7], visible biofilms grew in the meteorite solutions in days. To assess biological isotopic and chemical impacts, cultures were incubated 11 months and analyzed by PCR. The sequences for 2 isolates from EET 87770 and Leoville were of a good quality with long sequence reads. In EET 87770, the closest matches were in the genus Microbacterium. Soil and plant isolates were close relatives by sequence comparison. Bacillus, a common soil bacterial genus, grew in a Leoville culture. All SNCs exhibited biological activity measured independently by LAL but only 1 colony was successfully cultured from grains of the SNC Los Angeles. Isotopic analyses of samples with various amounts of microbial contamination could help quantified isotopic impact of microbes on protoplanetary chemistry in these rocks. References: [1] Gounelle, M.& Zolensky M. (2001) LPS XXXII, Abstract #999. [2] Fries, M. et al. (2005) Meteoritical Society Meeting 68, Abstract # 5201. [3] Burckle, L. H. & Delaney, J. S (1999) Meteoritics & Planet. Sci., 32, 475. [4] Whitby, C. et al. (2000) LPS XXXI, Abstract #1732. [5] Tyra M. et al., (2007) Geochim. Cosmochim. Acta, 71, 782 [6] Toporski, J. & Steele A., (2007) Astrobiology, 7, 389 [7]Airieau, S. et al (2005) Geochim. Cosmochim. Acta, 69, 4166.

Airieau, S.; Piceno, Y.; Andersen, G.

2007-08-01

280

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

SciTech Connect

Antarctic H chondrites show a different range of induced thermoluminescence properties compared with those of H chondrites that have fallen elsewhere in the world. Recent noble gas data show that this difference is displayed most dramatically by meteorites with cosmic-ray exposure ages less than 20 Ma, and they confirm that the differences cannot be attributed to weathering or to the presence of a great many fragments of an unusual Antarctic meteorite. Annealing experiments on an H5 chondrite, and other measurements on a variety of ordinary chondrites, have shown that induced TL properties are sensitive to the thermal histories of the meteorites. The authors conclude that the event(s) that released the less than 20 Ma samples, which are predominantly those with exposure ages of 8{plus minus}2 Ma, produced two groups with different thermal histories, one that came to earth several 10{sup 5} years ago and that are currently only found in Antarctica, and one that is currently falling on the earth.

Sears, D.W.G.; Benott, P.; Batchelor, J.D. (Univ. of Arkansas, Fayetteville (USA))

1991-04-01

281

Annuities: Ordinary? Due? What do I do?  

NSDL National Science Digital Library

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

Wachowicz, John M., Jr.

282

Chondritic Mg isotope composition of the Earth  

NASA Astrophysics Data System (ADS)

The processes of planetary accretion and differentiation have potentially been recorded as variations in the stable isotope ratios of the major elements between planetary objects. However, the magnitude of observed isotopic variations for several elements (Mg, Fe, Si) are at the limit of what current analytical precision and accuracy obtained by mass spectrometry are able to resolve. Here, we present a comprehensive data set of Mg isotope ratios measured by multiple collector ICP-MS in eighteen ocean island basalts and four mid-ocean ridge basalts, six peridotites and five chondrites. The basalt and peridotite samples span the whole compositional range described in the literature. The precision and accuracy of the measurements was verified by isotopic standard addition for two samples, one carbonaceous chondrite (Murchison) and one continental flood basalt (BCR-1). In contrast with some previous studies, our data from terrestrial and chondritic materials have invariant Mg isotope ratios within the uncertainty of the method (0.09‰ for the 26Mg/24Mg ratio, 2 S.D.). Although isotopic variations of less than about 0.1‰ could still be present, the data demonstrate that, at this level of uncertainty, the bulk silicate Earth and chondritic Mg reservoir have a homogeneous 26Mg/24Mg ratio equal to -0.23 ‰ (expressed as delta26Mg relative to DSM3). This observation is comparable with K, Fe and Li isotopes but contrasts with observations for Si isotopes and can be used to further constrain the conditions of moderately volatile element loss during terrestrial accretion and solar material evolution. The data for basalts and peridotites show that there is no detectable fractionation in Mg isotopes during mantle melting and subsequent melt evolution at the current level of precision and accuracy, and one could indifferently use basalts or peridotites to assess the Mg isotope composition of the bulk Earth. Our data also reveals the Mg isotopes cannot be used to argue that the Earth was built from preferential accumulation of chondrules as in Wiechert and Halliday (2007). Reference Wiechert U. and Halliday A.N. (2007) Earth Planet. Sci. Lett. 256, 360-371.

Bourdon, B.; Tipper, E. T.; Fitoussi, C.; Stracke, A.

2009-12-01

283

The Salem, Oregon L6 Chondrite  

Microsoft Academic Search

The Salem, Oregon meteorite fall of 1:05 a.m. (07:05 GMT) May 13, 1981 (lat. 44°58arcmin45arcsecN., long. 123°58arcmin10arcsecW) was heard by two observers. A 22.2 g fragment was recovered immediately from a total recovery of 61.4 g from a single individual. No other fall related phenomena were observed. It is a heavily fusion-crusted, shock-veined, L6 chondrite.

R. S. Clarke Jr.; R. N. Pugh

1988-01-01

284

The Salem, Oregon L6 Chondrite  

NASA Astrophysics Data System (ADS)

The Salem, Oregon meteorite fall of 1:05 a.m. (07:05 GMT) May 13, 1981 (lat. 44°58arcmin45arcsecN., long. 123°58arcmin10arcsecW) was heard by two observers. A 22.2 g fragment was recovered immediately from a total recovery of 61.4 g from a single individual. No other fall related phenomena were observed. It is a heavily fusion-crusted, shock-veined, L6 chondrite.

Clarke, R. S., Jr.; Pugh, R. N.

1988-06-01

285

Evolutionary history of CI and CM chondrites  

SciTech Connect

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

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

1984-01-01

286

Nucleosynthetic Nd isotope anomalies in primitive enstatite chondrites  

NASA Astrophysics Data System (ADS)

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

Boyet, M.; Gannoun, A.

2013-11-01

287

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

USGS Publications Warehouse

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

Unruh, D. M.

1982-01-01

288

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

289

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

290

Data Management in Ordinary English: Examples.  

ERIC Educational Resources Information Center

|The use of a system for on-line conversation in ordinary English grammatical patterns is illustrated by a number of examples showing how data bases of diverse content and structure may be described, interrogated, and modified. It is suggested that a system composed of a user extendable subset of English, a natural language compiler to translate…

Kellogg, Charles H.

291

Cell Dimensions of Ordinary and `Heavy' Ice  

Microsoft Academic Search

I HAVE recently made accurate determinations of the cell dimensions of crystals of ordinary and `heavy' ice (D2O). Single crystals were used. The apparatus consisted of a small Dewar flask mounted on the arcs of a Bernal photogoniometer, and filled with a mixture of acetone and solid carbon dioxide. A holder of copper wire attached to the bottom of the

H. D. Megaw

1934-01-01

292

Applications to Stochastic Ordinary Differential Equations  

Microsoft Academic Search

As mentioned in the introduction, the framework that we developed in Chapter 2 for the main purpose of solving stochastic\\u000a partial differential equations, can also be used to obtain new results – as well as new proofs of old results – for stochastic\\u000a ordinary differential equations. In this chapter we will illustrate this by discussing some important examples.

Helge Holden; Bernt Øksendal; Jan Ubøe; Tusheng Zhang

293

Relevant Alternatives Contextualism and Ordinary Contingent Knowledge  

Microsoft Academic Search

According to David Lewis' contextualist analysis of knowledge, there can be contexts in which a subject counts as knowing a proposition just because every possibility that this proposition might be false is irrelevant in these contexts. In this paper I argue that, in some cases at least, Lewis' analysis results in granting people non-evidentially based knowledge of ordinary contingent truths

Franck Lihoreau

2008-01-01

294

Chondrites: A Trace Fossil Indicator of Anoxia in Sediments  

NASA Astrophysics Data System (ADS)

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 carbonate units throughout the geologic column, Chondrites typically represents the last trace fossil in a bioturbation sequence. This indicates that the burrow system was produced deep within the sediment in the anaerobic zone below the surficial oxidized zone that was characterized by freely circulating and oxidizing pore waters.

Bromley, Richard G.; Ekdale, A. A.

1984-05-01

295

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

Microsoft Academic Search

Several differences between Antarctic and non-Antarctic meteorite populations have been recognized that are attributed to two main causes, namely a general difference in their parent meteoroid populations and\\/or secondary effects like weathering or pairing (see e.g.[1]). In the last few years several hundred new meteorites have become available from hot desert areas (Nullabor Plain, Roosevelt County, Sahara Desert). Compared to

P. Scherer; T. Loeken; L. Schultz

1992-01-01

296

Terrestrial Weathering of Ordinary Chondrites in Nature and Continuing During Laboratory Storage and Processing: Implications for Sample Integrity  

NASA Astrophysics Data System (ADS)

Terrestrial weathering has affected OC finds, samples of OC falls exposed in hot-deserts before recovery, and OC falls recovered promptly and curated promptly after recovery. Similar phenomena must be anticipated in planning for returned samples.

Velbel, M. A.

2013-09-01

297

The Trace-Element Composition of a Silica-rich Clast in the Bovedy (L3/4) Chondrite  

NASA Astrophysics Data System (ADS)

The discovery of a ~4 X 4.5 X 7 mm^3, igneous-textured, silica-rich clast in the Bovedy chondrite [1] may have important implications regarding igneous processes that occurred on chondritic parent bodies [1,2]. This clast, designated Bo-1, is comprised of orthopyroxene, a silica polymorph, two feldspars, pigeonite, and minor chromite and trace metal and sulfide [1]. Bulk SEM/EMPA analyses of the clast indicated superchondritic Si/Mg and Si/Fe ratios, which Ruzicka and Boynton [1] proposed was produced by extensive olivine fractionation from a melted L-chondrite precursor. The low Fe/Mn ratio and low metal and sulfide abundances also suggest that the clast is largely missing a chondritic complement of metal and sulfide. To test these hypotheses, we measured the bulk composition of the clast using INAA techniques and found that the siderophile elements were lost in a two-step process and that partial melting also depleted incompatible lithophile elements. Lithophile Elements: Two splits (2.94 and 2.39 mg) of Bo-1 were analyzed. The concentrations of major elements (Ca, Fe, Cr, K, Na) bracket those previously determined by SEM/EMPA [1], suggesting that the two splits are reasonably representative of the bulk clast. If olivine and metal had been removed from an ordinary chondrite melt to produce the clast, then incompatible lithophile trace elements should have been enriched. Contrary to this expectation, however, the REE, Zr, Hf, Th, Sr, Rb, Cs and Br are consistently depleted to a level of 0.5-1.0 X CI abundances, while all of them (except the highly volatile Cs and Br) have concentrations of ~1.0-2.0 X CI abundances in ordinary chondrites. If the clast had been derived from melted ordinary chondrite material, then an additional step that removed incompatible elements, such as the loss of a partial melt, must have occurred. Siderophile Elements: Unlike lithophile trace elements, which are relatively unfractionated, the siderophiles Ni, Co, and Au are dramatically fractionated from Re, Os, Ir, and Ru. Nickel, Co, Au, and the chalcophile element Se are present at approximately 0.004-0.015 X CI abundances, compared to Re, Os, Ir, and Ru at 0.1-0.3 X CI. All the former elements have high affinities for S- rich metallic liquids, while the latter elements prefer solid metal [3], implying that the petrogenesis of Bo-1 included the loss of a S-rich metallic liquid. An equilibrium batch melting model of these trace siderophile elements, using the partition coefficients of [3], was constructed assuming an ordinary chondrite precursor. In these models, the proportion of liquid to solid silicate or of silicate to metal is unimportant, because the siderophile elements partition almost entirely into the metallic phases. The model results suggest that the siderophile trace elements can be adequately accounted for by a two-step process: (1) loss of a S-rich metallic liquid at high degrees of melting; and (2) subsequent loss of much of the remaining solid metal fraction. For an L-chondrite precursor, an optimal model involves the complete removal of metallic liquid generated by 90% partial melting of the metal + sulfide system, followed by the loss of 80% of the remaining 10% of the solids. Together, these two steps remove all but 2% of the initial metal + sulfide complement, consistent with the presence of only trace metal and sulfide in Bo-1. The large fraction of metallic melt involved in the first step implies that metallic liquid segregated from the remainder of the system at relatively high temperatures (~1325 degrees C for an L-chondrite precursor, based on the Fe-S phase diagram of [4]). References: [1] Ruzicka A. and Boynton W. V. (1992) Meteoritics, 27, 283. [2] Ruzicka A. and Boynton W. V. (1992) Meteoritics, 27, 284. [3] Jones J. H. and Drake M. J. (1986) Nature, 322, 221-228. [4] Kellerud G. and Yoder H. (1959) Econ. Geol., 54, 533-572.

Ruzicka, A.; Kring, D. A.; Hill, D. H.; Boynton, W. V.

1993-07-01

298

Analysis of the Allende chondritic meteorite's remanence  

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

299

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

300

Magnetic Characterization of Tetrataenite in Mesosoderites and Chondrites  

NASA Astrophysics Data System (ADS)

We describe the magnetic domain configurations of tetratagonal L10 tetrataenite (Tt) found in chondritic and mesosiderite metal using Magnetic Force Microscopy to understand the relationships between magnetic domain state and the properties of Tt.

Bordeaux, N.; Mubarok, A.; Goldstein, J. I.; Lewis, L. H.

2012-09-01

301

Thermomagnetic analysis of meteorites, 2. C2 chondrites  

USGS Publications Warehouse

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

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

1975-01-01

302

Elemental Composition and Chemical Classification of Sutter's Mill Chondrites  

NASA Astrophysics Data System (ADS)

The elemental composition of the SM2 fragment of Sutter's Mill is consistent with a CM chondrite. Based on the content of thermally labile elements, our fragment of SM2 did not experience heating over ~500°C.

Friedrich, J. M.; Ebel, D. S.; Jenniskens, P.

2012-09-01

303

Strong Oxidants are Needed to form Sulfates in CM Chondrites  

NASA Astrophysics Data System (ADS)

Oxidants (O_2, H_2O_2, O_3, etc.) produced through radiolysis and photolysis of water ice in the solar nebula could be responsible for formation of sulfates and some ferric phases in carbonaceous chondrites.

Zolotov, M. Yu.

2013-09-01

304

Sm-Nd isotopic evolution of chondrites and achondrites. II  

NASA Astrophysics Data System (ADS)

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

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

1984-02-01

305

Bloomington (LL6) chondrite and its shock melt glasses  

SciTech Connect

The shock melt glasses of the Bloomington LL-group chondrite were examined using electron-beam microscopy and compared with data from studies of other shock melt glasses. Petrologic and mineralogic characterizations were also performed of the samples. The metal contents of the meteorite were almost wholly Ni-rich martensite. The glasses resembled shock melt glasses in L-group chondrites, and were indicative of isochemical melting during one melt phase, i.e., a very simple history. 12 references.

Dodd, R.T.; Olsen, E.J.; Clarke, R.S.,JR.

1985-09-01

306

Precious metal abundances in some carbonaceous and enstatite chondrites  

Microsoft Academic Search

Neutron activation analysis has been used to determine the concentrations of Ru, Pd, Os, Ir, Pt and Au in seven carbonaceous and two enstatite chondrites. The average atomic abundances relative to 10 6 silicon atoms are tabulated below: Chondrite Ru Pd Os Ir Pt Au Group Carbon- aceous 1.84±0.09 6 1.32± 0.21 0.79± 0.12 0.76 ± 0.28 1.4 ± 0.25

J. H. Crocket; R. R. Keays; S. Hsieh

1967-01-01

307

Sulfide-rich metallic impact melts from chondritic parent bodies  

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

308

Analysis of chondritic interplanetary dust thin-sections  

SciTech Connect

Chondritic interplanetary dust particles (IDPs) are heterogeneous aggregates of predominantly submicrometer mineral grains and carbonaceous material, whose bulk compositions agree within a factor of two with type CI/CM carbonaceous chondrites. The mineralogy and petrography of 25 such particles were studied by analytical electron microscopic examination of ultramicrotomed thin-sections (500-1,000 {angstrom} thick). Four classes of chondritic IDPs were recognized, referred to as pyroxene, olivine, smectite, and serpentine, and their relative abundances were 9:4:10:2 respectively. Pyroxene and olivine particles are porous assemblages of anhydrous mineral grains, glass, and carbonaceous material. Smectite and serpentine particles are low porosity objects whose matrices contain layer silicates and glassy material. Quantitative thin-film analyses indicate that pyroxene particles most closely resemble material emitted from comet Halley. Smectite particles may have formed from pyroxene particles by aqueous alteration of glass and enstatite crystals. Serpentine particles are the only class that are similar to the matrices of carbonaceous chondrites, but these are the least abundant chondritic IDPs. Collectively, chondritic particles are a mineralogically diverse group of extraterrestrial materials.

Bradley, J.P. (McCrone Associates, Inc., Westmont, IL (USA))

1988-04-01

309

Terrestrial microbes in martian and chondritic meteorites  

NASA Astrophysics Data System (ADS)

Introduction: The best extraterrestrial analogs for microbiology are meteorites. The chemistry and mineralogy of Asteroid Belt and martian (SNC) meteorites are used as tracers of processes that took place in the early solar system. Meteoritic falls, in particular those of carbonaceous chondrites, are regarded as pristine samples of planetesimal evolution as these rocks are primitive and mostly unprocessed since the formation of the solar system 4.56 billion years ago. Yet, questions about terrestrial contamination and its effects on the meteoritic isotopic, chemical and mineral characteristics often arise. Meteorites are hosts to biological activity as soon as they are in contact with the terrestrial biosphere, like all rocks. A wide biodiversity was found in 21 chondrites and 8 martian stones, and was investigated with cell culture, microscopy techniques, PCR, and LAL photoluminetry. Some preliminary results are presented here. The sample suite included carbonaceous chondrites of types CR, CV, CK, CO, CI, and CM, from ANSMET and Falls. Past studies documented the alteration of meteorites by weathering and biological activity [1]-[4]. Unpublished observations during aqueous extraction for oxygen isotopic analysis [5], noted the formation of biofilms in water in a matter of days. In order to address the potential modification of meteoritic isotopic and chemical signatures, the culture of microbial contaminating species was initiated in 2005, and after a prolonged incubation, some of the species obtained from cell culture were analyzed in 2006. The results are preliminary, and a systematic catalog of microbial contaminants is developing very slowly due to lack of funding. Methods: The primary method was cell culture and PCR. Chondrites. Chondritic meteorite fragments were obtained by breaking stones of approximately one gram in sterile mortars. The core of the rocks, presumably less contaminated than the surface, was used for the present microbial study, and the remaining fragments of the samples were used for amino acid and isotopic analyses [6]. Some samples were fragments of dried and wet meteorites isolated in centrifuge tubes after a 10-day water extraction. Sabouraud Dextrose (dilutions 1:10 and 1:1000), Bacto Agar, LB Broth Miller (dilutions 1:10 and 1:1000), and R2A agar (1:1 and 1:1000), were autoclaved and cooled in culture plates inside a clean hood for cell culture. Some controls retained sterile moist agar still adhering to the perimeter of the plates for up to 18 months, and validated the sterile technique. Cell culture, PCR and microscopy documented a diversity of archea, prokaryotes and eukaryotes in these samples [7]. The plates displaying microbial growth at room temperature after 6 weeks or less were used to produce streak plates and isolate colonies of individual species for long term freezing in Eppendorf tubes. Any plate with biological growth along the perimeter of the plate was discarded. The plates without microbial activity after 6 weeks were stored in a fridge for 18 months. Control plates, exposed to the clean hood, laboratory room, used gloves, and weighing paper used in the analyses, sustained the prolonged storage with no sign of microbial activity that could be related to the analysis method. Dust grains and water extracts from the meteorites were spread on agar surfaces in cell culture Petri dishes in a clean hood. SNC samples.In early 2005, the surface of SNC stones in the USNM curation facility were brushed with sterile swabs. Fallen dust grains were collected on weighing paper and isolated in sterile tubes. The sample suite included Zagami USNM 6545, Lafayette USNM 1505, Los Angeles USNM 7052, Shergotty USNM 321, Nakhla USNM 5892, Nakhla USNM 426 (117.4 g) and Nakhla USNM 426 (18.2 g), and Chassigny USNMMNHN 2524. The controls, worker's gloves, blank swabs, and weighing paper exhibited no microbial activity in subsequent months. The cell culture was conducted with Sabouraud Dextrose and R2A only, by deposition of dry grains onto the surface of agar in culture plates that were incubated a

Airieau, S.; Picenco, Y.; Andersen, G.

2007-08-01

310

High-precision Mg isotopic systematics of bulk chondrites  

NASA Astrophysics Data System (ADS)

Variations of the mass-independent abundance of 26Mg ( ?26Mg*) and stable Mg ( ?25Mg) isotope composition of chondrites are important because they constrain the homogeneity of 26Al and Mg isotopes in the proto-planetary disc and the validity of the short-lived 26Al-to- 26Mg chronometer applied to meteorites. We present high-precision Mg isotope data and Al/Mg ratios of chondrites representing nearly all major chondrite classes, including a step-leaching experiment on the CM2 chondrite Murchison. ?26Mg* variations in leachates of Murchison representing acid soluble material are ? 30 times smaller than reported for neutron-rich isotopes of Ti and Cr and do not reveal resolvable deficits in ?26Mg* (-0.002 to + 0.118‰). Very small variations in ?26Mg* anomalies in bulk chondrites (-0.006 to + 0.019‰) correlate with increasing 27Al/ 24Mg ratios and ?50Ti, reflecting the variable presence of calcium-aluminium-rich inclusions (CAIs) in some types of carbonaceous chondrites. Similarly, release of radiogenic 26Mg produced by 26Al decay from CAI material in the step-leaching of Murchison best explains the high ?26Mg* observed in the last, aggressive, leaching steps of this experiment. Overall, the observed variations in ?26Mg* are small and potential differences beyond that which result from the presence of CAI-like material cannot be detected within the analytical uncertainties of this study (± 0.004‰). The results do not allow radical heterogeneity of 26Al (?±30%) or measurable Mg nucleosynthetic heterogeneity (?±0.005‰) to have existed on a planetesimal scale in the proto-planetary disc. Combined with published ?26Mg* data for CAIs, the bulk chondrite data yield a precise initial ( 26Al/ 27Al) 0 = (5.21 ± 0.06) × 10 -5 and ?26Mg* = -0.0340 ± 0.0016‰ for the Solar System. However, it is not possible with the currently available data to determine with certainty whether CAIs and the material from which planetesimals accreted including chondrite parent bodies had precisely the same initial levels of 26Al, although planetesimals and planets appear to have accreted from material with a mean initial ( 26Al/ 27Al) 0 in the range of 2.1 to 6.7 × 10 - 5 . The average stable Mg isotope composition of all analysed chondrites, with the exception of a chondrule from the CBa chondrite Gujba ( ?25Mg DSM-3 = -0.032 ± 0.035‰), is ?25Mg DSM-3 = -0.152 ± 0.079‰ (2 sd) and is indistinguishable from that of the Earth's mantle.

Schiller, Martin; Handler, Monica R.; Baker, Joel A.

2010-08-01

311

Phyllosilicates in the Carbonaceous Chondrite Breccia Kaidun  

NASA Astrophysics Data System (ADS)

Kaidun appears to predominantly be a CR chondrite, containing other diverse components, including enstatite chondrites. Previous observations indicate that the dominant phyllosilicates in Kaidun are serpentine and saponite, suggesting that the Kaidun parent body has undergone aqueous alteration [1]. Phyllosilicates in the smectite group are important in that they act as ion exchangers, which can retain alkali metal, alkaline earth, or ammonium ions in their interlayers in exchangeable form while their structure may contain hydroxyl groups derived from the aqueous alteration process. The purpose of this investigation was to study the layer charge of these smectites and to make an attempt to understand the interlayer chemistry, which was the result of rock-water interaction in its parent body. An alkylammonium method coupled with high-resolution transmission electron microscope (HRTEM) was used to study layer charge and the electron microprobe was used to study the composition and the interlayer chemistry of phyllosilicates. Ultramicrotomed Kaidun matrix samples (on TEEM grids) were pretreated with C12-alkylammonium solutions [2]. This procedure was performed to expand and stabilize the smectite (e.g., saponite) for HRTEM study and permit characterization of the relative charge density of the interlayer sites. This latter feature is a potentially important indicator of the environment of the Kaidun parent body (probably a hydrous asteroid). Recent work by Ming et al. [2] shows that the basal lattice fringes of C12-alkylammonium treated saponites in Kaidun meteorite are typically 1.3-1.4 nm, which indicates low-charged interlayer sites. However, in this study saponites with much larger layer spacing (1.3-2.6 nm, mostly 2 nm) were observed. suggesting the presence of high-charge interlayer sites. Another distinct feature observed in this study is that saponite is clearly the dominant phyllosilicate phase in some Kaidun matrix lithologies, with serpentine being rarely observed. In contrast, most reported Kaidun and CR lithologies have approximately subequal amounts of saponite and serpentine in matrix. Phyllosilicates in Kaidun are commonly associated with sulfides; no phyllosilicates have been observed as direct overgrowths on olivine or pyroxene. Microprobe analyses of coarse-grained Kaidun saponites indicate that the majority of the exchangeable cations in the saponites studied are Mg2+ and Ca2+, with mior Na+. However, since the results of this study suggest that the saponite in Kaidun has a highly charged interlayer environment, one might speculate that any ammonium (NH4+) if present in the original parent body atmosphere or the reacting solution might be fixed in the interlayers. High- charge smectites are known to fix ammonium ions from solution [3]. There is spectroscopic evidence for ammonium-bearing phases on asteroid Ceres 1 [4]. Most carbonaceous chondrites are known to contain relatively high amounts of nitrogen (up to 3000 ppm) [5]. In order to detect if any of this N is in NH4+ form in the interlayers, we set up our Cameca electron microprobe to detect the nitrogen K-alpha X-ray peak using an ODPB crystal of a wavelength dispersive spectrometer. No nitrogen peak was positively identified on the carbonaceous matrix, nor on any saponites, although it is possible that the electron beam neutralized and evaporated any NH4+ cations before detection. In conclusion, the phyllosilicates in Kaidun are heterogeneously distributed from clast to clast, with highly charged saponite predominating in some clasts; serpentine and saponite are more nearly equally abundant in other clasts. No nitrogen was positively detected in the matrix or in any components in Kaidun by the electron microprobe in this study, although further studies of Kaidun phyllosilicates are in progress. References: [1] Zolensky M. and McSween H. Y. Jr. (1988) in Meteorites and the Early Solar System, Univ. of Arizona, 114-143. [2] Ming D. W. et. al. (1992) LPSC XXIII, 913-914. [3] Krishnamoorthy C. and Overstreet R. (1950) Soil Sci., 69, 41-53. [4] King T.

Yang, S. V.; Zolensky, M.; Golden, D. C.; Ming, D. W.; Ivanov, A.

1993-07-01

312

A Framework for Chondrite Formation in the Nebula  

NASA Astrophysics Data System (ADS)

More than a dozen subclasses of chondritic meteorites, the most primitive accessible samples of planetary material, are recognized. It has long been assumed that these subclasses formed at different times and/or places in what is now the asteroid belt. Recently the ages of individual chondrule in particularly primitive chondrites have been determined by radiometric techniques, and these data, though still fragmentary, permit placement of the subclasses in a crude time - radial distance matrix. Distances are related to spectral correspondences between the chondrite subclasses and present families of asteroids, and times to the age ranges found for chondrules in the various subclasses, which are unexpectedly long and which seem to be offset from one another. The variable abundance of refractory inclusions, which formed in a brief period at the beginning of nebular activity, in chondrite subclasses provide another age criterion. The mm-sized chondrules that comprise the bulk of most chondritic material were created by brief energetic events in the solar nebula, probably the action of energetic shock waves on precursor solids (this, at least, is the conventional wisdom). The process was modulated by the presence of carbon (probably presolar organic compounds; Nakano et al., 2003) in the precursor material, which during chondrule melting reduced Fe oxides to varying degrees, providing a basis for metal/silicate fractionation and the variability in bulk Fe/Si that is one of the properties differentiating the chondrite subclasses. Greatly enhanced system C/O was needed at the time and place when the end-member enstatite chondrite subclass were formed. The source of the putative chondrule-forming shocks constitutes an interesting problem. Chondrules were formed over too long a time period (3 Myr or more) for the shocks to have been caused by (early) gravitational instability in the nebula. Tidal disturbances by early stellar companions of the sun (Larson, 2002) are a more plausible mechanism, but they may be inconsistent with the present orderly geometry of the planetary system.

Wood, J. A.

2004-12-01

313

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

314

The Trace Element Chemistry of Northwest Africa 5958, a Curious Primitive Carbonaceous Chondrite  

NASA Astrophysics Data System (ADS)

NWA 5958 is a primitive, carbon-rich carbonaceous chondrite which exhibits refractory and volatile trace element chemistry indistinguishable from CI chondrite, but whose oxygen isotopic composition suggests it has not seen hydrous alteration.

Ash, R. D.; Walker, R. J.; Puchtel, I. S.; McDonough, W. F.; Irving, A. J.

2011-03-01

315

Carbon and Noble Gases in Sutter"s Mill: Relationship to CM Chondrites  

NASA Astrophysics Data System (ADS)

Sutter"s Mill fell in California in April 2012. Because of its fresh state, we are interested in the light element history of this meteorite, for comparison with other carbonaceous chondrites, particularly CM chondrites and the unusual Tagish Lake.

Grady, M. M.; Verchovsky, A. B.; Gilmour, I.; Yin, Q.-Z.

2012-09-01

316

Localized Chemical Redistribution During Aqueous Alteration in Cr2 Carbonaceous Chondrites EET 87770 and EET 92105.  

National Technical Information Service (NTIS)

Carbonaceous chondrites are primitive meteorites that are valuable because they preserve evidence of processes that occurred in the solar nebula and on asteroidal parent bodies. Among the carbonaceous chondrite groups, the CR group appears to contain a pa...

P. V. Burger A. J. Brearley

2005-01-01

317

Exposure history of H5 chondrite Gujargaon  

SciTech Connect

Cosmic-ray-produced tracks, He and Ne isotopes, and radionuclides have been studied in the recently fallen H5 chondrite Gujargaon. The results indicate an exposure age of about 7 Ma. The high track production rates of 0.25 to 690,000/sq cm per Ma suggest that the Gujargaon meteoroid had a small size, R(E) = 9-10 cm, in space and suffered 1-3 cm ablation in the atmosphere. The conclusion about the meteoroid size is supported by the low activity of neutron capture isotope Co-60 and high spallogenic Ne-22/Ne-21 ratio of about 1.25. The data on long lived isotopes Be-10, Mn-53, and Al-26 are used to derive production rates of these isotopes in a rock having a radius of 9 cm, and the activity levels of the short lived isotopes Na-22 and Mn-54 are used to estimate the effect of modulation of galactic cosmic rays at the time of solar maximum of 1982. 25 references.

Bhandari, N.; Padia, J.T.; Rao, M.N.; Shukla, P.N.; Suthar, K.M.

1988-06-01

318

Early Chronology of the H Chondrite Asteroid  

NASA Astrophysics Data System (ADS)

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

Pellas, P.

1992-07-01

319

Magnetism in the Carbonaceous Chondrite Meteorite Allende  

NASA Astrophysics Data System (ADS)

The intensity of magnetic fields in the early solar system are still largely unknown. Knowledge of these field intensities would provide a critical constraint on planet formation scenarios, because (a) magnetic fields may have strongly influenced the transfer of mass and momentum inward and outward in the protoplanetary disk and (b) may have played a key role in the formation of some of the earliest solids. The extent to which magnetic fields influenced these processes depended on what their intensity was through time. Many of these processes would have occurred during the first million years of the solar system, a time when it has been suggested that the Sun passed through a magnetically active phase like that observed for T Tauri stars. We have begun to study the magnetism of primitive constituents of CV carbonaceous chondrite meteorites to search for a signature of such early magnetism. We will present the results of a full suite of magnetic analyses on Allende calcium-aluminum-inclusions (CAIs) and chondrules.

Thomas, Cristina A.; Weiss, B.

2006-09-01

320

An investigation of chemical composition and chondritic texture of Lishui chondrite  

NASA Astrophysics Data System (ADS)

The chemical composition of the Lishui chondrite which fell to earth on Sept. 10, 1978, was examined. Having a total mass of 498 g, the meteorite contained 39.10% SiO2, 13.64% FeO, 0.112% TiO2, 1.691% CaO, 25.46% MgO, 0.106% Na2O, 0.255% P2O5, 0.325% MnO, 0.533% Cr2O3, 0.056% CO2, 7.488% Fe, 1.293% Ni, 0.003% Pb, 0.062% Zn, 6.405% FeS, and 0.10% H2O(+). Minerals which were identified were chrysolite, bonzite, quartz, hypersthene, kamacite, taenite, troilite, plagioclase, chromite, whitlockite, apatite, calcite, zircon, magnetite, and hematite. Olivine represented 43.46% and pyroxene 27.98%. The sample was classed as an L-group chondrite, and petrologically a type 5.

Wang, X.; Zhang, H.; Wang, S.

321

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

322

Impact cratering on the H chondrite parent asteroid  

NASA Astrophysics Data System (ADS)

This paper reports petrological data for LaPaz Icefield 02240, 03922, 031125, 031173, 031308, 04462, and 04751, which are meteoritic samples of clast-rich impact melt rocks from the H chondrite parent asteroid. The size distribution and metallographic characteristics of Fe-Ni metal in the melts indicate very rapid 1 to 40°C/s cooling in the temperature range between >1500 and ˜950°C when the clast-melt mixtures were thermally equilibrating. Cooling slowed to values between 10-3 and 10-2°C/s in the temperature range between 700 and 400°C when the melt rocks were cooling to their surroundings. These data suggest that the rocks cooled near the surface of the H chondrite asteroid within suevitic impact deposits. Integrating these data with the petrologic characteristics of other H chondrite melt rocks and their radioisotopic ages indicates that the H chondrite asteroid suffered at least one large impact event while still cooling from endogenous metamorphism at ˜4500 Ma; this impact must have degraded the asteroid's integrity but did not cause shattering. Impact events in the era between ˜4100 and ˜3600 Ma produced melt volumes large enough to allow segregation of metal and troilite from silicate melts, possibly within continuous impact melt sheets contained in craters. The impact record after 3600 Ma does not display such assemblages, which suggests a decrease in the rate of large impact events or a catastrophic size reduction of the H chondrite parent asteroid at around this time.

Wittmann, Axel; Swindle, Timothy D.; Cheek, Leah C.; Frank, Elizabeth A.; Kring, David A.

2010-07-01

323

Refractory Inclusions and Aluminum-rich Chondrules in the CB/CH-like Carbonaceous Chondrite Isheyevo  

NASA Astrophysics Data System (ADS)

The CAIs and Al-rich chondrules in Isheyevo are texturally and mineralogically similar to those in other previously studied CH chondrites and to a lesser degree to those in the CB chondrites and different from those in CO, CM, CR, and CV chondrites.

Krot, A. N.; Ulyanov, A. A.; Ivanova, M. A.

2006-03-01

324

Discovery of an Unmelted H-Chondrite Inclusion in an Iron Metorite  

Microsoft Academic Search

The link between H chondrites and silicate inclusions in group IIE iron meteorites has long been suspected, but direct evidence for a common parentage has remained elusive. The discovery of an unmelted chondritic inclusion in the Techado iron meteorite sheds light on the genetic relation between these two groups, providing clues on the origin of chondritic materials as inclusions in

Ignacio Casanova; Thomas Graf; Kurt Marti

1995-01-01

325

Constraints for chondrule formation from Ca–Al distribution in carbonaceous chondrites  

Microsoft Academic Search

Chondritic meteorites and their components formed in the protoplanetary disk surrounding the nascent sun. We show here that the two volumetrically dominating components of carbonaceous chondrites, chondrules and matrix did not form independently. They must have been derived from a single, common source. We analyzed Ca and Al in chondrules and matrix of the CV type carbonaceous chondrites Allende and

D. C. Hezel; H. Palme

2008-01-01

326

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

Microsoft Academic Search

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

J. W. Larimer; Edward Anders

1970-01-01

327

H4 and H5 chondrites from the Rub'al Khali desert  

NASA Astrophysics Data System (ADS)

Based on texture and mineral composition, the highly weathered al-Jimshan chondrite is classed as an S2-shock stage H4 chondrite. The Bir-Hadi and ad-Dahbubah H chondrites are probably not paired with al-Jimshan, and are here respectively classified as H5, shock stage S3 and H5, shock stage S2.

Krot, A. N.

1993-06-01

328

Tungsten Isotopes and the Origins of Enstatite Chondrites and the Earth  

Microsoft Academic Search

Enstatite chondrites are highly reduced and this has led scientists to believe that they might have formed from an accretionary feeding zone located relatively close to the Sun. Enstatite chondrites have also been linked with the origin of the Earth because of their similarity in O-isotopic compositions. It is, therefore, of interest to study enstatite chondrites with the newly developed

D.-C. Lee; A. N. Halliday

1998-01-01

329

Evidence for a Metallic Core in the CV Chondrite Parent Planetesimal  

Microsoft Academic Search

The aggregational texture and bulk chemical composition of chondrites demonstrate that they are not the products of planetary melting processes. As a result, carbonaceous chondrites have traditionally been thought to samples bodies that have not undergone large-scale differentiation. However, it has long been known that the meteorite Allende and other CV carbonaceous chondrites contain a natural remanent magnetization. This record

B. P. Weiss; L. Carporzen; D. S. Ebel; J. Gattacceca; D. L. Shuster

2009-01-01

330

Petrology and Geochemistry of LEW 88663 and PAT 91501: High Petrologic L Chondrites  

Microsoft Academic Search

Primitive achondrites (e.g., Acapulco, Lodran) are believed to be highly metamorphosed chondritic materials, perhaps up to the point of anatexis in some types. Low petrologic grade equivalents of these achondrites are unknown, so the petrologic transition from chondritic to achondritic material cannot be documented. However, there are rare L chondrites of petrologic grade 7 that may have experienced igneous processes,

D. W. Mittlefehldt; M. M. Lindstrom; S. W. Field

1993-01-01

331

Petrology and mineralogy of the Ningqiang carbonaceous chondrite  

NASA Astrophysics Data System (ADS)

We report detailed chemical, petrological, and mineralogical studies on the Ningqiang carbonaceous chondrite. Ningqiang is a unique ungrouped type 3 carbonaceous chondrite. Its bulk composition is similar to that of CV and CK chondrites, but refractory lithophile elements (1.01 × CI) are distinctly depleted relative to CV (1.29 × CI) and CK (1.20 × CI) chondrites. Ningqiang consists of 47.5 vol% chondrules, 2.0 vol% Ca,Al-rich inclusions (CAIs), 4.5 vol% amoeboid olivine aggregates (AOAs), and 46.0 vol% matrix. Most chondrules (95%) in Ningqiang are Mgrich. The abundances of Fe-rich and Al-rich chondrules are very low. Al-rich chondrules (ARCs) in Ningqiang are composed mainly of olivine, plagioclase, spinel, and pyroxenes. In ARCs, spinel and plagioclase are enriched in moderately volatile elements (Cr, Mn, and Na), and low-Ca pyroxenes are enriched in refractory elements (Al and Ti). The petrology and mineralogy of ARCs in Ningqiang indicate that they were formed from hybrid precursors of ferromagnesian chondrules mixed with refractory materials during chondrule formation processes. We found 294 CAIs (55.0% type A, 39.5% spinel-pyroxene-rich, 4.4% hibonite-rich, and several type C and anorthite-spinelrich inclusions) and 73 AOAs in 15 Ningqiang sections (equivalent to 20 cm2 surface area). This is the first report of hibonite-rich inclusions in Ningqiang. They are texturally similar to those in CM, CH, and CB chondrites, and exhibit three textural forms: aggregates of euhedral hibonite single crystals, fine-grained aggregates of subhedral hibonite with minor spinel, and hibonite ± Al,Ti-diopside ± spinel spherules. Evidence of secondary alteration is ubiquitous in Ningqiang. Opaque assemblages, formed by secondary alteration of pre-existing alloys on the parent body, are widespread in chondrules and matrix. On the other hand, nepheline and sodalite, existing in all chondritic components, formed by alkali-halogen metasomatism in the solar nebula.

Wang, Y.; Hsu, W.

2009-07-01

332

Major, trace element and oxygen isotope study of glass cosmic spherules of chondritic composition: The record of their source material and atmospheric entry heating  

NASA Astrophysics Data System (ADS)

New geochemical data on cosmic spherules (187 major element, 76 trace element, and 10 oxygen isotope compositions) and 273 analyses from the literature were used to assess the chemical diversity observed among glass cosmic spherules with chondritic composition. Three chemical groups of glass spherules are identified: normal chondritic spherules, CAT-like spherules (where CAT refers to Ca-Al-Ti-rich spherules), and high Ca-Al spherules. The transition from normal to high Ca-Al spherules occurs through a progressive enrichment in refractory major elements (on average from 2.3 wt.% to 7.0 wt.% for CaO, 2.8 wt.% to 7.2 wt.% for Al 2 O 3 , and 0.14 wt.% to 0.31 wt.% for TiO 2 ) and refractory trace elements (from 6.2 ?g/g to 19.3 ?g/g for Zr and 1.6CI-4.3CI for Rare Earth Elements-REEs) relative to moderately refractory elements (Mg, Si) and volatile elements (Rb, Na, Zn, Pb). Based on a comparison with experimental works from the literature, these chemical groups are thought to record progressive heating and evaporation during atmospheric entry. The evaporative mass losses evaluated for the high Ca-Al group (80-90%) supersede those of the CAT spherules which up to now have been considered as the most heated class of stony cosmic spherules. However, glass cosmic spherules still retain isotopic and elemental evidence of their source and precursor mineralogy. Four out of the 10 normal and high Ca-Al spherules analysed for oxygen isotopes are related to ordinary chondrites ( ? 18 O = 13.2-17.3‰ and ? 17 O = 7.6-9.2‰). They are systematically enriched in Ni and Co (Ni = 24-500 ?g/g) with respect to spherules related to carbonaceous chondrites (Ni < 1.2 ?g/g, ? 18 O = 13.1-28.0‰ and ? 17 O = 5.1-14.0‰). REE abundances in cosmic spherules, which are not fractionated according to parent body or atmospheric entry heating, can then be used to unravel the precursor mineralogy. Spherules with flat REE pattern close to unity when normalized to CI are the most abundant in our dataset (54%) and likely derive from homogeneous, fine-grained chondritic precursors. Other REE patterns fall into no more than five categories, a surprising reproducibility in view of the mineralogical heterogeneity of chondritic lithologies at the micrometeorite scale.

Cordier, Carole; Folco, Luigi; Suavet, Clément; Sonzogni, Corinne; Rochette, Pierre

2011-09-01

333

Nitrogen and light noble gases in Parsa enstatite chondrite  

NASA Astrophysics Data System (ADS)

Solar gases have been recently reported in Parsa, an EH3 chondrite. In an effort to check whether solar gases are uniformly distributed throughout Parsa or they are located in specific phases, we analyzed two additional samples of bulk Parsa and one aubritic nodule for N and noble gases. Nitrogen studies are intended for the understanding of the nitrogen components distribution in E-chondrites. The N-systematics of the nodule are entirely different from the bulk samples. The higher N contents in this nodule, as well as its complex delta15N structure, as compared to the normal aubrites, is suggestive that the nodule is not a genuine aubrite.

Murty, S. V. S.

1993-03-01

334

Breakup and structure of an H-chondrite parent body - The H-chondrite flux over the last million years  

NASA Astrophysics Data System (ADS)

Two distinct groups of H chondrites are identified which have respectively induced thermoluminescence peak temperatures above 190 C (AC) and below 190 C (BC). Metallographic cooling rate determinations confirm that the AC group cools at very high rates relative to the latter group. The AC group members have cosmic ray exposure ages of about 8 Myr. Antarctic meteorite of the BC group have cosmic ray exposure ages greater than 20 Myr. Modern H-chondrite falls, which are all of the BC group, have cosmic ray exposure ages of 8 and above 20 Myr. The data show that the abundance of the AC group is directly related to terrestrial age. It is suggested that both the AC group and part of BC group were produced by an impact event at approximately 8 Myr and that the small sizes of the AC group made them prone to destruction, allowing the BC group to dominate the modern H-chondrite flux.

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

1993-02-01

335

An investigation of chemical composition and chondritic texture of Lishui chondrite  

Microsoft Academic Search

The chemical composition of the Lishui chondrite which fell to earth on Sept. 10, 1978, was examined. Having a total mass of 498 g, the meteorite contained 39.10% SiO2, 13.64% FeO, 0.112% TiO2, 1.691% CaO, 25.46% MgO, 0.106% Na2O, 0.255% P2O5, 0.325% MnO, 0.533% Cr2O3, 0.056% CO2, 7.488% Fe, 1.293% Ni, 0.003% Pb, 0.062% Zn, 6.405% FeS, and 0.10% H2O(+).

X. Wang; H. Zhang; S. Wang

1981-01-01

336

Elemental and isotopic characterization of organic particles in carbonaceous chondrites by NanoSIMS imaging: assessment on the origin, accretion and preservation of organic matter in chondrites  

Microsoft Academic Search

Chondrites accreted primitive components, including organic compounds sampled from the proto-solar nebula. However, the molecular and isotopic fingerprints of organic matter extracted from chondrites are also potentially influenced by complex evolution on the parent bodies. We have performed NanoSIMS in situ characterisation of organic matter in the matrices of carbonaceous chondrites Orgueil (CI), Murchison (CM), Tagish Lake (C2), Renazzo (CR)

L. Remusat; Y. Guan; J. M. Eiler

2009-01-01

337

The robust beauty of ordinary information.  

PubMed

Heuristics embodying limited information search and noncompensatory processing of information can yield robust performance relative to computationally more complex models. One criticism raised against heuristics is the argument that complexity is hidden in the calculation of the cue order used to make predictions. We discuss ways to order cues that do not entail individual learning. Then we propose and test the thesis that when orders are learned individually, people's necessarily limited knowledge will curtail computational complexity while also achieving robustness. Using computer simulations, we compare the performance of the take-the-best heuristic--with dichotomized or undichotomized cues--to benchmarks such as the naïve Bayes algorithm across 19 environments. Even with minute sizes of training sets, take-the-best using undichotomized cues excels. For 10 environments, we probe people's intuitions about the direction of the correlation between cues and criterion. On the basis of these intuitions, in most of the environments take-the-best achieves the level of performance that would be expected from learning cue orders from 50% of the objects in the environments. Thus, ordinary information about cues--either gleaned from small training sets or intuited--can support robust performance without requiring Herculean computations. PMID:20822293

Katsikopoulos, Konstantinos V; Schooler, Lael J; Hertwig, Ralph

2010-10-01

338

Organic Carbon Inclusions in CR2 Chondrite Graves Nunataks 95229  

NASA Astrophysics Data System (ADS)

We report coordinated XANES, TEM, and nanoSIMS analysis of two large, carbon-rich veins in CR2 chondrite GRA 95229. The variability in morphological, isotopic, and chemical properties is compared to previous results on C-rich veins in CR3 QUE 99177.

Peeters, Z.; Changela, H.; Stroud, R. H.; Alexander, C. M. O'D.; Nittler, L. R.

2012-09-01

339

Al Rais Meteorite: A CR Chondrite or Close Relative.  

National Technical Information Service (NTIS)

Although the classificational group 'CR' was first put forth by McSween more than 10 years ago, it included only the Al Rais and Renazzo meteorites. It has only been the relatively recent discovery of several CR-related chondrites in Antarctica and the Sa...

G. W. Kallemeyn

1993-01-01

340

On the chemical evolution of the carbonaceous chondrites  

Microsoft Academic Search

X-ray diffraction microtechnique has been applied to nine carbonaceous chondrites, so that a definite knowledge of their mineral composition has been obtained. The existence of magnesium sulphate, elemental sulphur and a magnetic spinel containing Fe 3+ ion, has been confirmed. However, troilite is rare, and absent in many cases. Dolomite has been observed in meteorites for the first time, and

E. R. Dufresne; Edward Anders

1962-01-01

341

Water and the thermal evolution of carbonaceous chondrite parent bodies  

Microsoft Academic Search

Two hypotheses are proposed for the aqueous alteration of carbonaceous chondrites within their parent bodies, in which respectively the alteration occurs (1) throughout the parent body interior, or (2) in a postaccretional surface regolith; both models assume an initially homogeneous mixture of ice and rock that is heated through the decay of Al-26. Water is seen to exert a powerful

R. E. Grimm; H. Y. Jr. Mcsween

1989-01-01

342

The Sfax L6 chondrite - A new fall from Tunisia  

NASA Astrophysics Data System (ADS)

The Sfax meteorite fell on October 16, 1989. Four pieces totaling less than 10 kg were recovered from a much larger meteoroid, according to the cosmogenic gas measurements. It is an L6 chondrite, strongly degassed and shocked, with olivine of composition Fa24.

Amouri, M.; Ouazaa, N. L.; Michel-Levy, M. C.; Rekhiss, F.

1991-03-01

343

Shock and thermal history of iron and chondritic meteorites  

NASA Astrophysics Data System (ADS)

This research grant included a study of the shock and thermal history of iron and chondritic meteorites. The important research findings are to be found in the 20 publications that were published as a result of the research support. A complete bibliographic reference to all these papers is given.

Goldstein, Joseph I.

1994-10-01

344

Matrix mineralogy of the orgueil CI carbonaceous chondrite  

SciTech Connect

A petrographic and transmission electron microscopic study of the Orgueil CI carbonaceous chondrite shows that the matrix consists mainly of Fe-bearing, Mg-rich serpentine and smectite (saponite) as well as a poorly crystallized Fe-rich material that contains minor, variable S and Ni; the Fe-rich material is probably ferrihydrite. The ferrihydrite occurs in small particles, and the S and Ni are probably adsorbed on its surfaces. The serpentine and saponite occur in poorly crystallized, fine crystallites that are intimately associated with the ferrihydrite. Coarsely crystallized phyllosilicates occur in clusters relatively free of ferrihydrite. The ferrihydrite is a major matrix constitutent and probably accounts for most of the Fe{sub 3+} as well as the superparamagnetic fraction in the Orgueil matrix. The textures suggest that the fine phyllosilicates resulted from alteration of the coarse phyllosilicates. The alteration probably involved a substantial amount of water and coincided with the period of sulfate vein formation. During the aqueous alteration magnetite grains, disaggregated from framboids, and Fe-(Ni) sulfides were replaces by ferrihydrite. The matrix mineralogy of the Orgueil chondrite suggests that Orgueil experienced considerably different alteration conditions from the CM chondrites. The mineralogical and petrological differences between CI and CM chondrites can not simply be explained as the result of different degrees of aqueous alteration.

Tomeoka, K.; Buseck, P.R. (Arizona State Univ., Tempe (USA))

1988-06-01

345

Refractory solids in chondrites and comets: How similar  

Microsoft Academic Search

The grains of ice, dust, and organic material that came together to form the solar system have been preserved to differing degrees in the most primitive solar system bodies, asteroids and comets. The study of samples of asteroids (in the form of chondritic meteorites) reveals that the dust component was extensively altered by high-temperature events and processes in the early

John A. Wood

1989-01-01

346

The chondrite Senboku: Is this the same fall as Shiraiwa?  

NASA Astrophysics Data System (ADS)

A stone has been kept in a household altar of the Suda family in Takanashi, Senboku-machi, Senboku-gun, Akita-ken, Japan. The stone came from the sky into the chestnut grove in the dry Maruko river bed. The chondrite Shiraiwa was found in 1920 at approximately 60 cm depth under the field behind a Gosha shrine, at Shiraiwa, Kakunodate-machi, Senboku-gun, Akita-ken, Japan. We have checked the two chondrites to see whether they are from the same fall or not because Senboku and Shiraiwa are the only meteorites found in Akita-ken, and were found only 17 km apart; the time of fall of both are unknown; and both chondrites belong to the H group. Because both chondrites fell more than 70 years ago, cosmogenic radioactive nuclides other than Al-26 were not detected. Aluminum-26 data in both chondrites were compared with a gamma ray standard in respective samples. Obtained results are as follows: Shiraiwa 41.5 +/- 5.3 and Senboku 51.4 +/- 2.6. The concentration and isotopic composition of noble gases of Senboku were determined and compared with that of Shiraiwa. Production rates for He-3 and Ne-21 by Eugster and that for Ar-38 by Schultz et al. were used for age calculation. Although Shiraiwa has data by M. Watanabe as well as by Saga and Kano, who classified it as H4, we are now looking at their data for comparison. For Senboku, we have determined 30 grains of olivine and 40 grains of orthopyroxene and obtained mean Fa and Fs ratios by atomic percent as 18.4 +/- 0.5 and 16.3 +/- 0.6 respectively. From the presence of colorless clear plagioclase in matrix, Senboku was classified as H6. From the results, we have concluded that Shiraiwa and Senboku are completely different falls.

Shima, M.; Honda, M.; Okada, A.; Miura, Y. N.; Ebihara, M.

1994-07-01

347

The Philosophy of Ordinary Language Is a Naturalistic Philosophy  

Microsoft Academic Search

It is argued that the only response to the mereological objections of the ordinary language philosopher available to the scientistic philosopher of mind requires the adoption of the view that ordinary psychological talk is theoretical and falsified by the findings of brain science. The availability of this sort of response produces a kind of stalemate between these opposed views and

Jonathan Trigg

2010-01-01

348

A result on a feedback system of ordinary differential equations  

Microsoft Academic Search

A monotone system of ordinary differential equations is considered. It is shown that the omega limit set of a bounded trajectory of this system contains an equilibrium point or a nonconstant periodic orbit. As an application, a four-dimensional system of ordinary differential equations of Lotka-Volterra type is presented. It is shown that if the interior equilibrium point of this system

A. S. Elkhader

1992-01-01

349

Monograph - The Numerical Integration of Ordinary Differential Equations.  

ERIC Educational Resources Information Center

|The materials presented in this monograph are intended to be included in a course on ordinary differential equations at the upper division level in a college mathematics program. These materials provide an introduction to the numerical integration of ordinary differential equations, and they can be used to supplement a regular text on this…

Hull, T. E.

350

Fayalite Formation in Some Primitive Chondrites  

NASA Astrophysics Data System (ADS)

Fayalite (up to Fa(sub)99.9) occurs in the Kaba and Mokoia CV3 carbonaceous chondrites. The grains can reach up to 100 micrometers in diameter and are commonly associated with magnetite and sulfides. Since the fayalite is essentially pure, it must have formed in an environment where Mg is absent. We believe it formed by a two-step gas-solid reaction: (i) the decomposition of enstatite to release SiO (g); (ii) reaction of SiO (g) with magnetite or sulfides to form fayalite. Production of SiO (g) occurs via a reaction such as: 2 MgSiO3 (s) + H2 (g) = Mg2SiO4 (s) + SiO (g) + H2O (g) (1) for which the equilibrium constant is K = the equation which appears here in the hard copy. Using the JANAF tables, we can calculate Delta G for different temperatures, followed by a calculation of PSiO for various H2O/H2 ratios: equation appears here. For fayalite formation, we considered the following reactions: 2 Fe3O4 (s) + 3 SiO (g) + H2O (g) = 3 Fe2SiO4 (s) + H2 (g), and (2) 2 FeS (s) + SiO (g) +3 H2O = Fe2SiO4 (s) + H2(g) + 2 H2S (g) (3) Since sulfides will first react with H2O to form magnetite, reaction (3) will proceed via reaction (2), so our calculation is only for reaction (2). Following the same procedure as for reaction (1), we obtain: the equation, which appears here in the hard copy. After plotting the P(sub)SiO vs. temperature for different H2O/H2 ratios we found: (i) If the H2O/H2 ratio is 5.1 X 10^-4 (solar), fayalite starts to form at a temperature of 300 K, at which the vapor pressure of SiO is only 10^-86 atm. We presume under these conditions the reaction is kinetically prohibited. (ii) If H2O/H2 = 100, fayalite forms above 3000 K, which is also unlikely, because at such a high temperature all silicates will decompose. (iii) If H2O/H2 = 1, the formation temperature of fayalite is ~ 640 K, and the vapor pressure of SiO is 10^-36 atm. (iv) If H2O/H2 = 10, fayalite begins to form at 1100 K, and the vapor pressure of SiO is 10^-19 atm. After taking the reaction rates into consideration, we prefer the combination of H2O/H2 = 10 and starting temperature of 1100 K, because for these conditions P(sub)SiO is 17 orders of magnitude greater than that at ~640 K. If we put additional constraints on the temperature based on the coexistence of magnetite, then a maximum temperature of 1200 K for the reaction can also be determined [1] (Fig 4), because above this temperature magnetite is not stable when the H2O/H2 ratio equals 10. In an environment with H2O/H2 = 10 atm and T = 1100 or 1200 K, the vapor pressure of SiO released from the evaporation of enstatite is 10^-17 and 10^-14.8, respectively. The decomposition of forsterite under identical conditions will be negligible [2 log P(sub)Mgo + log P(sub)SiO = 10^-57.4 (at 1100 K) and 10^-50.3 (at 1200 K)]. References: [1] Larimer J. W. (1967) GCA, 1215-1238; JANAF Thermodunamical Tables (1971).

Hua, X.; Buseck, P. R.

1993-07-01

351

Magnesium isotopic constraints on the origin of CB b chondrites  

NASA Astrophysics Data System (ADS)

The magnesium isotopic composition of Calcium-, Aluminium-rich Inclusions (CAIs) and chondrules from the CB b chondrites HH237 and QUE94411 was measured using MC-ICPMS coupled with a laser ablation system. CAIs from CB b chondrites exhibit limited mass-dependent fractionation ( ?25Mg' (DSM3) < 1.3‰) and formed with undetectable 26Al ( 26Al/ 27Al < 4.6 × 10 - 6 ). Petrographic observations suggest that CB b CAIs are igneous. The magnesium isotopic composition of CB b igneous CAIs contrast with that of CV3 igneous CAIs which are usually mass fractionated and formed with an elevated initial abundance of 26Al. We contend that the absence of 26Al in CAIs is due either to a late formation in the case of a stellar origin of 26Al, or to a lack of exposure to impulsive flares in the case of an irradiation origin of 26Al. In both cases, it implies that a protoplanetary disk was present ˜ 4563 Ma ago, when CB b chondrites agglomerated. Chondrules have ?25Mg' (DSM3) varying from - 0.80 to 0.95‰. A rough negative correlation is observed between the ?25Mg' of chondrules and their 24Mg/ 27Al ratio. This correlation is attributed to evaporation rather than mixing. Contrary to CAIs, chondrules from CB b chondrites have a magnesium isotopic composition similar to that of CV3 chondrules. This last result is surprising as CB b chondrules are significantly different from CV3 chondrules in mineralogy and chemistry. If chondrules from CB b chondrites formed in an impact-related vapour plume as proposed by Krot et al. [A.N. Krot, Y. Amelin, P. Cassen and A. Meibom, Young chondrules in CB chondrites formed by a giant impact in the early Solar System, Nature 436 (2005) 989-992], our data show that physical conditions in the vapour plume were similar to those of the solar accretion disk at the time and location of the formation of CV chondrules. We note that the oxygen isotopic composition of CAIs is incompatible with their remelting in the putative impact vapour plume. Alternatively, it is possible that CB b chondrules formed in a protoplanetary disk as the differences between these and "normal" CV3 chondrules can also be explained in term of spatial and temporal variations of the protoplanetary disk. We show that their young Pb-Pb age is not an argument in favour of an impact origin as protoplanetary disks can last as long as 10 Myr around protostars. If CB b chondrites formed in the solar accretion disk, we speculate they might be the last formed chondrite group. Such a hypothesis might shed light on the unique properties of CB b chondrites.

Gounelle, Matthieu; Young, Edward D.; Shahar, Anat; Tonui, Eric; Kearsley, Anton

2007-04-01

352

A database of chondrite analyses including platinum group elements, Ni, Co, Au, and Cr: Implications for the identification of chondritic projectiles  

Microsoft Academic Search

Siderophile elements have been used to constrain projectile compositions in terrestrial and lunar impact melt rocks. To obtain a better knowledge of compositional differences between potential chondritic projectile types, meteorite analyses of the elements Ru, Rh, Pd, Os, Ir, Pt, Cr, Co, Ni, and Au were gathered into a database. The presented compilation comprises 806 analyses of 278 chondrites including

Roald Tagle; Jana Berlin

2008-01-01

353

Chondritic models of 4 Vesta: Comparison of data from the Dawn mission with predicted internal structure and surface composition/mineralogy.  

NASA Astrophysics Data System (ADS)

While the HEDs provide an extremely useful basis for interpreting data from the Dawn mission, there is no guarantee that they provide a complete vision of all possible crustal (and possibly mantle) lithologies that are exposed at the surface of Vesta. With this in mind, an alternative approach is to identify plausible bulk compositions and use mass-balance and geochemical modelling to predict possible internal structures and crust/mantle compositions and mineralogies. While such models must be consistent with known HED samples, this 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. This calculation is complicated by the fact that iron may occur in metallic form (in the core) and/or in oxidized form (in the mantle and crust). However, considering that the basaltic crust has the composition of Juvinas and assuming that this crust is in thermodynamic equilibrium with the residual mantle, it is possible to calculate a single solution to this problem for a given bulk composition. Of the nine bulk compositions tested, solutions corresponding to CI and LL groups predicted a negative metal fraction and were not considered further. Solutions for enstatite chondrites imply significant oxidation relative to the starting materials and these solutions too are considered unlikely. For the remaining bulk compositions, the relative proportion of crust to bulk silicate is typically in the range 15 to 20% corresponding to crustal thicknesses of 15 to 20 km for a porosity-free Vesta-sized body. The mantle is predicted to be largely dominated by olivine (>85%) for carbonaceous chondrites, but to be a roughly equal mixture of olivine and pyroxene for ordinary chondrite precursors. All bulk compositions have a significant core, but the relative proportions of metal and sulphide can be widely different. Using these data, total core size (metal+ sulphide) and average core densities can be calculated, providing a useful reference frame within which to consider geophysical/gravity data of the Dawn mission. Further to these mass-balance calculations, the MELTS thermodynamic calculator has been used to assess to what extent chondritic bulk compositions can produce Juvinas-like liquids at relevant degrees of partial melting/crystallization. This work will refine acceptable bulk compositions and predict the mineralogy and composition of the associated solid and liquid products over wide ranges of partial melting and crystallization, providing a useful and self-consistent reference frame for interpretation of the data from the VIR and GRaND instruments onboard the Dawn spacecraft.

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

2012-04-01

354

Refractory Inclusions From the Carbonaceous Chondrite ACFER 094  

NASA Astrophysics Data System (ADS)

Introduction: The meteorite Acfer 094 is a uniquely primitive carbonaceous chondrite from the Sahara, which was first classified as a CO(CM) chondrite [1,2]. Trace element abundances of Acfer 094 are closely related to those from CM2 chondrites [1,3], but the oxygen isotopes suggest a relationship to C03 chondrites [1]. Studies on stable isotopes indicate that Acfer 094 contains isotopically anomalous carbon and nitrogen [4,5]. Based on mineralogical and petrographical observations, Bischoffand Geiger [6] suggested that Acfer 094 may be the first CM3 chondrite, whereas Newton et al. [5] pointed out that this meteorite is indeed very primitive but may not be directly related to existing types of carbonaceous chondrites. This study on refractory inclusions contribute further informations on Acfer 094 in view of a possible relationship to other meteorites. Results: The modal abundance of refractory or calcium-aluminium-rich inclusions (CAIs) within Acfer 094 is below 2 vol.% and the sizes of the objects range from 40 to 500 micrometers. The most abundant phases within the inclusions are melilite and spinel. Other phases identified within 23 studied inclusions include perovskite, hibonite, Ca-pyroxene (diopsidic to fassaitic), anorthite, grossite (CaA1407), an Al-, Ti-, Zr-, Y-rich phase and metal particles rich in Os, Ir, and Ru (PGEs). Secondary alteration products, such as sodalite, nepheline, or grossular, do not occur. The most common types of CAIs are type A (compact and fluflo and spinel-rich inclusions (together 15 objects). However, some of these inclusions have modal melilite and spinel abundances which indicate a smooth transition between type A (= melilite-rich) and spinel-rich inclusions. Thus, a reasonable distinction between these two inclusion types is not possible in every case. Usually, the melilite- and/or spinel-rich inclusions are rimmed by an outermost layer made of Ca-pyroxene and sometimes by an inner indistinct layer enriched in spinel. Four inclusions are rich in anorthite, three in hibonite. Another CAI with an apparent size of 140 x 140 micrometers consists of an intergrowth of grossite, melilite, perovskite, and hibonite, which is surrounded by a mantle of spinel. This mantle is rimmed by an inner layer of melilite and an outer layer of Ca-pyroxene. Two of the investigated inclusions (one anorthite-rich and one hibonite-rich CAI) are enclosed in a several hundred microns thick aggregate of fine-grained olivines. In addition, 5 objects were found which resemble AOAs. Discussion: Comparing CAIs from Acfer 094 to those from CV, CM, and CH chondrites the following general differences are obvious: Refractory inclusions from CV chondrites usually are larger and often affected by secondary processes, those from CM chondrites do not show the high modal abundance of melilite, and CAIs from CH chondrites contain grossite as a common phase and are rare in PGE-enriched metal particles. Some of the studied objects are restricted to Acfer 094 (e.g. inclusions enclosed in a thick aggregate of olivines), but many CAIs exhibit mineralogical and petrographical features which are similar to those from CO and CR inclusions. Therefore, it seems that the Acfer 094 CAI population is more related to inclusions known from CO and CR chondrites than to CAI populations from other carbonaceous chondrites. However, refractory inclusions occurring in Acfer 094 and other meteorites show such a broad variety and complexity that a standardized CAI classification is impossible. Based on the investigations on CAIs, the question whether Acfer 094 fits into the known classification scheme for carbonaceous chondrites or not remains unsolved. References: [1] Bischoff A. et al. (1991) Meteoritics, 26, 318-319. [2] Wlotzka F. (1991) Meteoritics, 26, 255-262. [3] Spettel B. et al. (1992) Meteoritics, 27, 290-291. [4] Newton J. et al. (1992) Meteoritics, 27, 267-268. [5] Newton J. et al. (1995) Meteoritics, 30, 47-56. [6] Bischoff A. and Geiger T. (1994) LPS XXV, 115-116.

Weber, D.

1995-09-01

355

Quantitative methods for three-dimensional comparison and petrographic description of chondrites  

SciTech Connect

X-ray computed tomography can be used to generate three-dimensional (3D) volumetric representations of chondritic meteorites. One of the challenges of using collected X-ray tomographic data is the extraction of useful data for 3D petrographic analysis or description. Here, I examine computer-aided quantitative 3D texture metrics that can be used for the classification of chondritic meteorites. These quantitative techniques are extremely useful for discriminating between chondritic materials, but yield little information on the 3D morphology of chondrite components. To investigate the morphology of chondrite minerals such as Fe(Ni) metal and related sulfides, the homology descriptors known as Betti numbers, are examined. Both methodologies are illustrated with theoretical discussion and examples. Betti numbers may be valuable for examining the nature of metal-silicate structural changes within chondrites with increasing degrees of metamorphism.

Friedrich, J.M. (Fordham)

2008-10-20

356

Axtell, a new CV3 chondrite find from Texas  

NASA Astrophysics Data System (ADS)

We describe a previously unreported meteorite found in Axtell, Texas, in 1943. Based on the mineralogical composition and texture of its matrix and the sizes and abundance of chondrules, we classify it as a CV3 carbonaceous chondrite. The dominant opaque phase in the chondrules is magnetite, and that in refractory inclusions is Ni-rich metal (awaruite). Axtell, therefore, belongs to the oxidized subgroup of CV3 chondrites, although unlike Allende it escaped strong sulfidation. The meteorite bears a strong textural resemblance to Allende, and its chondrule population and matrix appear to be quite similar to those of Allende, but its refractory inclusions, thermoluminescence properties, and cosmogenic Co-60 abundances are not. Our data are consistent with a terrestrial age for Axtell of approximately 100 years and a metamorphic grade slightly lower than that of Allende.

Simon, S. B.; Grossman, L.; Casanova, I.; Symes, S.; Benoit, P.; Sears, D. W. G.; Wacker, J. F.

1995-01-01

357

Comparing amino acid abundances and distributions across carbonaceous chondrite groups  

NASA Astrophysics Data System (ADS)

Meteorites are grouped according to bulk properties such as chemical composition and mineralogy. These parameters can vary significantly among the different carbonaceous chondrite groups (CI, CM, CO, CR, CH, CB, CV and CK). We have determined the amino acid abundances of more than 30 primary amino acids in meteorites from each of the eight groups, revealing several interesting trends. There are noticeable differences in the structural diversity and overall abundances of amino acids between meteorites from the different chondrite groups. Because meteorites may have been an important source of amino acids to the prebiotic Earth and these organic compounds are essential for life as we know it, the observed variations of these molecules may have been important for the origins of life.

Burton, Aaron; Dworkin, Jason; Callahan, Michael; Glavin, Daniel; Elsila, Jamie

2012-07-01

358

Ragland - an LL3. 4 chondrite find from New Mexico  

SciTech Connect

The Ragland, New Mexico, chondrite was found in 1978. It consists of a single stone of 12.16 kg that broke into three pieces. The stone is moderately weathered and has a pronounced chondritic texture. Bulk composition favors an LL classification, and modal analysis and oxygen isotopic composition are consistent with this. The thermoluminescence sensitivity of 0.056 + or - 0.020 normalized to Dhajala, compositional variability of olivine (mean Fa 18.3, sigma = 10.1) and low-Ca pyroxene (mean Fs 14.6, sigma = 6.7), and Ca concentrations in olivine indicate metamorphic subtype 3.4 + or - 0.1. The isotopically heavy oxygen composition, which is characteristic of subtypes 3.0-3.1, may be a primary characteristic and not a result of weathering. Low concentrations of radiogenic Ar-40 and planetary Ar-36 suggest noble gas loss. 19 references.

Recca, S.I.; Scott, E.R.D.; Keil, K.; Clayton, R.N.; Mayeda, T.K.

1986-06-01

359

Geochromatography on the parent body of the carbonaceous chondrite Ivuna  

NASA Astrophysics Data System (ADS)

A model geochromatography experiment was conducted to test the hypothesis that leaching by hydrothermal fluids was the cause for the unique polycyclic aromatic hydrocarbon (PAH) compositions of Ivuna, a CI carbonaceous chondrite. In this experiment, naphthalene, phenanthrene, and pyrene were partially resolved at a low pressure and low flow rates, using columns containing crushed serpentine or beach sand, and water for elution. The results suggest that complete separation of PAHs could be expected to occur in the parent body of CI carbonaceous chondrites. It is proposed that aqueous fluids driven by heat in the parent body of Ivuna migrated from the interior to the surface, and, in the process, transported, separated, and concentrated PAHs at various zones in the parent body.

Wing, Michael R.; Bada, Jeffrey L.

1991-10-01

360

21 Lutetia as the likely parent body of CH chondrites  

NASA Astrophysics Data System (ADS)

The reflectance spectra of the different groups of carbonaceous chondrites (hereafter CCs) reflects a large compositional diversity. CC groups exhibit different components and distinctive abundance ratios that are the main reasons for a large spectral diversity [1, 2]. A precise visible reflectance spectra of asteroid 21 Lutetia was recently obtained by VIRTIS spectrometer on board the Rosetta (ESA) spacecraft [3]. All collected evidence suggests that 21 Lutetia is a primitive asteroid, but exhibiting far higher reflectance than the measured for the most common groups of CCs [3, 4]. In any case, Rosetta data can be compared with our recently taken laboratory spectra of rare CC groups from the NASA Antarctic collection. As a result we have found an excellent candidate to fit that reflectance pattern in the CH group of carbonaceous chondrites. We exemplify that presenting the UV to nIR spectrum of one of the most pristine CHs available in our collections: PCA 91467.

Trigo-Rodríguez, J. M.; Moyano-Cambero, C. E.; Llorca, J.; Barucci, A.; Fornasier, S.; Belskaya, I.; Binzel, R.; Rivkin, AS.

2012-09-01

361

Rhenium-osmium systematics of calcium-aluminium-rich inclusions in carbonaceous chondrites  

Microsoft Academic Search

The Re-Os isotopic systematics of calcium-aluminium-rich inclusions (CAIs) in chondrites were investigated in order to shed light on the behavior of the Re-Os system in bulk chondrites, and to constrain the timing of chemical fractionation in primitive chondrites. CAIs with relatively unfractionated rare earth element (REE) patterns (groups I, III, V, VI) define a narrow range of 187Re\\/188Os (0.3764–0.4443) and

Harry Becker; John W. Morgan; Richard J. Walker; Glenn J. MacPherson; Jeffrey N. Grossman

2001-01-01

362

Chondrite Barium, Neodymium, and Samarium Isotopic Heterogeneity and Early Earth Differentiation  

Microsoft Academic Search

Isotopic variability in barium, neodymium, and samarium in carbonaceous chondrites reflects the distinct stellar nucleosynthetic contributions to the early solar system. We used 148Nd\\/144Nd to correct for the observed s-process deficiency, which produced a chondrite 146Sm-142Nd isochron consistent with previous estimates of the initial solar system abundance of 146Sm and a 142Nd\\/144Nd at average chondrite Sm\\/Nd ratio that is lower

Richard W. Carlson; Maud Boyet; Mary Horan

2007-01-01

363

Hydrogen isotopic composition of the water in CR chondrites  

NASA Astrophysics Data System (ADS)

The thermal and aqueous alteration experienced by QUE 99177, MET 00426, EET 92042, GRA 95229, Renazzo and Al Rais CR chondrites was assessed through multi-technique characterization of their the carbonaceous matter and hydrated mineral phases. Each of the chondrites escaped long duration thermal metamorphism as reflected by the low structural order of the polyaromatic carbonaceous matter assessed by Raman spectroscopy. The infrared spectra of the matrix grains clearly reveal the presence of hydrated minerals in each of the CR chondrites. In particular, the extent of aqueous alteration experienced by QUE 99177 and MET 00426 may have been previously underestimated. The H isotopic compositions of the altering fluids were measured in situ in fine-grained phyllosilicates and individual coarse-grained hydrated silicates. In the analyzed CR chondrites, the main observations are that (i) the water is systematically enriched in D, and the enrichments (?Dwater up to 1600‰) can be even higher than the highest D-enrichments reported for cometary water; (ii) the isotopic composition of the water is highly variable at the micrometer scale; (iii) there is no clear trend observed in the isotopic composition of the water (maximum D-enrichment, range of variation) along the aqueous alteration sequence. The D-enrichments and spatial variability are easier to explain as secondary signatures acquired through parent body processes, rather than as being due to the accretion of at least two ices with distinct isotopic compositions and sources that did not fully mix when they melted at the start of the aqueous alteration process.

Bonal, L.; Alexander, C. M. O.'D.; Huss, G. R.; Nagashima, K.; Quirico, E.; Beck, P.

2013-04-01

364

Magnesium isotopic composition of the Earth and chondrites  

Microsoft Academic Search

To constrain further the Mg isotopic composition of the Earth and chondrites, and investigate the behavior of Mg isotopes during planetary formation and magmatic processes, we report high-precision (±0.06‰ on ?25Mg and ±0.07‰ on ?26Mg, 2SD) analyses of Mg isotopes for (1) 47 mid-ocean ridge basalts covering global major ridge segments and spanning a broad range in latitudes, geochemical and

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

2010-01-01

365

A model for the production of cosmogenic nuclides in chondrites  

Microsoft Academic Search

A model is presented for calculating the production rates of cosmic-ray-produced He, Ne, and Ar as well as Be-10, Al-26, and Mn-53 in chondrites of variable size and shape. The predictions of this model are compared with published data for the meteorites ALH78084, St. Severin, and Keyes. The agreement is found to be about 5 percent for the concentrations of

Th. Graf; H. Baur; P. Signer

1990-01-01

366

Cosmogenic radionuclides and noble gases in the Wethersfield (1982) chondrite  

SciTech Connect

The Wethersfield (1982) chondrite was assayed for a suite of cosmogenic radionuclides shortly after fall. Data are reported for Be-7, Na-22, All-26, Sc-46, V-48, Cr-51, Mn-54, Co-56, Co-57, and Co-60. A comparison is made with predicted results based on a scaling to the Deep River Neutron Monitor. Noble gases were also assayed in a subsample. The cosmic-ray-exposure age is estimated to be 45 Myr. 9 references.

Evans, J.C.; Reeves, J.H.; Bogard, D.D.

1986-09-01

367

Origin of plagioclase-olivine inclusions in carbonaceous chondrites  

Microsoft Academic Search

Plagioclase-Olivine Inclusions (POIs) are an abundant group of chondrule-like objects with igneous textures found in carbonaceous chondrites. POIs consist of plagioclase, olivine, pyroxene, and spinel, and cover a wide range of compositions between Type C Ca-Al-rich Inclusions (CAIs) and ferromagnesian chondrules. POIs are distinguished from CAIs by the absence of melilite, lack of refractory siderophile-rich opaque assemblages, more sodic plagioclase,

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

1991-01-01

368

Origin of zoned metal grains in the QUE94411 chondrite  

Microsoft Academic Search

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was used to measure distributions of the siderophile elements P, V, Cr, Fe, Co, Ni, Mo, Ru, Rh, Pd, W, Re, Os, Ir, and Pt in metal grains in the metal-rich chondrite QUE94411 with a spatial resolution of ?30 ?m. The platinum group elements (PGEs), except Pd, exhibit radial zoning in these

Andrew J. Campbell; Munir Humayun; Anders Meibom; Alexander N. Krot; Klaus Keil

2001-01-01

369

The Ruhobobo, Rwanda meteorite - A new L6 chondrite  

NASA Astrophysics Data System (ADS)

Ruhobobo is a new meteorite which fell in Rwanda, Africa, in 1976. Olivine (Fa 23.4), opx (Fs 19.7, Wo 1.4), cpx (Fs 7.5, Wo 44.0), plagioclase (An 11.7, Or 5.6), chromite, 'whitlockite', kamacite, taenite and troilite were found and analyzed. Based on these analyses and on microscopic observation, Ruhobobo is an unshocked L6 chondrite.

Klob, H.; Kracher, A.; Kurat, G.

1981-03-01

370

Timescales and settings for alteration of chondritic meteorites  

SciTech Connect

Most groups of chondritic meteorites experienced diverse styles of secondary alteration to various degrees that resulted in formation of hydrous and anhydrous minerals (e.g., phyllosilicates, magnetite, carbonates, ferrous olivine, hedenbergite, wollastonite, grossular, andradite, nepheline, sodalite, Fe,Ni-carbides, pentlandite, pyrrhotite, Ni-rich metal). Mineralogical, petrographic, and isotopic observations suggest that the alteration occurred in the presence of aqueous solutions under variable conditions (temperature, water/rock ratio, redox conditions, and fluid compositions) in an asteroidal setting, and, in many cases, was multistage. Although some alteration predated agglomeration of the final chondrite asteroidal bodies (i.e. was pre-accretionary), it seems highly unlikely that the alteration occurred in the solar nebula, nor in planetesimals of earlier generations. Short-lived isotope chronologies ({sup 26}Al-{sup 26}Mg, {sup 53}Mn-{sup 53}Cr, {sup 129}I-{sup 129}Xe) of the secondary minerals indicate that the alteration started within 1-2 Ma after formation of the Ca,Al-rich inclusions and lasted up to 15 Ma. These observations suggest that chondrite parent bodies must have accreted within the first 1-2 Ma after collapse of the protosolar molecular cloud and provide strong evidence for an early onset of aqueous activity on these bodies.

Krot, A N; Hutcheon, I D; Brearley, A J; Pravdivtseva, O V; Petaev, M I; Hohenberg, C M

2005-11-16

371

Chlorine isotope homogeneity of the mantle, crust and carbonaceous chondrites  

NASA Astrophysics Data System (ADS)

Chlorine in the Earth is highly depleted relative to carbonaceous chondrites and solar abundances. Knowledge of the Cl concentrations and distribution on Earth is essential for understanding the origin of these depletions. Large differences in the stable chlorine isotope ratios of meteoritic, mantle and crustal materials have been used as evidence for distinct reservoirs in the solar nebula and to calculate the relative proportions of Cl in the mantle and crust. Here we report that large isotopic differences do not exist, and that carbonaceous chondrites, mantle and crust all have the same 37Cl/35Cl ratios. We have further analysed crustal sediments from the early Archaean era to the Recent epoch and find no systematic isotopic variations with age, demonstrating that the mantle and crust have always had the same ?37Cl value. The similarity of mantle, crust and carbonaceous chondrites establishes that there were no nebular reservoirs with distinct isotopic compositions, no isotopic fractionation during differentiation of the Earth and no late (post-core formation) Cl-bearing volatile additions to the crustal veneer with a unique isotopic composition.

Sharp, Z. D.; Barnes, J. D.; Brearley, A. J.; Chaussidon, M.; Fischer, T. P.; Kamenetsky, V. S.

2007-04-01

372

Ordinary differential equations, transport theory and Sobolev spaces  

Microsoft Academic Search

Summary We obtain some new existence, uniqueness and stability results for ordinary differential equations with coefficients in Sobolev spaces. These results are deduced from corresponding results on linear transport equations which are analyzed by the method of renormalized solutions.

R. J. DiPerna; P. L. Lions

1989-01-01

373

39Ar? 40Ar age and petrology of Chico: Large-scale impact melting on the L chondrite parent body  

Microsoft Academic Search

Our studies of the 105 kg Chico L chondrite show that it contains ?60% impact melt and the largest volume of impact melt recognized in stony meteorites. We suggest that it is part of a much larger dike complex that formed when chondritic impact melt was intruded into host chondrite during a large, if not catastrophic, impact on the L

D. D. Bogard; D. H. Garrison; M. Norman; E. R. D. Scott; K. Keil

1995-01-01

374

Accretionary dust mantles in CM chondrites - Evidence for solar nebula processes  

Microsoft Academic Search

The origin of the various components of 14 carbonaceous chondrites of the CM group, and the evolution of their parent body (or bodies) were examined by studying the texture and the model composition of these chondrites. Evidence is presented for the existence of preaccretionary aqueous alteration of anhydrous primary products in the solar nebula. Based on the results of textural,

K. Metzler; A. Bischoff; D. Stoeffler

1992-01-01

375

The oxygen isotopic composition of olivine and pyroxene from CI chondrites  

Microsoft Academic Search

The CI chondrites are taken to represent average solar system material based on the similarity of their elemental compositions to that of the solar photosphere. However, their oxygen isotope geochemistry is dominated by secondary minerals that formed during aqueous alteration on the CI parent body. Precursors to this alteration, namely olivine and pyroxene, are extremely rare in CI chondrites, precluding

Laurie A. Leshin; Alan E. Rubin; Kevin D. McKeegan

1997-01-01

376

Rapid contamination during storage of carbonaceous chondrites prepared for micro FTIR measurements  

Microsoft Academic Search

Organic contamination (~2965 and ~1260 cm-1 peaks) was found on Tagish Lake (C2) and Murchison (CM2) carbonaceous chondrites containing abundant hydrous minerals by Fourier transform infrared (FTIR) microspectroscopy on the samples pressed on Al plates. On the other hand, anhydrous chondrite (Moss, CO3) was not contaminated. This contamination occurred within one day of storage, when the samples pressed on Al

Yoko KEBUKAWA; Satoru NAKASHIMA; Takahiro OTSUKA; Keiko NAKAMURA-MESSENGER; M. E. Zolensky

2009-01-01

377

Aqueous alteration of carbonaceous chondrites: Evidence for preaccretionary alteration. A review  

Microsoft Academic Search

In most groups of carbonaceous chondrites minerals occur that are formed due to aqueous alteration in the nebula or\\/and within meteorite parent bodies. For determining the evolution of materials in the early solar system it is of significant importance to clearly identify evidence for either nebular or planetary aqueous alteration. Therefore, results from the study of chondrites have fundamental implications

A. Bischoff

1998-01-01

378

New SSMS Techniques for the Determination of Rhodium and Other Platinum Group Elements in Carbonaceous Chondrites  

Microsoft Academic Search

We have developed new spark source mass spectrometric (SSMS) techniques for simultaneous analysis of platinum-group elements (PGE) together with other trace elements in stony meteorites. We have measured elemental abundances of Rh, Ru, Os, Ir, Pt, Au in carbonaceous chondrites of different types including the two CI chondrites Orgueil and Ivuna. These data are relevant for the determination of solar-system

K. P. Jochum; H. M. Seufert

1995-01-01

379

Aqueous alteration and brecciation in Bells, an unusual, saponite-bearing, CM chondrite  

Microsoft Academic Search

The petrological and mineralogical characteristics of the unusual CM2 chondrite, Bells, have been investigated in detail by scanning electron microscopy (SEM), electron microprobe analysis (EPMA), and transmission electron microscopy (TEM). Bells is a highly brecciated chondrite which contains few intact chondrules, a very low abundance of refractory inclusions, and is notable in having an unusually high abundance of magnetite, which

Adrian J. Brearley

1995-01-01

380

Crystallization Experiments on Amorphous Silicates with Chondritic Composition: Quantitative Formulation of the Crystallization  

Microsoft Academic Search

In order to make clear crystallization process of silicates in circumstellar environments of oxygen-rich young stars, we have performed laboratory experiments on crystallization of a silicate material by use of a synthetic sample with the chondritic composition for the first time. The aim of this work is to analyze the crystallization process quantitatively using the amorphous material with the chondritic

K. Murata; H. Chihara; A. Tsuchiyama; C. Koike; T. Takakura; T. Noguchi; T. Nakamura

2007-01-01

381

Dahmani, a highly oxidised LL6 chondrite bearing Ni-rich taenite  

NASA Astrophysics Data System (ADS)

Dahmani, an LL6 brecciated chondrite, which fell in May 1981 is examined. It is considered to be one of the most oxidized chondrites ever known accounting for the composition of silicates (olivine Fa(30-32.6), orthopyroxene Fs(24.5-26.3)) and metals (60 percent Ni taenite).

Michel-Levy, M. C.; Denise, M. B.

1992-06-01

382

Nature of volatile depletion and genetic relationships in enstatite chondrites and aubrites inferred from Zn isotopes  

Microsoft Academic Search

Enstatite meteorites include the undifferentiated enstatite chondrites and the differentiated enstatite achondrites (aubrites). They are the most reduced group of all meteorites. The oxygen isotope compositions of both enstatite chondrites and aubrites plot along the terrestrial mass fractionation line, which suggests some genetic links between these meteorites and the Earth as well.For this study, we measured the Zn isotopic composition

Frédéric Moynier; Randal C. Paniello; Matthieu Gounelle; Francis Albarède; Pierre Beck; Frank Podosek; Brigitte Zanda

2011-01-01

383

Abundances of New-PCP in Acfer 094 and Other Carbonaceous Chondrites  

NASA Astrophysics Data System (ADS)

We have measured abundances of new-PCP in various chemical groups of carbonaceous chondrites. The new-PCP has been commonly observed in Acfer 094, but not detected in the other chondrites, suggesting that asteroid process decomposed new-PCPs.

Abe, K.; Sakamoto, N.; Krot, A. N.; Yurimoto, H.

2008-03-01

384

Petrology and Geochemistry of Patuxent Range 91501, a Clast-Poor Impact-Melt from the L Chondrite Parent Body, and Lewis Cliff 88663, an L7 Chondrite.  

National Technical Information Service (NTIS)

We have performed petrologic and geochemical studies of Patuxent Range 91501, originally classified as an L7 chondrite. PAT 91501 is an unshocked homogeneous, igneous-textured ultramafic rock composed of euhedral to subhedral olivine, low-Ca pyroxene, aug...

D. W. Mittlefehldt M. M. Lindstrom

2001-01-01

385

Early core formation in asteroids and late accretion of chondrite parent bodies: Evidence from 182Hf 182W in CAIs, metal-rich chondrites, and iron meteorites  

Microsoft Academic Search

The 182Hf-182W isotopic systematics of Ca-Al-rich inclusions (CAIs), metal-rich chondrites, and iron meteorites were investigated to constrain the relative timing of accretion of their parent asteroids. A regression of the Hf-W data for two bulk CAIs, various fragments of a single CAI, and carbonaceous chondrites constrains the 182Hf\\/180Hf and ?W at the time of CAI formation to (1.07 ± 0.10)

Thorsten Kleine; Klaus Mezger; Herbert Palme; Erik Scherer; Carsten Münker

2005-01-01

386

Experiments on the consolidation of chondrites and the formation of dense rims around chondrules  

NASA Astrophysics Data System (ADS)

It is generally accepted, that chondrites are formed by coagulation of chondrules and the matrix dust. Such pre-chondrites can be formed in low-velocity collisions and would therefore be more porous than the typical chondrites are. Those chondrites have volume filling factors (porosity) ranging from ?=0.3 (70%) to ?=0.6 (40%). We will present impact experiments into mixtures of chondrule analogs and dust materials to determine the dynamic pressure range under which these can be compacted to achieve porosities found in chondritic meteorites. The second objective of the experiment was to test whether or not fine-grained dust rims around chondrules can be formed due to the dynamic compaction process. In our experiments, aluminum cylinders were used as projectiles to compact the chondrite-analog samples in a velocity range between 165 m/s and 1200 m/s. The resulting impact pressures in the samples fall between ~90 and ~2400 MPa. To measure the achieved porosities of our samples, 25 samples were analyzed using computer-aided tomography. We found volume filling factors to be between ?= 0.70 and ?= 0.99. Additionally, we determined the mean pressure range in which CM chondrites were likely to be compacted and found values between 60 and 150 MPa. As for the high-density rims found around chondrules, we can show that these do not form in dynamic compaction processes. Moreover, we found that for a collision between two pre-chondritic bodies of 0.4< ? < 0.5, the collision velocity for a pressure range of 0.05 GPa to 2 GPa falls between 100 m/s and 2000 m/s, which is within the typical velocity range of the of planetary growth models and agrees with a formation distance of chondrites between 2 and 3 AU at given orbital eccentricities of 0.02 and 0.1 for the pre-chondrites.

Beitz, Eike; Güttler, Carsten; Nakamura, Akiko; Blum, Jürgen

2013-07-01

387

Extraterrestrial amino acids identified in metal-rich CH and CB carbonaceous chondrites from Antarctica  

NASA Astrophysics Data System (ADS)

Carbonaceous chondrites contain numerous indigenous organic compounds and could have been an important source of prebiotic compounds required for the origin of life on Earth or elsewhere. Extraterrestrial amino acids have been reported in five of the eight groups of carbonaceous chondrites and are most abundant in CI, CM, and CR chondrites but are also present in the more thermally altered CV and CO chondrites. We report the abundance, distribution, and enantiomeric and isotopic compositions of simple primary amino acids in six metal-rich CH and CB carbonaceous chondrites that have not previously been investigated for amino acids: Allan Hills (ALH) 85085 (CH3), Pecora Escarpment (PCA) 91467 (CH3), Patuxent Range (PAT) 91546 (CH3), MacAlpine Hills (MAC) 02675 (CBb), Miller Range (MIL) 05082 (CB), and Miller Range (MIL) 07411 (CB). Amino acid abundances and carbon isotopic values were obtained by using both liquid chromatography time-of-flight mass spectrometry and fluorescence, and gas chromatography isotope ratio mass spectrometry. The ?13C/12C ratios of multiple amino acids fall outside of the terrestrial range and support their extraterrestrial origin. Extracts of CH chondrites were found to be particularly rich in amino acids (13-16 parts per million, ppm) while CB chondrite extracts had much lower abundances (0.2-2 ppm). The amino acid distributions of the CH and CB chondrites were distinct from the distributions observed in type 2 and 3 CM and CR chondrites and contained elevated levels of ?-, ?-, and ?-amino acids compared to the corresponding ?-amino acids, providing evidence that multiple amino acid formation mechanisms were important in CH and CB chondrites.

Burton, Aaron S.; Elsila, Jamie E.; Hein, Jason E.; Glavin, Daniel P.; Dworkin, Jason P.

2013-03-01

388

Highly oxidized and metamorphosed chondritic or igneous (?) clasts in the CV3 carbonaceous chondrite Mokoia - Excavated material from the interior of the CV3 asteroid or previously unsampled asteroid  

NASA Astrophysics Data System (ADS)

The Mokoia clasts are fragments of coarse-grained, granular, polymineralic rocks which consist of Ca-rich fayalitic olivine. Nepheline typically replaces plagioclase. The textures and mineralogy of the clasts indicate that they were extensively metamorphosed above 750-800 C prior to excavation from their parent asteroid and subsequently added to the Mokoia breccia; the last event postdates aqueous alteration of the host meteorite. The coexisting Al-diopside, anorthitic plagioclase and Cr-spinel in the clasts and high CaO contents in olivine suggest that precursor materials for the clasts were rich in Ca and Al; Fe-rich compositions of olivine, diopside, and mineralogy of the opaque assemblage suggest a high degree of oxidation. The mineralogy and mineral chemistry of the Mokoia clasts are unique among known metamorphosed ordinary and carbonaceous chondrites and achondrites and may represent material from a previously unsampled asteroid. Alternatively, the Mokoia clasts may have been excavated from the oxidized and metamorphosed interior of the CV3 asteroid.

Krot, A. N.; Hutcheon, I. D.

1997-03-01

389

Oxygen three-isotope ratios of silicate particles returned from asteroid Itokawa by the Hayabusa spacecraft: A strong link with equilibrated LL chondrites  

NASA Astrophysics Data System (ADS)

Oxygen three-isotope ratios of four mineral phases (olivine, low-Ca and high-Ca pyroxene, and plagioclase) in seven silicate particles from asteroid Itokawa were measured to investigate oxygen isotope systematics of asteroidal materials. In order to obtain highly precise and accurate oxygen isotope ratios (˜±0.3‰ in ?18O), we used a new indium mounting method that minimizes potential instrumental mass fractionation due to surface topography. The oxygen isotope data of the seven Itokawa particles are distributed above the terrestrial fractionation line with indistinguishable ?O17(=?O17-0.52×?O18) values of +1.34±0.36‰ (2SD; n=22), which is similar to those of Itokawa particles analyzed by Yurimoto et al. (2011) and Nakamura et al. (2012). However, ?18O values of the seven Itokawa particles are tightly clustered (+3.9‰ to +5.9‰ VSMOW) compared to previous analyses of the Itokawa particles (+1.4‰ to +8.8‰). The average ?17O values and 2SD of the two equilibrated ordinary chondrites (EOCs), which were analyzed for comparison, are +1.31±0.49‰ for St. Séverin (LL6) and +0.83±0.64‰ for Guareña (H6). The ?17O values of the seven Itokawa particles are similar to those of St. Séverin. The average bulk ?18O value of the seven Itokawa particles is estimated as +4.8‰, which is within the ?18O range of bulk LL5 and LL6 chondrites. It is suggested that Itokawa particles are similar to those of equilibrated LL chondrites, which strengthens a link between asteroid Itokawa and equilibrated LL chondrites that fell to Earth. The seven Itokawa particles and two EOCs have ?18O values of high-Ca pyroxene that are lower than those of olivine, indicating that oxygen isotopes between the two mineral phases are not in equilibrium. Apparent oxygen isotope equilibrium temperatures estimated from a pair of low-Ca pyroxene and olivine are excessively higher than those from a pair of plagioclase and high-Ca pyroxene (˜800 °C) and peak metamorphic temperatures. Oxygen isotopes in olivine and low-Ca pyroxene do not represent equilibrium. On the other hand, oxygen isotope ratios in high-Ca pyroxene and plagioclase were mass-dependently fractionated accompanied by recrystallization (and possibly by diffusion) during thermal metamorphism. Values of ?18O in high-Ca pyroxene were lowered by exchange, which may have resulted in the reverse ?18O fractionation between olivine and high-Ca pyroxene.

Nakashima, Daisuke; Kita, Noriko T.; Ushikubo, Takayuki; Noguchi, Takaaki; Nakamura, Tomoki; Valley, John W.

2013-10-01

390

Ce isotope abundance in chondritic and HED meteorites  

NASA Astrophysics Data System (ADS)

138La, 136Ce and 138Ce are p-process nuclides, and their isotopic abundances are generally low due to their modes of nucleosynthesis compared with other isotopes of La and Ce (139La, 140Ce and 142Ce). Tanimizu et al. (2004) mentioned that, using the 140Ce/142Ce ratio as the normalizing value, 136Ce isotope abundance could be acted as an indicator of p-process nuclide anomaly for extra-terrestrial materials to understand the nucleosynthetic origins of solar system matter. Then, meteoritic primordial composition of Ce isotope provides useful information related with 138La decay system. Especially, combined Ce/Nd isotope data in geological and cosmological materials enable us the modeling of the light REE profiles of the source material. We measured Ce isotope ratio for fifteen meteorites, using 140Ce/142Ce=7.941 as the normalizing value, in order to compare Ce isotope abundance between chondritic and HED meteorites. Of them, Ce isotope abundances from two chondritic meteorites were deviated from the average abundances of other 13 meteorites. In this report, we will discuss cosmochemical significance of Ce isotope anomaly.

Lee, S.; Asahara, Y.; Tanaka, T.; Lee, S. R.

2011-12-01

391

Fine-grained Chondrule Rims in the Murchison CM2 Chondrite: Compositional and Mineralogical Systematics  

NASA Astrophysics Data System (ADS)

The CM2 carbonaceous chondrites contain numerous chondrules, silicate grains, CAIs, etc, which are mantled by rims of fine- grained material [1]. These rims often consist of two or more layers that can be distinguished on chemical and textural criteria. The formation mechanisms of rims, and the timing and location (i.e., nebular vs planetary) of aqueous alteration of rim materials is the subject of some controversy. We are examining, in detail, the relationships between the mineralogy and bulk composition of individual rims in the Murchison CM2 chondrite in order to place constraints on their mechanisms of formation and alteration histories. We have carried out detailed SEM, electron microprobe and TEM studies of a number of rim sequences in Murchison. Our data provide further confirmation of some of the observations of [1]. For example, we have found that on any given chondrule, inner rims are almost invariably more Mg-rich than outer rims. However, when the entire population of rims is considered it is evident that the compositional field for inner rims overlaps that for outer rims in terms of Mg/Fe ratio. Na and K are also consistently enriched in inner rims, but all the other analyzed elements show variable behavior. Elemental ratio diagrams for rims show some variation in their shape, but in most cases are relatively flat. The elements that consistently show exceptions are Ca and S are frequently depleted relative to CI values in both inner and outer rims. We have also examined the interelement variations in inner and outer rims. One of the surprising results of this study is that some elements may be correlated in inner rims, but not in outer rims and vice versa. Fe and S show a strong positive correlation in outer rims, but have no correlation in inner rims. The reverse is true of Na and S. Our TEM studies of the fine-grained mineralogy of 5 rims have, so far, revealed consistent relationships between rim composition and mineralogy. All the inner rims studied consist dominantly of microcrystalline Mg-rich serpentine, rare platy cronstedtite crystals and poorly crystalline pentlandite and pyrrhotite. The sulfides are disseminated throughout the regions of microcrystalline serpentine. Tochilinite has not been found. The compositions of serpentine and cronstedtite in the different rims studied are very similar and define distinct, tightly clustered compositional groups on Si-Fe-Mg ternary diagrams. Outer rims are mineralogically distinct. For intermediate Mg/Fe ratios, outer rims are dominated by relatively coarse-grained platy cronstedtite, a minor amorphous component and sulfides, whereas the most Fe-rich outer rims contain tochilinite and minor cronstedtite. Our present data indicate clear relationships between bulk rim composition and mineralogy, which would appear to support a parent body location for aqueous alteration, rather than nebular. In addition, the evidence that some elements show variable correlations in inner and outer rims, indicates that there must be mineralogical controls on the major and minor element chemistry of rims. This may reflect variations in the mineralogy of the precursor components of rims, or the mineralogical constraints imposed on elemental mobility between rims and chondrules during alteration. The depletions in Ca and S in rims may be a reflection of the high mobility of these elements during alteration, as is certainly the case in CI chondrites. Finally the textural characteristics of inner rim materials appear to be inconsistent with alteration of a crystalline precursor, because there is no evidence of pseudomorphic replacement of phases. Many of the textures are similar to those produced during low temperature alteration of basaltic glass [2]. The possibility that the precursor was an amorphous material, perhaps of the type observed in ALH A77307 [3] and several of the least equilibrated ordinary chondrites [4], should be considered. Funded by NASA grant NAGW-3347 to J. J. Papike (P.I.). References: [1] Metzler K. et al. (1992) GCA, 65, 2873-2897. [2] Tazaki K. et al. (1989)

Brearley, A. J.; Geiger, T.

1993-07-01

392

Educating children with Down's Syndrome in an ordinary school  

Microsoft Academic Search

The article describes the attempts and achievements of a group of parents of children with Down's Syndrome to provide an education for their children in an ordinary school. Their efforts at interesting the local education authority in establishing a unit were thwarted and they turned to the private sector. The description of the education of the children is set in

Tony Booth

1981-01-01

393

The grey zone: the 'ordinary' violence of extraordinary times  

Microsoft Academic Search

The article analyses the 'ordinary' violence of revolutionary politics, particularly acts of gendered and sexual violence that tend to be neglected in the face of the 'extraordinariness' of political terror. Focusing on the extreme left Naxalbari movement of West Bengal, it points to those morally ambiguous 'grey zones' that confound the rigid distinctions between victim and victimizer in insurrectionary politics.

S rila R oy

2008-01-01

394

A minimax inequality and its applications to ordinary differential equations  

Microsoft Academic Search

The aim of this paper is to investigate the minimax inequality which plays a fundamental role in the critical points theorem of B. Ricceri below. Equivalent formulations are shown, and characterization is proved in particular for a special class of functionals. As an application, a multiplicity result for an ordinary Dirichlet problem is emphasized.

Gabriele Bonanno

2002-01-01

395

The numerical simulation for stiff systems of ordinary differential equations  

Microsoft Academic Search

In this paper, the variational iteration method is applied to solve systems of ordinary differential equations in both linear and nonlinear cases, focusing interest on stiff problems. Some examples are given to illustrate the accuracy and effectiveness of the method. We compare our results with results obtained by the Adomian decomposition method. This comparison reveals that the variational iteration method

M. T. Darvishi; F. Khani; A. A. Soliman

2007-01-01

396

The Democratic Firm: An Argument Based on Ordinary Jurisprudence  

Microsoft Academic Search

This paper presents an argument for the democratic (or 'labor-managed') firm based on ordinary jurisprudence. The standard principle of responsibility in jurisprudence ('Assign legal responsibility in accordance with de facto responsibility') implies that the people working in a firm should legally appropriate the assets and liabilities produced in the firm (the positive and negative fruits of their labor). This appropriation

David Ellerman

1999-01-01

397

Learning to Compute: Computerization and Ordinary, Everyday Life  

ERIC Educational Resources Information Center

This study utilizes the basic framework of classical sociology as a foundation for examining the intersection of the structural history of the computer revolution with ordinary, everyday life. Just as the classical forefathers of modern sociology--Marx, Durkheim, and Weber--attempted to understand their eras of structural transformation, this…

Sullivan, Joseph F.

2009-01-01

398

Water, Water, Everywhere: Phase Diagrams of Ordinary Water Substance  

NASA Astrophysics Data System (ADS)

A three-dimensional phase diagram for ordinary water substance, with its solid, liquid, and vapor phases, based on fitted authentic experimental data is presented. Such an authentic diagram appears not to have been presented for water before, and may improve the understanding of its phase relationships. The nature of the IAPWS-95 equations, fitted to data, is discussed.

Glasser, L.

2004-03-01

399

Does antimatter fall with the same acceleration as ordinary matter  

Microsoft Academic Search

Equivalence-principle experiments with ordinary matter probe the gravivector acceleration of antimatter in the same way as do direct measurements of antimatter in free fall and set stringent upper limits on the gravivector acceleration of antimatter predicted by certain quantum-gravity models.

E. G. Adelberger; B. R. Heckel; C. W. Stubbs; Y. Su

1991-01-01

400

Pricing differentials for organic, ordinary and genetically modified food  

Microsoft Academic Search

Purpose – Aims to conduct research on consumer willingness to buy genetically modified (GM) foods with a price advantage and other benefits, compared with organic and ordinary types of foods, employing a robust experimental method. The importance of this increases as the volume and range of GM foods grown and distributed globally increase, as consumer fears surrounding perceived risk decrease

Damien Mather; John Knight; David Holdsworth

2005-01-01

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